Merge pull request #1 from rust-lang/master

Pull from newest repo

71 files changed, 16113 insertions, 17160 deletions

diff --git a/src/libsyntax/Cargo.toml b/src/libsyntax/Cargo.toml
index b48f3c9b8b8..d4a9acc1569 100644
--- a/src/libsyntax/Cargo.toml
+++ b/src/libsyntax/Cargo.toml
@@ -7,17 +7,18 @@ edition = "2018"
 [lib]
 name = "syntax"
 path = "lib.rs"
-crate-type = ["dylib"]
+doctest = false
 
 [dependencies]
 bitflags = "1.0"
-serialize = { path = "../libserialize" }
+rustc_serialize = { path = "../libserialize", package = "serialize" }
 log = "0.4"
 scoped-tls = "1.0"
 lazy_static = "1.0.0"
 syntax_pos = { path = "../libsyntax_pos" }
 errors = { path = "../librustc_errors", package = "rustc_errors" }
 rustc_data_structures = { path = "../librustc_data_structures" }
+rustc_lexer = { path = "../librustc_lexer" }
 rustc_macros = { path = "../librustc_macros" }
 rustc_target = { path = "../librustc_target" }
 smallvec = { version = "0.6.7", features = ["union", "may_dangle"] }
diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index d12240655e6..50e428ea0cc 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -5,28 +5,31 @@ pub use UnsafeSource::*;
 pub use crate::symbol::{Ident, Symbol as Name};
 pub use crate::util::parser::ExprPrecedence;
 
-use crate::ext::hygiene::{Mark, SyntaxContext};
-use crate::parse::token;
+use crate::ext::hygiene::ExpnId;
+use crate::parse::token::{self, DelimToken};
 use crate::print::pprust;
 use crate::ptr::P;
 use crate::source_map::{dummy_spanned, respan, Spanned};
-use crate::symbol::{keywords, Symbol};
+use crate::symbol::{kw, sym, Symbol};
 use crate::tokenstream::TokenStream;
 use crate::ThinVec;
 
 use rustc_data_structures::indexed_vec::Idx;
 #[cfg(target_arch = "x86_64")]
-use rustc_data_structures::static_assert;
+use rustc_data_structures::static_assert_size;
 use rustc_target::spec::abi::Abi;
 use syntax_pos::{Span, DUMMY_SP};
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sync::Lrc;
-use serialize::{self, Decoder, Encoder};
+use rustc_serialize::{self, Decoder, Encoder};
 use std::fmt;
 
 pub use rustc_target::abi::FloatTy;
 
+#[cfg(test)]
+mod tests;
+
 #[derive(Clone, RustcEncodable, RustcDecodable, Copy)]
 pub struct Label {
     pub ident: Ident,
@@ -50,11 +53,17 @@ impl fmt::Debug for Lifetime {
             f,
             "lifetime({}: {})",
             self.id,
-            pprust::lifetime_to_string(self)
+            self
         )
     }
 }
 
+impl fmt::Display for Lifetime {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.ident.name.as_str())
+    }
+}
+
 /// A "Path" is essentially Rust's notion of a name.
 ///
 /// It's represented as a sequence of identifiers,
@@ -65,18 +74,14 @@ impl fmt::Debug for Lifetime {
 pub struct Path {
     pub span: Span,
     /// The segments in the path: the things separated by `::`.
-    /// Global paths begin with `keywords::PathRoot`.
+    /// Global paths begin with `kw::PathRoot`.
     pub segments: Vec<PathSegment>,
 }
 
 impl PartialEq<Symbol> for Path {
     fn eq(&self, symbol: &Symbol) -> bool {
         self.segments.len() == 1 && {
-            let name = self.segments[0].ident.name;
-            // Make sure these symbols are pure strings
-            debug_assert!(!symbol.is_gensymed());
-            debug_assert!(!name.is_gensymed());
-            name == *symbol
+            self.segments[0].ident.name == *symbol
         }
     }
 }
@@ -104,7 +109,7 @@ impl Path {
     }
 
     pub fn is_global(&self) -> bool {
-        !self.segments.is_empty() && self.segments[0].ident.name == keywords::PathRoot.name()
+        !self.segments.is_empty() && self.segments[0].ident.name == kw::PathRoot
     }
 }
 
@@ -132,7 +137,7 @@ impl PathSegment {
         PathSegment { ident, id: DUMMY_NODE_ID, args: None }
     }
     pub fn path_root(span: Span) -> Self {
-        PathSegment::from_ident(Ident::new(keywords::PathRoot.name(), span))
+        PathSegment::from_ident(Ident::new(kw::PathRoot, span))
     }
 }
 
@@ -194,9 +199,9 @@ pub struct AngleBracketedArgs {
     pub span: Span,
     /// The arguments for this path segment.
     pub args: Vec<GenericArg>,
-    /// Bindings (equality constraints) on associated types, if present.
-    /// E.g., `Foo<A = Bar>`.
-    pub bindings: Vec<TypeBinding>,
+    /// Constraints on associated types, if any.
+    /// E.g., `Foo<A = Bar, B: Baz>`.
+    pub constraints: Vec<AssocTyConstraint>,
 }
 
 impl Into<Option<P<GenericArgs>>> for AngleBracketedArgs {
@@ -217,7 +222,7 @@ pub struct ParenthesizedArgs {
     /// Overall span
     pub span: Span,
 
-    /// `(A,B)`
+    /// `(A, B)`
     pub inputs: Vec<P<Ty>>,
 
     /// `C`
@@ -229,7 +234,7 @@ impl ParenthesizedArgs {
         AngleBracketedArgs {
             span: self.span,
             args: self.inputs.iter().cloned().map(|input| GenericArg::Type(input)).collect(),
-            bindings: vec![],
+            constraints: vec![],
         }
     }
 }
@@ -249,12 +254,12 @@ mod node_id_inner {
 pub use node_id_inner::NodeId;
 
 impl NodeId {
-    pub fn placeholder_from_mark(mark: Mark) -> Self {
-        NodeId::from_u32(mark.as_u32())
+    pub fn placeholder_from_expn_id(expn_id: ExpnId) -> Self {
+        NodeId::from_u32(expn_id.as_u32())
     }
 
-    pub fn placeholder_to_mark(self) -> Mark {
-        Mark::from_u32(self.as_u32())
+    pub fn placeholder_to_expn_id(self) -> ExpnId {
+        ExpnId::from_u32(self.as_u32())
     }
 }
 
@@ -264,13 +269,13 @@ impl fmt::Display for NodeId {
     }
 }
 
-impl serialize::UseSpecializedEncodable for NodeId {
+impl rustc_serialize::UseSpecializedEncodable for NodeId {
     fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_u32(self.as_u32())
     }
 }
 
-impl serialize::UseSpecializedDecodable for NodeId {
+impl rustc_serialize::UseSpecializedDecodable for NodeId {
     fn default_decode<D: Decoder>(d: &mut D) -> Result<NodeId, D::Error> {
         d.read_u32().map(NodeId::from_u32)
     }
@@ -366,7 +371,6 @@ impl Default for Generics {
         Generics {
             params: Vec::new(),
             where_clause: WhereClause {
-                id: DUMMY_NODE_ID,
                 predicates: Vec::new(),
                 span: DUMMY_SP,
             },
@@ -378,7 +382,6 @@ impl Default for Generics {
 /// A where-clause in a definition.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct WhereClause {
-    pub id: NodeId,
     pub predicates: Vec<WherePredicate>,
     pub span: Span,
 }
@@ -519,21 +522,28 @@ impl fmt::Debug for Pat {
 }
 
 impl Pat {
+    /// Attempt reparsing the pattern as a type.
+    /// This is intended for use by diagnostics.
     pub(super) fn to_ty(&self) -> Option<P<Ty>> {
         let node = match &self.node {
+            // In a type expression `_` is an inference variable.
             PatKind::Wild => TyKind::Infer,
+            // An IDENT pattern with no binding mode would be valid as path to a type. E.g. `u32`.
             PatKind::Ident(BindingMode::ByValue(Mutability::Immutable), ident, None) => {
                 TyKind::Path(None, Path::from_ident(*ident))
             }
             PatKind::Path(qself, path) => TyKind::Path(qself.clone(), path.clone()),
             PatKind::Mac(mac) => TyKind::Mac(mac.clone()),
+            // `&mut? P` can be reinterpreted as `&mut? T` where `T` is `P` reparsed as a type.
             PatKind::Ref(pat, mutbl) => pat
                 .to_ty()
                 .map(|ty| TyKind::Rptr(None, MutTy { ty, mutbl: *mutbl }))?,
-            PatKind::Slice(pats, None, _) if pats.len() == 1 => {
-                pats[0].to_ty().map(TyKind::Slice)?
-            }
-            PatKind::Tuple(pats, None) => {
+            // A slice/array pattern `[P]` can be reparsed as `[T]`, an unsized array,
+            // when `P` can be reparsed as a type `T`.
+            PatKind::Slice(pats) if pats.len() == 1 => pats[0].to_ty().map(TyKind::Slice)?,
+            // A tuple pattern `(P0, .., Pn)` can be reparsed as `(T0, .., Tn)`
+            // assuming `T0` to `Tn` are all syntactically valid as types.
+            PatKind::Tuple(pats) => {
                 let mut tys = Vec::with_capacity(pats.len());
                 // FIXME(#48994) - could just be collected into an Option<Vec>
                 for pat in pats {
@@ -559,19 +569,16 @@ impl Pat {
             return false;
         }
 
-        match self.node {
-            PatKind::Ident(_, _, Some(ref p)) => p.walk(it),
-            PatKind::Struct(_, ref fields, _) => fields.iter().all(|field| field.node.pat.walk(it)),
-            PatKind::TupleStruct(_, ref s, _) | PatKind::Tuple(ref s, _) => {
-                s.iter().all(|p| p.walk(it))
-            }
-            PatKind::Box(ref s) | PatKind::Ref(ref s, _) | PatKind::Paren(ref s) => s.walk(it),
-            PatKind::Slice(ref before, ref slice, ref after) => {
-                before.iter().all(|p| p.walk(it))
-                    && slice.iter().all(|p| p.walk(it))
-                    && after.iter().all(|p| p.walk(it))
-            }
+        match &self.node {
+            PatKind::Ident(_, _, Some(p)) => p.walk(it),
+            PatKind::Struct(_, fields, _) => fields.iter().all(|field| field.pat.walk(it)),
+            PatKind::TupleStruct(_, s)
+            | PatKind::Tuple(s)
+            | PatKind::Slice(s)
+            | PatKind::Or(s) => s.iter().all(|p| p.walk(it)),
+            PatKind::Box(s) | PatKind::Ref(s, _) | PatKind::Paren(s) => s.walk(it),
             PatKind::Wild
+            | PatKind::Rest
             | PatKind::Lit(_)
             | PatKind::Range(..)
             | PatKind::Ident(..)
@@ -579,6 +586,14 @@ impl Pat {
             | PatKind::Mac(_) => true,
         }
     }
+
+    /// Is this a `..` pattern?
+    pub fn is_rest(&self) -> bool {
+        match self.node {
+            PatKind::Rest => true,
+            _ => false,
+        }
+    }
 }
 
 /// A single field in a struct pattern
@@ -594,6 +609,8 @@ pub struct FieldPat {
     pub pat: P<Pat>,
     pub is_shorthand: bool,
     pub attrs: ThinVec<Attribute>,
+    pub id: NodeId,
+    pub span: Span,
 }
 
 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Copy)]
@@ -627,12 +644,14 @@ pub enum PatKind {
 
     /// A struct or struct variant pattern (e.g., `Variant {x, y, ..}`).
     /// The `bool` is `true` in the presence of a `..`.
-    Struct(Path, Vec<Spanned<FieldPat>>, /* recovered */ bool),
+    Struct(Path, Vec<FieldPat>, /* recovered */ bool),
 
     /// A tuple struct/variant pattern (`Variant(x, y, .., z)`).
-    /// If the `..` pattern fragment is present, then `Option<usize>` denotes its position.
-    /// `0 <= position <= subpats.len()`.
-    TupleStruct(Path, Vec<P<Pat>>, Option<usize>),
+    TupleStruct(Path, Vec<P<Pat>>),
+
+    /// An or-pattern `A | B | C`.
+    /// Invariant: `pats.len() >= 2`.
+    Or(Vec<P<Pat>>),
 
     /// A possibly qualified path pattern.
     /// Unqualified path patterns `A::B::C` can legally refer to variants, structs, constants
@@ -641,9 +660,7 @@ pub enum PatKind {
     Path(Option<QSelf>, Path),
 
     /// A tuple pattern (`(a, b)`).
-    /// If the `..` pattern fragment is present, then `Option<usize>` denotes its position.
-    /// `0 <= position <= subpats.len()`.
-    Tuple(Vec<P<Pat>>, Option<usize>),
+    Tuple(Vec<P<Pat>>),
 
     /// A `box` pattern.
     Box(P<Pat>),
@@ -657,9 +674,22 @@ pub enum PatKind {
     /// A range pattern (e.g., `1...2`, `1..=2` or `1..2`).
     Range(P<Expr>, P<Expr>, Spanned<RangeEnd>),
 
-    /// `[a, b, ..i, y, z]` is represented as:
-    ///     `PatKind::Slice(box [a, b], Some(i), box [y, z])`
-    Slice(Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>),
+    /// A slice pattern `[a, b, c]`.
+    Slice(Vec<P<Pat>>),
+
+    /// A rest pattern `..`.
+    ///
+    /// Syntactically it is valid anywhere.
+    ///
+    /// Semantically however, it only has meaning immediately inside:
+    /// - a slice pattern: `[a, .., b]`,
+    /// - a binding pattern immediately inside a slice pattern: `[a, r @ ..]`,
+    /// - a tuple pattern: `(a, .., b)`,
+    /// - a tuple struct/variant pattern: `$path(a, .., b)`.
+    ///
+    /// In all of these cases, an additional restriction applies,
+    /// only one rest pattern may occur in the pattern sequences.
+    Rest,
 
     /// Parentheses in patterns used for grouping (i.e., `(PAT)`).
     Paren(P<Pat>),
@@ -883,17 +913,6 @@ pub struct Local {
     pub id: NodeId,
     pub span: Span,
     pub attrs: ThinVec<Attribute>,
-    /// Origin of this local variable.
-    pub source: LocalSource,
-}
-
-#[derive(Clone, Copy, RustcEncodable, RustcDecodable, Debug)]
-pub enum LocalSource {
-    /// Local was parsed from source.
-    Normal,
-    /// Within `ast::IsAsync::Async`, a local is generated that will contain the moved arguments
-    /// of an `async fn`.
-    AsyncFn,
 }
 
 /// An arm of a 'match'.
@@ -910,13 +929,10 @@ pub enum LocalSource {
 pub struct Arm {
     pub attrs: Vec<Attribute>,
     pub pats: Vec<P<Pat>>,
-    pub guard: Option<Guard>,
+    pub guard: Option<P<Expr>>,
     pub body: P<Expr>,
-}
-
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
-pub enum Guard {
-    If(P<Expr>),
+    pub span: Span,
+    pub id: NodeId,
 }
 
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
@@ -926,10 +942,9 @@ pub struct Field {
     pub span: Span,
     pub is_shorthand: bool,
     pub attrs: ThinVec<Attribute>,
+    pub id: NodeId,
 }
 
-pub type SpannedIdent = Spanned<Ident>;
-
 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Copy)]
 pub enum BlockCheckMode {
     Default,
@@ -964,7 +979,7 @@ pub struct Expr {
 
 // `Expr` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(target_arch = "x86_64")]
-static_assert!(MEM_SIZE_OF_EXPR: std::mem::size_of::<Expr>() == 96);
+static_assert_size!(Expr, 96);
 
 impl Expr {
     /// Whether this expression would be valid somewhere that expects a value; for example, an `if`
@@ -1040,7 +1055,6 @@ impl Expr {
     pub fn precedence(&self) -> ExprPrecedence {
         match self.node {
             ExprKind::Box(_) => ExprPrecedence::Box,
-            ExprKind::ObsoleteInPlace(..) => ExprPrecedence::ObsoleteInPlace,
             ExprKind::Array(_) => ExprPrecedence::Array,
             ExprKind::Call(..) => ExprPrecedence::Call,
             ExprKind::MethodCall(..) => ExprPrecedence::MethodCall,
@@ -1049,10 +1063,9 @@ impl Expr {
             ExprKind::Unary(..) => ExprPrecedence::Unary,
             ExprKind::Lit(_) => ExprPrecedence::Lit,
             ExprKind::Type(..) | ExprKind::Cast(..) => ExprPrecedence::Cast,
+            ExprKind::Let(..) => ExprPrecedence::Let,
             ExprKind::If(..) => ExprPrecedence::If,
-            ExprKind::IfLet(..) => ExprPrecedence::IfLet,
             ExprKind::While(..) => ExprPrecedence::While,
-            ExprKind::WhileLet(..) => ExprPrecedence::WhileLet,
             ExprKind::ForLoop(..) => ExprPrecedence::ForLoop,
             ExprKind::Loop(..) => ExprPrecedence::Loop,
             ExprKind::Match(..) => ExprPrecedence::Match,
@@ -1102,8 +1115,6 @@ pub enum RangeLimits {
 pub enum ExprKind {
     /// A `box x` expression.
     Box(P<Expr>),
-    /// First expr is the place; second expr is the value.
-    ObsoleteInPlace(P<Expr>, P<Expr>),
     /// An array (`[a, b, c, d]`)
     Array(Vec<P<Expr>>),
     /// A function call
@@ -1135,26 +1146,20 @@ pub enum ExprKind {
     Cast(P<Expr>, P<Ty>),
     /// A type ascription (e.g., `42: usize`).
     Type(P<Expr>, P<Ty>),
+    /// A `let pats = expr` expression that is only semantically allowed in the condition
+    /// of `if` / `while` expressions. (e.g., `if let 0 = x { .. }`).
+    ///
+    /// The `Vec<P<Pat>>` is for or-patterns at the top level.
+    /// FIXME(54883): Change this to just `P<Pat>`.
+    Let(Vec<P<Pat>>, P<Expr>),
     /// An `if` block, with an optional `else` block.
     ///
     /// `if expr { block } else { expr }`
     If(P<Expr>, P<Block>, Option<P<Expr>>),
-    /// An `if let` expression with an optional else block
-    ///
-    /// `if let pat = expr { block } else { expr }`
-    ///
-    /// This is desugared to a `match` expression.
-    IfLet(Vec<P<Pat>>, P<Expr>, P<Block>, Option<P<Expr>>),
-    /// A while loop, with an optional label
+    /// A while loop, with an optional label.
     ///
     /// `'label: while expr { block }`
     While(P<Expr>, P<Block>, Option<Label>),
-    /// A `while let` loop, with an optional label.
-    ///
-    /// `'label: while let pat = expr { block }`
-    ///
-    /// This is desugared to a combination of `loop` and `match` expressions.
-    WhileLet(Vec<P<Pat>>, P<Expr>, P<Block>, Option<Label>),
     /// A `for` loop, with an optional label.
     ///
     /// `'label: for pat in expr { block }`
@@ -1183,7 +1188,7 @@ pub enum ExprKind {
     /// preexisting defs.
     Async(CaptureBy, NodeId, P<Block>),
     /// An await expression (`my_future.await`).
-    Await(AwaitOrigin, P<Expr>),
+    Await(P<Expr>),
 
     /// A try block (`try { ... }`).
     TryBlock(P<Block>),
@@ -1198,7 +1203,7 @@ pub enum ExprKind {
     Field(P<Expr>, Ident),
     /// An indexing operation (e.g., `foo[2]`).
     Index(P<Expr>, P<Expr>),
-    /// A range (e.g., `1..2`, `1..`, `..2`, `1...2`, `1...`, `...2`).
+    /// A range (e.g., `1..2`, `1..`, `..2`, `1..=2`, `..=2`).
     Range(Option<P<Expr>>, Option<P<Expr>>, RangeLimits),
 
     /// Variable reference, possibly containing `::` and/or type
@@ -1286,17 +1291,6 @@ pub enum Movability {
     Movable,
 }
 
-/// Whether an `await` comes from `await!` or `.await` syntax.
-/// FIXME: this should be removed when support for legacy `await!` is removed.
-/// https://github.com/rust-lang/rust/issues/60610
-#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Copy)]
-pub enum AwaitOrigin {
-    FieldLike,
-    MacroLike,
-}
-
-pub type Mac = Spanned<Mac_>;
-
 /// Represents a macro invocation. The `Path` indicates which macro
 /// is being invoked, and the vector of token-trees contains the source
 /// of the macro invocation.
@@ -1304,10 +1298,12 @@ pub type Mac = Spanned<Mac_>;
 /// N.B., the additional ident for a `macro_rules`-style macro is actually
 /// stored in the enclosing item.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
-pub struct Mac_ {
+pub struct Mac {
     pub path: Path,
     pub delim: MacDelimiter,
     pub tts: TokenStream,
+    pub span: Span,
+    pub prior_type_ascription: Option<(Span, bool)>,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Debug)]
@@ -1317,12 +1313,22 @@ pub enum MacDelimiter {
     Brace,
 }
 
-impl Mac_ {
+impl Mac {
     pub fn stream(&self) -> TokenStream {
         self.tts.clone()
     }
 }
 
+impl MacDelimiter {
+    crate fn to_token(self) -> DelimToken {
+        match self {
+            MacDelimiter::Parenthesis => DelimToken::Paren,
+            MacDelimiter::Bracket => DelimToken::Bracket,
+            MacDelimiter::Brace => DelimToken::Brace,
+        }
+    }
+}
+
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct MacroDef {
     pub tokens: TokenStream,
@@ -1350,8 +1356,6 @@ pub enum StrStyle {
 pub struct Lit {
     /// The original literal token as written in source code.
     pub token: token::Lit,
-    /// The original literal suffix as written in source code.
-    pub suffix: Option<Symbol>,
     /// The "semantic" representation of the literal lowered from the original tokens.
     /// Strings are unescaped, hexadecimal forms are eliminated, etc.
     /// FIXME: Remove this and only create the semantic representation during lowering to HIR.
@@ -1387,7 +1391,7 @@ pub enum LitKind {
     FloatUnsuffixed(Symbol),
     /// A boolean literal.
     Bool(bool),
-    /// A recovered character literal that contains mutliple `char`s, most likely a typo.
+    /// Placeholder for a literal that wasn't well-formed in some way.
     Err(Symbol),
 }
 
@@ -1425,10 +1429,10 @@ impl LitKind {
             | LitKind::ByteStr(..)
             | LitKind::Byte(..)
             | LitKind::Char(..)
-            | LitKind::Err(..)
             | LitKind::Int(_, LitIntType::Unsuffixed)
             | LitKind::FloatUnsuffixed(..)
-            | LitKind::Bool(..) => true,
+            | LitKind::Bool(..)
+            | LitKind::Err(..) => true,
             // suffixed variants
             LitKind::Int(_, LitIntType::Signed(..))
             | LitKind::Int(_, LitIntType::Unsigned(..))
@@ -1482,6 +1486,7 @@ pub enum TraitItemKind {
     Macro(Mac),
 }
 
+/// Represents anything within an `impl` block.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct ImplItem {
     pub id: NodeId,
@@ -1496,12 +1501,13 @@ pub struct ImplItem {
     pub tokens: Option<TokenStream>,
 }
 
+/// Represents various kinds of content within an `impl`.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub enum ImplItemKind {
     Const(P<Ty>, P<Expr>),
     Method(MethodSig, P<Block>),
-    Type(P<Ty>),
-    Existential(GenericBounds),
+    TyAlias(P<Ty>),
+    OpaqueTy(GenericBounds),
     Macro(Mac),
 }
 
@@ -1539,6 +1545,17 @@ impl IntTy {
         }
     }
 
+    pub fn to_symbol(&self) -> Symbol {
+        match *self {
+            IntTy::Isize => sym::isize,
+            IntTy::I8 => sym::i8,
+            IntTy::I16 => sym::i16,
+            IntTy::I32 => sym::i32,
+            IntTy::I64 => sym::i64,
+            IntTy::I128 => sym::i128,
+        }
+    }
+
     pub fn val_to_string(&self, val: i128) -> String {
         // Cast to a `u128` so we can correctly print `INT128_MIN`. All integral types
         // are parsed as `u128`, so we wouldn't want to print an extra negative
@@ -1580,6 +1597,17 @@ impl UintTy {
         }
     }
 
+    pub fn to_symbol(&self) -> Symbol {
+        match *self {
+            UintTy::Usize => sym::usize,
+            UintTy::U8 => sym::u8,
+            UintTy::U16 => sym::u16,
+            UintTy::U32 => sym::u32,
+            UintTy::U64 => sym::u64,
+            UintTy::U128 => sym::u128,
+        }
+    }
+
     pub fn val_to_string(&self, val: u128) -> String {
         format!("{}{}", val, self.ty_to_string())
     }
@@ -1608,15 +1636,29 @@ impl fmt::Display for UintTy {
     }
 }
 
-// Bind a type to an associated type: `A = Foo`.
+/// A constraint on an associated type (e.g., `A = Bar` in `Foo<A = Bar>` or
+/// `A: TraitA + TraitB` in `Foo<A: TraitA + TraitB>`).
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
-pub struct TypeBinding {
+pub struct AssocTyConstraint {
     pub id: NodeId,
     pub ident: Ident,
-    pub ty: P<Ty>,
+    pub kind: AssocTyConstraintKind,
     pub span: Span,
 }
 
+/// The kinds of an `AssocTyConstraint`.
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+pub enum AssocTyConstraintKind {
+    /// E.g., `A = Bar` in `Foo<A = Bar>`.
+    Equality {
+        ty: P<Ty>,
+    },
+    /// E.g. `A: TraitA + TraitB` in `Foo<A: TraitA + TraitB>`.
+    Bound {
+        bounds: GenericBounds,
+    },
+}
+
 #[derive(Clone, RustcEncodable, RustcDecodable)]
 pub struct Ty {
     pub id: NodeId,
@@ -1668,7 +1710,7 @@ pub enum TyKind {
     ///
     /// The `NodeId` exists to prevent lowering from having to
     /// generate `NodeId`s on the fly, which would complicate
-    /// the generation of `existential type` items significantly.
+    /// the generation of opaque `type Foo = impl Trait` items significantly.
     ImplTrait(NodeId, GenericBounds),
     /// No-op; kept solely so that we can pretty-print faithfully.
     Paren(P<Ty>),
@@ -1745,7 +1787,6 @@ pub struct InlineAsm {
     pub volatile: bool,
     pub alignstack: bool,
     pub dialect: AsmDialect,
-    pub ctxt: SyntaxContext,
 }
 
 /// An argument in a function header.
@@ -1753,19 +1794,11 @@ pub struct InlineAsm {
 /// E.g., `bar: usize` as in `fn foo(bar: usize)`.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct Arg {
+    pub attrs: ThinVec<Attribute>,
     pub ty: P<Ty>,
     pub pat: P<Pat>,
     pub id: NodeId,
-    pub source: ArgSource,
-}
-
-/// The source of an argument in a function header.
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
-pub enum ArgSource {
-    /// Argument as written by the user.
-    Normal,
-    /// Argument from `async fn` lowering, contains the original binding pattern.
-    AsyncFn(P<Pat>),
+    pub span: Span,
 }
 
 /// Alternative representation for `Arg`s describing `self` parameter of methods.
@@ -1786,7 +1819,7 @@ pub type ExplicitSelf = Spanned<SelfKind>;
 impl Arg {
     pub fn to_self(&self) -> Option<ExplicitSelf> {
         if let PatKind::Ident(BindingMode::ByValue(mutbl), ident, _) = self.pat.node {
-            if ident.name == keywords::SelfLower.name() {
+            if ident.name == kw::SelfLower {
                 return match self.ty.node {
                     TyKind::ImplicitSelf => Some(respan(self.pat.span, SelfKind::Value(mutbl))),
                     TyKind::Rptr(lt, MutTy { ref ty, mutbl }) if ty.node.is_implicit_self() => {
@@ -1804,13 +1837,13 @@ impl Arg {
 
     pub fn is_self(&self) -> bool {
         if let PatKind::Ident(_, ident, _) = self.pat.node {
-            ident.name == keywords::SelfLower.name()
+            ident.name == kw::SelfLower
         } else {
             false
         }
     }
 
-    pub fn from_self(eself: ExplicitSelf, eself_ident: Ident) -> Arg {
+    pub fn from_self(attrs: ThinVec<Attribute>, eself: ExplicitSelf, eself_ident: Ident) -> Arg {
         let span = eself.span.to(eself_ident.span);
         let infer_ty = P(Ty {
             id: DUMMY_NODE_ID,
@@ -1818,14 +1851,15 @@ impl Arg {
             span,
         });
         let arg = |mutbl, ty| Arg {
+            attrs,
             pat: P(Pat {
                 id: DUMMY_NODE_ID,
                 node: PatKind::Ident(BindingMode::ByValue(mutbl), eself_ident, None),
                 span,
             }),
+            span,
             ty,
             id: DUMMY_NODE_ID,
-            source: ArgSource::Normal,
         };
         match eself.node {
             SelfKind::Explicit(ty, mutbl) => arg(mutbl, ty),
@@ -1838,7 +1872,7 @@ impl Arg {
                         lt,
                         MutTy {
                             ty: infer_ty,
-                            mutbl: mutbl,
+                            mutbl,
                         },
                     ),
                     span,
@@ -1848,7 +1882,7 @@ impl Arg {
     }
 }
 
-/// Header (not the body) of a function declaration.
+/// A header (not the body) of a function declaration.
 ///
 /// E.g., `fn foo(bar: baz)`.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
@@ -1880,39 +1914,18 @@ pub enum Unsafety {
     Normal,
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
-pub struct AsyncArgument {
-    /// `__arg0`
-    pub ident: Ident,
-    /// `__arg0: <ty>` argument to replace existing function argument `<pat>: <ty>`. Only if
-    /// argument is not a simple binding.
-    pub arg: Option<Arg>,
-    /// `let __arg0 = __arg0;` statement to be inserted at the start of the block.
-    pub move_stmt: Stmt,
-    /// `let <pat> = __arg0;` statement to be inserted at the start of the block, after matching
-    /// move statement. Only if argument is not a simple binding.
-    pub pat_stmt: Option<Stmt>,
-}
-
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Copy, Clone, RustcEncodable, RustcDecodable, Debug)]
 pub enum IsAsync {
     Async {
         closure_id: NodeId,
         return_impl_trait_id: NodeId,
-        /// This field stores the arguments and statements that are used in HIR lowering to
-        /// ensure that `async fn` arguments are dropped at the correct time.
-        ///
-        /// The argument and statements here are generated at parse time as they are required in
-        /// both the hir lowering, def collection and name resolution and this stops them needing
-        /// to be created in each place.
-        arguments: Vec<AsyncArgument>,
     },
     NotAsync,
 }
 
 impl IsAsync {
-    pub fn is_async(&self) -> bool {
-        if let IsAsync::Async { .. } = *self {
+    pub fn is_async(self) -> bool {
+        if let IsAsync::Async { .. } = self {
             true
         } else {
             false
@@ -1920,12 +1933,12 @@ impl IsAsync {
     }
 
     /// In ths case this is an `async` return, the `NodeId` for the generated `impl Trait` item.
-    pub fn opt_return_id(&self) -> Option<NodeId> {
+    pub fn opt_return_id(self) -> Option<NodeId> {
         match self {
             IsAsync::Async {
                 return_impl_trait_id,
                 ..
-            } => Some(*return_impl_trait_id),
+            } => Some(return_impl_trait_id),
             IsAsync::NotAsync => None,
         }
     }
@@ -2021,7 +2034,6 @@ pub struct ForeignMod {
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug, Copy)]
 pub struct GlobalAsm {
     pub asm: Symbol,
-    pub ctxt: SyntaxContext,
 }
 
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
@@ -2030,7 +2042,7 @@ pub struct EnumDef {
 }
 
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
-pub struct Variant_ {
+pub struct Variant {
     /// Name of the variant.
     pub ident: Ident,
     /// Attributes of the variant.
@@ -2041,10 +2053,10 @@ pub struct Variant_ {
     pub data: VariantData,
     /// Explicit discriminant, e.g., `Foo = 1`.
     pub disr_expr: Option<AnonConst>,
+    /// Span
+    pub span: Span,
 }
 
-pub type Variant = Spanned<Variant_>;
-
 /// Part of `use` item to the right of its prefix.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub enum UseTreeKind {
@@ -2093,9 +2105,7 @@ pub enum AttrStyle {
     Inner,
 }
 
-#[derive(
-    Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, PartialOrd, Ord, Copy,
-)]
+#[derive(Clone, PartialEq, Eq, Hash, Debug, PartialOrd, Ord, Copy)]
 pub struct AttrId(pub usize);
 
 impl Idx for AttrId {
@@ -2107,6 +2117,18 @@ impl Idx for AttrId {
     }
 }
 
+impl rustc_serialize::Encodable for AttrId {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_unit()
+    }
+}
+
+impl rustc_serialize::Decodable for AttrId {
+    fn decode<D: Decoder>(d: &mut D) -> Result<AttrId, D::Error> {
+        d.read_nil().map(|_| crate::attr::mk_attr_id())
+    }
+}
+
 /// Metadata associated with an item.
 /// Doc-comments are promoted to attributes that have `is_sugared_doc = true`.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
@@ -2133,10 +2155,10 @@ pub struct TraitRef {
 
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct PolyTraitRef {
-    /// The `'a` in `<'a> Foo<&'a T>`
+    /// The `'a` in `<'a> Foo<&'a T>`.
     pub bound_generic_params: Vec<GenericParam>,
 
-    /// The `Foo<&'a T>` in `<'a> Foo<&'a T>`
+    /// The `Foo<&'a T>` in `<'a> Foo<&'a T>`.
     pub trait_ref: TraitRef,
 
     pub span: Span,
@@ -2147,7 +2169,7 @@ impl PolyTraitRef {
         PolyTraitRef {
             bound_generic_params: generic_params,
             trait_ref: TraitRef {
-                path: path,
+                path,
                 ref_id: DUMMY_NODE_ID,
             },
             span,
@@ -2265,7 +2287,7 @@ impl Item {
 ///
 /// All the information between the visibility and the name of the function is
 /// included in this struct (e.g., `async unsafe fn` or `const extern "C" fn`).
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Clone, Copy, RustcEncodable, RustcDecodable, Debug)]
 pub struct FnHeader {
     pub unsafety: Unsafety,
     pub asyncness: Spanned<IsAsync>,
@@ -2319,11 +2341,11 @@ pub enum ItemKind {
     /// A type alias (`type` or `pub type`).
     ///
     /// E.g., `type Foo = Bar<u8>;`.
-    Ty(P<Ty>, Generics),
-    /// An existential type declaration (`existential type`).
+    TyAlias(P<Ty>, Generics),
+    /// An opaque `impl Trait` type alias.
     ///
-    /// E.g., `existential type Foo: Bar + Boo;`.
-    Existential(GenericBounds, Generics),
+    /// E.g., `type Foo = impl Bar + Boo;`.
+    OpaqueTy(GenericBounds, Generics),
     /// An enum definition (`enum` or `pub enum`).
     ///
     /// E.g., `enum Foo<A, B> { C<A>, D<B> }`.
@@ -2376,8 +2398,8 @@ impl ItemKind {
             ItemKind::Mod(..) => "module",
             ItemKind::ForeignMod(..) => "foreign module",
             ItemKind::GlobalAsm(..) => "global asm",
-            ItemKind::Ty(..) => "type alias",
-            ItemKind::Existential(..) => "existential type",
+            ItemKind::TyAlias(..) => "type alias",
+            ItemKind::OpaqueTy(..) => "opaque type",
             ItemKind::Enum(..) => "enum",
             ItemKind::Struct(..) => "struct",
             ItemKind::Union(..) => "union",
@@ -2421,16 +2443,3 @@ impl ForeignItemKind {
         }
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use serialize;
-
-    // Are ASTs encodable?
-    #[test]
-    fn check_asts_encodable() {
-        fn assert_encodable<T: serialize::Encodable>() {}
-        assert_encodable::<Crate>();
-    }
-}
diff --git a/src/libsyntax/ast/tests.rs b/src/libsyntax/ast/tests.rs
new file mode 100644
index 00000000000..7558e9cc3a3
--- /dev/null
+++ b/src/libsyntax/ast/tests.rs
@@ -0,0 +1,8 @@
+use super::*;
+
+// Are ASTs encodable?
+#[test]
+fn check_asts_encodable() {
+    fn assert_encodable<T: rustc_serialize::Encodable>() {}
+    assert_encodable::<Crate>();
+}
diff --git a/src/libsyntax/attr/builtin.rs b/src/libsyntax/attr/builtin.rs
index 65ca96afab1..5fb513783fb 100644
--- a/src/libsyntax/attr/builtin.rs
+++ b/src/libsyntax/attr/builtin.rs
@@ -1,10 +1,13 @@
 //! Parsing and validation of builtin attributes
 
 use crate::ast::{self, Attribute, MetaItem, NestedMetaItem};
+use crate::early_buffered_lints::BufferedEarlyLintId;
+use crate::ext::base::ExtCtxt;
 use crate::feature_gate::{Features, GatedCfg};
 use crate::parse::ParseSess;
 
 use errors::{Applicability, Handler};
+use syntax_pos::hygiene::Transparency;
 use syntax_pos::{symbol::Symbol, symbol::sym, Span};
 
 use super::{mark_used, MetaItemKind};
@@ -18,6 +21,27 @@ enum AttrError {
     UnsupportedLiteral(&'static str, /* is_bytestr */ bool),
 }
 
+/// A template that the attribute input must match.
+/// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
+#[derive(Clone, Copy)]
+pub struct AttributeTemplate {
+    crate word: bool,
+    crate list: Option<&'static str>,
+    crate name_value_str: Option<&'static str>,
+}
+
+impl AttributeTemplate {
+    /// Checks that the given meta-item is compatible with this template.
+    fn compatible(&self, meta_item_kind: &ast::MetaItemKind) -> bool {
+        match meta_item_kind {
+            ast::MetaItemKind::Word => self.word,
+            ast::MetaItemKind::List(..) => self.list.is_some(),
+            ast::MetaItemKind::NameValue(lit) if lit.node.is_str() => self.name_value_str.is_some(),
+            ast::MetaItemKind::NameValue(..) => false,
+        }
+    }
+}
+
 fn handle_errors(sess: &ParseSess, span: Span, error: AttrError) {
     let diag = &sess.span_diagnostic;
     match error {
@@ -92,7 +116,15 @@ pub fn find_unwind_attr(diagnostic: Option<&Handler>, attrs: &[Attribute]) -> Op
                     }
 
                     diagnostic.map(|d| {
-                        span_err!(d, attr.span, E0633, "malformed `#[unwind]` attribute");
+                        struct_span_err!(d, attr.span, E0633, "malformed `unwind` attribute input")
+                            .span_label(attr.span, "invalid argument")
+                            .span_suggestions(
+                                attr.span,
+                                "the allowed arguments are `allowed` and `aborts`",
+                                (vec!["allowed", "aborts"]).into_iter()
+                                    .map(|s| format!("#[unwind({})]", s)),
+                                Applicability::MachineApplicable,
+                            ).emit();
                     });
                 }
             }
@@ -103,7 +135,7 @@ pub fn find_unwind_attr(diagnostic: Option<&Handler>, attrs: &[Attribute]) -> Op
 }
 
 /// Represents the #[stable], #[unstable], #[rustc_{deprecated,const_unstable}] attributes.
-#[derive(RustcEncodable, RustcDecodable, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(RustcEncodable, RustcDecodable, Copy, Clone, Debug, PartialEq, Eq, Hash)]
 pub struct Stability {
     pub level: StabilityLevel,
     pub feature: Symbol,
@@ -119,13 +151,26 @@ pub struct Stability {
 }
 
 /// The available stability levels.
-#[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Clone, Debug, Eq, Hash)]
+#[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Copy, Clone, Debug, Eq, Hash)]
 pub enum StabilityLevel {
     // Reason for the current stability level and the relevant rust-lang issue
     Unstable { reason: Option<Symbol>, issue: u32 },
     Stable { since: Symbol },
 }
 
+impl Stability {
+    pub fn unstable(feature: Symbol, reason: Option<Symbol>, issue: u32) -> Stability {
+        Stability {
+            level: StabilityLevel::Unstable { reason, issue },
+            feature,
+            rustc_depr: None,
+            const_stability: None,
+            promotable: false,
+            allow_const_fn_ptr: false,
+        }
+    }
+}
+
 impl StabilityLevel {
     pub fn is_unstable(&self) -> bool {
         if let StabilityLevel::Unstable {..} = *self {
@@ -143,7 +188,7 @@ impl StabilityLevel {
     }
 }
 
-#[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Clone, Debug, Eq, Hash)]
+#[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Copy, Clone, Debug, Eq, Hash)]
 pub struct RustcDeprecation {
     pub since: Symbol,
     pub reason: Symbol,
@@ -162,7 +207,8 @@ pub fn contains_feature_attr(attrs: &[Attribute], feature_name: Symbol) -> bool
     })
 }
 
-/// Finds the first stability attribute. `None` if none exists.
+/// Collects stability info from all stability attributes in `attrs`.
+/// Returns `None` if no stability attributes are found.
 pub fn find_stability(sess: &ParseSess, attrs: &[Attribute],
                       item_sp: Span) -> Option<Stability> {
     find_stability_generic(sess, attrs.iter(), item_sp)
@@ -846,3 +892,108 @@ fn int_type_of_word(s: Symbol) -> Option<IntType> {
         _ => None
     }
 }
+
+pub enum TransparencyError {
+    UnknownTransparency(Symbol, Span),
+    MultipleTransparencyAttrs(Span, Span),
+}
+
+pub fn find_transparency(
+    attrs: &[Attribute], is_legacy: bool
+) -> (Transparency, Option<TransparencyError>) {
+    let mut transparency = None;
+    let mut error = None;
+    for attr in attrs {
+        if attr.check_name(sym::rustc_macro_transparency) {
+            if let Some((_, old_span)) = transparency {
+                error = Some(TransparencyError::MultipleTransparencyAttrs(old_span, attr.span));
+                break;
+            } else if let Some(value) = attr.value_str() {
+                transparency = Some((match &*value.as_str() {
+                    "transparent" => Transparency::Transparent,
+                    "semitransparent" => Transparency::SemiTransparent,
+                    "opaque" => Transparency::Opaque,
+                    _ => {
+                        error = Some(TransparencyError::UnknownTransparency(value, attr.span));
+                        continue;
+                    }
+                }, attr.span));
+            }
+        }
+    }
+    let fallback = if is_legacy { Transparency::SemiTransparent } else { Transparency::Opaque };
+    (transparency.map_or(fallback, |t| t.0), error)
+}
+
+pub fn check_builtin_macro_attribute(ecx: &ExtCtxt<'_>, meta_item: &MetaItem, name: Symbol) {
+    // All the built-in macro attributes are "words" at the moment.
+    let template = AttributeTemplate { word: true, list: None, name_value_str: None };
+    let attr = ecx.attribute(meta_item.clone());
+    check_builtin_attribute(ecx.parse_sess, &attr, name, template);
+}
+
+crate fn check_builtin_attribute(
+    sess: &ParseSess, attr: &ast::Attribute, name: Symbol, template: AttributeTemplate
+) {
+    // Some special attributes like `cfg` must be checked
+    // before the generic check, so we skip them here.
+    let should_skip = |name| name == sym::cfg;
+    // Some of previously accepted forms were used in practice,
+    // report them as warnings for now.
+    let should_warn = |name| name == sym::doc || name == sym::ignore ||
+                             name == sym::inline || name == sym::link ||
+                             name == sym::test || name == sym::bench;
+
+    match attr.parse_meta(sess) {
+        Ok(meta) => if !should_skip(name) && !template.compatible(&meta.node) {
+            let error_msg = format!("malformed `{}` attribute input", name);
+            let mut msg = "attribute must be of the form ".to_owned();
+            let mut suggestions = vec![];
+            let mut first = true;
+            if template.word {
+                first = false;
+                let code = format!("#[{}]", name);
+                msg.push_str(&format!("`{}`", &code));
+                suggestions.push(code);
+            }
+            if let Some(descr) = template.list {
+                if !first {
+                    msg.push_str(" or ");
+                }
+                first = false;
+                let code = format!("#[{}({})]", name, descr);
+                msg.push_str(&format!("`{}`", &code));
+                suggestions.push(code);
+            }
+            if let Some(descr) = template.name_value_str {
+                if !first {
+                    msg.push_str(" or ");
+                }
+                let code = format!("#[{} = \"{}\"]", name, descr);
+                msg.push_str(&format!("`{}`", &code));
+                suggestions.push(code);
+            }
+            if should_warn(name) {
+                sess.buffer_lint(
+                    BufferedEarlyLintId::IllFormedAttributeInput,
+                    meta.span,
+                    ast::CRATE_NODE_ID,
+                    &msg,
+                );
+            } else {
+                sess.span_diagnostic.struct_span_err(meta.span, &error_msg)
+                    .span_suggestions(
+                        meta.span,
+                        if suggestions.len() == 1 {
+                            "must be of the form"
+                        } else {
+                            "the following are the possible correct uses"
+                        },
+                        suggestions.into_iter(),
+                        Applicability::HasPlaceholders,
+                    ).emit();
+            }
+        }
+        Err(mut err) => err.emit(),
+    }
+}
diff --git a/src/libsyntax/attr/mod.rs b/src/libsyntax/attr/mod.rs
index 592b40df176..bcf03b5237a 100644
--- a/src/libsyntax/attr/mod.rs
+++ b/src/libsyntax/attr/mod.rs
@@ -2,27 +2,24 @@
 
 mod builtin;
 
-pub use builtin::{
-    cfg_matches, contains_feature_attr, eval_condition, find_crate_name, find_deprecation,
-    find_repr_attrs, find_stability, find_unwind_attr, Deprecation, InlineAttr, OptimizeAttr,
-    IntType, ReprAttr, RustcDeprecation, Stability, StabilityLevel, UnwindAttr,
-};
+pub use builtin::*;
 pub use IntType::*;
 pub use ReprAttr::*;
 pub use StabilityLevel::*;
+pub use crate::ast::Attribute;
 
 use crate::ast;
-use crate::ast::{AttrId, Attribute, AttrStyle, Name, Ident, Path, PathSegment};
+use crate::ast::{AttrId, AttrStyle, Name, Ident, Path, PathSegment};
 use crate::ast::{MetaItem, MetaItemKind, NestedMetaItem};
 use crate::ast::{Lit, LitKind, Expr, Item, Local, Stmt, StmtKind, GenericParam};
 use crate::mut_visit::visit_clobber;
-use crate::source_map::{BytePos, Spanned, dummy_spanned};
+use crate::source_map::{BytePos, Spanned, DUMMY_SP};
 use crate::parse::lexer::comments::{doc_comment_style, strip_doc_comment_decoration};
 use crate::parse::parser::Parser;
 use crate::parse::{self, ParseSess, PResult};
 use crate::parse::token::{self, Token};
 use crate::ptr::P;
-use crate::symbol::{keywords, Symbol, sym};
+use crate::symbol::{sym, Symbol};
 use crate::ThinVec;
 use crate::tokenstream::{TokenStream, TokenTree, DelimSpan};
 use crate::GLOBALS;
@@ -34,7 +31,7 @@ use std::iter;
 use std::ops::DerefMut;
 
 pub fn mark_used(attr: &Attribute) {
-    debug!("Marking {:?} as used.", attr);
+    debug!("marking {:?} as used", attr);
     GLOBALS.with(|globals| {
         globals.used_attrs.lock().insert(attr.id);
     });
@@ -47,7 +44,7 @@ pub fn is_used(attr: &Attribute) -> bool {
 }
 
 pub fn mark_known(attr: &Attribute) {
-    debug!("Marking {:?} as known.", attr);
+    debug!("marking {:?} as known", attr);
     GLOBALS.with(|globals| {
         globals.known_attrs.lock().insert(attr.id);
     });
@@ -60,7 +57,7 @@ pub fn is_known(attr: &Attribute) -> bool {
 }
 
 pub fn is_known_lint_tool(m_item: Ident) -> bool {
-    ["clippy"].contains(&m_item.as_str().as_ref())
+    [sym::clippy, sym::rustc].contains(&m_item.name)
 }
 
 impl NestedMetaItem {
@@ -90,7 +87,7 @@ impl NestedMetaItem {
         self.meta_item().and_then(|meta_item| meta_item.ident())
     }
     pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or(keywords::Invalid.ident()).name
+        self.ident().unwrap_or(Ident::invalid()).name
     }
 
     /// Gets the string value if self is a MetaItem and the MetaItem is a
@@ -168,7 +165,7 @@ impl Attribute {
         }
     }
     pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or(keywords::Invalid.ident()).name
+        self.ident().unwrap_or(Ident::invalid()).name
     }
 
     pub fn value_str(&self) -> Option<Symbol> {
@@ -206,7 +203,7 @@ impl MetaItem {
         }
     }
     pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or(keywords::Invalid.ident()).name
+        self.ident().unwrap_or(Ident::invalid()).name
     }
 
     // #[attribute(name = "value")]
@@ -278,7 +275,14 @@ impl Attribute {
     pub fn parse<'a, T, F>(&self, sess: &'a ParseSess, mut f: F) -> PResult<'a, T>
         where F: FnMut(&mut Parser<'a>) -> PResult<'a, T>,
     {
-        let mut parser = Parser::new(sess, self.tokens.clone(), None, false, false);
+        let mut parser = Parser::new(
+            sess,
+            self.tokens.clone(),
+            None,
+            false,
+            false,
+            Some("attribute"),
+        );
         let result = f(&mut parser)?;
         if parser.token != token::Eof {
             parser.unexpected()?;
@@ -323,15 +327,18 @@ impl Attribute {
         if self.is_sugared_doc {
             let comment = self.value_str().unwrap();
             let meta = mk_name_value_item_str(
-                Ident::with_empty_ctxt(sym::doc),
-                dummy_spanned(Symbol::intern(&strip_doc_comment_decoration(&comment.as_str()))));
-            let mut attr = if self.style == ast::AttrStyle::Outer {
-                mk_attr_outer(self.span, self.id, meta)
-            } else {
-                mk_attr_inner(self.span, self.id, meta)
-            };
-            attr.is_sugared_doc = true;
-            f(&attr)
+                Ident::with_dummy_span(sym::doc),
+                Symbol::intern(&strip_doc_comment_decoration(&comment.as_str())),
+                DUMMY_SP,
+            );
+            f(&Attribute {
+                id: self.id,
+                style: self.style,
+                path: meta.path,
+                tokens: meta.node.tokens(meta.span),
+                is_sugared_doc: true,
+                span: self.span,
+            })
         } else {
             f(self)
         }
@@ -340,18 +347,19 @@ impl Attribute {
 
 /* Constructors */
 
-pub fn mk_name_value_item_str(ident: Ident, value: Spanned<Symbol>) -> MetaItem {
-    let lit_kind = LitKind::Str(value.node, ast::StrStyle::Cooked);
-    mk_name_value_item(ident.span.to(value.span), ident, lit_kind, value.span)
+pub fn mk_name_value_item_str(ident: Ident, str: Symbol, str_span: Span) -> MetaItem {
+    let lit_kind = LitKind::Str(str, ast::StrStyle::Cooked);
+    mk_name_value_item(ident, lit_kind, str_span)
 }
 
-pub fn mk_name_value_item(span: Span, ident: Ident, lit_kind: LitKind, lit_span: Span) -> MetaItem {
+pub fn mk_name_value_item(ident: Ident, lit_kind: LitKind, lit_span: Span) -> MetaItem {
     let lit = Lit::from_lit_kind(lit_kind, lit_span);
+    let span = ident.span.to(lit_span);
     MetaItem { path: Path::from_ident(ident), span, node: MetaItemKind::NameValue(lit) }
 }
 
-pub fn mk_list_item(span: Span, ident: Ident, items: Vec<NestedMetaItem>) -> MetaItem {
-    MetaItem { path: Path::from_ident(ident), span, node: MetaItemKind::List(items) }
+pub fn mk_list_item(ident: Ident, items: Vec<NestedMetaItem>) -> MetaItem {
+    MetaItem { path: Path::from_ident(ident), span: ident.span, node: MetaItemKind::List(items) }
 }
 
 pub fn mk_word_item(ident: Ident) -> MetaItem {
@@ -362,7 +370,7 @@ pub fn mk_nested_word_item(ident: Ident) -> NestedMetaItem {
     NestedMetaItem::MetaItem(mk_word_item(ident))
 }
 
-pub fn mk_attr_id() -> AttrId {
+crate fn mk_attr_id() -> AttrId {
     use std::sync::atomic::AtomicUsize;
     use std::sync::atomic::Ordering;
 
@@ -373,48 +381,38 @@ pub fn mk_attr_id() -> AttrId {
     AttrId(id)
 }
 
-/// Returns an inner attribute with the given value.
-pub fn mk_attr_inner(span: Span, id: AttrId, item: MetaItem) -> Attribute {
-    mk_spanned_attr_inner(span, id, item)
-}
-
 /// Returns an inner attribute with the given value and span.
-pub fn mk_spanned_attr_inner(sp: Span, id: AttrId, item: MetaItem) -> Attribute {
+pub fn mk_attr_inner(item: MetaItem) -> Attribute {
     Attribute {
-        id,
+        id: mk_attr_id(),
         style: ast::AttrStyle::Inner,
         path: item.path,
         tokens: item.node.tokens(item.span),
         is_sugared_doc: false,
-        span: sp,
+        span: item.span,
     }
 }
 
-/// Returns an outer attribute with the given value.
-pub fn mk_attr_outer(span: Span, id: AttrId, item: MetaItem) -> Attribute {
-    mk_spanned_attr_outer(span, id, item)
-}
-
 /// Returns an outer attribute with the given value and span.
-pub fn mk_spanned_attr_outer(sp: Span, id: AttrId, item: MetaItem) -> Attribute {
+pub fn mk_attr_outer(item: MetaItem) -> Attribute {
     Attribute {
-        id,
+        id: mk_attr_id(),
         style: ast::AttrStyle::Outer,
         path: item.path,
         tokens: item.node.tokens(item.span),
         is_sugared_doc: false,
-        span: sp,
+        span: item.span,
     }
 }
 
-pub fn mk_sugared_doc_attr(id: AttrId, text: Symbol, span: Span) -> Attribute {
+pub fn mk_sugared_doc_attr(text: Symbol, span: Span) -> Attribute {
     let style = doc_comment_style(&text.as_str());
     let lit_kind = LitKind::Str(text, ast::StrStyle::Cooked);
     let lit = Lit::from_lit_kind(lit_kind, span);
     Attribute {
-        id,
+        id: mk_attr_id(),
         style,
-        path: Path::from_ident(Ident::with_empty_ctxt(sym::doc).with_span_pos(span)),
+        path: Path::from_ident(Ident::with_dummy_span(sym::doc).with_span_pos(span)),
         tokens: MetaItemKind::NameValue(lit).tokens(span),
         is_sugared_doc: true,
         span,
@@ -433,12 +431,12 @@ pub fn contains_name(attrs: &[Attribute], name: Symbol) -> bool {
     })
 }
 
-pub fn find_by_name<'a>(attrs: &'a [Attribute], name: Symbol) -> Option<&'a Attribute> {
+pub fn find_by_name(attrs: &[Attribute], name: Symbol) -> Option<&Attribute> {
     attrs.iter().find(|attr| attr.check_name(name))
 }
 
-pub fn filter_by_name<'a>(attrs: &'a [Attribute], name: Symbol)
-    -> impl Iterator<Item = &'a Attribute> {
+pub fn filter_by_name(attrs: &[Attribute], name: Symbol)
+                      -> impl Iterator<Item=&Attribute> {
     attrs.iter().filter(move |attr| attr.check_name(name))
 }
 
@@ -458,10 +456,9 @@ impl MetaItem {
                 let mod_sep_span = Span::new(last_pos,
                                              segment.ident.span.lo(),
                                              segment.ident.span.ctxt());
-                idents.push(TokenTree::Token(mod_sep_span, Token::ModSep).into());
+                idents.push(TokenTree::token(token::ModSep, mod_sep_span).into());
             }
-            idents.push(TokenTree::Token(segment.ident.span,
-                                         Token::from_ast_ident(segment.ident)).into());
+            idents.push(TokenTree::Token(Token::from_ast_ident(segment.ident)).into());
             last_pos = segment.ident.span.hi();
         }
         self.node.tokens(self.span).append_to_tree_and_joint_vec(&mut idents);
@@ -473,26 +470,28 @@ impl MetaItem {
     {
         // FIXME: Share code with `parse_path`.
         let path = match tokens.next() {
-            Some(TokenTree::Token(span, token @ Token::Ident(..))) |
-            Some(TokenTree::Token(span, token @ Token::ModSep)) => 'arm: {
-                let mut segments = if let Token::Ident(ident, _) = token {
-                    if let Some(TokenTree::Token(_, Token::ModSep)) = tokens.peek() {
+            Some(TokenTree::Token(Token { kind: kind @ token::Ident(..), span })) |
+            Some(TokenTree::Token(Token { kind: kind @ token::ModSep, span })) => 'arm: {
+                let mut segments = if let token::Ident(name, _) = kind {
+                    if let Some(TokenTree::Token(Token { kind: token::ModSep, .. }))
+                            = tokens.peek() {
                         tokens.next();
-                        vec![PathSegment::from_ident(ident.with_span_pos(span))]
+                        vec![PathSegment::from_ident(Ident::new(name, span))]
                     } else {
-                        break 'arm Path::from_ident(ident.with_span_pos(span));
+                        break 'arm Path::from_ident(Ident::new(name, span));
                     }
                 } else {
                     vec![PathSegment::path_root(span)]
                 };
                 loop {
-                    if let Some(TokenTree::Token(span,
-                                                    Token::Ident(ident, _))) = tokens.next() {
-                        segments.push(PathSegment::from_ident(ident.with_span_pos(span)));
+                    if let Some(TokenTree::Token(Token { kind: token::Ident(name, _), span }))
+                            = tokens.next() {
+                        segments.push(PathSegment::from_ident(Ident::new(name, span)));
                     } else {
                         return None;
                     }
-                    if let Some(TokenTree::Token(_, Token::ModSep)) = tokens.peek() {
+                    if let Some(TokenTree::Token(Token { kind: token::ModSep, .. }))
+                            = tokens.peek() {
                         tokens.next();
                     } else {
                         break;
@@ -501,7 +500,7 @@ impl MetaItem {
                 let span = span.with_hi(segments.last().unwrap().ident.span.hi());
                 Path { span, segments }
             }
-            Some(TokenTree::Token(_, Token::Interpolated(nt))) => match *nt {
+            Some(TokenTree::Token(Token { kind: token::Interpolated(nt), .. })) => match *nt {
                 token::Nonterminal::NtIdent(ident, _) => Path::from_ident(ident),
                 token::Nonterminal::NtMeta(ref meta) => return Some(meta.clone()),
                 token::Nonterminal::NtPath(ref path) => path.clone(),
@@ -526,7 +525,7 @@ impl MetaItemKind {
         match *self {
             MetaItemKind::Word => TokenStream::empty(),
             MetaItemKind::NameValue(ref lit) => {
-                let mut vec = vec![TokenTree::Token(span, Token::Eq).into()];
+                let mut vec = vec![TokenTree::token(token::Eq, span).into()];
                 lit.tokens().append_to_tree_and_joint_vec(&mut vec);
                 TokenStream::new(vec)
             }
@@ -534,7 +533,7 @@ impl MetaItemKind {
                 let mut tokens = Vec::new();
                 for (i, item) in list.iter().enumerate() {
                     if i > 0 {
-                        tokens.push(TokenTree::Token(span, Token::Comma).into());
+                        tokens.push(TokenTree::token(token::Comma, span).into());
                     }
                     item.tokens().append_to_tree_and_joint_vec(&mut tokens);
                 }
@@ -551,10 +550,10 @@ impl MetaItemKind {
         where I: Iterator<Item = TokenTree>,
     {
         let delimited = match tokens.peek().cloned() {
-            Some(TokenTree::Token(_, token::Eq)) => {
+            Some(TokenTree::Token(token)) if token == token::Eq => {
                 tokens.next();
-                return if let Some(TokenTree::Token(span, token)) = tokens.next() {
-                    Lit::from_token(&token, span, None).map(MetaItemKind::NameValue)
+                return if let Some(TokenTree::Token(token)) = tokens.next() {
+                    Lit::from_token(&token).ok().map(MetaItemKind::NameValue)
                 } else {
                     None
                 };
@@ -572,7 +571,7 @@ impl MetaItemKind {
             let item = NestedMetaItem::from_tokens(&mut tokens)?;
             result.push(item);
             match tokens.next() {
-                None | Some(TokenTree::Token(_, Token::Comma)) => {}
+                None | Some(TokenTree::Token(Token { kind: token::Comma, .. })) => {}
                 _ => return None,
             }
         }
@@ -598,8 +597,8 @@ impl NestedMetaItem {
     fn from_tokens<I>(tokens: &mut iter::Peekable<I>) -> Option<NestedMetaItem>
         where I: Iterator<Item = TokenTree>,
     {
-        if let Some(TokenTree::Token(span, token)) = tokens.peek().cloned() {
-            if let Some(lit) = Lit::from_token(&token, span, None) {
+        if let Some(TokenTree::Token(token)) = tokens.peek() {
+            if let Ok(lit) = Lit::from_token(token) {
                 tokens.next();
                 return Some(NestedMetaItem::Literal(lit));
             }
@@ -715,7 +714,7 @@ macro_rules! derive_has_attrs {
 
 derive_has_attrs! {
     Item, Expr, Local, ast::ForeignItem, ast::StructField, ast::ImplItem, ast::TraitItem, ast::Arm,
-    ast::Field, ast::FieldPat, ast::Variant_
+    ast::Field, ast::FieldPat, ast::Variant, ast::Arg
 }
 
 pub fn inject(mut krate: ast::Crate, parse_sess: &ParseSess, attrs: &[String]) -> ast::Crate {
@@ -726,9 +725,9 @@ pub fn inject(mut krate: ast::Crate, parse_sess: &ParseSess, attrs: &[String]) -
             raw_attr.clone(),
         );
 
-        let start_span = parser.span;
+        let start_span = parser.token.span;
         let (path, tokens) = panictry!(parser.parse_meta_item_unrestricted());
-        let end_span = parser.span;
+        let end_span = parser.token.span;
         if parser.token != token::Eof {
             parse_sess.span_diagnostic
                 .span_err(start_span.to(end_span), "invalid crate attribute");
diff --git a/src/libsyntax/config.rs b/src/libsyntax/config.rs
index c82936afa3d..7eeea4e7bdf 100644
--- a/src/libsyntax/config.rs
+++ b/src/libsyntax/config.rs
@@ -91,9 +91,25 @@ impl<'a> StripUnconfigured<'a> {
     /// is in the original source file. Gives a compiler error if the syntax of
     /// the attribute is incorrect.
     fn process_cfg_attr(&mut self, attr: ast::Attribute) -> Vec<ast::Attribute> {
-        if !attr.check_name(sym::cfg_attr) {
+        if attr.path != sym::cfg_attr {
             return vec![attr];
         }
+        if attr.tokens.is_empty() {
+            self.sess.span_diagnostic
+                .struct_span_err(
+                    attr.span,
+                    "malformed `cfg_attr` attribute input",
+                ).span_suggestion(
+                    attr.span,
+                    "missing condition and attribute",
+                    "#[cfg_attr(condition, attribute, other_attribute, ...)]".to_owned(),
+                    Applicability::HasPlaceholders,
+                ).note("for more information, visit \
+                       <https://doc.rust-lang.org/reference/conditional-compilation.html\
+                       #the-cfg_attr-attribute>")
+                .emit();
+            return vec![];
+        }
 
         let (cfg_predicate, expanded_attrs) = match attr.parse(self.sess, |parser| {
             parser.expect(&token::OpenDelim(token::Paren))?;
@@ -105,7 +121,7 @@ impl<'a> StripUnconfigured<'a> {
             let mut expanded_attrs = Vec::with_capacity(1);
 
             while !parser.check(&token::CloseDelim(token::Paren)) {
-                let lo = parser.span.lo();
+                let lo = parser.token.span.lo();
                 let (path, tokens) = parser.parse_meta_item_unrestricted()?;
                 expanded_attrs.push((path, tokens, parser.prev_span.with_lo(lo)));
                 parser.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Paren)])?;
@@ -117,17 +133,18 @@ impl<'a> StripUnconfigured<'a> {
             Ok(result) => result,
             Err(mut e) => {
                 e.emit();
-                return Vec::new();
+                return vec![];
             }
         };
 
-        // Check feature gate and lint on zero attributes in source. Even if the feature is gated,
-        // we still compute as if it wasn't, since the emitted error will stop compilation further
-        // along the compilation.
-        if expanded_attrs.len() == 0 {
-            // FIXME: Emit unused attribute lint here.
+        // Lint on zero attributes in source.
+        if expanded_attrs.is_empty() {
+            return vec![attr];
         }
 
+        // At this point we know the attribute is considered used.
+        attr::mark_used(&attr);
+
         if attr::cfg_matches(&cfg_predicate, self.sess, self.features) {
             // We call `process_cfg_attr` recursively in case there's a
             // `cfg_attr` inside of another `cfg_attr`. E.g.
@@ -143,7 +160,7 @@ impl<'a> StripUnconfigured<'a> {
             }))
             .collect()
         } else {
-            Vec::new()
+            vec![]
         }
     }
 
@@ -224,6 +241,10 @@ impl<'a> StripUnconfigured<'a> {
         items.flat_map_in_place(|item| self.configure(item));
     }
 
+    pub fn configure_generic_params(&mut self, params: &mut Vec<ast::GenericParam>) {
+        params.flat_map_in_place(|param| self.configure(param));
+    }
+
     fn configure_variant_data(&mut self, vdata: &mut ast::VariantData) {
         match vdata {
             ast::VariantData::Struct(fields, ..) | ast::VariantData::Tuple(fields, _) =>
@@ -239,7 +260,7 @@ impl<'a> StripUnconfigured<'a> {
             ast::ItemKind::Enum(ast::EnumDef { variants }, _generics) => {
                 variants.flat_map_in_place(|variant| self.configure(variant));
                 for variant in variants {
-                    self.configure_variant_data(&mut variant.node.data);
+                    self.configure_variant_data(&mut variant.data);
                 }
             }
             _ => {}
@@ -282,20 +303,8 @@ impl<'a> StripUnconfigured<'a> {
         }
     }
 
-    /// Denies `#[cfg]` on generic parameters until we decide what to do with it.
-    /// See issue #51279.
-    pub fn disallow_cfg_on_generic_param(&mut self, param: &ast::GenericParam) {
-        for attr in param.attrs() {
-            let offending_attr = if attr.check_name(sym::cfg) {
-                "cfg"
-            } else if attr.check_name(sym::cfg_attr) {
-                "cfg_attr"
-            } else {
-                continue;
-            };
-            let msg = format!("#[{}] cannot be applied on a generic parameter", offending_attr);
-            self.sess.span_diagnostic.span_err(attr.span, &msg);
-        }
+    pub fn configure_fn_decl(&mut self, fn_decl: &mut ast::FnDecl) {
+        fn_decl.inputs.flat_map_in_place(|arg| self.configure(arg));
     }
 }
 
@@ -348,6 +357,11 @@ impl<'a> MutVisitor for StripUnconfigured<'a> {
         self.configure_pat(pat);
         noop_visit_pat(pat, self)
     }
+
+    fn visit_fn_decl(&mut self, mut fn_decl: &mut P<ast::FnDecl>) {
+        self.configure_fn_decl(&mut fn_decl);
+        noop_visit_fn_decl(fn_decl, self);
+    }
 }
 
 fn is_cfg(attr: &ast::Attribute) -> bool {
diff --git a/src/libsyntax/diagnostics/macros.rs b/src/libsyntax/diagnostics/macros.rs
index 6f7493ad597..b754d083376 100644
--- a/src/libsyntax/diagnostics/macros.rs
+++ b/src/libsyntax/diagnostics/macros.rs
@@ -170,19 +170,19 @@ macro_rules! help {
 #[macro_export]
 macro_rules! register_diagnostics {
     ($($code:tt),*) => (
-        $(register_diagnostic! { $code })*
+        $($crate::register_diagnostic! { $code })*
     );
     ($($code:tt),*,) => (
-        $(register_diagnostic! { $code })*
+        $($crate::register_diagnostic! { $code })*
     )
 }
 
 #[macro_export]
 macro_rules! register_long_diagnostics {
     ($($code:tt: $description:tt),*) => (
-        $(register_diagnostic! { $code, $description })*
+        $($crate::register_diagnostic! { $code, $description })*
     );
     ($($code:tt: $description:tt),*,) => (
-        $(register_diagnostic! { $code, $description })*
+        $($crate::register_diagnostic! { $code, $description })*
     )
 }
diff --git a/src/libsyntax/diagnostics/plugin.rs b/src/libsyntax/diagnostics/plugin.rs
index 21024eb41ef..9618b5acfb0 100644
--- a/src/libsyntax/diagnostics/plugin.rs
+++ b/src/libsyntax/diagnostics/plugin.rs
@@ -4,10 +4,9 @@ use std::env;
 use crate::ast::{self, Ident, Name};
 use crate::source_map;
 use crate::ext::base::{ExtCtxt, MacEager, MacResult};
-use crate::ext::build::AstBuilder;
-use crate::parse::token;
+use crate::parse::token::{self, Token};
 use crate::ptr::P;
-use crate::symbol::{keywords, Symbol};
+use crate::symbol::kw;
 use crate::tokenstream::{TokenTree};
 
 use smallvec::smallvec;
@@ -33,13 +32,15 @@ pub fn expand_diagnostic_used<'cx>(ecx: &'cx mut ExtCtxt<'_>,
                                    span: Span,
                                    token_tree: &[TokenTree])
                                    -> Box<dyn MacResult+'cx> {
-    let code = match (token_tree.len(), token_tree.get(0)) {
-        (1, Some(&TokenTree::Token(_, token::Ident(code, _)))) => code,
+    let code = match token_tree {
+        [
+            TokenTree::Token(Token { kind: token::Ident(code, _), .. })
+        ] => code,
         _ => unreachable!()
     };
 
     ecx.parse_sess.registered_diagnostics.with_lock(|diagnostics| {
-        match diagnostics.get_mut(&code.name) {
+        match diagnostics.get_mut(&code) {
             // Previously used errors.
             Some(&mut ErrorInfo { description: _, use_site: Some(previous_span) }) => {
                 ecx.struct_span_warn(span, &format!(
@@ -66,20 +67,19 @@ pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt<'_>,
                                        span: Span,
                                        token_tree: &[TokenTree])
                                        -> Box<dyn MacResult+'cx> {
-    let (code, description) = match (
-        token_tree.len(),
-        token_tree.get(0),
-        token_tree.get(1),
-        token_tree.get(2)
-    ) {
-        (1, Some(&TokenTree::Token(_, token::Ident(ref code, _))), None, None) => {
-            (code, None)
+    let (code, description) = match  token_tree {
+        [
+            TokenTree::Token(Token { kind: token::Ident(code, _), .. })
+        ] => {
+            (*code, None)
+        },
+        [
+            TokenTree::Token(Token { kind: token::Ident(code, _), .. }),
+            TokenTree::Token(Token { kind: token::Comma, .. }),
+            TokenTree::Token(Token { kind: token::Literal(token::Lit { symbol, .. }), ..})
+        ] => {
+            (*code, Some(*symbol))
         },
-        (3, Some(&TokenTree::Token(_, token::Ident(ref code, _))),
-            Some(&TokenTree::Token(_, token::Comma)),
-            Some(&TokenTree::Token(_, token::Literal(token::StrRaw(description, _), None)))) => {
-            (code, Some(description))
-        }
         _ => unreachable!()
     };
 
@@ -112,41 +112,28 @@ pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt<'_>,
             description,
             use_site: None
         };
-        if diagnostics.insert(code.name, info).is_some() {
+        if diagnostics.insert(code, info).is_some() {
             ecx.span_err(span, &format!(
                 "diagnostic code {} already registered", code
             ));
         }
     });
 
-    let span = span.apply_mark(ecx.current_expansion.mark);
-
-    let sym = Ident::new(Symbol::gensym(&format!("__register_diagnostic_{}", code)), span);
-
-    MacEager::items(smallvec![
-        ecx.item_mod(
-            span,
-            span,
-            sym,
-            vec![],
-            vec![],
-        )
-    ])
+    MacEager::items(smallvec![])
 }
 
-#[allow(deprecated)]
 pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt<'_>,
                                           span: Span,
                                           token_tree: &[TokenTree])
                                           -> Box<dyn MacResult+'cx> {
     assert_eq!(token_tree.len(), 3);
-    let (crate_name, name) = match (&token_tree[0], &token_tree[2]) {
+    let (crate_name, ident) = match (&token_tree[0], &token_tree[2]) {
         (
             // Crate name.
-            &TokenTree::Token(_, token::Ident(ref crate_name, _)),
+            &TokenTree::Token(Token { kind: token::Ident(crate_name, _), .. }),
             // DIAGNOSTICS ident.
-            &TokenTree::Token(_, token::Ident(ref name, _))
-        ) => (*&crate_name, name),
+            &TokenTree::Token(Token { kind: token::Ident(name, _), span })
+        ) => (crate_name, Ident::new(name, span)),
         _ => unreachable!()
     };
 
@@ -160,7 +147,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt<'_>,
                 ecx.span_bug(span, &format!(
                     "error writing metadata for triple `{}` and crate `{}`, error: {}, \
                      cause: {:?}",
-                    target_triple, crate_name, e.description(), e.cause()
+                    target_triple, crate_name, e.description(), e.source()
                 ));
             }
         });
@@ -185,7 +172,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt<'_>,
             (descriptions.len(), ecx.expr_vec(span, descriptions))
         });
 
-    let static_ = ecx.lifetime(span, keywords::StaticLifetime.ident());
+    let static_ = ecx.lifetime(span, Ident::with_dummy_span(kw::StaticLifetime));
     let ty_str = ecx.ty_rptr(
         span,
         ecx.ty_ident(span, ecx.ident_of("str")),
@@ -209,7 +196,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt<'_>,
 
     MacEager::items(smallvec![
         P(ast::Item {
-            ident: *name,
+            ident,
             attrs: Vec::new(),
             id: ast::DUMMY_NODE_ID,
             node: ast::ItemKind::Const(
diff --git a/src/libsyntax/early_buffered_lints.rs b/src/libsyntax/early_buffered_lints.rs
index 977e6d45877..36c1da29299 100644
--- a/src/libsyntax/early_buffered_lints.rs
+++ b/src/libsyntax/early_buffered_lints.rs
@@ -3,15 +3,14 @@
 //! Since we cannot have a dependency on `librustc`, we implement some types here that are somewhat
 //! redundant. Later, these types can be converted to types for use by the rest of the compiler.
 
-use crate::syntax::ast::NodeId;
+use crate::ast::NodeId;
 use syntax_pos::MultiSpan;
 
 /// Since we cannot import `LintId`s from `rustc::lint`, we define some Ids here which can later be
 /// passed to `rustc::lint::Lint::from_parser_lint_id` to get a `rustc::lint::Lint`.
 pub enum BufferedEarlyLintId {
-    /// Usage of `?` as a macro separator is deprecated.
-    QuestionMarkMacroSep,
     IllFormedAttributeInput,
+    MetaVariableMisuse,
 }
 
 /// Stores buffered lint info which can later be passed to `librustc`.
diff --git a/src/libsyntax/error_codes.rs b/src/libsyntax/error_codes.rs
index e2d212eb721..1ba29011f75 100644
--- a/src/libsyntax/error_codes.rs
+++ b/src/libsyntax/error_codes.rs
@@ -1,5 +1,3 @@
-#![allow(non_snake_case)]
-
 // Error messages for EXXXX errors.
 // Each message should start and end with a new line, and be wrapped to 80 characters.
 // In vim you can `:set tw=80` and use `gq` to wrap paragraphs. Use `:set tw=0` to disable.
@@ -182,7 +180,7 @@ beta compilers will not comply.
 Example of erroneous code (on a stable compiler):
 
 ```ignore (depends on release channel)
-#![feature(non_ascii_idents)] // error: #![feature] may not be used on the
+#![feature(non_ascii_idents)] // error: `#![feature]` may not be used on the
                               //        stable release channel
 ```
 
diff --git a/src/libsyntax/ext/allocator.rs b/src/libsyntax/ext/allocator.rs
new file mode 100644
index 00000000000..99aeb5414c5
--- /dev/null
+++ b/src/libsyntax/ext/allocator.rs
@@ -0,0 +1,75 @@
+use crate::{ast, attr, visit};
+use crate::symbol::{sym, Symbol};
+use syntax_pos::Span;
+
+#[derive(Clone, Copy)]
+pub enum AllocatorKind {
+    Global,
+    DefaultLib,
+    DefaultExe,
+}
+
+impl AllocatorKind {
+    pub fn fn_name(&self, base: &str) -> String {
+        match *self {
+            AllocatorKind::Global => format!("__rg_{}", base),
+            AllocatorKind::DefaultLib => format!("__rdl_{}", base),
+            AllocatorKind::DefaultExe => format!("__rde_{}", base),
+        }
+    }
+}
+
+pub enum AllocatorTy {
+    Layout,
+    Ptr,
+    ResultPtr,
+    Unit,
+    Usize,
+}
+
+pub struct AllocatorMethod {
+    pub name: &'static str,
+    pub inputs: &'static [AllocatorTy],
+    pub output: AllocatorTy,
+}
+
+pub static ALLOCATOR_METHODS: &[AllocatorMethod] = &[
+    AllocatorMethod {
+        name: "alloc",
+        inputs: &[AllocatorTy::Layout],
+        output: AllocatorTy::ResultPtr,
+    },
+    AllocatorMethod {
+        name: "dealloc",
+        inputs: &[AllocatorTy::Ptr, AllocatorTy::Layout],
+        output: AllocatorTy::Unit,
+    },
+    AllocatorMethod {
+        name: "realloc",
+        inputs: &[AllocatorTy::Ptr, AllocatorTy::Layout, AllocatorTy::Usize],
+        output: AllocatorTy::ResultPtr,
+    },
+    AllocatorMethod {
+        name: "alloc_zeroed",
+        inputs: &[AllocatorTy::Layout],
+        output: AllocatorTy::ResultPtr,
+    },
+];
+
+pub fn global_allocator_spans(krate: &ast::Crate) -> Vec<Span> {
+    struct Finder { name: Symbol, spans: Vec<Span> }
+    impl<'ast> visit::Visitor<'ast> for Finder {
+        fn visit_item(&mut self, item: &'ast ast::Item) {
+            if item.ident.name == self.name &&
+               attr::contains_name(&item.attrs, sym::rustc_std_internal_symbol) {
+                self.spans.push(item.span);
+            }
+            visit::walk_item(self, item)
+        }
+    }
+
+    let name = Symbol::intern(&AllocatorKind::Global.fn_name("alloc"));
+    let mut f = Finder { name, spans: Vec::new() };
+    visit::walk_crate(&mut f, krate);
+    f.spans
+}
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 0a88d2f8824..b0a4a6af983 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -1,22 +1,21 @@
-pub use SyntaxExtension::*;
-
-use crate::ast::{self, Attribute, Name, PatKind, MetaItem};
-use crate::attr::HasAttrs;
-use crate::source_map::{SourceMap, Spanned, respan};
+use crate::ast::{self, NodeId, Attribute, Name, PatKind};
+use crate::attr::{HasAttrs, Stability, Deprecation};
+use crate::source_map::SourceMap;
 use crate::edition::Edition;
 use crate::ext::expand::{self, AstFragment, Invocation};
-use crate::ext::hygiene::{self, Mark, SyntaxContext, Transparency};
+use crate::ext::hygiene::{ExpnId, SyntaxContext, Transparency};
 use crate::mut_visit::{self, MutVisitor};
 use crate::parse::{self, parser, DirectoryOwnership};
 use crate::parse::token;
 use crate::ptr::P;
-use crate::symbol::{keywords, Ident, Symbol, sym};
-use crate::ThinVec;
-use crate::tokenstream::{self, TokenStream};
+use crate::symbol::{kw, sym, Ident, Symbol};
+use crate::{ThinVec, MACRO_ARGUMENTS};
+use crate::tokenstream::{self, TokenStream, TokenTree};
 
 use errors::{DiagnosticBuilder, DiagnosticId};
 use smallvec::{smallvec, SmallVec};
-use syntax_pos::{Span, MultiSpan, DUMMY_SP};
+use syntax_pos::{FileName, Span, MultiSpan, DUMMY_SP};
+use syntax_pos::hygiene::{ExpnData, ExpnKind};
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::{self, Lrc};
@@ -25,6 +24,7 @@ use std::path::PathBuf;
 use std::rc::Rc;
 use std::default::Default;
 
+pub use syntax_pos::hygiene::MacroKind;
 
 #[derive(Debug,Clone)]
 pub enum Annotatable {
@@ -137,29 +137,6 @@ impl Annotatable {
     }
 }
 
-// A more flexible ItemDecorator.
-pub trait MultiItemDecorator {
-    fn expand(&self,
-              ecx: &mut ExtCtxt<'_>,
-              sp: Span,
-              meta_item: &ast::MetaItem,
-              item: &Annotatable,
-              push: &mut dyn FnMut(Annotatable));
-}
-
-impl<F> MultiItemDecorator for F
-    where F : Fn(&mut ExtCtxt<'_>, Span, &ast::MetaItem, &Annotatable, &mut dyn FnMut(Annotatable))
-{
-    fn expand(&self,
-              ecx: &mut ExtCtxt<'_>,
-              sp: Span,
-              meta_item: &ast::MetaItem,
-              item: &Annotatable,
-              push: &mut dyn FnMut(Annotatable)) {
-        (*self)(ecx, sp, meta_item, item, push)
-    }
-}
-
 // `meta_item` is the annotation, and `item` is the item being modified.
 // FIXME Decorators should follow the same pattern too.
 pub trait MultiItemModifier {
@@ -242,7 +219,6 @@ pub trait TTMacroExpander {
         ecx: &'cx mut ExtCtxt<'_>,
         span: Span,
         input: TokenStream,
-        def_span: Option<Span>,
     ) -> Box<dyn MacResult+'cx>;
 }
 
@@ -259,16 +235,18 @@ impl<F> TTMacroExpander for F
         ecx: &'cx mut ExtCtxt<'_>,
         span: Span,
         input: TokenStream,
-        _def_span: Option<Span>,
     ) -> Box<dyn MacResult+'cx> {
         struct AvoidInterpolatedIdents;
 
         impl MutVisitor for AvoidInterpolatedIdents {
             fn visit_tt(&mut self, tt: &mut tokenstream::TokenTree) {
-                if let tokenstream::TokenTree::Token(_, token::Interpolated(nt)) = tt {
-                    if let token::NtIdent(ident, is_raw) = **nt {
-                        *tt = tokenstream::TokenTree::Token(ident.span,
-                                                            token::Ident(ident, is_raw));
+                if let tokenstream::TokenTree::Token(token) = tt {
+                    if let token::Interpolated(nt) = &token.kind {
+                        if let token::NtIdent(ident, is_raw) = **nt {
+                            *tt = tokenstream::TokenTree::token(
+                                token::Ident(ident.name, is_raw), ident.span
+                            );
+                        }
                     }
                 }
                 mut_visit::noop_visit_tt(tt, self)
@@ -285,34 +263,6 @@ impl<F> TTMacroExpander for F
     }
 }
 
-pub trait IdentMacroExpander {
-    fn expand<'cx>(&self,
-                   cx: &'cx mut ExtCtxt<'_>,
-                   sp: Span,
-                   ident: ast::Ident,
-                   token_tree: Vec<tokenstream::TokenTree>)
-                   -> Box<dyn MacResult+'cx>;
-}
-
-pub type IdentMacroExpanderFn =
-    for<'cx> fn(&'cx mut ExtCtxt<'_>, Span, ast::Ident, Vec<tokenstream::TokenTree>)
-                -> Box<dyn MacResult+'cx>;
-
-impl<F> IdentMacroExpander for F
-    where F : for<'cx> Fn(&'cx mut ExtCtxt<'_>, Span, ast::Ident,
-                          Vec<tokenstream::TokenTree>) -> Box<dyn MacResult+'cx>
-{
-    fn expand<'cx>(&self,
-                   cx: &'cx mut ExtCtxt<'_>,
-                   sp: Span,
-                   ident: ast::Ident,
-                   token_tree: Vec<tokenstream::TokenTree>)
-                   -> Box<dyn MacResult+'cx>
-    {
-        (*self)(cx, sp, ident, token_tree)
-    }
-}
-
 // Use a macro because forwarding to a simple function has type system issues
 macro_rules! make_stmts_default {
     ($me:expr) => {
@@ -455,7 +405,6 @@ impl MacResult for MacEager {
 /// after hitting errors.
 #[derive(Copy, Clone)]
 pub struct DummyResult {
-    expr_only: bool,
     is_error: bool,
     span: Span,
 }
@@ -466,21 +415,12 @@ impl DummyResult {
     /// Use this as a return value after hitting any errors and
     /// calling `span_err`.
     pub fn any(span: Span) -> Box<dyn MacResult+'static> {
-        Box::new(DummyResult { expr_only: false, is_error: true, span })
+        Box::new(DummyResult { is_error: true, span })
     }
 
     /// Same as `any`, but must be a valid fragment, not error.
     pub fn any_valid(span: Span) -> Box<dyn MacResult+'static> {
-        Box::new(DummyResult { expr_only: false, is_error: false, span })
-    }
-
-    /// Creates a default MacResult that can only be an expression.
-    ///
-    /// Use this for macros that must expand to an expression, so even
-    /// if an error is encountered internally, the user will receive
-    /// an error that they also used it in the wrong place.
-    pub fn expr(span: Span) -> Box<dyn MacResult+'static> {
-        Box::new(DummyResult { expr_only: true, is_error: true, span })
+        Box::new(DummyResult { is_error: false, span })
     }
 
     /// A plain dummy expression.
@@ -522,36 +462,19 @@ impl MacResult for DummyResult {
     }
 
     fn make_items(self: Box<DummyResult>) -> Option<SmallVec<[P<ast::Item>; 1]>> {
-        // this code needs a comment... why not always just return the Some() ?
-        if self.expr_only {
-            None
-        } else {
-            Some(SmallVec::new())
-        }
+        Some(SmallVec::new())
     }
 
     fn make_impl_items(self: Box<DummyResult>) -> Option<SmallVec<[ast::ImplItem; 1]>> {
-        if self.expr_only {
-            None
-        } else {
-            Some(SmallVec::new())
-        }
+        Some(SmallVec::new())
     }
 
     fn make_trait_items(self: Box<DummyResult>) -> Option<SmallVec<[ast::TraitItem; 1]>> {
-        if self.expr_only {
-            None
-        } else {
-            Some(SmallVec::new())
-        }
+        Some(SmallVec::new())
     }
 
     fn make_foreign_items(self: Box<Self>) -> Option<SmallVec<[ast::ForeignItem; 1]>> {
-        if self.expr_only {
-            None
-        } else {
-            Some(SmallVec::new())
-        }
+        Some(SmallVec::new())
     }
 
     fn make_stmts(self: Box<DummyResult>) -> Option<SmallVec<[ast::Stmt; 1]>> {
@@ -567,225 +490,205 @@ impl MacResult for DummyResult {
     }
 }
 
-pub type BuiltinDeriveFn =
-    for<'cx> fn(&'cx mut ExtCtxt<'_>, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable));
-
-/// Represents different kinds of macro invocations that can be resolved.
-#[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
-pub enum MacroKind {
-    /// A bang macro - foo!()
-    Bang,
-    /// An attribute macro - #[foo]
-    Attr,
-    /// A derive attribute macro - #[derive(Foo)]
-    Derive,
-    /// A view of a procedural macro from the same crate that defines it.
-    ProcMacroStub,
-}
+/// A syntax extension kind.
+pub enum SyntaxExtensionKind {
+    /// A token-based function-like macro.
+    Bang(
+        /// An expander with signature TokenStream -> TokenStream.
+        Box<dyn ProcMacro + sync::Sync + sync::Send>,
+    ),
+
+    /// An AST-based function-like macro.
+    LegacyBang(
+        /// An expander with signature TokenStream -> AST.
+        Box<dyn TTMacroExpander + sync::Sync + sync::Send>,
+    ),
+
+    /// A token-based attribute macro.
+    Attr(
+        /// An expander with signature (TokenStream, TokenStream) -> TokenStream.
+        /// The first TokenSteam is the attribute itself, the second is the annotated item.
+        /// The produced TokenSteam replaces the input TokenSteam.
+        Box<dyn AttrProcMacro + sync::Sync + sync::Send>,
+    ),
+
+    /// An AST-based attribute macro.
+    LegacyAttr(
+        /// An expander with signature (AST, AST) -> AST.
+        /// The first AST fragment is the attribute itself, the second is the annotated item.
+        /// The produced AST fragment replaces the input AST fragment.
+        Box<dyn MultiItemModifier + sync::Sync + sync::Send>,
+    ),
+
+    /// A trivial attribute "macro" that does nothing,
+    /// only keeps the attribute and marks it as inert,
+    /// thus making it ineligible for further expansion.
+    NonMacroAttr {
+        /// Suppresses the `unused_attributes` lint for this attribute.
+        mark_used: bool,
+    },
 
-impl MacroKind {
-    pub fn descr(self) -> &'static str {
+    /// A token-based derive macro.
+    Derive(
+        /// An expander with signature TokenStream -> TokenStream (not yet).
+        /// The produced TokenSteam is appended to the input TokenSteam.
+        Box<dyn MultiItemModifier + sync::Sync + sync::Send>,
+    ),
+
+    /// An AST-based derive macro.
+    LegacyDerive(
+        /// An expander with signature AST -> AST.
+        /// The produced AST fragment is appended to the input AST fragment.
+        Box<dyn MultiItemModifier + sync::Sync + sync::Send>,
+    ),
+}
+
+/// A struct representing a macro definition in "lowered" form ready for expansion.
+pub struct SyntaxExtension {
+    /// A syntax extension kind.
+    pub kind: SyntaxExtensionKind,
+    /// Span of the macro definition.
+    pub span: Span,
+    /// Hygienic properties of spans produced by this macro by default.
+    pub default_transparency: Transparency,
+    /// Whitelist of unstable features that are treated as stable inside this macro.
+    pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
+    /// Suppresses the `unsafe_code` lint for code produced by this macro.
+    pub allow_internal_unsafe: bool,
+    /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`) for this macro.
+    pub local_inner_macros: bool,
+    /// The macro's stability info.
+    pub stability: Option<Stability>,
+    /// The macro's deprecation info.
+    pub deprecation: Option<Deprecation>,
+    /// Names of helper attributes registered by this macro.
+    pub helper_attrs: Vec<Symbol>,
+    /// Edition of the crate in which this macro is defined.
+    pub edition: Edition,
+    /// Built-in macros have a couple of special properties like availability
+    /// in `#[no_implicit_prelude]` modules, so we have to keep this flag.
+    pub is_builtin: bool,
+    /// We have to identify macros providing a `Copy` impl early for compatibility reasons.
+    pub is_derive_copy: bool,
+}
+
+impl SyntaxExtensionKind {
+    /// When a syntax extension is constructed,
+    /// its transparency can often be inferred from its kind.
+    fn default_transparency(&self) -> Transparency {
         match self {
-            MacroKind::Bang => "macro",
-            MacroKind::Attr => "attribute macro",
-            MacroKind::Derive => "derive macro",
-            MacroKind::ProcMacroStub => "crate-local procedural macro",
+            SyntaxExtensionKind::Bang(..) |
+            SyntaxExtensionKind::Attr(..) |
+            SyntaxExtensionKind::Derive(..) |
+            SyntaxExtensionKind::NonMacroAttr { .. } => Transparency::Opaque,
+            SyntaxExtensionKind::LegacyBang(..) |
+            SyntaxExtensionKind::LegacyAttr(..) |
+            SyntaxExtensionKind::LegacyDerive(..) => Transparency::SemiTransparent,
         }
     }
+}
 
-    pub fn article(self) -> &'static str {
-        match self {
-            MacroKind::Attr => "an",
-            _ => "a",
+impl SyntaxExtension {
+    /// Returns which kind of macro calls this syntax extension.
+    pub fn macro_kind(&self) -> MacroKind {
+        match self.kind {
+            SyntaxExtensionKind::Bang(..) |
+            SyntaxExtensionKind::LegacyBang(..) => MacroKind::Bang,
+            SyntaxExtensionKind::Attr(..) |
+            SyntaxExtensionKind::LegacyAttr(..) |
+            SyntaxExtensionKind::NonMacroAttr { .. } => MacroKind::Attr,
+            SyntaxExtensionKind::Derive(..) |
+            SyntaxExtensionKind::LegacyDerive(..) => MacroKind::Derive,
         }
     }
-}
-
-/// An enum representing the different kinds of syntax extensions.
-pub enum SyntaxExtension {
-    /// A trivial "extension" that does nothing, only keeps the attribute and marks it as known.
-    NonMacroAttr { mark_used: bool },
 
-    /// A syntax extension that is attached to an item and creates new items
-    /// based upon it.
-    ///
-    /// `#[derive(...)]` is a `MultiItemDecorator`.
-    ///
-    /// Prefer ProcMacro or MultiModifier since they are more flexible.
-    MultiDecorator(Box<dyn MultiItemDecorator + sync::Sync + sync::Send>),
-
-    /// A syntax extension that is attached to an item and modifies it
-    /// in-place. Also allows decoration, i.e., creating new items.
-    MultiModifier(Box<dyn MultiItemModifier + sync::Sync + sync::Send>),
-
-    /// A function-like procedural macro. TokenStream -> TokenStream.
-    ProcMacro {
-        expander: Box<dyn ProcMacro + sync::Sync + sync::Send>,
-        /// Whitelist of unstable features that are treated as stable inside this macro
-        allow_internal_unstable: Option<Lrc<[Symbol]>>,
-        edition: Edition,
-    },
-
-    /// An attribute-like procedural macro. TokenStream, TokenStream -> TokenStream.
-    /// The first TokenSteam is the attribute, the second is the annotated item.
-    /// Allows modification of the input items and adding new items, similar to
-    /// MultiModifier, but uses TokenStreams, rather than AST nodes.
-    AttrProcMacro(Box<dyn AttrProcMacro + sync::Sync + sync::Send>, Edition),
-
-    /// A normal, function-like syntax extension.
-    ///
-    /// `bytes!` is a `NormalTT`.
-    NormalTT {
-        expander: Box<dyn TTMacroExpander + sync::Sync + sync::Send>,
-        def_info: Option<(ast::NodeId, Span)>,
-        /// Whether the contents of the macro can
-        /// directly use `#[unstable]` things.
-        ///
-        /// Only allows things that require a feature gate in the given whitelist
-        allow_internal_unstable: Option<Lrc<[Symbol]>>,
-        /// Whether the contents of the macro can use `unsafe`
-        /// without triggering the `unsafe_code` lint.
-        allow_internal_unsafe: bool,
-        /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
-        /// for a given macro.
-        local_inner_macros: bool,
-        /// The macro's feature name if it is unstable, and the stability feature
-        unstable_feature: Option<(Symbol, u32)>,
-        /// Edition of the crate in which the macro is defined
-        edition: Edition,
-    },
-
-    /// A function-like syntax extension that has an extra ident before
-    /// the block.
-    IdentTT {
-        expander: Box<dyn IdentMacroExpander + sync::Sync + sync::Send>,
-        span: Option<Span>,
-        allow_internal_unstable: Option<Lrc<[Symbol]>>,
-    },
-
-    /// An attribute-like procedural macro. TokenStream -> TokenStream.
-    /// The input is the annotated item.
-    /// Allows generating code to implement a Trait for a given struct
-    /// or enum item.
-    ProcMacroDerive(Box<dyn MultiItemModifier + sync::Sync + sync::Send>,
-                    Vec<Symbol> /* inert attribute names */, Edition),
-
-    /// An attribute-like procedural macro that derives a builtin trait.
-    BuiltinDerive(BuiltinDeriveFn),
-
-    /// A declarative macro, e.g., `macro m() {}`.
-    DeclMacro {
-        expander: Box<dyn TTMacroExpander + sync::Sync + sync::Send>,
-        def_info: Option<(ast::NodeId, Span)>,
-        is_transparent: bool,
-        edition: Edition,
+    /// Constructs a syntax extension with default properties.
+    pub fn default(kind: SyntaxExtensionKind, edition: Edition) -> SyntaxExtension {
+        SyntaxExtension {
+            span: DUMMY_SP,
+            default_transparency: kind.default_transparency(),
+            allow_internal_unstable: None,
+            allow_internal_unsafe: false,
+            local_inner_macros: false,
+            stability: None,
+            deprecation: None,
+            helper_attrs: Vec::new(),
+            edition,
+            is_builtin: false,
+            is_derive_copy: false,
+            kind,
+        }
     }
-}
 
-impl SyntaxExtension {
-    /// Returns which kind of macro calls this syntax extension.
-    pub fn kind(&self) -> MacroKind {
-        match *self {
-            SyntaxExtension::DeclMacro { .. } |
-            SyntaxExtension::NormalTT { .. } |
-            SyntaxExtension::IdentTT { .. } |
-            SyntaxExtension::ProcMacro { .. } =>
-                MacroKind::Bang,
-            SyntaxExtension::NonMacroAttr { .. } |
-            SyntaxExtension::MultiDecorator(..) |
-            SyntaxExtension::MultiModifier(..) |
-            SyntaxExtension::AttrProcMacro(..) =>
-                MacroKind::Attr,
-            SyntaxExtension::ProcMacroDerive(..) |
-            SyntaxExtension::BuiltinDerive(..) =>
-                MacroKind::Derive,
+    pub fn dummy_bang(edition: Edition) -> SyntaxExtension {
+        fn expander<'cx>(_: &'cx mut ExtCtxt<'_>, span: Span, _: &[TokenTree])
+                         -> Box<dyn MacResult + 'cx> {
+            DummyResult::any(span)
         }
+        SyntaxExtension::default(SyntaxExtensionKind::LegacyBang(Box::new(expander)), edition)
     }
 
-    pub fn default_transparency(&self) -> Transparency {
-        match *self {
-            SyntaxExtension::ProcMacro { .. } |
-            SyntaxExtension::AttrProcMacro(..) |
-            SyntaxExtension::ProcMacroDerive(..) |
-            SyntaxExtension::DeclMacro { is_transparent: false, .. } => Transparency::Opaque,
-            SyntaxExtension::DeclMacro { is_transparent: true, .. } => Transparency::Transparent,
-            _ => Transparency::SemiTransparent,
+    pub fn dummy_derive(edition: Edition) -> SyntaxExtension {
+        fn expander(_: &mut ExtCtxt<'_>, _: Span, _: &ast::MetaItem, _: Annotatable)
+                    -> Vec<Annotatable> {
+            Vec::new()
         }
+        SyntaxExtension::default(SyntaxExtensionKind::Derive(Box::new(expander)), edition)
     }
 
-    pub fn edition(&self) -> Edition {
-        match *self {
-            SyntaxExtension::NormalTT { edition, .. } |
-            SyntaxExtension::DeclMacro { edition, .. } |
-            SyntaxExtension::ProcMacro { edition, .. } |
-            SyntaxExtension::AttrProcMacro(.., edition) |
-            SyntaxExtension::ProcMacroDerive(.., edition) => edition,
-            // Unstable legacy stuff
-            SyntaxExtension::NonMacroAttr { .. } |
-            SyntaxExtension::IdentTT { .. } |
-            SyntaxExtension::MultiDecorator(..) |
-            SyntaxExtension::MultiModifier(..) |
-            SyntaxExtension::BuiltinDerive(..) => hygiene::default_edition(),
+    pub fn non_macro_attr(mark_used: bool, edition: Edition) -> SyntaxExtension {
+        SyntaxExtension::default(SyntaxExtensionKind::NonMacroAttr { mark_used }, edition)
+    }
+
+    pub fn expn_data(&self, parent: ExpnId, call_site: Span, descr: Symbol) -> ExpnData {
+        ExpnData {
+            kind: ExpnKind::Macro(self.macro_kind(), descr),
+            parent,
+            call_site,
+            def_site: self.span,
+            default_transparency: self.default_transparency,
+            allow_internal_unstable: self.allow_internal_unstable.clone(),
+            allow_internal_unsafe: self.allow_internal_unsafe,
+            local_inner_macros: self.local_inner_macros,
+            edition: self.edition,
         }
     }
 }
 
 pub type NamedSyntaxExtension = (Name, SyntaxExtension);
 
-pub trait Resolver {
-    fn next_node_id(&mut self) -> ast::NodeId;
-    fn get_module_scope(&mut self, id: ast::NodeId) -> Mark;
-
-    fn resolve_dollar_crates(&mut self, fragment: &AstFragment);
-    fn visit_ast_fragment_with_placeholders(&mut self, mark: Mark, fragment: &AstFragment,
-                                            derives: &[Mark]);
-    fn add_builtin(&mut self, ident: ast::Ident, ext: Lrc<SyntaxExtension>);
-
-    fn resolve_imports(&mut self);
-
-    fn resolve_macro_invocation(&mut self, invoc: &Invocation, invoc_id: Mark, force: bool)
-                                -> Result<Option<Lrc<SyntaxExtension>>, Determinacy>;
-    fn resolve_macro_path(&mut self, path: &ast::Path, kind: MacroKind, invoc_id: Mark,
-                          derives_in_scope: Vec<ast::Path>, force: bool)
-                          -> Result<Lrc<SyntaxExtension>, Determinacy>;
+/// Error type that denotes indeterminacy.
+pub struct Indeterminate;
 
-    fn check_unused_macros(&self);
+bitflags::bitflags! {
+    /// Built-in derives that need some extra tracking beyond the usual macro functionality.
+    #[derive(Default)]
+    pub struct SpecialDerives: u8 {
+        const PARTIAL_EQ = 1 << 0;
+        const EQ         = 1 << 1;
+        const COPY       = 1 << 2;
+    }
 }
 
-#[derive(Copy, Clone, PartialEq, Debug)]
-pub enum Determinacy {
-    Determined,
-    Undetermined,
-}
+pub trait Resolver {
+    fn next_node_id(&mut self) -> NodeId;
 
-impl Determinacy {
-    pub fn determined(determined: bool) -> Determinacy {
-        if determined { Determinacy::Determined } else { Determinacy::Undetermined }
-    }
-}
+    fn get_module_scope(&mut self, id: NodeId) -> ExpnId;
 
-pub struct DummyResolver;
+    fn resolve_dollar_crates(&mut self);
+    fn visit_ast_fragment_with_placeholders(&mut self, expn_id: ExpnId, fragment: &AstFragment,
+                                            extra_placeholders: &[NodeId]);
+    fn register_builtin_macro(&mut self, ident: ast::Ident, ext: SyntaxExtension);
 
-impl Resolver for DummyResolver {
-    fn next_node_id(&mut self) -> ast::NodeId { ast::DUMMY_NODE_ID }
-    fn get_module_scope(&mut self, _id: ast::NodeId) -> Mark { Mark::root() }
+    fn resolve_imports(&mut self);
 
-    fn resolve_dollar_crates(&mut self, _fragment: &AstFragment) {}
-    fn visit_ast_fragment_with_placeholders(&mut self, _invoc: Mark, _fragment: &AstFragment,
-                                            _derives: &[Mark]) {}
-    fn add_builtin(&mut self, _ident: ast::Ident, _ext: Lrc<SyntaxExtension>) {}
+    fn resolve_macro_invocation(&mut self, invoc: &Invocation, invoc_id: ExpnId, force: bool)
+                                -> Result<Option<Lrc<SyntaxExtension>>, Indeterminate>;
 
-    fn resolve_imports(&mut self) {}
-    fn resolve_macro_invocation(&mut self, _invoc: &Invocation, _invoc_id: Mark, _force: bool)
-                                -> Result<Option<Lrc<SyntaxExtension>>, Determinacy> {
-        Err(Determinacy::Determined)
-    }
-    fn resolve_macro_path(&mut self, _path: &ast::Path, _kind: MacroKind, _invoc_id: Mark,
-                          _derives_in_scope: Vec<ast::Path>, _force: bool)
-                          -> Result<Lrc<SyntaxExtension>, Determinacy> {
-        Err(Determinacy::Determined)
-    }
-    fn check_unused_macros(&self) {}
+    fn check_unused_macros(&self);
+
+    fn has_derives(&self, expn_id: ExpnId, derives: SpecialDerives) -> bool;
+    fn add_derives(&mut self, expn_id: ExpnId, derives: SpecialDerives);
 }
 
 #[derive(Clone)]
@@ -796,16 +699,16 @@ pub struct ModuleData {
 
 #[derive(Clone)]
 pub struct ExpansionData {
-    pub mark: Mark,
+    pub id: ExpnId,
     pub depth: usize,
     pub module: Rc<ModuleData>,
     pub directory_ownership: DirectoryOwnership,
-    pub crate_span: Option<Span>,
+    pub prior_type_ascription: Option<(Span, bool)>,
 }
 
 /// One of these is made during expansion and incrementally updated as we go;
 /// when a macro expansion occurs, the resulting nodes have the `backtrace()
-/// -> expn_info` of their expansion context stored into their span.
+/// -> expn_data` of their expansion context stored into their span.
 pub struct ExtCtxt<'a> {
     pub parse_sess: &'a parse::ParseSess,
     pub ecfg: expand::ExpansionConfig<'a>,
@@ -826,11 +729,11 @@ impl<'a> ExtCtxt<'a> {
             root_path: PathBuf::new(),
             resolver,
             current_expansion: ExpansionData {
-                mark: Mark::root(),
+                id: ExpnId::root(),
                 depth: 0,
                 module: Rc::new(ModuleData { mod_path: Vec::new(), directory: PathBuf::new() }),
                 directory_ownership: DirectoryOwnership::Owned { relative: None },
-                crate_span: None,
+                prior_type_ascription: None,
             },
             expansions: FxHashMap::default(),
         }
@@ -848,19 +751,16 @@ impl<'a> ExtCtxt<'a> {
     }
 
     pub fn new_parser_from_tts(&self, tts: &[tokenstream::TokenTree]) -> parser::Parser<'a> {
-        parse::stream_to_parser(self.parse_sess, tts.iter().cloned().collect())
+        parse::stream_to_parser(self.parse_sess, tts.iter().cloned().collect(), MACRO_ARGUMENTS)
     }
     pub fn source_map(&self) -> &'a SourceMap { self.parse_sess.source_map() }
     pub fn parse_sess(&self) -> &'a parse::ParseSess { self.parse_sess }
     pub fn cfg(&self) -> &ast::CrateConfig { &self.parse_sess.config }
     pub fn call_site(&self) -> Span {
-        match self.current_expansion.mark.expn_info() {
-            Some(expn_info) => expn_info.call_site,
-            None => DUMMY_SP,
-        }
+        self.current_expansion.id.expn_data().call_site
     }
     pub fn backtrace(&self) -> SyntaxContext {
-        SyntaxContext::empty().apply_mark(self.current_expansion.mark)
+        SyntaxContext::root().apply_mark(self.current_expansion.id)
     }
 
     /// Returns span for the macro which originally caused the current expansion to happen.
@@ -870,17 +770,13 @@ impl<'a> ExtCtxt<'a> {
         let mut ctxt = self.backtrace();
         let mut last_macro = None;
         loop {
-            if ctxt.outer().expn_info().map_or(None, |info| {
-                if info.format.name() == sym::include {
-                    // Stop going up the backtrace once include! is encountered
-                    return None;
-                }
-                ctxt = info.call_site.ctxt();
-                last_macro = Some(info.call_site);
-                Some(())
-            }).is_none() {
-                break
+            let expn_data = ctxt.outer_expn_data();
+            // Stop going up the backtrace once include! is encountered
+            if expn_data.is_root() || expn_data.kind.descr() == sym::include {
+                break;
             }
+            ctxt = expn_data.call_site.ctxt();
+            last_macro = Some(expn_data.call_site);
         }
         last_macro
     }
@@ -967,10 +863,10 @@ impl<'a> ExtCtxt<'a> {
     pub fn ident_of(&self, st: &str) -> ast::Ident {
         ast::Ident::from_str(st)
     }
-    pub fn std_path(&self, components: &[&str]) -> Vec<ast::Ident> {
-        let def_site = DUMMY_SP.apply_mark(self.current_expansion.mark);
-        iter::once(Ident::new(keywords::DollarCrate.name(), def_site))
-            .chain(components.iter().map(|s| self.ident_of(s)))
+    pub fn std_path(&self, components: &[Symbol]) -> Vec<ast::Ident> {
+        let def_site = DUMMY_SP.apply_mark(self.current_expansion.id);
+        iter::once(Ident::new(kw::DollarCrate, def_site))
+            .chain(components.iter().map(|&s| Ident::with_dummy_span(s)))
             .collect()
     }
     pub fn name_of(&self, st: &str) -> ast::Name {
@@ -980,6 +876,31 @@ impl<'a> ExtCtxt<'a> {
     pub fn check_unused_macros(&self) {
         self.resolver.check_unused_macros();
     }
+
+    /// Resolve a path mentioned inside Rust code.
+    ///
+    /// This unifies the logic used for resolving `include_X!`, and `#[doc(include)]` file paths.
+    ///
+    /// Returns an absolute path to the file that `path` refers to.
+    pub fn resolve_path(&self, path: impl Into<PathBuf>, span: Span) -> PathBuf {
+        let path = path.into();
+
+        // Relative paths are resolved relative to the file in which they are found
+        // after macro expansion (that is, they are unhygienic).
+        if !path.is_absolute() {
+            let callsite = span.source_callsite();
+            let mut result = match self.source_map().span_to_unmapped_path(callsite) {
+                FileName::Real(path) => path,
+                FileName::DocTest(path, _) => path,
+                other => panic!("cannot resolve relative path in non-file source `{}`", other),
+            };
+            result.pop();
+            result.push(path);
+            result
+        } else {
+            path
+        }
+    }
 }
 
 /// Extracts a string literal from the macro expanded version of `expr`,
@@ -989,15 +910,17 @@ pub fn expr_to_spanned_string<'a>(
     cx: &'a mut ExtCtxt<'_>,
     mut expr: P<ast::Expr>,
     err_msg: &str,
-) -> Result<Spanned<(Symbol, ast::StrStyle)>, Option<DiagnosticBuilder<'a>>> {
+) -> Result<(Symbol, ast::StrStyle, Span), Option<DiagnosticBuilder<'a>>> {
     // Update `expr.span`'s ctxt now in case expr is an `include!` macro invocation.
-    expr.span = expr.span.apply_mark(cx.current_expansion.mark);
+    expr.span = expr.span.apply_mark(cx.current_expansion.id);
+
+    // Perform eager expansion on the expression.
+    // We want to be able to handle e.g., `concat!("foo", "bar")`.
+    let expr = cx.expander().fully_expand_fragment(AstFragment::Expr(expr)).make_expr();
 
-    // we want to be able to handle e.g., `concat!("foo", "bar")`
-    cx.expander().visit_expr(&mut expr);
     Err(match expr.node {
         ast::ExprKind::Lit(ref l) => match l.node {
-            ast::LitKind::Str(s, style) => return Ok(respan(expr.span, (s, style))),
+            ast::LitKind::Str(s, style) => return Ok((s, style, expr.span)),
             ast::LitKind::Err(_) => None,
             _ => Some(cx.struct_span_err(l.span, err_msg))
         },
@@ -1011,7 +934,7 @@ pub fn expr_to_string(cx: &mut ExtCtxt<'_>, expr: P<ast::Expr>, err_msg: &str)
     expr_to_spanned_string(cx, expr, err_msg)
         .map_err(|err| err.map(|mut err| err.emit()))
         .ok()
-        .map(|s| s.node)
+        .map(|(symbol, style, _)| (symbol, style))
 }
 
 /// Non-fatally assert that `tts` is empty. Note that this function
@@ -1059,8 +982,12 @@ pub fn get_exprs_from_tts(cx: &mut ExtCtxt<'_>,
     let mut p = cx.new_parser_from_tts(tts);
     let mut es = Vec::new();
     while p.token != token::Eof {
-        let mut expr = panictry!(p.parse_expr());
-        cx.expander().visit_expr(&mut expr);
+        let expr = panictry!(p.parse_expr());
+
+        // Perform eager expansion on the expression.
+        // We want to be able to handle e.g., `concat!("foo", "bar")`.
+        let expr = cx.expander().fully_expand_fragment(AstFragment::Expr(expr)).make_expr();
+
         es.push(expr);
         if p.eat(&token::Comma) {
             continue;
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index d24106f697e..e2ac4d573a1 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -3,307 +3,31 @@ use crate::attr;
 use crate::source_map::{dummy_spanned, respan, Spanned};
 use crate::ext::base::ExtCtxt;
 use crate::ptr::P;
-use crate::symbol::{Symbol, keywords};
+use crate::symbol::{kw, sym, Symbol};
 use crate::ThinVec;
 
 use rustc_target::spec::abi::Abi;
-use syntax_pos::{Pos, Span, DUMMY_SP};
-
-pub trait AstBuilder {
-    // paths
-    fn path(&self, span: Span, strs: Vec<ast::Ident> ) -> ast::Path;
-    fn path_ident(&self, span: Span, id: ast::Ident) -> ast::Path;
-    fn path_global(&self, span: Span, strs: Vec<ast::Ident> ) -> ast::Path;
-    fn path_all(&self, sp: Span,
-                global: bool,
-                idents: Vec<ast::Ident>,
-                args: Vec<ast::GenericArg>,
-                bindings: Vec<ast::TypeBinding>)
-        -> ast::Path;
-
-    fn qpath(&self, self_type: P<ast::Ty>,
-             trait_path: ast::Path,
-             ident: ast::Ident)
-             -> (ast::QSelf, ast::Path);
-    fn qpath_all(&self, self_type: P<ast::Ty>,
-                trait_path: ast::Path,
-                ident: ast::Ident,
-                args: Vec<ast::GenericArg>,
-                bindings: Vec<ast::TypeBinding>)
-                -> (ast::QSelf, ast::Path);
-
-    // types and consts
-    fn ty_mt(&self, ty: P<ast::Ty>, mutbl: ast::Mutability) -> ast::MutTy;
-
-    fn ty(&self, span: Span, ty: ast::TyKind) -> P<ast::Ty>;
-    fn ty_path(&self, path: ast::Path) -> P<ast::Ty>;
-    fn ty_ident(&self, span: Span, idents: ast::Ident) -> P<ast::Ty>;
-    fn anon_const(&self, span: Span, expr: ast::ExprKind) -> ast::AnonConst;
-    fn const_ident(&self, span: Span, idents: ast::Ident) -> ast::AnonConst;
-
-    fn ty_rptr(&self, span: Span,
-               ty: P<ast::Ty>,
-               lifetime: Option<ast::Lifetime>,
-               mutbl: ast::Mutability) -> P<ast::Ty>;
-    fn ty_ptr(&self, span: Span,
-              ty: P<ast::Ty>,
-              mutbl: ast::Mutability) -> P<ast::Ty>;
-
-    fn ty_option(&self, ty: P<ast::Ty>) -> P<ast::Ty>;
-    fn ty_infer(&self, sp: Span) -> P<ast::Ty>;
-
-    fn typaram(&self,
-               span: Span,
-               id: ast::Ident,
-               attrs: Vec<ast::Attribute>,
-               bounds: ast::GenericBounds,
-               default: Option<P<ast::Ty>>) -> ast::GenericParam;
-
-    fn trait_ref(&self, path: ast::Path) -> ast::TraitRef;
-    fn poly_trait_ref(&self, span: Span, path: ast::Path) -> ast::PolyTraitRef;
-    fn trait_bound(&self, path: ast::Path) -> ast::GenericBound;
-    fn lifetime(&self, span: Span, ident: ast::Ident) -> ast::Lifetime;
-    fn lifetime_def(&self,
-                    span: Span,
-                    ident: ast::Ident,
-                    attrs: Vec<ast::Attribute>,
-                    bounds: ast::GenericBounds)
-                    -> ast::GenericParam;
-
-    // statements
-    fn stmt_expr(&self, expr: P<ast::Expr>) -> ast::Stmt;
-    fn stmt_semi(&self, expr: P<ast::Expr>) -> ast::Stmt;
-    fn stmt_let(&self, sp: Span, mutbl: bool, ident: ast::Ident, ex: P<ast::Expr>) -> ast::Stmt;
-    fn stmt_let_typed(&self,
-                      sp: Span,
-                      mutbl: bool,
-                      ident: ast::Ident,
-                      typ: P<ast::Ty>,
-                      ex: P<ast::Expr>)
-                      -> ast::Stmt;
-    fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt;
-    fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt;
-
-    // blocks
-    fn block(&self, span: Span, stmts: Vec<ast::Stmt>) -> P<ast::Block>;
-    fn block_expr(&self, expr: P<ast::Expr>) -> P<ast::Block>;
-
-    // expressions
-    fn expr(&self, span: Span, node: ast::ExprKind) -> P<ast::Expr>;
-    fn expr_path(&self, path: ast::Path) -> P<ast::Expr>;
-    fn expr_qpath(&self, span: Span, qself: ast::QSelf, path: ast::Path) -> P<ast::Expr>;
-    fn expr_ident(&self, span: Span, id: ast::Ident) -> P<ast::Expr>;
-
-    fn expr_self(&self, span: Span) -> P<ast::Expr>;
-    fn expr_binary(&self, sp: Span, op: ast::BinOpKind,
-                   lhs: P<ast::Expr>, rhs: P<ast::Expr>) -> P<ast::Expr>;
-    fn expr_deref(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr>;
-    fn expr_unary(&self, sp: Span, op: ast::UnOp, e: P<ast::Expr>) -> P<ast::Expr>;
-
-    fn expr_addr_of(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr>;
-    fn expr_mut_addr_of(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr>;
-    fn expr_field_access(&self, span: Span, expr: P<ast::Expr>, ident: ast::Ident) -> P<ast::Expr>;
-    fn expr_tup_field_access(&self, sp: Span, expr: P<ast::Expr>,
-                             idx: usize) -> P<ast::Expr>;
-    fn expr_call(&self, span: Span, expr: P<ast::Expr>, args: Vec<P<ast::Expr>>) -> P<ast::Expr>;
-    fn expr_call_ident(&self, span: Span, id: ast::Ident, args: Vec<P<ast::Expr>>) -> P<ast::Expr>;
-    fn expr_call_global(&self, sp: Span, fn_path: Vec<ast::Ident>,
-                        args: Vec<P<ast::Expr>> ) -> P<ast::Expr>;
-    fn expr_method_call(&self, span: Span,
-                        expr: P<ast::Expr>, ident: ast::Ident,
-                        args: Vec<P<ast::Expr>> ) -> P<ast::Expr>;
-    fn expr_block(&self, b: P<ast::Block>) -> P<ast::Expr>;
-    fn expr_cast(&self, sp: Span, expr: P<ast::Expr>, ty: P<ast::Ty>) -> P<ast::Expr>;
-
-    fn field_imm(&self, span: Span, name: Ident, e: P<ast::Expr>) -> ast::Field;
-    fn expr_struct(&self, span: Span, path: ast::Path, fields: Vec<ast::Field>) -> P<ast::Expr>;
-    fn expr_struct_ident(&self, span: Span, id: ast::Ident,
-                         fields: Vec<ast::Field>) -> P<ast::Expr>;
-
-    fn expr_lit(&self, sp: Span, lit: ast::LitKind) -> P<ast::Expr>;
-
-    fn expr_usize(&self, span: Span, i: usize) -> P<ast::Expr>;
-    fn expr_isize(&self, sp: Span, i: isize) -> P<ast::Expr>;
-    fn expr_u8(&self, sp: Span, u: u8) -> P<ast::Expr>;
-    fn expr_u16(&self, sp: Span, u: u16) -> P<ast::Expr>;
-    fn expr_u32(&self, sp: Span, u: u32) -> P<ast::Expr>;
-    fn expr_bool(&self, sp: Span, value: bool) -> P<ast::Expr>;
-
-    fn expr_vec(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr>;
-    fn expr_vec_ng(&self, sp: Span) -> P<ast::Expr>;
-    fn expr_vec_slice(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr>;
-    fn expr_str(&self, sp: Span, s: Symbol) -> P<ast::Expr>;
-
-    fn expr_some(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr>;
-    fn expr_none(&self, sp: Span) -> P<ast::Expr>;
-
-    fn expr_break(&self, sp: Span) -> P<ast::Expr>;
-
-    fn expr_tuple(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr>;
-
-    fn expr_fail(&self, span: Span, msg: Symbol) -> P<ast::Expr>;
-    fn expr_unreachable(&self, span: Span) -> P<ast::Expr>;
-
-    fn expr_ok(&self, span: Span, expr: P<ast::Expr>) -> P<ast::Expr>;
-    fn expr_err(&self, span: Span, expr: P<ast::Expr>) -> P<ast::Expr>;
-    fn expr_try(&self, span: Span, head: P<ast::Expr>) -> P<ast::Expr>;
-
-    fn pat(&self, span: Span, pat: PatKind) -> P<ast::Pat>;
-    fn pat_wild(&self, span: Span) -> P<ast::Pat>;
-    fn pat_lit(&self, span: Span, expr: P<ast::Expr>) -> P<ast::Pat>;
-    fn pat_ident(&self, span: Span, ident: ast::Ident) -> P<ast::Pat>;
-
-    fn pat_ident_binding_mode(&self,
-                              span: Span,
-                              ident: ast::Ident,
-                              bm: ast::BindingMode) -> P<ast::Pat>;
-    fn pat_path(&self, span: Span, path: ast::Path) -> P<ast::Pat>;
-    fn pat_tuple_struct(&self, span: Span, path: ast::Path,
-                        subpats: Vec<P<ast::Pat>>) -> P<ast::Pat>;
-    fn pat_struct(&self, span: Span, path: ast::Path,
-                  field_pats: Vec<Spanned<ast::FieldPat>>) -> P<ast::Pat>;
-    fn pat_tuple(&self, span: Span, pats: Vec<P<ast::Pat>>) -> P<ast::Pat>;
-
-    fn pat_some(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat>;
-    fn pat_none(&self, span: Span) -> P<ast::Pat>;
-
-    fn pat_ok(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat>;
-    fn pat_err(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat>;
-
-    fn arm(&self, span: Span, pats: Vec<P<ast::Pat>>, expr: P<ast::Expr>) -> ast::Arm;
-    fn arm_unreachable(&self, span: Span) -> ast::Arm;
-
-    fn expr_match(&self, span: Span, arg: P<ast::Expr>, arms: Vec<ast::Arm> ) -> P<ast::Expr>;
-    fn expr_if(&self, span: Span,
-               cond: P<ast::Expr>, then: P<ast::Expr>, els: Option<P<ast::Expr>>) -> P<ast::Expr>;
-    fn expr_loop(&self, span: Span, block: P<ast::Block>) -> P<ast::Expr>;
-
-    fn lambda_fn_decl(&self,
-                      span: Span,
-                      fn_decl: P<ast::FnDecl>,
-                      body: P<ast::Expr>,
-                      fn_decl_span: Span)
-                      -> P<ast::Expr>;
-
-    fn lambda(&self, span: Span, ids: Vec<ast::Ident>, body: P<ast::Expr>) -> P<ast::Expr>;
-    fn lambda0(&self, span: Span, body: P<ast::Expr>) -> P<ast::Expr>;
-    fn lambda1(&self, span: Span, body: P<ast::Expr>, ident: ast::Ident) -> P<ast::Expr>;
-
-    fn lambda_stmts(&self, span: Span, ids: Vec<ast::Ident>,
-                    blk: Vec<ast::Stmt>) -> P<ast::Expr>;
-    fn lambda_stmts_0(&self, span: Span, stmts: Vec<ast::Stmt>) -> P<ast::Expr>;
-    fn lambda_stmts_1(&self, span: Span, stmts: Vec<ast::Stmt>,
-                      ident: ast::Ident) -> P<ast::Expr>;
-
-    // items
-    fn item(&self, span: Span,
-            name: Ident, attrs: Vec<ast::Attribute> , node: ast::ItemKind) -> P<ast::Item>;
-
-    fn arg(&self, span: Span, name: Ident, ty: P<ast::Ty>) -> ast::Arg;
-    // FIXME unused self
-    fn fn_decl(&self, inputs: Vec<ast::Arg> , output: ast::FunctionRetTy) -> P<ast::FnDecl>;
-
-    fn item_fn_poly(&self,
-                    span: Span,
-                    name: Ident,
-                    inputs: Vec<ast::Arg> ,
-                    output: P<ast::Ty>,
-                    generics: Generics,
-                    body: P<ast::Block>) -> P<ast::Item>;
-    fn item_fn(&self,
-               span: Span,
-               name: Ident,
-               inputs: Vec<ast::Arg> ,
-               output: P<ast::Ty>,
-               body: P<ast::Block>) -> P<ast::Item>;
-
-    fn variant(&self, span: Span, name: Ident, tys: Vec<P<ast::Ty>> ) -> ast::Variant;
-    fn item_enum_poly(&self,
-                      span: Span,
-                      name: Ident,
-                      enum_definition: ast::EnumDef,
-                      generics: Generics) -> P<ast::Item>;
-    fn item_enum(&self, span: Span, name: Ident, enum_def: ast::EnumDef) -> P<ast::Item>;
-
-    fn item_struct_poly(&self,
-                        span: Span,
-                        name: Ident,
-                        struct_def: ast::VariantData,
-                        generics: Generics) -> P<ast::Item>;
-    fn item_struct(&self, span: Span, name: Ident, struct_def: ast::VariantData) -> P<ast::Item>;
-
-    fn item_mod(&self, span: Span, inner_span: Span,
-                name: Ident, attrs: Vec<ast::Attribute>,
-                items: Vec<P<ast::Item>>) -> P<ast::Item>;
-
-    fn item_extern_crate(&self, span: Span, name: Ident) -> P<ast::Item>;
-
-    fn item_static(&self,
-                   span: Span,
-                   name: Ident,
-                   ty: P<ast::Ty>,
-                   mutbl: ast::Mutability,
-                   expr: P<ast::Expr>)
-                   -> P<ast::Item>;
-
-    fn item_const(&self,
-                   span: Span,
-                   name: Ident,
-                   ty: P<ast::Ty>,
-                   expr: P<ast::Expr>)
-                   -> P<ast::Item>;
+use syntax_pos::{Pos, Span};
 
-    fn item_ty_poly(&self,
-                    span: Span,
-                    name: Ident,
-                    ty: P<ast::Ty>,
-                    generics: Generics) -> P<ast::Item>;
-    fn item_ty(&self, span: Span, name: Ident, ty: P<ast::Ty>) -> P<ast::Item>;
-
-    fn attribute(&self, sp: Span, mi: ast::MetaItem) -> ast::Attribute;
-
-    fn meta_word(&self, sp: Span, w: ast::Name) -> ast::MetaItem;
-
-    fn meta_list_item_word(&self, sp: Span, w: ast::Name) -> ast::NestedMetaItem;
-
-    fn meta_list(&self,
-                 sp: Span,
-                 name: ast::Name,
-                 mis: Vec<ast::NestedMetaItem> )
-                 -> ast::MetaItem;
-    fn meta_name_value(&self,
-                       sp: Span,
-                       name: ast::Name,
-                       value: ast::LitKind)
-                       -> ast::MetaItem;
-
-    fn item_use(&self, sp: Span,
-                vis: ast::Visibility, vp: P<ast::UseTree>) -> P<ast::Item>;
-    fn item_use_simple(&self, sp: Span, vis: ast::Visibility, path: ast::Path) -> P<ast::Item>;
-    fn item_use_simple_(&self, sp: Span, vis: ast::Visibility,
-                        ident: Option<ast::Ident>, path: ast::Path) -> P<ast::Item>;
-    fn item_use_list(&self, sp: Span, vis: ast::Visibility,
-                     path: Vec<ast::Ident>, imports: &[ast::Ident]) -> P<ast::Item>;
-    fn item_use_glob(&self, sp: Span,
-                     vis: ast::Visibility, path: Vec<ast::Ident>) -> P<ast::Item>;
-}
+// Left so that Cargo tests don't break, this can be removed once those no longer use it
+pub trait AstBuilder {}
 
-impl<'a> AstBuilder for ExtCtxt<'a> {
-    fn path(&self, span: Span, strs: Vec<ast::Ident> ) -> ast::Path {
+impl<'a> ExtCtxt<'a> {
+    pub fn path(&self, span: Span, strs: Vec<ast::Ident> ) -> ast::Path {
         self.path_all(span, false, strs, vec![], vec![])
     }
-    fn path_ident(&self, span: Span, id: ast::Ident) -> ast::Path {
+    pub fn path_ident(&self, span: Span, id: ast::Ident) -> ast::Path {
         self.path(span, vec![id])
     }
-    fn path_global(&self, span: Span, strs: Vec<ast::Ident> ) -> ast::Path {
+    pub fn path_global(&self, span: Span, strs: Vec<ast::Ident> ) -> ast::Path {
         self.path_all(span, true, strs, vec![], vec![])
     }
-    fn path_all(&self,
+    pub fn path_all(&self,
                 span: Span,
                 global: bool,
                 mut idents: Vec<ast::Ident> ,
                 args: Vec<ast::GenericArg>,
-                bindings: Vec<ast::TypeBinding> )
+                constraints: Vec<ast::AssocTyConstraint> )
                 -> ast::Path {
         assert!(!idents.is_empty());
         let add_root = global && !idents[0].is_path_segment_keyword();
@@ -315,8 +39,8 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         segments.extend(idents.into_iter().map(|ident| {
             ast::PathSegment::from_ident(ident.with_span_pos(span))
         }));
-        let args = if !args.is_empty() || !bindings.is_empty() {
-            ast::AngleBracketedArgs { args, bindings, span }.into()
+        let args = if !args.is_empty() || !constraints.is_empty() {
+            ast::AngleBracketedArgs { args, constraints, span }.into()
         } else {
             None
         };
@@ -331,7 +55,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
     /// Constructs a qualified path.
     ///
     /// Constructs a path like `<self_type as trait_path>::ident`.
-    fn qpath(&self,
+    pub fn qpath(&self,
              self_type: P<ast::Ty>,
              trait_path: ast::Path,
              ident: ast::Ident)
@@ -342,16 +66,16 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
     /// Constructs a qualified path.
     ///
     /// Constructs a path like `<self_type as trait_path>::ident<'a, T, A = Bar>`.
-    fn qpath_all(&self,
+    pub fn qpath_all(&self,
                  self_type: P<ast::Ty>,
                  trait_path: ast::Path,
                  ident: ast::Ident,
                  args: Vec<ast::GenericArg>,
-                 bindings: Vec<ast::TypeBinding>)
+                 constraints: Vec<ast::AssocTyConstraint>)
                  -> (ast::QSelf, ast::Path) {
         let mut path = trait_path;
-        let args = if !args.is_empty() || !bindings.is_empty() {
-            ast::AngleBracketedArgs { args, bindings, span: ident.span }.into()
+        let args = if !args.is_empty() || !constraints.is_empty() {
+            ast::AngleBracketedArgs { args, constraints, span: ident.span }.into()
         } else {
             None
         };
@@ -364,14 +88,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }, path)
     }
 
-    fn ty_mt(&self, ty: P<ast::Ty>, mutbl: ast::Mutability) -> ast::MutTy {
+    pub fn ty_mt(&self, ty: P<ast::Ty>, mutbl: ast::Mutability) -> ast::MutTy {
         ast::MutTy {
             ty,
             mutbl,
         }
     }
 
-    fn ty(&self, span: Span, ty: ast::TyKind) -> P<ast::Ty> {
+    pub fn ty(&self, span: Span, ty: ast::TyKind) -> P<ast::Ty> {
         P(ast::Ty {
             id: ast::DUMMY_NODE_ID,
             span,
@@ -379,18 +103,18 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         })
     }
 
-    fn ty_path(&self, path: ast::Path) -> P<ast::Ty> {
+    pub fn ty_path(&self, path: ast::Path) -> P<ast::Ty> {
         self.ty(path.span, ast::TyKind::Path(None, path))
     }
 
     // Might need to take bounds as an argument in the future, if you ever want
     // to generate a bounded existential trait type.
-    fn ty_ident(&self, span: Span, ident: ast::Ident)
+    pub fn ty_ident(&self, span: Span, ident: ast::Ident)
         -> P<ast::Ty> {
         self.ty_path(self.path_ident(span, ident))
     }
 
-    fn anon_const(&self, span: Span, expr: ast::ExprKind) -> ast::AnonConst {
+    pub fn anon_const(&self, span: Span, expr: ast::ExprKind) -> ast::AnonConst {
         ast::AnonConst {
             id: ast::DUMMY_NODE_ID,
             value: P(ast::Expr {
@@ -402,11 +126,11 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    fn const_ident(&self, span: Span, ident: ast::Ident) -> ast::AnonConst {
+    pub fn const_ident(&self, span: Span, ident: ast::Ident) -> ast::AnonConst {
         self.anon_const(span, ast::ExprKind::Path(None, self.path_ident(span, ident)))
     }
 
-    fn ty_rptr(&self,
+    pub fn ty_rptr(&self,
                span: Span,
                ty: P<ast::Ty>,
                lifetime: Option<ast::Lifetime>,
@@ -416,7 +140,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                 ast::TyKind::Rptr(lifetime, self.ty_mt(ty, mutbl)))
     }
 
-    fn ty_ptr(&self,
+    pub fn ty_ptr(&self,
               span: Span,
               ty: P<ast::Ty>,
               mutbl: ast::Mutability)
@@ -425,20 +149,11 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                 ast::TyKind::Ptr(self.ty_mt(ty, mutbl)))
     }
 
-    fn ty_option(&self, ty: P<ast::Ty>) -> P<ast::Ty> {
-        self.ty_path(
-            self.path_all(DUMMY_SP,
-                          true,
-                          self.std_path(&["option", "Option"]),
-                          vec![ast::GenericArg::Type(ty)],
-                          Vec::new()))
-    }
-
-    fn ty_infer(&self, span: Span) -> P<ast::Ty> {
+    pub fn ty_infer(&self, span: Span) -> P<ast::Ty> {
         self.ty(span, ast::TyKind::Infer)
     }
 
-    fn typaram(&self,
+    pub fn typaram(&self,
                span: Span,
                ident: ast::Ident,
                attrs: Vec<ast::Attribute>,
@@ -455,14 +170,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    fn trait_ref(&self, path: ast::Path) -> ast::TraitRef {
+    pub fn trait_ref(&self, path: ast::Path) -> ast::TraitRef {
         ast::TraitRef {
             path,
             ref_id: ast::DUMMY_NODE_ID,
         }
     }
 
-    fn poly_trait_ref(&self, span: Span, path: ast::Path) -> ast::PolyTraitRef {
+    pub fn poly_trait_ref(&self, span: Span, path: ast::Path) -> ast::PolyTraitRef {
         ast::PolyTraitRef {
             bound_generic_params: Vec::new(),
             trait_ref: self.trait_ref(path),
@@ -470,16 +185,16 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    fn trait_bound(&self, path: ast::Path) -> ast::GenericBound {
+    pub fn trait_bound(&self, path: ast::Path) -> ast::GenericBound {
         ast::GenericBound::Trait(self.poly_trait_ref(path.span, path),
                                  ast::TraitBoundModifier::None)
     }
 
-    fn lifetime(&self, span: Span, ident: ast::Ident) -> ast::Lifetime {
+    pub fn lifetime(&self, span: Span, ident: ast::Ident) -> ast::Lifetime {
         ast::Lifetime { id: ast::DUMMY_NODE_ID, ident: ident.with_span_pos(span) }
     }
 
-    fn lifetime_def(&self,
+    pub fn lifetime_def(&self,
                     span: Span,
                     ident: ast::Ident,
                     attrs: Vec<ast::Attribute>,
@@ -495,7 +210,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    fn stmt_expr(&self, expr: P<ast::Expr>) -> ast::Stmt {
+    pub fn stmt_expr(&self, expr: P<ast::Expr>) -> ast::Stmt {
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,
             span: expr.span,
@@ -503,7 +218,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    fn stmt_semi(&self, expr: P<ast::Expr>) -> ast::Stmt {
+    pub fn stmt_semi(&self, expr: P<ast::Expr>) -> ast::Stmt {
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,
             span: expr.span,
@@ -511,7 +226,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    fn stmt_let(&self, sp: Span, mutbl: bool, ident: ast::Ident,
+    pub fn stmt_let(&self, sp: Span, mutbl: bool, ident: ast::Ident,
                 ex: P<ast::Expr>) -> ast::Stmt {
         let pat = if mutbl {
             let binding_mode = ast::BindingMode::ByValue(ast::Mutability::Mutable);
@@ -526,7 +241,6 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             id: ast::DUMMY_NODE_ID,
             span: sp,
             attrs: ThinVec::new(),
-            source: ast::LocalSource::Normal,
         });
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,
@@ -535,7 +249,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    fn stmt_let_typed(&self,
+    pub fn stmt_let_typed(&self,
                       sp: Span,
                       mutbl: bool,
                       ident: ast::Ident,
@@ -555,7 +269,6 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             id: ast::DUMMY_NODE_ID,
             span: sp,
             attrs: ThinVec::new(),
-            source: ast::LocalSource::Normal,
         });
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,
@@ -564,8 +277,8 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    // Generate `let _: Type;`, usually used for type assertions.
-    fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt {
+    // Generates `let _: Type;`, which is usually used for type assertions.
+    pub fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt {
         let local = P(ast::Local {
             pat: self.pat_wild(span),
             ty: Some(ty),
@@ -573,7 +286,6 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             id: ast::DUMMY_NODE_ID,
             span,
             attrs: ThinVec::new(),
-            source: ast::LocalSource::Normal,
         });
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,
@@ -582,7 +294,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt {
+    pub fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt {
         ast::Stmt {
             id: ast::DUMMY_NODE_ID,
             node: ast::StmtKind::Item(item),
@@ -590,14 +302,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
     }
 
-    fn block_expr(&self, expr: P<ast::Expr>) -> P<ast::Block> {
+    pub fn block_expr(&self, expr: P<ast::Expr>) -> P<ast::Block> {
         self.block(expr.span, vec![ast::Stmt {
             id: ast::DUMMY_NODE_ID,
             span: expr.span,
             node: ast::StmtKind::Expr(expr),
         }])
     }
-    fn block(&self, span: Span, stmts: Vec<ast::Stmt>) -> P<ast::Block> {
+    pub fn block(&self, span: Span, stmts: Vec<ast::Stmt>) -> P<ast::Block> {
         P(ast::Block {
            stmts,
            id: ast::DUMMY_NODE_ID,
@@ -606,7 +318,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         })
     }
 
-    fn expr(&self, span: Span, node: ast::ExprKind) -> P<ast::Expr> {
+    pub fn expr(&self, span: Span, node: ast::ExprKind) -> P<ast::Expr> {
         P(ast::Expr {
             id: ast::DUMMY_NODE_ID,
             node,
@@ -615,61 +327,65 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         })
     }
 
-    fn expr_path(&self, path: ast::Path) -> P<ast::Expr> {
+    pub fn expr_path(&self, path: ast::Path) -> P<ast::Expr> {
         self.expr(path.span, ast::ExprKind::Path(None, path))
     }
 
-    /// Constructs a QPath expression.
-    fn expr_qpath(&self, span: Span, qself: ast::QSelf, path: ast::Path) -> P<ast::Expr> {
+    /// Constructs a `QPath` expression.
+    pub fn expr_qpath(&self, span: Span, qself: ast::QSelf, path: ast::Path) -> P<ast::Expr> {
         self.expr(span, ast::ExprKind::Path(Some(qself), path))
     }
 
-    fn expr_ident(&self, span: Span, id: ast::Ident) -> P<ast::Expr> {
+    pub fn expr_ident(&self, span: Span, id: ast::Ident) -> P<ast::Expr> {
         self.expr_path(self.path_ident(span, id))
     }
-    fn expr_self(&self, span: Span) -> P<ast::Expr> {
-        self.expr_ident(span, keywords::SelfLower.ident())
+    pub fn expr_self(&self, span: Span) -> P<ast::Expr> {
+        self.expr_ident(span, Ident::with_dummy_span(kw::SelfLower))
     }
 
-    fn expr_binary(&self, sp: Span, op: ast::BinOpKind,
+    pub fn expr_binary(&self, sp: Span, op: ast::BinOpKind,
                    lhs: P<ast::Expr>, rhs: P<ast::Expr>) -> P<ast::Expr> {
         self.expr(sp, ast::ExprKind::Binary(Spanned { node: op, span: sp }, lhs, rhs))
     }
 
-    fn expr_deref(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_deref(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr> {
         self.expr_unary(sp, UnOp::Deref, e)
     }
-    fn expr_unary(&self, sp: Span, op: ast::UnOp, e: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_unary(&self, sp: Span, op: ast::UnOp, e: P<ast::Expr>) -> P<ast::Expr> {
         self.expr(sp, ast::ExprKind::Unary(op, e))
     }
 
-    fn expr_field_access(&self, sp: Span, expr: P<ast::Expr>, ident: ast::Ident) -> P<ast::Expr> {
+    pub fn expr_field_access(
+        &self, sp: Span, expr: P<ast::Expr>, ident: ast::Ident,
+    ) -> P<ast::Expr> {
         self.expr(sp, ast::ExprKind::Field(expr, ident.with_span_pos(sp)))
     }
-    fn expr_tup_field_access(&self, sp: Span, expr: P<ast::Expr>, idx: usize) -> P<ast::Expr> {
+    pub fn expr_tup_field_access(&self, sp: Span, expr: P<ast::Expr>, idx: usize) -> P<ast::Expr> {
         let ident = Ident::from_str(&idx.to_string()).with_span_pos(sp);
         self.expr(sp, ast::ExprKind::Field(expr, ident))
     }
-    fn expr_addr_of(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_addr_of(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr> {
         self.expr(sp, ast::ExprKind::AddrOf(ast::Mutability::Immutable, e))
     }
-    fn expr_mut_addr_of(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_mut_addr_of(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr> {
         self.expr(sp, ast::ExprKind::AddrOf(ast::Mutability::Mutable, e))
     }
 
-    fn expr_call(&self, span: Span, expr: P<ast::Expr>, args: Vec<P<ast::Expr>>) -> P<ast::Expr> {
+    pub fn expr_call(
+        &self, span: Span, expr: P<ast::Expr>, args: Vec<P<ast::Expr>>,
+    ) -> P<ast::Expr> {
         self.expr(span, ast::ExprKind::Call(expr, args))
     }
-    fn expr_call_ident(&self, span: Span, id: ast::Ident,
+    pub fn expr_call_ident(&self, span: Span, id: ast::Ident,
                        args: Vec<P<ast::Expr>>) -> P<ast::Expr> {
         self.expr(span, ast::ExprKind::Call(self.expr_ident(span, id), args))
     }
-    fn expr_call_global(&self, sp: Span, fn_path: Vec<ast::Ident> ,
+    pub fn expr_call_global(&self, sp: Span, fn_path: Vec<ast::Ident> ,
                       args: Vec<P<ast::Expr>> ) -> P<ast::Expr> {
         let pathexpr = self.expr_path(self.path_global(sp, fn_path));
         self.expr_call(sp, pathexpr, args)
     }
-    fn expr_method_call(&self, span: Span,
+    pub fn expr_method_call(&self, span: Span,
                         expr: P<ast::Expr>,
                         ident: ast::Ident,
                         mut args: Vec<P<ast::Expr>> ) -> P<ast::Expr> {
@@ -677,35 +393,38 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         let segment = ast::PathSegment::from_ident(ident.with_span_pos(span));
         self.expr(span, ast::ExprKind::MethodCall(segment, args))
     }
-    fn expr_block(&self, b: P<ast::Block>) -> P<ast::Expr> {
+    pub fn expr_block(&self, b: P<ast::Block>) -> P<ast::Expr> {
         self.expr(b.span, ast::ExprKind::Block(b, None))
     }
-    fn field_imm(&self, span: Span, ident: Ident, e: P<ast::Expr>) -> ast::Field {
+    pub fn field_imm(&self, span: Span, ident: Ident, e: P<ast::Expr>) -> ast::Field {
         ast::Field {
             ident: ident.with_span_pos(span),
             expr: e,
             span,
             is_shorthand: false,
             attrs: ThinVec::new(),
+            id: ast::DUMMY_NODE_ID,
         }
     }
-    fn expr_struct(&self, span: Span, path: ast::Path, fields: Vec<ast::Field>) -> P<ast::Expr> {
+    pub fn expr_struct(
+        &self, span: Span, path: ast::Path, fields: Vec<ast::Field>
+    ) -> P<ast::Expr> {
         self.expr(span, ast::ExprKind::Struct(path, fields, None))
     }
-    fn expr_struct_ident(&self, span: Span,
+    pub fn expr_struct_ident(&self, span: Span,
                          id: ast::Ident, fields: Vec<ast::Field>) -> P<ast::Expr> {
         self.expr_struct(span, self.path_ident(span, id), fields)
     }
 
-    fn expr_lit(&self, span: Span, lit_kind: ast::LitKind) -> P<ast::Expr> {
+    pub fn expr_lit(&self, span: Span, lit_kind: ast::LitKind) -> P<ast::Expr> {
         let lit = ast::Lit::from_lit_kind(lit_kind, span);
         self.expr(span, ast::ExprKind::Lit(lit))
     }
-    fn expr_usize(&self, span: Span, i: usize) -> P<ast::Expr> {
+    pub fn expr_usize(&self, span: Span, i: usize) -> P<ast::Expr> {
         self.expr_lit(span, ast::LitKind::Int(i as u128,
                                               ast::LitIntType::Unsigned(ast::UintTy::Usize)))
     }
-    fn expr_isize(&self, sp: Span, i: isize) -> P<ast::Expr> {
+    pub fn expr_isize(&self, sp: Span, i: isize) -> P<ast::Expr> {
         if i < 0 {
             let i = (-i) as u128;
             let lit_ty = ast::LitIntType::Signed(ast::IntTy::Isize);
@@ -716,62 +435,59 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                                                 ast::LitIntType::Signed(ast::IntTy::Isize)))
         }
     }
-    fn expr_u32(&self, sp: Span, u: u32) -> P<ast::Expr> {
+    pub fn expr_u32(&self, sp: Span, u: u32) -> P<ast::Expr> {
         self.expr_lit(sp, ast::LitKind::Int(u as u128,
                                             ast::LitIntType::Unsigned(ast::UintTy::U32)))
     }
-    fn expr_u16(&self, sp: Span, u: u16) -> P<ast::Expr> {
+    pub fn expr_u16(&self, sp: Span, u: u16) -> P<ast::Expr> {
         self.expr_lit(sp, ast::LitKind::Int(u as u128,
                                             ast::LitIntType::Unsigned(ast::UintTy::U16)))
     }
-    fn expr_u8(&self, sp: Span, u: u8) -> P<ast::Expr> {
+    pub fn expr_u8(&self, sp: Span, u: u8) -> P<ast::Expr> {
         self.expr_lit(sp, ast::LitKind::Int(u as u128, ast::LitIntType::Unsigned(ast::UintTy::U8)))
     }
-    fn expr_bool(&self, sp: Span, value: bool) -> P<ast::Expr> {
+    pub fn expr_bool(&self, sp: Span, value: bool) -> P<ast::Expr> {
         self.expr_lit(sp, ast::LitKind::Bool(value))
     }
 
-    fn expr_vec(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr> {
+    pub fn expr_vec(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr> {
         self.expr(sp, ast::ExprKind::Array(exprs))
     }
-    fn expr_vec_ng(&self, sp: Span) -> P<ast::Expr> {
-        self.expr_call_global(sp, self.std_path(&["vec", "Vec", "new"]),
+    pub fn expr_vec_ng(&self, sp: Span) -> P<ast::Expr> {
+        self.expr_call_global(sp, self.std_path(&[sym::vec, sym::Vec, sym::new]),
                               Vec::new())
     }
-    fn expr_vec_slice(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr> {
+    pub fn expr_vec_slice(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr> {
         self.expr_addr_of(sp, self.expr_vec(sp, exprs))
     }
-    fn expr_str(&self, sp: Span, s: Symbol) -> P<ast::Expr> {
+    pub fn expr_str(&self, sp: Span, s: Symbol) -> P<ast::Expr> {
         self.expr_lit(sp, ast::LitKind::Str(s, ast::StrStyle::Cooked))
     }
 
-    fn expr_cast(&self, sp: Span, expr: P<ast::Expr>, ty: P<ast::Ty>) -> P<ast::Expr> {
+    pub fn expr_cast(&self, sp: Span, expr: P<ast::Expr>, ty: P<ast::Ty>) -> P<ast::Expr> {
         self.expr(sp, ast::ExprKind::Cast(expr, ty))
     }
 
-
-    fn expr_some(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
-        let some = self.std_path(&["option", "Option", "Some"]);
+    pub fn expr_some(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
+        let some = self.std_path(&[sym::option, sym::Option, sym::Some]);
         self.expr_call_global(sp, some, vec![expr])
     }
 
-    fn expr_none(&self, sp: Span) -> P<ast::Expr> {
-        let none = self.std_path(&["option", "Option", "None"]);
+    pub fn expr_none(&self, sp: Span) -> P<ast::Expr> {
+        let none = self.std_path(&[sym::option, sym::Option, sym::None]);
         let none = self.path_global(sp, none);
         self.expr_path(none)
     }
 
-
-    fn expr_break(&self, sp: Span) -> P<ast::Expr> {
+    pub fn expr_break(&self, sp: Span) -> P<ast::Expr> {
         self.expr(sp, ast::ExprKind::Break(None, None))
     }
 
-
-    fn expr_tuple(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr> {
+    pub fn expr_tuple(&self, sp: Span, exprs: Vec<P<ast::Expr>>) -> P<ast::Expr> {
         self.expr(sp, ast::ExprKind::Tup(exprs))
     }
 
-    fn expr_fail(&self, span: Span, msg: Symbol) -> P<ast::Expr> {
+    pub fn expr_fail(&self, span: Span, msg: Symbol) -> P<ast::Expr> {
         let loc = self.source_map().lookup_char_pos(span.lo());
         let expr_file = self.expr_str(span, Symbol::intern(&loc.file.name.to_string()));
         let expr_line = self.expr_u32(span, loc.line as u32);
@@ -780,144 +496,146 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         let expr_loc_ptr = self.expr_addr_of(span, expr_loc_tuple);
         self.expr_call_global(
             span,
-            self.std_path(&["rt", "begin_panic"]),
+            [sym::std, sym::rt, sym::begin_panic].iter().map(|s| Ident::new(*s, span)).collect(),
             vec![
                 self.expr_str(span, msg),
                 expr_loc_ptr])
     }
 
-    fn expr_unreachable(&self, span: Span) -> P<ast::Expr> {
+    pub fn expr_unreachable(&self, span: Span) -> P<ast::Expr> {
         self.expr_fail(span, Symbol::intern("internal error: entered unreachable code"))
     }
 
-    fn expr_ok(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
-        let ok = self.std_path(&["result", "Result", "Ok"]);
+    pub fn expr_ok(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
+        let ok = self.std_path(&[sym::result, sym::Result, sym::Ok]);
         self.expr_call_global(sp, ok, vec![expr])
     }
 
-    fn expr_err(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
-        let err = self.std_path(&["result", "Result", "Err"]);
+    pub fn expr_err(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
+        let err = self.std_path(&[sym::result, sym::Result, sym::Err]);
         self.expr_call_global(sp, err, vec![expr])
     }
 
-    fn expr_try(&self, sp: Span, head: P<ast::Expr>) -> P<ast::Expr> {
-        let ok = self.std_path(&["result", "Result", "Ok"]);
+    pub fn expr_try(&self, sp: Span, head: P<ast::Expr>) -> P<ast::Expr> {
+        let ok = self.std_path(&[sym::result, sym::Result, sym::Ok]);
         let ok_path = self.path_global(sp, ok);
-        let err = self.std_path(&["result", "Result", "Err"]);
+        let err = self.std_path(&[sym::result, sym::Result, sym::Err]);
         let err_path = self.path_global(sp, err);
 
         let binding_variable = self.ident_of("__try_var");
         let binding_pat = self.pat_ident(sp, binding_variable);
         let binding_expr = self.expr_ident(sp, binding_variable);
 
-        // Ok(__try_var) pattern
+        // `Ok(__try_var)` pattern
         let ok_pat = self.pat_tuple_struct(sp, ok_path, vec![binding_pat.clone()]);
 
-        // Err(__try_var)  (pattern and expression resp.)
+        // `Err(__try_var)` (pattern and expression respectively)
         let err_pat = self.pat_tuple_struct(sp, err_path.clone(), vec![binding_pat]);
         let err_inner_expr = self.expr_call(sp, self.expr_path(err_path),
                                             vec![binding_expr.clone()]);
-        // return Err(__try_var)
+        // `return Err(__try_var)`
         let err_expr = self.expr(sp, ast::ExprKind::Ret(Some(err_inner_expr)));
 
-        // Ok(__try_var) => __try_var
+        // `Ok(__try_var) => __try_var`
         let ok_arm = self.arm(sp, vec![ok_pat], binding_expr);
-        // Err(__try_var) => return Err(__try_var)
+        // `Err(__try_var) => return Err(__try_var)`
         let err_arm = self.arm(sp, vec![err_pat], err_expr);
 
-        // match head { Ok() => ..., Err() => ... }
+        // `match head { Ok() => ..., Err() => ... }`
         self.expr_match(sp, head, vec![ok_arm, err_arm])
     }
 
 
-    fn pat(&self, span: Span, pat: PatKind) -> P<ast::Pat> {
-        P(ast::Pat { id: ast::DUMMY_NODE_ID, node: pat, span: span })
+    pub fn pat(&self, span: Span, pat: PatKind) -> P<ast::Pat> {
+        P(ast::Pat { id: ast::DUMMY_NODE_ID, node: pat, span })
     }
-    fn pat_wild(&self, span: Span) -> P<ast::Pat> {
+    pub fn pat_wild(&self, span: Span) -> P<ast::Pat> {
         self.pat(span, PatKind::Wild)
     }
-    fn pat_lit(&self, span: Span, expr: P<ast::Expr>) -> P<ast::Pat> {
+    pub fn pat_lit(&self, span: Span, expr: P<ast::Expr>) -> P<ast::Pat> {
         self.pat(span, PatKind::Lit(expr))
     }
-    fn pat_ident(&self, span: Span, ident: ast::Ident) -> P<ast::Pat> {
+    pub fn pat_ident(&self, span: Span, ident: ast::Ident) -> P<ast::Pat> {
         let binding_mode = ast::BindingMode::ByValue(ast::Mutability::Immutable);
         self.pat_ident_binding_mode(span, ident, binding_mode)
     }
 
-    fn pat_ident_binding_mode(&self,
+    pub fn pat_ident_binding_mode(&self,
                               span: Span,
                               ident: ast::Ident,
                               bm: ast::BindingMode) -> P<ast::Pat> {
         let pat = PatKind::Ident(bm, ident.with_span_pos(span), None);
         self.pat(span, pat)
     }
-    fn pat_path(&self, span: Span, path: ast::Path) -> P<ast::Pat> {
+    pub fn pat_path(&self, span: Span, path: ast::Path) -> P<ast::Pat> {
         self.pat(span, PatKind::Path(None, path))
     }
-    fn pat_tuple_struct(&self, span: Span, path: ast::Path,
+    pub fn pat_tuple_struct(&self, span: Span, path: ast::Path,
                         subpats: Vec<P<ast::Pat>>) -> P<ast::Pat> {
-        self.pat(span, PatKind::TupleStruct(path, subpats, None))
+        self.pat(span, PatKind::TupleStruct(path, subpats))
     }
-    fn pat_struct(&self, span: Span, path: ast::Path,
-                  field_pats: Vec<Spanned<ast::FieldPat>>) -> P<ast::Pat> {
+    pub fn pat_struct(&self, span: Span, path: ast::Path,
+                      field_pats: Vec<ast::FieldPat>) -> P<ast::Pat> {
         self.pat(span, PatKind::Struct(path, field_pats, false))
     }
-    fn pat_tuple(&self, span: Span, pats: Vec<P<ast::Pat>>) -> P<ast::Pat> {
-        self.pat(span, PatKind::Tuple(pats, None))
+    pub fn pat_tuple(&self, span: Span, pats: Vec<P<ast::Pat>>) -> P<ast::Pat> {
+        self.pat(span, PatKind::Tuple(pats))
     }
 
-    fn pat_some(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat> {
-        let some = self.std_path(&["option", "Option", "Some"]);
+    pub fn pat_some(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat> {
+        let some = self.std_path(&[sym::option, sym::Option, sym::Some]);
         let path = self.path_global(span, some);
         self.pat_tuple_struct(span, path, vec![pat])
     }
 
-    fn pat_none(&self, span: Span) -> P<ast::Pat> {
-        let some = self.std_path(&["option", "Option", "None"]);
+    pub fn pat_none(&self, span: Span) -> P<ast::Pat> {
+        let some = self.std_path(&[sym::option, sym::Option, sym::None]);
         let path = self.path_global(span, some);
         self.pat_path(span, path)
     }
 
-    fn pat_ok(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat> {
-        let some = self.std_path(&["result", "Result", "Ok"]);
+    pub fn pat_ok(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat> {
+        let some = self.std_path(&[sym::result, sym::Result, sym::Ok]);
         let path = self.path_global(span, some);
         self.pat_tuple_struct(span, path, vec![pat])
     }
 
-    fn pat_err(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat> {
-        let some = self.std_path(&["result", "Result", "Err"]);
+    pub fn pat_err(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat> {
+        let some = self.std_path(&[sym::result, sym::Result, sym::Err]);
         let path = self.path_global(span, some);
         self.pat_tuple_struct(span, path, vec![pat])
     }
 
-    fn arm(&self, _span: Span, pats: Vec<P<ast::Pat>>, expr: P<ast::Expr>) -> ast::Arm {
+    pub fn arm(&self, span: Span, pats: Vec<P<ast::Pat>>, expr: P<ast::Expr>) -> ast::Arm {
         ast::Arm {
             attrs: vec![],
             pats,
             guard: None,
             body: expr,
+            span,
+            id: ast::DUMMY_NODE_ID,
         }
     }
 
-    fn arm_unreachable(&self, span: Span) -> ast::Arm {
+    pub fn arm_unreachable(&self, span: Span) -> ast::Arm {
         self.arm(span, vec![self.pat_wild(span)], self.expr_unreachable(span))
     }
 
-    fn expr_match(&self, span: Span, arg: P<ast::Expr>, arms: Vec<ast::Arm>) -> P<Expr> {
+    pub fn expr_match(&self, span: Span, arg: P<ast::Expr>, arms: Vec<ast::Arm>) -> P<Expr> {
         self.expr(span, ast::ExprKind::Match(arg, arms))
     }
 
-    fn expr_if(&self, span: Span, cond: P<ast::Expr>,
+    pub fn expr_if(&self, span: Span, cond: P<ast::Expr>,
                then: P<ast::Expr>, els: Option<P<ast::Expr>>) -> P<ast::Expr> {
         let els = els.map(|x| self.expr_block(self.block_expr(x)));
         self.expr(span, ast::ExprKind::If(cond, self.block_expr(then), els))
     }
 
-    fn expr_loop(&self, span: Span, block: P<ast::Block>) -> P<ast::Expr> {
+    pub fn expr_loop(&self, span: Span, block: P<ast::Block>) -> P<ast::Expr> {
         self.expr(span, ast::ExprKind::Loop(block, None))
     }
 
-    fn lambda_fn_decl(&self,
+    pub fn lambda_fn_decl(&self,
                       span: Span,
                       fn_decl: P<ast::FnDecl>,
                       body: P<ast::Expr>,
@@ -931,7 +649,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                                                fn_decl_span))
     }
 
-    fn lambda(&self,
+    pub fn lambda(&self,
               span: Span,
               ids: Vec<ast::Ident>,
               body: P<ast::Expr>)
@@ -952,41 +670,42 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                                                span))
     }
 
-    fn lambda0(&self, span: Span, body: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn lambda0(&self, span: Span, body: P<ast::Expr>) -> P<ast::Expr> {
         self.lambda(span, Vec::new(), body)
     }
 
-    fn lambda1(&self, span: Span, body: P<ast::Expr>, ident: ast::Ident) -> P<ast::Expr> {
+    pub fn lambda1(&self, span: Span, body: P<ast::Expr>, ident: ast::Ident) -> P<ast::Expr> {
         self.lambda(span, vec![ident], body)
     }
 
-    fn lambda_stmts(&self,
+    pub fn lambda_stmts(&self,
                     span: Span,
                     ids: Vec<ast::Ident>,
                     stmts: Vec<ast::Stmt>)
                     -> P<ast::Expr> {
         self.lambda(span, ids, self.expr_block(self.block(span, stmts)))
     }
-    fn lambda_stmts_0(&self, span: Span, stmts: Vec<ast::Stmt>) -> P<ast::Expr> {
+    pub fn lambda_stmts_0(&self, span: Span, stmts: Vec<ast::Stmt>) -> P<ast::Expr> {
         self.lambda0(span, self.expr_block(self.block(span, stmts)))
     }
-    fn lambda_stmts_1(&self, span: Span, stmts: Vec<ast::Stmt>,
+    pub fn lambda_stmts_1(&self, span: Span, stmts: Vec<ast::Stmt>,
                       ident: ast::Ident) -> P<ast::Expr> {
         self.lambda1(span, self.expr_block(self.block(span, stmts)), ident)
     }
 
-    fn arg(&self, span: Span, ident: ast::Ident, ty: P<ast::Ty>) -> ast::Arg {
+    pub fn arg(&self, span: Span, ident: ast::Ident, ty: P<ast::Ty>) -> ast::Arg {
         let arg_pat = self.pat_ident(span, ident);
         ast::Arg {
-            ty,
-            pat: arg_pat,
+            attrs: ThinVec::default(),
             id: ast::DUMMY_NODE_ID,
-            source: ast::ArgSource::Normal,
+            pat: arg_pat,
+            span,
+            ty,
         }
     }
 
-    // FIXME unused self
-    fn fn_decl(&self, inputs: Vec<ast::Arg>, output: ast::FunctionRetTy) -> P<ast::FnDecl> {
+    // FIXME: unused `self`
+    pub fn fn_decl(&self, inputs: Vec<ast::Arg>, output: ast::FunctionRetTy) -> P<ast::FnDecl> {
         P(ast::FnDecl {
             inputs,
             output,
@@ -994,7 +713,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         })
     }
 
-    fn item(&self, span: Span, name: Ident,
+    pub fn item(&self, span: Span, name: Ident,
             attrs: Vec<ast::Attribute>, node: ast::ItemKind) -> P<ast::Item> {
         // FIXME: Would be nice if our generated code didn't violate
         // Rust coding conventions
@@ -1009,7 +728,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         })
     }
 
-    fn item_fn_poly(&self,
+    pub fn item_fn_poly(&self,
                     span: Span,
                     name: Ident,
                     inputs: Vec<ast::Arg> ,
@@ -1030,7 +749,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                               body))
     }
 
-    fn item_fn(&self,
+    pub fn item_fn(&self,
                span: Span,
                name: Ident,
                inputs: Vec<ast::Arg> ,
@@ -1046,7 +765,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             body)
     }
 
-    fn variant(&self, span: Span, ident: Ident, tys: Vec<P<ast::Ty>> ) -> ast::Variant {
+    pub fn variant(&self, span: Span, ident: Ident, tys: Vec<P<ast::Ty>> ) -> ast::Variant {
         let fields: Vec<_> = tys.into_iter().map(|ty| {
             ast::StructField {
                 span: ty.span,
@@ -1064,29 +783,29 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             ast::VariantData::Tuple(fields, ast::DUMMY_NODE_ID)
         };
 
-        respan(span,
-               ast::Variant_ {
-                   ident,
-                   id: ast::DUMMY_NODE_ID,
-                   attrs: Vec::new(),
-                   data: vdata,
-                   disr_expr: None,
-               })
+        ast::Variant {
+            attrs: Vec::new(),
+            data: vdata,
+            disr_expr: None,
+            id: ast::DUMMY_NODE_ID,
+            ident,
+            span,
+        }
     }
 
-    fn item_enum_poly(&self, span: Span, name: Ident,
+    pub fn item_enum_poly(&self, span: Span, name: Ident,
                       enum_definition: ast::EnumDef,
                       generics: Generics) -> P<ast::Item> {
         self.item(span, name, Vec::new(), ast::ItemKind::Enum(enum_definition, generics))
     }
 
-    fn item_enum(&self, span: Span, name: Ident,
+    pub fn item_enum(&self, span: Span, name: Ident,
                  enum_definition: ast::EnumDef) -> P<ast::Item> {
         self.item_enum_poly(span, name, enum_definition,
                             Generics::default())
     }
 
-    fn item_struct(&self, span: Span, name: Ident,
+    pub fn item_struct(&self, span: Span, name: Ident,
                    struct_def: ast::VariantData) -> P<ast::Item> {
         self.item_struct_poly(
             span,
@@ -1096,12 +815,12 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         )
     }
 
-    fn item_struct_poly(&self, span: Span, name: Ident,
+    pub fn item_struct_poly(&self, span: Span, name: Ident,
         struct_def: ast::VariantData, generics: Generics) -> P<ast::Item> {
         self.item(span, name, Vec::new(), ast::ItemKind::Struct(struct_def, generics))
     }
 
-    fn item_mod(&self, span: Span, inner_span: Span, name: Ident,
+    pub fn item_mod(&self, span: Span, inner_span: Span, name: Ident,
                 attrs: Vec<ast::Attribute>,
                 items: Vec<P<ast::Item>>) -> P<ast::Item> {
         self.item(
@@ -1116,11 +835,11 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         )
     }
 
-    fn item_extern_crate(&self, span: Span, name: Ident) -> P<ast::Item> {
+    pub fn item_extern_crate(&self, span: Span, name: Ident) -> P<ast::Item> {
         self.item(span, name, Vec::new(), ast::ItemKind::ExternCrate(None))
     }
 
-    fn item_static(&self,
+    pub fn item_static(&self,
                    span: Span,
                    name: Ident,
                    ty: P<ast::Ty>,
@@ -1130,7 +849,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         self.item(span, name, Vec::new(), ast::ItemKind::Static(ty, mutbl, expr))
     }
 
-    fn item_const(&self,
+    pub fn item_const(&self,
                   span: Span,
                   name: Ident,
                   ty: P<ast::Ty>,
@@ -1139,43 +858,42 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         self.item(span, name, Vec::new(), ast::ItemKind::Const(ty, expr))
     }
 
-    fn item_ty_poly(&self, span: Span, name: Ident, ty: P<ast::Ty>,
+    pub fn item_ty_poly(&self, span: Span, name: Ident, ty: P<ast::Ty>,
                     generics: Generics) -> P<ast::Item> {
-        self.item(span, name, Vec::new(), ast::ItemKind::Ty(ty, generics))
+        self.item(span, name, Vec::new(), ast::ItemKind::TyAlias(ty, generics))
     }
 
-    fn item_ty(&self, span: Span, name: Ident, ty: P<ast::Ty>) -> P<ast::Item> {
+    pub fn item_ty(&self, span: Span, name: Ident, ty: P<ast::Ty>) -> P<ast::Item> {
         self.item_ty_poly(span, name, ty, Generics::default())
     }
 
-    fn attribute(&self, sp: Span, mi: ast::MetaItem) -> ast::Attribute {
-        attr::mk_spanned_attr_outer(sp, attr::mk_attr_id(), mi)
+    pub fn attribute(&self, mi: ast::MetaItem) -> ast::Attribute {
+        attr::mk_attr_outer(mi)
     }
 
-    fn meta_word(&self, sp: Span, w: ast::Name) -> ast::MetaItem {
-        attr::mk_word_item(Ident::with_empty_ctxt(w).with_span_pos(sp))
+    pub fn meta_word(&self, sp: Span, w: ast::Name) -> ast::MetaItem {
+        attr::mk_word_item(Ident::new(w, sp))
     }
 
-    fn meta_list_item_word(&self, sp: Span, w: ast::Name) -> ast::NestedMetaItem {
-        attr::mk_nested_word_item(Ident::with_empty_ctxt(w).with_span_pos(sp))
+    pub fn meta_list_item_word(&self, sp: Span, w: ast::Name) -> ast::NestedMetaItem {
+        attr::mk_nested_word_item(Ident::new(w, sp))
     }
 
-    fn meta_list(&self, sp: Span, name: ast::Name, mis: Vec<ast::NestedMetaItem>)
+    pub fn meta_list(&self, sp: Span, name: ast::Name, mis: Vec<ast::NestedMetaItem>)
                  -> ast::MetaItem {
-        attr::mk_list_item(sp, Ident::with_empty_ctxt(name).with_span_pos(sp), mis)
+        attr::mk_list_item(Ident::new(name, sp), mis)
     }
 
-    fn meta_name_value(&self, span: Span, name: ast::Name, lit_kind: ast::LitKind)
+    pub fn meta_name_value(&self, span: Span, name: ast::Name, lit_kind: ast::LitKind)
                        -> ast::MetaItem {
-        attr::mk_name_value_item(span, Ident::with_empty_ctxt(name).with_span_pos(span),
-                                 lit_kind, span)
+        attr::mk_name_value_item(Ident::new(name, span), lit_kind, span)
     }
 
-    fn item_use(&self, sp: Span,
+    pub fn item_use(&self, sp: Span,
                 vis: ast::Visibility, vp: P<ast::UseTree>) -> P<ast::Item> {
         P(ast::Item {
             id: ast::DUMMY_NODE_ID,
-            ident: keywords::Invalid.ident(),
+            ident: Ident::invalid(),
             attrs: vec![],
             node: ast::ItemKind::Use(vp),
             vis,
@@ -1184,11 +902,11 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         })
     }
 
-    fn item_use_simple(&self, sp: Span, vis: ast::Visibility, path: ast::Path) -> P<ast::Item> {
+    pub fn item_use_simple(&self, sp: Span, vis: ast::Visibility, path: ast::Path) -> P<ast::Item> {
         self.item_use_simple_(sp, vis, None, path)
     }
 
-    fn item_use_simple_(&self, sp: Span, vis: ast::Visibility,
+    pub fn item_use_simple_(&self, sp: Span, vis: ast::Visibility,
                         rename: Option<ast::Ident>, path: ast::Path) -> P<ast::Item> {
         self.item_use(sp, vis, P(ast::UseTree {
             span: sp,
@@ -1197,7 +915,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }))
     }
 
-    fn item_use_list(&self, sp: Span, vis: ast::Visibility,
+    pub fn item_use_list(&self, sp: Span, vis: ast::Visibility,
                      path: Vec<ast::Ident>, imports: &[ast::Ident]) -> P<ast::Item> {
         let imports = imports.iter().map(|id| {
             (ast::UseTree {
@@ -1214,7 +932,7 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }))
     }
 
-    fn item_use_glob(&self, sp: Span,
+    pub fn item_use_glob(&self, sp: Span,
                      vis: ast::Visibility, path: Vec<ast::Ident>) -> P<ast::Item> {
         self.item_use(sp, vis, P(ast::UseTree {
             span: sp,
diff --git a/src/libsyntax/ext/derive.rs b/src/libsyntax/ext/derive.rs
deleted file mode 100644
index a24e09f127e..00000000000
--- a/src/libsyntax/ext/derive.rs
+++ /dev/null
@@ -1,81 +0,0 @@
-use crate::attr::HasAttrs;
-use crate::ast;
-use crate::source_map::{hygiene, ExpnInfo, ExpnFormat};
-use crate::ext::base::ExtCtxt;
-use crate::ext::build::AstBuilder;
-use crate::parse::parser::PathStyle;
-use crate::symbol::{Symbol, sym};
-
-use syntax_pos::Span;
-
-use rustc_data_structures::fx::FxHashSet;
-
-pub fn collect_derives(cx: &mut ExtCtxt<'_>, attrs: &mut Vec<ast::Attribute>) -> Vec<ast::Path> {
-    let mut result = Vec::new();
-    attrs.retain(|attr| {
-        if attr.path != sym::derive {
-            return true;
-        }
-        if !attr.is_meta_item_list() {
-            cx.span_err(attr.span,
-                        "attribute must be of the form `#[derive(Trait1, Trait2, ...)]`");
-            return false;
-        }
-
-        match attr.parse_list(cx.parse_sess,
-                              |parser| parser.parse_path_allowing_meta(PathStyle::Mod)) {
-            Ok(ref traits) if traits.is_empty() => {
-                cx.span_warn(attr.span, "empty trait list in `derive`");
-                false
-            }
-            Ok(traits) => {
-                result.extend(traits);
-                true
-            }
-            Err(mut e) => {
-                e.emit();
-                false
-            }
-        }
-    });
-    result
-}
-
-pub fn add_derived_markers<T>(cx: &mut ExtCtxt<'_>, span: Span, traits: &[ast::Path], item: &mut T)
-    where T: HasAttrs,
-{
-    let (mut names, mut pretty_name) = (FxHashSet::default(), "derive(".to_owned());
-    for (i, path) in traits.iter().enumerate() {
-        if i > 0 {
-            pretty_name.push_str(", ");
-        }
-        pretty_name.push_str(&path.to_string());
-        names.insert(unwrap_or!(path.segments.get(0), continue).ident.name);
-    }
-    pretty_name.push(')');
-
-    cx.current_expansion.mark.set_expn_info(ExpnInfo {
-        call_site: span,
-        def_site: None,
-        format: ExpnFormat::MacroAttribute(Symbol::intern(&pretty_name)),
-        allow_internal_unstable: Some(vec![
-            Symbol::intern("rustc_attrs"),
-            Symbol::intern("structural_match"),
-        ].into()),
-        allow_internal_unsafe: false,
-        local_inner_macros: false,
-        edition: hygiene::default_edition(),
-    });
-
-    let span = span.with_ctxt(cx.backtrace());
-    item.visit_attrs(|attrs| {
-        if names.contains(&Symbol::intern("Eq")) && names.contains(&Symbol::intern("PartialEq")) {
-            let meta = cx.meta_word(span, Symbol::intern("structural_match"));
-            attrs.push(cx.attribute(span, meta));
-        }
-        if names.contains(&Symbol::intern("Copy")) {
-            let meta = cx.meta_word(span, Symbol::intern("rustc_copy_clone_marker"));
-            attrs.push(cx.attribute(span, meta));
-        }
-    });
-}
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 019ebc8566f..c1d52c97455 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -1,20 +1,20 @@
 use crate::ast::{self, Block, Ident, LitKind, NodeId, PatKind, Path};
 use crate::ast::{MacStmtStyle, StmtKind, ItemKind};
 use crate::attr::{self, HasAttrs};
-use crate::source_map::{ExpnInfo, MacroBang, MacroAttribute, dummy_spanned, respan};
+use crate::source_map::respan;
 use crate::config::StripUnconfigured;
 use crate::ext::base::*;
-use crate::ext::derive::{add_derived_markers, collect_derives};
-use crate::ext::hygiene::{self, Mark, SyntaxContext};
+use crate::ext::proc_macro::collect_derives;
+use crate::ext::hygiene::{ExpnId, SyntaxContext, ExpnData, ExpnKind};
+use crate::ext::tt::macro_rules::annotate_err_with_kind;
 use crate::ext::placeholders::{placeholder, PlaceholderExpander};
 use crate::feature_gate::{self, Features, GateIssue, is_builtin_attr, emit_feature_err};
 use crate::mut_visit::*;
 use crate::parse::{DirectoryOwnership, PResult, ParseSess};
-use crate::parse::token::{self, Token};
+use crate::parse::token;
 use crate::parse::parser::Parser;
 use crate::ptr::P;
-use crate::symbol::Symbol;
-use crate::symbol::{keywords, sym};
+use crate::symbol::{sym, Symbol};
 use crate::tokenstream::{TokenStream, TokenTree};
 use crate::visit::{self, Visitor};
 use crate::util::map_in_place::MapInPlace;
@@ -22,11 +22,9 @@ use crate::util::map_in_place::MapInPlace;
 use errors::{Applicability, FatalError};
 use smallvec::{smallvec, SmallVec};
 use syntax_pos::{Span, DUMMY_SP, FileName};
-use syntax_pos::hygiene::ExpnFormat;
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
-use std::fs;
 use std::io::ErrorKind;
 use std::{iter, mem};
 use std::ops::DerefMut;
@@ -99,9 +97,9 @@ macro_rules! ast_fragments {
                             }
                         });
                     }
-                    $($(AstFragment::$Kind(ast) => vis.$mut_visit_ast(ast),)*)*
+                    $($(AstFragment::$Kind(ast) => vis.$mut_visit_ast(ast),)?)*
                     $($(AstFragment::$Kind(ast) =>
-                        ast.flat_map_in_place(|ast| vis.$flat_map_ast_elt(ast)),)*)*
+                        ast.flat_map_in_place(|ast| vis.$flat_map_ast_elt(ast)),)?)*
                 }
             }
 
@@ -109,26 +107,14 @@ macro_rules! ast_fragments {
                 match *self {
                     AstFragment::OptExpr(Some(ref expr)) => visitor.visit_expr(expr),
                     AstFragment::OptExpr(None) => {}
-                    $($(AstFragment::$Kind(ref ast) => visitor.$visit_ast(ast),)*)*
+                    $($(AstFragment::$Kind(ref ast) => visitor.$visit_ast(ast),)?)*
                     $($(AstFragment::$Kind(ref ast) => for ast_elt in &ast[..] {
                         visitor.$visit_ast_elt(ast_elt);
-                    })*)*
+                    })?)*
                 }
             }
         }
 
-        impl<'a, 'b> MutVisitor for MacroExpander<'a, 'b> {
-            fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
-                self.expand_fragment(AstFragment::OptExpr(Some(expr))).make_opt_expr()
-            }
-            $($(fn $mut_visit_ast(&mut self, ast: &mut $AstTy) {
-                visit_clobber(ast, |ast| self.expand_fragment(AstFragment::$Kind(ast)).$make_ast());
-            })*)*
-            $($(fn $flat_map_ast_elt(&mut self, ast_elt: <$AstTy as IntoIterator>::Item) -> $AstTy {
-                self.expand_fragment(AstFragment::$Kind(smallvec![ast_elt])).$make_ast()
-            })*)*
-        }
-
         impl<'a> MacResult for crate::ext::tt::macro_rules::ParserAnyMacro<'a> {
             $(fn $make_ast(self: Box<crate::ext::tt::macro_rules::ParserAnyMacro<'a>>)
                            -> Option<$AstTy> {
@@ -160,8 +146,8 @@ ast_fragments! {
 }
 
 impl AstFragmentKind {
-    fn dummy(self, span: Span) -> Option<AstFragment> {
-        self.make_from(DummyResult::any(span))
+    fn dummy(self, span: Span) -> AstFragment {
+        self.make_from(DummyResult::any(span)).expect("couldn't create a dummy AST fragment")
     }
 
     fn expect_from_annotatables<I: IntoIterator<Item = Annotatable>>(self, items: I)
@@ -189,23 +175,6 @@ impl AstFragmentKind {
     }
 }
 
-fn macro_bang_format(path: &ast::Path) -> ExpnFormat {
-    // We don't want to format a path using pretty-printing,
-    // `format!("{}", path)`, because that tries to insert
-    // line-breaks and is slow.
-    let mut path_str = String::with_capacity(64);
-    for (i, segment) in path.segments.iter().enumerate() {
-        if i != 0 {
-            path_str.push_str("::");
-        }
-        if segment.ident.name != keywords::PathRoot.name() {
-            path_str.push_str(&segment.ident.as_str())
-        }
-    }
-
-    MacroBang(Symbol::intern(&path_str))
-}
-
 pub struct Invocation {
     pub kind: InvocationKind,
     fragment_kind: AstFragmentKind,
@@ -215,13 +184,13 @@ pub struct Invocation {
 pub enum InvocationKind {
     Bang {
         mac: ast::Mac,
-        ident: Option<Ident>,
         span: Span,
     },
     Attr {
-        attr: Option<ast::Attribute>,
-        traits: Vec<Path>,
+        attr: ast::Attribute,
         item: Annotatable,
+        // Required for resolving derive helper attributes.
+        derives: Vec<Path>,
         // We temporarily report errors for attribute macros placed after derives
         after_derive: bool,
     },
@@ -229,27 +198,34 @@ pub enum InvocationKind {
         path: Path,
         item: Annotatable,
     },
+    /// "Invocation" that contains all derives from an item,
+    /// broken into multiple `Derive` invocations when expanded.
+    /// FIXME: Find a way to remove it.
+    DeriveContainer {
+        derives: Vec<Path>,
+        item: Annotatable,
+    },
 }
 
 impl Invocation {
     pub fn span(&self) -> Span {
-        match self.kind {
-            InvocationKind::Bang { span, .. } => span,
-            InvocationKind::Attr { attr: Some(ref attr), .. } => attr.span,
-            InvocationKind::Attr { attr: None, .. } => DUMMY_SP,
-            InvocationKind::Derive { ref path, .. } => path.span,
+        match &self.kind {
+            InvocationKind::Bang { span, .. } => *span,
+            InvocationKind::Attr { attr, .. } => attr.span,
+            InvocationKind::Derive { path, .. } => path.span,
+            InvocationKind::DeriveContainer { item, .. } => item.span(),
         }
     }
 }
 
-pub struct MacroExpander<'a, 'b:'a> {
+pub struct MacroExpander<'a, 'b> {
     pub cx: &'a mut ExtCtxt<'b>,
     monotonic: bool, // cf. `cx.monotonic_expander()`
 }
 
 impl<'a, 'b> MacroExpander<'a, 'b> {
     pub fn new(cx: &'a mut ExtCtxt<'b>, monotonic: bool) -> Self {
-        MacroExpander { cx: cx, monotonic: monotonic }
+        MacroExpander { cx, monotonic }
     }
 
     pub fn expand_crate(&mut self, mut krate: ast::Crate) -> ast::Crate {
@@ -263,7 +239,6 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         module.directory.pop();
         self.cx.root_path = module.directory.clone();
         self.cx.current_expansion.module = Rc::new(module);
-        self.cx.current_expansion.crate_span = Some(krate.span);
 
         let orig_mod_span = krate.module.inner;
 
@@ -271,13 +246,13 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             attrs: krate.attrs,
             span: krate.span,
             node: ast::ItemKind::Mod(krate.module),
-            ident: keywords::Invalid.ident(),
+            ident: Ident::invalid(),
             id: ast::DUMMY_NODE_ID,
             vis: respan(krate.span.shrink_to_lo(), ast::VisibilityKind::Public),
             tokens: None,
         })]);
 
-        match self.expand_fragment(krate_item).make_items().pop().map(P::into_inner) {
+        match self.fully_expand_fragment(krate_item).make_items().pop().map(P::into_inner) {
             Some(ast::Item { attrs, node: ast::ItemKind::Mod(module), .. }) => {
                 krate.attrs = attrs;
                 krate.module = module;
@@ -297,8 +272,8 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         krate
     }
 
-    // Fully expand all macro invocations in this AST fragment.
-    fn expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragment {
+    // Recursively expand all macro invocations in this AST fragment.
+    pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragment {
         let orig_expansion_data = self.cx.current_expansion.clone();
         self.cx.current_expansion.depth = 0;
 
@@ -316,7 +291,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         // Unresolved macros produce dummy outputs as a recovery measure.
         invocations.reverse();
         let mut expanded_fragments = Vec::new();
-        let mut derives: FxHashMap<Mark, Vec<_>> = FxHashMap::default();
+        let mut all_derive_placeholders: FxHashMap<ExpnId, Vec<_>> = FxHashMap::default();
         let mut undetermined_invocations = Vec::new();
         let (mut progress, mut force) = (false, !self.monotonic);
         loop {
@@ -325,98 +300,81 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             } else {
                 self.resolve_imports();
                 if undetermined_invocations.is_empty() { break }
-                invocations = mem::replace(&mut undetermined_invocations, Vec::new());
+                invocations = mem::take(&mut undetermined_invocations);
                 force = !mem::replace(&mut progress, false);
                 continue
             };
 
             let scope =
-                if self.monotonic { invoc.expansion_data.mark } else { orig_expansion_data.mark };
+                if self.monotonic { invoc.expansion_data.id } else { orig_expansion_data.id };
             let ext = match self.cx.resolver.resolve_macro_invocation(&invoc, scope, force) {
-                Ok(ext) => Some(ext),
-                Err(Determinacy::Determined) => None,
-                Err(Determinacy::Undetermined) => {
+                Ok(ext) => ext,
+                Err(Indeterminate) => {
                     undetermined_invocations.push(invoc);
                     continue
                 }
             };
 
             progress = true;
-            let ExpansionData { depth, mark, .. } = invoc.expansion_data;
+            let ExpansionData { depth, id: expn_id, .. } = invoc.expansion_data;
             self.cx.current_expansion = invoc.expansion_data.clone();
+            self.cx.current_expansion.id = scope;
 
-            self.cx.current_expansion.mark = scope;
             // FIXME(jseyfried): Refactor out the following logic
             let (expanded_fragment, new_invocations) = if let Some(ext) = ext {
-                if let Some(ext) = ext {
-                    let (invoc_fragment_kind, invoc_span) = (invoc.fragment_kind, invoc.span());
-                    let fragment = self.expand_invoc(invoc, &*ext).unwrap_or_else(|| {
-                        invoc_fragment_kind.dummy(invoc_span).unwrap()
-                    });
-                    self.collect_invocations(fragment, &[])
-                } else if let InvocationKind::Attr { attr: None, traits, item, .. } = invoc.kind {
-                    if !item.derive_allowed() {
-                        let attr = attr::find_by_name(item.attrs(), sym::derive)
-                            .expect("`derive` attribute should exist");
-                        let span = attr.span;
-                        let mut err = self.cx.mut_span_err(span,
-                                                           "`derive` may only be applied to \
-                                                            structs, enums and unions");
-                        if let ast::AttrStyle::Inner = attr.style {
-                            let trait_list = traits.iter()
-                                .map(|t| t.to_string()).collect::<Vec<_>>();
-                            let suggestion = format!("#[derive({})]", trait_list.join(", "));
-                            err.span_suggestion(
-                                span, "try an outer attribute", suggestion,
-                                // We don't 𝑘𝑛𝑜𝑤 that the following item is an ADT
-                                Applicability::MaybeIncorrect
-                            );
-                        }
-                        err.emit();
+                let fragment = self.expand_invoc(invoc, &ext.kind);
+                self.collect_invocations(fragment, &[])
+            } else if let InvocationKind::DeriveContainer { derives: traits, item } = invoc.kind {
+                if !item.derive_allowed() {
+                    let attr = attr::find_by_name(item.attrs(), sym::derive)
+                        .expect("`derive` attribute should exist");
+                    let span = attr.span;
+                    let mut err = self.cx.mut_span_err(span,
+                                                        "`derive` may only be applied to \
+                                                        structs, enums and unions");
+                    if let ast::AttrStyle::Inner = attr.style {
+                        let trait_list = traits.iter()
+                            .map(|t| t.to_string()).collect::<Vec<_>>();
+                        let suggestion = format!("#[derive({})]", trait_list.join(", "));
+                        err.span_suggestion(
+                            span, "try an outer attribute", suggestion,
+                            // We don't 𝑘𝑛𝑜𝑤 that the following item is an ADT
+                            Applicability::MaybeIncorrect
+                        );
                     }
+                    err.emit();
+                }
 
-                    let mut item = self.fully_configure(item);
-                    item.visit_attrs(|attrs| attrs.retain(|a| a.path != sym::derive));
-                    let mut item_with_markers = item.clone();
-                    add_derived_markers(&mut self.cx, item.span(), &traits, &mut item_with_markers);
-                    let derives = derives.entry(invoc.expansion_data.mark).or_default();
-
-                    derives.reserve(traits.len());
-                    invocations.reserve(traits.len());
-                    for path in &traits {
-                        let mark = Mark::fresh(self.cx.current_expansion.mark);
-                        derives.push(mark);
-                        let item = match self.cx.resolver.resolve_macro_path(
-                                path, MacroKind::Derive, Mark::root(), Vec::new(), false) {
-                            Ok(ext) => match *ext {
-                                BuiltinDerive(..) => item_with_markers.clone(),
-                                _ => item.clone(),
-                            },
-                            _ => item.clone(),
-                        };
-                        invocations.push(Invocation {
-                            kind: InvocationKind::Derive { path: path.clone(), item: item },
-                            fragment_kind: invoc.fragment_kind,
-                            expansion_data: ExpansionData {
-                                mark,
-                                ..invoc.expansion_data.clone()
-                            },
-                        });
-                    }
-                    let fragment = invoc.fragment_kind
-                        .expect_from_annotatables(::std::iter::once(item_with_markers));
-                    self.collect_invocations(fragment, derives)
-                } else {
-                    unreachable!()
+                let mut item = self.fully_configure(item);
+                item.visit_attrs(|attrs| attrs.retain(|a| a.path != sym::derive));
+                let derive_placeholders =
+                    all_derive_placeholders.entry(invoc.expansion_data.id).or_default();
+
+                derive_placeholders.reserve(traits.len());
+                invocations.reserve(traits.len());
+                for path in traits {
+                    let expn_id = ExpnId::fresh(None);
+                    derive_placeholders.push(NodeId::placeholder_from_expn_id(expn_id));
+                    invocations.push(Invocation {
+                        kind: InvocationKind::Derive { path, item: item.clone() },
+                        fragment_kind: invoc.fragment_kind,
+                        expansion_data: ExpansionData {
+                            id: expn_id,
+                            ..invoc.expansion_data.clone()
+                        },
+                    });
                 }
+                let fragment = invoc.fragment_kind
+                    .expect_from_annotatables(::std::iter::once(item));
+                self.collect_invocations(fragment, derive_placeholders)
             } else {
-                self.collect_invocations(invoc.fragment_kind.dummy(invoc.span()).unwrap(), &[])
+                unreachable!()
             };
 
             if expanded_fragments.len() < depth {
                 expanded_fragments.push(Vec::new());
             }
-            expanded_fragments[depth - 1].push((mark, expanded_fragment));
+            expanded_fragments[depth - 1].push((expn_id, expanded_fragment));
             if !self.cx.ecfg.single_step {
                 invocations.extend(new_invocations.into_iter().rev());
             }
@@ -427,10 +385,11 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         // Finally incorporate all the expanded macros into the input AST fragment.
         let mut placeholder_expander = PlaceholderExpander::new(self.cx, self.monotonic);
         while let Some(expanded_fragments) = expanded_fragments.pop() {
-            for (mark, expanded_fragment) in expanded_fragments.into_iter().rev() {
-                let derives = derives.remove(&mark).unwrap_or_else(Vec::new);
-                placeholder_expander.add(NodeId::placeholder_from_mark(mark),
-                                         expanded_fragment, derives);
+            for (expn_id, expanded_fragment) in expanded_fragments.into_iter().rev() {
+                let derive_placeholders =
+                    all_derive_placeholders.remove(&expn_id).unwrap_or_else(Vec::new);
+                placeholder_expander.add(NodeId::placeholder_from_expn_id(expn_id),
+                                         expanded_fragment, derive_placeholders);
             }
         }
         fragment_with_placeholders.mut_visit_with(&mut placeholder_expander);
@@ -447,10 +406,10 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
     /// them with "placeholders" - dummy macro invocations with specially crafted `NodeId`s.
     /// Then call into resolver that builds a skeleton ("reduced graph") of the fragment and
     /// prepares data for resolving paths of macro invocations.
-    fn collect_invocations(&mut self, mut fragment: AstFragment, derives: &[Mark])
+    fn collect_invocations(&mut self, mut fragment: AstFragment, extra_placeholders: &[NodeId])
                            -> (AstFragment, Vec<Invocation>) {
         // Resolve `$crate`s in the fragment for pretty-printing.
-        self.cx.resolver.resolve_dollar_crates(&fragment);
+        self.cx.resolver.resolve_dollar_crates();
 
         let invocations = {
             let mut collector = InvocationCollector {
@@ -466,9 +425,10 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             collector.invocations
         };
 
+        // FIXME: Merge `extra_placeholders` into the `fragment` as regular placeholders.
         if self.monotonic {
             self.cx.resolver.visit_ast_fragment_with_placeholders(
-                self.cx.current_expansion.mark, &fragment, derives);
+                self.cx.current_expansion.id, &fragment, extra_placeholders);
         }
 
         (fragment, invocations)
@@ -506,28 +466,22 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         }
     }
 
-    fn expand_invoc(&mut self, invoc: Invocation, ext: &SyntaxExtension) -> Option<AstFragment> {
-        if invoc.fragment_kind == AstFragmentKind::ForeignItems &&
-           !self.cx.ecfg.macros_in_extern_enabled() {
-            if let SyntaxExtension::NonMacroAttr { .. } = *ext {} else {
+    fn expand_invoc(&mut self, invoc: Invocation, ext: &SyntaxExtensionKind) -> AstFragment {
+        let (fragment_kind, span) = (invoc.fragment_kind, invoc.span());
+        if fragment_kind == AstFragmentKind::ForeignItems && !self.cx.ecfg.macros_in_extern() {
+            if let SyntaxExtensionKind::NonMacroAttr { .. } = ext {} else {
                 emit_feature_err(&self.cx.parse_sess, sym::macros_in_extern,
-                                 invoc.span(), GateIssue::Language,
+                                 span, GateIssue::Language,
                                  "macro invocations in `extern {}` blocks are experimental");
             }
         }
 
-        let result = match invoc.kind {
-            InvocationKind::Bang { .. } => self.expand_bang_invoc(invoc, ext)?,
-            InvocationKind::Attr { .. } => self.expand_attr_invoc(invoc, ext)?,
-            InvocationKind::Derive { .. } => self.expand_derive_invoc(invoc, ext)?,
-        };
-
         if self.cx.current_expansion.depth > self.cx.ecfg.recursion_limit {
-            let info = self.cx.current_expansion.mark.expn_info().unwrap();
+            let expn_data = self.cx.current_expansion.id.expn_data();
             let suggested_limit = self.cx.ecfg.recursion_limit * 2;
-            let mut err = self.cx.struct_span_err(info.call_site,
+            let mut err = self.cx.struct_span_err(expn_data.call_site,
                 &format!("recursion limit reached while expanding the macro `{}`",
-                         info.format.name()));
+                         expn_data.kind.descr()));
             err.help(&format!(
                 "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
                 suggested_limit));
@@ -536,81 +490,87 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             FatalError.raise();
         }
 
-        Some(result)
-    }
-
-    fn expand_attr_invoc(&mut self,
-                         invoc: Invocation,
-                         ext: &SyntaxExtension)
-                         -> Option<AstFragment> {
-        let (attr, mut item) = match invoc.kind {
-            InvocationKind::Attr { attr, item, .. } => (attr?, item),
-            _ => unreachable!(),
-        };
-
-        if let NonMacroAttr { mark_used: false } = *ext {} else {
-            // Macro attrs are always used when expanded,
-            // non-macro attrs are considered used when the field says so.
-            attr::mark_used(&attr);
-        }
-        invoc.expansion_data.mark.set_expn_info(ExpnInfo {
-            call_site: attr.span,
-            def_site: None,
-            format: MacroAttribute(Symbol::intern(&attr.path.to_string())),
-            allow_internal_unstable: None,
-            allow_internal_unsafe: false,
-            local_inner_macros: false,
-            edition: ext.edition(),
-        });
-
-        match *ext {
-            NonMacroAttr { .. } => {
-                attr::mark_known(&attr);
-                item.visit_attrs(|attrs| attrs.push(attr));
-                Some(invoc.fragment_kind.expect_from_annotatables(iter::once(item)))
-            }
-            MultiModifier(ref mac) => {
-                let meta = attr.parse_meta(self.cx.parse_sess)
-                               .map_err(|mut e| { e.emit(); }).ok()?;
-                let item = mac.expand(self.cx, attr.span, &meta, item);
-                Some(invoc.fragment_kind.expect_from_annotatables(item))
-            }
-            MultiDecorator(ref mac) => {
-                let mut items = Vec::new();
-                let meta = attr.parse_meta(self.cx.parse_sess)
-                               .expect("derive meta should already have been parsed");
-                mac.expand(self.cx, attr.span, &meta, &item, &mut |item| items.push(item));
-                items.push(item);
-                Some(invoc.fragment_kind.expect_from_annotatables(items))
-            }
-            AttrProcMacro(ref mac, ..) => {
-                self.gate_proc_macro_attr_item(attr.span, &item);
-                let item_tok = TokenTree::Token(DUMMY_SP, Token::Interpolated(Lrc::new(match item {
-                    Annotatable::Item(item) => token::NtItem(item),
-                    Annotatable::TraitItem(item) => token::NtTraitItem(item.into_inner()),
-                    Annotatable::ImplItem(item) => token::NtImplItem(item.into_inner()),
-                    Annotatable::ForeignItem(item) => token::NtForeignItem(item.into_inner()),
-                    Annotatable::Stmt(stmt) => token::NtStmt(stmt.into_inner()),
-                    Annotatable::Expr(expr) => token::NtExpr(expr),
-                }))).into();
-                let input = self.extract_proc_macro_attr_input(attr.tokens, attr.span);
-                let tok_result = mac.expand(self.cx, attr.span, input, item_tok);
-                let res = self.parse_ast_fragment(tok_result, invoc.fragment_kind,
-                                                  &attr.path, attr.span);
-                self.gate_proc_macro_expansion(attr.span, &res);
-                res
-            }
-            ProcMacroDerive(..) | BuiltinDerive(..) => {
-                self.cx.span_err(attr.span, &format!("`{}` is a derive macro", attr.path));
-                self.cx.trace_macros_diag();
-                invoc.fragment_kind.dummy(attr.span)
+        match invoc.kind {
+            InvocationKind::Bang { mac, .. } => match ext {
+                SyntaxExtensionKind::Bang(expander) => {
+                    self.gate_proc_macro_expansion_kind(span, fragment_kind);
+                    let tok_result = expander.expand(self.cx, span, mac.stream());
+                    let result =
+                        self.parse_ast_fragment(tok_result, fragment_kind, &mac.path, span);
+                    self.gate_proc_macro_expansion(span, &result);
+                    result
+                }
+                SyntaxExtensionKind::LegacyBang(expander) => {
+                    let prev = self.cx.current_expansion.prior_type_ascription;
+                    self.cx.current_expansion.prior_type_ascription = mac.prior_type_ascription;
+                    let tok_result = expander.expand(self.cx, span, mac.stream());
+                    let result = if let Some(result) = fragment_kind.make_from(tok_result) {
+                        result
+                    } else {
+                        let msg = format!("non-{kind} macro in {kind} position: {path}",
+                                          kind = fragment_kind.name(), path = mac.path);
+                        self.cx.span_err(span, &msg);
+                        self.cx.trace_macros_diag();
+                        fragment_kind.dummy(span)
+                    };
+                    self.cx.current_expansion.prior_type_ascription = prev;
+                    result
+                }
+                _ => unreachable!()
+            }
+            InvocationKind::Attr { attr, mut item, .. } => match ext {
+                SyntaxExtensionKind::Attr(expander) => {
+                    self.gate_proc_macro_attr_item(span, &item);
+                    let item_tok = TokenTree::token(token::Interpolated(Lrc::new(match item {
+                        Annotatable::Item(item) => token::NtItem(item),
+                        Annotatable::TraitItem(item) => token::NtTraitItem(item.into_inner()),
+                        Annotatable::ImplItem(item) => token::NtImplItem(item.into_inner()),
+                        Annotatable::ForeignItem(item) => token::NtForeignItem(item.into_inner()),
+                        Annotatable::Stmt(stmt) => token::NtStmt(stmt.into_inner()),
+                        Annotatable::Expr(expr) => token::NtExpr(expr),
+                    })), DUMMY_SP).into();
+                    let input = self.extract_proc_macro_attr_input(attr.tokens, span);
+                    let tok_result = expander.expand(self.cx, span, input, item_tok);
+                    let res = self.parse_ast_fragment(tok_result, fragment_kind, &attr.path, span);
+                    self.gate_proc_macro_expansion(span, &res);
+                    res
+                }
+                SyntaxExtensionKind::LegacyAttr(expander) => {
+                    match attr.parse_meta(self.cx.parse_sess) {
+                        Ok(meta) => {
+                            let item = expander.expand(self.cx, span, &meta, item);
+                            fragment_kind.expect_from_annotatables(item)
+                        }
+                        Err(mut err) => {
+                            err.emit();
+                            fragment_kind.dummy(span)
+                        }
+                    }
+                }
+                SyntaxExtensionKind::NonMacroAttr { mark_used } => {
+                    attr::mark_known(&attr);
+                    if *mark_used {
+                        attr::mark_used(&attr);
+                    }
+                    item.visit_attrs(|attrs| attrs.push(attr));
+                    fragment_kind.expect_from_annotatables(iter::once(item))
+                }
+                _ => unreachable!()
             }
-            _ => {
-                let msg = &format!("macro `{}` may not be used in attributes", attr.path);
-                self.cx.span_err(attr.span, msg);
-                self.cx.trace_macros_diag();
-                invoc.fragment_kind.dummy(attr.span)
+            InvocationKind::Derive { path, item } => match ext {
+                SyntaxExtensionKind::Derive(expander) |
+                SyntaxExtensionKind::LegacyDerive(expander) => {
+                    if !item.derive_allowed() {
+                        return fragment_kind.dummy(span);
+                    }
+                    let meta = ast::MetaItem { node: ast::MetaItemKind::Word, span, path };
+                    let span = span.with_ctxt(self.cx.backtrace());
+                    let items = expander.expand(self.cx, span, &meta, item);
+                    fragment_kind.expect_from_annotatables(items)
+                }
+                _ => unreachable!()
             }
+            InvocationKind::DeriveContainer { .. } => unreachable!()
         }
     }
 
@@ -626,7 +586,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             None => return TokenStream::empty(),
         }
         self.cx.span_err(span, "custom attribute invocations must be \
-            of the form #[foo] or #[foo(..)], the macro name must only be \
+            of the form `#[foo]` or `#[foo(..)]`, the macro name must only be \
             followed by a delimiter token");
         TokenStream::empty()
     }
@@ -657,14 +617,10 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         );
     }
 
-    fn gate_proc_macro_expansion(&self, span: Span, fragment: &Option<AstFragment>) {
+    fn gate_proc_macro_expansion(&self, span: Span, fragment: &AstFragment) {
         if self.cx.ecfg.proc_macro_hygiene() {
             return
         }
-        let fragment = match fragment {
-            Some(fragment) => fragment,
-            None => return,
-        };
 
         fragment.visit_with(&mut DisallowMacros {
             span,
@@ -696,178 +652,6 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         }
     }
 
-    /// Expand a macro invocation. Returns the resulting expanded AST fragment.
-    fn expand_bang_invoc(&mut self,
-                         invoc: Invocation,
-                         ext: &SyntaxExtension)
-                         -> Option<AstFragment> {
-        let (mark, kind) = (invoc.expansion_data.mark, invoc.fragment_kind);
-        let (mac, ident, span) = match invoc.kind {
-            InvocationKind::Bang { mac, ident, span } => (mac, ident, span),
-            _ => unreachable!(),
-        };
-        let path = &mac.node.path;
-
-        let ident = ident.unwrap_or_else(|| keywords::Invalid.ident());
-        let validate_and_set_expn_info = |this: &mut Self, // arg instead of capture
-                                          def_site_span: Option<Span>,
-                                          allow_internal_unstable,
-                                          allow_internal_unsafe,
-                                          local_inner_macros,
-                                          // can't infer this type
-                                          unstable_feature: Option<(Symbol, u32)>,
-                                          edition| {
-
-            // feature-gate the macro invocation
-            if let Some((feature, issue)) = unstable_feature {
-                let crate_span = this.cx.current_expansion.crate_span.unwrap();
-                // don't stability-check macros in the same crate
-                // (the only time this is null is for syntax extensions registered as macros)
-                if def_site_span.map_or(false, |def_span| !crate_span.contains(def_span))
-                    && !span.allows_unstable(feature)
-                    && this.cx.ecfg.features.map_or(true, |feats| {
-                    // macro features will count as lib features
-                    !feats.declared_lib_features.iter().any(|&(feat, _)| feat == feature)
-                }) {
-                    let explain = format!("macro {}! is unstable", path);
-                    emit_feature_err(this.cx.parse_sess, feature, span,
-                                     GateIssue::Library(Some(issue)), &explain);
-                    this.cx.trace_macros_diag();
-                }
-            }
-
-            if ident.name != keywords::Invalid.name() {
-                let msg = format!("macro {}! expects no ident argument, given '{}'", path, ident);
-                this.cx.span_err(path.span, &msg);
-                this.cx.trace_macros_diag();
-                return Err(kind.dummy(span));
-            }
-            mark.set_expn_info(ExpnInfo {
-                call_site: span,
-                def_site: def_site_span,
-                format: macro_bang_format(path),
-                allow_internal_unstable,
-                allow_internal_unsafe,
-                local_inner_macros,
-                edition,
-            });
-            Ok(())
-        };
-
-        let opt_expanded = match *ext {
-            DeclMacro { ref expander, def_info, edition, .. } => {
-                if let Err(dummy_span) = validate_and_set_expn_info(self, def_info.map(|(_, s)| s),
-                                                                    None, false, false, None,
-                                                                    edition) {
-                    dummy_span
-                } else {
-                    kind.make_from(expander.expand(self.cx, span, mac.node.stream(), None))
-                }
-            }
-
-            NormalTT {
-                ref expander,
-                def_info,
-                ref allow_internal_unstable,
-                allow_internal_unsafe,
-                local_inner_macros,
-                unstable_feature,
-                edition,
-            } => {
-                if let Err(dummy_span) = validate_and_set_expn_info(self, def_info.map(|(_, s)| s),
-                                                                    allow_internal_unstable.clone(),
-                                                                    allow_internal_unsafe,
-                                                                    local_inner_macros,
-                                                                    unstable_feature,
-                                                                    edition) {
-                    dummy_span
-                } else {
-                    kind.make_from(expander.expand(
-                        self.cx,
-                        span,
-                        mac.node.stream(),
-                        def_info.map(|(_, s)| s),
-                    ))
-                }
-            }
-
-            IdentTT { ref expander, span: tt_span, ref allow_internal_unstable } => {
-                if ident.name == keywords::Invalid.name() {
-                    self.cx.span_err(path.span,
-                                    &format!("macro {}! expects an ident argument", path));
-                    self.cx.trace_macros_diag();
-                    kind.dummy(span)
-                } else {
-                    invoc.expansion_data.mark.set_expn_info(ExpnInfo {
-                        call_site: span,
-                        def_site: tt_span,
-                        format: macro_bang_format(path),
-                        allow_internal_unstable: allow_internal_unstable.clone(),
-                        allow_internal_unsafe: false,
-                        local_inner_macros: false,
-                        edition: hygiene::default_edition(),
-                    });
-
-                    let input: Vec<_> = mac.node.stream().into_trees().collect();
-                    kind.make_from(expander.expand(self.cx, span, ident, input))
-                }
-            }
-
-            MultiDecorator(..) | MultiModifier(..) |
-            AttrProcMacro(..) | SyntaxExtension::NonMacroAttr { .. } => {
-                self.cx.span_err(path.span,
-                                 &format!("`{}` can only be used in attributes", path));
-                self.cx.trace_macros_diag();
-                kind.dummy(span)
-            }
-
-            ProcMacroDerive(..) | BuiltinDerive(..) => {
-                self.cx.span_err(path.span, &format!("`{}` is a derive macro", path));
-                self.cx.trace_macros_diag();
-                kind.dummy(span)
-            }
-
-            SyntaxExtension::ProcMacro { ref expander, ref allow_internal_unstable, edition } => {
-                if ident.name != keywords::Invalid.name() {
-                    let msg =
-                        format!("macro {}! expects no ident argument, given '{}'", path, ident);
-                    self.cx.span_err(path.span, &msg);
-                    self.cx.trace_macros_diag();
-                    kind.dummy(span)
-                } else {
-                    self.gate_proc_macro_expansion_kind(span, kind);
-                    invoc.expansion_data.mark.set_expn_info(ExpnInfo {
-                        call_site: span,
-                        // FIXME procedural macros do not have proper span info
-                        // yet, when they do, we should use it here.
-                        def_site: None,
-                        format: macro_bang_format(path),
-                        // FIXME probably want to follow macro_rules macros here.
-                        allow_internal_unstable: allow_internal_unstable.clone(),
-                        allow_internal_unsafe: false,
-                        local_inner_macros: false,
-                        edition,
-                    });
-
-                    let tok_result = expander.expand(self.cx, span, mac.node.stream());
-                    let result = self.parse_ast_fragment(tok_result, kind, path, span);
-                    self.gate_proc_macro_expansion(span, &result);
-                    result
-                }
-            }
-        };
-
-        if opt_expanded.is_some() {
-            opt_expanded
-        } else {
-            let msg = format!("non-{kind} macro in {kind} position: {name}",
-                              name = path.segments[0].ident.name, kind = kind.name());
-            self.cx.span_err(path.span, &msg);
-            self.cx.trace_macros_diag();
-            kind.dummy(span)
-        }
-    }
-
     fn gate_proc_macro_expansion_kind(&self, span: Span, kind: AstFragmentKind) {
         let kind = match kind {
             AstFragmentKind::Expr => "expressions",
@@ -892,86 +676,22 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         );
     }
 
-    /// Expand a derive invocation. Returns the resulting expanded AST fragment.
-    fn expand_derive_invoc(&mut self,
-                           invoc: Invocation,
-                           ext: &SyntaxExtension)
-                           -> Option<AstFragment> {
-        let (path, item) = match invoc.kind {
-            InvocationKind::Derive { path, item } => (path, item),
-            _ => unreachable!(),
-        };
-        if !item.derive_allowed() {
-            return None;
-        }
-
-        let pretty_name = Symbol::intern(&format!("derive({})", path));
-        let span = path.span;
-        let attr = ast::Attribute {
-            path, span,
-            tokens: TokenStream::empty(),
-            // irrelevant:
-            id: ast::AttrId(0), style: ast::AttrStyle::Outer, is_sugared_doc: false,
-        };
-
-        let mut expn_info = ExpnInfo {
-            call_site: span,
-            def_site: None,
-            format: MacroAttribute(pretty_name),
-            allow_internal_unstable: None,
-            allow_internal_unsafe: false,
-            local_inner_macros: false,
-            edition: ext.edition(),
-        };
-
-        match *ext {
-            ProcMacroDerive(ref ext, ..) => {
-                invoc.expansion_data.mark.set_expn_info(expn_info);
-                let span = span.with_ctxt(self.cx.backtrace());
-                let dummy = ast::MetaItem { // FIXME(jseyfried) avoid this
-                    path: Path::from_ident(keywords::Invalid.ident()),
-                    span: DUMMY_SP,
-                    node: ast::MetaItemKind::Word,
-                };
-                let items = ext.expand(self.cx, span, &dummy, item);
-                Some(invoc.fragment_kind.expect_from_annotatables(items))
-            }
-            BuiltinDerive(func) => {
-                expn_info.allow_internal_unstable = Some(vec![
-                    Symbol::intern("rustc_attrs"),
-                    Symbol::intern("derive_clone_copy"),
-                    Symbol::intern("derive_eq"),
-                    Symbol::intern("libstd_sys_internals"), // RustcDeserialize and RustcSerialize
-                ].into());
-                invoc.expansion_data.mark.set_expn_info(expn_info);
-                let span = span.with_ctxt(self.cx.backtrace());
-                let mut items = Vec::new();
-                func(self.cx, span, &attr.meta()?, &item, &mut |a| items.push(a));
-                Some(invoc.fragment_kind.expect_from_annotatables(items))
-            }
-            _ => {
-                let msg = &format!("macro `{}` may not be used for derive attributes", attr.path);
-                self.cx.span_err(span, msg);
-                self.cx.trace_macros_diag();
-                invoc.fragment_kind.dummy(span)
-            }
-        }
-    }
-
-    fn parse_ast_fragment(&mut self,
-                          toks: TokenStream,
-                          kind: AstFragmentKind,
-                          path: &Path,
-                          span: Span)
-                          -> Option<AstFragment> {
+    fn parse_ast_fragment(
+        &mut self,
+        toks: TokenStream,
+        kind: AstFragmentKind,
+        path: &Path,
+        span: Span,
+    ) -> AstFragment {
         let mut parser = self.cx.new_parser_from_tts(&toks.into_trees().collect::<Vec<_>>());
         match parser.parse_ast_fragment(kind, false) {
             Ok(fragment) => {
                 parser.ensure_complete_parse(path, kind.name(), span);
-                Some(fragment)
+                fragment
             }
             Err(mut err) => {
                 err.set_span(span);
+                annotate_err_with_kind(&mut err, kind, span);
                 err.emit();
                 self.cx.trace_macros_diag();
                 kind.dummy(span)
@@ -1008,7 +728,7 @@ impl<'a> Parser<'a> {
             AstFragmentKind::ForeignItems => {
                 let mut items = SmallVec::new();
                 while self.token != token::Eof {
-                    items.push(self.parse_foreign_item()?);
+                    items.push(self.parse_foreign_item(DUMMY_SP)?);
                 }
                 AstFragment::ForeignItems(items)
             }
@@ -1041,7 +761,7 @@ impl<'a> Parser<'a> {
             let msg = format!("macro expansion ignores token `{}` and any following",
                               self.this_token_to_string());
             // Avoid emitting backtrace info twice.
-            let def_site_span = self.span.with_ctxt(SyntaxContext::empty());
+            let def_site_span = self.token.span.with_ctxt(SyntaxContext::root());
             let mut err = self.diagnostic().struct_span_err(def_site_span, &msg);
             err.span_label(span, "caused by the macro expansion here");
             let msg = format!(
@@ -1069,7 +789,7 @@ impl<'a> Parser<'a> {
     }
 }
 
-struct InvocationCollector<'a, 'b: 'a> {
+struct InvocationCollector<'a, 'b> {
     cx: &'a mut ExtCtxt<'b>,
     cfg: StripUnconfigured<'a>,
     invocations: Vec<Invocation>,
@@ -1078,31 +798,47 @@ struct InvocationCollector<'a, 'b: 'a> {
 
 impl<'a, 'b> InvocationCollector<'a, 'b> {
     fn collect(&mut self, fragment_kind: AstFragmentKind, kind: InvocationKind) -> AstFragment {
-        let mark = Mark::fresh(self.cx.current_expansion.mark);
+        // Expansion data for all the collected invocations is set upon their resolution,
+        // with exception of the derive container case which is not resolved and can get
+        // its expansion data immediately.
+        let expn_data = match &kind {
+            InvocationKind::DeriveContainer { item, .. } => Some(ExpnData {
+                parent: self.cx.current_expansion.id,
+                ..ExpnData::default(
+                    ExpnKind::Macro(MacroKind::Attr, sym::derive),
+                    item.span(), self.cx.parse_sess.edition,
+                )
+            }),
+            _ => None,
+        };
+        let expn_id = ExpnId::fresh(expn_data);
         self.invocations.push(Invocation {
             kind,
             fragment_kind,
             expansion_data: ExpansionData {
-                mark,
+                id: expn_id,
                 depth: self.cx.current_expansion.depth + 1,
                 ..self.cx.current_expansion.clone()
             },
         });
-        placeholder(fragment_kind, NodeId::placeholder_from_mark(mark))
+        placeholder(fragment_kind, NodeId::placeholder_from_expn_id(expn_id))
     }
 
     fn collect_bang(&mut self, mac: ast::Mac, span: Span, kind: AstFragmentKind) -> AstFragment {
-        self.collect(kind, InvocationKind::Bang { mac: mac, ident: None, span: span })
+        self.collect(kind, InvocationKind::Bang { mac, span })
     }
 
     fn collect_attr(&mut self,
                     attr: Option<ast::Attribute>,
-                    traits: Vec<Path>,
+                    derives: Vec<Path>,
                     item: Annotatable,
                     kind: AstFragmentKind,
                     after_derive: bool)
                     -> AstFragment {
-        self.collect(kind, InvocationKind::Attr { attr, traits, item, after_derive })
+        self.collect(kind, match attr {
+            Some(attr) => InvocationKind::Attr { attr, item, derives, after_derive },
+            None => InvocationKind::DeriveContainer { derives, item },
+        })
     }
 
     fn find_attr_invoc(&self, attrs: &mut Vec<ast::Attribute>, after_derive: &mut bool)
@@ -1116,7 +852,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                         })
                         .map(|i| attrs.remove(i));
         if let Some(attr) = &attr {
-            if !self.cx.ecfg.enable_custom_inner_attributes() &&
+            if !self.cx.ecfg.custom_inner_attributes() &&
                attr.style == ast::AttrStyle::Inner && attr.path != sym::test {
                 emit_feature_err(&self.cx.parse_sess, sym::custom_inner_attributes,
                                  attr.span, GateIssue::Language,
@@ -1327,18 +1063,14 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
             ast::ItemKind::Mac(..) => {
                 self.check_attributes(&item.attrs);
                 item.and_then(|item| match item.node {
-                    ItemKind::Mac(mac) => {
-                        self.collect(AstFragmentKind::Items, InvocationKind::Bang {
-                            mac,
-                            ident: Some(item.ident),
-                            span: item.span,
-                        }).make_items()
-                    }
+                    ItemKind::Mac(mac) => self.collect(
+                        AstFragmentKind::Items, InvocationKind::Bang { mac, span: item.span }
+                    ).make_items(),
                     _ => unreachable!(),
                 })
             }
             ast::ItemKind::Mod(ast::Mod { inner, .. }) => {
-                if item.ident == keywords::Invalid.ident() {
+                if item.ident == Ident::invalid() {
                     return noop_flat_map_item(item, self);
                 }
 
@@ -1477,9 +1209,9 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
         }
     }
 
-    fn visit_generic_param(&mut self, param: &mut ast::GenericParam) {
-        self.cfg.disallow_cfg_on_generic_param(&param);
-        noop_visit_generic_param(param, self)
+    fn visit_generic_params(&mut self, params: &mut Vec<ast::GenericParam>) {
+        self.cfg.configure_generic_params(params);
+        noop_visit_generic_params(params, self);
     }
 
     fn visit_attribute(&mut self, at: &mut ast::Attribute) {
@@ -1510,32 +1242,32 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
                         return noop_visit_attribute(at, self);
                     }
 
-                    let filename = self.cx.root_path.join(file.to_string());
-                    match fs::read_to_string(&filename) {
-                        Ok(src) => {
-                            let src_interned = Symbol::intern(&src);
-
-                            // Add this input file to the code map to make it available as
-                            // dependency information
-                            self.cx.source_map().new_source_file(filename.into(), src);
+                    let filename = self.cx.resolve_path(&*file.as_str(), it.span());
+                    match self.cx.source_map().load_file(&filename) {
+                        Ok(source_file) => {
+                            let src = source_file.src.as_ref()
+                                .expect("freshly loaded file should have a source");
+                            let src_interned = Symbol::intern(src.as_str());
 
                             let include_info = vec![
                                 ast::NestedMetaItem::MetaItem(
                                     attr::mk_name_value_item_str(
-                                        Ident::with_empty_ctxt(sym::file),
-                                        dummy_spanned(file),
+                                        Ident::with_dummy_span(sym::file),
+                                        file,
+                                        DUMMY_SP,
                                     ),
                                 ),
                                 ast::NestedMetaItem::MetaItem(
                                     attr::mk_name_value_item_str(
-                                        Ident::with_empty_ctxt(sym::contents),
-                                        dummy_spanned(src_interned),
+                                        Ident::with_dummy_span(sym::contents),
+                                        src_interned,
+                                        DUMMY_SP,
                                     ),
                                 ),
                             ];
 
-                            let include_ident = Ident::with_empty_ctxt(sym::include);
-                            let item = attr::mk_list_item(DUMMY_SP, include_ident, include_info);
+                            let include_ident = Ident::with_dummy_span(sym::include);
+                            let item = attr::mk_list_item(include_ident, include_info);
                             items.push(ast::NestedMetaItem::MetaItem(item));
                         }
                         Err(e) => {
@@ -1559,10 +1291,6 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
                                 );
                                 err.span_label(lit.span, "couldn't read file");
 
-                                if e.kind() == ErrorKind::NotFound {
-                                    err.help("external doc paths are relative to the crate root");
-                                }
-
                                 err.emit();
                             }
                         }
@@ -1600,11 +1328,15 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
                 }
             }
 
-            let meta = attr::mk_list_item(DUMMY_SP, Ident::with_empty_ctxt(sym::doc), items);
-            match at.style {
-                ast::AttrStyle::Inner => *at = attr::mk_spanned_attr_inner(at.span, at.id, meta),
-                ast::AttrStyle::Outer => *at = attr::mk_spanned_attr_outer(at.span, at.id, meta),
-            }
+            let meta = attr::mk_list_item(Ident::with_dummy_span(sym::doc), items);
+            *at = attr::Attribute {
+                span: at.span,
+                id: at.id,
+                style: at.style,
+                path: meta.path,
+                tokens: meta.node.tokens(meta.span),
+                is_sugared_doc: false,
+            };
         } else {
             noop_visit_attribute(at, self)
         }
@@ -1616,6 +1348,11 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
             *id = self.cx.resolver.next_node_id()
         }
     }
+
+    fn visit_fn_decl(&mut self, mut fn_decl: &mut P<ast::FnDecl>) {
+        self.cfg.configure_fn_decl(&mut fn_decl);
+        noop_visit_fn_decl(fn_decl, self);
+    }
 }
 
 pub struct ExpansionConfig<'feat> {
@@ -1628,19 +1365,6 @@ pub struct ExpansionConfig<'feat> {
     pub keep_macs: bool,
 }
 
-macro_rules! feature_tests {
-    ($( fn $getter:ident = $field:ident, )*) => {
-        $(
-            pub fn $getter(&self) -> bool {
-                match self.features {
-                    Some(&Features { $field: true, .. }) => true,
-                    _ => false,
-                }
-            }
-        )*
-    }
-}
-
 impl<'feat> ExpansionConfig<'feat> {
     pub fn default(crate_name: String) -> ExpansionConfig<'static> {
         ExpansionConfig {
@@ -1654,29 +1378,20 @@ impl<'feat> ExpansionConfig<'feat> {
         }
     }
 
-    feature_tests! {
-        fn enable_asm = asm,
-        fn enable_custom_test_frameworks = custom_test_frameworks,
-        fn enable_global_asm = global_asm,
-        fn enable_log_syntax = log_syntax,
-        fn enable_concat_idents = concat_idents,
-        fn enable_trace_macros = trace_macros,
-        fn enable_allow_internal_unstable = allow_internal_unstable,
-        fn enable_format_args_nl = format_args_nl,
-        fn macros_in_extern_enabled = macros_in_extern,
-        fn proc_macro_hygiene = proc_macro_hygiene,
+    fn macros_in_extern(&self) -> bool {
+        self.features.map_or(false, |features| features.macros_in_extern)
     }
-
-    fn enable_custom_inner_attributes(&self) -> bool {
-        self.features.map_or(false, |features| {
-            features.custom_inner_attributes || features.custom_attribute || features.rustc_attrs
-        })
+    fn proc_macro_hygiene(&self) -> bool {
+        self.features.map_or(false, |features| features.proc_macro_hygiene)
+    }
+    fn custom_inner_attributes(&self) -> bool {
+        self.features.map_or(false, |features| features.custom_inner_attributes)
     }
 }
 
 // A Marker adds the given mark to the syntax context.
 #[derive(Debug)]
-pub struct Marker(pub Mark);
+pub struct Marker(pub ExpnId);
 
 impl MutVisitor for Marker {
     fn visit_span(&mut self, span: &mut Span) {
diff --git a/src/libsyntax/ext/placeholders.rs b/src/libsyntax/ext/placeholders.rs
index f5e18e98436..d800cfedcfb 100644
--- a/src/libsyntax/ext/placeholders.rs
+++ b/src/libsyntax/ext/placeholders.rs
@@ -2,11 +2,9 @@ use crate::ast::{self, NodeId};
 use crate::source_map::{DUMMY_SP, dummy_spanned};
 use crate::ext::base::ExtCtxt;
 use crate::ext::expand::{AstFragment, AstFragmentKind};
-use crate::ext::hygiene::Mark;
 use crate::tokenstream::TokenStream;
 use crate::mut_visit::*;
 use crate::ptr::P;
-use crate::symbol::keywords;
 use crate::ThinVec;
 
 use smallvec::{smallvec, SmallVec};
@@ -15,14 +13,16 @@ use rustc_data_structures::fx::FxHashMap;
 
 pub fn placeholder(kind: AstFragmentKind, id: ast::NodeId) -> AstFragment {
     fn mac_placeholder() -> ast::Mac {
-        dummy_spanned(ast::Mac_ {
+        ast::Mac {
             path: ast::Path { span: DUMMY_SP, segments: Vec::new() },
             tts: TokenStream::empty().into(),
             delim: ast::MacDelimiter::Brace,
-        })
+            span: DUMMY_SP,
+            prior_type_ascription: None,
+        }
     }
 
-    let ident = keywords::Invalid.ident();
+    let ident = ast::Ident::invalid();
     let attrs = Vec::new();
     let generics = ast::Generics::default();
     let vis = dummy_spanned(ast::VisibilityKind::Inherited);
@@ -70,7 +70,7 @@ pub fn placeholder(kind: AstFragmentKind, id: ast::NodeId) -> AstFragment {
     }
 }
 
-pub struct PlaceholderExpander<'a, 'b: 'a> {
+pub struct PlaceholderExpander<'a, 'b> {
     expanded_fragments: FxHashMap<ast::NodeId, AstFragment>,
     cx: &'a mut ExtCtxt<'b>,
     monotonic: bool,
@@ -85,11 +85,11 @@ impl<'a, 'b> PlaceholderExpander<'a, 'b> {
         }
     }
 
-    pub fn add(&mut self, id: ast::NodeId, mut fragment: AstFragment, derives: Vec<Mark>) {
+    pub fn add(&mut self, id: ast::NodeId, mut fragment: AstFragment, placeholders: Vec<NodeId>) {
         fragment.mut_visit_with(self);
         if let AstFragment::Items(mut items) = fragment {
-            for derive in derives {
-                match self.remove(NodeId::placeholder_from_mark(derive)) {
+            for placeholder in placeholders {
+                match self.remove(placeholder) {
                     AstFragment::Items(derived_items) => items.extend(derived_items),
                     _ => unreachable!(),
                 }
@@ -102,13 +102,6 @@ impl<'a, 'b> PlaceholderExpander<'a, 'b> {
     fn remove(&mut self, id: ast::NodeId) -> AstFragment {
         self.expanded_fragments.remove(&id).unwrap()
     }
-
-    fn next_id(&mut self, id: &mut ast::NodeId) {
-        if self.monotonic {
-            assert_eq!(*id, ast::DUMMY_NODE_ID);
-            *id = self.cx.resolver.next_node_id()
-        }
-    }
 }
 
 impl<'a, 'b> MutVisitor for PlaceholderExpander<'a, 'b> {
@@ -190,19 +183,9 @@ impl<'a, 'b> MutVisitor for PlaceholderExpander<'a, 'b> {
         noop_visit_block(block, self);
 
         for stmt in block.stmts.iter_mut() {
-            self.next_id(&mut stmt.id);
-        }
-    }
-
-    fn visit_asyncness(&mut self, a: &mut ast::IsAsync) {
-        noop_visit_asyncness(a, self);
-
-        if let ast::IsAsync::Async { ref mut arguments, .. } = a {
-            for argument in arguments.iter_mut() {
-                self.next_id(&mut argument.move_stmt.id);
-                if let Some(ref mut pat_stmt) = &mut argument.pat_stmt {
-                    self.next_id(&mut pat_stmt.id);
-                }
+            if self.monotonic {
+                assert_eq!(stmt.id, ast::DUMMY_NODE_ID);
+                stmt.id = self.cx.resolver.next_node_id();
             }
         }
     }
diff --git a/src/libsyntax/ext/proc_macro.rs b/src/libsyntax/ext/proc_macro.rs
new file mode 100644
index 00000000000..c17b6f6b424
--- /dev/null
+++ b/src/libsyntax/ext/proc_macro.rs
@@ -0,0 +1,217 @@
+use crate::ast::{self, ItemKind, Attribute, Mac};
+use crate::attr::{mark_used, mark_known};
+use crate::errors::{Applicability, FatalError};
+use crate::ext::base::{self, *};
+use crate::ext::proc_macro_server;
+use crate::parse::{self, token};
+use crate::parse::parser::PathStyle;
+use crate::symbol::sym;
+use crate::tokenstream::{self, TokenStream};
+use crate::visit::Visitor;
+
+use rustc_data_structures::sync::Lrc;
+use syntax_pos::{Span, DUMMY_SP};
+
+const EXEC_STRATEGY: proc_macro::bridge::server::SameThread =
+    proc_macro::bridge::server::SameThread;
+
+pub struct BangProcMacro {
+    pub client: proc_macro::bridge::client::Client<
+        fn(proc_macro::TokenStream) -> proc_macro::TokenStream,
+    >,
+}
+
+impl base::ProcMacro for BangProcMacro {
+    fn expand<'cx>(&self,
+                   ecx: &'cx mut ExtCtxt<'_>,
+                   span: Span,
+                   input: TokenStream)
+                   -> TokenStream {
+        let server = proc_macro_server::Rustc::new(ecx);
+        match self.client.run(&EXEC_STRATEGY, server, input) {
+            Ok(stream) => stream,
+            Err(e) => {
+                let msg = "proc macro panicked";
+                let mut err = ecx.struct_span_fatal(span, msg);
+                if let Some(s) = e.as_str() {
+                    err.help(&format!("message: {}", s));
+                }
+
+                err.emit();
+                FatalError.raise();
+            }
+        }
+    }
+}
+
+pub struct AttrProcMacro {
+    pub client: proc_macro::bridge::client::Client<
+        fn(proc_macro::TokenStream, proc_macro::TokenStream) -> proc_macro::TokenStream,
+    >,
+}
+
+impl base::AttrProcMacro for AttrProcMacro {
+    fn expand<'cx>(&self,
+                   ecx: &'cx mut ExtCtxt<'_>,
+                   span: Span,
+                   annotation: TokenStream,
+                   annotated: TokenStream)
+                   -> TokenStream {
+        let server = proc_macro_server::Rustc::new(ecx);
+        match self.client.run(&EXEC_STRATEGY, server, annotation, annotated) {
+            Ok(stream) => stream,
+            Err(e) => {
+                let msg = "custom attribute panicked";
+                let mut err = ecx.struct_span_fatal(span, msg);
+                if let Some(s) = e.as_str() {
+                    err.help(&format!("message: {}", s));
+                }
+
+                err.emit();
+                FatalError.raise();
+            }
+        }
+    }
+}
+
+pub struct ProcMacroDerive {
+    pub client: proc_macro::bridge::client::Client<
+        fn(proc_macro::TokenStream) -> proc_macro::TokenStream,
+    >,
+    pub attrs: Vec<ast::Name>,
+}
+
+impl MultiItemModifier for ProcMacroDerive {
+    fn expand(&self,
+              ecx: &mut ExtCtxt<'_>,
+              span: Span,
+              _meta_item: &ast::MetaItem,
+              item: Annotatable)
+              -> Vec<Annotatable> {
+        let item = match item {
+            Annotatable::Item(item) => item,
+            Annotatable::ImplItem(_) |
+            Annotatable::TraitItem(_) |
+            Annotatable::ForeignItem(_) |
+            Annotatable::Stmt(_) |
+            Annotatable::Expr(_) => {
+                ecx.span_err(span, "proc-macro derives may only be \
+                                    applied to a struct, enum, or union");
+                return Vec::new()
+            }
+        };
+        match item.node {
+            ItemKind::Struct(..) |
+            ItemKind::Enum(..) |
+            ItemKind::Union(..) => {},
+            _ => {
+                ecx.span_err(span, "proc-macro derives may only be \
+                                    applied to a struct, enum, or union");
+                return Vec::new()
+            }
+        }
+
+        // Mark attributes as known, and used.
+        MarkAttrs(&self.attrs).visit_item(&item);
+
+        let token = token::Interpolated(Lrc::new(token::NtItem(item)));
+        let input = tokenstream::TokenTree::token(token, DUMMY_SP).into();
+
+        let server = proc_macro_server::Rustc::new(ecx);
+        let stream = match self.client.run(&EXEC_STRATEGY, server, input) {
+            Ok(stream) => stream,
+            Err(e) => {
+                let msg = "proc-macro derive panicked";
+                let mut err = ecx.struct_span_fatal(span, msg);
+                if let Some(s) = e.as_str() {
+                    err.help(&format!("message: {}", s));
+                }
+
+                err.emit();
+                FatalError.raise();
+            }
+        };
+
+        let error_count_before = ecx.parse_sess.span_diagnostic.err_count();
+        let msg = "proc-macro derive produced unparseable tokens";
+
+        let mut parser = parse::stream_to_parser(ecx.parse_sess, stream, Some("proc-macro derive"));
+        let mut items = vec![];
+
+        loop {
+            match parser.parse_item() {
+                Ok(None) => break,
+                Ok(Some(item)) => {
+                    items.push(Annotatable::Item(item))
+                }
+                Err(mut err) => {
+                    // FIXME: handle this better
+                    err.cancel();
+                    ecx.struct_span_fatal(span, msg).emit();
+                    FatalError.raise();
+                }
+            }
+        }
+
+
+        // fail if there have been errors emitted
+        if ecx.parse_sess.span_diagnostic.err_count() > error_count_before {
+            ecx.struct_span_fatal(span, msg).emit();
+            FatalError.raise();
+        }
+
+        items
+    }
+}
+
+struct MarkAttrs<'a>(&'a [ast::Name]);
+
+impl<'a> Visitor<'a> for MarkAttrs<'a> {
+    fn visit_attribute(&mut self, attr: &Attribute) {
+        if let Some(ident) = attr.ident() {
+            if self.0.contains(&ident.name) {
+                mark_used(attr);
+                mark_known(attr);
+            }
+        }
+    }
+
+    fn visit_mac(&mut self, _mac: &Mac) {}
+}
+
+pub fn is_proc_macro_attr(attr: &Attribute) -> bool {
+    [sym::proc_macro, sym::proc_macro_attribute, sym::proc_macro_derive]
+        .iter().any(|kind| attr.check_name(*kind))
+}
+
+crate fn collect_derives(cx: &mut ExtCtxt<'_>, attrs: &mut Vec<ast::Attribute>) -> Vec<ast::Path> {
+    let mut result = Vec::new();
+    attrs.retain(|attr| {
+        if attr.path != sym::derive {
+            return true;
+        }
+        if !attr.is_meta_item_list() {
+            cx.struct_span_err(attr.span, "malformed `derive` attribute input")
+                .span_suggestion(
+                    attr.span,
+                    "missing traits to be derived",
+                    "#[derive(Trait1, Trait2, ...)]".to_owned(),
+                    Applicability::HasPlaceholders,
+                ).emit();
+            return false;
+        }
+
+        match attr.parse_list(cx.parse_sess,
+                              |parser| parser.parse_path_allowing_meta(PathStyle::Mod)) {
+            Ok(traits) => {
+                result.extend(traits);
+                true
+            }
+            Err(mut e) => {
+                e.emit();
+                false
+            }
+        }
+    });
+    result
+}
diff --git a/src/libsyntax/ext/proc_macro_server.rs b/src/libsyntax/ext/proc_macro_server.rs
new file mode 100644
index 00000000000..1619fa69941
--- /dev/null
+++ b/src/libsyntax/ext/proc_macro_server.rs
@@ -0,0 +1,715 @@
+use crate::ast;
+use crate::ext::base::ExtCtxt;
+use crate::parse::{self, token, ParseSess};
+use crate::parse::lexer::comments;
+use crate::tokenstream::{self, DelimSpan, IsJoint::*, TokenStream, TreeAndJoint};
+
+use errors::{Diagnostic, DiagnosticBuilder};
+use rustc_data_structures::sync::Lrc;
+use syntax_pos::{BytePos, FileName, MultiSpan, Pos, SourceFile, Span};
+use syntax_pos::hygiene::{SyntaxContext, Transparency};
+use syntax_pos::symbol::{kw, sym, Symbol};
+
+use proc_macro::{Delimiter, Level, LineColumn, Spacing};
+use proc_macro::bridge::{server, TokenTree};
+use std::{ascii, panic};
+use std::ops::Bound;
+
+trait FromInternal<T> {
+    fn from_internal(x: T) -> Self;
+}
+
+trait ToInternal<T> {
+    fn to_internal(self) -> T;
+}
+
+impl FromInternal<token::DelimToken> for Delimiter {
+    fn from_internal(delim: token::DelimToken) -> Delimiter {
+        match delim {
+            token::Paren => Delimiter::Parenthesis,
+            token::Brace => Delimiter::Brace,
+            token::Bracket => Delimiter::Bracket,
+            token::NoDelim => Delimiter::None,
+        }
+    }
+}
+
+impl ToInternal<token::DelimToken> for Delimiter {
+    fn to_internal(self) -> token::DelimToken {
+        match self {
+            Delimiter::Parenthesis => token::Paren,
+            Delimiter::Brace => token::Brace,
+            Delimiter::Bracket => token::Bracket,
+            Delimiter::None => token::NoDelim,
+        }
+    }
+}
+
+impl FromInternal<(TreeAndJoint, &'_ ParseSess, &'_ mut Vec<Self>)>
+    for TokenTree<Group, Punct, Ident, Literal>
+{
+    fn from_internal(((tree, is_joint), sess, stack): (TreeAndJoint, &ParseSess, &mut Vec<Self>))
+                    -> Self {
+        use crate::parse::token::*;
+
+        let joint = is_joint == Joint;
+        let Token { kind, span } = match tree {
+            tokenstream::TokenTree::Delimited(span, delim, tts) => {
+                let delimiter = Delimiter::from_internal(delim);
+                return TokenTree::Group(Group {
+                    delimiter,
+                    stream: tts.into(),
+                    span,
+                });
+            }
+            tokenstream::TokenTree::Token(token) => token,
+        };
+
+        macro_rules! tt {
+            ($ty:ident { $($field:ident $(: $value:expr)*),+ $(,)? }) => (
+                TokenTree::$ty(self::$ty {
+                    $($field $(: $value)*,)+
+                    span,
+                })
+            );
+            ($ty:ident::$method:ident($($value:expr),*)) => (
+                TokenTree::$ty(self::$ty::$method($($value,)* span))
+            );
+        }
+        macro_rules! op {
+            ($a:expr) => {
+                tt!(Punct::new($a, joint))
+            };
+            ($a:expr, $b:expr) => {{
+                stack.push(tt!(Punct::new($b, joint)));
+                tt!(Punct::new($a, true))
+            }};
+            ($a:expr, $b:expr, $c:expr) => {{
+                stack.push(tt!(Punct::new($c, joint)));
+                stack.push(tt!(Punct::new($b, true)));
+                tt!(Punct::new($a, true))
+            }};
+        }
+
+        match kind {
+            Eq => op!('='),
+            Lt => op!('<'),
+            Le => op!('<', '='),
+            EqEq => op!('=', '='),
+            Ne => op!('!', '='),
+            Ge => op!('>', '='),
+            Gt => op!('>'),
+            AndAnd => op!('&', '&'),
+            OrOr => op!('|', '|'),
+            Not => op!('!'),
+            Tilde => op!('~'),
+            BinOp(Plus) => op!('+'),
+            BinOp(Minus) => op!('-'),
+            BinOp(Star) => op!('*'),
+            BinOp(Slash) => op!('/'),
+            BinOp(Percent) => op!('%'),
+            BinOp(Caret) => op!('^'),
+            BinOp(And) => op!('&'),
+            BinOp(Or) => op!('|'),
+            BinOp(Shl) => op!('<', '<'),
+            BinOp(Shr) => op!('>', '>'),
+            BinOpEq(Plus) => op!('+', '='),
+            BinOpEq(Minus) => op!('-', '='),
+            BinOpEq(Star) => op!('*', '='),
+            BinOpEq(Slash) => op!('/', '='),
+            BinOpEq(Percent) => op!('%', '='),
+            BinOpEq(Caret) => op!('^', '='),
+            BinOpEq(And) => op!('&', '='),
+            BinOpEq(Or) => op!('|', '='),
+            BinOpEq(Shl) => op!('<', '<', '='),
+            BinOpEq(Shr) => op!('>', '>', '='),
+            At => op!('@'),
+            Dot => op!('.'),
+            DotDot => op!('.', '.'),
+            DotDotDot => op!('.', '.', '.'),
+            DotDotEq => op!('.', '.', '='),
+            Comma => op!(','),
+            Semi => op!(';'),
+            Colon => op!(':'),
+            ModSep => op!(':', ':'),
+            RArrow => op!('-', '>'),
+            LArrow => op!('<', '-'),
+            FatArrow => op!('=', '>'),
+            Pound => op!('#'),
+            Dollar => op!('$'),
+            Question => op!('?'),
+            SingleQuote => op!('\''),
+
+            Ident(name, false) if name == kw::DollarCrate => tt!(Ident::dollar_crate()),
+            Ident(name, is_raw) => tt!(Ident::new(name, is_raw)),
+            Lifetime(name) => {
+                let ident = ast::Ident::new(name, span).without_first_quote();
+                stack.push(tt!(Ident::new(ident.name, false)));
+                tt!(Punct::new('\'', true))
+            }
+            Literal(lit) => tt!(Literal { lit }),
+            DocComment(c) => {
+                let style = comments::doc_comment_style(&c.as_str());
+                let stripped = comments::strip_doc_comment_decoration(&c.as_str());
+                let mut escaped = String::new();
+                for ch in stripped.chars() {
+                    escaped.extend(ch.escape_debug());
+                }
+                let stream = vec![
+                    Ident(sym::doc, false),
+                    Eq,
+                    TokenKind::lit(token::Str, Symbol::intern(&escaped), None),
+                ]
+                .into_iter()
+                .map(|kind| tokenstream::TokenTree::token(kind, span))
+                .collect();
+                stack.push(TokenTree::Group(Group {
+                    delimiter: Delimiter::Bracket,
+                    stream,
+                    span: DelimSpan::from_single(span),
+                }));
+                if style == ast::AttrStyle::Inner {
+                    stack.push(tt!(Punct::new('!', false)));
+                }
+                tt!(Punct::new('#', false))
+            }
+
+            Interpolated(nt) => {
+                let stream = nt.to_tokenstream(sess, span);
+                TokenTree::Group(Group {
+                    delimiter: Delimiter::None,
+                    stream,
+                    span: DelimSpan::from_single(span),
+                })
+            }
+
+            OpenDelim(..) | CloseDelim(..) => unreachable!(),
+            Whitespace | Comment | Shebang(..) | Unknown(..) | Eof => unreachable!(),
+        }
+    }
+}
+
+impl ToInternal<TokenStream> for TokenTree<Group, Punct, Ident, Literal> {
+    fn to_internal(self) -> TokenStream {
+        use crate::parse::token::*;
+
+        let (ch, joint, span) = match self {
+            TokenTree::Punct(Punct { ch, joint, span }) => (ch, joint, span),
+            TokenTree::Group(Group {
+                delimiter,
+                stream,
+                span,
+            }) => {
+                return tokenstream::TokenTree::Delimited(
+                    span,
+                    delimiter.to_internal(),
+                    stream.into(),
+                )
+                .into();
+            }
+            TokenTree::Ident(self::Ident { sym, is_raw, span }) => {
+                return tokenstream::TokenTree::token(Ident(sym, is_raw), span).into();
+            }
+            TokenTree::Literal(self::Literal {
+                lit: token::Lit { kind: token::Integer, symbol, suffix },
+                span,
+            }) if symbol.as_str().starts_with("-") => {
+                let minus = BinOp(BinOpToken::Minus);
+                let symbol = Symbol::intern(&symbol.as_str()[1..]);
+                let integer = TokenKind::lit(token::Integer, symbol, suffix);
+                let a = tokenstream::TokenTree::token(minus, span);
+                let b = tokenstream::TokenTree::token(integer, span);
+                return vec![a, b].into_iter().collect();
+            }
+            TokenTree::Literal(self::Literal {
+                lit: token::Lit { kind: token::Float, symbol, suffix },
+                span,
+            }) if symbol.as_str().starts_with("-") => {
+                let minus = BinOp(BinOpToken::Minus);
+                let symbol = Symbol::intern(&symbol.as_str()[1..]);
+                let float = TokenKind::lit(token::Float, symbol, suffix);
+                let a = tokenstream::TokenTree::token(minus, span);
+                let b = tokenstream::TokenTree::token(float, span);
+                return vec![a, b].into_iter().collect();
+            }
+            TokenTree::Literal(self::Literal { lit, span }) => {
+                return tokenstream::TokenTree::token(Literal(lit), span).into()
+            }
+        };
+
+        let kind = match ch {
+            '=' => Eq,
+            '<' => Lt,
+            '>' => Gt,
+            '!' => Not,
+            '~' => Tilde,
+            '+' => BinOp(Plus),
+            '-' => BinOp(Minus),
+            '*' => BinOp(Star),
+            '/' => BinOp(Slash),
+            '%' => BinOp(Percent),
+            '^' => BinOp(Caret),
+            '&' => BinOp(And),
+            '|' => BinOp(Or),
+            '@' => At,
+            '.' => Dot,
+            ',' => Comma,
+            ';' => Semi,
+            ':' => Colon,
+            '#' => Pound,
+            '$' => Dollar,
+            '?' => Question,
+            '\'' => SingleQuote,
+            _ => unreachable!(),
+        };
+
+        let tree = tokenstream::TokenTree::token(kind, span);
+        TokenStream::new(vec![(tree, if joint { Joint } else { NonJoint })])
+    }
+}
+
+impl ToInternal<errors::Level> for Level {
+    fn to_internal(self) -> errors::Level {
+        match self {
+            Level::Error => errors::Level::Error,
+            Level::Warning => errors::Level::Warning,
+            Level::Note => errors::Level::Note,
+            Level::Help => errors::Level::Help,
+            _ => unreachable!("unknown proc_macro::Level variant: {:?}", self),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub struct TokenStreamIter {
+    cursor: tokenstream::Cursor,
+    stack: Vec<TokenTree<Group, Punct, Ident, Literal>>,
+}
+
+#[derive(Clone)]
+pub struct Group {
+    delimiter: Delimiter,
+    stream: TokenStream,
+    span: DelimSpan,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+pub struct Punct {
+    ch: char,
+    // NB. not using `Spacing` here because it doesn't implement `Hash`.
+    joint: bool,
+    span: Span,
+}
+
+impl Punct {
+    fn new(ch: char, joint: bool, span: Span) -> Punct {
+        const LEGAL_CHARS: &[char] = &['=', '<', '>', '!', '~', '+', '-', '*', '/', '%', '^',
+                                       '&', '|', '@', '.', ',', ';', ':', '#', '$', '?', '\''];
+        if !LEGAL_CHARS.contains(&ch) {
+            panic!("unsupported character `{:?}`", ch)
+        }
+        Punct { ch, joint, span }
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+pub struct Ident {
+    sym: Symbol,
+    is_raw: bool,
+    span: Span,
+}
+
+impl Ident {
+    fn is_valid(string: &str) -> bool {
+        let mut chars = string.chars();
+        if let Some(start) = chars.next() {
+            (start == '_' || start.is_xid_start())
+                && chars.all(|cont| cont == '_' || cont.is_xid_continue())
+        } else {
+            false
+        }
+    }
+    fn new(sym: Symbol, is_raw: bool, span: Span) -> Ident {
+        let string = sym.as_str();
+        if !Self::is_valid(&string) {
+            panic!("`{:?}` is not a valid identifier", string)
+        }
+        // Get rid of gensyms to conservatively check rawness on the string contents only.
+        if is_raw && !sym.as_interned_str().as_symbol().can_be_raw() {
+            panic!("`{}` cannot be a raw identifier", string);
+        }
+        Ident { sym, is_raw, span }
+    }
+    fn dollar_crate(span: Span) -> Ident {
+        // `$crate` is accepted as an ident only if it comes from the compiler.
+        Ident { sym: kw::DollarCrate, is_raw: false, span }
+    }
+}
+
+// FIXME(eddyb) `Literal` should not expose internal `Debug` impls.
+#[derive(Clone, Debug)]
+pub struct Literal {
+    lit: token::Lit,
+    span: Span,
+}
+
+pub(crate) struct Rustc<'a> {
+    sess: &'a ParseSess,
+    def_site: Span,
+    call_site: Span,
+}
+
+impl<'a> Rustc<'a> {
+    pub fn new(cx: &'a ExtCtxt<'_>) -> Self {
+        // No way to determine def location for a proc macro right now, so use call location.
+        let location = cx.current_expansion.id.expn_data().call_site;
+        let to_span = |transparency| {
+            location.with_ctxt(
+                SyntaxContext::root()
+                    .apply_mark_with_transparency(cx.current_expansion.id, transparency),
+            )
+        };
+        Rustc {
+            sess: cx.parse_sess,
+            def_site: to_span(Transparency::Opaque),
+            call_site: to_span(Transparency::Transparent),
+        }
+    }
+
+    fn lit(&mut self, kind: token::LitKind, symbol: Symbol, suffix: Option<Symbol>) -> Literal {
+        Literal {
+            lit: token::Lit::new(kind, symbol, suffix),
+            span: server::Span::call_site(self),
+        }
+    }
+}
+
+impl server::Types for Rustc<'_> {
+    type TokenStream = TokenStream;
+    type TokenStreamBuilder = tokenstream::TokenStreamBuilder;
+    type TokenStreamIter = TokenStreamIter;
+    type Group = Group;
+    type Punct = Punct;
+    type Ident = Ident;
+    type Literal = Literal;
+    type SourceFile = Lrc<SourceFile>;
+    type MultiSpan = Vec<Span>;
+    type Diagnostic = Diagnostic;
+    type Span = Span;
+}
+
+impl server::TokenStream for Rustc<'_> {
+    fn new(&mut self) -> Self::TokenStream {
+        TokenStream::empty()
+    }
+    fn is_empty(&mut self, stream: &Self::TokenStream) -> bool {
+        stream.is_empty()
+    }
+    fn from_str(&mut self, src: &str) -> Self::TokenStream {
+        parse::parse_stream_from_source_str(
+            FileName::proc_macro_source_code(src),
+            src.to_string(),
+            self.sess,
+            Some(self.call_site),
+        )
+    }
+    fn to_string(&mut self, stream: &Self::TokenStream) -> String {
+        stream.to_string()
+    }
+    fn from_token_tree(
+        &mut self,
+        tree: TokenTree<Self::Group, Self::Punct, Self::Ident, Self::Literal>,
+    ) -> Self::TokenStream {
+        tree.to_internal()
+    }
+    fn into_iter(&mut self, stream: Self::TokenStream) -> Self::TokenStreamIter {
+        TokenStreamIter {
+            cursor: stream.trees(),
+            stack: vec![],
+        }
+    }
+}
+
+impl server::TokenStreamBuilder for Rustc<'_> {
+    fn new(&mut self) -> Self::TokenStreamBuilder {
+        tokenstream::TokenStreamBuilder::new()
+    }
+    fn push(&mut self, builder: &mut Self::TokenStreamBuilder, stream: Self::TokenStream) {
+        builder.push(stream);
+    }
+    fn build(&mut self, builder: Self::TokenStreamBuilder) -> Self::TokenStream {
+        builder.build()
+    }
+}
+
+impl server::TokenStreamIter for Rustc<'_> {
+    fn next(
+        &mut self,
+        iter: &mut Self::TokenStreamIter,
+    ) -> Option<TokenTree<Self::Group, Self::Punct, Self::Ident, Self::Literal>> {
+        loop {
+            let tree = iter.stack.pop().or_else(|| {
+                let next = iter.cursor.next_with_joint()?;
+                Some(TokenTree::from_internal((next, self.sess, &mut iter.stack)))
+            })?;
+            // HACK: The condition "dummy span + group with empty delimiter" represents an AST
+            // fragment approximately converted into a token stream. This may happen, for
+            // example, with inputs to proc macro attributes, including derives. Such "groups"
+            // need to flattened during iteration over stream's token trees.
+            // Eventually this needs to be removed in favor of keeping original token trees
+            // and not doing the roundtrip through AST.
+            if let TokenTree::Group(ref group) = tree {
+                if group.delimiter == Delimiter::None && group.span.entire().is_dummy() {
+                    iter.cursor.append(group.stream.clone());
+                    continue;
+                }
+            }
+            return Some(tree);
+        }
+    }
+}
+
+impl server::Group for Rustc<'_> {
+    fn new(&mut self, delimiter: Delimiter, stream: Self::TokenStream) -> Self::Group {
+        Group {
+            delimiter,
+            stream,
+            span: DelimSpan::from_single(server::Span::call_site(self)),
+        }
+    }
+    fn delimiter(&mut self, group: &Self::Group) -> Delimiter {
+        group.delimiter
+    }
+    fn stream(&mut self, group: &Self::Group) -> Self::TokenStream {
+        group.stream.clone()
+    }
+    fn span(&mut self, group: &Self::Group) -> Self::Span {
+        group.span.entire()
+    }
+    fn span_open(&mut self, group: &Self::Group) -> Self::Span {
+        group.span.open
+    }
+    fn span_close(&mut self, group: &Self::Group) -> Self::Span {
+        group.span.close
+    }
+    fn set_span(&mut self, group: &mut Self::Group, span: Self::Span) {
+        group.span = DelimSpan::from_single(span);
+    }
+}
+
+impl server::Punct for Rustc<'_> {
+    fn new(&mut self, ch: char, spacing: Spacing) -> Self::Punct {
+        Punct::new(ch, spacing == Spacing::Joint, server::Span::call_site(self))
+    }
+    fn as_char(&mut self, punct: Self::Punct) -> char {
+        punct.ch
+    }
+    fn spacing(&mut self, punct: Self::Punct) -> Spacing {
+        if punct.joint {
+            Spacing::Joint
+        } else {
+            Spacing::Alone
+        }
+    }
+    fn span(&mut self, punct: Self::Punct) -> Self::Span {
+        punct.span
+    }
+    fn with_span(&mut self, punct: Self::Punct, span: Self::Span) -> Self::Punct {
+        Punct { span, ..punct }
+    }
+}
+
+impl server::Ident for Rustc<'_> {
+    fn new(&mut self, string: &str, span: Self::Span, is_raw: bool) -> Self::Ident {
+        Ident::new(Symbol::intern(string), is_raw, span)
+    }
+    fn span(&mut self, ident: Self::Ident) -> Self::Span {
+        ident.span
+    }
+    fn with_span(&mut self, ident: Self::Ident, span: Self::Span) -> Self::Ident {
+        Ident { span, ..ident }
+    }
+}
+
+impl server::Literal for Rustc<'_> {
+    // FIXME(eddyb) `Literal` should not expose internal `Debug` impls.
+    fn debug(&mut self, literal: &Self::Literal) -> String {
+        format!("{:?}", literal)
+    }
+    fn integer(&mut self, n: &str) -> Self::Literal {
+        self.lit(token::Integer, Symbol::intern(n), None)
+    }
+    fn typed_integer(&mut self, n: &str, kind: &str) -> Self::Literal {
+        self.lit(token::Integer, Symbol::intern(n), Some(Symbol::intern(kind)))
+    }
+    fn float(&mut self, n: &str) -> Self::Literal {
+        self.lit(token::Float, Symbol::intern(n), None)
+    }
+    fn f32(&mut self, n: &str) -> Self::Literal {
+        self.lit(token::Float, Symbol::intern(n), Some(sym::f32))
+    }
+    fn f64(&mut self, n: &str) -> Self::Literal {
+        self.lit(token::Float, Symbol::intern(n), Some(sym::f64))
+    }
+    fn string(&mut self, string: &str) -> Self::Literal {
+        let mut escaped = String::new();
+        for ch in string.chars() {
+            escaped.extend(ch.escape_debug());
+        }
+        self.lit(token::Str, Symbol::intern(&escaped), None)
+    }
+    fn character(&mut self, ch: char) -> Self::Literal {
+        let mut escaped = String::new();
+        escaped.extend(ch.escape_unicode());
+        self.lit(token::Char, Symbol::intern(&escaped), None)
+    }
+    fn byte_string(&mut self, bytes: &[u8]) -> Self::Literal {
+        let string = bytes
+            .iter()
+            .cloned()
+            .flat_map(ascii::escape_default)
+            .map(Into::<char>::into)
+            .collect::<String>();
+        self.lit(token::ByteStr, Symbol::intern(&string), None)
+    }
+    fn span(&mut self, literal: &Self::Literal) -> Self::Span {
+        literal.span
+    }
+    fn set_span(&mut self, literal: &mut Self::Literal, span: Self::Span) {
+        literal.span = span;
+    }
+    fn subspan(
+        &mut self,
+        literal: &Self::Literal,
+        start: Bound<usize>,
+        end: Bound<usize>,
+    ) -> Option<Self::Span> {
+        let span = literal.span;
+        let length = span.hi().to_usize() - span.lo().to_usize();
+
+        let start = match start {
+            Bound::Included(lo) => lo,
+            Bound::Excluded(lo) => lo + 1,
+            Bound::Unbounded => 0,
+        };
+
+        let end = match end {
+            Bound::Included(hi) => hi + 1,
+            Bound::Excluded(hi) => hi,
+            Bound::Unbounded => length,
+        };
+
+        // Bounds check the values, preventing addition overflow and OOB spans.
+        if start > u32::max_value() as usize
+            || end > u32::max_value() as usize
+            || (u32::max_value() - start as u32) < span.lo().to_u32()
+            || (u32::max_value() - end as u32) < span.lo().to_u32()
+            || start >= end
+            || end > length
+        {
+            return None;
+        }
+
+        let new_lo = span.lo() + BytePos::from_usize(start);
+        let new_hi = span.lo() + BytePos::from_usize(end);
+        Some(span.with_lo(new_lo).with_hi(new_hi))
+    }
+}
+
+impl server::SourceFile for Rustc<'_> {
+    fn eq(&mut self, file1: &Self::SourceFile, file2: &Self::SourceFile) -> bool {
+        Lrc::ptr_eq(file1, file2)
+    }
+    fn path(&mut self, file: &Self::SourceFile) -> String {
+        match file.name {
+            FileName::Real(ref path) => path
+                .to_str()
+                .expect("non-UTF8 file path in `proc_macro::SourceFile::path`")
+                .to_string(),
+            _ => file.name.to_string(),
+        }
+    }
+    fn is_real(&mut self, file: &Self::SourceFile) -> bool {
+        file.is_real_file()
+    }
+}
+
+impl server::MultiSpan for Rustc<'_> {
+    fn new(&mut self) -> Self::MultiSpan {
+        vec![]
+    }
+    fn push(&mut self, spans: &mut Self::MultiSpan, span: Self::Span) {
+        spans.push(span)
+    }
+}
+
+impl server::Diagnostic for Rustc<'_> {
+    fn new(&mut self, level: Level, msg: &str, spans: Self::MultiSpan) -> Self::Diagnostic {
+        let mut diag = Diagnostic::new(level.to_internal(), msg);
+        diag.set_span(MultiSpan::from_spans(spans));
+        diag
+    }
+    fn sub(
+        &mut self,
+        diag: &mut Self::Diagnostic,
+        level: Level,
+        msg: &str,
+        spans: Self::MultiSpan,
+    ) {
+        diag.sub(level.to_internal(), msg, MultiSpan::from_spans(spans), None);
+    }
+    fn emit(&mut self, diag: Self::Diagnostic) {
+        DiagnosticBuilder::new_diagnostic(&self.sess.span_diagnostic, diag).emit()
+    }
+}
+
+impl server::Span for Rustc<'_> {
+    fn debug(&mut self, span: Self::Span) -> String {
+        format!("{:?} bytes({}..{})", span.ctxt(), span.lo().0, span.hi().0)
+    }
+    fn def_site(&mut self) -> Self::Span {
+        self.def_site
+    }
+    fn call_site(&mut self) -> Self::Span {
+        self.call_site
+    }
+    fn source_file(&mut self, span: Self::Span) -> Self::SourceFile {
+        self.sess.source_map().lookup_char_pos(span.lo()).file
+    }
+    fn parent(&mut self, span: Self::Span) -> Option<Self::Span> {
+        span.parent()
+    }
+    fn source(&mut self, span: Self::Span) -> Self::Span {
+        span.source_callsite()
+    }
+    fn start(&mut self, span: Self::Span) -> LineColumn {
+        let loc = self.sess.source_map().lookup_char_pos(span.lo());
+        LineColumn {
+            line: loc.line,
+            column: loc.col.to_usize(),
+        }
+    }
+    fn end(&mut self, span: Self::Span) -> LineColumn {
+        let loc = self.sess.source_map().lookup_char_pos(span.hi());
+        LineColumn {
+            line: loc.line,
+            column: loc.col.to_usize(),
+        }
+    }
+    fn join(&mut self, first: Self::Span, second: Self::Span) -> Option<Self::Span> {
+        let self_loc = self.sess.source_map().lookup_char_pos(first.lo());
+        let other_loc = self.sess.source_map().lookup_char_pos(second.lo());
+
+        if self_loc.file.name != other_loc.file.name {
+            return None;
+        }
+
+        Some(first.to(second))
+    }
+    fn resolved_at(&mut self, span: Self::Span, at: Self::Span) -> Self::Span {
+        span.with_ctxt(at.ctxt())
+    }
+    fn source_text(&mut self,  span: Self::Span) -> Option<String> {
+        self.sess.source_map().span_to_snippet(span).ok()
+    }
+}
diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
deleted file mode 100644
index e1cb90d9e71..00000000000
--- a/src/libsyntax/ext/source_util.rs
+++ /dev/null
@@ -1,197 +0,0 @@
-use crate::ast;
-use crate::ext::base::{self, *};
-use crate::ext::build::AstBuilder;
-use crate::parse::{self, token, DirectoryOwnership};
-use crate::print::pprust;
-use crate::ptr::P;
-use crate::symbol::{Symbol, sym};
-use crate::tokenstream;
-
-use smallvec::SmallVec;
-use syntax_pos::{self, Pos, Span, FileName};
-
-use std::fs;
-use std::io::ErrorKind;
-use std::path::PathBuf;
-use rustc_data_structures::sync::Lrc;
-
-// These macros all relate to the file system; they either return
-// the column/row/filename of the expression, or they include
-// a given file into the current one.
-
-/// line!(): expands to the current line number
-pub fn expand_line(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
-                   -> Box<dyn base::MacResult+'static> {
-    base::check_zero_tts(cx, sp, tts, "line!");
-
-    let topmost = cx.expansion_cause().unwrap_or(sp);
-    let loc = cx.source_map().lookup_char_pos(topmost.lo());
-
-    base::MacEager::expr(cx.expr_u32(topmost, loc.line as u32))
-}
-
-/* column!(): expands to the current column number */
-pub fn expand_column(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
-                  -> Box<dyn base::MacResult+'static> {
-    base::check_zero_tts(cx, sp, tts, "column!");
-
-    let topmost = cx.expansion_cause().unwrap_or(sp);
-    let loc = cx.source_map().lookup_char_pos(topmost.lo());
-
-    base::MacEager::expr(cx.expr_u32(topmost, loc.col.to_usize() as u32 + 1))
-}
-
-/* __rust_unstable_column!(): expands to the current column number */
-pub fn expand_column_gated(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
-                  -> Box<dyn base::MacResult+'static> {
-    if sp.allows_unstable(sym::__rust_unstable_column) {
-        expand_column(cx, sp, tts)
-    } else {
-        cx.span_fatal(sp, "the __rust_unstable_column macro is unstable");
-    }
-}
-
-/// file!(): expands to the current filename */
-/// The source_file (`loc.file`) contains a bunch more information we could spit
-/// out if we wanted.
-pub fn expand_file(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
-                   -> Box<dyn base::MacResult+'static> {
-    base::check_zero_tts(cx, sp, tts, "file!");
-
-    let topmost = cx.expansion_cause().unwrap_or(sp);
-    let loc = cx.source_map().lookup_char_pos(topmost.lo());
-    base::MacEager::expr(cx.expr_str(topmost, Symbol::intern(&loc.file.name.to_string())))
-}
-
-pub fn expand_stringify(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
-                        -> Box<dyn base::MacResult+'static> {
-    let s = pprust::tts_to_string(tts);
-    base::MacEager::expr(cx.expr_str(sp, Symbol::intern(&s)))
-}
-
-pub fn expand_mod(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
-                  -> Box<dyn base::MacResult+'static> {
-    base::check_zero_tts(cx, sp, tts, "module_path!");
-    let mod_path = &cx.current_expansion.module.mod_path;
-    let string = mod_path.iter().map(|x| x.to_string()).collect::<Vec<String>>().join("::");
-
-    base::MacEager::expr(cx.expr_str(sp, Symbol::intern(&string)))
-}
-
-/// include! : parse the given file as an expr
-/// This is generally a bad idea because it's going to behave
-/// unhygienically.
-pub fn expand_include<'cx>(cx: &'cx mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
-                           -> Box<dyn base::MacResult+'cx> {
-    let file = match get_single_str_from_tts(cx, sp, tts, "include!") {
-        Some(f) => f,
-        None => return DummyResult::any(sp),
-    };
-    // The file will be added to the code map by the parser
-    let path = res_rel_file(cx, sp, file);
-    let directory_ownership = DirectoryOwnership::Owned { relative: None };
-    let p = parse::new_sub_parser_from_file(cx.parse_sess(), &path, directory_ownership, None, sp);
-
-    struct ExpandResult<'a> {
-        p: parse::parser::Parser<'a>,
-    }
-    impl<'a> base::MacResult for ExpandResult<'a> {
-        fn make_expr(mut self: Box<ExpandResult<'a>>) -> Option<P<ast::Expr>> {
-            Some(panictry!(self.p.parse_expr()))
-        }
-
-        fn make_items(mut self: Box<ExpandResult<'a>>) -> Option<SmallVec<[P<ast::Item>; 1]>> {
-            let mut ret = SmallVec::new();
-            while self.p.token != token::Eof {
-                match panictry!(self.p.parse_item()) {
-                    Some(item) => ret.push(item),
-                    None => self.p.diagnostic().span_fatal(self.p.span,
-                                                           &format!("expected item, found `{}`",
-                                                                    self.p.this_token_to_string()))
-                                               .raise()
-                }
-            }
-            Some(ret)
-        }
-    }
-
-    Box::new(ExpandResult { p })
-}
-
-// include_str! : read the given file, insert it as a literal string expr
-pub fn expand_include_str(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
-                          -> Box<dyn base::MacResult+'static> {
-    let file = match get_single_str_from_tts(cx, sp, tts, "include_str!") {
-        Some(f) => f,
-        None => return DummyResult::expr(sp)
-    };
-    let file = res_rel_file(cx, sp, file);
-    match fs::read_to_string(&file) {
-        Ok(src) => {
-            let interned_src = Symbol::intern(&src);
-
-            // Add this input file to the code map to make it available as
-            // dependency information
-            cx.source_map().new_source_file(file.into(), src);
-
-            base::MacEager::expr(cx.expr_str(sp, interned_src))
-        },
-        Err(ref e) if e.kind() == ErrorKind::InvalidData => {
-            cx.span_err(sp, &format!("{} wasn't a utf-8 file", file.display()));
-            DummyResult::expr(sp)
-        }
-        Err(e) => {
-            cx.span_err(sp, &format!("couldn't read {}: {}", file.display(), e));
-            DummyResult::expr(sp)
-        }
-    }
-}
-
-pub fn expand_include_bytes(cx: &mut ExtCtxt<'_>, sp: Span, tts: &[tokenstream::TokenTree])
-                            -> Box<dyn base::MacResult+'static> {
-    let file = match get_single_str_from_tts(cx, sp, tts, "include_bytes!") {
-        Some(f) => f,
-        None => return DummyResult::expr(sp)
-    };
-    let file = res_rel_file(cx, sp, file);
-    match fs::read(&file) {
-        Ok(bytes) => {
-            // Add the contents to the source map if it contains UTF-8.
-            let (contents, bytes) = match String::from_utf8(bytes) {
-                Ok(s) => {
-                    let bytes = s.as_bytes().to_owned();
-                    (s, bytes)
-                },
-                Err(e) => (String::new(), e.into_bytes()),
-            };
-            cx.source_map().new_source_file(file.into(), contents);
-
-            base::MacEager::expr(cx.expr_lit(sp, ast::LitKind::ByteStr(Lrc::new(bytes))))
-        },
-        Err(e) => {
-            cx.span_err(sp, &format!("couldn't read {}: {}", file.display(), e));
-            DummyResult::expr(sp)
-        }
-    }
-}
-
-// resolve a file-system path to an absolute file-system path (if it
-// isn't already)
-fn res_rel_file(cx: &mut ExtCtxt<'_>, sp: syntax_pos::Span, arg: String) -> PathBuf {
-    let arg = PathBuf::from(arg);
-    // Relative paths are resolved relative to the file in which they are found
-    // after macro expansion (that is, they are unhygienic).
-    if !arg.is_absolute() {
-        let callsite = sp.source_callsite();
-        let mut path = match cx.source_map().span_to_unmapped_path(callsite) {
-            FileName::Real(path) => path,
-            FileName::DocTest(path, _) => path,
-            other => panic!("cannot resolve relative path in non-file source `{}`", other),
-        };
-        path.pop();
-        path.push(arg);
-        path
-    } else {
-        arg
-    }
-}
diff --git a/src/libsyntax/ext/tt/macro_check.rs b/src/libsyntax/ext/tt/macro_check.rs
new file mode 100644
index 00000000000..5af97199902
--- /dev/null
+++ b/src/libsyntax/ext/tt/macro_check.rs
@@ -0,0 +1,626 @@
+//! Checks that meta-variables in macro definition are correctly declared and used.
+//!
+//! # What is checked
+//!
+//! ## Meta-variables must not be bound twice
+//!
+//! ```
+//! macro_rules! foo { ($x:tt $x:tt) => { $x }; }
+//! ```
+//!
+//! This check is sound (no false-negative) and complete (no false-positive).
+//!
+//! ## Meta-variables must not be free
+//!
+//! ```
+//! macro_rules! foo { () => { $x }; }
+//! ```
+//!
+//! This check is also done at macro instantiation but only if the branch is taken.
+//!
+//! ## Meta-variables must repeat at least as many times as their binder
+//!
+//! ```
+//! macro_rules! foo { ($($x:tt)*) => { $x }; }
+//! ```
+//!
+//! This check is also done at macro instantiation but only if the branch is taken.
+//!
+//! ## Meta-variables must repeat with the same Kleene operators as their binder
+//!
+//! ```
+//! macro_rules! foo { ($($x:tt)+) => { $($x)* }; }
+//! ```
+//!
+//! This check is not done at macro instantiation.
+//!
+//! # Disclaimer
+//!
+//! In the presence of nested macros (a macro defined in a macro), those checks may have false
+//! positives and false negatives. We try to detect those cases by recognizing potential macro
+//! definitions in RHSes, but nested macros may be hidden through the use of particular values of
+//! meta-variables.
+//!
+//! ## Examples of false positive
+//!
+//! False positives can come from cases where we don't recognize a nested macro, because it depends
+//! on particular values of meta-variables. In the following example, we think both instances of
+//! `$x` are free, which is a correct statement if `$name` is anything but `macro_rules`. But when
+//! `$name` is `macro_rules`, like in the instantiation below, then `$x:tt` is actually a binder of
+//! the nested macro and `$x` is bound to it.
+//!
+//! ```
+//! macro_rules! foo { ($name:ident) => { $name! bar { ($x:tt) => { $x }; } }; }
+//! foo!(macro_rules);
+//! ```
+//!
+//! False positives can also come from cases where we think there is a nested macro while there
+//! isn't. In the following example, we think `$x` is free, which is incorrect because `bar` is not
+//! a nested macro since it is not evaluated as code by `stringify!`.
+//!
+//! ```
+//! macro_rules! foo { () => { stringify!(macro_rules! bar { () => { $x }; }) }; }
+//! ```
+//!
+//! ## Examples of false negative
+//!
+//! False negatives can come from cases where we don't recognize a meta-variable, because it depends
+//! on particular values of meta-variables. In the following examples, we don't see that if `$d` is
+//! instantiated with `$` then `$d z` becomes `$z` in the nested macro definition and is thus a free
+//! meta-variable. Note however, that if `foo` is instantiated, then we would check the definition
+//! of `bar` and would see the issue.
+//!
+//! ```
+//! macro_rules! foo { ($d:tt) => { macro_rules! bar { ($y:tt) => { $d z }; } }; }
+//! ```
+//!
+//! # How it is checked
+//!
+//! There are 3 main functions: `check_binders`, `check_occurrences`, and `check_nested_macro`. They
+//! all need some kind of environment.
+//!
+//! ## Environments
+//!
+//! Environments are used to pass information.
+//!
+//! ### From LHS to RHS
+//!
+//! When checking a LHS with `check_binders`, we produce (and use) an environment for binders,
+//! namely `Binders`. This is a mapping from binder name to information about that binder: the span
+//! of the binder for error messages and the stack of Kleene operators under which it was bound in
+//! the LHS.
+//!
+//! This environment is used by both the LHS and RHS. The LHS uses it to detect duplicate binders.
+//! The RHS uses it to detect the other errors.
+//!
+//! ### From outer macro to inner macro
+//!
+//! When checking the RHS of an outer macro and we detect a nested macro definition, we push the
+//! current state, namely `MacroState`, to an environment of nested macro definitions. Each state
+//! stores the LHS binders when entering the macro definition as well as the stack of Kleene
+//! operators under which the inner macro is defined in the RHS.
+//!
+//! This environment is a stack representing the nesting of macro definitions. As such, the stack of
+//! Kleene operators under which a meta-variable is repeating is the concatenation of the stacks
+//! stored when entering a macro definition starting from the state in which the meta-variable is
+//! bound.
+use crate::ast::NodeId;
+use crate::early_buffered_lints::BufferedEarlyLintId;
+use crate::ext::tt::quoted::{KleeneToken, TokenTree};
+use crate::parse::token::TokenKind;
+use crate::parse::token::{DelimToken, Token};
+use crate::parse::ParseSess;
+use crate::symbol::{kw, sym};
+
+use rustc_data_structures::fx::FxHashMap;
+use smallvec::SmallVec;
+use syntax_pos::{symbol::Ident, MultiSpan, Span};
+
+/// Stack represented as linked list.
+///
+/// Those are used for environments because they grow incrementally and are not mutable.
+enum Stack<'a, T> {
+    /// Empty stack.
+    Empty,
+    /// A non-empty stack.
+    Push {
+        /// The top element.
+        top: T,
+        /// The previous elements.
+        prev: &'a Stack<'a, T>,
+    },
+}
+
+impl<'a, T> Stack<'a, T> {
+    /// Returns whether a stack is empty.
+    fn is_empty(&self) -> bool {
+        match *self {
+            Stack::Empty => true,
+            _ => false,
+        }
+    }
+
+    /// Returns a new stack with an element of top.
+    fn push(&'a self, top: T) -> Stack<'a, T> {
+        Stack::Push { top, prev: self }
+    }
+}
+
+impl<'a, T> Iterator for &'a Stack<'a, T> {
+    type Item = &'a T;
+
+    // Iterates from top to bottom of the stack.
+    fn next(&mut self) -> Option<&'a T> {
+        match *self {
+            Stack::Empty => None,
+            Stack::Push { ref top, ref prev } => {
+                *self = prev;
+                Some(top)
+            }
+        }
+    }
+}
+
+impl From<&Stack<'_, KleeneToken>> for SmallVec<[KleeneToken; 1]> {
+    fn from(ops: &Stack<'_, KleeneToken>) -> SmallVec<[KleeneToken; 1]> {
+        let mut ops: SmallVec<[KleeneToken; 1]> = ops.cloned().collect();
+        // The stack is innermost on top. We want outermost first.
+        ops.reverse();
+        ops
+    }
+}
+
+/// Information attached to a meta-variable binder in LHS.
+struct BinderInfo {
+    /// The span of the meta-variable in LHS.
+    span: Span,
+    /// The stack of Kleene operators (outermost first).
+    ops: SmallVec<[KleeneToken; 1]>,
+}
+
+/// An environment of meta-variables to their binder information.
+type Binders = FxHashMap<Ident, BinderInfo>;
+
+/// The state at which we entered a macro definition in the RHS of another macro definition.
+struct MacroState<'a> {
+    /// The binders of the branch where we entered the macro definition.
+    binders: &'a Binders,
+    /// The stack of Kleene operators (outermost first) where we entered the macro definition.
+    ops: SmallVec<[KleeneToken; 1]>,
+}
+
+/// Checks that meta-variables are used correctly in a macro definition.
+///
+/// Arguments:
+/// - `sess` is used to emit diagnostics and lints
+/// - `node_id` is used to emit lints
+/// - `span` is used when no spans are available
+/// - `lhses` and `rhses` should have the same length and represent the macro definition
+pub fn check_meta_variables(
+    sess: &ParseSess,
+    node_id: NodeId,
+    span: Span,
+    lhses: &[TokenTree],
+    rhses: &[TokenTree],
+) -> bool {
+    if lhses.len() != rhses.len() {
+        sess.span_diagnostic.span_bug(span, "length mismatch between LHSes and RHSes")
+    }
+    let mut valid = true;
+    for (lhs, rhs) in lhses.iter().zip(rhses.iter()) {
+        let mut binders = Binders::default();
+        check_binders(sess, node_id, lhs, &Stack::Empty, &mut binders, &Stack::Empty, &mut valid);
+        check_occurrences(sess, node_id, rhs, &Stack::Empty, &binders, &Stack::Empty, &mut valid);
+    }
+    valid
+}
+
+/// Checks `lhs` as part of the LHS of a macro definition, extends `binders` with new binders, and
+/// sets `valid` to false in case of errors.
+///
+/// Arguments:
+/// - `sess` is used to emit diagnostics and lints
+/// - `node_id` is used to emit lints
+/// - `lhs` is checked as part of a LHS
+/// - `macros` is the stack of possible outer macros
+/// - `binders` contains the binders of the LHS
+/// - `ops` is the stack of Kleene operators from the LHS
+/// - `valid` is set in case of errors
+fn check_binders(
+    sess: &ParseSess,
+    node_id: NodeId,
+    lhs: &TokenTree,
+    macros: &Stack<'_, MacroState<'_>>,
+    binders: &mut Binders,
+    ops: &Stack<'_, KleeneToken>,
+    valid: &mut bool,
+) {
+    match *lhs {
+        TokenTree::Token(..) => {}
+        // This can only happen when checking a nested macro because this LHS is then in the RHS of
+        // the outer macro. See ui/macros/macro-of-higher-order.rs where $y:$fragment in the
+        // LHS of the nested macro (and RHS of the outer macro) is parsed as MetaVar(y) Colon
+        // MetaVar(fragment) and not as MetaVarDecl(y, fragment).
+        TokenTree::MetaVar(span, name) => {
+            if macros.is_empty() {
+                sess.span_diagnostic.span_bug(span, "unexpected MetaVar in lhs");
+            }
+            // There are 3 possibilities:
+            if let Some(prev_info) = binders.get(&name) {
+                // 1. The meta-variable is already bound in the current LHS: This is an error.
+                let mut span = MultiSpan::from_span(span);
+                span.push_span_label(prev_info.span, "previous declaration".into());
+                buffer_lint(sess, span, node_id, "duplicate matcher binding");
+            } else if get_binder_info(macros, binders, name).is_none() {
+                // 2. The meta-variable is free: This is a binder.
+                binders.insert(name, BinderInfo { span, ops: ops.into() });
+            } else {
+                // 3. The meta-variable is bound: This is an occurrence.
+                check_occurrences(sess, node_id, lhs, macros, binders, ops, valid);
+            }
+        }
+        // Similarly, this can only happen when checking a toplevel macro.
+        TokenTree::MetaVarDecl(span, name, _kind) => {
+            if !macros.is_empty() {
+                sess.span_diagnostic.span_bug(span, "unexpected MetaVarDecl in nested lhs");
+            }
+            if let Some(prev_info) = get_binder_info(macros, binders, name) {
+                // Duplicate binders at the top-level macro definition are errors. The lint is only
+                // for nested macro definitions.
+                sess.span_diagnostic
+                    .struct_span_err(span, "duplicate matcher binding")
+                    .span_note(prev_info.span, "previous declaration was here")
+                    .emit();
+                *valid = false;
+            } else {
+                binders.insert(name, BinderInfo { span, ops: ops.into() });
+            }
+        }
+        TokenTree::Delimited(_, ref del) => {
+            for tt in &del.tts {
+                check_binders(sess, node_id, tt, macros, binders, ops, valid);
+            }
+        }
+        TokenTree::Sequence(_, ref seq) => {
+            let ops = ops.push(seq.kleene);
+            for tt in &seq.tts {
+                check_binders(sess, node_id, tt, macros, binders, &ops, valid);
+            }
+        }
+    }
+}
+
+/// Returns the binder information of a meta-variable.
+///
+/// Arguments:
+/// - `macros` is the stack of possible outer macros
+/// - `binders` contains the current binders
+/// - `name` is the name of the meta-variable we are looking for
+fn get_binder_info<'a>(
+    mut macros: &'a Stack<'a, MacroState<'a>>,
+    binders: &'a Binders,
+    name: Ident,
+) -> Option<&'a BinderInfo> {
+    binders.get(&name).or_else(|| macros.find_map(|state| state.binders.get(&name)))
+}
+
+/// Checks `rhs` as part of the RHS of a macro definition and sets `valid` to false in case of
+/// errors.
+///
+/// Arguments:
+/// - `sess` is used to emit diagnostics and lints
+/// - `node_id` is used to emit lints
+/// - `rhs` is checked as part of a RHS
+/// - `macros` is the stack of possible outer macros
+/// - `binders` contains the binders of the associated LHS
+/// - `ops` is the stack of Kleene operators from the RHS
+/// - `valid` is set in case of errors
+fn check_occurrences(
+    sess: &ParseSess,
+    node_id: NodeId,
+    rhs: &TokenTree,
+    macros: &Stack<'_, MacroState<'_>>,
+    binders: &Binders,
+    ops: &Stack<'_, KleeneToken>,
+    valid: &mut bool,
+) {
+    match *rhs {
+        TokenTree::Token(..) => {}
+        TokenTree::MetaVarDecl(span, _name, _kind) => {
+            sess.span_diagnostic.span_bug(span, "unexpected MetaVarDecl in rhs")
+        }
+        TokenTree::MetaVar(span, name) => {
+            check_ops_is_prefix(sess, node_id, macros, binders, ops, span, name);
+        }
+        TokenTree::Delimited(_, ref del) => {
+            check_nested_occurrences(sess, node_id, &del.tts, macros, binders, ops, valid);
+        }
+        TokenTree::Sequence(_, ref seq) => {
+            let ops = ops.push(seq.kleene);
+            check_nested_occurrences(sess, node_id, &seq.tts, macros, binders, &ops, valid);
+        }
+    }
+}
+
+/// Represents the processed prefix of a nested macro.
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum NestedMacroState {
+    /// Nothing that matches a nested macro definition was processed yet.
+    Empty,
+    /// The token `macro_rules` was processed.
+    MacroRules,
+    /// The tokens `macro_rules!` were processed.
+    MacroRulesNot,
+    /// The tokens `macro_rules!` followed by a name were processed. The name may be either directly
+    /// an identifier or a meta-variable (that hopefully would be instantiated by an identifier).
+    MacroRulesNotName,
+    /// The keyword `macro` was processed.
+    Macro,
+    /// The keyword `macro` followed by a name was processed.
+    MacroName,
+    /// The keyword `macro` followed by a name and a token delimited by parentheses was processed.
+    MacroNameParen,
+}
+
+/// Checks `tts` as part of the RHS of a macro definition, tries to recognize nested macro
+/// definitions, and sets `valid` to false in case of errors.
+///
+/// Arguments:
+/// - `sess` is used to emit diagnostics and lints
+/// - `node_id` is used to emit lints
+/// - `tts` is checked as part of a RHS and may contain macro definitions
+/// - `macros` is the stack of possible outer macros
+/// - `binders` contains the binders of the associated LHS
+/// - `ops` is the stack of Kleene operators from the RHS
+/// - `valid` is set in case of errors
+fn check_nested_occurrences(
+    sess: &ParseSess,
+    node_id: NodeId,
+    tts: &[TokenTree],
+    macros: &Stack<'_, MacroState<'_>>,
+    binders: &Binders,
+    ops: &Stack<'_, KleeneToken>,
+    valid: &mut bool,
+) {
+    let mut state = NestedMacroState::Empty;
+    let nested_macros = macros.push(MacroState { binders, ops: ops.into() });
+    let mut nested_binders = Binders::default();
+    for tt in tts {
+        match (state, tt) {
+            (
+                NestedMacroState::Empty,
+                &TokenTree::Token(Token { kind: TokenKind::Ident(name, false), .. }),
+            ) => {
+                if name == sym::macro_rules {
+                    state = NestedMacroState::MacroRules;
+                } else if name == kw::Macro {
+                    state = NestedMacroState::Macro;
+                }
+            }
+            (
+                NestedMacroState::MacroRules,
+                &TokenTree::Token(Token { kind: TokenKind::Not, .. }),
+            ) => {
+                state = NestedMacroState::MacroRulesNot;
+            }
+            (
+                NestedMacroState::MacroRulesNot,
+                &TokenTree::Token(Token { kind: TokenKind::Ident(..), .. }),
+            ) => {
+                state = NestedMacroState::MacroRulesNotName;
+            }
+            (NestedMacroState::MacroRulesNot, &TokenTree::MetaVar(..)) => {
+                state = NestedMacroState::MacroRulesNotName;
+                // We check that the meta-variable is correctly used.
+                check_occurrences(sess, node_id, tt, macros, binders, ops, valid);
+            }
+            (NestedMacroState::MacroRulesNotName, &TokenTree::Delimited(_, ref del))
+            | (NestedMacroState::MacroName, &TokenTree::Delimited(_, ref del))
+                if del.delim == DelimToken::Brace =>
+            {
+                let legacy = state == NestedMacroState::MacroRulesNotName;
+                state = NestedMacroState::Empty;
+                let rest =
+                    check_nested_macro(sess, node_id, legacy, &del.tts, &nested_macros, valid);
+                // If we did not check the whole macro definition, then check the rest as if outside
+                // the macro definition.
+                check_nested_occurrences(
+                    sess,
+                    node_id,
+                    &del.tts[rest..],
+                    macros,
+                    binders,
+                    ops,
+                    valid,
+                );
+            }
+            (
+                NestedMacroState::Macro,
+                &TokenTree::Token(Token { kind: TokenKind::Ident(..), .. }),
+            ) => {
+                state = NestedMacroState::MacroName;
+            }
+            (NestedMacroState::Macro, &TokenTree::MetaVar(..)) => {
+                state = NestedMacroState::MacroName;
+                // We check that the meta-variable is correctly used.
+                check_occurrences(sess, node_id, tt, macros, binders, ops, valid);
+            }
+            (NestedMacroState::MacroName, &TokenTree::Delimited(_, ref del))
+                if del.delim == DelimToken::Paren =>
+            {
+                state = NestedMacroState::MacroNameParen;
+                nested_binders = Binders::default();
+                check_binders(
+                    sess,
+                    node_id,
+                    tt,
+                    &nested_macros,
+                    &mut nested_binders,
+                    &Stack::Empty,
+                    valid,
+                );
+            }
+            (NestedMacroState::MacroNameParen, &TokenTree::Delimited(_, ref del))
+                if del.delim == DelimToken::Brace =>
+            {
+                state = NestedMacroState::Empty;
+                check_occurrences(
+                    sess,
+                    node_id,
+                    tt,
+                    &nested_macros,
+                    &nested_binders,
+                    &Stack::Empty,
+                    valid,
+                );
+            }
+            (_, ref tt) => {
+                state = NestedMacroState::Empty;
+                check_occurrences(sess, node_id, tt, macros, binders, ops, valid);
+            }
+        }
+    }
+}
+
+/// Checks the body of nested macro, returns where the check stopped, and sets `valid` to false in
+/// case of errors.
+///
+/// The token trees are checked as long as they look like a list of (LHS) => {RHS} token trees. This
+/// check is a best-effort to detect a macro definition. It returns the position in `tts` where we
+/// stopped checking because we detected we were not in a macro definition anymore.
+///
+/// Arguments:
+/// - `sess` is used to emit diagnostics and lints
+/// - `node_id` is used to emit lints
+/// - `legacy` specifies whether the macro is legacy
+/// - `tts` is checked as a list of (LHS) => {RHS}
+/// - `macros` is the stack of outer macros
+/// - `valid` is set in case of errors
+fn check_nested_macro(
+    sess: &ParseSess,
+    node_id: NodeId,
+    legacy: bool,
+    tts: &[TokenTree],
+    macros: &Stack<'_, MacroState<'_>>,
+    valid: &mut bool,
+) -> usize {
+    let n = tts.len();
+    let mut i = 0;
+    let separator = if legacy { TokenKind::Semi } else { TokenKind::Comma };
+    loop {
+        // We expect 3 token trees: `(LHS) => {RHS}`. The separator is checked after.
+        if i + 2 >= n
+            || !tts[i].is_delimited()
+            || !tts[i + 1].is_token(&TokenKind::FatArrow)
+            || !tts[i + 2].is_delimited()
+        {
+            break;
+        }
+        let lhs = &tts[i];
+        let rhs = &tts[i + 2];
+        let mut binders = Binders::default();
+        check_binders(sess, node_id, lhs, macros, &mut binders, &Stack::Empty, valid);
+        check_occurrences(sess, node_id, rhs, macros, &binders, &Stack::Empty, valid);
+        // Since the last semicolon is optional for legacy macros and decl_macro are not terminated,
+        // we increment our checked position by how many token trees we already checked (the 3
+        // above) before checking for the separator.
+        i += 3;
+        if i == n || !tts[i].is_token(&separator) {
+            break;
+        }
+        // We increment our checked position for the semicolon.
+        i += 1;
+    }
+    i
+}
+
+/// Checks that a meta-variable occurrence is valid.
+///
+/// Arguments:
+/// - `sess` is used to emit diagnostics and lints
+/// - `node_id` is used to emit lints
+/// - `macros` is the stack of possible outer macros
+/// - `binders` contains the binders of the associated LHS
+/// - `ops` is the stack of Kleene operators from the RHS
+/// - `span` is the span of the meta-variable to check
+/// - `name` is the name of the meta-variable to check
+fn check_ops_is_prefix(
+    sess: &ParseSess,
+    node_id: NodeId,
+    macros: &Stack<'_, MacroState<'_>>,
+    binders: &Binders,
+    ops: &Stack<'_, KleeneToken>,
+    span: Span,
+    name: Ident,
+) {
+    let macros = macros.push(MacroState { binders, ops: ops.into() });
+    // Accumulates the stacks the operators of each state until (and including when) the
+    // meta-variable is found. The innermost stack is first.
+    let mut acc: SmallVec<[&SmallVec<[KleeneToken; 1]>; 1]> = SmallVec::new();
+    for state in &macros {
+        acc.push(&state.ops);
+        if let Some(binder) = state.binders.get(&name) {
+            // This variable concatenates the stack of operators from the RHS of the LHS where the
+            // meta-variable was defined to where it is used (in possibly nested macros). The
+            // outermost operator is first.
+            let mut occurrence_ops: SmallVec<[KleeneToken; 2]> = SmallVec::new();
+            // We need to iterate from the end to start with outermost stack.
+            for ops in acc.iter().rev() {
+                occurrence_ops.extend_from_slice(ops);
+            }
+            ops_is_prefix(sess, node_id, span, name, &binder.ops, &occurrence_ops);
+            return;
+        }
+    }
+    buffer_lint(sess, span.into(), node_id, &format!("unknown macro variable `{}`", name));
+}
+
+/// Returns whether `binder_ops` is a prefix of `occurrence_ops`.
+///
+/// The stack of Kleene operators of a meta-variable occurrence just needs to have the stack of
+/// Kleene operators of its binder as a prefix.
+///
+/// Consider $i in the following example:
+///
+///     ( $( $i:ident = $($j:ident),+ );* ) => { $($( $i += $j; )+)* }
+///
+/// It occurs under the Kleene stack ["*", "+"] and is bound under ["*"] only.
+///
+/// Arguments:
+/// - `sess` is used to emit diagnostics and lints
+/// - `node_id` is used to emit lints
+/// - `span` is the span of the meta-variable being check
+/// - `name` is the name of the meta-variable being check
+/// - `binder_ops` is the stack of Kleene operators for the binder
+/// - `occurrence_ops` is the stack of Kleene operators for the occurrence
+fn ops_is_prefix(
+    sess: &ParseSess,
+    node_id: NodeId,
+    span: Span,
+    name: Ident,
+    binder_ops: &[KleeneToken],
+    occurrence_ops: &[KleeneToken],
+) {
+    for (i, binder) in binder_ops.iter().enumerate() {
+        if i >= occurrence_ops.len() {
+            let mut span = MultiSpan::from_span(span);
+            span.push_span_label(binder.span, "expected repetition".into());
+            let message = &format!("variable '{}' is still repeating at this depth", name);
+            buffer_lint(sess, span, node_id, message);
+            return;
+        }
+        let occurrence = &occurrence_ops[i];
+        if occurrence.op != binder.op {
+            let mut span = MultiSpan::from_span(span);
+            span.push_span_label(binder.span, "expected repetition".into());
+            span.push_span_label(occurrence.span, "conflicting repetition".into());
+            let message = "meta-variable repeats with different Kleene operator";
+            buffer_lint(sess, span, node_id, message);
+            return;
+        }
+    }
+}
+
+fn buffer_lint(sess: &ParseSess, span: MultiSpan, node_id: NodeId, message: &str) {
+    sess.buffer_lint(BufferedEarlyLintId::MetaVariableMisuse, span, node_id, message);
+}
diff --git a/src/libsyntax/ext/tt/macro_parser.rs b/src/libsyntax/ext/tt/macro_parser.rs
index 084a69f4cda..dbf14daa30e 100644
--- a/src/libsyntax/ext/tt/macro_parser.rs
+++ b/src/libsyntax/ext/tt/macro_parser.rs
@@ -74,13 +74,13 @@ pub use NamedMatch::*;
 pub use ParseResult::*;
 use TokenTreeOrTokenTreeSlice::*;
 
-use crate::ast::Ident;
+use crate::ast::{Ident, Name};
 use crate::ext::tt::quoted::{self, TokenTree};
 use crate::parse::{Directory, ParseSess};
 use crate::parse::parser::{Parser, PathStyle};
 use crate::parse::token::{self, DocComment, Nonterminal, Token};
 use crate::print::pprust;
-use crate::symbol::keywords;
+use crate::symbol::{kw, sym, Symbol};
 use crate::tokenstream::{DelimSpan, TokenStream};
 
 use errors::FatalError;
@@ -92,7 +92,6 @@ use rustc_data_structures::sync::Lrc;
 use std::collections::hash_map::Entry::{Occupied, Vacant};
 use std::mem;
 use std::ops::{Deref, DerefMut};
-use std::rc::Rc;
 
 // To avoid costly uniqueness checks, we require that `MatchSeq` always has a nonempty body.
 
@@ -156,7 +155,7 @@ type NamedMatchVec = SmallVec<[NamedMatch; 4]>;
 /// all the elements in that `SmallVec` strictly outlive the root stack slot
 /// lifetime. By separating `'tt` from `'root`, we can show that.
 #[derive(Clone)]
-struct MatcherPos<'root, 'tt: 'root> {
+struct MatcherPos<'root, 'tt> {
     /// The token or sequence of tokens that make up the matcher
     top_elts: TokenTreeOrTokenTreeSlice<'tt>,
 
@@ -233,7 +232,7 @@ impl<'root, 'tt> MatcherPos<'root, 'tt> {
 // Therefore, the initial MatcherPos is always allocated on the stack,
 // subsequent ones (of which there aren't that many) are allocated on the heap,
 // and this type is used to encapsulate both cases.
-enum MatcherPosHandle<'root, 'tt: 'root> {
+enum MatcherPosHandle<'root, 'tt> {
     Ref(&'root mut MatcherPos<'root, 'tt>),
     Box(Box<MatcherPos<'root, 'tt>>),
 }
@@ -273,14 +272,14 @@ pub enum ParseResult<T> {
     Success(T),
     /// Arm failed to match. If the second parameter is `token::Eof`, it indicates an unexpected
     /// end of macro invocation. Otherwise, it indicates that no rules expected the given token.
-    Failure(syntax_pos::Span, Token, &'static str),
+    Failure(Token, &'static str),
     /// Fatal error (malformed macro?). Abort compilation.
     Error(syntax_pos::Span, String),
 }
 
 /// A `ParseResult` where the `Success` variant contains a mapping of `Ident`s to `NamedMatch`es.
 /// This represents the mapping of metavars to the token trees they bind to.
-pub type NamedParseResult = ParseResult<FxHashMap<Ident, Rc<NamedMatch>>>;
+pub type NamedParseResult = ParseResult<FxHashMap<Ident, NamedMatch>>;
 
 /// Count how many metavars are named in the given matcher `ms`.
 pub fn count_names(ms: &[TokenTree]) -> usize {
@@ -373,7 +372,7 @@ fn nameize<I: Iterator<Item = NamedMatch>>(
         sess: &ParseSess,
         m: &TokenTree,
         res: &mut I,
-        ret_val: &mut FxHashMap<Ident, Rc<NamedMatch>>,
+        ret_val: &mut FxHashMap<Ident, NamedMatch>,
     ) -> Result<(), (syntax_pos::Span, String)> {
         match *m {
             TokenTree::Sequence(_, ref seq) => for next_m in &seq.tts {
@@ -382,7 +381,7 @@ fn nameize<I: Iterator<Item = NamedMatch>>(
             TokenTree::Delimited(_, ref delim) => for next_m in &delim.tts {
                 n_rec(sess, next_m, res.by_ref(), ret_val)?;
             },
-            TokenTree::MetaVarDecl(span, _, id) if id.name == keywords::Invalid.name() => {
+            TokenTree::MetaVarDecl(span, _, id) if id.name == kw::Invalid => {
                 if sess.missing_fragment_specifiers.borrow_mut().remove(&span) {
                     return Err((span, "missing fragment specifier".to_string()));
                 }
@@ -390,8 +389,7 @@ fn nameize<I: Iterator<Item = NamedMatch>>(
             TokenTree::MetaVarDecl(sp, bind_name, _) => {
                 match ret_val.entry(bind_name) {
                     Vacant(spot) => {
-                        // FIXME(simulacrum): Don't construct Rc here
-                        spot.insert(Rc::new(res.next().unwrap()));
+                        spot.insert(res.next().unwrap());
                     }
                     Occupied(..) => {
                         return Err((sp, format!("duplicated bind name: {}", bind_name)))
@@ -417,24 +415,24 @@ fn nameize<I: Iterator<Item = NamedMatch>>(
 
 /// Generates an appropriate parsing failure message. For EOF, this is "unexpected end...". For
 /// other tokens, this is "unexpected token...".
-pub fn parse_failure_msg(tok: Token) -> String {
-    match tok {
+pub fn parse_failure_msg(tok: &Token) -> String {
+    match tok.kind {
         token::Eof => "unexpected end of macro invocation".to_string(),
         _ => format!(
             "no rules expected the token `{}`",
-            pprust::token_to_string(&tok)
+            pprust::token_to_string(tok)
         ),
     }
 }
 
 /// Performs a token equality check, ignoring syntax context (that is, an unhygienic comparison)
 fn token_name_eq(t1: &Token, t2: &Token) -> bool {
-    if let (Some((id1, is_raw1)), Some((id2, is_raw2))) = (t1.ident(), t2.ident()) {
-        id1.name == id2.name && is_raw1 == is_raw2
-    } else if let (Some(id1), Some(id2)) = (t1.lifetime(), t2.lifetime()) {
-        id1.name == id2.name
+    if let (Some((ident1, is_raw1)), Some((ident2, is_raw2))) = (t1.ident(), t2.ident()) {
+        ident1.name == ident2.name && is_raw1 == is_raw2
+    } else if let (Some(ident1), Some(ident2)) = (t1.lifetime(), t2.lifetime()) {
+        ident1.name == ident2.name
     } else {
-        *t1 == *t2
+        t1.kind == t2.kind
     }
 }
 
@@ -467,7 +465,6 @@ fn inner_parse_loop<'root, 'tt>(
     eof_items: &mut SmallVec<[MatcherPosHandle<'root, 'tt>; 1]>,
     bb_items: &mut SmallVec<[MatcherPosHandle<'root, 'tt>; 1]>,
     token: &Token,
-    span: syntax_pos::Span,
 ) -> ParseResult<()> {
     // Pop items from `cur_items` until it is empty.
     while let Some(mut item) = cur_items.pop() {
@@ -510,7 +507,7 @@ fn inner_parse_loop<'root, 'tt>(
                     // Add matches from this repetition to the `matches` of `up`
                     for idx in item.match_lo..item.match_hi {
                         let sub = item.matches[idx].clone();
-                        let span = DelimSpan::from_pair(item.sp_open, span);
+                        let span = DelimSpan::from_pair(item.sp_open, token.span);
                         new_pos.push_match(idx, MatchedSeq(sub, span));
                     }
 
@@ -558,8 +555,8 @@ fn inner_parse_loop<'root, 'tt>(
                     // implicitly disallowing OneOrMore from having 0 matches here. Thus, that will
                     // result in a "no rules expected token" error by virtue of this matcher not
                     // working.
-                    if seq.op == quoted::KleeneOp::ZeroOrMore
-                        || seq.op == quoted::KleeneOp::ZeroOrOne
+                    if seq.kleene.op == quoted::KleeneOp::ZeroOrMore
+                        || seq.kleene.op == quoted::KleeneOp::ZeroOrOne
                     {
                         let mut new_item = item.clone();
                         new_item.match_cur += seq.num_captures;
@@ -574,7 +571,7 @@ fn inner_parse_loop<'root, 'tt>(
                     cur_items.push(MatcherPosHandle::Box(Box::new(MatcherPos {
                         stack: smallvec![],
                         sep: seq.separator.clone(),
-                        seq_op: Some(seq.op),
+                        seq_op: Some(seq.kleene.op),
                         idx: 0,
                         matches,
                         match_lo: item.match_cur,
@@ -587,7 +584,7 @@ fn inner_parse_loop<'root, 'tt>(
                 }
 
                 // We need to match a metavar (but the identifier is invalid)... this is an error
-                TokenTree::MetaVarDecl(span, _, id) if id.name == keywords::Invalid.name() => {
+                TokenTree::MetaVarDecl(span, _, id) if id.name == kw::Invalid => {
                     if sess.missing_fragment_specifiers.borrow_mut().remove(&span) {
                         return Error(span, "missing fragment specifier".to_string());
                     }
@@ -598,7 +595,7 @@ fn inner_parse_loop<'root, 'tt>(
                 TokenTree::MetaVarDecl(_, _, id) => {
                     // Built-in nonterminals never start with these tokens,
                     // so we can eliminate them from consideration.
-                    if may_begin_with(&*id.as_str(), token) {
+                    if may_begin_with(token, id.name) {
                         bb_items.push(item);
                     }
                 }
@@ -609,7 +606,8 @@ fn inner_parse_loop<'root, 'tt>(
                 //
                 // At the beginning of the loop, if we reach the end of the delimited submatcher,
                 // we pop the stack to backtrack out of the descent.
-                seq @ TokenTree::Delimited(..) | seq @ TokenTree::Token(_, DocComment(..)) => {
+                seq @ TokenTree::Delimited(..) |
+                seq @ TokenTree::Token(Token { kind: DocComment(..), .. }) => {
                     let lower_elts = mem::replace(&mut item.top_elts, Tt(seq));
                     let idx = item.idx;
                     item.stack.push(MatcherTtFrame {
@@ -621,7 +619,7 @@ fn inner_parse_loop<'root, 'tt>(
                 }
 
                 // We just matched a normal token. We can just advance the parser.
-                TokenTree::Token(_, ref t) if token_name_eq(t, token) => {
+                TokenTree::Token(t) if token_name_eq(&t, token) => {
                     item.idx += 1;
                     next_items.push(item);
                 }
@@ -658,7 +656,14 @@ pub fn parse(
     recurse_into_modules: bool,
 ) -> NamedParseResult {
     // Create a parser that can be used for the "black box" parts.
-    let mut parser = Parser::new(sess, tts, directory, recurse_into_modules, true);
+    let mut parser = Parser::new(
+        sess,
+        tts,
+        directory,
+        recurse_into_modules,
+        true,
+        crate::MACRO_ARGUMENTS,
+    );
 
     // A queue of possible matcher positions. We initialize it with the matcher position in which
     // the "dot" is before the first token of the first token tree in `ms`. `inner_parse_loop` then
@@ -668,7 +673,7 @@ pub fn parse(
     //
     // This MatcherPos instance is allocated on the stack. All others -- and
     // there are frequently *no* others! -- are allocated on the heap.
-    let mut initial = initial_matcher_pos(ms, parser.span);
+    let mut initial = initial_matcher_pos(ms, parser.token.span);
     let mut cur_items = smallvec![MatcherPosHandle::Ref(&mut initial)];
     let mut next_items = Vec::new();
 
@@ -690,10 +695,9 @@ pub fn parse(
             &mut eof_items,
             &mut bb_items,
             &parser.token,
-            parser.span,
         ) {
             Success(_) => {}
-            Failure(sp, tok, t) => return Failure(sp, tok, t),
+            Failure(token, msg) => return Failure(token, msg),
             Error(sp, msg) => return Error(sp, msg),
         }
 
@@ -706,7 +710,7 @@ pub fn parse(
 
         // If we reached the EOF, check that there is EXACTLY ONE possible matcher. Otherwise,
         // either the parse is ambiguous (which should never happen) or there is a syntax error.
-        if token_name_eq(&parser.token, &token::Eof) {
+        if parser.token == token::Eof {
             if eof_items.len() == 1 {
                 let matches = eof_items[0]
                     .matches
@@ -715,17 +719,16 @@ pub fn parse(
                 return nameize(sess, ms, matches);
             } else if eof_items.len() > 1 {
                 return Error(
-                    parser.span,
+                    parser.token.span,
                     "ambiguity: multiple successful parses".to_string(),
                 );
             } else {
                 return Failure(
-                    if parser.span.is_dummy() {
-                        parser.span
+                    Token::new(token::Eof, if parser.token.span.is_dummy() {
+                        parser.token.span
                     } else {
-                        sess.source_map().next_point(parser.span)
-                    },
-                    token::Eof,
+                        sess.source_map().next_point(parser.token.span)
+                    }),
                     "missing tokens in macro arguments",
                 );
             }
@@ -748,7 +751,7 @@ pub fn parse(
                 .join(" or ");
 
             return Error(
-                parser.span,
+                parser.token.span,
                 format!(
                     "local ambiguity: multiple parsing options: {}",
                     match next_items.len() {
@@ -763,8 +766,7 @@ pub fn parse(
         // then there is a syntax error.
         else if bb_items.is_empty() && next_items.is_empty() {
             return Failure(
-                parser.span,
-                parser.token.clone(),
+                parser.token.take(),
                 "no rules expected this token in macro call",
             );
         }
@@ -784,7 +786,7 @@ pub fn parse(
                 let match_cur = item.match_cur;
                 item.push_match(
                     match_cur,
-                    MatchedNonterminal(Lrc::new(parse_nt(&mut parser, span, &ident.as_str()))),
+                    MatchedNonterminal(Lrc::new(parse_nt(&mut parser, span, ident.name))),
                 );
                 item.idx += 1;
                 item.match_cur += 1;
@@ -800,10 +802,9 @@ pub fn parse(
 
 /// The token is an identifier, but not `_`.
 /// We prohibit passing `_` to macros expecting `ident` for now.
-fn get_macro_ident(token: &Token) -> Option<(Ident, bool)> {
-    match *token {
-        token::Ident(ident, is_raw) if ident.name != keywords::Underscore.name() =>
-            Some((ident, is_raw)),
+fn get_macro_name(token: &Token) -> Option<(Name, bool)> {
+    match token.kind {
+        token::Ident(name, is_raw) if name != kw::Underscore => Some((name, is_raw)),
         _ => None,
     }
 }
@@ -812,7 +813,7 @@ fn get_macro_ident(token: &Token) -> Option<(Ident, bool)> {
 ///
 /// Returning `false` is a *stability guarantee* that such a matcher will *never* begin with that
 /// token. Be conservative (return true) if not sure.
-fn may_begin_with(name: &str, token: &Token) -> bool {
+fn may_begin_with(token: &Token, name: Name) -> bool {
     /// Checks whether the non-terminal may contain a single (non-keyword) identifier.
     fn may_be_ident(nt: &token::Nonterminal) -> bool {
         match *nt {
@@ -822,18 +823,20 @@ fn may_begin_with(name: &str, token: &Token) -> bool {
     }
 
     match name {
-        "expr" => token.can_begin_expr(),
-        "ty" => token.can_begin_type(),
-        "ident" => get_macro_ident(token).is_some(),
-        "literal" => token.can_begin_literal_or_bool(),
-        "vis" => match *token {
+        sym::expr => token.can_begin_expr()
+            // This exception is here for backwards compatibility.
+            && !token.is_keyword(kw::Let),
+        sym::ty => token.can_begin_type(),
+        sym::ident => get_macro_name(token).is_some(),
+        sym::literal => token.can_begin_literal_or_bool(),
+        sym::vis => match token.kind {
             // The follow-set of :vis + "priv" keyword + interpolated
-            Token::Comma | Token::Ident(..) | Token::Interpolated(_) => true,
+            token::Comma | token::Ident(..) | token::Interpolated(_) => true,
             _ => token.can_begin_type(),
         },
-        "block" => match *token {
-            Token::OpenDelim(token::Brace) => true,
-            Token::Interpolated(ref nt) => match **nt {
+        sym::block => match token.kind {
+            token::OpenDelim(token::Brace) => true,
+            token::Interpolated(ref nt) => match **nt {
                 token::NtItem(_)
                 | token::NtPat(_)
                 | token::NtTy(_)
@@ -845,39 +848,39 @@ fn may_begin_with(name: &str, token: &Token) -> bool {
             },
             _ => false,
         },
-        "path" | "meta" => match *token {
-            Token::ModSep | Token::Ident(..) => true,
-            Token::Interpolated(ref nt) => match **nt {
+        sym::path | sym::meta => match token.kind {
+            token::ModSep | token::Ident(..) => true,
+            token::Interpolated(ref nt) => match **nt {
                 token::NtPath(_) | token::NtMeta(_) => true,
                 _ => may_be_ident(&nt),
             },
             _ => false,
         },
-        "pat" => match *token {
-            Token::Ident(..) |               // box, ref, mut, and other identifiers (can stricten)
-            Token::OpenDelim(token::Paren) |    // tuple pattern
-            Token::OpenDelim(token::Bracket) |  // slice pattern
-            Token::BinOp(token::And) |          // reference
-            Token::BinOp(token::Minus) |        // negative literal
-            Token::AndAnd |                     // double reference
-            Token::Literal(..) |                // literal
-            Token::DotDot |                     // range pattern (future compat)
-            Token::DotDotDot |                  // range pattern (future compat)
-            Token::ModSep |                     // path
-            Token::Lt |                         // path (UFCS constant)
-            Token::BinOp(token::Shl) => true,   // path (double UFCS)
-            Token::Interpolated(ref nt) => may_be_ident(nt),
+        sym::pat => match token.kind {
+            token::Ident(..) |               // box, ref, mut, and other identifiers (can stricten)
+            token::OpenDelim(token::Paren) |    // tuple pattern
+            token::OpenDelim(token::Bracket) |  // slice pattern
+            token::BinOp(token::And) |          // reference
+            token::BinOp(token::Minus) |        // negative literal
+            token::AndAnd |                     // double reference
+            token::Literal(..) |                // literal
+            token::DotDot |                     // range pattern (future compat)
+            token::DotDotDot |                  // range pattern (future compat)
+            token::ModSep |                     // path
+            token::Lt |                         // path (UFCS constant)
+            token::BinOp(token::Shl) => true,   // path (double UFCS)
+            token::Interpolated(ref nt) => may_be_ident(nt),
             _ => false,
         },
-        "lifetime" => match *token {
-            Token::Lifetime(_) => true,
-            Token::Interpolated(ref nt) => match **nt {
+        sym::lifetime => match token.kind {
+            token::Lifetime(_) => true,
+            token::Interpolated(ref nt) => match **nt {
                 token::NtLifetime(_) | token::NtTT(_) => true,
                 _ => false,
             },
             _ => false,
         },
-        _ => match *token {
+        _ => match token.kind {
             token::CloseDelim(_) => false,
             _ => true,
         },
@@ -896,46 +899,46 @@ fn may_begin_with(name: &str, token: &Token) -> bool {
 /// # Returns
 ///
 /// The parsed non-terminal.
-fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: &str) -> Nonterminal {
-    if name == "tt" {
+fn parse_nt(p: &mut Parser<'_>, sp: Span, name: Symbol) -> Nonterminal {
+    if name == sym::tt {
         return token::NtTT(p.parse_token_tree());
     }
     // check at the beginning and the parser checks after each bump
     p.process_potential_macro_variable();
     match name {
-        "item" => match panictry!(p.parse_item()) {
+        sym::item => match panictry!(p.parse_item()) {
             Some(i) => token::NtItem(i),
             None => {
                 p.fatal("expected an item keyword").emit();
                 FatalError.raise();
             }
         },
-        "block" => token::NtBlock(panictry!(p.parse_block())),
-        "stmt" => match panictry!(p.parse_stmt()) {
+        sym::block => token::NtBlock(panictry!(p.parse_block())),
+        sym::stmt => match panictry!(p.parse_stmt()) {
             Some(s) => token::NtStmt(s),
             None => {
                 p.fatal("expected a statement").emit();
                 FatalError.raise();
             }
         },
-        "pat" => token::NtPat(panictry!(p.parse_pat(None))),
-        "expr" => token::NtExpr(panictry!(p.parse_expr())),
-        "literal" => token::NtLiteral(panictry!(p.parse_literal_maybe_minus())),
-        "ty" => token::NtTy(panictry!(p.parse_ty())),
+        sym::pat => token::NtPat(panictry!(p.parse_pat(None))),
+        sym::expr => token::NtExpr(panictry!(p.parse_expr())),
+        sym::literal => token::NtLiteral(panictry!(p.parse_literal_maybe_minus())),
+        sym::ty => token::NtTy(panictry!(p.parse_ty())),
         // this could be handled like a token, since it is one
-        "ident" => if let Some((ident, is_raw)) = get_macro_ident(&p.token) {
-            let span = p.span;
+        sym::ident => if let Some((name, is_raw)) = get_macro_name(&p.token) {
+            let span = p.token.span;
             p.bump();
-            token::NtIdent(Ident::new(ident.name, span), is_raw)
+            token::NtIdent(Ident::new(name, span), is_raw)
         } else {
             let token_str = pprust::token_to_string(&p.token);
             p.fatal(&format!("expected ident, found {}", &token_str)).emit();
             FatalError.raise()
         }
-        "path" => token::NtPath(panictry!(p.parse_path(PathStyle::Type))),
-        "meta" => token::NtMeta(panictry!(p.parse_meta_item())),
-        "vis" => token::NtVis(panictry!(p.parse_visibility(true))),
-        "lifetime" => if p.check_lifetime() {
+        sym::path => token::NtPath(panictry!(p.parse_path(PathStyle::Type))),
+        sym::meta => token::NtMeta(panictry!(p.parse_meta_item())),
+        sym::vis => token::NtVis(panictry!(p.parse_visibility(true))),
+        sym::lifetime => if p.check_lifetime() {
             token::NtLifetime(p.expect_lifetime().ident)
         } else {
             let token_str = pprust::token_to_string(&p.token);
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 06651750de7..b057a9ad44d 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -1,35 +1,37 @@
-use crate::{ast, attr};
 use crate::edition::Edition;
-use crate::ext::base::{DummyResult, ExtCtxt, MacResult, SyntaxExtension};
-use crate::ext::base::{NormalTT, TTMacroExpander};
+use crate::ext::base::{DummyResult, ExtCtxt, MacResult, TTMacroExpander};
+use crate::ext::base::{SyntaxExtension, SyntaxExtensionKind};
 use crate::ext::expand::{AstFragment, AstFragmentKind};
-use crate::ext::tt::macro_parser::{Success, Error, Failure};
-use crate::ext::tt::macro_parser::{MatchedSeq, MatchedNonterminal};
+use crate::ext::tt::macro_check;
 use crate::ext::tt::macro_parser::{parse, parse_failure_msg};
+use crate::ext::tt::macro_parser::{Error, Failure, Success};
+use crate::ext::tt::macro_parser::{MatchedNonterminal, MatchedSeq};
 use crate::ext::tt::quoted;
 use crate::ext::tt::transcribe::transcribe;
 use crate::feature_gate::Features;
-use crate::parse::{Directory, ParseSess};
 use crate::parse::parser::Parser;
-use crate::parse::token::{self, NtTT};
-use crate::parse::token::Token::*;
-use crate::symbol::{Symbol, keywords, sym};
+use crate::parse::token::TokenKind::*;
+use crate::parse::token::{self, NtTT, Token};
+use crate::parse::{Directory, ParseSess};
+use crate::symbol::{kw, sym, Symbol};
 use crate::tokenstream::{DelimSpan, TokenStream, TokenTree};
+use crate::{ast, attr, attr::TransparencyError};
 
-use errors::FatalError;
-use syntax_pos::{Span, DUMMY_SP, symbol::Ident};
+use errors::{DiagnosticBuilder, FatalError};
 use log::debug;
+use syntax_pos::Span;
 
-use rustc_data_structures::fx::{FxHashMap};
+use rustc_data_structures::fx::FxHashMap;
 use std::borrow::Cow;
 use std::collections::hash_map::Entry;
+use std::slice;
 
-use rustc_data_structures::sync::Lrc;
 use errors::Applicability;
+use rustc_data_structures::sync::Lrc;
 
 const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \
-    `ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, `literal`, \
-    `path`, `meta`, `tt`, `item` and `vis`";
+                                        `ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, \
+                                        `literal`, `path`, `meta`, `tt`, `item` and `vis`";
 
 pub struct ParserAnyMacro<'a> {
     parser: Parser<'a>,
@@ -41,13 +43,26 @@ pub struct ParserAnyMacro<'a> {
     arm_span: Span,
 }
 
+pub fn annotate_err_with_kind(err: &mut DiagnosticBuilder<'_>, kind: AstFragmentKind, span: Span) {
+    match kind {
+        AstFragmentKind::Ty => {
+            err.span_label(span, "this macro call doesn't expand to a type");
+        }
+        AstFragmentKind::Pat => {
+            err.span_label(span, "this macro call doesn't expand to a pattern");
+        }
+        _ => {}
+    };
+}
+
 impl<'a> ParserAnyMacro<'a> {
     pub fn make(mut self: Box<ParserAnyMacro<'a>>, kind: AstFragmentKind) -> AstFragment {
         let ParserAnyMacro { site_span, macro_ident, ref mut parser, arm_span } = *self;
         let fragment = panictry!(parser.parse_ast_fragment(kind, true).map_err(|mut e| {
             if parser.token == token::Eof && e.message().ends_with(", found `<eof>`") {
-                if !e.span.is_dummy() {  // early end of macro arm (#52866)
-                    e.replace_span_with(parser.sess.source_map().next_point(parser.span));
+                if !e.span.is_dummy() {
+                    // early end of macro arm (#52866)
+                    e.replace_span_with(parser.sess.source_map().next_point(parser.token.span));
                 }
                 let msg = &e.message[0];
                 e.message[0] = (
@@ -58,14 +73,41 @@ impl<'a> ParserAnyMacro<'a> {
                     msg.1,
                 );
             }
-            if e.span.is_dummy() {  // Get around lack of span in error (#30128)
+            if e.span.is_dummy() {
+                // Get around lack of span in error (#30128)
                 e.replace_span_with(site_span);
                 if parser.sess.source_map().span_to_filename(arm_span).is_real() {
                     e.span_label(arm_span, "in this macro arm");
                 }
-            } else if !parser.sess.source_map().span_to_filename(parser.span).is_real() {
+            } else if !parser.sess.source_map().span_to_filename(parser.token.span).is_real() {
                 e.span_label(site_span, "in this macro invocation");
             }
+            match kind {
+                AstFragmentKind::Pat if macro_ident.name == sym::vec => {
+                    let mut suggestion = None;
+                    if let Ok(code) = parser.sess.source_map().span_to_snippet(site_span) {
+                        if let Some(bang) = code.find('!') {
+                            suggestion = Some(code[bang + 1..].to_string());
+                        }
+                    }
+                    if let Some(suggestion) = suggestion {
+                        e.span_suggestion(
+                            site_span,
+                            "use a slice pattern here instead",
+                            suggestion,
+                            Applicability::MachineApplicable,
+                        );
+                    } else {
+                        e.span_label(
+                            site_span,
+                            "use a slice pattern here instead",
+                        );
+                    }
+                    e.help("for more information, see https://doc.rust-lang.org/edition-guide/\
+                            rust-2018/slice-patterns.html");
+                }
+                _ => annotate_err_with_kind(&mut e, kind, site_span),
+            };
             e
         }));
 
@@ -85,6 +127,7 @@ impl<'a> ParserAnyMacro<'a> {
 
 struct MacroRulesMacroExpander {
     name: ast::Ident,
+    span: Span,
     lhses: Vec<quoted::TokenTree>,
     rhses: Vec<quoted::TokenTree>,
     valid: bool,
@@ -96,18 +139,11 @@ impl TTMacroExpander for MacroRulesMacroExpander {
         cx: &'cx mut ExtCtxt<'_>,
         sp: Span,
         input: TokenStream,
-        def_span: Option<Span>,
-    ) -> Box<dyn MacResult+'cx> {
+    ) -> Box<dyn MacResult + 'cx> {
         if !self.valid {
             return DummyResult::any(sp);
         }
-        generic_extension(cx,
-                          sp,
-                          def_span,
-                          self.name,
-                          input,
-                          &self.lhses,
-                          &self.rhses)
+        generic_extension(cx, sp, self.span, self.name, input, &self.lhses, &self.rhses)
     }
 }
 
@@ -117,27 +153,27 @@ fn trace_macros_note(cx: &mut ExtCtxt<'_>, sp: Span, message: String) {
 }
 
 /// Given `lhses` and `rhses`, this is the new macro we create
-fn generic_extension<'cx>(cx: &'cx mut ExtCtxt<'_>,
-                          sp: Span,
-                          def_span: Option<Span>,
-                          name: ast::Ident,
-                          arg: TokenStream,
-                          lhses: &[quoted::TokenTree],
-                          rhses: &[quoted::TokenTree])
-                          -> Box<dyn MacResult+'cx> {
+fn generic_extension<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    def_span: Span,
+    name: ast::Ident,
+    arg: TokenStream,
+    lhses: &[quoted::TokenTree],
+    rhses: &[quoted::TokenTree],
+) -> Box<dyn MacResult + 'cx> {
     if cx.trace_macros() {
         trace_macros_note(cx, sp, format!("expanding `{}! {{ {} }}`", name, arg));
     }
 
     // Which arm's failure should we report? (the one furthest along)
-    let mut best_fail_spot = DUMMY_SP;
-    let mut best_fail_tok = None;
-    let mut best_fail_text = None;
+    let mut best_failure: Option<(Token, &str)> = None;
 
-    for (i, lhs) in lhses.iter().enumerate() { // try each arm's matchers
+    for (i, lhs) in lhses.iter().enumerate() {
+        // try each arm's matchers
         let lhs_tt = match *lhs {
             quoted::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
-            _ => cx.span_bug(sp, "malformed macro lhs")
+            _ => cx.span_bug(sp, "malformed macro lhs"),
         };
 
         match TokenTree::parse(cx, lhs_tt, arg.clone()) {
@@ -172,9 +208,10 @@ fn generic_extension<'cx>(cx: &'cx mut ExtCtxt<'_>,
                     path: Cow::from(cx.current_expansion.module.directory.as_path()),
                     ownership: cx.current_expansion.directory_ownership,
                 };
-                let mut p = Parser::new(cx.parse_sess(), tts, Some(directory), true, false);
-                p.root_module_name = cx.current_expansion.module.mod_path.last()
-                    .map(|id| id.as_str().to_string());
+                let mut p = Parser::new(cx.parse_sess(), tts, Some(directory), true, false, None);
+                p.root_module_name =
+                    cx.current_expansion.module.mod_path.last().map(|id| id.as_str().to_string());
+                p.last_type_ascription = cx.current_expansion.prior_type_ascription;
 
                 p.process_potential_macro_variable();
                 // Let the context choose how to interpret the result.
@@ -188,32 +225,28 @@ fn generic_extension<'cx>(cx: &'cx mut ExtCtxt<'_>,
                     site_span: sp,
                     macro_ident: name,
                     arm_span,
-                })
+                });
             }
-            Failure(sp, tok, t) => if sp.lo() >= best_fail_spot.lo() {
-                best_fail_spot = sp;
-                best_fail_tok = Some(tok);
-                best_fail_text = Some(t);
+            Failure(token, msg) => match best_failure {
+                Some((ref best_token, _)) if best_token.span.lo() >= token.span.lo() => {}
+                _ => best_failure = Some((token, msg)),
             },
-            Error(err_sp, ref msg) => {
-                cx.span_fatal(err_sp.substitute_dummy(sp), &msg[..])
-            }
+            Error(err_sp, ref msg) => cx.span_fatal(err_sp.substitute_dummy(sp), &msg[..]),
         }
     }
 
-    let best_fail_msg = parse_failure_msg(best_fail_tok.expect("ran no matchers"));
-    let span = best_fail_spot.substitute_dummy(sp);
-    let mut err = cx.struct_span_err(span, &best_fail_msg);
-    err.span_label(span, best_fail_text.unwrap_or(&best_fail_msg));
-    if let Some(sp) = def_span {
-        if cx.source_map().span_to_filename(sp).is_real() && !sp.is_dummy() {
-            err.span_label(cx.source_map().def_span(sp), "when calling this macro");
-        }
+    let (token, label) = best_failure.expect("ran no matchers");
+    let span = token.span.substitute_dummy(sp);
+    let mut err = cx.struct_span_err(span, &parse_failure_msg(&token));
+    err.span_label(span, label);
+    if !def_span.is_dummy() && cx.source_map().span_to_filename(def_span).is_real() {
+        err.span_label(cx.source_map().def_span(def_span), "when calling this macro");
     }
 
     // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
     if let Some((arg, comma_span)) = arg.add_comma() {
-        for lhs in lhses { // try each arm's matchers
+        for lhs in lhses {
+            // try each arm's matchers
             let lhs_tt = match *lhs {
                 quoted::TokenTree::Delimited(_, ref delim) => &delim.tts[..],
                 _ => continue,
@@ -250,10 +283,11 @@ pub fn compile(
     sess: &ParseSess,
     features: &Features,
     def: &ast::Item,
-    edition: Edition
+    edition: Edition,
 ) -> SyntaxExtension {
-    let lhs_nm = ast::Ident::with_empty_ctxt(Symbol::gensym("lhs"));
-    let rhs_nm = ast::Ident::with_empty_ctxt(Symbol::gensym("rhs"));
+    let lhs_nm = ast::Ident::new(sym::lhs, def.span);
+    let rhs_nm = ast::Ident::new(sym::rhs, def.span);
+    let tt_spec = ast::Ident::new(sym::tt, def.span);
 
     // Parse the macro_rules! invocation
     let body = match def.node {
@@ -267,32 +301,44 @@ pub fn compile(
     // ...quasiquoting this would be nice.
     // These spans won't matter, anyways
     let argument_gram = vec![
-        quoted::TokenTree::Sequence(DelimSpan::dummy(), Lrc::new(quoted::SequenceRepetition {
-            tts: vec![
-                quoted::TokenTree::MetaVarDecl(DUMMY_SP, lhs_nm, ast::Ident::from_str("tt")),
-                quoted::TokenTree::Token(DUMMY_SP, token::FatArrow),
-                quoted::TokenTree::MetaVarDecl(DUMMY_SP, rhs_nm, ast::Ident::from_str("tt")),
-            ],
-            separator: Some(if body.legacy { token::Semi } else { token::Comma }),
-            op: quoted::KleeneOp::OneOrMore,
-            num_captures: 2,
-        })),
+        quoted::TokenTree::Sequence(
+            DelimSpan::dummy(),
+            Lrc::new(quoted::SequenceRepetition {
+                tts: vec![
+                    quoted::TokenTree::MetaVarDecl(def.span, lhs_nm, tt_spec),
+                    quoted::TokenTree::token(token::FatArrow, def.span),
+                    quoted::TokenTree::MetaVarDecl(def.span, rhs_nm, tt_spec),
+                ],
+                separator: Some(Token::new(
+                    if body.legacy { token::Semi } else { token::Comma },
+                    def.span,
+                )),
+                kleene: quoted::KleeneToken::new(quoted::KleeneOp::OneOrMore, def.span),
+                num_captures: 2,
+            }),
+        ),
         // to phase into semicolon-termination instead of semicolon-separation
-        quoted::TokenTree::Sequence(DelimSpan::dummy(), Lrc::new(quoted::SequenceRepetition {
-            tts: vec![quoted::TokenTree::Token(DUMMY_SP, token::Semi)],
-            separator: None,
-            op: quoted::KleeneOp::ZeroOrMore,
-            num_captures: 0
-        })),
+        quoted::TokenTree::Sequence(
+            DelimSpan::dummy(),
+            Lrc::new(quoted::SequenceRepetition {
+                tts: vec![quoted::TokenTree::token(
+                    if body.legacy { token::Semi } else { token::Comma },
+                    def.span,
+                )],
+                separator: None,
+                kleene: quoted::KleeneToken::new(quoted::KleeneOp::ZeroOrMore, def.span),
+                num_captures: 0,
+            }),
+        ),
     ];
 
     let argument_map = match parse(sess, body.stream(), &argument_gram, None, true) {
         Success(m) => m,
-        Failure(sp, tok, t) => {
-            let s = parse_failure_msg(tok);
-            let sp = sp.substitute_dummy(def.span);
+        Failure(token, msg) => {
+            let s = parse_failure_msg(&token);
+            let sp = token.span.substitute_dummy(def.span);
             let mut err = sess.span_diagnostic.struct_span_fatal(sp, &s);
-            err.span_label(sp, t);
+            err.span_label(sp, msg);
             err.emit();
             FatalError.raise();
         }
@@ -304,9 +350,10 @@ pub fn compile(
     let mut valid = true;
 
     // Extract the arguments:
-    let lhses = match *argument_map[&lhs_nm] {
-        MatchedSeq(ref s, _) => {
-            s.iter().map(|m| {
+    let lhses = match argument_map[&lhs_nm] {
+        MatchedSeq(ref s, _) => s
+            .iter()
+            .map(|m| {
                 if let MatchedNonterminal(ref nt) = *m {
                     if let NtTT(ref tt) = **nt {
                         let tt = quoted::parse(
@@ -325,14 +372,15 @@ pub fn compile(
                     }
                 }
                 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
-            }).collect::<Vec<quoted::TokenTree>>()
-        }
-        _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
+            })
+            .collect::<Vec<quoted::TokenTree>>(),
+        _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs"),
     };
 
-    let rhses = match *argument_map[&rhs_nm] {
-        MatchedSeq(ref s, _) => {
-            s.iter().map(|m| {
+    let rhses = match argument_map[&rhs_nm] {
+        MatchedSeq(ref s, _) => s
+            .iter()
+            .map(|m| {
                 if let MatchedNonterminal(ref nt) = *m {
                     if let NtTT(ref tt) = **nt {
                         return quoted::parse(
@@ -343,14 +391,15 @@ pub fn compile(
                             &def.attrs,
                             edition,
                             def.id,
-                        ).pop()
-                         .unwrap();
+                        )
+                        .pop()
+                        .unwrap();
                     }
                 }
                 sess.span_diagnostic.span_bug(def.span, "wrong-structured lhs")
-            }).collect::<Vec<quoted::TokenTree>>()
-        }
-        _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured rhs")
+            })
+            .collect::<Vec<quoted::TokenTree>>(),
+        _ => sess.span_diagnostic.span_bug(def.span, "wrong-structured rhs"),
     };
 
     for rhs in &rhses {
@@ -359,88 +408,90 @@ pub fn compile(
 
     // don't abort iteration early, so that errors for multiple lhses can be reported
     for lhs in &lhses {
-        valid &= check_lhs_no_empty_seq(sess, &[lhs.clone()]);
-        valid &= check_lhs_duplicate_matcher_bindings(
-            sess,
-            &[lhs.clone()],
-            &mut FxHashMap::default(),
-            def.id
-        );
+        valid &= check_lhs_no_empty_seq(sess, slice::from_ref(lhs));
     }
 
-    let expander: Box<_> = Box::new(MacroRulesMacroExpander {
-        name: def.ident,
-        lhses,
-        rhses,
-        valid,
-    });
-
-    if body.legacy {
-        let allow_internal_unstable = attr::find_by_name(&def.attrs, sym::allow_internal_unstable)
-            .map(|attr| attr
-                .meta_item_list()
-                .map(|list| list.iter()
-                    .filter_map(|it| {
-                        let name = it.ident().map(|ident| ident.name);
-                        if name.is_none() {
-                            sess.span_diagnostic.span_err(it.span(),
-                                "allow internal unstable expects feature names")
-                        }
-                        name
-                    })
-                    .collect::<Vec<Symbol>>().into()
-                )
+    // We use CRATE_NODE_ID instead of `def.id` otherwise we may emit buffered lints for a node id
+    // that is not lint-checked and trigger the "failed to process buffered lint here" bug.
+    valid &= macro_check::check_meta_variables(sess, ast::CRATE_NODE_ID, def.span, &lhses, &rhses);
+
+    let expander: Box<_> =
+        Box::new(MacroRulesMacroExpander { name: def.ident, span: def.span, lhses, rhses, valid });
+
+    let (default_transparency, transparency_error) =
+        attr::find_transparency(&def.attrs, body.legacy);
+    match transparency_error {
+        Some(TransparencyError::UnknownTransparency(value, span)) =>
+            sess.span_diagnostic.span_err(
+                span, &format!("unknown macro transparency: `{}`", value)
+            ),
+        Some(TransparencyError::MultipleTransparencyAttrs(old_span, new_span)) =>
+            sess.span_diagnostic.span_err(
+                vec![old_span, new_span], "multiple macro transparency attributes"
+            ),
+        None => {}
+    }
+
+    let allow_internal_unstable =
+        attr::find_by_name(&def.attrs, sym::allow_internal_unstable).map(|attr| {
+            attr.meta_item_list()
+                .map(|list| {
+                    list.iter()
+                        .filter_map(|it| {
+                            let name = it.ident().map(|ident| ident.name);
+                            if name.is_none() {
+                                sess.span_diagnostic.span_err(
+                                    it.span(),
+                                    "allow internal unstable expects feature names",
+                                )
+                            }
+                            name
+                        })
+                        .collect::<Vec<Symbol>>()
+                        .into()
+                })
                 .unwrap_or_else(|| {
                     sess.span_diagnostic.span_warn(
-                        attr.span, "allow_internal_unstable expects list of feature names. In the \
-                        future this will become a hard error. Please use `allow_internal_unstable(\
-                        foo, bar)` to only allow the `foo` and `bar` features",
+                        attr.span,
+                        "allow_internal_unstable expects list of feature names. In the \
+                         future this will become a hard error. Please use `allow_internal_unstable(\
+                         foo, bar)` to only allow the `foo` and `bar` features",
                     );
-                    vec![Symbol::intern("allow_internal_unstable_backcompat_hack")].into()
+                    vec![sym::allow_internal_unstable_backcompat_hack].into()
                 })
-            );
-        let allow_internal_unsafe = attr::contains_name(&def.attrs, sym::allow_internal_unsafe);
-        let mut local_inner_macros = false;
-        if let Some(macro_export) = attr::find_by_name(&def.attrs, sym::macro_export) {
-            if let Some(l) = macro_export.meta_item_list() {
-                local_inner_macros = attr::list_contains_name(&l, sym::local_inner_macros);
-            }
-        }
-
-        let unstable_feature = attr::find_stability(&sess,
-                                                    &def.attrs, def.span).and_then(|stability| {
-            if let attr::StabilityLevel::Unstable { issue, .. } = stability.level {
-                Some((stability.feature, issue))
-            } else {
-                None
-            }
         });
 
-        NormalTT {
-            expander,
-            def_info: Some((def.id, def.span)),
-            allow_internal_unstable,
-            allow_internal_unsafe,
-            local_inner_macros,
-            unstable_feature,
-            edition,
+    let mut local_inner_macros = false;
+    if let Some(macro_export) = attr::find_by_name(&def.attrs, sym::macro_export) {
+        if let Some(l) = macro_export.meta_item_list() {
+            local_inner_macros = attr::list_contains_name(&l, sym::local_inner_macros);
         }
-    } else {
-        let is_transparent = attr::contains_name(&def.attrs, sym::rustc_transparent_macro);
+    }
 
-        SyntaxExtension::DeclMacro {
-            expander,
-            def_info: Some((def.id, def.span)),
-            is_transparent,
-            edition,
-        }
+    let is_builtin = attr::contains_name(&def.attrs, sym::rustc_builtin_macro);
+
+    SyntaxExtension {
+        kind: SyntaxExtensionKind::LegacyBang(expander),
+        span: def.span,
+        default_transparency,
+        allow_internal_unstable,
+        allow_internal_unsafe: attr::contains_name(&def.attrs, sym::allow_internal_unsafe),
+        local_inner_macros,
+        stability: attr::find_stability(&sess, &def.attrs, def.span),
+        deprecation: attr::find_deprecation(&sess, &def.attrs, def.span),
+        helper_attrs: Vec::new(),
+        edition,
+        is_builtin,
+        is_derive_copy: is_builtin && def.ident.name == sym::Copy,
     }
 }
 
-fn check_lhs_nt_follows(sess: &ParseSess,
-                        features: &Features,
-                        attrs: &[ast::Attribute],
-                        lhs: &quoted::TokenTree) -> bool {
+fn check_lhs_nt_follows(
+    sess: &ParseSess,
+    features: &Features,
+    attrs: &[ast::Attribute],
+    lhs: &quoted::TokenTree,
+) -> bool {
     // lhs is going to be like TokenTree::Delimited(...), where the
     // entire lhs is those tts. Or, it can be a "bare sequence", not wrapped in parens.
     if let quoted::TokenTree::Delimited(_, ref tts) = *lhs {
@@ -461,19 +512,22 @@ fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[quoted::TokenTree]) -> bool {
     for tt in tts {
         match *tt {
             TokenTree::Token(..) | TokenTree::MetaVar(..) | TokenTree::MetaVarDecl(..) => (),
-            TokenTree::Delimited(_, ref del) => if !check_lhs_no_empty_seq(sess, &del.tts) {
-                return false;
-            },
+            TokenTree::Delimited(_, ref del) => {
+                if !check_lhs_no_empty_seq(sess, &del.tts) {
+                    return false;
+                }
+            }
             TokenTree::Sequence(span, ref seq) => {
-                if seq.separator.is_none() && seq.tts.iter().all(|seq_tt| {
-                    match *seq_tt {
+                if seq.separator.is_none()
+                    && seq.tts.iter().all(|seq_tt| match *seq_tt {
                         TokenTree::MetaVarDecl(_, _, id) => id.name == sym::vis,
-                        TokenTree::Sequence(_, ref sub_seq) =>
-                            sub_seq.op == quoted::KleeneOp::ZeroOrMore
-                            || sub_seq.op == quoted::KleeneOp::ZeroOrOne,
+                        TokenTree::Sequence(_, ref sub_seq) => {
+                            sub_seq.kleene.op == quoted::KleeneOp::ZeroOrMore
+                                || sub_seq.kleene.op == quoted::KleeneOp::ZeroOrOne
+                        }
                         _ => false,
-                    }
-                }) {
+                    })
+                {
                     let sp = span.entire();
                     sess.span_diagnostic.span_err(sp, "repetition matches empty token tree");
                     return false;
@@ -488,57 +542,20 @@ fn check_lhs_no_empty_seq(sess: &ParseSess, tts: &[quoted::TokenTree]) -> bool {
     true
 }
 
-/// Check that the LHS contains no duplicate matcher bindings. e.g. `$a:expr, $a:expr` would be
-/// illegal, since it would be ambiguous which `$a` to use if we ever needed to.
-fn check_lhs_duplicate_matcher_bindings(
-    sess: &ParseSess,
-    tts: &[quoted::TokenTree],
-    metavar_names: &mut FxHashMap<Ident, Span>,
-    node_id: ast::NodeId,
-) -> bool {
-    use self::quoted::TokenTree;
-    for tt in tts {
-        match *tt {
-            TokenTree::MetaVarDecl(span, name, _kind) => {
-                if let Some(&prev_span) = metavar_names.get(&name) {
-                    sess.span_diagnostic
-                        .struct_span_err(span, "duplicate matcher binding")
-                        .span_note(prev_span, "previous declaration was here")
-                        .emit();
-                    return false;
-                } else {
-                    metavar_names.insert(name, span);
-                }
-            }
-            TokenTree::Delimited(_, ref del) => {
-                if !check_lhs_duplicate_matcher_bindings(sess, &del.tts, metavar_names, node_id) {
-                    return false;
-                }
-            },
-            TokenTree::Sequence(_, ref seq) => {
-                if !check_lhs_duplicate_matcher_bindings(sess, &seq.tts, metavar_names, node_id) {
-                    return false;
-                }
-            }
-            _ => {}
-        }
-    }
-
-    true
-}
-
 fn check_rhs(sess: &ParseSess, rhs: &quoted::TokenTree) -> bool {
     match *rhs {
         quoted::TokenTree::Delimited(..) => return true,
-        _ => sess.span_diagnostic.span_err(rhs.span(), "macro rhs must be delimited")
+        _ => sess.span_diagnostic.span_err(rhs.span(), "macro rhs must be delimited"),
     }
     false
 }
 
-fn check_matcher(sess: &ParseSess,
-                 features: &Features,
-                 attrs: &[ast::Attribute],
-                 matcher: &[quoted::TokenTree]) -> bool {
+fn check_matcher(
+    sess: &ParseSess,
+    features: &Features,
+    attrs: &[ast::Attribute],
+    matcher: &[quoted::TokenTree],
+) -> bool {
     let first_sets = FirstSets::new(matcher);
     let empty_suffix = TokenSet::empty();
     let err = sess.span_diagnostic.err_count();
@@ -611,15 +628,14 @@ impl FirstSets {
                         // If the sequence contents can be empty, then the first
                         // token could be the separator token itself.
 
-                        if let (Some(ref sep), true) = (seq_rep.separator.clone(),
-                                                        subfirst.maybe_empty) {
-                            first.add_one_maybe(TokenTree::Token(sp.entire(), sep.clone()));
+                        if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
+                            first.add_one_maybe(TokenTree::Token(sep.clone()));
                         }
 
                         // Reverse scan: Sequence comes before `first`.
                         if subfirst.maybe_empty
-                           || seq_rep.op == quoted::KleeneOp::ZeroOrMore
-                           || seq_rep.op == quoted::KleeneOp::ZeroOrOne
+                            || seq_rep.kleene.op == quoted::KleeneOp::ZeroOrMore
+                            || seq_rep.kleene.op == quoted::KleeneOp::ZeroOrOne
                         {
                             // If sequence is potentially empty, then
                             // union them (preserving first emptiness).
@@ -655,40 +671,37 @@ impl FirstSets {
                     return first;
                 }
                 TokenTree::Sequence(sp, ref seq_rep) => {
-                    match self.first.get(&sp.entire()) {
-                        Some(&Some(ref subfirst)) => {
-
-                            // If the sequence contents can be empty, then the first
-                            // token could be the separator token itself.
-
-                            if let (Some(ref sep), true) = (seq_rep.separator.clone(),
-                                                            subfirst.maybe_empty) {
-                                first.add_one_maybe(TokenTree::Token(sp.entire(), sep.clone()));
-                            }
-
-                            assert!(first.maybe_empty);
-                            first.add_all(subfirst);
-                            if subfirst.maybe_empty
-                               || seq_rep.op == quoted::KleeneOp::ZeroOrMore
-                               || seq_rep.op == quoted::KleeneOp::ZeroOrOne
-                            {
-                                // continue scanning for more first
-                                // tokens, but also make sure we
-                                // restore empty-tracking state
-                                first.maybe_empty = true;
-                                continue;
-                            } else {
-                                return first;
-                            }
-                        }
-
+                    let subfirst_owned;
+                    let subfirst = match self.first.get(&sp.entire()) {
+                        Some(&Some(ref subfirst)) => subfirst,
                         Some(&None) => {
-                            panic!("assume all sequences have (unique) spans for now");
+                            subfirst_owned = self.first(&seq_rep.tts[..]);
+                            &subfirst_owned
                         }
-
                         None => {
                             panic!("We missed a sequence during FirstSets construction");
                         }
+                    };
+
+                    // If the sequence contents can be empty, then the first
+                    // token could be the separator token itself.
+                    if let (Some(sep), true) = (&seq_rep.separator, subfirst.maybe_empty) {
+                        first.add_one_maybe(TokenTree::Token(sep.clone()));
+                    }
+
+                    assert!(first.maybe_empty);
+                    first.add_all(subfirst);
+                    if subfirst.maybe_empty
+                        || seq_rep.kleene.op == quoted::KleeneOp::ZeroOrMore
+                        || seq_rep.kleene.op == quoted::KleeneOp::ZeroOrOne
+                    {
+                        // Continue scanning for more first
+                        // tokens, but also make sure we
+                        // restore empty-tracking state.
+                        first.maybe_empty = true;
+                        continue;
+                    } else {
+                        return first;
                     }
                 }
             }
@@ -719,7 +732,9 @@ struct TokenSet {
 
 impl TokenSet {
     // Returns a set for the empty sequence.
-    fn empty() -> Self { TokenSet { tokens: Vec::new(), maybe_empty: true } }
+    fn empty() -> Self {
+        TokenSet { tokens: Vec::new(), maybe_empty: true }
+    }
 
     // Returns the set `{ tok }` for the single-token (and thus
     // non-empty) sequence [tok].
@@ -778,7 +793,7 @@ impl TokenSet {
 }
 
 // Checks that `matcher` is internally consistent and that it
-// can legally by followed by a token N, for all N in `follow`.
+// can legally be followed by a token `N`, for all `N` in `follow`.
 // (If `follow` is empty, then it imposes no constraint on
 // the `matcher`.)
 //
@@ -788,12 +803,14 @@ impl TokenSet {
 //
 // Requires that `first_sets` is pre-computed for `matcher`;
 // see `FirstSets::new`.
-fn check_matcher_core(sess: &ParseSess,
-                      features: &Features,
-                      attrs: &[ast::Attribute],
-                      first_sets: &FirstSets,
-                      matcher: &[quoted::TokenTree],
-                      follow: &TokenSet) -> TokenSet {
+fn check_matcher_core(
+    sess: &ParseSess,
+    features: &Features,
+    attrs: &[ast::Attribute],
+    first_sets: &FirstSets,
+    matcher: &[quoted::TokenTree],
+    follow: &TokenSet,
+) -> TokenSet {
     use quoted::TokenTree;
 
     let mut last = TokenSet::empty();
@@ -803,11 +820,13 @@ fn check_matcher_core(sess: &ParseSess,
     // then ensure T can also be followed by any element of FOLLOW.
     'each_token: for i in 0..matcher.len() {
         let token = &matcher[i];
-        let suffix = &matcher[i+1..];
+        let suffix = &matcher[i + 1..];
 
         let build_suffix_first = || {
             let mut s = first_sets.first(suffix);
-            if s.maybe_empty { s.add_all(follow); }
+            if s.maybe_empty {
+                s.add_all(follow);
+            }
             s
         };
 
@@ -823,7 +842,8 @@ fn check_matcher_core(sess: &ParseSess,
                 let can_be_followed_by_any;
                 if let Err(bad_frag) = has_legal_fragment_specifier(sess, features, attrs, token) {
                     let msg = format!("invalid fragment specifier `{}`", bad_frag);
-                    sess.span_diagnostic.struct_span_err(token.span(), &msg)
+                    sess.span_diagnostic
+                        .struct_span_err(token.span(), &msg)
                         .help(VALID_FRAGMENT_NAMES_MSG)
                         .emit();
                     // (This eliminates false positives and duplicates
@@ -854,7 +874,7 @@ fn check_matcher_core(sess: &ParseSess,
                 // against SUFFIX
                 continue 'each_token;
             }
-            TokenTree::Sequence(sp, ref seq_rep) => {
+            TokenTree::Sequence(_, ref seq_rep) => {
                 suffix_first = build_suffix_first();
                 // The trick here: when we check the interior, we want
                 // to include the separator (if any) as a potential
@@ -867,9 +887,9 @@ fn check_matcher_core(sess: &ParseSess,
                 // work of cloning it? But then again, this way I may
                 // get a "tighter" span?
                 let mut new;
-                let my_suffix = if let Some(ref u) = seq_rep.separator {
+                let my_suffix = if let Some(sep) = &seq_rep.separator {
                     new = suffix_first.clone();
-                    new.add_one_maybe(TokenTree::Token(sp.entire(), u.clone()));
+                    new.add_one_maybe(TokenTree::Token(sep.clone()));
                     &new
                 } else {
                     &suffix_first
@@ -878,12 +898,8 @@ fn check_matcher_core(sess: &ParseSess,
                 // At this point, `suffix_first` is built, and
                 // `my_suffix` is some TokenSet that we can use
                 // for checking the interior of `seq_rep`.
-                let next = check_matcher_core(sess,
-                                              features,
-                                              attrs,
-                                              first_sets,
-                                              &seq_rep.tts,
-                                              my_suffix);
+                let next =
+                    check_matcher_core(sess, features, attrs, first_sets, &seq_rep.tts, my_suffix);
                 if next.maybe_empty {
                     last.add_all(&next);
                 } else {
@@ -905,16 +921,17 @@ fn check_matcher_core(sess: &ParseSess,
                 for next_token in &suffix_first.tokens {
                     match is_in_follow(next_token, &frag_spec.as_str()) {
                         IsInFollow::Invalid(msg, help) => {
-                            sess.span_diagnostic.struct_span_err(next_token.span(), &msg)
-                                .help(help).emit();
+                            sess.span_diagnostic
+                                .struct_span_err(next_token.span(), &msg)
+                                .help(help)
+                                .emit();
                             // don't bother reporting every source of
                             // conflict for a particular element of `last`.
                             continue 'each_last;
                         }
                         IsInFollow::Yes => {}
-                        IsInFollow::No(ref possible) => {
-                            let may_be = if last.tokens.len() == 1 &&
-                                suffix_first.tokens.len() == 1
+                        IsInFollow::No(possible) => {
+                            let may_be = if last.tokens.len() == 1 && suffix_first.tokens.len() == 1
                             {
                                 "is"
                             } else {
@@ -924,33 +941,37 @@ fn check_matcher_core(sess: &ParseSess,
                             let sp = next_token.span();
                             let mut err = sess.span_diagnostic.struct_span_err(
                                 sp,
-                                &format!("`${name}:{frag}` {may_be} followed by `{next}`, which \
-                                          is not allowed for `{frag}` fragments",
-                                         name=name,
-                                         frag=frag_spec,
-                                         next=quoted_tt_to_string(next_token),
-                                         may_be=may_be),
+                                &format!(
+                                    "`${name}:{frag}` {may_be} followed by `{next}`, which \
+                                     is not allowed for `{frag}` fragments",
+                                    name = name,
+                                    frag = frag_spec,
+                                    next = quoted_tt_to_string(next_token),
+                                    may_be = may_be
+                                ),
                             );
                             err.span_label(
                                 sp,
                                 format!("not allowed after `{}` fragments", frag_spec),
                             );
                             let msg = "allowed there are: ";
-                            match &possible[..] {
+                            match possible {
                                 &[] => {}
                                 &[t] => {
                                     err.note(&format!(
                                         "only {} is allowed after `{}` fragments",
-                                        t,
-                                        frag_spec,
+                                        t, frag_spec,
                                     ));
                                 }
                                 ts => {
                                     err.note(&format!(
                                         "{}{} or {}",
                                         msg,
-                                        ts[..ts.len() - 1].iter().map(|s| *s)
-                                            .collect::<Vec<_>>().join(", "),
+                                        ts[..ts.len() - 1]
+                                            .iter()
+                                            .map(|s| *s)
+                                            .collect::<Vec<_>>()
+                                            .join(", "),
                                         ts[ts.len() - 1],
                                     ));
                                 }
@@ -1000,7 +1021,7 @@ fn frag_can_be_followed_by_any(frag: &str) -> bool {
 
 enum IsInFollow {
     Yes,
-    No(Vec<&'static str>),
+    No(&'static [&'static str]),
     Invalid(String, &'static str),
 }
 
@@ -1015,7 +1036,7 @@ enum IsInFollow {
 fn is_in_follow(tok: &quoted::TokenTree, frag: &str) -> IsInFollow {
     use quoted::TokenTree;
 
-    if let TokenTree::Token(_, token::CloseDelim(_)) = *tok {
+    if let TokenTree::Token(Token { kind: token::CloseDelim(_), .. }) = *tok {
         // closing a token tree can never be matched by any fragment;
         // iow, we always require that `(` and `)` match, etc.
         IsInFollow::Yes
@@ -1025,115 +1046,131 @@ fn is_in_follow(tok: &quoted::TokenTree, frag: &str) -> IsInFollow {
                 // since items *must* be followed by either a `;` or a `}`, we can
                 // accept anything after them
                 IsInFollow::Yes
-            },
+            }
             "block" => {
                 // anything can follow block, the braces provide an easy boundary to
                 // maintain
                 IsInFollow::Yes
-            },
-            "stmt" | "expr"  => {
-                let tokens = vec!["`=>`", "`,`", "`;`"];
-                match *tok {
-                    TokenTree::Token(_, ref tok) => match *tok {
+            }
+            "stmt" | "expr" => {
+                const TOKENS: &[&str] = &["`=>`", "`,`", "`;`"];
+                match tok {
+                    TokenTree::Token(token) => match token.kind {
                         FatArrow | Comma | Semi => IsInFollow::Yes,
-                        _ => IsInFollow::No(tokens),
+                        _ => IsInFollow::No(TOKENS),
                     },
-                    _ => IsInFollow::No(tokens),
+                    _ => IsInFollow::No(TOKENS),
                 }
-            },
+            }
             "pat" => {
-                let tokens = vec!["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
-                match *tok {
-                    TokenTree::Token(_, ref tok) => match *tok {
+                const TOKENS: &[&str] = &["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
+                match tok {
+                    TokenTree::Token(token) => match token.kind {
                         FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes,
-                        Ident(i, false) if i.name == keywords::If.name() ||
-                                           i.name == keywords::In.name() => IsInFollow::Yes,
-                        _ => IsInFollow::No(tokens),
+                        Ident(name, false) if name == kw::If || name == kw::In => IsInFollow::Yes,
+                        _ => IsInFollow::No(TOKENS),
                     },
-                    _ => IsInFollow::No(tokens),
+                    _ => IsInFollow::No(TOKENS),
                 }
-            },
+            }
             "path" | "ty" => {
-                let tokens = vec![
-                    "`{`", "`[`", "`=>`", "`,`", "`>`","`=`", "`:`", "`;`", "`|`", "`as`",
+                const TOKENS: &[&str] = &[
+                    "`{`", "`[`", "`=>`", "`,`", "`>`", "`=`", "`:`", "`;`", "`|`", "`as`",
                     "`where`",
                 ];
-                match *tok {
-                    TokenTree::Token(_, ref tok) => match *tok {
-                        OpenDelim(token::DelimToken::Brace) |
-                        OpenDelim(token::DelimToken::Bracket) |
-                        Comma | FatArrow | Colon | Eq | Gt | BinOp(token::Shr) | Semi |
-                        BinOp(token::Or) => IsInFollow::Yes,
-                        Ident(i, false) if i.name == keywords::As.name() ||
-                                           i.name == keywords::Where.name() => IsInFollow::Yes,
-                        _ => IsInFollow::No(tokens),
+                match tok {
+                    TokenTree::Token(token) => match token.kind {
+                        OpenDelim(token::DelimToken::Brace)
+                        | OpenDelim(token::DelimToken::Bracket)
+                        | Comma
+                        | FatArrow
+                        | Colon
+                        | Eq
+                        | Gt
+                        | BinOp(token::Shr)
+                        | Semi
+                        | BinOp(token::Or) => IsInFollow::Yes,
+                        Ident(name, false) if name == kw::As || name == kw::Where => {
+                            IsInFollow::Yes
+                        }
+                        _ => IsInFollow::No(TOKENS),
                     },
-                    TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::block =>
-                        IsInFollow::Yes,
-                    _ => IsInFollow::No(tokens),
+                    TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::block => {
+                        IsInFollow::Yes
+                    }
+                    _ => IsInFollow::No(TOKENS),
                 }
-            },
+            }
             "ident" | "lifetime" => {
                 // being a single token, idents and lifetimes are harmless
                 IsInFollow::Yes
-            },
+            }
             "literal" => {
                 // literals may be of a single token, or two tokens (negative numbers)
                 IsInFollow::Yes
-            },
+            }
             "meta" | "tt" => {
                 // being either a single token or a delimited sequence, tt is
                 // harmless
                 IsInFollow::Yes
-            },
+            }
             "vis" => {
                 // Explicitly disallow `priv`, on the off chance it comes back.
-                let tokens = vec!["`,`", "an ident", "a type"];
-                match *tok {
-                    TokenTree::Token(_, ref tok) => match *tok {
+                const TOKENS: &[&str] = &["`,`", "an ident", "a type"];
+                match tok {
+                    TokenTree::Token(token) => match token.kind {
                         Comma => IsInFollow::Yes,
-                        Ident(i, is_raw) if is_raw || i.name != keywords::Priv.name() =>
-                            IsInFollow::Yes,
-                        ref tok => if tok.can_begin_type() {
-                            IsInFollow::Yes
-                        } else {
-                            IsInFollow::No(tokens)
+                        Ident(name, is_raw) if is_raw || name != kw::Priv => IsInFollow::Yes,
+                        _ => {
+                            if token.can_begin_type() {
+                                IsInFollow::Yes
+                            } else {
+                                IsInFollow::No(TOKENS)
+                            }
                         }
                     },
-                    TokenTree::MetaVarDecl(_, _, frag) if frag.name == sym::ident
-                                                       || frag.name == sym::ty
-                                                       || frag.name == sym::path =>
-                        IsInFollow::Yes,
-                    _ => IsInFollow::No(tokens),
+                    TokenTree::MetaVarDecl(_, _, frag)
+                        if frag.name == sym::ident
+                            || frag.name == sym::ty
+                            || frag.name == sym::path =>
+                    {
+                        IsInFollow::Yes
+                    }
+                    _ => IsInFollow::No(TOKENS),
                 }
-            },
-            "" => IsInFollow::Yes, // keywords::Invalid
-            _ => IsInFollow::Invalid(format!("invalid fragment specifier `{}`", frag),
-                                     VALID_FRAGMENT_NAMES_MSG),
+            }
+            "" => IsInFollow::Yes, // kw::Invalid
+            _ => IsInFollow::Invalid(
+                format!("invalid fragment specifier `{}`", frag),
+                VALID_FRAGMENT_NAMES_MSG,
+            ),
         }
     }
 }
 
-fn has_legal_fragment_specifier(sess: &ParseSess,
-                                features: &Features,
-                                attrs: &[ast::Attribute],
-                                tok: &quoted::TokenTree) -> Result<(), String> {
+fn has_legal_fragment_specifier(
+    sess: &ParseSess,
+    features: &Features,
+    attrs: &[ast::Attribute],
+    tok: &quoted::TokenTree,
+) -> Result<(), String> {
     debug!("has_legal_fragment_specifier({:?})", tok);
     if let quoted::TokenTree::MetaVarDecl(_, _, ref frag_spec) = *tok {
-        let frag_name = frag_spec.as_str();
         let frag_span = tok.span();
-        if !is_legal_fragment_specifier(sess, features, attrs, &frag_name, frag_span) {
-            return Err(frag_name.to_string());
+        if !is_legal_fragment_specifier(sess, features, attrs, frag_spec.name, frag_span) {
+            return Err(frag_spec.to_string());
         }
     }
     Ok(())
 }
 
-fn is_legal_fragment_specifier(_sess: &ParseSess,
-                               _features: &Features,
-                               _attrs: &[ast::Attribute],
-                               frag_name: &str,
-                               _frag_span: Span) -> bool {
+fn is_legal_fragment_specifier(
+    _sess: &ParseSess,
+    _features: &Features,
+    _attrs: &[ast::Attribute],
+    frag_name: Symbol,
+    _frag_span: Span,
+) -> bool {
     /*
      * If new fragment specifiers are invented in nightly, `_sess`,
      * `_features`, `_attrs`, and `_frag_span` will be useful here
@@ -1141,19 +1178,32 @@ fn is_legal_fragment_specifier(_sess: &ParseSess,
      * this function.
      */
     match frag_name {
-        "item" | "block" | "stmt" | "expr" | "pat" | "lifetime" |
-        "path" | "ty" | "ident" | "meta" | "tt" | "vis" | "literal" |
-        "" => true,
+        sym::item
+        | sym::block
+        | sym::stmt
+        | sym::expr
+        | sym::pat
+        | sym::lifetime
+        | sym::path
+        | sym::ty
+        | sym::ident
+        | sym::meta
+        | sym::tt
+        | sym::vis
+        | sym::literal
+        | kw::Invalid => true,
         _ => false,
     }
 }
 
 fn quoted_tt_to_string(tt: &quoted::TokenTree) -> String {
     match *tt {
-        quoted::TokenTree::Token(_, ref tok) => crate::print::pprust::token_to_string(tok),
+        quoted::TokenTree::Token(ref token) => crate::print::pprust::token_to_string(&token),
         quoted::TokenTree::MetaVar(_, name) => format!("${}", name),
         quoted::TokenTree::MetaVarDecl(_, name, kind) => format!("${}:{}", name, kind),
-        _ => panic!("unexpected quoted::TokenTree::{{Sequence or Delimited}} \
-                     in follow set checker"),
+        _ => panic!(
+            "unexpected quoted::TokenTree::{{Sequence or Delimited}} \
+             in follow set checker"
+        ),
     }
 }
diff --git a/src/libsyntax/ext/tt/quoted.rs b/src/libsyntax/ext/tt/quoted.rs
index ed8395f11ad..cad94a0e4c1 100644
--- a/src/libsyntax/ext/tt/quoted.rs
+++ b/src/libsyntax/ext/tt/quoted.rs
@@ -1,12 +1,12 @@
+use crate::ast;
 use crate::ast::NodeId;
-use crate::early_buffered_lints::BufferedEarlyLintId;
 use crate::ext::tt::macro_parser;
 use crate::feature_gate::Features;
-use crate::parse::{token, ParseSess};
+use crate::parse::token::{self, Token, TokenKind};
+use crate::parse::ParseSess;
 use crate::print::pprust;
+use crate::symbol::kw;
 use crate::tokenstream::{self, DelimSpan};
-use crate::ast;
-use crate::symbol::keywords;
 
 use syntax_pos::{edition::Edition, BytePos, Span};
 
@@ -22,24 +22,14 @@ pub struct Delimited {
 }
 
 impl Delimited {
-    /// Returns the opening delimiter (possibly `NoDelim`).
-    pub fn open_token(&self) -> token::Token {
-        token::OpenDelim(self.delim)
-    }
-
-    /// Returns the closing delimiter (possibly `NoDelim`).
-    pub fn close_token(&self) -> token::Token {
-        token::CloseDelim(self.delim)
-    }
-
     /// Returns a `self::TokenTree` with a `Span` corresponding to the opening delimiter.
     pub fn open_tt(&self, span: Span) -> TokenTree {
         let open_span = if span.is_dummy() {
             span
         } else {
-            span.with_lo(span.lo() + BytePos(self.delim.len() as u32))
+            span.with_hi(span.lo() + BytePos(self.delim.len() as u32))
         };
-        TokenTree::Token(open_span, self.open_token())
+        TokenTree::token(token::OpenDelim(self.delim), open_span)
     }
 
     /// Returns a `self::TokenTree` with a `Span` corresponding to the closing delimiter.
@@ -49,7 +39,7 @@ impl Delimited {
         } else {
             span.with_lo(span.hi() - BytePos(self.delim.len() as u32))
         };
-        TokenTree::Token(close_span, self.close_token())
+        TokenTree::token(token::CloseDelim(self.delim), close_span)
     }
 }
 
@@ -58,13 +48,25 @@ pub struct SequenceRepetition {
     /// The sequence of token trees
     pub tts: Vec<TokenTree>,
     /// The optional separator
-    pub separator: Option<token::Token>,
+    pub separator: Option<Token>,
     /// Whether the sequence can be repeated zero (*), or one or more times (+)
-    pub op: KleeneOp,
+    pub kleene: KleeneToken,
     /// The number of `Match`s that appear in the sequence (and subsequences)
     pub num_captures: usize,
 }
 
+#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Copy)]
+pub struct KleeneToken {
+    pub span: Span,
+    pub op: KleeneOp,
+}
+
+impl KleeneToken {
+    pub fn new(op: KleeneOp, span: Span) -> KleeneToken {
+        KleeneToken { span, op }
+    }
+}
+
 /// A Kleene-style [repetition operator](http://en.wikipedia.org/wiki/Kleene_star)
 /// for token sequences.
 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
@@ -81,7 +83,7 @@ pub enum KleeneOp {
 /// are "first-class" token trees. Useful for parsing macros.
 #[derive(Debug, Clone, PartialEq, RustcEncodable, RustcDecodable)]
 pub enum TokenTree {
-    Token(Span, token::Token),
+    Token(Token),
     Delimited(DelimSpan, Lrc<Delimited>),
     /// A kleene-style repetition sequence
     Sequence(DelimSpan, Lrc<SequenceRepetition>),
@@ -121,6 +123,22 @@ impl TokenTree {
         }
     }
 
+    /// Returns `true` if the given token tree is delimited.
+    pub fn is_delimited(&self) -> bool {
+        match *self {
+            TokenTree::Delimited(..) => true,
+            _ => false,
+        }
+    }
+
+    /// Returns `true` if the given token tree is a token of the given kind.
+    pub fn is_token(&self, expected_kind: &TokenKind) -> bool {
+        match self {
+            TokenTree::Token(Token { kind: actual_kind, .. }) => actual_kind == expected_kind,
+            _ => false,
+        }
+    }
+
     /// Gets the `index`-th sub-token-tree. This only makes sense for delimited trees and sequences.
     pub fn get_tt(&self, index: usize) -> TokenTree {
         match (self, index) {
@@ -144,13 +162,16 @@ impl TokenTree {
     /// Retrieves the `TokenTree`'s span.
     pub fn span(&self) -> Span {
         match *self {
-            TokenTree::Token(sp, _)
-            | TokenTree::MetaVar(sp, _)
-            | TokenTree::MetaVarDecl(sp, _, _) => sp,
-            TokenTree::Delimited(sp, _)
-            | TokenTree::Sequence(sp, _) => sp.entire(),
+            TokenTree::Token(Token { span, .. })
+            | TokenTree::MetaVar(span, _)
+            | TokenTree::MetaVarDecl(span, _, _) => span,
+            TokenTree::Delimited(span, _) | TokenTree::Sequence(span, _) => span.entire(),
         }
     }
+
+    crate fn token(kind: TokenKind, span: Span) -> TokenTree {
+        TokenTree::Token(Token::new(kind, span))
+    }
 }
 
 /// Takes a `tokenstream::TokenStream` and returns a `Vec<self::TokenTree>`. Specifically, this
@@ -205,31 +226,23 @@ pub fn parse(
         match tree {
             TokenTree::MetaVar(start_sp, ident) if expect_matchers => {
                 let span = match trees.next() {
-                    Some(tokenstream::TokenTree::Token(span, token::Colon)) => match trees.next() {
-                        Some(tokenstream::TokenTree::Token(end_sp, ref tok)) => match tok.ident() {
-                            Some((kind, _)) => {
-                                let span = end_sp.with_lo(start_sp.lo());
-                                result.push(TokenTree::MetaVarDecl(span, ident, kind));
-                                continue;
-                            }
-                            _ => end_sp,
-                        },
-                        tree => tree
-                            .as_ref()
-                            .map(tokenstream::TokenTree::span)
-                            .unwrap_or(span),
-                    },
-                    tree => tree
-                        .as_ref()
-                        .map(tokenstream::TokenTree::span)
-                        .unwrap_or(start_sp),
+                    Some(tokenstream::TokenTree::Token(Token { kind: token::Colon, span })) => {
+                        match trees.next() {
+                            Some(tokenstream::TokenTree::Token(token)) => match token.ident() {
+                                Some((kind, _)) => {
+                                    let span = token.span.with_lo(start_sp.lo());
+                                    result.push(TokenTree::MetaVarDecl(span, ident, kind));
+                                    continue;
+                                }
+                                _ => token.span,
+                            },
+                            tree => tree.as_ref().map(tokenstream::TokenTree::span).unwrap_or(span),
+                        }
+                    }
+                    tree => tree.as_ref().map(tokenstream::TokenTree::span).unwrap_or(start_sp),
                 };
                 sess.missing_fragment_specifiers.borrow_mut().insert(span);
-                result.push(TokenTree::MetaVarDecl(
-                    span,
-                    ident,
-                    keywords::Invalid.ident(),
-                ));
+                result.push(TokenTree::MetaVarDecl(span, ident, ast::Ident::invalid()));
             }
 
             // Not a metavar or no matchers allowed, so just return the tree
@@ -254,29 +267,26 @@ pub fn parse(
 /// - `sess`: the parsing session. Any errors will be emitted to this session.
 /// - `features`, `attrs`: language feature flags and attributes so that we know whether to use
 ///   unstable features or not.
-fn parse_tree<I>(
+fn parse_tree(
     tree: tokenstream::TokenTree,
-    trees: &mut Peekable<I>,
+    trees: &mut Peekable<impl Iterator<Item = tokenstream::TokenTree>>,
     expect_matchers: bool,
     sess: &ParseSess,
     features: &Features,
     attrs: &[ast::Attribute],
     edition: Edition,
     macro_node_id: NodeId,
-) -> TokenTree
-where
-    I: Iterator<Item = tokenstream::TokenTree>,
-{
+) -> TokenTree {
     // Depending on what `tree` is, we could be parsing different parts of a macro
     match tree {
         // `tree` is a `$` token. Look at the next token in `trees`
-        tokenstream::TokenTree::Token(span, token::Dollar) => match trees.next() {
+        tokenstream::TokenTree::Token(Token { kind: token::Dollar, span }) => match trees.next() {
             // `tree` is followed by a delimited set of token trees. This indicates the beginning
             // of a repetition sequence in the macro (e.g. `$(pat)*`).
             Some(tokenstream::TokenTree::Delimited(span, delim, tts)) => {
                 // Must have `(` not `{` or `[`
                 if delim != token::Paren {
-                    let tok = pprust::token_to_string(&token::OpenDelim(delim));
+                    let tok = pprust::token_kind_to_string(&token::OpenDelim(delim));
                     let msg = format!("expected `(`, found `{}`", tok);
                     sess.span_diagnostic.span_err(span.entire(), &msg);
                 }
@@ -291,16 +301,7 @@ where
                     macro_node_id,
                 );
                 // Get the Kleene operator and optional separator
-                let (separator, op) =
-                    parse_sep_and_kleene_op(
-                        trees,
-                        span.entire(),
-                        sess,
-                        features,
-                        attrs,
-                        edition,
-                        macro_node_id,
-                    );
+                let (separator, kleene) = parse_sep_and_kleene_op(trees, span.entire(), sess);
                 // Count the number of captured "names" (i.e., named metavars)
                 let name_captures = macro_parser::count_names(&sequence);
                 TokenTree::Sequence(
@@ -308,7 +309,7 @@ where
                     Lrc::new(SequenceRepetition {
                         tts: sequence,
                         separator,
-                        op,
+                        kleene,
                         num_captures: name_captures,
                     }),
                 )
@@ -316,40 +317,37 @@ where
 
             // `tree` is followed by an `ident`. This could be `$meta_var` or the `$crate` special
             // metavariable that names the crate of the invocation.
-            Some(tokenstream::TokenTree::Token(ident_span, ref token)) if token.is_ident() => {
+            Some(tokenstream::TokenTree::Token(token)) if token.is_ident() => {
                 let (ident, is_raw) = token.ident().unwrap();
-                let span = ident_span.with_lo(span.lo());
-                if ident.name == keywords::Crate.name() && !is_raw {
-                    let ident = ast::Ident::new(keywords::DollarCrate.name(), ident.span);
-                    TokenTree::Token(span, token::Ident(ident, is_raw))
+                let span = ident.span.with_lo(span.lo());
+                if ident.name == kw::Crate && !is_raw {
+                    TokenTree::token(token::Ident(kw::DollarCrate, is_raw), span)
                 } else {
                     TokenTree::MetaVar(span, ident)
                 }
             }
 
             // `tree` is followed by a random token. This is an error.
-            Some(tokenstream::TokenTree::Token(span, tok)) => {
-                let msg = format!(
-                    "expected identifier, found `{}`",
-                    pprust::token_to_string(&tok)
-                );
-                sess.span_diagnostic.span_err(span, &msg);
-                TokenTree::MetaVar(span, keywords::Invalid.ident())
+            Some(tokenstream::TokenTree::Token(token)) => {
+                let msg =
+                    format!("expected identifier, found `{}`", pprust::token_to_string(&token),);
+                sess.span_diagnostic.span_err(token.span, &msg);
+                TokenTree::MetaVar(token.span, ast::Ident::invalid())
             }
 
             // There are no more tokens. Just return the `$` we already have.
-            None => TokenTree::Token(span, token::Dollar),
+            None => TokenTree::token(token::Dollar, span),
         },
 
         // `tree` is an arbitrary token. Keep it.
-        tokenstream::TokenTree::Token(span, tok) => TokenTree::Token(span, tok),
+        tokenstream::TokenTree::Token(token) => TokenTree::Token(token),
 
         // `tree` is the beginning of a delimited set of tokens (e.g., `(` or `{`). We need to
         // descend into the delimited set and further parse it.
         tokenstream::TokenTree::Delimited(span, delim, tts) => TokenTree::Delimited(
             span,
             Lrc::new(Delimited {
-                delim: delim,
+                delim,
                 tts: parse(
                     tts.into(),
                     expect_matchers,
@@ -366,8 +364,8 @@ where
 
 /// Takes a token and returns `Some(KleeneOp)` if the token is `+` `*` or `?`. Otherwise, return
 /// `None`.
-fn kleene_op(token: &token::Token) -> Option<KleeneOp> {
-    match *token {
+fn kleene_op(token: &Token) -> Option<KleeneOp> {
+    match token.kind {
         token::BinOp(token::Star) => Some(KleeneOp::ZeroOrMore),
         token::BinOp(token::Plus) => Some(KleeneOp::OneOrMore),
         token::Question => Some(KleeneOp::ZeroOrOne),
@@ -380,22 +378,16 @@ fn kleene_op(token: &token::Token) -> Option<KleeneOp> {
 /// - Ok(Ok((op, span))) if the next token tree is a KleeneOp
 /// - Ok(Err(tok, span)) if the next token tree is a token but not a KleeneOp
 /// - Err(span) if the next token tree is not a token
-fn parse_kleene_op<I>(
-    input: &mut I,
+fn parse_kleene_op(
+    input: &mut impl Iterator<Item = tokenstream::TokenTree>,
     span: Span,
-) -> Result<Result<(KleeneOp, Span), (token::Token, Span)>, Span>
-where
-    I: Iterator<Item = tokenstream::TokenTree>,
-{
+) -> Result<Result<(KleeneOp, Span), Token>, Span> {
     match input.next() {
-        Some(tokenstream::TokenTree::Token(span, tok)) => match kleene_op(&tok) {
-            Some(op) => Ok(Ok((op, span))),
-            None => Ok(Err((tok, span))),
+        Some(tokenstream::TokenTree::Token(token)) => match kleene_op(&token) {
+            Some(op) => Ok(Ok((op, token.span))),
+            None => Ok(Err(token)),
         },
-        tree => Err(tree
-            .as_ref()
-            .map(tokenstream::TokenTree::span)
-            .unwrap_or(span)),
+        tree => Err(tree.as_ref().map(tokenstream::TokenTree::span).unwrap_or(span)),
     }
 }
 
@@ -411,196 +403,35 @@ where
 /// session `sess`. If the next one (or possibly two) tokens in `input` correspond to a Kleene
 /// operator and separator, then a tuple with `(separator, KleeneOp)` is returned. Otherwise, an
 /// error with the appropriate span is emitted to `sess` and a dummy value is returned.
-///
-/// N.B., in the 2015 edition, `*` and `+` are the only Kleene operators, and `?` is a separator.
-/// In the 2018 edition however, `?` is a Kleene operator, and not a separator.
-fn parse_sep_and_kleene_op<I>(
-    input: &mut Peekable<I>,
+fn parse_sep_and_kleene_op(
+    input: &mut Peekable<impl Iterator<Item = tokenstream::TokenTree>>,
     span: Span,
     sess: &ParseSess,
-    features: &Features,
-    attrs: &[ast::Attribute],
-    edition: Edition,
-    macro_node_id: NodeId,
-) -> (Option<token::Token>, KleeneOp)
-where
-    I: Iterator<Item = tokenstream::TokenTree>,
-{
-    match edition {
-        Edition::Edition2015 => parse_sep_and_kleene_op_2015(
-            input,
-            span,
-            sess,
-            features,
-            attrs,
-            macro_node_id,
-        ),
-        Edition::Edition2018 => parse_sep_and_kleene_op_2018(input, span, sess, features, attrs),
-    }
-}
-
-// `?` is a separator (with a migration warning) and never a KleeneOp.
-fn parse_sep_and_kleene_op_2015<I>(
-    input: &mut Peekable<I>,
-    span: Span,
-    sess: &ParseSess,
-    _features: &Features,
-    _attrs: &[ast::Attribute],
-    macro_node_id: NodeId,
-) -> (Option<token::Token>, KleeneOp)
-where
-    I: Iterator<Item = tokenstream::TokenTree>,
-{
+) -> (Option<Token>, KleeneToken) {
     // We basically look at two token trees here, denoted as #1 and #2 below
     let span = match parse_kleene_op(input, span) {
-        // #1 is a `+` or `*` KleeneOp
-        //
-        // `?` is ambiguous: it could be a separator (warning) or a Kleene::ZeroOrOne (error), so
-        // we need to look ahead one more token to be sure.
-        Ok(Ok((op, _))) if op != KleeneOp::ZeroOrOne => return (None, op),
-
-        // #1 is `?` token, but it could be a Kleene::ZeroOrOne (error in 2015) without a separator
-        // or it could be a `?` separator followed by any Kleene operator. We need to look ahead 1
-        // token to find out which.
-        Ok(Ok((op, op1_span))) => {
-            assert_eq!(op, KleeneOp::ZeroOrOne);
-
-            // Lookahead at #2. If it is a KleenOp, then #1 is a separator.
-            let is_1_sep = if let Some(&tokenstream::TokenTree::Token(_, ref tok2)) = input.peek() {
-                kleene_op(tok2).is_some()
-            } else {
-                false
-            };
-
-            if is_1_sep {
-                // #1 is a separator and #2 should be a KleepeOp.
-                // (N.B. We need to advance the input iterator.)
-                match parse_kleene_op(input, span) {
-                    // #2 is `?`, which is not allowed as a Kleene op in 2015 edition,
-                    // but is allowed in the 2018 edition.
-                    Ok(Ok((op, op2_span))) if op == KleeneOp::ZeroOrOne => {
-                        sess.span_diagnostic
-                            .struct_span_err(op2_span, "expected `*` or `+`")
-                            .note("`?` is not a macro repetition operator in the 2015 edition, \
-                                 but is accepted in the 2018 edition")
-                            .emit();
-
-                        // Return a dummy
-                        return (None, KleeneOp::ZeroOrMore);
-                    }
-
-                    // #2 is a Kleene op, which is the only valid option
-                    Ok(Ok((op, _))) => {
-                        // Warn that `?` as a separator will be deprecated
-                        sess.buffer_lint(
-                            BufferedEarlyLintId::QuestionMarkMacroSep,
-                            op1_span,
-                            macro_node_id,
-                            "using `?` as a separator is deprecated and will be \
-                             a hard error in an upcoming edition",
-                        );
-
-                        return (Some(token::Question), op);
-                    }
-
-                    // #2 is a random token (this is an error) :(
-                    Ok(Err((_, _))) => op1_span,
-
-                    // #2 is not even a token at all :(
-                    Err(_) => op1_span,
-                }
-            } else {
-                // `?` is not allowed as a Kleene op in 2015,
-                // but is allowed in the 2018 edition
-                sess.span_diagnostic
-                    .struct_span_err(op1_span, "expected `*` or `+`")
-                    .note("`?` is not a macro repetition operator in the 2015 edition, \
-                         but is accepted in the 2018 edition")
-                    .emit();
-
-                // Return a dummy
-                return (None, KleeneOp::ZeroOrMore);
-            }
-        }
+        // #1 is a `?`, `+`, or `*` KleeneOp
+        Ok(Ok((op, span))) => return (None, KleeneToken::new(op, span)),
 
         // #1 is a separator followed by #2, a KleeneOp
-        Ok(Err((tok, span))) => match parse_kleene_op(input, span) {
-            // #2 is a `?`, which is not allowed as a Kleene op in 2015 edition,
-            // but is allowed in the 2018 edition
-            Ok(Ok((op, op2_span))) if op == KleeneOp::ZeroOrOne => {
-                sess.span_diagnostic
-                    .struct_span_err(op2_span, "expected `*` or `+`")
-                    .note("`?` is not a macro repetition operator in the 2015 edition, \
-                        but is accepted in the 2018 edition")
-                    .emit();
-
-                // Return a dummy
-                return (None, KleeneOp::ZeroOrMore);
-            }
-
-            // #2 is a KleeneOp :D
-            Ok(Ok((op, _))) => return (Some(tok), op),
-
-            // #2 is a random token :(
-            Ok(Err((_, span))) => span,
-
-            // #2 is not a token at all :(
-            Err(span) => span,
-        },
-
-        // #1 is not a token
-        Err(span) => span,
-    };
-
-    sess.span_diagnostic.span_err(span, "expected `*` or `+`");
-
-    // Return a dummy
-    (None, KleeneOp::ZeroOrMore)
-}
-
-// `?` is a Kleene op, not a separator
-fn parse_sep_and_kleene_op_2018<I>(
-    input: &mut Peekable<I>,
-    span: Span,
-    sess: &ParseSess,
-    _features: &Features,
-    _attrs: &[ast::Attribute],
-) -> (Option<token::Token>, KleeneOp)
-where
-    I: Iterator<Item = tokenstream::TokenTree>,
-{
-    // We basically look at two token trees here, denoted as #1 and #2 below
-    let span = match parse_kleene_op(input, span) {
-        // #1 is a `?` (needs feature gate)
-        Ok(Ok((op, _op1_span))) if op == KleeneOp::ZeroOrOne => {
-            return (None, op);
-        }
-
-        // #1 is a `+` or `*` KleeneOp
-        Ok(Ok((op, _))) => return (None, op),
-
-        // #1 is a separator followed by #2, a KleeneOp
-        Ok(Err((tok, span))) => match parse_kleene_op(input, span) {
+        Ok(Err(token)) => match parse_kleene_op(input, token.span) {
             // #2 is the `?` Kleene op, which does not take a separator (error)
-            Ok(Ok((op, _op2_span))) if op == KleeneOp::ZeroOrOne => {
+            Ok(Ok((KleeneOp::ZeroOrOne, span))) => {
                 // Error!
                 sess.span_diagnostic.span_err(
-                    span,
+                    token.span,
                     "the `?` macro repetition operator does not take a separator",
                 );
 
                 // Return a dummy
-                return (None, KleeneOp::ZeroOrMore);
+                return (None, KleeneToken::new(KleeneOp::ZeroOrMore, span));
             }
 
             // #2 is a KleeneOp :D
-            Ok(Ok((op, _))) => return (Some(tok), op),
-
-            // #2 is a random token :(
-            Ok(Err((_, span))) => span,
+            Ok(Ok((op, span))) => return (Some(token), KleeneToken::new(op, span)),
 
-            // #2 is not a token at all :(
-            Err(span) => span,
+            // #2 is a random token or not a token at all :(
+            Ok(Err(Token { span, .. })) | Err(span) => span,
         },
 
         // #1 is not a token
@@ -608,9 +439,8 @@ where
     };
 
     // If we ever get to this point, we have experienced an "unexpected token" error
-    sess.span_diagnostic
-        .span_err(span, "expected one of: `*`, `+`, or `?`");
+    sess.span_diagnostic.span_err(span, "expected one of: `*`, `+`, or `?`");
 
     // Return a dummy
-    (None, KleeneOp::ZeroOrMore)
+    (None, KleeneToken::new(KleeneOp::ZeroOrMore, span))
 }
diff --git a/src/libsyntax/ext/tt/transcribe.rs b/src/libsyntax/ext/tt/transcribe.rs
index e3586c1854c..214e721fd15 100644
--- a/src/libsyntax/ext/tt/transcribe.rs
+++ b/src/libsyntax/ext/tt/transcribe.rs
@@ -8,12 +8,10 @@ use crate::parse::token::{self, NtTT, Token};
 use crate::tokenstream::{DelimSpan, TokenStream, TokenTree, TreeAndJoint};
 
 use smallvec::{smallvec, SmallVec};
-use syntax_pos::DUMMY_SP;
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
 use std::mem;
-use std::rc::Rc;
 
 /// An iterator over the token trees in a delimited token tree (`{ ... }`) or a sequence (`$(...)`).
 enum Frame {
@@ -24,8 +22,8 @@ enum Frame {
 impl Frame {
     /// Construct a new frame around the delimited set of tokens.
     fn new(tts: Vec<quoted::TokenTree>) -> Frame {
-        let forest = Lrc::new(quoted::Delimited { delim: token::NoDelim, tts: tts });
-        Frame::Delimited { forest: forest, idx: 0, span: DelimSpan::dummy() }
+        let forest = Lrc::new(quoted::Delimited { delim: token::NoDelim, tts });
+        Frame::Delimited { forest, idx: 0, span: DelimSpan::dummy() }
     }
 }
 
@@ -66,9 +64,9 @@ impl Iterator for Frame {
 /// `transcribe` would return a `TokenStream` containing `println!("{}", stringify!(bar));`.
 ///
 /// Along the way, we do some additional error checking.
-pub fn transcribe(
+pub(super) fn transcribe(
     cx: &ExtCtxt<'_>,
-    interp: &FxHashMap<Ident, Rc<NamedMatch>>,
+    interp: &FxHashMap<Ident, NamedMatch>,
     src: Vec<quoted::TokenTree>,
 ) -> TokenStream {
     // Nothing for us to transcribe...
@@ -109,17 +107,13 @@ pub fn transcribe(
         else {
             // Otherwise, if we have just reached the end of a sequence and we can keep repeating,
             // go back to the beginning of the sequence.
-            if let Frame::Sequence { ref mut idx, ref sep, .. } = *stack.last_mut().unwrap() {
-                let (ref mut repeat_idx, repeat_len) = *repeats.last_mut().unwrap();
+            if let Frame::Sequence { idx, sep, .. } = stack.last_mut().unwrap() {
+                let (repeat_idx, repeat_len) = repeats.last_mut().unwrap();
                 *repeat_idx += 1;
-                if *repeat_idx < repeat_len {
+                if repeat_idx < repeat_len {
                     *idx = 0;
-                    if let Some(sep) = sep.clone() {
-                        let prev_span = match result.last() {
-                            Some((tt, _)) => tt.span(),
-                            None => DUMMY_SP,
-                        };
-                        result.push(TokenTree::Token(prev_span, sep).into());
+                    if let Some(sep) = sep {
+                        result.push(TokenTree::Token(sep.clone()).into());
                     }
                     continue;
                 }
@@ -170,9 +164,11 @@ pub fn transcribe(
                     }
 
                     LockstepIterSize::Contradiction(ref msg) => {
-                        // This should never happen because the macro parser should generate
-                        // properly-sized matches for all meta-vars.
-                        cx.span_bug(seq.span(), &msg[..]);
+                        // FIXME: this really ought to be caught at macro definition time... It
+                        // happens when two meta-variables are used in the same repetition in a
+                        // sequence, but they come from different sequence matchers and repeat
+                        // different amounts.
+                        cx.span_fatal(seq.span(), &msg[..]);
                     }
 
                     LockstepIterSize::Constraint(len, _) => {
@@ -186,10 +182,11 @@ pub fn transcribe(
 
                         // Is the repetition empty?
                         if len == 0 {
-                            if seq.op == quoted::KleeneOp::OneOrMore {
-                                // This should be impossible because the macro parser would not
-                                // match the given macro arm.
-                                cx.span_bug(sp.entire(), "this must repeat at least once");
+                            if seq.kleene.op == quoted::KleeneOp::OneOrMore {
+                                // FIXME: this really ought to be caught at macro definition
+                                // time... It happens when the Kleene operator in the matcher and
+                                // the body for the same meta-variable do not match.
+                                cx.span_fatal(sp.entire(), "this must repeat at least once");
                             }
                         } else {
                             // 0 is the initial counter (we have done 0 repretitions so far). `len`
@@ -214,15 +211,15 @@ pub fn transcribe(
                 // Find the matched nonterminal from the macro invocation, and use it to replace
                 // the meta-var.
                 if let Some(cur_matched) = lookup_cur_matched(ident, interp, &repeats) {
-                    if let MatchedNonterminal(ref nt) = *cur_matched {
+                    if let MatchedNonterminal(ref nt) = cur_matched {
                         // FIXME #2887: why do we apply a mark when matching a token tree meta-var
                         // (e.g. `$x:tt`), but not when we are matching any other type of token
                         // tree?
                         if let NtTT(ref tt) = **nt {
                             result.push(tt.clone().into());
                         } else {
-                            sp = sp.apply_mark(cx.current_expansion.mark);
-                            let token = TokenTree::Token(sp, Token::Interpolated(nt.clone()));
+                            sp = sp.apply_mark(cx.current_expansion.id);
+                            let token = TokenTree::token(token::Interpolated(nt.clone()), sp);
                             result.push(token.into());
                         }
                     } else {
@@ -236,10 +233,10 @@ pub fn transcribe(
                     // If we aren't able to match the meta-var, we push it back into the result but
                     // with modified syntax context. (I believe this supports nested macros).
                     let ident =
-                        Ident::new(ident.name, ident.span.apply_mark(cx.current_expansion.mark));
-                    sp = sp.apply_mark(cx.current_expansion.mark);
-                    result.push(TokenTree::Token(sp, token::Dollar).into());
-                    result.push(TokenTree::Token(sp, token::Token::from_ast_ident(ident)).into());
+                        Ident::new(ident.name, ident.span.apply_mark(cx.current_expansion.id));
+                    sp = sp.apply_mark(cx.current_expansion.id);
+                    result.push(TokenTree::token(token::Dollar, sp).into());
+                    result.push(TokenTree::Token(Token::from_ast_ident(ident)).into());
                 }
             }
 
@@ -249,16 +246,16 @@ pub fn transcribe(
             // jump back out of the Delimited, pop the result_stack and add the new results back to
             // the previous results (from outside the Delimited).
             quoted::TokenTree::Delimited(mut span, delimited) => {
-                span = span.apply_mark(cx.current_expansion.mark);
-                stack.push(Frame::Delimited { forest: delimited, idx: 0, span: span });
-                result_stack.push(mem::replace(&mut result, Vec::new()));
+                span = span.apply_mark(cx.current_expansion.id);
+                stack.push(Frame::Delimited { forest: delimited, idx: 0, span });
+                result_stack.push(mem::take(&mut result));
             }
 
             // Nothing much to do here. Just push the token to the result, being careful to
             // preserve syntax context.
-            quoted::TokenTree::Token(sp, tok) => {
-                let mut marker = Marker(cx.current_expansion.mark);
-                let mut tt = TokenTree::Token(sp, tok);
+            quoted::TokenTree::Token(token) => {
+                let mut marker = Marker(cx.current_expansion.id);
+                let mut tt = TokenTree::Token(token);
                 noop_visit_tt(&mut tt, &mut marker);
                 result.push(tt.into());
             }
@@ -275,18 +272,17 @@ pub fn transcribe(
 /// See the definition of `repeats` in the `transcribe` function. `repeats` is used to descend
 /// into the right place in nested matchers. If we attempt to descend too far, the macro writer has
 /// made a mistake, and we return `None`.
-fn lookup_cur_matched(
+fn lookup_cur_matched<'a>(
     ident: Ident,
-    interpolations: &FxHashMap<Ident, Rc<NamedMatch>>,
+    interpolations: &'a FxHashMap<Ident, NamedMatch>,
     repeats: &[(usize, usize)],
-) -> Option<Rc<NamedMatch>> {
+) -> Option<&'a NamedMatch> {
     interpolations.get(&ident).map(|matched| {
-        let mut matched = matched.clone();
+        let mut matched = matched;
         for &(idx, _) in repeats {
-            let m = matched.clone();
-            match *m {
+            match matched {
                 MatchedNonterminal(_) => break,
-                MatchedSeq(ref ads, _) => matched = Rc::new(ads[idx].clone()),
+                MatchedSeq(ref ads, _) => matched = ads.get(idx).unwrap(),
             }
         }
 
@@ -327,8 +323,7 @@ impl LockstepIterSize {
                 LockstepIterSize::Constraint(r_len, _) if l_len == r_len => self,
                 LockstepIterSize::Constraint(r_len, r_id) => {
                     let msg = format!(
-                        "inconsistent lockstep iteration: \
-                         '{}' has {} items, but '{}' has {}",
+                        "meta-variable `{}` repeats {} times, but `{}` repeats {} times",
                         l_id, l_len, r_id, r_len
                     );
                     LockstepIterSize::Contradiction(msg)
@@ -346,7 +341,7 @@ impl LockstepIterSize {
 /// multiple nested matcher sequences.
 fn lockstep_iter_size(
     tree: &quoted::TokenTree,
-    interpolations: &FxHashMap<Ident, Rc<NamedMatch>>,
+    interpolations: &FxHashMap<Ident, NamedMatch>,
     repeats: &[(usize, usize)],
 ) -> LockstepIterSize {
     use quoted::TokenTree;
@@ -363,7 +358,7 @@ fn lockstep_iter_size(
         }
         TokenTree::MetaVar(_, name) | TokenTree::MetaVarDecl(_, name, _) => {
             match lookup_cur_matched(name, interpolations, repeats) {
-                Some(matched) => match *matched {
+                Some(matched) => match matched {
                     MatchedNonterminal(_) => LockstepIterSize::Unconstrained,
                     MatchedSeq(ref ads, _) => LockstepIterSize::Constraint(ads.len(), name),
                 },
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 8a066f3f4a0..bbc3ae28225 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -15,20 +15,23 @@
 use AttributeType::*;
 use AttributeGate::*;
 
-use crate::ast::{self, NodeId, GenericParam, GenericParamKind, PatKind, RangeEnd};
-use crate::attr;
-use crate::early_buffered_lints::BufferedEarlyLintId;
+use crate::ast::{
+    self, AssocTyConstraint, AssocTyConstraintKind, NodeId, GenericParam, GenericParamKind,
+    PatKind, RangeEnd,
+};
+use crate::attr::{self, check_builtin_attribute, AttributeTemplate};
 use crate::source_map::Spanned;
 use crate::edition::{ALL_EDITIONS, Edition};
 use crate::visit::{self, FnKind, Visitor};
 use crate::parse::{token, ParseSess};
-use crate::symbol::{Symbol, keywords, sym};
+use crate::parse::parser::Parser;
+use crate::symbol::{Symbol, sym};
 use crate::tokenstream::TokenTree;
 
-use errors::{DiagnosticBuilder, Handler};
+use errors::{Applicability, DiagnosticBuilder, Handler};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_target::spec::abi::Abi;
-use syntax_pos::{Span, DUMMY_SP};
+use syntax_pos::{Span, DUMMY_SP, MultiSpan};
 use log::debug;
 use lazy_static::lazy_static;
 
@@ -121,6 +124,9 @@ declare_features! (
 
     // no-tracking-issue-start
 
+    // Allows using compiler's own crates.
+    (active, rustc_private, "1.0.0", Some(27812), None),
+
     // Allows using the `rust-intrinsic`'s "ABI".
     (active, intrinsics, "1.0.0", None, None),
 
@@ -194,9 +200,6 @@ declare_features! (
 
     // no-tracking-issue-end
 
-    // Allows using `#[unsafe_destructor_blind_to_params]` (RFC 1238).
-    (active, dropck_parametricity, "1.3.0", Some(28498), None),
-
     // no-tracking-issue-start
 
     // Allows using `#[omit_gdb_pretty_printer_section]`.
@@ -239,9 +242,6 @@ declare_features! (
     // Allows using `#![needs_allocator]`, an implementation detail of `#[global_allocator]`.
     (active, allocator_internals, "1.20.0", None, None),
 
-    // Allows using the `format_args_nl` macro.
-    (active, format_args_nl, "1.29.0", None, None),
-
     // no-tracking-issue-end
 
     // Added for testing E0705; perma-unstable.
@@ -282,12 +282,6 @@ declare_features! (
     // feature-group-start: actual feature gates
     // -------------------------------------------------------------------------
 
-    // Allows using `asm!` macro with which inline assembly can be embedded.
-    (active, asm, "1.0.0", Some(29722), None),
-
-    // Allows using the `concat_idents!` macro with which identifiers can be concatenated.
-    (active, concat_idents, "1.0.0", Some(29599), None),
-
     // Allows using the `#[link_args]` attribute.
     (active, link_args, "1.0.0", Some(29596), None),
 
@@ -303,12 +297,6 @@ declare_features! (
     // Allows using `#[thread_local]` on `static` items.
     (active, thread_local, "1.0.0", Some(29594), None),
 
-    // Allows using the `log_syntax!` macro.
-    (active, log_syntax, "1.0.0", Some(29598), None),
-
-    // Allows using the `trace_macros!` macro.
-    (active, trace_macros, "1.0.0", Some(29598), None),
-
     // Allows the use of SIMD types in functions declared in `extern` blocks.
     (active, simd_ffi, "1.0.0", Some(27731), None),
 
@@ -319,7 +307,7 @@ declare_features! (
     (active, nll, "1.0.0", Some(43234), None),
 
     // Allows using slice patterns.
-    (active, slice_patterns, "1.0.0", Some(23121), None),
+    (active, slice_patterns, "1.0.0", Some(62254), None),
 
     // Allows the definition of `const` functions with some advanced features.
     (active, const_fn, "1.2.0", Some(57563), None),
@@ -398,9 +386,6 @@ declare_features! (
     // Allows `extern "x86-interrupt" fn()`.
     (active, abi_x86_interrupt, "1.17.0", Some(40180), None),
 
-    // Allows module-level inline assembly by way of `global_asm!()`.
-    (active, global_asm, "1.18.0", Some(35119), None),
-
     // Allows overlapping impls of marker traits.
     (active, overlapping_marker_traits, "1.18.0", Some(29864), None),
 
@@ -467,9 +452,6 @@ declare_features! (
     // Allows `#[doc(alias = "...")]`.
     (active, doc_alias, "1.27.0", Some(50146), None),
 
-    // Allows defining `existential type`s.
-    (active, existential_type, "1.28.0", Some(34511), None),
-
     // Allows inconsistent bounds in where clauses.
     (active, trivial_bounds, "1.28.0", Some(48214), None),
 
@@ -482,10 +464,6 @@ declare_features! (
     // Allows async and await syntax.
     (active, async_await, "1.28.0", Some(50547), None),
 
-    // Allows await! macro-like syntax.
-    // This will likely be removed prior to stabilization of async/await.
-    (active, await_macro, "1.28.0", Some(50547), None),
-
     // Allows reinterpretation of the bits of a value of one type as another type during const eval.
     (active, const_transmute, "1.29.0", Some(53605), None),
 
@@ -521,17 +499,11 @@ declare_features! (
     (active, bind_by_move_pattern_guards, "1.30.0", Some(15287), None),
 
     // Allows `impl Trait` in bindings (`let`, `const`, `static`).
-    (active, impl_trait_in_bindings, "1.30.0", Some(34511), None),
-
-    // Allows `const _: TYPE = VALUE`.
-    (active, underscore_const_names, "1.31.0", Some(54912), None),
+    (active, impl_trait_in_bindings, "1.30.0", Some(63065), None),
 
     // Allows using `reason` in lint attributes and the `#[expect(lint)]` lint check.
     (active, lint_reasons, "1.31.0", Some(54503), None),
 
-    // Allows paths to enum variants on type aliases.
-    (active, type_alias_enum_variants, "1.31.0", Some(49683), None),
-
     // Allows exhaustive integer pattern matching on `usize` and `isize`.
     (active, precise_pointer_size_matching, "1.32.0", Some(56354), None),
 
@@ -548,24 +520,62 @@ declare_features! (
     // Allows using `#[optimize(X)]`.
     (active, optimize_attribute, "1.34.0", Some(54882), None),
 
-    // Allows using `#[repr(align(X))]` on enums.
-    (active, repr_align_enum, "1.34.0", Some(57996), None),
-
     // Allows using C-variadics.
     (active, c_variadic, "1.34.0", Some(44930), None),
 
+    // Allows the user of associated type bounds.
+    (active, associated_type_bounds, "1.34.0", Some(52662), None),
+
+    // Attributes on formal function params.
+    (active, param_attrs, "1.36.0", Some(60406), None),
+
+    // Allows calling constructor functions in `const fn`.
+    (active, const_constructor, "1.37.0", Some(61456), None),
+
+    // Allows `if/while p && let q = r && ...` chains.
+    (active, let_chains, "1.37.0", Some(53667), None),
+
+    // Allows #[repr(transparent)] on enums (RFC 2645).
+    (active, transparent_enums, "1.37.0", Some(60405), None),
+
+    // Allows #[repr(transparent)] on unions (RFC 2645).
+    (active, transparent_unions, "1.37.0", Some(60405), None),
+
+    // Allows explicit discriminants on non-unit enum variants.
+    (active, arbitrary_enum_discriminant, "1.37.0", Some(60553), None),
+
+    // Allows `impl Trait` with multiple unrelated lifetimes.
+    (active, member_constraints, "1.37.0", Some(61977), None),
+
+    // Allows `async || body` closures.
+    (active, async_closure, "1.37.0", Some(62290), None),
+
+    // Allows the use of `#[cfg(doctest)]`, set when rustdoc is collecting doctests
+    (active, cfg_doctest, "1.37.0", Some(62210), None),
+
+    // Allows `[x; N]` where `x` is a constant (RFC 2203).
+    (active, const_in_array_repeat_expressions, "1.37.0", Some(49147), None),
+
+    // Allows `impl Trait` to be used inside type aliases (RFC 2515).
+    (active, type_alias_impl_trait, "1.38.0", Some(63063), None),
+
+    // Allows the use of or-patterns, e.g. `0 | 1`.
+    (active, or_patterns, "1.38.0", Some(54883), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------
 );
 
-// Some features are known to be incomplete and using them is likely to have
-// unanticipated results, such as compiler crashes. We warn the user about these
-// to alert them.
-const INCOMPLETE_FEATURES: &[Symbol] = &[
+/// Some features are known to be incomplete and using them is likely to have
+/// unanticipated results, such as compiler crashes. We warn the user about these
+/// to alert them.
+pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::impl_trait_in_bindings,
     sym::generic_associated_types,
-    sym::const_generics
+    sym::const_generics,
+    sym::or_patterns,
+    sym::let_chains,
 ];
 
 declare_features! (
@@ -590,7 +600,7 @@ declare_features! (
     (removed, allocator, "1.0.0", None, None, None),
     (removed, simd, "1.0.0", Some(27731), None,
      Some("removed in favor of `#[repr(simd)]`")),
-    (removed, advanced_slice_patterns, "1.0.0", Some(23121), None,
+    (removed, advanced_slice_patterns, "1.0.0", Some(62254), None,
      Some("merged into `#![feature(slice_patterns)]`")),
     (removed, macro_reexport, "1.0.0", Some(29638), None,
      Some("subsumed by `pub use`")),
@@ -614,6 +624,13 @@ declare_features! (
     (removed, extern_in_paths, "1.33.0", Some(55600), None,
      Some("subsumed by `::foo::bar` paths")),
     (removed, quote, "1.33.0", Some(29601), None, None),
+    // Allows using `#[unsafe_destructor_blind_to_params]` (RFC 1238).
+    (removed, dropck_parametricity, "1.38.0", Some(28498), None, None),
+    (removed, await_macro, "1.38.0", Some(50547), None,
+     Some("subsumed by `.await` syntax")),
+    // Allows defining `existential type`s.
+    (removed, existential_type, "1.38.0", Some(63063), None,
+     Some("removed in favor of `#![feature(type_alias_impl_trait)]`")),
 
     // -------------------------------------------------------------------------
     // feature-group-end: removed features
@@ -833,6 +850,13 @@ declare_features! (
     (accepted, extern_crate_self, "1.34.0", Some(56409), None),
     // Allows arbitrary delimited token streams in non-macro attributes.
     (accepted, unrestricted_attribute_tokens, "1.34.0", Some(55208), None),
+    // Allows paths to enum variants on type aliases including `Self`.
+    (accepted, type_alias_enum_variants, "1.37.0", Some(49683), None),
+    // Allows using `#[repr(align(X))]` on enums with equivalent semantics
+    // to wrapping an enum in a wrapper struct with `#[repr(align(X))]`.
+    (accepted, repr_align_enum, "1.37.0", Some(57996), None),
+    // Allows `const _: TYPE = VALUE`.
+    (accepted, underscore_const_names, "1.37.0", Some(54912), None),
 
     // -------------------------------------------------------------------------
     // feature-group-end: accepted features
@@ -867,27 +891,6 @@ pub enum AttributeGate {
     Ungated,
 }
 
-/// A template that the attribute input must match.
-/// Only top-level shape (`#[attr]` vs `#[attr(...)]` vs `#[attr = ...]`) is considered now.
-#[derive(Clone, Copy)]
-pub struct AttributeTemplate {
-    word: bool,
-    list: Option<&'static str>,
-    name_value_str: Option<&'static str>,
-}
-
-impl AttributeTemplate {
-    /// Checks that the given meta-item is compatible with this template.
-    fn compatible(&self, meta_item_kind: &ast::MetaItemKind) -> bool {
-        match meta_item_kind {
-            ast::MetaItemKind::Word => self.word,
-            ast::MetaItemKind::List(..) => self.list.is_some(),
-            ast::MetaItemKind::NameValue(lit) if lit.node.is_str() => self.name_value_str.is_some(),
-            ast::MetaItemKind::NameValue(..) => false,
-        }
-    }
-}
-
 /// A convenience macro for constructing attribute templates.
 /// E.g., `template!(Word, List: "description")` means that the attribute
 /// supports forms `#[attr]` and `#[attr(description)]`.
@@ -998,7 +1001,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     (sym::repr, Normal, template!(List: "C, packed, ..."), Ungated),
     (sym::path, Normal, template!(NameValueStr: "file"), Ungated),
     (sym::automatically_derived, Normal, template!(Word), Ungated),
-    (sym::no_mangle, Normal, template!(Word), Ungated),
+    (sym::no_mangle, Whitelisted, template!(Word), Ungated),
     (sym::no_link, Normal, template!(Word), Ungated),
     (sym::derive, Normal, template!(List: "Trait1, Trait2, ..."), Ungated),
     (
@@ -1078,7 +1081,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
                                             "the `#[rustc_const_unstable]` attribute \
                                             is an internal feature",
                                             cfg_fn!(rustc_const_unstable))),
-    (sym::global_allocator, Normal, template!(Word), Ungated),
     (sym::default_lib_allocator, Whitelisted, template!(Word), Gated(Stability::Unstable,
                                             sym::allocator_internals,
                                             "the `#[default_lib_allocator]` \
@@ -1134,6 +1136,13 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
             is just used to enable niche optimizations in libcore \
             and will never be stable",
         cfg_fn!(rustc_attrs))),
+    (sym::rustc_nonnull_optimization_guaranteed, Whitelisted, template!(Word),
+    Gated(Stability::Unstable,
+        sym::rustc_attrs,
+        "the `#[rustc_nonnull_optimization_guaranteed]` attribute \
+            is just used to enable niche optimizations in libcore \
+            and will never be stable",
+        cfg_fn!(rustc_attrs))),
     (sym::rustc_regions, Normal, template!(Word), Gated(Stability::Unstable,
                                     sym::rustc_attrs,
                                     "the `#[rustc_regions]` attribute \
@@ -1258,12 +1267,26 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
                                                     attribute is just used for rustc unit \
                                                     tests and will never be stable",
                                                     cfg_fn!(rustc_attrs))),
+    (sym::rustc_dump_env_program_clauses, Whitelisted, template!(Word), Gated(Stability::Unstable,
+                                                    sym::rustc_attrs,
+                                                    "the `#[rustc_dump_env_program_clauses]` \
+                                                    attribute is just used for rustc unit \
+                                                    tests and will never be stable",
+                                                    cfg_fn!(rustc_attrs))),
+    (sym::rustc_object_lifetime_default, Whitelisted, template!(Word), Gated(Stability::Unstable,
+                                                    sym::rustc_attrs,
+                                                    "the `#[rustc_object_lifetime_default]` \
+                                                    attribute is just used for rustc unit \
+                                                    tests and will never be stable",
+                                                    cfg_fn!(rustc_attrs))),
     (sym::rustc_test_marker, Normal, template!(Word), Gated(Stability::Unstable,
                                     sym::rustc_attrs,
                                     "the `#[rustc_test_marker]` attribute \
                                     is used internally to track tests",
                                     cfg_fn!(rustc_attrs))),
-    (sym::rustc_transparent_macro, Whitelisted, template!(Word), Gated(Stability::Unstable,
+    (sym::rustc_macro_transparency, Whitelisted, template!(NameValueStr:
+                                                           "transparent|semitransparent|opaque"),
+                                                Gated(Stability::Unstable,
                                                 sym::rustc_attrs,
                                                 "used internally for testing macro hygiene",
                                                     cfg_fn!(rustc_attrs))),
@@ -1309,11 +1332,36 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
                                                 /*opt*/ attributes(name1, name2, ...)"),
                                     Ungated),
 
-    (sym::rustc_copy_clone_marker, Whitelisted, template!(Word), Gated(Stability::Unstable,
+    (sym::rustc_allocator, Whitelisted, template!(Word), Gated(Stability::Unstable,
+                                                sym::rustc_attrs,
+                                                "internal implementation detail",
+                                                cfg_fn!(rustc_attrs))),
+
+    (sym::rustc_allocator_nounwind, Whitelisted, template!(Word), Gated(Stability::Unstable,
+                                                sym::rustc_attrs,
+                                                "internal implementation detail",
+                                                cfg_fn!(rustc_attrs))),
+
+    (sym::rustc_builtin_macro, Whitelisted, template!(Word), Gated(Stability::Unstable,
+                                                sym::rustc_attrs,
+                                                "internal implementation detail",
+                                                cfg_fn!(rustc_attrs))),
+
+    (sym::rustc_promotable, Whitelisted, template!(Word), Gated(Stability::Unstable,
                                                 sym::rustc_attrs,
                                                 "internal implementation detail",
                                                 cfg_fn!(rustc_attrs))),
 
+    (sym::rustc_allow_const_fn_ptr, Whitelisted, template!(Word), Gated(Stability::Unstable,
+                                                sym::rustc_attrs,
+                                                "internal implementation detail",
+                                                cfg_fn!(rustc_attrs))),
+
+    (sym::rustc_dummy, Normal, template!(Word /* doesn't matter*/), Gated(Stability::Unstable,
+                                         sym::rustc_attrs,
+                                         "used by the test suite",
+                                         cfg_fn!(rustc_attrs))),
+
     // FIXME: #14408 whitelist docs since rustdoc looks at them
     (
         sym::doc,
@@ -1362,25 +1410,16 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
             cfg_fn!(omit_gdb_pretty_printer_section)
         )
     ),
-    (sym::unsafe_destructor_blind_to_params,
-    Normal,
-    template!(Word),
-    Gated(Stability::Deprecated("https://github.com/rust-lang/rust/issues/34761",
-                                Some("replace this attribute with `#[may_dangle]`")),
-        sym::dropck_parametricity,
-        "unsafe_destructor_blind_to_params has been replaced by \
-            may_dangle and will be removed in the future",
-        cfg_fn!(dropck_parametricity))),
     (sym::may_dangle,
     Normal,
     template!(Word),
     Gated(Stability::Unstable,
         sym::dropck_eyepatch,
-        "may_dangle has unstable semantics and may be removed in the future",
+        "`may_dangle` has unstable semantics and may be removed in the future",
         cfg_fn!(dropck_eyepatch))),
     (sym::unwind, Whitelisted, template!(List: "allowed|aborts"), Gated(Stability::Unstable,
                                 sym::unwind_attributes,
-                                "#[unwind] is experimental",
+                                "`#[unwind]` is experimental",
                                 cfg_fn!(unwind_attributes))),
     (sym::used, Whitelisted, template!(Word), Ungated),
 
@@ -1415,7 +1454,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         Normal,
         template!(
             Word,
-            List: r#"/*opt*/ since = "version", /*opt*/ note = "reason"#,
+            List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
             NameValueStr: "reason"
         ),
         Ungated
@@ -1466,13 +1505,13 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 
     (sym::alloc_error_handler, Normal, template!(Word), Gated(Stability::Unstable,
                         sym::alloc_error_handler,
-                        "#[alloc_error_handler] is an unstable feature",
+                        "`#[alloc_error_handler]` is an unstable feature",
                         cfg_fn!(alloc_error_handler))),
 
     // RFC 2412
     (sym::optimize, Whitelisted, template!(List: "size|speed"), Gated(Stability::Unstable,
                             sym::optimize_attribute,
-                            "#[optimize] attribute is an unstable feature",
+                            "`#[optimize]` attribute is an unstable feature",
                             cfg_fn!(optimize_attribute))),
 
     // Crate level attributes
@@ -1486,7 +1525,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     (sym::type_length_limit, CrateLevel, template!(NameValueStr: "N"), Ungated),
     (sym::test_runner, CrateLevel, template!(List: "path"), Gated(Stability::Unstable,
                     sym::custom_test_frameworks,
-                    EXPLAIN_CUSTOM_TEST_FRAMEWORKS,
+                    "custom test frameworks are an unstable feature",
                     cfg_fn!(custom_test_frameworks))),
 ];
 
@@ -1510,6 +1549,7 @@ const GATED_CFGS: &[(Symbol, Symbol, fn(&Features) -> bool)] = &[
     (sym::target_thread_local, sym::cfg_target_thread_local, cfg_fn!(cfg_target_thread_local)),
     (sym::target_has_atomic, sym::cfg_target_has_atomic, cfg_fn!(cfg_target_has_atomic)),
     (sym::rustdoc, sym::doc_cfg, cfg_fn!(doc_cfg)),
+    (sym::doctest, sym::cfg_doctest, cfg_fn!(cfg_doctest)),
 ];
 
 #[derive(Debug)]
@@ -1588,13 +1628,21 @@ impl<'a> Context<'a> {
                 if let Some(content) = attr.meta_item_list() {
                     if content.iter().any(|c| c.check_name(sym::include)) {
                         gate_feature!(self, external_doc, attr.span,
-                            "#[doc(include = \"...\")] is experimental"
+                            "`#[doc(include = \"...\")]` is experimental"
                         );
                     }
                 }
             }
             debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
             return;
+        } else {
+            for segment in &attr.path.segments {
+                if segment.ident.as_str().starts_with("rustc") {
+                    let msg = "attributes starting with `rustc` are \
+                               reserved for use by the `rustc` compiler";
+                    gate_feature!(self, rustc_attrs, segment.ident.span, msg);
+                }
+            }
         }
         for &(n, ty) in self.plugin_attributes {
             if attr.path == n {
@@ -1605,25 +1653,19 @@ impl<'a> Context<'a> {
                 return;
             }
         }
-        if !attr::is_known(attr) {
-            if attr.name_or_empty().as_str().starts_with("rustc_") {
-                let msg = "unless otherwise specified, attributes with the prefix `rustc_` \
-                           are reserved for internal compiler diagnostics";
-                gate_feature!(self, rustc_attrs, attr.span, msg);
-            } else if !is_macro {
-                // Only run the custom attribute lint during regular feature gate
-                // checking. Macro gating runs before the plugin attributes are
-                // registered, so we skip this in that case.
-                let msg = format!("The attribute `{}` is currently unknown to the compiler and \
-                                   may have meaning added to it in the future", attr.path);
-                gate_feature!(self, custom_attribute, attr.span, &msg);
-            }
+        if !is_macro && !attr::is_known(attr) {
+            // Only run the custom attribute lint during regular feature gate
+            // checking. Macro gating runs before the plugin attributes are
+            // registered, so we skip this in that case.
+            let msg = format!("the attribute `{}` is currently unknown to the compiler and \
+                               may have meaning added to it in the future", attr.path);
+            gate_feature!(self, custom_attribute, attr.span, &msg);
         }
     }
 }
 
 pub fn check_attribute(attr: &ast::Attribute, parse_sess: &ParseSess, features: &Features) {
-    let cx = Context { features: features, parse_sess: parse_sess, plugin_attributes: &[] };
+    let cx = Context { features, parse_sess, plugin_attributes: &[] };
     cx.check_attribute(
         attr,
         attr.ident().and_then(|ident| BUILTIN_ATTRIBUTE_MAP.get(&ident.name).map(|a| *a)),
@@ -1671,20 +1713,20 @@ pub fn emit_feature_err(
     feature_err(sess, feature, span, issue, explain).emit();
 }
 
-pub fn feature_err<'a>(
+pub fn feature_err<'a, S: Into<MultiSpan>>(
     sess: &'a ParseSess,
     feature: Symbol,
-    span: Span,
+    span: S,
     issue: GateIssue,
     explain: &str,
 ) -> DiagnosticBuilder<'a> {
     leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
 }
 
-fn leveled_feature_err<'a>(
+fn leveled_feature_err<'a, S: Into<MultiSpan>>(
     sess: &'a ParseSess,
     feature: Symbol,
-    span: Span,
+    span: S,
     issue: GateIssue,
     explain: &str,
     level: GateStrength,
@@ -1715,7 +1757,7 @@ fn leveled_feature_err<'a>(
 
     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
     if sess.unstable_features.is_nightly_build() {
-        err.help(&format!("add #![feature({})] to the crate attributes to enable", feature));
+        err.help(&format!("add `#![feature({})]` to the crate attributes to enable", feature));
     }
 
     // If we're on stable and only emitting a "soft" warning, add a note to
@@ -1735,26 +1777,6 @@ const EXPLAIN_BOX_SYNTAX: &str =
 pub const EXPLAIN_STMT_ATTR_SYNTAX: &str =
     "attributes on expressions are experimental";
 
-pub const EXPLAIN_ASM: &str =
-    "inline assembly is not stable enough for use and is subject to change";
-
-pub const EXPLAIN_GLOBAL_ASM: &str =
-    "`global_asm!` is not stable enough for use and is subject to change";
-
-pub const EXPLAIN_CUSTOM_TEST_FRAMEWORKS: &str =
-    "custom test frameworks are an unstable feature";
-
-pub const EXPLAIN_LOG_SYNTAX: &str =
-    "`log_syntax!` is not stable enough for use and is subject to change";
-
-pub const EXPLAIN_CONCAT_IDENTS: &str =
-    "`concat_idents` is not stable enough for use and is subject to change";
-
-pub const EXPLAIN_FORMAT_ARGS_NL: &str =
-    "`format_args_nl` is only for internal language use and is subject to change";
-
-pub const EXPLAIN_TRACE_MACROS: &str =
-    "`trace_macros` is not stable enough for use and is subject to change";
 pub const EXPLAIN_ALLOW_INTERNAL_UNSTABLE: &str =
     "allow_internal_unstable side-steps feature gating and stability checks";
 pub const EXPLAIN_ALLOW_INTERNAL_UNSAFE: &str =
@@ -1838,52 +1860,6 @@ impl<'a> PostExpansionVisitor<'a> {
             Abi::System => {}
         }
     }
-
-    fn check_builtin_attribute(&mut self, attr: &ast::Attribute, name: Symbol,
-                               template: AttributeTemplate) {
-        // Some special attributes like `cfg` must be checked
-        // before the generic check, so we skip them here.
-        let should_skip = |name| name == sym::cfg;
-        // Some of previously accepted forms were used in practice,
-        // report them as warnings for now.
-        let should_warn = |name| name == sym::doc || name == sym::ignore ||
-                                 name == sym::inline || name == sym::link;
-
-        match attr.parse_meta(self.context.parse_sess) {
-            Ok(meta) => if !should_skip(name) && !template.compatible(&meta.node) {
-                let mut msg = "attribute must be of the form ".to_owned();
-                let mut first = true;
-                if template.word {
-                    first = false;
-                    msg.push_str(&format!("`#[{}{}]`", name, ""));
-                }
-                if let Some(descr) = template.list {
-                    if !first {
-                        msg.push_str(" or ");
-                    }
-                    first = false;
-                    msg.push_str(&format!("`#[{}({})]`", name, descr));
-                }
-                if let Some(descr) = template.name_value_str {
-                    if !first {
-                        msg.push_str(" or ");
-                    }
-                    msg.push_str(&format!("`#[{} = \"{}\"]`", name, descr));
-                }
-                if should_warn(name) {
-                    self.context.parse_sess.buffer_lint(
-                        BufferedEarlyLintId::IllFormedAttributeInput,
-                        meta.span,
-                        ast::CRATE_NODE_ID,
-                        &msg,
-                    );
-                } else {
-                    self.context.parse_sess.span_diagnostic.span_err(meta.span, &msg);
-                }
-            }
-            Err(mut err) => err.emit(),
-        }
-    }
 }
 
 impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
@@ -1892,44 +1868,44 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             self.builtin_attributes.get(&ident.name).map(|a| *a)
         });
 
-        // check for gated attributes
+        // Check for gated attributes.
         self.context.check_attribute(attr, attr_info, false);
 
         if attr.check_name(sym::doc) {
             if let Some(content) = attr.meta_item_list() {
                 if content.len() == 1 && content[0].check_name(sym::cfg) {
                     gate_feature_post!(&self, doc_cfg, attr.span,
-                        "#[doc(cfg(...))] is experimental"
+                        "`#[doc(cfg(...))]` is experimental"
                     );
                 } else if content.iter().any(|c| c.check_name(sym::masked)) {
                     gate_feature_post!(&self, doc_masked, attr.span,
-                        "#[doc(masked)] is experimental"
+                        "`#[doc(masked)]` is experimental"
                     );
                 } else if content.iter().any(|c| c.check_name(sym::spotlight)) {
                     gate_feature_post!(&self, doc_spotlight, attr.span,
-                        "#[doc(spotlight)] is experimental"
+                        "`#[doc(spotlight)]` is experimental"
                     );
                 } else if content.iter().any(|c| c.check_name(sym::alias)) {
                     gate_feature_post!(&self, doc_alias, attr.span,
-                        "#[doc(alias = \"...\")] is experimental"
+                        "`#[doc(alias = \"...\")]` is experimental"
                     );
                 } else if content.iter().any(|c| c.check_name(sym::keyword)) {
                     gate_feature_post!(&self, doc_keyword, attr.span,
-                        "#[doc(keyword = \"...\")] is experimental"
+                        "`#[doc(keyword = \"...\")]` is experimental"
                     );
                 }
             }
         }
 
         match attr_info {
-            Some(&(name, _, template, _)) => self.check_builtin_attribute(
-                attr,
-                name,
-                template
-            ),
-            None => if let Some(TokenTree::Token(_, token::Eq)) = attr.tokens.trees().next() {
-                // All key-value attributes are restricted to meta-item syntax.
-                attr.parse_meta(self.context.parse_sess).map_err(|mut err| err.emit()).ok();
+            // `rustc_dummy` doesn't have any restrictions specific to built-in attributes.
+            Some(&(name, _, template, _)) if name != sym::rustc_dummy =>
+                check_builtin_attribute(self.context.parse_sess, attr, name, template),
+            _ => if let Some(TokenTree::Token(token)) = attr.tokens.trees().next() {
+                if token == token::Eq {
+                    // All key-value attributes are restricted to meta-item syntax.
+                    attr.parse_meta(self.context.parse_sess).map_err(|mut err| err.emit()).ok();
+                }
             }
         }
     }
@@ -1947,13 +1923,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 
     fn visit_item(&mut self, i: &'a ast::Item) {
         match i.node {
-            ast::ItemKind::Const(_,_) => {
-                if i.ident.name == keywords::Underscore.name() {
-                    gate_feature_post!(&self, underscore_const_names, i.span,
-                                        "naming constants with `_` is unstable");
-                }
-            }
-
             ast::ItemKind::ForeignMod(ref foreign_module) => {
                 self.check_abi(foreign_module.abi, i.span);
             }
@@ -1965,13 +1934,13 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
                 if attr::contains_name(&i.attrs[..], sym::start) {
                     gate_feature_post!(&self, start, i.span,
-                                      "a #[start] function is an experimental \
+                                      "a `#[start]` function is an experimental \
                                        feature whose signature may change \
                                        over time");
                 }
                 if attr::contains_name(&i.attrs[..], sym::main) {
                     gate_feature_post!(&self, main, i.span,
-                                       "declaration of a nonstandard #[main] \
+                                       "declaration of a non-standard `#[main]` \
                                         function may change over time, for now \
                                         a top-level `fn main()` is required");
                 }
@@ -1988,15 +1957,27 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
 
-            ast::ItemKind::Enum(..) => {
-                for attr in attr::filter_by_name(&i.attrs[..], sym::repr) {
-                    for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
-                        if item.check_name(sym::align) {
-                            gate_feature_post!(&self, repr_align_enum, attr.span,
-                                               "`#[repr(align(x))]` on enums is experimental");
-                        }
+            ast::ItemKind::Enum(ast::EnumDef{ref variants, ..}, ..) => {
+                for variant in variants {
+                    match (&variant.data, &variant.disr_expr) {
+                        (ast::VariantData::Unit(..), _) => {},
+                        (_, Some(disr_expr)) =>
+                            gate_feature_post!(
+                                &self,
+                                arbitrary_enum_discriminant,
+                                disr_expr.value.span,
+                                "discriminants on non-unit variants are experimental"),
+                        _ => {},
                     }
                 }
+
+                let has_feature = self.context.features.arbitrary_enum_discriminant;
+                if !has_feature && !i.span.allows_unstable(sym::arbitrary_enum_discriminant) {
+                    Parser::maybe_report_invalid_custom_discriminants(
+                        self.context.parse_sess,
+                        &variants,
+                    );
+                }
             }
 
             ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
@@ -2034,12 +2015,12 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 gate_feature_post!(&self, decl_macro, i.span, msg);
             }
 
-            ast::ItemKind::Existential(..) => {
+            ast::ItemKind::OpaqueTy(..) => {
                 gate_feature_post!(
                     &self,
-                    existential_type,
+                    type_alias_impl_trait,
                     i.span,
-                    "existential types are unstable"
+                    "`impl Trait` in type aliases is unstable"
                 );
             }
 
@@ -2090,7 +2071,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
     fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
         if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
             if let ast::TyKind::Never = output_ty.node {
-                // Do nothing
+                // Do nothing.
             } else {
                 self.visit_ty(output_ty)
             }
@@ -2110,14 +2091,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                                        "type ascription is experimental");
                 }
             }
-            ast::ExprKind::ObsoleteInPlace(..) => {
-                // these get a hard error in ast-validation
-            }
-            ast::ExprKind::Yield(..) => {
-                gate_feature_post!(&self, generators,
-                                  e.span,
-                                  "yield syntax is experimental");
-            }
             ast::ExprKind::TryBlock(_) => {
                 gate_feature_post!(&self, try_blocks, e.span, "`try` expression is experimental");
             }
@@ -2127,29 +2100,15 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                                     "labels on blocks are unstable");
                 }
             }
-            ast::ExprKind::Closure(_, ast::IsAsync::Async { .. }, ..) => {
-                gate_feature_post!(&self, async_await, e.span, "async closures are unstable");
-            }
             ast::ExprKind::Async(..) => {
                 gate_feature_post!(&self, async_await, e.span, "async blocks are unstable");
             }
-            ast::ExprKind::Await(origin, _) => {
-                match origin {
-                    ast::AwaitOrigin::FieldLike =>
-                        gate_feature_post!(&self, async_await, e.span, "async/await is unstable"),
-                    ast::AwaitOrigin::MacroLike =>
-                        gate_feature_post!(
-                            &self,
-                            await_macro,
-                            e.span,
-                            "`await!(<expr>)` macro syntax is unstable, and will soon be removed \
-                            in favor of `<expr>.await` syntax."
-                        ),
-                }
+            ast::ExprKind::Await(_) => {
+                gate_feature_post!(&self, async_await, e.span, "async/await is unstable");
             }
             _ => {}
         }
-        visit::walk_expr(self, e);
+        visit::walk_expr(self, e)
     }
 
     fn visit_arm(&mut self, arm: &'a ast::Arm) {
@@ -2157,11 +2116,23 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
     }
 
     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
-        match pattern.node {
-            PatKind::Slice(_, Some(ref subslice), _) => {
-                gate_feature_post!(&self, slice_patterns,
-                                   subslice.span,
-                                   "syntax for subslices in slice patterns is not yet stabilized");
+        match &pattern.node {
+            PatKind::Slice(pats) => {
+                for pat in &*pats {
+                    let span = pat.span;
+                    let inner_pat = match &pat.node {
+                        PatKind::Ident(.., Some(pat)) => pat,
+                        _ => pat,
+                    };
+                    if inner_pat.is_rest() {
+                        gate_feature_post!(
+                            &self,
+                            slice_patterns,
+                            span,
+                            "subslice patterns are unstable"
+                        );
+                    }
+                }
             }
             PatKind::Box(..) => {
                 gate_feature_post!(&self, box_patterns,
@@ -2198,15 +2169,27 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             gate_feature_post!(&self, c_variadic, span, "C-variadic functions are unstable");
         }
 
-        visit::walk_fn(self, fn_kind, fn_decl, span);
+        visit::walk_fn(self, fn_kind, fn_decl, span)
     }
 
     fn visit_generic_param(&mut self, param: &'a GenericParam) {
-        if let GenericParamKind::Const { .. } = param.kind {
-            gate_feature_post!(&self, const_generics, param.ident.span,
-                "const generics are unstable");
+        match param.kind {
+            GenericParamKind::Const { .. } =>
+                gate_feature_post!(&self, const_generics, param.ident.span,
+                    "const generics are unstable"),
+            _ => {}
         }
-        visit::walk_generic_param(self, param);
+        visit::walk_generic_param(self, param)
+    }
+
+    fn visit_assoc_ty_constraint(&mut self, constraint: &'a AssocTyConstraint) {
+        match constraint.kind {
+            AssocTyConstraintKind::Bound { .. } =>
+                gate_feature_post!(&self, associated_type_bounds, constraint.span,
+                    "associated type bounds are unstable"),
+            _ => {}
+        }
+        visit::walk_assoc_ty_constraint(self, constraint)
     }
 
     fn visit_trait_item(&mut self, ti: &'a ast::TraitItem) {
@@ -2244,7 +2227,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             }
             _ => {}
         }
-        visit::walk_trait_item(self, ti);
+        visit::walk_trait_item(self, ti)
     }
 
     fn visit_impl_item(&mut self, ii: &'a ast::ImplItem) {
@@ -2256,15 +2239,15 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 
         match ii.node {
             ast::ImplItemKind::Method(..) => {}
-            ast::ImplItemKind::Existential(..) => {
+            ast::ImplItemKind::OpaqueTy(..) => {
                 gate_feature_post!(
                     &self,
-                    existential_type,
+                    type_alias_impl_trait,
                     ii.span,
-                    "existential types are unstable"
+                    "`impl Trait` in type aliases is unstable"
                 );
             }
-            ast::ImplItemKind::Type(_) => {
+            ast::ImplItemKind::TyAlias(_) => {
                 if !ii.generics.params.is_empty() {
                     gate_feature_post!(&self, generic_associated_types, ii.span,
                                        "generic associated types are unstable");
@@ -2276,7 +2259,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             }
             _ => {}
         }
-        visit::walk_impl_item(self, ii);
+        visit::walk_impl_item(self, ii)
     }
 
     fn visit_vis(&mut self, vis: &'a ast::Visibility) {
@@ -2284,7 +2267,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             gate_feature_post!(&self, crate_visibility_modifier, vis.span,
                                "`crate` visibility modifier is experimental");
         }
-        visit::walk_vis(self, vis);
+        visit::walk_vis(self, vis)
     }
 }
 
@@ -2294,6 +2277,8 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
         let mut err = struct_span_err!(span_handler, span, E0557, "feature has been removed");
         if let Some(reason) = reason {
             err.span_note(span, reason);
+        } else {
+            err.span_label(span, "feature has been removed");
         }
         err.emit();
     }
@@ -2336,15 +2321,6 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
             }
 
             let name = mi.name_or_empty();
-            if INCOMPLETE_FEATURES.iter().any(|f| name == *f) {
-                span_handler.struct_span_warn(
-                    mi.span(),
-                    &format!(
-                        "the feature `{}` is incomplete and may cause the compiler to crash",
-                        name
-                    )
-                ).emit();
-            }
 
             if let Some(edition) = ALL_EDITIONS.iter().find(|e| name == e.feature_name()) {
                 if *edition <= crate_edition {
@@ -2375,12 +2351,24 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
             None => continue,
         };
 
+        let bad_input = |span| {
+            struct_span_err!(span_handler, span, E0556, "malformed `feature` attribute input")
+        };
+
         for mi in list {
             let name = match mi.ident() {
                 Some(ident) if mi.is_word() => ident.name,
-                _ => {
-                    span_err!(span_handler, mi.span(), E0556,
-                            "malformed feature, expected just one word");
+                Some(ident) => {
+                    bad_input(mi.span()).span_suggestion(
+                        mi.span(),
+                        "expected just one word",
+                        format!("{}", ident.name),
+                        Applicability::MaybeIncorrect,
+                    ).emit();
+                    continue
+                }
+                None => {
+                    bad_input(mi.span()).span_label(mi.span(), "expected just one word").emit();
                     continue
                 }
             };
@@ -2448,6 +2436,19 @@ pub fn check_crate(krate: &ast::Crate,
         parse_sess: sess,
         plugin_attributes,
     };
+
+    macro_rules! gate_all {
+        ($spans:ident, $gate:ident, $msg:literal) => {
+            for span in &*sess.$spans.borrow() { gate_feature!(&ctx, $gate, *span, $msg); }
+        }
+    }
+
+    gate_all!(param_attr_spans, param_attrs, "attributes on function parameters are unstable");
+    gate_all!(let_chains_spans, let_chains, "`let` expressions in this position are experimental");
+    gate_all!(async_closure_spans, async_closure, "async closures are unstable");
+    gate_all!(yield_spans, generators, "yield syntax is experimental");
+    gate_all!(or_pattern_spans, or_patterns, "or-patterns syntax is experimental");
+
     let visitor = &mut PostExpansionVisitor {
         context: &ctx,
         builtin_attributes: &*BUILTIN_ATTRIBUTE_MAP,
@@ -2501,7 +2502,7 @@ fn maybe_stage_features(span_handler: &Handler, krate: &ast::Crate,
             if attr.check_name(sym::feature) {
                 let release_channel = option_env!("CFG_RELEASE_CHANNEL").unwrap_or("(unknown)");
                 span_err!(span_handler, attr.span, E0554,
-                          "#![feature] may not be used on the {} release channel",
+                          "`#![feature]` may not be used on the {} release channel",
                           release_channel);
             }
         }
diff --git a/src/libsyntax/json.rs b/src/libsyntax/json.rs
index 2dd2ecb7493..83c9c692bd3 100644
--- a/src/libsyntax/json.rs
+++ b/src/libsyntax/json.rs
@@ -92,8 +92,8 @@ impl Emitter for JsonEmitter {
         }
     }
 
-    fn emit_artifact_notification(&mut self, path: &Path) {
-        let data = ArtifactNotification { artifact: path };
+    fn emit_artifact_notification(&mut self, path: &Path, artifact_type: &str) {
+        let data = ArtifactNotification { artifact: path, emit: artifact_type };
         let result = if self.pretty {
             writeln!(&mut self.dst, "{}", as_pretty_json(&data))
         } else {
@@ -122,7 +122,6 @@ struct Diagnostic {
 }
 
 #[derive(RustcEncodable)]
-#[allow(unused_attributes)]
 struct DiagnosticSpan {
     file_name: String,
     byte_start: u32,
@@ -170,7 +169,7 @@ struct DiagnosticSpanMacroExpansion {
     macro_decl_name: String,
 
     /// span where macro was defined (if known)
-    def_site_span: Option<DiagnosticSpan>,
+    def_site_span: DiagnosticSpan,
 }
 
 #[derive(RustcEncodable)]
@@ -185,6 +184,8 @@ struct DiagnosticCode {
 struct ArtifactNotification<'a> {
     /// The path of the artifact.
     artifact: &'a Path,
+    /// What kind of artifact we're emitting.
+    emit: &'a str,
 }
 
 impl Diagnostic {
@@ -298,14 +299,13 @@ impl DiagnosticSpan {
                                      None,
                                      backtrace,
                                      je);
-            let def_site_span = bt.def_site_span.map(|sp| {
-                Self::from_span_full(sp,
+            let def_site_span =
+                Self::from_span_full(bt.def_site_span,
                                      false,
                                      None,
                                      None,
                                      vec![].into_iter(),
-                                     je)
-            });
+                                     je);
             Box::new(DiagnosticSpanMacroExpansion {
                 span: call_site,
                 macro_decl_name: bt.macro_decl_name,
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index db10ab7af5a..8ac48d8d74a 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -7,33 +7,42 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/",
        test(attr(deny(warnings))))]
 
-#![deny(rust_2018_idioms)]
-#![deny(internal)]
-
+#![feature(bind_by_move_pattern_guards)]
+#![feature(box_syntax)]
+#![feature(const_fn)]
+#![feature(const_transmute)]
 #![feature(crate_visibility_modifier)]
 #![feature(label_break_value)]
+#![feature(mem_take)]
 #![feature(nll)]
-#![feature(rustc_attrs)]
+#![feature(proc_macro_diagnostic)]
+#![feature(proc_macro_internals)]
+#![feature(proc_macro_span)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(step_trait)]
 #![feature(try_trait)]
 #![feature(unicode_internals)]
 
 #![recursion_limit="256"]
 
-#[allow(unused_extern_crates)]
-extern crate serialize as rustc_serialize; // used by deriving
+extern crate proc_macro;
 
 pub use errors;
 use rustc_data_structures::sync::Lock;
 use rustc_data_structures::bit_set::GrowableBitSet;
 pub use rustc_data_structures::thin_vec::ThinVec;
 use ast::AttrId;
+use syntax_pos::edition::Edition;
+
+#[cfg(test)]
+mod tests;
+
+const MACRO_ARGUMENTS: Option<&'static str> = Some("macro arguments");
 
 // A variant of 'try!' that panics on an Err. This is used as a crutch on the
 // way towards a non-panic!-prone parser. It should be used for fatal parsing
 // errors; eventually we plan to convert all code using panictry to just use
 // normal try.
+#[macro_export]
 macro_rules! panictry {
     ($e:expr) => ({
         use std::result::Result::{Ok, Err};
@@ -82,26 +91,32 @@ pub struct Globals {
 }
 
 impl Globals {
-    fn new() -> Globals {
+    fn new(edition: Edition) -> Globals {
         Globals {
             // We have no idea how many attributes their will be, so just
             // initiate the vectors with 0 bits. We'll grow them as necessary.
             used_attrs: Lock::new(GrowableBitSet::new_empty()),
             known_attrs: Lock::new(GrowableBitSet::new_empty()),
-            syntax_pos_globals: syntax_pos::Globals::new(),
+            syntax_pos_globals: syntax_pos::Globals::new(edition),
         }
     }
 }
 
-pub fn with_globals<F, R>(f: F) -> R
+pub fn with_globals<F, R>(edition: Edition, f: F) -> R
     where F: FnOnce() -> R
 {
-    let globals = Globals::new();
+    let globals = Globals::new(edition);
     GLOBALS.set(&globals, || {
         syntax_pos::GLOBALS.set(&globals.syntax_pos_globals, f)
     })
 }
 
+pub fn with_default_globals<F, R>(f: F) -> R
+    where F: FnOnce() -> R
+{
+    with_globals(edition::DEFAULT_EDITION, f)
+}
+
 scoped_tls::scoped_thread_local!(pub static GLOBALS: Globals);
 
 #[macro_use]
@@ -120,19 +135,11 @@ pub mod util {
     pub mod lev_distance;
     pub mod node_count;
     pub mod parser;
-    #[cfg(test)]
-    pub mod parser_testing;
     pub mod map_in_place;
 }
 
 pub mod json;
 
-pub mod syntax {
-    pub use crate::ext;
-    pub use crate::parse;
-    pub use crate::ast;
-}
-
 pub mod ast;
 pub mod attr;
 pub mod source_map;
@@ -144,29 +151,31 @@ pub mod mut_visit;
 pub mod parse;
 pub mod ptr;
 pub mod show_span;
-pub mod std_inject;
 pub use syntax_pos::edition;
 pub use syntax_pos::symbol;
-pub mod test;
 pub mod tokenstream;
 pub mod visit;
 
 pub mod print {
     pub mod pp;
     pub mod pprust;
+    mod helpers;
 }
 
 pub mod ext {
+    mod placeholders;
+    mod proc_macro_server;
+
     pub use syntax_pos::hygiene;
+    pub mod allocator;
     pub mod base;
     pub mod build;
-    pub mod derive;
     pub mod expand;
-    pub mod placeholders;
-    pub mod source_util;
+    pub mod proc_macro;
 
     pub mod tt {
         pub mod transcribe;
+        pub mod macro_check;
         pub mod macro_parser;
         pub mod macro_rules;
         pub mod quoted;
@@ -175,7 +184,4 @@ pub mod ext {
 
 pub mod early_buffered_lints;
 
-#[cfg(test)]
-mod test_snippet;
-
 __build_diagnostic_array! { libsyntax, DIAGNOSTICS }
diff --git a/src/libsyntax/mut_visit.rs b/src/libsyntax/mut_visit.rs
index f587e63e12b..9785f8e2de0 100644
--- a/src/libsyntax/mut_visit.rs
+++ b/src/libsyntax/mut_visit.rs
@@ -11,7 +11,6 @@ use crate::ast::*;
 use crate::source_map::{Spanned, respan};
 use crate::parse::token::{self, Token};
 use crate::ptr::P;
-use crate::symbol::keywords;
 use crate::ThinVec;
 use crate::tokenstream::*;
 use crate::util::map_in_place::MapInPlace;
@@ -23,6 +22,9 @@ use rustc_data_structures::sync::Lrc;
 use std::ops::DerefMut;
 use std::{panic, process, ptr};
 
+#[cfg(test)]
+mod tests;
+
 pub trait ExpectOne<A: Array> {
     fn expect_one(self, err: &'static str) -> A::Item;
 }
@@ -132,10 +134,6 @@ pub trait MutVisitor: Sized {
         noop_visit_arm(a, self);
     }
 
-    fn visit_guard(&mut self, g: &mut Guard) {
-        noop_visit_guard(g, self);
-    }
-
     fn visit_pat(&mut self, p: &mut P<Pat>) {
         noop_visit_pat(p, self);
     }
@@ -164,8 +162,8 @@ pub trait MutVisitor: Sized {
         noop_visit_lifetime(l, self);
     }
 
-    fn visit_ty_binding(&mut self, t: &mut TypeBinding) {
-        noop_visit_ty_binding(t, self);
+    fn visit_ty_constraint(&mut self, t: &mut AssocTyConstraint) {
+        noop_visit_ty_constraint(t, self);
     }
 
     fn visit_mod(&mut self, m: &mut Mod) {
@@ -208,10 +206,6 @@ pub trait MutVisitor: Sized {
         noop_visit_local(l, self);
     }
 
-    fn visit_local_source(&mut self, l: &mut LocalSource) {
-        noop_visit_local_source(l, self);
-    }
-
     fn visit_mac(&mut self, _mac: &mut Mac) {
         panic!("visit_mac disabled by default");
         // N.B., see note about macros above. If you really want a visitor that
@@ -235,10 +229,6 @@ pub trait MutVisitor: Sized {
         noop_visit_arg(a, self);
     }
 
-    fn visit_arg_source(&mut self, a: &mut ArgSource) {
-        noop_visit_arg_source(a, self);
-    }
-
     fn visit_generics(&mut self, generics: &mut Generics) {
         noop_visit_generics(generics, self);
     }
@@ -392,24 +382,32 @@ pub fn noop_visit_use_tree<T: MutVisitor>(use_tree: &mut UseTree, vis: &mut T) {
     vis.visit_span(span);
 }
 
-pub fn noop_visit_arm<T: MutVisitor>(Arm { attrs, pats, guard, body }: &mut Arm, vis: &mut T) {
+pub fn noop_visit_arm<T: MutVisitor>(
+    Arm { attrs, pats, guard, body, span, id }: &mut Arm,
+    vis: &mut T,
+) {
     visit_attrs(attrs, vis);
+    vis.visit_id(id);
     visit_vec(pats, |pat| vis.visit_pat(pat));
-    visit_opt(guard, |guard| vis.visit_guard(guard));
+    visit_opt(guard, |guard| vis.visit_expr(guard));
     vis.visit_expr(body);
+    vis.visit_span(span);
 }
 
-pub fn noop_visit_guard<T: MutVisitor>(g: &mut Guard, vis: &mut T) {
-    match g {
-        Guard::If(e) => vis.visit_expr(e),
-    }
-}
-
-pub fn noop_visit_ty_binding<T: MutVisitor>(TypeBinding { id, ident, ty, span }: &mut TypeBinding,
-                                            vis: &mut T) {
+pub fn noop_visit_ty_constraint<T: MutVisitor>(
+    AssocTyConstraint { id, ident, kind, span }: &mut AssocTyConstraint,
+    vis: &mut T
+) {
     vis.visit_id(id);
     vis.visit_ident(ident);
-    vis.visit_ty(ty);
+    match kind {
+        AssocTyConstraintKind::Equality { ref mut ty } => {
+            vis.visit_ty(ty);
+        }
+        AssocTyConstraintKind::Bound { ref mut bounds } => {
+            visit_bounds(bounds, vis);
+        }
+    }
     vis.visit_span(span);
 }
 
@@ -458,7 +456,7 @@ pub fn noop_visit_foreign_mod<T: MutVisitor>(foreign_mod: &mut ForeignMod, vis:
 }
 
 pub fn noop_visit_variant<T: MutVisitor>(variant: &mut Variant, vis: &mut T) {
-    let Spanned { node: Variant_ { ident, attrs, id, data, disr_expr }, span } = variant;
+    let Variant { ident, attrs, id, data, disr_expr, span } = variant;
     vis.visit_ident(ident);
     visit_attrs(attrs, vis);
     vis.visit_id(id);
@@ -504,9 +502,9 @@ pub fn noop_visit_generic_arg<T: MutVisitor>(arg: &mut GenericArg, vis: &mut T)
 
 pub fn noop_visit_angle_bracketed_parameter_data<T: MutVisitor>(data: &mut AngleBracketedArgs,
                                                                 vis: &mut T) {
-    let AngleBracketedArgs { args, bindings, span } = data;
+    let AngleBracketedArgs { args, constraints, span } = data;
     visit_vec(args, |arg| vis.visit_generic_arg(arg));
-    visit_vec(bindings, |binding| vis.visit_ty_binding(binding));
+    visit_vec(constraints, |constraint| vis.visit_ty_constraint(constraint));
     vis.visit_span(span);
 }
 
@@ -519,17 +517,13 @@ pub fn noop_visit_parenthesized_parameter_data<T: MutVisitor>(args: &mut Parenth
 }
 
 pub fn noop_visit_local<T: MutVisitor>(local: &mut P<Local>, vis: &mut T) {
-    let Local { id, pat, ty, init, span, attrs, source } = local.deref_mut();
+    let Local { id, pat, ty, init, span, attrs } = local.deref_mut();
     vis.visit_id(id);
     vis.visit_pat(pat);
     visit_opt(ty, |ty| vis.visit_ty(ty));
     visit_opt(init, |init| vis.visit_expr(init));
     vis.visit_span(span);
     visit_thin_attrs(attrs, vis);
-    vis.visit_local_source(source);
-}
-
-pub fn noop_visit_local_source<T: MutVisitor>(_local_source: &mut LocalSource, _vis: &mut T) {
 }
 
 pub fn noop_visit_attribute<T: MutVisitor>(attr: &mut Attribute, vis: &mut T) {
@@ -539,8 +533,8 @@ pub fn noop_visit_attribute<T: MutVisitor>(attr: &mut Attribute, vis: &mut T) {
     vis.visit_span(span);
 }
 
-pub fn noop_visit_mac<T: MutVisitor>(Spanned { node, span }: &mut Mac, vis: &mut T) {
-    let Mac_ { path, delim: _, tts } = node;
+pub fn noop_visit_mac<T: MutVisitor>(mac: &mut Mac, vis: &mut T) {
+    let Mac { path, delim: _, tts, span, prior_type_ascription: _ } = mac;
     vis.visit_path(path);
     vis.visit_tts(tts);
     vis.visit_span(span);
@@ -568,25 +562,18 @@ pub fn noop_visit_meta_item<T: MutVisitor>(mi: &mut MetaItem, vis: &mut T) {
     vis.visit_span(span);
 }
 
-pub fn noop_visit_arg<T: MutVisitor>(Arg { id, pat, ty, source }: &mut Arg, vis: &mut T) {
+pub fn noop_visit_arg<T: MutVisitor>(Arg { attrs, id, pat, span, ty }: &mut Arg, vis: &mut T) {
     vis.visit_id(id);
+    visit_thin_attrs(attrs, vis);
     vis.visit_pat(pat);
+    vis.visit_span(span);
     vis.visit_ty(ty);
-    vis.visit_arg_source(source);
-}
-
-pub fn noop_visit_arg_source<T: MutVisitor>(source: &mut ArgSource, vis: &mut T) {
-    match source {
-        ArgSource::Normal => {},
-        ArgSource::AsyncFn(pat) => vis.visit_pat(pat),
-    }
 }
 
 pub fn noop_visit_tt<T: MutVisitor>(tt: &mut TokenTree, vis: &mut T) {
     match tt {
-        TokenTree::Token(span, tok) => {
-            vis.visit_span(span);
-            vis.visit_token(tok);
+        TokenTree::Token(token) => {
+            vis.visit_token(token);
         }
         TokenTree::Delimited(DelimSpan { open, close }, _delim, tts) => {
             vis.visit_span(open);
@@ -603,17 +590,26 @@ pub fn noop_visit_tts<T: MutVisitor>(TokenStream(tts): &mut TokenStream, vis: &m
     })
 }
 
-// apply ident visitor if it's an ident, apply other visits to interpolated nodes
+// Apply ident visitor if it's an ident, apply other visits to interpolated nodes.
+// In practice the ident part is not actually used by specific visitors right now,
+// but there's a test below checking that it works.
 pub fn noop_visit_token<T: MutVisitor>(t: &mut Token, vis: &mut T) {
-    match t {
-        token::Ident(id, _is_raw) => vis.visit_ident(id),
-        token::Lifetime(id) => vis.visit_ident(id),
+    let Token { kind, span } = t;
+    match kind {
+        token::Ident(name, _) | token::Lifetime(name) => {
+            let mut ident = Ident::new(*name, *span);
+            vis.visit_ident(&mut ident);
+            *name = ident.name;
+            *span = ident.span;
+            return; // avoid visiting the span for the second time
+        }
         token::Interpolated(nt) => {
             let mut nt = Lrc::make_mut(nt);
             vis.visit_interpolated(&mut nt);
         }
         _ => {}
     }
+    vis.visit_span(span);
 }
 
 /// Apply visitor to elements of interpolated nodes.
@@ -687,25 +683,9 @@ pub fn noop_visit_interpolated<T: MutVisitor>(nt: &mut token::Nonterminal, vis:
 
 pub fn noop_visit_asyncness<T: MutVisitor>(asyncness: &mut IsAsync, vis: &mut T) {
     match asyncness {
-        IsAsync::Async { closure_id, return_impl_trait_id, ref mut arguments } => {
+        IsAsync::Async { closure_id, return_impl_trait_id } => {
             vis.visit_id(closure_id);
             vis.visit_id(return_impl_trait_id);
-            for AsyncArgument { ident, arg, pat_stmt, move_stmt } in arguments.iter_mut() {
-                vis.visit_ident(ident);
-                if let Some(arg) = arg {
-                    vis.visit_arg(arg);
-                }
-                visit_clobber(move_stmt, |stmt| {
-                    vis.flat_map_stmt(stmt)
-                        .expect_one("expected visitor to produce exactly one item")
-                });
-                visit_opt(pat_stmt, |stmt| {
-                    visit_clobber(stmt, |stmt| {
-                        vis.flat_map_stmt(stmt)
-                            .expect_one("expected visitor to produce exactly one item")
-                    })
-                });
-            }
         }
         IsAsync::NotAsync => {}
     }
@@ -765,8 +745,7 @@ pub fn noop_visit_generics<T: MutVisitor>(generics: &mut Generics, vis: &mut T)
 }
 
 pub fn noop_visit_where_clause<T: MutVisitor>(wc: &mut WhereClause, vis: &mut T) {
-    let WhereClause { id, predicates, span } = wc;
-    vis.visit_id(id);
+    let WhereClause { predicates, span } = wc;
     visit_vec(predicates, |predicate| vis.visit_where_predicate(predicate));
     vis.visit_span(span);
 }
@@ -830,9 +809,10 @@ pub fn noop_visit_struct_field<T: MutVisitor>(f: &mut StructField, visitor: &mut
 }
 
 pub fn noop_visit_field<T: MutVisitor>(f: &mut Field, vis: &mut T) {
-    let Field { ident, expr, span, is_shorthand: _, attrs } = f;
+    let Field { ident, expr, span, is_shorthand: _, attrs, id } = f;
     vis.visit_ident(ident);
     vis.visit_expr(expr);
+    vis.visit_id(id);
     vis.visit_span(span);
     visit_thin_attrs(attrs, vis);
 }
@@ -869,11 +849,11 @@ pub fn noop_visit_item_kind<T: MutVisitor>(kind: &mut ItemKind, vis: &mut T) {
         ItemKind::Mod(m) => vis.visit_mod(m),
         ItemKind::ForeignMod(nm) => vis.visit_foreign_mod(nm),
         ItemKind::GlobalAsm(_ga) => {}
-        ItemKind::Ty(ty, generics) => {
+        ItemKind::TyAlias(ty, generics) => {
             vis.visit_ty(ty);
             vis.visit_generics(generics);
         }
-        ItemKind::Existential(bounds, generics) => {
+        ItemKind::OpaqueTy(bounds, generics) => {
             visit_bounds(bounds, vis);
             vis.visit_generics(generics);
         }
@@ -955,8 +935,8 @@ pub fn noop_flat_map_impl_item<T: MutVisitor>(mut item: ImplItem, visitor: &mut
             visit_method_sig(sig, visitor);
             visitor.visit_block(body);
         }
-        ImplItemKind::Type(ty) => visitor.visit_ty(ty),
-        ImplItemKind::Existential(bounds) => visit_bounds(bounds, visitor),
+        ImplItemKind::TyAlias(ty) => visitor.visit_ty(ty),
+        ImplItemKind::OpaqueTy(bounds) => visit_bounds(bounds, visitor),
         ImplItemKind::Macro(mac) => visitor.visit_mac(mac),
     }
     visitor.visit_span(span);
@@ -977,7 +957,7 @@ pub fn noop_visit_mod<T: MutVisitor>(Mod { inner, items, inline: _ }: &mut Mod,
 pub fn noop_visit_crate<T: MutVisitor>(krate: &mut Crate, vis: &mut T) {
     visit_clobber(krate, |Crate { module, attrs, span }| {
         let item = P(Item {
-            ident: keywords::Invalid.ident(),
+            ident: Ident::invalid(),
             attrs,
             id: DUMMY_NODE_ID,
             vis: respan(span.shrink_to_lo(), VisibilityKind::Public),
@@ -1046,15 +1026,15 @@ pub fn noop_visit_pat<T: MutVisitor>(pat: &mut P<Pat>, vis: &mut T) {
     let Pat { id, node, span } = pat.deref_mut();
     vis.visit_id(id);
     match node {
-        PatKind::Wild => {}
+        PatKind::Wild | PatKind::Rest => {}
         PatKind::Ident(_binding_mode, ident, sub) => {
             vis.visit_ident(ident);
             visit_opt(sub, |sub| vis.visit_pat(sub));
         }
         PatKind::Lit(e) => vis.visit_expr(e),
-        PatKind::TupleStruct(path, pats, _ddpos) => {
+        PatKind::TupleStruct(path, elems) => {
             vis.visit_path(path);
-            visit_vec(pats, |pat| vis.visit_pat(pat));
+            visit_vec(elems, |elem| vis.visit_pat(elem));
         }
         PatKind::Path(qself, path) => {
             vis.visit_qself(qself);
@@ -1062,14 +1042,14 @@ pub fn noop_visit_pat<T: MutVisitor>(pat: &mut P<Pat>, vis: &mut T) {
         }
         PatKind::Struct(path, fields, _etc) => {
             vis.visit_path(path);
-            for Spanned { node: FieldPat { ident, pat, is_shorthand: _, attrs }, span } in fields {
+            for FieldPat { ident, pat, is_shorthand: _, attrs, id, span } in fields {
                 vis.visit_ident(ident);
+                vis.visit_id(id);
                 vis.visit_pat(pat);
                 visit_thin_attrs(attrs, vis);
                 vis.visit_span(span);
             };
         }
-        PatKind::Tuple(elts, _ddpos) => visit_vec(elts, |elt| vis.visit_pat(elt)),
         PatKind::Box(inner) => vis.visit_pat(inner),
         PatKind::Ref(inner, _mutbl) => vis.visit_pat(inner),
         PatKind::Range(e1, e2, Spanned { span: _, node: _ }) => {
@@ -1077,11 +1057,9 @@ pub fn noop_visit_pat<T: MutVisitor>(pat: &mut P<Pat>, vis: &mut T) {
             vis.visit_expr(e2);
             vis.visit_span(span);
         }
-        PatKind::Slice(before, slice, after) => {
-            visit_vec(before, |pat| vis.visit_pat(pat));
-            visit_opt(slice, |slice| vis.visit_pat(slice));
-            visit_vec(after, |pat| vis.visit_pat(pat));
-        }
+        PatKind::Tuple(elems)
+        | PatKind::Slice(elems)
+        | PatKind::Or(elems) => visit_vec(elems, |elem| vis.visit_pat(elem)),
         PatKind::Paren(inner) => vis.visit_pat(inner),
         PatKind::Mac(mac) => vis.visit_mac(mac),
     }
@@ -1096,10 +1074,6 @@ pub fn noop_visit_anon_const<T: MutVisitor>(AnonConst { id, value }: &mut AnonCo
 pub fn noop_visit_expr<T: MutVisitor>(Expr { node, id, span, attrs }: &mut Expr, vis: &mut T) {
     match node {
         ExprKind::Box(expr) => vis.visit_expr(expr),
-        ExprKind::ObsoleteInPlace(a, b) => {
-            vis.visit_expr(a);
-            vis.visit_expr(b);
-        }
         ExprKind::Array(exprs) => visit_exprs(exprs, vis),
         ExprKind::Repeat(expr, count) => {
             vis.visit_expr(expr);
@@ -1121,7 +1095,6 @@ pub fn noop_visit_expr<T: MutVisitor>(Expr { node, id, span, attrs }: &mut Expr,
             vis.visit_expr(rhs);
         }
         ExprKind::Unary(_unop, ohs) => vis.visit_expr(ohs),
-        ExprKind::Lit(_lit) => {}
         ExprKind::Cast(expr, ty) => {
             vis.visit_expr(expr);
             vis.visit_ty(ty);
@@ -1131,28 +1104,20 @@ pub fn noop_visit_expr<T: MutVisitor>(Expr { node, id, span, attrs }: &mut Expr,
             vis.visit_ty(ty);
         }
         ExprKind::AddrOf(_m, ohs) => vis.visit_expr(ohs),
+        ExprKind::Let(pats, scrutinee) => {
+            visit_vec(pats, |pat| vis.visit_pat(pat));
+            vis.visit_expr(scrutinee);
+        }
         ExprKind::If(cond, tr, fl) => {
             vis.visit_expr(cond);
             vis.visit_block(tr);
             visit_opt(fl, |fl| vis.visit_expr(fl));
         }
-        ExprKind::IfLet(pats, expr, tr, fl) => {
-            visit_vec(pats, |pat| vis.visit_pat(pat));
-            vis.visit_expr(expr);
-            vis.visit_block(tr);
-            visit_opt(fl, |fl| vis.visit_expr(fl));
-        }
         ExprKind::While(cond, body, label) => {
             vis.visit_expr(cond);
             vis.visit_block(body);
             visit_opt(label, |label| vis.visit_label(label));
         }
-        ExprKind::WhileLet(pats, expr, body, label) => {
-            visit_vec(pats, |pat| vis.visit_pat(pat));
-            vis.visit_expr(expr);
-            vis.visit_block(body);
-            visit_opt(label, |label| vis.visit_label(label));
-        }
         ExprKind::ForLoop(pat, iter, body, label) => {
             vis.visit_pat(pat);
             vis.visit_expr(iter);
@@ -1181,7 +1146,7 @@ pub fn noop_visit_expr<T: MutVisitor>(Expr { node, id, span, attrs }: &mut Expr,
             vis.visit_id(node_id);
             vis.visit_block(body);
         }
-        ExprKind::Await(_origin, expr) => vis.visit_expr(expr),
+        ExprKind::Await(expr) => vis.visit_expr(expr),
         ExprKind::Assign(el, er) => {
             vis.visit_expr(el);
             vis.visit_expr(er);
@@ -1218,7 +1183,7 @@ pub fn noop_visit_expr<T: MutVisitor>(Expr { node, id, span, attrs }: &mut Expr,
         }
         ExprKind::InlineAsm(asm) => {
             let InlineAsm { asm: _, asm_str_style: _, outputs, inputs, clobbers: _, volatile: _,
-                            alignstack: _, dialect: _, ctxt: _ } = asm.deref_mut();
+                            alignstack: _, dialect: _ } = asm.deref_mut();
             for out in outputs {
                 let InlineAsmOutput { constraint: _, expr, is_rw: _, is_indirect: _ } = out;
                 vis.visit_expr(expr);
@@ -1245,7 +1210,7 @@ pub fn noop_visit_expr<T: MutVisitor>(Expr { node, id, span, attrs }: &mut Expr,
         }
         ExprKind::Try(expr) => vis.visit_expr(expr),
         ExprKind::TryBlock(body) => vis.visit_block(body),
-        ExprKind::Err => {}
+        ExprKind::Lit(_) | ExprKind::Err => {}
     }
     vis.visit_id(id);
     vis.visit_span(span);
@@ -1297,78 +1262,3 @@ pub fn noop_visit_vis<T: MutVisitor>(Spanned { node, span }: &mut Visibility, vi
     }
     vis.visit_span(span);
 }
-
-#[cfg(test)]
-mod tests {
-    use std::io;
-    use crate::ast::{self, Ident};
-    use crate::util::parser_testing::{string_to_crate, matches_codepattern};
-    use crate::print::pprust;
-    use crate::mut_visit;
-    use crate::with_globals;
-    use super::*;
-
-    // this version doesn't care about getting comments or docstrings in.
-    fn fake_print_crate(s: &mut pprust::State<'_>,
-                        krate: &ast::Crate) -> io::Result<()> {
-        s.print_mod(&krate.module, &krate.attrs)
-    }
-
-    // change every identifier to "zz"
-    struct ToZzIdentMutVisitor;
-
-    impl MutVisitor for ToZzIdentMutVisitor {
-        fn visit_ident(&mut self, ident: &mut ast::Ident) {
-            *ident = Ident::from_str("zz");
-        }
-        fn visit_mac(&mut self, mac: &mut ast::Mac) {
-            mut_visit::noop_visit_mac(mac, self)
-        }
-    }
-
-    // maybe add to expand.rs...
-    macro_rules! assert_pred {
-        ($pred:expr, $predname:expr, $a:expr , $b:expr) => (
-            {
-                let pred_val = $pred;
-                let a_val = $a;
-                let b_val = $b;
-                if !(pred_val(&a_val, &b_val)) {
-                    panic!("expected args satisfying {}, got {} and {}",
-                          $predname, a_val, b_val);
-                }
-            }
-        )
-    }
-
-    // make sure idents get transformed everywhere
-    #[test] fn ident_transformation () {
-        with_globals(|| {
-            let mut zz_visitor = ToZzIdentMutVisitor;
-            let mut krate = string_to_crate(
-                "#[a] mod b {fn c (d : e, f : g) {h!(i,j,k);l;m}}".to_string());
-            zz_visitor.visit_crate(&mut krate);
-            assert_pred!(
-                matches_codepattern,
-                "matches_codepattern",
-                pprust::to_string(|s| fake_print_crate(s, &krate)),
-                "#[zz]mod zz{fn zz(zz:zz,zz:zz){zz!(zz,zz,zz);zz;zz}}".to_string());
-        })
-    }
-
-    // even inside macro defs....
-    #[test] fn ident_transformation_in_defs () {
-        with_globals(|| {
-            let mut zz_visitor = ToZzIdentMutVisitor;
-            let mut krate = string_to_crate(
-                "macro_rules! a {(b $c:expr $(d $e:token)f+ => \
-                (g $(d $d $e)+))} ".to_string());
-            zz_visitor.visit_crate(&mut krate);
-            assert_pred!(
-                matches_codepattern,
-                "matches_codepattern",
-                pprust::to_string(|s| fake_print_crate(s, &krate)),
-                "macro_rules! zz((zz$zz:zz$(zz $zz:zz)zz+=>(zz$(zz$zz$zz)+)));".to_string());
-        })
-    }
-}
diff --git a/src/libsyntax/mut_visit/tests.rs b/src/libsyntax/mut_visit/tests.rs
new file mode 100644
index 00000000000..6868736976b
--- /dev/null
+++ b/src/libsyntax/mut_visit/tests.rs
@@ -0,0 +1,71 @@
+use super::*;
+
+use crate::ast::{self, Ident};
+use crate::tests::{string_to_crate, matches_codepattern};
+use crate::print::pprust;
+use crate::mut_visit;
+use crate::with_default_globals;
+
+// this version doesn't care about getting comments or docstrings in.
+fn fake_print_crate(s: &mut pprust::State<'_>,
+                    krate: &ast::Crate) {
+    s.print_mod(&krate.module, &krate.attrs)
+}
+
+// change every identifier to "zz"
+struct ToZzIdentMutVisitor;
+
+impl MutVisitor for ToZzIdentMutVisitor {
+    fn visit_ident(&mut self, ident: &mut ast::Ident) {
+        *ident = Ident::from_str("zz");
+    }
+    fn visit_mac(&mut self, mac: &mut ast::Mac) {
+        mut_visit::noop_visit_mac(mac, self)
+    }
+}
+
+// maybe add to expand.rs...
+macro_rules! assert_pred {
+    ($pred:expr, $predname:expr, $a:expr , $b:expr) => (
+        {
+            let pred_val = $pred;
+            let a_val = $a;
+            let b_val = $b;
+            if !(pred_val(&a_val, &b_val)) {
+                panic!("expected args satisfying {}, got {} and {}",
+                        $predname, a_val, b_val);
+            }
+        }
+    )
+}
+
+// make sure idents get transformed everywhere
+#[test] fn ident_transformation () {
+    with_default_globals(|| {
+        let mut zz_visitor = ToZzIdentMutVisitor;
+        let mut krate = string_to_crate(
+            "#[a] mod b {fn c (d : e, f : g) {h!(i,j,k);l;m}}".to_string());
+        zz_visitor.visit_crate(&mut krate);
+        assert_pred!(
+            matches_codepattern,
+            "matches_codepattern",
+            pprust::to_string(|s| fake_print_crate(s, &krate)),
+            "#[zz]mod zz{fn zz(zz:zz,zz:zz){zz!(zz,zz,zz);zz;zz}}".to_string());
+    })
+}
+
+// even inside macro defs....
+#[test] fn ident_transformation_in_defs () {
+    with_default_globals(|| {
+        let mut zz_visitor = ToZzIdentMutVisitor;
+        let mut krate = string_to_crate(
+            "macro_rules! a {(b $c:expr $(d $e:token)f+ => \
+            (g $(d $d $e)+))} ".to_string());
+        zz_visitor.visit_crate(&mut krate);
+        assert_pred!(
+            matches_codepattern,
+            "matches_codepattern",
+            pprust::to_string(|s| fake_print_crate(s, &krate)),
+            "macro_rules! zz{(zz$zz:zz$(zz $zz:zz)zz+=>(zz$(zz$zz$zz)+))}".to_string());
+    })
+}
diff --git a/src/libsyntax/parse/attr.rs b/src/libsyntax/parse/attr.rs
index e99a86e807f..a42da112360 100644
--- a/src/libsyntax/parse/attr.rs
+++ b/src/libsyntax/parse/attr.rs
@@ -4,6 +4,7 @@ use crate::parse::{SeqSep, PResult};
 use crate::parse::token::{self, Nonterminal, DelimToken};
 use crate::parse::parser::{Parser, TokenType, PathStyle};
 use crate::tokenstream::{TokenStream, TokenTree};
+use crate::source_map::Span;
 
 use log::debug;
 use smallvec::smallvec;
@@ -11,20 +12,28 @@ use smallvec::smallvec;
 #[derive(Debug)]
 enum InnerAttributeParsePolicy<'a> {
     Permitted,
-    NotPermitted { reason: &'a str },
+    NotPermitted { reason: &'a str, saw_doc_comment: bool, prev_attr_sp: Option<Span> },
 }
 
 const DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG: &str = "an inner attribute is not \
                                                      permitted in this context";
 
 impl<'a> Parser<'a> {
+    crate fn parse_arg_attributes(&mut self) -> PResult<'a, Vec<ast::Attribute>> {
+        let attrs = self.parse_outer_attributes()?;
+        attrs.iter().for_each(|a|
+            self.sess.param_attr_spans.borrow_mut().push(a.span)
+        );
+        Ok(attrs)
+    }
+
     /// Parse attributes that appear before an item
     crate fn parse_outer_attributes(&mut self) -> PResult<'a, Vec<ast::Attribute>> {
         let mut attrs: Vec<ast::Attribute> = Vec::new();
         let mut just_parsed_doc_comment = false;
         loop {
             debug!("parse_outer_attributes: self.token={:?}", self.token);
-            match self.token {
+            match self.token.kind {
                 token::Pound => {
                     let inner_error_reason = if just_parsed_doc_comment {
                         "an inner attribute is not permitted following an outer doc comment"
@@ -34,12 +43,17 @@ impl<'a> Parser<'a> {
                         DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG
                     };
                     let inner_parse_policy =
-                        InnerAttributeParsePolicy::NotPermitted { reason: inner_error_reason };
-                    attrs.push(self.parse_attribute_with_inner_parse_policy(inner_parse_policy)?);
+                        InnerAttributeParsePolicy::NotPermitted {
+                            reason: inner_error_reason,
+                            saw_doc_comment: just_parsed_doc_comment,
+                            prev_attr_sp: attrs.last().and_then(|a| Some(a.span))
+                        };
+                    let attr = self.parse_attribute_with_inner_parse_policy(inner_parse_policy)?;
+                    attrs.push(attr);
                     just_parsed_doc_comment = false;
                 }
                 token::DocComment(s) => {
-                    let attr = attr::mk_sugared_doc_attr(attr::mk_attr_id(), s, self.span);
+                    let attr = attr::mk_sugared_doc_attr(s, self.token.span);
                     if attr.style != ast::AttrStyle::Outer {
                         let mut err = self.fatal("expected outer doc comment");
                         err.note("inner doc comments like this (starting with \
@@ -67,8 +81,11 @@ impl<'a> Parser<'a> {
         let inner_parse_policy = if permit_inner {
             InnerAttributeParsePolicy::Permitted
         } else {
-            InnerAttributeParsePolicy::NotPermitted
-                { reason: DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG }
+            InnerAttributeParsePolicy::NotPermitted {
+                reason: DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG,
+                saw_doc_comment: false,
+                prev_attr_sp: None
+            }
         };
         self.parse_attribute_with_inner_parse_policy(inner_parse_policy)
     }
@@ -81,27 +98,17 @@ impl<'a> Parser<'a> {
         debug!("parse_attribute_with_inner_parse_policy: inner_parse_policy={:?} self.token={:?}",
                inner_parse_policy,
                self.token);
-        let (span, path, tokens, style) = match self.token {
+        let (span, path, tokens, style) = match self.token.kind {
             token::Pound => {
-                let lo = self.span;
+                let lo = self.token.span;
                 self.bump();
 
                 if let InnerAttributeParsePolicy::Permitted = inner_parse_policy {
                     self.expected_tokens.push(TokenType::Token(token::Not));
                 }
+
                 let style = if self.token == token::Not {
                     self.bump();
-                    if let InnerAttributeParsePolicy::NotPermitted { reason } = inner_parse_policy
-                    {
-                        let span = self.span;
-                        self.diagnostic()
-                            .struct_span_err(span, reason)
-                            .note("inner attributes, like `#![no_std]`, annotate the item \
-                                   enclosing them, and are usually found at the beginning of \
-                                   source files. Outer attributes, like `#[test]`, annotate the \
-                                   item following them.")
-                            .emit()
-                    }
                     ast::AttrStyle::Inner
                 } else {
                     ast::AttrStyle::Outer
@@ -112,7 +119,38 @@ impl<'a> Parser<'a> {
                 self.expect(&token::CloseDelim(token::Bracket))?;
                 let hi = self.prev_span;
 
-                (lo.to(hi), path, tokens, style)
+                let attr_sp = lo.to(hi);
+
+                // Emit error if inner attribute is encountered and not permitted
+                if style == ast::AttrStyle::Inner {
+                    if let InnerAttributeParsePolicy::NotPermitted { reason,
+                        saw_doc_comment, prev_attr_sp } = inner_parse_policy {
+                        let prev_attr_note = if saw_doc_comment {
+                            "previous doc comment"
+                        } else {
+                            "previous outer attribute"
+                        };
+
+                        let mut diagnostic = self
+                            .diagnostic()
+                            .struct_span_err(attr_sp, reason);
+
+                        if let Some(prev_attr_sp) = prev_attr_sp {
+                            diagnostic
+                                .span_label(attr_sp, "not permitted following an outer attibute")
+                                .span_label(prev_attr_sp, prev_attr_note);
+                        }
+
+                        diagnostic
+                            .note("inner attributes, like `#![no_std]`, annotate the item \
+                                   enclosing them, and are usually found at the beginning of \
+                                   source files. Outer attributes, like `#[test]`, annotate the \
+                                   item following them.")
+                            .emit()
+                    }
+                }
+
+                (attr_sp, path, tokens, style)
             }
             _ => {
                 let token_str = self.this_token_to_string();
@@ -140,7 +178,7 @@ impl<'a> Parser<'a> {
     /// PATH `=` TOKEN_TREE
     /// The delimiters or `=` are still put into the resulting token stream.
     crate fn parse_meta_item_unrestricted(&mut self) -> PResult<'a, (ast::Path, TokenStream)> {
-        let meta = match self.token {
+        let meta = match self.token.kind {
             token::Interpolated(ref nt) => match **nt {
                 Nonterminal::NtMeta(ref meta) => Some(meta.clone()),
                 _ => None,
@@ -157,9 +195,9 @@ impl<'a> Parser<'a> {
                self.check(&token::OpenDelim(DelimToken::Brace)) {
                    self.parse_token_tree().into()
             } else if self.eat(&token::Eq) {
-                let eq = TokenTree::Token(self.prev_span, token::Eq);
+                let eq = TokenTree::token(token::Eq, self.prev_span);
                 let mut is_interpolated_expr = false;
-                if let token::Interpolated(nt) = &self.token {
+                if let token::Interpolated(nt) = &self.token.kind {
                     if let token::NtExpr(..) = **nt {
                         is_interpolated_expr = true;
                     }
@@ -188,7 +226,7 @@ impl<'a> Parser<'a> {
     crate fn parse_inner_attributes(&mut self) -> PResult<'a, Vec<ast::Attribute>> {
         let mut attrs: Vec<ast::Attribute> = vec![];
         loop {
-            match self.token {
+            match self.token.kind {
                 token::Pound => {
                     // Don't even try to parse if it's not an inner attribute.
                     if !self.look_ahead(1, |t| t == &token::Not) {
@@ -201,7 +239,7 @@ impl<'a> Parser<'a> {
                 }
                 token::DocComment(s) => {
                     // we need to get the position of this token before we bump.
-                    let attr = attr::mk_sugared_doc_attr(attr::mk_attr_id(), s, self.span);
+                    let attr = attr::mk_sugared_doc_attr(s, self.token.span);
                     if attr.style == ast::AttrStyle::Inner {
                         attrs.push(attr);
                         self.bump();
@@ -217,7 +255,7 @@ impl<'a> Parser<'a> {
 
     fn parse_unsuffixed_lit(&mut self) -> PResult<'a, ast::Lit> {
         let lit = self.parse_lit()?;
-        debug!("Checking if {:?} is unusuffixed.", lit);
+        debug!("checking if {:?} is unusuffixed", lit);
 
         if !lit.node.is_unsuffixed() {
             let msg = "suffixed literals are not allowed in attributes";
@@ -236,7 +274,7 @@ impl<'a> Parser<'a> {
     /// meta_item : IDENT ( '=' UNSUFFIXED_LIT | '(' meta_item_inner? ')' )? ;
     /// meta_item_inner : (meta_item | UNSUFFIXED_LIT) (',' meta_item_inner)? ;
     pub fn parse_meta_item(&mut self) -> PResult<'a, ast::MetaItem> {
-        let nt_meta = match self.token {
+        let nt_meta = match self.token.kind {
             token::Interpolated(ref nt) => match **nt {
                 token::NtMeta(ref e) => Some(e.clone()),
                 _ => None,
@@ -249,7 +287,7 @@ impl<'a> Parser<'a> {
             return Ok(meta);
         }
 
-        let lo = self.span;
+        let lo = self.token.span;
         let path = self.parse_path(PathStyle::Mod)?;
         let node = self.parse_meta_item_kind()?;
         let span = lo.to(self.prev_span);
@@ -284,7 +322,7 @@ impl<'a> Parser<'a> {
 
         let found = self.this_token_to_string();
         let msg = format!("expected unsuffixed literal or identifier, found `{}`", found);
-        Err(self.diagnostic().struct_span_err(self.span, &msg))
+        Err(self.diagnostic().struct_span_err(self.token.span, &msg))
     }
 
     /// matches meta_seq = ( COMMASEP(meta_item_inner) )
diff --git a/src/libsyntax/parse/classify.rs b/src/libsyntax/parse/classify.rs
index dfd6f451c28..6ebfab3a133 100644
--- a/src/libsyntax/parse/classify.rs
+++ b/src/libsyntax/parse/classify.rs
@@ -14,11 +14,9 @@ use crate::ast;
 pub fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool {
     match e.node {
         ast::ExprKind::If(..) |
-        ast::ExprKind::IfLet(..) |
         ast::ExprKind::Match(..) |
         ast::ExprKind::Block(..) |
         ast::ExprKind::While(..) |
-        ast::ExprKind::WhileLet(..) |
         ast::ExprKind::Loop(..) |
         ast::ExprKind::ForLoop(..) |
         ast::ExprKind::TryBlock(..) => false,
diff --git a/src/libsyntax/parse/diagnostics.rs b/src/libsyntax/parse/diagnostics.rs
index 1a2393be806..1fbf28fb830 100644
--- a/src/libsyntax/parse/diagnostics.rs
+++ b/src/libsyntax/parse/diagnostics.rs
@@ -1,16 +1,118 @@
-use crate::ast;
-use crate::ast::{BlockCheckMode, Expr, ExprKind, Item, ItemKind, Pat, PatKind, QSelf, Ty, TyKind};
-use crate::parse::parser::{BlockMode, PathStyle, TokenType, SemiColonMode};
-use crate::parse::token;
-use crate::parse::PResult;
-use crate::parse::Parser;
+use crate::ast::{
+    self, Arg, BinOpKind, BindingMode, BlockCheckMode, Expr, ExprKind, Ident, Item, ItemKind,
+    Mutability, Pat, PatKind, PathSegment, QSelf, Ty, TyKind, VariantData,
+};
+use crate::feature_gate::{feature_err, UnstableFeatures};
+use crate::parse::{SeqSep, PResult, Parser, ParseSess};
+use crate::parse::parser::{BlockMode, PathStyle, SemiColonMode, TokenType, TokenExpectType};
+use crate::parse::token::{self, TokenKind};
 use crate::print::pprust;
 use crate::ptr::P;
-use crate::symbol::keywords;
+use crate::symbol::{kw, sym};
 use crate::ThinVec;
-use errors::{Applicability, DiagnosticBuilder};
-use syntax_pos::Span;
-use log::debug;
+use crate::util::parser::AssocOp;
+use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
+use rustc_data_structures::fx::FxHashSet;
+use syntax_pos::{Span, DUMMY_SP, MultiSpan, SpanSnippetError};
+use log::{debug, trace};
+use std::mem;
+
+/// Creates a placeholder argument.
+crate fn dummy_arg(ident: Ident) -> Arg {
+    let pat = P(Pat {
+        id: ast::DUMMY_NODE_ID,
+        node: PatKind::Ident(BindingMode::ByValue(Mutability::Immutable), ident, None),
+        span: ident.span,
+    });
+    let ty = Ty {
+        node: TyKind::Err,
+        span: ident.span,
+        id: ast::DUMMY_NODE_ID
+    };
+    Arg { attrs: ThinVec::default(), id: ast::DUMMY_NODE_ID, pat, span: ident.span, ty: P(ty) }
+}
+
+pub enum Error {
+    FileNotFoundForModule {
+        mod_name: String,
+        default_path: String,
+        secondary_path: String,
+        dir_path: String,
+    },
+    DuplicatePaths {
+        mod_name: String,
+        default_path: String,
+        secondary_path: String,
+    },
+    UselessDocComment,
+    InclusiveRangeWithNoEnd,
+}
+
+impl Error {
+    fn span_err<S: Into<MultiSpan>>(
+        self,
+        sp: S,
+        handler: &errors::Handler,
+    ) -> DiagnosticBuilder<'_> {
+        match self {
+            Error::FileNotFoundForModule {
+                ref mod_name,
+                ref default_path,
+                ref secondary_path,
+                ref dir_path,
+            } => {
+                let mut err = struct_span_err!(
+                    handler,
+                    sp,
+                    E0583,
+                    "file not found for module `{}`",
+                    mod_name,
+                );
+                err.help(&format!(
+                    "name the file either {} or {} inside the directory \"{}\"",
+                    default_path,
+                    secondary_path,
+                    dir_path,
+                ));
+                err
+            }
+            Error::DuplicatePaths { ref mod_name, ref default_path, ref secondary_path } => {
+                let mut err = struct_span_err!(
+                    handler,
+                    sp,
+                    E0584,
+                    "file for module `{}` found at both {} and {}",
+                    mod_name,
+                    default_path,
+                    secondary_path,
+                );
+                err.help("delete or rename one of them to remove the ambiguity");
+                err
+            }
+            Error::UselessDocComment => {
+                let mut err = struct_span_err!(
+                    handler,
+                    sp,
+                    E0585,
+                    "found a documentation comment that doesn't document anything",
+                );
+                err.help("doc comments must come before what they document, maybe a comment was \
+                          intended with `//`?");
+                err
+            }
+            Error::InclusiveRangeWithNoEnd => {
+                let mut err = struct_span_err!(
+                    handler,
+                    sp,
+                    E0586,
+                    "inclusive range with no end",
+                );
+                err.help("inclusive ranges must be bounded at the end (`..=b` or `a..=b`)");
+                err
+            }
+        }
+    }
+}
 
 pub trait RecoverQPath: Sized + 'static {
     const PATH_STYLE: PathStyle = PathStyle::Expr;
@@ -60,6 +162,414 @@ impl RecoverQPath for Expr {
 }
 
 impl<'a> Parser<'a> {
+    pub fn fatal(&self, m: &str) -> DiagnosticBuilder<'a> {
+        self.span_fatal(self.token.span, m)
+    }
+
+    pub fn span_fatal<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> DiagnosticBuilder<'a> {
+        self.sess.span_diagnostic.struct_span_fatal(sp, m)
+    }
+
+    pub fn span_fatal_err<S: Into<MultiSpan>>(&self, sp: S, err: Error) -> DiagnosticBuilder<'a> {
+        err.span_err(sp, self.diagnostic())
+    }
+
+    pub fn bug(&self, m: &str) -> ! {
+        self.sess.span_diagnostic.span_bug(self.token.span, m)
+    }
+
+    pub fn span_err<S: Into<MultiSpan>>(&self, sp: S, m: &str) {
+        self.sess.span_diagnostic.span_err(sp, m)
+    }
+
+    crate fn struct_span_err<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> DiagnosticBuilder<'a> {
+        self.sess.span_diagnostic.struct_span_err(sp, m)
+    }
+
+    crate fn span_bug<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> ! {
+        self.sess.span_diagnostic.span_bug(sp, m)
+    }
+
+    crate fn cancel(&self, err: &mut DiagnosticBuilder<'_>) {
+        self.sess.span_diagnostic.cancel(err)
+    }
+
+    crate fn diagnostic(&self) -> &'a errors::Handler {
+        &self.sess.span_diagnostic
+    }
+
+    crate fn span_to_snippet(&self, span: Span) -> Result<String, SpanSnippetError> {
+        self.sess.source_map().span_to_snippet(span)
+    }
+
+    crate fn expected_ident_found(&self) -> DiagnosticBuilder<'a> {
+        let mut err = self.struct_span_err(
+            self.token.span,
+            &format!("expected identifier, found {}", self.this_token_descr()),
+        );
+        if let token::Ident(name, false) = self.token.kind {
+            if Ident::new(name, self.token.span).is_raw_guess() {
+                err.span_suggestion(
+                    self.token.span,
+                    "you can escape reserved keywords to use them as identifiers",
+                    format!("r#{}", name),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+        }
+        if let Some(token_descr) = self.token_descr() {
+            err.span_label(self.token.span, format!("expected identifier, found {}", token_descr));
+        } else {
+            err.span_label(self.token.span, "expected identifier");
+            if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
+                err.span_suggestion(
+                    self.token.span,
+                    "remove this comma",
+                    String::new(),
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+        err
+    }
+
+    pub fn expected_one_of_not_found(
+        &mut self,
+        edible: &[TokenKind],
+        inedible: &[TokenKind],
+    ) -> PResult<'a, bool /* recovered */> {
+        fn tokens_to_string(tokens: &[TokenType]) -> String {
+            let mut i = tokens.iter();
+            // This might be a sign we need a connect method on Iterator.
+            let b = i.next()
+                     .map_or(String::new(), |t| t.to_string());
+            i.enumerate().fold(b, |mut b, (i, a)| {
+                if tokens.len() > 2 && i == tokens.len() - 2 {
+                    b.push_str(", or ");
+                } else if tokens.len() == 2 && i == tokens.len() - 2 {
+                    b.push_str(" or ");
+                } else {
+                    b.push_str(", ");
+                }
+                b.push_str(&a.to_string());
+                b
+            })
+        }
+
+        let mut expected = edible.iter()
+            .map(|x| TokenType::Token(x.clone()))
+            .chain(inedible.iter().map(|x| TokenType::Token(x.clone())))
+            .chain(self.expected_tokens.iter().cloned())
+            .collect::<Vec<_>>();
+        expected.sort_by_cached_key(|x| x.to_string());
+        expected.dedup();
+        let expect = tokens_to_string(&expected[..]);
+        let actual = self.this_token_to_string();
+        let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
+            let short_expect = if expected.len() > 6 {
+                format!("{} possible tokens", expected.len())
+            } else {
+                expect.clone()
+            };
+            (format!("expected one of {}, found `{}`", expect, actual),
+                (self.sess.source_map().next_point(self.prev_span),
+                format!("expected one of {} here", short_expect)))
+        } else if expected.is_empty() {
+            (format!("unexpected token: `{}`", actual),
+                (self.prev_span, "unexpected token after this".to_string()))
+        } else {
+            (format!("expected {}, found `{}`", expect, actual),
+                (self.sess.source_map().next_point(self.prev_span),
+                format!("expected {} here", expect)))
+        };
+        self.last_unexpected_token_span = Some(self.token.span);
+        let mut err = self.fatal(&msg_exp);
+        if self.token.is_ident_named(sym::and) {
+            err.span_suggestion_short(
+                self.token.span,
+                "use `&&` instead of `and` for the boolean operator",
+                "&&".to_string(),
+                Applicability::MaybeIncorrect,
+            );
+        }
+        if self.token.is_ident_named(sym::or) {
+            err.span_suggestion_short(
+                self.token.span,
+                "use `||` instead of `or` for the boolean operator",
+                "||".to_string(),
+                Applicability::MaybeIncorrect,
+            );
+        }
+        let sp = if self.token == token::Eof {
+            // This is EOF, don't want to point at the following char, but rather the last token
+            self.prev_span
+        } else {
+            label_sp
+        };
+        match self.recover_closing_delimiter(&expected.iter().filter_map(|tt| match tt {
+            TokenType::Token(t) => Some(t.clone()),
+            _ => None,
+        }).collect::<Vec<_>>(), err) {
+            Err(e) => err = e,
+            Ok(recovered) => {
+                return Ok(recovered);
+            }
+        }
+
+        let is_semi_suggestable = expected.iter().any(|t| match t {
+            TokenType::Token(token::Semi) => true, // we expect a `;` here
+            _ => false,
+        }) && ( // a `;` would be expected before the current keyword
+            self.token.is_keyword(kw::Break) ||
+            self.token.is_keyword(kw::Continue) ||
+            self.token.is_keyword(kw::For) ||
+            self.token.is_keyword(kw::If) ||
+            self.token.is_keyword(kw::Let) ||
+            self.token.is_keyword(kw::Loop) ||
+            self.token.is_keyword(kw::Match) ||
+            self.token.is_keyword(kw::Return) ||
+            self.token.is_keyword(kw::While)
+        );
+        let sm = self.sess.source_map();
+        match (sm.lookup_line(self.token.span.lo()), sm.lookup_line(sp.lo())) {
+            (Ok(ref a), Ok(ref b)) if a.line != b.line && is_semi_suggestable => {
+                // The spans are in different lines, expected `;` and found `let` or `return`.
+                // High likelihood that it is only a missing `;`.
+                err.span_suggestion_short(
+                    label_sp,
+                    "a semicolon may be missing here",
+                    ";".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+                err.emit();
+                return Ok(true);
+            }
+            (Ok(ref a), Ok(ref b)) if a.line == b.line => {
+                // When the spans are in the same line, it means that the only content between
+                // them is whitespace, point at the found token in that case:
+                //
+                // X |     () => { syntax error };
+                //   |                    ^^^^^ expected one of 8 possible tokens here
+                //
+                // instead of having:
+                //
+                // X |     () => { syntax error };
+                //   |                   -^^^^^ unexpected token
+                //   |                   |
+                //   |                   expected one of 8 possible tokens here
+                err.span_label(self.token.span, label_exp);
+            }
+            _ if self.prev_span == syntax_pos::DUMMY_SP => {
+                // Account for macro context where the previous span might not be
+                // available to avoid incorrect output (#54841).
+                err.span_label(self.token.span, "unexpected token");
+            }
+            _ => {
+                err.span_label(sp, label_exp);
+                err.span_label(self.token.span, "unexpected token");
+            }
+        }
+        self.maybe_annotate_with_ascription(&mut err, false);
+        Err(err)
+    }
+
+    pub fn maybe_annotate_with_ascription(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        maybe_expected_semicolon: bool,
+    ) {
+        if let Some((sp, likely_path)) = self.last_type_ascription {
+            let sm = self.sess.source_map();
+            let next_pos = sm.lookup_char_pos(self.token.span.lo());
+            let op_pos = sm.lookup_char_pos(sp.hi());
+
+            if likely_path {
+                err.span_suggestion(
+                    sp,
+                    "maybe write a path separator here",
+                    "::".to_string(),
+                    match self.sess.unstable_features {
+                        UnstableFeatures::Disallow => Applicability::MachineApplicable,
+                        _ => Applicability::MaybeIncorrect,
+                    },
+                );
+            } else if op_pos.line != next_pos.line && maybe_expected_semicolon {
+                err.span_suggestion(
+                    sp,
+                    "try using a semicolon",
+                    ";".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            } else if let UnstableFeatures::Disallow = self.sess.unstable_features {
+                err.span_label(sp, "tried to parse a type due to this");
+            } else {
+                err.span_label(sp, "tried to parse a type due to this type ascription");
+            }
+            if let UnstableFeatures::Disallow = self.sess.unstable_features {
+                // Give extra information about type ascription only if it's a nightly compiler.
+            } else {
+                err.note("`#![feature(type_ascription)]` lets you annotate an expression with a \
+                          type: `<expr>: <type>`");
+                err.note("for more information, see \
+                          https://github.com/rust-lang/rust/issues/23416");
+            }
+        }
+    }
+
+    /// Eats and discards tokens until one of `kets` is encountered. Respects token trees,
+    /// passes through any errors encountered. Used for error recovery.
+    crate fn eat_to_tokens(&mut self, kets: &[&TokenKind]) {
+        let handler = self.diagnostic();
+
+        if let Err(ref mut err) = self.parse_seq_to_before_tokens(
+            kets,
+            SeqSep::none(),
+            TokenExpectType::Expect,
+            |p| Ok(p.parse_token_tree()),
+        ) {
+            handler.cancel(err);
+        }
+    }
+
+    /// This function checks if there are trailing angle brackets and produces
+    /// a diagnostic to suggest removing them.
+    ///
+    /// ```ignore (diagnostic)
+    /// let _ = vec![1, 2, 3].into_iter().collect::<Vec<usize>>>>();
+    ///                                                        ^^ help: remove extra angle brackets
+    /// ```
+    crate fn check_trailing_angle_brackets(&mut self, segment: &PathSegment, end: TokenKind) {
+        // This function is intended to be invoked after parsing a path segment where there are two
+        // cases:
+        //
+        // 1. A specific token is expected after the path segment.
+        //    eg. `x.foo(`, `x.foo::<u32>(` (parenthesis - method call),
+        //        `Foo::`, or `Foo::<Bar>::` (mod sep - continued path).
+        // 2. No specific token is expected after the path segment.
+        //    eg. `x.foo` (field access)
+        //
+        // This function is called after parsing `.foo` and before parsing the token `end` (if
+        // present). This includes any angle bracket arguments, such as `.foo::<u32>` or
+        // `Foo::<Bar>`.
+
+        // We only care about trailing angle brackets if we previously parsed angle bracket
+        // arguments. This helps stop us incorrectly suggesting that extra angle brackets be
+        // removed in this case:
+        //
+        // `x.foo >> (3)` (where `x.foo` is a `u32` for example)
+        //
+        // This case is particularly tricky as we won't notice it just looking at the tokens -
+        // it will appear the same (in terms of upcoming tokens) as below (since the `::<u32>` will
+        // have already been parsed):
+        //
+        // `x.foo::<u32>>>(3)`
+        let parsed_angle_bracket_args = segment.args
+            .as_ref()
+            .map(|args| args.is_angle_bracketed())
+            .unwrap_or(false);
+
+        debug!(
+            "check_trailing_angle_brackets: parsed_angle_bracket_args={:?}",
+            parsed_angle_bracket_args,
+        );
+        if !parsed_angle_bracket_args {
+            return;
+        }
+
+        // Keep the span at the start so we can highlight the sequence of `>` characters to be
+        // removed.
+        let lo = self.token.span;
+
+        // We need to look-ahead to see if we have `>` characters without moving the cursor forward
+        // (since we might have the field access case and the characters we're eating are
+        // actual operators and not trailing characters - ie `x.foo >> 3`).
+        let mut position = 0;
+
+        // We can encounter `>` or `>>` tokens in any order, so we need to keep track of how
+        // many of each (so we can correctly pluralize our error messages) and continue to
+        // advance.
+        let mut number_of_shr = 0;
+        let mut number_of_gt = 0;
+        while self.look_ahead(position, |t| {
+            trace!("check_trailing_angle_brackets: t={:?}", t);
+            if *t == token::BinOp(token::BinOpToken::Shr) {
+                number_of_shr += 1;
+                true
+            } else if *t == token::Gt {
+                number_of_gt += 1;
+                true
+            } else {
+                false
+            }
+        }) {
+            position += 1;
+        }
+
+        // If we didn't find any trailing `>` characters, then we have nothing to error about.
+        debug!(
+            "check_trailing_angle_brackets: number_of_gt={:?} number_of_shr={:?}",
+            number_of_gt, number_of_shr,
+        );
+        if number_of_gt < 1 && number_of_shr < 1 {
+            return;
+        }
+
+        // Finally, double check that we have our end token as otherwise this is the
+        // second case.
+        if self.look_ahead(position, |t| {
+            trace!("check_trailing_angle_brackets: t={:?}", t);
+            *t == end
+        }) {
+            // Eat from where we started until the end token so that parsing can continue
+            // as if we didn't have those extra angle brackets.
+            self.eat_to_tokens(&[&end]);
+            let span = lo.until(self.token.span);
+
+            let plural = number_of_gt > 1 || number_of_shr >= 1;
+            self.diagnostic()
+                .struct_span_err(
+                    span,
+                    &format!("unmatched angle bracket{}", if plural { "s" } else { "" }),
+                )
+                .span_suggestion(
+                    span,
+                    &format!("remove extra angle bracket{}", if plural { "s" } else { "" }),
+                    String::new(),
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+        }
+    }
+
+    /// Produce an error if comparison operators are chained (RFC #558).
+    /// We only need to check lhs, not rhs, because all comparison ops
+    /// have same precedence and are left-associative
+    crate fn check_no_chained_comparison(&self, lhs: &Expr, outer_op: &AssocOp) {
+        debug_assert!(outer_op.is_comparison(),
+                      "check_no_chained_comparison: {:?} is not comparison",
+                      outer_op);
+        match lhs.node {
+            ExprKind::Binary(op, _, _) if op.node.is_comparison() => {
+                // respan to include both operators
+                let op_span = op.span.to(self.token.span);
+                let mut err = self.struct_span_err(
+                    op_span,
+                    "chained comparison operators require parentheses",
+                );
+                if op.node == BinOpKind::Lt &&
+                    *outer_op == AssocOp::Less ||  // Include `<` to provide this recommendation
+                    *outer_op == AssocOp::Greater  // even in a case like the following:
+                {                                  //     Foo<Bar<Baz<Qux, ()>>>
+                    err.help(
+                        "use `::<...>` instead of `<...>` if you meant to specify type arguments");
+                    err.help("or use `(...)` if you meant to specify fn arguments");
+                }
+                err.emit();
+            }
+            _ => {}
+        }
+    }
+
     crate fn maybe_report_ambiguous_plus(
         &mut self,
         allow_plus: bool,
@@ -79,6 +589,54 @@ impl<'a> Parser<'a> {
         }
     }
 
+    crate fn maybe_report_invalid_custom_discriminants(
+        sess: &ParseSess,
+        variants: &[ast::Variant],
+    ) {
+        let has_fields = variants.iter().any(|variant| match variant.data {
+            VariantData::Tuple(..) | VariantData::Struct(..) => true,
+            VariantData::Unit(..) => false,
+        });
+
+        let discriminant_spans = variants.iter().filter(|variant| match variant.data {
+            VariantData::Tuple(..) | VariantData::Struct(..) => false,
+            VariantData::Unit(..) => true,
+        })
+        .filter_map(|variant| variant.disr_expr.as_ref().map(|c| c.value.span))
+        .collect::<Vec<_>>();
+
+        if !discriminant_spans.is_empty() && has_fields {
+            let mut err = feature_err(
+                sess,
+                sym::arbitrary_enum_discriminant,
+                discriminant_spans.clone(),
+                crate::feature_gate::GateIssue::Language,
+                "custom discriminant values are not allowed in enums with tuple or struct variants",
+            );
+            for sp in discriminant_spans {
+                err.span_label(sp, "disallowed custom discriminant");
+            }
+            for variant in variants.iter() {
+                match &variant.data {
+                    VariantData::Struct(..) => {
+                        err.span_label(
+                            variant.span,
+                            "struct variant defined here",
+                        );
+                    }
+                    VariantData::Tuple(..) => {
+                        err.span_label(
+                            variant.span,
+                            "tuple variant defined here",
+                        );
+                    }
+                    VariantData::Unit(..) => {}
+                }
+            }
+            err.emit();
+        }
+    }
+
     crate fn maybe_recover_from_bad_type_plus(
         &mut self,
         allow_plus: bool,
@@ -104,14 +662,12 @@ impl<'a> Parser<'a> {
         match ty.node {
             TyKind::Rptr(ref lifetime, ref mut_ty) => {
                 let sum_with_parens = pprust::to_string(|s| {
-                    use crate::print::pprust::PrintState;
-
-                    s.s.word("&")?;
-                    s.print_opt_lifetime(lifetime)?;
-                    s.print_mutability(mut_ty.mutbl)?;
-                    s.popen()?;
-                    s.print_type(&mut_ty.ty)?;
-                    s.print_type_bounds(" +", &bounds)?;
+                    s.s.word("&");
+                    s.print_opt_lifetime(lifetime);
+                    s.print_mutability(mut_ty.mutbl);
+                    s.popen();
+                    s.print_type(&mut_ty.ty);
+                    s.print_type_bounds(" +", &bounds);
                     s.pclose()
                 });
                 err.span_suggestion(
@@ -160,14 +716,12 @@ impl<'a> Parser<'a> {
 
         let mut path = ast::Path {
             segments: Vec::new(),
-            span: syntax_pos::DUMMY_SP,
+            span: DUMMY_SP,
         };
         self.parse_path_segments(&mut path.segments, T::PATH_STYLE)?;
         path.span = ty_span.to(self.prev_span);
 
         let ty_str = self
-            .sess
-            .source_map()
             .span_to_snippet(ty_span)
             .unwrap_or_else(|_| pprust::ty_to_string(&ty));
         self.diagnostic()
@@ -226,13 +780,111 @@ impl<'a> Parser<'a> {
         }
     }
 
-    /// Consume alternative await syntaxes like `await <expr>`, `await? <expr>`, `await(<expr>)`
-    /// and `await { <expr> }`.
+    /// Create a `DiagnosticBuilder` for an unexpected token `t` and try to recover if it is a
+    /// closing delimiter.
+    pub fn unexpected_try_recover(
+        &mut self,
+        t: &TokenKind,
+    ) -> PResult<'a, bool /* recovered */> {
+        let token_str = pprust::token_kind_to_string(t);
+        let this_token_str = self.this_token_descr();
+        let (prev_sp, sp) = match (&self.token.kind, self.subparser_name) {
+            // Point at the end of the macro call when reaching end of macro arguments.
+            (token::Eof, Some(_)) => {
+                let sp = self.sess.source_map().next_point(self.token.span);
+                (sp, sp)
+            }
+            // We don't want to point at the following span after DUMMY_SP.
+            // This happens when the parser finds an empty TokenStream.
+            _ if self.prev_span == DUMMY_SP => (self.token.span, self.token.span),
+            // EOF, don't want to point at the following char, but rather the last token.
+            (token::Eof, None) => (self.prev_span, self.token.span),
+            _ => (self.sess.source_map().next_point(self.prev_span), self.token.span),
+        };
+        let msg = format!(
+            "expected `{}`, found {}",
+            token_str,
+            match (&self.token.kind, self.subparser_name) {
+                (token::Eof, Some(origin)) => format!("end of {}", origin),
+                _ => this_token_str,
+            },
+        );
+        let mut err = self.struct_span_err(sp, &msg);
+        let label_exp = format!("expected `{}`", token_str);
+        match self.recover_closing_delimiter(&[t.clone()], err) {
+            Err(e) => err = e,
+            Ok(recovered) => {
+                return Ok(recovered);
+            }
+        }
+        let sm = self.sess.source_map();
+        match (sm.lookup_line(prev_sp.lo()), sm.lookup_line(sp.lo())) {
+            (Ok(ref a), Ok(ref b)) if a.line == b.line => {
+                // When the spans are in the same line, it means that the only content
+                // between them is whitespace, point only at the found token.
+                err.span_label(sp, label_exp);
+            }
+            _ => {
+                err.span_label(prev_sp, label_exp);
+                err.span_label(sp, "unexpected token");
+            }
+        }
+        Err(err)
+    }
+
+    crate fn parse_semi_or_incorrect_foreign_fn_body(
+        &mut self,
+        ident: &Ident,
+        extern_sp: Span,
+    ) -> PResult<'a, ()> {
+        if self.token != token::Semi {
+            // this might be an incorrect fn definition (#62109)
+            let parser_snapshot = self.clone();
+            match self.parse_inner_attrs_and_block() {
+                Ok((_, body)) => {
+                    self.struct_span_err(ident.span, "incorrect `fn` inside `extern` block")
+                        .span_label(ident.span, "can't have a body")
+                        .span_label(body.span, "this body is invalid here")
+                        .span_label(
+                            extern_sp,
+                            "`extern` blocks define existing foreign functions and `fn`s \
+                             inside of them cannot have a body")
+                        .help("you might have meant to write a function accessible through ffi, \
+                               which can be done by writing `extern fn` outside of the \
+                               `extern` block")
+                        .note("for more information, visit \
+                               https://doc.rust-lang.org/std/keyword.extern.html")
+                        .emit();
+                }
+                Err(mut err) => {
+                    err.cancel();
+                    mem::replace(self, parser_snapshot);
+                    self.expect(&token::Semi)?;
+                }
+            }
+        } else {
+            self.bump();
+        }
+        Ok(())
+    }
+
+    /// Consume alternative await syntaxes like `await!(<expr>)`, `await <expr>`,
+    /// `await? <expr>`, `await(<expr>)`, and `await { <expr> }`.
     crate fn parse_incorrect_await_syntax(
         &mut self,
         lo: Span,
         await_sp: Span,
     ) -> PResult<'a, (Span, ExprKind)> {
+        if self.token == token::Not {
+            // Handle `await!(<expr>)`.
+            self.expect(&token::Not)?;
+            self.expect(&token::OpenDelim(token::Paren))?;
+            let expr = self.parse_expr()?;
+            self.expect(&token::CloseDelim(token::Paren))?;
+            let sp = self.error_on_incorrect_await(lo, self.prev_span, &expr, false);
+            return Ok((sp, ExprKind::Await(expr)))
+        }
+
         let is_question = self.eat(&token::Question); // Handle `await? <expr>`.
         let expr = if self.token == token::OpenDelim(token::Brace) {
             // Handle `await { <expr> }`.
@@ -240,7 +892,7 @@ impl<'a> Parser<'a> {
             // interpreting `await { <expr> }?` as `<expr>?.await`.
             self.parse_block_expr(
                 None,
-                self.span,
+                self.token.span,
                 BlockCheckMode::Default,
                 ThinVec::new(),
             )
@@ -250,10 +902,15 @@ impl<'a> Parser<'a> {
             err.span_label(await_sp, "while parsing this incorrect await expression");
             err
         })?;
-        let expr_str = self.sess.source_map().span_to_snippet(expr.span)
+        let sp = self.error_on_incorrect_await(lo, expr.span, &expr, is_question);
+        Ok((sp, ExprKind::Await(expr)))
+    }
+
+    fn error_on_incorrect_await(&self, lo: Span, hi: Span, expr: &Expr, is_question: bool) -> Span {
+        let expr_str = self.span_to_snippet(expr.span)
             .unwrap_or_else(|_| pprust::expr_to_string(&expr));
         let suggestion = format!("{}.await{}", expr_str, if is_question { "?" } else { "" });
-        let sp = lo.to(expr.span);
+        let sp = lo.to(hi);
         let app = match expr.node {
             ExprKind::Try(_) => Applicability::MaybeIncorrect, // `await <expr>?`
             _ => Applicability::MachineApplicable,
@@ -261,7 +918,7 @@ impl<'a> Parser<'a> {
         self.struct_span_err(sp, "incorrect use of `await`")
             .span_suggestion(sp, "`await` is a postfix operation", suggestion, app)
             .emit();
-        Ok((sp, ExprKind::Await(ast::AwaitOrigin::FieldLike, expr)))
+        sp
     }
 
     /// If encountering `future.await()`, consume and emit error.
@@ -270,9 +927,9 @@ impl<'a> Parser<'a> {
             self.look_ahead(1, |t| t == &token::CloseDelim(token::Paren))
         {
             // future.await()
-            let lo = self.span;
+            let lo = self.token.span;
             self.bump(); // (
-            let sp = lo.to(self.span);
+            let sp = lo.to(self.token.span);
             self.bump(); // )
             self.struct_span_err(sp, "incorrect use of `await`")
                 .span_suggestion(
@@ -284,6 +941,48 @@ impl<'a> Parser<'a> {
         }
     }
 
+    /// Recover a situation like `for ( $pat in $expr )`
+    /// and suggest writing `for $pat in $expr` instead.
+    ///
+    /// This should be called before parsing the `$block`.
+    crate fn recover_parens_around_for_head(
+        &mut self,
+        pat: P<Pat>,
+        expr: &Expr,
+        begin_paren: Option<Span>,
+    ) -> P<Pat> {
+        match (&self.token.kind, begin_paren) {
+            (token::CloseDelim(token::Paren), Some(begin_par_sp)) => {
+                self.bump();
+
+                let pat_str = self
+                    // Remove the `(` from the span of the pattern:
+                    .span_to_snippet(pat.span.trim_start(begin_par_sp).unwrap())
+                    .unwrap_or_else(|_| pprust::pat_to_string(&pat));
+
+                self.struct_span_err(self.prev_span, "unexpected closing `)`")
+                    .span_label(begin_par_sp, "opening `(`")
+                    .span_suggestion(
+                        begin_par_sp.to(self.prev_span),
+                        "remove parenthesis in `for` loop",
+                        format!("{} in {}", pat_str, pprust::expr_to_string(&expr)),
+                        // With e.g. `for (x) in y)` this would replace `(x) in y)`
+                        // with `x) in y)` which is syntactically invalid.
+                        // However, this is prevented before we get here.
+                        Applicability::MachineApplicable,
+                    )
+                    .emit();
+
+                // Unwrap `(pat)` into `pat` to avoid the `unused_parens` lint.
+                pat.and_then(|pat| match pat.node {
+                    PatKind::Paren(pat) => pat,
+                    _ => P(pat),
+                })
+            }
+            _ => pat,
+        }
+    }
+
     crate fn could_ascription_be_path(&self, node: &ast::ExprKind) -> bool {
         self.token.is_ident() &&
             if let ast::ExprKind::Path(..) = node { true } else { false } &&
@@ -293,47 +992,9 @@ impl<'a> Parser<'a> {
             self.look_ahead(2, |t| t.is_ident()) ||
             self.look_ahead(1, |t| t == &token::Colon) &&  // `foo:bar:baz`
             self.look_ahead(2, |t| t.is_ident()) ||
-            self.look_ahead(1, |t| t == &token::ModSep) &&  // `foo:bar::baz`
-            self.look_ahead(2, |t| t.is_ident())
-    }
-
-    crate fn bad_type_ascription(
-        &self,
-        err: &mut DiagnosticBuilder<'a>,
-        lhs_span: Span,
-        cur_op_span: Span,
-        next_sp: Span,
-        maybe_path: bool,
-    ) {
-        err.span_label(self.span, "expecting a type here because of type ascription");
-        let cm = self.sess.source_map();
-        let next_pos = cm.lookup_char_pos(next_sp.lo());
-        let op_pos = cm.lookup_char_pos(cur_op_span.hi());
-        if op_pos.line != next_pos.line {
-            err.span_suggestion(
-                cur_op_span,
-                "try using a semicolon",
-                ";".to_string(),
-                Applicability::MaybeIncorrect,
-            );
-        } else {
-            if maybe_path {
-                err.span_suggestion(
-                    cur_op_span,
-                    "maybe you meant to write a path separator here",
-                    "::".to_string(),
-                    Applicability::MaybeIncorrect,
-                );
-            } else {
-                err.note("type ascription is a nightly-only feature that lets \
-                          you annotate an expression with a type: `<expr>: <type>`")
-                    .span_note(
-                        lhs_span,
-                        "this expression expects an ascribed type after the colon",
-                    )
-                    .help("this might be indicative of a syntax error elsewhere");
-            }
-        }
+            self.look_ahead(1, |t| t == &token::ModSep) &&
+            (self.look_ahead(2, |t| t.is_ident()) ||   // `foo:bar::baz`
+             self.look_ahead(2, |t| t == &token::Lt))  // `foo:bar::<baz>`
     }
 
     crate fn recover_seq_parse_error(
@@ -355,14 +1016,14 @@ impl<'a> Parser<'a> {
 
     crate fn recover_closing_delimiter(
         &mut self,
-        tokens: &[token::Token],
+        tokens: &[TokenKind],
         mut err: DiagnosticBuilder<'a>,
     ) -> PResult<'a, bool> {
         let mut pos = None;
         // we want to use the last closing delim that would apply
         for (i, unmatched) in self.unclosed_delims.iter().enumerate().rev() {
             if tokens.contains(&token::CloseDelim(unmatched.expected_delim))
-                && Some(self.span) > unmatched.unclosed_span
+                && Some(self.token.span) > unmatched.unclosed_span
             {
                 pos = Some(i);
             }
@@ -383,7 +1044,7 @@ impl<'a> Parser<'a> {
                 //  {foo(bar {}}
                 //      -      ^
                 //      |      |
-                //      |      help: `)` may belong here (FIXME: #58270)
+                //      |      help: `)` may belong here
                 //      |
                 //      unclosed delimiter
                 if let Some(sp) = unmatched.unclosed_span {
@@ -405,7 +1066,7 @@ impl<'a> Parser<'a> {
 
     /// Recover from `pub` keyword in places where it seems _reasonable_ but isn't valid.
     crate fn eat_bad_pub(&mut self) {
-        if self.token.is_keyword(keywords::Pub) {
+        if self.token.is_keyword(kw::Pub) {
             match self.parse_visibility(false) {
                 Ok(vis) => {
                     self.diagnostic()
@@ -441,7 +1102,7 @@ impl<'a> Parser<'a> {
                break_on_semi, break_on_block);
         loop {
             debug!("recover_stmt_ loop {:?}", self.token);
-            match self.token {
+            match self.token.kind {
                 token::OpenDelim(token::DelimToken::Brace) => {
                     brace_depth += 1;
                     self.bump();
@@ -501,6 +1162,148 @@ impl<'a> Parser<'a> {
         }
     }
 
+    crate fn check_for_for_in_in_typo(&mut self, in_span: Span) {
+        if self.eat_keyword(kw::In) {
+            // a common typo: `for _ in in bar {}`
+            self.struct_span_err(self.prev_span, "expected iterable, found keyword `in`")
+                .span_suggestion_short(
+                    in_span.until(self.prev_span),
+                    "remove the duplicated `in`",
+                    String::new(),
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+        }
+    }
+
+    crate fn expected_semi_or_open_brace(&mut self) -> PResult<'a, ast::TraitItem> {
+        let token_str = self.this_token_descr();
+        let mut err = self.fatal(&format!("expected `;` or `{{`, found {}", token_str));
+        err.span_label(self.token.span, "expected `;` or `{`");
+        Err(err)
+    }
+
+    crate fn eat_incorrect_doc_comment_for_arg_type(&mut self) {
+        if let token::DocComment(_) = self.token.kind {
+            self.struct_span_err(
+                self.token.span,
+                "documentation comments cannot be applied to a function parameter's type",
+            )
+            .span_label(self.token.span, "doc comments are not allowed here")
+            .emit();
+            self.bump();
+        } else if self.token == token::Pound && self.look_ahead(1, |t| {
+            *t == token::OpenDelim(token::Bracket)
+        }) {
+            let lo = self.token.span;
+            // Skip every token until next possible arg.
+            while self.token != token::CloseDelim(token::Bracket) {
+                self.bump();
+            }
+            let sp = lo.to(self.token.span);
+            self.bump();
+            self.struct_span_err(
+                sp,
+                "attributes cannot be applied to a function parameter's type",
+            )
+            .span_label(sp, "attributes are not allowed here")
+            .emit();
+        }
+    }
+
+    crate fn argument_without_type(
+        &mut self,
+        err: &mut DiagnosticBuilder<'_>,
+        pat: P<ast::Pat>,
+        require_name: bool,
+        is_trait_item: bool,
+    ) -> Option<Ident> {
+        // If we find a pattern followed by an identifier, it could be an (incorrect)
+        // C-style parameter declaration.
+        if self.check_ident() && self.look_ahead(1, |t| {
+            *t == token::Comma || *t == token::CloseDelim(token::Paren)
+        }) { // `fn foo(String s) {}`
+            let ident = self.parse_ident().unwrap();
+            let span = pat.span.with_hi(ident.span.hi());
+
+            err.span_suggestion(
+                span,
+                "declare the type after the parameter binding",
+                String::from("<identifier>: <type>"),
+                Applicability::HasPlaceholders,
+            );
+            return Some(ident);
+        } else if let PatKind::Ident(_, ident, _) = pat.node {
+            if require_name && (
+                is_trait_item ||
+                self.token == token::Comma ||
+                self.token == token::CloseDelim(token::Paren)
+            ) { // `fn foo(a, b) {}` or `fn foo(usize, usize) {}`
+                err.span_suggestion(
+                    pat.span,
+                    "if this was a parameter name, give it a type",
+                    format!("{}: TypeName", ident),
+                    Applicability::HasPlaceholders,
+                );
+                err.span_suggestion(
+                    pat.span,
+                    "if this is a type, explicitly ignore the parameter name",
+                    format!("_: {}", ident),
+                    Applicability::MachineApplicable,
+                );
+                err.note("anonymous parameters are removed in the 2018 edition (see RFC 1685)");
+                return Some(ident);
+            }
+        }
+        None
+    }
+
+    crate fn recover_arg_parse(&mut self) -> PResult<'a, (P<ast::Pat>, P<ast::Ty>)> {
+        let pat = self.parse_pat(Some("argument name"))?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+
+        self.diagnostic()
+            .struct_span_err_with_code(
+                pat.span,
+                "patterns aren't allowed in methods without bodies",
+                DiagnosticId::Error("E0642".into()),
+            )
+            .span_suggestion_short(
+                pat.span,
+                "give this argument a name or use an underscore to ignore it",
+                "_".to_owned(),
+                Applicability::MachineApplicable,
+            )
+            .emit();
+
+        // Pretend the pattern is `_`, to avoid duplicate errors from AST validation.
+        let pat = P(Pat {
+            node: PatKind::Wild,
+            span: pat.span,
+            id: ast::DUMMY_NODE_ID
+        });
+        Ok((pat, ty))
+    }
+
+    crate fn recover_bad_self_arg(
+        &mut self,
+        mut arg: ast::Arg,
+        is_trait_item: bool,
+    ) -> PResult<'a, ast::Arg> {
+        let sp = arg.pat.span;
+        arg.ty.node = TyKind::Err;
+        let mut err = self.struct_span_err(sp, "unexpected `self` parameter in function");
+        if is_trait_item {
+            err.span_label(sp, "must be the first associated function parameter");
+        } else {
+            err.span_label(sp, "not valid as function parameter");
+            err.note("`self` is only valid as the first parameter of an associated function");
+        }
+        err.emit();
+        Ok(arg)
+    }
+
     crate fn consume_block(&mut self, delim: token::DelimToken) {
         let mut brace_depth = 0;
         loop {
@@ -521,4 +1324,50 @@ impl<'a> Parser<'a> {
         }
     }
 
+    crate fn expected_expression_found(&self) -> DiagnosticBuilder<'a> {
+        let (span, msg) = match (&self.token.kind, self.subparser_name) {
+            (&token::Eof, Some(origin)) => {
+                let sp = self.sess.source_map().next_point(self.token.span);
+                (sp, format!("expected expression, found end of {}", origin))
+            }
+            _ => (self.token.span, format!(
+                "expected expression, found {}",
+                self.this_token_descr(),
+            )),
+        };
+        let mut err = self.struct_span_err(span, &msg);
+        let sp = self.sess.source_map().start_point(self.token.span);
+        if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
+            self.sess.expr_parentheses_needed(&mut err, *sp, None);
+        }
+        err.span_label(span, "expected expression");
+        err
+    }
+
+    /// Replace duplicated recovered arguments with `_` pattern to avoid unecessary errors.
+    ///
+    /// This is necessary because at this point we don't know whether we parsed a function with
+    /// anonymous arguments or a function with names but no types. In order to minimize
+    /// unecessary errors, we assume the arguments are in the shape of `fn foo(a, b, c)` where
+    /// the arguments are *names* (so we don't emit errors about not being able to find `b` in
+    /// the local scope), but if we find the same name multiple times, like in `fn foo(i8, i8)`,
+    /// we deduplicate them to not complain about duplicated argument names.
+    crate fn deduplicate_recovered_arg_names(&self, fn_inputs: &mut Vec<Arg>) {
+        let mut seen_inputs = FxHashSet::default();
+        for input in fn_inputs.iter_mut() {
+            let opt_ident = if let (PatKind::Ident(_, ident, _), TyKind::Err) = (
+                &input.pat.node, &input.ty.node,
+            ) {
+                Some(*ident)
+            } else {
+                None
+            };
+            if let Some(ident) = opt_ident {
+                if seen_inputs.contains(&ident) {
+                    input.pat.node = PatKind::Wild;
+                }
+                seen_inputs.insert(ident);
+            }
+        }
+    }
 }
diff --git a/src/libsyntax/parse/lexer/comments.rs b/src/libsyntax/parse/lexer/comments.rs
index 97d3fc002e9..5121a9ef7b5 100644
--- a/src/libsyntax/parse/lexer/comments.rs
+++ b/src/libsyntax/parse/lexer/comments.rs
@@ -2,15 +2,16 @@ pub use CommentStyle::*;
 
 use crate::ast;
 use crate::source_map::SourceMap;
-use crate::parse::lexer::{is_block_doc_comment, is_pattern_whitespace};
-use crate::parse::lexer::{self, ParseSess, StringReader};
+use crate::parse::lexer::is_block_doc_comment;
+use crate::parse::lexer::ParseSess;
 
 use syntax_pos::{BytePos, CharPos, Pos, FileName};
-use log::debug;
 
-use std::io::Read;
 use std::usize;
 
+#[cfg(test)]
+mod tests;
+
 #[derive(Clone, Copy, PartialEq, Debug)]
 pub enum CommentStyle {
     /// No code on either side of each line of the comment
@@ -136,66 +137,6 @@ pub fn strip_doc_comment_decoration(comment: &str) -> String {
     panic!("not a doc-comment: {}", comment);
 }
 
-fn push_blank_line_comment(rdr: &StringReader<'_>, comments: &mut Vec<Comment>) {
-    debug!(">>> blank-line comment");
-    comments.push(Comment {
-        style: BlankLine,
-        lines: Vec::new(),
-        pos: rdr.pos,
-    });
-}
-
-fn consume_whitespace_counting_blank_lines(
-    rdr: &mut StringReader<'_>,
-    comments: &mut Vec<Comment>
-) {
-    while is_pattern_whitespace(rdr.ch) && !rdr.is_eof() {
-        if rdr.ch_is('\n') {
-            push_blank_line_comment(rdr, &mut *comments);
-        }
-        rdr.bump();
-    }
-}
-
-fn read_shebang_comment(rdr: &mut StringReader<'_>,
-                        code_to_the_left: bool,
-                        comments: &mut Vec<Comment>) {
-    debug!(">>> shebang comment");
-    let p = rdr.pos;
-    debug!("<<< shebang comment");
-    comments.push(Comment {
-        style: if code_to_the_left { Trailing } else { Isolated },
-        lines: vec![rdr.read_one_line_comment()],
-        pos: p,
-    });
-}
-
-fn read_line_comments(rdr: &mut StringReader<'_>,
-                      code_to_the_left: bool,
-                      comments: &mut Vec<Comment>) {
-    debug!(">>> line comments");
-    let p = rdr.pos;
-    let mut lines: Vec<String> = Vec::new();
-    while rdr.ch_is('/') && rdr.nextch_is('/') {
-        let line = rdr.read_one_line_comment();
-        debug!("{}", line);
-        // Doc comments are not put in comments.
-        if is_doc_comment(&line[..]) {
-            break;
-        }
-        lines.push(line);
-        rdr.consume_non_eol_whitespace();
-    }
-    debug!("<<< line comments");
-    if !lines.is_empty() {
-        comments.push(Comment {
-            style: if code_to_the_left { Trailing } else { Isolated },
-            lines,
-            pos: p,
-        });
-    }
-}
-
 /// Returns `None` if the first `col` chars of `s` contain a non-whitespace char.
 /// Otherwise returns `Some(k)` where `k` is first char offset after that leading
 /// whitespace. Note that `k` may be outside bounds of `s`.
@@ -210,224 +151,104 @@ fn all_whitespace(s: &str, col: CharPos) -> Option<usize> {
     Some(idx)
 }
 
-fn trim_whitespace_prefix_and_push_line(lines: &mut Vec<String>, s: String, col: CharPos) {
+fn trim_whitespace_prefix(s: &str, col: CharPos) -> &str {
     let len = s.len();
-    let s1 = match all_whitespace(&s[..], col) {
-        Some(col) => {
-            if col < len {
-                s[col..len].to_string()
-            } else {
-                String::new()
-            }
-        }
+    match all_whitespace(&s, col) {
+        Some(col) => if col < len { &s[col..] } else { "" },
         None => s,
-    };
-    debug!("pushing line: {}", s1);
-    lines.push(s1);
-}
-
-fn read_block_comment(rdr: &mut StringReader<'_>,
-                      code_to_the_left: bool,
-                      comments: &mut Vec<Comment>) {
-    debug!(">>> block comment");
-    let p = rdr.pos;
-    let mut lines: Vec<String> = Vec::new();
-
-    // Count the number of chars since the start of the line by rescanning.
-    let src_index = rdr.src_index(rdr.source_file.line_begin_pos(rdr.pos));
-    let end_src_index = rdr.src_index(rdr.pos);
-    assert!(src_index <= end_src_index,
-        "src_index={}, end_src_index={}, line_begin_pos={}",
-        src_index, end_src_index, rdr.source_file.line_begin_pos(rdr.pos).to_u32());
-
-    let col = CharPos(rdr.src[src_index..end_src_index].chars().count());
-
-    rdr.bump();
-    rdr.bump();
-
-    let mut curr_line = String::from("/*");
-
-    // doc-comments are not really comments, they are attributes
-    if (rdr.ch_is('*') && !rdr.nextch_is('*')) || rdr.ch_is('!') {
-        while !(rdr.ch_is('*') && rdr.nextch_is('/')) && !rdr.is_eof() {
-            curr_line.push(rdr.ch.unwrap());
-            rdr.bump();
-        }
-        if !rdr.is_eof() {
-            curr_line.push_str("*/");
-            rdr.bump();
-            rdr.bump();
-        }
-        if is_block_doc_comment(&curr_line[..]) {
-            return;
-        }
-        assert!(!curr_line.contains('\n'));
-        lines.push(curr_line);
-    } else {
-        let mut level: isize = 1;
-        while level > 0 {
-            debug!("=== block comment level {}", level);
-            if rdr.is_eof() {
-                rdr.fatal("unterminated block comment").raise();
-            }
-            if rdr.ch_is('\n') {
-                trim_whitespace_prefix_and_push_line(&mut lines, curr_line, col);
-                curr_line = String::new();
-                rdr.bump();
-            } else {
-                curr_line.push(rdr.ch.unwrap());
-                if rdr.ch_is('/') && rdr.nextch_is('*') {
-                    rdr.bump();
-                    rdr.bump();
-                    curr_line.push('*');
-                    level += 1;
-                } else {
-                    if rdr.ch_is('*') && rdr.nextch_is('/') {
-                        rdr.bump();
-                        rdr.bump();
-                        curr_line.push('/');
-                        level -= 1;
-                    } else {
-                        rdr.bump();
-                    }
-                }
-            }
-        }
-        if !curr_line.is_empty() {
-            trim_whitespace_prefix_and_push_line(&mut lines, curr_line, col);
-        }
     }
-
-    let mut style = if code_to_the_left {
-        Trailing
-    } else {
-        Isolated
-    };
-    rdr.consume_non_eol_whitespace();
-    if !rdr.is_eof() && !rdr.ch_is('\n') && lines.len() == 1 {
-        style = Mixed;
-    }
-    debug!("<<< block comment");
-    comments.push(Comment {
-        style,
-        lines,
-        pos: p,
-    });
 }
 
-
-fn consume_comment(rdr: &mut StringReader<'_>,
-                   comments: &mut Vec<Comment>,
-                   code_to_the_left: &mut bool,
-                   anything_to_the_left: &mut bool) {
-    debug!(">>> consume comment");
-    if rdr.ch_is('/') && rdr.nextch_is('/') {
-        read_line_comments(rdr, *code_to_the_left, comments);
-        *code_to_the_left = false;
-        *anything_to_the_left = false;
-    } else if rdr.ch_is('/') && rdr.nextch_is('*') {
-        read_block_comment(rdr, *code_to_the_left, comments);
-        *anything_to_the_left = true;
-    } else if rdr.ch_is('#') && rdr.nextch_is('!') {
-        read_shebang_comment(rdr, *code_to_the_left, comments);
-        *code_to_the_left = false;
-        *anything_to_the_left = false;
-    } else {
-        panic!();
-    }
-    debug!("<<< consume comment");
+fn split_block_comment_into_lines(
+    text: &str,
+    col: CharPos,
+) -> Vec<String> {
+    let mut res: Vec<String> = vec![];
+    let mut lines = text.lines();
+    // just push the first line
+    res.extend(lines.next().map(|it| it.to_string()));
+    // for other lines, strip common whitespace prefix
+    for line in lines {
+        res.push(trim_whitespace_prefix(line, col).to_string())
+    }
+    res
 }
 
 // it appears this function is called only from pprust... that's
 // probably not a good thing.
-pub fn gather_comments(sess: &ParseSess, path: FileName, srdr: &mut dyn Read) -> Vec<Comment>
-{
-    let mut src = String::new();
-    srdr.read_to_string(&mut src).unwrap();
+pub fn gather_comments(sess: &ParseSess, path: FileName, src: String) -> Vec<Comment> {
     let cm = SourceMap::new(sess.source_map().path_mapping().clone());
     let source_file = cm.new_source_file(path, src);
-    let mut rdr = lexer::StringReader::new_raw(sess, source_file, None);
+    let text = (*source_file.src.as_ref().unwrap()).clone();
 
+    let text: &str = text.as_str();
+    let start_bpos = source_file.start_pos;
+    let mut pos = 0;
     let mut comments: Vec<Comment> = Vec::new();
-    let mut code_to_the_left = false; // Only code
-    let mut anything_to_the_left = false; // Code or comments
+    let mut code_to_the_left = false;
 
-    while !rdr.is_eof() {
-        loop {
-            // Eat all the whitespace and count blank lines.
-            rdr.consume_non_eol_whitespace();
-            if rdr.ch_is('\n') {
-                if anything_to_the_left {
-                    rdr.bump(); // The line is not blank, do not count.
+    if let Some(shebang_len) = rustc_lexer::strip_shebang(text) {
+        comments.push(Comment {
+            style: Isolated,
+            lines: vec![text[..shebang_len].to_string()],
+            pos: start_bpos,
+        });
+        pos += shebang_len;
+    }
+
+    for token in rustc_lexer::tokenize(&text[pos..]) {
+        let token_text = &text[pos..pos + token.len];
+        match token.kind {
+            rustc_lexer::TokenKind::Whitespace => {
+                if let Some(mut idx) = token_text.find('\n') {
+                    code_to_the_left = false;
+                    while let Some(next_newline) = &token_text[idx + 1..].find('\n') {
+                        idx = idx + 1 + next_newline;
+                        comments.push(Comment {
+                            style: BlankLine,
+                            lines: vec![],
+                            pos: start_bpos + BytePos((pos + idx) as u32),
+                        });
+                    }
+                }
+            }
+            rustc_lexer::TokenKind::BlockComment { terminated: _ } => {
+                if !is_block_doc_comment(token_text) {
+                    let code_to_the_right = match text[pos + token.len..].chars().next() {
+                        Some('\r') | Some('\n') => false,
+                        _ => true,
+                    };
+                    let style = match (code_to_the_left, code_to_the_right) {
+                        (true, true) | (false, true) => Mixed,
+                        (false, false) => Isolated,
+                        (true, false) => Trailing,
+                    };
+
+                    // Count the number of chars since the start of the line by rescanning.
+                    let pos_in_file = start_bpos + BytePos(pos as u32);
+                    let line_begin_in_file = source_file.line_begin_pos(pos_in_file);
+                    let line_begin_pos = (line_begin_in_file - start_bpos).to_usize();
+                    let col = CharPos(text[line_begin_pos..pos].chars().count());
+
+                    let lines = split_block_comment_into_lines(token_text, col);
+                    comments.push(Comment { style, lines, pos: pos_in_file })
                 }
-                consume_whitespace_counting_blank_lines(&mut rdr, &mut comments);
-                code_to_the_left = false;
-                anything_to_the_left = false;
             }
-            // Eat one comment group
-            if rdr.peeking_at_comment() {
-                consume_comment(&mut rdr, &mut comments,
-                                &mut code_to_the_left, &mut anything_to_the_left);
-            } else {
-                break
+            rustc_lexer::TokenKind::LineComment => {
+                if !is_doc_comment(token_text) {
+                    comments.push(Comment {
+                        style: if code_to_the_left { Trailing } else { Isolated },
+                        lines: vec![token_text.to_string()],
+                        pos: start_bpos + BytePos(pos as u32),
+                    })
+                }
+            }
+            _ => {
+                code_to_the_left = true;
             }
         }
-
-        rdr.next_token();
-        code_to_the_left = true;
-        anything_to_the_left = true;
+        pos += token.len;
     }
 
     comments
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_block_doc_comment_1() {
-        let comment = "/**\n * Test \n **  Test\n *   Test\n*/";
-        let stripped = strip_doc_comment_decoration(comment);
-        assert_eq!(stripped, " Test \n*  Test\n   Test");
-    }
-
-    #[test]
-    fn test_block_doc_comment_2() {
-        let comment = "/**\n * Test\n *  Test\n*/";
-        let stripped = strip_doc_comment_decoration(comment);
-        assert_eq!(stripped, " Test\n  Test");
-    }
-
-    #[test]
-    fn test_block_doc_comment_3() {
-        let comment = "/**\n let a: *i32;\n *a = 5;\n*/";
-        let stripped = strip_doc_comment_decoration(comment);
-        assert_eq!(stripped, " let a: *i32;\n *a = 5;");
-    }
-
-    #[test]
-    fn test_block_doc_comment_4() {
-        let comment = "/*******************\n test\n *********************/";
-        let stripped = strip_doc_comment_decoration(comment);
-        assert_eq!(stripped, " test");
-    }
-
-    #[test]
-    fn test_line_doc_comment() {
-        let stripped = strip_doc_comment_decoration("/// test");
-        assert_eq!(stripped, " test");
-        let stripped = strip_doc_comment_decoration("///! test");
-        assert_eq!(stripped, " test");
-        let stripped = strip_doc_comment_decoration("// test");
-        assert_eq!(stripped, " test");
-        let stripped = strip_doc_comment_decoration("// test");
-        assert_eq!(stripped, " test");
-        let stripped = strip_doc_comment_decoration("///test");
-        assert_eq!(stripped, "test");
-        let stripped = strip_doc_comment_decoration("///!test");
-        assert_eq!(stripped, "test");
-        let stripped = strip_doc_comment_decoration("//test");
-        assert_eq!(stripped, "test");
-    }
-}
diff --git a/src/libsyntax/parse/lexer/comments/tests.rs b/src/libsyntax/parse/lexer/comments/tests.rs
new file mode 100644
index 00000000000..f9cd69fb50d
--- /dev/null
+++ b/src/libsyntax/parse/lexer/comments/tests.rs
@@ -0,0 +1,47 @@
+use super::*;
+
+#[test]
+fn test_block_doc_comment_1() {
+    let comment = "/**\n * Test \n **  Test\n *   Test\n*/";
+    let stripped = strip_doc_comment_decoration(comment);
+    assert_eq!(stripped, " Test \n*  Test\n   Test");
+}
+
+#[test]
+fn test_block_doc_comment_2() {
+    let comment = "/**\n * Test\n *  Test\n*/";
+    let stripped = strip_doc_comment_decoration(comment);
+    assert_eq!(stripped, " Test\n  Test");
+}
+
+#[test]
+fn test_block_doc_comment_3() {
+    let comment = "/**\n let a: *i32;\n *a = 5;\n*/";
+    let stripped = strip_doc_comment_decoration(comment);
+    assert_eq!(stripped, " let a: *i32;\n *a = 5;");
+}
+
+#[test]
+fn test_block_doc_comment_4() {
+    let comment = "/*******************\n test\n *********************/";
+    let stripped = strip_doc_comment_decoration(comment);
+    assert_eq!(stripped, " test");
+}
+
+#[test]
+fn test_line_doc_comment() {
+    let stripped = strip_doc_comment_decoration("/// test");
+    assert_eq!(stripped, " test");
+    let stripped = strip_doc_comment_decoration("///! test");
+    assert_eq!(stripped, " test");
+    let stripped = strip_doc_comment_decoration("// test");
+    assert_eq!(stripped, " test");
+    let stripped = strip_doc_comment_decoration("// test");
+    assert_eq!(stripped, " test");
+    let stripped = strip_doc_comment_decoration("///test");
+    assert_eq!(stripped, "test");
+    let stripped = strip_doc_comment_decoration("///!test");
+    assert_eq!(stripped, "test");
+    let stripped = strip_doc_comment_decoration("//test");
+    assert_eq!(stripped, "test");
+}
diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 47da3ee6a6c..bdf468a52bb 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -1,40 +1,26 @@
-use crate::ast::{self, Ident};
-use crate::parse::{token, ParseSess};
-use crate::symbol::Symbol;
-use crate::parse::unescape;
+use crate::parse::ParseSess;
+use crate::parse::token::{self, Token, TokenKind};
+use crate::symbol::{sym, Symbol};
 use crate::parse::unescape_error_reporting::{emit_unescape_error, push_escaped_char};
 
-use errors::{FatalError, Diagnostic, DiagnosticBuilder};
-use syntax_pos::{BytePos, Pos, Span, NO_EXPANSION};
-use core::unicode::property::Pattern_White_Space;
+use errors::{FatalError, DiagnosticBuilder};
+use syntax_pos::{BytePos, Pos, Span};
+use rustc_lexer::Base;
+use rustc_lexer::unescape;
 
-use std::borrow::Cow;
 use std::char;
-use std::iter;
-use std::mem::replace;
+use std::convert::TryInto;
 use rustc_data_structures::sync::Lrc;
 use log::debug;
 
+#[cfg(test)]
+mod tests;
+
 pub mod comments;
 mod tokentrees;
 mod unicode_chars;
 
 #[derive(Clone, Debug)]
-pub struct TokenAndSpan {
-    pub tok: token::Token,
-    pub sp: Span,
-}
-
-impl Default for TokenAndSpan {
-    fn default() -> Self {
-        TokenAndSpan {
-            tok: token::Whitespace,
-            sp: syntax_pos::DUMMY_SP,
-        }
-    }
-}
-
-#[derive(Clone, Debug)]
 pub struct UnmatchedBrace {
     pub expected_delim: token::DelimToken,
     pub found_delim: token::DelimToken,
@@ -44,176 +30,22 @@ pub struct UnmatchedBrace {
 }
 
 pub struct StringReader<'a> {
-    crate sess: &'a ParseSess,
-    /// The absolute offset within the source_map of the next character to read
-    crate next_pos: BytePos,
-    /// The absolute offset within the source_map of the current character
-    crate pos: BytePos,
-    /// The current character (which has been read from self.pos)
-    crate ch: Option<char>,
-    crate source_file: Lrc<syntax_pos::SourceFile>,
+    sess: &'a ParseSess,
+    /// Initial position, read-only.
+    start_pos: BytePos,
+    /// The absolute offset within the source_map of the current character.
+    pos: BytePos,
     /// Stop reading src at this index.
-    crate end_src_index: usize,
-    // cached:
-    peek_tok: token::Token,
-    peek_span: Span,
-    peek_span_src_raw: Span,
-    fatal_errs: Vec<DiagnosticBuilder<'a>>,
-    // cache a direct reference to the source text, so that we don't have to
-    // retrieve it via `self.source_file.src.as_ref().unwrap()` all the time.
+    end_src_index: usize,
+    /// Source text to tokenize.
     src: Lrc<String>,
     override_span: Option<Span>,
 }
 
 impl<'a> StringReader<'a> {
-    fn mk_sp(&self, lo: BytePos, hi: BytePos) -> Span {
-        self.mk_sp_and_raw(lo, hi).0
-    }
-
-    fn mk_sp_and_raw(&self, lo: BytePos, hi: BytePos) -> (Span, Span) {
-        let raw = Span::new(lo, hi, NO_EXPANSION);
-        let real = self.override_span.unwrap_or(raw);
-
-        (real, raw)
-    }
-
-    fn mk_ident(&self, string: &str) -> Ident {
-        let mut ident = Ident::from_str(string);
-        if let Some(span) = self.override_span {
-            ident.span = span;
-        }
-
-        ident
-    }
-
-    fn unwrap_or_abort(&mut self, res: Result<TokenAndSpan, ()>) -> TokenAndSpan {
-        match res {
-            Ok(tok) => tok,
-            Err(_) => {
-                self.emit_fatal_errors();
-                FatalError.raise();
-            }
-        }
-    }
-
-    fn next_token(&mut self) -> TokenAndSpan where Self: Sized {
-        let res = self.try_next_token();
-        self.unwrap_or_abort(res)
-    }
-
-    /// Returns the next token. EFFECT: advances the string_reader.
-    pub fn try_next_token(&mut self) -> Result<TokenAndSpan, ()> {
-        assert!(self.fatal_errs.is_empty());
-        let ret_val = TokenAndSpan {
-            tok: replace(&mut self.peek_tok, token::Whitespace),
-            sp: self.peek_span,
-        };
-        self.advance_token()?;
-        Ok(ret_val)
-    }
-
-    /// Immutably extract string if found at current position with given delimiters
-    fn peek_delimited(&self, from_ch: char, to_ch: char) -> Option<String> {
-        let mut pos = self.pos;
-        let mut idx = self.src_index(pos);
-        let mut ch = char_at(&self.src, idx);
-        if ch != from_ch {
-            return None;
-        }
-        pos = pos + Pos::from_usize(ch.len_utf8());
-        let start_pos = pos;
-        idx = self.src_index(pos);
-        while idx < self.end_src_index {
-            ch = char_at(&self.src, idx);
-            if ch == to_ch {
-                return Some(self.src[self.src_index(start_pos)..self.src_index(pos)].to_string());
-            }
-            pos = pos + Pos::from_usize(ch.len_utf8());
-            idx = self.src_index(pos);
-        }
-        return None;
-    }
-
-    fn try_real_token(&mut self) -> Result<TokenAndSpan, ()> {
-        let mut t = self.try_next_token()?;
-        loop {
-            match t.tok {
-                token::Whitespace | token::Comment | token::Shebang(_) => {
-                    t = self.try_next_token()?;
-                }
-                _ => break,
-            }
-        }
-
-        Ok(t)
-    }
-
-    pub fn real_token(&mut self) -> TokenAndSpan {
-        let res = self.try_real_token();
-        self.unwrap_or_abort(res)
-    }
-
-    #[inline]
-    fn is_eof(&self) -> bool {
-        self.ch.is_none()
-    }
-
-    fn fail_unterminated_raw_string(&self, pos: BytePos, hash_count: u16) {
-        let mut err = self.struct_span_fatal(pos, pos, "unterminated raw string");
-        err.span_label(self.mk_sp(pos, pos), "unterminated raw string");
-
-        if hash_count > 0 {
-            err.note(&format!("this raw string should be terminated with `\"{}`",
-                              "#".repeat(hash_count as usize)));
-        }
-
-        err.emit();
-        FatalError.raise();
-    }
-
-    fn fatal(&self, m: &str) -> FatalError {
-        self.fatal_span(self.peek_span, m)
-    }
-
-    crate fn emit_fatal_errors(&mut self) {
-        for err in &mut self.fatal_errs {
-            err.emit();
-        }
-
-        self.fatal_errs.clear();
-    }
-
-    pub fn buffer_fatal_errors(&mut self) -> Vec<Diagnostic> {
-        let mut buffer = Vec::new();
-
-        for err in self.fatal_errs.drain(..) {
-            err.buffer(&mut buffer);
-        }
-
-        buffer
-    }
-
-    pub fn peek(&self) -> TokenAndSpan {
-        // FIXME(pcwalton): Bad copy!
-        TokenAndSpan {
-            tok: self.peek_tok.clone(),
-            sp: self.peek_span,
-        }
-    }
-
-    /// For comments.rs, which hackily pokes into next_pos and ch
-    fn new_raw(sess: &'a ParseSess,
+    pub fn new(sess: &'a ParseSess,
                source_file: Lrc<syntax_pos::SourceFile>,
                override_span: Option<Span>) -> Self {
-        let mut sr = StringReader::new_raw_internal(sess, source_file, override_span);
-        sr.bump();
-
-        sr
-    }
-
-    fn new_raw_internal(sess: &'a ParseSess, source_file: Lrc<syntax_pos::SourceFile>,
-        override_span: Option<Span>) -> Self
-    {
         if source_file.src.is_none() {
             sess.span_diagnostic.bug(&format!("Cannot lex source_file without source: {}",
                                               source_file.name));
@@ -223,32 +55,14 @@ impl<'a> StringReader<'a> {
 
         StringReader {
             sess,
-            next_pos: source_file.start_pos,
+            start_pos: source_file.start_pos,
             pos: source_file.start_pos,
-            ch: Some('\n'),
-            source_file,
             end_src_index: src.len(),
-            // dummy values; not read
-            peek_tok: token::Eof,
-            peek_span: syntax_pos::DUMMY_SP,
-            peek_span_src_raw: syntax_pos::DUMMY_SP,
             src,
-            fatal_errs: Vec::new(),
             override_span,
         }
     }
 
-    pub fn new_or_buffered_errs(sess: &'a ParseSess,
-                                source_file: Lrc<syntax_pos::SourceFile>,
-                                override_span: Option<Span>) -> Result<Self, Vec<Diagnostic>> {
-        let mut sr = StringReader::new_raw(sess, source_file, override_span);
-        if sr.advance_token().is_err() {
-            Err(sr.buffer_fatal_errors())
-        } else {
-            Ok(sr)
-        }
-    }
-
     pub fn retokenize(sess: &'a ParseSess, mut span: Span) -> Self {
         let begin = sess.source_map().lookup_byte_offset(span.lo());
         let end = sess.source_map().lookup_byte_offset(span.hi());
@@ -258,25 +72,61 @@ impl<'a> StringReader<'a> {
             span = span.shrink_to_lo();
         }
 
-        let mut sr = StringReader::new_raw_internal(sess, begin.sf, None);
+        let mut sr = StringReader::new(sess, begin.sf, None);
 
         // Seek the lexer to the right byte range.
-        sr.next_pos = span.lo();
         sr.end_src_index = sr.src_index(span.hi());
 
-        sr.bump();
+        sr
+    }
 
-        if sr.advance_token().is_err() {
-            sr.emit_fatal_errors();
-            FatalError.raise();
-        }
 
-        sr
+    fn mk_sp(&self, lo: BytePos, hi: BytePos) -> Span {
+        self.override_span.unwrap_or_else(|| Span::with_root_ctxt(lo, hi))
     }
 
-    #[inline]
-    fn ch_is(&self, c: char) -> bool {
-        self.ch == Some(c)
+    /// Returns the next token, including trivia like whitespace or comments.
+    ///
+    /// `Err(())` means that some errors were encountered, which can be
+    /// retrieved using `buffer_fatal_errors`.
+    pub fn next_token(&mut self) -> Token {
+        let start_src_index = self.src_index(self.pos);
+        let text: &str = &self.src[start_src_index..self.end_src_index];
+
+        if text.is_empty() {
+            let span = self.mk_sp(self.pos, self.pos);
+            return Token::new(token::Eof, span);
+        }
+
+        {
+            let is_beginning_of_file = self.pos == self.start_pos;
+            if is_beginning_of_file {
+                if let Some(shebang_len) = rustc_lexer::strip_shebang(text) {
+                    let start = self.pos;
+                    self.pos = self.pos + BytePos::from_usize(shebang_len);
+
+                    let sym = self.symbol_from(start + BytePos::from_usize("#!".len()));
+                    let kind = token::Shebang(sym);
+
+                    let span = self.mk_sp(start, self.pos);
+                    return Token::new(kind, span);
+                }
+            }
+        }
+
+        let token = rustc_lexer::first_token(text);
+
+        let start = self.pos;
+        self.pos = self.pos + BytePos::from_usize(token.len);
+
+        debug!("try_next_token: {:?}({:?})", token.kind, self.str_from(start));
+
+        // This could use `?`, but that makes code significantly (10-20%) slower.
+        // https://github.com/rust-lang/rust/issues/37939
+        let kind = self.cook_lexer_token(token.kind, start);
+
+        let span = self.mk_sp(start, self.pos);
+        Token::new(kind, span)
     }
 
     /// Report a fatal lexical error with a given span.
@@ -300,16 +150,6 @@ impl<'a> StringReader<'a> {
         self.err_span(self.mk_sp(from_pos, to_pos), m)
     }
 
-    /// Report a lexical error spanning [`from_pos`, `to_pos`), appending an
-    /// escaped character to the error message
-    fn fatal_span_char(&self, from_pos: BytePos, to_pos: BytePos, m: &str, c: char) -> FatalError {
-        let mut m = m.to_string();
-        m.push_str(": ");
-        push_escaped_char(&mut m, c);
-
-        self.fatal_span_(from_pos, to_pos, &m[..])
-    }
-
     fn struct_span_fatal(&self, from_pos: BytePos, to_pos: BytePos, m: &str)
         -> DiagnosticBuilder<'a>
     {
@@ -326,1186 +166,506 @@ impl<'a> StringReader<'a> {
         self.sess.span_diagnostic.struct_span_fatal(self.mk_sp(from_pos, to_pos), &m[..])
     }
 
-    /// Report a lexical error spanning [`from_pos`, `to_pos`), appending an
-    /// escaped character to the error message
-    fn err_span_char(&self, from_pos: BytePos, to_pos: BytePos, m: &str, c: char) {
-        let mut m = m.to_string();
-        m.push_str(": ");
-        push_escaped_char(&mut m, c);
-        self.err_span_(from_pos, to_pos, &m[..]);
-    }
-
-    /// Advance peek_tok and peek_span to refer to the next token, and
-    /// possibly update the interner.
-    fn advance_token(&mut self) -> Result<(), ()> {
-        match self.scan_whitespace_or_comment() {
-            Some(comment) => {
-                self.peek_span_src_raw = comment.sp;
-                self.peek_span = comment.sp;
-                self.peek_tok = comment.tok;
-            }
-            None => {
-                if self.is_eof() {
-                    self.peek_tok = token::Eof;
-                    let (real, raw) = self.mk_sp_and_raw(
-                        self.source_file.end_pos,
-                        self.source_file.end_pos,
-                    );
-                    self.peek_span = real;
-                    self.peek_span_src_raw = raw;
+    /// Turns simple `rustc_lexer::TokenKind` enum into a rich
+    /// `libsyntax::TokenKind`. This turns strings into interned
+    /// symbols and runs additional validation.
+    fn cook_lexer_token(
+        &self,
+        token: rustc_lexer::TokenKind,
+        start: BytePos,
+    ) -> TokenKind {
+        match token {
+            rustc_lexer::TokenKind::LineComment => {
+                let string = self.str_from(start);
+                // comments with only more "/"s are not doc comments
+                let tok = if is_doc_comment(string) {
+                    self.forbid_bare_cr(start, string, "bare CR not allowed in doc-comment");
+                    token::DocComment(Symbol::intern(string))
                 } else {
-                    let start_bytepos = self.pos;
-                    self.peek_tok = self.next_token_inner()?;
-                    let (real, raw) = self.mk_sp_and_raw(start_bytepos, self.pos);
-                    self.peek_span = real;
-                    self.peek_span_src_raw = raw;
+                    token::Comment
                 };
-            }
-        }
-
-        Ok(())
-    }
-
-    #[inline]
-    fn src_index(&self, pos: BytePos) -> usize {
-        (pos - self.source_file.start_pos).to_usize()
-    }
-
-    /// Calls `f` with a string slice of the source text spanning from `start`
-    /// up to but excluding `self.pos`, meaning the slice does not include
-    /// the character `self.ch`.
-    fn with_str_from<T, F>(&self, start: BytePos, f: F) -> T
-        where F: FnOnce(&str) -> T
-    {
-        self.with_str_from_to(start, self.pos, f)
-    }
 
-    /// Creates a Name from a given offset to the current offset.
-    fn name_from(&self, start: BytePos) -> ast::Name {
-        debug!("taking an ident from {:?} to {:?}", start, self.pos);
-        self.with_str_from(start, Symbol::intern)
-    }
-
-    /// As name_from, with an explicit endpoint.
-    fn name_from_to(&self, start: BytePos, end: BytePos) -> ast::Name {
-        debug!("taking an ident from {:?} to {:?}", start, end);
-        self.with_str_from_to(start, end, Symbol::intern)
-    }
-
-    /// Calls `f` with a string slice of the source text spanning from `start`
-    /// up to but excluding `end`.
-    fn with_str_from_to<T, F>(&self, start: BytePos, end: BytePos, f: F) -> T
-        where F: FnOnce(&str) -> T
-    {
-        f(&self.src[self.src_index(start)..self.src_index(end)])
-    }
-
-    /// Converts CRLF to LF in the given string, raising an error on bare CR.
-    fn translate_crlf<'b>(&self, start: BytePos, s: &'b str, errmsg: &'b str) -> Cow<'b, str> {
-        let mut chars = s.char_indices().peekable();
-        while let Some((i, ch)) = chars.next() {
-            if ch == '\r' {
-                if let Some((lf_idx, '\n')) = chars.peek() {
-                    return translate_crlf_(self, start, s, *lf_idx, chars, errmsg).into();
-                }
-                let pos = start + BytePos(i as u32);
-                let end_pos = start + BytePos((i + ch.len_utf8()) as u32);
-                self.err_span_(pos, end_pos, errmsg);
-            }
-        }
-        return s.into();
-
-        fn translate_crlf_(rdr: &StringReader<'_>,
-                           start: BytePos,
-                           s: &str,
-                           mut j: usize,
-                           mut chars: iter::Peekable<impl Iterator<Item = (usize, char)>>,
-                           errmsg: &str)
-                           -> String {
-            let mut buf = String::with_capacity(s.len());
-            // Skip first CR
-            buf.push_str(&s[.. j - 1]);
-            while let Some((i, ch)) = chars.next() {
-                if ch == '\r' {
-                    if j < i {
-                        buf.push_str(&s[j..i]);
-                    }
-                    let next = i + ch.len_utf8();
-                    j = next;
-                    if chars.peek().map(|(_, ch)| *ch) != Some('\n') {
-                        let pos = start + BytePos(i as u32);
-                        let end_pos = start + BytePos(next as u32);
-                        rdr.err_span_(pos, end_pos, errmsg);
-                    }
-                }
+                tok
             }
-            if j < s.len() {
-                buf.push_str(&s[j..]);
-            }
-            buf
-        }
-    }
+            rustc_lexer::TokenKind::BlockComment { terminated } => {
+                let string = self.str_from(start);
+                // block comments starting with "/**" or "/*!" are doc-comments
+                // but comments with only "*"s between two "/"s are not
+                let is_doc_comment = is_block_doc_comment(string);
 
-    /// Advance the StringReader by one character.
-    crate fn bump(&mut self) {
-        let next_src_index = self.src_index(self.next_pos);
-        if next_src_index < self.end_src_index {
-            let next_ch = char_at(&self.src, next_src_index);
-            let next_ch_len = next_ch.len_utf8();
-
-            self.ch = Some(next_ch);
-            self.pos = self.next_pos;
-            self.next_pos = self.next_pos + Pos::from_usize(next_ch_len);
-        } else {
-            self.ch = None;
-            self.pos = self.next_pos;
-        }
-    }
-
-    fn nextch(&self) -> Option<char> {
-        let next_src_index = self.src_index(self.next_pos);
-        if next_src_index < self.end_src_index {
-            Some(char_at(&self.src, next_src_index))
-        } else {
-            None
-        }
-    }
-
-    #[inline]
-    fn nextch_is(&self, c: char) -> bool {
-        self.nextch() == Some(c)
-    }
-
-    fn nextnextch(&self) -> Option<char> {
-        let next_src_index = self.src_index(self.next_pos);
-        if next_src_index < self.end_src_index {
-            let next_next_src_index =
-                next_src_index + char_at(&self.src, next_src_index).len_utf8();
-            if next_next_src_index < self.end_src_index {
-                return Some(char_at(&self.src, next_next_src_index));
-            }
-        }
-        None
-    }
-
-    #[inline]
-    fn nextnextch_is(&self, c: char) -> bool {
-        self.nextnextch() == Some(c)
-    }
-
-    /// Eats <XID_start><XID_continue>*, if possible.
-    fn scan_optional_raw_name(&mut self) -> Option<ast::Name> {
-        if !ident_start(self.ch) {
-            return None;
-        }
-
-        let start = self.pos;
-        self.bump();
-
-        while ident_continue(self.ch) {
-            self.bump();
-        }
-
-        self.with_str_from(start, |string| {
-            if string == "_" {
-                self.sess.span_diagnostic
-                    .struct_span_warn(self.mk_sp(start, self.pos),
-                                      "underscore literal suffix is not allowed")
-                    .warn("this was previously accepted by the compiler but is \
-                          being phased out; it will become a hard error in \
-                          a future release!")
-                    .note("for more information, see issue #42326 \
-                          <https://github.com/rust-lang/rust/issues/42326>")
-                    .emit();
-                None
-            } else {
-                Some(Symbol::intern(string))
-            }
-        })
-    }
-
-    /// PRECONDITION: self.ch is not whitespace
-    /// Eats any kind of comment.
-    fn scan_comment(&mut self) -> Option<TokenAndSpan> {
-        if let Some(c) = self.ch {
-            if c.is_whitespace() {
-                let msg = "called consume_any_line_comment, but there was whitespace";
-                self.sess.span_diagnostic.span_err(self.mk_sp(self.pos, self.pos), msg);
-            }
-        }
-
-        if self.ch_is('/') {
-            match self.nextch() {
-                Some('/') => {
-                    self.bump();
-                    self.bump();
-
-                    // line comments starting with "///" or "//!" are doc-comments
-                    let doc_comment = (self.ch_is('/') && !self.nextch_is('/')) || self.ch_is('!');
-                    let start_bpos = self.pos - BytePos(2);
-
-                    while !self.is_eof() {
-                        match self.ch.unwrap() {
-                            '\n' => break,
-                            '\r' => {
-                                if self.nextch_is('\n') {
-                                    // CRLF
-                                    break;
-                                } else if doc_comment {
-                                    self.err_span_(self.pos,
-                                                   self.next_pos,
-                                                   "bare CR not allowed in doc-comment");
-                                }
-                            }
-                            _ => (),
-                        }
-                        self.bump();
-                    }
-
-                    let tok = if doc_comment {
-                        self.with_str_from(start_bpos, |string| {
-                            token::DocComment(Symbol::intern(string))
-                        })
+                if !terminated {
+                    let msg = if is_doc_comment {
+                        "unterminated block doc-comment"
                     } else {
-                        token::Comment
+                        "unterminated block comment"
                     };
-                    Some(TokenAndSpan { tok, sp: self.mk_sp(start_bpos, self.pos) })
-                }
-                Some('*') => {
-                    self.bump();
-                    self.bump();
-                    self.scan_block_comment()
-                }
-                _ => None,
-            }
-        } else if self.ch_is('#') {
-            if self.nextch_is('!') {
-
-                // Parse an inner attribute.
-                if self.nextnextch_is('[') {
-                    return None;
-                }
-
-                let is_beginning_of_file = self.pos == self.source_file.start_pos;
-                if is_beginning_of_file {
-                    debug!("Skipping a shebang");
-                    let start = self.pos;
-                    while !self.ch_is('\n') && !self.is_eof() {
-                        self.bump();
-                    }
-                    return Some(TokenAndSpan {
-                        tok: token::Shebang(self.name_from(start)),
-                        sp: self.mk_sp(start, self.pos),
-                    });
-                }
-            }
-            None
-        } else {
-            None
-        }
-    }
-
-    /// If there is whitespace, shebang, or a comment, scan it. Otherwise,
-    /// return `None`.
-    fn scan_whitespace_or_comment(&mut self) -> Option<TokenAndSpan> {
-        match self.ch.unwrap_or('\0') {
-            // # to handle shebang at start of file -- this is the entry point
-            // for skipping over all "junk"
-            '/' | '#' => {
-                let c = self.scan_comment();
-                debug!("scanning a comment {:?}", c);
-                c
-            },
-            c if is_pattern_whitespace(Some(c)) => {
-                let start_bpos = self.pos;
-                while is_pattern_whitespace(self.ch) {
-                    self.bump();
-                }
-                let c = Some(TokenAndSpan {
-                    tok: token::Whitespace,
-                    sp: self.mk_sp(start_bpos, self.pos),
-                });
-                debug!("scanning whitespace: {:?}", c);
-                c
-            }
-            _ => None,
-        }
-    }
-
-    /// Might return a sugared-doc-attr
-    fn scan_block_comment(&mut self) -> Option<TokenAndSpan> {
-        // block comments starting with "/**" or "/*!" are doc-comments
-        let is_doc_comment = self.ch_is('*') || self.ch_is('!');
-        let start_bpos = self.pos - BytePos(2);
-
-        let mut level: isize = 1;
-        let mut has_cr = false;
-        while level > 0 {
-            if self.is_eof() {
-                let msg = if is_doc_comment {
-                    "unterminated block doc-comment"
-                } else {
-                    "unterminated block comment"
-                };
-                let last_bpos = self.pos;
-                self.fatal_span_(start_bpos, last_bpos, msg).raise();
-            }
-            let n = self.ch.unwrap();
-            match n {
-                '/' if self.nextch_is('*') => {
-                    level += 1;
-                    self.bump();
-                }
-                '*' if self.nextch_is('/') => {
-                    level -= 1;
-                    self.bump();
-                }
-                '\r' => {
-                    has_cr = true;
+                    let last_bpos = self.pos;
+                    self.fatal_span_(start, last_bpos, msg).raise();
                 }
-                _ => (),
-            }
-            self.bump();
-        }
 
-        self.with_str_from(start_bpos, |string| {
-            // but comments with only "*"s between two "/"s are not
-            let tok = if is_block_doc_comment(string) {
-                let string = if has_cr {
-                    self.translate_crlf(start_bpos,
+                let tok = if is_doc_comment {
+                    self.forbid_bare_cr(start,
                                         string,
-                                        "bare CR not allowed in block doc-comment")
+                                        "bare CR not allowed in block doc-comment");
+                    token::DocComment(Symbol::intern(string))
                 } else {
-                    string.into()
+                    token::Comment
                 };
-                token::DocComment(Symbol::intern(&string[..]))
-            } else {
-                token::Comment
-            };
-
-            Some(TokenAndSpan {
-                tok,
-                sp: self.mk_sp(start_bpos, self.pos),
-            })
-        })
-    }
-
-    /// Scan through any digits (base `scan_radix`) or underscores,
-    /// and return how many digits there were.
-    ///
-    /// `real_radix` represents the true radix of the number we're
-    /// interested in, and errors will be emitted for any digits
-    /// between `real_radix` and `scan_radix`.
-    fn scan_digits(&mut self, real_radix: u32, scan_radix: u32) -> usize {
-        assert!(real_radix <= scan_radix);
-        let mut len = 0;
-
-        loop {
-            let c = self.ch;
-            if c == Some('_') {
-                debug!("skipping a _");
-                self.bump();
-                continue;
-            }
-            match c.and_then(|cc| cc.to_digit(scan_radix)) {
-                Some(_) => {
-                    debug!("{:?} in scan_digits", c);
-                    // check that the hypothetical digit is actually
-                    // in range for the true radix
-                    if c.unwrap().to_digit(real_radix).is_none() {
-                        self.err_span_(self.pos,
-                                       self.next_pos,
-                                       &format!("invalid digit for a base {} literal", real_radix));
-                    }
-                    len += 1;
-                    self.bump();
-                }
-                _ => return len,
-            }
-        }
-    }
 
-    /// Lex a LIT_INTEGER or a LIT_FLOAT
-    fn scan_number(&mut self, c: char) -> token::Lit {
-        let mut base = 10;
-        let start_bpos = self.pos;
-        self.bump();
-
-        let num_digits = if c == '0' {
-            match self.ch.unwrap_or('\0') {
-                'b' => {
-                    self.bump();
-                    base = 2;
-                    self.scan_digits(2, 10)
-                }
-                'o' => {
-                    self.bump();
-                    base = 8;
-                    self.scan_digits(8, 10)
-                }
-                'x' => {
-                    self.bump();
-                    base = 16;
-                    self.scan_digits(16, 16)
-                }
-                '0'..='9' | '_' | '.' | 'e' | 'E' => {
-                    self.scan_digits(10, 10) + 1
-                }
-                _ => {
-                    // just a 0
-                    return token::Integer(self.name_from(start_bpos));
-                }
+                tok
             }
-        } else if c.is_digit(10) {
-            self.scan_digits(10, 10) + 1
-        } else {
-            0
-        };
-
-        if num_digits == 0 {
-            self.err_span_(start_bpos, self.pos, "no valid digits found for number");
-
-            return token::Integer(Symbol::intern("0"));
-        }
-
-        // might be a float, but don't be greedy if this is actually an
-        // integer literal followed by field/method access or a range pattern
-        // (`0..2` and `12.foo()`)
-        if self.ch_is('.') && !self.nextch_is('.') &&
-           !ident_start(self.nextch()) {
-            // might have stuff after the ., and if it does, it needs to start
-            // with a number
-            self.bump();
-            if self.ch.unwrap_or('\0').is_digit(10) {
-                self.scan_digits(10, 10);
-                self.scan_float_exponent();
-            }
-            let pos = self.pos;
-            self.check_float_base(start_bpos, pos, base);
-
-            token::Float(self.name_from(start_bpos))
-        } else {
-            // it might be a float if it has an exponent
-            if self.ch_is('e') || self.ch_is('E') {
-                self.scan_float_exponent();
-                let pos = self.pos;
-                self.check_float_base(start_bpos, pos, base);
-                return token::Float(self.name_from(start_bpos));
-            }
-            // but we certainly have an integer!
-            token::Integer(self.name_from(start_bpos))
-        }
-    }
-
-    /// Scan over a float exponent.
-    fn scan_float_exponent(&mut self) {
-        if self.ch_is('e') || self.ch_is('E') {
-            self.bump();
-
-            if self.ch_is('-') || self.ch_is('+') {
-                self.bump();
-            }
-
-            if self.scan_digits(10, 10) == 0 {
-                let mut err = self.struct_span_fatal(
-                    self.pos, self.next_pos,
-                    "expected at least one digit in exponent"
-                );
-                if let Some(ch) = self.ch {
-                    // check for e.g., Unicode minus '−' (Issue #49746)
-                    if unicode_chars::check_for_substitution(self, ch, &mut err) {
-                        self.bump();
-                        self.scan_digits(10, 10);
-                    }
-                }
-                err.emit();
-            }
-        }
-    }
-
-    /// Checks that a base is valid for a floating literal, emitting a nice
-    /// error if it isn't.
-    fn check_float_base(&mut self, start_bpos: BytePos, last_bpos: BytePos, base: usize) {
-        match base {
-            16 => {
-                self.err_span_(start_bpos,
-                               last_bpos,
-                               "hexadecimal float literal is not supported")
-            }
-            8 => {
-                self.err_span_(start_bpos,
-                               last_bpos,
-                               "octal float literal is not supported")
-            }
-            2 => {
-                self.err_span_(start_bpos,
-                               last_bpos,
-                               "binary float literal is not supported")
-            }
-            _ => (),
-        }
-    }
-
-    fn binop(&mut self, op: token::BinOpToken) -> token::Token {
-        self.bump();
-        if self.ch_is('=') {
-            self.bump();
-            token::BinOpEq(op)
-        } else {
-            token::BinOp(op)
-        }
-    }
-
-    /// Returns the next token from the string, advances the input past that
-    /// token, and updates the interner
-    fn next_token_inner(&mut self) -> Result<token::Token, ()> {
-        let c = self.ch;
-
-        if ident_start(c) {
-            let (is_ident_start, is_raw_ident) =
-                match (c.unwrap(), self.nextch(), self.nextnextch()) {
-                    // r# followed by an identifier starter is a raw identifier.
-                    // This is an exception to the r# case below.
-                    ('r', Some('#'), x) if ident_start(x) => (true, true),
-                    // r as in r" or r#" is part of a raw string literal.
-                    // b as in b' is part of a byte literal.
-                    // They are not identifiers, and are handled further down.
-                    ('r', Some('"'), _) |
-                    ('r', Some('#'), _) |
-                    ('b', Some('"'), _) |
-                    ('b', Some('\''), _) |
-                    ('b', Some('r'), Some('"')) |
-                    ('b', Some('r'), Some('#')) => (false, false),
-                    _ => (true, false),
-                };
-
-            if is_ident_start {
-                let raw_start = self.pos;
+            rustc_lexer::TokenKind::Whitespace => token::Whitespace,
+            rustc_lexer::TokenKind::Ident | rustc_lexer::TokenKind::RawIdent => {
+                let is_raw_ident = token == rustc_lexer::TokenKind::RawIdent;
+                let mut ident_start = start;
                 if is_raw_ident {
-                    // Consume the 'r#' characters.
-                    self.bump();
-                    self.bump();
-                }
-
-                let start = self.pos;
-                self.bump();
-
-                while ident_continue(self.ch) {
-                    self.bump();
+                    ident_start = ident_start + BytePos(2);
                 }
-
-                return Ok(self.with_str_from(start, |string| {
-                    // FIXME: perform NFKC normalization here. (Issue #2253)
-                    let ident = self.mk_ident(string);
-
-                    if is_raw_ident {
-                        let span = self.mk_sp(raw_start, self.pos);
-                        if !ident.can_be_raw() {
-                            self.err_span(span, &format!("`{}` cannot be a raw identifier", ident));
-                        }
-                        self.sess.raw_identifier_spans.borrow_mut().push(span);
+                // FIXME: perform NFKC normalization here. (Issue #2253)
+                let sym = self.symbol_from(ident_start);
+                if is_raw_ident {
+                    let span = self.mk_sp(start, self.pos);
+                    if !sym.can_be_raw() {
+                        self.err_span(span, &format!("`{}` cannot be a raw identifier", sym));
                     }
-
-                    token::Ident(ident, is_raw_ident)
-                }));
-            }
-        }
-
-        if is_dec_digit(c) {
-            let num = self.scan_number(c.unwrap());
-            let suffix = self.scan_optional_raw_name();
-            debug!("next_token_inner: scanned number {:?}, {:?}", num, suffix);
-            return Ok(token::Literal(num, suffix));
-        }
-
-        match c.expect("next_token_inner called at EOF") {
-            // One-byte tokens.
-            ';' => {
-                self.bump();
-                Ok(token::Semi)
-            }
-            ',' => {
-                self.bump();
-                Ok(token::Comma)
-            }
-            '.' => {
-                self.bump();
-                if self.ch_is('.') {
-                    self.bump();
-                    if self.ch_is('.') {
-                        self.bump();
-                        Ok(token::DotDotDot)
-                    } else if self.ch_is('=') {
-                        self.bump();
-                        Ok(token::DotDotEq)
+                    self.sess.raw_identifier_spans.borrow_mut().push(span);
+                }
+                token::Ident(sym, is_raw_ident)
+            }
+            rustc_lexer::TokenKind::Literal { kind, suffix_start } => {
+                let suffix_start = start + BytePos(suffix_start as u32);
+                let (kind, symbol) = self.cook_lexer_literal(start, suffix_start, kind);
+                let suffix = if suffix_start < self.pos {
+                    let string = self.str_from(suffix_start);
+                    if string == "_" {
+                        self.sess.span_diagnostic
+                            .struct_span_warn(self.mk_sp(suffix_start, self.pos),
+                                              "underscore literal suffix is not allowed")
+                            .warn("this was previously accepted by the compiler but is \
+                                   being phased out; it will become a hard error in \
+                                   a future release!")
+                            .note("for more information, see issue #42326 \
+                                   <https://github.com/rust-lang/rust/issues/42326>")
+                            .emit();
+                        None
                     } else {
-                        Ok(token::DotDot)
+                        Some(Symbol::intern(string))
                     }
                 } else {
-                    Ok(token::Dot)
-                }
-            }
-            '(' => {
-                self.bump();
-                Ok(token::OpenDelim(token::Paren))
-            }
-            ')' => {
-                self.bump();
-                Ok(token::CloseDelim(token::Paren))
-            }
-            '{' => {
-                self.bump();
-                Ok(token::OpenDelim(token::Brace))
-            }
-            '}' => {
-                self.bump();
-                Ok(token::CloseDelim(token::Brace))
-            }
-            '[' => {
-                self.bump();
-                Ok(token::OpenDelim(token::Bracket))
-            }
-            ']' => {
-                self.bump();
-                Ok(token::CloseDelim(token::Bracket))
-            }
-            '@' => {
-                self.bump();
-                Ok(token::At)
-            }
-            '#' => {
-                self.bump();
-                Ok(token::Pound)
-            }
-            '~' => {
-                self.bump();
-                Ok(token::Tilde)
-            }
-            '?' => {
-                self.bump();
-                Ok(token::Question)
-            }
-            ':' => {
-                self.bump();
-                if self.ch_is(':') {
-                    self.bump();
-                    Ok(token::ModSep)
-                } else {
-                    Ok(token::Colon)
+                    None
+                };
+                token::Literal(token::Lit { kind, symbol, suffix })
+            }
+            rustc_lexer::TokenKind::Lifetime { starts_with_number } => {
+                // Include the leading `'` in the real identifier, for macro
+                // expansion purposes. See #12512 for the gory details of why
+                // this is necessary.
+                let lifetime_name = self.str_from(start);
+                if starts_with_number {
+                    self.err_span_(
+                        start,
+                        self.pos,
+                        "lifetimes cannot start with a number",
+                    );
                 }
+                let ident = Symbol::intern(lifetime_name);
+                token::Lifetime(ident)
+            }
+            rustc_lexer::TokenKind::Semi => token::Semi,
+            rustc_lexer::TokenKind::Comma => token::Comma,
+            rustc_lexer::TokenKind::DotDotDot => token::DotDotDot,
+            rustc_lexer::TokenKind::DotDotEq => token::DotDotEq,
+            rustc_lexer::TokenKind::DotDot => token::DotDot,
+            rustc_lexer::TokenKind::Dot => token::Dot,
+            rustc_lexer::TokenKind::OpenParen => token::OpenDelim(token::Paren),
+            rustc_lexer::TokenKind::CloseParen => token::CloseDelim(token::Paren),
+            rustc_lexer::TokenKind::OpenBrace => token::OpenDelim(token::Brace),
+            rustc_lexer::TokenKind::CloseBrace => token::CloseDelim(token::Brace),
+            rustc_lexer::TokenKind::OpenBracket => token::OpenDelim(token::Bracket),
+            rustc_lexer::TokenKind::CloseBracket => token::CloseDelim(token::Bracket),
+            rustc_lexer::TokenKind::At => token::At,
+            rustc_lexer::TokenKind::Pound => token::Pound,
+            rustc_lexer::TokenKind::Tilde => token::Tilde,
+            rustc_lexer::TokenKind::Question => token::Question,
+            rustc_lexer::TokenKind::ColonColon => token::ModSep,
+            rustc_lexer::TokenKind::Colon => token::Colon,
+            rustc_lexer::TokenKind::Dollar => token::Dollar,
+            rustc_lexer::TokenKind::EqEq => token::EqEq,
+            rustc_lexer::TokenKind::Eq => token::Eq,
+            rustc_lexer::TokenKind::FatArrow => token::FatArrow,
+            rustc_lexer::TokenKind::Ne => token::Ne,
+            rustc_lexer::TokenKind::Not => token::Not,
+            rustc_lexer::TokenKind::Le => token::Le,
+            rustc_lexer::TokenKind::LArrow => token::LArrow,
+            rustc_lexer::TokenKind::Lt => token::Lt,
+            rustc_lexer::TokenKind::ShlEq => token::BinOpEq(token::Shl),
+            rustc_lexer::TokenKind::Shl => token::BinOp(token::Shl),
+            rustc_lexer::TokenKind::Ge => token::Ge,
+            rustc_lexer::TokenKind::Gt => token::Gt,
+            rustc_lexer::TokenKind::ShrEq => token::BinOpEq(token::Shr),
+            rustc_lexer::TokenKind::Shr => token::BinOp(token::Shr),
+            rustc_lexer::TokenKind::RArrow => token::RArrow,
+            rustc_lexer::TokenKind::Minus => token::BinOp(token::Minus),
+            rustc_lexer::TokenKind::MinusEq => token::BinOpEq(token::Minus),
+            rustc_lexer::TokenKind::And => token::BinOp(token::And),
+            rustc_lexer::TokenKind::AndEq => token::BinOpEq(token::And),
+            rustc_lexer::TokenKind::AndAnd => token::AndAnd,
+            rustc_lexer::TokenKind::Or => token::BinOp(token::Or),
+            rustc_lexer::TokenKind::OrEq => token::BinOpEq(token::Or),
+            rustc_lexer::TokenKind::OrOr => token::OrOr,
+            rustc_lexer::TokenKind::Plus => token::BinOp(token::Plus),
+            rustc_lexer::TokenKind::PlusEq => token::BinOpEq(token::Plus),
+            rustc_lexer::TokenKind::Star => token::BinOp(token::Star),
+            rustc_lexer::TokenKind::StarEq => token::BinOpEq(token::Star),
+            rustc_lexer::TokenKind::Slash => token::BinOp(token::Slash),
+            rustc_lexer::TokenKind::SlashEq => token::BinOpEq(token::Slash),
+            rustc_lexer::TokenKind::Caret => token::BinOp(token::Caret),
+            rustc_lexer::TokenKind::CaretEq => token::BinOpEq(token::Caret),
+            rustc_lexer::TokenKind::Percent => token::BinOp(token::Percent),
+            rustc_lexer::TokenKind::PercentEq => token::BinOpEq(token::Percent),
+
+            rustc_lexer::TokenKind::Unknown => {
+                let c = self.str_from(start).chars().next().unwrap();
+                let mut err = self.struct_fatal_span_char(start,
+                                                          self.pos,
+                                                          "unknown start of token",
+                                                          c);
+                // FIXME: the lexer could be used to turn the ASCII version of unicode homoglyphs,
+                // instead of keeping a table in `check_for_substitution`into the token. Ideally,
+                // this should be inside `rustc_lexer`. However, we should first remove compound
+                // tokens like `<<` from `rustc_lexer`, and then add fancier error recovery to it,
+                // as there will be less overall work to do this way.
+                let token = unicode_chars::check_for_substitution(self, start, c, &mut err)
+                    .unwrap_or_else(|| token::Unknown(self.symbol_from(start)));
+                err.emit();
+                token
             }
+        }
+    }
 
-            '$' => {
-                self.bump();
-                Ok(token::Dollar)
-            }
-
-            // Multi-byte tokens.
-            '=' => {
-                self.bump();
-                if self.ch_is('=') {
-                    self.bump();
-                    Ok(token::EqEq)
-                } else if self.ch_is('>') {
-                    self.bump();
-                    Ok(token::FatArrow)
-                } else {
-                    Ok(token::Eq)
+    fn cook_lexer_literal(
+        &self,
+        start: BytePos,
+        suffix_start: BytePos,
+        kind: rustc_lexer::LiteralKind
+    ) -> (token::LitKind, Symbol) {
+        match kind {
+            rustc_lexer::LiteralKind::Char { terminated } => {
+                if !terminated {
+                    self.fatal_span_(start, suffix_start,
+                                     "unterminated character literal".into())
+                        .raise()
                 }
-            }
-            '!' => {
-                self.bump();
-                if self.ch_is('=') {
-                    self.bump();
-                    Ok(token::Ne)
+                let content_start = start + BytePos(1);
+                let content_end = suffix_start - BytePos(1);
+                self.validate_char_escape(content_start, content_end);
+                let id = self.symbol_from_to(content_start, content_end);
+                (token::Char, id)
+            },
+            rustc_lexer::LiteralKind::Byte { terminated } => {
+                if !terminated {
+                    self.fatal_span_(start + BytePos(1), suffix_start,
+                                     "unterminated byte constant".into())
+                        .raise()
+                }
+                let content_start = start + BytePos(2);
+                let content_end = suffix_start - BytePos(1);
+                self.validate_byte_escape(content_start, content_end);
+                let id = self.symbol_from_to(content_start, content_end);
+                (token::Byte, id)
+            },
+            rustc_lexer::LiteralKind::Str { terminated } => {
+                if !terminated {
+                    self.fatal_span_(start, suffix_start,
+                                     "unterminated double quote string".into())
+                        .raise()
+                }
+                let content_start = start + BytePos(1);
+                let content_end = suffix_start - BytePos(1);
+                self.validate_str_escape(content_start, content_end);
+                let id = self.symbol_from_to(content_start, content_end);
+                (token::Str, id)
+            }
+            rustc_lexer::LiteralKind::ByteStr { terminated } => {
+                if !terminated {
+                    self.fatal_span_(start + BytePos(1), suffix_start,
+                                     "unterminated double quote byte string".into())
+                        .raise()
+                }
+                let content_start = start + BytePos(2);
+                let content_end = suffix_start - BytePos(1);
+                self.validate_byte_str_escape(content_start, content_end);
+                let id = self.symbol_from_to(content_start, content_end);
+                (token::ByteStr, id)
+            }
+            rustc_lexer::LiteralKind::RawStr { n_hashes, started, terminated } => {
+                if !started {
+                    self.report_non_started_raw_string(start);
+                }
+                if !terminated {
+                    self.report_unterminated_raw_string(start, n_hashes)
+                }
+                let n_hashes: u16 = self.restrict_n_hashes(start, n_hashes);
+                let n = u32::from(n_hashes);
+                let content_start = start + BytePos(2 + n);
+                let content_end = suffix_start - BytePos(1 + n);
+                self.validate_raw_str_escape(content_start, content_end);
+                let id = self.symbol_from_to(content_start, content_end);
+                (token::StrRaw(n_hashes), id)
+            }
+            rustc_lexer::LiteralKind::RawByteStr { n_hashes, started, terminated } => {
+                if !started {
+                    self.report_non_started_raw_string(start);
+                }
+                if !terminated {
+                    self.report_unterminated_raw_string(start, n_hashes)
+                }
+                let n_hashes: u16 = self.restrict_n_hashes(start, n_hashes);
+                let n = u32::from(n_hashes);
+                let content_start = start + BytePos(3 + n);
+                let content_end = suffix_start - BytePos(1 + n);
+                self.validate_raw_byte_str_escape(content_start, content_end);
+                let id = self.symbol_from_to(content_start, content_end);
+                (token::ByteStrRaw(n_hashes), id)
+            }
+            rustc_lexer::LiteralKind::Int { base, empty_int } => {
+                if empty_int {
+                    self.err_span_(start, suffix_start, "no valid digits found for number");
+                    (token::Integer, sym::integer(0))
                 } else {
-                    Ok(token::Not)
-                }
-            }
-            '<' => {
-                self.bump();
-                match self.ch.unwrap_or('\x00') {
-                    '=' => {
-                        self.bump();
-                        Ok(token::Le)
-                    }
-                    '<' => {
-                        Ok(self.binop(token::Shl))
-                    }
-                    '-' => {
-                        self.bump();
-                        Ok(token::LArrow)
-                    }
-                    _ => {
-                        Ok(token::Lt)
-                    }
+                    self.validate_int_literal(base, start, suffix_start);
+                    (token::Integer, self.symbol_from_to(start, suffix_start))
                 }
-            }
-            '>' => {
-                self.bump();
-                match self.ch.unwrap_or('\x00') {
-                    '=' => {
-                        self.bump();
-                        Ok(token::Ge)
-                    }
-                    '>' => {
-                        Ok(self.binop(token::Shr))
-                    }
-                    _ => {
-                        Ok(token::Gt)
-                    }
-                }
-            }
-            '\'' => {
-                // Either a character constant 'a' OR a lifetime name 'abc
-                let start_with_quote = self.pos;
-                self.bump();
-                let start = self.pos;
-
-                // If the character is an ident start not followed by another single
-                // quote, then this is a lifetime name:
-                let starts_with_number = self.ch.unwrap_or('\x00').is_numeric();
-                if (ident_start(self.ch) || starts_with_number) && !self.nextch_is('\'') {
-                    self.bump();
-                    while ident_continue(self.ch) {
-                        self.bump();
-                    }
-                    // lifetimes shouldn't end with a single quote
-                    // if we find one, then this is an invalid character literal
-                    if self.ch_is('\'') {
-                        let id = self.name_from(start);
-                        self.bump();
-                        self.validate_char_escape(start_with_quote);
-                        return Ok(token::Literal(token::Char(id), None))
-                    }
-
-                    // Include the leading `'` in the real identifier, for macro
-                    // expansion purposes. See #12512 for the gory details of why
-                    // this is necessary.
-                    let ident = self.with_str_from(start_with_quote, |lifetime_name| {
-                        self.mk_ident(lifetime_name)
-                    });
-
-                    if starts_with_number {
-                        // this is a recovered lifetime written `'1`, error but accept it
-                        self.err_span_(
-                            start_with_quote,
-                            self.pos,
-                            "lifetimes cannot start with a number",
-                        );
-                    }
-
-                    return Ok(token::Lifetime(ident));
-                }
-                let msg = "unterminated character literal";
-                let id = self.scan_single_quoted_string(start_with_quote, msg);
-                self.validate_char_escape(start_with_quote);
-                let suffix = self.scan_optional_raw_name();
-                Ok(token::Literal(token::Char(id), suffix))
-            }
-            'b' => {
-                self.bump();
-                let lit = match self.ch {
-                    Some('\'') => {
-                        let start_with_quote = self.pos;
-                        self.bump();
-                        let msg = "unterminated byte constant";
-                        let id = self.scan_single_quoted_string(start_with_quote, msg);
-                        self.validate_byte_escape(start_with_quote);
-                        token::Byte(id)
-                    },
-                    Some('"') => {
-                        let start_with_quote = self.pos;
-                        let msg = "unterminated double quote byte string";
-                        let id = self.scan_double_quoted_string(msg);
-                        self.validate_byte_str_escape(start_with_quote);
-                        token::ByteStr(id)
-                    },
-                    Some('r') => self.scan_raw_byte_string(),
-                    _ => unreachable!(),  // Should have been a token::Ident above.
-                };
-                let suffix = self.scan_optional_raw_name();
-
-                Ok(token::Literal(lit, suffix))
-            }
-            '"' => {
-                let start_with_quote = self.pos;
-                let msg = "unterminated double quote string";
-                let id = self.scan_double_quoted_string(msg);
-                self.validate_str_escape(start_with_quote);
-                let suffix = self.scan_optional_raw_name();
-                Ok(token::Literal(token::Str_(id), suffix))
-            }
-            'r' => {
-                let start_bpos = self.pos;
-                self.bump();
-                let mut hash_count: u16 = 0;
-                while self.ch_is('#') {
-                    if hash_count == 65535 {
-                        let bpos = self.next_pos;
-                        self.fatal_span_(start_bpos,
-                                         bpos,
-                                         "too many `#` symbols: raw strings may be \
-                                         delimited by up to 65535 `#` symbols").raise();
-                    }
-                    self.bump();
-                    hash_count += 1;
+            },
+            rustc_lexer::LiteralKind::Float { base, empty_exponent } => {
+                if empty_exponent {
+                    let mut err = self.struct_span_fatal(
+                        start, self.pos,
+                        "expected at least one digit in exponent"
+                    );
+                    err.emit();
                 }
 
-                if self.is_eof() {
-                    self.fail_unterminated_raw_string(start_bpos, hash_count);
-                } else if !self.ch_is('"') {
-                    let last_bpos = self.pos;
-                    let curr_char = self.ch.unwrap();
-                    self.fatal_span_char(start_bpos,
-                                         last_bpos,
-                                         "found invalid character; only `#` is allowed \
-                                         in raw string delimitation",
-                                         curr_char).raise();
-                }
-                self.bump();
-                let content_start_bpos = self.pos;
-                let mut content_end_bpos;
-                let mut valid = true;
-                'outer: loop {
-                    if self.is_eof() {
-                        self.fail_unterminated_raw_string(start_bpos, hash_count);
+                match base {
+                    Base::Hexadecimal => {
+                        self.err_span_(start, suffix_start,
+                                       "hexadecimal float literal is not supported")
                     }
-                    // if self.ch_is('"') {
-                    // content_end_bpos = self.pos;
-                    // for _ in 0..hash_count {
-                    // self.bump();
-                    // if !self.ch_is('#') {
-                    // continue 'outer;
-                    let c = self.ch.unwrap();
-                    match c {
-                        '"' => {
-                            content_end_bpos = self.pos;
-                            for _ in 0..hash_count {
-                                self.bump();
-                                if !self.ch_is('#') {
-                                    continue 'outer;
-                                }
-                            }
-                            break;
-                        }
-                        '\r' => {
-                            if !self.nextch_is('\n') {
-                                let last_bpos = self.pos;
-                                self.err_span_(start_bpos,
-                                               last_bpos,
-                                               "bare CR not allowed in raw string, use \\r \
-                                                instead");
-                                valid = false;
-                            }
-                        }
-                        _ => (),
-                    }
-                    self.bump();
-                }
-
-                self.bump();
-                let id = if valid {
-                    self.name_from_to(content_start_bpos, content_end_bpos)
-                } else {
-                    Symbol::intern("??")
-                };
-                let suffix = self.scan_optional_raw_name();
-
-                Ok(token::Literal(token::StrRaw(id, hash_count), suffix))
-            }
-            '-' => {
-                if self.nextch_is('>') {
-                    self.bump();
-                    self.bump();
-                    Ok(token::RArrow)
-                } else {
-                    Ok(self.binop(token::Minus))
-                }
-            }
-            '&' => {
-                if self.nextch_is('&') {
-                    self.bump();
-                    self.bump();
-                    Ok(token::AndAnd)
-                } else {
-                    Ok(self.binop(token::And))
-                }
-            }
-            '|' => {
-                match self.nextch() {
-                    Some('|') => {
-                        self.bump();
-                        self.bump();
-                        Ok(token::OrOr)
+                    Base::Octal => {
+                        self.err_span_(start, suffix_start,
+                                       "octal float literal is not supported")
                     }
-                    _ => {
-                        Ok(self.binop(token::Or))
+                    Base::Binary => {
+                        self.err_span_(start, suffix_start,
+                                       "binary float literal is not supported")
                     }
+                    _ => ()
                 }
-            }
-            '+' => {
-                Ok(self.binop(token::Plus))
-            }
-            '*' => {
-                Ok(self.binop(token::Star))
-            }
-            '/' => {
-                Ok(self.binop(token::Slash))
-            }
-            '^' => {
-                Ok(self.binop(token::Caret))
-            }
-            '%' => {
-                Ok(self.binop(token::Percent))
-            }
-            c => {
-                let last_bpos = self.pos;
-                let bpos = self.next_pos;
-                let mut err = self.struct_fatal_span_char(last_bpos,
-                                                          bpos,
-                                                          "unknown start of token",
-                                                          c);
-                unicode_chars::check_for_substitution(self, c, &mut err);
-                self.fatal_errs.push(err);
 
-                Err(())
-            }
+                let id = self.symbol_from_to(start, suffix_start);
+                (token::Float, id)
+            },
         }
     }
 
-    fn read_to_eol(&mut self) -> String {
-        let mut val = String::new();
-        while !self.ch_is('\n') && !self.is_eof() {
-            val.push(self.ch.unwrap());
-            self.bump();
-        }
-
-        if self.ch_is('\n') {
-            self.bump();
-        }
+    #[inline]
+    fn src_index(&self, pos: BytePos) -> usize {
+        (pos - self.start_pos).to_usize()
+    }
 
-        val
+    /// Slice of the source text from `start` up to but excluding `self.pos`,
+    /// meaning the slice does not include the character `self.ch`.
+    fn str_from(&self, start: BytePos) -> &str
+    {
+        self.str_from_to(start, self.pos)
     }
 
-    fn read_one_line_comment(&mut self) -> String {
-        let val = self.read_to_eol();
-        assert!((val.as_bytes()[0] == b'/' && val.as_bytes()[1] == b'/') ||
-                (val.as_bytes()[0] == b'#' && val.as_bytes()[1] == b'!'));
-        val
+    /// Creates a Symbol from a given offset to the current offset.
+    fn symbol_from(&self, start: BytePos) -> Symbol {
+        debug!("taking an ident from {:?} to {:?}", start, self.pos);
+        Symbol::intern(self.str_from(start))
     }
 
-    fn consume_non_eol_whitespace(&mut self) {
-        while is_pattern_whitespace(self.ch) && !self.ch_is('\n') && !self.is_eof() {
-            self.bump();
-        }
+    /// As symbol_from, with an explicit endpoint.
+    fn symbol_from_to(&self, start: BytePos, end: BytePos) -> Symbol {
+        debug!("taking an ident from {:?} to {:?}", start, end);
+        Symbol::intern(self.str_from_to(start, end))
     }
 
-    fn peeking_at_comment(&self) -> bool {
-        (self.ch_is('/') && self.nextch_is('/')) || (self.ch_is('/') && self.nextch_is('*')) ||
-        // consider shebangs comments, but not inner attributes
-        (self.ch_is('#') && self.nextch_is('!') && !self.nextnextch_is('['))
+    /// Slice of the source text spanning from `start` up to but excluding `end`.
+    fn str_from_to(&self, start: BytePos, end: BytePos) -> &str
+    {
+        &self.src[self.src_index(start)..self.src_index(end)]
     }
 
-    fn scan_single_quoted_string(&mut self,
-                                 start_with_quote: BytePos,
-                                 unterminated_msg: &str) -> ast::Name {
-        // assumes that first `'` is consumed
-        let start = self.pos;
-        // lex `'''` as a single char, for recovery
-        if self.ch_is('\'') && self.nextch_is('\'') {
-            self.bump();
-        } else {
-            let mut first = true;
-            loop {
-                if self.ch_is('\'') {
-                    break;
-                }
-                if self.ch_is('\\') && (self.nextch_is('\'') || self.nextch_is('\\')) {
-                    self.bump();
-                    self.bump();
-                } else {
-                    // Only attempt to infer single line string literals. If we encounter
-                    // a slash, bail out in order to avoid nonsensical suggestion when
-                    // involving comments.
-                    if self.is_eof()
-                        || (self.ch_is('/') && !first)
-                        || (self.ch_is('\n') && !self.nextch_is('\'')) {
-
-                        self.fatal_span_(start_with_quote, self.pos, unterminated_msg.into())
-                            .raise()
-                    }
-                    self.bump();
-                }
-                first = false;
-            }
+    fn forbid_bare_cr(&self, start: BytePos, s: &str, errmsg: &str) {
+        let mut idx = 0;
+        loop {
+            idx = match s[idx..].find('\r') {
+                None => break,
+                Some(it) => idx + it + 1
+            };
+            self.err_span_(start + BytePos(idx as u32 - 1),
+                           start + BytePos(idx as u32),
+                           errmsg);
+        }
+    }
+
+    fn report_non_started_raw_string(&self, start: BytePos) -> ! {
+        let bad_char = self.str_from(start).chars().last().unwrap();
+        self
+            .struct_fatal_span_char(
+                start,
+                self.pos,
+                "found invalid character; only `#` is allowed \
+                 in raw string delimitation",
+                bad_char,
+            )
+            .emit();
+        FatalError.raise()
+    }
+
+    fn report_unterminated_raw_string(&self, start: BytePos, n_hashes: usize) -> ! {
+        let mut err = self.struct_span_fatal(
+            start, start,
+            "unterminated raw string",
+        );
+        err.span_label(
+            self.mk_sp(start, start),
+            "unterminated raw string",
+        );
+
+        if n_hashes > 0 {
+            err.note(&format!("this raw string should be terminated with `\"{}`",
+                                "#".repeat(n_hashes as usize)));
         }
 
-        let id = self.name_from(start);
-        self.bump();
-        id
+        err.emit();
+        FatalError.raise()
     }
 
-    fn scan_double_quoted_string(&mut self, unterminated_msg: &str) -> ast::Name {
-        debug_assert!(self.ch_is('\"'));
-        let start_with_quote = self.pos;
-        self.bump();
-        let start = self.pos;
-        while !self.ch_is('"') {
-            if self.is_eof() {
-                let pos = self.pos;
-                self.fatal_span_(start_with_quote, pos, unterminated_msg).raise();
-            }
-            if self.ch_is('\\') && (self.nextch_is('\\') || self.nextch_is('"')) {
-                self.bump();
+    fn restrict_n_hashes(&self, start: BytePos, n_hashes: usize) -> u16 {
+        match n_hashes.try_into() {
+            Ok(n_hashes) => n_hashes,
+            Err(_) => {
+                self.fatal_span_(start,
+                                 self.pos,
+                                 "too many `#` symbols: raw strings may be \
+                                  delimited by up to 65535 `#` symbols").raise();
             }
-            self.bump();
         }
-        let id = self.name_from(start);
-        self.bump();
-        id
     }
 
-    fn scan_raw_byte_string(&mut self) -> token::Lit {
-        let start_bpos = self.pos;
-        self.bump();
-        let mut hash_count = 0;
-        while self.ch_is('#') {
-            if hash_count == 65535 {
-                let bpos = self.next_pos;
-                self.fatal_span_(start_bpos,
-                                 bpos,
-                                 "too many `#` symbols: raw byte strings may be \
-                                 delimited by up to 65535 `#` symbols").raise();
-            }
-            self.bump();
-            hash_count += 1;
+    fn validate_char_escape(&self, content_start: BytePos, content_end: BytePos) {
+        let lit = self.str_from_to(content_start, content_end);
+        if let Err((off, err)) = unescape::unescape_char(lit) {
+            emit_unescape_error(
+                &self.sess.span_diagnostic,
+                lit,
+                self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
+                unescape::Mode::Char,
+                0..off,
+                err,
+            )
         }
+    }
 
-        if self.is_eof() {
-            self.fail_unterminated_raw_string(start_bpos, hash_count);
-        } else if !self.ch_is('"') {
-            let pos = self.pos;
-            let ch = self.ch.unwrap();
-            self.fatal_span_char(start_bpos,
-                                        pos,
-                                        "found invalid character; only `#` is allowed in raw \
-                                         string delimitation",
-                                        ch).raise();
+    fn validate_byte_escape(&self, content_start: BytePos, content_end: BytePos) {
+        let lit = self.str_from_to(content_start, content_end);
+        if let Err((off, err)) = unescape::unescape_byte(lit) {
+            emit_unescape_error(
+                &self.sess.span_diagnostic,
+                lit,
+                self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
+                unescape::Mode::Byte,
+                0..off,
+                err,
+            )
         }
-        self.bump();
-        let content_start_bpos = self.pos;
-        let mut content_end_bpos;
-        'outer: loop {
-            match self.ch {
-                None => {
-                    self.fail_unterminated_raw_string(start_bpos, hash_count);
-                }
-                Some('"') => {
-                    content_end_bpos = self.pos;
-                    for _ in 0..hash_count {
-                        self.bump();
-                        if !self.ch_is('#') {
-                            continue 'outer;
-                        }
-                    }
-                    break;
-                }
-                Some(c) => {
-                    if c > '\x7F' {
-                        let pos = self.pos;
-                        self.err_span_char(pos, pos, "raw byte string must be ASCII", c);
-                    }
-                }
-            }
-            self.bump();
-        }
-
-        self.bump();
-
-        token::ByteStrRaw(self.name_from_to(content_start_bpos, content_end_bpos), hash_count)
     }
 
-    fn validate_char_escape(&self, start_with_quote: BytePos) {
-        self.with_str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1), |lit| {
-            if let Err((off, err)) = unescape::unescape_char(lit) {
+    fn validate_str_escape(&self, content_start: BytePos, content_end: BytePos) {
+        let lit = self.str_from_to(content_start, content_end);
+        unescape::unescape_str(lit, &mut |range, c| {
+            if let Err(err) = c {
                 emit_unescape_error(
                     &self.sess.span_diagnostic,
                     lit,
-                    self.mk_sp(start_with_quote, self.pos),
-                    unescape::Mode::Char,
-                    0..off,
+                    self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
+                    unescape::Mode::Str,
+                    range,
                     err,
                 )
             }
-        });
+        })
     }
 
-    fn validate_byte_escape(&self, start_with_quote: BytePos) {
-        self.with_str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1), |lit| {
-            if let Err((off, err)) = unescape::unescape_byte(lit) {
+    fn validate_raw_str_escape(&self, content_start: BytePos, content_end: BytePos) {
+        let lit = self.str_from_to(content_start, content_end);
+        unescape::unescape_raw_str(lit, &mut |range, c| {
+            if let Err(err) = c {
                 emit_unescape_error(
                     &self.sess.span_diagnostic,
                     lit,
-                    self.mk_sp(start_with_quote, self.pos),
-                    unescape::Mode::Byte,
-                    0..off,
+                    self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
+                    unescape::Mode::Str,
+                    range,
                     err,
                 )
             }
-        });
+        })
     }
 
-    fn validate_str_escape(&self, start_with_quote: BytePos) {
-        self.with_str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1), |lit| {
-            unescape::unescape_str(lit, &mut |range, c| {
-                if let Err(err) = c {
-                    emit_unescape_error(
-                        &self.sess.span_diagnostic,
-                        lit,
-                        self.mk_sp(start_with_quote, self.pos),
-                        unescape::Mode::Str,
-                        range,
-                        err,
-                    )
-                }
-            })
-        });
+    fn validate_raw_byte_str_escape(&self, content_start: BytePos, content_end: BytePos) {
+        let lit = self.str_from_to(content_start, content_end);
+        unescape::unescape_raw_byte_str(lit, &mut |range, c| {
+            if let Err(err) = c {
+                emit_unescape_error(
+                    &self.sess.span_diagnostic,
+                    lit,
+                    self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
+                    unescape::Mode::ByteStr,
+                    range,
+                    err,
+                )
+            }
+        })
     }
 
-    fn validate_byte_str_escape(&self, start_with_quote: BytePos) {
-        self.with_str_from_to(start_with_quote + BytePos(1), self.pos - BytePos(1), |lit| {
-            unescape::unescape_byte_str(lit, &mut |range, c| {
-                if let Err(err) = c {
-                    emit_unescape_error(
-                        &self.sess.span_diagnostic,
-                        lit,
-                        self.mk_sp(start_with_quote, self.pos),
-                        unescape::Mode::ByteStr,
-                        range,
-                        err,
-                    )
-                }
-            })
-        });
+    fn validate_byte_str_escape(&self, content_start: BytePos, content_end: BytePos) {
+        let lit = self.str_from_to(content_start, content_end);
+        unescape::unescape_byte_str(lit, &mut |range, c| {
+            if let Err(err) = c {
+                emit_unescape_error(
+                    &self.sess.span_diagnostic,
+                    lit,
+                    self.mk_sp(content_start - BytePos(1), content_end + BytePos(1)),
+                    unescape::Mode::ByteStr,
+                    range,
+                    err,
+                )
+            }
+        })
     }
-}
 
-// This tests the character for the unicode property 'PATTERN_WHITE_SPACE' which
-// is guaranteed to be forward compatible. http://unicode.org/reports/tr31/#R3
-#[inline]
-crate fn is_pattern_whitespace(c: Option<char>) -> bool {
-    c.map_or(false, Pattern_White_Space)
-}
-
-#[inline]
-fn in_range(c: Option<char>, lo: char, hi: char) -> bool {
-    c.map_or(false, |c| lo <= c && c <= hi)
-}
+    fn validate_int_literal(&self, base: Base, content_start: BytePos, content_end: BytePos) {
+        let base = match base {
+            Base::Binary => 2,
+            Base::Octal => 8,
+            _ => return,
+        };
+        let s = self.str_from_to(content_start + BytePos(2), content_end);
+        for (idx, c) in s.char_indices() {
+            let idx = idx as u32;
+            if c != '_' && c.to_digit(base).is_none() {
+                let lo = content_start + BytePos(2 + idx);
+                let hi = content_start + BytePos(2 + idx + c.len_utf8() as u32);
+                self.err_span_(lo, hi,
+                               &format!("invalid digit for a base {} literal", base));
 
-#[inline]
-fn is_dec_digit(c: Option<char>) -> bool {
-    in_range(c, '0', '9')
+            }
+        }
+    }
 }
 
 fn is_doc_comment(s: &str) -> bool {
@@ -1522,296 +682,3 @@ fn is_block_doc_comment(s: &str) -> bool {
     debug!("is {:?} a doc comment? {}", s, res);
     res
 }
-
-/// Determine whether `c` is a valid start for an ident.
-fn ident_start(c: Option<char>) -> bool {
-    let c = match c {
-        Some(c) => c,
-        None => return false,
-    };
-
-    (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || (c > '\x7f' && c.is_xid_start())
-}
-
-fn ident_continue(c: Option<char>) -> bool {
-    let c = match c {
-        Some(c) => c,
-        None => return false,
-    };
-
-    (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_' ||
-    (c > '\x7f' && c.is_xid_continue())
-}
-
-#[inline]
-fn char_at(s: &str, byte: usize) -> char {
-    s[byte..].chars().next().unwrap()
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    use crate::ast::{Ident, CrateConfig};
-    use crate::symbol::Symbol;
-    use crate::source_map::{SourceMap, FilePathMapping};
-    use crate::feature_gate::UnstableFeatures;
-    use crate::parse::token;
-    use crate::diagnostics::plugin::ErrorMap;
-    use crate::with_globals;
-    use std::io;
-    use std::path::PathBuf;
-    use syntax_pos::{BytePos, Span, NO_EXPANSION};
-    use rustc_data_structures::fx::{FxHashSet, FxHashMap};
-    use rustc_data_structures::sync::Lock;
-
-    fn mk_sess(sm: Lrc<SourceMap>) -> ParseSess {
-        let emitter = errors::emitter::EmitterWriter::new(Box::new(io::sink()),
-                                                          Some(sm.clone()),
-                                                          false,
-                                                          false,
-                                                          false);
-        ParseSess {
-            span_diagnostic: errors::Handler::with_emitter(true, None, Box::new(emitter)),
-            unstable_features: UnstableFeatures::from_environment(),
-            config: CrateConfig::default(),
-            included_mod_stack: Lock::new(Vec::new()),
-            source_map: sm,
-            missing_fragment_specifiers: Lock::new(FxHashSet::default()),
-            raw_identifier_spans: Lock::new(Vec::new()),
-            registered_diagnostics: Lock::new(ErrorMap::new()),
-            buffered_lints: Lock::new(vec![]),
-            ambiguous_block_expr_parse: Lock::new(FxHashMap::default()),
-        }
-    }
-
-    // open a string reader for the given string
-    fn setup<'a>(sm: &SourceMap,
-                 sess: &'a ParseSess,
-                 teststr: String)
-                 -> StringReader<'a> {
-        let sf = sm.new_source_file(PathBuf::from(teststr.clone()).into(), teststr);
-        let mut sr = StringReader::new_raw(sess, sf, None);
-        if sr.advance_token().is_err() {
-            sr.emit_fatal_errors();
-            FatalError.raise();
-        }
-        sr
-    }
-
-    #[test]
-    fn t1() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            let mut string_reader = setup(&sm,
-                                        &sh,
-                                        "/* my source file */ fn main() { println!(\"zebra\"); }\n"
-                                            .to_string());
-            let id = Ident::from_str("fn");
-            assert_eq!(string_reader.next_token().tok, token::Comment);
-            assert_eq!(string_reader.next_token().tok, token::Whitespace);
-            let tok1 = string_reader.next_token();
-            let tok2 = TokenAndSpan {
-                tok: token::Ident(id, false),
-                sp: Span::new(BytePos(21), BytePos(23), NO_EXPANSION),
-            };
-            assert_eq!(tok1.tok, tok2.tok);
-            assert_eq!(tok1.sp, tok2.sp);
-            assert_eq!(string_reader.next_token().tok, token::Whitespace);
-            // the 'main' id is already read:
-            assert_eq!(string_reader.pos.clone(), BytePos(28));
-            // read another token:
-            let tok3 = string_reader.next_token();
-            let tok4 = TokenAndSpan {
-                tok: mk_ident("main"),
-                sp: Span::new(BytePos(24), BytePos(28), NO_EXPANSION),
-            };
-            assert_eq!(tok3.tok, tok4.tok);
-            assert_eq!(tok3.sp, tok4.sp);
-            // the lparen is already read:
-            assert_eq!(string_reader.pos.clone(), BytePos(29))
-        })
-    }
-
-    // check that the given reader produces the desired stream
-    // of tokens (stop checking after exhausting the expected vec)
-    fn check_tokenization(mut string_reader: StringReader<'_>, expected: Vec<token::Token>) {
-        for expected_tok in &expected {
-            assert_eq!(&string_reader.next_token().tok, expected_tok);
-        }
-    }
-
-    // make the identifier by looking up the string in the interner
-    fn mk_ident(id: &str) -> token::Token {
-        token::Token::from_ast_ident(Ident::from_str(id))
-    }
-
-    #[test]
-    fn doublecolonparsing() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            check_tokenization(setup(&sm, &sh, "a b".to_string()),
-                            vec![mk_ident("a"), token::Whitespace, mk_ident("b")]);
-        })
-    }
-
-    #[test]
-    fn dcparsing_2() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            check_tokenization(setup(&sm, &sh, "a::b".to_string()),
-                            vec![mk_ident("a"), token::ModSep, mk_ident("b")]);
-        })
-    }
-
-    #[test]
-    fn dcparsing_3() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            check_tokenization(setup(&sm, &sh, "a ::b".to_string()),
-                            vec![mk_ident("a"), token::Whitespace, token::ModSep, mk_ident("b")]);
-        })
-    }
-
-    #[test]
-    fn dcparsing_4() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            check_tokenization(setup(&sm, &sh, "a:: b".to_string()),
-                            vec![mk_ident("a"), token::ModSep, token::Whitespace, mk_ident("b")]);
-        })
-    }
-
-    #[test]
-    fn character_a() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            assert_eq!(setup(&sm, &sh, "'a'".to_string()).next_token().tok,
-                    token::Literal(token::Char(Symbol::intern("a")), None));
-        })
-    }
-
-    #[test]
-    fn character_space() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            assert_eq!(setup(&sm, &sh, "' '".to_string()).next_token().tok,
-                    token::Literal(token::Char(Symbol::intern(" ")), None));
-        })
-    }
-
-    #[test]
-    fn character_escaped() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            assert_eq!(setup(&sm, &sh, "'\\n'".to_string()).next_token().tok,
-                    token::Literal(token::Char(Symbol::intern("\\n")), None));
-        })
-    }
-
-    #[test]
-    fn lifetime_name() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            assert_eq!(setup(&sm, &sh, "'abc".to_string()).next_token().tok,
-                    token::Lifetime(Ident::from_str("'abc")));
-        })
-    }
-
-    #[test]
-    fn raw_string() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            assert_eq!(setup(&sm, &sh, "r###\"\"#a\\b\x00c\"\"###".to_string())
-                        .next_token()
-                        .tok,
-                    token::Literal(token::StrRaw(Symbol::intern("\"#a\\b\x00c\""), 3), None));
-        })
-    }
-
-    #[test]
-    fn literal_suffixes() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            macro_rules! test {
-                ($input: expr, $tok_type: ident, $tok_contents: expr) => {{
-                    assert_eq!(setup(&sm, &sh, format!("{}suffix", $input)).next_token().tok,
-                            token::Literal(token::$tok_type(Symbol::intern($tok_contents)),
-                                            Some(Symbol::intern("suffix"))));
-                    // with a whitespace separator:
-                    assert_eq!(setup(&sm, &sh, format!("{} suffix", $input)).next_token().tok,
-                            token::Literal(token::$tok_type(Symbol::intern($tok_contents)),
-                                            None));
-                }}
-            }
-
-            test!("'a'", Char, "a");
-            test!("b'a'", Byte, "a");
-            test!("\"a\"", Str_, "a");
-            test!("b\"a\"", ByteStr, "a");
-            test!("1234", Integer, "1234");
-            test!("0b101", Integer, "0b101");
-            test!("0xABC", Integer, "0xABC");
-            test!("1.0", Float, "1.0");
-            test!("1.0e10", Float, "1.0e10");
-
-            assert_eq!(setup(&sm, &sh, "2us".to_string()).next_token().tok,
-                    token::Literal(token::Integer(Symbol::intern("2")),
-                                    Some(Symbol::intern("us"))));
-            assert_eq!(setup(&sm, &sh, "r###\"raw\"###suffix".to_string()).next_token().tok,
-                    token::Literal(token::StrRaw(Symbol::intern("raw"), 3),
-                                    Some(Symbol::intern("suffix"))));
-            assert_eq!(setup(&sm, &sh, "br###\"raw\"###suffix".to_string()).next_token().tok,
-                    token::Literal(token::ByteStrRaw(Symbol::intern("raw"), 3),
-                                    Some(Symbol::intern("suffix"))));
-        })
-    }
-
-    #[test]
-    fn line_doc_comments() {
-        assert!(is_doc_comment("///"));
-        assert!(is_doc_comment("/// blah"));
-        assert!(!is_doc_comment("////"));
-    }
-
-    #[test]
-    fn nested_block_comments() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            let mut lexer = setup(&sm, &sh, "/* /* */ */'a'".to_string());
-            match lexer.next_token().tok {
-                token::Comment => {}
-                _ => panic!("expected a comment!"),
-            }
-            assert_eq!(lexer.next_token().tok,
-                    token::Literal(token::Char(Symbol::intern("a")), None));
-        })
-    }
-
-    #[test]
-    fn crlf_comments() {
-        with_globals(|| {
-            let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-            let sh = mk_sess(sm.clone());
-            let mut lexer = setup(&sm, &sh, "// test\r\n/// test\r\n".to_string());
-            let comment = lexer.next_token();
-            assert_eq!(comment.tok, token::Comment);
-            assert_eq!((comment.sp.lo(), comment.sp.hi()), (BytePos(0), BytePos(7)));
-            assert_eq!(lexer.next_token().tok, token::Whitespace);
-            assert_eq!(lexer.next_token().tok,
-                    token::DocComment(Symbol::intern("/// test")));
-        })
-    }
-}
diff --git a/src/libsyntax/parse/lexer/tests.rs b/src/libsyntax/parse/lexer/tests.rs
new file mode 100644
index 00000000000..94570140996
--- /dev/null
+++ b/src/libsyntax/parse/lexer/tests.rs
@@ -0,0 +1,231 @@
+use super::*;
+
+use crate::symbol::Symbol;
+use crate::source_map::{SourceMap, FilePathMapping};
+use crate::parse::token;
+use crate::with_default_globals;
+use std::io;
+use std::path::PathBuf;
+use errors::{Handler, emitter::EmitterWriter};
+use syntax_pos::{BytePos, Span};
+
+fn mk_sess(sm: Lrc<SourceMap>) -> ParseSess {
+    let emitter = EmitterWriter::new(Box::new(io::sink()), Some(sm.clone()), false, false, false);
+    ParseSess::with_span_handler(Handler::with_emitter(true, None, Box::new(emitter)), sm)
+}
+
+// open a string reader for the given string
+fn setup<'a>(sm: &SourceMap,
+                sess: &'a ParseSess,
+                teststr: String)
+                -> StringReader<'a> {
+    let sf = sm.new_source_file(PathBuf::from(teststr.clone()).into(), teststr);
+    StringReader::new(sess, sf, None)
+}
+
+#[test]
+fn t1() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        let mut string_reader = setup(&sm,
+                                    &sh,
+                                    "/* my source file */ fn main() { println!(\"zebra\"); }\n"
+                                        .to_string());
+        assert_eq!(string_reader.next_token(), token::Comment);
+        assert_eq!(string_reader.next_token(), token::Whitespace);
+        let tok1 = string_reader.next_token();
+        let tok2 = Token::new(
+            mk_ident("fn"),
+            Span::with_root_ctxt(BytePos(21), BytePos(23)),
+        );
+        assert_eq!(tok1.kind, tok2.kind);
+        assert_eq!(tok1.span, tok2.span);
+        assert_eq!(string_reader.next_token(), token::Whitespace);
+        // read another token:
+        let tok3 = string_reader.next_token();
+        assert_eq!(string_reader.pos.clone(), BytePos(28));
+        let tok4 = Token::new(
+            mk_ident("main"),
+            Span::with_root_ctxt(BytePos(24), BytePos(28)),
+        );
+        assert_eq!(tok3.kind, tok4.kind);
+        assert_eq!(tok3.span, tok4.span);
+
+        assert_eq!(string_reader.next_token(), token::OpenDelim(token::Paren));
+        assert_eq!(string_reader.pos.clone(), BytePos(29))
+    })
+}
+
+// check that the given reader produces the desired stream
+// of tokens (stop checking after exhausting the expected vec)
+fn check_tokenization(mut string_reader: StringReader<'_>, expected: Vec<TokenKind>) {
+    for expected_tok in &expected {
+        assert_eq!(&string_reader.next_token(), expected_tok);
+    }
+}
+
+// make the identifier by looking up the string in the interner
+fn mk_ident(id: &str) -> TokenKind {
+    token::Ident(Symbol::intern(id), false)
+}
+
+fn mk_lit(kind: token::LitKind, symbol: &str, suffix: Option<&str>) -> TokenKind {
+    TokenKind::lit(kind, Symbol::intern(symbol), suffix.map(Symbol::intern))
+}
+
+#[test]
+fn doublecolonparsing() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        check_tokenization(setup(&sm, &sh, "a b".to_string()),
+                        vec![mk_ident("a"), token::Whitespace, mk_ident("b")]);
+    })
+}
+
+#[test]
+fn dcparsing_2() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        check_tokenization(setup(&sm, &sh, "a::b".to_string()),
+                        vec![mk_ident("a"), token::ModSep, mk_ident("b")]);
+    })
+}
+
+#[test]
+fn dcparsing_3() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        check_tokenization(setup(&sm, &sh, "a ::b".to_string()),
+                        vec![mk_ident("a"), token::Whitespace, token::ModSep, mk_ident("b")]);
+    })
+}
+
+#[test]
+fn dcparsing_4() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        check_tokenization(setup(&sm, &sh, "a:: b".to_string()),
+                        vec![mk_ident("a"), token::ModSep, token::Whitespace, mk_ident("b")]);
+    })
+}
+
+#[test]
+fn character_a() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        assert_eq!(setup(&sm, &sh, "'a'".to_string()).next_token(),
+                    mk_lit(token::Char, "a", None));
+    })
+}
+
+#[test]
+fn character_space() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        assert_eq!(setup(&sm, &sh, "' '".to_string()).next_token(),
+                    mk_lit(token::Char, " ", None));
+    })
+}
+
+#[test]
+fn character_escaped() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        assert_eq!(setup(&sm, &sh, "'\\n'".to_string()).next_token(),
+                    mk_lit(token::Char, "\\n", None));
+    })
+}
+
+#[test]
+fn lifetime_name() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        assert_eq!(setup(&sm, &sh, "'abc".to_string()).next_token(),
+                    token::Lifetime(Symbol::intern("'abc")));
+    })
+}
+
+#[test]
+fn raw_string() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        assert_eq!(setup(&sm, &sh, "r###\"\"#a\\b\x00c\"\"###".to_string()).next_token(),
+                    mk_lit(token::StrRaw(3), "\"#a\\b\x00c\"", None));
+    })
+}
+
+#[test]
+fn literal_suffixes() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        macro_rules! test {
+            ($input: expr, $tok_type: ident, $tok_contents: expr) => {{
+                assert_eq!(setup(&sm, &sh, format!("{}suffix", $input)).next_token(),
+                            mk_lit(token::$tok_type, $tok_contents, Some("suffix")));
+                // with a whitespace separator:
+                assert_eq!(setup(&sm, &sh, format!("{} suffix", $input)).next_token(),
+                            mk_lit(token::$tok_type, $tok_contents, None));
+            }}
+        }
+
+        test!("'a'", Char, "a");
+        test!("b'a'", Byte, "a");
+        test!("\"a\"", Str, "a");
+        test!("b\"a\"", ByteStr, "a");
+        test!("1234", Integer, "1234");
+        test!("0b101", Integer, "0b101");
+        test!("0xABC", Integer, "0xABC");
+        test!("1.0", Float, "1.0");
+        test!("1.0e10", Float, "1.0e10");
+
+        assert_eq!(setup(&sm, &sh, "2us".to_string()).next_token(),
+                    mk_lit(token::Integer, "2", Some("us")));
+        assert_eq!(setup(&sm, &sh, "r###\"raw\"###suffix".to_string()).next_token(),
+                    mk_lit(token::StrRaw(3), "raw", Some("suffix")));
+        assert_eq!(setup(&sm, &sh, "br###\"raw\"###suffix".to_string()).next_token(),
+                    mk_lit(token::ByteStrRaw(3), "raw", Some("suffix")));
+    })
+}
+
+#[test]
+fn line_doc_comments() {
+    assert!(is_doc_comment("///"));
+    assert!(is_doc_comment("/// blah"));
+    assert!(!is_doc_comment("////"));
+}
+
+#[test]
+fn nested_block_comments() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        let mut lexer = setup(&sm, &sh, "/* /* */ */'a'".to_string());
+        assert_eq!(lexer.next_token(), token::Comment);
+        assert_eq!(lexer.next_token(), mk_lit(token::Char, "a", None));
+    })
+}
+
+#[test]
+fn crlf_comments() {
+    with_default_globals(|| {
+        let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
+        let sh = mk_sess(sm.clone());
+        let mut lexer = setup(&sm, &sh, "// test\r\n/// test\r\n".to_string());
+        let comment = lexer.next_token();
+        assert_eq!(comment.kind, token::Comment);
+        assert_eq!((comment.span.lo(), comment.span.hi()), (BytePos(0), BytePos(7)));
+        assert_eq!(lexer.next_token(), token::Whitespace);
+        assert_eq!(lexer.next_token(), token::DocComment(Symbol::intern("/// test")));
+    })
+}
diff --git a/src/libsyntax/parse/lexer/tokentrees.rs b/src/libsyntax/parse/lexer/tokentrees.rs
index 4bfc5bb16c0..37e67a2729e 100644
--- a/src/libsyntax/parse/lexer/tokentrees.rs
+++ b/src/libsyntax/parse/lexer/tokentrees.rs
@@ -2,15 +2,16 @@ use syntax_pos::Span;
 
 use crate::print::pprust::token_to_string;
 use crate::parse::lexer::{StringReader, UnmatchedBrace};
-use crate::parse::{token, PResult};
-use crate::tokenstream::{DelimSpan, IsJoint::*, TokenStream, TokenTree, TreeAndJoint};
+use crate::parse::token::{self, Token};
+use crate::parse::PResult;
+use crate::tokenstream::{DelimSpan, IsJoint::{self, *}, TokenStream, TokenTree, TreeAndJoint};
 
 impl<'a> StringReader<'a> {
     crate fn into_token_trees(self) -> (PResult<'a, TokenStream>, Vec<UnmatchedBrace>) {
         let mut tt_reader = TokenTreesReader {
             string_reader: self,
-            token: token::Eof,
-            span: syntax_pos::DUMMY_SP,
+            token: Token::dummy(),
+            joint_to_prev: Joint,
             open_braces: Vec::new(),
             unmatched_braces: Vec::new(),
             matching_delim_spans: Vec::new(),
@@ -23,8 +24,8 @@ impl<'a> StringReader<'a> {
 
 struct TokenTreesReader<'a> {
     string_reader: StringReader<'a>,
-    token: token::Token,
-    span: Span,
+    token: Token,
+    joint_to_prev: IsJoint,
     /// Stack of open delimiters and their spans. Used for error message.
     open_braces: Vec<(token::DelimToken, Span)>,
     unmatched_braces: Vec<UnmatchedBrace>,
@@ -52,7 +53,7 @@ impl<'a> TokenTreesReader<'a> {
     fn parse_token_trees_until_close_delim(&mut self) -> TokenStream {
         let mut tts = vec![];
         loop {
-            if let token::CloseDelim(..) = self.token {
+            if let token::CloseDelim(..) = self.token.kind {
                 return TokenStream::new(tts);
             }
 
@@ -68,11 +69,11 @@ impl<'a> TokenTreesReader<'a> {
 
     fn parse_token_tree(&mut self) -> PResult<'a, TreeAndJoint> {
         let sm = self.string_reader.sess.source_map();
-        match self.token {
+        match self.token.kind {
             token::Eof => {
                 let msg = "this file contains an un-closed delimiter";
                 let mut err = self.string_reader.sess.span_diagnostic
-                    .struct_span_err(self.span, msg);
+                    .struct_span_err(self.token.span, msg);
                 for &(_, sp) in &self.open_braces {
                     err.span_label(sp, "un-closed delimiter");
                 }
@@ -102,10 +103,10 @@ impl<'a> TokenTreesReader<'a> {
             },
             token::OpenDelim(delim) => {
                 // The span for beginning of the delimited section
-                let pre_span = self.span;
+                let pre_span = self.token.span;
 
                 // Parse the open delimiter.
-                self.open_braces.push((delim, self.span));
+                self.open_braces.push((delim, self.token.span));
                 self.real_token();
 
                 // Parse the token trees within the delimiters.
@@ -114,9 +115,9 @@ impl<'a> TokenTreesReader<'a> {
                 let tts = self.parse_token_trees_until_close_delim();
 
                 // Expand to cover the entire delimited token tree
-                let delim_span = DelimSpan::from_pair(pre_span, self.span);
+                let delim_span = DelimSpan::from_pair(pre_span, self.token.span);
 
-                match self.token {
+                match self.token.kind {
                     // Correct delimiter.
                     token::CloseDelim(d) if d == delim => {
                         let (open_brace, open_brace_span) = self.open_braces.pop().unwrap();
@@ -126,7 +127,7 @@ impl<'a> TokenTreesReader<'a> {
                             self.matching_delim_spans.clear();
                         } else {
                             self.matching_delim_spans.push(
-                                (open_brace, open_brace_span, self.span),
+                                (open_brace, open_brace_span, self.token.span),
                             );
                         }
                         // Parse the close delimiter.
@@ -136,16 +137,16 @@ impl<'a> TokenTreesReader<'a> {
                     token::CloseDelim(other) => {
                         let mut unclosed_delimiter = None;
                         let mut candidate = None;
-                        if self.last_unclosed_found_span != Some(self.span) {
+                        if self.last_unclosed_found_span != Some(self.token.span) {
                             // do not complain about the same unclosed delimiter multiple times
-                            self.last_unclosed_found_span = Some(self.span);
+                            self.last_unclosed_found_span = Some(self.token.span);
                             // This is a conservative error: only report the last unclosed
                             // delimiter. The previous unclosed delimiters could actually be
                             // closed! The parser just hasn't gotten to them yet.
                             if let Some(&(_, sp)) = self.open_braces.last() {
                                 unclosed_delimiter = Some(sp);
                             };
-                            if let Some(current_padding) = sm.span_to_margin(self.span) {
+                            if let Some(current_padding) = sm.span_to_margin(self.token.span) {
                                 for (brace, brace_span) in &self.open_braces {
                                     if let Some(padding) = sm.span_to_margin(*brace_span) {
                                         // high likelihood of these two corresponding
@@ -159,7 +160,7 @@ impl<'a> TokenTreesReader<'a> {
                             self.unmatched_braces.push(UnmatchedBrace {
                                 expected_delim: tok,
                                 found_delim: other,
-                                found_span: self.span,
+                                found_span: self.token.span,
                                 unclosed_span: unclosed_delimiter,
                                 candidate_span: candidate,
                             });
@@ -198,29 +199,32 @@ impl<'a> TokenTreesReader<'a> {
                 let token_str = token_to_string(&self.token);
                 let msg = format!("unexpected close delimiter: `{}`", token_str);
                 let mut err = self.string_reader.sess.span_diagnostic
-                    .struct_span_err(self.span, &msg);
-                err.span_label(self.span, "unexpected close delimiter");
+                    .struct_span_err(self.token.span, &msg);
+                err.span_label(self.token.span, "unexpected close delimiter");
                 Err(err)
             },
             _ => {
-                let tt = TokenTree::Token(self.span, self.token.clone());
-                // Note that testing for joint-ness here is done via the raw
-                // source span as the joint-ness is a property of the raw source
-                // rather than wanting to take `override_span` into account.
-                // Additionally, we actually check if the *next* pair of tokens
-                // is joint, but this is equivalent to checking the current pair.
-                let raw = self.string_reader.peek_span_src_raw;
+                let tt = TokenTree::Token(self.token.take());
                 self.real_token();
-                let is_joint = raw.hi() == self.string_reader.peek_span_src_raw.lo()
-                    && token::is_op(&self.token);
+                let is_joint = self.joint_to_prev == Joint && self.token.is_op();
                 Ok((tt, if is_joint { Joint } else { NonJoint }))
             }
         }
     }
 
     fn real_token(&mut self) {
-        let t = self.string_reader.real_token();
-        self.token = t.tok;
-        self.span = t.sp;
+        self.joint_to_prev = Joint;
+        loop {
+            let token = self.string_reader.next_token();
+            match token.kind {
+                token::Whitespace | token::Comment | token::Shebang(_) | token::Unknown(_) => {
+                    self.joint_to_prev = NonJoint;
+                }
+                _ => {
+                    self.token = token;
+                    return;
+                },
+            }
+        }
     }
 }
diff --git a/src/libsyntax/parse/lexer/unicode_chars.rs b/src/libsyntax/parse/lexer/unicode_chars.rs
index 94ce6297fbe..525b4215aff 100644
--- a/src/libsyntax/parse/lexer/unicode_chars.rs
+++ b/src/libsyntax/parse/lexer/unicode_chars.rs
@@ -1,10 +1,12 @@
 // Characters and their corresponding confusables were collected from
 // http://www.unicode.org/Public/security/10.0.0/confusables.txt
 
-use syntax_pos::{Span, Pos, NO_EXPANSION};
-use errors::{Applicability, DiagnosticBuilder};
 use super::StringReader;
+use errors::{Applicability, DiagnosticBuilder};
+use syntax_pos::{BytePos, Pos, Span, symbol::kw};
+use crate::parse::token;
 
+#[rustfmt::skip] // for line breaks
 const UNICODE_ARRAY: &[(char, &str, char)] = &[
     ('
', "Line Separator", ' '),
     ('
', "Paragraph Separator", ' '),
@@ -49,7 +51,7 @@ const UNICODE_ARRAY: &[(char, &str, char)] = &[
     ('─', "Box Drawings Light Horizontal", '-'),
     ('━', "Box Drawings Heavy Horizontal", '-'),
     ('㇐', "CJK Stroke H", '-'),
-    ('ꟷ', "Latin Epigraphic Letter Dideways", '-'),
+    ('ꟷ', "Latin Epigraphic Letter Sideways I", '-'),
     ('ᅳ', "Hangul Jungseong Eu", '-'),
     ('ㅡ', "Hangul Letter Eu", '-'),
     ('一', "CJK Unified Ideograph-4E00", '-'),
@@ -293,74 +295,98 @@ const UNICODE_ARRAY: &[(char, &str, char)] = &[
     ('〉', "Right-Pointing Angle Bracket", '>'),
     ('〉', "Right Angle Bracket", '>'),
     ('》', "Right Double Angle Bracket", '>'),
-    ('＞', "Fullwidth Greater-Than Sign", '>'), ];
-
-
-const ASCII_ARRAY: &[(char, &str)] = &[
-    (' ', "Space"),
-    ('_', "Underscore"),
-    ('-', "Minus/Hyphen"),
-    (',', "Comma"),
-    (';', "Semicolon"),
-    (':', "Colon"),
-    ('!', "Exclamation Mark"),
-    ('?', "Question Mark"),
-    ('.', "Period"),
-    ('\'', "Single Quote"),
-    ('"', "Quotation Mark"),
-    ('(', "Left Parenthesis"),
-    (')', "Right Parenthesis"),
-    ('[', "Left Square Bracket"),
-    (']', "Right Square Bracket"),
-    ('{', "Left Curly Brace"),
-    ('}', "Right Curly Brace"),
-    ('*', "Asterisk"),
-    ('/', "Slash"),
-    ('\\', "Backslash"),
-    ('&', "Ampersand"),
-    ('+', "Plus Sign"),
-    ('<', "Less-Than Sign"),
-    ('=', "Equals Sign"),
-    ('>', "Greater-Than Sign"), ];
-
-crate fn check_for_substitution<'a>(reader: &StringReader<'a>,
-                                  ch: char,
-                                  err: &mut DiagnosticBuilder<'a>) -> bool {
-    UNICODE_ARRAY
-    .iter()
-    .find(|&&(c, _, _)| c == ch)
-    .map(|&(_, u_name, ascii_char)| {
-        let span = Span::new(reader.pos, reader.next_pos, NO_EXPANSION);
-        match ASCII_ARRAY.iter().find(|&&(c, _)| c == ascii_char) {
-            Some(&(ascii_char, ascii_name)) => {
-                // special help suggestion for "directed" double quotes
-                if let Some(s) = reader.peek_delimited('“', '”') {
-                    let msg = format!("Unicode characters '“' (Left Double Quotation Mark) and \
-                        '”' (Right Double Quotation Mark) look like '{}' ({}), but are not",
-                                ascii_char, ascii_name);
-                    err.span_suggestion(
-                        Span::new(reader.pos, reader.next_pos + Pos::from_usize(s.len()) +
-                            Pos::from_usize('”'.len_utf8()), NO_EXPANSION),
-                        &msg,
-                        format!("\"{}\"", s),
-                        Applicability::MaybeIncorrect);
-                } else {
-                    let msg =
-                        format!("Unicode character '{}' ({}) looks like '{}' ({}), but it is not",
-                                ch, u_name, ascii_char, ascii_name);
-                    err.span_suggestion(
-                        span,
-                        &msg,
-                        ascii_char.to_string(),
-                        Applicability::MaybeIncorrect);
-                }
-                true
-            },
-            None => {
-                let msg = format!("substitution character not found for '{}'", ch);
-                reader.sess.span_diagnostic.span_bug_no_panic(span, &msg);
-                false
-            }
+    ('＞', "Fullwidth Greater-Than Sign", '>'),
+];
+
+// FIXME: the lexer could be used to turn the ASCII version of unicode homoglyphs, instead of
+// keeping the substitution token in this table. Ideally, this should be inside `rustc_lexer`.
+// However, we should first remove compound tokens like `<<` from `rustc_lexer`, and then add
+// fancier error recovery to it, as there will be less overall work to do this way.
+const ASCII_ARRAY: &[(char, &str, Option<token::TokenKind>)] = &[
+    (' ', "Space", Some(token::Whitespace)),
+    ('_', "Underscore", Some(token::Ident(kw::Underscore, false))),
+    ('-', "Minus/Hyphen", Some(token::BinOp(token::Minus))),
+    (',', "Comma", Some(token::Comma)),
+    (';', "Semicolon", Some(token::Semi)),
+    (':', "Colon", Some(token::Colon)),
+    ('!', "Exclamation Mark", Some(token::Not)),
+    ('?', "Question Mark", Some(token::Question)),
+    ('.', "Period", Some(token::Dot)),
+    ('(', "Left Parenthesis", Some(token::OpenDelim(token::Paren))),
+    (')', "Right Parenthesis", Some(token::CloseDelim(token::Paren))),
+    ('[', "Left Square Bracket", Some(token::OpenDelim(token::Bracket))),
+    (']', "Right Square Bracket", Some(token::CloseDelim(token::Bracket))),
+    ('{', "Left Curly Brace", Some(token::OpenDelim(token::Brace))),
+    ('}', "Right Curly Brace", Some(token::CloseDelim(token::Brace))),
+    ('*', "Asterisk", Some(token::BinOp(token::Star))),
+    ('/', "Slash", Some(token::BinOp(token::Slash))),
+    ('\\', "Backslash", None),
+    ('&', "Ampersand", Some(token::BinOp(token::And))),
+    ('+', "Plus Sign", Some(token::BinOp(token::Plus))),
+    ('<', "Less-Than Sign", Some(token::Lt)),
+    ('=', "Equals Sign", Some(token::Eq)),
+    ('>', "Greater-Than Sign", Some(token::Gt)),
+    // FIXME: Literals are already lexed by this point, so we can't recover gracefully just by
+    // spitting the correct token out.
+    ('\'', "Single Quote", None),
+    ('"', "Quotation Mark", None),
+];
+
+crate fn check_for_substitution<'a>(
+    reader: &StringReader<'a>,
+    pos: BytePos,
+    ch: char,
+    err: &mut DiagnosticBuilder<'a>,
+) -> Option<token::TokenKind> {
+    let (u_name, ascii_char) = match UNICODE_ARRAY.iter().find(|&&(c, _, _)| c == ch) {
+        Some(&(_u_char, u_name, ascii_char)) => (u_name, ascii_char),
+        None => return None,
+    };
+
+    let span = Span::with_root_ctxt(pos, pos + Pos::from_usize(ch.len_utf8()));
+
+    let (ascii_name, token) = match ASCII_ARRAY.iter().find(|&&(c, _, _)| c == ascii_char) {
+        Some((_ascii_char, ascii_name, token)) => (ascii_name, token),
+        None => {
+            let msg = format!("substitution character not found for '{}'", ch);
+            reader.sess.span_diagnostic.span_bug_no_panic(span, &msg);
+            return None;
         }
-    }).unwrap_or(false)
+    };
+
+    // special help suggestion for "directed" double quotes
+    if let Some(s) = peek_delimited(&reader.src[reader.src_index(pos)..], '“', '”') {
+        let msg = format!(
+            "Unicode characters '“' (Left Double Quotation Mark) and \
+             '”' (Right Double Quotation Mark) look like '{}' ({}), but are not",
+            ascii_char, ascii_name
+        );
+        err.span_suggestion(
+            Span::with_root_ctxt(
+                pos,
+                pos + Pos::from_usize('“'.len_utf8() + s.len() + '”'.len_utf8()),
+            ),
+            &msg,
+            format!("\"{}\"", s),
+            Applicability::MaybeIncorrect,
+        );
+    } else {
+        let msg = format!(
+            "Unicode character '{}' ({}) looks like '{}' ({}), but it is not",
+            ch, u_name, ascii_char, ascii_name
+        );
+        err.span_suggestion(span, &msg, ascii_char.to_string(), Applicability::MaybeIncorrect);
+    }
+    token.clone()
+}
+
+/// Extract string if found at current position with given delimiters
+fn peek_delimited(text: &str, from_ch: char, to_ch: char) -> Option<&str> {
+    let mut chars = text.chars();
+    let first_char = chars.next()?;
+    if first_char != from_ch {
+        return None;
+    }
+    let last_char_idx = chars.as_str().find(to_ch)?;
+    Some(&chars.as_str()[..last_char_idx])
 }
diff --git a/src/libsyntax/parse/literal.rs b/src/libsyntax/parse/literal.rs
index 53195421ddc..6409acba573 100644
--- a/src/libsyntax/parse/literal.rs
+++ b/src/libsyntax/parse/literal.rs
@@ -1,487 +1,470 @@
 //! Code related to parsing literals.
 
-use crate::ast::{self, Ident, Lit, LitKind};
+use crate::ast::{self, Lit, LitKind};
 use crate::parse::parser::Parser;
 use crate::parse::PResult;
-use crate::parse::token::{self, Token};
-use crate::parse::unescape::{unescape_str, unescape_char, unescape_byte_str, unescape_byte};
+use crate::parse::token::{self, Token, TokenKind};
 use crate::print::pprust;
-use crate::symbol::{keywords, Symbol};
+use crate::symbol::{kw, sym, Symbol};
 use crate::tokenstream::{TokenStream, TokenTree};
 
 use errors::{Applicability, Handler};
 use log::debug;
 use rustc_data_structures::sync::Lrc;
 use syntax_pos::Span;
+use rustc_lexer::unescape::{unescape_char, unescape_byte};
+use rustc_lexer::unescape::{unescape_str, unescape_byte_str};
+use rustc_lexer::unescape::{unescape_raw_str, unescape_raw_byte_str};
 
 use std::ascii;
 
-macro_rules! err {
-    ($opt_diag:expr, |$span:ident, $diag:ident| $($body:tt)*) => {
-        match $opt_diag {
-            Some(($span, $diag)) => { $($body)* }
-            None => return None,
+crate enum LitError {
+    NotLiteral,
+    LexerError,
+    InvalidSuffix,
+    InvalidIntSuffix,
+    InvalidFloatSuffix,
+    NonDecimalFloat(u32),
+    IntTooLarge,
+}
+
+impl LitError {
+    fn report(&self, diag: &Handler, lit: token::Lit, span: Span) {
+        let token::Lit { kind, suffix, .. } = lit;
+        match *self {
+            // `NotLiteral` is not an error by itself, so we don't report
+            // it and give the parser opportunity to try something else.
+            LitError::NotLiteral => {}
+            // `LexerError` *is* an error, but it was already reported
+            // by lexer, so here we don't report it the second time.
+            LitError::LexerError => {}
+            LitError::InvalidSuffix => {
+                expect_no_suffix(
+                    diag, span, &format!("{} {} literal", kind.article(), kind.descr()), suffix
+                );
+            }
+            LitError::InvalidIntSuffix => {
+                let suf = suffix.expect("suffix error with no suffix").as_str();
+                if looks_like_width_suffix(&['i', 'u'], &suf) {
+                    // If it looks like a width, try to be helpful.
+                    let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
+                    diag.struct_span_err(span, &msg)
+                        .help("valid widths are 8, 16, 32, 64 and 128")
+                        .emit();
+                } else {
+                    let msg = format!("invalid suffix `{}` for integer literal", suf);
+                    diag.struct_span_err(span, &msg)
+                        .span_label(span, format!("invalid suffix `{}`", suf))
+                        .help("the suffix must be one of the integral types (`u32`, `isize`, etc)")
+                        .emit();
+                }
+            }
+            LitError::InvalidFloatSuffix => {
+                let suf = suffix.expect("suffix error with no suffix").as_str();
+                if looks_like_width_suffix(&['f'], &suf) {
+                    // If it looks like a width, try to be helpful.
+                    let msg = format!("invalid width `{}` for float literal", &suf[1..]);
+                    diag.struct_span_err(span, &msg)
+                        .help("valid widths are 32 and 64")
+                        .emit();
+                } else {
+                    let msg = format!("invalid suffix `{}` for float literal", suf);
+                    diag.struct_span_err(span, &msg)
+                        .span_label(span, format!("invalid suffix `{}`", suf))
+                        .help("valid suffixes are `f32` and `f64`")
+                        .emit();
+                }
+            }
+            LitError::NonDecimalFloat(base) => {
+                let descr = match base {
+                    16 => "hexadecimal",
+                    8 => "octal",
+                    2 => "binary",
+                    _ => unreachable!(),
+                };
+                diag.struct_span_err(span, &format!("{} float literal is not supported", descr))
+                    .span_label(span, "not supported")
+                    .emit();
+            }
+            LitError::IntTooLarge => {
+                diag.struct_span_err(span, "integer literal is too large")
+                    .emit();
+            }
         }
     }
 }
 
 impl LitKind {
-    /// Converts literal token with a suffix into a semantic literal.
-    /// Works speculatively and may return `None` if diagnostic handler is not passed.
-    /// If diagnostic handler is passed, always returns `Some`,
-    /// possibly after reporting non-fatal errors and recovery.
-    fn from_lit_token(
-        lit: token::Lit,
-        suf: Option<Symbol>,
-        diag: Option<(Span, &Handler)>
-    ) -> Option<LitKind> {
-        if suf.is_some() && !lit.may_have_suffix() {
-            err!(diag, |span, diag| {
-                expect_no_suffix(span, diag, &format!("a {}", lit.literal_name()), suf)
-            });
+    /// Converts literal token into a semantic literal.
+    fn from_lit_token(lit: token::Lit) -> Result<LitKind, LitError> {
+        let token::Lit { kind, symbol, suffix } = lit;
+        if suffix.is_some() && !kind.may_have_suffix() {
+            return Err(LitError::InvalidSuffix);
         }
 
-        Some(match lit {
-            token::Bool(i) => {
-                assert!(i == keywords::True.name() || i == keywords::False.name());
-                LitKind::Bool(i == keywords::True.name())
+        Ok(match kind {
+            token::Bool => {
+                assert!(symbol == kw::True || symbol == kw::False);
+                LitKind::Bool(symbol == kw::True)
             }
-            token::Byte(i) => {
-                match unescape_byte(&i.as_str()) {
-                    Ok(c) => LitKind::Byte(c),
-                    Err(_) => LitKind::Err(i),
-                }
-            },
-            token::Char(i) => {
-                match unescape_char(&i.as_str()) {
-                    Ok(c) => LitKind::Char(c),
-                    Err(_) => LitKind::Err(i),
-                }
-            },
-            token::Err(i) => LitKind::Err(i),
+            token::Byte => return unescape_byte(&symbol.as_str())
+                .map(LitKind::Byte).map_err(|_| LitError::LexerError),
+            token::Char => return unescape_char(&symbol.as_str())
+                .map(LitKind::Char).map_err(|_| LitError::LexerError),
 
             // There are some valid suffixes for integer and float literals,
             // so all the handling is done internally.
-            token::Integer(s) => return integer_lit(&s.as_str(), suf, diag),
-            token::Float(s) => return float_lit(&s.as_str(), suf, diag),
+            token::Integer => return integer_lit(symbol, suffix),
+            token::Float => return float_lit(symbol, suffix),
 
-            token::Str_(mut sym) => {
+            token::Str => {
                 // If there are no characters requiring special treatment we can
-                // reuse the symbol from the Token. Otherwise, we must generate a
+                // reuse the symbol from the token. Otherwise, we must generate a
                 // new symbol because the string in the LitKind is different to the
-                // string in the Token.
-                let mut has_error = false;
-                let s = &sym.as_str();
-                if s.as_bytes().iter().any(|&c| c == b'\\' || c == b'\r') {
+                // string in the token.
+                let s = symbol.as_str();
+                let symbol = if s.contains(&['\\', '\r'][..]) {
                     let mut buf = String::with_capacity(s.len());
-                    unescape_str(s, &mut |_, unescaped_char| {
+                    let mut error = Ok(());
+                    unescape_str(&s, &mut |_, unescaped_char| {
                         match unescaped_char {
                             Ok(c) => buf.push(c),
-                            Err(_) => has_error = true,
+                            Err(_) => error = Err(LitError::LexerError),
                         }
                     });
-                    if has_error {
-                        return Some(LitKind::Err(sym));
-                    }
-                    sym = Symbol::intern(&buf)
-                }
-
-                LitKind::Str(sym, ast::StrStyle::Cooked)
+                    error?;
+                    Symbol::intern(&buf)
+                } else {
+                    symbol
+                };
+                LitKind::Str(symbol, ast::StrStyle::Cooked)
             }
-            token::StrRaw(mut sym, n) => {
+            token::StrRaw(n) => {
                 // Ditto.
-                let s = &sym.as_str();
-                if s.contains('\r') {
-                    sym = Symbol::intern(&raw_str_lit(s));
-                }
-                LitKind::Str(sym, ast::StrStyle::Raw(n))
+                let s = symbol.as_str();
+                let symbol = if s.contains('\r') {
+                    let mut buf = String::with_capacity(s.len());
+                    let mut error = Ok(());
+                    unescape_raw_str(&s, &mut |_, unescaped_char| {
+                        match unescaped_char {
+                            Ok(c) => buf.push(c),
+                            Err(_) => error = Err(LitError::LexerError),
+                        }
+                    });
+                    error?;
+                    buf.shrink_to_fit();
+                    Symbol::intern(&buf)
+                } else {
+                    symbol
+                };
+                LitKind::Str(symbol, ast::StrStyle::Raw(n))
             }
-            token::ByteStr(i) => {
-                let s = &i.as_str();
+            token::ByteStr => {
+                let s = symbol.as_str();
                 let mut buf = Vec::with_capacity(s.len());
-                let mut has_error = false;
-                unescape_byte_str(s, &mut |_, unescaped_byte| {
+                let mut error = Ok(());
+                unescape_byte_str(&s, &mut |_, unescaped_byte| {
                     match unescaped_byte {
                         Ok(c) => buf.push(c),
-                        Err(_) => has_error = true,
+                        Err(_) => error = Err(LitError::LexerError),
                     }
                 });
-                if has_error {
-                    return Some(LitKind::Err(i));
-                }
+                error?;
                 buf.shrink_to_fit();
                 LitKind::ByteStr(Lrc::new(buf))
             }
-            token::ByteStrRaw(i, _) => {
-                LitKind::ByteStr(Lrc::new(i.to_string().into_bytes()))
-            }
+            token::ByteStrRaw(_) => {
+                let s = symbol.as_str();
+                let bytes = if s.contains('\r') {
+                    let mut buf = Vec::with_capacity(s.len());
+                    let mut error = Ok(());
+                    unescape_raw_byte_str(&s, &mut |_, unescaped_byte| {
+                        match unescaped_byte {
+                            Ok(c) => buf.push(c),
+                            Err(_) => error = Err(LitError::LexerError),
+                        }
+                    });
+                    error?;
+                    buf.shrink_to_fit();
+                    buf
+                } else {
+                    symbol.to_string().into_bytes()
+                };
+
+                LitKind::ByteStr(Lrc::new(bytes))
+            },
+            token::Err => LitKind::Err(symbol),
         })
     }
 
     /// Attempts to recover a token from semantic literal.
     /// This function is used when the original token doesn't exist (e.g. the literal is created
     /// by an AST-based macro) or unavailable (e.g. from HIR pretty-printing).
-    pub fn to_lit_token(&self) -> (token::Lit, Option<Symbol>) {
-        match *self {
-            LitKind::Str(string, ast::StrStyle::Cooked) => {
-                let escaped = string.as_str().escape_default().to_string();
-                (token::Lit::Str_(Symbol::intern(&escaped)), None)
+    pub fn to_lit_token(&self) -> token::Lit {
+        let (kind, symbol, suffix) = match *self {
+            LitKind::Str(symbol, ast::StrStyle::Cooked) => {
+                // Don't re-intern unless the escaped string is different.
+                let s = &symbol.as_str();
+                let escaped = s.escape_default().to_string();
+                let symbol = if escaped == *s { symbol } else { Symbol::intern(&escaped) };
+                (token::Str, symbol, None)
             }
-            LitKind::Str(string, ast::StrStyle::Raw(n)) => {
-                (token::Lit::StrRaw(string, n), None)
+            LitKind::Str(symbol, ast::StrStyle::Raw(n)) => {
+                (token::StrRaw(n), symbol, None)
             }
             LitKind::ByteStr(ref bytes) => {
                 let string = bytes.iter().cloned().flat_map(ascii::escape_default)
                     .map(Into::<char>::into).collect::<String>();
-                (token::Lit::ByteStr(Symbol::intern(&string)), None)
+                (token::ByteStr, Symbol::intern(&string), None)
             }
             LitKind::Byte(byte) => {
                 let string: String = ascii::escape_default(byte).map(Into::<char>::into).collect();
-                (token::Lit::Byte(Symbol::intern(&string)), None)
+                (token::Byte, Symbol::intern(&string), None)
             }
             LitKind::Char(ch) => {
                 let string: String = ch.escape_default().map(Into::<char>::into).collect();
-                (token::Lit::Char(Symbol::intern(&string)), None)
+                (token::Char, Symbol::intern(&string), None)
             }
             LitKind::Int(n, ty) => {
                 let suffix = match ty {
-                    ast::LitIntType::Unsigned(ty) => Some(Symbol::intern(ty.ty_to_string())),
-                    ast::LitIntType::Signed(ty) => Some(Symbol::intern(ty.ty_to_string())),
+                    ast::LitIntType::Unsigned(ty) => Some(ty.to_symbol()),
+                    ast::LitIntType::Signed(ty) => Some(ty.to_symbol()),
                     ast::LitIntType::Unsuffixed => None,
                 };
-                (token::Lit::Integer(Symbol::intern(&n.to_string())), suffix)
+                (token::Integer, sym::integer(n), suffix)
             }
             LitKind::Float(symbol, ty) => {
-                (token::Lit::Float(symbol), Some(Symbol::intern(ty.ty_to_string())))
+                (token::Float, symbol, Some(ty.to_symbol()))
+            }
+            LitKind::FloatUnsuffixed(symbol) => {
+                (token::Float, symbol, None)
             }
-            LitKind::FloatUnsuffixed(symbol) => (token::Lit::Float(symbol), None),
             LitKind::Bool(value) => {
-                let kw = if value { keywords::True } else { keywords::False };
-                (token::Lit::Bool(kw.name()), None)
+                let symbol = if value { kw::True } else { kw::False };
+                (token::Bool, symbol, None)
             }
-            LitKind::Err(val) => (token::Lit::Err(val), None),
-        }
+            LitKind::Err(symbol) => {
+                (token::Err, symbol, None)
+            }
+        };
+
+        token::Lit::new(kind, symbol, suffix)
     }
 }
 
 impl Lit {
-    /// Converts literal token with a suffix into an AST literal.
-    /// Works speculatively and may return `None` if diagnostic handler is not passed.
-    /// If diagnostic handler is passed, may return `Some`,
-    /// possibly after reporting non-fatal errors and recovery, or `None` for irrecoverable errors.
-    crate fn from_token(
-        token: &token::Token,
-        span: Span,
-        diag: Option<(Span, &Handler)>,
-    ) -> Option<Lit> {
-        let (token, suffix) = match *token {
-            token::Ident(ident, false) if ident.name == keywords::True.name() ||
-                                          ident.name == keywords::False.name() =>
-                (token::Bool(ident.name), None),
-            token::Literal(token, suffix) =>
-                (token, suffix),
+    /// Converts literal token into an AST literal.
+    fn from_lit_token(token: token::Lit, span: Span) -> Result<Lit, LitError> {
+        Ok(Lit { token, node: LitKind::from_lit_token(token)?, span })
+    }
+
+    /// Converts arbitrary token into an AST literal.
+    crate fn from_token(token: &Token) -> Result<Lit, LitError> {
+        let lit = match token.kind {
+            token::Ident(name, false) if name == kw::True || name == kw::False =>
+                token::Lit::new(token::Bool, name, None),
+            token::Literal(lit) =>
+                lit,
             token::Interpolated(ref nt) => {
                 if let token::NtExpr(expr) | token::NtLiteral(expr) = &**nt {
                     if let ast::ExprKind::Lit(lit) = &expr.node {
-                        return Some(lit.clone());
+                        return Ok(lit.clone());
                     }
                 }
-                return None;
+                return Err(LitError::NotLiteral);
             }
-            _ => return None,
+            _ => return Err(LitError::NotLiteral)
         };
 
-        let node = LitKind::from_lit_token(token, suffix, diag)?;
-        Some(Lit { node, token, suffix, span })
+        Lit::from_lit_token(lit, token.span)
     }
 
     /// Attempts to recover an AST literal from semantic literal.
     /// This function is used when the original token doesn't exist (e.g. the literal is created
     /// by an AST-based macro) or unavailable (e.g. from HIR pretty-printing).
     pub fn from_lit_kind(node: LitKind, span: Span) -> Lit {
-        let (token, suffix) = node.to_lit_token();
-        Lit { node, token, suffix, span }
+        Lit { token: node.to_lit_token(), node, span }
     }
 
     /// Losslessly convert an AST literal into a token stream.
     crate fn tokens(&self) -> TokenStream {
-        let token = match self.token {
-            token::Bool(symbol) => Token::Ident(Ident::with_empty_ctxt(symbol), false),
-            token => Token::Literal(token, self.suffix),
+        let token = match self.token.kind {
+            token::Bool => token::Ident(self.token.symbol, false),
+            _ => token::Literal(self.token),
         };
-        TokenTree::Token(self.span, token).into()
+        TokenTree::token(token, self.span).into()
     }
 }
 
 impl<'a> Parser<'a> {
     /// Matches `lit = true | false | token_lit`.
     crate fn parse_lit(&mut self) -> PResult<'a, Lit> {
-        let diag = Some((self.span, &self.sess.span_diagnostic));
-        if let Some(lit) = Lit::from_token(&self.token, self.span, diag) {
-            self.bump();
-            return Ok(lit);
-        } else if self.token == token::Dot {
-            // Recover `.4` as `0.4`.
-            let recovered = self.look_ahead(1, |t| {
-                if let token::Literal(token::Integer(val), suf) = *t {
-                    let next_span = self.look_ahead_span(1);
-                    if self.span.hi() == next_span.lo() {
-                        let sym = String::from("0.") + &val.as_str();
-                        let token = token::Literal(token::Float(Symbol::intern(&sym)), suf);
-                        return Some((token, self.span.to(next_span)));
+        let mut recovered = None;
+        if self.token == token::Dot {
+            // Attempt to recover `.4` as `0.4`.
+            recovered = self.look_ahead(1, |next_token| {
+                if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix })
+                        = next_token.kind {
+                    if self.token.span.hi() == next_token.span.lo() {
+                        let s = String::from("0.") + &symbol.as_str();
+                        let kind = TokenKind::lit(token::Float, Symbol::intern(&s), suffix);
+                        return Some(Token::new(kind, self.token.span.to(next_token.span)));
                     }
                 }
                 None
             });
-            if let Some((token, span)) = recovered {
+            if let Some(token) = &recovered {
+                self.bump();
                 self.diagnostic()
-                    .struct_span_err(span, "float literals must have an integer part")
+                    .struct_span_err(token.span, "float literals must have an integer part")
                     .span_suggestion(
-                        span,
+                        token.span,
                         "must have an integer part",
-                        pprust::token_to_string(&token),
+                        pprust::token_to_string(token),
                         Applicability::MachineApplicable,
                     )
                     .emit();
-                let diag = Some((span, &self.sess.span_diagnostic));
-                if let Some(lit) = Lit::from_token(&token, span, diag) {
-                    self.bump();
-                    self.bump();
-                    return Ok(lit);
-                }
             }
         }
 
-        Err(self.span_fatal(self.span, &format!("unexpected token: {}", self.this_token_descr())))
-    }
-}
-
-crate fn expect_no_suffix(sp: Span, diag: &Handler, kind: &str, suffix: Option<ast::Name>) {
-    match suffix {
-        None => {/* everything ok */}
-        Some(suf) => {
-            let text = suf.as_str();
-            if text.is_empty() {
-                diag.span_bug(sp, "found empty literal suffix in Some")
+        let token = recovered.as_ref().unwrap_or(&self.token);
+        match Lit::from_token(token) {
+            Ok(lit) => {
+                self.bump();
+                Ok(lit)
+            }
+            Err(LitError::NotLiteral) => {
+                let msg = format!("unexpected token: {}", self.this_token_descr());
+                Err(self.span_fatal(token.span, &msg))
+            }
+            Err(err) => {
+                let (lit, span) = (token.expect_lit(), token.span);
+                self.bump();
+                err.report(&self.sess.span_diagnostic, lit, span);
+                // Pack possible quotes and prefixes from the original literal into
+                // the error literal's symbol so they can be pretty-printed faithfully.
+                let suffixless_lit = token::Lit::new(lit.kind, lit.symbol, None);
+                let symbol = Symbol::intern(&suffixless_lit.to_string());
+                let lit = token::Lit::new(token::Err, symbol, lit.suffix);
+                Lit::from_lit_token(lit, span).map_err(|_| unreachable!())
             }
-            let mut err = if kind == "a tuple index" &&
-                ["i32", "u32", "isize", "usize"].contains(&text.to_string().as_str())
-            {
-                // #59553: warn instead of reject out of hand to allow the fix to percolate
-                // through the ecosystem when people fix their macros
-                let mut err = diag.struct_span_warn(
-                    sp,
-                    &format!("suffixes on {} are invalid", kind),
-                );
-                err.note(&format!(
-                    "`{}` is *temporarily* accepted on tuple index fields as it was \
-                        incorrectly accepted on stable for a few releases",
-                    text,
-                ));
-                err.help(
-                    "on proc macros, you'll want to use `syn::Index::from` or \
-                        `proc_macro::Literal::*_unsuffixed` for code that will desugar \
-                        to tuple field access",
-                );
-                err.note(
-                    "for more context, see https://github.com/rust-lang/rust/issues/60210",
-                );
-                err
-            } else {
-                diag.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
-            };
-            err.span_label(sp, format!("invalid suffix `{}`", text));
-            err.emit();
         }
     }
 }
 
-/// Parses a string representing a raw string literal into its final form. The
-/// only operation this does is convert embedded CRLF into a single LF.
-fn raw_str_lit(lit: &str) -> String {
-    debug!("raw_str_lit: given {}", lit.escape_default());
-    let mut res = String::with_capacity(lit.len());
-
-    let mut chars = lit.chars().peekable();
-    while let Some(c) = chars.next() {
-        if c == '\r' {
-            if *chars.peek().unwrap() != '\n' {
-                panic!("lexer accepted bare CR");
-            }
-            chars.next();
-            res.push('\n');
+crate fn expect_no_suffix(diag: &Handler, sp: Span, kind: &str, suffix: Option<Symbol>) {
+    if let Some(suf) = suffix {
+        let mut err = if kind == "a tuple index" &&
+                         [sym::i32, sym::u32, sym::isize, sym::usize].contains(&suf) {
+            // #59553: warn instead of reject out of hand to allow the fix to percolate
+            // through the ecosystem when people fix their macros
+            let mut err = diag.struct_span_warn(
+                sp,
+                &format!("suffixes on {} are invalid", kind),
+            );
+            err.note(&format!(
+                "`{}` is *temporarily* accepted on tuple index fields as it was \
+                    incorrectly accepted on stable for a few releases",
+                suf,
+            ));
+            err.help(
+                "on proc macros, you'll want to use `syn::Index::from` or \
+                    `proc_macro::Literal::*_unsuffixed` for code that will desugar \
+                    to tuple field access",
+            );
+            err.note(
+                "for more context, see https://github.com/rust-lang/rust/issues/60210",
+            );
+            err
         } else {
-            res.push(c);
-        }
+            diag.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
+        };
+        err.span_label(sp, format!("invalid suffix `{}`", suf));
+        err.emit();
     }
-
-    res.shrink_to_fit();
-    res
 }
 
-// check if `s` looks like i32 or u1234 etc.
+// Checks if `s` looks like i32 or u1234 etc.
 fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
-    s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
+    s.len() > 1 && s.starts_with(first_chars) && s[1..].chars().all(|c| c.is_ascii_digit())
 }
 
-fn filtered_float_lit(data: Symbol, suffix: Option<Symbol>, diag: Option<(Span, &Handler)>)
-                      -> Option<LitKind> {
-    debug!("filtered_float_lit: {}, {:?}", data, suffix);
-    let suffix = match suffix {
-        Some(suffix) => suffix,
-        None => return Some(LitKind::FloatUnsuffixed(data)),
-    };
-
-    Some(match &*suffix.as_str() {
-        "f32" => LitKind::Float(data, ast::FloatTy::F32),
-        "f64" => LitKind::Float(data, ast::FloatTy::F64),
-        suf => {
-            err!(diag, |span, diag| {
-                if suf.len() >= 2 && looks_like_width_suffix(&['f'], suf) {
-                    // if it looks like a width, lets try to be helpful.
-                    let msg = format!("invalid width `{}` for float literal", &suf[1..]);
-                    diag.struct_span_err(span, &msg).help("valid widths are 32 and 64").emit()
-                } else {
-                    let msg = format!("invalid suffix `{}` for float literal", suf);
-                    diag.struct_span_err(span, &msg)
-                        .span_label(span, format!("invalid suffix `{}`", suf))
-                        .help("valid suffixes are `f32` and `f64`")
-                        .emit();
-                }
-            });
+fn strip_underscores(symbol: Symbol) -> Symbol {
+    // Do not allocate a new string unless necessary.
+    let s = symbol.as_str();
+    if s.contains('_') {
+        let mut s = s.to_string();
+        s.retain(|c| c != '_');
+        return Symbol::intern(&s);
+    }
+    symbol
+}
 
-            LitKind::FloatUnsuffixed(data)
+fn filtered_float_lit(symbol: Symbol, suffix: Option<Symbol>, base: u32)
+                      -> Result<LitKind, LitError> {
+    debug!("filtered_float_lit: {:?}, {:?}, {:?}", symbol, suffix, base);
+    if base != 10 {
+        return Err(LitError::NonDecimalFloat(base));
+    }
+    Ok(match suffix {
+        Some(suf) => match suf {
+            sym::f32 => LitKind::Float(symbol, ast::FloatTy::F32),
+            sym::f64 => LitKind::Float(symbol, ast::FloatTy::F64),
+            _ => return Err(LitError::InvalidFloatSuffix),
         }
+        None => LitKind::FloatUnsuffixed(symbol)
     })
 }
-fn float_lit(s: &str, suffix: Option<Symbol>, diag: Option<(Span, &Handler)>)
-                 -> Option<LitKind> {
-    debug!("float_lit: {:?}, {:?}", s, suffix);
-    // FIXME #2252: bounds checking float literals is deferred until trans
-
-    // Strip underscores without allocating a new String unless necessary.
-    let s2;
-    let s = if s.chars().any(|c| c == '_') {
-        s2 = s.chars().filter(|&c| c != '_').collect::<String>();
-        &s2
-    } else {
-        s
-    };
 
-    filtered_float_lit(Symbol::intern(s), suffix, diag)
+fn float_lit(symbol: Symbol, suffix: Option<Symbol>) -> Result<LitKind, LitError> {
+    debug!("float_lit: {:?}, {:?}", symbol, suffix);
+    filtered_float_lit(strip_underscores(symbol), suffix, 10)
 }
 
-fn integer_lit(s: &str, suffix: Option<Symbol>, diag: Option<(Span, &Handler)>)
-                   -> Option<LitKind> {
-    // s can only be ascii, byte indexing is fine
-
-    // Strip underscores without allocating a new String unless necessary.
-    let s2;
-    let mut s = if s.chars().any(|c| c == '_') {
-        s2 = s.chars().filter(|&c| c != '_').collect::<String>();
-        &s2
-    } else {
-        s
-    };
-
-    debug!("integer_lit: {}, {:?}", s, suffix);
+fn integer_lit(symbol: Symbol, suffix: Option<Symbol>) -> Result<LitKind, LitError> {
+    debug!("integer_lit: {:?}, {:?}", symbol, suffix);
+    let symbol = strip_underscores(symbol);
+    let s = symbol.as_str();
 
     let mut base = 10;
-    let orig = s;
-    let mut ty = ast::LitIntType::Unsuffixed;
-
-    if s.starts_with('0') && s.len() > 1 {
+    if s.len() > 1 && s.as_bytes()[0] == b'0' {
         match s.as_bytes()[1] {
             b'x' => base = 16,
             b'o' => base = 8,
             b'b' => base = 2,
-            _ => { }
-        }
-    }
-
-    // 1f64 and 2f32 etc. are valid float literals.
-    if let Some(suf) = suffix {
-        if looks_like_width_suffix(&['f'], &suf.as_str()) {
-            let err = match base {
-                16 => Some("hexadecimal float literal is not supported"),
-                8 => Some("octal float literal is not supported"),
-                2 => Some("binary float literal is not supported"),
-                _ => None,
-            };
-            if let Some(err) = err {
-                err!(diag, |span, diag| {
-                    diag.struct_span_err(span, err)
-                        .span_label(span, "not supported")
-                        .emit();
-                });
-            }
-            return filtered_float_lit(Symbol::intern(s), Some(suf), diag)
+            _ => {}
         }
     }
 
-    if base != 10 {
-        s = &s[2..];
-    }
-
-    if let Some(suf) = suffix {
-        if suf.as_str().is_empty() {
-            err!(diag, |span, diag| diag.span_bug(span, "found empty literal suffix in Some"));
+    let ty = match suffix {
+        Some(suf) => match suf {
+            sym::isize => ast::LitIntType::Signed(ast::IntTy::Isize),
+            sym::i8  => ast::LitIntType::Signed(ast::IntTy::I8),
+            sym::i16 => ast::LitIntType::Signed(ast::IntTy::I16),
+            sym::i32 => ast::LitIntType::Signed(ast::IntTy::I32),
+            sym::i64 => ast::LitIntType::Signed(ast::IntTy::I64),
+            sym::i128 => ast::LitIntType::Signed(ast::IntTy::I128),
+            sym::usize => ast::LitIntType::Unsigned(ast::UintTy::Usize),
+            sym::u8  => ast::LitIntType::Unsigned(ast::UintTy::U8),
+            sym::u16 => ast::LitIntType::Unsigned(ast::UintTy::U16),
+            sym::u32 => ast::LitIntType::Unsigned(ast::UintTy::U32),
+            sym::u64 => ast::LitIntType::Unsigned(ast::UintTy::U64),
+            sym::u128 => ast::LitIntType::Unsigned(ast::UintTy::U128),
+            // `1f64` and `2f32` etc. are valid float literals, and
+            // `fxxx` looks more like an invalid float literal than invalid integer literal.
+            _ if suf.as_str().starts_with('f') => return filtered_float_lit(symbol, suffix, base),
+            _ => return Err(LitError::InvalidIntSuffix),
         }
-        ty = match &*suf.as_str() {
-            "isize" => ast::LitIntType::Signed(ast::IntTy::Isize),
-            "i8"  => ast::LitIntType::Signed(ast::IntTy::I8),
-            "i16" => ast::LitIntType::Signed(ast::IntTy::I16),
-            "i32" => ast::LitIntType::Signed(ast::IntTy::I32),
-            "i64" => ast::LitIntType::Signed(ast::IntTy::I64),
-            "i128" => ast::LitIntType::Signed(ast::IntTy::I128),
-            "usize" => ast::LitIntType::Unsigned(ast::UintTy::Usize),
-            "u8"  => ast::LitIntType::Unsigned(ast::UintTy::U8),
-            "u16" => ast::LitIntType::Unsigned(ast::UintTy::U16),
-            "u32" => ast::LitIntType::Unsigned(ast::UintTy::U32),
-            "u64" => ast::LitIntType::Unsigned(ast::UintTy::U64),
-            "u128" => ast::LitIntType::Unsigned(ast::UintTy::U128),
-            suf => {
-                // i<digits> and u<digits> look like widths, so lets
-                // give an error message along those lines
-                err!(diag, |span, diag| {
-                    if looks_like_width_suffix(&['i', 'u'], suf) {
-                        let msg = format!("invalid width `{}` for integer literal", &suf[1..]);
-                        diag.struct_span_err(span, &msg)
-                            .help("valid widths are 8, 16, 32, 64 and 128")
-                            .emit();
-                    } else {
-                        let msg = format!("invalid suffix `{}` for numeric literal", suf);
-                        diag.struct_span_err(span, &msg)
-                            .span_label(span, format!("invalid suffix `{}`", suf))
-                            .help("the suffix must be one of the integral types \
-                                   (`u32`, `isize`, etc)")
-                            .emit();
-                    }
-                });
-
-                ty
-            }
-        }
-    }
-
-    debug!("integer_lit: the type is {:?}, base {:?}, the new string is {:?}, the original \
-           string was {:?}, the original suffix was {:?}", ty, base, s, orig, suffix);
-
-    Some(match u128::from_str_radix(s, base) {
-        Ok(r) => LitKind::Int(r, ty),
-        Err(_) => {
-            // small bases are lexed as if they were base 10, e.g, the string
-            // might be `0b10201`. This will cause the conversion above to fail,
-            // but these cases have errors in the lexer: we don't want to emit
-            // two errors, and we especially don't want to emit this error since
-            // it isn't necessarily true.
-            let already_errored = base < 10 &&
-                s.chars().any(|c| c.to_digit(10).map_or(false, |d| d >= base));
+        _ => ast::LitIntType::Unsuffixed
+    };
 
-            if !already_errored {
-                err!(diag, |span, diag| diag.span_err(span, "int literal is too large"));
-            }
-            LitKind::Int(0, ty)
-        }
+    let s = &s[if base != 10 { 2 } else { 0 } ..];
+    u128::from_str_radix(s, base).map(|i| LitKind::Int(i, ty)).map_err(|_| {
+        // Small bases are lexed as if they were base 10, e.g, the string
+        // might be `0b10201`. This will cause the conversion above to fail,
+        // but these kinds of errors are already reported by the lexer.
+        let from_lexer =
+            base < 10 && s.chars().any(|c| c.to_digit(10).map_or(false, |d| d >= base));
+        if from_lexer { LitError::LexerError } else { LitError::IntTooLarge }
     })
 }
diff --git a/src/libsyntax/parse/mod.rs b/src/libsyntax/parse/mod.rs
index 0611c1d9b42..b1f3612a839 100644
--- a/src/libsyntax/parse/mod.rs
+++ b/src/libsyntax/parse/mod.rs
@@ -5,21 +5,26 @@ use crate::early_buffered_lints::{BufferedEarlyLint, BufferedEarlyLintId};
 use crate::source_map::{SourceMap, FilePathMapping};
 use crate::feature_gate::UnstableFeatures;
 use crate::parse::parser::Parser;
-use crate::syntax::parse::parser::emit_unclosed_delims;
+use crate::parse::parser::emit_unclosed_delims;
+use crate::parse::token::TokenKind;
 use crate::tokenstream::{TokenStream, TokenTree};
 use crate::diagnostics::plugin::ErrorMap;
-use crate::print::pprust::token_to_string;
+use crate::print::pprust;
+use crate::symbol::Symbol;
 
 use errors::{Applicability, FatalError, Level, Handler, ColorConfig, Diagnostic, DiagnosticBuilder};
-use rustc_data_structures::sync::{Lrc, Lock};
+use rustc_data_structures::sync::{Lrc, Lock, Once};
 use syntax_pos::{Span, SourceFile, FileName, MultiSpan};
+use syntax_pos::edition::Edition;
+use syntax_pos::hygiene::ExpnId;
 
 use rustc_data_structures::fx::{FxHashSet, FxHashMap};
 use std::borrow::Cow;
 use std::path::{Path, PathBuf};
 use std::str;
 
-pub type PResult<'a, T> = Result<T, DiagnosticBuilder<'a>>;
+#[cfg(test)]
+mod tests;
 
 #[macro_use]
 pub mod parser;
@@ -30,14 +35,16 @@ pub mod token;
 crate mod classify;
 crate mod diagnostics;
 crate mod literal;
-crate mod unescape;
 crate mod unescape_error_reporting;
 
+pub type PResult<'a, T> = Result<T, DiagnosticBuilder<'a>>;
+
 /// Info about a parsing session.
 pub struct ParseSess {
     pub span_diagnostic: Handler,
     pub unstable_features: UnstableFeatures,
     pub config: CrateConfig,
+    pub edition: Edition,
     pub missing_fragment_specifiers: Lock<FxHashSet<Span>>,
     /// Places where raw identifiers were used. This is used for feature-gating raw identifiers.
     pub raw_identifier_spans: Lock<Vec<Span>>,
@@ -51,6 +58,16 @@ pub struct ParseSess {
     /// operation token that followed it, but that the parser cannot identify without further
     /// analysis.
     pub ambiguous_block_expr_parse: Lock<FxHashMap<Span, Span>>,
+    pub param_attr_spans: Lock<Vec<Span>>,
+    // Places where `let` exprs were used and should be feature gated according to `let_chains`.
+    pub let_chains_spans: Lock<Vec<Span>>,
+    // Places where `async || ..` exprs were used and should be feature gated.
+    pub async_closure_spans: Lock<Vec<Span>>,
+    // Places where `yield e?` exprs were used and should be feature gated.
+    pub yield_spans: Lock<Vec<Span>>,
+    pub injected_crate_name: Once<Symbol>,
+    // Places where or-patterns e.g. `Some(Foo | Bar)` were used and should be feature gated.
+    pub or_pattern_spans: Lock<Vec<Span>>,
 }
 
 impl ParseSess {
@@ -74,7 +91,14 @@ impl ParseSess {
             included_mod_stack: Lock::new(vec![]),
             source_map,
             buffered_lints: Lock::new(vec![]),
+            edition: ExpnId::root().expn_data().edition,
             ambiguous_block_expr_parse: Lock::new(FxHashMap::default()),
+            param_attr_spans: Lock::new(Vec::new()),
+            let_chains_spans: Lock::new(Vec::new()),
+            async_closure_spans: Lock::new(Vec::new()),
+            yield_spans: Lock::new(Vec::new()),
+            injected_crate_name: Once::new(),
+            or_pattern_spans: Lock::new(Vec::new()),
         }
     }
 
@@ -233,10 +257,10 @@ fn maybe_source_file_to_parser(
 ) -> Result<Parser<'_>, Vec<Diagnostic>> {
     let end_pos = source_file.end_pos;
     let (stream, unclosed_delims) = maybe_file_to_stream(sess, source_file, None)?;
-    let mut parser = stream_to_parser(sess, stream);
+    let mut parser = stream_to_parser(sess, stream, None);
     parser.unclosed_delims = unclosed_delims;
-    if parser.token == token::Eof && parser.span.is_dummy() {
-        parser.span = Span::new(end_pos, end_pos, parser.span.ctxt());
+    if parser.token == token::Eof && parser.token.span.is_dummy() {
+        parser.token.span = Span::new(end_pos, end_pos, parser.token.span.ctxt());
     }
 
     Ok(parser)
@@ -245,7 +269,7 @@ fn maybe_source_file_to_parser(
 // must preserve old name for now, because quote! from the *existing*
 // compiler expands into it
 pub fn new_parser_from_tts(sess: &ParseSess, tts: Vec<TokenTree>) -> Parser<'_> {
-    stream_to_parser(sess, tts.into_iter().collect())
+    stream_to_parser(sess, tts.into_iter().collect(), crate::MACRO_ARGUMENTS)
 }
 
 
@@ -296,7 +320,7 @@ pub fn maybe_file_to_stream(
     source_file: Lrc<SourceFile>,
     override_span: Option<Span>,
 ) -> Result<(TokenStream, Vec<lexer::UnmatchedBrace>), Vec<Diagnostic>> {
-    let srdr = lexer::StringReader::new_or_buffered_errs(sess, source_file, override_span)?;
+    let srdr = lexer::StringReader::new(sess, source_file, override_span);
     let (token_trees, unmatched_braces) = srdr.into_token_trees();
 
     match token_trees {
@@ -308,7 +332,7 @@ pub fn maybe_file_to_stream(
             for unmatched in unmatched_braces {
                 let mut db = sess.span_diagnostic.struct_span_err(unmatched.found_span, &format!(
                     "incorrect close delimiter: `{}`",
-                    token_to_string(&token::Token::CloseDelim(unmatched.found_delim)),
+                    pprust::token_kind_to_string(&token::CloseDelim(unmatched.found_delim)),
                 ));
                 db.span_label(unmatched.found_span, "incorrect close delimiter");
                 if let Some(sp) = unmatched.candidate_span {
@@ -325,20 +349,43 @@ pub fn maybe_file_to_stream(
 }
 
 /// Given stream and the `ParseSess`, produces a parser.
-pub fn stream_to_parser(sess: &ParseSess, stream: TokenStream) -> Parser<'_> {
-    Parser::new(sess, stream, None, true, false)
+pub fn stream_to_parser<'a>(
+    sess: &'a ParseSess,
+    stream: TokenStream,
+    subparser_name: Option<&'static str>,
+) -> Parser<'a> {
+    Parser::new(sess, stream, None, true, false, subparser_name)
+}
+
+/// Given stream, the `ParseSess` and the base directory, produces a parser.
+///
+/// Use this function when you are creating a parser from the token stream
+/// and also care about the current working directory of the parser (e.g.,
+/// you are trying to resolve modules defined inside a macro invocation).
+///
+/// # Note
+///
+/// The main usage of this function is outside of rustc, for those who uses
+/// libsyntax as a library. Please do not remove this function while refactoring
+/// just because it is not used in rustc codebase!
+pub fn stream_to_parser_with_base_dir<'a>(
+    sess: &'a ParseSess,
+    stream: TokenStream,
+    base_dir: Directory<'a>,
+) -> Parser<'a> {
+    Parser::new(sess, stream, Some(base_dir), true, false, None)
 }
 
 /// A sequence separator.
 pub struct SeqSep {
-    /// The seperator token.
-    pub sep: Option<token::Token>,
+    /// The separator token.
+    pub sep: Option<TokenKind>,
     /// `true` if a trailing separator is allowed.
     pub trailing_sep_allowed: bool,
 }
 
 impl SeqSep {
-    pub fn trailing_allowed(t: token::Token) -> SeqSep {
+    pub fn trailing_allowed(t: TokenKind) -> SeqSep {
         SeqSep {
             sep: Some(t),
             trailing_sep_allowed: true,
@@ -352,304 +399,3 @@ impl SeqSep {
         }
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::ast::{self, Ident, PatKind};
-    use crate::attr::first_attr_value_str_by_name;
-    use crate::ptr::P;
-    use crate::print::pprust::item_to_string;
-    use crate::tokenstream::{DelimSpan, TokenTree};
-    use crate::util::parser_testing::string_to_stream;
-    use crate::util::parser_testing::{string_to_expr, string_to_item};
-    use crate::with_globals;
-    use syntax_pos::{Span, BytePos, Pos, NO_EXPANSION};
-
-    /// Parses an item.
-    ///
-    /// Returns `Ok(Some(item))` when successful, `Ok(None)` when no item was found, and `Err`
-    /// when a syntax error occurred.
-    fn parse_item_from_source_str(name: FileName, source: String, sess: &ParseSess)
-                                        -> PResult<'_, Option<P<ast::Item>>> {
-        new_parser_from_source_str(sess, name, source).parse_item()
-    }
-
-    // produce a syntax_pos::span
-    fn sp(a: u32, b: u32) -> Span {
-        Span::new(BytePos(a), BytePos(b), NO_EXPANSION)
-    }
-
-    #[should_panic]
-    #[test] fn bad_path_expr_1() {
-        with_globals(|| {
-            string_to_expr("::abc::def::return".to_string());
-        })
-    }
-
-    // check the token-tree-ization of macros
-    #[test]
-    fn string_to_tts_macro () {
-        with_globals(|| {
-            use crate::symbol::sym;
-
-            let tts: Vec<_> =
-                string_to_stream("macro_rules! zip (($a)=>($a))".to_string()).trees().collect();
-            let tts: &[TokenTree] = &tts[..];
-
-            match (tts.len(), tts.get(0), tts.get(1), tts.get(2), tts.get(3)) {
-                (
-                    4,
-                    Some(&TokenTree::Token(_, token::Ident(name_macro_rules, false))),
-                    Some(&TokenTree::Token(_, token::Not)),
-                    Some(&TokenTree::Token(_, token::Ident(name_zip, false))),
-                    Some(&TokenTree::Delimited(_, macro_delim, ref macro_tts)),
-                )
-                if name_macro_rules.name == sym::macro_rules
-                && name_zip.name.as_str() == "zip" => {
-                    let tts = &macro_tts.trees().collect::<Vec<_>>();
-                    match (tts.len(), tts.get(0), tts.get(1), tts.get(2)) {
-                        (
-                            3,
-                            Some(&TokenTree::Delimited(_, first_delim, ref first_tts)),
-                            Some(&TokenTree::Token(_, token::FatArrow)),
-                            Some(&TokenTree::Delimited(_, second_delim, ref second_tts)),
-                        )
-                        if macro_delim == token::Paren => {
-                            let tts = &first_tts.trees().collect::<Vec<_>>();
-                            match (tts.len(), tts.get(0), tts.get(1)) {
-                                (
-                                    2,
-                                    Some(&TokenTree::Token(_, token::Dollar)),
-                                    Some(&TokenTree::Token(_, token::Ident(ident, false))),
-                                )
-                                if first_delim == token::Paren && ident.name.as_str() == "a" => {},
-                                _ => panic!("value 3: {:?} {:?}", first_delim, first_tts),
-                            }
-                            let tts = &second_tts.trees().collect::<Vec<_>>();
-                            match (tts.len(), tts.get(0), tts.get(1)) {
-                                (
-                                    2,
-                                    Some(&TokenTree::Token(_, token::Dollar)),
-                                    Some(&TokenTree::Token(_, token::Ident(ident, false))),
-                                )
-                                if second_delim == token::Paren && ident.name.as_str() == "a" => {},
-                                _ => panic!("value 4: {:?} {:?}", second_delim, second_tts),
-                            }
-                        },
-                        _ => panic!("value 2: {:?} {:?}", macro_delim, macro_tts),
-                    }
-                },
-                _ => panic!("value: {:?}",tts),
-            }
-        })
-    }
-
-    #[test]
-    fn string_to_tts_1() {
-        with_globals(|| {
-            let tts = string_to_stream("fn a (b : i32) { b; }".to_string());
-
-            let expected = TokenStream::new(vec![
-                TokenTree::Token(sp(0, 2), token::Ident(Ident::from_str("fn"), false)).into(),
-                TokenTree::Token(sp(3, 4), token::Ident(Ident::from_str("a"), false)).into(),
-                TokenTree::Delimited(
-                    DelimSpan::from_pair(sp(5, 6), sp(13, 14)),
-                    token::DelimToken::Paren,
-                    TokenStream::new(vec![
-                        TokenTree::Token(sp(6, 7),
-                                         token::Ident(Ident::from_str("b"), false)).into(),
-                        TokenTree::Token(sp(8, 9), token::Colon).into(),
-                        TokenTree::Token(sp(10, 13),
-                                         token::Ident(Ident::from_str("i32"), false)).into(),
-                    ]).into(),
-                ).into(),
-                TokenTree::Delimited(
-                    DelimSpan::from_pair(sp(15, 16), sp(20, 21)),
-                    token::DelimToken::Brace,
-                    TokenStream::new(vec![
-                        TokenTree::Token(sp(17, 18),
-                                         token::Ident(Ident::from_str("b"), false)).into(),
-                        TokenTree::Token(sp(18, 19), token::Semi).into(),
-                    ]).into(),
-                ).into()
-            ]);
-
-            assert_eq!(tts, expected);
-        })
-    }
-
-    #[test] fn parse_use() {
-        with_globals(|| {
-            let use_s = "use foo::bar::baz;";
-            let vitem = string_to_item(use_s.to_string()).unwrap();
-            let vitem_s = item_to_string(&vitem);
-            assert_eq!(&vitem_s[..], use_s);
-
-            let use_s = "use foo::bar as baz;";
-            let vitem = string_to_item(use_s.to_string()).unwrap();
-            let vitem_s = item_to_string(&vitem);
-            assert_eq!(&vitem_s[..], use_s);
-        })
-    }
-
-    #[test] fn parse_extern_crate() {
-        with_globals(|| {
-            let ex_s = "extern crate foo;";
-            let vitem = string_to_item(ex_s.to_string()).unwrap();
-            let vitem_s = item_to_string(&vitem);
-            assert_eq!(&vitem_s[..], ex_s);
-
-            let ex_s = "extern crate foo as bar;";
-            let vitem = string_to_item(ex_s.to_string()).unwrap();
-            let vitem_s = item_to_string(&vitem);
-            assert_eq!(&vitem_s[..], ex_s);
-        })
-    }
-
-    fn get_spans_of_pat_idents(src: &str) -> Vec<Span> {
-        let item = string_to_item(src.to_string()).unwrap();
-
-        struct PatIdentVisitor {
-            spans: Vec<Span>
-        }
-        impl<'a> crate::visit::Visitor<'a> for PatIdentVisitor {
-            fn visit_pat(&mut self, p: &'a ast::Pat) {
-                match p.node {
-                    PatKind::Ident(_ , ref spannedident, _) => {
-                        self.spans.push(spannedident.span.clone());
-                    }
-                    _ => {
-                        crate::visit::walk_pat(self, p);
-                    }
-                }
-            }
-        }
-        let mut v = PatIdentVisitor { spans: Vec::new() };
-        crate::visit::walk_item(&mut v, &item);
-        return v.spans;
-    }
-
-    #[test] fn span_of_self_arg_pat_idents_are_correct() {
-        with_globals(|| {
-
-            let srcs = ["impl z { fn a (&self, &myarg: i32) {} }",
-                        "impl z { fn a (&mut self, &myarg: i32) {} }",
-                        "impl z { fn a (&'a self, &myarg: i32) {} }",
-                        "impl z { fn a (self, &myarg: i32) {} }",
-                        "impl z { fn a (self: Foo, &myarg: i32) {} }",
-                        ];
-
-            for &src in &srcs {
-                let spans = get_spans_of_pat_idents(src);
-                let (lo, hi) = (spans[0].lo(), spans[0].hi());
-                assert!("self" == &src[lo.to_usize()..hi.to_usize()],
-                        "\"{}\" != \"self\". src=\"{}\"",
-                        &src[lo.to_usize()..hi.to_usize()], src)
-            }
-        })
-    }
-
-    #[test] fn parse_exprs () {
-        with_globals(|| {
-            // just make sure that they parse....
-            string_to_expr("3 + 4".to_string());
-            string_to_expr("a::z.froob(b,&(987+3))".to_string());
-        })
-    }
-
-    #[test] fn attrs_fix_bug () {
-        with_globals(|| {
-            string_to_item("pub fn mk_file_writer(path: &Path, flags: &[FileFlag])
-                   -> Result<Box<Writer>, String> {
-    #[cfg(windows)]
-    fn wb() -> c_int {
-      (O_WRONLY | libc::consts::os::extra::O_BINARY) as c_int
-    }
-
-    #[cfg(unix)]
-    fn wb() -> c_int { O_WRONLY as c_int }
-
-    let mut fflags: c_int = wb();
-}".to_string());
-        })
-    }
-
-    #[test] fn crlf_doc_comments() {
-        with_globals(|| {
-            use crate::symbol::sym;
-
-            let sess = ParseSess::new(FilePathMapping::empty());
-
-            let name_1 = FileName::Custom("crlf_source_1".to_string());
-            let source = "/// doc comment\r\nfn foo() {}".to_string();
-            let item = parse_item_from_source_str(name_1, source, &sess)
-                .unwrap().unwrap();
-            let doc = first_attr_value_str_by_name(&item.attrs, sym::doc).unwrap();
-            assert_eq!(doc.as_str(), "/// doc comment");
-
-            let name_2 = FileName::Custom("crlf_source_2".to_string());
-            let source = "/// doc comment\r\n/// line 2\r\nfn foo() {}".to_string();
-            let item = parse_item_from_source_str(name_2, source, &sess)
-                .unwrap().unwrap();
-            let docs = item.attrs.iter().filter(|a| a.path == sym::doc)
-                        .map(|a| a.value_str().unwrap().to_string()).collect::<Vec<_>>();
-            let b: &[_] = &["/// doc comment".to_string(), "/// line 2".to_string()];
-            assert_eq!(&docs[..], b);
-
-            let name_3 = FileName::Custom("clrf_source_3".to_string());
-            let source = "/** doc comment\r\n *  with CRLF */\r\nfn foo() {}".to_string();
-            let item = parse_item_from_source_str(name_3, source, &sess).unwrap().unwrap();
-            let doc = first_attr_value_str_by_name(&item.attrs, sym::doc).unwrap();
-            assert_eq!(doc.as_str(), "/** doc comment\n *  with CRLF */");
-        });
-    }
-
-    #[test]
-    fn ttdelim_span() {
-        fn parse_expr_from_source_str(
-            name: FileName, source: String, sess: &ParseSess
-        ) -> PResult<'_, P<ast::Expr>> {
-            new_parser_from_source_str(sess, name, source).parse_expr()
-        }
-
-        with_globals(|| {
-            let sess = ParseSess::new(FilePathMapping::empty());
-            let expr = parse_expr_from_source_str(PathBuf::from("foo").into(),
-                "foo!( fn main() { body } )".to_string(), &sess).unwrap();
-
-            let tts: Vec<_> = match expr.node {
-                ast::ExprKind::Mac(ref mac) => mac.node.stream().trees().collect(),
-                _ => panic!("not a macro"),
-            };
-
-            let span = tts.iter().rev().next().unwrap().span();
-
-            match sess.source_map().span_to_snippet(span) {
-                Ok(s) => assert_eq!(&s[..], "{ body }"),
-                Err(_) => panic!("could not get snippet"),
-            }
-        });
-    }
-
-    // This tests that when parsing a string (rather than a file) we don't try
-    // and read in a file for a module declaration and just parse a stub.
-    // See `recurse_into_file_modules` in the parser.
-    #[test]
-    fn out_of_line_mod() {
-        with_globals(|| {
-            let sess = ParseSess::new(FilePathMapping::empty());
-            let item = parse_item_from_source_str(
-                PathBuf::from("foo").into(),
-                "mod foo { struct S; mod this_does_not_exist; }".to_owned(),
-                &sess,
-            ).unwrap().unwrap();
-
-            if let ast::ItemKind::Mod(ref m) = item.node {
-                assert!(m.items.len() == 2);
-            } else {
-                panic!();
-            }
-        });
-    }
-}
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 24d120376de..89725d8b339 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -1,75 +1,40 @@
-// ignore-tidy-filelength
-
-use crate::ast::{AngleBracketedArgs, AsyncArgument, ParenthesizedArgs, AttrStyle, BareFnTy};
-use crate::ast::{GenericBound, TraitBoundModifier};
-use crate::ast::Unsafety;
-use crate::ast::{Mod, AnonConst, Arg, ArgSource, Arm, Guard, Attribute, BindingMode, TraitItemKind};
-use crate::ast::Block;
-use crate::ast::{BlockCheckMode, CaptureBy, Movability};
-use crate::ast::{Constness, Crate};
-use crate::ast::Defaultness;
-use crate::ast::EnumDef;
-use crate::ast::{Expr, ExprKind, RangeLimits};
-use crate::ast::{Field, FnDecl, FnHeader};
-use crate::ast::{ForeignItem, ForeignItemKind, FunctionRetTy};
-use crate::ast::{GenericParam, GenericParamKind};
-use crate::ast::GenericArg;
-use crate::ast::{Ident, ImplItem, IsAsync, IsAuto, Item, ItemKind};
-use crate::ast::{Label, Lifetime};
-use crate::ast::{Local, LocalSource};
-use crate::ast::MacStmtStyle;
-use crate::ast::{Mac, Mac_, MacDelimiter};
-use crate::ast::{MutTy, Mutability};
-use crate::ast::{Pat, PatKind, PathSegment};
-use crate::ast::{PolyTraitRef, QSelf};
-use crate::ast::{Stmt, StmtKind};
-use crate::ast::{VariantData, StructField};
-use crate::ast::StrStyle;
-use crate::ast::SelfKind;
-use crate::ast::{TraitItem, TraitRef, TraitObjectSyntax};
-use crate::ast::{Ty, TyKind, TypeBinding, GenericBounds};
-use crate::ast::{Visibility, VisibilityKind, WhereClause, CrateSugar};
-use crate::ast::{UseTree, UseTreeKind};
-use crate::ast::{BinOpKind, UnOp};
-use crate::ast::{RangeEnd, RangeSyntax};
-use crate::{ast, attr};
-use crate::ext::base::DummyResult;
-use crate::source_map::{self, SourceMap, Spanned, respan};
-use crate::parse::{SeqSep, classify, literal, token};
-use crate::parse::lexer::{TokenAndSpan, UnmatchedBrace};
+mod expr;
+mod pat;
+mod item;
+pub use item::AliasKind;
+mod module;
+pub use module::{ModulePath, ModulePathSuccess};
+mod ty;
+mod path;
+pub use path::PathStyle;
+mod stmt;
+mod generics;
+
+use crate::ast::{self, AttrStyle, Attribute, Arg, BindingMode, StrStyle, SelfKind};
+use crate::ast::{FnDecl, Ident, IsAsync, MacDelimiter, Mutability, TyKind};
+use crate::ast::{Visibility, VisibilityKind, Unsafety, CrateSugar};
+use crate::source_map::{self, respan};
+use crate::parse::{SeqSep, literal, token};
+use crate::parse::lexer::UnmatchedBrace;
 use crate::parse::lexer::comments::{doc_comment_style, strip_doc_comment_decoration};
-use crate::parse::token::DelimToken;
-use crate::parse::{new_sub_parser_from_file, ParseSess, Directory, DirectoryOwnership};
-use crate::util::parser::{AssocOp, Fixity};
+use crate::parse::token::{Token, TokenKind, DelimToken};
+use crate::parse::{ParseSess, Directory, DirectoryOwnership};
 use crate::print::pprust;
 use crate::ptr::P;
 use crate::parse::PResult;
 use crate::ThinVec;
 use crate::tokenstream::{self, DelimSpan, TokenTree, TokenStream, TreeAndJoint};
-use crate::symbol::{keywords, sym, Symbol};
+use crate::symbol::{kw, sym, Symbol};
+use crate::parse::diagnostics::{Error, dummy_arg};
 
-use errors::{Applicability, DiagnosticBuilder, DiagnosticId, FatalError};
+use errors::{Applicability, DiagnosticId, FatalError};
 use rustc_target::spec::abi::{self, Abi};
-use syntax_pos::{
-    Span, MultiSpan, BytePos, FileName,
-    hygiene::CompilerDesugaringKind,
-};
-use log::{debug, trace};
+use syntax_pos::{Span, BytePos, DUMMY_SP, FileName};
+use log::debug;
 
 use std::borrow::Cow;
-use std::cmp;
-use std::mem;
-use std::path::{self, Path, PathBuf};
-use std::slice;
-
-#[derive(Debug)]
-/// Whether the type alias or associated type is a concrete type or an existential type
-pub enum AliasKind {
-    /// Just a new name for the same type
-    Weak(P<Ty>),
-    /// Only trait impls of the type will be usable, not the actual type itself
-    Existential(GenericBounds),
-}
+use std::{cmp, mem, slice};
+use std::path::PathBuf;
 
 bitflags::bitflags! {
     struct Restrictions: u8 {
@@ -78,31 +43,6 @@ bitflags::bitflags! {
     }
 }
 
-type ItemInfo = (Ident, ItemKind, Option<Vec<Attribute>>);
-
-/// Specifies how to parse a path.
-#[derive(Copy, Clone, PartialEq)]
-pub enum PathStyle {
-    /// In some contexts, notably in expressions, paths with generic arguments are ambiguous
-    /// with something else. For example, in expressions `segment < ....` can be interpreted
-    /// as a comparison and `segment ( ....` can be interpreted as a function call.
-    /// In all such contexts the non-path interpretation is preferred by default for practical
-    /// reasons, but the path interpretation can be forced by the disambiguator `::`, e.g.
-    /// `x<y>` - comparisons, `x::<y>` - unambiguously a path.
-    Expr,
-    /// In other contexts, notably in types, no ambiguity exists and paths can be written
-    /// without the disambiguator, e.g., `x<y>` - unambiguously a path.
-    /// Paths with disambiguators are still accepted, `x::<Y>` - unambiguously a path too.
-    Type,
-    /// A path with generic arguments disallowed, e.g., `foo::bar::Baz`, used in imports,
-    /// visibilities or attributes.
-    /// Technically, this variant is unnecessary and e.g., `Expr` can be used instead
-    /// (paths in "mod" contexts have to be checked later for absence of generic arguments
-    /// anyway, due to macros), but it is used to avoid weird suggestions about expected
-    /// tokens when something goes wrong.
-    Mod,
-}
-
 #[derive(Clone, Copy, PartialEq, Debug)]
 crate enum SemiColonMode {
     Break,
@@ -116,40 +56,11 @@ crate enum BlockMode {
     Ignore,
 }
 
-/// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
-/// dropped into the token stream, which happens while parsing the result of
-/// macro expansion). Placement of these is not as complex as I feared it would
-/// be. The important thing is to make sure that lookahead doesn't balk at
-/// `token::Interpolated` tokens.
-macro_rules! maybe_whole_expr {
-    ($p:expr) => {
-        if let token::Interpolated(nt) = &$p.token {
-            match &**nt {
-                token::NtExpr(e) | token::NtLiteral(e) => {
-                    let e = e.clone();
-                    $p.bump();
-                    return Ok(e);
-                }
-                token::NtPath(path) => {
-                    let path = path.clone();
-                    $p.bump();
-                    return Ok($p.mk_expr($p.span, ExprKind::Path(None, path), ThinVec::new()));
-                }
-                token::NtBlock(block) => {
-                    let block = block.clone();
-                    $p.bump();
-                    return Ok($p.mk_expr($p.span, ExprKind::Block(block, None), ThinVec::new()));
-                }
-                _ => {},
-            };
-        }
-    }
-}
-
 /// As maybe_whole_expr, but for things other than expressions
+#[macro_export]
 macro_rules! maybe_whole {
     ($p:expr, $constructor:ident, |$x:ident| $e:expr) => {
-        if let token::Interpolated(nt) = &$p.token {
+        if let token::Interpolated(nt) = &$p.token.kind {
             if let token::$constructor(x) = &**nt {
                 let $x = x.clone();
                 $p.bump();
@@ -160,10 +71,11 @@ macro_rules! maybe_whole {
 }
 
 /// If the next tokens are ill-formed `$ty::` recover them as `<$ty>::`.
+#[macro_export]
 macro_rules! maybe_recover_from_interpolated_ty_qpath {
     ($self: expr, $allow_qpath_recovery: expr) => {
         if $allow_qpath_recovery && $self.look_ahead(1, |t| t == &token::ModSep) {
-            if let token::Interpolated(nt) = &$self.token {
+            if let token::Interpolated(nt) = &$self.token.kind {
                 if let token::NtTy(ty) = &**nt {
                     let ty = ty.clone();
                     $self.bump();
@@ -193,33 +105,36 @@ enum PrevTokenKind {
     Other,
 }
 
-/* ident is handled by common.rs */
+// NOTE: `Ident`s are handled by `common.rs`.
 
 #[derive(Clone)]
 pub struct Parser<'a> {
     pub sess: &'a ParseSess,
-    /// the current token:
-    pub token: token::Token,
-    /// the span of the current token:
-    pub span: Span,
-    /// the span of the previous token:
+    /// The current normalized token.
+    /// "Normalized" means that some interpolated tokens
+    /// (`$i: ident` and `$l: lifetime` meta-variables) are replaced
+    /// with non-interpolated identifier and lifetime tokens they refer to.
+    /// Perhaps the normalized / non-normalized setup can be simplified somehow.
+    pub token: Token,
+    /// Span of the current non-normalized token.
     meta_var_span: Option<Span>,
+    /// Span of the previous non-normalized token.
     pub prev_span: Span,
-    /// the previous token kind
+    /// Kind of the previous normalized token (in simplified form).
     prev_token_kind: PrevTokenKind,
     restrictions: Restrictions,
-    /// Used to determine the path to externally loaded source files
+    /// Used to determine the path to externally loaded source files.
     crate directory: Directory<'a>,
-    /// Whether to parse sub-modules in other files.
+    /// `true` to parse sub-modules in other files.
     pub recurse_into_file_modules: bool,
     /// Name of the root module this parser originated from. If `None`, then the
     /// name is not known. This does not change while the parser is descending
     /// into modules, and sub-parsers have new values for this name.
     pub root_module_name: Option<String>,
     crate expected_tokens: Vec<TokenType>,
-    token_cursor: TokenCursor,
+    crate token_cursor: TokenCursor,
     desugar_doc_comments: bool,
-    /// Whether we should configure out of line modules as we parse.
+    /// `true` we should configure out of line modules as we parse.
     pub cfg_mods: bool,
     /// This field is used to keep track of how many left angle brackets we have seen. This is
     /// required in order to detect extra leading left angle brackets (`<` characters) and error
@@ -232,7 +147,10 @@ pub struct Parser<'a> {
     /// it gets removed from here. Every entry left at the end gets emitted as an independent
     /// error.
     crate unclosed_delims: Vec<UnmatchedBrace>,
-    last_unexpected_token_span: Option<Span>,
+    crate last_unexpected_token_span: Option<Span>,
+    crate last_type_ascription: Option<(Span, bool /* likely path typo */)>,
+    /// If present, this `Parser` is not parsing Rust code but rather a macro call.
+    crate subparser_name: Option<&'static str>,
 }
 
 impl<'a> Drop for Parser<'a> {
@@ -243,19 +161,19 @@ impl<'a> Drop for Parser<'a> {
 }
 
 #[derive(Clone)]
-struct TokenCursor {
-    frame: TokenCursorFrame,
-    stack: Vec<TokenCursorFrame>,
+crate struct TokenCursor {
+    crate frame: TokenCursorFrame,
+    crate stack: Vec<TokenCursorFrame>,
 }
 
 #[derive(Clone)]
-struct TokenCursorFrame {
-    delim: token::DelimToken,
-    span: DelimSpan,
-    open_delim: bool,
-    tree_cursor: tokenstream::Cursor,
-    close_delim: bool,
-    last_token: LastToken,
+crate struct TokenCursorFrame {
+    crate delim: token::DelimToken,
+    crate span: DelimSpan,
+    crate open_delim: bool,
+    crate tree_cursor: tokenstream::Cursor,
+    crate close_delim: bool,
+    crate last_token: LastToken,
 }
 
 /// This is used in `TokenCursorFrame` above to track tokens that are consumed
@@ -276,16 +194,16 @@ struct TokenCursorFrame {
 /// You can find some more example usage of this in the `collect_tokens` method
 /// on the parser.
 #[derive(Clone)]
-enum LastToken {
+crate enum LastToken {
     Collecting(Vec<TreeAndJoint>),
     Was(Option<TreeAndJoint>),
 }
 
 impl TokenCursorFrame {
-    fn new(sp: DelimSpan, delim: DelimToken, tts: &TokenStream) -> Self {
+    fn new(span: DelimSpan, delim: DelimToken, tts: &TokenStream) -> Self {
         TokenCursorFrame {
-            delim: delim,
-            span: sp,
+            delim,
+            span,
             open_delim: delim == token::NoDelim,
             tree_cursor: tts.clone().into_trees(),
             close_delim: delim == token::NoDelim,
@@ -295,7 +213,7 @@ impl TokenCursorFrame {
 }
 
 impl TokenCursor {
-    fn next(&mut self) -> TokenAndSpan {
+    fn next(&mut self) -> Token {
         loop {
             let tree = if !self.frame.open_delim {
                 self.frame.open_delim = true;
@@ -309,7 +227,7 @@ impl TokenCursor {
                 self.frame = frame;
                 continue
             } else {
-                return TokenAndSpan { tok: token::Eof, sp: syntax_pos::DUMMY_SP }
+                return Token::new(token::Eof, DUMMY_SP);
             };
 
             match self.frame.last_token {
@@ -318,7 +236,7 @@ impl TokenCursor {
             }
 
             match tree {
-                TokenTree::Token(sp, tok) => return TokenAndSpan { tok: tok, sp: sp },
+                TokenTree::Token(token) => return token,
                 TokenTree::Delimited(sp, delim, tts) => {
                     let frame = TokenCursorFrame::new(sp, delim, &tts);
                     self.stack.push(mem::replace(&mut self.frame, frame));
@@ -327,9 +245,9 @@ impl TokenCursor {
         }
     }
 
-    fn next_desugared(&mut self) -> TokenAndSpan {
-        let (sp, name) = match self.next() {
-            TokenAndSpan { sp, tok: token::DocComment(name) } => (sp, name),
+    fn next_desugared(&mut self) -> Token {
+        let (name, sp) = match self.next() {
+            Token { kind: token::DocComment(name), span } => (name, span),
             tok => return tok,
         };
 
@@ -352,10 +270,12 @@ impl TokenCursor {
         let body = TokenTree::Delimited(
             delim_span,
             token::Bracket,
-            [TokenTree::Token(sp, token::Ident(ast::Ident::with_empty_ctxt(sym::doc), false)),
-             TokenTree::Token(sp, token::Eq),
-             TokenTree::Token(sp, token::Literal(
-                token::StrRaw(Symbol::intern(&stripped), num_of_hashes), None))
+            [
+                TokenTree::token(token::Ident(sym::doc, false), sp),
+                TokenTree::token(token::Eq, sp),
+                TokenTree::token(TokenKind::lit(
+                    token::StrRaw(num_of_hashes), Symbol::intern(&stripped), None
+                ), sp),
             ]
             .iter().cloned().collect::<TokenStream>().into(),
         );
@@ -364,10 +284,10 @@ impl TokenCursor {
             delim_span,
             token::NoDelim,
             &if doc_comment_style(&name.as_str()) == AttrStyle::Inner {
-                [TokenTree::Token(sp, token::Pound), TokenTree::Token(sp, token::Not), body]
+                [TokenTree::token(token::Pound, sp), TokenTree::token(token::Not, sp), body]
                     .iter().cloned().collect::<TokenStream>().into()
             } else {
-                [TokenTree::Token(sp, token::Pound), body]
+                [TokenTree::token(token::Pound, sp), body]
                     .iter().cloned().collect::<TokenStream>().into()
             },
         )));
@@ -378,8 +298,8 @@ impl TokenCursor {
 
 #[derive(Clone, PartialEq)]
 crate enum TokenType {
-    Token(token::Token),
-    Keyword(keywords::Keyword),
+    Token(TokenKind),
+    Keyword(Symbol),
     Operator,
     Lifetime,
     Ident,
@@ -391,8 +311,8 @@ crate enum TokenType {
 impl TokenType {
     crate fn to_string(&self) -> String {
         match *self {
-            TokenType::Token(ref t) => format!("`{}`", pprust::token_to_string(t)),
-            TokenType::Keyword(kw) => format!("`{}`", kw.name()),
+            TokenType::Token(ref t) => format!("`{}`", pprust::token_kind_to_string(t)),
+            TokenType::Keyword(kw) => format!("`{}`", kw),
             TokenType::Operator => "an operator".to_string(),
             TokenType::Lifetime => "lifetime".to_string(),
             TokenType::Ident => "identifier".to_string(),
@@ -403,145 +323,25 @@ impl TokenType {
     }
 }
 
-/// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
-/// `IDENT<<u8 as Trait>::AssocTy>`.
-///
-/// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
-/// that `IDENT` is not the ident of a fn trait.
-fn can_continue_type_after_non_fn_ident(t: &token::Token) -> bool {
-    t == &token::ModSep || t == &token::Lt ||
-    t == &token::BinOp(token::Shl)
-}
-
-/// Information about the path to a module.
-pub struct ModulePath {
-    name: String,
-    path_exists: bool,
-    pub result: Result<ModulePathSuccess, Error>,
-}
-
-pub struct ModulePathSuccess {
-    pub path: PathBuf,
-    pub directory_ownership: DirectoryOwnership,
-    warn: bool,
-}
-
-pub enum Error {
-    FileNotFoundForModule {
-        mod_name: String,
-        default_path: String,
-        secondary_path: String,
-        dir_path: String,
-    },
-    DuplicatePaths {
-        mod_name: String,
-        default_path: String,
-        secondary_path: String,
-    },
-    UselessDocComment,
-    InclusiveRangeWithNoEnd,
-}
-
-impl Error {
-    fn span_err<S: Into<MultiSpan>>(self,
-                                        sp: S,
-                                        handler: &errors::Handler) -> DiagnosticBuilder<'_> {
-        match self {
-            Error::FileNotFoundForModule { ref mod_name,
-                                           ref default_path,
-                                           ref secondary_path,
-                                           ref dir_path } => {
-                let mut err = struct_span_err!(handler, sp, E0583,
-                                               "file not found for module `{}`", mod_name);
-                err.help(&format!("name the file either {} or {} inside the directory \"{}\"",
-                                  default_path,
-                                  secondary_path,
-                                  dir_path));
-                err
-            }
-            Error::DuplicatePaths { ref mod_name, ref default_path, ref secondary_path } => {
-                let mut err = struct_span_err!(handler, sp, E0584,
-                                               "file for module `{}` found at both {} and {}",
-                                               mod_name,
-                                               default_path,
-                                               secondary_path);
-                err.help("delete or rename one of them to remove the ambiguity");
-                err
-            }
-            Error::UselessDocComment => {
-                let mut err = struct_span_err!(handler, sp, E0585,
-                                  "found a documentation comment that doesn't document anything");
-                err.help("doc comments must come before what they document, maybe a comment was \
-                          intended with `//`?");
-                err
-            }
-            Error::InclusiveRangeWithNoEnd => {
-                let mut err = struct_span_err!(handler, sp, E0586,
-                                               "inclusive range with no end");
-                err.help("inclusive ranges must be bounded at the end (`..=b` or `a..=b`)");
-                err
-            }
-        }
-    }
-}
-
-#[derive(Debug)]
-enum LhsExpr {
-    NotYetParsed,
-    AttributesParsed(ThinVec<Attribute>),
-    AlreadyParsed(P<Expr>),
-}
-
-impl From<Option<ThinVec<Attribute>>> for LhsExpr {
-    fn from(o: Option<ThinVec<Attribute>>) -> Self {
-        if let Some(attrs) = o {
-            LhsExpr::AttributesParsed(attrs)
-        } else {
-            LhsExpr::NotYetParsed
-        }
-    }
-}
-
-impl From<P<Expr>> for LhsExpr {
-    fn from(expr: P<Expr>) -> Self {
-        LhsExpr::AlreadyParsed(expr)
-    }
-}
-
-/// Creates a placeholder argument.
-fn dummy_arg(span: Span) -> Arg {
-    let ident = Ident::new(keywords::Invalid.name(), span);
-    let pat = P(Pat {
-        id: ast::DUMMY_NODE_ID,
-        node: PatKind::Ident(BindingMode::ByValue(Mutability::Immutable), ident, None),
-        span,
-    });
-    let ty = Ty {
-        node: TyKind::Err,
-        span,
-        id: ast::DUMMY_NODE_ID
-    };
-    Arg { ty: P(ty), pat: pat, id: ast::DUMMY_NODE_ID, source: ast::ArgSource::Normal }
-}
-
 #[derive(Copy, Clone, Debug)]
-enum TokenExpectType {
+crate enum TokenExpectType {
     Expect,
     NoExpect,
 }
 
 impl<'a> Parser<'a> {
-    pub fn new(sess: &'a ParseSess,
-               tokens: TokenStream,
-               directory: Option<Directory<'a>>,
-               recurse_into_file_modules: bool,
-               desugar_doc_comments: bool)
-               -> Self {
+    pub fn new(
+        sess: &'a ParseSess,
+        tokens: TokenStream,
+        directory: Option<Directory<'a>>,
+        recurse_into_file_modules: bool,
+        desugar_doc_comments: bool,
+        subparser_name: Option<&'static str>,
+    ) -> Self {
         let mut parser = Parser {
             sess,
-            token: token::Whitespace,
-            span: syntax_pos::DUMMY_SP,
-            prev_span: syntax_pos::DUMMY_SP,
+            token: Token::dummy(),
+            prev_span: DUMMY_SP,
             meta_var_span: None,
             prev_token_kind: PrevTokenKind::Other,
             restrictions: Restrictions::empty(),
@@ -566,16 +366,17 @@ impl<'a> Parser<'a> {
             max_angle_bracket_count: 0,
             unclosed_delims: Vec::new(),
             last_unexpected_token_span: None,
+            last_type_ascription: None,
+            subparser_name,
         };
 
-        let tok = parser.next_tok();
-        parser.token = tok.tok;
-        parser.span = tok.sp;
+        parser.token = parser.next_tok();
 
         if let Some(directory) = directory {
             parser.directory = directory;
-        } else if !parser.span.is_dummy() {
-            if let FileName::Real(mut path) = sess.source_map().span_to_unmapped_path(parser.span) {
+        } else if !parser.token.span.is_dummy() {
+            if let FileName::Real(mut path) =
+                    sess.source_map().span_to_unmapped_path(parser.token.span) {
                 path.pop();
                 parser.directory.path = Cow::from(path);
             }
@@ -585,15 +386,15 @@ impl<'a> Parser<'a> {
         parser
     }
 
-    fn next_tok(&mut self) -> TokenAndSpan {
+    fn next_tok(&mut self) -> Token {
         let mut next = if self.desugar_doc_comments {
             self.token_cursor.next_desugared()
         } else {
             self.token_cursor.next()
         };
-        if next.sp.is_dummy() {
+        if next.span.is_dummy() {
             // Tweak the location for better diagnostics, but keep syntactic context intact.
-            next.sp = self.prev_span.with_ctxt(next.sp.ctxt());
+            next.span = self.prev_span.with_ctxt(next.span.ctxt());
         }
         next
     }
@@ -603,11 +404,11 @@ impl<'a> Parser<'a> {
         pprust::token_to_string(&self.token)
     }
 
-    fn token_descr(&self) -> Option<&'static str> {
-        Some(match &self.token {
-            t if t.is_special_ident() => "reserved identifier",
-            t if t.is_used_keyword() => "keyword",
-            t if t.is_unused_keyword() => "reserved keyword",
+    crate fn token_descr(&self) -> Option<&'static str> {
+        Some(match &self.token.kind {
+            _ if self.token.is_special_ident() => "reserved identifier",
+            _ if self.token.is_used_keyword() => "keyword",
+            _ if self.token.is_unused_keyword() => "reserved keyword",
             token::DocComment(..) => "doc comment",
             _ => return None,
         })
@@ -629,44 +430,13 @@ impl<'a> Parser<'a> {
     }
 
     /// Expects and consumes the token `t`. Signals an error if the next token is not `t`.
-    pub fn expect(&mut self, t: &token::Token) -> PResult<'a,  bool /* recovered */> {
+    pub fn expect(&mut self, t: &TokenKind) -> PResult<'a, bool /* recovered */> {
         if self.expected_tokens.is_empty() {
             if self.token == *t {
                 self.bump();
                 Ok(false)
             } else {
-                let token_str = pprust::token_to_string(t);
-                let this_token_str = self.this_token_descr();
-                let mut err = self.fatal(&format!("expected `{}`, found {}",
-                                                  token_str,
-                                                  this_token_str));
-
-                let sp = if self.token == token::Token::Eof {
-                    // EOF, don't want to point at the following char, but rather the last token
-                    self.prev_span
-                } else {
-                    self.sess.source_map().next_point(self.prev_span)
-                };
-                let label_exp = format!("expected `{}`", token_str);
-                match self.recover_closing_delimiter(&[t.clone()], err) {
-                    Err(e) => err = e,
-                    Ok(recovered) => {
-                        return Ok(recovered);
-                    }
-                }
-                let cm = self.sess.source_map();
-                match (cm.lookup_line(self.span.lo()), cm.lookup_line(sp.lo())) {
-                    (Ok(ref a), Ok(ref b)) if a.line == b.line => {
-                        // When the spans are in the same line, it means that the only content
-                        // between them is whitespace, point only at the found token.
-                        err.span_label(self.span, label_exp);
-                    }
-                    _ => {
-                        err.span_label(sp, label_exp);
-                        err.span_label(self.span, "unexpected token");
-                    }
-                }
-                Err(err)
+                self.unexpected_try_recover(t)
             }
         } else {
             self.expect_one_of(slice::from_ref(t), &[])
@@ -678,193 +448,20 @@ impl<'a> Parser<'a> {
     /// anything.  Signal a fatal error if next token is unexpected.
     pub fn expect_one_of(
         &mut self,
-        edible: &[token::Token],
-        inedible: &[token::Token],
+        edible: &[TokenKind],
+        inedible: &[TokenKind],
     ) -> PResult<'a, bool /* recovered */> {
-        fn tokens_to_string(tokens: &[TokenType]) -> String {
-            let mut i = tokens.iter();
-            // This might be a sign we need a connect method on Iterator.
-            let b = i.next()
-                     .map_or(String::new(), |t| t.to_string());
-            i.enumerate().fold(b, |mut b, (i, a)| {
-                if tokens.len() > 2 && i == tokens.len() - 2 {
-                    b.push_str(", or ");
-                } else if tokens.len() == 2 && i == tokens.len() - 2 {
-                    b.push_str(" or ");
-                } else {
-                    b.push_str(", ");
-                }
-                b.push_str(&a.to_string());
-                b
-            })
-        }
-        if edible.contains(&self.token) {
+        if edible.contains(&self.token.kind) {
             self.bump();
             Ok(false)
-        } else if inedible.contains(&self.token) {
+        } else if inedible.contains(&self.token.kind) {
             // leave it in the input
             Ok(false)
-        } else if self.last_unexpected_token_span == Some(self.span) {
+        } else if self.last_unexpected_token_span == Some(self.token.span) {
             FatalError.raise();
         } else {
-            let mut expected = edible.iter()
-                .map(|x| TokenType::Token(x.clone()))
-                .chain(inedible.iter().map(|x| TokenType::Token(x.clone())))
-                .chain(self.expected_tokens.iter().cloned())
-                .collect::<Vec<_>>();
-            expected.sort_by_cached_key(|x| x.to_string());
-            expected.dedup();
-            let expect = tokens_to_string(&expected[..]);
-            let actual = self.this_token_to_string();
-            let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
-                let short_expect = if expected.len() > 6 {
-                    format!("{} possible tokens", expected.len())
-                } else {
-                    expect.clone()
-                };
-                (format!("expected one of {}, found `{}`", expect, actual),
-                 (self.sess.source_map().next_point(self.prev_span),
-                  format!("expected one of {} here", short_expect)))
-            } else if expected.is_empty() {
-                (format!("unexpected token: `{}`", actual),
-                 (self.prev_span, "unexpected token after this".to_string()))
-            } else {
-                (format!("expected {}, found `{}`", expect, actual),
-                 (self.sess.source_map().next_point(self.prev_span),
-                  format!("expected {} here", expect)))
-            };
-            self.last_unexpected_token_span = Some(self.span);
-            let mut err = self.fatal(&msg_exp);
-            if self.token.is_ident_named("and") {
-                err.span_suggestion_short(
-                    self.span,
-                    "use `&&` instead of `and` for the boolean operator",
-                    "&&".to_string(),
-                    Applicability::MaybeIncorrect,
-                );
-            }
-            if self.token.is_ident_named("or") {
-                err.span_suggestion_short(
-                    self.span,
-                    "use `||` instead of `or` for the boolean operator",
-                    "||".to_string(),
-                    Applicability::MaybeIncorrect,
-                );
-            }
-            let sp = if self.token == token::Token::Eof {
-                // This is EOF, don't want to point at the following char, but rather the last token
-                self.prev_span
-            } else {
-                label_sp
-            };
-            match self.recover_closing_delimiter(&expected.iter().filter_map(|tt| match tt {
-                TokenType::Token(t) => Some(t.clone()),
-                _ => None,
-            }).collect::<Vec<_>>(), err) {
-                Err(e) => err = e,
-                Ok(recovered) => {
-                    return Ok(recovered);
-                }
-            }
-
-            let is_semi_suggestable = expected.iter().any(|t| match t {
-                TokenType::Token(token::Semi) => true, // we expect a `;` here
-                _ => false,
-            }) && ( // a `;` would be expected before the current keyword
-                self.token.is_keyword(keywords::Break) ||
-                self.token.is_keyword(keywords::Continue) ||
-                self.token.is_keyword(keywords::For) ||
-                self.token.is_keyword(keywords::If) ||
-                self.token.is_keyword(keywords::Let) ||
-                self.token.is_keyword(keywords::Loop) ||
-                self.token.is_keyword(keywords::Match) ||
-                self.token.is_keyword(keywords::Return) ||
-                self.token.is_keyword(keywords::While)
-            );
-            let cm = self.sess.source_map();
-            match (cm.lookup_line(self.span.lo()), cm.lookup_line(sp.lo())) {
-                (Ok(ref a), Ok(ref b)) if a.line != b.line && is_semi_suggestable => {
-                    // The spans are in different lines, expected `;` and found `let` or `return`.
-                    // High likelihood that it is only a missing `;`.
-                    err.span_suggestion_short(
-                        label_sp,
-                        "a semicolon may be missing here",
-                        ";".to_string(),
-                        Applicability::MaybeIncorrect,
-                    );
-                    err.emit();
-                    return Ok(true);
-                }
-                (Ok(ref a), Ok(ref b)) if a.line == b.line => {
-                    // When the spans are in the same line, it means that the only content between
-                    // them is whitespace, point at the found token in that case:
-                    //
-                    // X |     () => { syntax error };
-                    //   |                    ^^^^^ expected one of 8 possible tokens here
-                    //
-                    // instead of having:
-                    //
-                    // X |     () => { syntax error };
-                    //   |                   -^^^^^ unexpected token
-                    //   |                   |
-                    //   |                   expected one of 8 possible tokens here
-                    err.span_label(self.span, label_exp);
-                }
-                _ if self.prev_span == syntax_pos::DUMMY_SP => {
-                    // Account for macro context where the previous span might not be
-                    // available to avoid incorrect output (#54841).
-                    err.span_label(self.span, "unexpected token");
-                }
-                _ => {
-                    err.span_label(sp, label_exp);
-                    err.span_label(self.span, "unexpected token");
-                }
-            }
-            Err(err)
-        }
-    }
-
-    /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
-    fn interpolated_or_expr_span(&self,
-                                 expr: PResult<'a, P<Expr>>)
-                                 -> PResult<'a, (Span, P<Expr>)> {
-        expr.map(|e| {
-            if self.prev_token_kind == PrevTokenKind::Interpolated {
-                (self.prev_span, e)
-            } else {
-                (e.span, e)
-            }
-        })
-    }
-
-    fn expected_ident_found(&self) -> DiagnosticBuilder<'a> {
-        let mut err = self.struct_span_err(self.span,
-                                           &format!("expected identifier, found {}",
-                                                    self.this_token_descr()));
-        if let token::Ident(ident, false) = &self.token {
-            if ident.is_raw_guess() {
-                err.span_suggestion(
-                    self.span,
-                    "you can escape reserved keywords to use them as identifiers",
-                    format!("r#{}", ident),
-                    Applicability::MaybeIncorrect,
-                );
-            }
+            self.expected_one_of_not_found(edible, inedible)
         }
-        if let Some(token_descr) = self.token_descr() {
-            err.span_label(self.span, format!("expected identifier, found {}", token_descr));
-        } else {
-            err.span_label(self.span, "expected identifier");
-            if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
-                err.span_suggestion(
-                    self.span,
-                    "remove this comma",
-                    String::new(),
-                    Applicability::MachineApplicable,
-                );
-            }
-        }
-        err
     }
 
     pub fn parse_ident(&mut self) -> PResult<'a, ast::Ident> {
@@ -872,8 +469,8 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_ident_common(&mut self, recover: bool) -> PResult<'a, ast::Ident> {
-        match self.token {
-            token::Ident(ident, _) => {
+        match self.token.kind {
+            token::Ident(name, _) => {
                 if self.token.is_reserved_ident() {
                     let mut err = self.expected_ident_found();
                     if recover {
@@ -882,16 +479,16 @@ impl<'a> Parser<'a> {
                         return Err(err);
                     }
                 }
-                let span = self.span;
+                let span = self.token.span;
                 self.bump();
-                Ok(Ident::new(ident.name, span))
+                Ok(Ident::new(name, span))
             }
             _ => {
                 Err(if self.prev_token_kind == PrevTokenKind::DocComment {
-                        self.span_fatal_err(self.prev_span, Error::UselessDocComment)
-                    } else {
-                        self.expected_ident_found()
-                    })
+                    self.span_fatal_err(self.prev_span, Error::UselessDocComment)
+                } else {
+                    self.expected_ident_found()
+                })
             }
         }
     }
@@ -900,27 +497,27 @@ impl<'a> Parser<'a> {
     ///
     /// This method will automatically add `tok` to `expected_tokens` if `tok` is not
     /// encountered.
-    crate fn check(&mut self, tok: &token::Token) -> bool {
+    crate fn check(&mut self, tok: &TokenKind) -> bool {
         let is_present = self.token == *tok;
         if !is_present { self.expected_tokens.push(TokenType::Token(tok.clone())); }
         is_present
     }
 
     /// Consumes a token 'tok' if it exists. Returns whether the given token was present.
-    pub fn eat(&mut self, tok: &token::Token) -> bool {
+    pub fn eat(&mut self, tok: &TokenKind) -> bool {
         let is_present = self.check(tok);
         if is_present { self.bump() }
         is_present
     }
 
-    fn check_keyword(&mut self, kw: keywords::Keyword) -> bool {
+    fn check_keyword(&mut self, kw: Symbol) -> bool {
         self.expected_tokens.push(TokenType::Keyword(kw));
         self.token.is_keyword(kw)
     }
 
     /// If the next token is the given keyword, eats it and returns
     /// `true`. Otherwise, returns `false`.
-    pub fn eat_keyword(&mut self, kw: keywords::Keyword) -> bool {
+    pub fn eat_keyword(&mut self, kw: Symbol) -> bool {
         if self.check_keyword(kw) {
             self.bump();
             true
@@ -929,7 +526,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn eat_keyword_noexpect(&mut self, kw: keywords::Keyword) -> bool {
+    fn eat_keyword_noexpect(&mut self, kw: Symbol) -> bool {
         if self.token.is_keyword(kw) {
             self.bump();
             true
@@ -941,7 +538,7 @@ impl<'a> Parser<'a> {
     /// If the given word is not a keyword, signals an error.
     /// If the next token is not the given word, signals an error.
     /// Otherwise, eats it.
-    fn expect_keyword(&mut self, kw: keywords::Keyword) -> PResult<'a, ()> {
+    fn expect_keyword(&mut self, kw: Symbol) -> PResult<'a, ()> {
         if !self.eat_keyword(kw) {
             self.unexpected()
         } else {
@@ -949,7 +546,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn check_ident(&mut self) -> bool {
+    crate fn check_ident(&mut self) -> bool {
         if self.token.is_ident() {
             true
         } else {
@@ -992,13 +589,13 @@ impl<'a> Parser<'a> {
     /// See issue #47856 for an example of when this may occur.
     fn eat_plus(&mut self) -> bool {
         self.expected_tokens.push(TokenType::Token(token::BinOp(token::Plus)));
-        match self.token {
+        match self.token.kind {
             token::BinOp(token::Plus) => {
                 self.bump();
                 true
             }
             token::BinOpEq(token::Plus) => {
-                let span = self.span.with_lo(self.span.lo() + BytePos(1));
+                let span = self.token.span.with_lo(self.token.span.lo() + BytePos(1));
                 self.bump_with(token::Eq, span);
                 true
             }
@@ -1006,7 +603,6 @@ impl<'a> Parser<'a> {
         }
     }
 
-
     /// Checks to see if the next token is either `+` or `+=`.
     /// Otherwise returns `false`.
     fn check_plus(&mut self) -> bool {
@@ -1023,13 +619,13 @@ impl<'a> Parser<'a> {
     /// `&` and continues. If an `&` is not seen, signals an error.
     fn expect_and(&mut self) -> PResult<'a, ()> {
         self.expected_tokens.push(TokenType::Token(token::BinOp(token::And)));
-        match self.token {
+        match self.token.kind {
             token::BinOp(token::And) => {
                 self.bump();
                 Ok(())
             }
             token::AndAnd => {
-                let span = self.span.with_lo(self.span.lo() + BytePos(1));
+                let span = self.token.span.with_lo(self.token.span.lo() + BytePos(1));
                 Ok(self.bump_with(token::BinOp(token::And), span))
             }
             _ => self.unexpected()
@@ -1040,13 +636,13 @@ impl<'a> Parser<'a> {
     /// `|` and continues. If an `|` is not seen, signals an error.
     fn expect_or(&mut self) -> PResult<'a, ()> {
         self.expected_tokens.push(TokenType::Token(token::BinOp(token::Or)));
-        match self.token {
+        match self.token.kind {
             token::BinOp(token::Or) => {
                 self.bump();
                 Ok(())
             }
             token::OrOr => {
-                let span = self.span.with_lo(self.span.lo() + BytePos(1));
+                let span = self.token.span.with_lo(self.token.span.lo() + BytePos(1));
                 Ok(self.bump_with(token::BinOp(token::Or), span))
             }
             _ => self.unexpected()
@@ -1054,7 +650,7 @@ impl<'a> Parser<'a> {
     }
 
     fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<ast::Name>) {
-        literal::expect_no_suffix(sp, &self.sess.span_diagnostic, kind, suffix)
+        literal::expect_no_suffix(&self.sess.span_diagnostic, sp, kind, suffix)
     }
 
     /// Attempts to consume a `<`. If `<<` is seen, replaces it with a single
@@ -1065,18 +661,18 @@ impl<'a> Parser<'a> {
     /// starting token.
     fn eat_lt(&mut self) -> bool {
         self.expected_tokens.push(TokenType::Token(token::Lt));
-        let ate = match self.token {
+        let ate = match self.token.kind {
             token::Lt => {
                 self.bump();
                 true
             }
             token::BinOp(token::Shl) => {
-                let span = self.span.with_lo(self.span.lo() + BytePos(1));
+                let span = self.token.span.with_lo(self.token.span.lo() + BytePos(1));
                 self.bump_with(token::Lt, span);
                 true
             }
             token::LArrow => {
-                let span = self.span.with_lo(self.span.lo() + BytePos(1));
+                let span = self.token.span.with_lo(self.token.span.lo() + BytePos(1));
                 self.bump_with(token::BinOp(token::Minus), span);
                 true
             }
@@ -1105,21 +701,21 @@ impl<'a> Parser<'a> {
     /// with a single `>` and continues. If a `>` is not seen, signals an error.
     fn expect_gt(&mut self) -> PResult<'a, ()> {
         self.expected_tokens.push(TokenType::Token(token::Gt));
-        let ate = match self.token {
+        let ate = match self.token.kind {
             token::Gt => {
                 self.bump();
                 Some(())
             }
             token::BinOp(token::Shr) => {
-                let span = self.span.with_lo(self.span.lo() + BytePos(1));
+                let span = self.token.span.with_lo(self.token.span.lo() + BytePos(1));
                 Some(self.bump_with(token::Gt, span))
             }
             token::BinOpEq(token::Shr) => {
-                let span = self.span.with_lo(self.span.lo() + BytePos(1));
+                let span = self.token.span.with_lo(self.token.span.lo() + BytePos(1));
                 Some(self.bump_with(token::Ge, span))
             }
             token::Ge => {
-                let span = self.span.with_lo(self.span.lo() + BytePos(1));
+                let span = self.token.span.with_lo(self.token.span.lo() + BytePos(1));
                 Some(self.bump_with(token::Eq, span))
             }
             _ => None,
@@ -1139,30 +735,16 @@ impl<'a> Parser<'a> {
         }
     }
 
-    /// Eats and discards tokens until one of `kets` is encountered. Respects token trees,
-    /// passes through any errors encountered. Used for error recovery.
-    fn eat_to_tokens(&mut self, kets: &[&token::Token]) {
-        let handler = self.diagnostic();
-
-        if let Err(ref mut err) = self.parse_seq_to_before_tokens(kets,
-                                                                  SeqSep::none(),
-                                                                  TokenExpectType::Expect,
-                                                                  |p| Ok(p.parse_token_tree())) {
-            handler.cancel(err);
-        }
-    }
-
     /// Parses a sequence, including the closing delimiter. The function
     /// `f` must consume tokens until reaching the next separator or
     /// closing bracket.
-    pub fn parse_seq_to_end<T, F>(&mut self,
-                                  ket: &token::Token,
-                                  sep: SeqSep,
-                                  f: F)
-                                  -> PResult<'a, Vec<T>> where
-        F: FnMut(&mut Parser<'a>) -> PResult<'a,  T>,
-    {
-        let (val, recovered) = self.parse_seq_to_before_end(ket, sep, f)?;
+    pub fn parse_seq_to_end<T>(
+        &mut self,
+        ket: &TokenKind,
+        sep: SeqSep,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a,  T>,
+    ) -> PResult<'a, Vec<T>> {
+        let (val, _, recovered) = self.parse_seq_to_before_end(ket, sep, f)?;
         if !recovered {
             self.bump();
         }
@@ -1172,39 +754,39 @@ impl<'a> Parser<'a> {
     /// Parses a sequence, not including the closing delimiter. The function
     /// `f` must consume tokens until reaching the next separator or
     /// closing bracket.
-    pub fn parse_seq_to_before_end<T, F>(
+    pub fn parse_seq_to_before_end<T>(
         &mut self,
-        ket: &token::Token,
+        ket: &TokenKind,
         sep: SeqSep,
-        f: F,
-    ) -> PResult<'a, (Vec<T>, bool)>
-        where F: FnMut(&mut Parser<'a>) -> PResult<'a, T>
-    {
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (Vec<T>, bool, bool)> {
         self.parse_seq_to_before_tokens(&[ket], sep, TokenExpectType::Expect, f)
     }
 
-    fn parse_seq_to_before_tokens<T, F>(
+    fn expect_any_with_type(&mut self, kets: &[&TokenKind], expect: TokenExpectType) -> bool {
+        kets.iter().any(|k| {
+            match expect {
+                TokenExpectType::Expect => self.check(k),
+                TokenExpectType::NoExpect => self.token == **k,
+            }
+        })
+    }
+
+    crate fn parse_seq_to_before_tokens<T>(
         &mut self,
-        kets: &[&token::Token],
+        kets: &[&TokenKind],
         sep: SeqSep,
         expect: TokenExpectType,
-        mut f: F,
-    ) -> PResult<'a, (Vec<T>, bool /* recovered */)>
-        where F: FnMut(&mut Parser<'a>) -> PResult<'a, T>
-    {
+        mut f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (Vec<T>, bool /* trailing */, bool /* recovered */)> {
         let mut first = true;
         let mut recovered = false;
+        let mut trailing = false;
         let mut v = vec![];
-        while !kets.iter().any(|k| {
-                match expect {
-                    TokenExpectType::Expect => self.check(k),
-                    TokenExpectType::NoExpect => self.token == **k,
-                }
-            }) {
-            match self.token {
-                token::CloseDelim(..) | token::Eof => break,
-                _ => {}
-            };
+        while !self.expect_any_with_type(kets, expect) {
+            if let token::CloseDelim(..) | token::Eof = self.token.kind {
+                break
+            }
             if let Some(ref t) = sep.sep {
                 if first {
                     first = false;
@@ -1218,7 +800,7 @@ impl<'a> Parser<'a> {
                         Err(mut e) => {
                             // Attempt to keep parsing if it was a similar separator
                             if let Some(ref tokens) = t.similar_tokens() {
-                                if tokens.contains(&self.token) {
+                                if tokens.contains(&self.token.kind) {
                                     self.bump();
                                 }
                             }
@@ -1238,12 +820,8 @@ impl<'a> Parser<'a> {
                     }
                 }
             }
-            if sep.trailing_sep_allowed && kets.iter().any(|k| {
-                match expect {
-                    TokenExpectType::Expect => self.check(k),
-                    TokenExpectType::NoExpect => self.token == **k,
-                }
-            }) {
+            if sep.trailing_sep_allowed && self.expect_any_with_type(kets, expect) {
+                trailing = true;
                 break;
             }
 
@@ -1251,27 +829,45 @@ impl<'a> Parser<'a> {
             v.push(t);
         }
 
-        Ok((v, recovered))
+        Ok((v, trailing, recovered))
     }
 
     /// Parses a sequence, including the closing delimiter. The function
     /// `f` must consume tokens until reaching the next separator or
     /// closing bracket.
-    fn parse_unspanned_seq<T, F>(
+    fn parse_unspanned_seq<T>(
         &mut self,
-        bra: &token::Token,
-        ket: &token::Token,
+        bra: &TokenKind,
+        ket: &TokenKind,
         sep: SeqSep,
-        f: F,
-    ) -> PResult<'a, Vec<T>> where
-        F: FnMut(&mut Parser<'a>) -> PResult<'a, T>,
-    {
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (Vec<T>, bool)> {
         self.expect(bra)?;
-        let (result, recovered) = self.parse_seq_to_before_end(ket, sep, f)?;
+        let (result, trailing, recovered) = self.parse_seq_to_before_end(ket, sep, f)?;
         if !recovered {
             self.eat(ket);
         }
-        Ok(result)
+        Ok((result, trailing))
+    }
+
+    fn parse_delim_comma_seq<T>(
+        &mut self,
+        delim: DelimToken,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (Vec<T>, bool)> {
+        self.parse_unspanned_seq(
+            &token::OpenDelim(delim),
+            &token::CloseDelim(delim),
+            SeqSep::trailing_allowed(token::Comma),
+            f,
+        )
+    }
+
+    fn parse_paren_comma_seq<T>(
+        &mut self,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (Vec<T>, bool)> {
+        self.parse_delim_comma_seq(token::Paren, f)
     }
 
     /// Advance the parser by one token
@@ -1281,10 +877,10 @@ impl<'a> Parser<'a> {
             self.bug("attempted to bump the parser past EOF (may be stuck in a loop)");
         }
 
-        self.prev_span = self.meta_var_span.take().unwrap_or(self.span);
+        self.prev_span = self.meta_var_span.take().unwrap_or(self.token.span);
 
         // Record last token kind for possible error recovery.
-        self.prev_token_kind = match self.token {
+        self.prev_token_kind = match self.token.kind {
             token::DocComment(..) => PrevTokenKind::DocComment,
             token::Comma => PrevTokenKind::Comma,
             token::BinOp(token::Plus) => PrevTokenKind::Plus,
@@ -1295,9 +891,7 @@ impl<'a> Parser<'a> {
             _ => PrevTokenKind::Other,
         };
 
-        let next = self.next_tok();
-        self.span = next.sp;
-        self.token = next.tok;
+        self.token = self.next_tok();
         self.expected_tokens.clear();
         // check after each token
         self.process_potential_macro_variable();
@@ -1305,125 +899,45 @@ impl<'a> Parser<'a> {
 
     /// Advance the parser using provided token as a next one. Use this when
     /// consuming a part of a token. For example a single `<` from `<<`.
-    fn bump_with(&mut self, next: token::Token, span: Span) {
-        self.prev_span = self.span.with_hi(span.lo());
+    fn bump_with(&mut self, next: TokenKind, span: Span) {
+        self.prev_span = self.token.span.with_hi(span.lo());
         // It would be incorrect to record the kind of the current token, but
         // fortunately for tokens currently using `bump_with`, the
         // prev_token_kind will be of no use anyway.
         self.prev_token_kind = PrevTokenKind::Other;
-        self.span = span;
-        self.token = next;
+        self.token = Token::new(next, span);
         self.expected_tokens.clear();
     }
 
     pub fn look_ahead<R, F>(&self, dist: usize, f: F) -> R where
-        F: FnOnce(&token::Token) -> R,
+        F: FnOnce(&Token) -> R,
     {
         if dist == 0 {
-            return f(&self.token)
+            return f(&self.token);
         }
 
-        f(&match self.token_cursor.frame.tree_cursor.look_ahead(dist - 1) {
+        let frame = &self.token_cursor.frame;
+        f(&match frame.tree_cursor.look_ahead(dist - 1) {
             Some(tree) => match tree {
-                TokenTree::Token(_, tok) => tok,
-                TokenTree::Delimited(_, delim, _) => token::OpenDelim(delim),
-            },
-            None => token::CloseDelim(self.token_cursor.frame.delim),
+                TokenTree::Token(token) => token,
+                TokenTree::Delimited(dspan, delim, _) =>
+                    Token::new(token::OpenDelim(delim), dspan.open),
+            }
+            None => Token::new(token::CloseDelim(frame.delim), frame.span.close)
         })
     }
 
-    crate fn look_ahead_span(&self, dist: usize) -> Span {
-        if dist == 0 {
-            return self.span
-        }
-
-        match self.token_cursor.frame.tree_cursor.look_ahead(dist - 1) {
-            Some(TokenTree::Token(span, _)) => span,
-            Some(TokenTree::Delimited(span, ..)) => span.entire(),
-            None => self.look_ahead_span(dist - 1),
-        }
-    }
-    pub fn fatal(&self, m: &str) -> DiagnosticBuilder<'a> {
-        self.sess.span_diagnostic.struct_span_fatal(self.span, m)
-    }
-    pub fn span_fatal<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> DiagnosticBuilder<'a> {
-        self.sess.span_diagnostic.struct_span_fatal(sp, m)
-    }
-    fn span_fatal_err<S: Into<MultiSpan>>(&self, sp: S, err: Error) -> DiagnosticBuilder<'a> {
-        err.span_err(sp, self.diagnostic())
-    }
-    fn bug(&self, m: &str) -> ! {
-        self.sess.span_diagnostic.span_bug(self.span, m)
-    }
-    fn span_err<S: Into<MultiSpan>>(&self, sp: S, m: &str) {
-        self.sess.span_diagnostic.span_err(sp, m)
-    }
-    crate fn struct_span_err<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> DiagnosticBuilder<'a> {
-        self.sess.span_diagnostic.struct_span_err(sp, m)
-    }
-    crate fn span_bug<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> ! {
-        self.sess.span_diagnostic.span_bug(sp, m)
-    }
-
-    fn cancel(&self, err: &mut DiagnosticBuilder<'_>) {
-        self.sess.span_diagnostic.cancel(err)
-    }
-
-    crate fn diagnostic(&self) -> &'a errors::Handler {
-        &self.sess.span_diagnostic
-    }
-
-    /// Is the current token one of the keywords that signals a bare function type?
-    fn token_is_bare_fn_keyword(&mut self) -> bool {
-        self.check_keyword(keywords::Fn) ||
-            self.check_keyword(keywords::Unsafe) ||
-            self.check_keyword(keywords::Extern)
-    }
-
-    /// Parses a `TyKind::BareFn` type.
-    fn parse_ty_bare_fn(&mut self, generic_params: Vec<GenericParam>) -> PResult<'a, TyKind> {
-        /*
-
-        [unsafe] [extern "ABI"] fn (S) -> T
-         ^~~~^           ^~~~^     ^~^    ^
-           |               |        |     |
-           |               |        |   Return type
-           |               |      Argument types
-           |               |
-           |              ABI
-        Function Style
-        */
-
-        let unsafety = self.parse_unsafety();
-        let abi = if self.eat_keyword(keywords::Extern) {
-            self.parse_opt_abi()?.unwrap_or(Abi::C)
-        } else {
-            Abi::Rust
-        };
-
-        self.expect_keyword(keywords::Fn)?;
-        let (inputs, c_variadic) = self.parse_fn_args(false, true)?;
-        let ret_ty = self.parse_ret_ty(false)?;
-        let decl = P(FnDecl {
-            inputs,
-            output: ret_ty,
-            c_variadic,
-        });
-        Ok(TyKind::BareFn(P(BareFnTy {
-            abi,
-            unsafety,
-            generic_params,
-            decl,
-        })))
+    /// Returns whether any of the given keywords are `dist` tokens ahead of the current one.
+    fn is_keyword_ahead(&self, dist: usize, kws: &[Symbol]) -> bool {
+        self.look_ahead(dist, |t| kws.iter().any(|&kw| t.is_keyword(kw)))
     }
 
     /// Parses asyncness: `async` or nothing.
     fn parse_asyncness(&mut self) -> IsAsync {
-        if self.eat_keyword(keywords::Async) {
+        if self.eat_keyword(kw::Async) {
             IsAsync::Async {
                 closure_id: ast::DUMMY_NODE_ID,
                 return_impl_trait_id: ast::DUMMY_NODE_ID,
-                arguments: Vec::new(),
             }
         } else {
             IsAsync::NotAsync
@@ -1432,365 +946,21 @@ impl<'a> Parser<'a> {
 
     /// Parses unsafety: `unsafe` or nothing.
     fn parse_unsafety(&mut self) -> Unsafety {
-        if self.eat_keyword(keywords::Unsafe) {
+        if self.eat_keyword(kw::Unsafe) {
             Unsafety::Unsafe
         } else {
             Unsafety::Normal
         }
     }
 
-    /// Parses the items in a trait declaration.
-    pub fn parse_trait_item(&mut self, at_end: &mut bool) -> PResult<'a, TraitItem> {
-        maybe_whole!(self, NtTraitItem, |x| x);
-        let attrs = self.parse_outer_attributes()?;
-        let mut unclosed_delims = vec![];
-        let (mut item, tokens) = self.collect_tokens(|this| {
-            let item = this.parse_trait_item_(at_end, attrs);
-            unclosed_delims.append(&mut this.unclosed_delims);
-            item
-        })?;
-        self.unclosed_delims.append(&mut unclosed_delims);
-        // See `parse_item` for why this clause is here.
-        if !item.attrs.iter().any(|attr| attr.style == AttrStyle::Inner) {
-            item.tokens = Some(tokens);
-        }
-        Ok(item)
-    }
-
-    fn parse_trait_item_(&mut self,
-                         at_end: &mut bool,
-                         mut attrs: Vec<Attribute>) -> PResult<'a, TraitItem> {
-        let lo = self.span;
-        self.eat_bad_pub();
-        let (name, node, generics) = if self.eat_keyword(keywords::Type) {
-            self.parse_trait_item_assoc_ty()?
-        } else if self.is_const_item() {
-            self.expect_keyword(keywords::Const)?;
-            let ident = self.parse_ident()?;
-            self.expect(&token::Colon)?;
-            let ty = self.parse_ty()?;
-            let default = if self.eat(&token::Eq) {
-                let expr = self.parse_expr()?;
-                self.expect(&token::Semi)?;
-                Some(expr)
-            } else {
-                self.expect(&token::Semi)?;
-                None
-            };
-            (ident, TraitItemKind::Const(ty, default), ast::Generics::default())
-        } else if let Some(mac) = self.parse_assoc_macro_invoc("trait", None, &mut false)? {
-            // trait item macro.
-            (keywords::Invalid.ident(), ast::TraitItemKind::Macro(mac), ast::Generics::default())
-        } else {
-            let (constness, unsafety, mut asyncness, abi) = self.parse_fn_front_matter()?;
-
-            let ident = self.parse_ident()?;
-            let mut generics = self.parse_generics()?;
-
-            let mut decl = self.parse_fn_decl_with_self(|p: &mut Parser<'a>| {
-                // This is somewhat dubious; We don't want to allow
-                // argument names to be left off if there is a
-                // definition...
-
-                // We don't allow argument names to be left off in edition 2018.
-                p.parse_arg_general(p.span.rust_2018(), true, false)
-            })?;
-            generics.where_clause = self.parse_where_clause()?;
-            self.construct_async_arguments(&mut asyncness, &mut decl);
-
-            let sig = ast::MethodSig {
-                header: FnHeader {
-                    unsafety,
-                    constness,
-                    abi,
-                    asyncness,
-                },
-                decl,
-            };
-
-            let body = match self.token {
-                token::Semi => {
-                    self.bump();
-                    *at_end = true;
-                    debug!("parse_trait_methods(): parsing required method");
-                    None
-                }
-                token::OpenDelim(token::Brace) => {
-                    debug!("parse_trait_methods(): parsing provided method");
-                    *at_end = true;
-                    let (inner_attrs, body) = self.parse_inner_attrs_and_block()?;
-                    attrs.extend(inner_attrs.iter().cloned());
-                    Some(body)
-                }
-                token::Interpolated(ref nt) => {
-                    match **nt {
-                        token::NtBlock(..) => {
-                            *at_end = true;
-                            let (inner_attrs, body) = self.parse_inner_attrs_and_block()?;
-                            attrs.extend(inner_attrs.iter().cloned());
-                            Some(body)
-                        }
-                        _ => {
-                            let token_str = self.this_token_descr();
-                            let mut err = self.fatal(&format!("expected `;` or `{{`, found {}",
-                                                              token_str));
-                            err.span_label(self.span, "expected `;` or `{`");
-                            return Err(err);
-                        }
-                    }
-                }
-                _ => {
-                    let token_str = self.this_token_descr();
-                    let mut err = self.fatal(&format!("expected `;` or `{{`, found {}",
-                                                      token_str));
-                    err.span_label(self.span, "expected `;` or `{`");
-                    return Err(err);
-                }
-            };
-            (ident, ast::TraitItemKind::Method(sig, body), generics)
-        };
-
-        Ok(TraitItem {
-            id: ast::DUMMY_NODE_ID,
-            ident: name,
-            attrs,
-            generics,
-            node,
-            span: lo.to(self.prev_span),
-            tokens: None,
-        })
-    }
-
-    /// Parses an optional return type `[ -> TY ]` in a function declaration.
-    fn parse_ret_ty(&mut self, allow_plus: bool) -> PResult<'a, FunctionRetTy> {
-        if self.eat(&token::RArrow) {
-            Ok(FunctionRetTy::Ty(self.parse_ty_common(allow_plus, true, false)?))
-        } else {
-            Ok(FunctionRetTy::Default(self.span.shrink_to_lo()))
-        }
-    }
-
-    /// Parses a type.
-    pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
-        self.parse_ty_common(true, true, false)
-    }
-
-    /// Parses a type in restricted contexts where `+` is not permitted.
-    ///
-    /// Example 1: `&'a TYPE`
-    ///     `+` is prohibited to maintain operator priority (P(+) < P(&)).
-    /// Example 2: `value1 as TYPE + value2`
-    ///     `+` is prohibited to avoid interactions with expression grammar.
-    fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
-        self.parse_ty_common(false, true, false)
-    }
-
-    fn parse_ty_common(&mut self, allow_plus: bool, allow_qpath_recovery: bool,
-                       allow_c_variadic: bool) -> PResult<'a, P<Ty>> {
-        maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
-        maybe_whole!(self, NtTy, |x| x);
-
-        let lo = self.span;
-        let mut impl_dyn_multi = false;
-        let node = if self.eat(&token::OpenDelim(token::Paren)) {
-            // `(TYPE)` is a parenthesized type.
-            // `(TYPE,)` is a tuple with a single field of type TYPE.
-            let mut ts = vec![];
-            let mut last_comma = false;
-            while self.token != token::CloseDelim(token::Paren) {
-                ts.push(self.parse_ty()?);
-                if self.eat(&token::Comma) {
-                    last_comma = true;
-                } else {
-                    last_comma = false;
-                    break;
-                }
-            }
-            let trailing_plus = self.prev_token_kind == PrevTokenKind::Plus;
-            self.expect(&token::CloseDelim(token::Paren))?;
-
-            if ts.len() == 1 && !last_comma {
-                let ty = ts.into_iter().nth(0).unwrap().into_inner();
-                let maybe_bounds = allow_plus && self.token.is_like_plus();
-                match ty.node {
-                    // `(TY_BOUND_NOPAREN) + BOUND + ...`.
-                    TyKind::Path(None, ref path) if maybe_bounds => {
-                        self.parse_remaining_bounds(Vec::new(), path.clone(), lo, true)?
-                    }
-                    TyKind::TraitObject(ref bounds, TraitObjectSyntax::None)
-                            if maybe_bounds && bounds.len() == 1 && !trailing_plus => {
-                        let path = match bounds[0] {
-                            GenericBound::Trait(ref pt, ..) => pt.trait_ref.path.clone(),
-                            GenericBound::Outlives(..) => self.bug("unexpected lifetime bound"),
-                        };
-                        self.parse_remaining_bounds(Vec::new(), path, lo, true)?
-                    }
-                    // `(TYPE)`
-                    _ => TyKind::Paren(P(ty))
-                }
-            } else {
-                TyKind::Tup(ts)
-            }
-        } else if self.eat(&token::Not) {
-            // Never type `!`
-            TyKind::Never
-        } else if self.eat(&token::BinOp(token::Star)) {
-            // Raw pointer
-            TyKind::Ptr(self.parse_ptr()?)
-        } else if self.eat(&token::OpenDelim(token::Bracket)) {
-            // Array or slice
-            let t = self.parse_ty()?;
-            // Parse optional `; EXPR` in `[TYPE; EXPR]`
-            let t = match self.maybe_parse_fixed_length_of_vec()? {
-                None => TyKind::Slice(t),
-                Some(length) => TyKind::Array(t, AnonConst {
-                    id: ast::DUMMY_NODE_ID,
-                    value: length,
-                }),
-            };
-            self.expect(&token::CloseDelim(token::Bracket))?;
-            t
-        } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
-            // Reference
-            self.expect_and()?;
-            self.parse_borrowed_pointee()?
-        } else if self.eat_keyword_noexpect(keywords::Typeof) {
-            // `typeof(EXPR)`
-            // In order to not be ambiguous, the type must be surrounded by parens.
-            self.expect(&token::OpenDelim(token::Paren))?;
-            let e = AnonConst {
-                id: ast::DUMMY_NODE_ID,
-                value: self.parse_expr()?,
-            };
-            self.expect(&token::CloseDelim(token::Paren))?;
-            TyKind::Typeof(e)
-        } else if self.eat_keyword(keywords::Underscore) {
-            // A type to be inferred `_`
-            TyKind::Infer
-        } else if self.token_is_bare_fn_keyword() {
-            // Function pointer type
-            self.parse_ty_bare_fn(Vec::new())?
-        } else if self.check_keyword(keywords::For) {
-            // Function pointer type or bound list (trait object type) starting with a poly-trait.
-            //   `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
-            //   `for<'lt> Trait1<'lt> + Trait2 + 'a`
-            let lo = self.span;
-            let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
-            if self.token_is_bare_fn_keyword() {
-                self.parse_ty_bare_fn(lifetime_defs)?
-            } else {
-                let path = self.parse_path(PathStyle::Type)?;
-                let parse_plus = allow_plus && self.check_plus();
-                self.parse_remaining_bounds(lifetime_defs, path, lo, parse_plus)?
-            }
-        } else if self.eat_keyword(keywords::Impl) {
-            // Always parse bounds greedily for better error recovery.
-            let bounds = self.parse_generic_bounds(None)?;
-            impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
-            TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds)
-        } else if self.check_keyword(keywords::Dyn) &&
-                  (self.span.rust_2018() ||
-                   self.look_ahead(1, |t| t.can_begin_bound() &&
-                                          !can_continue_type_after_non_fn_ident(t))) {
-            self.bump(); // `dyn`
-            // Always parse bounds greedily for better error recovery.
-            let bounds = self.parse_generic_bounds(None)?;
-            impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
-            TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn)
-        } else if self.check(&token::Question) ||
-                  self.check_lifetime() && self.look_ahead(1, |t| t.is_like_plus()) {
-            // Bound list (trait object type)
-            TyKind::TraitObject(self.parse_generic_bounds_common(allow_plus, None)?,
-                                TraitObjectSyntax::None)
-        } else if self.eat_lt() {
-            // Qualified path
-            let (qself, path) = self.parse_qpath(PathStyle::Type)?;
-            TyKind::Path(Some(qself), path)
-        } else if self.token.is_path_start() {
-            // Simple path
-            let path = self.parse_path(PathStyle::Type)?;
-            if self.eat(&token::Not) {
-                // Macro invocation in type position
-                let (delim, tts) = self.expect_delimited_token_tree()?;
-                let node = Mac_ { path, tts, delim };
-                TyKind::Mac(respan(lo.to(self.prev_span), node))
-            } else {
-                // Just a type path or bound list (trait object type) starting with a trait.
-                //   `Type`
-                //   `Trait1 + Trait2 + 'a`
-                if allow_plus && self.check_plus() {
-                    self.parse_remaining_bounds(Vec::new(), path, lo, true)?
-                } else {
-                    TyKind::Path(None, path)
-                }
-            }
-        } else if self.check(&token::DotDotDot) {
-            if allow_c_variadic {
-                self.eat(&token::DotDotDot);
-                TyKind::CVarArgs
-            } else {
-                return Err(self.fatal(
-                    "only foreign functions are allowed to be C-variadic"
-                ));
-            }
-        } else {
-            let msg = format!("expected type, found {}", self.this_token_descr());
-            return Err(self.fatal(&msg));
-        };
-
-        let span = lo.to(self.prev_span);
-        let ty = P(Ty { node, span, id: ast::DUMMY_NODE_ID });
-
-        // Try to recover from use of `+` with incorrect priority.
-        self.maybe_report_ambiguous_plus(allow_plus, impl_dyn_multi, &ty);
-        self.maybe_recover_from_bad_type_plus(allow_plus, &ty)?;
-        self.maybe_recover_from_bad_qpath(ty, allow_qpath_recovery)
-    }
-
-    fn parse_remaining_bounds(&mut self, generic_params: Vec<GenericParam>, path: ast::Path,
-                              lo: Span, parse_plus: bool) -> PResult<'a, TyKind> {
-        let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_span));
-        let mut bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
-        if parse_plus {
-            self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
-            bounds.append(&mut self.parse_generic_bounds(Some(self.prev_span))?);
-        }
-        Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
-    }
-
-    fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
-        let opt_lifetime = if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
-        let mutbl = self.parse_mutability();
-        let ty = self.parse_ty_no_plus()?;
-        return Ok(TyKind::Rptr(opt_lifetime, MutTy { ty: ty, mutbl: mutbl }));
-    }
-
-    fn parse_ptr(&mut self) -> PResult<'a, MutTy> {
-        let mutbl = if self.eat_keyword(keywords::Mut) {
-            Mutability::Mutable
-        } else if self.eat_keyword(keywords::Const) {
-            Mutability::Immutable
-        } else {
-            let span = self.prev_span;
-            let msg = "expected mut or const in raw pointer type";
-            self.struct_span_err(span, msg)
-                .span_label(span, msg)
-                .help("use `*mut T` or `*const T` as appropriate")
-                .emit();
-            Mutability::Immutable
-        };
-        let t = self.parse_ty_no_plus()?;
-        Ok(MutTy { ty: t, mutbl: mutbl })
-    }
-
     fn is_named_argument(&self) -> bool {
-        let offset = match self.token {
+        let offset = match self.token.kind {
             token::Interpolated(ref nt) => match **nt {
                 token::NtPat(..) => return self.look_ahead(1, |t| t == &token::Colon),
                 _ => 0,
             }
             token::BinOp(token::And) | token::AndAnd => 1,
-            _ if self.token.is_keyword(keywords::Mut) => 1,
+            _ if self.token.is_keyword(kw::Mut) => 1,
             _ => 0,
         };
 
@@ -1800,88 +970,48 @@ impl<'a> Parser<'a> {
 
     /// Skips unexpected attributes and doc comments in this position and emits an appropriate
     /// error.
-    fn eat_incorrect_doc_comment(&mut self, applied_to: &str) {
-        if let token::DocComment(_) = self.token {
-            let mut err = self.diagnostic().struct_span_err(
-                self.span,
-                &format!("documentation comments cannot be applied to {}", applied_to),
-            );
-            err.span_label(self.span, "doc comments are not allowed here");
-            err.emit();
-            self.bump();
-        } else if self.token == token::Pound && self.look_ahead(1, |t| {
-            *t == token::OpenDelim(token::Bracket)
-        }) {
-            let lo = self.span;
-            // Skip every token until next possible arg.
-            while self.token != token::CloseDelim(token::Bracket) {
-                self.bump();
-            }
-            let sp = lo.to(self.span);
-            self.bump();
-            let mut err = self.diagnostic().struct_span_err(
-                sp,
-                &format!("attributes cannot be applied to {}", applied_to),
-            );
-            err.span_label(sp, "attributes are not allowed here");
-            err.emit();
-        }
-    }
-
     /// This version of parse arg doesn't necessarily require identifier names.
-    fn parse_arg_general(&mut self, require_name: bool, is_trait_item: bool,
-                         allow_c_variadic: bool) -> PResult<'a, Arg> {
-        if let Ok(Some(_)) = self.parse_self_arg() {
-            let mut err = self.struct_span_err(self.prev_span,
-                "unexpected `self` argument in function");
-            err.span_label(self.prev_span,
-                "`self` is only valid as the first argument of an associated function");
-            return Err(err);
+    fn parse_arg_general<F>(
+        &mut self,
+        is_trait_item: bool,
+        allow_c_variadic: bool,
+        is_name_required: F,
+    ) -> PResult<'a, Arg>
+    where
+        F: Fn(&token::Token) -> bool
+    {
+        let lo = self.token.span;
+        let attrs = self.parse_arg_attributes()?;
+        if let Some(mut arg) = self.parse_self_arg()? {
+            arg.attrs = attrs.into();
+            return self.recover_bad_self_arg(arg, is_trait_item);
         }
 
-        let (pat, ty) = if require_name || self.is_named_argument() {
-            debug!("parse_arg_general parse_pat (require_name:{})",
-                   require_name);
-            self.eat_incorrect_doc_comment("method arguments");
-            let pat = self.parse_pat(Some("argument name"))?;
+        let is_name_required = is_name_required(&self.token);
+        let (pat, ty) = if is_name_required || self.is_named_argument() {
+            debug!("parse_arg_general parse_pat (is_name_required:{})", is_name_required);
 
+            let pat = self.parse_pat(Some("argument name"))?;
             if let Err(mut err) = self.expect(&token::Colon) {
-                // If we find a pattern followed by an identifier, it could be an (incorrect)
-                // C-style parameter declaration.
-                if self.check_ident() && self.look_ahead(1, |t| {
-                    *t == token::Comma || *t == token::CloseDelim(token::Paren)
-                }) {
-                    let ident = self.parse_ident().unwrap();
-                    let span = pat.span.with_hi(ident.span.hi());
-
-                    err.span_suggestion(
-                        span,
-                        "declare the type after the parameter binding",
-                        String::from("<identifier>: <type>"),
-                        Applicability::HasPlaceholders,
-                    );
-                } else if require_name && is_trait_item {
-                    if let PatKind::Ident(_, ident, _) = pat.node {
-                        err.span_suggestion(
-                            pat.span,
-                            "explicitly ignore parameter",
-                            format!("_: {}", ident),
-                            Applicability::MachineApplicable,
-                        );
-                    }
-
-                    err.note("anonymous parameters are removed in the 2018 edition (see RFC 1685)");
+                if let Some(ident) = self.argument_without_type(
+                    &mut err,
+                    pat,
+                    is_name_required,
+                    is_trait_item,
+                ) {
+                    err.emit();
+                    return Ok(dummy_arg(ident));
+                } else {
+                    return Err(err);
                 }
-
-                return Err(err);
             }
 
-            self.eat_incorrect_doc_comment("a method argument's type");
+            self.eat_incorrect_doc_comment_for_arg_type();
             (pat, self.parse_ty_common(true, true, allow_c_variadic)?)
         } else {
             debug!("parse_arg_general ident_to_pat");
             let parser_snapshot_before_ty = self.clone();
-            self.eat_incorrect_doc_comment("a method argument's type");
+            self.eat_incorrect_doc_comment_for_arg_type();
             let mut ty = self.parse_ty_common(true, true, allow_c_variadic);
             if ty.is_ok() && self.token != token::Comma &&
                self.token != token::CloseDelim(token::Paren) {
@@ -1891,13 +1021,9 @@ impl<'a> Parser<'a> {
             }
             match ty {
                 Ok(ty) => {
-                    let ident = Ident::new(keywords::Invalid.name(), self.prev_span);
-                    let pat = P(Pat {
-                        id: ast::DUMMY_NODE_ID,
-                        node: PatKind::Ident(
-                            BindingMode::ByValue(Mutability::Immutable), ident, None),
-                        span: ty.span,
-                    });
+                    let ident = Ident::new(kw::Invalid, self.prev_span);
+                    let bm = BindingMode::ByValue(Mutability::Immutable);
+                    let pat = self.mk_pat_ident(ty.span, bm, ident);
                     (pat, ty)
                 }
                 Err(mut err) => {
@@ -1909,331 +1035,19 @@ impl<'a> Parser<'a> {
                     // Recover from attempting to parse the argument as a type without pattern.
                     err.cancel();
                     mem::replace(self, parser_snapshot_before_ty);
-                    let pat = self.parse_pat(Some("argument name"))?;
-                    self.expect(&token::Colon)?;
-                    let ty = self.parse_ty()?;
-
-                    let mut err = self.diagnostic().struct_span_err_with_code(
-                        pat.span,
-                        "patterns aren't allowed in methods without bodies",
-                        DiagnosticId::Error("E0642".into()),
-                    );
-                    err.span_suggestion_short(
-                        pat.span,
-                        "give this argument a name or use an underscore to ignore it",
-                        "_".to_owned(),
-                        Applicability::MachineApplicable,
-                    );
-                    err.emit();
-
-                    // Pretend the pattern is `_`, to avoid duplicate errors from AST validation.
-                    let pat = P(Pat {
-                        node: PatKind::Wild,
-                        span: pat.span,
-                        id: ast::DUMMY_NODE_ID
-                    });
-                    (pat, ty)
+                    self.recover_arg_parse()?
                 }
             }
         };
 
-        Ok(Arg { ty, pat, id: ast::DUMMY_NODE_ID, source: ast::ArgSource::Normal })
-    }
-
-    /// Parses a single function argument.
-    crate fn parse_arg(&mut self) -> PResult<'a, Arg> {
-        self.parse_arg_general(true, false, false)
-    }
+        let span = lo.to(self.token.span);
 
-    /// Parses an argument in a lambda header (e.g., `|arg, arg|`).
-    fn parse_fn_block_arg(&mut self) -> PResult<'a, Arg> {
-        let pat = self.parse_pat(Some("argument name"))?;
-        let t = if self.eat(&token::Colon) {
-            self.parse_ty()?
-        } else {
-            P(Ty {
-                id: ast::DUMMY_NODE_ID,
-                node: TyKind::Infer,
-                span: self.prev_span,
-            })
-        };
-        Ok(Arg {
-            ty: t,
-            pat,
-            id: ast::DUMMY_NODE_ID,
-            source: ast::ArgSource::Normal,
-        })
-    }
-
-    fn maybe_parse_fixed_length_of_vec(&mut self) -> PResult<'a, Option<P<ast::Expr>>> {
-        if self.eat(&token::Semi) {
-            Ok(Some(self.parse_expr()?))
-        } else {
-            Ok(None)
-        }
-    }
-
-    /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
-    crate fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
-        maybe_whole_expr!(self);
-
-        let minus_lo = self.span;
-        let minus_present = self.eat(&token::BinOp(token::Minus));
-        let lo = self.span;
-        let literal = self.parse_lit()?;
-        let hi = self.prev_span;
-        let expr = self.mk_expr(lo.to(hi), ExprKind::Lit(literal), ThinVec::new());
-
-        if minus_present {
-            let minus_hi = self.prev_span;
-            let unary = self.mk_unary(UnOp::Neg, expr);
-            Ok(self.mk_expr(minus_lo.to(minus_hi), unary, ThinVec::new()))
-        } else {
-            Ok(expr)
-        }
-    }
-
-    fn parse_path_segment_ident(&mut self) -> PResult<'a, ast::Ident> {
-        match self.token {
-            token::Ident(ident, _) if self.token.is_path_segment_keyword() => {
-                let span = self.span;
-                self.bump();
-                Ok(Ident::new(ident.name, span))
-            }
-            _ => self.parse_ident(),
-        }
-    }
-
-    fn parse_ident_or_underscore(&mut self) -> PResult<'a, ast::Ident> {
-        match self.token {
-            token::Ident(ident, false) if ident.name == keywords::Underscore.name() => {
-                let span = self.span;
-                self.bump();
-                Ok(Ident::new(ident.name, span))
-            }
-            _ => self.parse_ident(),
-        }
-    }
-
-    /// Parses a qualified path.
-    /// Assumes that the leading `<` has been parsed already.
-    ///
-    /// `qualified_path = <type [as trait_ref]>::path`
-    ///
-    /// # Examples
-    /// `<T>::default`
-    /// `<T as U>::a`
-    /// `<T as U>::F::a<S>` (without disambiguator)
-    /// `<T as U>::F::a::<S>` (with disambiguator)
-    fn parse_qpath(&mut self, style: PathStyle) -> PResult<'a, (QSelf, ast::Path)> {
-        let lo = self.prev_span;
-        let ty = self.parse_ty()?;
-
-        // `path` will contain the prefix of the path up to the `>`,
-        // if any (e.g., `U` in the `<T as U>::*` examples
-        // above). `path_span` has the span of that path, or an empty
-        // span in the case of something like `<T>::Bar`.
-        let (mut path, path_span);
-        if self.eat_keyword(keywords::As) {
-            let path_lo = self.span;
-            path = self.parse_path(PathStyle::Type)?;
-            path_span = path_lo.to(self.prev_span);
-        } else {
-            path = ast::Path { segments: Vec::new(), span: syntax_pos::DUMMY_SP };
-            path_span = self.span.to(self.span);
-        }
-
-        // See doc comment for `unmatched_angle_bracket_count`.
-        self.expect(&token::Gt)?;
-        if self.unmatched_angle_bracket_count > 0 {
-            self.unmatched_angle_bracket_count -= 1;
-            debug!("parse_qpath: (decrement) count={:?}", self.unmatched_angle_bracket_count);
-        }
-
-        self.expect(&token::ModSep)?;
-
-        let qself = QSelf { ty, path_span, position: path.segments.len() };
-        self.parse_path_segments(&mut path.segments, style)?;
-
-        Ok((qself, ast::Path { segments: path.segments, span: lo.to(self.prev_span) }))
-    }
-
-    /// Parses simple paths.
-    ///
-    /// `path = [::] segment+`
-    /// `segment = ident | ident[::]<args> | ident[::](args) [-> type]`
-    ///
-    /// # Examples
-    /// `a::b::C<D>` (without disambiguator)
-    /// `a::b::C::<D>` (with disambiguator)
-    /// `Fn(Args)` (without disambiguator)
-    /// `Fn::(Args)` (with disambiguator)
-    pub fn parse_path(&mut self, style: PathStyle) -> PResult<'a, ast::Path> {
-        maybe_whole!(self, NtPath, |path| {
-            if style == PathStyle::Mod &&
-               path.segments.iter().any(|segment| segment.args.is_some()) {
-                self.diagnostic().span_err(path.span, "unexpected generic arguments in path");
-            }
-            path
-        });
-
-        let lo = self.meta_var_span.unwrap_or(self.span);
-        let mut segments = Vec::new();
-        let mod_sep_ctxt = self.span.ctxt();
-        if self.eat(&token::ModSep) {
-            segments.push(PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt)));
-        }
-        self.parse_path_segments(&mut segments, style)?;
-
-        Ok(ast::Path { segments, span: lo.to(self.prev_span) })
-    }
-
-    /// Like `parse_path`, but also supports parsing `Word` meta items into paths for
-    /// backwards-compatibility. This is used when parsing derive macro paths in `#[derive]`
-    /// attributes.
-    pub fn parse_path_allowing_meta(&mut self, style: PathStyle) -> PResult<'a, ast::Path> {
-        let meta_ident = match self.token {
-            token::Interpolated(ref nt) => match **nt {
-                token::NtMeta(ref meta) => match meta.node {
-                    ast::MetaItemKind::Word => Some(meta.path.clone()),
-                    _ => None,
-                },
-                _ => None,
-            },
-            _ => None,
-        };
-        if let Some(path) = meta_ident {
-            self.bump();
-            return Ok(path);
-        }
-        self.parse_path(style)
-    }
-
-    crate fn parse_path_segments(&mut self,
-                           segments: &mut Vec<PathSegment>,
-                           style: PathStyle)
-                           -> PResult<'a, ()> {
-        loop {
-            let segment = self.parse_path_segment(style)?;
-            if style == PathStyle::Expr {
-                // In order to check for trailing angle brackets, we must have finished
-                // recursing (`parse_path_segment` can indirectly call this function),
-                // that is, the next token must be the highlighted part of the below example:
-                //
-                // `Foo::<Bar as Baz<T>>::Qux`
-                //                      ^ here
-                //
-                // As opposed to the below highlight (if we had only finished the first
-                // recursion):
-                //
-                // `Foo::<Bar as Baz<T>>::Qux`
-                //                     ^ here
-                //
-                // `PathStyle::Expr` is only provided at the root invocation and never in
-                // `parse_path_segment` to recurse and therefore can be checked to maintain
-                // this invariant.
-                self.check_trailing_angle_brackets(&segment, token::ModSep);
-            }
-            segments.push(segment);
-
-            if self.is_import_coupler() || !self.eat(&token::ModSep) {
-                return Ok(());
-            }
-        }
-    }
-
-    fn parse_path_segment(&mut self, style: PathStyle) -> PResult<'a, PathSegment> {
-        let ident = self.parse_path_segment_ident()?;
-
-        let is_args_start = |token: &token::Token| match *token {
-            token::Lt | token::BinOp(token::Shl) | token::OpenDelim(token::Paren)
-            | token::LArrow => true,
-            _ => false,
-        };
-        let check_args_start = |this: &mut Self| {
-            this.expected_tokens.extend_from_slice(
-                &[TokenType::Token(token::Lt), TokenType::Token(token::OpenDelim(token::Paren))]
-            );
-            is_args_start(&this.token)
-        };
-
-        Ok(if style == PathStyle::Type && check_args_start(self) ||
-              style != PathStyle::Mod && self.check(&token::ModSep)
-                                      && self.look_ahead(1, |t| is_args_start(t)) {
-            // We use `style == PathStyle::Expr` to check if this is in a recursion or not. If
-            // it isn't, then we reset the unmatched angle bracket count as we're about to start
-            // parsing a new path.
-            if style == PathStyle::Expr {
-                self.unmatched_angle_bracket_count = 0;
-                self.max_angle_bracket_count = 0;
-            }
-
-            // Generic arguments are found - `<`, `(`, `::<` or `::(`.
-            self.eat(&token::ModSep);
-            let lo = self.span;
-            let args = if self.eat_lt() {
-                // `<'a, T, A = U>`
-                let (args, bindings) =
-                    self.parse_generic_args_with_leaning_angle_bracket_recovery(style, lo)?;
-                self.expect_gt()?;
-                let span = lo.to(self.prev_span);
-                AngleBracketedArgs { args, bindings, span }.into()
-            } else {
-                // `(T, U) -> R`
-                self.bump(); // `(`
-                let (inputs, recovered) = self.parse_seq_to_before_tokens(
-                    &[&token::CloseDelim(token::Paren)],
-                    SeqSep::trailing_allowed(token::Comma),
-                    TokenExpectType::Expect,
-                    |p| p.parse_ty())?;
-                if !recovered {
-                    self.bump(); // `)`
-                }
-                let span = lo.to(self.prev_span);
-                let output = if self.eat(&token::RArrow) {
-                    Some(self.parse_ty_common(false, false, false)?)
-                } else {
-                    None
-                };
-                ParenthesizedArgs { inputs, output, span }.into()
-            };
-
-            PathSegment { ident, args, id: ast::DUMMY_NODE_ID }
-        } else {
-            // Generic arguments are not found.
-            PathSegment::from_ident(ident)
-        })
-    }
-
-    crate fn check_lifetime(&mut self) -> bool {
-        self.expected_tokens.push(TokenType::Lifetime);
-        self.token.is_lifetime()
-    }
-
-    /// Parses a single lifetime `'a` or panics.
-    crate fn expect_lifetime(&mut self) -> Lifetime {
-        if let Some(ident) = self.token.lifetime() {
-            let span = self.span;
-            self.bump();
-            Lifetime { ident: Ident::new(ident.name, span), id: ast::DUMMY_NODE_ID }
-        } else {
-            self.span_bug(self.span, "not a lifetime")
-        }
-    }
-
-    fn eat_label(&mut self) -> Option<Label> {
-        if let Some(ident) = self.token.lifetime() {
-            let span = self.span;
-            self.bump();
-            Some(Label { ident: Ident::new(ident.name, span) })
-        } else {
-            None
-        }
+        Ok(Arg { attrs: attrs.into(), id: ast::DUMMY_NODE_ID, pat, span, ty })
     }
 
     /// Parses mutability (`mut` or nothing).
     fn parse_mutability(&mut self) -> Mutability {
-        if self.eat_keyword(keywords::Mut) {
+        if self.eat_keyword(kw::Mut) {
             Mutability::Mutable
         } else {
             Mutability::Immutable
@@ -2241,102 +1055,23 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_field_name(&mut self) -> PResult<'a, Ident> {
-        if let token::Literal(token::Integer(name), suffix) = self.token {
-            self.expect_no_suffix(self.span, "a tuple index", suffix);
+        if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) =
+                self.token.kind {
+            self.expect_no_suffix(self.token.span, "a tuple index", suffix);
             self.bump();
-            Ok(Ident::new(name, self.prev_span))
+            Ok(Ident::new(symbol, self.prev_span))
         } else {
             self.parse_ident_common(false)
         }
     }
 
-    /// Parse ident (COLON expr)?
-    fn parse_field(&mut self) -> PResult<'a, Field> {
-        let attrs = self.parse_outer_attributes()?;
-        let lo = self.span;
-
-        // Check if a colon exists one ahead. This means we're parsing a fieldname.
-        let (fieldname, expr, is_shorthand) = if self.look_ahead(1, |t| {
-            t == &token::Colon || t == &token::Eq
-        }) {
-            let fieldname = self.parse_field_name()?;
-
-            // Check for an equals token. This means the source incorrectly attempts to
-            // initialize a field with an eq rather than a colon.
-            if self.token == token::Eq {
-                self.diagnostic()
-                    .struct_span_err(self.span, "expected `:`, found `=`")
-                    .span_suggestion(
-                        fieldname.span.shrink_to_hi().to(self.span),
-                        "replace equals symbol with a colon",
-                        ":".to_string(),
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
-            }
-            self.bump(); // `:`
-            (fieldname, self.parse_expr()?, false)
-        } else {
-            let fieldname = self.parse_ident_common(false)?;
-
-            // Mimic `x: x` for the `x` field shorthand.
-            let path = ast::Path::from_ident(fieldname);
-            let expr = self.mk_expr(fieldname.span, ExprKind::Path(None, path), ThinVec::new());
-            (fieldname, expr, true)
-        };
-        Ok(ast::Field {
-            ident: fieldname,
-            span: lo.to(expr.span),
-            expr,
-            is_shorthand,
-            attrs: attrs.into(),
-        })
-    }
-
-    crate fn mk_expr(&self, span: Span, node: ExprKind, attrs: ThinVec<Attribute>) -> P<Expr> {
-        P(Expr { node, span, attrs, id: ast::DUMMY_NODE_ID })
-    }
-
-    fn mk_unary(&self, unop: ast::UnOp, expr: P<Expr>) -> ast::ExprKind {
-        ExprKind::Unary(unop, expr)
-    }
-
-    fn mk_binary(&self, binop: ast::BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ast::ExprKind {
-        ExprKind::Binary(binop, lhs, rhs)
-    }
-
-    fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ast::ExprKind {
-        ExprKind::Call(f, args)
-    }
-
-    fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ast::ExprKind {
-        ExprKind::Index(expr, idx)
-    }
-
-    fn mk_range(&self,
-                    start: Option<P<Expr>>,
-                    end: Option<P<Expr>>,
-                    limits: RangeLimits)
-                    -> PResult<'a, ast::ExprKind> {
-        if end.is_none() && limits == RangeLimits::Closed {
-            Err(self.span_fatal_err(self.span, Error::InclusiveRangeWithNoEnd))
-        } else {
-            Ok(ExprKind::Range(start, end, limits))
-        }
-    }
-
-    fn mk_assign_op(&self, binop: ast::BinOp,
-                        lhs: P<Expr>, rhs: P<Expr>) -> ast::ExprKind {
-        ExprKind::AssignOp(binop, lhs, rhs)
-    }
-
     fn expect_delimited_token_tree(&mut self) -> PResult<'a, (MacDelimiter, TokenStream)> {
-        let delim = match self.token {
+        let delim = match self.token.kind {
             token::OpenDelim(delim) => delim,
             _ => {
                 let msg = "expected open delimiter";
                 let mut err = self.fatal(msg);
-                err.span_label(self.span, msg);
+                err.span_label(self.token.span, msg);
                 return Err(err)
             }
         };
@@ -2353,461 +1088,6 @@ impl<'a> Parser<'a> {
         Ok((delim, tts.into()))
     }
 
-    /// At the bottom (top?) of the precedence hierarchy,
-    /// Parses things like parenthesized exprs, macros, `return`, etc.
-    ///
-    /// N.B., this does not parse outer attributes, and is private because it only works
-    /// correctly if called from `parse_dot_or_call_expr()`.
-    fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
-        maybe_recover_from_interpolated_ty_qpath!(self, true);
-        maybe_whole_expr!(self);
-
-        // Outer attributes are already parsed and will be
-        // added to the return value after the fact.
-        //
-        // Therefore, prevent sub-parser from parsing
-        // attributes by giving them a empty "already parsed" list.
-        let mut attrs = ThinVec::new();
-
-        let lo = self.span;
-        let mut hi = self.span;
-
-        let ex: ExprKind;
-
-        // Note: when adding new syntax here, don't forget to adjust Token::can_begin_expr().
-        match self.token {
-            token::OpenDelim(token::Paren) => {
-                self.bump();
-
-                attrs.extend(self.parse_inner_attributes()?);
-
-                // (e) is parenthesized e
-                // (e,) is a tuple with only one field, e
-                let mut es = vec![];
-                let mut trailing_comma = false;
-                let mut recovered = false;
-                while self.token != token::CloseDelim(token::Paren) {
-                    es.push(match self.parse_expr() {
-                        Ok(es) => es,
-                        Err(err) => {
-                            // recover from parse error in tuple list
-                            return Ok(self.recover_seq_parse_error(token::Paren, lo, Err(err)));
-                        }
-                    });
-                    recovered = self.expect_one_of(
-                        &[],
-                        &[token::Comma, token::CloseDelim(token::Paren)],
-                    )?;
-                    if self.eat(&token::Comma) {
-                        trailing_comma = true;
-                    } else {
-                        trailing_comma = false;
-                        break;
-                    }
-                }
-                if !recovered {
-                    self.bump();
-                }
-
-                hi = self.prev_span;
-                ex = if es.len() == 1 && !trailing_comma {
-                    ExprKind::Paren(es.into_iter().nth(0).unwrap())
-                } else {
-                    ExprKind::Tup(es)
-                };
-            }
-            token::OpenDelim(token::Brace) => {
-                return self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs);
-            }
-            token::BinOp(token::Or) | token::OrOr => {
-                return self.parse_lambda_expr(attrs);
-            }
-            token::OpenDelim(token::Bracket) => {
-                self.bump();
-
-                attrs.extend(self.parse_inner_attributes()?);
-
-                if self.eat(&token::CloseDelim(token::Bracket)) {
-                    // Empty vector.
-                    ex = ExprKind::Array(Vec::new());
-                } else {
-                    // Nonempty vector.
-                    let first_expr = self.parse_expr()?;
-                    if self.eat(&token::Semi) {
-                        // Repeating array syntax: [ 0; 512 ]
-                        let count = AnonConst {
-                            id: ast::DUMMY_NODE_ID,
-                            value: self.parse_expr()?,
-                        };
-                        self.expect(&token::CloseDelim(token::Bracket))?;
-                        ex = ExprKind::Repeat(first_expr, count);
-                    } else if self.eat(&token::Comma) {
-                        // Vector with two or more elements.
-                        let remaining_exprs = self.parse_seq_to_end(
-                            &token::CloseDelim(token::Bracket),
-                            SeqSep::trailing_allowed(token::Comma),
-                            |p| Ok(p.parse_expr()?)
-                        )?;
-                        let mut exprs = vec![first_expr];
-                        exprs.extend(remaining_exprs);
-                        ex = ExprKind::Array(exprs);
-                    } else {
-                        // Vector with one element.
-                        self.expect(&token::CloseDelim(token::Bracket))?;
-                        ex = ExprKind::Array(vec![first_expr]);
-                    }
-                }
-                hi = self.prev_span;
-            }
-            _ => {
-                if self.eat_lt() {
-                    let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
-                    hi = path.span;
-                    return Ok(self.mk_expr(lo.to(hi), ExprKind::Path(Some(qself), path), attrs));
-                }
-                if self.span.rust_2018() && self.check_keyword(keywords::Async) {
-                    return if self.is_async_block() { // check for `async {` and `async move {`
-                        self.parse_async_block(attrs)
-                    } else {
-                        self.parse_lambda_expr(attrs)
-                    };
-                }
-                if self.check_keyword(keywords::Move) || self.check_keyword(keywords::Static) {
-                    return self.parse_lambda_expr(attrs);
-                }
-                if self.eat_keyword(keywords::If) {
-                    return self.parse_if_expr(attrs);
-                }
-                if self.eat_keyword(keywords::For) {
-                    let lo = self.prev_span;
-                    return self.parse_for_expr(None, lo, attrs);
-                }
-                if self.eat_keyword(keywords::While) {
-                    let lo = self.prev_span;
-                    return self.parse_while_expr(None, lo, attrs);
-                }
-                if let Some(label) = self.eat_label() {
-                    let lo = label.ident.span;
-                    self.expect(&token::Colon)?;
-                    if self.eat_keyword(keywords::While) {
-                        return self.parse_while_expr(Some(label), lo, attrs)
-                    }
-                    if self.eat_keyword(keywords::For) {
-                        return self.parse_for_expr(Some(label), lo, attrs)
-                    }
-                    if self.eat_keyword(keywords::Loop) {
-                        return self.parse_loop_expr(Some(label), lo, attrs)
-                    }
-                    if self.token == token::OpenDelim(token::Brace) {
-                        return self.parse_block_expr(Some(label),
-                                                     lo,
-                                                     BlockCheckMode::Default,
-                                                     attrs);
-                    }
-                    let msg = "expected `while`, `for`, `loop` or `{` after a label";
-                    let mut err = self.fatal(msg);
-                    err.span_label(self.span, msg);
-                    return Err(err);
-                }
-                if self.eat_keyword(keywords::Loop) {
-                    let lo = self.prev_span;
-                    return self.parse_loop_expr(None, lo, attrs);
-                }
-                if self.eat_keyword(keywords::Continue) {
-                    let label = self.eat_label();
-                    let ex = ExprKind::Continue(label);
-                    let hi = self.prev_span;
-                    return Ok(self.mk_expr(lo.to(hi), ex, attrs));
-                }
-                if self.eat_keyword(keywords::Match) {
-                    let match_sp = self.prev_span;
-                    return self.parse_match_expr(attrs).map_err(|mut err| {
-                        err.span_label(match_sp, "while parsing this match expression");
-                        err
-                    });
-                }
-                if self.eat_keyword(keywords::Unsafe) {
-                    return self.parse_block_expr(
-                        None,
-                        lo,
-                        BlockCheckMode::Unsafe(ast::UserProvided),
-                        attrs);
-                }
-                if self.is_do_catch_block() {
-                    let mut db = self.fatal("found removed `do catch` syntax");
-                    db.help("Following RFC #2388, the new non-placeholder syntax is `try`");
-                    return Err(db);
-                }
-                if self.is_try_block() {
-                    let lo = self.span;
-                    assert!(self.eat_keyword(keywords::Try));
-                    return self.parse_try_block(lo, attrs);
-                }
-                if self.eat_keyword(keywords::Return) {
-                    if self.token.can_begin_expr() {
-                        let e = self.parse_expr()?;
-                        hi = e.span;
-                        ex = ExprKind::Ret(Some(e));
-                    } else {
-                        ex = ExprKind::Ret(None);
-                    }
-                } else if self.eat_keyword(keywords::Break) {
-                    let label = self.eat_label();
-                    let e = if self.token.can_begin_expr()
-                               && !(self.token == token::OpenDelim(token::Brace)
-                                    && self.restrictions.contains(
-                                           Restrictions::NO_STRUCT_LITERAL)) {
-                        Some(self.parse_expr()?)
-                    } else {
-                        None
-                    };
-                    ex = ExprKind::Break(label, e);
-                    hi = self.prev_span;
-                } else if self.eat_keyword(keywords::Yield) {
-                    if self.token.can_begin_expr() {
-                        let e = self.parse_expr()?;
-                        hi = e.span;
-                        ex = ExprKind::Yield(Some(e));
-                    } else {
-                        ex = ExprKind::Yield(None);
-                    }
-                } else if self.token.is_keyword(keywords::Let) {
-                    // Catch this syntax error here, instead of in `parse_ident`, so
-                    // that we can explicitly mention that let is not to be used as an expression
-                    let mut db = self.fatal("expected expression, found statement (`let`)");
-                    db.span_label(self.span, "expected expression");
-                    db.note("variable declaration using `let` is a statement");
-                    return Err(db);
-                } else if self.span.rust_2018() && self.eat_keyword(keywords::Await) {
-                    let (await_hi, e_kind) = self.parse_await_macro_or_alt(lo, self.prev_span)?;
-                    hi = await_hi;
-                    ex = e_kind;
-                } else if self.token.is_path_start() {
-                    let path = self.parse_path(PathStyle::Expr)?;
-
-                    // `!`, as an operator, is prefix, so we know this isn't that
-                    if self.eat(&token::Not) {
-                        // MACRO INVOCATION expression
-                        let (delim, tts) = self.expect_delimited_token_tree()?;
-                        hi = self.prev_span;
-                        ex = ExprKind::Mac(respan(lo.to(hi), Mac_ { path, tts, delim }));
-                    } else if self.check(&token::OpenDelim(token::Brace)) {
-                        if let Some(expr) = self.maybe_parse_struct_expr(lo, &path, &attrs) {
-                            return expr;
-                        } else {
-                            hi = path.span;
-                            ex = ExprKind::Path(None, path);
-                        }
-                    } else {
-                        hi = path.span;
-                        ex = ExprKind::Path(None, path);
-                    }
-                } else {
-                    if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
-                        // Don't complain about bare semicolons after unclosed braces
-                        // recovery in order to keep the error count down. Fixing the
-                        // delimiters will possibly also fix the bare semicolon found in
-                        // expression context. For example, silence the following error:
-                        // ```
-                        // error: expected expression, found `;`
-                        //  --> file.rs:2:13
-                        //   |
-                        // 2 |     foo(bar(;
-                        //   |             ^ expected expression
-                        // ```
-                        self.bump();
-                        return Ok(self.mk_expr(self.span, ExprKind::Err, ThinVec::new()));
-                    }
-                    match self.parse_literal_maybe_minus() {
-                        Ok(expr) => {
-                            hi = expr.span;
-                            ex = expr.node.clone();
-                        }
-                        Err(mut err) => {
-                            self.cancel(&mut err);
-                            let msg = format!("expected expression, found {}",
-                                              self.this_token_descr());
-                            let mut err = self.fatal(&msg);
-                            let sp = self.sess.source_map().start_point(self.span);
-                            if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow()
-                                .get(&sp)
-                            {
-                                self.sess.expr_parentheses_needed(&mut err, *sp, None);
-                            }
-                            err.span_label(self.span, "expected expression");
-                            return Err(err);
-                        }
-                    }
-                }
-            }
-        }
-
-        let expr = self.mk_expr(lo.to(hi), ex, attrs);
-        self.maybe_recover_from_bad_qpath(expr, true)
-    }
-
-    /// Parse `await!(<expr>)` calls, or alternatively recover from incorrect but reasonable
-    /// alternative syntaxes `await <expr>`, `await? <expr>`, `await(<expr>)` and
-    /// `await { <expr> }`.
-    fn parse_await_macro_or_alt(
-        &mut self,
-        lo: Span,
-        await_sp: Span,
-    ) -> PResult<'a, (Span, ExprKind)> {
-        if self.token == token::Not {
-            // Handle correct `await!(<expr>)`.
-            // FIXME: make this an error when `await!` is no longer supported
-            // https://github.com/rust-lang/rust/issues/60610
-            self.expect(&token::Not)?;
-            self.expect(&token::OpenDelim(token::Paren))?;
-            let expr = self.parse_expr().map_err(|mut err| {
-                err.span_label(await_sp, "while parsing this await macro call");
-                err
-            })?;
-            self.expect(&token::CloseDelim(token::Paren))?;
-            Ok((self.prev_span, ExprKind::Await(ast::AwaitOrigin::MacroLike, expr)))
-        } else { // Handle `await <expr>`.
-            self.parse_incorrect_await_syntax(lo, await_sp)
-        }
-    }
-
-    fn maybe_parse_struct_expr(
-        &mut self,
-        lo: Span,
-        path: &ast::Path,
-        attrs: &ThinVec<Attribute>,
-    ) -> Option<PResult<'a, P<Expr>>> {
-        let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
-        let certainly_not_a_block = || self.look_ahead(1, |t| t.is_ident()) && (
-            // `{ ident, ` cannot start a block
-            self.look_ahead(2, |t| t == &token::Comma) ||
-            self.look_ahead(2, |t| t == &token::Colon) && (
-                // `{ ident: token, ` cannot start a block
-                self.look_ahead(4, |t| t == &token::Comma) ||
-                // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`
-                self.look_ahead(3, |t| !t.can_begin_type())
-            )
-        );
-
-        if struct_allowed || certainly_not_a_block() {
-            // This is a struct literal, but we don't can't accept them here
-            let expr = self.parse_struct_expr(lo, path.clone(), attrs.clone());
-            if let (Ok(expr), false) = (&expr, struct_allowed) {
-                let mut err = self.diagnostic().struct_span_err(
-                    expr.span,
-                    "struct literals are not allowed here",
-                );
-                err.multipart_suggestion(
-                    "surround the struct literal with parentheses",
-                    vec![
-                        (lo.shrink_to_lo(), "(".to_string()),
-                        (expr.span.shrink_to_hi(), ")".to_string()),
-                    ],
-                    Applicability::MachineApplicable,
-                );
-                err.emit();
-            }
-            return Some(expr);
-        }
-        None
-    }
-
-    fn parse_struct_expr(&mut self, lo: Span, pth: ast::Path, mut attrs: ThinVec<Attribute>)
-                         -> PResult<'a, P<Expr>> {
-        let struct_sp = lo.to(self.prev_span);
-        self.bump();
-        let mut fields = Vec::new();
-        let mut base = None;
-
-        attrs.extend(self.parse_inner_attributes()?);
-
-        while self.token != token::CloseDelim(token::Brace) {
-            if self.eat(&token::DotDot) {
-                let exp_span = self.prev_span;
-                match self.parse_expr() {
-                    Ok(e) => {
-                        base = Some(e);
-                    }
-                    Err(mut e) => {
-                        e.emit();
-                        self.recover_stmt();
-                    }
-                }
-                if self.token == token::Comma {
-                    let mut err = self.sess.span_diagnostic.mut_span_err(
-                        exp_span.to(self.prev_span),
-                        "cannot use a comma after the base struct",
-                    );
-                    err.span_suggestion_short(
-                        self.span,
-                        "remove this comma",
-                        String::new(),
-                        Applicability::MachineApplicable
-                    );
-                    err.note("the base struct must always be the last field");
-                    err.emit();
-                    self.recover_stmt();
-                }
-                break;
-            }
-
-            let mut recovery_field = None;
-            if let token::Ident(ident, _) = self.token {
-                if !self.token.is_reserved_ident() && self.look_ahead(1, |t| *t == token::Colon) {
-                    // Use in case of error after field-looking code: `S { foo: () with a }`
-                    let mut ident = ident.clone();
-                    ident.span = self.span;
-                    recovery_field = Some(ast::Field {
-                        ident,
-                        span: self.span,
-                        expr: self.mk_expr(self.span, ExprKind::Err, ThinVec::new()),
-                        is_shorthand: false,
-                        attrs: ThinVec::new(),
-                    });
-                }
-            }
-            let mut parsed_field = None;
-            match self.parse_field() {
-                Ok(f) => parsed_field = Some(f),
-                Err(mut e) => {
-                    e.span_label(struct_sp, "while parsing this struct");
-                    e.emit();
-
-                    // If the next token is a comma, then try to parse
-                    // what comes next as additional fields, rather than
-                    // bailing out until next `}`.
-                    if self.token != token::Comma {
-                        self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
-                        if self.token != token::Comma {
-                            break;
-                        }
-                    }
-                }
-            }
-
-            match self.expect_one_of(&[token::Comma],
-                                     &[token::CloseDelim(token::Brace)]) {
-                Ok(_) => if let Some(f) = parsed_field.or(recovery_field) {
-                    // only include the field if there's no parse error for the field name
-                    fields.push(f);
-                }
-                Err(mut e) => {
-                    if let Some(f) = recovery_field {
-                        fields.push(f);
-                    }
-                    e.span_label(struct_sp, "while parsing this struct");
-                    e.emit();
-                    self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
-                    self.eat(&token::Comma);
-                }
-            }
-        }
-
-        let span = lo.to(self.span);
-        self.expect(&token::CloseDelim(token::Brace))?;
-        return Ok(self.mk_expr(span, ExprKind::Struct(pth, fields, base), attrs));
-    }
-
     fn parse_or_use_outer_attributes(&mut self,
                                      already_parsed_attrs: Option<ThinVec<Attribute>>)
                                      -> PResult<'a, ThinVec<Attribute>> {
@@ -2818,351 +1098,46 @@ impl<'a> Parser<'a> {
         }
     }
 
-    /// Parses a block or unsafe block.
-    crate fn parse_block_expr(
-        &mut self,
-        opt_label: Option<Label>,
-        lo: Span,
-        blk_mode: BlockCheckMode,
-        outer_attrs: ThinVec<Attribute>,
-    ) -> PResult<'a, P<Expr>> {
-        self.expect(&token::OpenDelim(token::Brace))?;
-
-        let mut attrs = outer_attrs;
-        attrs.extend(self.parse_inner_attributes()?);
-
-        let blk = self.parse_block_tail(lo, blk_mode)?;
-        return Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs));
-    }
-
-    /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
-    fn parse_dot_or_call_expr(&mut self,
-                                  already_parsed_attrs: Option<ThinVec<Attribute>>)
-                                  -> PResult<'a, P<Expr>> {
-        let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
-
-        let b = self.parse_bottom_expr();
-        let (span, b) = self.interpolated_or_expr_span(b)?;
-        self.parse_dot_or_call_expr_with(b, span, attrs)
-    }
-
-    fn parse_dot_or_call_expr_with(&mut self,
-                                       e0: P<Expr>,
-                                       lo: Span,
-                                       mut attrs: ThinVec<Attribute>)
-                                       -> PResult<'a, P<Expr>> {
-        // Stitch the list of outer attributes onto the return value.
-        // A little bit ugly, but the best way given the current code
-        // structure
-        self.parse_dot_or_call_expr_with_(e0, lo)
-        .map(|expr|
-            expr.map(|mut expr| {
-                attrs.extend::<Vec<_>>(expr.attrs.into());
-                expr.attrs = attrs;
-                match expr.node {
-                    ExprKind::If(..) | ExprKind::IfLet(..) => {
-                        if !expr.attrs.is_empty() {
-                            // Just point to the first attribute in there...
-                            let span = expr.attrs[0].span;
-
-                            self.span_err(span,
-                                "attributes are not yet allowed on `if` \
-                                expressions");
-                        }
-                    }
-                    _ => {}
-                }
-                expr
-            })
-        )
-    }
-
-    // Assuming we have just parsed `.`, continue parsing into an expression.
-    fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
-        if self.span.rust_2018() && self.eat_keyword(keywords::Await) {
-            let span = lo.to(self.prev_span);
-            let await_expr = self.mk_expr(
-                span,
-                ExprKind::Await(ast::AwaitOrigin::FieldLike, self_arg),
-                ThinVec::new(),
-            );
-            self.recover_from_await_method_call();
-            return Ok(await_expr);
-        }
-        let segment = self.parse_path_segment(PathStyle::Expr)?;
-        self.check_trailing_angle_brackets(&segment, token::OpenDelim(token::Paren));
-
-        Ok(match self.token {
-            token::OpenDelim(token::Paren) => {
-                // Method call `expr.f()`
-                let mut args = self.parse_unspanned_seq(
-                    &token::OpenDelim(token::Paren),
-                    &token::CloseDelim(token::Paren),
-                    SeqSep::trailing_allowed(token::Comma),
-                    |p| Ok(p.parse_expr()?)
-                )?;
-                args.insert(0, self_arg);
-
-                let span = lo.to(self.prev_span);
-                self.mk_expr(span, ExprKind::MethodCall(segment, args), ThinVec::new())
-            }
-            _ => {
-                // Field access `expr.f`
-                if let Some(args) = segment.args {
-                    self.span_err(args.span(),
-                                  "field expressions may not have generic arguments");
-                }
-
-                let span = lo.to(self.prev_span);
-                self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), ThinVec::new())
-            }
-        })
-    }
-
-    /// This function checks if there are trailing angle brackets and produces
-    /// a diagnostic to suggest removing them.
-    ///
-    /// ```ignore (diagnostic)
-    /// let _ = vec![1, 2, 3].into_iter().collect::<Vec<usize>>>>();
-    ///                                                        ^^ help: remove extra angle brackets
-    /// ```
-    fn check_trailing_angle_brackets(&mut self, segment: &PathSegment, end: token::Token) {
-        // This function is intended to be invoked after parsing a path segment where there are two
-        // cases:
-        //
-        // 1. A specific token is expected after the path segment.
-        //    eg. `x.foo(`, `x.foo::<u32>(` (parenthesis - method call),
-        //        `Foo::`, or `Foo::<Bar>::` (mod sep - continued path).
-        // 2. No specific token is expected after the path segment.
-        //    eg. `x.foo` (field access)
-        //
-        // This function is called after parsing `.foo` and before parsing the token `end` (if
-        // present). This includes any angle bracket arguments, such as `.foo::<u32>` or
-        // `Foo::<Bar>`.
-
-        // We only care about trailing angle brackets if we previously parsed angle bracket
-        // arguments. This helps stop us incorrectly suggesting that extra angle brackets be
-        // removed in this case:
-        //
-        // `x.foo >> (3)` (where `x.foo` is a `u32` for example)
-        //
-        // This case is particularly tricky as we won't notice it just looking at the tokens -
-        // it will appear the same (in terms of upcoming tokens) as below (since the `::<u32>` will
-        // have already been parsed):
-        //
-        // `x.foo::<u32>>>(3)`
-        let parsed_angle_bracket_args = segment.args
-            .as_ref()
-            .map(|args| args.is_angle_bracketed())
-            .unwrap_or(false);
-
-        debug!(
-            "check_trailing_angle_brackets: parsed_angle_bracket_args={:?}",
-            parsed_angle_bracket_args,
-        );
-        if !parsed_angle_bracket_args {
-            return;
-        }
-
-        // Keep the span at the start so we can highlight the sequence of `>` characters to be
-        // removed.
-        let lo = self.span;
-
-        // We need to look-ahead to see if we have `>` characters without moving the cursor forward
-        // (since we might have the field access case and the characters we're eating are
-        // actual operators and not trailing characters - ie `x.foo >> 3`).
-        let mut position = 0;
-
-        // We can encounter `>` or `>>` tokens in any order, so we need to keep track of how
-        // many of each (so we can correctly pluralize our error messages) and continue to
-        // advance.
-        let mut number_of_shr = 0;
-        let mut number_of_gt = 0;
-        while self.look_ahead(position, |t| {
-            trace!("check_trailing_angle_brackets: t={:?}", t);
-            if *t == token::BinOp(token::BinOpToken::Shr) {
-                number_of_shr += 1;
-                true
-            } else if *t == token::Gt {
-                number_of_gt += 1;
-                true
-            } else {
-                false
-            }
-        }) {
-            position += 1;
-        }
-
-        // If we didn't find any trailing `>` characters, then we have nothing to error about.
-        debug!(
-            "check_trailing_angle_brackets: number_of_gt={:?} number_of_shr={:?}",
-            number_of_gt, number_of_shr,
-        );
-        if number_of_gt < 1 && number_of_shr < 1 {
-            return;
-        }
-
-        // Finally, double check that we have our end token as otherwise this is the
-        // second case.
-        if self.look_ahead(position, |t| {
-            trace!("check_trailing_angle_brackets: t={:?}", t);
-            *t == end
-        }) {
-            // Eat from where we started until the end token so that parsing can continue
-            // as if we didn't have those extra angle brackets.
-            self.eat_to_tokens(&[&end]);
-            let span = lo.until(self.span);
-
-            let plural = number_of_gt > 1 || number_of_shr >= 1;
-            self.diagnostic()
-                .struct_span_err(
-                    span,
-                    &format!("unmatched angle bracket{}", if plural { "s" } else { "" }),
-                )
-                .span_suggestion(
-                    span,
-                    &format!("remove extra angle bracket{}", if plural { "s" } else { "" }),
-                    String::new(),
-                    Applicability::MachineApplicable,
-                )
-                .emit();
-        }
-    }
-
-    fn parse_dot_or_call_expr_with_(&mut self, e0: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
-        let mut e = e0;
-        let mut hi;
-        loop {
-            // expr?
-            while self.eat(&token::Question) {
-                let hi = self.prev_span;
-                e = self.mk_expr(lo.to(hi), ExprKind::Try(e), ThinVec::new());
-            }
-
-            // expr.f
-            if self.eat(&token::Dot) {
-                match self.token {
-                    token::Ident(..) => {
-                        e = self.parse_dot_suffix(e, lo)?;
-                    }
-                    token::Literal(token::Integer(name), suffix) => {
-                        let span = self.span;
-                        self.bump();
-                        let field = ExprKind::Field(e, Ident::new(name, span));
-                        e = self.mk_expr(lo.to(span), field, ThinVec::new());
-
-                        self.expect_no_suffix(span, "a tuple index", suffix);
-                    }
-                    token::Literal(token::Float(n), _suf) => {
-                      self.bump();
-                      let fstr = n.as_str();
-                      let mut err = self.diagnostic()
-                          .struct_span_err(self.prev_span, &format!("unexpected token: `{}`", n));
-                      err.span_label(self.prev_span, "unexpected token");
-                      if fstr.chars().all(|x| "0123456789.".contains(x)) {
-                          let float = match fstr.parse::<f64>().ok() {
-                              Some(f) => f,
-                              None => continue,
-                          };
-                          let sugg = pprust::to_string(|s| {
-                              use crate::print::pprust::PrintState;
-                              s.popen()?;
-                              s.print_expr(&e)?;
-                              s.s.word( ".")?;
-                              s.print_usize(float.trunc() as usize)?;
-                              s.pclose()?;
-                              s.s.word(".")?;
-                              s.s.word(fstr.splitn(2, ".").last().unwrap().to_string())
-                          });
-                          err.span_suggestion(
-                              lo.to(self.prev_span),
-                              "try parenthesizing the first index",
-                              sugg,
-                              Applicability::MachineApplicable
-                          );
-                      }
-                      return Err(err);
-
-                    }
-                    _ => {
-                        // FIXME Could factor this out into non_fatal_unexpected or something.
-                        let actual = self.this_token_to_string();
-                        self.span_err(self.span, &format!("unexpected token: `{}`", actual));
-                    }
-                }
-                continue;
-            }
-            if self.expr_is_complete(&e) { break; }
-            match self.token {
-                // expr(...)
-                token::OpenDelim(token::Paren) => {
-                    let seq = self.parse_unspanned_seq(
-                        &token::OpenDelim(token::Paren),
-                        &token::CloseDelim(token::Paren),
-                        SeqSep::trailing_allowed(token::Comma),
-                        |p| Ok(p.parse_expr()?)
-                    ).map(|es| {
-                        let nd = self.mk_call(e, es);
-                        let hi = self.prev_span;
-                        self.mk_expr(lo.to(hi), nd, ThinVec::new())
-                    });
-                    e = self.recover_seq_parse_error(token::Paren, lo, seq);
-                }
-
-                // expr[...]
-                // Could be either an index expression or a slicing expression.
-                token::OpenDelim(token::Bracket) => {
-                    self.bump();
-                    let ix = self.parse_expr()?;
-                    hi = self.span;
-                    self.expect(&token::CloseDelim(token::Bracket))?;
-                    let index = self.mk_index(e, ix);
-                    e = self.mk_expr(lo.to(hi), index, ThinVec::new())
-                }
-                _ => return Ok(e)
-            }
-        }
-        return Ok(e);
-    }
-
     crate fn process_potential_macro_variable(&mut self) {
-        let (token, span) = match self.token {
-            token::Dollar if self.span.ctxt() != syntax_pos::hygiene::SyntaxContext::empty() &&
+        self.token = match self.token.kind {
+            token::Dollar if self.token.span.from_expansion() &&
                              self.look_ahead(1, |t| t.is_ident()) => {
                 self.bump();
-                let name = match self.token {
-                    token::Ident(ident, _) => ident,
+                let name = match self.token.kind {
+                    token::Ident(name, _) => name,
                     _ => unreachable!()
                 };
-                let mut err = self.fatal(&format!("unknown macro variable `{}`", name));
-                err.span_label(self.span, "unknown macro variable");
-                err.emit();
+                let span = self.prev_span.to(self.token.span);
+                self.diagnostic()
+                    .struct_span_fatal(span, &format!("unknown macro variable `{}`", name))
+                    .span_label(span, "unknown macro variable")
+                    .emit();
                 self.bump();
                 return
             }
             token::Interpolated(ref nt) => {
-                self.meta_var_span = Some(self.span);
+                self.meta_var_span = Some(self.token.span);
                 // Interpolated identifier and lifetime tokens are replaced with usual identifier
                 // and lifetime tokens, so the former are never encountered during normal parsing.
                 match **nt {
-                    token::NtIdent(ident, is_raw) => (token::Ident(ident, is_raw), ident.span),
-                    token::NtLifetime(ident) => (token::Lifetime(ident), ident.span),
+                    token::NtIdent(ident, is_raw) =>
+                        Token::new(token::Ident(ident.name, is_raw), ident.span),
+                    token::NtLifetime(ident) =>
+                        Token::new(token::Lifetime(ident.name), ident.span),
                     _ => return,
                 }
             }
             _ => return,
         };
-        self.token = token;
-        self.span = span;
     }
 
     /// Parses a single token tree from the input.
     crate fn parse_token_tree(&mut self) -> TokenTree {
-        match self.token {
+        match self.token.kind {
             token::OpenDelim(..) => {
                 let frame = mem::replace(&mut self.token_cursor.frame,
                                          self.token_cursor.stack.pop().unwrap());
-                self.span = frame.span.entire();
+                self.token.span = frame.span.entire();
                 self.bump();
                 TokenTree::Delimited(
                     frame.span,
@@ -3172,15 +1147,14 @@ impl<'a> Parser<'a> {
             },
             token::CloseDelim(_) | token::Eof => unreachable!(),
             _ => {
-                let (token, span) = (mem::replace(&mut self.token, token::Whitespace), self.span);
+                let token = self.token.take();
                 self.bump();
-                TokenTree::Token(span, token)
+                TokenTree::Token(token)
             }
         }
     }
 
-    // parse a stream of tokens into a list of TokenTree's,
-    // up to EOF.
+    /// Parses a stream of tokens into a list of `TokenTree`s, up to EOF.
     pub fn parse_all_token_trees(&mut self) -> PResult<'a, Vec<TokenTree>> {
         let mut tts = Vec::new();
         while self.token != token::Eof {
@@ -3192,7 +1166,7 @@ impl<'a> Parser<'a> {
     pub fn parse_tokens(&mut self) -> TokenStream {
         let mut result = Vec::new();
         loop {
-            match self.token {
+            match self.token.kind {
                 token::Eof | token::CloseDelim(..) => break,
                 _ => result.push(self.parse_token_tree().into()),
             }
@@ -3200,823 +1174,6 @@ impl<'a> Parser<'a> {
         TokenStream::new(result)
     }
 
-    /// Parse a prefix-unary-operator expr
-    fn parse_prefix_expr(&mut self,
-                             already_parsed_attrs: Option<ThinVec<Attribute>>)
-                             -> PResult<'a, P<Expr>> {
-        let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
-        let lo = self.span;
-        // Note: when adding new unary operators, don't forget to adjust Token::can_begin_expr()
-        let (hi, ex) = match self.token {
-            token::Not => {
-                self.bump();
-                let e = self.parse_prefix_expr(None);
-                let (span, e) = self.interpolated_or_expr_span(e)?;
-                (lo.to(span), self.mk_unary(UnOp::Not, e))
-            }
-            // Suggest `!` for bitwise negation when encountering a `~`
-            token::Tilde => {
-                self.bump();
-                let e = self.parse_prefix_expr(None);
-                let (span, e) = self.interpolated_or_expr_span(e)?;
-                let span_of_tilde = lo;
-                let mut err = self.diagnostic()
-                    .struct_span_err(span_of_tilde, "`~` cannot be used as a unary operator");
-                err.span_suggestion_short(
-                    span_of_tilde,
-                    "use `!` to perform bitwise negation",
-                    "!".to_owned(),
-                    Applicability::MachineApplicable
-                );
-                err.emit();
-                (lo.to(span), self.mk_unary(UnOp::Not, e))
-            }
-            token::BinOp(token::Minus) => {
-                self.bump();
-                let e = self.parse_prefix_expr(None);
-                let (span, e) = self.interpolated_or_expr_span(e)?;
-                (lo.to(span), self.mk_unary(UnOp::Neg, e))
-            }
-            token::BinOp(token::Star) => {
-                self.bump();
-                let e = self.parse_prefix_expr(None);
-                let (span, e) = self.interpolated_or_expr_span(e)?;
-                (lo.to(span), self.mk_unary(UnOp::Deref, e))
-            }
-            token::BinOp(token::And) | token::AndAnd => {
-                self.expect_and()?;
-                let m = self.parse_mutability();
-                let e = self.parse_prefix_expr(None);
-                let (span, e) = self.interpolated_or_expr_span(e)?;
-                (lo.to(span), ExprKind::AddrOf(m, e))
-            }
-            token::Ident(..) if self.token.is_keyword(keywords::In) => {
-                self.bump();
-                let place = self.parse_expr_res(
-                    Restrictions::NO_STRUCT_LITERAL,
-                    None,
-                )?;
-                let blk = self.parse_block()?;
-                let span = blk.span;
-                let blk_expr = self.mk_expr(span, ExprKind::Block(blk, None), ThinVec::new());
-                (lo.to(span), ExprKind::ObsoleteInPlace(place, blk_expr))
-            }
-            token::Ident(..) if self.token.is_keyword(keywords::Box) => {
-                self.bump();
-                let e = self.parse_prefix_expr(None);
-                let (span, e) = self.interpolated_or_expr_span(e)?;
-                (lo.to(span), ExprKind::Box(e))
-            }
-            token::Ident(..) if self.token.is_ident_named("not") => {
-                // `not` is just an ordinary identifier in Rust-the-language,
-                // but as `rustc`-the-compiler, we can issue clever diagnostics
-                // for confused users who really want to say `!`
-                let token_cannot_continue_expr = |t: &token::Token| match *t {
-                    // These tokens can start an expression after `!`, but
-                    // can't continue an expression after an ident
-                    token::Ident(ident, is_raw) => token::ident_can_begin_expr(ident, is_raw),
-                    token::Literal(..) | token::Pound => true,
-                    token::Interpolated(ref nt) => match **nt {
-                        token::NtIdent(..) | token::NtExpr(..) |
-                        token::NtBlock(..) | token::NtPath(..) => true,
-                        _ => false,
-                    },
-                    _ => false
-                };
-                let cannot_continue_expr = self.look_ahead(1, token_cannot_continue_expr);
-                if cannot_continue_expr {
-                    self.bump();
-                    // Emit the error ...
-                    let mut err = self.diagnostic()
-                        .struct_span_err(self.span,
-                                         &format!("unexpected {} after identifier",
-                                                  self.this_token_descr()));
-                    // span the `not` plus trailing whitespace to avoid
-                    // trailing whitespace after the `!` in our suggestion
-                    let to_replace = self.sess.source_map()
-                        .span_until_non_whitespace(lo.to(self.span));
-                    err.span_suggestion_short(
-                        to_replace,
-                        "use `!` to perform logical negation",
-                        "!".to_owned(),
-                        Applicability::MachineApplicable
-                    );
-                    err.emit();
-                    // —and recover! (just as if we were in the block
-                    // for the `token::Not` arm)
-                    let e = self.parse_prefix_expr(None);
-                    let (span, e) = self.interpolated_or_expr_span(e)?;
-                    (lo.to(span), self.mk_unary(UnOp::Not, e))
-                } else {
-                    return self.parse_dot_or_call_expr(Some(attrs));
-                }
-            }
-            _ => { return self.parse_dot_or_call_expr(Some(attrs)); }
-        };
-        return Ok(self.mk_expr(lo.to(hi), ex, attrs));
-    }
-
-    /// Parses an associative expression.
-    ///
-    /// This parses an expression accounting for associativity and precedence of the operators in
-    /// the expression.
-    #[inline]
-    fn parse_assoc_expr(&mut self,
-                            already_parsed_attrs: Option<ThinVec<Attribute>>)
-                            -> PResult<'a, P<Expr>> {
-        self.parse_assoc_expr_with(0, already_parsed_attrs.into())
-    }
-
-    /// Parses an associative expression with operators of at least `min_prec` precedence.
-    fn parse_assoc_expr_with(&mut self,
-                                 min_prec: usize,
-                                 lhs: LhsExpr)
-                                 -> PResult<'a, P<Expr>> {
-        let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs {
-            expr
-        } else {
-            let attrs = match lhs {
-                LhsExpr::AttributesParsed(attrs) => Some(attrs),
-                _ => None,
-            };
-            if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token) {
-                return self.parse_prefix_range_expr(attrs);
-            } else {
-                self.parse_prefix_expr(attrs)?
-            }
-        };
-
-        match (self.expr_is_complete(&lhs), AssocOp::from_token(&self.token)) {
-            (true, None) => {
-                // Semi-statement forms are odd. See https://github.com/rust-lang/rust/issues/29071
-                return Ok(lhs);
-            }
-            (false, _) => {} // continue parsing the expression
-            // An exhaustive check is done in the following block, but these are checked first
-            // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
-            // want to keep their span info to improve diagnostics in these cases in a later stage.
-            (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
-            (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
-            (true, Some(AssocOp::Add)) => { // `{ 42 } + 42
-                // These cases are ambiguous and can't be identified in the parser alone
-                let sp = self.sess.source_map().start_point(self.span);
-                self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
-                return Ok(lhs);
-            }
-            (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => {
-                return Ok(lhs);
-            }
-            (true, Some(_)) => {
-                // We've found an expression that would be parsed as a statement, but the next
-                // token implies this should be parsed as an expression.
-                // For example: `if let Some(x) = x { x } else { 0 } / 2`
-                let mut err = self.sess.span_diagnostic.struct_span_err(self.span, &format!(
-                    "expected expression, found `{}`",
-                    pprust::token_to_string(&self.token),
-                ));
-                err.span_label(self.span, "expected expression");
-                self.sess.expr_parentheses_needed(
-                    &mut err,
-                    lhs.span,
-                    Some(pprust::expr_to_string(&lhs),
-                ));
-                err.emit();
-            }
-        }
-        self.expected_tokens.push(TokenType::Operator);
-        while let Some(op) = AssocOp::from_token(&self.token) {
-
-            // Adjust the span for interpolated LHS to point to the `$lhs` token and not to what
-            // it refers to. Interpolated identifiers are unwrapped early and never show up here
-            // as `PrevTokenKind::Interpolated` so if LHS is a single identifier we always process
-            // it as "interpolated", it doesn't change the answer for non-interpolated idents.
-            let lhs_span = match (self.prev_token_kind, &lhs.node) {
-                (PrevTokenKind::Interpolated, _) => self.prev_span,
-                (PrevTokenKind::Ident, &ExprKind::Path(None, ref path))
-                    if path.segments.len() == 1 => self.prev_span,
-                _ => lhs.span,
-            };
-
-            let cur_op_span = self.span;
-            let restrictions = if op.is_assign_like() {
-                self.restrictions & Restrictions::NO_STRUCT_LITERAL
-            } else {
-                self.restrictions
-            };
-            let prec = op.precedence();
-            if prec < min_prec {
-                break;
-            }
-            // Check for deprecated `...` syntax
-            if self.token == token::DotDotDot && op == AssocOp::DotDotEq {
-                self.err_dotdotdot_syntax(self.span);
-            }
-
-            self.bump();
-            if op.is_comparison() {
-                self.check_no_chained_comparison(&lhs, &op);
-            }
-            // Special cases:
-            if op == AssocOp::As {
-                lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
-                continue
-            } else if op == AssocOp::Colon {
-                let maybe_path = self.could_ascription_be_path(&lhs.node);
-                let next_sp = self.span;
-
-                lhs = match self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type) {
-                    Ok(lhs) => lhs,
-                    Err(mut err) => {
-                        self.bad_type_ascription(
-                            &mut err,
-                            lhs_span,
-                            cur_op_span,
-                            next_sp,
-                            maybe_path,
-                        );
-                        return Err(err);
-                    }
-                };
-                continue
-            } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
-                // If we didn’t have to handle `x..`/`x..=`, it would be pretty easy to
-                // generalise it to the Fixity::None code.
-                //
-                // We have 2 alternatives here: `x..y`/`x..=y` and `x..`/`x..=` The other
-                // two variants are handled with `parse_prefix_range_expr` call above.
-                let rhs = if self.is_at_start_of_range_notation_rhs() {
-                    Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
-                } else {
-                    None
-                };
-                let (lhs_span, rhs_span) = (lhs.span, if let Some(ref x) = rhs {
-                    x.span
-                } else {
-                    cur_op_span
-                });
-                let limits = if op == AssocOp::DotDot {
-                    RangeLimits::HalfOpen
-                } else {
-                    RangeLimits::Closed
-                };
-
-                let r = self.mk_range(Some(lhs), rhs, limits)?;
-                lhs = self.mk_expr(lhs_span.to(rhs_span), r, ThinVec::new());
-                break
-            }
-
-            let fixity = op.fixity();
-            let prec_adjustment = match fixity {
-                Fixity::Right => 0,
-                Fixity::Left => 1,
-                // We currently have no non-associative operators that are not handled above by
-                // the special cases. The code is here only for future convenience.
-                Fixity::None => 1,
-            };
-            let rhs = self.with_res(
-                restrictions - Restrictions::STMT_EXPR,
-                |this| this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
-            )?;
-
-            // Make sure that the span of the parent node is larger than the span of lhs and rhs,
-            // including the attributes.
-            let lhs_span = lhs
-                .attrs
-                .iter()
-                .filter(|a| a.style == AttrStyle::Outer)
-                .next()
-                .map_or(lhs_span, |a| a.span);
-            let span = lhs_span.to(rhs.span);
-            lhs = match op {
-                AssocOp::Add | AssocOp::Subtract | AssocOp::Multiply | AssocOp::Divide |
-                AssocOp::Modulus | AssocOp::LAnd | AssocOp::LOr | AssocOp::BitXor |
-                AssocOp::BitAnd | AssocOp::BitOr | AssocOp::ShiftLeft | AssocOp::ShiftRight |
-                AssocOp::Equal | AssocOp::Less | AssocOp::LessEqual | AssocOp::NotEqual |
-                AssocOp::Greater | AssocOp::GreaterEqual => {
-                    let ast_op = op.to_ast_binop().unwrap();
-                    let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
-                    self.mk_expr(span, binary, ThinVec::new())
-                }
-                AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs), ThinVec::new()),
-                AssocOp::ObsoleteInPlace =>
-                    self.mk_expr(span, ExprKind::ObsoleteInPlace(lhs, rhs), ThinVec::new()),
-                AssocOp::AssignOp(k) => {
-                    let aop = match k {
-                        token::Plus =>    BinOpKind::Add,
-                        token::Minus =>   BinOpKind::Sub,
-                        token::Star =>    BinOpKind::Mul,
-                        token::Slash =>   BinOpKind::Div,
-                        token::Percent => BinOpKind::Rem,
-                        token::Caret =>   BinOpKind::BitXor,
-                        token::And =>     BinOpKind::BitAnd,
-                        token::Or =>      BinOpKind::BitOr,
-                        token::Shl =>     BinOpKind::Shl,
-                        token::Shr =>     BinOpKind::Shr,
-                    };
-                    let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
-                    self.mk_expr(span, aopexpr, ThinVec::new())
-                }
-                AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
-                    self.bug("AssocOp should have been handled by special case")
-                }
-            };
-
-            if let Fixity::None = fixity { break }
-        }
-        Ok(lhs)
-    }
-
-    fn parse_assoc_op_cast(&mut self, lhs: P<Expr>, lhs_span: Span,
-                           expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind)
-                           -> PResult<'a, P<Expr>> {
-        let mk_expr = |this: &mut Self, rhs: P<Ty>| {
-            this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs), ThinVec::new())
-        };
-
-        // Save the state of the parser before parsing type normally, in case there is a
-        // LessThan comparison after this cast.
-        let parser_snapshot_before_type = self.clone();
-        match self.parse_ty_no_plus() {
-            Ok(rhs) => {
-                Ok(mk_expr(self, rhs))
-            }
-            Err(mut type_err) => {
-                // Rewind to before attempting to parse the type with generics, to recover
-                // from situations like `x as usize < y` in which we first tried to parse
-                // `usize < y` as a type with generic arguments.
-                let parser_snapshot_after_type = self.clone();
-                mem::replace(self, parser_snapshot_before_type);
-
-                match self.parse_path(PathStyle::Expr) {
-                    Ok(path) => {
-                        let (op_noun, op_verb) = match self.token {
-                            token::Lt => ("comparison", "comparing"),
-                            token::BinOp(token::Shl) => ("shift", "shifting"),
-                            _ => {
-                                // We can end up here even without `<` being the next token, for
-                                // example because `parse_ty_no_plus` returns `Err` on keywords,
-                                // but `parse_path` returns `Ok` on them due to error recovery.
-                                // Return original error and parser state.
-                                mem::replace(self, parser_snapshot_after_type);
-                                return Err(type_err);
-                            }
-                        };
-
-                        // Successfully parsed the type path leaving a `<` yet to parse.
-                        type_err.cancel();
-
-                        // Report non-fatal diagnostics, keep `x as usize` as an expression
-                        // in AST and continue parsing.
-                        let msg = format!("`<` is interpreted as a start of generic \
-                                           arguments for `{}`, not a {}", path, op_noun);
-                        let mut err = self.sess.span_diagnostic.struct_span_err(self.span, &msg);
-                        err.span_label(self.look_ahead_span(1).to(parser_snapshot_after_type.span),
-                                       "interpreted as generic arguments");
-                        err.span_label(self.span, format!("not interpreted as {}", op_noun));
-
-                        let expr = mk_expr(self, P(Ty {
-                            span: path.span,
-                            node: TyKind::Path(None, path),
-                            id: ast::DUMMY_NODE_ID
-                        }));
-
-                        let expr_str = self.sess.source_map().span_to_snippet(expr.span)
-                                                .unwrap_or_else(|_| pprust::expr_to_string(&expr));
-                        err.span_suggestion(
-                            expr.span,
-                            &format!("try {} the cast value", op_verb),
-                            format!("({})", expr_str),
-                            Applicability::MachineApplicable
-                        );
-                        err.emit();
-
-                        Ok(expr)
-                    }
-                    Err(mut path_err) => {
-                        // Couldn't parse as a path, return original error and parser state.
-                        path_err.cancel();
-                        mem::replace(self, parser_snapshot_after_type);
-                        Err(type_err)
-                    }
-                }
-            }
-        }
-    }
-
-    /// Produce an error if comparison operators are chained (RFC #558).
-    /// We only need to check lhs, not rhs, because all comparison ops
-    /// have same precedence and are left-associative
-    fn check_no_chained_comparison(&self, lhs: &Expr, outer_op: &AssocOp) {
-        debug_assert!(outer_op.is_comparison(),
-                      "check_no_chained_comparison: {:?} is not comparison",
-                      outer_op);
-        match lhs.node {
-            ExprKind::Binary(op, _, _) if op.node.is_comparison() => {
-                // respan to include both operators
-                let op_span = op.span.to(self.span);
-                let mut err = self.diagnostic().struct_span_err(op_span,
-                    "chained comparison operators require parentheses");
-                if op.node == BinOpKind::Lt &&
-                    *outer_op == AssocOp::Less ||  // Include `<` to provide this recommendation
-                    *outer_op == AssocOp::Greater  // even in a case like the following:
-                {                                  //     Foo<Bar<Baz<Qux, ()>>>
-                    err.help(
-                        "use `::<...>` instead of `<...>` if you meant to specify type arguments");
-                    err.help("or use `(...)` if you meant to specify fn arguments");
-                }
-                err.emit();
-            }
-            _ => {}
-        }
-    }
-
-    /// Parse prefix-forms of range notation: `..expr`, `..`, `..=expr`
-    fn parse_prefix_range_expr(&mut self,
-                               already_parsed_attrs: Option<ThinVec<Attribute>>)
-                               -> PResult<'a, P<Expr>> {
-        // Check for deprecated `...` syntax
-        if self.token == token::DotDotDot {
-            self.err_dotdotdot_syntax(self.span);
-        }
-
-        debug_assert!([token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token),
-                      "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
-                      self.token);
-        let tok = self.token.clone();
-        let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
-        let lo = self.span;
-        let mut hi = self.span;
-        self.bump();
-        let opt_end = if self.is_at_start_of_range_notation_rhs() {
-            // RHS must be parsed with more associativity than the dots.
-            let next_prec = AssocOp::from_token(&tok).unwrap().precedence() + 1;
-            Some(self.parse_assoc_expr_with(next_prec,
-                                            LhsExpr::NotYetParsed)
-                .map(|x|{
-                    hi = x.span;
-                    x
-                })?)
-         } else {
-            None
-        };
-        let limits = if tok == token::DotDot {
-            RangeLimits::HalfOpen
-        } else {
-            RangeLimits::Closed
-        };
-
-        let r = self.mk_range(None, opt_end, limits)?;
-        Ok(self.mk_expr(lo.to(hi), r, attrs))
-    }
-
-    fn is_at_start_of_range_notation_rhs(&self) -> bool {
-        if self.token.can_begin_expr() {
-            // parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
-            if self.token == token::OpenDelim(token::Brace) {
-                return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
-            }
-            true
-        } else {
-            false
-        }
-    }
-
-    /// Parses an `if` or `if let` expression (`if` token already eaten).
-    fn parse_if_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
-        if self.check_keyword(keywords::Let) {
-            return self.parse_if_let_expr(attrs);
-        }
-        let lo = self.prev_span;
-        let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
-
-        // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
-        // verify that the last statement is either an implicit return (no `;`) or an explicit
-        // return. This won't catch blocks with an explicit `return`, but that would be caught by
-        // the dead code lint.
-        if self.eat_keyword(keywords::Else) || !cond.returns() {
-            let sp = self.sess.source_map().next_point(lo);
-            let mut err = self.diagnostic()
-                .struct_span_err(sp, "missing condition for `if` statemement");
-            err.span_label(sp, "expected if condition here");
-            return Err(err)
-        }
-        let not_block = self.token != token::OpenDelim(token::Brace);
-        let thn = self.parse_block().map_err(|mut err| {
-            if not_block {
-                err.span_label(lo, "this `if` statement has a condition, but no block");
-            }
-            err
-        })?;
-        let mut els: Option<P<Expr>> = None;
-        let mut hi = thn.span;
-        if self.eat_keyword(keywords::Else) {
-            let elexpr = self.parse_else_expr()?;
-            hi = elexpr.span;
-            els = Some(elexpr);
-        }
-        Ok(self.mk_expr(lo.to(hi), ExprKind::If(cond, thn, els), attrs))
-    }
-
-    /// Parses an `if let` expression (`if` token already eaten).
-    fn parse_if_let_expr(&mut self, attrs: ThinVec<Attribute>)
-                             -> PResult<'a, P<Expr>> {
-        let lo = self.prev_span;
-        self.expect_keyword(keywords::Let)?;
-        let pats = self.parse_pats()?;
-        self.expect(&token::Eq)?;
-        let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
-        let thn = self.parse_block()?;
-        let (hi, els) = if self.eat_keyword(keywords::Else) {
-            let expr = self.parse_else_expr()?;
-            (expr.span, Some(expr))
-        } else {
-            (thn.span, None)
-        };
-        Ok(self.mk_expr(lo.to(hi), ExprKind::IfLet(pats, expr, thn, els), attrs))
-    }
-
-    /// Parses `move |args| expr`.
-    fn parse_lambda_expr(&mut self,
-                             attrs: ThinVec<Attribute>)
-                             -> PResult<'a, P<Expr>>
-    {
-        let lo = self.span;
-        let movability = if self.eat_keyword(keywords::Static) {
-            Movability::Static
-        } else {
-            Movability::Movable
-        };
-        let asyncness = if self.span.rust_2018() {
-            self.parse_asyncness()
-        } else {
-            IsAsync::NotAsync
-        };
-        let capture_clause = if self.eat_keyword(keywords::Move) {
-            CaptureBy::Value
-        } else {
-            CaptureBy::Ref
-        };
-        let decl = self.parse_fn_block_decl()?;
-        let decl_hi = self.prev_span;
-        let body = match decl.output {
-            FunctionRetTy::Default(_) => {
-                let restrictions = self.restrictions - Restrictions::STMT_EXPR;
-                self.parse_expr_res(restrictions, None)?
-            },
-            _ => {
-                // If an explicit return type is given, require a
-                // block to appear (RFC 968).
-                let body_lo = self.span;
-                self.parse_block_expr(None, body_lo, BlockCheckMode::Default, ThinVec::new())?
-            }
-        };
-
-        Ok(self.mk_expr(
-            lo.to(body.span),
-            ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)),
-            attrs))
-    }
-
-    // `else` token already eaten
-    fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
-        if self.eat_keyword(keywords::If) {
-            return self.parse_if_expr(ThinVec::new());
-        } else {
-            let blk = self.parse_block()?;
-            return Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), ThinVec::new()));
-        }
-    }
-
-    /// Parse a 'for' .. 'in' expression ('for' token already eaten)
-    fn parse_for_expr(&mut self, opt_label: Option<Label>,
-                          span_lo: Span,
-                          mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
-        // Parse: `for <src_pat> in <src_expr> <src_loop_block>`
-
-        let pat = self.parse_top_level_pat()?;
-        if !self.eat_keyword(keywords::In) {
-            let in_span = self.prev_span.between(self.span);
-            let mut err = self.sess.span_diagnostic
-                .struct_span_err(in_span, "missing `in` in `for` loop");
-            err.span_suggestion_short(
-                in_span, "try adding `in` here", " in ".into(),
-                // has been misleading, at least in the past (closed Issue #48492)
-                Applicability::MaybeIncorrect
-            );
-            err.emit();
-        }
-        let in_span = self.prev_span;
-        if self.eat_keyword(keywords::In) {
-            // a common typo: `for _ in in bar {}`
-            let mut err = self.sess.span_diagnostic.struct_span_err(
-                self.prev_span,
-                "expected iterable, found keyword `in`",
-            );
-            err.span_suggestion_short(
-                in_span.until(self.prev_span),
-                "remove the duplicated `in`",
-                String::new(),
-                Applicability::MachineApplicable,
-            );
-            err.note("if you meant to use emplacement syntax, it is obsolete (for now, anyway)");
-            err.note("for more information on the status of emplacement syntax, see <\
-                      https://github.com/rust-lang/rust/issues/27779#issuecomment-378416911>");
-            err.emit();
-        }
-        let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
-        let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
-        attrs.extend(iattrs);
-
-        let hi = self.prev_span;
-        Ok(self.mk_expr(span_lo.to(hi), ExprKind::ForLoop(pat, expr, loop_block, opt_label), attrs))
-    }
-
-    /// Parses a `while` or `while let` expression (`while` token already eaten).
-    fn parse_while_expr(&mut self, opt_label: Option<Label>,
-                            span_lo: Span,
-                            mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
-        if self.token.is_keyword(keywords::Let) {
-            return self.parse_while_let_expr(opt_label, span_lo, attrs);
-        }
-        let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
-        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
-        attrs.extend(iattrs);
-        let span = span_lo.to(body.span);
-        return Ok(self.mk_expr(span, ExprKind::While(cond, body, opt_label), attrs));
-    }
-
-    /// Parses a `while let` expression (`while` token already eaten).
-    fn parse_while_let_expr(&mut self, opt_label: Option<Label>,
-                                span_lo: Span,
-                                mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
-        self.expect_keyword(keywords::Let)?;
-        let pats = self.parse_pats()?;
-        self.expect(&token::Eq)?;
-        let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
-        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
-        attrs.extend(iattrs);
-        let span = span_lo.to(body.span);
-        return Ok(self.mk_expr(span, ExprKind::WhileLet(pats, expr, body, opt_label), attrs));
-    }
-
-    // parse `loop {...}`, `loop` token already eaten
-    fn parse_loop_expr(&mut self, opt_label: Option<Label>,
-                           span_lo: Span,
-                           mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
-        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
-        attrs.extend(iattrs);
-        let span = span_lo.to(body.span);
-        Ok(self.mk_expr(span, ExprKind::Loop(body, opt_label), attrs))
-    }
-
-    /// Parses an `async move {...}` expression.
-    pub fn parse_async_block(&mut self, mut attrs: ThinVec<Attribute>)
-        -> PResult<'a, P<Expr>>
-    {
-        let span_lo = self.span;
-        self.expect_keyword(keywords::Async)?;
-        let capture_clause = if self.eat_keyword(keywords::Move) {
-            CaptureBy::Value
-        } else {
-            CaptureBy::Ref
-        };
-        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
-        attrs.extend(iattrs);
-        Ok(self.mk_expr(
-            span_lo.to(body.span),
-            ExprKind::Async(capture_clause, ast::DUMMY_NODE_ID, body), attrs))
-    }
-
-    /// Parses a `try {...}` expression (`try` token already eaten).
-    fn parse_try_block(&mut self, span_lo: Span, mut attrs: ThinVec<Attribute>)
-        -> PResult<'a, P<Expr>>
-    {
-        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
-        attrs.extend(iattrs);
-        if self.eat_keyword(keywords::Catch) {
-            let mut error = self.struct_span_err(self.prev_span,
-                                                 "keyword `catch` cannot follow a `try` block");
-            error.help("try using `match` on the result of the `try` block instead");
-            error.emit();
-            Err(error)
-        } else {
-            Ok(self.mk_expr(span_lo.to(body.span), ExprKind::TryBlock(body), attrs))
-        }
-    }
-
-    // `match` token already eaten
-    fn parse_match_expr(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
-        let match_span = self.prev_span;
-        let lo = self.prev_span;
-        let discriminant = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL,
-                                               None)?;
-        if let Err(mut e) = self.expect(&token::OpenDelim(token::Brace)) {
-            if self.token == token::Token::Semi {
-                e.span_suggestion_short(
-                    match_span,
-                    "try removing this `match`",
-                    String::new(),
-                    Applicability::MaybeIncorrect // speculative
-                );
-            }
-            return Err(e)
-        }
-        attrs.extend(self.parse_inner_attributes()?);
-
-        let mut arms: Vec<Arm> = Vec::new();
-        while self.token != token::CloseDelim(token::Brace) {
-            match self.parse_arm() {
-                Ok(arm) => arms.push(arm),
-                Err(mut e) => {
-                    // Recover by skipping to the end of the block.
-                    e.emit();
-                    self.recover_stmt();
-                    let span = lo.to(self.span);
-                    if self.token == token::CloseDelim(token::Brace) {
-                        self.bump();
-                    }
-                    return Ok(self.mk_expr(span, ExprKind::Match(discriminant, arms), attrs));
-                }
-            }
-        }
-        let hi = self.span;
-        self.bump();
-        return Ok(self.mk_expr(lo.to(hi), ExprKind::Match(discriminant, arms), attrs));
-    }
-
-    crate fn parse_arm(&mut self) -> PResult<'a, Arm> {
-        let attrs = self.parse_outer_attributes()?;
-        let pats = self.parse_pats()?;
-        let guard = if self.eat_keyword(keywords::If) {
-            Some(Guard::If(self.parse_expr()?))
-        } else {
-            None
-        };
-        let arrow_span = self.span;
-        self.expect(&token::FatArrow)?;
-        let arm_start_span = self.span;
-
-        let expr = self.parse_expr_res(Restrictions::STMT_EXPR, None)
-            .map_err(|mut err| {
-                err.span_label(arrow_span, "while parsing the `match` arm starting here");
-                err
-            })?;
-
-        let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
-            && self.token != token::CloseDelim(token::Brace);
-
-        if require_comma {
-            let cm = self.sess.source_map();
-            self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)])
-                .map_err(|mut err| {
-                    match (cm.span_to_lines(expr.span), cm.span_to_lines(arm_start_span)) {
-                        (Ok(ref expr_lines), Ok(ref arm_start_lines))
-                        if arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
-                            && expr_lines.lines.len() == 2
-                            && self.token == token::FatArrow => {
-                            // We check whether there's any trailing code in the parse span,
-                            // if there isn't, we very likely have the following:
-                            //
-                            // X |     &Y => "y"
-                            //   |        --    - missing comma
-                            //   |        |
-                            //   |        arrow_span
-                            // X |     &X => "x"
-                            //   |      - ^^ self.span
-                            //   |      |
-                            //   |      parsed until here as `"y" & X`
-                            err.span_suggestion_short(
-                                cm.next_point(arm_start_span),
-                                "missing a comma here to end this `match` arm",
-                                ",".to_owned(),
-                                Applicability::MachineApplicable
-                            );
-                        }
-                        _ => {
-                            err.span_label(arrow_span,
-                                           "while parsing the `match` arm starting here");
-                        }
-                    }
-                    err
-                })?;
-        } else {
-            self.eat(&token::Comma);
-        }
-
-        Ok(ast::Arm {
-            attrs,
-            pats,
-            guard,
-            body: expr,
-        })
-    }
-
-    /// Parses an expression.
-    #[inline]
-    pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
-        self.parse_expr_res(Restrictions::empty(), None)
-    }
-
     /// Evaluates the closure with restrictions in place.
     ///
     /// Afters the closure is evaluated, restrictions are reset.
@@ -4031,1963 +1188,54 @@ impl<'a> Parser<'a> {
 
     }
 
-    /// Parses an expression, subject to the given restrictions.
-    #[inline]
-    fn parse_expr_res(&mut self, r: Restrictions,
-                          already_parsed_attrs: Option<ThinVec<Attribute>>)
-                          -> PResult<'a, P<Expr>> {
-        self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
-    }
-
-    /// Parses the RHS of a local variable declaration (e.g., '= 14;').
-    fn parse_initializer(&mut self, skip_eq: bool) -> PResult<'a, Option<P<Expr>>> {
-        if self.eat(&token::Eq) {
-            Ok(Some(self.parse_expr()?))
-        } else if skip_eq {
-            Ok(Some(self.parse_expr()?))
-        } else {
-            Ok(None)
-        }
-    }
-
-    /// Parses patterns, separated by '|' s.
-    fn parse_pats(&mut self) -> PResult<'a, Vec<P<Pat>>> {
-        // Allow a '|' before the pats (RFC 1925 + RFC 2530)
-        self.eat(&token::BinOp(token::Or));
-
-        let mut pats = Vec::new();
-        loop {
-            pats.push(self.parse_top_level_pat()?);
-
-            if self.token == token::OrOr {
-                let mut err = self.struct_span_err(self.span,
-                                                   "unexpected token `||` after pattern");
-                err.span_suggestion(
-                    self.span,
-                    "use a single `|` to specify multiple patterns",
-                    "|".to_owned(),
-                    Applicability::MachineApplicable
-                );
-                err.emit();
-                self.bump();
-            } else if self.eat(&token::BinOp(token::Or)) {
-                // This is a No-op. Continue the loop to parse the next
-                // pattern.
-            } else {
-                return Ok(pats);
-            }
-        };
-    }
-
-    // Parses a parenthesized list of patterns like
-    // `()`, `(p)`, `(p,)`, `(p, q)`, or `(p, .., q)`. Returns:
-    // - a vector of the patterns that were parsed
-    // - an option indicating the index of the `..` element
-    // - a boolean indicating whether a trailing comma was present.
-    // Trailing commas are significant because (p) and (p,) are different patterns.
-    fn parse_parenthesized_pat_list(&mut self) -> PResult<'a, (Vec<P<Pat>>, Option<usize>, bool)> {
-        self.expect(&token::OpenDelim(token::Paren))?;
-        let result = match self.parse_pat_list() {
-            Ok(result) => result,
-            Err(mut err) => { // recover from parse error in tuple pattern list
-                err.emit();
-                self.consume_block(token::Paren);
-                return Ok((vec![], Some(0), false));
-            }
-        };
-        self.expect(&token::CloseDelim(token::Paren))?;
-        Ok(result)
-    }
-
-    fn parse_pat_list(&mut self) -> PResult<'a, (Vec<P<Pat>>, Option<usize>, bool)> {
-        let mut fields = Vec::new();
-        let mut ddpos = None;
-        let mut prev_dd_sp = None;
-        let mut trailing_comma = false;
-        loop {
-            if self.eat(&token::DotDot) {
-                if ddpos.is_none() {
-                    ddpos = Some(fields.len());
-                    prev_dd_sp = Some(self.prev_span);
-                } else {
-                    // Emit a friendly error, ignore `..` and continue parsing
-                    let mut err = self.struct_span_err(
-                        self.prev_span,
-                        "`..` can only be used once per tuple or tuple struct pattern",
-                    );
-                    err.span_label(self.prev_span, "can only be used once per pattern");
-                    if let Some(sp) = prev_dd_sp {
-                        err.span_label(sp, "previously present here");
-                    }
-                    err.emit();
-                }
-            } else if !self.check(&token::CloseDelim(token::Paren)) {
-                fields.push(self.parse_pat(None)?);
-            } else {
-                break
-            }
-
-            trailing_comma = self.eat(&token::Comma);
-            if !trailing_comma {
-                break
-            }
-        }
-
-        if ddpos == Some(fields.len()) && trailing_comma {
-            // `..` needs to be followed by `)` or `, pat`, `..,)` is disallowed.
-            let msg = "trailing comma is not permitted after `..`";
-            self.struct_span_err(self.prev_span, msg)
-                .span_label(self.prev_span, msg)
-                .emit();
-        }
-
-        Ok((fields, ddpos, trailing_comma))
-    }
-
-    fn parse_pat_vec_elements(
-        &mut self,
-    ) -> PResult<'a, (Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>)> {
-        let mut before = Vec::new();
-        let mut slice = None;
-        let mut after = Vec::new();
-        let mut first = true;
-        let mut before_slice = true;
-
-        while self.token != token::CloseDelim(token::Bracket) {
-            if first {
-                first = false;
-            } else {
-                self.expect(&token::Comma)?;
-
-                if self.token == token::CloseDelim(token::Bracket)
-                        && (before_slice || !after.is_empty()) {
-                    break
-                }
-            }
-
-            if before_slice {
-                if self.eat(&token::DotDot) {
-
-                    if self.check(&token::Comma) ||
-                            self.check(&token::CloseDelim(token::Bracket)) {
-                        slice = Some(P(Pat {
-                            id: ast::DUMMY_NODE_ID,
-                            node: PatKind::Wild,
-                            span: self.prev_span,
-                        }));
-                        before_slice = false;
-                    }
-                    continue
-                }
-            }
-
-            let subpat = self.parse_pat(None)?;
-            if before_slice && self.eat(&token::DotDot) {
-                slice = Some(subpat);
-                before_slice = false;
-            } else if before_slice {
-                before.push(subpat);
-            } else {
-                after.push(subpat);
-            }
-        }
-
-        Ok((before, slice, after))
-    }
-
-    fn parse_pat_field(
-        &mut self,
-        lo: Span,
-        attrs: Vec<Attribute>
-    ) -> PResult<'a, source_map::Spanned<ast::FieldPat>> {
-        // Check if a colon exists one ahead. This means we're parsing a fieldname.
-        let hi;
-        let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
-            // Parsing a pattern of the form "fieldname: pat"
-            let fieldname = self.parse_field_name()?;
-            self.bump();
-            let pat = self.parse_pat(None)?;
-            hi = pat.span;
-            (pat, fieldname, false)
-        } else {
-            // Parsing a pattern of the form "(box) (ref) (mut) fieldname"
-            let is_box = self.eat_keyword(keywords::Box);
-            let boxed_span = self.span;
-            let is_ref = self.eat_keyword(keywords::Ref);
-            let is_mut = self.eat_keyword(keywords::Mut);
-            let fieldname = self.parse_ident()?;
-            hi = self.prev_span;
-
-            let bind_type = match (is_ref, is_mut) {
-                (true, true) => BindingMode::ByRef(Mutability::Mutable),
-                (true, false) => BindingMode::ByRef(Mutability::Immutable),
-                (false, true) => BindingMode::ByValue(Mutability::Mutable),
-                (false, false) => BindingMode::ByValue(Mutability::Immutable),
-            };
-            let fieldpat = P(Pat {
-                id: ast::DUMMY_NODE_ID,
-                node: PatKind::Ident(bind_type, fieldname, None),
-                span: boxed_span.to(hi),
-            });
-
-            let subpat = if is_box {
-                P(Pat {
-                    id: ast::DUMMY_NODE_ID,
-                    node: PatKind::Box(fieldpat),
-                    span: lo.to(hi),
-                })
-            } else {
-                fieldpat
-            };
-            (subpat, fieldname, true)
-        };
-
-        Ok(source_map::Spanned {
-            span: lo.to(hi),
-            node: ast::FieldPat {
-                ident: fieldname,
-                pat: subpat,
-                is_shorthand,
-                attrs: attrs.into(),
-           }
-        })
-    }
-
-    /// Parses the fields of a struct-like pattern.
-    fn parse_pat_fields(&mut self) -> PResult<'a, (Vec<source_map::Spanned<ast::FieldPat>>, bool)> {
-        let mut fields = Vec::new();
-        let mut etc = false;
-        let mut ate_comma = true;
-        let mut delayed_err: Option<DiagnosticBuilder<'a>> = None;
-        let mut etc_span = None;
-
-        while self.token != token::CloseDelim(token::Brace) {
-            let attrs = self.parse_outer_attributes()?;
-            let lo = self.span;
-
-            // check that a comma comes after every field
-            if !ate_comma {
-                let err = self.struct_span_err(self.prev_span, "expected `,`");
-                if let Some(mut delayed) = delayed_err {
-                    delayed.emit();
-                }
-                return Err(err);
-            }
-            ate_comma = false;
-
-            if self.check(&token::DotDot) || self.token == token::DotDotDot {
-                etc = true;
-                let mut etc_sp = self.span;
-
-                if self.token == token::DotDotDot { // Issue #46718
-                    // Accept `...` as if it were `..` to avoid further errors
-                    let mut err = self.struct_span_err(self.span,
-                                                       "expected field pattern, found `...`");
-                    err.span_suggestion(
-                        self.span,
-                        "to omit remaining fields, use one fewer `.`",
-                        "..".to_owned(),
-                        Applicability::MachineApplicable
-                    );
-                    err.emit();
-                }
-                self.bump();  // `..` || `...`
-
-                if self.token == token::CloseDelim(token::Brace) {
-                    etc_span = Some(etc_sp);
-                    break;
-                }
-                let token_str = self.this_token_descr();
-                let mut err = self.fatal(&format!("expected `}}`, found {}", token_str));
-
-                err.span_label(self.span, "expected `}`");
-                let mut comma_sp = None;
-                if self.token == token::Comma { // Issue #49257
-                    etc_sp = etc_sp.to(self.sess.source_map().span_until_non_whitespace(self.span));
-                    err.span_label(etc_sp,
-                                   "`..` must be at the end and cannot have a trailing comma");
-                    comma_sp = Some(self.span);
-                    self.bump();
-                    ate_comma = true;
-                }
-
-                etc_span = Some(etc_sp.until(self.span));
-                if self.token == token::CloseDelim(token::Brace) {
-                    // If the struct looks otherwise well formed, recover and continue.
-                    if let Some(sp) = comma_sp {
-                        err.span_suggestion_short(
-                            sp,
-                            "remove this comma",
-                            String::new(),
-                            Applicability::MachineApplicable,
-                        );
-                    }
-                    err.emit();
-                    break;
-                } else if self.token.is_ident() && ate_comma {
-                    // Accept fields coming after `..,`.
-                    // This way we avoid "pattern missing fields" errors afterwards.
-                    // We delay this error until the end in order to have a span for a
-                    // suggested fix.
-                    if let Some(mut delayed_err) = delayed_err {
-                        delayed_err.emit();
-                        return Err(err);
+    fn parse_fn_args(&mut self, named_args: bool, allow_c_variadic: bool)
+                     -> PResult<'a, (Vec<Arg> , bool)> {
+        let sp = self.token.span;
+        let mut c_variadic = false;
+        let (args, _): (Vec<Option<Arg>>, _) = self.parse_paren_comma_seq(|p| {
+            let do_not_enforce_named_arguments_for_c_variadic =
+                |token: &token::Token| -> bool {
+                    if token == &token::DotDotDot {
+                        false
                     } else {
-                        delayed_err = Some(err);
-                    }
-                } else {
-                    if let Some(mut err) = delayed_err {
-                        err.emit();
-                    }
-                    return Err(err);
-                }
-            }
-
-            fields.push(match self.parse_pat_field(lo, attrs) {
-                Ok(field) => field,
-                Err(err) => {
-                    if let Some(mut delayed_err) = delayed_err {
-                        delayed_err.emit();
+                        named_args
                     }
-                    return Err(err);
-                }
-            });
-            ate_comma = self.eat(&token::Comma);
-        }
-
-        if let Some(mut err) = delayed_err {
-            if let Some(etc_span) = etc_span {
-                err.multipart_suggestion(
-                    "move the `..` to the end of the field list",
-                    vec![
-                        (etc_span, String::new()),
-                        (self.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
-                    ],
-                    Applicability::MachineApplicable,
-                );
-            }
-            err.emit();
-        }
-        return Ok((fields, etc));
-    }
-
-    fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
-        if self.token.is_path_start() {
-            let lo = self.span;
-            let (qself, path) = if self.eat_lt() {
-                // Parse a qualified path
-                let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
-                (Some(qself), path)
-            } else {
-                // Parse an unqualified path
-                (None, self.parse_path(PathStyle::Expr)?)
-            };
-            let hi = self.prev_span;
-            Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path), ThinVec::new()))
-        } else {
-            self.parse_literal_maybe_minus()
-        }
-    }
-
-    // helper function to decide whether to parse as ident binding or to try to do
-    // something more complex like range patterns
-    fn parse_as_ident(&mut self) -> bool {
-        self.look_ahead(1, |t| match *t {
-            token::OpenDelim(token::Paren) | token::OpenDelim(token::Brace) |
-            token::DotDotDot | token::DotDotEq | token::ModSep | token::Not => Some(false),
-            // ensure slice patterns [a, b.., c] and [a, b, c..] don't go into the
-            // range pattern branch
-            token::DotDot => None,
-            _ => Some(true),
-        }).unwrap_or_else(|| self.look_ahead(2, |t| match *t {
-            token::Comma | token::CloseDelim(token::Bracket) => true,
-            _ => false,
-        }))
-    }
-
-    /// A wrapper around `parse_pat` with some special error handling for the
-    /// "top-level" patterns in a match arm, `for` loop, `let`, &c. (in contrast
-    /// to subpatterns within such).
-    fn parse_top_level_pat(&mut self) -> PResult<'a, P<Pat>> {
-        let pat = self.parse_pat(None)?;
-        if self.token == token::Comma {
-            // An unexpected comma after a top-level pattern is a clue that the
-            // user (perhaps more accustomed to some other language) forgot the
-            // parentheses in what should have been a tuple pattern; return a
-            // suggestion-enhanced error here rather than choking on the comma
-            // later.
-            let comma_span = self.span;
-            self.bump();
-            if let Err(mut err) = self.parse_pat_list() {
-                // We didn't expect this to work anyway; we just wanted
-                // to advance to the end of the comma-sequence so we know
-                // the span to suggest parenthesizing
-                err.cancel();
-            }
-            let seq_span = pat.span.to(self.prev_span);
-            let mut err = self.struct_span_err(comma_span,
-                                               "unexpected `,` in pattern");
-            if let Ok(seq_snippet) = self.sess.source_map().span_to_snippet(seq_span) {
-                err.span_suggestion(
-                    seq_span,
-                    "try adding parentheses to match on a tuple..",
-                    format!("({})", seq_snippet),
-                    Applicability::MachineApplicable
-                ).span_suggestion(
-                    seq_span,
-                    "..or a vertical bar to match on multiple alternatives",
-                    format!("{}", seq_snippet.replace(",", " |")),
-                    Applicability::MachineApplicable
-                );
-            }
-            return Err(err);
-        }
-        Ok(pat)
-    }
-
-    /// Parses a pattern.
-    pub fn parse_pat(&mut self, expected: Option<&'static str>) -> PResult<'a, P<Pat>> {
-        self.parse_pat_with_range_pat(true, expected)
-    }
-
-    /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
-    /// allowed).
-    fn parse_pat_with_range_pat(
-        &mut self,
-        allow_range_pat: bool,
-        expected: Option<&'static str>,
-    ) -> PResult<'a, P<Pat>> {
-        maybe_recover_from_interpolated_ty_qpath!(self, true);
-        maybe_whole!(self, NtPat, |x| x);
-
-        let lo = self.span;
-        let pat;
-        match self.token {
-            token::BinOp(token::And) | token::AndAnd => {
-                // Parse &pat / &mut pat
-                self.expect_and()?;
-                let mutbl = self.parse_mutability();
-                if let token::Lifetime(ident) = self.token {
-                    let mut err = self.fatal(&format!("unexpected lifetime `{}` in pattern",
-                                                      ident));
-                    err.span_label(self.span, "unexpected lifetime");
-                    return Err(err);
-                }
-                let subpat = self.parse_pat_with_range_pat(false, expected)?;
-                pat = PatKind::Ref(subpat, mutbl);
-            }
-            token::OpenDelim(token::Paren) => {
-                // Parse (pat,pat,pat,...) as tuple pattern
-                let (fields, ddpos, trailing_comma) = self.parse_parenthesized_pat_list()?;
-                pat = if fields.len() == 1 && ddpos.is_none() && !trailing_comma {
-                    PatKind::Paren(fields.into_iter().nth(0).unwrap())
-                } else {
-                    PatKind::Tuple(fields, ddpos)
-                };
-            }
-            token::OpenDelim(token::Bracket) => {
-                // Parse [pat,pat,...] as slice pattern
-                self.bump();
-                let (before, slice, after) = self.parse_pat_vec_elements()?;
-                self.expect(&token::CloseDelim(token::Bracket))?;
-                pat = PatKind::Slice(before, slice, after);
-            }
-            // At this point, token != &, &&, (, [
-            _ => if self.eat_keyword(keywords::Underscore) {
-                // Parse _
-                pat = PatKind::Wild;
-            } else if self.eat_keyword(keywords::Mut) {
-                // Parse mut ident @ pat / mut ref ident @ pat
-                let mutref_span = self.prev_span.to(self.span);
-                let binding_mode = if self.eat_keyword(keywords::Ref) {
-                    self.diagnostic()
-                        .struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
-                        .span_suggestion(
-                            mutref_span,
-                            "try switching the order",
-                            "ref mut".into(),
-                            Applicability::MachineApplicable
-                        ).emit();
-                    BindingMode::ByRef(Mutability::Mutable)
-                } else {
-                    BindingMode::ByValue(Mutability::Mutable)
-                };
-                pat = self.parse_pat_ident(binding_mode)?;
-            } else if self.eat_keyword(keywords::Ref) {
-                // Parse ref ident @ pat / ref mut ident @ pat
-                let mutbl = self.parse_mutability();
-                pat = self.parse_pat_ident(BindingMode::ByRef(mutbl))?;
-            } else if self.eat_keyword(keywords::Box) {
-                // Parse box pat
-                let subpat = self.parse_pat_with_range_pat(false, None)?;
-                pat = PatKind::Box(subpat);
-            } else if self.token.is_ident() && !self.token.is_reserved_ident() &&
-                      self.parse_as_ident() {
-                // Parse ident @ pat
-                // This can give false positives and parse nullary enums,
-                // they are dealt with later in resolve
-                let binding_mode = BindingMode::ByValue(Mutability::Immutable);
-                pat = self.parse_pat_ident(binding_mode)?;
-            } else if self.token.is_path_start() {
-                // Parse pattern starting with a path
-                let (qself, path) = if self.eat_lt() {
-                    // Parse a qualified path
-                    let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
-                    (Some(qself), path)
-                } else {
-                    // Parse an unqualified path
-                    (None, self.parse_path(PathStyle::Expr)?)
                 };
-                match self.token {
-                    token::Not if qself.is_none() => {
-                        // Parse macro invocation
-                        self.bump();
-                        let (delim, tts) = self.expect_delimited_token_tree()?;
-                        let mac = respan(lo.to(self.prev_span), Mac_ { path, tts, delim });
-                        pat = PatKind::Mac(mac);
-                    }
-                    token::DotDotDot | token::DotDotEq | token::DotDot => {
-                        let end_kind = match self.token {
-                            token::DotDot => RangeEnd::Excluded,
-                            token::DotDotDot => RangeEnd::Included(RangeSyntax::DotDotDot),
-                            token::DotDotEq => RangeEnd::Included(RangeSyntax::DotDotEq),
-                            _ => panic!("can only parse `..`/`...`/`..=` for ranges \
-                                         (checked above)"),
-                        };
-                        let op_span = self.span;
-                        // Parse range
-                        let span = lo.to(self.prev_span);
-                        let begin = self.mk_expr(span, ExprKind::Path(qself, path), ThinVec::new());
-                        self.bump();
-                        let end = self.parse_pat_range_end()?;
-                        let op = Spanned { span: op_span, node: end_kind };
-                        pat = PatKind::Range(begin, end, op);
-                    }
-                    token::OpenDelim(token::Brace) => {
-                        if qself.is_some() {
-                            let msg = "unexpected `{` after qualified path";
-                            let mut err = self.fatal(msg);
-                            err.span_label(self.span, msg);
-                            return Err(err);
-                        }
-                        // Parse struct pattern
-                        self.bump();
-                        let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
-                            e.emit();
-                            self.recover_stmt();
-                            (vec![], true)
-                        });
-                        self.bump();
-                        pat = PatKind::Struct(path, fields, etc);
-                    }
-                    token::OpenDelim(token::Paren) => {
-                        if qself.is_some() {
-                            let msg = "unexpected `(` after qualified path";
-                            let mut err = self.fatal(msg);
-                            err.span_label(self.span, msg);
-                            return Err(err);
-                        }
-                        // Parse tuple struct or enum pattern
-                        let (fields, ddpos, _) = self.parse_parenthesized_pat_list()?;
-                        pat = PatKind::TupleStruct(path, fields, ddpos)
-                    }
-                    _ => pat = PatKind::Path(qself, path),
-                }
-            } else {
-                // Try to parse everything else as literal with optional minus
-                match self.parse_literal_maybe_minus() {
-                    Ok(begin) => {
-                        let op_span = self.span;
-                        if self.check(&token::DotDot) || self.check(&token::DotDotEq) ||
-                                self.check(&token::DotDotDot) {
-                            let end_kind = if self.eat(&token::DotDotDot) {
-                                RangeEnd::Included(RangeSyntax::DotDotDot)
-                            } else if self.eat(&token::DotDotEq) {
-                                RangeEnd::Included(RangeSyntax::DotDotEq)
-                            } else if self.eat(&token::DotDot) {
-                                RangeEnd::Excluded
-                            } else {
-                                panic!("impossible case: we already matched \
-                                        on a range-operator token")
-                            };
-                            let end = self.parse_pat_range_end()?;
-                            let op = Spanned { span: op_span, node: end_kind };
-                            pat = PatKind::Range(begin, end, op);
+            match p.parse_arg_general(
+                false,
+                allow_c_variadic,
+                do_not_enforce_named_arguments_for_c_variadic
+            ) {
+                Ok(arg) => {
+                    if let TyKind::CVarArgs = arg.ty.node {
+                        c_variadic = true;
+                        if p.token != token::CloseDelim(token::Paren) {
+                            let span = p.token.span;
+                            p.span_err(span,
+                                "`...` must be the last argument of a C-variadic function");
+                            Ok(None)
                         } else {
-                            pat = PatKind::Lit(begin);
-                        }
-                    }
-                    Err(mut err) => {
-                        self.cancel(&mut err);
-                        let expected = expected.unwrap_or("pattern");
-                        let msg = format!(
-                            "expected {}, found {}",
-                            expected,
-                            self.this_token_descr(),
-                        );
-                        let mut err = self.fatal(&msg);
-                        err.span_label(self.span, format!("expected {}", expected));
-                        let sp = self.sess.source_map().start_point(self.span);
-                        if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
-                            self.sess.expr_parentheses_needed(&mut err, *sp, None);
-                        }
-                        return Err(err);
-                    }
-                }
-            }
-        }
-
-        let pat = P(Pat { node: pat, span: lo.to(self.prev_span), id: ast::DUMMY_NODE_ID });
-        let pat = self.maybe_recover_from_bad_qpath(pat, true)?;
-
-        if !allow_range_pat {
-            match pat.node {
-                PatKind::Range(
-                    _, _, Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. }
-                ) => {},
-                PatKind::Range(..) => {
-                    let mut err = self.struct_span_err(
-                        pat.span,
-                        "the range pattern here has ambiguous interpretation",
-                    );
-                    err.span_suggestion(
-                        pat.span,
-                        "add parentheses to clarify the precedence",
-                        format!("({})", pprust::pat_to_string(&pat)),
-                        // "ambiguous interpretation" implies that we have to be guessing
-                        Applicability::MaybeIncorrect
-                    );
-                    return Err(err);
-                }
-                _ => {}
-            }
-        }
-
-        Ok(pat)
-    }
-
-    /// Parses `ident` or `ident @ pat`.
-    /// used by the copy foo and ref foo patterns to give a good
-    /// error message when parsing mistakes like `ref foo(a, b)`.
-    fn parse_pat_ident(&mut self,
-                       binding_mode: ast::BindingMode)
-                       -> PResult<'a, PatKind> {
-        let ident = self.parse_ident()?;
-        let sub = if self.eat(&token::At) {
-            Some(self.parse_pat(Some("binding pattern"))?)
-        } else {
-            None
-        };
-
-        // just to be friendly, if they write something like
-        //   ref Some(i)
-        // we end up here with ( as the current token.  This shortly
-        // leads to a parse error.  Note that if there is no explicit
-        // binding mode then we do not end up here, because the lookahead
-        // will direct us over to parse_enum_variant()
-        if self.token == token::OpenDelim(token::Paren) {
-            return Err(self.span_fatal(
-                self.prev_span,
-                "expected identifier, found enum pattern"))
-        }
-
-        Ok(PatKind::Ident(binding_mode, ident, sub))
-    }
-
-    /// Parses a local variable declaration.
-    fn parse_local(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Local>> {
-        let lo = self.prev_span;
-        let pat = self.parse_top_level_pat()?;
-
-        let (err, ty) = if self.eat(&token::Colon) {
-            // Save the state of the parser before parsing type normally, in case there is a `:`
-            // instead of an `=` typo.
-            let parser_snapshot_before_type = self.clone();
-            let colon_sp = self.prev_span;
-            match self.parse_ty() {
-                Ok(ty) => (None, Some(ty)),
-                Err(mut err) => {
-                    // Rewind to before attempting to parse the type and continue parsing
-                    let parser_snapshot_after_type = self.clone();
-                    mem::replace(self, parser_snapshot_before_type);
-
-                    let snippet = self.sess.source_map().span_to_snippet(pat.span).unwrap();
-                    err.span_label(pat.span, format!("while parsing the type for `{}`", snippet));
-                    (Some((parser_snapshot_after_type, colon_sp, err)), None)
-                }
-            }
-        } else {
-            (None, None)
-        };
-        let init = match (self.parse_initializer(err.is_some()), err) {
-            (Ok(init), None) => {  // init parsed, ty parsed
-                init
-            }
-            (Ok(init), Some((_, colon_sp, mut err))) => {  // init parsed, ty error
-                // Could parse the type as if it were the initializer, it is likely there was a
-                // typo in the code: `:` instead of `=`. Add suggestion and emit the error.
-                err.span_suggestion_short(
-                    colon_sp,
-                    "use `=` if you meant to assign",
-                    "=".to_string(),
-                    Applicability::MachineApplicable
-                );
-                err.emit();
-                // As this was parsed successfully, continue as if the code has been fixed for the
-                // rest of the file. It will still fail due to the emitted error, but we avoid
-                // extra noise.
-                init
-            }
-            (Err(mut init_err), Some((snapshot, _, ty_err))) => {  // init error, ty error
-                init_err.cancel();
-                // Couldn't parse the type nor the initializer, only raise the type error and
-                // return to the parser state before parsing the type as the initializer.
-                // let x: <parse_error>;
-                mem::replace(self, snapshot);
-                return Err(ty_err);
-            }
-            (Err(err), None) => {  // init error, ty parsed
-                // Couldn't parse the initializer and we're not attempting to recover a failed
-                // parse of the type, return the error.
-                return Err(err);
-            }
-        };
-        let hi = if self.token == token::Semi {
-            self.span
-        } else {
-            self.prev_span
-        };
-        Ok(P(ast::Local {
-            ty,
-            pat,
-            init,
-            id: ast::DUMMY_NODE_ID,
-            span: lo.to(hi),
-            attrs,
-            source: LocalSource::Normal,
-        }))
-    }
-
-    /// Parses a structure field.
-    fn parse_name_and_ty(&mut self,
-                         lo: Span,
-                         vis: Visibility,
-                         attrs: Vec<Attribute>)
-                         -> PResult<'a, StructField> {
-        let name = self.parse_ident()?;
-        self.expect(&token::Colon)?;
-        let ty = self.parse_ty()?;
-        Ok(StructField {
-            span: lo.to(self.prev_span),
-            ident: Some(name),
-            vis,
-            id: ast::DUMMY_NODE_ID,
-            ty,
-            attrs,
-        })
-    }
-
-    /// Emits an expected-item-after-attributes error.
-    fn expected_item_err(&mut self, attrs: &[Attribute]) -> PResult<'a,  ()> {
-        let message = match attrs.last() {
-            Some(&Attribute { is_sugared_doc: true, .. }) => "expected item after doc comment",
-            _ => "expected item after attributes",
-        };
-
-        let mut err = self.diagnostic().struct_span_err(self.prev_span, message);
-        if attrs.last().unwrap().is_sugared_doc {
-            err.span_label(self.prev_span, "this doc comment doesn't document anything");
-        }
-        Err(err)
-    }
-
-    /// Parse a statement. This stops just before trailing semicolons on everything but items.
-    /// e.g., a `StmtKind::Semi` parses to a `StmtKind::Expr`, leaving the trailing `;` unconsumed.
-    pub fn parse_stmt(&mut self) -> PResult<'a, Option<Stmt>> {
-        Ok(self.parse_stmt_(true))
-    }
-
-    fn parse_stmt_(&mut self, macro_legacy_warnings: bool) -> Option<Stmt> {
-        self.parse_stmt_without_recovery(macro_legacy_warnings).unwrap_or_else(|mut e| {
-            e.emit();
-            self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
-            None
-        })
-    }
-
-    fn is_async_block(&self) -> bool {
-        self.token.is_keyword(keywords::Async) &&
-        (
-            ( // `async move {`
-                self.look_ahead(1, |t| t.is_keyword(keywords::Move)) &&
-                self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
-            ) || ( // `async {`
-                self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
-            )
-        )
-    }
-
-    fn is_async_fn(&self) -> bool {
-        self.token.is_keyword(keywords::Async) &&
-            self.look_ahead(1, |t| t.is_keyword(keywords::Fn))
-    }
-
-    fn is_do_catch_block(&self) -> bool {
-        self.token.is_keyword(keywords::Do) &&
-        self.look_ahead(1, |t| t.is_keyword(keywords::Catch)) &&
-        self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace)) &&
-        !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
-    }
-
-    fn is_try_block(&self) -> bool {
-        self.token.is_keyword(keywords::Try) &&
-        self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) &&
-        self.span.rust_2018() &&
-        // prevent `while try {} {}`, `if try {} {} else {}`, etc.
-        !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
-    }
-
-    fn is_union_item(&self) -> bool {
-        self.token.is_keyword(keywords::Union) &&
-        self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident())
-    }
-
-    fn is_crate_vis(&self) -> bool {
-        self.token.is_keyword(keywords::Crate) && self.look_ahead(1, |t| t != &token::ModSep)
-    }
-
-    fn is_existential_type_decl(&self) -> bool {
-        self.token.is_keyword(keywords::Existential) &&
-        self.look_ahead(1, |t| t.is_keyword(keywords::Type))
-    }
-
-    fn is_auto_trait_item(&self) -> bool {
-        // auto trait
-        (self.token.is_keyword(keywords::Auto)
-            && self.look_ahead(1, |t| t.is_keyword(keywords::Trait)))
-        || // unsafe auto trait
-        (self.token.is_keyword(keywords::Unsafe) &&
-         self.look_ahead(1, |t| t.is_keyword(keywords::Auto)) &&
-         self.look_ahead(2, |t| t.is_keyword(keywords::Trait)))
-    }
-
-    fn eat_macro_def(&mut self, attrs: &[Attribute], vis: &Visibility, lo: Span)
-                     -> PResult<'a, Option<P<Item>>> {
-        let token_lo = self.span;
-        let (ident, def) = match self.token {
-            token::Ident(ident, false) if ident.name == keywords::Macro.name() => {
-                self.bump();
-                let ident = self.parse_ident()?;
-                let tokens = if self.check(&token::OpenDelim(token::Brace)) {
-                    match self.parse_token_tree() {
-                        TokenTree::Delimited(_, _, tts) => tts,
-                        _ => unreachable!(),
-                    }
-                } else if self.check(&token::OpenDelim(token::Paren)) {
-                    let args = self.parse_token_tree();
-                    let body = if self.check(&token::OpenDelim(token::Brace)) {
-                        self.parse_token_tree()
-                    } else {
-                        self.unexpected()?;
-                        unreachable!()
-                    };
-                    TokenStream::new(vec![
-                        args.into(),
-                        TokenTree::Token(token_lo.to(self.prev_span), token::FatArrow).into(),
-                        body.into(),
-                    ])
-                } else {
-                    self.unexpected()?;
-                    unreachable!()
-                };
-
-                (ident, ast::MacroDef { tokens: tokens.into(), legacy: false })
-            }
-            token::Ident(ident, _) if ident.name == sym::macro_rules &&
-                                   self.look_ahead(1, |t| *t == token::Not) => {
-                let prev_span = self.prev_span;
-                self.complain_if_pub_macro(&vis.node, prev_span);
-                self.bump();
-                self.bump();
-
-                let ident = self.parse_ident()?;
-                let (delim, tokens) = self.expect_delimited_token_tree()?;
-                if delim != MacDelimiter::Brace && !self.eat(&token::Semi) {
-                    self.report_invalid_macro_expansion_item();
-                }
-
-                (ident, ast::MacroDef { tokens: tokens, legacy: true })
-            }
-            _ => return Ok(None),
-        };
-
-        let span = lo.to(self.prev_span);
-        Ok(Some(self.mk_item(span, ident, ItemKind::MacroDef(def), vis.clone(), attrs.to_vec())))
-    }
-
-    fn parse_stmt_without_recovery(&mut self,
-                                   macro_legacy_warnings: bool)
-                                   -> PResult<'a, Option<Stmt>> {
-        maybe_whole!(self, NtStmt, |x| Some(x));
-
-        let attrs = self.parse_outer_attributes()?;
-        let lo = self.span;
-
-        Ok(Some(if self.eat_keyword(keywords::Let) {
-            Stmt {
-                id: ast::DUMMY_NODE_ID,
-                node: StmtKind::Local(self.parse_local(attrs.into())?),
-                span: lo.to(self.prev_span),
-            }
-        } else if let Some(macro_def) = self.eat_macro_def(
-            &attrs,
-            &source_map::respan(lo, VisibilityKind::Inherited),
-            lo,
-        )? {
-            Stmt {
-                id: ast::DUMMY_NODE_ID,
-                node: StmtKind::Item(macro_def),
-                span: lo.to(self.prev_span),
-            }
-        // Starts like a simple path, being careful to avoid contextual keywords
-        // such as a union items, item with `crate` visibility or auto trait items.
-        // Our goal here is to parse an arbitrary path `a::b::c` but not something that starts
-        // like a path (1 token), but it fact not a path.
-        // `union::b::c` - path, `union U { ... }` - not a path.
-        // `crate::b::c` - path, `crate struct S;` - not a path.
-        } else if self.token.is_path_start() &&
-                  !self.token.is_qpath_start() &&
-                  !self.is_union_item() &&
-                  !self.is_crate_vis() &&
-                  !self.is_existential_type_decl() &&
-                  !self.is_auto_trait_item() &&
-                  !self.is_async_fn() {
-            let pth = self.parse_path(PathStyle::Expr)?;
-
-            if !self.eat(&token::Not) {
-                let expr = if self.check(&token::OpenDelim(token::Brace)) {
-                    self.parse_struct_expr(lo, pth, ThinVec::new())?
-                } else {
-                    let hi = self.prev_span;
-                    self.mk_expr(lo.to(hi), ExprKind::Path(None, pth), ThinVec::new())
-                };
-
-                let expr = self.with_res(Restrictions::STMT_EXPR, |this| {
-                    let expr = this.parse_dot_or_call_expr_with(expr, lo, attrs.into())?;
-                    this.parse_assoc_expr_with(0, LhsExpr::AlreadyParsed(expr))
-                })?;
-
-                return Ok(Some(Stmt {
-                    id: ast::DUMMY_NODE_ID,
-                    node: StmtKind::Expr(expr),
-                    span: lo.to(self.prev_span),
-                }));
-            }
-
-            // it's a macro invocation
-            let id = match self.token {
-                token::OpenDelim(_) => keywords::Invalid.ident(), // no special identifier
-                _ => self.parse_ident()?,
-            };
-
-            // check that we're pointing at delimiters (need to check
-            // again after the `if`, because of `parse_ident`
-            // consuming more tokens).
-            match self.token {
-                token::OpenDelim(_) => {}
-                _ => {
-                    // we only expect an ident if we didn't parse one
-                    // above.
-                    let ident_str = if id.name == keywords::Invalid.name() {
-                        "identifier, "
-                    } else {
-                        ""
-                    };
-                    let tok_str = self.this_token_descr();
-                    let mut err = self.fatal(&format!("expected {}`(` or `{{`, found {}",
-                                                      ident_str,
-                                                      tok_str));
-                    err.span_label(self.span, format!("expected {}`(` or `{{`", ident_str));
-                    return Err(err)
-                },
-            }
-
-            let (delim, tts) = self.expect_delimited_token_tree()?;
-            let hi = self.prev_span;
-
-            let style = if delim == MacDelimiter::Brace {
-                MacStmtStyle::Braces
-            } else {
-                MacStmtStyle::NoBraces
-            };
-
-            if id.name == keywords::Invalid.name() {
-                let mac = respan(lo.to(hi), Mac_ { path: pth, tts, delim });
-                let node = if delim == MacDelimiter::Brace ||
-                              self.token == token::Semi || self.token == token::Eof {
-                    StmtKind::Mac(P((mac, style, attrs.into())))
-                }
-                // We used to incorrectly stop parsing macro-expanded statements here.
-                // If the next token will be an error anyway but could have parsed with the
-                // earlier behavior, stop parsing here and emit a warning to avoid breakage.
-                else if macro_legacy_warnings && self.token.can_begin_expr() && match self.token {
-                    // These can continue an expression, so we can't stop parsing and warn.
-                    token::OpenDelim(token::Paren) | token::OpenDelim(token::Bracket) |
-                    token::BinOp(token::Minus) | token::BinOp(token::Star) |
-                    token::BinOp(token::And) | token::BinOp(token::Or) |
-                    token::AndAnd | token::OrOr |
-                    token::DotDot | token::DotDotDot | token::DotDotEq => false,
-                    _ => true,
-                } {
-                    self.warn_missing_semicolon();
-                    StmtKind::Mac(P((mac, style, attrs.into())))
-                } else {
-                    let e = self.mk_expr(mac.span, ExprKind::Mac(mac), ThinVec::new());
-                    let e = self.maybe_recover_from_bad_qpath(e, true)?;
-                    let e = self.parse_dot_or_call_expr_with(e, lo, attrs.into())?;
-                    let e = self.parse_assoc_expr_with(0, LhsExpr::AlreadyParsed(e))?;
-                    StmtKind::Expr(e)
-                };
-                Stmt {
-                    id: ast::DUMMY_NODE_ID,
-                    span: lo.to(hi),
-                    node,
-                }
-            } else {
-                // if it has a special ident, it's definitely an item
-                //
-                // Require a semicolon or braces.
-                if style != MacStmtStyle::Braces && !self.eat(&token::Semi) {
-                    self.report_invalid_macro_expansion_item();
-                }
-                let span = lo.to(hi);
-                Stmt {
-                    id: ast::DUMMY_NODE_ID,
-                    span,
-                    node: StmtKind::Item({
-                        self.mk_item(
-                            span, id /*id is good here*/,
-                            ItemKind::Mac(respan(span, Mac_ { path: pth, tts, delim })),
-                            respan(lo, VisibilityKind::Inherited),
-                            attrs)
-                    }),
-                }
-            }
-        } else {
-            // FIXME: Bad copy of attrs
-            let old_directory_ownership =
-                mem::replace(&mut self.directory.ownership, DirectoryOwnership::UnownedViaBlock);
-            let item = self.parse_item_(attrs.clone(), false, true)?;
-            self.directory.ownership = old_directory_ownership;
-
-            match item {
-                Some(i) => Stmt {
-                    id: ast::DUMMY_NODE_ID,
-                    span: lo.to(i.span),
-                    node: StmtKind::Item(i),
-                },
-                None => {
-                    let unused_attrs = |attrs: &[Attribute], s: &mut Self| {
-                        if !attrs.is_empty() {
-                            if s.prev_token_kind == PrevTokenKind::DocComment {
-                                s.span_fatal_err(s.prev_span, Error::UselessDocComment).emit();
-                            } else if attrs.iter().any(|a| a.style == AttrStyle::Outer) {
-                                s.span_err(s.span, "expected statement after outer attribute");
-                            }
-                        }
-                    };
-
-                    // Do not attempt to parse an expression if we're done here.
-                    if self.token == token::Semi {
-                        unused_attrs(&attrs, self);
-                        self.bump();
-                        return Ok(None);
-                    }
-
-                    if self.token == token::CloseDelim(token::Brace) {
-                        unused_attrs(&attrs, self);
-                        return Ok(None);
-                    }
-
-                    // Remainder are line-expr stmts.
-                    let e = self.parse_expr_res(
-                        Restrictions::STMT_EXPR, Some(attrs.into()))?;
-                    Stmt {
-                        id: ast::DUMMY_NODE_ID,
-                        span: lo.to(e.span),
-                        node: StmtKind::Expr(e),
-                    }
-                }
-            }
-        }))
-    }
-
-    /// Checks if this expression is a successfully parsed statement.
-    fn expr_is_complete(&self, e: &Expr) -> bool {
-        self.restrictions.contains(Restrictions::STMT_EXPR) &&
-            !classify::expr_requires_semi_to_be_stmt(e)
-    }
-
-    /// Parses a block. No inner attributes are allowed.
-    pub fn parse_block(&mut self) -> PResult<'a, P<Block>> {
-        maybe_whole!(self, NtBlock, |x| x);
-
-        let lo = self.span;
-
-        if !self.eat(&token::OpenDelim(token::Brace)) {
-            let sp = self.span;
-            let tok = self.this_token_descr();
-            let mut e = self.span_fatal(sp, &format!("expected `{{`, found {}", tok));
-            let do_not_suggest_help =
-                self.token.is_keyword(keywords::In) || self.token == token::Colon;
-
-            if self.token.is_ident_named("and") {
-                e.span_suggestion_short(
-                    self.span,
-                    "use `&&` instead of `and` for the boolean operator",
-                    "&&".to_string(),
-                    Applicability::MaybeIncorrect,
-                );
-            }
-            if self.token.is_ident_named("or") {
-                e.span_suggestion_short(
-                    self.span,
-                    "use `||` instead of `or` for the boolean operator",
-                    "||".to_string(),
-                    Applicability::MaybeIncorrect,
-                );
-            }
-
-            // Check to see if the user has written something like
-            //
-            //    if (cond)
-            //      bar;
-            //
-            // Which is valid in other languages, but not Rust.
-            match self.parse_stmt_without_recovery(false) {
-                Ok(Some(stmt)) => {
-                    if self.look_ahead(1, |t| t == &token::OpenDelim(token::Brace))
-                        || do_not_suggest_help {
-                        // if the next token is an open brace (e.g., `if a b {`), the place-
-                        // inside-a-block suggestion would be more likely wrong than right
-                        e.span_label(sp, "expected `{`");
-                        return Err(e);
-                    }
-                    let mut stmt_span = stmt.span;
-                    // expand the span to include the semicolon, if it exists
-                    if self.eat(&token::Semi) {
-                        stmt_span = stmt_span.with_hi(self.prev_span.hi());
-                    }
-                    let sugg = pprust::to_string(|s| {
-                        use crate::print::pprust::{PrintState, INDENT_UNIT};
-                        s.ibox(INDENT_UNIT)?;
-                        s.bopen()?;
-                        s.print_stmt(&stmt)?;
-                        s.bclose_maybe_open(stmt.span, INDENT_UNIT, false)
-                    });
-                    e.span_suggestion(
-                        stmt_span,
-                        "try placing this code inside a block",
-                        sugg,
-                        // speculative, has been misleading in the past (closed Issue #46836)
-                        Applicability::MaybeIncorrect
-                    );
-                }
-                Err(mut e) => {
-                    self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
-                    self.cancel(&mut e);
-                }
-                _ => ()
-            }
-            e.span_label(sp, "expected `{`");
-            return Err(e);
-        }
-
-        self.parse_block_tail(lo, BlockCheckMode::Default)
-    }
-
-    /// Parses a block. Inner attributes are allowed.
-    fn parse_inner_attrs_and_block(&mut self) -> PResult<'a, (Vec<Attribute>, P<Block>)> {
-        maybe_whole!(self, NtBlock, |x| (Vec::new(), x));
-
-        let lo = self.span;
-        self.expect(&token::OpenDelim(token::Brace))?;
-        Ok((self.parse_inner_attributes()?,
-            self.parse_block_tail(lo, BlockCheckMode::Default)?))
-    }
-
-    /// Parses the rest of a block expression or function body.
-    /// Precondition: already parsed the '{'.
-    fn parse_block_tail(&mut self, lo: Span, s: BlockCheckMode) -> PResult<'a, P<Block>> {
-        let mut stmts = vec![];
-        while !self.eat(&token::CloseDelim(token::Brace)) {
-            let stmt = match self.parse_full_stmt(false) {
-                Err(mut err) => {
-                    err.emit();
-                    self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
-                    Some(Stmt {
-                        id: ast::DUMMY_NODE_ID,
-                        node: StmtKind::Expr(DummyResult::raw_expr(self.span, true)),
-                        span: self.span,
-                    })
-                }
-                Ok(stmt) => stmt,
-            };
-            if let Some(stmt) = stmt {
-                stmts.push(stmt);
-            } else if self.token == token::Eof {
-                break;
-            } else {
-                // Found only `;` or `}`.
-                continue;
-            };
-        }
-        Ok(P(ast::Block {
-            stmts,
-            id: ast::DUMMY_NODE_ID,
-            rules: s,
-            span: lo.to(self.prev_span),
-        }))
-    }
-
-    /// Parses a statement, including the trailing semicolon.
-    crate fn parse_full_stmt(&mut self, macro_legacy_warnings: bool) -> PResult<'a, Option<Stmt>> {
-        // skip looking for a trailing semicolon when we have an interpolated statement
-        maybe_whole!(self, NtStmt, |x| Some(x));
-
-        let mut stmt = match self.parse_stmt_without_recovery(macro_legacy_warnings)? {
-            Some(stmt) => stmt,
-            None => return Ok(None),
-        };
-
-        match stmt.node {
-            StmtKind::Expr(ref expr) if self.token != token::Eof => {
-                // expression without semicolon
-                if classify::expr_requires_semi_to_be_stmt(expr) {
-                    // Just check for errors and recover; do not eat semicolon yet.
-                    if let Err(mut e) =
-                        self.expect_one_of(&[], &[token::Semi, token::CloseDelim(token::Brace)])
-                    {
-                        e.emit();
-                        self.recover_stmt();
-                    }
-                }
-            }
-            StmtKind::Local(..) => {
-                // We used to incorrectly allow a macro-expanded let statement to lack a semicolon.
-                if macro_legacy_warnings && self.token != token::Semi {
-                    self.warn_missing_semicolon();
-                } else {
-                    self.expect_one_of(&[], &[token::Semi])?;
-                }
-            }
-            _ => {}
-        }
-
-        if self.eat(&token::Semi) {
-            stmt = stmt.add_trailing_semicolon();
-        }
-
-        stmt.span = stmt.span.with_hi(self.prev_span.hi());
-        Ok(Some(stmt))
-    }
-
-    fn warn_missing_semicolon(&self) {
-        self.diagnostic().struct_span_warn(self.span, {
-            &format!("expected `;`, found {}", self.this_token_descr())
-        }).note({
-            "This was erroneously allowed and will become a hard error in a future release"
-        }).emit();
-    }
-
-    fn err_dotdotdot_syntax(&self, span: Span) {
-        self.diagnostic().struct_span_err(span, {
-            "unexpected token: `...`"
-        }).span_suggestion(
-            span, "use `..` for an exclusive range", "..".to_owned(),
-            Applicability::MaybeIncorrect
-        ).span_suggestion(
-            span, "or `..=` for an inclusive range", "..=".to_owned(),
-            Applicability::MaybeIncorrect
-        ).emit();
-    }
-
-    /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
-    ///
-    /// ```
-    /// BOUND = TY_BOUND | LT_BOUND
-    /// LT_BOUND = LIFETIME (e.g., `'a`)
-    /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
-    /// TY_BOUND_NOPAREN = [?] [for<LT_PARAM_DEFS>] SIMPLE_PATH (e.g., `?for<'a: 'b> m::Trait<'a>`)
-    /// ```
-    fn parse_generic_bounds_common(&mut self,
-                                   allow_plus: bool,
-                                   colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
-        let mut bounds = Vec::new();
-        let mut negative_bounds = Vec::new();
-        let mut last_plus_span = None;
-        let mut was_negative = false;
-        loop {
-            // This needs to be synchronized with `Token::can_begin_bound`.
-            let is_bound_start = self.check_path() || self.check_lifetime() ||
-                                 self.check(&token::Not) || // used for error reporting only
-                                 self.check(&token::Question) ||
-                                 self.check_keyword(keywords::For) ||
-                                 self.check(&token::OpenDelim(token::Paren));
-            if is_bound_start {
-                let lo = self.span;
-                let has_parens = self.eat(&token::OpenDelim(token::Paren));
-                let inner_lo = self.span;
-                let is_negative = self.eat(&token::Not);
-                let question = if self.eat(&token::Question) { Some(self.prev_span) } else { None };
-                if self.token.is_lifetime() {
-                    if let Some(question_span) = question {
-                        self.span_err(question_span,
-                                      "`?` may only modify trait bounds, not lifetime bounds");
-                    }
-                    bounds.push(GenericBound::Outlives(self.expect_lifetime()));
-                    if has_parens {
-                        let inner_span = inner_lo.to(self.prev_span);
-                        self.expect(&token::CloseDelim(token::Paren))?;
-                        let mut err = self.struct_span_err(
-                            lo.to(self.prev_span),
-                            "parenthesized lifetime bounds are not supported"
-                        );
-                        if let Ok(snippet) = self.sess.source_map().span_to_snippet(inner_span) {
-                            err.span_suggestion_short(
-                                lo.to(self.prev_span),
-                                "remove the parentheses",
-                                snippet.to_owned(),
-                                Applicability::MachineApplicable
-                            );
-                        }
-                        err.emit();
-                    }
-                } else {
-                    let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
-                    let path = self.parse_path(PathStyle::Type)?;
-                    if has_parens {
-                        self.expect(&token::CloseDelim(token::Paren))?;
-                    }
-                    let poly_span = lo.to(self.prev_span);
-                    if is_negative {
-                        was_negative = true;
-                        if let Some(sp) = last_plus_span.or(colon_span) {
-                            negative_bounds.push(sp.to(poly_span));
+                            Ok(Some(arg))
                         }
                     } else {
-                        let poly_trait = PolyTraitRef::new(lifetime_defs, path, poly_span);
-                        let modifier = if question.is_some() {
-                            TraitBoundModifier::Maybe
-                        } else {
-                            TraitBoundModifier::None
-                        };
-                        bounds.push(GenericBound::Trait(poly_trait, modifier));
+                        Ok(Some(arg))
                     }
-                }
-            } else {
-                break
-            }
-
-            if !allow_plus || !self.eat_plus() {
-                break
-            } else {
-                last_plus_span = Some(self.prev_span);
-            }
-        }
-
-        if !negative_bounds.is_empty() || was_negative {
-            let plural = negative_bounds.len() > 1;
-            let last_span = negative_bounds.last().map(|sp| *sp);
-            let mut err = self.struct_span_err(
-                negative_bounds,
-                "negative trait bounds are not supported",
-            );
-            if let Some(sp) = last_span {
-                err.span_label(sp, "negative trait bounds are not supported");
-            }
-            if let Some(bound_list) = colon_span {
-                let bound_list = bound_list.to(self.prev_span);
-                let mut new_bound_list = String::new();
-                if !bounds.is_empty() {
-                    let mut snippets = bounds.iter().map(|bound| bound.span())
-                        .map(|span| self.sess.source_map().span_to_snippet(span));
-                    while let Some(Ok(snippet)) = snippets.next() {
-                        new_bound_list.push_str(" + ");
-                        new_bound_list.push_str(&snippet);
-                    }
-                    new_bound_list = new_bound_list.replacen(" +", ":", 1);
-                }
-                err.span_suggestion_hidden(
-                    bound_list,
-                    &format!("remove the trait bound{}", if plural { "s" } else { "" }),
-                    new_bound_list,
-                    Applicability::MachineApplicable,
-                );
-            }
-            err.emit();
-        }
-
-        return Ok(bounds);
-    }
-
-    crate fn parse_generic_bounds(&mut self,
-                                  colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
-        self.parse_generic_bounds_common(true, colon_span)
-    }
-
-    /// Parses bounds of a lifetime parameter `BOUND + BOUND + BOUND`, possibly with trailing `+`.
-    ///
-    /// ```
-    /// BOUND = LT_BOUND (e.g., `'a`)
-    /// ```
-    fn parse_lt_param_bounds(&mut self) -> GenericBounds {
-        let mut lifetimes = Vec::new();
-        while self.check_lifetime() {
-            lifetimes.push(ast::GenericBound::Outlives(self.expect_lifetime()));
-
-            if !self.eat_plus() {
-                break
-            }
-        }
-        lifetimes
-    }
-
-    /// Matches `typaram = IDENT (`?` unbound)? optbounds ( EQ ty )?`.
-    fn parse_ty_param(&mut self,
-                      preceding_attrs: Vec<Attribute>)
-                      -> PResult<'a, GenericParam> {
-        let ident = self.parse_ident()?;
-
-        // Parse optional colon and param bounds.
-        let bounds = if self.eat(&token::Colon) {
-            self.parse_generic_bounds(Some(self.prev_span))?
-        } else {
-            Vec::new()
-        };
-
-        let default = if self.eat(&token::Eq) {
-            Some(self.parse_ty()?)
-        } else {
-            None
-        };
-
-        Ok(GenericParam {
-            ident,
-            id: ast::DUMMY_NODE_ID,
-            attrs: preceding_attrs.into(),
-            bounds,
-            kind: GenericParamKind::Type {
-                default,
-            }
-        })
-    }
-
-    /// Parses the following grammar:
-    ///
-    ///     TraitItemAssocTy = Ident ["<"...">"] [":" [GenericBounds]] ["where" ...] ["=" Ty]
-    fn parse_trait_item_assoc_ty(&mut self)
-        -> PResult<'a, (Ident, TraitItemKind, ast::Generics)> {
-        let ident = self.parse_ident()?;
-        let mut generics = self.parse_generics()?;
-
-        // Parse optional colon and param bounds.
-        let bounds = if self.eat(&token::Colon) {
-            self.parse_generic_bounds(None)?
-        } else {
-            Vec::new()
-        };
-        generics.where_clause = self.parse_where_clause()?;
-
-        let default = if self.eat(&token::Eq) {
-            Some(self.parse_ty()?)
-        } else {
-            None
-        };
-        self.expect(&token::Semi)?;
-
-        Ok((ident, TraitItemKind::Type(bounds, default), generics))
-    }
-
-    fn parse_const_param(&mut self, preceding_attrs: Vec<Attribute>) -> PResult<'a, GenericParam> {
-        self.expect_keyword(keywords::Const)?;
-        let ident = self.parse_ident()?;
-        self.expect(&token::Colon)?;
-        let ty = self.parse_ty()?;
-
-        Ok(GenericParam {
-            ident,
-            id: ast::DUMMY_NODE_ID,
-            attrs: preceding_attrs.into(),
-            bounds: Vec::new(),
-            kind: GenericParamKind::Const {
-                ty,
-            }
-        })
-    }
-
-    /// Parses a (possibly empty) list of lifetime and type parameters, possibly including
-    /// a trailing comma and erroneous trailing attributes.
-    crate fn parse_generic_params(&mut self) -> PResult<'a, Vec<ast::GenericParam>> {
-        let mut params = Vec::new();
-        loop {
-            let attrs = self.parse_outer_attributes()?;
-            if self.check_lifetime() {
-                let lifetime = self.expect_lifetime();
-                // Parse lifetime parameter.
-                let bounds = if self.eat(&token::Colon) {
-                    self.parse_lt_param_bounds()
-                } else {
-                    Vec::new()
-                };
-                params.push(ast::GenericParam {
-                    ident: lifetime.ident,
-                    id: lifetime.id,
-                    attrs: attrs.into(),
-                    bounds,
-                    kind: ast::GenericParamKind::Lifetime,
-                });
-            } else if self.check_keyword(keywords::Const) {
-                // Parse const parameter.
-                params.push(self.parse_const_param(attrs)?);
-            } else if self.check_ident() {
-                // Parse type parameter.
-                params.push(self.parse_ty_param(attrs)?);
-            } else {
-                // Check for trailing attributes and stop parsing.
-                if !attrs.is_empty() {
-                    if !params.is_empty() {
-                        self.struct_span_err(
-                            attrs[0].span,
-                            &format!("trailing attribute after generic parameter"),
-                        )
-                        .span_label(attrs[0].span, "attributes must go before parameters")
-                        .emit();
-                    } else {
-                        self.struct_span_err(
-                            attrs[0].span,
-                            &format!("attribute without generic parameters"),
-                        )
-                        .span_label(
-                            attrs[0].span,
-                            "attributes are only permitted when preceding parameters",
-                        )
-                        .emit();
-                    }
-                }
-                break
-            }
-
-            if !self.eat(&token::Comma) {
-                break
-            }
-        }
-        Ok(params)
-    }
-
-    /// Parses a set of optional generic type parameter declarations. Where
-    /// clauses are not parsed here, and must be added later via
-    /// `parse_where_clause()`.
-    ///
-    /// matches generics = ( ) | ( < > ) | ( < typaramseq ( , )? > ) | ( < lifetimes ( , )? > )
-    ///                  | ( < lifetimes , typaramseq ( , )? > )
-    /// where   typaramseq = ( typaram ) | ( typaram , typaramseq )
-    fn parse_generics(&mut self) -> PResult<'a, ast::Generics> {
-        let span_lo = self.span;
-        if self.eat_lt() {
-            let params = self.parse_generic_params()?;
-            self.expect_gt()?;
-            Ok(ast::Generics {
-                params,
-                where_clause: WhereClause {
-                    id: ast::DUMMY_NODE_ID,
-                    predicates: Vec::new(),
-                    span: syntax_pos::DUMMY_SP,
                 },
-                span: span_lo.to(self.prev_span),
-            })
-        } else {
-            Ok(ast::Generics::default())
-        }
-    }
-
-    /// Parses generic args (within a path segment) with recovery for extra leading angle brackets.
-    /// For the purposes of understanding the parsing logic of generic arguments, this function
-    /// can be thought of being the same as just calling `self.parse_generic_args()` if the source
-    /// had the correct amount of leading angle brackets.
-    ///
-    /// ```ignore (diagnostics)
-    /// bar::<<<<T as Foo>::Output>();
-    ///      ^^ help: remove extra angle brackets
-    /// ```
-    fn parse_generic_args_with_leaning_angle_bracket_recovery(
-        &mut self,
-        style: PathStyle,
-        lo: Span,
-    ) -> PResult<'a, (Vec<GenericArg>, Vec<TypeBinding>)> {
-        // We need to detect whether there are extra leading left angle brackets and produce an
-        // appropriate error and suggestion. This cannot be implemented by looking ahead at
-        // upcoming tokens for a matching `>` character - if there are unmatched `<` tokens
-        // then there won't be matching `>` tokens to find.
-        //
-        // To explain how this detection works, consider the following example:
-        //
-        // ```ignore (diagnostics)
-        // bar::<<<<T as Foo>::Output>();
-        //      ^^ help: remove extra angle brackets
-        // ```
-        //
-        // Parsing of the left angle brackets starts in this function. We start by parsing the
-        // `<` token (incrementing the counter of unmatched angle brackets on `Parser` via
-        // `eat_lt`):
-        //
-        // *Upcoming tokens:* `<<<<T as Foo>::Output>;`
-        // *Unmatched count:* 1
-        // *`parse_path_segment` calls deep:* 0
-        //
-        // This has the effect of recursing as this function is called if a `<` character
-        // is found within the expected generic arguments:
-        //
-        // *Upcoming tokens:* `<<<T as Foo>::Output>;`
-        // *Unmatched count:* 2
-        // *`parse_path_segment` calls deep:* 1
-        //
-        // Eventually we will have recursed until having consumed all of the `<` tokens and
-        // this will be reflected in the count:
-        //
-        // *Upcoming tokens:* `T as Foo>::Output>;`
-        // *Unmatched count:* 4
-        // `parse_path_segment` calls deep:* 3
-        //
-        // The parser will continue until reaching the first `>` - this will decrement the
-        // unmatched angle bracket count and return to the parent invocation of this function
-        // having succeeded in parsing:
-        //
-        // *Upcoming tokens:* `::Output>;`
-        // *Unmatched count:* 3
-        // *`parse_path_segment` calls deep:* 2
-        //
-        // This will continue until the next `>` character which will also return successfully
-        // to the parent invocation of this function and decrement the count:
-        //
-        // *Upcoming tokens:* `;`
-        // *Unmatched count:* 2
-        // *`parse_path_segment` calls deep:* 1
-        //
-        // At this point, this function will expect to find another matching `>` character but
-        // won't be able to and will return an error. This will continue all the way up the
-        // call stack until the first invocation:
-        //
-        // *Upcoming tokens:* `;`
-        // *Unmatched count:* 2
-        // *`parse_path_segment` calls deep:* 0
-        //
-        // In doing this, we have managed to work out how many unmatched leading left angle
-        // brackets there are, but we cannot recover as the unmatched angle brackets have
-        // already been consumed. To remedy this, we keep a snapshot of the parser state
-        // before we do the above. We can then inspect whether we ended up with a parsing error
-        // and unmatched left angle brackets and if so, restore the parser state before we
-        // consumed any `<` characters to emit an error and consume the erroneous tokens to
-        // recover by attempting to parse again.
-        //
-        // In practice, the recursion of this function is indirect and there will be other
-        // locations that consume some `<` characters - as long as we update the count when
-        // this happens, it isn't an issue.
-
-        let is_first_invocation = style == PathStyle::Expr;
-        // Take a snapshot before attempting to parse - we can restore this later.
-        let snapshot = if is_first_invocation {
-            Some(self.clone())
-        } else {
-            None
-        };
-
-        debug!("parse_generic_args_with_leading_angle_bracket_recovery: (snapshotting)");
-        match self.parse_generic_args() {
-            Ok(value) => Ok(value),
-            Err(ref mut e) if is_first_invocation && self.unmatched_angle_bracket_count > 0 => {
-                // Cancel error from being unable to find `>`. We know the error
-                // must have been this due to a non-zero unmatched angle bracket
-                // count.
-                e.cancel();
-
-                // Swap `self` with our backup of the parser state before attempting to parse
-                // generic arguments.
-                let snapshot = mem::replace(self, snapshot.unwrap());
-
-                debug!(
-                    "parse_generic_args_with_leading_angle_bracket_recovery: (snapshot failure) \
-                     snapshot.count={:?}",
-                    snapshot.unmatched_angle_bracket_count,
-                );
-
-                // Eat the unmatched angle brackets.
-                for _ in 0..snapshot.unmatched_angle_bracket_count {
-                    self.eat_lt();
-                }
-
-                // Make a span over ${unmatched angle bracket count} characters.
-                let span = lo.with_hi(
-                    lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count)
-                );
-                let plural = snapshot.unmatched_angle_bracket_count > 1;
-                self.diagnostic()
-                    .struct_span_err(
-                        span,
-                        &format!(
-                            "unmatched angle bracket{}",
-                            if plural { "s" } else { "" }
-                        ),
-                    )
-                    .span_suggestion(
-                        span,
-                        &format!(
-                            "remove extra angle bracket{}",
-                            if plural { "s" } else { "" }
-                        ),
-                        String::new(),
-                        Applicability::MachineApplicable,
-                    )
-                    .emit();
-
-                // Try again without unmatched angle bracket characters.
-                self.parse_generic_args()
-            },
-            Err(e) => Err(e),
-        }
-    }
-
-    /// Parses (possibly empty) list of lifetime and type arguments and associated type bindings,
-    /// possibly including trailing comma.
-    fn parse_generic_args(&mut self) -> PResult<'a, (Vec<GenericArg>, Vec<TypeBinding>)> {
-        let mut args = Vec::new();
-        let mut bindings = Vec::new();
-        let mut misplaced_assoc_ty_bindings: Vec<Span> = Vec::new();
-        let mut assoc_ty_bindings: Vec<Span> = Vec::new();
-
-        let args_lo = self.span;
-
-        loop {
-            if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) {
-                // Parse lifetime argument.
-                args.push(GenericArg::Lifetime(self.expect_lifetime()));
-                misplaced_assoc_ty_bindings.append(&mut assoc_ty_bindings);
-            } else if self.check_ident() && self.look_ahead(1, |t| t == &token::Eq) {
-                // Parse associated type binding.
-                let lo = self.span;
-                let ident = self.parse_ident()?;
-                self.bump();
-                let ty = self.parse_ty()?;
-                let span = lo.to(self.prev_span);
-                bindings.push(TypeBinding {
-                    id: ast::DUMMY_NODE_ID,
-                    ident,
-                    ty,
-                    span,
-                });
-                assoc_ty_bindings.push(span);
-            } else if self.check_const_arg() {
-                // Parse const argument.
-                let expr = if let token::OpenDelim(token::Brace) = self.token {
-                    self.parse_block_expr(None, self.span, BlockCheckMode::Default, ThinVec::new())?
-                } else if self.token.is_ident() {
-                    // FIXME(const_generics): to distinguish between idents for types and consts,
-                    // we should introduce a GenericArg::Ident in the AST and distinguish when
-                    // lowering to the HIR. For now, idents for const args are not permitted.
-                    return Err(
-                        self.fatal("identifiers may currently not be used for const generics")
-                    );
-                } else {
-                    self.parse_literal_maybe_minus()?
-                };
-                let value = AnonConst {
-                    id: ast::DUMMY_NODE_ID,
-                    value: expr,
-                };
-                args.push(GenericArg::Const(value));
-                misplaced_assoc_ty_bindings.append(&mut assoc_ty_bindings);
-            } else if self.check_type() {
-                // Parse type argument.
-                args.push(GenericArg::Type(self.parse_ty()?));
-                misplaced_assoc_ty_bindings.append(&mut assoc_ty_bindings);
-            } else {
-                break
-            }
-
-            if !self.eat(&token::Comma) {
-                break
-            }
-        }
-
-        // FIXME: we would like to report this in ast_validation instead, but we currently do not
-        // preserve ordering of generic parameters with respect to associated type binding, so we
-        // lose that information after parsing.
-        if misplaced_assoc_ty_bindings.len() > 0 {
-            let mut err = self.struct_span_err(
-                args_lo.to(self.prev_span),
-                "associated type bindings must be declared after generic parameters",
-            );
-            for span in misplaced_assoc_ty_bindings {
-                err.span_label(
-                    span,
-                    "this associated type binding should be moved after the generic parameters",
-                );
-            }
-            err.emit();
-        }
-
-        Ok((args, bindings))
-    }
-
-    /// Parses an optional where-clause and places it in `generics`.
-    ///
-    /// ```ignore (only-for-syntax-highlight)
-    /// where T : Trait<U, V> + 'b, 'a : 'b
-    /// ```
-    fn parse_where_clause(&mut self) -> PResult<'a, WhereClause> {
-        let mut where_clause = WhereClause {
-            id: ast::DUMMY_NODE_ID,
-            predicates: Vec::new(),
-            span: syntax_pos::DUMMY_SP,
-        };
-
-        if !self.eat_keyword(keywords::Where) {
-            return Ok(where_clause);
-        }
-        let lo = self.prev_span;
-
-        // We are considering adding generics to the `where` keyword as an alternative higher-rank
-        // parameter syntax (as in `where<'a>` or `where<T>`. To avoid that being a breaking
-        // change we parse those generics now, but report an error.
-        if self.choose_generics_over_qpath() {
-            let generics = self.parse_generics()?;
-            self.struct_span_err(
-                generics.span,
-                "generic parameters on `where` clauses are reserved for future use",
-            )
-                .span_label(generics.span, "currently unsupported")
-                .emit();
-        }
-
-        loop {
-            let lo = self.span;
-            if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) {
-                let lifetime = self.expect_lifetime();
-                // Bounds starting with a colon are mandatory, but possibly empty.
-                self.expect(&token::Colon)?;
-                let bounds = self.parse_lt_param_bounds();
-                where_clause.predicates.push(ast::WherePredicate::RegionPredicate(
-                    ast::WhereRegionPredicate {
-                        span: lo.to(self.prev_span),
-                        lifetime,
-                        bounds,
-                    }
-                ));
-            } else if self.check_type() {
-                // Parse optional `for<'a, 'b>`.
-                // This `for` is parsed greedily and applies to the whole predicate,
-                // the bounded type can have its own `for` applying only to it.
-                // Example 1: for<'a> Trait1<'a>: Trait2<'a /*ok*/>
-                // Example 2: (for<'a> Trait1<'a>): Trait2<'a /*not ok*/>
-                // Example 3: for<'a> for<'b> Trait1<'a, 'b>: Trait2<'a /*ok*/, 'b /*not ok*/>
-                let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
-
-                // Parse type with mandatory colon and (possibly empty) bounds,
-                // or with mandatory equality sign and the second type.
-                let ty = self.parse_ty()?;
-                if self.eat(&token::Colon) {
-                    let bounds = self.parse_generic_bounds(Some(self.prev_span))?;
-                    where_clause.predicates.push(ast::WherePredicate::BoundPredicate(
-                        ast::WhereBoundPredicate {
-                            span: lo.to(self.prev_span),
-                            bound_generic_params: lifetime_defs,
-                            bounded_ty: ty,
-                            bounds,
-                        }
-                    ));
-                // FIXME: Decide what should be used here, `=` or `==`.
-                // FIXME: We are just dropping the binders in lifetime_defs on the floor here.
-                } else if self.eat(&token::Eq) || self.eat(&token::EqEq) {
-                    let rhs_ty = self.parse_ty()?;
-                    where_clause.predicates.push(ast::WherePredicate::EqPredicate(
-                        ast::WhereEqPredicate {
-                            span: lo.to(self.prev_span),
-                            lhs_ty: ty,
-                            rhs_ty,
-                            id: ast::DUMMY_NODE_ID,
-                        }
-                    ));
-                } else {
-                    return self.unexpected();
+                Err(mut e) => {
+                    e.emit();
+                    let lo = p.prev_span;
+                    // Skip every token until next possible arg or end.
+                    p.eat_to_tokens(&[&token::Comma, &token::CloseDelim(token::Paren)]);
+                    // Create a placeholder argument for proper arg count (issue #34264).
+                    let span = lo.to(p.prev_span);
+                    Ok(Some(dummy_arg(Ident::new(kw::Invalid, span))))
                 }
-            } else {
-                break
             }
-
-            if !self.eat(&token::Comma) {
-                break
-            }
-        }
-
-        where_clause.span = lo.to(self.prev_span);
-        Ok(where_clause)
-    }
-
-    fn parse_fn_args(&mut self, named_args: bool, allow_c_variadic: bool)
-                     -> PResult<'a, (Vec<Arg> , bool)> {
-        self.expect(&token::OpenDelim(token::Paren))?;
-
-        let sp = self.span;
-        let mut c_variadic = false;
-        let (args, recovered): (Vec<Option<Arg>>, bool) =
-            self.parse_seq_to_before_end(
-                &token::CloseDelim(token::Paren),
-                SeqSep::trailing_allowed(token::Comma),
-                |p| {
-                    // If the argument is a C-variadic argument we should not
-                    // enforce named arguments.
-                    let enforce_named_args = if p.token == token::DotDotDot {
-                        false
-                    } else {
-                        named_args
-                    };
-                    match p.parse_arg_general(enforce_named_args, false,
-                                              allow_c_variadic) {
-                        Ok(arg) => {
-                            if let TyKind::CVarArgs = arg.ty.node {
-                                c_variadic = true;
-                                if p.token != token::CloseDelim(token::Paren) {
-                                    let span = p.span;
-                                    p.span_err(span,
-                                        "`...` must be the last argument of a C-variadic function");
-                                    Ok(None)
-                                } else {
-                                    Ok(Some(arg))
-                                }
-                            } else {
-                                Ok(Some(arg))
-                            }
-                        },
-                        Err(mut e) => {
-                            e.emit();
-                            let lo = p.prev_span;
-                            // Skip every token until next possible arg or end.
-                            p.eat_to_tokens(&[&token::Comma, &token::CloseDelim(token::Paren)]);
-                            // Create a placeholder argument for proper arg count (issue #34264).
-                            let span = lo.to(p.prev_span);
-                            Ok(Some(dummy_arg(span)))
-                        }
-                    }
-                }
-            )?;
-
-        if !recovered {
-            self.eat(&token::CloseDelim(token::Paren));
-        }
+        })?;
 
         let args: Vec<_> = args.into_iter().filter_map(|x| x).collect();
 
-        if c_variadic && args.is_empty() {
+        if c_variadic && args.len() <= 1 {
             self.span_err(sp,
                           "C-variadic function must be declared with at least one named argument");
         }
@@ -5995,47 +1243,36 @@ impl<'a> Parser<'a> {
         Ok((args, c_variadic))
     }
 
-    /// Parses the argument list and result type of a function declaration.
-    fn parse_fn_decl(&mut self, allow_c_variadic: bool) -> PResult<'a, P<FnDecl>> {
-
-        let (args, c_variadic) = self.parse_fn_args(true, allow_c_variadic)?;
-        let ret_ty = self.parse_ret_ty(true)?;
-
-        Ok(P(FnDecl {
-            inputs: args,
-            output: ret_ty,
-            c_variadic,
-        }))
-    }
-
     /// Returns the parsed optional self argument and whether a self shortcut was used.
+    ///
+    /// See `parse_self_arg_with_attrs` to collect attributes.
     fn parse_self_arg(&mut self) -> PResult<'a, Option<Arg>> {
-        let expect_ident = |this: &mut Self| match this.token {
+        let expect_ident = |this: &mut Self| match this.token.kind {
             // Preserve hygienic context.
-            token::Ident(ident, _) =>
-                { let span = this.span; this.bump(); Ident::new(ident.name, span) }
+            token::Ident(name, _) =>
+                { let span = this.token.span; this.bump(); Ident::new(name, span) }
             _ => unreachable!()
         };
         let isolated_self = |this: &mut Self, n| {
-            this.look_ahead(n, |t| t.is_keyword(keywords::SelfLower)) &&
+            this.look_ahead(n, |t| t.is_keyword(kw::SelfLower)) &&
             this.look_ahead(n + 1, |t| t != &token::ModSep)
         };
 
-        // Parse optional self parameter of a method.
-        // Only a limited set of initial token sequences is considered self parameters, anything
+        // Parse optional `self` parameter of a method.
+        // Only a limited set of initial token sequences is considered `self` parameters; anything
         // else is parsed as a normal function parameter list, so some lookahead is required.
-        let eself_lo = self.span;
-        let (eself, eself_ident, eself_hi) = match self.token {
+        let eself_lo = self.token.span;
+        let (eself, eself_ident, eself_hi) = match self.token.kind {
             token::BinOp(token::And) => {
-                // &self
-                // &mut self
-                // &'lt self
-                // &'lt mut self
-                // &not_self
+                // `&self`
+                // `&mut self`
+                // `&'lt self`
+                // `&'lt mut self`
+                // `&not_self`
                 (if isolated_self(self, 1) {
                     self.bump();
                     SelfKind::Region(None, Mutability::Immutable)
-                } else if self.look_ahead(1, |t| t.is_keyword(keywords::Mut)) &&
+                } else if self.is_keyword_ahead(1, &[kw::Mut]) &&
                           isolated_self(self, 2) {
                     self.bump();
                     self.bump();
@@ -6046,7 +1283,7 @@ impl<'a> Parser<'a> {
                     let lt = self.expect_lifetime();
                     SelfKind::Region(Some(lt), Mutability::Immutable)
                 } else if self.look_ahead(1, |t| t.is_lifetime()) &&
-                          self.look_ahead(2, |t| t.is_keyword(keywords::Mut)) &&
+                          self.is_keyword_ahead(2, &[kw::Mut]) &&
                           isolated_self(self, 3) {
                     self.bump();
                     let lt = self.expect_lifetime();
@@ -6057,24 +1294,24 @@ impl<'a> Parser<'a> {
                 }, expect_ident(self), self.prev_span)
             }
             token::BinOp(token::Star) => {
-                // *self
-                // *const self
-                // *mut self
-                // *not_self
+                // `*self`
+                // `*const self`
+                // `*mut self`
+                // `*not_self`
                 // Emit special error for `self` cases.
                 let msg = "cannot pass `self` by raw pointer";
                 (if isolated_self(self, 1) {
                     self.bump();
-                    self.struct_span_err(self.span, msg)
-                        .span_label(self.span, msg)
+                    self.struct_span_err(self.token.span, msg)
+                        .span_label(self.token.span, msg)
                         .emit();
                     SelfKind::Value(Mutability::Immutable)
                 } else if self.look_ahead(1, |t| t.is_mutability()) &&
                           isolated_self(self, 2) {
                     self.bump();
                     self.bump();
-                    self.struct_span_err(self.span, msg)
-                        .span_label(self.span, msg)
+                    self.struct_span_err(self.token.span, msg)
+                        .span_label(self.token.span, msg)
                         .emit();
                     SelfKind::Value(Mutability::Immutable)
                 } else {
@@ -6083,8 +1320,8 @@ impl<'a> Parser<'a> {
             }
             token::Ident(..) => {
                 if isolated_self(self, 0) {
-                    // self
-                    // self: TYPE
+                    // `self`
+                    // `self: TYPE`
                     let eself_ident = expect_ident(self);
                     let eself_hi = self.prev_span;
                     (if self.eat(&token::Colon) {
@@ -6093,10 +1330,10 @@ impl<'a> Parser<'a> {
                     } else {
                         SelfKind::Value(Mutability::Immutable)
                     }, eself_ident, eself_hi)
-                } else if self.token.is_keyword(keywords::Mut) &&
+                } else if self.token.is_keyword(kw::Mut) &&
                           isolated_self(self, 1) {
-                    // mut self
-                    // mut self: TYPE
+                    // `mut self`
+                    // `mut self: TYPE`
                     self.bump();
                     let eself_ident = expect_ident(self);
                     let eself_hi = self.prev_span;
@@ -6114,7 +1351,18 @@ impl<'a> Parser<'a> {
         };
 
         let eself = source_map::respan(eself_lo.to(eself_hi), eself);
-        Ok(Some(Arg::from_self(eself, eself_ident)))
+        Ok(Some(Arg::from_self(ThinVec::default(), eself, eself_ident)))
+    }
+
+    /// Returns the parsed optional self argument with attributes and whether a self
+    /// shortcut was used.
+    fn parse_self_arg_with_attrs(&mut self) -> PResult<'a, Option<Arg>> {
+        let attrs = self.parse_arg_attributes()?;
+        let arg_opt = self.parse_self_arg()?;
+        Ok(arg_opt.map(|mut arg| {
+            arg.attrs = attrs.into();
+            arg
+        }))
     }
 
     /// Parses the parameter list and result type of a function that may have a `self` parameter.
@@ -6123,17 +1371,17 @@ impl<'a> Parser<'a> {
     {
         self.expect(&token::OpenDelim(token::Paren))?;
 
-        // Parse optional self argument
-        let self_arg = self.parse_self_arg()?;
+        // Parse optional self argument.
+        let self_arg = self.parse_self_arg_with_attrs()?;
 
         // Parse the rest of the function parameter list.
         let sep = SeqSep::trailing_allowed(token::Comma);
-        let (fn_inputs, recovered) = if let Some(self_arg) = self_arg {
+        let (mut fn_inputs, recovered) = if let Some(self_arg) = self_arg {
             if self.check(&token::CloseDelim(token::Paren)) {
                 (vec![self_arg], false)
             } else if self.eat(&token::Comma) {
                 let mut fn_inputs = vec![self_arg];
-                let (mut input, recovered) = self.parse_seq_to_before_end(
+                let (mut input, _, recovered) = self.parse_seq_to_before_end(
                     &token::CloseDelim(token::Paren), sep, parse_arg_fn)?;
                 fn_inputs.append(&mut input);
                 (fn_inputs, recovered)
@@ -6144,13 +1392,18 @@ impl<'a> Parser<'a> {
                 }
             }
         } else {
-            self.parse_seq_to_before_end(&token::CloseDelim(token::Paren), sep, parse_arg_fn)?
+            let (input, _, recovered) =
+                self.parse_seq_to_before_end(&token::CloseDelim(token::Paren), sep, parse_arg_fn)?;
+            (input, recovered)
         };
 
         if !recovered {
             // Parse closing paren and return type.
             self.expect(&token::CloseDelim(token::Paren))?;
         }
+        // Replace duplicated recovered arguments with `_` pattern to avoid unecessary errors.
+        self.deduplicate_recovered_arg_names(&mut fn_inputs);
+
         Ok(P(FnDecl {
             inputs: fn_inputs,
             output: self.parse_ret_ty(true)?,
@@ -6158,682 +1411,8 @@ impl<'a> Parser<'a> {
         }))
     }
 
-    /// Parses the `|arg, arg|` header of a closure.
-    fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
-        let inputs_captures = {
-            if self.eat(&token::OrOr) {
-                Vec::new()
-            } else {
-                self.expect(&token::BinOp(token::Or))?;
-                let args = self.parse_seq_to_before_tokens(
-                    &[&token::BinOp(token::Or), &token::OrOr],
-                    SeqSep::trailing_allowed(token::Comma),
-                    TokenExpectType::NoExpect,
-                    |p| p.parse_fn_block_arg()
-                )?.0;
-                self.expect_or()?;
-                args
-            }
-        };
-        let output = self.parse_ret_ty(true)?;
-
-        Ok(P(FnDecl {
-            inputs: inputs_captures,
-            output,
-            c_variadic: false
-        }))
-    }
-
-    /// Parses the name and optional generic types of a function header.
-    fn parse_fn_header(&mut self) -> PResult<'a, (Ident, ast::Generics)> {
-        let id = self.parse_ident()?;
-        let generics = self.parse_generics()?;
-        Ok((id, generics))
-    }
-
-    fn mk_item(&self, span: Span, ident: Ident, node: ItemKind, vis: Visibility,
-               attrs: Vec<Attribute>) -> P<Item> {
-        P(Item {
-            ident,
-            attrs,
-            id: ast::DUMMY_NODE_ID,
-            node,
-            vis,
-            span,
-            tokens: None,
-        })
-    }
-
-    /// Parses an item-position function declaration.
-    fn parse_item_fn(&mut self,
-                     unsafety: Unsafety,
-                     mut asyncness: Spanned<IsAsync>,
-                     constness: Spanned<Constness>,
-                     abi: Abi)
-                     -> PResult<'a, ItemInfo> {
-        let (ident, mut generics) = self.parse_fn_header()?;
-        let allow_c_variadic = abi == Abi::C && unsafety == Unsafety::Unsafe;
-        let mut decl = self.parse_fn_decl(allow_c_variadic)?;
-        generics.where_clause = self.parse_where_clause()?;
-        let (inner_attrs, body) = self.parse_inner_attrs_and_block()?;
-        self.construct_async_arguments(&mut asyncness, &mut decl);
-        let header = FnHeader { unsafety, asyncness, constness, abi };
-        Ok((ident, ItemKind::Fn(decl, header, generics, body), Some(inner_attrs)))
-    }
-
-    /// Returns `true` if we are looking at `const ID`
-    /// (returns `false` for things like `const fn`, etc.).
-    fn is_const_item(&self) -> bool {
-        self.token.is_keyword(keywords::Const) &&
-            !self.look_ahead(1, |t| t.is_keyword(keywords::Fn)) &&
-            !self.look_ahead(1, |t| t.is_keyword(keywords::Unsafe))
-    }
-
-    /// Parses all the "front matter" for a `fn` declaration, up to
-    /// and including the `fn` keyword:
-    ///
-    /// - `const fn`
-    /// - `unsafe fn`
-    /// - `const unsafe fn`
-    /// - `extern fn`
-    /// - etc.
-    fn parse_fn_front_matter(&mut self)
-        -> PResult<'a, (
-            Spanned<Constness>,
-            Unsafety,
-            Spanned<IsAsync>,
-            Abi
-        )>
-    {
-        let is_const_fn = self.eat_keyword(keywords::Const);
-        let const_span = self.prev_span;
-        let unsafety = self.parse_unsafety();
-        let asyncness = self.parse_asyncness();
-        let asyncness = respan(self.prev_span, asyncness);
-        let (constness, unsafety, abi) = if is_const_fn {
-            (respan(const_span, Constness::Const), unsafety, Abi::Rust)
-        } else {
-            let abi = if self.eat_keyword(keywords::Extern) {
-                self.parse_opt_abi()?.unwrap_or(Abi::C)
-            } else {
-                Abi::Rust
-            };
-            (respan(self.prev_span, Constness::NotConst), unsafety, abi)
-        };
-        if !self.eat_keyword(keywords::Fn) {
-            // It is possible for `expect_one_of` to recover given the contents of
-            // `self.expected_tokens`, therefore, do not use `self.unexpected()` which doesn't
-            // account for this.
-            if !self.expect_one_of(&[], &[])? { unreachable!() }
-        }
-        Ok((constness, unsafety, asyncness, abi))
-    }
-
-    /// Parses an impl item.
-    pub fn parse_impl_item(&mut self, at_end: &mut bool) -> PResult<'a, ImplItem> {
-        maybe_whole!(self, NtImplItem, |x| x);
-        let attrs = self.parse_outer_attributes()?;
-        let mut unclosed_delims = vec![];
-        let (mut item, tokens) = self.collect_tokens(|this| {
-            let item = this.parse_impl_item_(at_end, attrs);
-            unclosed_delims.append(&mut this.unclosed_delims);
-            item
-        })?;
-        self.unclosed_delims.append(&mut unclosed_delims);
-
-        // See `parse_item` for why this clause is here.
-        if !item.attrs.iter().any(|attr| attr.style == AttrStyle::Inner) {
-            item.tokens = Some(tokens);
-        }
-        Ok(item)
-    }
-
-    fn parse_impl_item_(&mut self,
-                        at_end: &mut bool,
-                        mut attrs: Vec<Attribute>) -> PResult<'a, ImplItem> {
-        let lo = self.span;
-        let vis = self.parse_visibility(false)?;
-        let defaultness = self.parse_defaultness();
-        let (name, node, generics) = if let Some(type_) = self.eat_type() {
-            let (name, alias, generics) = type_?;
-            let kind = match alias {
-                AliasKind::Weak(typ) => ast::ImplItemKind::Type(typ),
-                AliasKind::Existential(bounds) => ast::ImplItemKind::Existential(bounds),
-            };
-            (name, kind, generics)
-        } else if self.is_const_item() {
-            // This parses the grammar:
-            //     ImplItemConst = "const" Ident ":" Ty "=" Expr ";"
-            self.expect_keyword(keywords::Const)?;
-            let name = self.parse_ident()?;
-            self.expect(&token::Colon)?;
-            let typ = self.parse_ty()?;
-            self.expect(&token::Eq)?;
-            let expr = self.parse_expr()?;
-            self.expect(&token::Semi)?;
-            (name, ast::ImplItemKind::Const(typ, expr), ast::Generics::default())
-        } else {
-            let (name, inner_attrs, generics, node) = self.parse_impl_method(&vis, at_end)?;
-            attrs.extend(inner_attrs);
-            (name, node, generics)
-        };
-
-        Ok(ImplItem {
-            id: ast::DUMMY_NODE_ID,
-            span: lo.to(self.prev_span),
-            ident: name,
-            vis,
-            defaultness,
-            attrs,
-            generics,
-            node,
-            tokens: None,
-        })
-    }
-
-    fn complain_if_pub_macro(&self, vis: &VisibilityKind, sp: Span) {
-        match *vis {
-            VisibilityKind::Inherited => {}
-            _ => {
-                let is_macro_rules: bool = match self.token {
-                    token::Ident(sid, _) => sid.name == Symbol::intern("macro_rules"),
-                    _ => false,
-                };
-                let mut err = if is_macro_rules {
-                    let mut err = self.diagnostic()
-                        .struct_span_err(sp, "can't qualify macro_rules invocation with `pub`");
-                    err.span_suggestion(
-                        sp,
-                        "try exporting the macro",
-                        "#[macro_export]".to_owned(),
-                        Applicability::MaybeIncorrect // speculative
-                    );
-                    err
-                } else {
-                    let mut err = self.diagnostic()
-                        .struct_span_err(sp, "can't qualify macro invocation with `pub`");
-                    err.help("try adjusting the macro to put `pub` inside the invocation");
-                    err
-                };
-                err.emit();
-            }
-        }
-    }
-
-    fn missing_assoc_item_kind_err(&self, item_type: &str, prev_span: Span)
-                                   -> DiagnosticBuilder<'a>
-    {
-        let expected_kinds = if item_type == "extern" {
-            "missing `fn`, `type`, or `static`"
-        } else {
-            "missing `fn`, `type`, or `const`"
-        };
-
-        // Given this code `path(`, it seems like this is not
-        // setting the visibility of a macro invocation, but rather
-        // a mistyped method declaration.
-        // Create a diagnostic pointing out that `fn` is missing.
-        //
-        // x |     pub path(&self) {
-        //   |        ^ missing `fn`, `type`, or `const`
-        //     pub  path(
-        //        ^^ `sp` below will point to this
-        let sp = prev_span.between(self.prev_span);
-        let mut err = self.diagnostic().struct_span_err(
-            sp,
-            &format!("{} for {}-item declaration",
-                     expected_kinds, item_type));
-        err.span_label(sp, expected_kinds);
-        err
-    }
-
-    /// Parse a method or a macro invocation in a trait impl.
-    fn parse_impl_method(&mut self, vis: &Visibility, at_end: &mut bool)
-                         -> PResult<'a, (Ident, Vec<Attribute>, ast::Generics,
-                             ast::ImplItemKind)> {
-        // code copied from parse_macro_use_or_failure... abstraction!
-        if let Some(mac) = self.parse_assoc_macro_invoc("impl", Some(vis), at_end)? {
-            // method macro
-            Ok((keywords::Invalid.ident(), vec![], ast::Generics::default(),
-                ast::ImplItemKind::Macro(mac)))
-        } else {
-            let (constness, unsafety, mut asyncness, abi) = self.parse_fn_front_matter()?;
-            let ident = self.parse_ident()?;
-            let mut generics = self.parse_generics()?;
-            let mut decl = self.parse_fn_decl_with_self(|p| p.parse_arg())?;
-            generics.where_clause = self.parse_where_clause()?;
-            self.construct_async_arguments(&mut asyncness, &mut decl);
-            *at_end = true;
-            let (inner_attrs, body) = self.parse_inner_attrs_and_block()?;
-            let header = ast::FnHeader { abi, unsafety, constness, asyncness };
-            Ok((ident, inner_attrs, generics, ast::ImplItemKind::Method(
-                ast::MethodSig { header, decl },
-                body
-            )))
-        }
-    }
-
-    /// Parses `trait Foo { ... }` or `trait Foo = Bar;`.
-    fn parse_item_trait(&mut self, is_auto: IsAuto, unsafety: Unsafety) -> PResult<'a, ItemInfo> {
-        let ident = self.parse_ident()?;
-        let mut tps = self.parse_generics()?;
-
-        // Parse optional colon and supertrait bounds.
-        let bounds = if self.eat(&token::Colon) {
-            self.parse_generic_bounds(Some(self.prev_span))?
-        } else {
-            Vec::new()
-        };
-
-        if self.eat(&token::Eq) {
-            // it's a trait alias
-            let bounds = self.parse_generic_bounds(None)?;
-            tps.where_clause = self.parse_where_clause()?;
-            self.expect(&token::Semi)?;
-            if is_auto == IsAuto::Yes {
-                let msg = "trait aliases cannot be `auto`";
-                self.struct_span_err(self.prev_span, msg)
-                    .span_label(self.prev_span, msg)
-                    .emit();
-            }
-            if unsafety != Unsafety::Normal {
-                let msg = "trait aliases cannot be `unsafe`";
-                self.struct_span_err(self.prev_span, msg)
-                    .span_label(self.prev_span, msg)
-                    .emit();
-            }
-            Ok((ident, ItemKind::TraitAlias(tps, bounds), None))
-        } else {
-            // it's a normal trait
-            tps.where_clause = self.parse_where_clause()?;
-            self.expect(&token::OpenDelim(token::Brace))?;
-            let mut trait_items = vec![];
-            while !self.eat(&token::CloseDelim(token::Brace)) {
-                if let token::DocComment(_) = self.token {
-                    if self.look_ahead(1,
-                    |tok| tok == &token::Token::CloseDelim(token::Brace)) {
-                        let mut err = self.diagnostic().struct_span_err_with_code(
-                            self.span,
-                            "found a documentation comment that doesn't document anything",
-                            DiagnosticId::Error("E0584".into()),
-                        );
-                        err.help("doc comments must come before what they document, maybe a \
-                            comment was intended with `//`?",
-                        );
-                        err.emit();
-                        self.bump();
-                        continue;
-                    }
-                }
-                let mut at_end = false;
-                match self.parse_trait_item(&mut at_end) {
-                    Ok(item) => trait_items.push(item),
-                    Err(mut e) => {
-                        e.emit();
-                        if !at_end {
-                            self.recover_stmt_(SemiColonMode::Break, BlockMode::Break);
-                        }
-                    }
-                }
-            }
-            Ok((ident, ItemKind::Trait(is_auto, unsafety, tps, bounds, trait_items), None))
-        }
-    }
-
-    fn choose_generics_over_qpath(&self) -> bool {
-        // There's an ambiguity between generic parameters and qualified paths in impls.
-        // If we see `<` it may start both, so we have to inspect some following tokens.
-        // The following combinations can only start generics,
-        // but not qualified paths (with one exception):
-        //     `<` `>` - empty generic parameters
-        //     `<` `#` - generic parameters with attributes
-        //     `<` (LIFETIME|IDENT) `>` - single generic parameter
-        //     `<` (LIFETIME|IDENT) `,` - first generic parameter in a list
-        //     `<` (LIFETIME|IDENT) `:` - generic parameter with bounds
-        //     `<` (LIFETIME|IDENT) `=` - generic parameter with a default
-        //     `<` const                - generic const parameter
-        // The only truly ambiguous case is
-        //     `<` IDENT `>` `::` IDENT ...
-        // we disambiguate it in favor of generics (`impl<T> ::absolute::Path<T> { ... }`)
-        // because this is what almost always expected in practice, qualified paths in impls
-        // (`impl <Type>::AssocTy { ... }`) aren't even allowed by type checker at the moment.
-        self.token == token::Lt &&
-            (self.look_ahead(1, |t| t == &token::Pound || t == &token::Gt) ||
-             self.look_ahead(1, |t| t.is_lifetime() || t.is_ident()) &&
-                self.look_ahead(2, |t| t == &token::Gt || t == &token::Comma ||
-                                       t == &token::Colon || t == &token::Eq) ||
-             self.look_ahead(1, |t| t.is_keyword(keywords::Const)))
-    }
-
-    fn parse_impl_body(&mut self) -> PResult<'a, (Vec<ImplItem>, Vec<Attribute>)> {
-        self.expect(&token::OpenDelim(token::Brace))?;
-        let attrs = self.parse_inner_attributes()?;
-
-        let mut impl_items = Vec::new();
-        while !self.eat(&token::CloseDelim(token::Brace)) {
-            let mut at_end = false;
-            match self.parse_impl_item(&mut at_end) {
-                Ok(impl_item) => impl_items.push(impl_item),
-                Err(mut err) => {
-                    err.emit();
-                    if !at_end {
-                        self.recover_stmt_(SemiColonMode::Break, BlockMode::Break);
-                    }
-                }
-            }
-        }
-        Ok((impl_items, attrs))
-    }
-
-    /// Parses an implementation item, `impl` keyword is already parsed.
-    ///
-    ///    impl<'a, T> TYPE { /* impl items */ }
-    ///    impl<'a, T> TRAIT for TYPE { /* impl items */ }
-    ///    impl<'a, T> !TRAIT for TYPE { /* impl items */ }
-    ///
-    /// We actually parse slightly more relaxed grammar for better error reporting and recovery.
-    ///     `impl` GENERICS `!`? TYPE `for`? (TYPE | `..`) (`where` PREDICATES)? `{` BODY `}`
-    ///     `impl` GENERICS `!`? TYPE (`where` PREDICATES)? `{` BODY `}`
-    fn parse_item_impl(&mut self, unsafety: Unsafety, defaultness: Defaultness)
-                       -> PResult<'a, ItemInfo> {
-        // First, parse generic parameters if necessary.
-        let mut generics = if self.choose_generics_over_qpath() {
-            self.parse_generics()?
-        } else {
-            ast::Generics::default()
-        };
-
-        // Disambiguate `impl !Trait for Type { ... }` and `impl ! { ... }` for the never type.
-        let polarity = if self.check(&token::Not) && self.look_ahead(1, |t| t.can_begin_type()) {
-            self.bump(); // `!`
-            ast::ImplPolarity::Negative
-        } else {
-            ast::ImplPolarity::Positive
-        };
-
-        // Parse both types and traits as a type, then reinterpret if necessary.
-        let err_path = |span| ast::Path::from_ident(Ident::new(keywords::Invalid.name(), span));
-        let ty_first = if self.token.is_keyword(keywords::For) &&
-                          self.look_ahead(1, |t| t != &token::Lt) {
-            let span = self.prev_span.between(self.span);
-            self.struct_span_err(span, "missing trait in a trait impl").emit();
-            P(Ty { node: TyKind::Path(None, err_path(span)), span, id: ast::DUMMY_NODE_ID })
-        } else {
-            self.parse_ty()?
-        };
-
-        // If `for` is missing we try to recover.
-        let has_for = self.eat_keyword(keywords::For);
-        let missing_for_span = self.prev_span.between(self.span);
-
-        let ty_second = if self.token == token::DotDot {
-            // We need to report this error after `cfg` expansion for compatibility reasons
-            self.bump(); // `..`, do not add it to expected tokens
-            Some(DummyResult::raw_ty(self.prev_span, true))
-        } else if has_for || self.token.can_begin_type() {
-            Some(self.parse_ty()?)
-        } else {
-            None
-        };
-
-        generics.where_clause = self.parse_where_clause()?;
-
-        let (impl_items, attrs) = self.parse_impl_body()?;
-
-        let item_kind = match ty_second {
-            Some(ty_second) => {
-                // impl Trait for Type
-                if !has_for {
-                    self.struct_span_err(missing_for_span, "missing `for` in a trait impl")
-                        .span_suggestion_short(
-                            missing_for_span,
-                            "add `for` here",
-                            " for ".to_string(),
-                            Applicability::MachineApplicable,
-                        ).emit();
-                }
-
-                let ty_first = ty_first.into_inner();
-                let path = match ty_first.node {
-                    // This notably includes paths passed through `ty` macro fragments (#46438).
-                    TyKind::Path(None, path) => path,
-                    _ => {
-                        self.span_err(ty_first.span, "expected a trait, found type");
-                        err_path(ty_first.span)
-                    }
-                };
-                let trait_ref = TraitRef { path, ref_id: ty_first.id };
-
-                ItemKind::Impl(unsafety, polarity, defaultness,
-                               generics, Some(trait_ref), ty_second, impl_items)
-            }
-            None => {
-                // impl Type
-                ItemKind::Impl(unsafety, polarity, defaultness,
-                               generics, None, ty_first, impl_items)
-            }
-        };
-
-        Ok((keywords::Invalid.ident(), item_kind, Some(attrs)))
-    }
-
-    fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
-        if self.eat_keyword(keywords::For) {
-            self.expect_lt()?;
-            let params = self.parse_generic_params()?;
-            self.expect_gt()?;
-            // We rely on AST validation to rule out invalid cases: There must not be type
-            // parameters, and the lifetime parameters must not have bounds.
-            Ok(params)
-        } else {
-            Ok(Vec::new())
-        }
-    }
-
-    /// Parses `struct Foo { ... }`.
-    fn parse_item_struct(&mut self) -> PResult<'a, ItemInfo> {
-        let class_name = self.parse_ident()?;
-
-        let mut generics = self.parse_generics()?;
-
-        // There is a special case worth noting here, as reported in issue #17904.
-        // If we are parsing a tuple struct it is the case that the where clause
-        // should follow the field list. Like so:
-        //
-        // struct Foo<T>(T) where T: Copy;
-        //
-        // If we are parsing a normal record-style struct it is the case
-        // that the where clause comes before the body, and after the generics.
-        // So if we look ahead and see a brace or a where-clause we begin
-        // parsing a record style struct.
-        //
-        // Otherwise if we look ahead and see a paren we parse a tuple-style
-        // struct.
-
-        let vdata = if self.token.is_keyword(keywords::Where) {
-            generics.where_clause = self.parse_where_clause()?;
-            if self.eat(&token::Semi) {
-                // If we see a: `struct Foo<T> where T: Copy;` style decl.
-                VariantData::Unit(ast::DUMMY_NODE_ID)
-            } else {
-                // If we see: `struct Foo<T> where T: Copy { ... }`
-                let (fields, recovered) = self.parse_record_struct_body()?;
-                VariantData::Struct(fields, recovered)
-            }
-        // No `where` so: `struct Foo<T>;`
-        } else if self.eat(&token::Semi) {
-            VariantData::Unit(ast::DUMMY_NODE_ID)
-        // Record-style struct definition
-        } else if self.token == token::OpenDelim(token::Brace) {
-            let (fields, recovered) = self.parse_record_struct_body()?;
-            VariantData::Struct(fields, recovered)
-        // Tuple-style struct definition with optional where-clause.
-        } else if self.token == token::OpenDelim(token::Paren) {
-            let body = VariantData::Tuple(self.parse_tuple_struct_body()?, ast::DUMMY_NODE_ID);
-            generics.where_clause = self.parse_where_clause()?;
-            self.expect(&token::Semi)?;
-            body
-        } else {
-            let token_str = self.this_token_descr();
-            let mut err = self.fatal(&format!(
-                "expected `where`, `{{`, `(`, or `;` after struct name, found {}",
-                token_str
-            ));
-            err.span_label(self.span, "expected `where`, `{`, `(`, or `;` after struct name");
-            return Err(err);
-        };
-
-        Ok((class_name, ItemKind::Struct(vdata, generics), None))
-    }
-
-    /// Parses `union Foo { ... }`.
-    fn parse_item_union(&mut self) -> PResult<'a, ItemInfo> {
-        let class_name = self.parse_ident()?;
-
-        let mut generics = self.parse_generics()?;
-
-        let vdata = if self.token.is_keyword(keywords::Where) {
-            generics.where_clause = self.parse_where_clause()?;
-            let (fields, recovered) = self.parse_record_struct_body()?;
-            VariantData::Struct(fields, recovered)
-        } else if self.token == token::OpenDelim(token::Brace) {
-            let (fields, recovered) = self.parse_record_struct_body()?;
-            VariantData::Struct(fields, recovered)
-        } else {
-            let token_str = self.this_token_descr();
-            let mut err = self.fatal(&format!(
-                "expected `where` or `{{` after union name, found {}", token_str));
-            err.span_label(self.span, "expected `where` or `{` after union name");
-            return Err(err);
-        };
-
-        Ok((class_name, ItemKind::Union(vdata, generics), None))
-    }
-
-    fn parse_record_struct_body(
-        &mut self,
-    ) -> PResult<'a, (Vec<StructField>, /* recovered */ bool)> {
-        let mut fields = Vec::new();
-        let mut recovered = false;
-        if self.eat(&token::OpenDelim(token::Brace)) {
-            while self.token != token::CloseDelim(token::Brace) {
-                let field = self.parse_struct_decl_field().map_err(|e| {
-                    self.recover_stmt();
-                    recovered = true;
-                    e
-                });
-                match field {
-                    Ok(field) => fields.push(field),
-                    Err(mut err) => {
-                        err.emit();
-                    }
-                }
-            }
-            self.eat(&token::CloseDelim(token::Brace));
-        } else {
-            let token_str = self.this_token_descr();
-            let mut err = self.fatal(&format!(
-                    "expected `where`, or `{{` after struct name, found {}", token_str));
-            err.span_label(self.span, "expected `where`, or `{` after struct name");
-            return Err(err);
-        }
-
-        Ok((fields, recovered))
-    }
-
-    fn parse_tuple_struct_body(&mut self) -> PResult<'a, Vec<StructField>> {
-        // This is the case where we find `struct Foo<T>(T) where T: Copy;`
-        // Unit like structs are handled in parse_item_struct function
-        let fields = self.parse_unspanned_seq(
-            &token::OpenDelim(token::Paren),
-            &token::CloseDelim(token::Paren),
-            SeqSep::trailing_allowed(token::Comma),
-            |p| {
-                let attrs = p.parse_outer_attributes()?;
-                let lo = p.span;
-                let vis = p.parse_visibility(true)?;
-                let ty = p.parse_ty()?;
-                Ok(StructField {
-                    span: lo.to(ty.span),
-                    vis,
-                    ident: None,
-                    id: ast::DUMMY_NODE_ID,
-                    ty,
-                    attrs,
-                })
-            })?;
-
-        Ok(fields)
-    }
-
-    /// Parses a structure field declaration.
-    fn parse_single_struct_field(&mut self,
-                                     lo: Span,
-                                     vis: Visibility,
-                                     attrs: Vec<Attribute> )
-                                     -> PResult<'a, StructField> {
-        let mut seen_comma: bool = false;
-        let a_var = self.parse_name_and_ty(lo, vis, attrs)?;
-        if self.token == token::Comma {
-            seen_comma = true;
-        }
-        match self.token {
-            token::Comma => {
-                self.bump();
-            }
-            token::CloseDelim(token::Brace) => {}
-            token::DocComment(_) => {
-                let previous_span = self.prev_span;
-                let mut err = self.span_fatal_err(self.span, Error::UselessDocComment);
-                self.bump(); // consume the doc comment
-                let comma_after_doc_seen = self.eat(&token::Comma);
-                // `seen_comma` is always false, because we are inside doc block
-                // condition is here to make code more readable
-                if seen_comma == false && comma_after_doc_seen == true {
-                    seen_comma = true;
-                }
-                if comma_after_doc_seen || self.token == token::CloseDelim(token::Brace) {
-                    err.emit();
-                } else {
-                    if seen_comma == false {
-                        let sp = self.sess.source_map().next_point(previous_span);
-                        err.span_suggestion(
-                            sp,
-                            "missing comma here",
-                            ",".into(),
-                            Applicability::MachineApplicable
-                        );
-                    }
-                    return Err(err);
-                }
-            }
-            _ => {
-                let sp = self.sess.source_map().next_point(self.prev_span);
-                let mut err = self.struct_span_err(sp, &format!("expected `,`, or `}}`, found {}",
-                                                                self.this_token_descr()));
-                if self.token.is_ident() {
-                    // This is likely another field; emit the diagnostic and keep going
-                    err.span_suggestion(
-                        sp,
-                        "try adding a comma",
-                        ",".into(),
-                        Applicability::MachineApplicable,
-                    );
-                    err.emit();
-                } else {
-                    return Err(err)
-                }
-            }
-        }
-        Ok(a_var)
-    }
-
-    /// Parses an element of a struct declaration.
-    fn parse_struct_decl_field(&mut self) -> PResult<'a, StructField> {
-        let attrs = self.parse_outer_attributes()?;
-        let lo = self.span;
-        let vis = self.parse_visibility(false)?;
-        self.parse_single_struct_field(lo, vis, attrs)
+    fn is_crate_vis(&self) -> bool {
+        self.token.is_keyword(kw::Crate) && self.look_ahead(1, |t| t != &token::ModSep)
     }
 
     /// Parses `pub`, `pub(crate)` and `pub(in path)` plus shortcuts `crate` for `pub(crate)`,
@@ -6844,17 +1423,17 @@ impl<'a> Parser<'a> {
     pub fn parse_visibility(&mut self, can_take_tuple: bool) -> PResult<'a, Visibility> {
         maybe_whole!(self, NtVis, |x| x);
 
-        self.expected_tokens.push(TokenType::Keyword(keywords::Crate));
+        self.expected_tokens.push(TokenType::Keyword(kw::Crate));
         if self.is_crate_vis() {
             self.bump(); // `crate`
             return Ok(respan(self.prev_span, VisibilityKind::Crate(CrateSugar::JustCrate)));
         }
 
-        if !self.eat_keyword(keywords::Pub) {
+        if !self.eat_keyword(kw::Pub) {
             // We need a span for our `Spanned<VisibilityKind>`, but there's inherently no
             // keyword to grab a span from for inherited visibility; an empty span at the
             // beginning of the current token would seem to be the "Schelling span".
-            return Ok(respan(self.span.shrink_to_lo(), VisibilityKind::Inherited))
+            return Ok(respan(self.token.span.shrink_to_lo(), VisibilityKind::Inherited))
         }
         let lo = self.prev_span;
 
@@ -6863,7 +1442,7 @@ impl<'a> Parser<'a> {
             // `()` or a tuple might be allowed. For example, `struct Struct(pub (), pub (usize));`.
             // Because of this, we only `bump` the `(` if we're assured it is appropriate to do so
             // by the following tokens.
-            if self.look_ahead(1, |t| t.is_keyword(keywords::Crate)) &&
+            if self.is_keyword_ahead(1, &[kw::Crate]) &&
                 self.look_ahead(2, |t| t != &token::ModSep) // account for `pub(crate::foo)`
             {
                 // `pub(crate)`
@@ -6875,7 +1454,7 @@ impl<'a> Parser<'a> {
                     VisibilityKind::Crate(CrateSugar::PubCrate),
                 );
                 return Ok(vis)
-            } else if self.look_ahead(1, |t| t.is_keyword(keywords::In)) {
+            } else if self.is_keyword_ahead(1, &[kw::In]) {
                 // `pub(in path)`
                 self.bump(); // `(`
                 self.bump(); // `in`
@@ -6887,8 +1466,7 @@ impl<'a> Parser<'a> {
                 });
                 return Ok(vis)
             } else if self.look_ahead(2, |t| t == &token::CloseDelim(token::Paren)) &&
-                      self.look_ahead(1, |t| t.is_keyword(keywords::Super) ||
-                                             t.is_keyword(keywords::SelfLower))
+                      self.is_keyword_ahead(1, &[kw::Super, kw::SelfLower])
             {
                 // `pub(self)` or `pub(super)`
                 self.bump(); // `(`
@@ -6911,665 +1489,44 @@ impl<'a> Parser<'a> {
                 let sp = path.span;
                 let help_msg = format!("make this visible only to module `{}` with `in`", path);
                 self.expect(&token::CloseDelim(token::Paren))?;  // `)`
-                let mut err = struct_span_err!(self.sess.span_diagnostic, sp, E0704, "{}", msg);
-                err.help(suggestion);
-                err.span_suggestion(
-                    sp, &help_msg, format!("in {}", path), Applicability::MachineApplicable
-                );
-                err.emit();  // emit diagnostic, but continue with public visibility
-            }
-        }
-
-        Ok(respan(lo, VisibilityKind::Public))
-    }
-
-    /// Parses defaultness (i.e., `default` or nothing).
-    fn parse_defaultness(&mut self) -> Defaultness {
-        // `pub` is included for better error messages
-        if self.check_keyword(keywords::Default) &&
-           self.look_ahead(1, |t| t.is_keyword(keywords::Impl) ||
-                                  t.is_keyword(keywords::Const) ||
-                                  t.is_keyword(keywords::Fn) ||
-                                  t.is_keyword(keywords::Unsafe) ||
-                                  t.is_keyword(keywords::Extern) ||
-                                  t.is_keyword(keywords::Type) ||
-                                  t.is_keyword(keywords::Pub)) {
-            self.bump(); // `default`
-            Defaultness::Default
-        } else {
-            Defaultness::Final
-        }
-    }
-
-    /// Given a termination token, parses all of the items in a module.
-    fn parse_mod_items(&mut self, term: &token::Token, inner_lo: Span) -> PResult<'a, Mod> {
-        let mut items = vec![];
-        while let Some(item) = self.parse_item()? {
-            items.push(item);
-            self.maybe_consume_incorrect_semicolon(&items);
-        }
-
-        if !self.eat(term) {
-            let token_str = self.this_token_descr();
-            if !self.maybe_consume_incorrect_semicolon(&items) {
-                let mut err = self.fatal(&format!("expected item, found {}", token_str));
-                err.span_label(self.span, "expected item");
-                return Err(err);
-            }
-        }
-
-        let hi = if self.span.is_dummy() {
-            inner_lo
-        } else {
-            self.prev_span
-        };
-
-        Ok(ast::Mod {
-            inner: inner_lo.to(hi),
-            items,
-            inline: true
-        })
-    }
-
-    fn parse_item_const(&mut self, m: Option<Mutability>) -> PResult<'a, ItemInfo> {
-        let id = if m.is_none() { self.parse_ident_or_underscore() } else { self.parse_ident() }?;
-        self.expect(&token::Colon)?;
-        let ty = self.parse_ty()?;
-        self.expect(&token::Eq)?;
-        let e = self.parse_expr()?;
-        self.expect(&token::Semi)?;
-        let item = match m {
-            Some(m) => ItemKind::Static(ty, m, e),
-            None => ItemKind::Const(ty, e),
-        };
-        Ok((id, item, None))
-    }
-
-    /// Parse a `mod <foo> { ... }` or `mod <foo>;` item
-    fn parse_item_mod(&mut self, outer_attrs: &[Attribute]) -> PResult<'a, ItemInfo> {
-        let (in_cfg, outer_attrs) = {
-            let mut strip_unconfigured = crate::config::StripUnconfigured {
-                sess: self.sess,
-                features: None, // don't perform gated feature checking
-            };
-            let mut outer_attrs = outer_attrs.to_owned();
-            strip_unconfigured.process_cfg_attrs(&mut outer_attrs);
-            (!self.cfg_mods || strip_unconfigured.in_cfg(&outer_attrs), outer_attrs)
-        };
-
-        let id_span = self.span;
-        let id = self.parse_ident()?;
-        if self.eat(&token::Semi) {
-            if in_cfg && self.recurse_into_file_modules {
-                // This mod is in an external file. Let's go get it!
-                let ModulePathSuccess { path, directory_ownership, warn } =
-                    self.submod_path(id, &outer_attrs, id_span)?;
-                let (module, mut attrs) =
-                    self.eval_src_mod(path, directory_ownership, id.to_string(), id_span)?;
-                // Record that we fetched the mod from an external file
-                if warn {
-                    let attr = Attribute {
-                        id: attr::mk_attr_id(),
-                        style: ast::AttrStyle::Outer,
-                        path: ast::Path::from_ident(
-                            Ident::with_empty_ctxt(sym::warn_directory_ownership)),
-                        tokens: TokenStream::empty(),
-                        is_sugared_doc: false,
-                        span: syntax_pos::DUMMY_SP,
-                    };
-                    attr::mark_known(&attr);
-                    attrs.push(attr);
-                }
-                Ok((id, ItemKind::Mod(module), Some(attrs)))
-            } else {
-                let placeholder = ast::Mod {
-                    inner: syntax_pos::DUMMY_SP,
-                    items: Vec::new(),
-                    inline: false
-                };
-                Ok((id, ItemKind::Mod(placeholder), None))
-            }
-        } else {
-            let old_directory = self.directory.clone();
-            self.push_directory(id, &outer_attrs);
-
-            self.expect(&token::OpenDelim(token::Brace))?;
-            let mod_inner_lo = self.span;
-            let attrs = self.parse_inner_attributes()?;
-            let module = self.parse_mod_items(&token::CloseDelim(token::Brace), mod_inner_lo)?;
-
-            self.directory = old_directory;
-            Ok((id, ItemKind::Mod(module), Some(attrs)))
-        }
-    }
-
-    fn push_directory(&mut self, id: Ident, attrs: &[Attribute]) {
-        if let Some(path) = attr::first_attr_value_str_by_name(attrs, sym::path) {
-            self.directory.path.to_mut().push(&path.as_str());
-            self.directory.ownership = DirectoryOwnership::Owned { relative: None };
-        } else {
-            // We have to push on the current module name in the case of relative
-            // paths in order to ensure that any additional module paths from inline
-            // `mod x { ... }` come after the relative extension.
-            //
-            // For example, a `mod z { ... }` inside `x/y.rs` should set the current
-            // directory path to `/x/y/z`, not `/x/z` with a relative offset of `y`.
-            if let DirectoryOwnership::Owned { relative } = &mut self.directory.ownership {
-                if let Some(ident) = relative.take() { // remove the relative offset
-                    self.directory.path.to_mut().push(ident.as_str());
-                }
-            }
-            self.directory.path.to_mut().push(&id.as_str());
-        }
-    }
-
-    pub fn submod_path_from_attr(attrs: &[Attribute], dir_path: &Path) -> Option<PathBuf> {
-        if let Some(s) = attr::first_attr_value_str_by_name(attrs, sym::path) {
-            let s = s.as_str();
-
-            // On windows, the base path might have the form
-            // `\\?\foo\bar` in which case it does not tolerate
-            // mixed `/` and `\` separators, so canonicalize
-            // `/` to `\`.
-            #[cfg(windows)]
-            let s = s.replace("/", "\\");
-            Some(dir_path.join(s))
-        } else {
-            None
-        }
-    }
-
-    /// Returns a path to a module.
-    pub fn default_submod_path(
-        id: ast::Ident,
-        relative: Option<ast::Ident>,
-        dir_path: &Path,
-        source_map: &SourceMap) -> ModulePath
-    {
-        // If we're in a foo.rs file instead of a mod.rs file,
-        // we need to look for submodules in
-        // `./foo/<id>.rs` and `./foo/<id>/mod.rs` rather than
-        // `./<id>.rs` and `./<id>/mod.rs`.
-        let relative_prefix_string;
-        let relative_prefix = if let Some(ident) = relative {
-            relative_prefix_string = format!("{}{}", ident.as_str(), path::MAIN_SEPARATOR);
-            &relative_prefix_string
-        } else {
-            ""
-        };
-
-        let mod_name = id.to_string();
-        let default_path_str = format!("{}{}.rs", relative_prefix, mod_name);
-        let secondary_path_str = format!("{}{}{}mod.rs",
-                                         relative_prefix, mod_name, path::MAIN_SEPARATOR);
-        let default_path = dir_path.join(&default_path_str);
-        let secondary_path = dir_path.join(&secondary_path_str);
-        let default_exists = source_map.file_exists(&default_path);
-        let secondary_exists = source_map.file_exists(&secondary_path);
-
-        let result = match (default_exists, secondary_exists) {
-            (true, false) => Ok(ModulePathSuccess {
-                path: default_path,
-                directory_ownership: DirectoryOwnership::Owned {
-                    relative: Some(id),
-                },
-                warn: false,
-            }),
-            (false, true) => Ok(ModulePathSuccess {
-                path: secondary_path,
-                directory_ownership: DirectoryOwnership::Owned {
-                    relative: None,
-                },
-                warn: false,
-            }),
-            (false, false) => Err(Error::FileNotFoundForModule {
-                mod_name: mod_name.clone(),
-                default_path: default_path_str,
-                secondary_path: secondary_path_str,
-                dir_path: dir_path.display().to_string(),
-            }),
-            (true, true) => Err(Error::DuplicatePaths {
-                mod_name: mod_name.clone(),
-                default_path: default_path_str,
-                secondary_path: secondary_path_str,
-            }),
-        };
-
-        ModulePath {
-            name: mod_name,
-            path_exists: default_exists || secondary_exists,
-            result,
-        }
-    }
-
-    fn submod_path(&mut self,
-                   id: ast::Ident,
-                   outer_attrs: &[Attribute],
-                   id_sp: Span)
-                   -> PResult<'a, ModulePathSuccess> {
-        if let Some(path) = Parser::submod_path_from_attr(outer_attrs, &self.directory.path) {
-            return Ok(ModulePathSuccess {
-                directory_ownership: match path.file_name().and_then(|s| s.to_str()) {
-                    // All `#[path]` files are treated as though they are a `mod.rs` file.
-                    // This means that `mod foo;` declarations inside `#[path]`-included
-                    // files are siblings,
-                    //
-                    // Note that this will produce weirdness when a file named `foo.rs` is
-                    // `#[path]` included and contains a `mod foo;` declaration.
-                    // If you encounter this, it's your own darn fault :P
-                    Some(_) => DirectoryOwnership::Owned { relative: None },
-                    _ => DirectoryOwnership::UnownedViaMod(true),
-                },
-                path,
-                warn: false,
-            });
-        }
-
-        let relative = match self.directory.ownership {
-            DirectoryOwnership::Owned { relative } => relative,
-            DirectoryOwnership::UnownedViaBlock |
-            DirectoryOwnership::UnownedViaMod(_) => None,
-        };
-        let paths = Parser::default_submod_path(
-                        id, relative, &self.directory.path, self.sess.source_map());
-
-        match self.directory.ownership {
-            DirectoryOwnership::Owned { .. } => {
-                paths.result.map_err(|err| self.span_fatal_err(id_sp, err))
-            },
-            DirectoryOwnership::UnownedViaBlock => {
-                let msg =
-                    "Cannot declare a non-inline module inside a block \
-                    unless it has a path attribute";
-                let mut err = self.diagnostic().struct_span_err(id_sp, msg);
-                if paths.path_exists {
-                    let msg = format!("Maybe `use` the module `{}` instead of redeclaring it",
-                                      paths.name);
-                    err.span_note(id_sp, &msg);
-                }
-                Err(err)
-            }
-            DirectoryOwnership::UnownedViaMod(warn) => {
-                if warn {
-                    if let Ok(result) = paths.result {
-                        return Ok(ModulePathSuccess { warn: true, ..result });
-                    }
-                }
-                let mut err = self.diagnostic().struct_span_err(id_sp,
-                    "cannot declare a new module at this location");
-                if !id_sp.is_dummy() {
-                    let src_path = self.sess.source_map().span_to_filename(id_sp);
-                    if let FileName::Real(src_path) = src_path {
-                        if let Some(stem) = src_path.file_stem() {
-                            let mut dest_path = src_path.clone();
-                            dest_path.set_file_name(stem);
-                            dest_path.push("mod.rs");
-                            err.span_note(id_sp,
-                                    &format!("maybe move this module `{}` to its own \
-                                                directory via `{}`", src_path.display(),
-                                            dest_path.display()));
-                        }
-                    }
-                }
-                if paths.path_exists {
-                    err.span_note(id_sp,
-                                  &format!("... or maybe `use` the module `{}` instead \
-                                            of possibly redeclaring it",
-                                           paths.name));
-                }
-                Err(err)
-            }
-        }
-    }
-
-    /// Reads a module from a source file.
-    fn eval_src_mod(&mut self,
-                    path: PathBuf,
-                    directory_ownership: DirectoryOwnership,
-                    name: String,
-                    id_sp: Span)
-                    -> PResult<'a, (ast::Mod, Vec<Attribute> )> {
-        let mut included_mod_stack = self.sess.included_mod_stack.borrow_mut();
-        if let Some(i) = included_mod_stack.iter().position(|p| *p == path) {
-            let mut err = String::from("circular modules: ");
-            let len = included_mod_stack.len();
-            for p in &included_mod_stack[i.. len] {
-                err.push_str(&p.to_string_lossy());
-                err.push_str(" -> ");
-            }
-            err.push_str(&path.to_string_lossy());
-            return Err(self.span_fatal(id_sp, &err[..]));
-        }
-        included_mod_stack.push(path.clone());
-        drop(included_mod_stack);
-
-        let mut p0 =
-            new_sub_parser_from_file(self.sess, &path, directory_ownership, Some(name), id_sp);
-        p0.cfg_mods = self.cfg_mods;
-        let mod_inner_lo = p0.span;
-        let mod_attrs = p0.parse_inner_attributes()?;
-        let mut m0 = p0.parse_mod_items(&token::Eof, mod_inner_lo)?;
-        m0.inline = false;
-        self.sess.included_mod_stack.borrow_mut().pop();
-        Ok((m0, mod_attrs))
-    }
-
-    /// Parses a function declaration from a foreign module.
-    fn parse_item_foreign_fn(&mut self, vis: ast::Visibility, lo: Span, attrs: Vec<Attribute>)
-                             -> PResult<'a, ForeignItem> {
-        self.expect_keyword(keywords::Fn)?;
-
-        let (ident, mut generics) = self.parse_fn_header()?;
-        let decl = self.parse_fn_decl(true)?;
-        generics.where_clause = self.parse_where_clause()?;
-        let hi = self.span;
-        self.expect(&token::Semi)?;
-        Ok(ast::ForeignItem {
-            ident,
-            attrs,
-            node: ForeignItemKind::Fn(decl, generics),
-            id: ast::DUMMY_NODE_ID,
-            span: lo.to(hi),
-            vis,
-        })
-    }
-
-    /// Parses a static item from a foreign module.
-    /// Assumes that the `static` keyword is already parsed.
-    fn parse_item_foreign_static(&mut self, vis: ast::Visibility, lo: Span, attrs: Vec<Attribute>)
-                                 -> PResult<'a, ForeignItem> {
-        let mutbl = self.parse_mutability();
-        let ident = self.parse_ident()?;
-        self.expect(&token::Colon)?;
-        let ty = self.parse_ty()?;
-        let hi = self.span;
-        self.expect(&token::Semi)?;
-        Ok(ForeignItem {
-            ident,
-            attrs,
-            node: ForeignItemKind::Static(ty, mutbl),
-            id: ast::DUMMY_NODE_ID,
-            span: lo.to(hi),
-            vis,
-        })
-    }
-
-    /// Parses a type from a foreign module.
-    fn parse_item_foreign_type(&mut self, vis: ast::Visibility, lo: Span, attrs: Vec<Attribute>)
-                             -> PResult<'a, ForeignItem> {
-        self.expect_keyword(keywords::Type)?;
-
-        let ident = self.parse_ident()?;
-        let hi = self.span;
-        self.expect(&token::Semi)?;
-        Ok(ast::ForeignItem {
-            ident: ident,
-            attrs: attrs,
-            node: ForeignItemKind::Ty,
-            id: ast::DUMMY_NODE_ID,
-            span: lo.to(hi),
-            vis: vis
-        })
-    }
-
-    fn parse_crate_name_with_dashes(&mut self) -> PResult<'a, ast::Ident> {
-        let error_msg = "crate name using dashes are not valid in `extern crate` statements";
-        let suggestion_msg = "if the original crate name uses dashes you need to use underscores \
-                              in the code";
-        let mut ident = if self.token.is_keyword(keywords::SelfLower) {
-            self.parse_path_segment_ident()
-        } else {
-            self.parse_ident()
-        }?;
-        let mut idents = vec![];
-        let mut replacement = vec![];
-        let mut fixed_crate_name = false;
-        // Accept `extern crate name-like-this` for better diagnostics
-        let dash = token::Token::BinOp(token::BinOpToken::Minus);
-        if self.token == dash {  // Do not include `-` as part of the expected tokens list
-            while self.eat(&dash) {
-                fixed_crate_name = true;
-                replacement.push((self.prev_span, "_".to_string()));
-                idents.push(self.parse_ident()?);
-            }
-        }
-        if fixed_crate_name {
-            let fixed_name_sp = ident.span.to(idents.last().unwrap().span);
-            let mut fixed_name = format!("{}", ident.name);
-            for part in idents {
-                fixed_name.push_str(&format!("_{}", part.name));
-            }
-            ident = Ident::from_str(&fixed_name).with_span_pos(fixed_name_sp);
-
-            let mut err = self.struct_span_err(fixed_name_sp, error_msg);
-            err.span_label(fixed_name_sp, "dash-separated idents are not valid");
-            err.multipart_suggestion(
-                suggestion_msg,
-                replacement,
-                Applicability::MachineApplicable,
-            );
-            err.emit();
-        }
-        Ok(ident)
-    }
-
-    /// Parses `extern crate` links.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// extern crate foo;
-    /// extern crate bar as foo;
-    /// ```
-    fn parse_item_extern_crate(&mut self,
-                               lo: Span,
-                               visibility: Visibility,
-                               attrs: Vec<Attribute>)
-                               -> PResult<'a, P<Item>> {
-        // Accept `extern crate name-like-this` for better diagnostics
-        let orig_name = self.parse_crate_name_with_dashes()?;
-        let (item_name, orig_name) = if let Some(rename) = self.parse_rename()? {
-            (rename, Some(orig_name.name))
-        } else {
-            (orig_name, None)
-        };
-        self.expect(&token::Semi)?;
-
-        let span = lo.to(self.prev_span);
-        Ok(self.mk_item(span, item_name, ItemKind::ExternCrate(orig_name), visibility, attrs))
-    }
-
-    /// Parses `extern` for foreign ABIs modules.
-    ///
-    /// `extern` is expected to have been
-    /// consumed before calling this method.
-    ///
-    /// # Examples
-    ///
-    /// ```ignore (only-for-syntax-highlight)
-    /// extern "C" {}
-    /// extern {}
-    /// ```
-    fn parse_item_foreign_mod(&mut self,
-                              lo: Span,
-                              opt_abi: Option<Abi>,
-                              visibility: Visibility,
-                              mut attrs: Vec<Attribute>)
-                              -> PResult<'a, P<Item>> {
-        self.expect(&token::OpenDelim(token::Brace))?;
-
-        let abi = opt_abi.unwrap_or(Abi::C);
-
-        attrs.extend(self.parse_inner_attributes()?);
-
-        let mut foreign_items = vec![];
-        while !self.eat(&token::CloseDelim(token::Brace)) {
-            foreign_items.push(self.parse_foreign_item()?);
-        }
-
-        let prev_span = self.prev_span;
-        let m = ast::ForeignMod {
-            abi,
-            items: foreign_items
-        };
-        let invalid = keywords::Invalid.ident();
-        Ok(self.mk_item(lo.to(prev_span), invalid, ItemKind::ForeignMod(m), visibility, attrs))
-    }
-
-    /// Parses `type Foo = Bar;`
-    /// or
-    /// `existential type Foo: Bar;`
-    /// or
-    /// `return `None``
-    /// without modifying the parser state.
-    fn eat_type(&mut self) -> Option<PResult<'a, (Ident, AliasKind, ast::Generics)>> {
-        // This parses the grammar:
-        //     Ident ["<"...">"] ["where" ...] ("=" | ":") Ty ";"
-        if self.check_keyword(keywords::Type) ||
-           self.check_keyword(keywords::Existential) &&
-                self.look_ahead(1, |t| t.is_keyword(keywords::Type)) {
-            let existential = self.eat_keyword(keywords::Existential);
-            assert!(self.eat_keyword(keywords::Type));
-            Some(self.parse_existential_or_alias(existential))
-        } else {
-            None
-        }
-    }
-
-    /// Parses a type alias or existential type.
-    fn parse_existential_or_alias(
-        &mut self,
-        existential: bool,
-    ) -> PResult<'a, (Ident, AliasKind, ast::Generics)> {
-        let ident = self.parse_ident()?;
-        let mut tps = self.parse_generics()?;
-        tps.where_clause = self.parse_where_clause()?;
-        let alias = if existential {
-            self.expect(&token::Colon)?;
-            let bounds = self.parse_generic_bounds(Some(self.prev_span))?;
-            AliasKind::Existential(bounds)
-        } else {
-            self.expect(&token::Eq)?;
-            let ty = self.parse_ty()?;
-            AliasKind::Weak(ty)
-        };
-        self.expect(&token::Semi)?;
-        Ok((ident, alias, tps))
-    }
-
-    /// Parses the part of an enum declaration following the `{`.
-    fn parse_enum_def(&mut self, _generics: &ast::Generics) -> PResult<'a, EnumDef> {
-        let mut variants = Vec::new();
-        let mut all_nullary = true;
-        let mut any_disr = vec![];
-        while self.token != token::CloseDelim(token::Brace) {
-            let variant_attrs = self.parse_outer_attributes()?;
-            let vlo = self.span;
-
-            let struct_def;
-            let mut disr_expr = None;
-            self.eat_bad_pub();
-            let ident = self.parse_ident()?;
-            if self.check(&token::OpenDelim(token::Brace)) {
-                // Parse a struct variant.
-                all_nullary = false;
-                let (fields, recovered) = self.parse_record_struct_body()?;
-                struct_def = VariantData::Struct(fields, recovered);
-            } else if self.check(&token::OpenDelim(token::Paren)) {
-                all_nullary = false;
-                struct_def = VariantData::Tuple(
-                    self.parse_tuple_struct_body()?,
-                    ast::DUMMY_NODE_ID,
-                );
-            } else if self.eat(&token::Eq) {
-                disr_expr = Some(AnonConst {
-                    id: ast::DUMMY_NODE_ID,
-                    value: self.parse_expr()?,
-                });
-                if let Some(sp) = disr_expr.as_ref().map(|c| c.value.span) {
-                    any_disr.push(sp);
-                }
-                struct_def = VariantData::Unit(ast::DUMMY_NODE_ID);
-            } else {
-                struct_def = VariantData::Unit(ast::DUMMY_NODE_ID);
-            }
-
-            let vr = ast::Variant_ {
-                ident,
-                id: ast::DUMMY_NODE_ID,
-                attrs: variant_attrs,
-                data: struct_def,
-                disr_expr,
-            };
-            variants.push(respan(vlo.to(self.prev_span), vr));
-
-            if !self.eat(&token::Comma) {
-                if self.token.is_ident() && !self.token.is_reserved_ident() {
-                    let sp = self.sess.source_map().next_point(self.prev_span);
-                    let mut err = self.struct_span_err(sp, "missing comma");
-                    err.span_suggestion_short(
+                struct_span_err!(self.sess.span_diagnostic, sp, E0704, "{}", msg)
+                    .help(suggestion)
+                    .span_suggestion(
                         sp,
-                        "missing comma",
-                        ",".to_owned(),
-                        Applicability::MaybeIncorrect,
-                    );
-                    err.emit();
-                } else {
-                    break;
-                }
-            }
-        }
-        self.expect(&token::CloseDelim(token::Brace))?;
-        if !any_disr.is_empty() && !all_nullary {
-            let mut err = self.struct_span_err(
-                any_disr.clone(),
-                "discriminator values can only be used with a field-less enum",
-            );
-            for sp in any_disr {
-                err.span_label(sp, "only valid in field-less enums");
+                        &help_msg,
+                        format!("in {}", path),
+                        Applicability::MachineApplicable,
+                    )
+                    .emit();  // emit diagnostic, but continue with public visibility
             }
-            err.emit();
         }
 
-        Ok(ast::EnumDef { variants })
-    }
-
-    /// Parses an enum declaration.
-    fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
-        let id = self.parse_ident()?;
-        let mut generics = self.parse_generics()?;
-        generics.where_clause = self.parse_where_clause()?;
-        self.expect(&token::OpenDelim(token::Brace))?;
-
-        let enum_definition = self.parse_enum_def(&generics).map_err(|e| {
-            self.recover_stmt();
-            self.eat(&token::CloseDelim(token::Brace));
-            e
-        })?;
-        Ok((id, ItemKind::Enum(enum_definition, generics), None))
+        Ok(respan(lo, VisibilityKind::Public))
     }
 
     /// Parses a string as an ABI spec on an extern type or module. Consumes
     /// the `extern` keyword, if one is found.
     fn parse_opt_abi(&mut self) -> PResult<'a, Option<Abi>> {
-        match self.token {
-            token::Literal(token::Str_(s), suf) | token::Literal(token::StrRaw(s, _), suf) => {
-                let sp = self.span;
-                self.expect_no_suffix(sp, "an ABI spec", suf);
+        match self.token.kind {
+            token::Literal(token::Lit { kind: token::Str, symbol, suffix }) |
+            token::Literal(token::Lit { kind: token::StrRaw(..), symbol, suffix }) => {
+                let sp = self.token.span;
+                self.expect_no_suffix(sp, "an ABI spec", suffix);
                 self.bump();
-                match abi::lookup(&s.as_str()) {
+                match abi::lookup(&symbol.as_str()) {
                     Some(abi) => Ok(Some(abi)),
                     None => {
                         let prev_span = self.prev_span;
-                        let mut err = struct_span_err!(
+                        struct_span_err!(
                             self.sess.span_diagnostic,
                             prev_span,
                             E0703,
                             "invalid ABI: found `{}`",
-                            s);
-                        err.span_label(prev_span, "invalid ABI");
-                        err.help(&format!("valid ABIs: {}", abi::all_names().join(", ")));
-                        err.emit();
+                            symbol
+                        )
+                        .span_label(prev_span, "invalid ABI")
+                        .help(&format!("valid ABIs: {}", abi::all_names().join(", ")))
+                        .emit();
                         Ok(None)
                     }
                 }
@@ -7579,640 +1536,16 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn is_static_global(&mut self) -> bool {
-        if self.check_keyword(keywords::Static) {
-            // Check if this could be a closure
-            !self.look_ahead(1, |token| {
-                if token.is_keyword(keywords::Move) {
-                    return true;
-                }
-                match *token {
-                    token::BinOp(token::Or) | token::OrOr => true,
-                    _ => false,
-                }
-            })
-        } else {
-            false
-        }
-    }
-
-    fn parse_item_(
-        &mut self,
-        attrs: Vec<Attribute>,
-        macros_allowed: bool,
-        attributes_allowed: bool,
-    ) -> PResult<'a, Option<P<Item>>> {
-        let mut unclosed_delims = vec![];
-        let (ret, tokens) = self.collect_tokens(|this| {
-            let item = this.parse_item_implementation(attrs, macros_allowed, attributes_allowed);
-            unclosed_delims.append(&mut this.unclosed_delims);
-            item
-        })?;
-        self.unclosed_delims.append(&mut unclosed_delims);
-
-        // Once we've parsed an item and recorded the tokens we got while
-        // parsing we may want to store `tokens` into the item we're about to
-        // return. Note, though, that we specifically didn't capture tokens
-        // related to outer attributes. The `tokens` field here may later be
-        // used with procedural macros to convert this item back into a token
-        // stream, but during expansion we may be removing attributes as we go
-        // along.
-        //
-        // If we've got inner attributes then the `tokens` we've got above holds
-        // these inner attributes. If an inner attribute is expanded we won't
-        // actually remove it from the token stream, so we'll just keep yielding
-        // it (bad!). To work around this case for now we just avoid recording
-        // `tokens` if we detect any inner attributes. This should help keep
-        // expansion correct, but we should fix this bug one day!
-        Ok(ret.map(|item| {
-            item.map(|mut i| {
-                if !i.attrs.iter().any(|attr| attr.style == AttrStyle::Inner) {
-                    i.tokens = Some(tokens);
-                }
-                i
-            })
-        }))
-    }
-
-    /// Parses one of the items allowed by the flags.
-    fn parse_item_implementation(
-        &mut self,
-        attrs: Vec<Attribute>,
-        macros_allowed: bool,
-        attributes_allowed: bool,
-    ) -> PResult<'a, Option<P<Item>>> {
-        maybe_whole!(self, NtItem, |item| {
-            let mut item = item.into_inner();
-            let mut attrs = attrs;
-            mem::swap(&mut item.attrs, &mut attrs);
-            item.attrs.extend(attrs);
-            Some(P(item))
-        });
-
-        let lo = self.span;
-
-        let visibility = self.parse_visibility(false)?;
-
-        if self.eat_keyword(keywords::Use) {
-            // USE ITEM
-            let item_ = ItemKind::Use(P(self.parse_use_tree()?));
-            self.expect(&token::Semi)?;
-
-            let span = lo.to(self.prev_span);
-            let item = self.mk_item(span, keywords::Invalid.ident(), item_, visibility, attrs);
-            return Ok(Some(item));
-        }
-
-        if self.eat_keyword(keywords::Extern) {
-            if self.eat_keyword(keywords::Crate) {
-                return Ok(Some(self.parse_item_extern_crate(lo, visibility, attrs)?));
-            }
-
-            let opt_abi = self.parse_opt_abi()?;
-
-            if self.eat_keyword(keywords::Fn) {
-                // EXTERN FUNCTION ITEM
-                let fn_span = self.prev_span;
-                let abi = opt_abi.unwrap_or(Abi::C);
-                let (ident, item_, extra_attrs) =
-                    self.parse_item_fn(Unsafety::Normal,
-                                       respan(fn_span, IsAsync::NotAsync),
-                                       respan(fn_span, Constness::NotConst),
-                                       abi)?;
-                let prev_span = self.prev_span;
-                let item = self.mk_item(lo.to(prev_span),
-                                        ident,
-                                        item_,
-                                        visibility,
-                                        maybe_append(attrs, extra_attrs));
-                return Ok(Some(item));
-            } else if self.check(&token::OpenDelim(token::Brace)) {
-                return Ok(Some(self.parse_item_foreign_mod(lo, opt_abi, visibility, attrs)?));
-            }
-
-            self.unexpected()?;
-        }
-
-        if self.is_static_global() {
-            self.bump();
-            // STATIC ITEM
-            let m = if self.eat_keyword(keywords::Mut) {
-                Mutability::Mutable
-            } else {
-                Mutability::Immutable
-            };
-            let (ident, item_, extra_attrs) = self.parse_item_const(Some(m))?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if self.eat_keyword(keywords::Const) {
-            let const_span = self.prev_span;
-            if self.check_keyword(keywords::Fn)
-                || (self.check_keyword(keywords::Unsafe)
-                    && self.look_ahead(1, |t| t.is_keyword(keywords::Fn))) {
-                // CONST FUNCTION ITEM
-                let unsafety = self.parse_unsafety();
-                self.bump();
-                let (ident, item_, extra_attrs) =
-                    self.parse_item_fn(unsafety,
-                                       respan(const_span, IsAsync::NotAsync),
-                                       respan(const_span, Constness::Const),
-                                       Abi::Rust)?;
-                let prev_span = self.prev_span;
-                let item = self.mk_item(lo.to(prev_span),
-                                        ident,
-                                        item_,
-                                        visibility,
-                                        maybe_append(attrs, extra_attrs));
-                return Ok(Some(item));
-            }
-
-            // CONST ITEM
-            if self.eat_keyword(keywords::Mut) {
-                let prev_span = self.prev_span;
-                let mut err = self.diagnostic()
-                    .struct_span_err(prev_span, "const globals cannot be mutable");
-                err.span_label(prev_span, "cannot be mutable");
-                err.span_suggestion(
-                    const_span,
-                    "you might want to declare a static instead",
-                    "static".to_owned(),
-                    Applicability::MaybeIncorrect,
-                );
-                err.emit();
-            }
-            let (ident, item_, extra_attrs) = self.parse_item_const(None)?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-
-        // `unsafe async fn` or `async fn`
-        if (
-            self.check_keyword(keywords::Unsafe) &&
-            self.look_ahead(1, |t| t.is_keyword(keywords::Async))
-        ) || (
-            self.check_keyword(keywords::Async) &&
-            self.look_ahead(1, |t| t.is_keyword(keywords::Fn))
-        )
-        {
-            // ASYNC FUNCTION ITEM
-            let unsafety = self.parse_unsafety();
-            self.expect_keyword(keywords::Async)?;
-            let async_span = self.prev_span;
-            self.expect_keyword(keywords::Fn)?;
-            let fn_span = self.prev_span;
-            let (ident, item_, extra_attrs) =
-                self.parse_item_fn(unsafety,
-                                   respan(async_span, IsAsync::Async {
-                                       closure_id: ast::DUMMY_NODE_ID,
-                                       return_impl_trait_id: ast::DUMMY_NODE_ID,
-                                       arguments: Vec::new(),
-                                   }),
-                                   respan(fn_span, Constness::NotConst),
-                                   Abi::Rust)?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            if self.span.rust_2015() {
-                self.diagnostic().struct_span_err_with_code(
+    /// We are parsing `async fn`. If we are on Rust 2015, emit an error.
+    fn ban_async_in_2015(&self, async_span: Span) {
+        if async_span.rust_2015() {
+            self.diagnostic()
+                .struct_span_err_with_code(
                     async_span,
                     "`async fn` is not permitted in the 2015 edition",
                     DiagnosticId::Error("E0670".into())
-                ).emit();
-            }
-            return Ok(Some(item));
-        }
-        if self.check_keyword(keywords::Unsafe) &&
-            (self.look_ahead(1, |t| t.is_keyword(keywords::Trait)) ||
-            self.look_ahead(1, |t| t.is_keyword(keywords::Auto)))
-        {
-            // UNSAFE TRAIT ITEM
-            self.bump(); // `unsafe`
-            let is_auto = if self.eat_keyword(keywords::Trait) {
-                IsAuto::No
-            } else {
-                self.expect_keyword(keywords::Auto)?;
-                self.expect_keyword(keywords::Trait)?;
-                IsAuto::Yes
-            };
-            let (ident, item_, extra_attrs) =
-                self.parse_item_trait(is_auto, Unsafety::Unsafe)?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if self.check_keyword(keywords::Impl) ||
-           self.check_keyword(keywords::Unsafe) &&
-                self.look_ahead(1, |t| t.is_keyword(keywords::Impl)) ||
-           self.check_keyword(keywords::Default) &&
-                self.look_ahead(1, |t| t.is_keyword(keywords::Impl)) ||
-           self.check_keyword(keywords::Default) &&
-                self.look_ahead(1, |t| t.is_keyword(keywords::Unsafe)) {
-            // IMPL ITEM
-            let defaultness = self.parse_defaultness();
-            let unsafety = self.parse_unsafety();
-            self.expect_keyword(keywords::Impl)?;
-            let (ident, item, extra_attrs) = self.parse_item_impl(unsafety, defaultness)?;
-            let span = lo.to(self.prev_span);
-            return Ok(Some(self.mk_item(span, ident, item, visibility,
-                                        maybe_append(attrs, extra_attrs))));
-        }
-        if self.check_keyword(keywords::Fn) {
-            // FUNCTION ITEM
-            self.bump();
-            let fn_span = self.prev_span;
-            let (ident, item_, extra_attrs) =
-                self.parse_item_fn(Unsafety::Normal,
-                                   respan(fn_span, IsAsync::NotAsync),
-                                   respan(fn_span, Constness::NotConst),
-                                   Abi::Rust)?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if self.check_keyword(keywords::Unsafe)
-            && self.look_ahead(1, |t| *t != token::OpenDelim(token::Brace)) {
-            // UNSAFE FUNCTION ITEM
-            self.bump(); // `unsafe`
-            // `{` is also expected after `unsafe`, in case of error, include it in the diagnostic
-            self.check(&token::OpenDelim(token::Brace));
-            let abi = if self.eat_keyword(keywords::Extern) {
-                self.parse_opt_abi()?.unwrap_or(Abi::C)
-            } else {
-                Abi::Rust
-            };
-            self.expect_keyword(keywords::Fn)?;
-            let fn_span = self.prev_span;
-            let (ident, item_, extra_attrs) =
-                self.parse_item_fn(Unsafety::Unsafe,
-                                   respan(fn_span, IsAsync::NotAsync),
-                                   respan(fn_span, Constness::NotConst),
-                                   abi)?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if self.eat_keyword(keywords::Mod) {
-            // MODULE ITEM
-            let (ident, item_, extra_attrs) =
-                self.parse_item_mod(&attrs[..])?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if let Some(type_) = self.eat_type() {
-            let (ident, alias, generics) = type_?;
-            // TYPE ITEM
-            let item_ = match alias {
-                AliasKind::Weak(ty) => ItemKind::Ty(ty, generics),
-                AliasKind::Existential(bounds) => ItemKind::Existential(bounds, generics),
-            };
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    attrs);
-            return Ok(Some(item));
-        }
-        if self.eat_keyword(keywords::Enum) {
-            // ENUM ITEM
-            let (ident, item_, extra_attrs) = self.parse_item_enum()?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if self.check_keyword(keywords::Trait)
-            || (self.check_keyword(keywords::Auto)
-                && self.look_ahead(1, |t| t.is_keyword(keywords::Trait)))
-        {
-            let is_auto = if self.eat_keyword(keywords::Trait) {
-                IsAuto::No
-            } else {
-                self.expect_keyword(keywords::Auto)?;
-                self.expect_keyword(keywords::Trait)?;
-                IsAuto::Yes
-            };
-            // TRAIT ITEM
-            let (ident, item_, extra_attrs) =
-                self.parse_item_trait(is_auto, Unsafety::Normal)?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if self.eat_keyword(keywords::Struct) {
-            // STRUCT ITEM
-            let (ident, item_, extra_attrs) = self.parse_item_struct()?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if self.is_union_item() {
-            // UNION ITEM
-            self.bump();
-            let (ident, item_, extra_attrs) = self.parse_item_union()?;
-            let prev_span = self.prev_span;
-            let item = self.mk_item(lo.to(prev_span),
-                                    ident,
-                                    item_,
-                                    visibility,
-                                    maybe_append(attrs, extra_attrs));
-            return Ok(Some(item));
-        }
-        if let Some(macro_def) = self.eat_macro_def(&attrs, &visibility, lo)? {
-            return Ok(Some(macro_def));
-        }
-
-        // Verify whether we have encountered a struct or method definition where the user forgot to
-        // add the `struct` or `fn` keyword after writing `pub`: `pub S {}`
-        if visibility.node.is_pub() &&
-            self.check_ident() &&
-            self.look_ahead(1, |t| *t != token::Not)
-        {
-            // Space between `pub` keyword and the identifier
-            //
-            //     pub   S {}
-            //        ^^^ `sp` points here
-            let sp = self.prev_span.between(self.span);
-            let full_sp = self.prev_span.to(self.span);
-            let ident_sp = self.span;
-            if self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) {
-                // possible public struct definition where `struct` was forgotten
-                let ident = self.parse_ident().unwrap();
-                let msg = format!("add `struct` here to parse `{}` as a public struct",
-                                  ident);
-                let mut err = self.diagnostic()
-                    .struct_span_err(sp, "missing `struct` for struct definition");
-                err.span_suggestion_short(
-                    sp, &msg, " struct ".into(), Applicability::MaybeIncorrect // speculative
-                );
-                return Err(err);
-            } else if self.look_ahead(1, |t| *t == token::OpenDelim(token::Paren)) {
-                let ident = self.parse_ident().unwrap();
-                self.bump();  // `(`
-                let kw_name = if let Ok(Some(_)) = self.parse_self_arg() {
-                    "method"
-                } else {
-                    "function"
-                };
-                self.consume_block(token::Paren);
-                let (kw, kw_name, ambiguous) = if self.check(&token::RArrow) {
-                    self.eat_to_tokens(&[&token::OpenDelim(token::Brace)]);
-                    self.bump();  // `{`
-                    ("fn", kw_name, false)
-                } else if self.check(&token::OpenDelim(token::Brace)) {
-                    self.bump();  // `{`
-                    ("fn", kw_name, false)
-                } else if self.check(&token::Colon) {
-                    let kw = "struct";
-                    (kw, kw, false)
-                } else {
-                    ("fn` or `struct", "function or struct", true)
-                };
-
-                let msg = format!("missing `{}` for {} definition", kw, kw_name);
-                let mut err = self.diagnostic().struct_span_err(sp, &msg);
-                if !ambiguous {
-                    self.consume_block(token::Brace);
-                    let suggestion = format!("add `{}` here to parse `{}` as a public {}",
-                                             kw,
-                                             ident,
-                                             kw_name);
-                    err.span_suggestion_short(
-                        sp, &suggestion, format!(" {} ", kw), Applicability::MachineApplicable
-                    );
-                } else {
-                    if let Ok(snippet) = self.sess.source_map().span_to_snippet(ident_sp) {
-                        err.span_suggestion(
-                            full_sp,
-                            "if you meant to call a macro, try",
-                            format!("{}!", snippet),
-                            // this is the `ambiguous` conditional branch
-                            Applicability::MaybeIncorrect
-                        );
-                    } else {
-                        err.help("if you meant to call a macro, remove the `pub` \
-                                  and add a trailing `!` after the identifier");
-                    }
-                }
-                return Err(err);
-            } else if self.look_ahead(1, |t| *t == token::Lt) {
-                let ident = self.parse_ident().unwrap();
-                self.eat_to_tokens(&[&token::Gt]);
-                self.bump();  // `>`
-                let (kw, kw_name, ambiguous) = if self.eat(&token::OpenDelim(token::Paren)) {
-                    if let Ok(Some(_)) = self.parse_self_arg() {
-                        ("fn", "method", false)
-                    } else {
-                        ("fn", "function", false)
-                    }
-                } else if self.check(&token::OpenDelim(token::Brace)) {
-                    ("struct", "struct", false)
-                } else {
-                    ("fn` or `struct", "function or struct", true)
-                };
-                let msg = format!("missing `{}` for {} definition", kw, kw_name);
-                let mut err = self.diagnostic().struct_span_err(sp, &msg);
-                if !ambiguous {
-                    err.span_suggestion_short(
-                        sp,
-                        &format!("add `{}` here to parse `{}` as a public {}", kw, ident, kw_name),
-                        format!(" {} ", kw),
-                        Applicability::MachineApplicable,
-                    );
-                }
-                return Err(err);
-            }
-        }
-        self.parse_macro_use_or_failure(attrs, macros_allowed, attributes_allowed, lo, visibility)
-    }
-
-    /// Parses a foreign item.
-    crate fn parse_foreign_item(&mut self) -> PResult<'a, ForeignItem> {
-        maybe_whole!(self, NtForeignItem, |ni| ni);
-
-        let attrs = self.parse_outer_attributes()?;
-        let lo = self.span;
-        let visibility = self.parse_visibility(false)?;
-
-        // FOREIGN STATIC ITEM
-        // Treat `const` as `static` for error recovery, but don't add it to expected tokens.
-        if self.check_keyword(keywords::Static) || self.token.is_keyword(keywords::Const) {
-            if self.token.is_keyword(keywords::Const) {
-                self.diagnostic()
-                    .struct_span_err(self.span, "extern items cannot be `const`")
-                    .span_suggestion(
-                        self.span,
-                        "try using a static value",
-                        "static".to_owned(),
-                        Applicability::MachineApplicable
-                    ).emit();
-            }
-            self.bump(); // `static` or `const`
-            return Ok(self.parse_item_foreign_static(visibility, lo, attrs)?);
-        }
-        // FOREIGN FUNCTION ITEM
-        if self.check_keyword(keywords::Fn) {
-            return Ok(self.parse_item_foreign_fn(visibility, lo, attrs)?);
-        }
-        // FOREIGN TYPE ITEM
-        if self.check_keyword(keywords::Type) {
-            return Ok(self.parse_item_foreign_type(visibility, lo, attrs)?);
-        }
-
-        match self.parse_assoc_macro_invoc("extern", Some(&visibility), &mut false)? {
-            Some(mac) => {
-                Ok(
-                    ForeignItem {
-                        ident: keywords::Invalid.ident(),
-                        span: lo.to(self.prev_span),
-                        id: ast::DUMMY_NODE_ID,
-                        attrs,
-                        vis: visibility,
-                        node: ForeignItemKind::Macro(mac),
-                    }
                 )
-            }
-            None => {
-                if !attrs.is_empty()  {
-                    self.expected_item_err(&attrs)?;
-                }
-
-                self.unexpected()
-            }
-        }
-    }
-
-    /// This is the fall-through for parsing items.
-    fn parse_macro_use_or_failure(
-        &mut self,
-        attrs: Vec<Attribute> ,
-        macros_allowed: bool,
-        attributes_allowed: bool,
-        lo: Span,
-        visibility: Visibility
-    ) -> PResult<'a, Option<P<Item>>> {
-        if macros_allowed && self.token.is_path_start() &&
-                !(self.is_async_fn() && self.span.rust_2015()) {
-            // MACRO INVOCATION ITEM
-
-            let prev_span = self.prev_span;
-            self.complain_if_pub_macro(&visibility.node, prev_span);
-
-            let mac_lo = self.span;
-
-            // item macro.
-            let pth = self.parse_path(PathStyle::Mod)?;
-            self.expect(&token::Not)?;
-
-            // a 'special' identifier (like what `macro_rules!` uses)
-            // is optional. We should eventually unify invoc syntax
-            // and remove this.
-            let id = if self.token.is_ident() {
-                self.parse_ident()?
-            } else {
-                keywords::Invalid.ident() // no special identifier
-            };
-            // eat a matched-delimiter token tree:
-            let (delim, tts) = self.expect_delimited_token_tree()?;
-            if delim != MacDelimiter::Brace && !self.eat(&token::Semi) {
-                self.report_invalid_macro_expansion_item();
-            }
-
-            let hi = self.prev_span;
-            let mac = respan(mac_lo.to(hi), Mac_ { path: pth, tts, delim });
-            let item = self.mk_item(lo.to(hi), id, ItemKind::Mac(mac), visibility, attrs);
-            return Ok(Some(item));
-        }
-
-        // FAILURE TO PARSE ITEM
-        match visibility.node {
-            VisibilityKind::Inherited => {}
-            _ => {
-                return Err(self.span_fatal(self.prev_span, "unmatched visibility `pub`"));
-            }
-        }
-
-        if !attributes_allowed && !attrs.is_empty() {
-            self.expected_item_err(&attrs)?;
-        }
-        Ok(None)
-    }
-
-    /// Parses a macro invocation inside a `trait`, `impl` or `extern` block.
-    fn parse_assoc_macro_invoc(&mut self, item_kind: &str, vis: Option<&Visibility>,
-                               at_end: &mut bool) -> PResult<'a, Option<Mac>>
-    {
-        if self.token.is_path_start() &&
-                !(self.is_async_fn() && self.span.rust_2015()) {
-            let prev_span = self.prev_span;
-            let lo = self.span;
-            let pth = self.parse_path(PathStyle::Mod)?;
-
-            if pth.segments.len() == 1 {
-                if !self.eat(&token::Not) {
-                    return Err(self.missing_assoc_item_kind_err(item_kind, prev_span));
-                }
-            } else {
-                self.expect(&token::Not)?;
-            }
-
-            if let Some(vis) = vis {
-                self.complain_if_pub_macro(&vis.node, prev_span);
-            }
-
-            *at_end = true;
-
-            // eat a matched-delimiter token tree:
-            let (delim, tts) = self.expect_delimited_token_tree()?;
-            if delim != MacDelimiter::Brace {
-                self.expect(&token::Semi)?;
-            }
-
-            Ok(Some(respan(lo.to(self.prev_span), Mac_ { path: pth, tts, delim })))
-        } else {
-            Ok(None)
+                .emit();
         }
     }
 
@@ -8223,7 +1556,7 @@ impl<'a> Parser<'a> {
         let mut tokens = Vec::new();
         let prev_collecting = match self.token_cursor.frame.last_token {
             LastToken::Collecting(ref mut list) => {
-                Some(mem::replace(list, Vec::new()))
+                Some(mem::take(list))
             }
             LastToken::Was(ref mut last) => {
                 tokens.extend(last.take());
@@ -8235,14 +1568,27 @@ impl<'a> Parser<'a> {
         let ret = f(self);
         let last_token = if self.token_cursor.stack.len() == prev {
             &mut self.token_cursor.frame.last_token
+        } else if self.token_cursor.stack.get(prev).is_none() {
+            // This can happen due to a bad interaction of two unrelated recovery mechanisms with
+            // mismatched delimiters *and* recovery lookahead on the likely typo `pub ident(`
+            // (#62881).
+            return Ok((ret?, TokenStream::new(vec![])));
         } else {
             &mut self.token_cursor.stack[prev].last_token
         };
 
         // Pull out the tokens that we've collected from the call to `f` above.
         let mut collected_tokens = match *last_token {
-            LastToken::Collecting(ref mut v) => mem::replace(v, Vec::new()),
-            LastToken::Was(_) => panic!("our vector went away?"),
+            LastToken::Collecting(ref mut v) => mem::take(v),
+            LastToken::Was(ref was) => {
+                let msg = format!("our vector went away? - found Was({:?})", was);
+                debug!("collect_tokens: {}", msg);
+                self.sess.span_diagnostic.delay_span_bug(self.token.span, &msg);
+                // This can happen due to a bad interaction of two unrelated recovery mechanisms
+                // with mismatched delimiters *and* recovery lookahead on the likely typo
+                // `pub ident(` (#62895, different but similar to the case above).
+                return Ok((ret?, TokenStream::new(vec![])));
+            }
         };
 
         // If we're not at EOF our current token wasn't actually consumed by
@@ -8272,11 +1618,6 @@ impl<'a> Parser<'a> {
         Ok((ret?, TokenStream::new(collected_tokens)))
     }
 
-    pub fn parse_item(&mut self) -> PResult<'a, Option<P<Item>>> {
-        let attrs = self.parse_outer_attributes()?;
-        self.parse_item_(attrs, true, false)
-    }
-
     /// `::{` or `::*`
     fn is_import_coupler(&mut self) -> bool {
         self.check(&token::ModSep) &&
@@ -8284,89 +1625,12 @@ impl<'a> Parser<'a> {
                                    *t == token::BinOp(token::Star))
     }
 
-    /// Parses a `UseTree`.
-    ///
-    /// ```
-    /// USE_TREE = [`::`] `*` |
-    ///            [`::`] `{` USE_TREE_LIST `}` |
-    ///            PATH `::` `*` |
-    ///            PATH `::` `{` USE_TREE_LIST `}` |
-    ///            PATH [`as` IDENT]
-    /// ```
-    fn parse_use_tree(&mut self) -> PResult<'a, UseTree> {
-        let lo = self.span;
-
-        let mut prefix = ast::Path { segments: Vec::new(), span: lo.shrink_to_lo() };
-        let kind = if self.check(&token::OpenDelim(token::Brace)) ||
-                      self.check(&token::BinOp(token::Star)) ||
-                      self.is_import_coupler() {
-            // `use *;` or `use ::*;` or `use {...};` or `use ::{...};`
-            let mod_sep_ctxt = self.span.ctxt();
-            if self.eat(&token::ModSep) {
-                prefix.segments.push(
-                    PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt))
-                );
-            }
-
-            if self.eat(&token::BinOp(token::Star)) {
-                UseTreeKind::Glob
-            } else {
-                UseTreeKind::Nested(self.parse_use_tree_list()?)
-            }
-        } else {
-            // `use path::*;` or `use path::{...};` or `use path;` or `use path as bar;`
-            prefix = self.parse_path(PathStyle::Mod)?;
-
-            if self.eat(&token::ModSep) {
-                if self.eat(&token::BinOp(token::Star)) {
-                    UseTreeKind::Glob
-                } else {
-                    UseTreeKind::Nested(self.parse_use_tree_list()?)
-                }
-            } else {
-                UseTreeKind::Simple(self.parse_rename()?, ast::DUMMY_NODE_ID, ast::DUMMY_NODE_ID)
-            }
-        };
-
-        Ok(UseTree { prefix, kind, span: lo.to(self.prev_span) })
-    }
-
-    /// Parses a `UseTreeKind::Nested(list)`.
-    ///
-    /// ```
-    /// USE_TREE_LIST = Ø | (USE_TREE `,`)* USE_TREE [`,`]
-    /// ```
-    fn parse_use_tree_list(&mut self) -> PResult<'a, Vec<(UseTree, ast::NodeId)>> {
-        self.parse_unspanned_seq(&token::OpenDelim(token::Brace),
-                                 &token::CloseDelim(token::Brace),
-                                 SeqSep::trailing_allowed(token::Comma), |this| {
-            Ok((this.parse_use_tree()?, ast::DUMMY_NODE_ID))
-        })
-    }
-
-    fn parse_rename(&mut self) -> PResult<'a, Option<Ident>> {
-        if self.eat_keyword(keywords::As) {
-            self.parse_ident_or_underscore().map(Some)
-        } else {
-            Ok(None)
-        }
-    }
-
-    /// Parses a source module as a crate. This is the main entry point for the parser.
-    pub fn parse_crate_mod(&mut self) -> PResult<'a, Crate> {
-        let lo = self.span;
-        let krate = Ok(ast::Crate {
-            attrs: self.parse_inner_attributes()?,
-            module: self.parse_mod_items(&token::Eof, lo)?,
-            span: lo.to(self.span),
-        });
-        krate
-    }
-
     pub fn parse_optional_str(&mut self) -> Option<(Symbol, ast::StrStyle, Option<ast::Name>)> {
-        let ret = match self.token {
-            token::Literal(token::Str_(s), suf) => (s, ast::StrStyle::Cooked, suf),
-            token::Literal(token::StrRaw(s, n), suf) => (s, ast::StrStyle::Raw(n), suf),
+        let ret = match self.token.kind {
+            token::Literal(token::Lit { kind: token::Str, symbol, suffix }) =>
+                (symbol, ast::StrStyle::Cooked, suffix),
+            token::Literal(token::Lit { kind: token::StrRaw(n), symbol, suffix }) =>
+                (symbol, ast::StrStyle::Raw(n), suffix),
             _ => return None
         };
         self.bump();
@@ -8383,7 +1647,7 @@ impl<'a> Parser<'a> {
             _ => {
                 let msg = "expected string literal";
                 let mut err = self.fatal(msg);
-                err.span_label(self.span, msg);
+                err.span_label(self.token.span, msg);
                 Err(err)
             }
         }
@@ -8407,122 +1671,13 @@ impl<'a> Parser<'a> {
             Applicability::MaybeIncorrect,
         ).emit();
     }
-
-    /// When lowering a `async fn` to the HIR, we need to move all of the arguments of the function
-    /// into the generated closure so that they are dropped when the future is polled and not when
-    /// it is created.
-    ///
-    /// The arguments of the function are replaced in HIR lowering with the arguments created by
-    /// this function and the statements created here are inserted at the top of the closure body.
-    fn construct_async_arguments(&mut self, asyncness: &mut Spanned<IsAsync>, decl: &mut FnDecl) {
-        // FIXME(davidtwco): This function should really live in the HIR lowering but because
-        // the types constructed here need to be used in parts of resolve so that the correct
-        // locals are considered upvars, it is currently easier for it to live here in the parser,
-        // where it can be constructed once.
-        if let IsAsync::Async { ref mut arguments, .. } = asyncness.node {
-            for (index, input) in decl.inputs.iter_mut().enumerate() {
-                let id = ast::DUMMY_NODE_ID;
-                let span = input.pat.span;
-
-                // Construct a name for our temporary argument.
-                let name = format!("__arg{}", index);
-                let ident = Ident::from_str(&name).gensym();
-
-                // Check if this is a ident pattern, if so, we can optimize and avoid adding a
-                // `let <pat> = __argN;` statement, instead just adding a `let <pat> = <pat>;`
-                // statement.
-                let (binding_mode, ident, is_simple_pattern) = match input.pat.node {
-                    PatKind::Ident(binding_mode @ BindingMode::ByValue(_), ident, _) => {
-                        // Simple patterns like this don't have a generated argument, but they are
-                        // moved into the closure with a statement, so any `mut` bindings on the
-                        // argument will be unused. This binding mode can't be removed, because
-                        // this would affect the input to procedural macros, but they can have
-                        // their span marked as being the result of a compiler desugaring so
-                        // that they aren't linted against.
-                        input.pat.span = self.sess.source_map().mark_span_with_reason(
-                            CompilerDesugaringKind::Async, span, None);
-
-                        (binding_mode, ident, true)
-                    }
-                    _ => (BindingMode::ByValue(Mutability::Mutable), ident, false),
-                };
-
-                // Construct an argument representing `__argN: <ty>` to replace the argument of the
-                // async function if it isn't a simple pattern.
-                let arg = if is_simple_pattern {
-                    None
-                } else {
-                    Some(Arg {
-                        ty: input.ty.clone(),
-                        id,
-                        pat: P(Pat {
-                            id,
-                            node: PatKind::Ident(
-                                BindingMode::ByValue(Mutability::Immutable), ident, None,
-                            ),
-                            span,
-                        }),
-                        source: ArgSource::AsyncFn(input.pat.clone()),
-                    })
-                };
-
-                // Construct a `let __argN = __argN;` statement to insert at the top of the
-                // async closure. This makes sure that the argument is captured by the closure and
-                // that the drop order is correct.
-                let move_local = Local {
-                    pat: P(Pat {
-                        id,
-                        node: PatKind::Ident(binding_mode, ident, None),
-                        span,
-                    }),
-                    // We explicitly do not specify the type for this statement. When the user's
-                    // argument type is `impl Trait` then this would require the
-                    // `impl_trait_in_bindings` feature to also be present for that same type to
-                    // be valid in this binding. At the time of writing (13 Mar 19),
-                    // `impl_trait_in_bindings` is not stable.
-                    ty: None,
-                    init: Some(P(Expr {
-                        id,
-                        node: ExprKind::Path(None, ast::Path {
-                            span,
-                            segments: vec![PathSegment { ident, id, args: None }],
-                        }),
-                        span,
-                        attrs: ThinVec::new(),
-                    })),
-                    id,
-                    span,
-                    attrs: ThinVec::new(),
-                    source: LocalSource::AsyncFn,
-                };
-
-                // Construct a `let <pat> = __argN;` statement to insert at the top of the
-                // async closure if this isn't a simple pattern.
-                let pat_stmt = if is_simple_pattern {
-                    None
-                } else {
-                    Some(Stmt {
-                        id,
-                        node: StmtKind::Local(P(Local {
-                            pat: input.pat.clone(),
-                            ..move_local.clone()
-                        })),
-                        span,
-                    })
-                };
-
-                let move_stmt = Stmt { id, node: StmtKind::Local(P(move_local)), span };
-                arguments.push(AsyncArgument { ident, arg, pat_stmt, move_stmt });
-            }
-        }
-    }
 }
 
 pub fn emit_unclosed_delims(unclosed_delims: &mut Vec<UnmatchedBrace>, handler: &errors::Handler) {
     for unmatched in unclosed_delims.iter() {
         let mut err = handler.struct_span_err(unmatched.found_span, &format!(
             "incorrect close delimiter: `{}`",
-            pprust::token_to_string(&token::Token::CloseDelim(unmatched.found_delim)),
+            pprust::token_kind_to_string(&token::CloseDelim(unmatched.found_delim)),
         ));
         err.span_label(unmatched.found_span, "incorrect close delimiter");
         if let Some(sp) = unmatched.candidate_span {
diff --git a/src/libsyntax/parse/parser/expr.rs b/src/libsyntax/parse/parser/expr.rs
new file mode 100644
index 00000000000..ccc6bd15067
--- /dev/null
+++ b/src/libsyntax/parse/parser/expr.rs
@@ -0,0 +1,1772 @@
+use super::{Parser, PResult, Restrictions, PrevTokenKind, TokenType, PathStyle};
+use super::{BlockMode, SemiColonMode};
+use super::{SeqSep, TokenExpectType};
+
+use crate::maybe_recover_from_interpolated_ty_qpath;
+use crate::ptr::P;
+use crate::ast::{self, Attribute, AttrStyle, Ident, CaptureBy, BlockCheckMode};
+use crate::ast::{Expr, ExprKind, RangeLimits, Label, Movability, IsAsync, Arm};
+use crate::ast::{Ty, TyKind, FunctionRetTy, Arg, FnDecl};
+use crate::ast::{BinOpKind, BinOp, UnOp};
+use crate::ast::{Mac, AnonConst, Field};
+
+use crate::parse::classify;
+use crate::parse::token::{self, Token};
+use crate::parse::diagnostics::{Error};
+use crate::print::pprust;
+use crate::source_map::{self, Span};
+use crate::symbol::{kw, sym};
+use crate::util::parser::{AssocOp, Fixity, prec_let_scrutinee_needs_par};
+
+use std::mem;
+use errors::Applicability;
+use rustc_data_structures::thin_vec::ThinVec;
+
+/// Possibly accepts an `token::Interpolated` expression (a pre-parsed expression
+/// dropped into the token stream, which happens while parsing the result of
+/// macro expansion). Placement of these is not as complex as I feared it would
+/// be. The important thing is to make sure that lookahead doesn't balk at
+/// `token::Interpolated` tokens.
+macro_rules! maybe_whole_expr {
+    ($p:expr) => {
+        if let token::Interpolated(nt) = &$p.token.kind {
+            match &**nt {
+                token::NtExpr(e) | token::NtLiteral(e) => {
+                    let e = e.clone();
+                    $p.bump();
+                    return Ok(e);
+                }
+                token::NtPath(path) => {
+                    let path = path.clone();
+                    $p.bump();
+                    return Ok($p.mk_expr(
+                        $p.token.span, ExprKind::Path(None, path), ThinVec::new()
+                    ));
+                }
+                token::NtBlock(block) => {
+                    let block = block.clone();
+                    $p.bump();
+                    return Ok($p.mk_expr(
+                        $p.token.span, ExprKind::Block(block, None), ThinVec::new()
+                    ));
+                }
+                // N.B: `NtIdent(ident)` is normalized to `Ident` in `fn bump`.
+                _ => {},
+            };
+        }
+    }
+}
+
+#[derive(Debug)]
+pub(super) enum LhsExpr {
+    NotYetParsed,
+    AttributesParsed(ThinVec<Attribute>),
+    AlreadyParsed(P<Expr>),
+}
+
+impl From<Option<ThinVec<Attribute>>> for LhsExpr {
+    fn from(o: Option<ThinVec<Attribute>>) -> Self {
+        if let Some(attrs) = o {
+            LhsExpr::AttributesParsed(attrs)
+        } else {
+            LhsExpr::NotYetParsed
+        }
+    }
+}
+
+impl From<P<Expr>> for LhsExpr {
+    fn from(expr: P<Expr>) -> Self {
+        LhsExpr::AlreadyParsed(expr)
+    }
+}
+
+impl<'a> Parser<'a> {
+    /// Parses an expression.
+    #[inline]
+    pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
+        self.parse_expr_res(Restrictions::empty(), None)
+    }
+
+    fn parse_paren_expr_seq(&mut self) -> PResult<'a, Vec<P<Expr>>> {
+        self.parse_paren_comma_seq(|p| {
+            match p.parse_expr() {
+                Ok(expr) => Ok(expr),
+                Err(mut err) => match p.token.kind {
+                    token::Ident(name, false)
+                    if name == kw::Underscore && p.look_ahead(1, |t| {
+                        t == &token::Comma
+                    }) => {
+                        // Special-case handling of `foo(_, _, _)`
+                        err.emit();
+                        let sp = p.token.span;
+                        p.bump();
+                        Ok(p.mk_expr(sp, ExprKind::Err, ThinVec::new()))
+                    }
+                    _ => Err(err),
+                },
+            }
+        }).map(|(r, _)| r)
+    }
+
+    /// Parses an expression, subject to the given restrictions.
+    #[inline]
+    pub(super) fn parse_expr_res(
+        &mut self,
+        r: Restrictions,
+        already_parsed_attrs: Option<ThinVec<Attribute>>
+    ) -> PResult<'a, P<Expr>> {
+        self.with_res(r, |this| this.parse_assoc_expr(already_parsed_attrs))
+    }
+
+    /// Parses an associative expression.
+    ///
+    /// This parses an expression accounting for associativity and precedence of the operators in
+    /// the expression.
+    #[inline]
+    fn parse_assoc_expr(
+        &mut self,
+        already_parsed_attrs: Option<ThinVec<Attribute>>,
+    ) -> PResult<'a, P<Expr>> {
+        self.parse_assoc_expr_with(0, already_parsed_attrs.into())
+    }
+
+    /// Parses an associative expression with operators of at least `min_prec` precedence.
+    pub(super) fn parse_assoc_expr_with(
+        &mut self,
+        min_prec: usize,
+        lhs: LhsExpr,
+    ) -> PResult<'a, P<Expr>> {
+        let mut lhs = if let LhsExpr::AlreadyParsed(expr) = lhs {
+            expr
+        } else {
+            let attrs = match lhs {
+                LhsExpr::AttributesParsed(attrs) => Some(attrs),
+                _ => None,
+            };
+            if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) {
+                return self.parse_prefix_range_expr(attrs);
+            } else {
+                self.parse_prefix_expr(attrs)?
+            }
+        };
+        let last_type_ascription_set = self.last_type_ascription.is_some();
+
+        match (self.expr_is_complete(&lhs), AssocOp::from_token(&self.token)) {
+            (true, None) => {
+                self.last_type_ascription = None;
+                // Semi-statement forms are odd. See https://github.com/rust-lang/rust/issues/29071
+                return Ok(lhs);
+            }
+            (false, _) => {} // continue parsing the expression
+            // An exhaustive check is done in the following block, but these are checked first
+            // because they *are* ambiguous but also reasonable looking incorrect syntax, so we
+            // want to keep their span info to improve diagnostics in these cases in a later stage.
+            (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3`
+            (true, Some(AssocOp::Subtract)) | // `{ 42 } -5`
+            (true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475)
+            (true, Some(AssocOp::Add)) // `{ 42 } + 42
+            // If the next token is a keyword, then the tokens above *are* unambiguously incorrect:
+            // `if x { a } else { b } && if y { c } else { d }`
+            if !self.look_ahead(1, |t| t.is_reserved_ident()) => {
+                self.last_type_ascription = None;
+                // These cases are ambiguous and can't be identified in the parser alone
+                let sp = self.sess.source_map().start_point(self.token.span);
+                self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span);
+                return Ok(lhs);
+            }
+            (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => {
+                self.last_type_ascription = None;
+                return Ok(lhs);
+            }
+            (true, Some(_)) => {
+                // We've found an expression that would be parsed as a statement, but the next
+                // token implies this should be parsed as an expression.
+                // For example: `if let Some(x) = x { x } else { 0 } / 2`
+                let mut err = self.struct_span_err(self.token.span, &format!(
+                    "expected expression, found `{}`",
+                    pprust::token_to_string(&self.token),
+                ));
+                err.span_label(self.token.span, "expected expression");
+                self.sess.expr_parentheses_needed(
+                    &mut err,
+                    lhs.span,
+                    Some(pprust::expr_to_string(&lhs),
+                ));
+                err.emit();
+            }
+        }
+        self.expected_tokens.push(TokenType::Operator);
+        while let Some(op) = AssocOp::from_token(&self.token) {
+
+            // Adjust the span for interpolated LHS to point to the `$lhs` token and not to what
+            // it refers to. Interpolated identifiers are unwrapped early and never show up here
+            // as `PrevTokenKind::Interpolated` so if LHS is a single identifier we always process
+            // it as "interpolated", it doesn't change the answer for non-interpolated idents.
+            let lhs_span = match (self.prev_token_kind, &lhs.node) {
+                (PrevTokenKind::Interpolated, _) => self.prev_span,
+                (PrevTokenKind::Ident, &ExprKind::Path(None, ref path))
+                    if path.segments.len() == 1 => self.prev_span,
+                _ => lhs.span,
+            };
+
+            let cur_op_span = self.token.span;
+            let restrictions = if op.is_assign_like() {
+                self.restrictions & Restrictions::NO_STRUCT_LITERAL
+            } else {
+                self.restrictions
+            };
+            let prec = op.precedence();
+            if prec < min_prec {
+                break;
+            }
+            // Check for deprecated `...` syntax
+            if self.token == token::DotDotDot && op == AssocOp::DotDotEq {
+                self.err_dotdotdot_syntax(self.token.span);
+            }
+
+            if self.token == token::LArrow {
+                self.err_larrow_operator(self.token.span);
+            }
+
+            self.bump();
+            if op.is_comparison() {
+                self.check_no_chained_comparison(&lhs, &op);
+            }
+            // Special cases:
+            if op == AssocOp::As {
+                lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Cast)?;
+                continue
+            } else if op == AssocOp::Colon {
+                let maybe_path = self.could_ascription_be_path(&lhs.node);
+                self.last_type_ascription = Some((self.prev_span, maybe_path));
+
+                lhs = self.parse_assoc_op_cast(lhs, lhs_span, ExprKind::Type)?;
+                continue
+            } else if op == AssocOp::DotDot || op == AssocOp::DotDotEq {
+                // If we didn’t have to handle `x..`/`x..=`, it would be pretty easy to
+                // generalise it to the Fixity::None code.
+                //
+                // We have 2 alternatives here: `x..y`/`x..=y` and `x..`/`x..=` The other
+                // two variants are handled with `parse_prefix_range_expr` call above.
+                let rhs = if self.is_at_start_of_range_notation_rhs() {
+                    Some(self.parse_assoc_expr_with(prec + 1, LhsExpr::NotYetParsed)?)
+                } else {
+                    None
+                };
+                let (lhs_span, rhs_span) = (lhs.span, if let Some(ref x) = rhs {
+                    x.span
+                } else {
+                    cur_op_span
+                });
+                let limits = if op == AssocOp::DotDot {
+                    RangeLimits::HalfOpen
+                } else {
+                    RangeLimits::Closed
+                };
+
+                let r = self.mk_range(Some(lhs), rhs, limits)?;
+                lhs = self.mk_expr(lhs_span.to(rhs_span), r, ThinVec::new());
+                break
+            }
+
+            let fixity = op.fixity();
+            let prec_adjustment = match fixity {
+                Fixity::Right => 0,
+                Fixity::Left => 1,
+                // We currently have no non-associative operators that are not handled above by
+                // the special cases. The code is here only for future convenience.
+                Fixity::None => 1,
+            };
+            let rhs = self.with_res(
+                restrictions - Restrictions::STMT_EXPR,
+                |this| this.parse_assoc_expr_with(prec + prec_adjustment, LhsExpr::NotYetParsed)
+            )?;
+
+            // Make sure that the span of the parent node is larger than the span of lhs and rhs,
+            // including the attributes.
+            let lhs_span = lhs
+                .attrs
+                .iter()
+                .filter(|a| a.style == AttrStyle::Outer)
+                .next()
+                .map_or(lhs_span, |a| a.span);
+            let span = lhs_span.to(rhs.span);
+            lhs = match op {
+                AssocOp::Add | AssocOp::Subtract | AssocOp::Multiply | AssocOp::Divide |
+                AssocOp::Modulus | AssocOp::LAnd | AssocOp::LOr | AssocOp::BitXor |
+                AssocOp::BitAnd | AssocOp::BitOr | AssocOp::ShiftLeft | AssocOp::ShiftRight |
+                AssocOp::Equal | AssocOp::Less | AssocOp::LessEqual | AssocOp::NotEqual |
+                AssocOp::Greater | AssocOp::GreaterEqual => {
+                    let ast_op = op.to_ast_binop().unwrap();
+                    let binary = self.mk_binary(source_map::respan(cur_op_span, ast_op), lhs, rhs);
+                    self.mk_expr(span, binary, ThinVec::new())
+                }
+                AssocOp::Assign => self.mk_expr(span, ExprKind::Assign(lhs, rhs), ThinVec::new()),
+                AssocOp::AssignOp(k) => {
+                    let aop = match k {
+                        token::Plus =>    BinOpKind::Add,
+                        token::Minus =>   BinOpKind::Sub,
+                        token::Star =>    BinOpKind::Mul,
+                        token::Slash =>   BinOpKind::Div,
+                        token::Percent => BinOpKind::Rem,
+                        token::Caret =>   BinOpKind::BitXor,
+                        token::And =>     BinOpKind::BitAnd,
+                        token::Or =>      BinOpKind::BitOr,
+                        token::Shl =>     BinOpKind::Shl,
+                        token::Shr =>     BinOpKind::Shr,
+                    };
+                    let aopexpr = self.mk_assign_op(source_map::respan(cur_op_span, aop), lhs, rhs);
+                    self.mk_expr(span, aopexpr, ThinVec::new())
+                }
+                AssocOp::As | AssocOp::Colon | AssocOp::DotDot | AssocOp::DotDotEq => {
+                    self.bug("AssocOp should have been handled by special case")
+                }
+            };
+
+            if let Fixity::None = fixity { break }
+        }
+        if last_type_ascription_set {
+            self.last_type_ascription = None;
+        }
+        Ok(lhs)
+    }
+
+    /// Checks if this expression is a successfully parsed statement.
+    fn expr_is_complete(&self, e: &Expr) -> bool {
+        self.restrictions.contains(Restrictions::STMT_EXPR) &&
+            !classify::expr_requires_semi_to_be_stmt(e)
+    }
+
+    fn is_at_start_of_range_notation_rhs(&self) -> bool {
+        if self.token.can_begin_expr() {
+            // parse `for i in 1.. { }` as infinite loop, not as `for i in (1..{})`.
+            if self.token == token::OpenDelim(token::Brace) {
+                return !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
+            }
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Parse prefix-forms of range notation: `..expr`, `..`, `..=expr`
+    fn parse_prefix_range_expr(
+        &mut self,
+        already_parsed_attrs: Option<ThinVec<Attribute>>
+    ) -> PResult<'a, P<Expr>> {
+        // Check for deprecated `...` syntax
+        if self.token == token::DotDotDot {
+            self.err_dotdotdot_syntax(self.token.span);
+        }
+
+        debug_assert!([token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind),
+                      "parse_prefix_range_expr: token {:?} is not DotDot/DotDotEq",
+                      self.token);
+        let tok = self.token.clone();
+        let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
+        let lo = self.token.span;
+        let mut hi = self.token.span;
+        self.bump();
+        let opt_end = if self.is_at_start_of_range_notation_rhs() {
+            // RHS must be parsed with more associativity than the dots.
+            let next_prec = AssocOp::from_token(&tok).unwrap().precedence() + 1;
+            Some(self.parse_assoc_expr_with(next_prec, LhsExpr::NotYetParsed)
+                .map(|x| {
+                    hi = x.span;
+                    x
+                })?)
+        } else {
+            None
+        };
+        let limits = if tok == token::DotDot {
+            RangeLimits::HalfOpen
+        } else {
+            RangeLimits::Closed
+        };
+
+        let r = self.mk_range(None, opt_end, limits)?;
+        Ok(self.mk_expr(lo.to(hi), r, attrs))
+    }
+
+    /// Parse a prefix-unary-operator expr
+    fn parse_prefix_expr(
+        &mut self,
+        already_parsed_attrs: Option<ThinVec<Attribute>>
+    ) -> PResult<'a, P<Expr>> {
+        let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
+        let lo = self.token.span;
+        // Note: when adding new unary operators, don't forget to adjust TokenKind::can_begin_expr()
+        let (hi, ex) = match self.token.kind {
+            token::Not => {
+                self.bump();
+                let e = self.parse_prefix_expr(None);
+                let (span, e) = self.interpolated_or_expr_span(e)?;
+                (lo.to(span), self.mk_unary(UnOp::Not, e))
+            }
+            // Suggest `!` for bitwise negation when encountering a `~`
+            token::Tilde => {
+                self.bump();
+                let e = self.parse_prefix_expr(None);
+                let (span, e) = self.interpolated_or_expr_span(e)?;
+                let span_of_tilde = lo;
+                self.struct_span_err(span_of_tilde, "`~` cannot be used as a unary operator")
+                    .span_suggestion_short(
+                        span_of_tilde,
+                        "use `!` to perform bitwise negation",
+                        "!".to_owned(),
+                        Applicability::MachineApplicable
+                    )
+                    .emit();
+                (lo.to(span), self.mk_unary(UnOp::Not, e))
+            }
+            token::BinOp(token::Minus) => {
+                self.bump();
+                let e = self.parse_prefix_expr(None);
+                let (span, e) = self.interpolated_or_expr_span(e)?;
+                (lo.to(span), self.mk_unary(UnOp::Neg, e))
+            }
+            token::BinOp(token::Star) => {
+                self.bump();
+                let e = self.parse_prefix_expr(None);
+                let (span, e) = self.interpolated_or_expr_span(e)?;
+                (lo.to(span), self.mk_unary(UnOp::Deref, e))
+            }
+            token::BinOp(token::And) | token::AndAnd => {
+                self.expect_and()?;
+                let m = self.parse_mutability();
+                let e = self.parse_prefix_expr(None);
+                let (span, e) = self.interpolated_or_expr_span(e)?;
+                (lo.to(span), ExprKind::AddrOf(m, e))
+            }
+            token::Ident(..) if self.token.is_keyword(kw::Box) => {
+                self.bump();
+                let e = self.parse_prefix_expr(None);
+                let (span, e) = self.interpolated_or_expr_span(e)?;
+                (lo.to(span), ExprKind::Box(e))
+            }
+            token::Ident(..) if self.token.is_ident_named(sym::not) => {
+                // `not` is just an ordinary identifier in Rust-the-language,
+                // but as `rustc`-the-compiler, we can issue clever diagnostics
+                // for confused users who really want to say `!`
+                let token_cannot_continue_expr = |t: &Token| match t.kind {
+                    // These tokens can start an expression after `!`, but
+                    // can't continue an expression after an ident
+                    token::Ident(name, is_raw) => token::ident_can_begin_expr(name, t.span, is_raw),
+                    token::Literal(..) | token::Pound => true,
+                    _ => t.is_whole_expr(),
+                };
+                let cannot_continue_expr = self.look_ahead(1, token_cannot_continue_expr);
+                if cannot_continue_expr {
+                    self.bump();
+                    // Emit the error ...
+                    self.struct_span_err(
+                        self.token.span,
+                        &format!("unexpected {} after identifier",self.this_token_descr())
+                    )
+                    .span_suggestion_short(
+                        // Span the `not` plus trailing whitespace to avoid
+                        // trailing whitespace after the `!` in our suggestion
+                        self.sess.source_map()
+                            .span_until_non_whitespace(lo.to(self.token.span)),
+                        "use `!` to perform logical negation",
+                        "!".to_owned(),
+                        Applicability::MachineApplicable
+                    )
+                    .emit();
+                    // —and recover! (just as if we were in the block
+                    // for the `token::Not` arm)
+                    let e = self.parse_prefix_expr(None);
+                    let (span, e) = self.interpolated_or_expr_span(e)?;
+                    (lo.to(span), self.mk_unary(UnOp::Not, e))
+                } else {
+                    return self.parse_dot_or_call_expr(Some(attrs));
+                }
+            }
+            _ => { return self.parse_dot_or_call_expr(Some(attrs)); }
+        };
+        return Ok(self.mk_expr(lo.to(hi), ex, attrs));
+    }
+
+    /// Returns the span of expr, if it was not interpolated or the span of the interpolated token.
+    fn interpolated_or_expr_span(
+        &self,
+        expr: PResult<'a, P<Expr>>,
+    ) -> PResult<'a, (Span, P<Expr>)> {
+        expr.map(|e| {
+            if self.prev_token_kind == PrevTokenKind::Interpolated {
+                (self.prev_span, e)
+            } else {
+                (e.span, e)
+            }
+        })
+    }
+
+    fn parse_assoc_op_cast(&mut self, lhs: P<Expr>, lhs_span: Span,
+                           expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind)
+                           -> PResult<'a, P<Expr>> {
+        let mk_expr = |this: &mut Self, rhs: P<Ty>| {
+            this.mk_expr(lhs_span.to(rhs.span), expr_kind(lhs, rhs), ThinVec::new())
+        };
+
+        // Save the state of the parser before parsing type normally, in case there is a
+        // LessThan comparison after this cast.
+        let parser_snapshot_before_type = self.clone();
+        match self.parse_ty_no_plus() {
+            Ok(rhs) => {
+                Ok(mk_expr(self, rhs))
+            }
+            Err(mut type_err) => {
+                // Rewind to before attempting to parse the type with generics, to recover
+                // from situations like `x as usize < y` in which we first tried to parse
+                // `usize < y` as a type with generic arguments.
+                let parser_snapshot_after_type = self.clone();
+                mem::replace(self, parser_snapshot_before_type);
+
+                match self.parse_path(PathStyle::Expr) {
+                    Ok(path) => {
+                        let (op_noun, op_verb) = match self.token.kind {
+                            token::Lt => ("comparison", "comparing"),
+                            token::BinOp(token::Shl) => ("shift", "shifting"),
+                            _ => {
+                                // We can end up here even without `<` being the next token, for
+                                // example because `parse_ty_no_plus` returns `Err` on keywords,
+                                // but `parse_path` returns `Ok` on them due to error recovery.
+                                // Return original error and parser state.
+                                mem::replace(self, parser_snapshot_after_type);
+                                return Err(type_err);
+                            }
+                        };
+
+                        // Successfully parsed the type path leaving a `<` yet to parse.
+                        type_err.cancel();
+
+                        // Report non-fatal diagnostics, keep `x as usize` as an expression
+                        // in AST and continue parsing.
+                        let msg = format!("`<` is interpreted as a start of generic \
+                                           arguments for `{}`, not a {}", path, op_noun);
+                        let span_after_type = parser_snapshot_after_type.token.span;
+                        let expr = mk_expr(self, P(Ty {
+                            span: path.span,
+                            node: TyKind::Path(None, path),
+                            id: ast::DUMMY_NODE_ID
+                        }));
+
+                        let expr_str = self.span_to_snippet(expr.span)
+                            .unwrap_or_else(|_| pprust::expr_to_string(&expr));
+
+                        self.struct_span_err(self.token.span, &msg)
+                            .span_label(
+                                self.look_ahead(1, |t| t.span).to(span_after_type),
+                                "interpreted as generic arguments"
+                            )
+                            .span_label(self.token.span, format!("not interpreted as {}", op_noun))
+                            .span_suggestion(
+                                expr.span,
+                                &format!("try {} the cast value", op_verb),
+                                format!("({})", expr_str),
+                                Applicability::MachineApplicable
+                            )
+                            .emit();
+
+                        Ok(expr)
+                    }
+                    Err(mut path_err) => {
+                        // Couldn't parse as a path, return original error and parser state.
+                        path_err.cancel();
+                        mem::replace(self, parser_snapshot_after_type);
+                        Err(type_err)
+                    }
+                }
+            }
+        }
+    }
+
+    /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
+    fn parse_dot_or_call_expr(
+        &mut self,
+        already_parsed_attrs: Option<ThinVec<Attribute>>,
+    ) -> PResult<'a, P<Expr>> {
+        let attrs = self.parse_or_use_outer_attributes(already_parsed_attrs)?;
+
+        let b = self.parse_bottom_expr();
+        let (span, b) = self.interpolated_or_expr_span(b)?;
+        self.parse_dot_or_call_expr_with(b, span, attrs)
+    }
+
+    pub(super) fn parse_dot_or_call_expr_with(
+        &mut self,
+        e0: P<Expr>,
+        lo: Span,
+        mut attrs: ThinVec<Attribute>,
+    ) -> PResult<'a, P<Expr>> {
+        // Stitch the list of outer attributes onto the return value.
+        // A little bit ugly, but the best way given the current code
+        // structure
+        self.parse_dot_or_call_expr_with_(e0, lo).map(|expr|
+            expr.map(|mut expr| {
+                attrs.extend::<Vec<_>>(expr.attrs.into());
+                expr.attrs = attrs;
+                match expr.node {
+                    ExprKind::If(..) if !expr.attrs.is_empty() => {
+                        // Just point to the first attribute in there...
+                        let span = expr.attrs[0].span;
+                        self.span_err(span, "attributes are not yet allowed on `if` expressions");
+                    }
+                    _ => {}
+                }
+                expr
+            })
+        )
+    }
+
+    fn parse_dot_or_call_expr_with_(&mut self, e0: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
+        let mut e = e0;
+        let mut hi;
+        loop {
+            // expr?
+            while self.eat(&token::Question) {
+                let hi = self.prev_span;
+                e = self.mk_expr(lo.to(hi), ExprKind::Try(e), ThinVec::new());
+            }
+
+            // expr.f
+            if self.eat(&token::Dot) {
+                match self.token.kind {
+                    token::Ident(..) => {
+                        e = self.parse_dot_suffix(e, lo)?;
+                    }
+                    token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {
+                        let span = self.token.span;
+                        self.bump();
+                        let field = ExprKind::Field(e, Ident::new(symbol, span));
+                        e = self.mk_expr(lo.to(span), field, ThinVec::new());
+
+                        self.expect_no_suffix(span, "a tuple index", suffix);
+                    }
+                    token::Literal(token::Lit { kind: token::Float, symbol, .. }) => {
+                      self.bump();
+                      let fstr = symbol.as_str();
+                      let msg = format!("unexpected token: `{}`", symbol);
+                      let mut err = self.diagnostic().struct_span_err(self.prev_span, &msg);
+                      err.span_label(self.prev_span, "unexpected token");
+                      if fstr.chars().all(|x| "0123456789.".contains(x)) {
+                          let float = match fstr.parse::<f64>().ok() {
+                              Some(f) => f,
+                              None => continue,
+                          };
+                          let sugg = pprust::to_string(|s| {
+                              s.popen();
+                              s.print_expr(&e);
+                              s.s.word( ".");
+                              s.print_usize(float.trunc() as usize);
+                              s.pclose();
+                              s.s.word(".");
+                              s.s.word(fstr.splitn(2, ".").last().unwrap().to_string())
+                          });
+                          err.span_suggestion(
+                              lo.to(self.prev_span),
+                              "try parenthesizing the first index",
+                              sugg,
+                              Applicability::MachineApplicable
+                          );
+                      }
+                      return Err(err);
+
+                    }
+                    _ => {
+                        // FIXME Could factor this out into non_fatal_unexpected or something.
+                        let actual = self.this_token_to_string();
+                        self.span_err(self.token.span, &format!("unexpected token: `{}`", actual));
+                    }
+                }
+                continue;
+            }
+            if self.expr_is_complete(&e) { break; }
+            match self.token.kind {
+                // expr(...)
+                token::OpenDelim(token::Paren) => {
+                    let seq = self.parse_paren_expr_seq().map(|es| {
+                        let nd = self.mk_call(e, es);
+                        let hi = self.prev_span;
+                        self.mk_expr(lo.to(hi), nd, ThinVec::new())
+                    });
+                    e = self.recover_seq_parse_error(token::Paren, lo, seq);
+                }
+
+                // expr[...]
+                // Could be either an index expression or a slicing expression.
+                token::OpenDelim(token::Bracket) => {
+                    self.bump();
+                    let ix = self.parse_expr()?;
+                    hi = self.token.span;
+                    self.expect(&token::CloseDelim(token::Bracket))?;
+                    let index = self.mk_index(e, ix);
+                    e = self.mk_expr(lo.to(hi), index, ThinVec::new())
+                }
+                _ => return Ok(e)
+            }
+        }
+        return Ok(e);
+    }
+
+    /// Assuming we have just parsed `.`, continue parsing into an expression.
+    fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
+        if self.token.span.rust_2018() && self.eat_keyword(kw::Await) {
+            return self.mk_await_expr(self_arg, lo);
+        }
+
+        let segment = self.parse_path_segment(PathStyle::Expr)?;
+        self.check_trailing_angle_brackets(&segment, token::OpenDelim(token::Paren));
+
+        Ok(match self.token.kind {
+            token::OpenDelim(token::Paren) => {
+                // Method call `expr.f()`
+                let mut args = self.parse_paren_expr_seq()?;
+                args.insert(0, self_arg);
+
+                let span = lo.to(self.prev_span);
+                self.mk_expr(span, ExprKind::MethodCall(segment, args), ThinVec::new())
+            }
+            _ => {
+                // Field access `expr.f`
+                if let Some(args) = segment.args {
+                    self.span_err(args.span(),
+                                  "field expressions may not have generic arguments");
+                }
+
+                let span = lo.to(self.prev_span);
+                self.mk_expr(span, ExprKind::Field(self_arg, segment.ident), ThinVec::new())
+            }
+        })
+    }
+
+
+    /// At the bottom (top?) of the precedence hierarchy,
+    /// Parses things like parenthesized exprs, macros, `return`, etc.
+    ///
+    /// N.B., this does not parse outer attributes, and is private because it only works
+    /// correctly if called from `parse_dot_or_call_expr()`.
+    fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {
+        maybe_recover_from_interpolated_ty_qpath!(self, true);
+        maybe_whole_expr!(self);
+
+        // Outer attributes are already parsed and will be
+        // added to the return value after the fact.
+        //
+        // Therefore, prevent sub-parser from parsing
+        // attributes by giving them a empty "already parsed" list.
+        let mut attrs = ThinVec::new();
+
+        let lo = self.token.span;
+        let mut hi = self.token.span;
+
+        let ex: ExprKind;
+
+        macro_rules! parse_lit {
+            () => {
+                match self.parse_lit() {
+                    Ok(literal) => {
+                        hi = self.prev_span;
+                        ex = ExprKind::Lit(literal);
+                    }
+                    Err(mut err) => {
+                        self.cancel(&mut err);
+                        return Err(self.expected_expression_found());
+                    }
+                }
+            }
+        }
+
+        // Note: when adding new syntax here, don't forget to adjust TokenKind::can_begin_expr().
+        match self.token.kind {
+            // This match arm is a special-case of the `_` match arm below and
+            // could be removed without changing functionality, but it's faster
+            // to have it here, especially for programs with large constants.
+            token::Literal(_) => {
+                parse_lit!()
+            }
+            token::OpenDelim(token::Paren) => {
+                self.bump();
+
+                attrs.extend(self.parse_inner_attributes()?);
+
+                // (e) is parenthesized e
+                // (e,) is a tuple with only one field, e
+                let mut es = vec![];
+                let mut trailing_comma = false;
+                let mut recovered = false;
+                while self.token != token::CloseDelim(token::Paren) {
+                    es.push(match self.parse_expr() {
+                        Ok(es) => es,
+                        Err(mut err) => {
+                            // recover from parse error in tuple list
+                            match self.token.kind {
+                                token::Ident(name, false)
+                                if name == kw::Underscore && self.look_ahead(1, |t| {
+                                    t == &token::Comma
+                                }) => {
+                                    // Special-case handling of `Foo<(_, _, _)>`
+                                    err.emit();
+                                    let sp = self.token.span;
+                                    self.bump();
+                                    self.mk_expr(sp, ExprKind::Err, ThinVec::new())
+                                }
+                                _ => return Ok(
+                                    self.recover_seq_parse_error(token::Paren, lo, Err(err)),
+                                ),
+                            }
+                        }
+                    });
+                    recovered = self.expect_one_of(
+                        &[],
+                        &[token::Comma, token::CloseDelim(token::Paren)],
+                    )?;
+                    if self.eat(&token::Comma) {
+                        trailing_comma = true;
+                    } else {
+                        trailing_comma = false;
+                        break;
+                    }
+                }
+                if !recovered {
+                    self.bump();
+                }
+
+                hi = self.prev_span;
+                ex = if es.len() == 1 && !trailing_comma {
+                    ExprKind::Paren(es.into_iter().nth(0).unwrap())
+                } else {
+                    ExprKind::Tup(es)
+                };
+            }
+            token::OpenDelim(token::Brace) => {
+                return self.parse_block_expr(None, lo, BlockCheckMode::Default, attrs);
+            }
+            token::BinOp(token::Or) | token::OrOr => {
+                return self.parse_lambda_expr(attrs);
+            }
+            token::OpenDelim(token::Bracket) => {
+                self.bump();
+
+                attrs.extend(self.parse_inner_attributes()?);
+
+                if self.eat(&token::CloseDelim(token::Bracket)) {
+                    // Empty vector.
+                    ex = ExprKind::Array(Vec::new());
+                } else {
+                    // Nonempty vector.
+                    let first_expr = self.parse_expr()?;
+                    if self.eat(&token::Semi) {
+                        // Repeating array syntax: [ 0; 512 ]
+                        let count = AnonConst {
+                            id: ast::DUMMY_NODE_ID,
+                            value: self.parse_expr()?,
+                        };
+                        self.expect(&token::CloseDelim(token::Bracket))?;
+                        ex = ExprKind::Repeat(first_expr, count);
+                    } else if self.eat(&token::Comma) {
+                        // Vector with two or more elements.
+                        let remaining_exprs = self.parse_seq_to_end(
+                            &token::CloseDelim(token::Bracket),
+                            SeqSep::trailing_allowed(token::Comma),
+                            |p| Ok(p.parse_expr()?)
+                        )?;
+                        let mut exprs = vec![first_expr];
+                        exprs.extend(remaining_exprs);
+                        ex = ExprKind::Array(exprs);
+                    } else {
+                        // Vector with one element.
+                        self.expect(&token::CloseDelim(token::Bracket))?;
+                        ex = ExprKind::Array(vec![first_expr]);
+                    }
+                }
+                hi = self.prev_span;
+            }
+            _ => {
+                if self.eat_lt() {
+                    let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
+                    hi = path.span;
+                    return Ok(self.mk_expr(lo.to(hi), ExprKind::Path(Some(qself), path), attrs));
+                }
+                if self.check_keyword(kw::Move) || self.check_keyword(kw::Static) {
+                    return self.parse_lambda_expr(attrs);
+                }
+                if self.eat_keyword(kw::If) {
+                    return self.parse_if_expr(attrs);
+                }
+                if self.eat_keyword(kw::For) {
+                    let lo = self.prev_span;
+                    return self.parse_for_expr(None, lo, attrs);
+                }
+                if self.eat_keyword(kw::While) {
+                    let lo = self.prev_span;
+                    return self.parse_while_expr(None, lo, attrs);
+                }
+                if let Some(label) = self.eat_label() {
+                    let lo = label.ident.span;
+                    self.expect(&token::Colon)?;
+                    if self.eat_keyword(kw::While) {
+                        return self.parse_while_expr(Some(label), lo, attrs)
+                    }
+                    if self.eat_keyword(kw::For) {
+                        return self.parse_for_expr(Some(label), lo, attrs)
+                    }
+                    if self.eat_keyword(kw::Loop) {
+                        return self.parse_loop_expr(Some(label), lo, attrs)
+                    }
+                    if self.token == token::OpenDelim(token::Brace) {
+                        return self.parse_block_expr(Some(label),
+                                                     lo,
+                                                     BlockCheckMode::Default,
+                                                     attrs);
+                    }
+                    let msg = "expected `while`, `for`, `loop` or `{` after a label";
+                    let mut err = self.fatal(msg);
+                    err.span_label(self.token.span, msg);
+                    return Err(err);
+                }
+                if self.eat_keyword(kw::Loop) {
+                    let lo = self.prev_span;
+                    return self.parse_loop_expr(None, lo, attrs);
+                }
+                if self.eat_keyword(kw::Continue) {
+                    let label = self.eat_label();
+                    let ex = ExprKind::Continue(label);
+                    let hi = self.prev_span;
+                    return Ok(self.mk_expr(lo.to(hi), ex, attrs));
+                }
+                if self.eat_keyword(kw::Match) {
+                    let match_sp = self.prev_span;
+                    return self.parse_match_expr(attrs).map_err(|mut err| {
+                        err.span_label(match_sp, "while parsing this match expression");
+                        err
+                    });
+                }
+                if self.eat_keyword(kw::Unsafe) {
+                    return self.parse_block_expr(
+                        None,
+                        lo,
+                        BlockCheckMode::Unsafe(ast::UserProvided),
+                        attrs);
+                }
+                if self.is_do_catch_block() {
+                    let mut db = self.fatal("found removed `do catch` syntax");
+                    db.help("Following RFC #2388, the new non-placeholder syntax is `try`");
+                    return Err(db);
+                }
+                if self.is_try_block() {
+                    let lo = self.token.span;
+                    assert!(self.eat_keyword(kw::Try));
+                    return self.parse_try_block(lo, attrs);
+                }
+
+                // Span::rust_2018() is somewhat expensive; don't get it repeatedly.
+                let is_span_rust_2018 = self.token.span.rust_2018();
+                if is_span_rust_2018 && self.check_keyword(kw::Async) {
+                    return if self.is_async_block() { // check for `async {` and `async move {`
+                        self.parse_async_block(attrs)
+                    } else {
+                        self.parse_lambda_expr(attrs)
+                    };
+                }
+                if self.eat_keyword(kw::Return) {
+                    if self.token.can_begin_expr() {
+                        let e = self.parse_expr()?;
+                        hi = e.span;
+                        ex = ExprKind::Ret(Some(e));
+                    } else {
+                        ex = ExprKind::Ret(None);
+                    }
+                } else if self.eat_keyword(kw::Break) {
+                    let label = self.eat_label();
+                    let e = if self.token.can_begin_expr()
+                               && !(self.token == token::OpenDelim(token::Brace)
+                                    && self.restrictions.contains(
+                                           Restrictions::NO_STRUCT_LITERAL)) {
+                        Some(self.parse_expr()?)
+                    } else {
+                        None
+                    };
+                    ex = ExprKind::Break(label, e);
+                    hi = self.prev_span;
+                } else if self.eat_keyword(kw::Yield) {
+                    if self.token.can_begin_expr() {
+                        let e = self.parse_expr()?;
+                        hi = e.span;
+                        ex = ExprKind::Yield(Some(e));
+                    } else {
+                        ex = ExprKind::Yield(None);
+                    }
+
+                    let span = lo.to(hi);
+                    self.sess.yield_spans.borrow_mut().push(span);
+                } else if self.eat_keyword(kw::Let) {
+                    return self.parse_let_expr(attrs);
+                } else if is_span_rust_2018 && self.eat_keyword(kw::Await) {
+                    let (await_hi, e_kind) = self.parse_incorrect_await_syntax(lo, self.prev_span)?;
+                    hi = await_hi;
+                    ex = e_kind;
+                } else if self.token.is_path_start() {
+                    let path = self.parse_path(PathStyle::Expr)?;
+
+                    // `!`, as an operator, is prefix, so we know this isn't that
+                    if self.eat(&token::Not) {
+                        // MACRO INVOCATION expression
+                        let (delim, tts) = self.expect_delimited_token_tree()?;
+                        hi = self.prev_span;
+                        ex = ExprKind::Mac(Mac {
+                            path,
+                            tts,
+                            delim,
+                            span: lo.to(hi),
+                            prior_type_ascription: self.last_type_ascription,
+                        });
+                    } else if self.check(&token::OpenDelim(token::Brace)) {
+                        if let Some(expr) = self.maybe_parse_struct_expr(lo, &path, &attrs) {
+                            return expr;
+                        } else {
+                            hi = path.span;
+                            ex = ExprKind::Path(None, path);
+                        }
+                    } else {
+                        hi = path.span;
+                        ex = ExprKind::Path(None, path);
+                    }
+                } else {
+                    if !self.unclosed_delims.is_empty() && self.check(&token::Semi) {
+                        // Don't complain about bare semicolons after unclosed braces
+                        // recovery in order to keep the error count down. Fixing the
+                        // delimiters will possibly also fix the bare semicolon found in
+                        // expression context. For example, silence the following error:
+                        // ```
+                        // error: expected expression, found `;`
+                        //  --> file.rs:2:13
+                        //   |
+                        // 2 |     foo(bar(;
+                        //   |             ^ expected expression
+                        // ```
+                        self.bump();
+                        return Ok(self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()));
+                    }
+                    parse_lit!()
+                }
+            }
+        }
+
+        let expr = self.mk_expr(lo.to(hi), ex, attrs);
+        self.maybe_recover_from_bad_qpath(expr, true)
+    }
+
+    /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
+    crate fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
+        maybe_whole_expr!(self);
+
+        let minus_lo = self.token.span;
+        let minus_present = self.eat(&token::BinOp(token::Minus));
+        let lo = self.token.span;
+        let literal = self.parse_lit()?;
+        let hi = self.prev_span;
+        let expr = self.mk_expr(lo.to(hi), ExprKind::Lit(literal), ThinVec::new());
+
+        if minus_present {
+            let minus_hi = self.prev_span;
+            let unary = self.mk_unary(UnOp::Neg, expr);
+            Ok(self.mk_expr(minus_lo.to(minus_hi), unary, ThinVec::new()))
+        } else {
+            Ok(expr)
+        }
+    }
+
+    /// Parses a block or unsafe block.
+    crate fn parse_block_expr(
+        &mut self,
+        opt_label: Option<Label>,
+        lo: Span,
+        blk_mode: BlockCheckMode,
+        outer_attrs: ThinVec<Attribute>,
+    ) -> PResult<'a, P<Expr>> {
+        self.expect(&token::OpenDelim(token::Brace))?;
+
+        let mut attrs = outer_attrs;
+        attrs.extend(self.parse_inner_attributes()?);
+
+        let blk = self.parse_block_tail(lo, blk_mode)?;
+        return Ok(self.mk_expr(blk.span, ExprKind::Block(blk, opt_label), attrs));
+    }
+
+    /// Parses `move |args| expr`.
+    fn parse_lambda_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
+        let lo = self.token.span;
+
+        let movability = if self.eat_keyword(kw::Static) {
+            Movability::Static
+        } else {
+            Movability::Movable
+        };
+
+        let asyncness = if self.token.span.rust_2018() {
+            self.parse_asyncness()
+        } else {
+            IsAsync::NotAsync
+        };
+        if asyncness.is_async() {
+            // Feature gate `async ||` closures.
+            self.sess.async_closure_spans.borrow_mut().push(self.prev_span);
+        }
+
+        let capture_clause = self.parse_capture_clause();
+        let decl = self.parse_fn_block_decl()?;
+        let decl_hi = self.prev_span;
+        let body = match decl.output {
+            FunctionRetTy::Default(_) => {
+                let restrictions = self.restrictions - Restrictions::STMT_EXPR;
+                self.parse_expr_res(restrictions, None)?
+            },
+            _ => {
+                // If an explicit return type is given, require a
+                // block to appear (RFC 968).
+                let body_lo = self.token.span;
+                self.parse_block_expr(None, body_lo, BlockCheckMode::Default, ThinVec::new())?
+            }
+        };
+
+        Ok(self.mk_expr(
+            lo.to(body.span),
+            ExprKind::Closure(capture_clause, asyncness, movability, decl, body, lo.to(decl_hi)),
+            attrs))
+    }
+
+    /// Parse an optional `move` prefix to a closure lke construct.
+    fn parse_capture_clause(&mut self) -> CaptureBy {
+        if self.eat_keyword(kw::Move) {
+            CaptureBy::Value
+        } else {
+            CaptureBy::Ref
+        }
+    }
+
+    /// Parses the `|arg, arg|` header of a closure.
+    fn parse_fn_block_decl(&mut self) -> PResult<'a, P<FnDecl>> {
+        let inputs_captures = {
+            if self.eat(&token::OrOr) {
+                Vec::new()
+            } else {
+                self.expect(&token::BinOp(token::Or))?;
+                let args = self.parse_seq_to_before_tokens(
+                    &[&token::BinOp(token::Or), &token::OrOr],
+                    SeqSep::trailing_allowed(token::Comma),
+                    TokenExpectType::NoExpect,
+                    |p| p.parse_fn_block_arg()
+                )?.0;
+                self.expect_or()?;
+                args
+            }
+        };
+        let output = self.parse_ret_ty(true)?;
+
+        Ok(P(FnDecl {
+            inputs: inputs_captures,
+            output,
+            c_variadic: false
+        }))
+    }
+
+    /// Parses an argument in a lambda header (e.g., `|arg, arg|`).
+    fn parse_fn_block_arg(&mut self) -> PResult<'a, Arg> {
+        let lo = self.token.span;
+        let attrs = self.parse_arg_attributes()?;
+        let pat = self.parse_pat(Some("argument name"))?;
+        let t = if self.eat(&token::Colon) {
+            self.parse_ty()?
+        } else {
+            P(Ty {
+                id: ast::DUMMY_NODE_ID,
+                node: TyKind::Infer,
+                span: self.prev_span,
+            })
+        };
+        let span = lo.to(self.token.span);
+        Ok(Arg {
+            attrs: attrs.into(),
+            ty: t,
+            pat,
+            span,
+            id: ast::DUMMY_NODE_ID
+        })
+    }
+
+    /// Parses an `if` expression (`if` token already eaten).
+    fn parse_if_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
+        let lo = self.prev_span;
+        let cond = self.parse_cond_expr()?;
+
+        // Verify that the parsed `if` condition makes sense as a condition. If it is a block, then
+        // verify that the last statement is either an implicit return (no `;`) or an explicit
+        // return. This won't catch blocks with an explicit `return`, but that would be caught by
+        // the dead code lint.
+        if self.eat_keyword(kw::Else) || !cond.returns() {
+            let sp = self.sess.source_map().next_point(lo);
+            let mut err = self.diagnostic()
+                .struct_span_err(sp, "missing condition for `if` expression");
+            err.span_label(sp, "expected if condition here");
+            return Err(err)
+        }
+        let not_block = self.token != token::OpenDelim(token::Brace);
+        let thn = self.parse_block().map_err(|mut err| {
+            if not_block {
+                err.span_label(lo, "this `if` statement has a condition, but no block");
+            }
+            err
+        })?;
+        let mut els: Option<P<Expr>> = None;
+        let mut hi = thn.span;
+        if self.eat_keyword(kw::Else) {
+            let elexpr = self.parse_else_expr()?;
+            hi = elexpr.span;
+            els = Some(elexpr);
+        }
+        Ok(self.mk_expr(lo.to(hi), ExprKind::If(cond, thn, els), attrs))
+    }
+
+    /// Parse the condition of a `if`- or `while`-expression
+    fn parse_cond_expr(&mut self) -> PResult<'a, P<Expr>> {
+        let cond = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
+
+        if let ExprKind::Let(..) = cond.node {
+            // Remove the last feature gating of a `let` expression since it's stable.
+            let last = self.sess.let_chains_spans.borrow_mut().pop();
+            debug_assert_eq!(cond.span, last.unwrap());
+        }
+
+        Ok(cond)
+    }
+
+    /// Parses a `let $pats = $expr` pseudo-expression.
+    /// The `let` token has already been eaten.
+    fn parse_let_expr(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
+        let lo = self.prev_span;
+        let pats = self.parse_pats()?;
+        self.expect(&token::Eq)?;
+        let expr = self.with_res(
+            Restrictions::NO_STRUCT_LITERAL,
+            |this| this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
+        )?;
+        let span = lo.to(expr.span);
+        self.sess.let_chains_spans.borrow_mut().push(span);
+        Ok(self.mk_expr(span, ExprKind::Let(pats, expr), attrs))
+    }
+
+    /// `else` token already eaten
+    fn parse_else_expr(&mut self) -> PResult<'a, P<Expr>> {
+        if self.eat_keyword(kw::If) {
+            return self.parse_if_expr(ThinVec::new());
+        } else {
+            let blk = self.parse_block()?;
+            return Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None), ThinVec::new()));
+        }
+    }
+
+    /// Parse a 'for' .. 'in' expression ('for' token already eaten)
+    fn parse_for_expr(
+        &mut self,
+        opt_label: Option<Label>,
+        span_lo: Span,
+        mut attrs: ThinVec<Attribute>
+    ) -> PResult<'a, P<Expr>> {
+        // Parse: `for <src_pat> in <src_expr> <src_loop_block>`
+
+        // Record whether we are about to parse `for (`.
+        // This is used below for recovery in case of `for ( $stuff ) $block`
+        // in which case we will suggest `for $stuff $block`.
+        let begin_paren = match self.token.kind {
+            token::OpenDelim(token::Paren) => Some(self.token.span),
+            _ => None,
+        };
+
+        let pat = self.parse_top_level_pat()?;
+        if !self.eat_keyword(kw::In) {
+            let in_span = self.prev_span.between(self.token.span);
+            self.struct_span_err(in_span, "missing `in` in `for` loop")
+                .span_suggestion_short(
+                    in_span,
+                    "try adding `in` here", " in ".into(),
+                    // has been misleading, at least in the past (closed Issue #48492)
+                    Applicability::MaybeIncorrect
+                )
+                .emit();
+        }
+        let in_span = self.prev_span;
+        self.check_for_for_in_in_typo(in_span);
+        let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
+
+        let pat = self.recover_parens_around_for_head(pat, &expr, begin_paren);
+
+        let (iattrs, loop_block) = self.parse_inner_attrs_and_block()?;
+        attrs.extend(iattrs);
+
+        let hi = self.prev_span;
+        Ok(self.mk_expr(span_lo.to(hi), ExprKind::ForLoop(pat, expr, loop_block, opt_label), attrs))
+    }
+
+    /// Parses a `while` or `while let` expression (`while` token already eaten).
+    fn parse_while_expr(
+        &mut self,
+        opt_label: Option<Label>,
+        span_lo: Span,
+        mut attrs: ThinVec<Attribute>
+    ) -> PResult<'a, P<Expr>> {
+        let cond = self.parse_cond_expr()?;
+        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
+        attrs.extend(iattrs);
+        let span = span_lo.to(body.span);
+        Ok(self.mk_expr(span, ExprKind::While(cond, body, opt_label), attrs))
+    }
+
+    /// Parse `loop {...}`, `loop` token already eaten.
+    fn parse_loop_expr(
+        &mut self,
+        opt_label: Option<Label>,
+        span_lo: Span,
+        mut attrs: ThinVec<Attribute>
+    ) -> PResult<'a, P<Expr>> {
+        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
+        attrs.extend(iattrs);
+        let span = span_lo.to(body.span);
+        Ok(self.mk_expr(span, ExprKind::Loop(body, opt_label), attrs))
+    }
+
+    fn eat_label(&mut self) -> Option<Label> {
+        if let Some(ident) = self.token.lifetime() {
+            let span = self.token.span;
+            self.bump();
+            Some(Label { ident: Ident::new(ident.name, span) })
+        } else {
+            None
+        }
+    }
+
+    // `match` token already eaten
+    fn parse_match_expr(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
+        let match_span = self.prev_span;
+        let lo = self.prev_span;
+        let discriminant = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
+        if let Err(mut e) = self.expect(&token::OpenDelim(token::Brace)) {
+            if self.token == token::Semi {
+                e.span_suggestion_short(
+                    match_span,
+                    "try removing this `match`",
+                    String::new(),
+                    Applicability::MaybeIncorrect // speculative
+                );
+            }
+            return Err(e)
+        }
+        attrs.extend(self.parse_inner_attributes()?);
+
+        let mut arms: Vec<Arm> = Vec::new();
+        while self.token != token::CloseDelim(token::Brace) {
+            match self.parse_arm() {
+                Ok(arm) => arms.push(arm),
+                Err(mut e) => {
+                    // Recover by skipping to the end of the block.
+                    e.emit();
+                    self.recover_stmt();
+                    let span = lo.to(self.token.span);
+                    if self.token == token::CloseDelim(token::Brace) {
+                        self.bump();
+                    }
+                    return Ok(self.mk_expr(span, ExprKind::Match(discriminant, arms), attrs));
+                }
+            }
+        }
+        let hi = self.token.span;
+        self.bump();
+        return Ok(self.mk_expr(lo.to(hi), ExprKind::Match(discriminant, arms), attrs));
+    }
+
+    crate fn parse_arm(&mut self) -> PResult<'a, Arm> {
+        let attrs = self.parse_outer_attributes()?;
+        let lo = self.token.span;
+        let pats = self.parse_pats()?;
+        let guard = if self.eat_keyword(kw::If) {
+            Some(self.parse_expr()?)
+        } else {
+            None
+        };
+        let arrow_span = self.token.span;
+        self.expect(&token::FatArrow)?;
+        let arm_start_span = self.token.span;
+
+        let expr = self.parse_expr_res(Restrictions::STMT_EXPR, None)
+            .map_err(|mut err| {
+                err.span_label(arrow_span, "while parsing the `match` arm starting here");
+                err
+            })?;
+
+        let require_comma = classify::expr_requires_semi_to_be_stmt(&expr)
+            && self.token != token::CloseDelim(token::Brace);
+
+        let hi = self.token.span;
+
+        if require_comma {
+            let cm = self.sess.source_map();
+            self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Brace)])
+                .map_err(|mut err| {
+                    match (cm.span_to_lines(expr.span), cm.span_to_lines(arm_start_span)) {
+                        (Ok(ref expr_lines), Ok(ref arm_start_lines))
+                        if arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
+                            && expr_lines.lines.len() == 2
+                            && self.token == token::FatArrow => {
+                            // We check whether there's any trailing code in the parse span,
+                            // if there isn't, we very likely have the following:
+                            //
+                            // X |     &Y => "y"
+                            //   |        --    - missing comma
+                            //   |        |
+                            //   |        arrow_span
+                            // X |     &X => "x"
+                            //   |      - ^^ self.token.span
+                            //   |      |
+                            //   |      parsed until here as `"y" & X`
+                            err.span_suggestion_short(
+                                cm.next_point(arm_start_span),
+                                "missing a comma here to end this `match` arm",
+                                ",".to_owned(),
+                                Applicability::MachineApplicable
+                            );
+                        }
+                        _ => {
+                            err.span_label(arrow_span,
+                                           "while parsing the `match` arm starting here");
+                        }
+                    }
+                    err
+                })?;
+        } else {
+            self.eat(&token::Comma);
+        }
+
+        Ok(ast::Arm {
+            attrs,
+            pats,
+            guard,
+            body: expr,
+            span: lo.to(hi),
+            id: ast::DUMMY_NODE_ID,
+        })
+    }
+
+    /// Parses a `try {...}` expression (`try` token already eaten).
+    fn parse_try_block(
+        &mut self,
+        span_lo: Span,
+        mut attrs: ThinVec<Attribute>
+    ) -> PResult<'a, P<Expr>> {
+        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
+        attrs.extend(iattrs);
+        if self.eat_keyword(kw::Catch) {
+            let mut error = self.struct_span_err(self.prev_span,
+                                                 "keyword `catch` cannot follow a `try` block");
+            error.help("try using `match` on the result of the `try` block instead");
+            error.emit();
+            Err(error)
+        } else {
+            Ok(self.mk_expr(span_lo.to(body.span), ExprKind::TryBlock(body), attrs))
+        }
+    }
+
+    fn is_do_catch_block(&self) -> bool {
+        self.token.is_keyword(kw::Do) &&
+        self.is_keyword_ahead(1, &[kw::Catch]) &&
+        self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace)) &&
+        !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
+    }
+
+    fn is_try_block(&self) -> bool {
+        self.token.is_keyword(kw::Try) &&
+        self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) &&
+        self.token.span.rust_2018() &&
+        // prevent `while try {} {}`, `if try {} {} else {}`, etc.
+        !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
+    }
+
+    /// Parses an `async move? {...}` expression.
+    pub fn parse_async_block(&mut self, mut attrs: ThinVec<Attribute>) -> PResult<'a, P<Expr>> {
+        let span_lo = self.token.span;
+        self.expect_keyword(kw::Async)?;
+        let capture_clause = self.parse_capture_clause();
+        let (iattrs, body) = self.parse_inner_attrs_and_block()?;
+        attrs.extend(iattrs);
+        Ok(self.mk_expr(
+            span_lo.to(body.span),
+            ExprKind::Async(capture_clause, ast::DUMMY_NODE_ID, body), attrs))
+    }
+
+    fn is_async_block(&self) -> bool {
+        self.token.is_keyword(kw::Async) &&
+        (
+            ( // `async move {`
+                self.is_keyword_ahead(1, &[kw::Move]) &&
+                self.look_ahead(2, |t| *t == token::OpenDelim(token::Brace))
+            ) || ( // `async {`
+                self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace))
+            )
+        )
+    }
+
+    fn maybe_parse_struct_expr(
+        &mut self,
+        lo: Span,
+        path: &ast::Path,
+        attrs: &ThinVec<Attribute>,
+    ) -> Option<PResult<'a, P<Expr>>> {
+        let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
+        let certainly_not_a_block = || self.look_ahead(1, |t| t.is_ident()) && (
+            // `{ ident, ` cannot start a block
+            self.look_ahead(2, |t| t == &token::Comma) ||
+            self.look_ahead(2, |t| t == &token::Colon) && (
+                // `{ ident: token, ` cannot start a block
+                self.look_ahead(4, |t| t == &token::Comma) ||
+                // `{ ident: ` cannot start a block unless it's a type ascription `ident: Type`
+                self.look_ahead(3, |t| !t.can_begin_type())
+            )
+        );
+
+        if struct_allowed || certainly_not_a_block() {
+            // This is a struct literal, but we don't can't accept them here
+            let expr = self.parse_struct_expr(lo, path.clone(), attrs.clone());
+            if let (Ok(expr), false) = (&expr, struct_allowed) {
+                self.struct_span_err(
+                    expr.span,
+                    "struct literals are not allowed here",
+                )
+                .multipart_suggestion(
+                    "surround the struct literal with parentheses",
+                    vec![
+                        (lo.shrink_to_lo(), "(".to_string()),
+                        (expr.span.shrink_to_hi(), ")".to_string()),
+                    ],
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+            }
+            return Some(expr);
+        }
+        None
+    }
+
+    pub(super) fn parse_struct_expr(
+        &mut self,
+        lo: Span,
+        pth: ast::Path,
+        mut attrs: ThinVec<Attribute>
+    ) -> PResult<'a, P<Expr>> {
+        let struct_sp = lo.to(self.prev_span);
+        self.bump();
+        let mut fields = Vec::new();
+        let mut base = None;
+
+        attrs.extend(self.parse_inner_attributes()?);
+
+        while self.token != token::CloseDelim(token::Brace) {
+            if self.eat(&token::DotDot) {
+                let exp_span = self.prev_span;
+                match self.parse_expr() {
+                    Ok(e) => {
+                        base = Some(e);
+                    }
+                    Err(mut e) => {
+                        e.emit();
+                        self.recover_stmt();
+                    }
+                }
+                if self.token == token::Comma {
+                    self.struct_span_err(
+                        exp_span.to(self.prev_span),
+                        "cannot use a comma after the base struct",
+                    )
+                    .span_suggestion_short(
+                        self.token.span,
+                        "remove this comma",
+                        String::new(),
+                        Applicability::MachineApplicable
+                    )
+                    .note("the base struct must always be the last field")
+                    .emit();
+                    self.recover_stmt();
+                }
+                break;
+            }
+
+            let mut recovery_field = None;
+            if let token::Ident(name, _) = self.token.kind {
+                if !self.token.is_reserved_ident() && self.look_ahead(1, |t| *t == token::Colon) {
+                    // Use in case of error after field-looking code: `S { foo: () with a }`
+                    recovery_field = Some(ast::Field {
+                        ident: Ident::new(name, self.token.span),
+                        span: self.token.span,
+                        expr: self.mk_expr(self.token.span, ExprKind::Err, ThinVec::new()),
+                        is_shorthand: false,
+                        attrs: ThinVec::new(),
+                        id: ast::DUMMY_NODE_ID,
+                    });
+                }
+            }
+            let mut parsed_field = None;
+            match self.parse_field() {
+                Ok(f) => parsed_field = Some(f),
+                Err(mut e) => {
+                    e.span_label(struct_sp, "while parsing this struct");
+                    e.emit();
+
+                    // If the next token is a comma, then try to parse
+                    // what comes next as additional fields, rather than
+                    // bailing out until next `}`.
+                    if self.token != token::Comma {
+                        self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
+                        if self.token != token::Comma {
+                            break;
+                        }
+                    }
+                }
+            }
+
+            match self.expect_one_of(&[token::Comma],
+                                     &[token::CloseDelim(token::Brace)]) {
+                Ok(_) => if let Some(f) = parsed_field.or(recovery_field) {
+                    // only include the field if there's no parse error for the field name
+                    fields.push(f);
+                }
+                Err(mut e) => {
+                    if let Some(f) = recovery_field {
+                        fields.push(f);
+                    }
+                    e.span_label(struct_sp, "while parsing this struct");
+                    e.emit();
+                    self.recover_stmt_(SemiColonMode::Comma, BlockMode::Ignore);
+                    self.eat(&token::Comma);
+                }
+            }
+        }
+
+        let span = lo.to(self.token.span);
+        self.expect(&token::CloseDelim(token::Brace))?;
+        return Ok(self.mk_expr(span, ExprKind::Struct(pth, fields, base), attrs));
+    }
+
+    /// Parse ident (COLON expr)?
+    fn parse_field(&mut self) -> PResult<'a, Field> {
+        let attrs = self.parse_outer_attributes()?;
+        let lo = self.token.span;
+
+        // Check if a colon exists one ahead. This means we're parsing a fieldname.
+        let (fieldname, expr, is_shorthand) = if self.look_ahead(1, |t| {
+            t == &token::Colon || t == &token::Eq
+        }) {
+            let fieldname = self.parse_field_name()?;
+
+            // Check for an equals token. This means the source incorrectly attempts to
+            // initialize a field with an eq rather than a colon.
+            if self.token == token::Eq {
+                self.diagnostic()
+                    .struct_span_err(self.token.span, "expected `:`, found `=`")
+                    .span_suggestion(
+                        fieldname.span.shrink_to_hi().to(self.token.span),
+                        "replace equals symbol with a colon",
+                        ":".to_string(),
+                        Applicability::MachineApplicable,
+                    )
+                    .emit();
+            }
+            self.bump(); // `:`
+            (fieldname, self.parse_expr()?, false)
+        } else {
+            let fieldname = self.parse_ident_common(false)?;
+
+            // Mimic `x: x` for the `x` field shorthand.
+            let path = ast::Path::from_ident(fieldname);
+            let expr = self.mk_expr(fieldname.span, ExprKind::Path(None, path), ThinVec::new());
+            (fieldname, expr, true)
+        };
+        Ok(ast::Field {
+            ident: fieldname,
+            span: lo.to(expr.span),
+            expr,
+            is_shorthand,
+            attrs: attrs.into(),
+            id: ast::DUMMY_NODE_ID,
+        })
+    }
+
+    fn err_dotdotdot_syntax(&self, span: Span) {
+        self.struct_span_err(span, "unexpected token: `...`")
+            .span_suggestion(
+                span,
+                "use `..` for an exclusive range", "..".to_owned(),
+                Applicability::MaybeIncorrect
+            )
+            .span_suggestion(
+                span,
+                "or `..=` for an inclusive range", "..=".to_owned(),
+                Applicability::MaybeIncorrect
+            )
+            .emit();
+    }
+
+    fn err_larrow_operator(&self, span: Span) {
+        self.struct_span_err(
+            span,
+            "unexpected token: `<-`"
+        ).span_suggestion(
+            span,
+            "if you meant to write a comparison against a negative value, add a \
+             space in between `<` and `-`",
+            "< -".to_string(),
+            Applicability::MaybeIncorrect
+        ).emit();
+    }
+
+    fn mk_assign_op(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
+        ExprKind::AssignOp(binop, lhs, rhs)
+    }
+
+    fn mk_range(
+        &self,
+        start: Option<P<Expr>>,
+        end: Option<P<Expr>>,
+        limits: RangeLimits
+    ) -> PResult<'a, ExprKind> {
+        if end.is_none() && limits == RangeLimits::Closed {
+            Err(self.span_fatal_err(self.token.span, Error::InclusiveRangeWithNoEnd))
+        } else {
+            Ok(ExprKind::Range(start, end, limits))
+        }
+    }
+
+    fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
+        ExprKind::Unary(unop, expr)
+    }
+
+    fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
+        ExprKind::Binary(binop, lhs, rhs)
+    }
+
+    fn mk_index(&self, expr: P<Expr>, idx: P<Expr>) -> ExprKind {
+        ExprKind::Index(expr, idx)
+    }
+
+    fn mk_call(&self, f: P<Expr>, args: Vec<P<Expr>>) -> ExprKind {
+        ExprKind::Call(f, args)
+    }
+
+    fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
+        let span = lo.to(self.prev_span);
+        let await_expr = self.mk_expr(span, ExprKind::Await(self_arg), ThinVec::new());
+        self.recover_from_await_method_call();
+        Ok(await_expr)
+    }
+
+    crate fn mk_expr(&self, span: Span, node: ExprKind, attrs: ThinVec<Attribute>) -> P<Expr> {
+        P(Expr { node, span, attrs, id: ast::DUMMY_NODE_ID })
+    }
+}
diff --git a/src/libsyntax/parse/parser/generics.rs b/src/libsyntax/parse/parser/generics.rs
new file mode 100644
index 00000000000..54f24f8ef2b
--- /dev/null
+++ b/src/libsyntax/parse/parser/generics.rs
@@ -0,0 +1,276 @@
+use super::{Parser, PResult};
+
+use crate::ast::{self, WhereClause, GenericParam, GenericParamKind, GenericBounds, Attribute};
+use crate::parse::token;
+use crate::source_map::DUMMY_SP;
+use crate::symbol::kw;
+
+impl<'a> Parser<'a> {
+    /// Parses bounds of a lifetime parameter `BOUND + BOUND + BOUND`, possibly with trailing `+`.
+    ///
+    /// ```
+    /// BOUND = LT_BOUND (e.g., `'a`)
+    /// ```
+    fn parse_lt_param_bounds(&mut self) -> GenericBounds {
+        let mut lifetimes = Vec::new();
+        while self.check_lifetime() {
+            lifetimes.push(ast::GenericBound::Outlives(self.expect_lifetime()));
+
+            if !self.eat_plus() {
+                break
+            }
+        }
+        lifetimes
+    }
+
+    /// Matches `typaram = IDENT (`?` unbound)? optbounds ( EQ ty )?`.
+    fn parse_ty_param(&mut self,
+                      preceding_attrs: Vec<Attribute>)
+                      -> PResult<'a, GenericParam> {
+        let ident = self.parse_ident()?;
+
+        // Parse optional colon and param bounds.
+        let bounds = if self.eat(&token::Colon) {
+            self.parse_generic_bounds(Some(self.prev_span))?
+        } else {
+            Vec::new()
+        };
+
+        let default = if self.eat(&token::Eq) {
+            Some(self.parse_ty()?)
+        } else {
+            None
+        };
+
+        Ok(GenericParam {
+            ident,
+            id: ast::DUMMY_NODE_ID,
+            attrs: preceding_attrs.into(),
+            bounds,
+            kind: GenericParamKind::Type {
+                default,
+            }
+        })
+    }
+
+    fn parse_const_param(&mut self, preceding_attrs: Vec<Attribute>) -> PResult<'a, GenericParam> {
+        self.expect_keyword(kw::Const)?;
+        let ident = self.parse_ident()?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+
+        Ok(GenericParam {
+            ident,
+            id: ast::DUMMY_NODE_ID,
+            attrs: preceding_attrs.into(),
+            bounds: Vec::new(),
+            kind: GenericParamKind::Const {
+                ty,
+            }
+        })
+    }
+
+    /// Parses a (possibly empty) list of lifetime and type parameters, possibly including
+    /// a trailing comma and erroneous trailing attributes.
+    crate fn parse_generic_params(&mut self) -> PResult<'a, Vec<ast::GenericParam>> {
+        let mut params = Vec::new();
+        loop {
+            let attrs = self.parse_outer_attributes()?;
+            if self.check_lifetime() {
+                let lifetime = self.expect_lifetime();
+                // Parse lifetime parameter.
+                let bounds = if self.eat(&token::Colon) {
+                    self.parse_lt_param_bounds()
+                } else {
+                    Vec::new()
+                };
+                params.push(ast::GenericParam {
+                    ident: lifetime.ident,
+                    id: lifetime.id,
+                    attrs: attrs.into(),
+                    bounds,
+                    kind: ast::GenericParamKind::Lifetime,
+                });
+            } else if self.check_keyword(kw::Const) {
+                // Parse const parameter.
+                params.push(self.parse_const_param(attrs)?);
+            } else if self.check_ident() {
+                // Parse type parameter.
+                params.push(self.parse_ty_param(attrs)?);
+            } else {
+                // Check for trailing attributes and stop parsing.
+                if !attrs.is_empty() {
+                    if !params.is_empty() {
+                        self.struct_span_err(
+                            attrs[0].span,
+                            &format!("trailing attribute after generic parameter"),
+                        )
+                        .span_label(attrs[0].span, "attributes must go before parameters")
+                        .emit();
+                    } else {
+                        self.struct_span_err(
+                            attrs[0].span,
+                            &format!("attribute without generic parameters"),
+                        )
+                        .span_label(
+                            attrs[0].span,
+                            "attributes are only permitted when preceding parameters",
+                        )
+                        .emit();
+                    }
+                }
+                break
+            }
+
+            if !self.eat(&token::Comma) {
+                break
+            }
+        }
+        Ok(params)
+    }
+
+    /// Parses a set of optional generic type parameter declarations. Where
+    /// clauses are not parsed here, and must be added later via
+    /// `parse_where_clause()`.
+    ///
+    /// matches generics = ( ) | ( < > ) | ( < typaramseq ( , )? > ) | ( < lifetimes ( , )? > )
+    ///                  | ( < lifetimes , typaramseq ( , )? > )
+    /// where   typaramseq = ( typaram ) | ( typaram , typaramseq )
+    pub(super) fn parse_generics(&mut self) -> PResult<'a, ast::Generics> {
+        let span_lo = self.token.span;
+        let (params, span) = if self.eat_lt() {
+            let params = self.parse_generic_params()?;
+            self.expect_gt()?;
+            (params, span_lo.to(self.prev_span))
+        } else {
+            (vec![], self.prev_span.between(self.token.span))
+        };
+        Ok(ast::Generics {
+            params,
+            where_clause: WhereClause {
+                predicates: Vec::new(),
+                span: DUMMY_SP,
+            },
+            span,
+        })
+    }
+
+    /// Parses an optional where-clause and places it in `generics`.
+    ///
+    /// ```ignore (only-for-syntax-highlight)
+    /// where T : Trait<U, V> + 'b, 'a : 'b
+    /// ```
+    pub(super) fn parse_where_clause(&mut self) -> PResult<'a, WhereClause> {
+        let mut where_clause = WhereClause {
+            predicates: Vec::new(),
+            span: self.prev_span.to(self.prev_span),
+        };
+
+        if !self.eat_keyword(kw::Where) {
+            return Ok(where_clause);
+        }
+        let lo = self.prev_span;
+
+        // We are considering adding generics to the `where` keyword as an alternative higher-rank
+        // parameter syntax (as in `where<'a>` or `where<T>`. To avoid that being a breaking
+        // change we parse those generics now, but report an error.
+        if self.choose_generics_over_qpath() {
+            let generics = self.parse_generics()?;
+            self.struct_span_err(
+                generics.span,
+                "generic parameters on `where` clauses are reserved for future use",
+            )
+                .span_label(generics.span, "currently unsupported")
+                .emit();
+        }
+
+        loop {
+            let lo = self.token.span;
+            if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) {
+                let lifetime = self.expect_lifetime();
+                // Bounds starting with a colon are mandatory, but possibly empty.
+                self.expect(&token::Colon)?;
+                let bounds = self.parse_lt_param_bounds();
+                where_clause.predicates.push(ast::WherePredicate::RegionPredicate(
+                    ast::WhereRegionPredicate {
+                        span: lo.to(self.prev_span),
+                        lifetime,
+                        bounds,
+                    }
+                ));
+            } else if self.check_type() {
+                // Parse optional `for<'a, 'b>`.
+                // This `for` is parsed greedily and applies to the whole predicate,
+                // the bounded type can have its own `for` applying only to it.
+                // Examples:
+                // * `for<'a> Trait1<'a>: Trait2<'a /* ok */>`
+                // * `(for<'a> Trait1<'a>): Trait2<'a /* not ok */>`
+                // * `for<'a> for<'b> Trait1<'a, 'b>: Trait2<'a /* ok */, 'b /* not ok */>`
+                let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
+
+                // Parse type with mandatory colon and (possibly empty) bounds,
+                // or with mandatory equality sign and the second type.
+                let ty = self.parse_ty()?;
+                if self.eat(&token::Colon) {
+                    let bounds = self.parse_generic_bounds(Some(self.prev_span))?;
+                    where_clause.predicates.push(ast::WherePredicate::BoundPredicate(
+                        ast::WhereBoundPredicate {
+                            span: lo.to(self.prev_span),
+                            bound_generic_params: lifetime_defs,
+                            bounded_ty: ty,
+                            bounds,
+                        }
+                    ));
+                // FIXME: Decide what should be used here, `=` or `==`.
+                // FIXME: We are just dropping the binders in lifetime_defs on the floor here.
+                } else if self.eat(&token::Eq) || self.eat(&token::EqEq) {
+                    let rhs_ty = self.parse_ty()?;
+                    where_clause.predicates.push(ast::WherePredicate::EqPredicate(
+                        ast::WhereEqPredicate {
+                            span: lo.to(self.prev_span),
+                            lhs_ty: ty,
+                            rhs_ty,
+                            id: ast::DUMMY_NODE_ID,
+                        }
+                    ));
+                } else {
+                    return self.unexpected();
+                }
+            } else {
+                break
+            }
+
+            if !self.eat(&token::Comma) {
+                break
+            }
+        }
+
+        where_clause.span = lo.to(self.prev_span);
+        Ok(where_clause)
+    }
+
+    pub(super) fn choose_generics_over_qpath(&self) -> bool {
+        // There's an ambiguity between generic parameters and qualified paths in impls.
+        // If we see `<` it may start both, so we have to inspect some following tokens.
+        // The following combinations can only start generics,
+        // but not qualified paths (with one exception):
+        //     `<` `>` - empty generic parameters
+        //     `<` `#` - generic parameters with attributes
+        //     `<` (LIFETIME|IDENT) `>` - single generic parameter
+        //     `<` (LIFETIME|IDENT) `,` - first generic parameter in a list
+        //     `<` (LIFETIME|IDENT) `:` - generic parameter with bounds
+        //     `<` (LIFETIME|IDENT) `=` - generic parameter with a default
+        //     `<` const                - generic const parameter
+        // The only truly ambiguous case is
+        //     `<` IDENT `>` `::` IDENT ...
+        // we disambiguate it in favor of generics (`impl<T> ::absolute::Path<T> { ... }`)
+        // because this is what almost always expected in practice, qualified paths in impls
+        // (`impl <Type>::AssocTy { ... }`) aren't even allowed by type checker at the moment.
+        self.token == token::Lt &&
+            (self.look_ahead(1, |t| t == &token::Pound || t == &token::Gt) ||
+             self.look_ahead(1, |t| t.is_lifetime() || t.is_ident()) &&
+                self.look_ahead(2, |t| t == &token::Gt || t == &token::Comma ||
+                                       t == &token::Colon || t == &token::Eq) ||
+            self.is_keyword_ahead(1, &[kw::Const]))
+    }
+}
diff --git a/src/libsyntax/parse/parser/item.rs b/src/libsyntax/parse/parser/item.rs
new file mode 100644
index 00000000000..72819c99660
--- /dev/null
+++ b/src/libsyntax/parse/parser/item.rs
@@ -0,0 +1,1918 @@
+use super::{Parser, PResult, PathStyle, SemiColonMode, BlockMode};
+
+use crate::maybe_whole;
+use crate::ptr::P;
+use crate::ast::{self, Ident, Attribute, AttrStyle};
+use crate::ast::{Item, ItemKind, ImplItem, TraitItem, TraitItemKind};
+use crate::ast::{UseTree, UseTreeKind, PathSegment};
+use crate::ast::{IsAuto, Constness, IsAsync, Unsafety, Defaultness};
+use crate::ast::{Visibility, VisibilityKind, Mutability, FnDecl, FnHeader};
+use crate::ast::{ForeignItem, ForeignItemKind};
+use crate::ast::{Ty, TyKind, GenericBounds, TraitRef};
+use crate::ast::{EnumDef, VariantData, StructField, AnonConst};
+use crate::ast::{Mac, MacDelimiter};
+use crate::ext::base::DummyResult;
+use crate::parse::token;
+use crate::parse::parser::maybe_append;
+use crate::parse::diagnostics::{Error};
+use crate::tokenstream::{TokenTree, TokenStream};
+use crate::source_map::{respan, Span, Spanned};
+use crate::symbol::{kw, sym};
+
+use std::mem;
+use log::debug;
+use rustc_target::spec::abi::{Abi};
+use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
+
+/// Whether the type alias or associated type is a concrete type or an opaque type
+#[derive(Debug)]
+pub enum AliasKind {
+    /// Just a new name for the same type
+    Weak(P<Ty>),
+    /// Only trait impls of the type will be usable, not the actual type itself
+    OpaqueTy(GenericBounds),
+}
+
+pub(super) type ItemInfo = (Ident, ItemKind, Option<Vec<Attribute>>);
+
+impl<'a> Parser<'a> {
+    pub fn parse_item(&mut self) -> PResult<'a, Option<P<Item>>> {
+        let attrs = self.parse_outer_attributes()?;
+        self.parse_item_(attrs, true, false)
+    }
+
+    pub(super) fn parse_item_(
+        &mut self,
+        attrs: Vec<Attribute>,
+        macros_allowed: bool,
+        attributes_allowed: bool,
+    ) -> PResult<'a, Option<P<Item>>> {
+        let mut unclosed_delims = vec![];
+        let (ret, tokens) = self.collect_tokens(|this| {
+            let item = this.parse_item_implementation(attrs, macros_allowed, attributes_allowed);
+            unclosed_delims.append(&mut this.unclosed_delims);
+            item
+        })?;
+        self.unclosed_delims.append(&mut unclosed_delims);
+
+        // Once we've parsed an item and recorded the tokens we got while
+        // parsing we may want to store `tokens` into the item we're about to
+        // return. Note, though, that we specifically didn't capture tokens
+        // related to outer attributes. The `tokens` field here may later be
+        // used with procedural macros to convert this item back into a token
+        // stream, but during expansion we may be removing attributes as we go
+        // along.
+        //
+        // If we've got inner attributes then the `tokens` we've got above holds
+        // these inner attributes. If an inner attribute is expanded we won't
+        // actually remove it from the token stream, so we'll just keep yielding
+        // it (bad!). To work around this case for now we just avoid recording
+        // `tokens` if we detect any inner attributes. This should help keep
+        // expansion correct, but we should fix this bug one day!
+        Ok(ret.map(|item| {
+            item.map(|mut i| {
+                if !i.attrs.iter().any(|attr| attr.style == AttrStyle::Inner) {
+                    i.tokens = Some(tokens);
+                }
+                i
+            })
+        }))
+    }
+
+    /// Parses one of the items allowed by the flags.
+    fn parse_item_implementation(
+        &mut self,
+        attrs: Vec<Attribute>,
+        macros_allowed: bool,
+        attributes_allowed: bool,
+    ) -> PResult<'a, Option<P<Item>>> {
+        maybe_whole!(self, NtItem, |item| {
+            let mut item = item.into_inner();
+            let mut attrs = attrs;
+            mem::swap(&mut item.attrs, &mut attrs);
+            item.attrs.extend(attrs);
+            Some(P(item))
+        });
+
+        let lo = self.token.span;
+
+        let visibility = self.parse_visibility(false)?;
+
+        if self.eat_keyword(kw::Use) {
+            // USE ITEM
+            let item_ = ItemKind::Use(P(self.parse_use_tree()?));
+            self.expect(&token::Semi)?;
+
+            let span = lo.to(self.prev_span);
+            let item =
+                self.mk_item(span, Ident::invalid(), item_, visibility, attrs);
+            return Ok(Some(item));
+        }
+
+        if self.eat_keyword(kw::Extern) {
+            let extern_sp = self.prev_span;
+            if self.eat_keyword(kw::Crate) {
+                return Ok(Some(self.parse_item_extern_crate(lo, visibility, attrs)?));
+            }
+
+            let opt_abi = self.parse_opt_abi()?;
+
+            if self.eat_keyword(kw::Fn) {
+                // EXTERN FUNCTION ITEM
+                let fn_span = self.prev_span;
+                let abi = opt_abi.unwrap_or(Abi::C);
+                let (ident, item_, extra_attrs) =
+                    self.parse_item_fn(Unsafety::Normal,
+                                       respan(fn_span, IsAsync::NotAsync),
+                                       respan(fn_span, Constness::NotConst),
+                                       abi)?;
+                let prev_span = self.prev_span;
+                let item = self.mk_item(lo.to(prev_span),
+                                        ident,
+                                        item_,
+                                        visibility,
+                                        maybe_append(attrs, extra_attrs));
+                return Ok(Some(item));
+            } else if self.check(&token::OpenDelim(token::Brace)) {
+                return Ok(Some(
+                    self.parse_item_foreign_mod(lo, opt_abi, visibility, attrs, extern_sp)?,
+                ));
+            }
+
+            self.unexpected()?;
+        }
+
+        if self.is_static_global() {
+            self.bump();
+            // STATIC ITEM
+            let m = self.parse_mutability();
+            let (ident, item_, extra_attrs) = self.parse_item_const(Some(m))?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if self.eat_keyword(kw::Const) {
+            let const_span = self.prev_span;
+            if self.check_keyword(kw::Fn)
+                || (self.check_keyword(kw::Unsafe)
+                    && self.is_keyword_ahead(1, &[kw::Fn])) {
+                // CONST FUNCTION ITEM
+                let unsafety = self.parse_unsafety();
+                self.bump();
+                let (ident, item_, extra_attrs) =
+                    self.parse_item_fn(unsafety,
+                                       respan(const_span, IsAsync::NotAsync),
+                                       respan(const_span, Constness::Const),
+                                       Abi::Rust)?;
+                let prev_span = self.prev_span;
+                let item = self.mk_item(lo.to(prev_span),
+                                        ident,
+                                        item_,
+                                        visibility,
+                                        maybe_append(attrs, extra_attrs));
+                return Ok(Some(item));
+            }
+
+            // CONST ITEM
+            if self.eat_keyword(kw::Mut) {
+                let prev_span = self.prev_span;
+                self.struct_span_err(prev_span, "const globals cannot be mutable")
+                    .span_label(prev_span, "cannot be mutable")
+                    .span_suggestion(
+                        const_span,
+                        "you might want to declare a static instead",
+                        "static".to_owned(),
+                        Applicability::MaybeIncorrect,
+                    )
+                    .emit();
+            }
+            let (ident, item_, extra_attrs) = self.parse_item_const(None)?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+
+        // Parse `async unsafe? fn`.
+        if self.check_keyword(kw::Async) {
+            let async_span = self.token.span;
+            if self.is_keyword_ahead(1, &[kw::Fn])
+                || self.is_keyword_ahead(2, &[kw::Fn])
+            {
+                // ASYNC FUNCTION ITEM
+                self.bump(); // `async`
+                let unsafety = self.parse_unsafety(); // `unsafe`?
+                self.expect_keyword(kw::Fn)?; // `fn`
+                let fn_span = self.prev_span;
+                let (ident, item_, extra_attrs) =
+                    self.parse_item_fn(unsafety,
+                                    respan(async_span, IsAsync::Async {
+                                        closure_id: ast::DUMMY_NODE_ID,
+                                        return_impl_trait_id: ast::DUMMY_NODE_ID,
+                                    }),
+                                    respan(fn_span, Constness::NotConst),
+                                    Abi::Rust)?;
+                let prev_span = self.prev_span;
+                let item = self.mk_item(lo.to(prev_span),
+                                        ident,
+                                        item_,
+                                        visibility,
+                                        maybe_append(attrs, extra_attrs));
+                self.ban_async_in_2015(async_span);
+                return Ok(Some(item));
+            }
+        }
+        if self.check_keyword(kw::Unsafe) &&
+            self.is_keyword_ahead(1, &[kw::Trait, kw::Auto])
+        {
+            // UNSAFE TRAIT ITEM
+            self.bump(); // `unsafe`
+            let is_auto = if self.eat_keyword(kw::Trait) {
+                IsAuto::No
+            } else {
+                self.expect_keyword(kw::Auto)?;
+                self.expect_keyword(kw::Trait)?;
+                IsAuto::Yes
+            };
+            let (ident, item_, extra_attrs) =
+                self.parse_item_trait(is_auto, Unsafety::Unsafe)?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if self.check_keyword(kw::Impl) ||
+           self.check_keyword(kw::Unsafe) &&
+                self.is_keyword_ahead(1, &[kw::Impl]) ||
+           self.check_keyword(kw::Default) &&
+                self.is_keyword_ahead(1, &[kw::Impl, kw::Unsafe]) {
+            // IMPL ITEM
+            let defaultness = self.parse_defaultness();
+            let unsafety = self.parse_unsafety();
+            self.expect_keyword(kw::Impl)?;
+            let (ident, item, extra_attrs) = self.parse_item_impl(unsafety, defaultness)?;
+            let span = lo.to(self.prev_span);
+            return Ok(Some(self.mk_item(span, ident, item, visibility,
+                                        maybe_append(attrs, extra_attrs))));
+        }
+        if self.check_keyword(kw::Fn) {
+            // FUNCTION ITEM
+            self.bump();
+            let fn_span = self.prev_span;
+            let (ident, item_, extra_attrs) =
+                self.parse_item_fn(Unsafety::Normal,
+                                   respan(fn_span, IsAsync::NotAsync),
+                                   respan(fn_span, Constness::NotConst),
+                                   Abi::Rust)?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if self.check_keyword(kw::Unsafe)
+            && self.look_ahead(1, |t| *t != token::OpenDelim(token::Brace)) {
+            // UNSAFE FUNCTION ITEM
+            self.bump(); // `unsafe`
+            // `{` is also expected after `unsafe`, in case of error, include it in the diagnostic
+            self.check(&token::OpenDelim(token::Brace));
+            let abi = if self.eat_keyword(kw::Extern) {
+                self.parse_opt_abi()?.unwrap_or(Abi::C)
+            } else {
+                Abi::Rust
+            };
+            self.expect_keyword(kw::Fn)?;
+            let fn_span = self.prev_span;
+            let (ident, item_, extra_attrs) =
+                self.parse_item_fn(Unsafety::Unsafe,
+                                   respan(fn_span, IsAsync::NotAsync),
+                                   respan(fn_span, Constness::NotConst),
+                                   abi)?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if self.eat_keyword(kw::Mod) {
+            // MODULE ITEM
+            let (ident, item_, extra_attrs) =
+                self.parse_item_mod(&attrs[..])?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if let Some(type_) = self.eat_type() {
+            let (ident, alias, generics) = type_?;
+            // TYPE ITEM
+            let item_ = match alias {
+                AliasKind::Weak(ty) => ItemKind::TyAlias(ty, generics),
+                AliasKind::OpaqueTy(bounds) => ItemKind::OpaqueTy(bounds, generics),
+            };
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    attrs);
+            return Ok(Some(item));
+        }
+        if self.eat_keyword(kw::Enum) {
+            // ENUM ITEM
+            let (ident, item_, extra_attrs) = self.parse_item_enum()?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if self.check_keyword(kw::Trait)
+            || (self.check_keyword(kw::Auto)
+                && self.is_keyword_ahead(1, &[kw::Trait]))
+        {
+            let is_auto = if self.eat_keyword(kw::Trait) {
+                IsAuto::No
+            } else {
+                self.expect_keyword(kw::Auto)?;
+                self.expect_keyword(kw::Trait)?;
+                IsAuto::Yes
+            };
+            // TRAIT ITEM
+            let (ident, item_, extra_attrs) =
+                self.parse_item_trait(is_auto, Unsafety::Normal)?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if self.eat_keyword(kw::Struct) {
+            // STRUCT ITEM
+            let (ident, item_, extra_attrs) = self.parse_item_struct()?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if self.is_union_item() {
+            // UNION ITEM
+            self.bump();
+            let (ident, item_, extra_attrs) = self.parse_item_union()?;
+            let prev_span = self.prev_span;
+            let item = self.mk_item(lo.to(prev_span),
+                                    ident,
+                                    item_,
+                                    visibility,
+                                    maybe_append(attrs, extra_attrs));
+            return Ok(Some(item));
+        }
+        if let Some(macro_def) = self.eat_macro_def(&attrs, &visibility, lo)? {
+            return Ok(Some(macro_def));
+        }
+
+        // Verify whether we have encountered a struct or method definition where the user forgot to
+        // add the `struct` or `fn` keyword after writing `pub`: `pub S {}`
+        if visibility.node.is_pub() &&
+            self.check_ident() &&
+            self.look_ahead(1, |t| *t != token::Not)
+        {
+            // Space between `pub` keyword and the identifier
+            //
+            //     pub   S {}
+            //        ^^^ `sp` points here
+            let sp = self.prev_span.between(self.token.span);
+            let full_sp = self.prev_span.to(self.token.span);
+            let ident_sp = self.token.span;
+            if self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) {
+                // possible public struct definition where `struct` was forgotten
+                let ident = self.parse_ident().unwrap();
+                let msg = format!("add `struct` here to parse `{}` as a public struct",
+                                  ident);
+                let mut err = self.diagnostic()
+                    .struct_span_err(sp, "missing `struct` for struct definition");
+                err.span_suggestion_short(
+                    sp, &msg, " struct ".into(), Applicability::MaybeIncorrect // speculative
+                );
+                return Err(err);
+            } else if self.look_ahead(1, |t| *t == token::OpenDelim(token::Paren)) {
+                let ident = self.parse_ident().unwrap();
+                self.bump();  // `(`
+                let kw_name = if let Ok(Some(_)) = self.parse_self_arg_with_attrs()
+                    .map_err(|mut e| e.cancel())
+                {
+                    "method"
+                } else {
+                    "function"
+                };
+                self.consume_block(token::Paren);
+                let (kw, kw_name, ambiguous) = if self.check(&token::RArrow) {
+                    self.eat_to_tokens(&[&token::OpenDelim(token::Brace)]);
+                    self.bump();  // `{`
+                    ("fn", kw_name, false)
+                } else if self.check(&token::OpenDelim(token::Brace)) {
+                    self.bump();  // `{`
+                    ("fn", kw_name, false)
+                } else if self.check(&token::Colon) {
+                    let kw = "struct";
+                    (kw, kw, false)
+                } else {
+                    ("fn` or `struct", "function or struct", true)
+                };
+
+                let msg = format!("missing `{}` for {} definition", kw, kw_name);
+                let mut err = self.diagnostic().struct_span_err(sp, &msg);
+                if !ambiguous {
+                    self.consume_block(token::Brace);
+                    let suggestion = format!("add `{}` here to parse `{}` as a public {}",
+                                             kw,
+                                             ident,
+                                             kw_name);
+                    err.span_suggestion_short(
+                        sp, &suggestion, format!(" {} ", kw), Applicability::MachineApplicable
+                    );
+                } else {
+                    if let Ok(snippet) = self.span_to_snippet(ident_sp) {
+                        err.span_suggestion(
+                            full_sp,
+                            "if you meant to call a macro, try",
+                            format!("{}!", snippet),
+                            // this is the `ambiguous` conditional branch
+                            Applicability::MaybeIncorrect
+                        );
+                    } else {
+                        err.help("if you meant to call a macro, remove the `pub` \
+                                  and add a trailing `!` after the identifier");
+                    }
+                }
+                return Err(err);
+            } else if self.look_ahead(1, |t| *t == token::Lt) {
+                let ident = self.parse_ident().unwrap();
+                self.eat_to_tokens(&[&token::Gt]);
+                self.bump();  // `>`
+                let (kw, kw_name, ambiguous) = if self.eat(&token::OpenDelim(token::Paren)) {
+                    if let Ok(Some(_)) = self.parse_self_arg_with_attrs()
+                        .map_err(|mut e| e.cancel())
+                    {
+                        ("fn", "method", false)
+                    } else {
+                        ("fn", "function", false)
+                    }
+                } else if self.check(&token::OpenDelim(token::Brace)) {
+                    ("struct", "struct", false)
+                } else {
+                    ("fn` or `struct", "function or struct", true)
+                };
+                let msg = format!("missing `{}` for {} definition", kw, kw_name);
+                let mut err = self.diagnostic().struct_span_err(sp, &msg);
+                if !ambiguous {
+                    err.span_suggestion_short(
+                        sp,
+                        &format!("add `{}` here to parse `{}` as a public {}", kw, ident, kw_name),
+                        format!(" {} ", kw),
+                        Applicability::MachineApplicable,
+                    );
+                }
+                return Err(err);
+            }
+        }
+        self.parse_macro_use_or_failure(attrs, macros_allowed, attributes_allowed, lo, visibility)
+    }
+
+    /// This is the fall-through for parsing items.
+    fn parse_macro_use_or_failure(
+        &mut self,
+        attrs: Vec<Attribute> ,
+        macros_allowed: bool,
+        attributes_allowed: bool,
+        lo: Span,
+        visibility: Visibility
+    ) -> PResult<'a, Option<P<Item>>> {
+        if macros_allowed && self.token.is_path_start() &&
+                !(self.is_async_fn() && self.token.span.rust_2015()) {
+            // MACRO INVOCATION ITEM
+
+            let prev_span = self.prev_span;
+            self.complain_if_pub_macro(&visibility.node, prev_span);
+
+            let mac_lo = self.token.span;
+
+            // item macro.
+            let path = self.parse_path(PathStyle::Mod)?;
+            self.expect(&token::Not)?;
+            let (delim, tts) = self.expect_delimited_token_tree()?;
+            if delim != MacDelimiter::Brace && !self.eat(&token::Semi) {
+                self.report_invalid_macro_expansion_item();
+            }
+
+            let hi = self.prev_span;
+            let mac = Mac {
+                path,
+                tts,
+                delim,
+                span: mac_lo.to(hi),
+                prior_type_ascription: self.last_type_ascription,
+            };
+            let item =
+                self.mk_item(lo.to(hi), Ident::invalid(), ItemKind::Mac(mac), visibility, attrs);
+            return Ok(Some(item));
+        }
+
+        // FAILURE TO PARSE ITEM
+        match visibility.node {
+            VisibilityKind::Inherited => {}
+            _ => {
+                return Err(self.span_fatal(self.prev_span, "unmatched visibility `pub`"));
+            }
+        }
+
+        if !attributes_allowed && !attrs.is_empty() {
+            self.expected_item_err(&attrs)?;
+        }
+        Ok(None)
+    }
+
+    /// Emits an expected-item-after-attributes error.
+    fn expected_item_err(&mut self, attrs: &[Attribute]) -> PResult<'a,  ()> {
+        let message = match attrs.last() {
+            Some(&Attribute { is_sugared_doc: true, .. }) => "expected item after doc comment",
+            _ => "expected item after attributes",
+        };
+
+        let mut err = self.diagnostic().struct_span_err(self.prev_span, message);
+        if attrs.last().unwrap().is_sugared_doc {
+            err.span_label(self.prev_span, "this doc comment doesn't document anything");
+        }
+        Err(err)
+    }
+
+    pub(super) fn is_async_fn(&self) -> bool {
+        self.token.is_keyword(kw::Async) &&
+            self.is_keyword_ahead(1, &[kw::Fn])
+    }
+
+    /// Parses a macro invocation inside a `trait`, `impl` or `extern` block.
+    fn parse_assoc_macro_invoc(&mut self, item_kind: &str, vis: Option<&Visibility>,
+                               at_end: &mut bool) -> PResult<'a, Option<Mac>>
+    {
+        if self.token.is_path_start() &&
+                !(self.is_async_fn() && self.token.span.rust_2015()) {
+            let prev_span = self.prev_span;
+            let lo = self.token.span;
+            let path = self.parse_path(PathStyle::Mod)?;
+
+            if path.segments.len() == 1 {
+                if !self.eat(&token::Not) {
+                    return Err(self.missing_assoc_item_kind_err(item_kind, prev_span));
+                }
+            } else {
+                self.expect(&token::Not)?;
+            }
+
+            if let Some(vis) = vis {
+                self.complain_if_pub_macro(&vis.node, prev_span);
+            }
+
+            *at_end = true;
+
+            // eat a matched-delimiter token tree:
+            let (delim, tts) = self.expect_delimited_token_tree()?;
+            if delim != MacDelimiter::Brace {
+                self.expect(&token::Semi)?;
+            }
+
+            Ok(Some(Mac {
+                path,
+                tts,
+                delim,
+                span: lo.to(self.prev_span),
+                prior_type_ascription: self.last_type_ascription,
+            }))
+        } else {
+            Ok(None)
+        }
+    }
+
+    fn missing_assoc_item_kind_err(&self, item_type: &str, prev_span: Span)
+                                   -> DiagnosticBuilder<'a>
+    {
+        let expected_kinds = if item_type == "extern" {
+            "missing `fn`, `type`, or `static`"
+        } else {
+            "missing `fn`, `type`, or `const`"
+        };
+
+        // Given this code `path(`, it seems like this is not
+        // setting the visibility of a macro invocation, but rather
+        // a mistyped method declaration.
+        // Create a diagnostic pointing out that `fn` is missing.
+        //
+        // x |     pub path(&self) {
+        //   |        ^ missing `fn`, `type`, or `const`
+        //     pub  path(
+        //        ^^ `sp` below will point to this
+        let sp = prev_span.between(self.prev_span);
+        let mut err = self.diagnostic().struct_span_err(
+            sp,
+            &format!("{} for {}-item declaration",
+                     expected_kinds, item_type));
+        err.span_label(sp, expected_kinds);
+        err
+    }
+
+    /// Parses an implementation item, `impl` keyword is already parsed.
+    ///
+    ///    impl<'a, T> TYPE { /* impl items */ }
+    ///    impl<'a, T> TRAIT for TYPE { /* impl items */ }
+    ///    impl<'a, T> !TRAIT for TYPE { /* impl items */ }
+    ///
+    /// We actually parse slightly more relaxed grammar for better error reporting and recovery.
+    ///     `impl` GENERICS `!`? TYPE `for`? (TYPE | `..`) (`where` PREDICATES)? `{` BODY `}`
+    ///     `impl` GENERICS `!`? TYPE (`where` PREDICATES)? `{` BODY `}`
+    fn parse_item_impl(&mut self, unsafety: Unsafety, defaultness: Defaultness)
+                       -> PResult<'a, ItemInfo> {
+        // First, parse generic parameters if necessary.
+        let mut generics = if self.choose_generics_over_qpath() {
+            self.parse_generics()?
+        } else {
+            ast::Generics::default()
+        };
+
+        // Disambiguate `impl !Trait for Type { ... }` and `impl ! { ... }` for the never type.
+        let polarity = if self.check(&token::Not) && self.look_ahead(1, |t| t.can_begin_type()) {
+            self.bump(); // `!`
+            ast::ImplPolarity::Negative
+        } else {
+            ast::ImplPolarity::Positive
+        };
+
+        // Parse both types and traits as a type, then reinterpret if necessary.
+        let err_path = |span| ast::Path::from_ident(Ident::new(kw::Invalid, span));
+        let ty_first = if self.token.is_keyword(kw::For) &&
+                          self.look_ahead(1, |t| t != &token::Lt) {
+            let span = self.prev_span.between(self.token.span);
+            self.struct_span_err(span, "missing trait in a trait impl").emit();
+            P(Ty { node: TyKind::Path(None, err_path(span)), span, id: ast::DUMMY_NODE_ID })
+        } else {
+            self.parse_ty()?
+        };
+
+        // If `for` is missing we try to recover.
+        let has_for = self.eat_keyword(kw::For);
+        let missing_for_span = self.prev_span.between(self.token.span);
+
+        let ty_second = if self.token == token::DotDot {
+            // We need to report this error after `cfg` expansion for compatibility reasons
+            self.bump(); // `..`, do not add it to expected tokens
+            Some(DummyResult::raw_ty(self.prev_span, true))
+        } else if has_for || self.token.can_begin_type() {
+            Some(self.parse_ty()?)
+        } else {
+            None
+        };
+
+        generics.where_clause = self.parse_where_clause()?;
+
+        let (impl_items, attrs) = self.parse_impl_body()?;
+
+        let item_kind = match ty_second {
+            Some(ty_second) => {
+                // impl Trait for Type
+                if !has_for {
+                    self.struct_span_err(missing_for_span, "missing `for` in a trait impl")
+                        .span_suggestion_short(
+                            missing_for_span,
+                            "add `for` here",
+                            " for ".to_string(),
+                            Applicability::MachineApplicable,
+                        ).emit();
+                }
+
+                let ty_first = ty_first.into_inner();
+                let path = match ty_first.node {
+                    // This notably includes paths passed through `ty` macro fragments (#46438).
+                    TyKind::Path(None, path) => path,
+                    _ => {
+                        self.span_err(ty_first.span, "expected a trait, found type");
+                        err_path(ty_first.span)
+                    }
+                };
+                let trait_ref = TraitRef { path, ref_id: ty_first.id };
+
+                ItemKind::Impl(unsafety, polarity, defaultness,
+                               generics, Some(trait_ref), ty_second, impl_items)
+            }
+            None => {
+                // impl Type
+                ItemKind::Impl(unsafety, polarity, defaultness,
+                               generics, None, ty_first, impl_items)
+            }
+        };
+
+        Ok((Ident::invalid(), item_kind, Some(attrs)))
+    }
+
+    fn parse_impl_body(&mut self) -> PResult<'a, (Vec<ImplItem>, Vec<Attribute>)> {
+        self.expect(&token::OpenDelim(token::Brace))?;
+        let attrs = self.parse_inner_attributes()?;
+
+        let mut impl_items = Vec::new();
+        while !self.eat(&token::CloseDelim(token::Brace)) {
+            let mut at_end = false;
+            match self.parse_impl_item(&mut at_end) {
+                Ok(impl_item) => impl_items.push(impl_item),
+                Err(mut err) => {
+                    err.emit();
+                    if !at_end {
+                        self.recover_stmt_(SemiColonMode::Break, BlockMode::Break);
+                    }
+                }
+            }
+        }
+        Ok((impl_items, attrs))
+    }
+
+    /// Parses an impl item.
+    pub fn parse_impl_item(&mut self, at_end: &mut bool) -> PResult<'a, ImplItem> {
+        maybe_whole!(self, NtImplItem, |x| x);
+        let attrs = self.parse_outer_attributes()?;
+        let mut unclosed_delims = vec![];
+        let (mut item, tokens) = self.collect_tokens(|this| {
+            let item = this.parse_impl_item_(at_end, attrs);
+            unclosed_delims.append(&mut this.unclosed_delims);
+            item
+        })?;
+        self.unclosed_delims.append(&mut unclosed_delims);
+
+        // See `parse_item` for why this clause is here.
+        if !item.attrs.iter().any(|attr| attr.style == AttrStyle::Inner) {
+            item.tokens = Some(tokens);
+        }
+        Ok(item)
+    }
+
+    fn parse_impl_item_(&mut self,
+                        at_end: &mut bool,
+                        mut attrs: Vec<Attribute>) -> PResult<'a, ImplItem> {
+        let lo = self.token.span;
+        let vis = self.parse_visibility(false)?;
+        let defaultness = self.parse_defaultness();
+        let (name, node, generics) = if let Some(type_) = self.eat_type() {
+            let (name, alias, generics) = type_?;
+            let kind = match alias {
+                AliasKind::Weak(typ) => ast::ImplItemKind::TyAlias(typ),
+                AliasKind::OpaqueTy(bounds) => ast::ImplItemKind::OpaqueTy(bounds),
+            };
+            (name, kind, generics)
+        } else if self.is_const_item() {
+            // This parses the grammar:
+            //     ImplItemConst = "const" Ident ":" Ty "=" Expr ";"
+            self.expect_keyword(kw::Const)?;
+            let name = self.parse_ident()?;
+            self.expect(&token::Colon)?;
+            let typ = self.parse_ty()?;
+            self.expect(&token::Eq)?;
+            let expr = self.parse_expr()?;
+            self.expect(&token::Semi)?;
+            (name, ast::ImplItemKind::Const(typ, expr), ast::Generics::default())
+        } else {
+            let (name, inner_attrs, generics, node) = self.parse_impl_method(&vis, at_end)?;
+            attrs.extend(inner_attrs);
+            (name, node, generics)
+        };
+
+        Ok(ImplItem {
+            id: ast::DUMMY_NODE_ID,
+            span: lo.to(self.prev_span),
+            ident: name,
+            vis,
+            defaultness,
+            attrs,
+            generics,
+            node,
+            tokens: None,
+        })
+    }
+
+    /// Parses defaultness (i.e., `default` or nothing).
+    fn parse_defaultness(&mut self) -> Defaultness {
+        // `pub` is included for better error messages
+        if self.check_keyword(kw::Default) &&
+            self.is_keyword_ahead(1, &[
+                kw::Impl,
+                kw::Const,
+                kw::Fn,
+                kw::Unsafe,
+                kw::Extern,
+                kw::Type,
+                kw::Pub,
+            ])
+        {
+            self.bump(); // `default`
+            Defaultness::Default
+        } else {
+            Defaultness::Final
+        }
+    }
+
+    /// Returns `true` if we are looking at `const ID`
+    /// (returns `false` for things like `const fn`, etc.).
+    fn is_const_item(&self) -> bool {
+        self.token.is_keyword(kw::Const) &&
+            !self.is_keyword_ahead(1, &[kw::Fn, kw::Unsafe])
+    }
+
+    /// Parse a method or a macro invocation in a trait impl.
+    fn parse_impl_method(&mut self, vis: &Visibility, at_end: &mut bool)
+                         -> PResult<'a, (Ident, Vec<Attribute>, ast::Generics,
+                             ast::ImplItemKind)> {
+        // code copied from parse_macro_use_or_failure... abstraction!
+        if let Some(mac) = self.parse_assoc_macro_invoc("impl", Some(vis), at_end)? {
+            // method macro
+            Ok((Ident::invalid(), vec![], ast::Generics::default(),
+                ast::ImplItemKind::Macro(mac)))
+        } else {
+            let (constness, unsafety, asyncness, abi) = self.parse_fn_front_matter()?;
+            let ident = self.parse_ident()?;
+            let mut generics = self.parse_generics()?;
+            let decl = self.parse_fn_decl_with_self(|p| {
+                p.parse_arg_general(true, false, |_| true)
+            })?;
+            generics.where_clause = self.parse_where_clause()?;
+            *at_end = true;
+            let (inner_attrs, body) = self.parse_inner_attrs_and_block()?;
+            let header = ast::FnHeader { abi, unsafety, constness, asyncness };
+            Ok((ident, inner_attrs, generics, ast::ImplItemKind::Method(
+                ast::MethodSig { header, decl },
+                body
+            )))
+        }
+    }
+
+    /// Parses all the "front matter" for a `fn` declaration, up to
+    /// and including the `fn` keyword:
+    ///
+    /// - `const fn`
+    /// - `unsafe fn`
+    /// - `const unsafe fn`
+    /// - `extern fn`
+    /// - etc.
+    fn parse_fn_front_matter(&mut self)
+        -> PResult<'a, (
+            Spanned<Constness>,
+            Unsafety,
+            Spanned<IsAsync>,
+            Abi
+        )>
+    {
+        let is_const_fn = self.eat_keyword(kw::Const);
+        let const_span = self.prev_span;
+        let asyncness = self.parse_asyncness();
+        if let IsAsync::Async { .. } = asyncness {
+            self.ban_async_in_2015(self.prev_span);
+        }
+        let asyncness = respan(self.prev_span, asyncness);
+        let unsafety = self.parse_unsafety();
+        let (constness, unsafety, abi) = if is_const_fn {
+            (respan(const_span, Constness::Const), unsafety, Abi::Rust)
+        } else {
+            let abi = if self.eat_keyword(kw::Extern) {
+                self.parse_opt_abi()?.unwrap_or(Abi::C)
+            } else {
+                Abi::Rust
+            };
+            (respan(self.prev_span, Constness::NotConst), unsafety, abi)
+        };
+        if !self.eat_keyword(kw::Fn) {
+            // It is possible for `expect_one_of` to recover given the contents of
+            // `self.expected_tokens`, therefore, do not use `self.unexpected()` which doesn't
+            // account for this.
+            if !self.expect_one_of(&[], &[])? { unreachable!() }
+        }
+        Ok((constness, unsafety, asyncness, abi))
+    }
+
+    /// Parses `trait Foo { ... }` or `trait Foo = Bar;`.
+    fn parse_item_trait(&mut self, is_auto: IsAuto, unsafety: Unsafety) -> PResult<'a, ItemInfo> {
+        let ident = self.parse_ident()?;
+        let mut tps = self.parse_generics()?;
+
+        // Parse optional colon and supertrait bounds.
+        let bounds = if self.eat(&token::Colon) {
+            self.parse_generic_bounds(Some(self.prev_span))?
+        } else {
+            Vec::new()
+        };
+
+        if self.eat(&token::Eq) {
+            // it's a trait alias
+            let bounds = self.parse_generic_bounds(None)?;
+            tps.where_clause = self.parse_where_clause()?;
+            self.expect(&token::Semi)?;
+            if is_auto == IsAuto::Yes {
+                let msg = "trait aliases cannot be `auto`";
+                self.struct_span_err(self.prev_span, msg)
+                    .span_label(self.prev_span, msg)
+                    .emit();
+            }
+            if unsafety != Unsafety::Normal {
+                let msg = "trait aliases cannot be `unsafe`";
+                self.struct_span_err(self.prev_span, msg)
+                    .span_label(self.prev_span, msg)
+                    .emit();
+            }
+            Ok((ident, ItemKind::TraitAlias(tps, bounds), None))
+        } else {
+            // it's a normal trait
+            tps.where_clause = self.parse_where_clause()?;
+            self.expect(&token::OpenDelim(token::Brace))?;
+            let mut trait_items = vec![];
+            while !self.eat(&token::CloseDelim(token::Brace)) {
+                if let token::DocComment(_) = self.token.kind {
+                    if self.look_ahead(1,
+                    |tok| tok == &token::CloseDelim(token::Brace)) {
+                        self.diagnostic().struct_span_err_with_code(
+                            self.token.span,
+                            "found a documentation comment that doesn't document anything",
+                            DiagnosticId::Error("E0584".into()),
+                        )
+                        .help(
+                            "doc comments must come before what they document, maybe a \
+                            comment was intended with `//`?",
+                        )
+                        .emit();
+                        self.bump();
+                        continue;
+                    }
+                }
+                let mut at_end = false;
+                match self.parse_trait_item(&mut at_end) {
+                    Ok(item) => trait_items.push(item),
+                    Err(mut e) => {
+                        e.emit();
+                        if !at_end {
+                            self.recover_stmt_(SemiColonMode::Break, BlockMode::Break);
+                        }
+                    }
+                }
+            }
+            Ok((ident, ItemKind::Trait(is_auto, unsafety, tps, bounds, trait_items), None))
+        }
+    }
+
+    /// Parses the items in a trait declaration.
+    pub fn parse_trait_item(&mut self, at_end: &mut bool) -> PResult<'a, TraitItem> {
+        maybe_whole!(self, NtTraitItem, |x| x);
+        let attrs = self.parse_outer_attributes()?;
+        let mut unclosed_delims = vec![];
+        let (mut item, tokens) = self.collect_tokens(|this| {
+            let item = this.parse_trait_item_(at_end, attrs);
+            unclosed_delims.append(&mut this.unclosed_delims);
+            item
+        })?;
+        self.unclosed_delims.append(&mut unclosed_delims);
+        // See `parse_item` for why this clause is here.
+        if !item.attrs.iter().any(|attr| attr.style == AttrStyle::Inner) {
+            item.tokens = Some(tokens);
+        }
+        Ok(item)
+    }
+
+    fn parse_trait_item_(&mut self,
+                         at_end: &mut bool,
+                         mut attrs: Vec<Attribute>) -> PResult<'a, TraitItem> {
+        let lo = self.token.span;
+        self.eat_bad_pub();
+        let (name, node, generics) = if self.eat_keyword(kw::Type) {
+            self.parse_trait_item_assoc_ty()?
+        } else if self.is_const_item() {
+            self.expect_keyword(kw::Const)?;
+            let ident = self.parse_ident()?;
+            self.expect(&token::Colon)?;
+            let ty = self.parse_ty()?;
+            let default = if self.eat(&token::Eq) {
+                let expr = self.parse_expr()?;
+                self.expect(&token::Semi)?;
+                Some(expr)
+            } else {
+                self.expect(&token::Semi)?;
+                None
+            };
+            (ident, TraitItemKind::Const(ty, default), ast::Generics::default())
+        } else if let Some(mac) = self.parse_assoc_macro_invoc("trait", None, &mut false)? {
+            // trait item macro.
+            (Ident::invalid(), ast::TraitItemKind::Macro(mac), ast::Generics::default())
+        } else {
+            let (constness, unsafety, asyncness, abi) = self.parse_fn_front_matter()?;
+
+            let ident = self.parse_ident()?;
+            let mut generics = self.parse_generics()?;
+
+            let decl = self.parse_fn_decl_with_self(|p: &mut Parser<'a>| {
+                // This is somewhat dubious; We don't want to allow
+                // argument names to be left off if there is a
+                // definition...
+
+                // We don't allow argument names to be left off in edition 2018.
+                let is_name_required = p.token.span.rust_2018();
+                p.parse_arg_general(true, false, |_| is_name_required)
+            })?;
+            generics.where_clause = self.parse_where_clause()?;
+
+            let sig = ast::MethodSig {
+                header: FnHeader {
+                    unsafety,
+                    constness,
+                    abi,
+                    asyncness,
+                },
+                decl,
+            };
+
+            let body = match self.token.kind {
+                token::Semi => {
+                    self.bump();
+                    *at_end = true;
+                    debug!("parse_trait_methods(): parsing required method");
+                    None
+                }
+                token::OpenDelim(token::Brace) => {
+                    debug!("parse_trait_methods(): parsing provided method");
+                    *at_end = true;
+                    let (inner_attrs, body) = self.parse_inner_attrs_and_block()?;
+                    attrs.extend(inner_attrs.iter().cloned());
+                    Some(body)
+                }
+                token::Interpolated(ref nt) => {
+                    match **nt {
+                        token::NtBlock(..) => {
+                            *at_end = true;
+                            let (inner_attrs, body) = self.parse_inner_attrs_and_block()?;
+                            attrs.extend(inner_attrs.iter().cloned());
+                            Some(body)
+                        }
+                        _ => {
+                            return self.expected_semi_or_open_brace();
+                        }
+                    }
+                }
+                _ => {
+                    return self.expected_semi_or_open_brace();
+                }
+            };
+            (ident, ast::TraitItemKind::Method(sig, body), generics)
+        };
+
+        Ok(TraitItem {
+            id: ast::DUMMY_NODE_ID,
+            ident: name,
+            attrs,
+            generics,
+            node,
+            span: lo.to(self.prev_span),
+            tokens: None,
+        })
+    }
+
+    /// Parses the following grammar:
+    ///
+    ///     TraitItemAssocTy = Ident ["<"...">"] [":" [GenericBounds]] ["where" ...] ["=" Ty]
+    fn parse_trait_item_assoc_ty(&mut self)
+        -> PResult<'a, (Ident, TraitItemKind, ast::Generics)> {
+        let ident = self.parse_ident()?;
+        let mut generics = self.parse_generics()?;
+
+        // Parse optional colon and param bounds.
+        let bounds = if self.eat(&token::Colon) {
+            self.parse_generic_bounds(None)?
+        } else {
+            Vec::new()
+        };
+        generics.where_clause = self.parse_where_clause()?;
+
+        let default = if self.eat(&token::Eq) {
+            Some(self.parse_ty()?)
+        } else {
+            None
+        };
+        self.expect(&token::Semi)?;
+
+        Ok((ident, TraitItemKind::Type(bounds, default), generics))
+    }
+
+    /// Parses a `UseTree`.
+    ///
+    /// ```
+    /// USE_TREE = [`::`] `*` |
+    ///            [`::`] `{` USE_TREE_LIST `}` |
+    ///            PATH `::` `*` |
+    ///            PATH `::` `{` USE_TREE_LIST `}` |
+    ///            PATH [`as` IDENT]
+    /// ```
+    fn parse_use_tree(&mut self) -> PResult<'a, UseTree> {
+        let lo = self.token.span;
+
+        let mut prefix = ast::Path { segments: Vec::new(), span: lo.shrink_to_lo() };
+        let kind = if self.check(&token::OpenDelim(token::Brace)) ||
+                      self.check(&token::BinOp(token::Star)) ||
+                      self.is_import_coupler() {
+            // `use *;` or `use ::*;` or `use {...};` or `use ::{...};`
+            let mod_sep_ctxt = self.token.span.ctxt();
+            if self.eat(&token::ModSep) {
+                prefix.segments.push(
+                    PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt))
+                );
+            }
+
+            if self.eat(&token::BinOp(token::Star)) {
+                UseTreeKind::Glob
+            } else {
+                UseTreeKind::Nested(self.parse_use_tree_list()?)
+            }
+        } else {
+            // `use path::*;` or `use path::{...};` or `use path;` or `use path as bar;`
+            prefix = self.parse_path(PathStyle::Mod)?;
+
+            if self.eat(&token::ModSep) {
+                if self.eat(&token::BinOp(token::Star)) {
+                    UseTreeKind::Glob
+                } else {
+                    UseTreeKind::Nested(self.parse_use_tree_list()?)
+                }
+            } else {
+                UseTreeKind::Simple(self.parse_rename()?, ast::DUMMY_NODE_ID, ast::DUMMY_NODE_ID)
+            }
+        };
+
+        Ok(UseTree { prefix, kind, span: lo.to(self.prev_span) })
+    }
+
+    /// Parses a `UseTreeKind::Nested(list)`.
+    ///
+    /// ```
+    /// USE_TREE_LIST = Ø | (USE_TREE `,`)* USE_TREE [`,`]
+    /// ```
+    fn parse_use_tree_list(&mut self) -> PResult<'a, Vec<(UseTree, ast::NodeId)>> {
+        self.parse_delim_comma_seq(token::Brace, |p| Ok((p.parse_use_tree()?, ast::DUMMY_NODE_ID)))
+            .map(|(r, _)| r)
+    }
+
+    fn parse_rename(&mut self) -> PResult<'a, Option<Ident>> {
+        if self.eat_keyword(kw::As) {
+            self.parse_ident_or_underscore().map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+
+    fn parse_ident_or_underscore(&mut self) -> PResult<'a, ast::Ident> {
+        match self.token.kind {
+            token::Ident(name, false) if name == kw::Underscore => {
+                let span = self.token.span;
+                self.bump();
+                Ok(Ident::new(name, span))
+            }
+            _ => self.parse_ident(),
+        }
+    }
+
+    /// Parses `extern crate` links.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// extern crate foo;
+    /// extern crate bar as foo;
+    /// ```
+    fn parse_item_extern_crate(
+        &mut self,
+        lo: Span,
+        visibility: Visibility,
+        attrs: Vec<Attribute>
+    ) -> PResult<'a, P<Item>> {
+        // Accept `extern crate name-like-this` for better diagnostics
+        let orig_name = self.parse_crate_name_with_dashes()?;
+        let (item_name, orig_name) = if let Some(rename) = self.parse_rename()? {
+            (rename, Some(orig_name.name))
+        } else {
+            (orig_name, None)
+        };
+        self.expect(&token::Semi)?;
+
+        let span = lo.to(self.prev_span);
+        Ok(self.mk_item(span, item_name, ItemKind::ExternCrate(orig_name), visibility, attrs))
+    }
+
+    fn parse_crate_name_with_dashes(&mut self) -> PResult<'a, ast::Ident> {
+        let error_msg = "crate name using dashes are not valid in `extern crate` statements";
+        let suggestion_msg = "if the original crate name uses dashes you need to use underscores \
+                              in the code";
+        let mut ident = if self.token.is_keyword(kw::SelfLower) {
+            self.parse_path_segment_ident()
+        } else {
+            self.parse_ident()
+        }?;
+        let mut idents = vec![];
+        let mut replacement = vec![];
+        let mut fixed_crate_name = false;
+        // Accept `extern crate name-like-this` for better diagnostics
+        let dash = token::BinOp(token::BinOpToken::Minus);
+        if self.token == dash {  // Do not include `-` as part of the expected tokens list
+            while self.eat(&dash) {
+                fixed_crate_name = true;
+                replacement.push((self.prev_span, "_".to_string()));
+                idents.push(self.parse_ident()?);
+            }
+        }
+        if fixed_crate_name {
+            let fixed_name_sp = ident.span.to(idents.last().unwrap().span);
+            let mut fixed_name = format!("{}", ident.name);
+            for part in idents {
+                fixed_name.push_str(&format!("_{}", part.name));
+            }
+            ident = Ident::from_str(&fixed_name).with_span_pos(fixed_name_sp);
+
+            self.struct_span_err(fixed_name_sp, error_msg)
+                .span_label(fixed_name_sp, "dash-separated idents are not valid")
+                .multipart_suggestion(suggestion_msg, replacement, Applicability::MachineApplicable)
+                .emit();
+        }
+        Ok(ident)
+    }
+
+    /// Parses an item-position function declaration.
+    fn parse_item_fn(
+        &mut self,
+        unsafety: Unsafety,
+        asyncness: Spanned<IsAsync>,
+        constness: Spanned<Constness>,
+        abi: Abi
+    ) -> PResult<'a, ItemInfo> {
+        let (ident, mut generics) = self.parse_fn_header()?;
+        let allow_c_variadic = abi == Abi::C && unsafety == Unsafety::Unsafe;
+        let decl = self.parse_fn_decl(allow_c_variadic)?;
+        generics.where_clause = self.parse_where_clause()?;
+        let (inner_attrs, body) = self.parse_inner_attrs_and_block()?;
+        let header = FnHeader { unsafety, asyncness, constness, abi };
+        Ok((ident, ItemKind::Fn(decl, header, generics, body), Some(inner_attrs)))
+    }
+
+    /// Parses the name and optional generic types of a function header.
+    fn parse_fn_header(&mut self) -> PResult<'a, (Ident, ast::Generics)> {
+        let id = self.parse_ident()?;
+        let generics = self.parse_generics()?;
+        Ok((id, generics))
+    }
+
+    /// Parses the argument list and result type of a function declaration.
+    fn parse_fn_decl(&mut self, allow_c_variadic: bool) -> PResult<'a, P<FnDecl>> {
+        let (args, c_variadic) = self.parse_fn_args(true, allow_c_variadic)?;
+        let ret_ty = self.parse_ret_ty(true)?;
+
+        Ok(P(FnDecl {
+            inputs: args,
+            output: ret_ty,
+            c_variadic,
+        }))
+    }
+
+    /// Parses `extern` for foreign ABIs modules.
+    ///
+    /// `extern` is expected to have been
+    /// consumed before calling this method.
+    ///
+    /// # Examples
+    ///
+    /// ```ignore (only-for-syntax-highlight)
+    /// extern "C" {}
+    /// extern {}
+    /// ```
+    fn parse_item_foreign_mod(
+        &mut self,
+        lo: Span,
+        opt_abi: Option<Abi>,
+        visibility: Visibility,
+        mut attrs: Vec<Attribute>,
+        extern_sp: Span,
+    ) -> PResult<'a, P<Item>> {
+        self.expect(&token::OpenDelim(token::Brace))?;
+
+        let abi = opt_abi.unwrap_or(Abi::C);
+
+        attrs.extend(self.parse_inner_attributes()?);
+
+        let mut foreign_items = vec![];
+        while !self.eat(&token::CloseDelim(token::Brace)) {
+            foreign_items.push(self.parse_foreign_item(extern_sp)?);
+        }
+
+        let prev_span = self.prev_span;
+        let m = ast::ForeignMod {
+            abi,
+            items: foreign_items
+        };
+        let invalid = Ident::invalid();
+        Ok(self.mk_item(lo.to(prev_span), invalid, ItemKind::ForeignMod(m), visibility, attrs))
+    }
+
+    /// Parses a foreign item.
+    crate fn parse_foreign_item(&mut self, extern_sp: Span) -> PResult<'a, ForeignItem> {
+        maybe_whole!(self, NtForeignItem, |ni| ni);
+
+        let attrs = self.parse_outer_attributes()?;
+        let lo = self.token.span;
+        let visibility = self.parse_visibility(false)?;
+
+        // FOREIGN STATIC ITEM
+        // Treat `const` as `static` for error recovery, but don't add it to expected tokens.
+        if self.check_keyword(kw::Static) || self.token.is_keyword(kw::Const) {
+            if self.token.is_keyword(kw::Const) {
+                self.diagnostic()
+                    .struct_span_err(self.token.span, "extern items cannot be `const`")
+                    .span_suggestion(
+                        self.token.span,
+                        "try using a static value",
+                        "static".to_owned(),
+                        Applicability::MachineApplicable
+                    ).emit();
+            }
+            self.bump(); // `static` or `const`
+            return Ok(self.parse_item_foreign_static(visibility, lo, attrs)?);
+        }
+        // FOREIGN FUNCTION ITEM
+        if self.check_keyword(kw::Fn) {
+            return Ok(self.parse_item_foreign_fn(visibility, lo, attrs, extern_sp)?);
+        }
+        // FOREIGN TYPE ITEM
+        if self.check_keyword(kw::Type) {
+            return Ok(self.parse_item_foreign_type(visibility, lo, attrs)?);
+        }
+
+        match self.parse_assoc_macro_invoc("extern", Some(&visibility), &mut false)? {
+            Some(mac) => {
+                Ok(
+                    ForeignItem {
+                        ident: Ident::invalid(),
+                        span: lo.to(self.prev_span),
+                        id: ast::DUMMY_NODE_ID,
+                        attrs,
+                        vis: visibility,
+                        node: ForeignItemKind::Macro(mac),
+                    }
+                )
+            }
+            None => {
+                if !attrs.is_empty()  {
+                    self.expected_item_err(&attrs)?;
+                }
+
+                self.unexpected()
+            }
+        }
+    }
+
+    /// Parses a function declaration from a foreign module.
+    fn parse_item_foreign_fn(
+        &mut self,
+        vis: ast::Visibility,
+        lo: Span,
+        attrs: Vec<Attribute>,
+        extern_sp: Span,
+    ) -> PResult<'a, ForeignItem> {
+        self.expect_keyword(kw::Fn)?;
+
+        let (ident, mut generics) = self.parse_fn_header()?;
+        let decl = self.parse_fn_decl(true)?;
+        generics.where_clause = self.parse_where_clause()?;
+        let hi = self.token.span;
+        self.parse_semi_or_incorrect_foreign_fn_body(&ident, extern_sp)?;
+        Ok(ast::ForeignItem {
+            ident,
+            attrs,
+            node: ForeignItemKind::Fn(decl, generics),
+            id: ast::DUMMY_NODE_ID,
+            span: lo.to(hi),
+            vis,
+        })
+    }
+
+    /// Parses a static item from a foreign module.
+    /// Assumes that the `static` keyword is already parsed.
+    fn parse_item_foreign_static(&mut self, vis: ast::Visibility, lo: Span, attrs: Vec<Attribute>)
+                                 -> PResult<'a, ForeignItem> {
+        let mutbl = self.parse_mutability();
+        let ident = self.parse_ident()?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+        let hi = self.token.span;
+        self.expect(&token::Semi)?;
+        Ok(ForeignItem {
+            ident,
+            attrs,
+            node: ForeignItemKind::Static(ty, mutbl),
+            id: ast::DUMMY_NODE_ID,
+            span: lo.to(hi),
+            vis,
+        })
+    }
+
+    /// Parses a type from a foreign module.
+    fn parse_item_foreign_type(&mut self, vis: ast::Visibility, lo: Span, attrs: Vec<Attribute>)
+                             -> PResult<'a, ForeignItem> {
+        self.expect_keyword(kw::Type)?;
+
+        let ident = self.parse_ident()?;
+        let hi = self.token.span;
+        self.expect(&token::Semi)?;
+        Ok(ast::ForeignItem {
+            ident,
+            attrs,
+            node: ForeignItemKind::Ty,
+            id: ast::DUMMY_NODE_ID,
+            span: lo.to(hi),
+            vis
+        })
+    }
+
+    fn is_static_global(&mut self) -> bool {
+        if self.check_keyword(kw::Static) {
+            // Check if this could be a closure
+            !self.look_ahead(1, |token| {
+                if token.is_keyword(kw::Move) {
+                    return true;
+                }
+                match token.kind {
+                    token::BinOp(token::Or) | token::OrOr => true,
+                    _ => false,
+                }
+            })
+        } else {
+            false
+        }
+    }
+
+    fn parse_item_const(&mut self, m: Option<Mutability>) -> PResult<'a, ItemInfo> {
+        let id = if m.is_none() { self.parse_ident_or_underscore() } else { self.parse_ident() }?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+        self.expect(&token::Eq)?;
+        let e = self.parse_expr()?;
+        self.expect(&token::Semi)?;
+        let item = match m {
+            Some(m) => ItemKind::Static(ty, m, e),
+            None => ItemKind::Const(ty, e),
+        };
+        Ok((id, item, None))
+    }
+
+    /// Parses `type Foo = Bar;` or returns `None`
+    /// without modifying the parser state.
+    fn eat_type(&mut self) -> Option<PResult<'a, (Ident, AliasKind, ast::Generics)>> {
+        // This parses the grammar:
+        //     Ident ["<"...">"] ["where" ...] ("=" | ":") Ty ";"
+        if self.eat_keyword(kw::Type) {
+            Some(self.parse_type_alias())
+        } else {
+            None
+        }
+    }
+
+    /// Parses a type alias or opaque type.
+    fn parse_type_alias(&mut self) -> PResult<'a, (Ident, AliasKind, ast::Generics)> {
+        let ident = self.parse_ident()?;
+        let mut tps = self.parse_generics()?;
+        tps.where_clause = self.parse_where_clause()?;
+        self.expect(&token::Eq)?;
+        let alias = if self.check_keyword(kw::Impl) {
+            self.bump();
+            let bounds = self.parse_generic_bounds(Some(self.prev_span))?;
+            AliasKind::OpaqueTy(bounds)
+        } else {
+            let ty = self.parse_ty()?;
+            AliasKind::Weak(ty)
+        };
+        self.expect(&token::Semi)?;
+        Ok((ident, alias, tps))
+    }
+
+    /// Parses an enum declaration.
+    fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
+        let id = self.parse_ident()?;
+        let mut generics = self.parse_generics()?;
+        generics.where_clause = self.parse_where_clause()?;
+        self.expect(&token::OpenDelim(token::Brace))?;
+
+        let enum_definition = self.parse_enum_def(&generics).map_err(|e| {
+            self.recover_stmt();
+            self.eat(&token::CloseDelim(token::Brace));
+            e
+        })?;
+        Ok((id, ItemKind::Enum(enum_definition, generics), None))
+    }
+
+    /// Parses the part of an enum declaration following the `{`.
+    fn parse_enum_def(&mut self, _generics: &ast::Generics) -> PResult<'a, EnumDef> {
+        let mut variants = Vec::new();
+        while self.token != token::CloseDelim(token::Brace) {
+            let variant_attrs = self.parse_outer_attributes()?;
+            let vlo = self.token.span;
+
+            self.eat_bad_pub();
+            let ident = self.parse_ident()?;
+
+            let struct_def = if self.check(&token::OpenDelim(token::Brace)) {
+                // Parse a struct variant.
+                let (fields, recovered) = self.parse_record_struct_body()?;
+                VariantData::Struct(fields, recovered)
+            } else if self.check(&token::OpenDelim(token::Paren)) {
+                VariantData::Tuple(
+                    self.parse_tuple_struct_body()?,
+                    ast::DUMMY_NODE_ID,
+                )
+            } else {
+                VariantData::Unit(ast::DUMMY_NODE_ID)
+            };
+
+            let disr_expr = if self.eat(&token::Eq) {
+                Some(AnonConst {
+                    id: ast::DUMMY_NODE_ID,
+                    value: self.parse_expr()?,
+                })
+            } else {
+                None
+            };
+
+            let vr = ast::Variant {
+                ident,
+                id: ast::DUMMY_NODE_ID,
+                attrs: variant_attrs,
+                data: struct_def,
+                disr_expr,
+                span: vlo.to(self.prev_span),
+            };
+            variants.push(vr);
+
+            if !self.eat(&token::Comma) {
+                if self.token.is_ident() && !self.token.is_reserved_ident() {
+                    let sp = self.sess.source_map().next_point(self.prev_span);
+                    self.struct_span_err(sp, "missing comma")
+                        .span_suggestion_short(
+                            sp,
+                            "missing comma",
+                            ",".to_owned(),
+                            Applicability::MaybeIncorrect,
+                        )
+                        .emit();
+                } else {
+                    break;
+                }
+            }
+        }
+        self.expect(&token::CloseDelim(token::Brace))?;
+
+        Ok(ast::EnumDef { variants })
+    }
+
+    /// Parses `struct Foo { ... }`.
+    fn parse_item_struct(&mut self) -> PResult<'a, ItemInfo> {
+        let class_name = self.parse_ident()?;
+
+        let mut generics = self.parse_generics()?;
+
+        // There is a special case worth noting here, as reported in issue #17904.
+        // If we are parsing a tuple struct it is the case that the where clause
+        // should follow the field list. Like so:
+        //
+        // struct Foo<T>(T) where T: Copy;
+        //
+        // If we are parsing a normal record-style struct it is the case
+        // that the where clause comes before the body, and after the generics.
+        // So if we look ahead and see a brace or a where-clause we begin
+        // parsing a record style struct.
+        //
+        // Otherwise if we look ahead and see a paren we parse a tuple-style
+        // struct.
+
+        let vdata = if self.token.is_keyword(kw::Where) {
+            generics.where_clause = self.parse_where_clause()?;
+            if self.eat(&token::Semi) {
+                // If we see a: `struct Foo<T> where T: Copy;` style decl.
+                VariantData::Unit(ast::DUMMY_NODE_ID)
+            } else {
+                // If we see: `struct Foo<T> where T: Copy { ... }`
+                let (fields, recovered) = self.parse_record_struct_body()?;
+                VariantData::Struct(fields, recovered)
+            }
+        // No `where` so: `struct Foo<T>;`
+        } else if self.eat(&token::Semi) {
+            VariantData::Unit(ast::DUMMY_NODE_ID)
+        // Record-style struct definition
+        } else if self.token == token::OpenDelim(token::Brace) {
+            let (fields, recovered) = self.parse_record_struct_body()?;
+            VariantData::Struct(fields, recovered)
+        // Tuple-style struct definition with optional where-clause.
+        } else if self.token == token::OpenDelim(token::Paren) {
+            let body = VariantData::Tuple(self.parse_tuple_struct_body()?, ast::DUMMY_NODE_ID);
+            generics.where_clause = self.parse_where_clause()?;
+            self.expect(&token::Semi)?;
+            body
+        } else {
+            let token_str = self.this_token_descr();
+            let mut err = self.fatal(&format!(
+                "expected `where`, `{{`, `(`, or `;` after struct name, found {}",
+                token_str
+            ));
+            err.span_label(self.token.span, "expected `where`, `{`, `(`, or `;` after struct name");
+            return Err(err);
+        };
+
+        Ok((class_name, ItemKind::Struct(vdata, generics), None))
+    }
+
+    /// Parses `union Foo { ... }`.
+    fn parse_item_union(&mut self) -> PResult<'a, ItemInfo> {
+        let class_name = self.parse_ident()?;
+
+        let mut generics = self.parse_generics()?;
+
+        let vdata = if self.token.is_keyword(kw::Where) {
+            generics.where_clause = self.parse_where_clause()?;
+            let (fields, recovered) = self.parse_record_struct_body()?;
+            VariantData::Struct(fields, recovered)
+        } else if self.token == token::OpenDelim(token::Brace) {
+            let (fields, recovered) = self.parse_record_struct_body()?;
+            VariantData::Struct(fields, recovered)
+        } else {
+            let token_str = self.this_token_descr();
+            let mut err = self.fatal(&format!(
+                "expected `where` or `{{` after union name, found {}", token_str));
+            err.span_label(self.token.span, "expected `where` or `{` after union name");
+            return Err(err);
+        };
+
+        Ok((class_name, ItemKind::Union(vdata, generics), None))
+    }
+
+    pub(super) fn is_union_item(&self) -> bool {
+        self.token.is_keyword(kw::Union) &&
+        self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident())
+    }
+
+    fn parse_record_struct_body(
+        &mut self,
+    ) -> PResult<'a, (Vec<StructField>, /* recovered */ bool)> {
+        let mut fields = Vec::new();
+        let mut recovered = false;
+        if self.eat(&token::OpenDelim(token::Brace)) {
+            while self.token != token::CloseDelim(token::Brace) {
+                let field = self.parse_struct_decl_field().map_err(|e| {
+                    self.recover_stmt();
+                    recovered = true;
+                    e
+                });
+                match field {
+                    Ok(field) => fields.push(field),
+                    Err(mut err) => {
+                        err.emit();
+                    }
+                }
+            }
+            self.eat(&token::CloseDelim(token::Brace));
+        } else {
+            let token_str = self.this_token_descr();
+            let mut err = self.fatal(&format!(
+                    "expected `where`, or `{{` after struct name, found {}", token_str));
+            err.span_label(self.token.span, "expected `where`, or `{` after struct name");
+            return Err(err);
+        }
+
+        Ok((fields, recovered))
+    }
+
+    fn parse_tuple_struct_body(&mut self) -> PResult<'a, Vec<StructField>> {
+        // This is the case where we find `struct Foo<T>(T) where T: Copy;`
+        // Unit like structs are handled in parse_item_struct function
+        self.parse_paren_comma_seq(|p| {
+            let attrs = p.parse_outer_attributes()?;
+            let lo = p.token.span;
+            let vis = p.parse_visibility(true)?;
+            let ty = p.parse_ty()?;
+            Ok(StructField {
+                span: lo.to(ty.span),
+                vis,
+                ident: None,
+                id: ast::DUMMY_NODE_ID,
+                ty,
+                attrs,
+            })
+        }).map(|(r, _)| r)
+    }
+
+    /// Parses an element of a struct declaration.
+    fn parse_struct_decl_field(&mut self) -> PResult<'a, StructField> {
+        let attrs = self.parse_outer_attributes()?;
+        let lo = self.token.span;
+        let vis = self.parse_visibility(false)?;
+        self.parse_single_struct_field(lo, vis, attrs)
+    }
+
+    /// Parses a structure field declaration.
+    fn parse_single_struct_field(&mut self,
+                                     lo: Span,
+                                     vis: Visibility,
+                                     attrs: Vec<Attribute> )
+                                     -> PResult<'a, StructField> {
+        let mut seen_comma: bool = false;
+        let a_var = self.parse_name_and_ty(lo, vis, attrs)?;
+        if self.token == token::Comma {
+            seen_comma = true;
+        }
+        match self.token.kind {
+            token::Comma => {
+                self.bump();
+            }
+            token::CloseDelim(token::Brace) => {}
+            token::DocComment(_) => {
+                let previous_span = self.prev_span;
+                let mut err = self.span_fatal_err(self.token.span, Error::UselessDocComment);
+                self.bump(); // consume the doc comment
+                let comma_after_doc_seen = self.eat(&token::Comma);
+                // `seen_comma` is always false, because we are inside doc block
+                // condition is here to make code more readable
+                if seen_comma == false && comma_after_doc_seen == true {
+                    seen_comma = true;
+                }
+                if comma_after_doc_seen || self.token == token::CloseDelim(token::Brace) {
+                    err.emit();
+                } else {
+                    if seen_comma == false {
+                        let sp = self.sess.source_map().next_point(previous_span);
+                        err.span_suggestion(
+                            sp,
+                            "missing comma here",
+                            ",".into(),
+                            Applicability::MachineApplicable
+                        );
+                    }
+                    return Err(err);
+                }
+            }
+            _ => {
+                let sp = self.sess.source_map().next_point(self.prev_span);
+                let mut err = self.struct_span_err(sp, &format!("expected `,`, or `}}`, found {}",
+                                                                self.this_token_descr()));
+                if self.token.is_ident() {
+                    // This is likely another field; emit the diagnostic and keep going
+                    err.span_suggestion(
+                        sp,
+                        "try adding a comma",
+                        ",".into(),
+                        Applicability::MachineApplicable,
+                    );
+                    err.emit();
+                } else {
+                    return Err(err)
+                }
+            }
+        }
+        Ok(a_var)
+    }
+
+    /// Parses a structure field.
+    fn parse_name_and_ty(
+        &mut self,
+        lo: Span,
+        vis: Visibility,
+        attrs: Vec<Attribute>
+    ) -> PResult<'a, StructField> {
+        let name = self.parse_ident()?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+        Ok(StructField {
+            span: lo.to(self.prev_span),
+            ident: Some(name),
+            vis,
+            id: ast::DUMMY_NODE_ID,
+            ty,
+            attrs,
+        })
+    }
+
+    pub(super) fn eat_macro_def(
+        &mut self,
+        attrs: &[Attribute],
+        vis: &Visibility,
+        lo: Span
+    ) -> PResult<'a, Option<P<Item>>> {
+        let token_lo = self.token.span;
+        let (ident, def) = if self.eat_keyword(kw::Macro) {
+            let ident = self.parse_ident()?;
+            let tokens = if self.check(&token::OpenDelim(token::Brace)) {
+                match self.parse_token_tree() {
+                    TokenTree::Delimited(_, _, tts) => tts,
+                    _ => unreachable!(),
+                }
+            } else if self.check(&token::OpenDelim(token::Paren)) {
+                let args = self.parse_token_tree();
+                let body = if self.check(&token::OpenDelim(token::Brace)) {
+                    self.parse_token_tree()
+                } else {
+                    self.unexpected()?;
+                    unreachable!()
+                };
+                TokenStream::new(vec![
+                    args.into(),
+                    TokenTree::token(token::FatArrow, token_lo.to(self.prev_span)).into(),
+                    body.into(),
+                ])
+            } else {
+                self.unexpected()?;
+                unreachable!()
+            };
+
+            (ident, ast::MacroDef { tokens: tokens.into(), legacy: false })
+        } else if self.check_keyword(sym::macro_rules) &&
+                  self.look_ahead(1, |t| *t == token::Not) &&
+                  self.look_ahead(2, |t| t.is_ident()) {
+            let prev_span = self.prev_span;
+            self.complain_if_pub_macro(&vis.node, prev_span);
+            self.bump();
+            self.bump();
+
+            let ident = self.parse_ident()?;
+            let (delim, tokens) = self.expect_delimited_token_tree()?;
+            if delim != MacDelimiter::Brace && !self.eat(&token::Semi) {
+                self.report_invalid_macro_expansion_item();
+            }
+
+            (ident, ast::MacroDef { tokens, legacy: true })
+        } else {
+            return Ok(None);
+        };
+
+        let span = lo.to(self.prev_span);
+        Ok(Some(self.mk_item(span, ident, ItemKind::MacroDef(def), vis.clone(), attrs.to_vec())))
+    }
+
+    fn complain_if_pub_macro(&self, vis: &VisibilityKind, sp: Span) {
+        match *vis {
+            VisibilityKind::Inherited => {}
+            _ => {
+                let mut err = if self.token.is_keyword(sym::macro_rules) {
+                    let mut err = self.diagnostic()
+                        .struct_span_err(sp, "can't qualify macro_rules invocation with `pub`");
+                    err.span_suggestion(
+                        sp,
+                        "try exporting the macro",
+                        "#[macro_export]".to_owned(),
+                        Applicability::MaybeIncorrect // speculative
+                    );
+                    err
+                } else {
+                    let mut err = self.diagnostic()
+                        .struct_span_err(sp, "can't qualify macro invocation with `pub`");
+                    err.help("try adjusting the macro to put `pub` inside the invocation");
+                    err
+                };
+                err.emit();
+            }
+        }
+    }
+
+    fn mk_item(&self, span: Span, ident: Ident, node: ItemKind, vis: Visibility,
+               attrs: Vec<Attribute>) -> P<Item> {
+        P(Item {
+            ident,
+            attrs,
+            id: ast::DUMMY_NODE_ID,
+            node,
+            vis,
+            span,
+            tokens: None,
+        })
+    }
+}
diff --git a/src/libsyntax/parse/parser/module.rs b/src/libsyntax/parse/parser/module.rs
new file mode 100644
index 00000000000..3f6f87b1c44
--- /dev/null
+++ b/src/libsyntax/parse/parser/module.rs
@@ -0,0 +1,332 @@
+use super::{Parser, PResult};
+use super::item::ItemInfo;
+
+use crate::attr;
+use crate::ast::{self, Ident, Attribute, ItemKind, Mod, Crate};
+use crate::parse::{new_sub_parser_from_file, DirectoryOwnership};
+use crate::parse::token::{self, TokenKind};
+use crate::parse::diagnostics::{Error};
+use crate::source_map::{SourceMap, Span, DUMMY_SP, FileName};
+use crate::symbol::sym;
+
+use std::path::{self, Path, PathBuf};
+
+/// Information about the path to a module.
+pub struct ModulePath {
+    name: String,
+    path_exists: bool,
+    pub result: Result<ModulePathSuccess, Error>,
+}
+
+pub struct ModulePathSuccess {
+    pub path: PathBuf,
+    pub directory_ownership: DirectoryOwnership,
+    warn: bool,
+}
+
+impl<'a> Parser<'a> {
+    /// Parses a source module as a crate. This is the main entry point for the parser.
+    pub fn parse_crate_mod(&mut self) -> PResult<'a, Crate> {
+        let lo = self.token.span;
+        let krate = Ok(ast::Crate {
+            attrs: self.parse_inner_attributes()?,
+            module: self.parse_mod_items(&token::Eof, lo)?,
+            span: lo.to(self.token.span),
+        });
+        krate
+    }
+
+    /// Parse a `mod <foo> { ... }` or `mod <foo>;` item
+    pub(super) fn parse_item_mod(&mut self, outer_attrs: &[Attribute]) -> PResult<'a, ItemInfo> {
+        let (in_cfg, outer_attrs) = {
+            let mut strip_unconfigured = crate::config::StripUnconfigured {
+                sess: self.sess,
+                features: None, // don't perform gated feature checking
+            };
+            let mut outer_attrs = outer_attrs.to_owned();
+            strip_unconfigured.process_cfg_attrs(&mut outer_attrs);
+            (!self.cfg_mods || strip_unconfigured.in_cfg(&outer_attrs), outer_attrs)
+        };
+
+        let id_span = self.token.span;
+        let id = self.parse_ident()?;
+        if self.eat(&token::Semi) {
+            if in_cfg && self.recurse_into_file_modules {
+                // This mod is in an external file. Let's go get it!
+                let ModulePathSuccess { path, directory_ownership, warn } =
+                    self.submod_path(id, &outer_attrs, id_span)?;
+                let (module, mut attrs) =
+                    self.eval_src_mod(path, directory_ownership, id.to_string(), id_span)?;
+                // Record that we fetched the mod from an external file
+                if warn {
+                    let attr = attr::mk_attr_outer(
+                        attr::mk_word_item(Ident::with_dummy_span(sym::warn_directory_ownership)));
+                    attr::mark_known(&attr);
+                    attrs.push(attr);
+                }
+                Ok((id, ItemKind::Mod(module), Some(attrs)))
+            } else {
+                let placeholder = ast::Mod {
+                    inner: DUMMY_SP,
+                    items: Vec::new(),
+                    inline: false
+                };
+                Ok((id, ItemKind::Mod(placeholder), None))
+            }
+        } else {
+            let old_directory = self.directory.clone();
+            self.push_directory(id, &outer_attrs);
+
+            self.expect(&token::OpenDelim(token::Brace))?;
+            let mod_inner_lo = self.token.span;
+            let attrs = self.parse_inner_attributes()?;
+            let module = self.parse_mod_items(&token::CloseDelim(token::Brace), mod_inner_lo)?;
+
+            self.directory = old_directory;
+            Ok((id, ItemKind::Mod(module), Some(attrs)))
+        }
+    }
+
+    /// Given a termination token, parses all of the items in a module.
+    fn parse_mod_items(&mut self, term: &TokenKind, inner_lo: Span) -> PResult<'a, Mod> {
+        let mut items = vec![];
+        while let Some(item) = self.parse_item()? {
+            items.push(item);
+            self.maybe_consume_incorrect_semicolon(&items);
+        }
+
+        if !self.eat(term) {
+            let token_str = self.this_token_descr();
+            if !self.maybe_consume_incorrect_semicolon(&items) {
+                let mut err = self.fatal(&format!("expected item, found {}", token_str));
+                err.span_label(self.token.span, "expected item");
+                return Err(err);
+            }
+        }
+
+        let hi = if self.token.span.is_dummy() {
+            inner_lo
+        } else {
+            self.prev_span
+        };
+
+        Ok(Mod {
+            inner: inner_lo.to(hi),
+            items,
+            inline: true
+        })
+    }
+
+    fn submod_path(
+        &mut self,
+        id: ast::Ident,
+        outer_attrs: &[Attribute],
+        id_sp: Span
+    ) -> PResult<'a, ModulePathSuccess> {
+        if let Some(path) = Parser::submod_path_from_attr(outer_attrs, &self.directory.path) {
+            return Ok(ModulePathSuccess {
+                directory_ownership: match path.file_name().and_then(|s| s.to_str()) {
+                    // All `#[path]` files are treated as though they are a `mod.rs` file.
+                    // This means that `mod foo;` declarations inside `#[path]`-included
+                    // files are siblings,
+                    //
+                    // Note that this will produce weirdness when a file named `foo.rs` is
+                    // `#[path]` included and contains a `mod foo;` declaration.
+                    // If you encounter this, it's your own darn fault :P
+                    Some(_) => DirectoryOwnership::Owned { relative: None },
+                    _ => DirectoryOwnership::UnownedViaMod(true),
+                },
+                path,
+                warn: false,
+            });
+        }
+
+        let relative = match self.directory.ownership {
+            DirectoryOwnership::Owned { relative } => relative,
+            DirectoryOwnership::UnownedViaBlock |
+            DirectoryOwnership::UnownedViaMod(_) => None,
+        };
+        let paths = Parser::default_submod_path(
+                        id, relative, &self.directory.path, self.sess.source_map());
+
+        match self.directory.ownership {
+            DirectoryOwnership::Owned { .. } => {
+                paths.result.map_err(|err| self.span_fatal_err(id_sp, err))
+            },
+            DirectoryOwnership::UnownedViaBlock => {
+                let msg =
+                    "Cannot declare a non-inline module inside a block \
+                    unless it has a path attribute";
+                let mut err = self.diagnostic().struct_span_err(id_sp, msg);
+                if paths.path_exists {
+                    let msg = format!("Maybe `use` the module `{}` instead of redeclaring it",
+                                      paths.name);
+                    err.span_note(id_sp, &msg);
+                }
+                Err(err)
+            }
+            DirectoryOwnership::UnownedViaMod(warn) => {
+                if warn {
+                    if let Ok(result) = paths.result {
+                        return Ok(ModulePathSuccess { warn: true, ..result });
+                    }
+                }
+                let mut err = self.diagnostic().struct_span_err(id_sp,
+                    "cannot declare a new module at this location");
+                if !id_sp.is_dummy() {
+                    let src_path = self.sess.source_map().span_to_filename(id_sp);
+                    if let FileName::Real(src_path) = src_path {
+                        if let Some(stem) = src_path.file_stem() {
+                            let mut dest_path = src_path.clone();
+                            dest_path.set_file_name(stem);
+                            dest_path.push("mod.rs");
+                            err.span_note(id_sp,
+                                    &format!("maybe move this module `{}` to its own \
+                                                directory via `{}`", src_path.display(),
+                                            dest_path.display()));
+                        }
+                    }
+                }
+                if paths.path_exists {
+                    err.span_note(id_sp,
+                                  &format!("... or maybe `use` the module `{}` instead \
+                                            of possibly redeclaring it",
+                                           paths.name));
+                }
+                Err(err)
+            }
+        }
+    }
+
+    pub fn submod_path_from_attr(attrs: &[Attribute], dir_path: &Path) -> Option<PathBuf> {
+        if let Some(s) = attr::first_attr_value_str_by_name(attrs, sym::path) {
+            let s = s.as_str();
+
+            // On windows, the base path might have the form
+            // `\\?\foo\bar` in which case it does not tolerate
+            // mixed `/` and `\` separators, so canonicalize
+            // `/` to `\`.
+            #[cfg(windows)]
+            let s = s.replace("/", "\\");
+            Some(dir_path.join(s))
+        } else {
+            None
+        }
+    }
+
+    /// Returns a path to a module.
+    pub fn default_submod_path(
+        id: ast::Ident,
+        relative: Option<ast::Ident>,
+        dir_path: &Path,
+        source_map: &SourceMap) -> ModulePath
+    {
+        // If we're in a foo.rs file instead of a mod.rs file,
+        // we need to look for submodules in
+        // `./foo/<id>.rs` and `./foo/<id>/mod.rs` rather than
+        // `./<id>.rs` and `./<id>/mod.rs`.
+        let relative_prefix_string;
+        let relative_prefix = if let Some(ident) = relative {
+            relative_prefix_string = format!("{}{}", ident.as_str(), path::MAIN_SEPARATOR);
+            &relative_prefix_string
+        } else {
+            ""
+        };
+
+        let mod_name = id.to_string();
+        let default_path_str = format!("{}{}.rs", relative_prefix, mod_name);
+        let secondary_path_str = format!("{}{}{}mod.rs",
+                                         relative_prefix, mod_name, path::MAIN_SEPARATOR);
+        let default_path = dir_path.join(&default_path_str);
+        let secondary_path = dir_path.join(&secondary_path_str);
+        let default_exists = source_map.file_exists(&default_path);
+        let secondary_exists = source_map.file_exists(&secondary_path);
+
+        let result = match (default_exists, secondary_exists) {
+            (true, false) => Ok(ModulePathSuccess {
+                path: default_path,
+                directory_ownership: DirectoryOwnership::Owned {
+                    relative: Some(id),
+                },
+                warn: false,
+            }),
+            (false, true) => Ok(ModulePathSuccess {
+                path: secondary_path,
+                directory_ownership: DirectoryOwnership::Owned {
+                    relative: None,
+                },
+                warn: false,
+            }),
+            (false, false) => Err(Error::FileNotFoundForModule {
+                mod_name: mod_name.clone(),
+                default_path: default_path_str,
+                secondary_path: secondary_path_str,
+                dir_path: dir_path.display().to_string(),
+            }),
+            (true, true) => Err(Error::DuplicatePaths {
+                mod_name: mod_name.clone(),
+                default_path: default_path_str,
+                secondary_path: secondary_path_str,
+            }),
+        };
+
+        ModulePath {
+            name: mod_name,
+            path_exists: default_exists || secondary_exists,
+            result,
+        }
+    }
+
+    /// Reads a module from a source file.
+    fn eval_src_mod(
+        &mut self,
+        path: PathBuf,
+        directory_ownership: DirectoryOwnership,
+        name: String,
+        id_sp: Span,
+    ) -> PResult<'a, (Mod, Vec<Attribute>)> {
+        let mut included_mod_stack = self.sess.included_mod_stack.borrow_mut();
+        if let Some(i) = included_mod_stack.iter().position(|p| *p == path) {
+            let mut err = String::from("circular modules: ");
+            let len = included_mod_stack.len();
+            for p in &included_mod_stack[i.. len] {
+                err.push_str(&p.to_string_lossy());
+                err.push_str(" -> ");
+            }
+            err.push_str(&path.to_string_lossy());
+            return Err(self.span_fatal(id_sp, &err[..]));
+        }
+        included_mod_stack.push(path.clone());
+        drop(included_mod_stack);
+
+        let mut p0 =
+            new_sub_parser_from_file(self.sess, &path, directory_ownership, Some(name), id_sp);
+        p0.cfg_mods = self.cfg_mods;
+        let mod_inner_lo = p0.token.span;
+        let mod_attrs = p0.parse_inner_attributes()?;
+        let mut m0 = p0.parse_mod_items(&token::Eof, mod_inner_lo)?;
+        m0.inline = false;
+        self.sess.included_mod_stack.borrow_mut().pop();
+        Ok((m0, mod_attrs))
+    }
+
+    fn push_directory(&mut self, id: Ident, attrs: &[Attribute]) {
+        if let Some(path) = attr::first_attr_value_str_by_name(attrs, sym::path) {
+            self.directory.path.to_mut().push(&path.as_str());
+            self.directory.ownership = DirectoryOwnership::Owned { relative: None };
+        } else {
+            // We have to push on the current module name in the case of relative
+            // paths in order to ensure that any additional module paths from inline
+            // `mod x { ... }` come after the relative extension.
+            //
+            // For example, a `mod z { ... }` inside `x/y.rs` should set the current
+            // directory path to `/x/y/z`, not `/x/z` with a relative offset of `y`.
+            if let DirectoryOwnership::Owned { relative } = &mut self.directory.ownership {
+                if let Some(ident) = relative.take() { // remove the relative offset
+                    self.directory.path.to_mut().push(ident.as_str());
+                }
+            }
+            self.directory.path.to_mut().push(&id.as_str());
+        }
+    }
+}
diff --git a/src/libsyntax/parse/parser/pat.rs b/src/libsyntax/parse/parser/pat.rs
new file mode 100644
index 00000000000..fd458aec743
--- /dev/null
+++ b/src/libsyntax/parse/parser/pat.rs
@@ -0,0 +1,708 @@
+use super::{Parser, PResult, PathStyle};
+
+use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
+use crate::ptr::P;
+use crate::ast::{self, Attribute, Pat, PatKind, FieldPat, RangeEnd, RangeSyntax, Mac};
+use crate::ast::{BindingMode, Ident, Mutability, Path, QSelf, Expr, ExprKind};
+use crate::parse::token::{self};
+use crate::print::pprust;
+use crate::source_map::{respan, Span, Spanned};
+use crate::symbol::kw;
+use crate::ThinVec;
+
+use errors::{Applicability, DiagnosticBuilder};
+
+impl<'a> Parser<'a> {
+    /// Parses a pattern.
+    pub fn parse_pat(
+        &mut self,
+        expected: Option<&'static str>
+    ) -> PResult<'a, P<Pat>> {
+        self.parse_pat_with_range_pat(true, expected)
+    }
+
+    /// Parses patterns, separated by '|' s.
+    pub(super) fn parse_pats(&mut self) -> PResult<'a, Vec<P<Pat>>> {
+        // Allow a '|' before the pats (RFC 1925 + RFC 2530)
+        self.eat(&token::BinOp(token::Or));
+
+        let mut pats = Vec::new();
+        loop {
+            pats.push(self.parse_top_level_pat()?);
+
+            if self.token == token::OrOr {
+                self.struct_span_err(self.token.span, "unexpected token `||` after pattern")
+                    .span_suggestion(
+                        self.token.span,
+                        "use a single `|` to specify multiple patterns",
+                        "|".to_owned(),
+                        Applicability::MachineApplicable
+                    )
+                    .emit();
+                self.bump();
+            } else if self.eat(&token::BinOp(token::Or)) {
+                // This is a No-op. Continue the loop to parse the next
+                // pattern.
+            } else {
+                return Ok(pats);
+            }
+        };
+    }
+
+    /// A wrapper around `parse_pat` with some special error handling for the
+    /// "top-level" patterns in a match arm, `for` loop, `let`, &c. (in contrast
+    /// to subpatterns within such).
+    pub(super) fn parse_top_level_pat(&mut self) -> PResult<'a, P<Pat>> {
+        let pat = self.parse_pat(None)?;
+        if self.token == token::Comma {
+            // An unexpected comma after a top-level pattern is a clue that the
+            // user (perhaps more accustomed to some other language) forgot the
+            // parentheses in what should have been a tuple pattern; return a
+            // suggestion-enhanced error here rather than choking on the comma
+            // later.
+            let comma_span = self.token.span;
+            self.bump();
+            if let Err(mut err) = self.skip_pat_list() {
+                // We didn't expect this to work anyway; we just wanted
+                // to advance to the end of the comma-sequence so we know
+                // the span to suggest parenthesizing
+                err.cancel();
+            }
+            let seq_span = pat.span.to(self.prev_span);
+            let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
+            if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
+                err.span_suggestion(
+                    seq_span,
+                    "try adding parentheses to match on a tuple..",
+                    format!("({})", seq_snippet),
+                    Applicability::MachineApplicable
+                ).span_suggestion(
+                    seq_span,
+                    "..or a vertical bar to match on multiple alternatives",
+                    format!("{}", seq_snippet.replace(",", " |")),
+                    Applicability::MachineApplicable
+                );
+            }
+            return Err(err);
+        }
+        Ok(pat)
+    }
+
+    /// Parse and throw away a parentesized comma separated
+    /// sequence of patterns until `)` is reached.
+    fn skip_pat_list(&mut self) -> PResult<'a, ()> {
+        while !self.check(&token::CloseDelim(token::Paren)) {
+            self.parse_pat(None)?;
+            if !self.eat(&token::Comma) {
+                return Ok(())
+            }
+        }
+        Ok(())
+    }
+
+    /// Parses a pattern, that may be a or-pattern (e.g. `Some(Foo | Bar)`).
+    fn parse_pat_with_or(&mut self, expected: Option<&'static str>) -> PResult<'a, P<Pat>> {
+        // Parse the first pattern.
+        let first_pat = self.parse_pat(expected)?;
+
+        // If the next token is not a `|`, this is not an or-pattern and
+        // we should exit here.
+        if !self.check(&token::BinOp(token::Or)) {
+            return Ok(first_pat)
+        }
+
+        let lo = first_pat.span;
+
+        let mut pats = vec![first_pat];
+
+        while self.eat(&token::BinOp(token::Or)) {
+            pats.push(self.parse_pat_with_range_pat(
+                true, expected
+            )?);
+        }
+
+        let or_pattern_span = lo.to(self.prev_span);
+
+        self.sess.or_pattern_spans.borrow_mut().push(or_pattern_span);
+
+        Ok(self.mk_pat(or_pattern_span, PatKind::Or(pats)))
+    }
+
+    /// Parses a pattern, with a setting whether modern range patterns (e.g., `a..=b`, `a..b` are
+    /// allowed).
+    fn parse_pat_with_range_pat(
+        &mut self,
+        allow_range_pat: bool,
+        expected: Option<&'static str>,
+    ) -> PResult<'a, P<Pat>> {
+        maybe_recover_from_interpolated_ty_qpath!(self, true);
+        maybe_whole!(self, NtPat, |x| x);
+
+        let lo = self.token.span;
+        let pat = match self.token.kind {
+            token::BinOp(token::And) | token::AndAnd => self.parse_pat_deref(expected)?,
+            token::OpenDelim(token::Paren) => self.parse_pat_tuple_or_parens()?,
+            token::OpenDelim(token::Bracket) => {
+                // Parse `[pat, pat,...]` as a slice pattern.
+                PatKind::Slice(self.parse_delim_comma_seq(token::Bracket, |p| p.parse_pat(None))?.0)
+            }
+            token::DotDot => {
+                self.bump();
+                if self.is_pat_range_end_start() {
+                    // Parse `..42` for recovery.
+                    self.parse_pat_range_to(RangeEnd::Excluded, "..")?
+                } else {
+                    // A rest pattern `..`.
+                    PatKind::Rest
+                }
+            }
+            token::DotDotEq => {
+                // Parse `..=42` for recovery.
+                self.bump();
+                self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotEq), "..=")?
+            }
+            token::DotDotDot => {
+                // Parse `...42` for recovery.
+                self.bump();
+                self.parse_pat_range_to(RangeEnd::Included(RangeSyntax::DotDotDot), "...")?
+            }
+            // At this point, token != &, &&, (, [
+            _ => if self.eat_keyword(kw::Underscore) {
+                // Parse _
+                PatKind::Wild
+            } else if self.eat_keyword(kw::Mut) {
+                self.recover_pat_ident_mut_first()?
+            } else if self.eat_keyword(kw::Ref) {
+                // Parse ref ident @ pat / ref mut ident @ pat
+                let mutbl = self.parse_mutability();
+                self.parse_pat_ident(BindingMode::ByRef(mutbl))?
+            } else if self.eat_keyword(kw::Box) {
+                // Parse `box pat`
+                PatKind::Box(self.parse_pat_with_range_pat(false, None)?)
+            } else if self.token.is_ident() && !self.token.is_reserved_ident() &&
+                      self.parse_as_ident() {
+                // Parse `ident @ pat`
+                // This can give false positives and parse nullary enums,
+                // they are dealt with later in resolve.
+                self.parse_pat_ident(BindingMode::ByValue(Mutability::Immutable))?
+            } else if self.token.is_path_start() {
+                // Parse pattern starting with a path
+                let (qself, path) = if self.eat_lt() {
+                    // Parse a qualified path
+                    let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
+                    (Some(qself), path)
+                } else {
+                    // Parse an unqualified path
+                    (None, self.parse_path(PathStyle::Expr)?)
+                };
+                match self.token.kind {
+                    token::Not if qself.is_none() => self.parse_pat_mac_invoc(lo, path)?,
+                    token::DotDotDot | token::DotDotEq | token::DotDot => {
+                        self.parse_pat_range_starting_with_path(lo, qself, path)?
+                    }
+                    token::OpenDelim(token::Brace) => self.parse_pat_struct(qself, path)?,
+                    token::OpenDelim(token::Paren) => self.parse_pat_tuple_struct(qself, path)?,
+                    _ => PatKind::Path(qself, path),
+                }
+            } else {
+                // Try to parse everything else as literal with optional minus
+                match self.parse_literal_maybe_minus() {
+                    Ok(begin)
+                        if self.check(&token::DotDot)
+                            || self.check(&token::DotDotEq)
+                            || self.check(&token::DotDotDot) =>
+                    {
+                        self.parse_pat_range_starting_with_lit(begin)?
+                    }
+                    Ok(begin) => PatKind::Lit(begin),
+                    Err(err) => return self.fatal_unexpected_non_pat(err, expected),
+                }
+            }
+        };
+
+        let pat = self.mk_pat(lo.to(self.prev_span), pat);
+        let pat = self.maybe_recover_from_bad_qpath(pat, true)?;
+
+        if !allow_range_pat {
+            self.ban_pat_range_if_ambiguous(&pat)?
+        }
+
+        Ok(pat)
+    }
+
+    /// Ban a range pattern if it has an ambiguous interpretation.
+    fn ban_pat_range_if_ambiguous(&self, pat: &Pat) -> PResult<'a, ()> {
+        match pat.node {
+            PatKind::Range(
+                .., Spanned { node: RangeEnd::Included(RangeSyntax::DotDotDot), .. }
+            ) => return Ok(()),
+            PatKind::Range(..) => {}
+            _ => return Ok(()),
+        }
+
+        let mut err = self.struct_span_err(
+            pat.span,
+            "the range pattern here has ambiguous interpretation",
+        );
+        err.span_suggestion(
+            pat.span,
+            "add parentheses to clarify the precedence",
+            format!("({})", pprust::pat_to_string(&pat)),
+            // "ambiguous interpretation" implies that we have to be guessing
+            Applicability::MaybeIncorrect
+        );
+        Err(err)
+    }
+
+    /// Parse `&pat` / `&mut pat`.
+    fn parse_pat_deref(&mut self, expected: Option<&'static str>) -> PResult<'a, PatKind> {
+        self.expect_and()?;
+        let mutbl = self.parse_mutability();
+
+        if let token::Lifetime(name) = self.token.kind {
+            let mut err = self.fatal(&format!("unexpected lifetime `{}` in pattern", name));
+            err.span_label(self.token.span, "unexpected lifetime");
+            return Err(err);
+        }
+
+        let subpat = self.parse_pat_with_range_pat(false, expected)?;
+        Ok(PatKind::Ref(subpat, mutbl))
+    }
+
+    /// Parse a tuple or parenthesis pattern.
+    fn parse_pat_tuple_or_parens(&mut self) -> PResult<'a, PatKind> {
+        let (fields, trailing_comma) = self.parse_paren_comma_seq(|p| {
+            p.parse_pat_with_or(None)
+        })?;
+
+        // Here, `(pat,)` is a tuple pattern.
+        // For backward compatibility, `(..)` is a tuple pattern as well.
+        Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
+            PatKind::Paren(fields.into_iter().nth(0).unwrap())
+        } else {
+            PatKind::Tuple(fields)
+        })
+    }
+
+    /// Recover on `mut ref? ident @ pat` and suggest
+    /// that the order of `mut` and `ref` is incorrect.
+    fn recover_pat_ident_mut_first(&mut self) -> PResult<'a, PatKind> {
+        let mutref_span = self.prev_span.to(self.token.span);
+        let binding_mode = if self.eat_keyword(kw::Ref) {
+            self.struct_span_err(mutref_span, "the order of `mut` and `ref` is incorrect")
+                .span_suggestion(
+                    mutref_span,
+                    "try switching the order",
+                    "ref mut".into(),
+                    Applicability::MachineApplicable
+                )
+                .emit();
+            BindingMode::ByRef(Mutability::Mutable)
+        } else {
+            BindingMode::ByValue(Mutability::Mutable)
+        };
+        self.parse_pat_ident(binding_mode)
+    }
+
+    /// Parse macro invocation
+    fn parse_pat_mac_invoc(&mut self, lo: Span, path: Path) -> PResult<'a, PatKind> {
+        self.bump();
+        let (delim, tts) = self.expect_delimited_token_tree()?;
+        let mac = Mac {
+            path,
+            tts,
+            delim,
+            span: lo.to(self.prev_span),
+            prior_type_ascription: self.last_type_ascription,
+        };
+        Ok(PatKind::Mac(mac))
+    }
+
+    /// Parse a range pattern `$path $form $end?` where `$form = ".." | "..." | "..=" ;`.
+    /// The `$path` has already been parsed and the next token is the `$form`.
+    fn parse_pat_range_starting_with_path(
+        &mut self,
+        lo: Span,
+        qself: Option<QSelf>,
+        path: Path
+    ) -> PResult<'a, PatKind> {
+        let (end_kind, form) = match self.token.kind {
+            token::DotDot => (RangeEnd::Excluded, ".."),
+            token::DotDotDot => (RangeEnd::Included(RangeSyntax::DotDotDot), "..."),
+            token::DotDotEq => (RangeEnd::Included(RangeSyntax::DotDotEq), "..="),
+            _ => panic!("can only parse `..`/`...`/`..=` for ranges (checked above)"),
+        };
+        let op_span = self.token.span;
+        // Parse range
+        let span = lo.to(self.prev_span);
+        let begin = self.mk_expr(span, ExprKind::Path(qself, path), ThinVec::new());
+        self.bump();
+        let end = self.parse_pat_range_end_opt(&begin, form)?;
+        Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
+    }
+
+    /// Parse a range pattern `$literal $form $end?` where `$form = ".." | "..." | "..=" ;`.
+    /// The `$path` has already been parsed and the next token is the `$form`.
+    fn parse_pat_range_starting_with_lit(&mut self, begin: P<Expr>) -> PResult<'a, PatKind> {
+        let op_span = self.token.span;
+        let (end_kind, form) = if self.eat(&token::DotDotDot) {
+            (RangeEnd::Included(RangeSyntax::DotDotDot), "...")
+        } else if self.eat(&token::DotDotEq) {
+            (RangeEnd::Included(RangeSyntax::DotDotEq), "..=")
+        } else if self.eat(&token::DotDot) {
+            (RangeEnd::Excluded, "..")
+        } else {
+            panic!("impossible case: we already matched on a range-operator token")
+        };
+        let end = self.parse_pat_range_end_opt(&begin, form)?;
+        Ok(PatKind::Range(begin, end, respan(op_span, end_kind)))
+    }
+
+    fn fatal_unexpected_non_pat(
+        &mut self,
+        mut err: DiagnosticBuilder<'a>,
+        expected: Option<&'static str>,
+    ) -> PResult<'a, P<Pat>> {
+        self.cancel(&mut err);
+
+        let expected = expected.unwrap_or("pattern");
+        let msg = format!("expected {}, found {}", expected, self.this_token_descr());
+
+        let mut err = self.fatal(&msg);
+        err.span_label(self.token.span, format!("expected {}", expected));
+
+        let sp = self.sess.source_map().start_point(self.token.span);
+        if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
+            self.sess.expr_parentheses_needed(&mut err, *sp, None);
+        }
+
+        Err(err)
+    }
+
+    // Helper function to decide whether to parse as ident binding
+    // or to try to do something more complex like range patterns.
+    fn parse_as_ident(&mut self) -> bool {
+        self.look_ahead(1, |t| match t.kind {
+            token::OpenDelim(token::Paren) | token::OpenDelim(token::Brace) |
+            token::DotDotDot | token::DotDotEq | token::DotDot |
+            token::ModSep | token::Not => false,
+            _ => true,
+        })
+    }
+
+    /// Is the current token suitable as the start of a range patterns end?
+    fn is_pat_range_end_start(&self) -> bool {
+        self.token.is_path_start() // e.g. `MY_CONST`;
+            || self.token == token::Dot // e.g. `.5` for recovery;
+            || self.token.can_begin_literal_or_bool() // e.g. `42`.
+            || self.token.is_whole_expr()
+    }
+
+    /// Parse a range-to pattern, e.g. `..X` and `..=X` for recovery.
+    fn parse_pat_range_to(&mut self, re: RangeEnd, form: &str) -> PResult<'a, PatKind> {
+        let lo = self.prev_span;
+        let end = self.parse_pat_range_end()?;
+        let range_span = lo.to(end.span);
+        let begin = self.mk_expr(range_span, ExprKind::Err, ThinVec::new());
+
+        self.diagnostic()
+            .struct_span_err(range_span, &format!("`{}X` range patterns are not supported", form))
+            .span_suggestion(
+                range_span,
+                "try using the minimum value for the type",
+                format!("MIN{}{}", form, pprust::expr_to_string(&end)),
+                Applicability::HasPlaceholders,
+            )
+            .emit();
+
+        Ok(PatKind::Range(begin, end, respan(lo, re)))
+    }
+
+    /// Parse the end of a `X..Y`, `X..=Y`, or `X...Y` range pattern  or recover
+    /// if that end is missing treating it as `X..`, `X..=`, or `X...` respectively.
+    fn parse_pat_range_end_opt(&mut self, begin: &Expr, form: &str) -> PResult<'a, P<Expr>> {
+        if self.is_pat_range_end_start() {
+            // Parsing e.g. `X..=Y`.
+            self.parse_pat_range_end()
+        } else {
+            // Parsing e.g. `X..`.
+            let range_span = begin.span.to(self.prev_span);
+
+            self.diagnostic()
+                .struct_span_err(
+                    range_span,
+                    &format!("`X{}` range patterns are not supported", form),
+                )
+                .span_suggestion(
+                    range_span,
+                    "try using the maximum value for the type",
+                    format!("{}{}MAX", pprust::expr_to_string(&begin), form),
+                    Applicability::HasPlaceholders,
+                )
+                .emit();
+
+            Ok(self.mk_expr(range_span, ExprKind::Err, ThinVec::new()))
+        }
+    }
+
+    fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
+        if self.token.is_path_start() {
+            let lo = self.token.span;
+            let (qself, path) = if self.eat_lt() {
+                // Parse a qualified path
+                let (qself, path) = self.parse_qpath(PathStyle::Expr)?;
+                (Some(qself), path)
+            } else {
+                // Parse an unqualified path
+                (None, self.parse_path(PathStyle::Expr)?)
+            };
+            let hi = self.prev_span;
+            Ok(self.mk_expr(lo.to(hi), ExprKind::Path(qself, path), ThinVec::new()))
+        } else {
+            self.parse_literal_maybe_minus()
+        }
+    }
+
+    /// Parses `ident` or `ident @ pat`.
+    /// Used by the copy foo and ref foo patterns to give a good
+    /// error message when parsing mistakes like `ref foo(a, b)`.
+    fn parse_pat_ident(&mut self, binding_mode: BindingMode) -> PResult<'a, PatKind> {
+        let ident = self.parse_ident()?;
+        let sub = if self.eat(&token::At) {
+            Some(self.parse_pat(Some("binding pattern"))?)
+        } else {
+            None
+        };
+
+        // Just to be friendly, if they write something like `ref Some(i)`,
+        // we end up here with `(` as the current token.
+        // This shortly leads to a parse error. Note that if there is no explicit
+        // binding mode then we do not end up here, because the lookahead
+        // will direct us over to `parse_enum_variant()`.
+        if self.token == token::OpenDelim(token::Paren) {
+            return Err(self.span_fatal(
+                self.prev_span,
+                "expected identifier, found enum pattern",
+            ))
+        }
+
+        Ok(PatKind::Ident(binding_mode, ident, sub))
+    }
+
+    /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
+    fn parse_pat_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
+        if qself.is_some() {
+            let msg = "unexpected `{` after qualified path";
+            let mut err = self.fatal(msg);
+            err.span_label(self.token.span, msg);
+            return Err(err);
+        }
+
+        self.bump();
+        let (fields, etc) = self.parse_pat_fields().unwrap_or_else(|mut e| {
+            e.emit();
+            self.recover_stmt();
+            (vec![], true)
+        });
+        self.bump();
+        Ok(PatKind::Struct(path, fields, etc))
+    }
+
+    /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
+    fn parse_pat_tuple_struct(&mut self, qself: Option<QSelf>, path: Path) -> PResult<'a, PatKind> {
+        if qself.is_some() {
+            let msg = "unexpected `(` after qualified path";
+            let mut err = self.fatal(msg);
+            err.span_label(self.token.span, msg);
+            return Err(err);
+        }
+        let (fields, _) = self.parse_paren_comma_seq(|p| p.parse_pat_with_or(None))?;
+        Ok(PatKind::TupleStruct(path, fields))
+    }
+
+    /// Parses the fields of a struct-like pattern.
+    fn parse_pat_fields(&mut self) -> PResult<'a, (Vec<FieldPat>, bool)> {
+        let mut fields = Vec::new();
+        let mut etc = false;
+        let mut ate_comma = true;
+        let mut delayed_err: Option<DiagnosticBuilder<'a>> = None;
+        let mut etc_span = None;
+
+        while self.token != token::CloseDelim(token::Brace) {
+            let attrs = match self.parse_outer_attributes() {
+                Ok(attrs) => attrs,
+                Err(err) => {
+                    if let Some(mut delayed) = delayed_err {
+                        delayed.emit();
+                    }
+                    return Err(err);
+                },
+            };
+            let lo = self.token.span;
+
+            // check that a comma comes after every field
+            if !ate_comma {
+                let err = self.struct_span_err(self.prev_span, "expected `,`");
+                if let Some(mut delayed) = delayed_err {
+                    delayed.emit();
+                }
+                return Err(err);
+            }
+            ate_comma = false;
+
+            if self.check(&token::DotDot) || self.token == token::DotDotDot {
+                etc = true;
+                let mut etc_sp = self.token.span;
+
+                self.recover_one_fewer_dotdot();
+                self.bump();  // `..` || `...`
+
+                if self.token == token::CloseDelim(token::Brace) {
+                    etc_span = Some(etc_sp);
+                    break;
+                }
+                let token_str = self.this_token_descr();
+                let mut err = self.fatal(&format!("expected `}}`, found {}", token_str));
+
+                err.span_label(self.token.span, "expected `}`");
+                let mut comma_sp = None;
+                if self.token == token::Comma { // Issue #49257
+                    let nw_span = self.sess.source_map().span_until_non_whitespace(self.token.span);
+                    etc_sp = etc_sp.to(nw_span);
+                    err.span_label(etc_sp,
+                                   "`..` must be at the end and cannot have a trailing comma");
+                    comma_sp = Some(self.token.span);
+                    self.bump();
+                    ate_comma = true;
+                }
+
+                etc_span = Some(etc_sp.until(self.token.span));
+                if self.token == token::CloseDelim(token::Brace) {
+                    // If the struct looks otherwise well formed, recover and continue.
+                    if let Some(sp) = comma_sp {
+                        err.span_suggestion_short(
+                            sp,
+                            "remove this comma",
+                            String::new(),
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                    err.emit();
+                    break;
+                } else if self.token.is_ident() && ate_comma {
+                    // Accept fields coming after `..,`.
+                    // This way we avoid "pattern missing fields" errors afterwards.
+                    // We delay this error until the end in order to have a span for a
+                    // suggested fix.
+                    if let Some(mut delayed_err) = delayed_err {
+                        delayed_err.emit();
+                        return Err(err);
+                    } else {
+                        delayed_err = Some(err);
+                    }
+                } else {
+                    if let Some(mut err) = delayed_err {
+                        err.emit();
+                    }
+                    return Err(err);
+                }
+            }
+
+            fields.push(match self.parse_pat_field(lo, attrs) {
+                Ok(field) => field,
+                Err(err) => {
+                    if let Some(mut delayed_err) = delayed_err {
+                        delayed_err.emit();
+                    }
+                    return Err(err);
+                }
+            });
+            ate_comma = self.eat(&token::Comma);
+        }
+
+        if let Some(mut err) = delayed_err {
+            if let Some(etc_span) = etc_span {
+                err.multipart_suggestion(
+                    "move the `..` to the end of the field list",
+                    vec![
+                        (etc_span, String::new()),
+                        (self.token.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
+                    ],
+                    Applicability::MachineApplicable,
+                );
+            }
+            err.emit();
+        }
+        return Ok((fields, etc));
+    }
+
+    /// Recover on `...` as if it were `..` to avoid further errors.
+    /// See issue #46718.
+    fn recover_one_fewer_dotdot(&self) {
+        if self.token != token::DotDotDot {
+            return;
+        }
+
+        self.struct_span_err(self.token.span, "expected field pattern, found `...`")
+            .span_suggestion(
+                self.token.span,
+                "to omit remaining fields, use one fewer `.`",
+                "..".to_owned(),
+                Applicability::MachineApplicable
+            )
+            .emit();
+    }
+
+    fn parse_pat_field(&mut self, lo: Span, attrs: Vec<Attribute>) -> PResult<'a, FieldPat> {
+        // Check if a colon exists one ahead. This means we're parsing a fieldname.
+        let hi;
+        let (subpat, fieldname, is_shorthand) = if self.look_ahead(1, |t| t == &token::Colon) {
+            // Parsing a pattern of the form "fieldname: pat"
+            let fieldname = self.parse_field_name()?;
+            self.bump();
+            let pat = self.parse_pat_with_or(None)?;
+            hi = pat.span;
+            (pat, fieldname, false)
+        } else {
+            // Parsing a pattern of the form "(box) (ref) (mut) fieldname"
+            let is_box = self.eat_keyword(kw::Box);
+            let boxed_span = self.token.span;
+            let is_ref = self.eat_keyword(kw::Ref);
+            let is_mut = self.eat_keyword(kw::Mut);
+            let fieldname = self.parse_ident()?;
+            hi = self.prev_span;
+
+            let bind_type = match (is_ref, is_mut) {
+                (true, true) => BindingMode::ByRef(Mutability::Mutable),
+                (true, false) => BindingMode::ByRef(Mutability::Immutable),
+                (false, true) => BindingMode::ByValue(Mutability::Mutable),
+                (false, false) => BindingMode::ByValue(Mutability::Immutable),
+            };
+
+            let fieldpat = self.mk_pat_ident(boxed_span.to(hi), bind_type, fieldname);
+            let subpat = if is_box {
+                self.mk_pat(lo.to(hi), PatKind::Box(fieldpat))
+            } else {
+                fieldpat
+            };
+            (subpat, fieldname, true)
+        };
+
+        Ok(FieldPat {
+            ident: fieldname,
+            pat: subpat,
+            is_shorthand,
+            attrs: attrs.into(),
+            id: ast::DUMMY_NODE_ID,
+            span: lo.to(hi),
+        })
+    }
+
+    pub(super) fn mk_pat_ident(&self, span: Span, bm: BindingMode, ident: Ident) -> P<Pat> {
+        self.mk_pat(span, PatKind::Ident(bm, ident, None))
+    }
+
+    fn mk_pat(&self, span: Span, node: PatKind) -> P<Pat> {
+        P(Pat { node, span, id: ast::DUMMY_NODE_ID })
+    }
+}
diff --git a/src/libsyntax/parse/parser/path.rs b/src/libsyntax/parse/parser/path.rs
new file mode 100644
index 00000000000..3eb4d45045a
--- /dev/null
+++ b/src/libsyntax/parse/parser/path.rs
@@ -0,0 +1,474 @@
+use super::{Parser, PResult, TokenType};
+
+use crate::{maybe_whole, ThinVec};
+use crate::ast::{self, QSelf, Path, PathSegment, Ident, ParenthesizedArgs, AngleBracketedArgs};
+use crate::ast::{AnonConst, GenericArg, AssocTyConstraint, AssocTyConstraintKind, BlockCheckMode};
+use crate::parse::token::{self, Token};
+use crate::source_map::{Span, BytePos};
+use crate::symbol::kw;
+
+use std::mem;
+use log::debug;
+use errors::{Applicability};
+
+/// Specifies how to parse a path.
+#[derive(Copy, Clone, PartialEq)]
+pub enum PathStyle {
+    /// In some contexts, notably in expressions, paths with generic arguments are ambiguous
+    /// with something else. For example, in expressions `segment < ....` can be interpreted
+    /// as a comparison and `segment ( ....` can be interpreted as a function call.
+    /// In all such contexts the non-path interpretation is preferred by default for practical
+    /// reasons, but the path interpretation can be forced by the disambiguator `::`, e.g.
+    /// `x<y>` - comparisons, `x::<y>` - unambiguously a path.
+    Expr,
+    /// In other contexts, notably in types, no ambiguity exists and paths can be written
+    /// without the disambiguator, e.g., `x<y>` - unambiguously a path.
+    /// Paths with disambiguators are still accepted, `x::<Y>` - unambiguously a path too.
+    Type,
+    /// A path with generic arguments disallowed, e.g., `foo::bar::Baz`, used in imports,
+    /// visibilities or attributes.
+    /// Technically, this variant is unnecessary and e.g., `Expr` can be used instead
+    /// (paths in "mod" contexts have to be checked later for absence of generic arguments
+    /// anyway, due to macros), but it is used to avoid weird suggestions about expected
+    /// tokens when something goes wrong.
+    Mod,
+}
+
+impl<'a> Parser<'a> {
+    /// Parses a qualified path.
+    /// Assumes that the leading `<` has been parsed already.
+    ///
+    /// `qualified_path = <type [as trait_ref]>::path`
+    ///
+    /// # Examples
+    /// `<T>::default`
+    /// `<T as U>::a`
+    /// `<T as U>::F::a<S>` (without disambiguator)
+    /// `<T as U>::F::a::<S>` (with disambiguator)
+    pub(super) fn parse_qpath(&mut self, style: PathStyle) -> PResult<'a, (QSelf, Path)> {
+        let lo = self.prev_span;
+        let ty = self.parse_ty()?;
+
+        // `path` will contain the prefix of the path up to the `>`,
+        // if any (e.g., `U` in the `<T as U>::*` examples
+        // above). `path_span` has the span of that path, or an empty
+        // span in the case of something like `<T>::Bar`.
+        let (mut path, path_span);
+        if self.eat_keyword(kw::As) {
+            let path_lo = self.token.span;
+            path = self.parse_path(PathStyle::Type)?;
+            path_span = path_lo.to(self.prev_span);
+        } else {
+            path_span = self.token.span.to(self.token.span);
+            path = ast::Path { segments: Vec::new(), span: path_span };
+        }
+
+        // See doc comment for `unmatched_angle_bracket_count`.
+        self.expect(&token::Gt)?;
+        if self.unmatched_angle_bracket_count > 0 {
+            self.unmatched_angle_bracket_count -= 1;
+            debug!("parse_qpath: (decrement) count={:?}", self.unmatched_angle_bracket_count);
+        }
+
+        self.expect(&token::ModSep)?;
+
+        let qself = QSelf { ty, path_span, position: path.segments.len() };
+        self.parse_path_segments(&mut path.segments, style)?;
+
+        Ok((qself, Path { segments: path.segments, span: lo.to(self.prev_span) }))
+    }
+
+    /// Parses simple paths.
+    ///
+    /// `path = [::] segment+`
+    /// `segment = ident | ident[::]<args> | ident[::](args) [-> type]`
+    ///
+    /// # Examples
+    /// `a::b::C<D>` (without disambiguator)
+    /// `a::b::C::<D>` (with disambiguator)
+    /// `Fn(Args)` (without disambiguator)
+    /// `Fn::(Args)` (with disambiguator)
+    pub fn parse_path(&mut self, style: PathStyle) -> PResult<'a, Path> {
+        maybe_whole!(self, NtPath, |path| {
+            if style == PathStyle::Mod &&
+               path.segments.iter().any(|segment| segment.args.is_some()) {
+                self.diagnostic().span_err(path.span, "unexpected generic arguments in path");
+            }
+            path
+        });
+
+        let lo = self.meta_var_span.unwrap_or(self.token.span);
+        let mut segments = Vec::new();
+        let mod_sep_ctxt = self.token.span.ctxt();
+        if self.eat(&token::ModSep) {
+            segments.push(PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt)));
+        }
+        self.parse_path_segments(&mut segments, style)?;
+
+        Ok(Path { segments, span: lo.to(self.prev_span) })
+    }
+
+    /// Like `parse_path`, but also supports parsing `Word` meta items into paths for
+    /// backwards-compatibility. This is used when parsing derive macro paths in `#[derive]`
+    /// attributes.
+    pub fn parse_path_allowing_meta(&mut self, style: PathStyle) -> PResult<'a, Path> {
+        let meta_ident = match self.token.kind {
+            token::Interpolated(ref nt) => match **nt {
+                token::NtMeta(ref meta) => match meta.node {
+                    ast::MetaItemKind::Word => Some(meta.path.clone()),
+                    _ => None,
+                },
+                _ => None,
+            },
+            _ => None,
+        };
+        if let Some(path) = meta_ident {
+            self.bump();
+            return Ok(path);
+        }
+        self.parse_path(style)
+    }
+
+    crate fn parse_path_segments(&mut self,
+                           segments: &mut Vec<PathSegment>,
+                           style: PathStyle)
+                           -> PResult<'a, ()> {
+        loop {
+            let segment = self.parse_path_segment(style)?;
+            if style == PathStyle::Expr {
+                // In order to check for trailing angle brackets, we must have finished
+                // recursing (`parse_path_segment` can indirectly call this function),
+                // that is, the next token must be the highlighted part of the below example:
+                //
+                // `Foo::<Bar as Baz<T>>::Qux`
+                //                      ^ here
+                //
+                // As opposed to the below highlight (if we had only finished the first
+                // recursion):
+                //
+                // `Foo::<Bar as Baz<T>>::Qux`
+                //                     ^ here
+                //
+                // `PathStyle::Expr` is only provided at the root invocation and never in
+                // `parse_path_segment` to recurse and therefore can be checked to maintain
+                // this invariant.
+                self.check_trailing_angle_brackets(&segment, token::ModSep);
+            }
+            segments.push(segment);
+
+            if self.is_import_coupler() || !self.eat(&token::ModSep) {
+                return Ok(());
+            }
+        }
+    }
+
+    pub(super) fn parse_path_segment(&mut self, style: PathStyle) -> PResult<'a, PathSegment> {
+        let ident = self.parse_path_segment_ident()?;
+
+        let is_args_start = |token: &Token| match token.kind {
+            token::Lt | token::BinOp(token::Shl) | token::OpenDelim(token::Paren)
+            | token::LArrow => true,
+            _ => false,
+        };
+        let check_args_start = |this: &mut Self| {
+            this.expected_tokens.extend_from_slice(
+                &[TokenType::Token(token::Lt), TokenType::Token(token::OpenDelim(token::Paren))]
+            );
+            is_args_start(&this.token)
+        };
+
+        Ok(if style == PathStyle::Type && check_args_start(self) ||
+              style != PathStyle::Mod && self.check(&token::ModSep)
+                                      && self.look_ahead(1, |t| is_args_start(t)) {
+            // We use `style == PathStyle::Expr` to check if this is in a recursion or not. If
+            // it isn't, then we reset the unmatched angle bracket count as we're about to start
+            // parsing a new path.
+            if style == PathStyle::Expr {
+                self.unmatched_angle_bracket_count = 0;
+                self.max_angle_bracket_count = 0;
+            }
+
+            // Generic arguments are found - `<`, `(`, `::<` or `::(`.
+            self.eat(&token::ModSep);
+            let lo = self.token.span;
+            let args = if self.eat_lt() {
+                // `<'a, T, A = U>`
+                let (args, constraints) =
+                    self.parse_generic_args_with_leaning_angle_bracket_recovery(style, lo)?;
+                self.expect_gt()?;
+                let span = lo.to(self.prev_span);
+                AngleBracketedArgs { args, constraints, span }.into()
+            } else {
+                // `(T, U) -> R`
+                let (inputs, _) = self.parse_paren_comma_seq(|p| p.parse_ty())?;
+                let span = lo.to(self.prev_span);
+                let output = if self.eat(&token::RArrow) {
+                    Some(self.parse_ty_common(false, false, false)?)
+                } else {
+                    None
+                };
+                ParenthesizedArgs { inputs, output, span }.into()
+            };
+
+            PathSegment { ident, args, id: ast::DUMMY_NODE_ID }
+        } else {
+            // Generic arguments are not found.
+            PathSegment::from_ident(ident)
+        })
+    }
+
+    pub(super) fn parse_path_segment_ident(&mut self) -> PResult<'a, Ident> {
+        match self.token.kind {
+            token::Ident(name, _) if name.is_path_segment_keyword() => {
+                let span = self.token.span;
+                self.bump();
+                Ok(Ident::new(name, span))
+            }
+            _ => self.parse_ident(),
+        }
+    }
+
+    /// Parses generic args (within a path segment) with recovery for extra leading angle brackets.
+    /// For the purposes of understanding the parsing logic of generic arguments, this function
+    /// can be thought of being the same as just calling `self.parse_generic_args()` if the source
+    /// had the correct amount of leading angle brackets.
+    ///
+    /// ```ignore (diagnostics)
+    /// bar::<<<<T as Foo>::Output>();
+    ///      ^^ help: remove extra angle brackets
+    /// ```
+    fn parse_generic_args_with_leaning_angle_bracket_recovery(
+        &mut self,
+        style: PathStyle,
+        lo: Span,
+    ) -> PResult<'a, (Vec<GenericArg>, Vec<AssocTyConstraint>)> {
+        // We need to detect whether there are extra leading left angle brackets and produce an
+        // appropriate error and suggestion. This cannot be implemented by looking ahead at
+        // upcoming tokens for a matching `>` character - if there are unmatched `<` tokens
+        // then there won't be matching `>` tokens to find.
+        //
+        // To explain how this detection works, consider the following example:
+        //
+        // ```ignore (diagnostics)
+        // bar::<<<<T as Foo>::Output>();
+        //      ^^ help: remove extra angle brackets
+        // ```
+        //
+        // Parsing of the left angle brackets starts in this function. We start by parsing the
+        // `<` token (incrementing the counter of unmatched angle brackets on `Parser` via
+        // `eat_lt`):
+        //
+        // *Upcoming tokens:* `<<<<T as Foo>::Output>;`
+        // *Unmatched count:* 1
+        // *`parse_path_segment` calls deep:* 0
+        //
+        // This has the effect of recursing as this function is called if a `<` character
+        // is found within the expected generic arguments:
+        //
+        // *Upcoming tokens:* `<<<T as Foo>::Output>;`
+        // *Unmatched count:* 2
+        // *`parse_path_segment` calls deep:* 1
+        //
+        // Eventually we will have recursed until having consumed all of the `<` tokens and
+        // this will be reflected in the count:
+        //
+        // *Upcoming tokens:* `T as Foo>::Output>;`
+        // *Unmatched count:* 4
+        // `parse_path_segment` calls deep:* 3
+        //
+        // The parser will continue until reaching the first `>` - this will decrement the
+        // unmatched angle bracket count and return to the parent invocation of this function
+        // having succeeded in parsing:
+        //
+        // *Upcoming tokens:* `::Output>;`
+        // *Unmatched count:* 3
+        // *`parse_path_segment` calls deep:* 2
+        //
+        // This will continue until the next `>` character which will also return successfully
+        // to the parent invocation of this function and decrement the count:
+        //
+        // *Upcoming tokens:* `;`
+        // *Unmatched count:* 2
+        // *`parse_path_segment` calls deep:* 1
+        //
+        // At this point, this function will expect to find another matching `>` character but
+        // won't be able to and will return an error. This will continue all the way up the
+        // call stack until the first invocation:
+        //
+        // *Upcoming tokens:* `;`
+        // *Unmatched count:* 2
+        // *`parse_path_segment` calls deep:* 0
+        //
+        // In doing this, we have managed to work out how many unmatched leading left angle
+        // brackets there are, but we cannot recover as the unmatched angle brackets have
+        // already been consumed. To remedy this, we keep a snapshot of the parser state
+        // before we do the above. We can then inspect whether we ended up with a parsing error
+        // and unmatched left angle brackets and if so, restore the parser state before we
+        // consumed any `<` characters to emit an error and consume the erroneous tokens to
+        // recover by attempting to parse again.
+        //
+        // In practice, the recursion of this function is indirect and there will be other
+        // locations that consume some `<` characters - as long as we update the count when
+        // this happens, it isn't an issue.
+
+        let is_first_invocation = style == PathStyle::Expr;
+        // Take a snapshot before attempting to parse - we can restore this later.
+        let snapshot = if is_first_invocation {
+            Some(self.clone())
+        } else {
+            None
+        };
+
+        debug!("parse_generic_args_with_leading_angle_bracket_recovery: (snapshotting)");
+        match self.parse_generic_args() {
+            Ok(value) => Ok(value),
+            Err(ref mut e) if is_first_invocation && self.unmatched_angle_bracket_count > 0 => {
+                // Cancel error from being unable to find `>`. We know the error
+                // must have been this due to a non-zero unmatched angle bracket
+                // count.
+                e.cancel();
+
+                // Swap `self` with our backup of the parser state before attempting to parse
+                // generic arguments.
+                let snapshot = mem::replace(self, snapshot.unwrap());
+
+                debug!(
+                    "parse_generic_args_with_leading_angle_bracket_recovery: (snapshot failure) \
+                     snapshot.count={:?}",
+                    snapshot.unmatched_angle_bracket_count,
+                );
+
+                // Eat the unmatched angle brackets.
+                for _ in 0..snapshot.unmatched_angle_bracket_count {
+                    self.eat_lt();
+                }
+
+                // Make a span over ${unmatched angle bracket count} characters.
+                let span = lo.with_hi(
+                    lo.lo() + BytePos(snapshot.unmatched_angle_bracket_count)
+                );
+                let plural = snapshot.unmatched_angle_bracket_count > 1;
+                self.diagnostic()
+                    .struct_span_err(
+                        span,
+                        &format!(
+                            "unmatched angle bracket{}",
+                            if plural { "s" } else { "" }
+                        ),
+                    )
+                    .span_suggestion(
+                        span,
+                        &format!(
+                            "remove extra angle bracket{}",
+                            if plural { "s" } else { "" }
+                        ),
+                        String::new(),
+                        Applicability::MachineApplicable,
+                    )
+                    .emit();
+
+                // Try again without unmatched angle bracket characters.
+                self.parse_generic_args()
+            },
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Parses (possibly empty) list of lifetime and type arguments and associated type bindings,
+    /// possibly including trailing comma.
+    fn parse_generic_args(&mut self) -> PResult<'a, (Vec<GenericArg>, Vec<AssocTyConstraint>)> {
+        let mut args = Vec::new();
+        let mut constraints = Vec::new();
+        let mut misplaced_assoc_ty_constraints: Vec<Span> = Vec::new();
+        let mut assoc_ty_constraints: Vec<Span> = Vec::new();
+
+        let args_lo = self.token.span;
+
+        loop {
+            if self.check_lifetime() && self.look_ahead(1, |t| !t.is_like_plus()) {
+                // Parse lifetime argument.
+                args.push(GenericArg::Lifetime(self.expect_lifetime()));
+                misplaced_assoc_ty_constraints.append(&mut assoc_ty_constraints);
+            } else if self.check_ident() && self.look_ahead(1,
+                    |t| t == &token::Eq || t == &token::Colon) {
+                // Parse associated type constraint.
+                let lo = self.token.span;
+                let ident = self.parse_ident()?;
+                let kind = if self.eat(&token::Eq) {
+                    AssocTyConstraintKind::Equality {
+                        ty: self.parse_ty()?,
+                    }
+                } else if self.eat(&token::Colon) {
+                    AssocTyConstraintKind::Bound {
+                        bounds: self.parse_generic_bounds(Some(self.prev_span))?,
+                    }
+                } else {
+                    unreachable!();
+                };
+                let span = lo.to(self.prev_span);
+                constraints.push(AssocTyConstraint {
+                    id: ast::DUMMY_NODE_ID,
+                    ident,
+                    kind,
+                    span,
+                });
+                assoc_ty_constraints.push(span);
+            } else if self.check_const_arg() {
+                // Parse const argument.
+                let expr = if let token::OpenDelim(token::Brace) = self.token.kind {
+                    self.parse_block_expr(
+                        None, self.token.span, BlockCheckMode::Default, ThinVec::new()
+                    )?
+                } else if self.token.is_ident() {
+                    // FIXME(const_generics): to distinguish between idents for types and consts,
+                    // we should introduce a GenericArg::Ident in the AST and distinguish when
+                    // lowering to the HIR. For now, idents for const args are not permitted.
+                    if self.token.is_keyword(kw::True) || self.token.is_keyword(kw::False) {
+                        self.parse_literal_maybe_minus()?
+                    } else {
+                        return Err(
+                            self.fatal("identifiers may currently not be used for const generics")
+                        );
+                    }
+                } else {
+                    self.parse_literal_maybe_minus()?
+                };
+                let value = AnonConst {
+                    id: ast::DUMMY_NODE_ID,
+                    value: expr,
+                };
+                args.push(GenericArg::Const(value));
+                misplaced_assoc_ty_constraints.append(&mut assoc_ty_constraints);
+            } else if self.check_type() {
+                // Parse type argument.
+                args.push(GenericArg::Type(self.parse_ty()?));
+                misplaced_assoc_ty_constraints.append(&mut assoc_ty_constraints);
+            } else {
+                break
+            }
+
+            if !self.eat(&token::Comma) {
+                break
+            }
+        }
+
+        // FIXME: we would like to report this in ast_validation instead, but we currently do not
+        // preserve ordering of generic parameters with respect to associated type binding, so we
+        // lose that information after parsing.
+        if misplaced_assoc_ty_constraints.len() > 0 {
+            let mut err = self.struct_span_err(
+                args_lo.to(self.prev_span),
+                "associated type bindings must be declared after generic parameters",
+            );
+            for span in misplaced_assoc_ty_constraints {
+                err.span_label(
+                    span,
+                    "this associated type binding should be moved after the generic parameters",
+                );
+            }
+            err.emit();
+        }
+
+        Ok((args, constraints))
+    }
+}
diff --git a/src/libsyntax/parse/parser/stmt.rs b/src/libsyntax/parse/parser/stmt.rs
new file mode 100644
index 00000000000..c911caba4cd
--- /dev/null
+++ b/src/libsyntax/parse/parser/stmt.rs
@@ -0,0 +1,474 @@
+use super::{Parser, PResult, Restrictions, PrevTokenKind, SemiColonMode, BlockMode};
+use super::expr::LhsExpr;
+use super::path::PathStyle;
+
+use crate::ptr::P;
+use crate::{maybe_whole, ThinVec};
+use crate::ast::{self, Stmt, StmtKind, Local, Block, BlockCheckMode, Expr, ExprKind};
+use crate::ast::{Attribute, AttrStyle, VisibilityKind, MacStmtStyle, Mac, MacDelimiter};
+use crate::ext::base::DummyResult;
+use crate::parse::{classify, DirectoryOwnership};
+use crate::parse::diagnostics::Error;
+use crate::parse::token::{self};
+use crate::source_map::{respan, Span};
+use crate::symbol::{kw, sym};
+
+use std::mem;
+use errors::Applicability;
+
+impl<'a> Parser<'a> {
+    /// Parse a statement. This stops just before trailing semicolons on everything but items.
+    /// e.g., a `StmtKind::Semi` parses to a `StmtKind::Expr`, leaving the trailing `;` unconsumed.
+    pub fn parse_stmt(&mut self) -> PResult<'a, Option<Stmt>> {
+        Ok(self.parse_stmt_(true))
+    }
+
+    fn parse_stmt_(&mut self, macro_legacy_warnings: bool) -> Option<Stmt> {
+        self.parse_stmt_without_recovery(macro_legacy_warnings).unwrap_or_else(|mut e| {
+            e.emit();
+            self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
+            None
+        })
+    }
+
+    fn parse_stmt_without_recovery(
+        &mut self,
+        macro_legacy_warnings: bool,
+    ) -> PResult<'a, Option<Stmt>> {
+        maybe_whole!(self, NtStmt, |x| Some(x));
+
+        let attrs = self.parse_outer_attributes()?;
+        let lo = self.token.span;
+
+        Ok(Some(if self.eat_keyword(kw::Let) {
+            Stmt {
+                id: ast::DUMMY_NODE_ID,
+                node: StmtKind::Local(self.parse_local(attrs.into())?),
+                span: lo.to(self.prev_span),
+            }
+        } else if let Some(macro_def) = self.eat_macro_def(
+            &attrs,
+            &respan(lo, VisibilityKind::Inherited),
+            lo,
+        )? {
+            Stmt {
+                id: ast::DUMMY_NODE_ID,
+                node: StmtKind::Item(macro_def),
+                span: lo.to(self.prev_span),
+            }
+        // Starts like a simple path, being careful to avoid contextual keywords
+        // such as a union items, item with `crate` visibility or auto trait items.
+        // Our goal here is to parse an arbitrary path `a::b::c` but not something that starts
+        // like a path (1 token), but it fact not a path.
+        // `union::b::c` - path, `union U { ... }` - not a path.
+        // `crate::b::c` - path, `crate struct S;` - not a path.
+        } else if self.token.is_path_start() &&
+                  !self.token.is_qpath_start() &&
+                  !self.is_union_item() &&
+                  !self.is_crate_vis() &&
+                  !self.is_auto_trait_item() &&
+                  !self.is_async_fn() {
+            let path = self.parse_path(PathStyle::Expr)?;
+
+            if !self.eat(&token::Not) {
+                let expr = if self.check(&token::OpenDelim(token::Brace)) {
+                    self.parse_struct_expr(lo, path, ThinVec::new())?
+                } else {
+                    let hi = self.prev_span;
+                    self.mk_expr(lo.to(hi), ExprKind::Path(None, path), ThinVec::new())
+                };
+
+                let expr = self.with_res(Restrictions::STMT_EXPR, |this| {
+                    let expr = this.parse_dot_or_call_expr_with(expr, lo, attrs.into())?;
+                    this.parse_assoc_expr_with(0, LhsExpr::AlreadyParsed(expr))
+                })?;
+
+                return Ok(Some(Stmt {
+                    id: ast::DUMMY_NODE_ID,
+                    node: StmtKind::Expr(expr),
+                    span: lo.to(self.prev_span),
+                }));
+            }
+
+            let (delim, tts) = self.expect_delimited_token_tree()?;
+            let hi = self.prev_span;
+
+            let style = if delim == MacDelimiter::Brace {
+                MacStmtStyle::Braces
+            } else {
+                MacStmtStyle::NoBraces
+            };
+
+            let mac = Mac {
+                path,
+                tts,
+                delim,
+                span: lo.to(hi),
+                prior_type_ascription: self.last_type_ascription,
+            };
+            let node = if delim == MacDelimiter::Brace ||
+                          self.token == token::Semi || self.token == token::Eof {
+                StmtKind::Mac(P((mac, style, attrs.into())))
+            }
+            // We used to incorrectly stop parsing macro-expanded statements here.
+            // If the next token will be an error anyway but could have parsed with the
+            // earlier behavior, stop parsing here and emit a warning to avoid breakage.
+            else if macro_legacy_warnings &&
+                    self.token.can_begin_expr() &&
+                    match self.token.kind {
+                // These can continue an expression, so we can't stop parsing and warn.
+                token::OpenDelim(token::Paren) | token::OpenDelim(token::Bracket) |
+                token::BinOp(token::Minus) | token::BinOp(token::Star) |
+                token::BinOp(token::And) | token::BinOp(token::Or) |
+                token::AndAnd | token::OrOr |
+                token::DotDot | token::DotDotDot | token::DotDotEq => false,
+                _ => true,
+            } {
+                self.warn_missing_semicolon();
+                StmtKind::Mac(P((mac, style, attrs.into())))
+            } else {
+                let e = self.mk_expr(mac.span, ExprKind::Mac(mac), ThinVec::new());
+                let e = self.maybe_recover_from_bad_qpath(e, true)?;
+                let e = self.parse_dot_or_call_expr_with(e, lo, attrs.into())?;
+                let e = self.parse_assoc_expr_with(0, LhsExpr::AlreadyParsed(e))?;
+                StmtKind::Expr(e)
+            };
+            Stmt {
+                id: ast::DUMMY_NODE_ID,
+                span: lo.to(hi),
+                node,
+            }
+        } else {
+            // FIXME: Bad copy of attrs
+            let old_directory_ownership =
+                mem::replace(&mut self.directory.ownership, DirectoryOwnership::UnownedViaBlock);
+            let item = self.parse_item_(attrs.clone(), false, true)?;
+            self.directory.ownership = old_directory_ownership;
+
+            match item {
+                Some(i) => Stmt {
+                    id: ast::DUMMY_NODE_ID,
+                    span: lo.to(i.span),
+                    node: StmtKind::Item(i),
+                },
+                None => {
+                    let unused_attrs = |attrs: &[Attribute], s: &mut Self| {
+                        if !attrs.is_empty() {
+                            if s.prev_token_kind == PrevTokenKind::DocComment {
+                                s.span_fatal_err(s.prev_span, Error::UselessDocComment).emit();
+                            } else if attrs.iter().any(|a| a.style == AttrStyle::Outer) {
+                                s.span_err(
+                                    s.token.span, "expected statement after outer attribute"
+                                );
+                            }
+                        }
+                    };
+
+                    // Do not attempt to parse an expression if we're done here.
+                    if self.token == token::Semi {
+                        unused_attrs(&attrs, self);
+                        self.bump();
+                        let mut last_semi = lo;
+                        while self.token == token::Semi {
+                            last_semi = self.token.span;
+                            self.bump();
+                        }
+                        // We are encoding a string of semicolons as an
+                        // an empty tuple that spans the excess semicolons
+                        // to preserve this info until the lint stage
+                        return Ok(Some(Stmt {
+                            id: ast::DUMMY_NODE_ID,
+                            span: lo.to(last_semi),
+                            node: StmtKind::Semi(self.mk_expr(lo.to(last_semi),
+                                ExprKind::Tup(Vec::new()),
+                                ThinVec::new()
+                            )),
+                        }));
+                    }
+
+                    if self.token == token::CloseDelim(token::Brace) {
+                        unused_attrs(&attrs, self);
+                        return Ok(None);
+                    }
+
+                    // Remainder are line-expr stmts.
+                    let e = self.parse_expr_res(
+                        Restrictions::STMT_EXPR, Some(attrs.into()))?;
+                    Stmt {
+                        id: ast::DUMMY_NODE_ID,
+                        span: lo.to(e.span),
+                        node: StmtKind::Expr(e),
+                    }
+                }
+            }
+        }))
+    }
+
+    /// Parses a local variable declaration.
+    fn parse_local(&mut self, attrs: ThinVec<Attribute>) -> PResult<'a, P<Local>> {
+        let lo = self.prev_span;
+        let pat = self.parse_top_level_pat()?;
+
+        let (err, ty) = if self.eat(&token::Colon) {
+            // Save the state of the parser before parsing type normally, in case there is a `:`
+            // instead of an `=` typo.
+            let parser_snapshot_before_type = self.clone();
+            let colon_sp = self.prev_span;
+            match self.parse_ty() {
+                Ok(ty) => (None, Some(ty)),
+                Err(mut err) => {
+                    // Rewind to before attempting to parse the type and continue parsing
+                    let parser_snapshot_after_type = self.clone();
+                    mem::replace(self, parser_snapshot_before_type);
+
+                    let snippet = self.span_to_snippet(pat.span).unwrap();
+                    err.span_label(pat.span, format!("while parsing the type for `{}`", snippet));
+                    (Some((parser_snapshot_after_type, colon_sp, err)), None)
+                }
+            }
+        } else {
+            (None, None)
+        };
+        let init = match (self.parse_initializer(err.is_some()), err) {
+            (Ok(init), None) => {  // init parsed, ty parsed
+                init
+            }
+            (Ok(init), Some((_, colon_sp, mut err))) => {  // init parsed, ty error
+                // Could parse the type as if it were the initializer, it is likely there was a
+                // typo in the code: `:` instead of `=`. Add suggestion and emit the error.
+                err.span_suggestion_short(
+                    colon_sp,
+                    "use `=` if you meant to assign",
+                    "=".to_string(),
+                    Applicability::MachineApplicable
+                );
+                err.emit();
+                // As this was parsed successfully, continue as if the code has been fixed for the
+                // rest of the file. It will still fail due to the emitted error, but we avoid
+                // extra noise.
+                init
+            }
+            (Err(mut init_err), Some((snapshot, _, ty_err))) => {  // init error, ty error
+                init_err.cancel();
+                // Couldn't parse the type nor the initializer, only raise the type error and
+                // return to the parser state before parsing the type as the initializer.
+                // let x: <parse_error>;
+                mem::replace(self, snapshot);
+                return Err(ty_err);
+            }
+            (Err(err), None) => {  // init error, ty parsed
+                // Couldn't parse the initializer and we're not attempting to recover a failed
+                // parse of the type, return the error.
+                return Err(err);
+            }
+        };
+        let hi = if self.token == token::Semi {
+            self.token.span
+        } else {
+            self.prev_span
+        };
+        Ok(P(ast::Local {
+            ty,
+            pat,
+            init,
+            id: ast::DUMMY_NODE_ID,
+            span: lo.to(hi),
+            attrs,
+        }))
+    }
+
+    /// Parses the RHS of a local variable declaration (e.g., '= 14;').
+    fn parse_initializer(&mut self, skip_eq: bool) -> PResult<'a, Option<P<Expr>>> {
+        if self.eat(&token::Eq) {
+            Ok(Some(self.parse_expr()?))
+        } else if skip_eq {
+            Ok(Some(self.parse_expr()?))
+        } else {
+            Ok(None)
+        }
+    }
+
+    fn is_auto_trait_item(&self) -> bool {
+        // auto trait
+        (self.token.is_keyword(kw::Auto) &&
+            self.is_keyword_ahead(1, &[kw::Trait]))
+        || // unsafe auto trait
+        (self.token.is_keyword(kw::Unsafe) &&
+         self.is_keyword_ahead(1, &[kw::Auto]) &&
+         self.is_keyword_ahead(2, &[kw::Trait]))
+    }
+
+    /// Parses a block. No inner attributes are allowed.
+    pub fn parse_block(&mut self) -> PResult<'a, P<Block>> {
+        maybe_whole!(self, NtBlock, |x| x);
+
+        let lo = self.token.span;
+
+        if !self.eat(&token::OpenDelim(token::Brace)) {
+            let sp = self.token.span;
+            let tok = self.this_token_descr();
+            let mut e = self.span_fatal(sp, &format!("expected `{{`, found {}", tok));
+            let do_not_suggest_help =
+                self.token.is_keyword(kw::In) || self.token == token::Colon;
+
+            if self.token.is_ident_named(sym::and) {
+                e.span_suggestion_short(
+                    self.token.span,
+                    "use `&&` instead of `and` for the boolean operator",
+                    "&&".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            if self.token.is_ident_named(sym::or) {
+                e.span_suggestion_short(
+                    self.token.span,
+                    "use `||` instead of `or` for the boolean operator",
+                    "||".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+
+            // Check to see if the user has written something like
+            //
+            //    if (cond)
+            //      bar;
+            //
+            // Which is valid in other languages, but not Rust.
+            match self.parse_stmt_without_recovery(false) {
+                Ok(Some(stmt)) => {
+                    if self.look_ahead(1, |t| t == &token::OpenDelim(token::Brace))
+                        || do_not_suggest_help {
+                        // if the next token is an open brace (e.g., `if a b {`), the place-
+                        // inside-a-block suggestion would be more likely wrong than right
+                        e.span_label(sp, "expected `{`");
+                        return Err(e);
+                    }
+                    let mut stmt_span = stmt.span;
+                    // expand the span to include the semicolon, if it exists
+                    if self.eat(&token::Semi) {
+                        stmt_span = stmt_span.with_hi(self.prev_span.hi());
+                    }
+                    if let Ok(snippet) = self.span_to_snippet(stmt_span) {
+                        e.span_suggestion(
+                            stmt_span,
+                            "try placing this code inside a block",
+                            format!("{{ {} }}", snippet),
+                            // speculative, has been misleading in the past (#46836)
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                }
+                Err(mut e) => {
+                    self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
+                    self.cancel(&mut e);
+                }
+                _ => ()
+            }
+            e.span_label(sp, "expected `{`");
+            return Err(e);
+        }
+
+        self.parse_block_tail(lo, BlockCheckMode::Default)
+    }
+
+    /// Parses a block. Inner attributes are allowed.
+    crate fn parse_inner_attrs_and_block(&mut self) -> PResult<'a, (Vec<Attribute>, P<Block>)> {
+        maybe_whole!(self, NtBlock, |x| (Vec::new(), x));
+
+        let lo = self.token.span;
+        self.expect(&token::OpenDelim(token::Brace))?;
+        Ok((self.parse_inner_attributes()?,
+            self.parse_block_tail(lo, BlockCheckMode::Default)?))
+    }
+
+    /// Parses the rest of a block expression or function body.
+    /// Precondition: already parsed the '{'.
+    pub(super) fn parse_block_tail(
+        &mut self,
+        lo: Span,
+        s: BlockCheckMode
+    ) -> PResult<'a, P<Block>> {
+        let mut stmts = vec![];
+        while !self.eat(&token::CloseDelim(token::Brace)) {
+            if self.token == token::Eof {
+                break;
+            }
+            let stmt = match self.parse_full_stmt(false) {
+                Err(mut err) => {
+                    err.emit();
+                    self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
+                    Some(Stmt {
+                        id: ast::DUMMY_NODE_ID,
+                        node: StmtKind::Expr(DummyResult::raw_expr(self.token.span, true)),
+                        span: self.token.span,
+                    })
+                }
+                Ok(stmt) => stmt,
+            };
+            if let Some(stmt) = stmt {
+                stmts.push(stmt);
+            } else {
+                // Found only `;` or `}`.
+                continue;
+            };
+        }
+        Ok(P(ast::Block {
+            stmts,
+            id: ast::DUMMY_NODE_ID,
+            rules: s,
+            span: lo.to(self.prev_span),
+        }))
+    }
+
+    /// Parses a statement, including the trailing semicolon.
+    crate fn parse_full_stmt(&mut self, macro_legacy_warnings: bool) -> PResult<'a, Option<Stmt>> {
+        // skip looking for a trailing semicolon when we have an interpolated statement
+        maybe_whole!(self, NtStmt, |x| Some(x));
+
+        let mut stmt = match self.parse_stmt_without_recovery(macro_legacy_warnings)? {
+            Some(stmt) => stmt,
+            None => return Ok(None),
+        };
+
+        match stmt.node {
+            StmtKind::Expr(ref expr) if self.token != token::Eof => {
+                // expression without semicolon
+                if classify::expr_requires_semi_to_be_stmt(expr) {
+                    // Just check for errors and recover; do not eat semicolon yet.
+                    if let Err(mut e) =
+                        self.expect_one_of(&[], &[token::Semi, token::CloseDelim(token::Brace)])
+                    {
+                        e.emit();
+                        self.recover_stmt();
+                        // Don't complain about type errors in body tail after parse error (#57383).
+                        let sp = expr.span.to(self.prev_span);
+                        stmt.node = StmtKind::Expr(DummyResult::raw_expr(sp, true));
+                    }
+                }
+            }
+            StmtKind::Local(..) => {
+                // We used to incorrectly allow a macro-expanded let statement to lack a semicolon.
+                if macro_legacy_warnings && self.token != token::Semi {
+                    self.warn_missing_semicolon();
+                } else {
+                    self.expect_one_of(&[], &[token::Semi])?;
+                }
+            }
+            _ => {}
+        }
+
+        if self.eat(&token::Semi) {
+            stmt = stmt.add_trailing_semicolon();
+        }
+        stmt.span = stmt.span.to(self.prev_span);
+        Ok(Some(stmt))
+    }
+
+    fn warn_missing_semicolon(&self) {
+        self.diagnostic().struct_span_warn(self.token.span, {
+            &format!("expected `;`, found {}", self.this_token_descr())
+        }).note({
+            "This was erroneously allowed and will become a hard error in a future release"
+        }).emit();
+    }
+}
diff --git a/src/libsyntax/parse/parser/ty.rs b/src/libsyntax/parse/parser/ty.rs
new file mode 100644
index 00000000000..337702b8d30
--- /dev/null
+++ b/src/libsyntax/parse/parser/ty.rs
@@ -0,0 +1,462 @@
+use super::{Parser, PResult, PathStyle, PrevTokenKind, TokenType};
+
+use crate::{maybe_whole, maybe_recover_from_interpolated_ty_qpath};
+use crate::ptr::P;
+use crate::ast::{self, Ty, TyKind, MutTy, BareFnTy, FunctionRetTy, GenericParam, Lifetime, Ident};
+use crate::ast::{TraitBoundModifier, TraitObjectSyntax, GenericBound, GenericBounds, PolyTraitRef};
+use crate::ast::{Mutability, AnonConst, FnDecl, Mac};
+use crate::parse::token::{self, Token};
+use crate::source_map::Span;
+use crate::symbol::{kw};
+
+use rustc_target::spec::abi::Abi;
+
+use errors::{Applicability};
+
+/// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
+/// `IDENT<<u8 as Trait>::AssocTy>`.
+///
+/// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
+/// that `IDENT` is not the ident of a fn trait.
+fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
+    t == &token::ModSep || t == &token::Lt ||
+    t == &token::BinOp(token::Shl)
+}
+
+impl<'a> Parser<'a> {
+    /// Parses a type.
+    pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
+        self.parse_ty_common(true, true, false)
+    }
+
+    /// Parses a type in restricted contexts where `+` is not permitted.
+    ///
+    /// Example 1: `&'a TYPE`
+    ///     `+` is prohibited to maintain operator priority (P(+) < P(&)).
+    /// Example 2: `value1 as TYPE + value2`
+    ///     `+` is prohibited to avoid interactions with expression grammar.
+    pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
+        self.parse_ty_common(false, true, false)
+    }
+
+    /// Parses an optional return type `[ -> TY ]` in a function declaration.
+    pub(super) fn parse_ret_ty(&mut self, allow_plus: bool) -> PResult<'a, FunctionRetTy> {
+        if self.eat(&token::RArrow) {
+            Ok(FunctionRetTy::Ty(self.parse_ty_common(allow_plus, true, false)?))
+        } else {
+            Ok(FunctionRetTy::Default(self.token.span.shrink_to_lo()))
+        }
+    }
+
+    pub(super) fn parse_ty_common(&mut self, allow_plus: bool, allow_qpath_recovery: bool,
+                       allow_c_variadic: bool) -> PResult<'a, P<Ty>> {
+        maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
+        maybe_whole!(self, NtTy, |x| x);
+
+        let lo = self.token.span;
+        let mut impl_dyn_multi = false;
+        let node = if self.eat(&token::OpenDelim(token::Paren)) {
+            // `(TYPE)` is a parenthesized type.
+            // `(TYPE,)` is a tuple with a single field of type TYPE.
+            let mut ts = vec![];
+            let mut last_comma = false;
+            while self.token != token::CloseDelim(token::Paren) {
+                ts.push(self.parse_ty()?);
+                if self.eat(&token::Comma) {
+                    last_comma = true;
+                } else {
+                    last_comma = false;
+                    break;
+                }
+            }
+            let trailing_plus = self.prev_token_kind == PrevTokenKind::Plus;
+            self.expect(&token::CloseDelim(token::Paren))?;
+
+            if ts.len() == 1 && !last_comma {
+                let ty = ts.into_iter().nth(0).unwrap().into_inner();
+                let maybe_bounds = allow_plus && self.token.is_like_plus();
+                match ty.node {
+                    // `(TY_BOUND_NOPAREN) + BOUND + ...`.
+                    TyKind::Path(None, ref path) if maybe_bounds => {
+                        self.parse_remaining_bounds(Vec::new(), path.clone(), lo, true)?
+                    }
+                    TyKind::TraitObject(ref bounds, TraitObjectSyntax::None)
+                            if maybe_bounds && bounds.len() == 1 && !trailing_plus => {
+                        let path = match bounds[0] {
+                            GenericBound::Trait(ref pt, ..) => pt.trait_ref.path.clone(),
+                            GenericBound::Outlives(..) => self.bug("unexpected lifetime bound"),
+                        };
+                        self.parse_remaining_bounds(Vec::new(), path, lo, true)?
+                    }
+                    // `(TYPE)`
+                    _ => TyKind::Paren(P(ty))
+                }
+            } else {
+                TyKind::Tup(ts)
+            }
+        } else if self.eat(&token::Not) {
+            // Never type `!`
+            TyKind::Never
+        } else if self.eat(&token::BinOp(token::Star)) {
+            // Raw pointer
+            TyKind::Ptr(self.parse_ptr()?)
+        } else if self.eat(&token::OpenDelim(token::Bracket)) {
+            // Array or slice
+            let t = self.parse_ty()?;
+            // Parse optional `; EXPR` in `[TYPE; EXPR]`
+            let t = match self.maybe_parse_fixed_length_of_vec()? {
+                None => TyKind::Slice(t),
+                Some(length) => TyKind::Array(t, AnonConst {
+                    id: ast::DUMMY_NODE_ID,
+                    value: length,
+                }),
+            };
+            self.expect(&token::CloseDelim(token::Bracket))?;
+            t
+        } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
+            // Reference
+            self.expect_and()?;
+            self.parse_borrowed_pointee()?
+        } else if self.eat_keyword_noexpect(kw::Typeof) {
+            // `typeof(EXPR)`
+            // In order to not be ambiguous, the type must be surrounded by parens.
+            self.expect(&token::OpenDelim(token::Paren))?;
+            let e = AnonConst {
+                id: ast::DUMMY_NODE_ID,
+                value: self.parse_expr()?,
+            };
+            self.expect(&token::CloseDelim(token::Paren))?;
+            TyKind::Typeof(e)
+        } else if self.eat_keyword(kw::Underscore) {
+            // A type to be inferred `_`
+            TyKind::Infer
+        } else if self.token_is_bare_fn_keyword() {
+            // Function pointer type
+            self.parse_ty_bare_fn(Vec::new())?
+        } else if self.check_keyword(kw::For) {
+            // Function pointer type or bound list (trait object type) starting with a poly-trait.
+            //   `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
+            //   `for<'lt> Trait1<'lt> + Trait2 + 'a`
+            let lo = self.token.span;
+            let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
+            if self.token_is_bare_fn_keyword() {
+                self.parse_ty_bare_fn(lifetime_defs)?
+            } else {
+                let path = self.parse_path(PathStyle::Type)?;
+                let parse_plus = allow_plus && self.check_plus();
+                self.parse_remaining_bounds(lifetime_defs, path, lo, parse_plus)?
+            }
+        } else if self.eat_keyword(kw::Impl) {
+            // Always parse bounds greedily for better error recovery.
+            let bounds = self.parse_generic_bounds(None)?;
+            impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
+            TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds)
+        } else if self.check_keyword(kw::Dyn) &&
+                  (self.token.span.rust_2018() ||
+                   self.look_ahead(1, |t| t.can_begin_bound() &&
+                                          !can_continue_type_after_non_fn_ident(t))) {
+            self.bump(); // `dyn`
+            // Always parse bounds greedily for better error recovery.
+            let bounds = self.parse_generic_bounds(None)?;
+            impl_dyn_multi = bounds.len() > 1 || self.prev_token_kind == PrevTokenKind::Plus;
+            TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn)
+        } else if self.check(&token::Question) ||
+                  self.check_lifetime() && self.look_ahead(1, |t| t.is_like_plus()) {
+            // Bound list (trait object type)
+            TyKind::TraitObject(self.parse_generic_bounds_common(allow_plus, None)?,
+                                TraitObjectSyntax::None)
+        } else if self.eat_lt() {
+            // Qualified path
+            let (qself, path) = self.parse_qpath(PathStyle::Type)?;
+            TyKind::Path(Some(qself), path)
+        } else if self.token.is_path_start() {
+            // Simple path
+            let path = self.parse_path(PathStyle::Type)?;
+            if self.eat(&token::Not) {
+                // Macro invocation in type position
+                let (delim, tts) = self.expect_delimited_token_tree()?;
+                let mac = Mac {
+                    path,
+                    tts,
+                    delim,
+                    span: lo.to(self.prev_span),
+                    prior_type_ascription: self.last_type_ascription,
+                };
+                TyKind::Mac(mac)
+            } else {
+                // Just a type path or bound list (trait object type) starting with a trait.
+                //   `Type`
+                //   `Trait1 + Trait2 + 'a`
+                if allow_plus && self.check_plus() {
+                    self.parse_remaining_bounds(Vec::new(), path, lo, true)?
+                } else {
+                    TyKind::Path(None, path)
+                }
+            }
+        } else if self.check(&token::DotDotDot) {
+            if allow_c_variadic {
+                self.eat(&token::DotDotDot);
+                TyKind::CVarArgs
+            } else {
+                return Err(self.fatal(
+                    "only foreign functions are allowed to be C-variadic"
+                ));
+            }
+        } else {
+            let msg = format!("expected type, found {}", self.this_token_descr());
+            let mut err = self.fatal(&msg);
+            err.span_label(self.token.span, "expected type");
+            self.maybe_annotate_with_ascription(&mut err, true);
+            return Err(err);
+        };
+
+        let span = lo.to(self.prev_span);
+        let ty = P(Ty { node, span, id: ast::DUMMY_NODE_ID });
+
+        // Try to recover from use of `+` with incorrect priority.
+        self.maybe_report_ambiguous_plus(allow_plus, impl_dyn_multi, &ty);
+        self.maybe_recover_from_bad_type_plus(allow_plus, &ty)?;
+        self.maybe_recover_from_bad_qpath(ty, allow_qpath_recovery)
+    }
+
+    fn parse_remaining_bounds(&mut self, generic_params: Vec<GenericParam>, path: ast::Path,
+                              lo: Span, parse_plus: bool) -> PResult<'a, TyKind> {
+        let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_span));
+        let mut bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
+        if parse_plus {
+            self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
+            bounds.append(&mut self.parse_generic_bounds(Some(self.prev_span))?);
+        }
+        Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
+    }
+
+    fn parse_ptr(&mut self) -> PResult<'a, MutTy> {
+        let mutbl = if self.eat_keyword(kw::Mut) {
+            Mutability::Mutable
+        } else if self.eat_keyword(kw::Const) {
+            Mutability::Immutable
+        } else {
+            let span = self.prev_span;
+            let msg = "expected mut or const in raw pointer type";
+            self.struct_span_err(span, msg)
+                .span_label(span, msg)
+                .help("use `*mut T` or `*const T` as appropriate")
+                .emit();
+            Mutability::Immutable
+        };
+        let t = self.parse_ty_no_plus()?;
+        Ok(MutTy { ty: t, mutbl })
+    }
+
+    fn maybe_parse_fixed_length_of_vec(&mut self) -> PResult<'a, Option<P<ast::Expr>>> {
+        if self.eat(&token::Semi) {
+            Ok(Some(self.parse_expr()?))
+        } else {
+            Ok(None)
+        }
+    }
+
+    fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
+        let opt_lifetime = if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
+        let mutbl = self.parse_mutability();
+        let ty = self.parse_ty_no_plus()?;
+        return Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }));
+    }
+
+    /// Is the current token one of the keywords that signals a bare function type?
+    fn token_is_bare_fn_keyword(&mut self) -> bool {
+        self.check_keyword(kw::Fn) ||
+            self.check_keyword(kw::Unsafe) ||
+            self.check_keyword(kw::Extern)
+    }
+
+    /// Parses a `TyKind::BareFn` type.
+    fn parse_ty_bare_fn(&mut self, generic_params: Vec<GenericParam>) -> PResult<'a, TyKind> {
+        /*
+
+        [unsafe] [extern "ABI"] fn (S) -> T
+         ^~~~^           ^~~~^     ^~^    ^
+           |               |        |     |
+           |               |        |   Return type
+           |               |      Argument types
+           |               |
+           |              ABI
+        Function Style
+        */
+
+        let unsafety = self.parse_unsafety();
+        let abi = if self.eat_keyword(kw::Extern) {
+            self.parse_opt_abi()?.unwrap_or(Abi::C)
+        } else {
+            Abi::Rust
+        };
+
+        self.expect_keyword(kw::Fn)?;
+        let (inputs, c_variadic) = self.parse_fn_args(false, true)?;
+        let ret_ty = self.parse_ret_ty(false)?;
+        let decl = P(FnDecl {
+            inputs,
+            output: ret_ty,
+            c_variadic,
+        });
+        Ok(TyKind::BareFn(P(BareFnTy {
+            abi,
+            unsafety,
+            generic_params,
+            decl,
+        })))
+    }
+
+    crate fn parse_generic_bounds(&mut self,
+                                  colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
+        self.parse_generic_bounds_common(true, colon_span)
+    }
+
+    /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
+    ///
+    /// ```
+    /// BOUND = TY_BOUND | LT_BOUND
+    /// LT_BOUND = LIFETIME (e.g., `'a`)
+    /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
+    /// TY_BOUND_NOPAREN = [?] [for<LT_PARAM_DEFS>] SIMPLE_PATH (e.g., `?for<'a: 'b> m::Trait<'a>`)
+    /// ```
+    fn parse_generic_bounds_common(&mut self,
+                                   allow_plus: bool,
+                                   colon_span: Option<Span>) -> PResult<'a, GenericBounds> {
+        let mut bounds = Vec::new();
+        let mut negative_bounds = Vec::new();
+        let mut last_plus_span = None;
+        let mut was_negative = false;
+        loop {
+            // This needs to be synchronized with `TokenKind::can_begin_bound`.
+            let is_bound_start = self.check_path() || self.check_lifetime() ||
+                                 self.check(&token::Not) || // used for error reporting only
+                                 self.check(&token::Question) ||
+                                 self.check_keyword(kw::For) ||
+                                 self.check(&token::OpenDelim(token::Paren));
+            if is_bound_start {
+                let lo = self.token.span;
+                let has_parens = self.eat(&token::OpenDelim(token::Paren));
+                let inner_lo = self.token.span;
+                let is_negative = self.eat(&token::Not);
+                let question = if self.eat(&token::Question) { Some(self.prev_span) } else { None };
+                if self.token.is_lifetime() {
+                    if let Some(question_span) = question {
+                        self.span_err(question_span,
+                                      "`?` may only modify trait bounds, not lifetime bounds");
+                    }
+                    bounds.push(GenericBound::Outlives(self.expect_lifetime()));
+                    if has_parens {
+                        let inner_span = inner_lo.to(self.prev_span);
+                        self.expect(&token::CloseDelim(token::Paren))?;
+                        let mut err = self.struct_span_err(
+                            lo.to(self.prev_span),
+                            "parenthesized lifetime bounds are not supported"
+                        );
+                        if let Ok(snippet) = self.span_to_snippet(inner_span) {
+                            err.span_suggestion_short(
+                                lo.to(self.prev_span),
+                                "remove the parentheses",
+                                snippet.to_owned(),
+                                Applicability::MachineApplicable
+                            );
+                        }
+                        err.emit();
+                    }
+                } else {
+                    let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
+                    let path = self.parse_path(PathStyle::Type)?;
+                    if has_parens {
+                        self.expect(&token::CloseDelim(token::Paren))?;
+                    }
+                    let poly_span = lo.to(self.prev_span);
+                    if is_negative {
+                        was_negative = true;
+                        if let Some(sp) = last_plus_span.or(colon_span) {
+                            negative_bounds.push(sp.to(poly_span));
+                        }
+                    } else {
+                        let poly_trait = PolyTraitRef::new(lifetime_defs, path, poly_span);
+                        let modifier = if question.is_some() {
+                            TraitBoundModifier::Maybe
+                        } else {
+                            TraitBoundModifier::None
+                        };
+                        bounds.push(GenericBound::Trait(poly_trait, modifier));
+                    }
+                }
+            } else {
+                break
+            }
+
+            if !allow_plus || !self.eat_plus() {
+                break
+            } else {
+                last_plus_span = Some(self.prev_span);
+            }
+        }
+
+        if !negative_bounds.is_empty() || was_negative {
+            let plural = negative_bounds.len() > 1;
+            let last_span = negative_bounds.last().map(|sp| *sp);
+            let mut err = self.struct_span_err(
+                negative_bounds,
+                "negative trait bounds are not supported",
+            );
+            if let Some(sp) = last_span {
+                err.span_label(sp, "negative trait bounds are not supported");
+            }
+            if let Some(bound_list) = colon_span {
+                let bound_list = bound_list.to(self.prev_span);
+                let mut new_bound_list = String::new();
+                if !bounds.is_empty() {
+                    let mut snippets = bounds.iter().map(|bound| bound.span())
+                        .map(|span| self.span_to_snippet(span));
+                    while let Some(Ok(snippet)) = snippets.next() {
+                        new_bound_list.push_str(" + ");
+                        new_bound_list.push_str(&snippet);
+                    }
+                    new_bound_list = new_bound_list.replacen(" +", ":", 1);
+                }
+                err.span_suggestion_hidden(
+                    bound_list,
+                    &format!("remove the trait bound{}", if plural { "s" } else { "" }),
+                    new_bound_list,
+                    Applicability::MachineApplicable,
+                );
+            }
+            err.emit();
+        }
+
+        return Ok(bounds);
+    }
+
+    pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
+        if self.eat_keyword(kw::For) {
+            self.expect_lt()?;
+            let params = self.parse_generic_params()?;
+            self.expect_gt()?;
+            // We rely on AST validation to rule out invalid cases: There must not be type
+            // parameters, and the lifetime parameters must not have bounds.
+            Ok(params)
+        } else {
+            Ok(Vec::new())
+        }
+    }
+
+    crate fn check_lifetime(&mut self) -> bool {
+        self.expected_tokens.push(TokenType::Lifetime);
+        self.token.is_lifetime()
+    }
+
+    /// Parses a single lifetime `'a` or panics.
+    crate fn expect_lifetime(&mut self) -> Lifetime {
+        if let Some(ident) = self.token.lifetime() {
+            let span = self.token.span;
+            self.bump();
+            Lifetime { ident: Ident::new(ident.name, span), id: ast::DUMMY_NODE_ID }
+        } else {
+            self.span_bug(self.token.span, "not a lifetime")
+        }
+    }
+}
diff --git a/src/libsyntax/parse/tests.rs b/src/libsyntax/parse/tests.rs
new file mode 100644
index 00000000000..6a789ef99d6
--- /dev/null
+++ b/src/libsyntax/parse/tests.rs
@@ -0,0 +1,339 @@
+use super::*;
+
+use crate::ast::{self, Name, PatKind};
+use crate::attr::first_attr_value_str_by_name;
+use crate::parse::{ParseSess, PResult};
+use crate::parse::new_parser_from_source_str;
+use crate::parse::token::Token;
+use crate::print::pprust::item_to_string;
+use crate::ptr::P;
+use crate::source_map::FilePathMapping;
+use crate::symbol::{kw, sym};
+use crate::tests::{matches_codepattern, string_to_stream, with_error_checking_parse};
+use crate::tokenstream::{DelimSpan, TokenTree, TokenStream};
+use crate::with_default_globals;
+use syntax_pos::{Span, BytePos, Pos};
+
+use std::path::PathBuf;
+
+/// Parses an item.
+///
+/// Returns `Ok(Some(item))` when successful, `Ok(None)` when no item was found, and `Err`
+/// when a syntax error occurred.
+fn parse_item_from_source_str(name: FileName, source: String, sess: &ParseSess)
+                                    -> PResult<'_, Option<P<ast::Item>>> {
+    new_parser_from_source_str(sess, name, source).parse_item()
+}
+
+// produce a syntax_pos::span
+fn sp(a: u32, b: u32) -> Span {
+    Span::with_root_ctxt(BytePos(a), BytePos(b))
+}
+
+/// Parse a string, return an expr
+fn string_to_expr(source_str : String) -> P<ast::Expr> {
+    let ps = ParseSess::new(FilePathMapping::empty());
+    with_error_checking_parse(source_str, &ps, |p| {
+        p.parse_expr()
+    })
+}
+
+/// Parse a string, return an item
+fn string_to_item(source_str : String) -> Option<P<ast::Item>> {
+    let ps = ParseSess::new(FilePathMapping::empty());
+    with_error_checking_parse(source_str, &ps, |p| {
+        p.parse_item()
+    })
+}
+
+#[should_panic]
+#[test] fn bad_path_expr_1() {
+    with_default_globals(|| {
+        string_to_expr("::abc::def::return".to_string());
+    })
+}
+
+// check the token-tree-ization of macros
+#[test]
+fn string_to_tts_macro () {
+    with_default_globals(|| {
+        let tts: Vec<_> =
+            string_to_stream("macro_rules! zip (($a)=>($a))".to_string()).trees().collect();
+        let tts: &[TokenTree] = &tts[..];
+
+        match tts {
+            [
+                TokenTree::Token(Token { kind: token::Ident(name_macro_rules, false), .. }),
+                TokenTree::Token(Token { kind: token::Not, .. }),
+                TokenTree::Token(Token { kind: token::Ident(name_zip, false), .. }),
+                TokenTree::Delimited(_, macro_delim,  macro_tts)
+            ]
+            if name_macro_rules == &sym::macro_rules && name_zip.as_str() == "zip" => {
+                let tts = &macro_tts.trees().collect::<Vec<_>>();
+                match &tts[..] {
+                    [
+                        TokenTree::Delimited(_, first_delim, first_tts),
+                        TokenTree::Token(Token { kind: token::FatArrow, .. }),
+                        TokenTree::Delimited(_, second_delim, second_tts),
+                    ]
+                    if macro_delim == &token::Paren => {
+                        let tts = &first_tts.trees().collect::<Vec<_>>();
+                        match &tts[..] {
+                            [
+                                TokenTree::Token(Token { kind: token::Dollar, .. }),
+                                TokenTree::Token(Token { kind: token::Ident(name, false), .. }),
+                            ]
+                            if first_delim == &token::Paren && name.as_str() == "a" => {},
+                            _ => panic!("value 3: {:?} {:?}", first_delim, first_tts),
+                        }
+                        let tts = &second_tts.trees().collect::<Vec<_>>();
+                        match &tts[..] {
+                            [
+                                TokenTree::Token(Token { kind: token::Dollar, .. }),
+                                TokenTree::Token(Token { kind: token::Ident(name, false), .. }),
+                            ]
+                            if second_delim == &token::Paren && name.as_str() == "a" => {},
+                            _ => panic!("value 4: {:?} {:?}", second_delim, second_tts),
+                        }
+                    },
+                    _ => panic!("value 2: {:?} {:?}", macro_delim, macro_tts),
+                }
+            },
+            _ => panic!("value: {:?}",tts),
+        }
+    })
+}
+
+#[test]
+fn string_to_tts_1() {
+    with_default_globals(|| {
+        let tts = string_to_stream("fn a (b : i32) { b; }".to_string());
+
+        let expected = TokenStream::new(vec![
+            TokenTree::token(token::Ident(kw::Fn, false), sp(0, 2)).into(),
+            TokenTree::token(token::Ident(Name::intern("a"), false), sp(3, 4)).into(),
+            TokenTree::Delimited(
+                DelimSpan::from_pair(sp(5, 6), sp(13, 14)),
+                token::DelimToken::Paren,
+                TokenStream::new(vec![
+                    TokenTree::token(token::Ident(Name::intern("b"), false), sp(6, 7)).into(),
+                    TokenTree::token(token::Colon, sp(8, 9)).into(),
+                    TokenTree::token(token::Ident(sym::i32, false), sp(10, 13)).into(),
+                ]).into(),
+            ).into(),
+            TokenTree::Delimited(
+                DelimSpan::from_pair(sp(15, 16), sp(20, 21)),
+                token::DelimToken::Brace,
+                TokenStream::new(vec![
+                    TokenTree::token(token::Ident(Name::intern("b"), false), sp(17, 18)).into(),
+                    TokenTree::token(token::Semi, sp(18, 19)).into(),
+                ]).into(),
+            ).into()
+        ]);
+
+        assert_eq!(tts, expected);
+    })
+}
+
+#[test] fn parse_use() {
+    with_default_globals(|| {
+        let use_s = "use foo::bar::baz;";
+        let vitem = string_to_item(use_s.to_string()).unwrap();
+        let vitem_s = item_to_string(&vitem);
+        assert_eq!(&vitem_s[..], use_s);
+
+        let use_s = "use foo::bar as baz;";
+        let vitem = string_to_item(use_s.to_string()).unwrap();
+        let vitem_s = item_to_string(&vitem);
+        assert_eq!(&vitem_s[..], use_s);
+    })
+}
+
+#[test] fn parse_extern_crate() {
+    with_default_globals(|| {
+        let ex_s = "extern crate foo;";
+        let vitem = string_to_item(ex_s.to_string()).unwrap();
+        let vitem_s = item_to_string(&vitem);
+        assert_eq!(&vitem_s[..], ex_s);
+
+        let ex_s = "extern crate foo as bar;";
+        let vitem = string_to_item(ex_s.to_string()).unwrap();
+        let vitem_s = item_to_string(&vitem);
+        assert_eq!(&vitem_s[..], ex_s);
+    })
+}
+
+fn get_spans_of_pat_idents(src: &str) -> Vec<Span> {
+    let item = string_to_item(src.to_string()).unwrap();
+
+    struct PatIdentVisitor {
+        spans: Vec<Span>
+    }
+    impl<'a> crate::visit::Visitor<'a> for PatIdentVisitor {
+        fn visit_pat(&mut self, p: &'a ast::Pat) {
+            match p.node {
+                PatKind::Ident(_ , ref ident, _) => {
+                    self.spans.push(ident.span.clone());
+                }
+                _ => {
+                    crate::visit::walk_pat(self, p);
+                }
+            }
+        }
+    }
+    let mut v = PatIdentVisitor { spans: Vec::new() };
+    crate::visit::walk_item(&mut v, &item);
+    return v.spans;
+}
+
+#[test] fn span_of_self_arg_pat_idents_are_correct() {
+    with_default_globals(|| {
+
+        let srcs = ["impl z { fn a (&self, &myarg: i32) {} }",
+                    "impl z { fn a (&mut self, &myarg: i32) {} }",
+                    "impl z { fn a (&'a self, &myarg: i32) {} }",
+                    "impl z { fn a (self, &myarg: i32) {} }",
+                    "impl z { fn a (self: Foo, &myarg: i32) {} }",
+                    ];
+
+        for &src in &srcs {
+            let spans = get_spans_of_pat_idents(src);
+            let (lo, hi) = (spans[0].lo(), spans[0].hi());
+            assert!("self" == &src[lo.to_usize()..hi.to_usize()],
+                    "\"{}\" != \"self\". src=\"{}\"",
+                    &src[lo.to_usize()..hi.to_usize()], src)
+        }
+    })
+}
+
+#[test] fn parse_exprs () {
+    with_default_globals(|| {
+        // just make sure that they parse....
+        string_to_expr("3 + 4".to_string());
+        string_to_expr("a::z.froob(b,&(987+3))".to_string());
+    })
+}
+
+#[test] fn attrs_fix_bug () {
+    with_default_globals(|| {
+        string_to_item("pub fn mk_file_writer(path: &Path, flags: &[FileFlag])
+                -> Result<Box<Writer>, String> {
+#[cfg(windows)]
+fn wb() -> c_int {
+    (O_WRONLY | libc::consts::os::extra::O_BINARY) as c_int
+}
+
+#[cfg(unix)]
+fn wb() -> c_int { O_WRONLY as c_int }
+
+let mut fflags: c_int = wb();
+}".to_string());
+    })
+}
+
+#[test] fn crlf_doc_comments() {
+    with_default_globals(|| {
+        let sess = ParseSess::new(FilePathMapping::empty());
+
+        let name_1 = FileName::Custom("crlf_source_1".to_string());
+        let source = "/// doc comment\r\nfn foo() {}".to_string();
+        let item = parse_item_from_source_str(name_1, source, &sess)
+            .unwrap().unwrap();
+        let doc = first_attr_value_str_by_name(&item.attrs, sym::doc).unwrap();
+        assert_eq!(doc.as_str(), "/// doc comment");
+
+        let name_2 = FileName::Custom("crlf_source_2".to_string());
+        let source = "/// doc comment\r\n/// line 2\r\nfn foo() {}".to_string();
+        let item = parse_item_from_source_str(name_2, source, &sess)
+            .unwrap().unwrap();
+        let docs = item.attrs.iter().filter(|a| a.path == sym::doc)
+                    .map(|a| a.value_str().unwrap().to_string()).collect::<Vec<_>>();
+        let b: &[_] = &["/// doc comment".to_string(), "/// line 2".to_string()];
+        assert_eq!(&docs[..], b);
+
+        let name_3 = FileName::Custom("clrf_source_3".to_string());
+        let source = "/** doc comment\r\n *  with CRLF */\r\nfn foo() {}".to_string();
+        let item = parse_item_from_source_str(name_3, source, &sess).unwrap().unwrap();
+        let doc = first_attr_value_str_by_name(&item.attrs, sym::doc).unwrap();
+        assert_eq!(doc.as_str(), "/** doc comment\n *  with CRLF */");
+    });
+}
+
+#[test]
+fn ttdelim_span() {
+    fn parse_expr_from_source_str(
+        name: FileName, source: String, sess: &ParseSess
+    ) -> PResult<'_, P<ast::Expr>> {
+        new_parser_from_source_str(sess, name, source).parse_expr()
+    }
+
+    with_default_globals(|| {
+        let sess = ParseSess::new(FilePathMapping::empty());
+        let expr = parse_expr_from_source_str(PathBuf::from("foo").into(),
+            "foo!( fn main() { body } )".to_string(), &sess).unwrap();
+
+        let tts: Vec<_> = match expr.node {
+            ast::ExprKind::Mac(ref mac) => mac.stream().trees().collect(),
+            _ => panic!("not a macro"),
+        };
+
+        let span = tts.iter().rev().next().unwrap().span();
+
+        match sess.source_map().span_to_snippet(span) {
+            Ok(s) => assert_eq!(&s[..], "{ body }"),
+            Err(_) => panic!("could not get snippet"),
+        }
+    });
+}
+
+// This tests that when parsing a string (rather than a file) we don't try
+// and read in a file for a module declaration and just parse a stub.
+// See `recurse_into_file_modules` in the parser.
+#[test]
+fn out_of_line_mod() {
+    with_default_globals(|| {
+        let sess = ParseSess::new(FilePathMapping::empty());
+        let item = parse_item_from_source_str(
+            PathBuf::from("foo").into(),
+            "mod foo { struct S; mod this_does_not_exist; }".to_owned(),
+            &sess,
+        ).unwrap().unwrap();
+
+        if let ast::ItemKind::Mod(ref m) = item.node {
+            assert!(m.items.len() == 2);
+        } else {
+            panic!();
+        }
+    });
+}
+
+#[test]
+fn eqmodws() {
+    assert_eq!(matches_codepattern("",""),true);
+    assert_eq!(matches_codepattern("","a"),false);
+    assert_eq!(matches_codepattern("a",""),false);
+    assert_eq!(matches_codepattern("a","a"),true);
+    assert_eq!(matches_codepattern("a b","a   \n\t\r  b"),true);
+    assert_eq!(matches_codepattern("a b ","a   \n\t\r  b"),true);
+    assert_eq!(matches_codepattern("a b","a   \n\t\r  b "),false);
+    assert_eq!(matches_codepattern("a   b","a b"),true);
+    assert_eq!(matches_codepattern("ab","a b"),false);
+    assert_eq!(matches_codepattern("a   b","ab"),true);
+    assert_eq!(matches_codepattern(" a   b","ab"),true);
+}
+
+#[test]
+fn pattern_whitespace() {
+    assert_eq!(matches_codepattern("","\x0C"), false);
+    assert_eq!(matches_codepattern("a b ","a   \u{0085}\n\t\r  b"),true);
+    assert_eq!(matches_codepattern("a b","a   \u{0085}\n\t\r  b "),false);
+}
+
+#[test]
+fn non_pattern_whitespace() {
+    // These have the property 'White_Space' but not 'Pattern_White_Space'
+    assert_eq!(matches_codepattern("a b","a\u{2002}b"), false);
+    assert_eq!(matches_codepattern("a   b","a\u{2002}b"), false);
+    assert_eq!(matches_codepattern("\u{205F}a   b","ab"), false);
+    assert_eq!(matches_codepattern("a  \u{3000}b","ab"), false);
+}
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 049fb6cb78b..be800b4de66 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -1,25 +1,24 @@
 pub use BinOpToken::*;
 pub use Nonterminal::*;
 pub use DelimToken::*;
-pub use Lit::*;
-pub use Token::*;
+pub use LitKind::*;
+pub use TokenKind::*;
 
 use crate::ast::{self};
-use crate::parse::ParseSess;
+use crate::parse::{parse_stream_from_source_str, ParseSess};
 use crate::print::pprust;
 use crate::ptr::P;
-use crate::symbol::keywords;
-use crate::syntax::parse::parse_stream_from_source_str;
+use crate::symbol::kw;
 use crate::tokenstream::{self, DelimSpan, TokenStream, TokenTree};
 
-use syntax_pos::symbol::{self, Symbol};
-use syntax_pos::{self, Span, FileName};
+use syntax_pos::symbol::Symbol;
+use syntax_pos::{self, Span, FileName, DUMMY_SP};
 use log::info;
 
 use std::fmt;
 use std::mem;
 #[cfg(target_arch = "x86_64")]
-use rustc_data_structures::static_assert;
+use rustc_data_structures::static_assert_size;
 use rustc_data_structures::sync::Lrc;
 
 #[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
@@ -59,101 +58,143 @@ impl DelimToken {
     }
 }
 
-#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
-pub enum Lit {
-    Bool(ast::Name), // AST only, must never appear in a `Token`
-    Byte(ast::Name),
-    Char(ast::Name),
-    Err(ast::Name),
-    Integer(ast::Name),
-    Float(ast::Name),
-    Str_(ast::Name),
-    StrRaw(ast::Name, u16), /* raw str delimited by n hash symbols */
-    ByteStr(ast::Name),
-    ByteStrRaw(ast::Name, u16), /* raw byte str delimited by n hash symbols */
+#[derive(Clone, Copy, PartialEq, RustcEncodable, RustcDecodable, Debug)]
+pub enum LitKind {
+    Bool, // AST only, must never appear in a `Token`
+    Byte,
+    Char,
+    Integer,
+    Float,
+    Str,
+    StrRaw(u16), // raw string delimited by `n` hash symbols
+    ByteStr,
+    ByteStrRaw(u16), // raw byte string delimited by `n` hash symbols
+    Err,
 }
 
-#[cfg(target_arch = "x86_64")]
-static_assert!(MEM_SIZE_OF_LIT: mem::size_of::<Lit>() == 8);
+/// A literal token.
+#[derive(Clone, Copy, PartialEq, RustcEncodable, RustcDecodable, Debug)]
+pub struct Lit {
+    pub kind: LitKind,
+    pub symbol: Symbol,
+    pub suffix: Option<Symbol>,
+}
 
-impl Lit {
-    crate fn literal_name(&self) -> &'static str {
-        match *self {
-            Bool(_) => panic!("literal token contains `Lit::Bool`"),
-            Byte(_) => "byte literal",
-            Char(_) => "char literal",
-            Err(_) => "invalid literal",
-            Integer(_) => "integer literal",
-            Float(_) => "float literal",
-            Str_(_) | StrRaw(..) => "string literal",
-            ByteStr(_) | ByteStrRaw(..) => "byte string literal"
+impl fmt::Display for Lit {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Lit { kind, symbol, suffix } = *self;
+        match kind {
+            Byte          => write!(f, "b'{}'", symbol)?,
+            Char          => write!(f, "'{}'", symbol)?,
+            Str           => write!(f, "\"{}\"", symbol)?,
+            StrRaw(n)     => write!(f, "r{delim}\"{string}\"{delim}",
+                                     delim="#".repeat(n as usize),
+                                     string=symbol)?,
+            ByteStr       => write!(f, "b\"{}\"", symbol)?,
+            ByteStrRaw(n) => write!(f, "br{delim}\"{string}\"{delim}",
+                                     delim="#".repeat(n as usize),
+                                     string=symbol)?,
+            Integer       |
+            Float         |
+            Bool          |
+            Err           => write!(f, "{}", symbol)?,
         }
+
+        if let Some(suffix) = suffix {
+            write!(f, "{}", suffix)?;
+        }
+
+        Ok(())
     }
+}
 
-    crate fn may_have_suffix(&self) -> bool {
-        match *self {
-            Integer(..) | Float(..) => true,
+impl LitKind {
+    /// An English article for the literal token kind.
+    crate fn article(self) -> &'static str {
+        match self {
+            Integer | Err => "an",
+            _ => "a",
+        }
+    }
+
+    crate fn descr(self) -> &'static str {
+        match self {
+            Bool => panic!("literal token contains `Lit::Bool`"),
+            Byte => "byte",
+            Char => "char",
+            Integer => "integer",
+            Float => "float",
+            Str | StrRaw(..) => "string",
+            ByteStr | ByteStrRaw(..) => "byte string",
+            Err => "error",
+        }
+    }
+
+    crate fn may_have_suffix(self) -> bool {
+        match self {
+            Integer | Float | Err => true,
             _ => false,
         }
     }
+}
 
-    // See comments in `Nonterminal::to_tokenstream` for why we care about
-    // *probably* equal here rather than actual equality
-    fn probably_equal_for_proc_macro(&self, other: &Lit) -> bool {
-        mem::discriminant(self) == mem::discriminant(other)
+impl Lit {
+    pub fn new(kind: LitKind, symbol: Symbol, suffix: Option<Symbol>) -> Lit {
+        Lit { kind, symbol, suffix }
     }
 }
 
-pub(crate) fn ident_can_begin_expr(ident: ast::Ident, is_raw: bool) -> bool {
-    let ident_token: Token = Ident(ident, is_raw);
+pub(crate) fn ident_can_begin_expr(name: ast::Name, span: Span, is_raw: bool) -> bool {
+    let ident_token = Token::new(Ident(name, is_raw), span);
 
     !ident_token.is_reserved_ident() ||
     ident_token.is_path_segment_keyword() ||
     [
-        keywords::Async.name(),
+        kw::Async,
 
         // FIXME: remove when `await!(..)` syntax is removed
         // https://github.com/rust-lang/rust/issues/60610
-        keywords::Await.name(),
-
-        keywords::Do.name(),
-        keywords::Box.name(),
-        keywords::Break.name(),
-        keywords::Continue.name(),
-        keywords::False.name(),
-        keywords::For.name(),
-        keywords::If.name(),
-        keywords::Loop.name(),
-        keywords::Match.name(),
-        keywords::Move.name(),
-        keywords::Return.name(),
-        keywords::True.name(),
-        keywords::Unsafe.name(),
-        keywords::While.name(),
-        keywords::Yield.name(),
-        keywords::Static.name(),
-    ].contains(&ident.name)
+        kw::Await,
+
+        kw::Do,
+        kw::Box,
+        kw::Break,
+        kw::Continue,
+        kw::False,
+        kw::For,
+        kw::If,
+        kw::Let,
+        kw::Loop,
+        kw::Match,
+        kw::Move,
+        kw::Return,
+        kw::True,
+        kw::Unsafe,
+        kw::While,
+        kw::Yield,
+        kw::Static,
+    ].contains(&name)
 }
 
-fn ident_can_begin_type(ident: ast::Ident, is_raw: bool) -> bool {
-    let ident_token: Token = Ident(ident, is_raw);
+fn ident_can_begin_type(name: ast::Name, span: Span, is_raw: bool) -> bool {
+    let ident_token = Token::new(Ident(name, is_raw), span);
 
     !ident_token.is_reserved_ident() ||
     ident_token.is_path_segment_keyword() ||
     [
-        keywords::Underscore.name(),
-        keywords::For.name(),
-        keywords::Impl.name(),
-        keywords::Fn.name(),
-        keywords::Unsafe.name(),
-        keywords::Extern.name(),
-        keywords::Typeof.name(),
-        keywords::Dyn.name(),
-    ].contains(&ident.name)
+        kw::Underscore,
+        kw::For,
+        kw::Impl,
+        kw::Fn,
+        kw::Unsafe,
+        kw::Extern,
+        kw::Typeof,
+        kw::Dyn,
+    ].contains(&name)
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Debug)]
-pub enum Token {
+#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug)]
+pub enum TokenKind {
     /* Expression-operator symbols. */
     Eq,
     Lt,
@@ -193,11 +234,11 @@ pub enum Token {
     CloseDelim(DelimToken),
 
     /* Literals */
-    Literal(Lit, Option<ast::Name>),
+    Literal(Lit),
 
     /* Name components */
-    Ident(ast::Ident, /* is_raw */ bool),
-    Lifetime(ast::Ident),
+    Ident(ast::Name, /* is_raw */ bool),
+    Lifetime(ast::Name),
 
     Interpolated(Lrc<Nonterminal>),
 
@@ -214,22 +255,69 @@ pub enum Token {
     /// A comment.
     Comment,
     Shebang(ast::Name),
+    /// A completely invalid token which should be skipped.
+    Unknown(ast::Name),
 
     Eof,
 }
 
-// `Token` is used a lot. Make sure it doesn't unintentionally get bigger.
+// `TokenKind` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(target_arch = "x86_64")]
-static_assert!(MEM_SIZE_OF_STATEMENT: mem::size_of::<Token>() == 16);
+static_assert_size!(TokenKind, 16);
+
+#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug)]
+pub struct Token {
+    pub kind: TokenKind,
+    pub span: Span,
+}
+
+impl TokenKind {
+    pub fn lit(kind: LitKind, symbol: Symbol, suffix: Option<Symbol>) -> TokenKind {
+        Literal(Lit::new(kind, symbol, suffix))
+    }
+
+    /// Returns tokens that are likely to be typed accidentally instead of the current token.
+    /// Enables better error recovery when the wrong token is found.
+    crate fn similar_tokens(&self) -> Option<Vec<TokenKind>> {
+        match *self {
+            Comma => Some(vec![Dot, Lt, Semi]),
+            Semi => Some(vec![Colon, Comma]),
+            _ => None
+        }
+    }
+}
 
 impl Token {
+    crate fn new(kind: TokenKind, span: Span) -> Self {
+        Token { kind, span }
+    }
+
+    /// Some token that will be thrown away later.
+    crate fn dummy() -> Self {
+        Token::new(TokenKind::Whitespace, DUMMY_SP)
+    }
+
     /// Recovers a `Token` from an `ast::Ident`. This creates a raw identifier if necessary.
-    pub fn from_ast_ident(ident: ast::Ident) -> Token {
-        Ident(ident, ident.is_raw_guess())
+    crate fn from_ast_ident(ident: ast::Ident) -> Self {
+        Token::new(Ident(ident.name, ident.is_raw_guess()), ident.span)
+    }
+
+    /// Return this token by value and leave a dummy token in its place.
+    crate fn take(&mut self) -> Self {
+        mem::replace(self, Token::dummy())
+    }
+
+    crate fn is_op(&self) -> bool {
+        match self.kind {
+            OpenDelim(..) | CloseDelim(..) | Literal(..) | DocComment(..) |
+            Ident(..) | Lifetime(..) | Interpolated(..) |
+            Whitespace | Comment | Shebang(..) | Eof => false,
+            _ => true,
+        }
     }
 
     crate fn is_like_plus(&self) -> bool {
-        match *self {
+        match self.kind {
             BinOp(Plus) | BinOpEq(Plus) => true,
             _ => false,
         }
@@ -237,9 +325,9 @@ impl Token {
 
     /// Returns `true` if the token can appear at the start of an expression.
     crate fn can_begin_expr(&self) -> bool {
-        match *self {
-            Ident(ident, is_raw)              =>
-                ident_can_begin_expr(ident, is_raw), // value name or keyword
+        match self.kind {
+            Ident(name, is_raw)              =>
+                ident_can_begin_expr(name, self.span, is_raw), // value name or keyword
             OpenDelim(..)                     | // tuple, array or block
             Literal(..)                       | // literal
             Not                               | // operator not
@@ -269,9 +357,9 @@ impl Token {
 
     /// Returns `true` if the token can appear at the start of a type.
     crate fn can_begin_type(&self) -> bool {
-        match *self {
-            Ident(ident, is_raw)        =>
-                ident_can_begin_type(ident, is_raw), // type name or keyword
+        match self.kind {
+            Ident(name, is_raw)        =>
+                ident_can_begin_type(name, self.span, is_raw), // type name or keyword
             OpenDelim(Paren)            | // tuple
             OpenDelim(Bracket)          | // array
             Not                         | // never
@@ -291,8 +379,8 @@ impl Token {
     }
 
     /// Returns `true` if the token can appear at the start of a const param.
-    pub fn can_begin_const_arg(&self) -> bool {
-        match self {
+    crate fn can_begin_const_arg(&self) -> bool {
+        match self.kind {
             OpenDelim(Brace) => true,
             Interpolated(ref nt) => match **nt {
                 NtExpr(..) => true,
@@ -306,26 +394,33 @@ impl Token {
 
     /// Returns `true` if the token can appear at the start of a generic bound.
     crate fn can_begin_bound(&self) -> bool {
-        self.is_path_start() || self.is_lifetime() || self.is_keyword(keywords::For) ||
+        self.is_path_start() || self.is_lifetime() || self.is_keyword(kw::For) ||
         self == &Question || self == &OpenDelim(Paren)
     }
 
     /// Returns `true` if the token is any literal
     crate fn is_lit(&self) -> bool {
-        match *self {
+        match self.kind {
             Literal(..) => true,
             _           => false,
         }
     }
 
+    crate fn expect_lit(&self) -> Lit {
+        match self.kind {
+            Literal(lit) => lit,
+            _=> panic!("`expect_lit` called on non-literal"),
+        }
+    }
+
     /// Returns `true` if the token is any literal, a minus (which can prefix a literal,
     /// for example a '-42', or one of the boolean idents).
     crate fn can_begin_literal_or_bool(&self) -> bool {
-        match *self {
+        match self.kind {
             Literal(..)  => true,
             BinOp(Minus) => true,
-            Ident(ident, false) if ident.name == keywords::True.name() => true,
-            Ident(ident, false) if ident.name == keywords::False.name() => true,
+            Ident(name, false) if name == kw::True => true,
+            Ident(name, false) if name == kw::False => true,
             Interpolated(ref nt) => match **nt {
                 NtLiteral(..) => true,
                 _             => false,
@@ -336,8 +431,8 @@ impl Token {
 
     /// Returns an identifier if this token is an identifier.
     pub fn ident(&self) -> Option<(ast::Ident, /* is_raw */ bool)> {
-        match *self {
-            Ident(ident, is_raw) => Some((ident, is_raw)),
+        match self.kind {
+            Ident(name, is_raw) => Some((ast::Ident::new(name, self.span), is_raw)),
             Interpolated(ref nt) => match **nt {
                 NtIdent(ident, is_raw) => Some((ident, is_raw)),
                 _ => None,
@@ -345,10 +440,11 @@ impl Token {
             _ => None,
         }
     }
+
     /// Returns a lifetime identifier if this token is a lifetime.
     pub fn lifetime(&self) -> Option<ast::Ident> {
-        match *self {
-            Lifetime(ident) => Some(ident),
+        match self.kind {
+            Lifetime(name) => Some(ast::Ident::new(name, self.span)),
             Interpolated(ref nt) => match **nt {
                 NtLifetime(ident) => Some(ident),
                 _ => None,
@@ -356,6 +452,7 @@ impl Token {
             _ => None,
         }
     }
+
     /// Returns `true` if the token is an identifier.
     pub fn is_ident(&self) -> bool {
         self.ident().is_some()
@@ -367,16 +464,13 @@ impl Token {
 
     /// Returns `true` if the token is a identifier whose name is the given
     /// string slice.
-    crate fn is_ident_named(&self, name: &str) -> bool {
-        match self.ident() {
-            Some((ident, _)) => ident.as_str() == name,
-            None => false
-        }
+    crate fn is_ident_named(&self, name: Symbol) -> bool {
+        self.ident().map_or(false, |(ident, _)| ident.name == name)
     }
 
     /// Returns `true` if the token is an interpolated path.
     fn is_path(&self) -> bool {
-        if let Interpolated(ref nt) = *self {
+        if let Interpolated(ref nt) = self.kind {
             if let NtPath(..) = **nt {
                 return true;
             }
@@ -384,10 +478,23 @@ impl Token {
         false
     }
 
+    /// Would `maybe_whole_expr` in `parser.rs` return `Ok(..)`?
+    /// That is, is this a pre-parsed expression dropped into the token stream
+    /// (which happens while parsing the result of macro expansion)?
+    crate fn is_whole_expr(&self) -> bool {
+        if let Interpolated(ref nt) = self.kind {
+            if let NtExpr(_) | NtLiteral(_) | NtPath(_) | NtIdent(..) | NtBlock(_) = **nt {
+                return true;
+            }
+        }
+
+        false
+    }
+
     /// Returns `true` if the token is either the `mut` or `const` keyword.
     crate fn is_mutability(&self) -> bool {
-        self.is_keyword(keywords::Mut) ||
-        self.is_keyword(keywords::Const)
+        self.is_keyword(kw::Mut) ||
+        self.is_keyword(kw::Const)
     }
 
     crate fn is_qpath_start(&self) -> bool {
@@ -400,11 +507,11 @@ impl Token {
     }
 
     /// Returns `true` if the token is a given keyword, `kw`.
-    pub fn is_keyword(&self, kw: keywords::Keyword) -> bool {
-        self.ident().map(|(ident, is_raw)| ident.name == kw.name() && !is_raw).unwrap_or(false)
+    pub fn is_keyword(&self, kw: Symbol) -> bool {
+        self.ident().map(|(id, is_raw)| id.name == kw && !is_raw).unwrap_or(false)
     }
 
-    pub fn is_path_segment_keyword(&self) -> bool {
+    crate fn is_path_segment_keyword(&self) -> bool {
         match self.ident() {
             Some((id, false)) => id.is_path_segment_keyword(),
             _ => false,
@@ -413,7 +520,7 @@ impl Token {
 
     // Returns true for reserved identifiers used internally for elided lifetimes,
     // unnamed method parameters, crate root module, error recovery etc.
-    pub fn is_special_ident(&self) -> bool {
+    crate fn is_special_ident(&self) -> bool {
         match self.ident() {
             Some((id, false)) => id.is_special(),
             _ => false,
@@ -445,58 +552,52 @@ impl Token {
     }
 
     crate fn glue(self, joint: Token) -> Option<Token> {
-        Some(match self {
-            Eq => match joint {
+        let kind = match self.kind {
+            Eq => match joint.kind {
                 Eq => EqEq,
                 Gt => FatArrow,
                 _ => return None,
             },
-            Lt => match joint {
+            Lt => match joint.kind {
                 Eq => Le,
                 Lt => BinOp(Shl),
                 Le => BinOpEq(Shl),
                 BinOp(Minus) => LArrow,
                 _ => return None,
             },
-            Gt => match joint {
+            Gt => match joint.kind {
                 Eq => Ge,
                 Gt => BinOp(Shr),
                 Ge => BinOpEq(Shr),
                 _ => return None,
             },
-            Not => match joint {
+            Not => match joint.kind {
                 Eq => Ne,
                 _ => return None,
             },
-            BinOp(op) => match joint {
+            BinOp(op) => match joint.kind {
                 Eq => BinOpEq(op),
                 BinOp(And) if op == And => AndAnd,
                 BinOp(Or) if op == Or => OrOr,
                 Gt if op == Minus => RArrow,
                 _ => return None,
             },
-            Dot => match joint {
+            Dot => match joint.kind {
                 Dot => DotDot,
                 DotDot => DotDotDot,
                 _ => return None,
             },
-            DotDot => match joint {
+            DotDot => match joint.kind {
                 Dot => DotDotDot,
                 Eq => DotDotEq,
                 _ => return None,
             },
-            Colon => match joint {
+            Colon => match joint.kind {
                 Colon => ModSep,
                 _ => return None,
             },
-            SingleQuote => match joint {
-                Ident(ident, false) => {
-                    let name = Symbol::intern(&format!("'{}", ident));
-                    Lifetime(symbol::Ident {
-                        name,
-                        span: ident.span,
-                    })
-                }
+            SingleQuote => match joint.kind {
+                Ident(name, false) => Lifetime(Symbol::intern(&format!("'{}", name))),
                 _ => return None,
             },
 
@@ -504,27 +605,19 @@ impl Token {
             DotDotEq | Comma | Semi | ModSep | RArrow | LArrow | FatArrow | Pound | Dollar |
             Question | OpenDelim(..) | CloseDelim(..) |
             Literal(..) | Ident(..) | Lifetime(..) | Interpolated(..) | DocComment(..) |
-            Whitespace | Comment | Shebang(..) | Eof => return None,
-        })
-    }
+            Whitespace | Comment | Shebang(..) | Unknown(..) | Eof => return None,
+        };
 
-    /// Returns tokens that are likely to be typed accidentally instead of the current token.
-    /// Enables better error recovery when the wrong token is found.
-    crate fn similar_tokens(&self) -> Option<Vec<Token>> {
-        match *self {
-            Comma => Some(vec![Dot, Lt, Semi]),
-            Semi => Some(vec![Colon, Comma]),
-            _ => None
-        }
+        Some(Token::new(kind, self.span.to(joint.span)))
     }
 
     // See comments in `Nonterminal::to_tokenstream` for why we care about
     // *probably* equal here rather than actual equality
     crate fn probably_equal_for_proc_macro(&self, other: &Token) -> bool {
-        if mem::discriminant(self) != mem::discriminant(other) {
+        if mem::discriminant(&self.kind) != mem::discriminant(&other.kind) {
             return false
         }
-        match (self, other) {
+        match (&self.kind, &other.kind) {
             (&Eq, &Eq) |
             (&Lt, &Lt) |
             (&Le, &Le) |
@@ -564,14 +657,12 @@ impl Token {
             (&DocComment(a), &DocComment(b)) |
             (&Shebang(a), &Shebang(b)) => a == b,
 
-            (&Lifetime(a), &Lifetime(b)) => a.name == b.name,
-            (&Ident(a, b), &Ident(c, d)) => b == d && (a.name == c.name ||
-                                                       a.name == keywords::DollarCrate.name() ||
-                                                       c.name == keywords::DollarCrate.name()),
+            (&Literal(a), &Literal(b)) => a == b,
 
-            (&Literal(ref a, b), &Literal(ref c, d)) => {
-                b == d && a.probably_equal_for_proc_macro(c)
-            }
+            (&Lifetime(a), &Lifetime(b)) => a == b,
+            (&Ident(a, b), &Ident(c, d)) => b == d && (a == c ||
+                                                       a == kw::DollarCrate ||
+                                                       c == kw::DollarCrate),
 
             (&Interpolated(_), &Interpolated(_)) => false,
 
@@ -580,6 +671,12 @@ impl Token {
     }
 }
 
+impl PartialEq<TokenKind> for Token {
+    fn eq(&self, rhs: &TokenKind) -> bool {
+        self.kind == *rhs
+    }
+}
+
 #[derive(Clone, RustcEncodable, RustcDecodable)]
 /// For interpolation during macro expansion.
 pub enum Nonterminal {
@@ -669,12 +766,10 @@ impl Nonterminal {
                 prepend_attrs(sess, &item.attrs, item.tokens.as_ref(), span)
             }
             Nonterminal::NtIdent(ident, is_raw) => {
-                let token = Token::Ident(ident, is_raw);
-                Some(TokenTree::Token(ident.span, token).into())
+                Some(TokenTree::token(Ident(ident.name, is_raw), ident.span).into())
             }
             Nonterminal::NtLifetime(ident) => {
-                let token = Token::Lifetime(ident);
-                Some(TokenTree::Token(ident.span, token).into())
+                Some(TokenTree::token(Lifetime(ident.name), ident.span).into())
             }
             Nonterminal::NtTT(ref tt) => {
                 Some(tt.clone().into())
@@ -721,15 +816,6 @@ impl Nonterminal {
     }
 }
 
-crate fn is_op(tok: &Token) -> bool {
-    match *tok {
-        OpenDelim(..) | CloseDelim(..) | Literal(..) | DocComment(..) |
-        Ident(..) | Lifetime(..) | Interpolated(..) |
-        Whitespace | Comment | Shebang(..) | Eof => false,
-        _ => true,
-    }
-}
-
 fn prepend_attrs(sess: &ParseSess,
                  attrs: &[ast::Attribute],
                  tokens: Option<&tokenstream::TokenStream>,
@@ -745,7 +831,7 @@ fn prepend_attrs(sess: &ParseSess,
         assert_eq!(attr.style, ast::AttrStyle::Outer,
                    "inner attributes should prevent cached tokens from existing");
 
-        let source = pprust::attr_to_string(attr);
+        let source = pprust::attribute_to_string(attr);
         let macro_filename = FileName::macro_expansion_source_code(&source);
         if attr.is_sugared_doc {
             let stream = parse_stream_from_source_str(macro_filename, source, sess, Some(span));
@@ -759,8 +845,8 @@ fn prepend_attrs(sess: &ParseSess,
         // For simple paths, push the identifier directly
         if attr.path.segments.len() == 1 && attr.path.segments[0].args.is_none() {
             let ident = attr.path.segments[0].ident;
-            let token = Ident(ident, ident.as_str().starts_with("r#"));
-            brackets.push(tokenstream::TokenTree::Token(ident.span, token));
+            let token = Ident(ident.name, ident.as_str().starts_with("r#"));
+            brackets.push(tokenstream::TokenTree::token(token, ident.span));
 
         // ... and for more complicated paths, fall back to a reparse hack that
         // should eventually be removed.
@@ -774,7 +860,7 @@ fn prepend_attrs(sess: &ParseSess,
         // The span we list here for `#` and for `[ ... ]` are both wrong in
         // that it encompasses more than each token, but it hopefully is "good
         // enough" for now at least.
-        builder.push(tokenstream::TokenTree::Token(attr.span, Pound));
+        builder.push(tokenstream::TokenTree::token(Pound, attr.span));
         let delim_span = DelimSpan::from_single(attr.span);
         builder.push(tokenstream::TokenTree::Delimited(
             delim_span, DelimToken::Bracket, brackets.build().into()));
diff --git a/src/libsyntax/parse/unescape.rs b/src/libsyntax/parse/unescape.rs
deleted file mode 100644
index 90ee549db01..00000000000
--- a/src/libsyntax/parse/unescape.rs
+++ /dev/null
@@ -1,515 +0,0 @@
-//! Utilities for validating  string and char literals and turning them into
-//! values they represent.
-
-use std::str::Chars;
-use std::ops::Range;
-
-#[derive(Debug, PartialEq, Eq)]
-pub(crate) enum EscapeError {
-    ZeroChars,
-    MoreThanOneChar,
-
-    LoneSlash,
-    InvalidEscape,
-    BareCarriageReturn,
-    EscapeOnlyChar,
-
-    TooShortHexEscape,
-    InvalidCharInHexEscape,
-    OutOfRangeHexEscape,
-
-    NoBraceInUnicodeEscape,
-    InvalidCharInUnicodeEscape,
-    EmptyUnicodeEscape,
-    UnclosedUnicodeEscape,
-    LeadingUnderscoreUnicodeEscape,
-    OverlongUnicodeEscape,
-    LoneSurrogateUnicodeEscape,
-    OutOfRangeUnicodeEscape,
-
-    UnicodeEscapeInByte,
-    NonAsciiCharInByte,
-}
-
-/// Takes a contents of a char literal (without quotes), and returns an
-/// unescaped char or an error
-pub(crate) fn unescape_char(literal_text: &str) -> Result<char, (usize, EscapeError)> {
-    let mut chars = literal_text.chars();
-    unescape_char_or_byte(&mut chars, Mode::Char)
-        .map_err(|err| (literal_text.len() - chars.as_str().len(), err))
-}
-
-/// Takes a contents of a string literal (without quotes) and produces a
-/// sequence of escaped characters or errors.
-pub(crate) fn unescape_str<F>(literal_text: &str, callback: &mut F)
-where
-    F: FnMut(Range<usize>, Result<char, EscapeError>),
-{
-    unescape_str_or_byte_str(literal_text, Mode::Str, callback)
-}
-
-pub(crate) fn unescape_byte(literal_text: &str) -> Result<u8, (usize, EscapeError)> {
-    let mut chars = literal_text.chars();
-    unescape_char_or_byte(&mut chars, Mode::Byte)
-        .map(byte_from_char)
-        .map_err(|err| (literal_text.len() - chars.as_str().len(), err))
-}
-
-/// Takes a contents of a string literal (without quotes) and produces a
-/// sequence of escaped characters or errors.
-pub(crate) fn unescape_byte_str<F>(literal_text: &str, callback: &mut F)
-where
-    F: FnMut(Range<usize>, Result<u8, EscapeError>),
-{
-    unescape_str_or_byte_str(literal_text, Mode::ByteStr, &mut |range, char| {
-        callback(range, char.map(byte_from_char))
-    })
-}
-
-#[derive(Debug, Clone, Copy)]
-pub(crate) enum Mode {
-    Char,
-    Str,
-    Byte,
-    ByteStr,
-}
-
-impl Mode {
-    fn in_single_quotes(self) -> bool {
-        match self {
-            Mode::Char | Mode::Byte => true,
-            Mode::Str | Mode::ByteStr => false,
-        }
-    }
-
-    pub(crate) fn in_double_quotes(self) -> bool {
-        !self.in_single_quotes()
-    }
-
-    pub(crate) fn is_bytes(self) -> bool {
-        match self {
-            Mode::Byte | Mode::ByteStr => true,
-            Mode::Char | Mode::Str => false,
-        }
-    }
-}
-
-
-fn scan_escape(first_char: char, chars: &mut Chars<'_>, mode: Mode) -> Result<char, EscapeError> {
-    if first_char != '\\' {
-        return match first_char {
-            '\t' | '\n' => Err(EscapeError::EscapeOnlyChar),
-            '\r' => Err(if chars.clone().next() == Some('\n') {
-                EscapeError::EscapeOnlyChar
-            } else {
-                EscapeError::BareCarriageReturn
-            }),
-            '\'' if mode.in_single_quotes() => Err(EscapeError::EscapeOnlyChar),
-            '"' if mode.in_double_quotes() => Err(EscapeError::EscapeOnlyChar),
-            _ => {
-                if mode.is_bytes() && !first_char.is_ascii() {
-                    return Err(EscapeError::NonAsciiCharInByte);
-                }
-                Ok(first_char)
-            }
-        };
-    }
-
-    let second_char = chars.next().ok_or(EscapeError::LoneSlash)?;
-
-    let res = match second_char {
-        '"' => '"',
-        'n' => '\n',
-        'r' => '\r',
-        't' => '\t',
-        '\\' => '\\',
-        '\'' => '\'',
-        '0' => '\0',
-
-        'x' => {
-            let hi = chars.next().ok_or(EscapeError::TooShortHexEscape)?;
-            let hi = hi.to_digit(16).ok_or(EscapeError::InvalidCharInHexEscape)?;
-
-            let lo = chars.next().ok_or(EscapeError::TooShortHexEscape)?;
-            let lo = lo.to_digit(16).ok_or(EscapeError::InvalidCharInHexEscape)?;
-
-            let value = hi * 16 + lo;
-
-            if !mode.is_bytes() && !is_ascii(value) {
-                return Err(EscapeError::OutOfRangeHexEscape);
-            }
-            let value = value as u8;
-
-            value as char
-        }
-
-        'u' => {
-            if chars.next() != Some('{') {
-                return Err(EscapeError::NoBraceInUnicodeEscape);
-            }
-
-            let mut n_digits = 1;
-            let mut value: u32 = match chars.next().ok_or(EscapeError::UnclosedUnicodeEscape)? {
-                '_' => return Err(EscapeError::LeadingUnderscoreUnicodeEscape),
-                '}' => return Err(EscapeError::EmptyUnicodeEscape),
-                c => c.to_digit(16).ok_or(EscapeError::InvalidCharInUnicodeEscape)?,
-            };
-
-            loop {
-                match chars.next() {
-                    None => return Err(EscapeError::UnclosedUnicodeEscape),
-                    Some('_') => continue,
-                    Some('}') => {
-                        if n_digits > 6 {
-                            return Err(EscapeError::OverlongUnicodeEscape);
-                        }
-                        if mode.is_bytes() {
-                            return Err(EscapeError::UnicodeEscapeInByte);
-                        }
-
-                        break std::char::from_u32(value).ok_or_else(|| {
-                            if value > 0x10FFFF {
-                                EscapeError::OutOfRangeUnicodeEscape
-                            } else {
-                                EscapeError::LoneSurrogateUnicodeEscape
-                            }
-                        })?;
-                    }
-                    Some(c) => {
-                        let digit = c.to_digit(16).ok_or(EscapeError::InvalidCharInUnicodeEscape)?;
-                        n_digits += 1;
-                        if n_digits > 6 {
-                            continue;
-                        }
-                        let digit = digit as u32;
-                        value = value * 16 + digit;
-                    }
-                };
-            }
-        }
-        _ => return Err(EscapeError::InvalidEscape),
-    };
-    Ok(res)
-}
-
-fn unescape_char_or_byte(chars: &mut Chars<'_>, mode: Mode) -> Result<char, EscapeError> {
-    let first_char = chars.next().ok_or(EscapeError::ZeroChars)?;
-    let res = scan_escape(first_char, chars, mode)?;
-    if chars.next().is_some() {
-        return Err(EscapeError::MoreThanOneChar);
-    }
-    Ok(res)
-}
-
-/// Takes a contents of a string literal (without quotes) and produces a
-/// sequence of escaped characters or errors.
-fn unescape_str_or_byte_str<F>(src: &str, mode: Mode, callback: &mut F)
-where
-    F: FnMut(Range<usize>, Result<char, EscapeError>),
-{
-    assert!(mode.in_double_quotes());
-    let initial_len = src.len();
-    let mut chars = src.chars();
-    while let Some(first_char) = chars.next() {
-        let start = initial_len - chars.as_str().len() - first_char.len_utf8();
-
-        let unescaped_char = match first_char {
-            '\\' => {
-                let (second_char, third_char) = {
-                    let mut chars = chars.clone();
-                    (chars.next(), chars.next())
-                };
-                match (second_char, third_char) {
-                    (Some('\n'), _) | (Some('\r'), Some('\n')) => {
-                        skip_ascii_whitespace(&mut chars);
-                        continue;
-                    }
-                    _ => scan_escape(first_char, &mut chars, mode),
-                }
-            }
-            '\r' => {
-                let second_char = chars.clone().next();
-                if second_char == Some('\n') {
-                    chars.next();
-                    Ok('\n')
-                } else {
-                    scan_escape(first_char, &mut chars, mode)
-                }
-            }
-            '\n' => Ok('\n'),
-            '\t' => Ok('\t'),
-            _ => scan_escape(first_char, &mut chars, mode),
-        };
-        let end = initial_len - chars.as_str().len();
-        callback(start..end, unescaped_char);
-    }
-
-    fn skip_ascii_whitespace(chars: &mut Chars<'_>) {
-        let str = chars.as_str();
-        let first_non_space = str
-            .bytes()
-            .position(|b| b != b' ' && b != b'\t' && b != b'\n' && b != b'\r')
-            .unwrap_or(str.len());
-        *chars = str[first_non_space..].chars()
-    }
-}
-
-fn byte_from_char(c: char) -> u8 {
-    let res = c as u32;
-    assert!(res <= u8::max_value() as u32, "guaranteed because of Mode::Byte");
-    res as u8
-}
-
-fn is_ascii(x: u32) -> bool {
-    x <= 0x7F
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_unescape_char_bad() {
-        fn check(literal_text: &str, expected_error: EscapeError) {
-            let actual_result = unescape_char(literal_text).map_err(|(_offset, err)| err);
-            assert_eq!(actual_result, Err(expected_error));
-        }
-
-        check("", EscapeError::ZeroChars);
-        check(r"\", EscapeError::LoneSlash);
-
-        check("\n", EscapeError::EscapeOnlyChar);
-        check("\r\n", EscapeError::EscapeOnlyChar);
-        check("\t", EscapeError::EscapeOnlyChar);
-        check("'", EscapeError::EscapeOnlyChar);
-        check("\r", EscapeError::BareCarriageReturn);
-
-        check("spam", EscapeError::MoreThanOneChar);
-        check(r"\x0ff", EscapeError::MoreThanOneChar);
-        check(r#"\"a"#, EscapeError::MoreThanOneChar);
-        check(r"\na", EscapeError::MoreThanOneChar);
-        check(r"\ra", EscapeError::MoreThanOneChar);
-        check(r"\ta", EscapeError::MoreThanOneChar);
-        check(r"\\a", EscapeError::MoreThanOneChar);
-        check(r"\'a", EscapeError::MoreThanOneChar);
-        check(r"\0a", EscapeError::MoreThanOneChar);
-        check(r"\u{0}x", EscapeError::MoreThanOneChar);
-        check(r"\u{1F63b}}", EscapeError::MoreThanOneChar);
-
-        check(r"\v", EscapeError::InvalidEscape);
-        check(r"\💩", EscapeError::InvalidEscape);
-        check(r"\●", EscapeError::InvalidEscape);
-
-        check(r"\x", EscapeError::TooShortHexEscape);
-        check(r"\x0", EscapeError::TooShortHexEscape);
-        check(r"\xf", EscapeError::TooShortHexEscape);
-        check(r"\xa", EscapeError::TooShortHexEscape);
-        check(r"\xx", EscapeError::InvalidCharInHexEscape);
-        check(r"\xы", EscapeError::InvalidCharInHexEscape);
-        check(r"\x🦀", EscapeError::InvalidCharInHexEscape);
-        check(r"\xtt", EscapeError::InvalidCharInHexEscape);
-        check(r"\xff", EscapeError::OutOfRangeHexEscape);
-        check(r"\xFF", EscapeError::OutOfRangeHexEscape);
-        check(r"\x80", EscapeError::OutOfRangeHexEscape);
-
-        check(r"\u", EscapeError::NoBraceInUnicodeEscape);
-        check(r"\u[0123]", EscapeError::NoBraceInUnicodeEscape);
-        check(r"\u{0x}", EscapeError::InvalidCharInUnicodeEscape);
-        check(r"\u{", EscapeError::UnclosedUnicodeEscape);
-        check(r"\u{0000", EscapeError::UnclosedUnicodeEscape);
-        check(r"\u{}", EscapeError::EmptyUnicodeEscape);
-        check(r"\u{_0000}", EscapeError::LeadingUnderscoreUnicodeEscape);
-        check(r"\u{0000000}", EscapeError::OverlongUnicodeEscape);
-        check(r"\u{FFFFFF}", EscapeError::OutOfRangeUnicodeEscape);
-        check(r"\u{ffffff}", EscapeError::OutOfRangeUnicodeEscape);
-        check(r"\u{ffffff}", EscapeError::OutOfRangeUnicodeEscape);
-
-        check(r"\u{DC00}", EscapeError::LoneSurrogateUnicodeEscape);
-        check(r"\u{DDDD}", EscapeError::LoneSurrogateUnicodeEscape);
-        check(r"\u{DFFF}", EscapeError::LoneSurrogateUnicodeEscape);
-
-        check(r"\u{D800}", EscapeError::LoneSurrogateUnicodeEscape);
-        check(r"\u{DAAA}", EscapeError::LoneSurrogateUnicodeEscape);
-        check(r"\u{DBFF}", EscapeError::LoneSurrogateUnicodeEscape);
-    }
-
-    #[test]
-    fn test_unescape_char_good() {
-        fn check(literal_text: &str, expected_char: char) {
-            let actual_result = unescape_char(literal_text);
-            assert_eq!(actual_result, Ok(expected_char));
-        }
-
-        check("a", 'a');
-        check("ы", 'ы');
-        check("🦀", '🦀');
-
-        check(r#"\""#, '"');
-        check(r"\n", '\n');
-        check(r"\r", '\r');
-        check(r"\t", '\t');
-        check(r"\\", '\\');
-        check(r"\'", '\'');
-        check(r"\0", '\0');
-
-        check(r"\x00", '\0');
-        check(r"\x5a", 'Z');
-        check(r"\x5A", 'Z');
-        check(r"\x7f", 127 as char);
-
-        check(r"\u{0}", '\0');
-        check(r"\u{000000}", '\0');
-        check(r"\u{41}", 'A');
-        check(r"\u{0041}", 'A');
-        check(r"\u{00_41}", 'A');
-        check(r"\u{4__1__}", 'A');
-        check(r"\u{1F63b}", '😻');
-    }
-
-    #[test]
-    fn test_unescape_str_good() {
-        fn check(literal_text: &str, expected: &str) {
-            let mut buf = Ok(String::with_capacity(literal_text.len()));
-            unescape_str(literal_text, &mut |range, c| {
-                if let Ok(b) = &mut buf {
-                    match c {
-                        Ok(c) => b.push(c),
-                        Err(e) => buf = Err((range, e)),
-                    }
-                }
-            });
-            let buf = buf.as_ref().map(|it| it.as_ref());
-            assert_eq!(buf, Ok(expected))
-        }
-
-        check("foo", "foo");
-        check("", "");
-        check(" \t\n\r\n", " \t\n\n");
-
-        check("hello \\\n     world", "hello world");
-        check("hello \\\r\n     world", "hello world");
-        check("thread's", "thread's")
-    }
-
-    #[test]
-    fn test_unescape_byte_bad() {
-        fn check(literal_text: &str, expected_error: EscapeError) {
-            let actual_result = unescape_byte(literal_text).map_err(|(_offset, err)| err);
-            assert_eq!(actual_result, Err(expected_error));
-        }
-
-        check("", EscapeError::ZeroChars);
-        check(r"\", EscapeError::LoneSlash);
-
-        check("\n", EscapeError::EscapeOnlyChar);
-        check("\r\n", EscapeError::EscapeOnlyChar);
-        check("\t", EscapeError::EscapeOnlyChar);
-        check("'", EscapeError::EscapeOnlyChar);
-        check("\r", EscapeError::BareCarriageReturn);
-
-        check("spam", EscapeError::MoreThanOneChar);
-        check(r"\x0ff", EscapeError::MoreThanOneChar);
-        check(r#"\"a"#, EscapeError::MoreThanOneChar);
-        check(r"\na", EscapeError::MoreThanOneChar);
-        check(r"\ra", EscapeError::MoreThanOneChar);
-        check(r"\ta", EscapeError::MoreThanOneChar);
-        check(r"\\a", EscapeError::MoreThanOneChar);
-        check(r"\'a", EscapeError::MoreThanOneChar);
-        check(r"\0a", EscapeError::MoreThanOneChar);
-
-        check(r"\v", EscapeError::InvalidEscape);
-        check(r"\💩", EscapeError::InvalidEscape);
-        check(r"\●", EscapeError::InvalidEscape);
-
-        check(r"\x", EscapeError::TooShortHexEscape);
-        check(r"\x0", EscapeError::TooShortHexEscape);
-        check(r"\xa", EscapeError::TooShortHexEscape);
-        check(r"\xf", EscapeError::TooShortHexEscape);
-        check(r"\xx", EscapeError::InvalidCharInHexEscape);
-        check(r"\xы", EscapeError::InvalidCharInHexEscape);
-        check(r"\x🦀", EscapeError::InvalidCharInHexEscape);
-        check(r"\xtt", EscapeError::InvalidCharInHexEscape);
-
-        check(r"\u", EscapeError::NoBraceInUnicodeEscape);
-        check(r"\u[0123]", EscapeError::NoBraceInUnicodeEscape);
-        check(r"\u{0x}", EscapeError::InvalidCharInUnicodeEscape);
-        check(r"\u{", EscapeError::UnclosedUnicodeEscape);
-        check(r"\u{0000", EscapeError::UnclosedUnicodeEscape);
-        check(r"\u{}", EscapeError::EmptyUnicodeEscape);
-        check(r"\u{_0000}", EscapeError::LeadingUnderscoreUnicodeEscape);
-        check(r"\u{0000000}", EscapeError::OverlongUnicodeEscape);
-
-        check("ы", EscapeError::NonAsciiCharInByte);
-        check("🦀", EscapeError::NonAsciiCharInByte);
-
-        check(r"\u{0}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{000000}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{41}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{0041}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{00_41}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{4__1__}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{1F63b}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{0}x", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{1F63b}}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{FFFFFF}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{ffffff}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{ffffff}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{DC00}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{DDDD}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{DFFF}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{D800}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{DAAA}", EscapeError::UnicodeEscapeInByte);
-        check(r"\u{DBFF}", EscapeError::UnicodeEscapeInByte);
-    }
-
-    #[test]
-    fn test_unescape_byte_good() {
-        fn check(literal_text: &str, expected_byte: u8) {
-            let actual_result = unescape_byte(literal_text);
-            assert_eq!(actual_result, Ok(expected_byte));
-        }
-
-        check("a", b'a');
-
-        check(r#"\""#, b'"');
-        check(r"\n", b'\n');
-        check(r"\r", b'\r');
-        check(r"\t", b'\t');
-        check(r"\\", b'\\');
-        check(r"\'", b'\'');
-        check(r"\0", b'\0');
-
-        check(r"\x00", b'\0');
-        check(r"\x5a", b'Z');
-        check(r"\x5A", b'Z');
-        check(r"\x7f", 127);
-        check(r"\x80", 128);
-        check(r"\xff", 255);
-        check(r"\xFF", 255);
-    }
-
-    #[test]
-    fn test_unescape_byte_str_good() {
-        fn check(literal_text: &str, expected: &[u8]) {
-            let mut buf = Ok(Vec::with_capacity(literal_text.len()));
-            unescape_byte_str(literal_text, &mut |range, c| {
-                if let Ok(b) = &mut buf {
-                    match c {
-                        Ok(c) => b.push(c),
-                        Err(e) => buf = Err((range, e)),
-                    }
-                }
-            });
-            let buf = buf.as_ref().map(|it| it.as_ref());
-            assert_eq!(buf, Ok(expected))
-        }
-
-        check("foo", b"foo");
-        check("", b"");
-        check(" \t\n\r\n", b" \t\n\n");
-
-        check("hello \\\n     world", b"hello world");
-        check("hello \\\r\n     world", b"hello world");
-        check("thread's", b"thread's")
-    }
-}
diff --git a/src/libsyntax/parse/unescape_error_reporting.rs b/src/libsyntax/parse/unescape_error_reporting.rs
index 22777c0884f..7eee07e61a9 100644
--- a/src/libsyntax/parse/unescape_error_reporting.rs
+++ b/src/libsyntax/parse/unescape_error_reporting.rs
@@ -3,12 +3,11 @@
 use std::ops::Range;
 use std::iter::once;
 
+use rustc_lexer::unescape::{EscapeError, Mode};
 use syntax_pos::{Span, BytePos};
 
 use crate::errors::{Handler, Applicability};
 
-use super::unescape::{EscapeError, Mode};
-
 pub(crate) fn emit_unescape_error(
     handler: &Handler,
     // interior part of the literal, without quotes
@@ -80,6 +79,11 @@ pub(crate) fn emit_unescape_error(
             };
             handler.span_err(span, msg);
         }
+        EscapeError::BareCarriageReturnInRawString => {
+            assert!(mode.in_double_quotes());
+            let msg = "bare CR not allowed in raw string";
+            handler.span_err(span, msg);
+        }
         EscapeError::InvalidEscape => {
             let (c, span) = last_char();
 
@@ -124,6 +128,11 @@ pub(crate) fn emit_unescape_error(
             handler.span_err(span, "byte constant must be ASCII. \
                                     Use a \\xHH escape for a non-ASCII byte")
         }
+        EscapeError::NonAsciiCharInByteString => {
+            assert!(mode.is_bytes());
+            let (_c, span) = last_char();
+            handler.span_err(span, "raw byte string must be ASCII")
+        }
         EscapeError::OutOfRangeHexEscape => {
             handler.span_err(span, "this form of character escape may only be used \
                                     with characters in the range [\\x00-\\x7f]")
@@ -181,7 +190,7 @@ pub(crate) fn emit_unescape_error(
             handler.span_err(span, "empty character literal")
         }
         EscapeError::LoneSlash => {
-            panic!("lexer accepted unterminated literal with trailing slash")
+            handler.span_err(span, "invalid trailing slash in literal")
         }
     }
 }
diff --git a/src/libsyntax/print/helpers.rs b/src/libsyntax/print/helpers.rs
new file mode 100644
index 00000000000..3449e07f456
--- /dev/null
+++ b/src/libsyntax/print/helpers.rs
@@ -0,0 +1,34 @@
+use std::borrow::Cow;
+use crate::print::pp::Printer;
+
+impl Printer {
+    pub fn word_space<W: Into<Cow<'static, str>>>(&mut self, w: W) {
+        self.word(w);
+        self.space();
+    }
+
+    pub fn popen(&mut self) {
+        self.word("(");
+    }
+
+    pub fn pclose(&mut self) {
+        self.word(")");
+    }
+
+    pub fn hardbreak_if_not_bol(&mut self) {
+        if !self.is_beginning_of_line() {
+            self.hardbreak()
+        }
+    }
+
+    pub fn space_if_not_bol(&mut self) {
+        if !self.is_beginning_of_line() { self.space(); }
+    }
+
+    pub fn nbsp(&mut self) { self.word(" ") }
+
+    pub fn word_nbsp<S: Into<Cow<'static, str>>>(&mut self, w: S) {
+        self.word(w);
+        self.nbsp()
+    }
+}
diff --git a/src/libsyntax/print/pp.rs b/src/libsyntax/print/pp.rs
index 45eb6995a76..660e77f77d0 100644
--- a/src/libsyntax/print/pp.rs
+++ b/src/libsyntax/print/pp.rs
@@ -131,12 +131,11 @@
 //! it.
 //!
 //! In this implementation (following the paper, again) the SCAN process is the
-//! methods called `Printer::pretty_print_*`, and the 'PRINT' process is the
+//! methods called `Printer::scan_*`, and the 'PRINT' process is the
 //! method called `Printer::print`.
 
 use std::collections::VecDeque;
 use std::fmt;
-use std::io;
 use std::borrow::Cow;
 use log::debug;
 
@@ -164,7 +163,7 @@ pub enum Token {
     // In practice a string token contains either a `&'static str` or a
     // `String`. `Cow` is overkill for this because we never modify the data,
     // but it's more convenient than rolling our own more specialized type.
-    String(Cow<'static, str>, isize),
+    String(Cow<'static, str>),
     Break(BreakToken),
     Begin(BeginToken),
     End,
@@ -172,7 +171,7 @@ pub enum Token {
 }
 
 impl Token {
-    pub fn is_eof(&self) -> bool {
+    crate fn is_eof(&self) -> bool {
         match *self {
             Token::Eof => true,
             _ => false,
@@ -195,7 +194,7 @@ impl Token {
 impl fmt::Display for Token {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
-            Token::String(ref s, len) => write!(f, "STR({},{})", s, len),
+            Token::String(ref s) => write!(f, "STR({},{})", s, s.len()),
             Token::Break(_) => f.write_str("BREAK"),
             Token::Begin(_) => f.write_str("BEGIN"),
             Token::End => f.write_str("END"),
@@ -223,25 +222,26 @@ fn buf_str(buf: &[BufEntry], left: usize, right: usize, lim: usize) -> String {
 }
 
 #[derive(Copy, Clone)]
-pub enum PrintStackBreak {
+enum PrintStackBreak {
     Fits,
     Broken(Breaks),
 }
 
 #[derive(Copy, Clone)]
-pub struct PrintStackElem {
+struct PrintStackElem {
     offset: isize,
     pbreak: PrintStackBreak
 }
 
 const SIZE_INFINITY: isize = 0xffff;
 
-pub fn mk_printer<'a>(out: Box<dyn io::Write+'a>, linewidth: usize) -> Printer<'a> {
+pub fn mk_printer() -> Printer {
+    let linewidth = 78;
     // Yes 55, it makes the ring buffers big enough to never fall behind.
     let n: usize = 55 * linewidth;
     debug!("mk_printer {}", linewidth);
     Printer {
-        out,
+        out: String::new(),
         buf_max_len: n,
         margin: linewidth as isize,
         space: linewidth as isize,
@@ -258,8 +258,8 @@ pub fn mk_printer<'a>(out: Box<dyn io::Write+'a>, linewidth: usize) -> Printer<'
     }
 }
 
-pub struct Printer<'a> {
-    out: Box<dyn io::Write+'a>,
+pub struct Printer {
+    out: String,
     buf_max_len: usize,
     /// Width of lines we're constrained to
     margin: isize,
@@ -300,10 +300,8 @@ impl Default for BufEntry {
     }
 }
 
-const SPACES: [u8; 128] = [b' '; 128];
-
-impl<'a> Printer<'a> {
-    pub fn last_token(&mut self) -> Token {
+impl Printer {
+    pub fn last_token(&self) -> Token {
         self.buf[self.right].token.clone()
     }
 
@@ -312,16 +310,14 @@ impl<'a> Printer<'a> {
         self.buf[self.right].token = t;
     }
 
-    fn pretty_print_eof(&mut self) -> io::Result<()> {
+    fn scan_eof(&mut self) {
         if !self.scan_stack.is_empty() {
             self.check_stack(0);
-            self.advance_left()?;
+            self.advance_left();
         }
-        self.indent(0);
-        Ok(())
     }
 
-    fn pretty_print_begin(&mut self, b: BeginToken) -> io::Result<()> {
+    fn scan_begin(&mut self, b: BeginToken) {
         if self.scan_stack.is_empty() {
             self.left_total = 1;
             self.right_total = 1;
@@ -332,27 +328,21 @@ impl<'a> Printer<'a> {
         }
         debug!("pp Begin({})/buffer Vec<{},{}>",
                b.offset, self.left, self.right);
-        self.buf[self.right] = BufEntry { token: Token::Begin(b), size: -self.right_total };
-        let right = self.right;
-        self.scan_push(right);
-        Ok(())
+        self.scan_push(BufEntry { token: Token::Begin(b), size: -self.right_total });
     }
 
-    fn pretty_print_end(&mut self) -> io::Result<()> {
+    fn scan_end(&mut self) {
         if self.scan_stack.is_empty() {
             debug!("pp End/print Vec<{},{}>", self.left, self.right);
-            self.print_end()
+            self.print_end();
         } else {
             debug!("pp End/buffer Vec<{},{}>", self.left, self.right);
             self.advance_right();
-            self.buf[self.right] = BufEntry { token: Token::End, size: -1 };
-            let right = self.right;
-            self.scan_push(right);
-            Ok(())
+            self.scan_push(BufEntry { token: Token::End, size: -1 });
         }
     }
 
-    fn pretty_print_break(&mut self, b: BreakToken) -> io::Result<()> {
+    fn scan_break(&mut self, b: BreakToken) {
         if self.scan_stack.is_empty() {
             self.left_total = 1;
             self.right_total = 1;
@@ -364,29 +354,27 @@ impl<'a> Printer<'a> {
         debug!("pp Break({})/buffer Vec<{},{}>",
                b.offset, self.left, self.right);
         self.check_stack(0);
-        let right = self.right;
-        self.scan_push(right);
-        self.buf[self.right] = BufEntry { token: Token::Break(b), size: -self.right_total };
+        self.scan_push(BufEntry { token: Token::Break(b), size: -self.right_total });
         self.right_total += b.blank_space;
-        Ok(())
     }
 
-    fn pretty_print_string(&mut self, s: Cow<'static, str>, len: isize) -> io::Result<()> {
+    fn scan_string(&mut self, s: Cow<'static, str>) {
         if self.scan_stack.is_empty() {
             debug!("pp String('{}')/print Vec<{},{}>",
                    s, self.left, self.right);
-            self.print_string(s, len)
+            self.print_string(s);
         } else {
             debug!("pp String('{}')/buffer Vec<{},{}>",
                    s, self.left, self.right);
             self.advance_right();
-            self.buf[self.right] = BufEntry { token: Token::String(s, len), size: len };
+            let len = s.len() as isize;
+            self.buf[self.right] = BufEntry { token: Token::String(s), size: len };
             self.right_total += len;
-            self.check_stream()
+            self.check_stream();
         }
     }
 
-    pub fn check_stream(&mut self) -> io::Result<()> {
+    fn check_stream(&mut self) {
         debug!("check_stream Vec<{}, {}> with left_total={}, right_total={}",
                self.left, self.right, self.left_total, self.right_total);
         if self.right_total - self.left_total > self.space {
@@ -397,32 +385,32 @@ impl<'a> Printer<'a> {
                 let scanned = self.scan_pop_bottom();
                 self.buf[scanned].size = SIZE_INFINITY;
             }
-            self.advance_left()?;
+            self.advance_left();
             if self.left != self.right {
-                self.check_stream()?;
+                self.check_stream();
             }
         }
-        Ok(())
     }
 
-    pub fn scan_push(&mut self, x: usize) {
-        debug!("scan_push {}", x);
-        self.scan_stack.push_front(x);
+    fn scan_push(&mut self, entry: BufEntry) {
+        debug!("scan_push {}", self.right);
+        self.buf[self.right] = entry;
+        self.scan_stack.push_front(self.right);
     }
 
-    pub fn scan_pop(&mut self) -> usize {
+    fn scan_pop(&mut self) -> usize {
         self.scan_stack.pop_front().unwrap()
     }
 
-    pub fn scan_top(&mut self) -> usize {
+    fn scan_top(&mut self) -> usize {
         *self.scan_stack.front().unwrap()
     }
 
-    pub fn scan_pop_bottom(&mut self) -> usize {
+    fn scan_pop_bottom(&mut self) -> usize {
         self.scan_stack.pop_back().unwrap()
     }
 
-    pub fn advance_right(&mut self) {
+    fn advance_right(&mut self) {
         self.right += 1;
         self.right %= self.buf_max_len;
         // Extend the buf if necessary.
@@ -432,7 +420,7 @@ impl<'a> Printer<'a> {
         assert_ne!(self.right, self.left);
     }
 
-    pub fn advance_left(&mut self) -> io::Result<()> {
+    fn advance_left(&mut self) {
         debug!("advance_left Vec<{},{}>, sizeof({})={}", self.left, self.right,
                self.left, self.buf[self.left].size);
 
@@ -443,14 +431,15 @@ impl<'a> Printer<'a> {
 
             let len = match left {
                 Token::Break(b) => b.blank_space,
-                Token::String(_, len) => {
+                Token::String(ref s) => {
+                    let len = s.len() as isize;
                     assert_eq!(len, left_size);
                     len
                 }
                 _ => 0
             };
 
-            self.print(left, left_size)?;
+            self.print(left, left_size);
 
             self.left_total += len;
 
@@ -463,30 +452,28 @@ impl<'a> Printer<'a> {
 
             left_size = self.buf[self.left].size;
         }
-
-        Ok(())
     }
 
-    pub fn check_stack(&mut self, k: isize) {
+    fn check_stack(&mut self, k: usize) {
         if !self.scan_stack.is_empty() {
             let x = self.scan_top();
             match self.buf[x].token {
                 Token::Begin(_) => {
                     if k > 0 {
-                        let popped = self.scan_pop();
-                        self.buf[popped].size = self.buf[x].size + self.right_total;
+                        self.scan_pop();
+                        self.buf[x].size += self.right_total;
                         self.check_stack(k - 1);
                     }
                 }
                 Token::End => {
                     // paper says + not =, but that makes no sense.
-                    let popped = self.scan_pop();
-                    self.buf[popped].size = 1;
+                    self.scan_pop();
+                    self.buf[x].size = 1;
                     self.check_stack(k + 1);
                 }
                 _ => {
-                    let popped = self.scan_pop();
-                    self.buf[popped].size = self.buf[x].size + self.right_total;
+                    self.scan_pop();
+                    self.buf[x].size += self.right_total;
                     if k > 0 {
                         self.check_stack(k);
                     }
@@ -495,20 +482,19 @@ impl<'a> Printer<'a> {
         }
     }
 
-    pub fn print_newline(&mut self, amount: isize) -> io::Result<()> {
+    fn print_newline(&mut self, amount: isize) {
         debug!("NEWLINE {}", amount);
-        let ret = write!(self.out, "\n");
+        self.out.push('\n');
         self.pending_indentation = 0;
         self.indent(amount);
-        ret
     }
 
-    pub fn indent(&mut self, amount: isize) {
+    fn indent(&mut self, amount: isize) {
         debug!("INDENT {}", amount);
         self.pending_indentation += amount;
     }
 
-    pub fn get_top(&mut self) -> PrintStackElem {
+    fn get_top(&mut self) -> PrintStackElem {
         match self.print_stack.last() {
             Some(el) => *el,
             None => PrintStackElem {
@@ -518,7 +504,7 @@ impl<'a> Printer<'a> {
         }
     }
 
-    pub fn print_begin(&mut self, b: BeginToken, l: isize) -> io::Result<()> {
+    fn print_begin(&mut self, b: BeginToken, l: isize) {
         if l > self.space {
             let col = self.margin - self.space + b.offset;
             debug!("print Begin -> push broken block at col {}", col);
@@ -533,52 +519,45 @@ impl<'a> Printer<'a> {
                 pbreak: PrintStackBreak::Fits
             });
         }
-        Ok(())
     }
 
-    pub fn print_end(&mut self) -> io::Result<()> {
+    fn print_end(&mut self) {
         debug!("print End -> pop End");
-        let print_stack = &mut self.print_stack;
-        assert!(!print_stack.is_empty());
-        print_stack.pop().unwrap();
-        Ok(())
+        self.print_stack.pop().unwrap();
     }
 
-    pub fn print_break(&mut self, b: BreakToken, l: isize) -> io::Result<()> {
+    fn print_break(&mut self, b: BreakToken, l: isize) {
         let top = self.get_top();
         match top.pbreak {
             PrintStackBreak::Fits => {
                 debug!("print Break({}) in fitting block", b.blank_space);
                 self.space -= b.blank_space;
                 self.indent(b.blank_space);
-                Ok(())
             }
             PrintStackBreak::Broken(Breaks::Consistent) => {
                 debug!("print Break({}+{}) in consistent block",
                        top.offset, b.offset);
-                let ret = self.print_newline(top.offset + b.offset);
+                self.print_newline(top.offset + b.offset);
                 self.space = self.margin - (top.offset + b.offset);
-                ret
             }
             PrintStackBreak::Broken(Breaks::Inconsistent) => {
                 if l > self.space {
                     debug!("print Break({}+{}) w/ newline in inconsistent",
                            top.offset, b.offset);
-                    let ret = self.print_newline(top.offset + b.offset);
+                    self.print_newline(top.offset + b.offset);
                     self.space = self.margin - (top.offset + b.offset);
-                    ret
                 } else {
                     debug!("print Break({}) w/o newline in inconsistent",
                            b.blank_space);
                     self.indent(b.blank_space);
                     self.space -= b.blank_space;
-                    Ok(())
                 }
             }
         }
     }
 
-    pub fn print_string(&mut self, s: Cow<'static, str>, len: isize) -> io::Result<()> {
+    fn print_string(&mut self, s: Cow<'static, str>) {
+        let len = s.len() as isize;
         debug!("print String({})", s);
         // assert!(len <= space);
         self.space -= len;
@@ -587,23 +566,15 @@ impl<'a> Printer<'a> {
         //
         //   write!(self.out, "{: >n$}", "", n = self.pending_indentation as usize)?;
         //
-        // But that is significantly slower than using `SPACES`. This code is
-        // sufficiently hot, and indents can get sufficiently large, that the
-        // difference is significant on some workloads.
-        let spaces_len = SPACES.len() as isize;
-        while self.pending_indentation >= spaces_len {
-            self.out.write_all(&SPACES)?;
-            self.pending_indentation -= spaces_len;
-        }
-        if self.pending_indentation > 0 {
-            self.out.write_all(&SPACES[0..self.pending_indentation as usize])?;
-            self.pending_indentation = 0;
-        }
-
-        write!(self.out, "{}", s)
+        // But that is significantly slower. This code is sufficiently hot, and indents can get
+        // sufficiently large, that the difference is significant on some workloads.
+        self.out.reserve(self.pending_indentation as usize);
+        self.out.extend(std::iter::repeat(' ').take(self.pending_indentation as usize));
+        self.pending_indentation = 0;
+        self.out.push_str(&s);
     }
 
-    pub fn print(&mut self, token: Token, l: isize) -> io::Result<()> {
+    fn print(&mut self, token: Token, l: isize) {
         debug!("print {} {} (remaining line space={})", token, l,
                self.space);
         debug!("{}", buf_str(&self.buf,
@@ -614,9 +585,10 @@ impl<'a> Printer<'a> {
             Token::Begin(b) => self.print_begin(b, l),
             Token::End => self.print_end(),
             Token::Break(b) => self.print_break(b, l),
-            Token::String(s, len) => {
+            Token::String(s) => {
+                let len = s.len() as isize;
                 assert_eq!(len, l);
-                self.print_string(s, len)
+                self.print_string(s);
             }
             Token::Eof => panic!(), // Eof should never get here.
         }
@@ -625,65 +597,65 @@ impl<'a> Printer<'a> {
     // Convenience functions to talk to the printer.
 
     /// "raw box"
-    pub fn rbox(&mut self, indent: usize, b: Breaks) -> io::Result<()> {
-        self.pretty_print_begin(BeginToken {
+    pub fn rbox(&mut self, indent: usize, b: Breaks) {
+        self.scan_begin(BeginToken {
             offset: indent as isize,
             breaks: b
         })
     }
 
     /// Inconsistent breaking box
-    pub fn ibox(&mut self, indent: usize) -> io::Result<()> {
+    pub fn ibox(&mut self, indent: usize) {
         self.rbox(indent, Breaks::Inconsistent)
     }
 
     /// Consistent breaking box
-    pub fn cbox(&mut self, indent: usize) -> io::Result<()> {
+    pub fn cbox(&mut self, indent: usize) {
         self.rbox(indent, Breaks::Consistent)
     }
 
-    pub fn break_offset(&mut self, n: usize, off: isize) -> io::Result<()> {
-        self.pretty_print_break(BreakToken {
+    pub fn break_offset(&mut self, n: usize, off: isize) {
+        self.scan_break(BreakToken {
             offset: off,
             blank_space: n as isize
         })
     }
 
-    pub fn end(&mut self) -> io::Result<()> {
-        self.pretty_print_end()
+    pub fn end(&mut self) {
+        self.scan_end()
     }
 
-    pub fn eof(&mut self) -> io::Result<()> {
-        self.pretty_print_eof()
+    pub fn eof(mut self) -> String {
+        self.scan_eof();
+        self.out
     }
 
-    pub fn word<S: Into<Cow<'static, str>>>(&mut self, wrd: S) -> io::Result<()> {
+    pub fn word<S: Into<Cow<'static, str>>>(&mut self, wrd: S) {
         let s = wrd.into();
-        let len = s.len() as isize;
-        self.pretty_print_string(s, len)
+        self.scan_string(s)
     }
 
-    fn spaces(&mut self, n: usize) -> io::Result<()> {
+    fn spaces(&mut self, n: usize) {
         self.break_offset(n, 0)
     }
 
-    pub fn zerobreak(&mut self) -> io::Result<()> {
+    crate fn zerobreak(&mut self) {
         self.spaces(0)
     }
 
-    pub fn space(&mut self) -> io::Result<()> {
+    pub fn space(&mut self) {
         self.spaces(1)
     }
 
-    pub fn hardbreak(&mut self) -> io::Result<()> {
+    pub fn hardbreak(&mut self) {
         self.spaces(SIZE_INFINITY as usize)
     }
 
-    pub fn hardbreak_tok_offset(off: isize) -> Token {
-        Token::Break(BreakToken {offset: off, blank_space: SIZE_INFINITY})
+    pub fn is_beginning_of_line(&self) -> bool {
+        self.last_token().is_eof() || self.last_token().is_hardbreak_tok()
     }
 
-    pub fn hardbreak_tok() -> Token {
-        Self::hardbreak_tok_offset(0)
+    pub fn hardbreak_tok_offset(off: isize) -> Token {
+        Token::Break(BreakToken {offset: off, blank_space: SIZE_INFINITY})
     }
 }
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index cd86d94f4b8..4dc00af4860 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1,28 +1,31 @@
-// ignore-tidy-filelength
-
 use crate::ast::{self, BlockCheckMode, PatKind, RangeEnd, RangeSyntax};
 use crate::ast::{SelfKind, GenericBound, TraitBoundModifier};
 use crate::ast::{Attribute, MacDelimiter, GenericArg};
 use crate::util::parser::{self, AssocOp, Fixity};
 use crate::attr;
 use crate::source_map::{self, SourceMap, Spanned};
-use crate::parse::token::{self, BinOpToken, Nonterminal, Token};
+use crate::parse::token::{self, BinOpToken, DelimToken, Nonterminal, Token, TokenKind};
 use crate::parse::lexer::comments;
 use crate::parse::{self, ParseSess};
 use crate::print::pp::{self, Breaks};
 use crate::print::pp::Breaks::{Consistent, Inconsistent};
 use crate::ptr::P;
-use crate::std_inject;
-use crate::symbol::{keywords, sym};
+use crate::symbol::{kw, sym};
 use crate::tokenstream::{self, TokenStream, TokenTree};
 
 use rustc_target::spec::abi::{self, Abi};
 use syntax_pos::{self, BytePos};
-use syntax_pos::{DUMMY_SP, FileName};
+use syntax_pos::{FileName, Span};
 
 use std::borrow::Cow;
-use std::io::{self, Write, Read};
-use std::vec;
+
+#[cfg(test)]
+mod tests;
+
+pub enum MacHeader<'a> {
+    Path(&'a ast::Path),
+    Keyword(&'static str),
+}
 
 pub enum AnnNode<'a> {
     Ident(&'a ast::Ident),
@@ -35,8 +38,8 @@ pub enum AnnNode<'a> {
 }
 
 pub trait PpAnn {
-    fn pre(&self, _state: &mut State<'_>, _node: AnnNode<'_>) -> io::Result<()> { Ok(()) }
-    fn post(&self, _state: &mut State<'_>, _node: AnnNode<'_>) -> io::Result<()> { Ok(()) }
+    fn pre(&self, _state: &mut State<'_>, _node: AnnNode<'_>) { }
+    fn post(&self, _state: &mut State<'_>, _node: AnnNode<'_>) { }
 }
 
 #[derive(Copy, Clone)]
@@ -44,31 +47,58 @@ pub struct NoAnn;
 
 impl PpAnn for NoAnn {}
 
-pub struct State<'a> {
-    pub s: pp::Printer<'a>,
-    cm: Option<&'a SourceMap>,
-    comments: Option<Vec<comments::Comment>>,
-    cur_cmnt: usize,
-    boxes: Vec<pp::Breaks>,
-    ann: &'a (dyn PpAnn+'a),
-    is_expanded: bool
+pub struct Comments<'a> {
+    cm: &'a SourceMap,
+    comments: Vec<comments::Comment>,
+    current: usize,
 }
 
-fn rust_printer<'a>(writer: Box<dyn Write+'a>, ann: &'a dyn PpAnn) -> State<'a> {
-    State {
-        s: pp::mk_printer(writer, DEFAULT_COLUMNS),
-        cm: None,
-        comments: None,
-        cur_cmnt: 0,
-        boxes: Vec::new(),
-        ann,
-        is_expanded: false
+impl<'a> Comments<'a> {
+    pub fn new(
+        cm: &'a SourceMap,
+        sess: &ParseSess,
+        filename: FileName,
+        input: String,
+    ) -> Comments<'a> {
+        let comments = comments::gather_comments(sess, filename, input);
+        Comments {
+            cm,
+            comments,
+            current: 0,
+        }
+    }
+
+    pub fn next(&self) -> Option<comments::Comment> {
+        self.comments.get(self.current).cloned()
+    }
+
+    pub fn trailing_comment(
+        &mut self,
+        span: syntax_pos::Span,
+        next_pos: Option<BytePos>,
+    ) -> Option<comments::Comment> {
+        if let Some(cmnt) = self.next() {
+            if cmnt.style != comments::Trailing { return None; }
+            let span_line = self.cm.lookup_char_pos(span.hi());
+            let comment_line = self.cm.lookup_char_pos(cmnt.pos);
+            let next = next_pos.unwrap_or_else(|| cmnt.pos + BytePos(1));
+            if span.hi() < cmnt.pos && cmnt.pos < next && span_line.line == comment_line.line {
+                return Some(cmnt);
+            }
+        }
+
+        None
     }
 }
 
-pub const INDENT_UNIT: usize = 4;
+pub struct State<'a> {
+    pub s: pp::Printer,
+    comments: Option<Comments<'a>>,
+    ann: &'a (dyn PpAnn+'a),
+    is_expanded: bool
+}
 
-pub const DEFAULT_COLUMNS: usize = 78;
+crate const INDENT_UNIT: usize = 4;
 
 /// Requires you to pass an input filename and reader so that
 /// it can scan the input text for comments to copy forward.
@@ -76,76 +106,50 @@ pub fn print_crate<'a>(cm: &'a SourceMap,
                        sess: &ParseSess,
                        krate: &ast::Crate,
                        filename: FileName,
-                       input: &mut dyn Read,
-                       out: Box<dyn Write+'a>,
+                       input: String,
                        ann: &'a dyn PpAnn,
-                       is_expanded: bool) -> io::Result<()> {
-    let mut s = State::new_from_input(cm, sess, filename, input, out, ann, is_expanded);
+                       is_expanded: bool) -> String {
+    let mut s = State {
+        s: pp::mk_printer(),
+        comments: Some(Comments::new(cm, sess, filename, input)),
+        ann,
+        is_expanded,
+    };
 
-    if is_expanded && std_inject::injected_crate_name().is_some() {
+    if is_expanded && sess.injected_crate_name.try_get().is_some() {
         // We need to print `#![no_std]` (and its feature gate) so that
         // compiling pretty-printed source won't inject libstd again.
         // However we don't want these attributes in the AST because
         // of the feature gate, so we fake them up here.
 
         // #![feature(prelude_import)]
-        let pi_nested = attr::mk_nested_word_item(ast::Ident::with_empty_ctxt(sym::prelude_import));
-        let list = attr::mk_list_item(
-            DUMMY_SP, ast::Ident::with_empty_ctxt(sym::feature), vec![pi_nested]);
-        let fake_attr = attr::mk_attr_inner(DUMMY_SP, attr::mk_attr_id(), list);
-        s.print_attribute(&fake_attr)?;
+        let pi_nested = attr::mk_nested_word_item(ast::Ident::with_dummy_span(sym::prelude_import));
+        let list = attr::mk_list_item(ast::Ident::with_dummy_span(sym::feature), vec![pi_nested]);
+        let fake_attr = attr::mk_attr_inner(list);
+        s.print_attribute(&fake_attr);
 
         // #![no_std]
-        let no_std_meta = attr::mk_word_item(ast::Ident::with_empty_ctxt(sym::no_std));
-        let fake_attr = attr::mk_attr_inner(DUMMY_SP, attr::mk_attr_id(), no_std_meta);
-        s.print_attribute(&fake_attr)?;
+        let no_std_meta = attr::mk_word_item(ast::Ident::with_dummy_span(sym::no_std));
+        let fake_attr = attr::mk_attr_inner(no_std_meta);
+        s.print_attribute(&fake_attr);
     }
 
-    s.print_mod(&krate.module, &krate.attrs)?;
-    s.print_remaining_comments()?;
+    s.print_mod(&krate.module, &krate.attrs);
+    s.print_remaining_comments();
     s.s.eof()
 }
 
-impl<'a> State<'a> {
-    pub fn new_from_input(cm: &'a SourceMap,
-                          sess: &ParseSess,
-                          filename: FileName,
-                          input: &mut dyn Read,
-                          out: Box<dyn Write+'a>,
-                          ann: &'a dyn PpAnn,
-                          is_expanded: bool) -> State<'a> {
-        let comments = comments::gather_comments(sess, filename, input);
-        State::new(cm, out, ann, Some(comments), is_expanded)
-    }
-
-    pub fn new(cm: &'a SourceMap,
-               out: Box<dyn Write+'a>,
-               ann: &'a dyn PpAnn,
-               comments: Option<Vec<comments::Comment>>,
-               is_expanded: bool) -> State<'a> {
-        State {
-            s: pp::mk_printer(out, DEFAULT_COLUMNS),
-            cm: Some(cm),
-            comments,
-            cur_cmnt: 0,
-            boxes: Vec::new(),
-            ann,
-            is_expanded,
-        }
-    }
-}
-
 pub fn to_string<F>(f: F) -> String where
-    F: FnOnce(&mut State<'_>) -> io::Result<()>,
+    F: FnOnce(&mut State<'_>),
 {
-    let mut wr = Vec::new();
-    {
-        let ann = NoAnn;
-        let mut printer = rust_printer(Box::new(&mut wr), &ann);
-        f(&mut printer).unwrap();
-        printer.s.eof().unwrap();
-    }
-    String::from_utf8(wr).unwrap()
+    let mut printer = State {
+        s: pp::mk_printer(),
+        comments: None,
+        ann: &NoAnn,
+        is_expanded: false
+    };
+    f(&mut printer);
+    printer.s.eof()
 }
 
 fn binop_to_string(op: BinOpToken) -> &'static str {
@@ -163,22 +167,23 @@ fn binop_to_string(op: BinOpToken) -> &'static str {
     }
 }
 
-pub fn literal_to_string(lit: token::Lit, suffix: Option<ast::Name>) -> String {
-    let mut out = match lit {
-        token::Byte(b)           => format!("b'{}'", b),
-        token::Char(c)           => format!("'{}'", c),
-        token::Err(c)            => format!("'{}'", c),
-        token::Bool(c)           |
-        token::Float(c)          |
-        token::Integer(c)        => c.to_string(),
-        token::Str_(s)           => format!("\"{}\"", s),
-        token::StrRaw(s, n)      => format!("r{delim}\"{string}\"{delim}",
-                                            delim="#".repeat(n as usize),
-                                            string=s),
-        token::ByteStr(v)        => format!("b\"{}\"", v),
-        token::ByteStrRaw(s, n)  => format!("br{delim}\"{string}\"{delim}",
-                                            delim="#".repeat(n as usize),
-                                            string=s),
+pub fn literal_to_string(lit: token::Lit) -> String {
+    let token::Lit { kind, symbol, suffix } = lit;
+    let mut out = match kind {
+        token::Byte          => format!("b'{}'", symbol),
+        token::Char          => format!("'{}'", symbol),
+        token::Str           => format!("\"{}\"", symbol),
+        token::StrRaw(n)     => format!("r{delim}\"{string}\"{delim}",
+                                        delim="#".repeat(n as usize),
+                                        string=symbol),
+        token::ByteStr       => format!("b\"{}\"", symbol),
+        token::ByteStrRaw(n) => format!("br{delim}\"{string}\"{delim}",
+                                        delim="#".repeat(n as usize),
+                                        string=symbol),
+        token::Integer       |
+        token::Float         |
+        token::Bool          |
+        token::Err           => symbol.to_string(),
     };
 
     if let Some(suffix) = suffix {
@@ -188,7 +193,46 @@ pub fn literal_to_string(lit: token::Lit, suffix: Option<ast::Name>) -> String {
     out
 }
 
-pub fn token_to_string(tok: &Token) -> String {
+/// Print an ident from AST, `$crate` is converted into its respective crate name.
+pub fn ast_ident_to_string(ident: ast::Ident, is_raw: bool) -> String {
+    ident_to_string(ident.name, is_raw, Some(ident.span))
+}
+
+// AST pretty-printer is used as a fallback for turning AST structures into token streams for
+// proc macros. Additionally, proc macros may stringify their input and expect it survive the
+// stringification (especially true for proc macro derives written between Rust 1.15 and 1.30).
+// So we need to somehow pretty-print `$crate` in a way preserving at least some of its
+// hygiene data, most importantly name of the crate it refers to.
+// As a result we print `$crate` as `crate` if it refers to the local crate
+// and as `::other_crate_name` if it refers to some other crate.
+// Note, that this is only done if the ident token is printed from inside of AST pretty-pringing,
+// but not otherwise. Pretty-printing is the only way for proc macros to discover token contents,
+// so we should not perform this lossy conversion if the top level call to the pretty-printer was
+// done for a token stream or a single token.
+fn ident_to_string(name: ast::Name, is_raw: bool, convert_dollar_crate: Option<Span>) -> String {
+    if is_raw {
+        format!("r#{}", name)
+    } else {
+        if name == kw::DollarCrate {
+            if let Some(span) = convert_dollar_crate {
+                let converted = span.ctxt().dollar_crate_name();
+                return if converted.is_path_segment_keyword() {
+                    converted.to_string()
+                } else {
+                    format!("::{}", converted)
+                }
+            }
+        }
+        name.to_string()
+    }
+}
+
+/// Print the token kind precisely, without converting `$crate` into its respective crate name.
+pub fn token_kind_to_string(tok: &TokenKind) -> String {
+    token_kind_to_string_ext(tok, None)
+}
+
+fn token_kind_to_string_ext(tok: &TokenKind, convert_dollar_crate: Option<Span>) -> String {
     match *tok {
         token::Eq                   => "=".to_string(),
         token::Lt                   => "<".to_string(),
@@ -231,11 +275,10 @@ pub fn token_to_string(tok: &Token) -> String {
         token::SingleQuote          => "'".to_string(),
 
         /* Literals */
-        token::Literal(lit, suf) => literal_to_string(lit, suf),
+        token::Literal(lit) => literal_to_string(lit),
 
         /* Name components */
-        token::Ident(s, false)      => s.to_string(),
-        token::Ident(s, true)       => format!("r#{}", s),
+        token::Ident(s, is_raw)     => ident_to_string(s, is_raw, convert_dollar_crate),
         token::Lifetime(s)          => s.to_string(),
 
         /* Other */
@@ -244,12 +287,23 @@ pub fn token_to_string(tok: &Token) -> String {
         token::Whitespace           => " ".to_string(),
         token::Comment              => "/* */".to_string(),
         token::Shebang(s)           => format!("/* shebang: {}*/", s),
+        token::Unknown(s)           => s.to_string(),
 
         token::Interpolated(ref nt) => nonterminal_to_string(nt),
     }
 }
 
-pub fn nonterminal_to_string(nt: &Nonterminal) -> String {
+/// Print the token precisely, without converting `$crate` into its respective crate name.
+pub fn token_to_string(token: &Token) -> String {
+    token_to_string_ext(token, false)
+}
+
+fn token_to_string_ext(token: &Token, convert_dollar_crate: bool) -> String {
+    let convert_dollar_crate = if convert_dollar_crate { Some(token.span) } else { None };
+    token_kind_to_string_ext(&token.kind, convert_dollar_crate)
+}
+
+crate fn nonterminal_to_string(nt: &Nonterminal) -> String {
     match *nt {
         token::NtExpr(ref e)        => expr_to_string(e),
         token::NtMeta(ref e)        => meta_item_to_string(e),
@@ -259,9 +313,8 @@ pub fn nonterminal_to_string(nt: &Nonterminal) -> String {
         token::NtBlock(ref e)       => block_to_string(e),
         token::NtStmt(ref e)        => stmt_to_string(e),
         token::NtPat(ref e)         => pat_to_string(e),
-        token::NtIdent(e, false)    => ident_to_string(e),
-        token::NtIdent(e, true)     => format!("r#{}", ident_to_string(e)),
-        token::NtLifetime(e)        => ident_to_string(e),
+        token::NtIdent(e, is_raw)   => ast_ident_to_string(e, is_raw),
+        token::NtLifetime(e)        => e.to_string(),
         token::NtLiteral(ref e)     => expr_to_string(e),
         token::NtTT(ref tree)       => tt_to_string(tree.clone()),
         token::NtImplItem(ref e)    => impl_item_to_string(e),
@@ -283,47 +336,35 @@ pub fn pat_to_string(pat: &ast::Pat) -> String {
     to_string(|s| s.print_pat(pat))
 }
 
-pub fn arm_to_string(arm: &ast::Arm) -> String {
-    to_string(|s| s.print_arm(arm))
-}
-
 pub fn expr_to_string(e: &ast::Expr) -> String {
     to_string(|s| s.print_expr(e))
 }
 
-pub fn lifetime_to_string(lt: &ast::Lifetime) -> String {
-    to_string(|s| s.print_lifetime(*lt))
-}
-
 pub fn tt_to_string(tt: tokenstream::TokenTree) -> String {
-    to_string(|s| s.print_tt(tt))
+    to_string(|s| s.print_tt(tt, false))
 }
 
 pub fn tts_to_string(tts: &[tokenstream::TokenTree]) -> String {
-    to_string(|s| s.print_tts(tts.iter().cloned().collect()))
+    tokens_to_string(tts.iter().cloned().collect())
 }
 
 pub fn tokens_to_string(tokens: TokenStream) -> String {
-    to_string(|s| s.print_tts(tokens))
+    to_string(|s| s.print_tts(tokens, false))
 }
 
 pub fn stmt_to_string(stmt: &ast::Stmt) -> String {
     to_string(|s| s.print_stmt(stmt))
 }
 
-pub fn attr_to_string(attr: &ast::Attribute) -> String {
-    to_string(|s| s.print_attribute(attr))
-}
-
 pub fn item_to_string(i: &ast::Item) -> String {
     to_string(|s| s.print_item(i))
 }
 
-pub fn impl_item_to_string(i: &ast::ImplItem) -> String {
+fn impl_item_to_string(i: &ast::ImplItem) -> String {
     to_string(|s| s.print_impl_item(i))
 }
 
-pub fn trait_item_to_string(i: &ast::TraitItem) -> String {
+fn trait_item_to_string(i: &ast::TraitItem) -> String {
     to_string(|s| s.print_trait_item(i))
 }
 
@@ -331,14 +372,6 @@ pub fn generic_params_to_string(generic_params: &[ast::GenericParam]) -> String
     to_string(|s| s.print_generic_params(generic_params))
 }
 
-pub fn where_clause_to_string(i: &ast::WhereClause) -> String {
-    to_string(|s| s.print_where_clause(i))
-}
-
-pub fn fn_block_to_string(p: &ast::FnDecl) -> String {
-    to_string(|s| s.print_fn_block_args(p))
-}
-
 pub fn path_to_string(p: &ast::Path) -> String {
     to_string(|s| s.print_path(p, false, 0))
 }
@@ -347,34 +380,16 @@ pub fn path_segment_to_string(p: &ast::PathSegment) -> String {
     to_string(|s| s.print_path_segment(p, false))
 }
 
-pub fn ident_to_string(id: ast::Ident) -> String {
-    to_string(|s| s.print_ident(id))
-}
-
 pub fn vis_to_string(v: &ast::Visibility) -> String {
     to_string(|s| s.print_visibility(v))
 }
 
-pub fn fun_to_string(decl: &ast::FnDecl,
-                     header: &ast::FnHeader,
-                     name: ast::Ident,
-                     generics: &ast::Generics)
-                     -> String {
-    to_string(|s| {
-        s.head("")?;
-        s.print_fn(decl, header, Some(name),
-                   generics, &source_map::dummy_spanned(ast::VisibilityKind::Inherited))?;
-        s.end()?; // Close the head box
-        s.end() // Close the outer box
-    })
-}
-
-pub fn block_to_string(blk: &ast::Block) -> String {
+fn block_to_string(blk: &ast::Block) -> String {
     to_string(|s| {
         // containing cbox, will be closed by print-block at }
-        s.cbox(INDENT_UNIT)?;
+        s.cbox(INDENT_UNIT);
         // head-ibox, will be closed by print-block after {
-        s.ibox(0)?;
+        s.ibox(0);
         s.print_block(blk)
     })
 }
@@ -391,191 +406,138 @@ pub fn attribute_to_string(attr: &ast::Attribute) -> String {
     to_string(|s| s.print_attribute(attr))
 }
 
-pub fn lit_to_string(l: &ast::Lit) -> String {
-    to_string(|s| s.print_literal(l))
-}
-
-pub fn variant_to_string(var: &ast::Variant) -> String {
-    to_string(|s| s.print_variant(var))
-}
-
 pub fn arg_to_string(arg: &ast::Arg) -> String {
     to_string(|s| s.print_arg(arg, false))
 }
 
-pub fn mac_to_string(arg: &ast::Mac) -> String {
-    to_string(|s| s.print_mac(arg))
-}
-
-pub fn foreign_item_to_string(arg: &ast::ForeignItem) -> String {
+fn foreign_item_to_string(arg: &ast::ForeignItem) -> String {
     to_string(|s| s.print_foreign_item(arg))
 }
 
-pub fn visibility_qualified(vis: &ast::Visibility, s: &str) -> String {
+fn visibility_qualified(vis: &ast::Visibility, s: &str) -> String {
     format!("{}{}", to_string(|s| s.print_visibility(vis)), s)
 }
 
-pub trait PrintState<'a> {
-    fn writer(&mut self) -> &mut pp::Printer<'a>;
-    fn boxes(&mut self) -> &mut Vec<pp::Breaks>;
-    fn comments(&mut self) -> &mut Option<Vec<comments::Comment>>;
-    fn cur_cmnt(&mut self) -> &mut usize;
-
-    fn word_space<S: Into<Cow<'static, str>>>(&mut self, w: S) -> io::Result<()> {
-        self.writer().word(w)?;
-        self.writer().space()
-    }
-
-    fn popen(&mut self) -> io::Result<()> { self.writer().word("(") }
-
-    fn pclose(&mut self) -> io::Result<()> { self.writer().word(")") }
-
-    fn is_begin(&mut self) -> bool {
-        match self.writer().last_token() {
-            pp::Token::Begin(_) => true,
-            _ => false,
-        }
+impl std::ops::Deref for State<'_> {
+    type Target = pp::Printer;
+    fn deref(&self) -> &Self::Target {
+        &self.s
     }
+}
 
-    fn is_end(&mut self) -> bool {
-        match self.writer().last_token() {
-            pp::Token::End => true,
-            _ => false,
-        }
+impl std::ops::DerefMut for State<'_> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.s
     }
+}
 
-    // is this the beginning of a line?
-    fn is_bol(&mut self) -> bool {
-        self.writer().last_token().is_eof() || self.writer().last_token().is_hardbreak_tok()
-    }
+pub trait PrintState<'a>: std::ops::Deref<Target=pp::Printer> + std::ops::DerefMut {
+    fn comments(&mut self) -> &mut Option<Comments<'a>>;
+    fn print_ident(&mut self, ident: ast::Ident);
+    fn print_generic_args(&mut self, args: &ast::GenericArgs, colons_before_params: bool);
 
-    fn hardbreak_if_not_bol(&mut self) -> io::Result<()> {
-        if !self.is_bol() {
-            self.writer().hardbreak()?
+    fn strsep<T, F>(&mut self, sep: &'static str, space_before: bool,
+                    b: Breaks, elts: &[T], mut op: F)
+        where F: FnMut(&mut Self, &T),
+    {
+        self.rbox(0, b);
+        if let Some((first, rest)) = elts.split_first() {
+            op(self, first);
+            for elt in rest {
+                if space_before {
+                    self.space();
+                }
+                self.word_space(sep);
+                op(self, elt);
+            }
         }
-        Ok(())
-    }
-
-    // "raw box"
-    fn rbox(&mut self, u: usize, b: pp::Breaks) -> io::Result<()> {
-        self.boxes().push(b);
-        self.writer().rbox(u, b)
-    }
-
-    fn ibox(&mut self, u: usize) -> io::Result<()> {
-        self.boxes().push(pp::Breaks::Inconsistent);
-        self.writer().ibox(u)
-    }
-
-    fn end(&mut self) -> io::Result<()> {
-        self.boxes().pop().unwrap();
-        self.writer().end()
+        self.end();
     }
 
-    fn commasep<T, F>(&mut self, b: Breaks, elts: &[T], mut op: F) -> io::Result<()>
-        where F: FnMut(&mut Self, &T) -> io::Result<()>,
+    fn commasep<T, F>(&mut self, b: Breaks, elts: &[T], op: F)
+        where F: FnMut(&mut Self, &T),
     {
-        self.rbox(0, b)?;
-        let mut first = true;
-        for elt in elts {
-            if first { first = false; } else { self.word_space(",")?; }
-            op(self, elt)?;
-        }
-        self.end()
+        self.strsep(",", false, b, elts, op)
     }
 
-    fn maybe_print_comment(&mut self, pos: BytePos) -> io::Result<()> {
+    fn maybe_print_comment(&mut self, pos: BytePos) {
         while let Some(ref cmnt) = self.next_comment() {
             if cmnt.pos < pos {
-                self.print_comment(cmnt)?;
+                self.print_comment(cmnt);
             } else {
                 break
             }
         }
-        Ok(())
     }
 
     fn print_comment(&mut self,
-                     cmnt: &comments::Comment) -> io::Result<()> {
-        let r = match cmnt.style {
+                     cmnt: &comments::Comment) {
+        match cmnt.style {
             comments::Mixed => {
                 assert_eq!(cmnt.lines.len(), 1);
-                self.writer().zerobreak()?;
-                self.writer().word(cmnt.lines[0].clone())?;
-                self.writer().zerobreak()
+                self.zerobreak();
+                self.word(cmnt.lines[0].clone());
+                self.zerobreak()
             }
             comments::Isolated => {
-                self.hardbreak_if_not_bol()?;
+                self.hardbreak_if_not_bol();
                 for line in &cmnt.lines {
                     // Don't print empty lines because they will end up as trailing
                     // whitespace
                     if !line.is_empty() {
-                        self.writer().word(line.clone())?;
+                        self.word(line.clone());
                     }
-                    self.writer().hardbreak()?;
+                    self.hardbreak();
                 }
-                Ok(())
             }
             comments::Trailing => {
-                if !self.is_bol() {
-                    self.writer().word(" ")?;
+                if !self.is_beginning_of_line() {
+                    self.word(" ");
                 }
                 if cmnt.lines.len() == 1 {
-                    self.writer().word(cmnt.lines[0].clone())?;
-                    self.writer().hardbreak()
+                    self.word(cmnt.lines[0].clone());
+                    self.hardbreak()
                 } else {
-                    self.ibox(0)?;
+                    self.ibox(0);
                     for line in &cmnt.lines {
                         if !line.is_empty() {
-                            self.writer().word(line.clone())?;
+                            self.word(line.clone());
                         }
-                        self.writer().hardbreak()?;
+                        self.hardbreak();
                     }
-                    self.end()
+                    self.end();
                 }
             }
             comments::BlankLine => {
                 // We need to do at least one, possibly two hardbreaks.
-                let is_semi = match self.writer().last_token() {
-                    pp::Token::String(s, _) => ";" == s,
+                let twice = match self.last_token() {
+                    pp::Token::String(s) => ";" == s,
+                    pp::Token::Begin(_) => true,
+                    pp::Token::End => true,
                     _ => false
                 };
-                if is_semi || self.is_begin() || self.is_end() {
-                    self.writer().hardbreak()?;
+                if twice {
+                    self.hardbreak();
                 }
-                self.writer().hardbreak()
+                self.hardbreak();
             }
-        };
-        match r {
-            Ok(()) => {
-                *self.cur_cmnt() = *self.cur_cmnt() + 1;
-                Ok(())
-            }
-            Err(e) => Err(e),
+        }
+        if let Some(cm) = self.comments() {
+            cm.current += 1;
         }
     }
 
     fn next_comment(&mut self) -> Option<comments::Comment> {
-        let cur_cmnt = *self.cur_cmnt();
-        match *self.comments() {
-            Some(ref cmnts) => {
-                if cur_cmnt < cmnts.len() {
-                    Some(cmnts[cur_cmnt].clone())
-                } else {
-                    None
-                }
-            }
-            _ => None
-        }
+        self.comments().as_mut().and_then(|c| c.next())
     }
 
-    fn print_literal(&mut self, lit: &ast::Lit) -> io::Result<()> {
-        self.maybe_print_comment(lit.span.lo())?;
-        self.writer().word(literal_to_string(lit.token, lit.suffix))
+    fn print_literal(&mut self, lit: &ast::Lit) {
+        self.maybe_print_comment(lit.span.lo());
+        self.word(lit.token.to_string())
     }
 
     fn print_string(&mut self, st: &str,
-                    style: ast::StrStyle) -> io::Result<()> {
+                    style: ast::StrStyle) {
         let st = match style {
             ast::StrStyle::Cooked => {
                 (format!("\"{}\"", st.escape_debug()))
@@ -586,32 +548,32 @@ pub trait PrintState<'a> {
                          string=st))
             }
         };
-        self.writer().word(st)
+        self.word(st)
     }
 
     fn print_inner_attributes(&mut self,
-                              attrs: &[ast::Attribute]) -> io::Result<()> {
+                              attrs: &[ast::Attribute]) {
         self.print_either_attributes(attrs, ast::AttrStyle::Inner, false, true)
     }
 
     fn print_inner_attributes_no_trailing_hardbreak(&mut self,
                                                    attrs: &[ast::Attribute])
-                                                   -> io::Result<()> {
+                                                   {
         self.print_either_attributes(attrs, ast::AttrStyle::Inner, false, false)
     }
 
     fn print_outer_attributes(&mut self,
-                              attrs: &[ast::Attribute]) -> io::Result<()> {
+                              attrs: &[ast::Attribute]) {
         self.print_either_attributes(attrs, ast::AttrStyle::Outer, false, true)
     }
 
     fn print_inner_attributes_inline(&mut self,
-                                     attrs: &[ast::Attribute]) -> io::Result<()> {
+                                     attrs: &[ast::Attribute]) {
         self.print_either_attributes(attrs, ast::AttrStyle::Inner, true, true)
     }
 
     fn print_outer_attributes_inline(&mut self,
-                                     attrs: &[ast::Attribute]) -> io::Result<()> {
+                                     attrs: &[ast::Attribute]) {
         self.print_either_attributes(attrs, ast::AttrStyle::Outer, true, true)
     }
 
@@ -619,69 +581,61 @@ pub trait PrintState<'a> {
                               attrs: &[ast::Attribute],
                               kind: ast::AttrStyle,
                               is_inline: bool,
-                              trailing_hardbreak: bool) -> io::Result<()> {
+                              trailing_hardbreak: bool) {
         let mut count = 0;
         for attr in attrs {
             if attr.style == kind {
-                self.print_attribute_inline(attr, is_inline)?;
+                self.print_attribute_inline(attr, is_inline);
                 if is_inline {
-                    self.nbsp()?;
+                    self.nbsp();
                 }
                 count += 1;
             }
         }
         if count > 0 && trailing_hardbreak && !is_inline {
-            self.hardbreak_if_not_bol()?;
+            self.hardbreak_if_not_bol();
         }
-        Ok(())
     }
 
-    fn print_attribute_path(&mut self, path: &ast::Path) -> io::Result<()> {
-        for (i, segment) in path.segments.iter().enumerate() {
-            if i > 0 {
-                self.writer().word("::")?
-            }
-            if segment.ident.name != keywords::PathRoot.name() {
-                if segment.ident.name == keywords::DollarCrate.name() {
-                    self.print_dollar_crate(segment.ident)?;
-                } else {
-                    self.writer().word(segment.ident.as_str().to_string())?;
-                }
-            }
-        }
-        Ok(())
-    }
-
-    fn print_attribute(&mut self, attr: &ast::Attribute) -> io::Result<()> {
+    fn print_attribute(&mut self, attr: &ast::Attribute) {
         self.print_attribute_inline(attr, false)
     }
 
     fn print_attribute_inline(&mut self, attr: &ast::Attribute,
-                              is_inline: bool) -> io::Result<()> {
+                              is_inline: bool) {
         if !is_inline {
-            self.hardbreak_if_not_bol()?;
+            self.hardbreak_if_not_bol();
         }
-        self.maybe_print_comment(attr.span.lo())?;
+        self.maybe_print_comment(attr.span.lo());
         if attr.is_sugared_doc {
-            self.writer().word(attr.value_str().unwrap().as_str().to_string())?;
-            self.writer().hardbreak()
+            self.word(attr.value_str().unwrap().as_str().to_string());
+            self.hardbreak()
         } else {
             match attr.style {
-                ast::AttrStyle::Inner => self.writer().word("#![")?,
-                ast::AttrStyle::Outer => self.writer().word("#[")?,
-            }
-            if let Some(mi) = attr.meta() {
-                self.print_meta_item(&mi)?
-            } else {
-                self.print_attribute_path(&attr.path)?;
-                self.writer().space()?;
-                self.print_tts(attr.tokens.clone())?;
+                ast::AttrStyle::Inner => self.word("#!["),
+                ast::AttrStyle::Outer => self.word("#["),
+            }
+            self.ibox(0);
+            match attr.tokens.trees().next() {
+                Some(TokenTree::Delimited(_, delim, tts)) => {
+                    self.print_mac_common(
+                        Some(MacHeader::Path(&attr.path)), false, None, delim, tts, true, attr.span
+                    );
+                }
+                tree => {
+                    self.print_path(&attr.path, false, 0);
+                    if tree.is_some() {
+                        self.space();
+                        self.print_tts(attr.tokens.clone(), true);
+                    }
+                }
             }
-            self.writer().word("]")
+            self.end();
+            self.word("]");
         }
     }
 
-    fn print_meta_list_item(&mut self, item: &ast::NestedMetaItem) -> io::Result<()> {
+    fn print_meta_list_item(&mut self, item: &ast::NestedMetaItem) {
         match item {
             ast::NestedMetaItem::MetaItem(ref mi) => {
                 self.print_meta_item(mi)
@@ -692,26 +646,26 @@ pub trait PrintState<'a> {
         }
     }
 
-    fn print_meta_item(&mut self, item: &ast::MetaItem) -> io::Result<()> {
-        self.ibox(INDENT_UNIT)?;
+    fn print_meta_item(&mut self, item: &ast::MetaItem) {
+        self.ibox(INDENT_UNIT);
         match item.node {
-            ast::MetaItemKind::Word => self.print_attribute_path(&item.path)?,
+            ast::MetaItemKind::Word => self.print_path(&item.path, false, 0),
             ast::MetaItemKind::NameValue(ref value) => {
-                self.print_attribute_path(&item.path)?;
-                self.writer().space()?;
-                self.word_space("=")?;
-                self.print_literal(value)?;
+                self.print_path(&item.path, false, 0);
+                self.space();
+                self.word_space("=");
+                self.print_literal(value);
             }
             ast::MetaItemKind::List(ref items) => {
-                self.print_attribute_path(&item.path)?;
-                self.popen()?;
+                self.print_path(&item.path, false, 0);
+                self.popen();
                 self.commasep(Consistent,
                               &items[..],
-                              |s, i| s.print_meta_list_item(i))?;
-                self.pclose()?;
+                              |s, i| s.print_meta_list_item(i));
+                self.pclose();
             }
         }
-        self.end()
+        self.end();
     }
 
     /// This doesn't deserve to be called "pretty" printing, but it should be
@@ -721,217 +675,275 @@ pub trait PrintState<'a> {
     /// appropriate macro, transcribe back into the grammar we just parsed from,
     /// and then pretty-print the resulting AST nodes (so, e.g., we print
     /// expression arguments as expressions). It can be done! I think.
-    fn print_tt(&mut self, tt: tokenstream::TokenTree) -> io::Result<()> {
+    fn print_tt(&mut self, tt: tokenstream::TokenTree, convert_dollar_crate: bool) {
         match tt {
-            TokenTree::Token(_, ref tk) => {
-                self.writer().word(token_to_string(tk))?;
-                match *tk {
-                    parse::token::DocComment(..) => {
-                        self.writer().hardbreak()
+            TokenTree::Token(ref token) => {
+                self.word(token_to_string_ext(&token, convert_dollar_crate));
+                match token.kind {
+                    token::DocComment(..) => {
+                        self.hardbreak()
                     }
-                    _ => Ok(())
+                    _ => {}
                 }
             }
-            TokenTree::Delimited(_, delim, tts) => {
-                self.writer().word(token_to_string(&token::OpenDelim(delim)))?;
-                self.writer().space()?;
-                self.print_tts(tts)?;
-                self.writer().space()?;
-                self.writer().word(token_to_string(&token::CloseDelim(delim)))
-            },
+            TokenTree::Delimited(dspan, delim, tts) => {
+                self.print_mac_common(
+                    None, false, None, delim, tts, convert_dollar_crate, dspan.entire()
+                );
+            }
         }
     }
 
-    fn print_tts(&mut self, tts: tokenstream::TokenStream) -> io::Result<()> {
-        self.ibox(0)?;
+    fn print_tts(&mut self, tts: tokenstream::TokenStream, convert_dollar_crate: bool) {
         for (i, tt) in tts.into_trees().enumerate() {
             if i != 0 {
-                self.writer().space()?;
+                self.space();
             }
-            self.print_tt(tt)?;
+            self.print_tt(tt, convert_dollar_crate);
         }
-        self.end()
-    }
-
-    fn space_if_not_bol(&mut self) -> io::Result<()> {
-        if !self.is_bol() { self.writer().space()?; }
-        Ok(())
     }
 
-    fn nbsp(&mut self) -> io::Result<()> { self.writer().word(" ") }
-
-    // AST pretty-printer is used as a fallback for turning AST structures into token streams for
-    // proc macros. Additionally, proc macros may stringify their input and expect it survive the
-    // stringification (especially true for proc macro derives written between Rust 1.15 and 1.30).
-    // So we need to somehow pretty-print `$crate` in paths in a way preserving at least some of
-    // its hygiene data, most importantly name of the crate it refers to.
-    // As a result we print `$crate` as `crate` if it refers to the local crate
-    // and as `::other_crate_name` if it refers to some other crate.
-    fn print_dollar_crate(&mut self, ident: ast::Ident) -> io::Result<()> {
-        let name = ident.span.ctxt().dollar_crate_name();
-        if !ast::Ident::with_empty_ctxt(name).is_path_segment_keyword() {
-            self.writer().word("::")?;
+    fn print_mac_common(
+        &mut self,
+        header: Option<MacHeader<'_>>,
+        has_bang: bool,
+        ident: Option<ast::Ident>,
+        delim: DelimToken,
+        tts: TokenStream,
+        convert_dollar_crate: bool,
+        span: Span,
+    ) {
+        if delim == DelimToken::Brace {
+            self.cbox(INDENT_UNIT);
+        }
+        match header {
+            Some(MacHeader::Path(path)) => self.print_path(path, false, 0),
+            Some(MacHeader::Keyword(kw)) => self.word(kw),
+            None => {}
+        }
+        if has_bang {
+            self.word("!");
+        }
+        if let Some(ident) = ident {
+            self.nbsp();
+            self.print_ident(ident);
+        }
+        match delim {
+            DelimToken::Brace => {
+                if header.is_some() || has_bang || ident.is_some() {
+                    self.nbsp();
+                }
+                self.word("{");
+                if !tts.is_empty() {
+                    self.space();
+                }
+            }
+            _ => self.word(token_kind_to_string(&token::OpenDelim(delim))),
+        }
+        self.ibox(0);
+        self.print_tts(tts, convert_dollar_crate);
+        self.end();
+        match delim {
+            DelimToken::Brace => self.bclose(span),
+            _ => self.word(token_kind_to_string(&token::CloseDelim(delim))),
         }
-        self.writer().word(name.as_str().to_string())
-    }
-}
-
-impl<'a> PrintState<'a> for State<'a> {
-    fn writer(&mut self) -> &mut pp::Printer<'a> {
-        &mut self.s
-    }
-
-    fn boxes(&mut self) -> &mut Vec<pp::Breaks> {
-        &mut self.boxes
-    }
-
-    fn comments(&mut self) -> &mut Option<Vec<comments::Comment>> {
-        &mut self.comments
     }
 
-    fn cur_cmnt(&mut self) -> &mut usize {
-        &mut self.cur_cmnt
-    }
-}
+    fn print_path(&mut self, path: &ast::Path, colons_before_params: bool, depth: usize) {
+        self.maybe_print_comment(path.span.lo());
 
-impl<'a> State<'a> {
-    pub fn cbox(&mut self, u: usize) -> io::Result<()> {
-        self.boxes.push(pp::Breaks::Consistent);
-        self.s.cbox(u)
+        for (i, segment) in path.segments[..path.segments.len() - depth].iter().enumerate() {
+            if i > 0 {
+                self.word("::")
+            }
+            self.print_path_segment(segment, colons_before_params);
+        }
     }
 
-    pub fn word_nbsp<S: Into<Cow<'static, str>>>(&mut self, w: S) -> io::Result<()> {
-        self.s.word(w)?;
-        self.nbsp()
+    fn print_path_segment(&mut self, segment: &ast::PathSegment, colons_before_params: bool) {
+        if segment.ident.name != kw::PathRoot {
+            self.print_ident(segment.ident);
+            if let Some(ref args) = segment.args {
+                self.print_generic_args(args, colons_before_params);
+            }
+        }
     }
 
-    pub fn head<S: Into<Cow<'static, str>>>(&mut self, w: S) -> io::Result<()> {
+    fn head<S: Into<Cow<'static, str>>>(&mut self, w: S) {
         let w = w.into();
         // outer-box is consistent
-        self.cbox(INDENT_UNIT)?;
+        self.cbox(INDENT_UNIT);
         // head-box is inconsistent
-        self.ibox(w.len() + 1)?;
+        self.ibox(w.len() + 1);
         // keyword that starts the head
         if !w.is_empty() {
-            self.word_nbsp(w)?;
+            self.word_nbsp(w);
         }
-        Ok(())
     }
 
-    pub fn bopen(&mut self) -> io::Result<()> {
-        self.s.word("{")?;
-        self.end() // close the head-box
+    fn bopen(&mut self) {
+        self.word("{");
+        self.end(); // close the head-box
     }
 
-    pub fn bclose_(&mut self, span: syntax_pos::Span,
-                   indented: usize) -> io::Result<()> {
-        self.bclose_maybe_open(span, indented, true)
-    }
-    pub fn bclose_maybe_open(&mut self, span: syntax_pos::Span,
-                             indented: usize, close_box: bool) -> io::Result<()> {
-        self.maybe_print_comment(span.hi())?;
-        self.break_offset_if_not_bol(1, -(indented as isize))?;
-        self.s.word("}")?;
+    fn bclose_maybe_open(&mut self, span: syntax_pos::Span, close_box: bool) {
+        self.maybe_print_comment(span.hi());
+        self.break_offset_if_not_bol(1, -(INDENT_UNIT as isize));
+        self.word("}");
         if close_box {
-            self.end()?; // close the outer-box
+            self.end(); // close the outer-box
         }
-        Ok(())
-    }
-    pub fn bclose(&mut self, span: syntax_pos::Span) -> io::Result<()> {
-        self.bclose_(span, INDENT_UNIT)
     }
 
-    pub fn in_cbox(&self) -> bool {
-        match self.boxes.last() {
-            Some(&last_box) => last_box == pp::Breaks::Consistent,
-            None => false
-        }
+    fn bclose(&mut self, span: syntax_pos::Span) {
+        self.bclose_maybe_open(span, true)
     }
 
-    pub fn break_offset_if_not_bol(&mut self, n: usize,
-                                   off: isize) -> io::Result<()> {
-        if !self.is_bol() {
-            self.s.break_offset(n, off)
+    fn break_offset_if_not_bol(&mut self, n: usize, off: isize) {
+        if !self.is_beginning_of_line() {
+            self.break_offset(n, off)
         } else {
-            if off != 0 && self.s.last_token().is_hardbreak_tok() {
+            if off != 0 && self.last_token().is_hardbreak_tok() {
                 // We do something pretty sketchy here: tuck the nonzero
                 // offset-adjustment we were going to deposit along with the
                 // break into the previous hardbreak.
-                self.s.replace_last_token(pp::Printer::hardbreak_tok_offset(off));
+                self.replace_last_token(pp::Printer::hardbreak_tok_offset(off));
             }
-            Ok(())
         }
     }
+}
+
+impl<'a> PrintState<'a> for State<'a> {
+    fn comments(&mut self) -> &mut Option<Comments<'a>> {
+        &mut self.comments
+    }
 
+    fn print_ident(&mut self, ident: ast::Ident) {
+        self.s.word(ast_ident_to_string(ident, ident.is_raw_guess()));
+        self.ann.post(self, AnnNode::Ident(&ident))
+    }
+
+    fn print_generic_args(&mut self, args: &ast::GenericArgs, colons_before_params: bool) {
+        if colons_before_params {
+            self.s.word("::")
+        }
+
+        match *args {
+            ast::GenericArgs::AngleBracketed(ref data) => {
+                self.s.word("<");
+
+                self.commasep(Inconsistent, &data.args, |s, generic_arg| {
+                    s.print_generic_arg(generic_arg)
+                });
+
+                let mut comma = data.args.len() != 0;
+
+                for constraint in data.constraints.iter() {
+                    if comma {
+                        self.word_space(",")
+                    }
+                    self.print_ident(constraint.ident);
+                    self.s.space();
+                    match constraint.kind {
+                        ast::AssocTyConstraintKind::Equality { ref ty } => {
+                            self.word_space("=");
+                            self.print_type(ty);
+                        }
+                        ast::AssocTyConstraintKind::Bound { ref bounds } => {
+                            self.print_type_bounds(":", &*bounds);
+                        }
+                    }
+                    comma = true;
+                }
+
+                self.s.word(">")
+            }
+
+            ast::GenericArgs::Parenthesized(ref data) => {
+                self.s.word("(");
+                self.commasep(
+                    Inconsistent,
+                    &data.inputs,
+                    |s, ty| s.print_type(ty));
+                self.s.word(")");
+
+                if let Some(ref ty) = data.output {
+                    self.space_if_not_bol();
+                    self.word_space("->");
+                    self.print_type(ty);
+                }
+            }
+        }
+    }
+}
+
+impl<'a> State<'a> {
     // Synthesizes a comment that was not textually present in the original source
     // file.
-    pub fn synth_comment(&mut self, text: String) -> io::Result<()> {
-        self.s.word("/*")?;
-        self.s.space()?;
-        self.s.word(text)?;
-        self.s.space()?;
+    pub fn synth_comment(&mut self, text: String) {
+        self.s.word("/*");
+        self.s.space();
+        self.s.word(text);
+        self.s.space();
         self.s.word("*/")
     }
 
 
 
-    pub fn commasep_cmnt<T, F, G>(&mut self,
+    crate fn commasep_cmnt<T, F, G>(&mut self,
                                   b: Breaks,
                                   elts: &[T],
                                   mut op: F,
-                                  mut get_span: G) -> io::Result<()> where
-        F: FnMut(&mut State<'_>, &T) -> io::Result<()>,
+                                  mut get_span: G) where
+        F: FnMut(&mut State<'_>, &T),
         G: FnMut(&T) -> syntax_pos::Span,
     {
-        self.rbox(0, b)?;
+        self.rbox(0, b);
         let len = elts.len();
         let mut i = 0;
         for elt in elts {
-            self.maybe_print_comment(get_span(elt).hi())?;
-            op(self, elt)?;
+            self.maybe_print_comment(get_span(elt).hi());
+            op(self, elt);
             i += 1;
             if i < len {
-                self.s.word(",")?;
+                self.s.word(",");
                 self.maybe_print_trailing_comment(get_span(elt),
-                                                  Some(get_span(&elts[i]).hi()))?;
-                self.space_if_not_bol()?;
+                                                  Some(get_span(&elts[i]).hi()));
+                self.space_if_not_bol();
             }
         }
-        self.end()
+        self.end();
     }
 
-    pub fn commasep_exprs(&mut self, b: Breaks,
-                          exprs: &[P<ast::Expr>]) -> io::Result<()> {
+    crate fn commasep_exprs(&mut self, b: Breaks,
+                          exprs: &[P<ast::Expr>]) {
         self.commasep_cmnt(b, exprs, |s, e| s.print_expr(e), |e| e.span)
     }
 
-    pub fn print_mod(&mut self, _mod: &ast::Mod,
-                     attrs: &[ast::Attribute]) -> io::Result<()> {
-        self.print_inner_attributes(attrs)?;
+    crate fn print_mod(&mut self, _mod: &ast::Mod,
+                     attrs: &[ast::Attribute]) {
+        self.print_inner_attributes(attrs);
         for item in &_mod.items {
-            self.print_item(item)?;
+            self.print_item(item);
         }
-        Ok(())
     }
 
-    pub fn print_foreign_mod(&mut self, nmod: &ast::ForeignMod,
-                             attrs: &[ast::Attribute]) -> io::Result<()> {
-        self.print_inner_attributes(attrs)?;
+    crate fn print_foreign_mod(&mut self, nmod: &ast::ForeignMod,
+                             attrs: &[ast::Attribute]) {
+        self.print_inner_attributes(attrs);
         for item in &nmod.items {
-            self.print_foreign_item(item)?;
+            self.print_foreign_item(item);
         }
-        Ok(())
     }
 
-    pub fn print_opt_lifetime(&mut self, lifetime: &Option<ast::Lifetime>) -> io::Result<()> {
+    crate fn print_opt_lifetime(&mut self, lifetime: &Option<ast::Lifetime>) {
         if let Some(lt) = *lifetime {
-            self.print_lifetime(lt)?;
-            self.nbsp()?;
+            self.print_lifetime(lt);
+            self.nbsp();
         }
-        Ok(())
     }
 
-    pub fn print_generic_arg(&mut self, generic_arg: &GenericArg) -> io::Result<()> {
+    crate fn print_generic_arg(&mut self, generic_arg: &GenericArg) {
         match generic_arg {
             GenericArg::Lifetime(lt) => self.print_lifetime(*lt),
             GenericArg::Type(ty) => self.print_type(ty),
@@ -939,136 +951,136 @@ impl<'a> State<'a> {
         }
     }
 
-    pub fn print_type(&mut self, ty: &ast::Ty) -> io::Result<()> {
-        self.maybe_print_comment(ty.span.lo())?;
-        self.ibox(0)?;
+    crate fn print_type(&mut self, ty: &ast::Ty) {
+        self.maybe_print_comment(ty.span.lo());
+        self.ibox(0);
         match ty.node {
             ast::TyKind::Slice(ref ty) => {
-                self.s.word("[")?;
-                self.print_type(ty)?;
-                self.s.word("]")?;
+                self.s.word("[");
+                self.print_type(ty);
+                self.s.word("]");
             }
             ast::TyKind::Ptr(ref mt) => {
-                self.s.word("*")?;
+                self.s.word("*");
                 match mt.mutbl {
-                    ast::Mutability::Mutable => self.word_nbsp("mut")?,
-                    ast::Mutability::Immutable => self.word_nbsp("const")?,
+                    ast::Mutability::Mutable => self.word_nbsp("mut"),
+                    ast::Mutability::Immutable => self.word_nbsp("const"),
                 }
-                self.print_type(&mt.ty)?;
+                self.print_type(&mt.ty);
             }
             ast::TyKind::Rptr(ref lifetime, ref mt) => {
-                self.s.word("&")?;
-                self.print_opt_lifetime(lifetime)?;
-                self.print_mt(mt)?;
+                self.s.word("&");
+                self.print_opt_lifetime(lifetime);
+                self.print_mt(mt);
             }
             ast::TyKind::Never => {
-                self.s.word("!")?;
+                self.s.word("!");
             },
             ast::TyKind::Tup(ref elts) => {
-                self.popen()?;
+                self.popen();
                 self.commasep(Inconsistent, &elts[..],
-                              |s, ty| s.print_type(ty))?;
+                              |s, ty| s.print_type(ty));
                 if elts.len() == 1 {
-                    self.s.word(",")?;
+                    self.s.word(",");
                 }
-                self.pclose()?;
+                self.pclose();
             }
             ast::TyKind::Paren(ref typ) => {
-                self.popen()?;
-                self.print_type(typ)?;
-                self.pclose()?;
+                self.popen();
+                self.print_type(typ);
+                self.pclose();
             }
             ast::TyKind::BareFn(ref f) => {
                 self.print_ty_fn(f.abi,
                                  f.unsafety,
                                  &f.decl,
                                  None,
-                                 &f.generic_params)?;
+                                 &f.generic_params);
             }
             ast::TyKind::Path(None, ref path) => {
-                self.print_path(path, false, 0)?;
+                self.print_path(path, false, 0);
             }
             ast::TyKind::Path(Some(ref qself), ref path) => {
-                self.print_qpath(path, qself, false)?
+                self.print_qpath(path, qself, false)
             }
             ast::TyKind::TraitObject(ref bounds, syntax) => {
                 let prefix = if syntax == ast::TraitObjectSyntax::Dyn { "dyn" } else { "" };
-                self.print_type_bounds(prefix, &bounds[..])?;
+                self.print_type_bounds(prefix, &bounds[..]);
             }
             ast::TyKind::ImplTrait(_, ref bounds) => {
-                self.print_type_bounds("impl", &bounds[..])?;
+                self.print_type_bounds("impl", &bounds[..]);
             }
             ast::TyKind::Array(ref ty, ref length) => {
-                self.s.word("[")?;
-                self.print_type(ty)?;
-                self.s.word("; ")?;
-                self.print_expr(&length.value)?;
-                self.s.word("]")?;
+                self.s.word("[");
+                self.print_type(ty);
+                self.s.word("; ");
+                self.print_expr(&length.value);
+                self.s.word("]");
             }
             ast::TyKind::Typeof(ref e) => {
-                self.s.word("typeof(")?;
-                self.print_expr(&e.value)?;
-                self.s.word(")")?;
+                self.s.word("typeof(");
+                self.print_expr(&e.value);
+                self.s.word(")");
             }
             ast::TyKind::Infer => {
-                self.s.word("_")?;
+                self.s.word("_");
             }
             ast::TyKind::Err => {
-                self.popen()?;
-                self.s.word("/*ERROR*/")?;
-                self.pclose()?;
+                self.popen();
+                self.s.word("/*ERROR*/");
+                self.pclose();
             }
             ast::TyKind::ImplicitSelf => {
-                self.s.word("Self")?;
+                self.s.word("Self");
             }
             ast::TyKind::Mac(ref m) => {
-                self.print_mac(m)?;
+                self.print_mac(m);
             }
             ast::TyKind::CVarArgs => {
-                self.s.word("...")?;
+                self.s.word("...");
             }
         }
-        self.end()
+        self.end();
     }
 
-    pub fn print_foreign_item(&mut self,
-                              item: &ast::ForeignItem) -> io::Result<()> {
-        self.hardbreak_if_not_bol()?;
-        self.maybe_print_comment(item.span.lo())?;
-        self.print_outer_attributes(&item.attrs)?;
+    crate fn print_foreign_item(&mut self,
+                              item: &ast::ForeignItem) {
+        self.hardbreak_if_not_bol();
+        self.maybe_print_comment(item.span.lo());
+        self.print_outer_attributes(&item.attrs);
         match item.node {
             ast::ForeignItemKind::Fn(ref decl, ref generics) => {
-                self.head("")?;
-                self.print_fn(decl, &ast::FnHeader::default(),
+                self.head("");
+                self.print_fn(decl, ast::FnHeader::default(),
                               Some(item.ident),
-                              generics, &item.vis)?;
-                self.end()?; // end head-ibox
-                self.s.word(";")?;
-                self.end() // end the outer fn box
+                              generics, &item.vis);
+                self.end(); // end head-ibox
+                self.s.word(";");
+                self.end(); // end the outer fn box
             }
             ast::ForeignItemKind::Static(ref t, m) => {
-                self.head(visibility_qualified(&item.vis, "static"))?;
+                self.head(visibility_qualified(&item.vis, "static"));
                 if m == ast::Mutability::Mutable {
-                    self.word_space("mut")?;
+                    self.word_space("mut");
                 }
-                self.print_ident(item.ident)?;
-                self.word_space(":")?;
-                self.print_type(t)?;
-                self.s.word(";")?;
-                self.end()?; // end the head-ibox
-                self.end() // end the outer cbox
+                self.print_ident(item.ident);
+                self.word_space(":");
+                self.print_type(t);
+                self.s.word(";");
+                self.end(); // end the head-ibox
+                self.end(); // end the outer cbox
             }
             ast::ForeignItemKind::Ty => {
-                self.head(visibility_qualified(&item.vis, "type"))?;
-                self.print_ident(item.ident)?;
-                self.s.word(";")?;
-                self.end()?; // end the head-ibox
-                self.end() // end the outer cbox
+                self.head(visibility_qualified(&item.vis, "type"));
+                self.print_ident(item.ident);
+                self.s.word(";");
+                self.end(); // end the head-ibox
+                self.end(); // end the outer cbox
             }
             ast::ForeignItemKind::Macro(ref m) => {
-                self.print_mac(m)?;
-                match m.node.delim {
-                    MacDelimiter::Brace => Ok(()),
+                self.print_mac(m);
+                match m.delim {
+                    MacDelimiter::Brace => {},
                     _ => self.s.word(";")
                 }
             }
@@ -1080,17 +1092,16 @@ impl<'a> State<'a> {
                               ty: &ast::Ty,
                               default: Option<&ast::Expr>,
                               vis: &ast::Visibility)
-                              -> io::Result<()>
     {
-        self.s.word(visibility_qualified(vis, ""))?;
-        self.word_space("const")?;
-        self.print_ident(ident)?;
-        self.word_space(":")?;
-        self.print_type(ty)?;
+        self.s.word(visibility_qualified(vis, ""));
+        self.word_space("const");
+        self.print_ident(ident);
+        self.word_space(":");
+        self.print_type(ty);
         if let Some(expr) = default {
-            self.s.space()?;
-            self.word_space("=")?;
-            self.print_expr(expr)?;
+            self.s.space();
+            self.word_space("=");
+            self.print_expr(expr);
         }
         self.s.word(";")
     }
@@ -1099,140 +1110,141 @@ impl<'a> State<'a> {
                              ident: ast::Ident,
                              bounds: Option<&ast::GenericBounds>,
                              ty: Option<&ast::Ty>)
-                             -> io::Result<()> {
-        self.word_space("type")?;
-        self.print_ident(ident)?;
+                             {
+        self.word_space("type");
+        self.print_ident(ident);
         if let Some(bounds) = bounds {
-            self.print_type_bounds(":", bounds)?;
+            self.print_type_bounds(":", bounds);
         }
         if let Some(ty) = ty {
-            self.s.space()?;
-            self.word_space("=")?;
-            self.print_type(ty)?;
+            self.s.space();
+            self.word_space("=");
+            self.print_type(ty);
         }
         self.s.word(";")
     }
 
     /// Pretty-print an item
-    pub fn print_item(&mut self, item: &ast::Item) -> io::Result<()> {
-        self.hardbreak_if_not_bol()?;
-        self.maybe_print_comment(item.span.lo())?;
-        self.print_outer_attributes(&item.attrs)?;
-        self.ann.pre(self, AnnNode::Item(item))?;
+    crate fn print_item(&mut self, item: &ast::Item) {
+        self.hardbreak_if_not_bol();
+        self.maybe_print_comment(item.span.lo());
+        self.print_outer_attributes(&item.attrs);
+        self.ann.pre(self, AnnNode::Item(item));
         match item.node {
             ast::ItemKind::ExternCrate(orig_name) => {
-                self.head(visibility_qualified(&item.vis, "extern crate"))?;
+                self.head(visibility_qualified(&item.vis, "extern crate"));
                 if let Some(orig_name) = orig_name {
-                    self.print_name(orig_name)?;
-                    self.s.space()?;
-                    self.s.word("as")?;
-                    self.s.space()?;
+                    self.print_name(orig_name);
+                    self.s.space();
+                    self.s.word("as");
+                    self.s.space();
                 }
-                self.print_ident(item.ident)?;
-                self.s.word(";")?;
-                self.end()?; // end inner head-block
-                self.end()?; // end outer head-block
+                self.print_ident(item.ident);
+                self.s.word(";");
+                self.end(); // end inner head-block
+                self.end(); // end outer head-block
             }
             ast::ItemKind::Use(ref tree) => {
-                self.head(visibility_qualified(&item.vis, "use"))?;
-                self.print_use_tree(tree)?;
-                self.s.word(";")?;
-                self.end()?; // end inner head-block
-                self.end()?; // end outer head-block
+                self.head(visibility_qualified(&item.vis, "use"));
+                self.print_use_tree(tree);
+                self.s.word(";");
+                self.end(); // end inner head-block
+                self.end(); // end outer head-block
             }
             ast::ItemKind::Static(ref ty, m, ref expr) => {
-                self.head(visibility_qualified(&item.vis, "static"))?;
+                self.head(visibility_qualified(&item.vis, "static"));
                 if m == ast::Mutability::Mutable {
-                    self.word_space("mut")?;
+                    self.word_space("mut");
                 }
-                self.print_ident(item.ident)?;
-                self.word_space(":")?;
-                self.print_type(ty)?;
-                self.s.space()?;
-                self.end()?; // end the head-ibox
+                self.print_ident(item.ident);
+                self.word_space(":");
+                self.print_type(ty);
+                self.s.space();
+                self.end(); // end the head-ibox
 
-                self.word_space("=")?;
-                self.print_expr(expr)?;
-                self.s.word(";")?;
-                self.end()?; // end the outer cbox
+                self.word_space("=");
+                self.print_expr(expr);
+                self.s.word(";");
+                self.end(); // end the outer cbox
             }
             ast::ItemKind::Const(ref ty, ref expr) => {
-                self.head(visibility_qualified(&item.vis, "const"))?;
-                self.print_ident(item.ident)?;
-                self.word_space(":")?;
-                self.print_type(ty)?;
-                self.s.space()?;
-                self.end()?; // end the head-ibox
-
-                self.word_space("=")?;
-                self.print_expr(expr)?;
-                self.s.word(";")?;
-                self.end()?; // end the outer cbox
-            }
-            ast::ItemKind::Fn(ref decl, ref header, ref param_names, ref body) => {
-                self.head("")?;
+                self.head(visibility_qualified(&item.vis, "const"));
+                self.print_ident(item.ident);
+                self.word_space(":");
+                self.print_type(ty);
+                self.s.space();
+                self.end(); // end the head-ibox
+
+                self.word_space("=");
+                self.print_expr(expr);
+                self.s.word(";");
+                self.end(); // end the outer cbox
+            }
+            ast::ItemKind::Fn(ref decl, header, ref param_names, ref body) => {
+                self.head("");
                 self.print_fn(
                     decl,
                     header,
                     Some(item.ident),
                     param_names,
                     &item.vis
-                )?;
-                self.s.word(" ")?;
-                self.print_block_with_attrs(body, &item.attrs)?;
+                );
+                self.s.word(" ");
+                self.print_block_with_attrs(body, &item.attrs);
             }
             ast::ItemKind::Mod(ref _mod) => {
-                self.head(visibility_qualified(&item.vis, "mod"))?;
-                self.print_ident(item.ident)?;
+                self.head(visibility_qualified(&item.vis, "mod"));
+                self.print_ident(item.ident);
 
                 if _mod.inline || self.is_expanded {
-                    self.nbsp()?;
-                    self.bopen()?;
-                    self.print_mod(_mod, &item.attrs)?;
-                    self.bclose(item.span)?;
+                    self.nbsp();
+                    self.bopen();
+                    self.print_mod(_mod, &item.attrs);
+                    self.bclose(item.span);
                 } else {
-                    self.s.word(";")?;
-                    self.end()?; // end inner head-block
-                    self.end()?; // end outer head-block
+                    self.s.word(";");
+                    self.end(); // end inner head-block
+                    self.end(); // end outer head-block
                 }
 
             }
             ast::ItemKind::ForeignMod(ref nmod) => {
-                self.head("extern")?;
-                self.word_nbsp(nmod.abi.to_string())?;
-                self.bopen()?;
-                self.print_foreign_mod(nmod, &item.attrs)?;
-                self.bclose(item.span)?;
+                self.head("extern");
+                self.word_nbsp(nmod.abi.to_string());
+                self.bopen();
+                self.print_foreign_mod(nmod, &item.attrs);
+                self.bclose(item.span);
             }
             ast::ItemKind::GlobalAsm(ref ga) => {
-                self.head(visibility_qualified(&item.vis, "global_asm!"))?;
-                self.s.word(ga.asm.as_str().to_string())?;
-                self.end()?;
-            }
-            ast::ItemKind::Ty(ref ty, ref generics) => {
-                self.head(visibility_qualified(&item.vis, "type"))?;
-                self.print_ident(item.ident)?;
-                self.print_generic_params(&generics.params)?;
-                self.end()?; // end the inner ibox
-
-                self.print_where_clause(&generics.where_clause)?;
-                self.s.space()?;
-                self.word_space("=")?;
-                self.print_type(ty)?;
-                self.s.word(";")?;
-                self.end()?; // end the outer ibox
-            }
-            ast::ItemKind::Existential(ref bounds, ref generics) => {
-                self.head(visibility_qualified(&item.vis, "existential type"))?;
-                self.print_ident(item.ident)?;
-                self.print_generic_params(&generics.params)?;
-                self.end()?; // end the inner ibox
-
-                self.print_where_clause(&generics.where_clause)?;
-                self.s.space()?;
-                self.print_type_bounds(":", bounds)?;
-                self.s.word(";")?;
-                self.end()?; // end the outer ibox
+                self.head(visibility_qualified(&item.vis, "global_asm!"));
+                self.s.word(ga.asm.as_str().to_string());
+                self.end();
+            }
+            ast::ItemKind::TyAlias(ref ty, ref generics) => {
+                self.head(visibility_qualified(&item.vis, "type"));
+                self.print_ident(item.ident);
+                self.print_generic_params(&generics.params);
+                self.end(); // end the inner ibox
+
+                self.print_where_clause(&generics.where_clause);
+                self.s.space();
+                self.word_space("=");
+                self.print_type(ty);
+                self.s.word(";");
+                self.end(); // end the outer ibox
+            }
+            ast::ItemKind::OpaqueTy(ref bounds, ref generics) => {
+                self.head(visibility_qualified(&item.vis, "type"));
+                self.print_ident(item.ident);
+                self.word_space("= impl");
+                self.print_generic_params(&generics.params);
+                self.end(); // end the inner ibox
+
+                self.print_where_clause(&generics.where_clause);
+                self.s.space();
+                self.print_type_bounds(":", bounds);
+                self.s.word(";");
+                self.end(); // end the outer ibox
             }
             ast::ItemKind::Enum(ref enum_definition, ref params) => {
                 self.print_enum_def(
@@ -1241,15 +1253,15 @@ impl<'a> State<'a> {
                     item.ident,
                     item.span,
                     &item.vis
-                )?;
+                );
             }
             ast::ItemKind::Struct(ref struct_def, ref generics) => {
-                self.head(visibility_qualified(&item.vis, "struct"))?;
-                self.print_struct(struct_def, generics, item.ident, item.span, true)?;
+                self.head(visibility_qualified(&item.vis, "struct"));
+                self.print_struct(struct_def, generics, item.ident, item.span, true);
             }
             ast::ItemKind::Union(ref struct_def, ref generics) => {
-                self.head(visibility_qualified(&item.vis, "union"))?;
-                self.print_struct(struct_def, generics, item.ident, item.span, true)?;
+                self.head(visibility_qualified(&item.vis, "union"));
+                self.print_struct(struct_def, generics, item.ident, item.span, true);
             }
             ast::ItemKind::Impl(unsafety,
                           polarity,
@@ -1258,171 +1270,161 @@ impl<'a> State<'a> {
                           ref opt_trait,
                           ref ty,
                           ref impl_items) => {
-                self.head("")?;
-                self.print_visibility(&item.vis)?;
-                self.print_defaultness(defaultness)?;
-                self.print_unsafety(unsafety)?;
-                self.word_nbsp("impl")?;
+                self.head("");
+                self.print_visibility(&item.vis);
+                self.print_defaultness(defaultness);
+                self.print_unsafety(unsafety);
+                self.word_nbsp("impl");
 
                 if !generics.params.is_empty() {
-                    self.print_generic_params(&generics.params)?;
-                    self.s.space()?;
+                    self.print_generic_params(&generics.params);
+                    self.s.space();
                 }
 
                 if polarity == ast::ImplPolarity::Negative {
-                    self.s.word("!")?;
+                    self.s.word("!");
                 }
 
                 if let Some(ref t) = *opt_trait {
-                    self.print_trait_ref(t)?;
-                    self.s.space()?;
-                    self.word_space("for")?;
+                    self.print_trait_ref(t);
+                    self.s.space();
+                    self.word_space("for");
                 }
 
-                self.print_type(ty)?;
-                self.print_where_clause(&generics.where_clause)?;
+                self.print_type(ty);
+                self.print_where_clause(&generics.where_clause);
 
-                self.s.space()?;
-                self.bopen()?;
-                self.print_inner_attributes(&item.attrs)?;
+                self.s.space();
+                self.bopen();
+                self.print_inner_attributes(&item.attrs);
                 for impl_item in impl_items {
-                    self.print_impl_item(impl_item)?;
+                    self.print_impl_item(impl_item);
                 }
-                self.bclose(item.span)?;
+                self.bclose(item.span);
             }
             ast::ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, ref trait_items) => {
-                self.head("")?;
-                self.print_visibility(&item.vis)?;
-                self.print_unsafety(unsafety)?;
-                self.print_is_auto(is_auto)?;
-                self.word_nbsp("trait")?;
-                self.print_ident(item.ident)?;
-                self.print_generic_params(&generics.params)?;
+                self.head("");
+                self.print_visibility(&item.vis);
+                self.print_unsafety(unsafety);
+                self.print_is_auto(is_auto);
+                self.word_nbsp("trait");
+                self.print_ident(item.ident);
+                self.print_generic_params(&generics.params);
                 let mut real_bounds = Vec::with_capacity(bounds.len());
                 for b in bounds.iter() {
                     if let GenericBound::Trait(ref ptr, ast::TraitBoundModifier::Maybe) = *b {
-                        self.s.space()?;
-                        self.word_space("for ?")?;
-                        self.print_trait_ref(&ptr.trait_ref)?;
+                        self.s.space();
+                        self.word_space("for ?");
+                        self.print_trait_ref(&ptr.trait_ref);
                     } else {
                         real_bounds.push(b.clone());
                     }
                 }
-                self.print_type_bounds(":", &real_bounds[..])?;
-                self.print_where_clause(&generics.where_clause)?;
-                self.s.word(" ")?;
-                self.bopen()?;
+                self.print_type_bounds(":", &real_bounds[..]);
+                self.print_where_clause(&generics.where_clause);
+                self.s.word(" ");
+                self.bopen();
                 for trait_item in trait_items {
-                    self.print_trait_item(trait_item)?;
+                    self.print_trait_item(trait_item);
                 }
-                self.bclose(item.span)?;
+                self.bclose(item.span);
             }
             ast::ItemKind::TraitAlias(ref generics, ref bounds) => {
-                self.head("")?;
-                self.print_visibility(&item.vis)?;
-                self.word_nbsp("trait")?;
-                self.print_ident(item.ident)?;
-                self.print_generic_params(&generics.params)?;
+                self.head("");
+                self.print_visibility(&item.vis);
+                self.word_nbsp("trait");
+                self.print_ident(item.ident);
+                self.print_generic_params(&generics.params);
                 let mut real_bounds = Vec::with_capacity(bounds.len());
                 // FIXME(durka) this seems to be some quite outdated syntax
                 for b in bounds.iter() {
                     if let GenericBound::Trait(ref ptr, ast::TraitBoundModifier::Maybe) = *b {
-                        self.s.space()?;
-                        self.word_space("for ?")?;
-                        self.print_trait_ref(&ptr.trait_ref)?;
+                        self.s.space();
+                        self.word_space("for ?");
+                        self.print_trait_ref(&ptr.trait_ref);
                     } else {
                         real_bounds.push(b.clone());
                     }
                 }
-                self.nbsp()?;
-                self.print_type_bounds("=", &real_bounds[..])?;
-                self.print_where_clause(&generics.where_clause)?;
-                self.s.word(";")?;
+                self.nbsp();
+                self.print_type_bounds("=", &real_bounds[..]);
+                self.print_where_clause(&generics.where_clause);
+                self.s.word(";");
             }
             ast::ItemKind::Mac(ref mac) => {
-                if item.ident.name == keywords::Invalid.name() {
-                    self.print_mac(mac)?;
-                    match mac.node.delim {
-                        MacDelimiter::Brace => {}
-                        _ => self.s.word(";")?,
-                    }
-                } else {
-                    self.print_path(&mac.node.path, false, 0)?;
-                    self.s.word("! ")?;
-                    self.print_ident(item.ident)?;
-                    self.cbox(INDENT_UNIT)?;
-                    self.popen()?;
-                    self.print_tts(mac.node.stream())?;
-                    self.pclose()?;
-                    self.s.word(";")?;
-                    self.end()?;
-                }
-            }
-            ast::ItemKind::MacroDef(ref tts) => {
-                self.s.word("macro_rules! ")?;
-                self.print_ident(item.ident)?;
-                self.cbox(INDENT_UNIT)?;
-                self.popen()?;
-                self.print_tts(tts.stream())?;
-                self.pclose()?;
-                self.s.word(";")?;
-                self.end()?;
+                self.print_mac(mac);
+                match mac.delim {
+                    MacDelimiter::Brace => {}
+                    _ => self.s.word(";"),
+                }
+            }
+            ast::ItemKind::MacroDef(ref macro_def) => {
+                let (kw, has_bang) =
+                    if macro_def.legacy { ("macro_rules", true) } else { ("macro", false) };
+                self.print_mac_common(
+                    Some(MacHeader::Keyword(kw)),
+                    has_bang,
+                    Some(item.ident),
+                    DelimToken::Brace,
+                    macro_def.stream(),
+                    true,
+                    item.span,
+                );
             }
         }
         self.ann.post(self, AnnNode::Item(item))
     }
 
-    fn print_trait_ref(&mut self, t: &ast::TraitRef) -> io::Result<()> {
+    fn print_trait_ref(&mut self, t: &ast::TraitRef) {
         self.print_path(&t.path, false, 0)
     }
 
     fn print_formal_generic_params(
         &mut self,
         generic_params: &[ast::GenericParam]
-    ) -> io::Result<()> {
+    ) {
         if !generic_params.is_empty() {
-            self.s.word("for")?;
-            self.print_generic_params(generic_params)?;
-            self.nbsp()?;
+            self.s.word("for");
+            self.print_generic_params(generic_params);
+            self.nbsp();
         }
-        Ok(())
     }
 
-    fn print_poly_trait_ref(&mut self, t: &ast::PolyTraitRef) -> io::Result<()> {
-        self.print_formal_generic_params(&t.bound_generic_params)?;
+    fn print_poly_trait_ref(&mut self, t: &ast::PolyTraitRef) {
+        self.print_formal_generic_params(&t.bound_generic_params);
         self.print_trait_ref(&t.trait_ref)
     }
 
-    pub fn print_enum_def(&mut self, enum_definition: &ast::EnumDef,
+    crate fn print_enum_def(&mut self, enum_definition: &ast::EnumDef,
                           generics: &ast::Generics, ident: ast::Ident,
                           span: syntax_pos::Span,
-                          visibility: &ast::Visibility) -> io::Result<()> {
-        self.head(visibility_qualified(visibility, "enum"))?;
-        self.print_ident(ident)?;
-        self.print_generic_params(&generics.params)?;
-        self.print_where_clause(&generics.where_clause)?;
-        self.s.space()?;
+                          visibility: &ast::Visibility) {
+        self.head(visibility_qualified(visibility, "enum"));
+        self.print_ident(ident);
+        self.print_generic_params(&generics.params);
+        self.print_where_clause(&generics.where_clause);
+        self.s.space();
         self.print_variants(&enum_definition.variants, span)
     }
 
-    pub fn print_variants(&mut self,
+    crate fn print_variants(&mut self,
                           variants: &[ast::Variant],
-                          span: syntax_pos::Span) -> io::Result<()> {
-        self.bopen()?;
+                          span: syntax_pos::Span) {
+        self.bopen();
         for v in variants {
-            self.space_if_not_bol()?;
-            self.maybe_print_comment(v.span.lo())?;
-            self.print_outer_attributes(&v.node.attrs)?;
-            self.ibox(INDENT_UNIT)?;
-            self.print_variant(v)?;
-            self.s.word(",")?;
-            self.end()?;
-            self.maybe_print_trailing_comment(v.span, None)?;
+            self.space_if_not_bol();
+            self.maybe_print_comment(v.span.lo());
+            self.print_outer_attributes(&v.attrs);
+            self.ibox(INDENT_UNIT);
+            self.print_variant(v);
+            self.s.word(",");
+            self.end();
+            self.maybe_print_trailing_comment(v.span, None);
         }
         self.bclose(span)
     }
 
-    pub fn print_visibility(&mut self, vis: &ast::Visibility) -> io::Result<()> {
+    crate fn print_visibility(&mut self, vis: &ast::Visibility) {
         match vis.node {
             ast::VisibilityKind::Public => self.word_nbsp("pub"),
             ast::VisibilityKind::Crate(sugar) => match sugar {
@@ -1437,62 +1439,61 @@ impl<'a> State<'a> {
                     self.word_nbsp(format!("pub(in {})", path))
                 }
             }
-            ast::VisibilityKind::Inherited => Ok(())
+            ast::VisibilityKind::Inherited => {}
         }
     }
 
-    pub fn print_defaultness(&mut self, defaultness: ast::Defaultness) -> io::Result<()> {
+    crate fn print_defaultness(&mut self, defaultness: ast::Defaultness) {
         if let ast::Defaultness::Default = defaultness {
-            self.word_nbsp("default")?;
+            self.word_nbsp("default");
         }
-        Ok(())
     }
 
-    pub fn print_struct(&mut self,
+    crate fn print_struct(&mut self,
                         struct_def: &ast::VariantData,
                         generics: &ast::Generics,
                         ident: ast::Ident,
                         span: syntax_pos::Span,
-                        print_finalizer: bool) -> io::Result<()> {
-        self.print_ident(ident)?;
-        self.print_generic_params(&generics.params)?;
+                        print_finalizer: bool) {
+        self.print_ident(ident);
+        self.print_generic_params(&generics.params);
         match struct_def {
             ast::VariantData::Tuple(..) | ast::VariantData::Unit(..) => {
                 if let ast::VariantData::Tuple(..) = struct_def {
-                    self.popen()?;
+                    self.popen();
                     self.commasep(
                         Inconsistent, struct_def.fields(),
                         |s, field| {
-                            s.maybe_print_comment(field.span.lo())?;
-                            s.print_outer_attributes(&field.attrs)?;
-                            s.print_visibility(&field.vis)?;
+                            s.maybe_print_comment(field.span.lo());
+                            s.print_outer_attributes(&field.attrs);
+                            s.print_visibility(&field.vis);
                             s.print_type(&field.ty)
                         }
-                    )?;
-                    self.pclose()?;
+                    );
+                    self.pclose();
                 }
-                self.print_where_clause(&generics.where_clause)?;
+                self.print_where_clause(&generics.where_clause);
                 if print_finalizer {
-                    self.s.word(";")?;
+                    self.s.word(";");
                 }
-                self.end()?;
-                self.end() // close the outer-box
+                self.end();
+                self.end(); // close the outer-box
             }
             ast::VariantData::Struct(..) => {
-                self.print_where_clause(&generics.where_clause)?;
-                self.nbsp()?;
-                self.bopen()?;
-                self.hardbreak_if_not_bol()?;
+                self.print_where_clause(&generics.where_clause);
+                self.nbsp();
+                self.bopen();
+                self.hardbreak_if_not_bol();
 
                 for field in struct_def.fields() {
-                    self.hardbreak_if_not_bol()?;
-                    self.maybe_print_comment(field.span.lo())?;
-                    self.print_outer_attributes(&field.attrs)?;
-                    self.print_visibility(&field.vis)?;
-                    self.print_ident(field.ident.unwrap())?;
-                    self.word_nbsp(":")?;
-                    self.print_type(&field.ty)?;
-                    self.s.word(",")?;
+                    self.hardbreak_if_not_bol();
+                    self.maybe_print_comment(field.span.lo());
+                    self.print_outer_attributes(&field.attrs);
+                    self.print_visibility(&field.vis);
+                    self.print_ident(field.ident.unwrap());
+                    self.word_nbsp(":");
+                    self.print_type(&field.ty);
+                    self.s.word(",");
                 }
 
                 self.bclose(span)
@@ -1500,39 +1501,39 @@ impl<'a> State<'a> {
         }
     }
 
-    pub fn print_variant(&mut self, v: &ast::Variant) -> io::Result<()> {
-        self.head("")?;
+    crate fn print_variant(&mut self, v: &ast::Variant) {
+        self.head("");
         let generics = ast::Generics::default();
-        self.print_struct(&v.node.data, &generics, v.node.ident, v.span, false)?;
-        match v.node.disr_expr {
+        self.print_struct(&v.data, &generics, v.ident, v.span, false);
+        match v.disr_expr {
             Some(ref d) => {
-                self.s.space()?;
-                self.word_space("=")?;
+                self.s.space();
+                self.word_space("=");
                 self.print_expr(&d.value)
             }
-            _ => Ok(())
+            _ => {}
         }
     }
 
-    pub fn print_method_sig(&mut self,
+    crate fn print_method_sig(&mut self,
                             ident: ast::Ident,
                             generics: &ast::Generics,
                             m: &ast::MethodSig,
                             vis: &ast::Visibility)
-                            -> io::Result<()> {
+                            {
         self.print_fn(&m.decl,
-                      &m.header,
+                      m.header,
                       Some(ident),
                       &generics,
                       vis)
     }
 
-    pub fn print_trait_item(&mut self, ti: &ast::TraitItem)
-                            -> io::Result<()> {
-        self.ann.pre(self, AnnNode::SubItem(ti.id))?;
-        self.hardbreak_if_not_bol()?;
-        self.maybe_print_comment(ti.span.lo())?;
-        self.print_outer_attributes(&ti.attrs)?;
+    crate fn print_trait_item(&mut self, ti: &ast::TraitItem)
+                            {
+        self.ann.pre(self, AnnNode::SubItem(ti.id));
+        self.hardbreak_if_not_bol();
+        self.maybe_print_comment(ti.span.lo());
+        self.print_outer_attributes(&ti.attrs);
         match ti.node {
             ast::TraitItemKind::Const(ref ty, ref default) => {
                 self.print_associated_const(
@@ -1540,283 +1541,255 @@ impl<'a> State<'a> {
                     ty,
                     default.as_ref().map(|expr| &**expr),
                     &source_map::respan(ti.span.shrink_to_lo(), ast::VisibilityKind::Inherited),
-                )?;
+                );
             }
             ast::TraitItemKind::Method(ref sig, ref body) => {
                 if body.is_some() {
-                    self.head("")?;
+                    self.head("");
                 }
                 self.print_method_sig(
                     ti.ident,
                     &ti.generics,
                     sig,
                     &source_map::respan(ti.span.shrink_to_lo(), ast::VisibilityKind::Inherited),
-                )?;
+                );
                 if let Some(ref body) = *body {
-                    self.nbsp()?;
-                    self.print_block_with_attrs(body, &ti.attrs)?;
+                    self.nbsp();
+                    self.print_block_with_attrs(body, &ti.attrs);
                 } else {
-                    self.s.word(";")?;
+                    self.s.word(";");
                 }
             }
             ast::TraitItemKind::Type(ref bounds, ref default) => {
                 self.print_associated_type(ti.ident, Some(bounds),
-                                           default.as_ref().map(|ty| &**ty))?;
+                                           default.as_ref().map(|ty| &**ty));
             }
             ast::TraitItemKind::Macro(ref mac) => {
-                self.print_mac(mac)?;
-                match mac.node.delim {
+                self.print_mac(mac);
+                match mac.delim {
                     MacDelimiter::Brace => {}
-                    _ => self.s.word(";")?,
+                    _ => self.s.word(";"),
                 }
             }
         }
         self.ann.post(self, AnnNode::SubItem(ti.id))
     }
 
-    pub fn print_impl_item(&mut self, ii: &ast::ImplItem) -> io::Result<()> {
-        self.ann.pre(self, AnnNode::SubItem(ii.id))?;
-        self.hardbreak_if_not_bol()?;
-        self.maybe_print_comment(ii.span.lo())?;
-        self.print_outer_attributes(&ii.attrs)?;
-        self.print_defaultness(ii.defaultness)?;
+    crate fn print_impl_item(&mut self, ii: &ast::ImplItem) {
+        self.ann.pre(self, AnnNode::SubItem(ii.id));
+        self.hardbreak_if_not_bol();
+        self.maybe_print_comment(ii.span.lo());
+        self.print_outer_attributes(&ii.attrs);
+        self.print_defaultness(ii.defaultness);
         match ii.node {
             ast::ImplItemKind::Const(ref ty, ref expr) => {
-                self.print_associated_const(ii.ident, ty, Some(expr), &ii.vis)?;
+                self.print_associated_const(ii.ident, ty, Some(expr), &ii.vis);
             }
             ast::ImplItemKind::Method(ref sig, ref body) => {
-                self.head("")?;
-                self.print_method_sig(ii.ident, &ii.generics, sig, &ii.vis)?;
-                self.nbsp()?;
-                self.print_block_with_attrs(body, &ii.attrs)?;
+                self.head("");
+                self.print_method_sig(ii.ident, &ii.generics, sig, &ii.vis);
+                self.nbsp();
+                self.print_block_with_attrs(body, &ii.attrs);
             }
-            ast::ImplItemKind::Type(ref ty) => {
-                self.print_associated_type(ii.ident, None, Some(ty))?;
+            ast::ImplItemKind::TyAlias(ref ty) => {
+                self.print_associated_type(ii.ident, None, Some(ty));
             }
-            ast::ImplItemKind::Existential(ref bounds) => {
-                self.word_space("existential")?;
-                self.print_associated_type(ii.ident, Some(bounds), None)?;
+            ast::ImplItemKind::OpaqueTy(ref bounds) => {
+                self.word_space("type");
+                self.print_ident(ii.ident);
+                self.word_space("= impl");
+                self.print_type_bounds(":", bounds);
+                self.s.word(";");
             }
             ast::ImplItemKind::Macro(ref mac) => {
-                self.print_mac(mac)?;
-                match mac.node.delim {
+                self.print_mac(mac);
+                match mac.delim {
                     MacDelimiter::Brace => {}
-                    _ => self.s.word(";")?,
+                    _ => self.s.word(";"),
                 }
             }
         }
         self.ann.post(self, AnnNode::SubItem(ii.id))
     }
 
-    pub fn print_stmt(&mut self, st: &ast::Stmt) -> io::Result<()> {
-        self.maybe_print_comment(st.span.lo())?;
+    crate fn print_stmt(&mut self, st: &ast::Stmt) {
+        self.maybe_print_comment(st.span.lo());
         match st.node {
             ast::StmtKind::Local(ref loc) => {
-                self.print_outer_attributes(&loc.attrs)?;
-                self.space_if_not_bol()?;
-                self.ibox(INDENT_UNIT)?;
-                self.word_nbsp("let")?;
-
-                self.ibox(INDENT_UNIT)?;
-                self.print_local_decl(loc)?;
-                self.end()?;
+                self.print_outer_attributes(&loc.attrs);
+                self.space_if_not_bol();
+                self.ibox(INDENT_UNIT);
+                self.word_nbsp("let");
+
+                self.ibox(INDENT_UNIT);
+                self.print_local_decl(loc);
+                self.end();
                 if let Some(ref init) = loc.init {
-                    self.nbsp()?;
-                    self.word_space("=")?;
-                    self.print_expr(init)?;
+                    self.nbsp();
+                    self.word_space("=");
+                    self.print_expr(init);
                 }
-                self.s.word(";")?;
-                self.end()?;
+                self.s.word(";");
+                self.end();
             }
-            ast::StmtKind::Item(ref item) => self.print_item(item)?,
+            ast::StmtKind::Item(ref item) => self.print_item(item),
             ast::StmtKind::Expr(ref expr) => {
-                self.space_if_not_bol()?;
-                self.print_expr_outer_attr_style(expr, false)?;
+                self.space_if_not_bol();
+                self.print_expr_outer_attr_style(expr, false);
                 if parse::classify::expr_requires_semi_to_be_stmt(expr) {
-                    self.s.word(";")?;
+                    self.s.word(";");
                 }
             }
             ast::StmtKind::Semi(ref expr) => {
-                self.space_if_not_bol()?;
-                self.print_expr_outer_attr_style(expr, false)?;
-                self.s.word(";")?;
+                self.space_if_not_bol();
+                self.print_expr_outer_attr_style(expr, false);
+                self.s.word(";");
             }
             ast::StmtKind::Mac(ref mac) => {
                 let (ref mac, style, ref attrs) = **mac;
-                self.space_if_not_bol()?;
-                self.print_outer_attributes(attrs)?;
-                self.print_mac(mac)?;
+                self.space_if_not_bol();
+                self.print_outer_attributes(attrs);
+                self.print_mac(mac);
                 if style == ast::MacStmtStyle::Semicolon {
-                    self.s.word(";")?;
+                    self.s.word(";");
                 }
             }
         }
         self.maybe_print_trailing_comment(st.span, None)
     }
 
-    pub fn print_block(&mut self, blk: &ast::Block) -> io::Result<()> {
+    crate fn print_block(&mut self, blk: &ast::Block) {
         self.print_block_with_attrs(blk, &[])
     }
 
-    pub fn print_block_unclosed(&mut self, blk: &ast::Block) -> io::Result<()> {
-        self.print_block_unclosed_indent(blk, INDENT_UNIT)
-    }
-
-    pub fn print_block_unclosed_with_attrs(&mut self, blk: &ast::Block,
-                                            attrs: &[ast::Attribute])
-                                           -> io::Result<()> {
-        self.print_block_maybe_unclosed(blk, INDENT_UNIT, attrs, false)
+    crate fn print_block_unclosed_indent(&mut self, blk: &ast::Block) {
+        self.print_block_maybe_unclosed(blk, &[], false)
     }
 
-    pub fn print_block_unclosed_indent(&mut self, blk: &ast::Block,
-                                       indented: usize) -> io::Result<()> {
-        self.print_block_maybe_unclosed(blk, indented, &[], false)
-    }
-
-    pub fn print_block_with_attrs(&mut self,
+    crate fn print_block_with_attrs(&mut self,
                                   blk: &ast::Block,
-                                  attrs: &[ast::Attribute]) -> io::Result<()> {
-        self.print_block_maybe_unclosed(blk, INDENT_UNIT, attrs, true)
+                                  attrs: &[ast::Attribute]) {
+        self.print_block_maybe_unclosed(blk, attrs, true)
     }
 
-    pub fn print_block_maybe_unclosed(&mut self,
+    crate fn print_block_maybe_unclosed(&mut self,
                                       blk: &ast::Block,
-                                      indented: usize,
                                       attrs: &[ast::Attribute],
-                                      close_box: bool) -> io::Result<()> {
+                                      close_box: bool) {
         match blk.rules {
-            BlockCheckMode::Unsafe(..) => self.word_space("unsafe")?,
+            BlockCheckMode::Unsafe(..) => self.word_space("unsafe"),
             BlockCheckMode::Default => ()
         }
-        self.maybe_print_comment(blk.span.lo())?;
-        self.ann.pre(self, AnnNode::Block(blk))?;
-        self.bopen()?;
+        self.maybe_print_comment(blk.span.lo());
+        self.ann.pre(self, AnnNode::Block(blk));
+        self.bopen();
 
-        self.print_inner_attributes(attrs)?;
+        self.print_inner_attributes(attrs);
 
         for (i, st) in blk.stmts.iter().enumerate() {
             match st.node {
                 ast::StmtKind::Expr(ref expr) if i == blk.stmts.len() - 1 => {
-                    self.maybe_print_comment(st.span.lo())?;
-                    self.space_if_not_bol()?;
-                    self.print_expr_outer_attr_style(expr, false)?;
-                    self.maybe_print_trailing_comment(expr.span, Some(blk.span.hi()))?;
+                    self.maybe_print_comment(st.span.lo());
+                    self.space_if_not_bol();
+                    self.print_expr_outer_attr_style(expr, false);
+                    self.maybe_print_trailing_comment(expr.span, Some(blk.span.hi()));
                 }
-                _ => self.print_stmt(st)?,
+                _ => self.print_stmt(st),
             }
         }
 
-        self.bclose_maybe_open(blk.span, indented, close_box)?;
+        self.bclose_maybe_open(blk.span, close_box);
         self.ann.post(self, AnnNode::Block(blk))
     }
 
-    fn print_else(&mut self, els: Option<&ast::Expr>) -> io::Result<()> {
+    /// Print a `let pats = scrutinee` expression.
+    crate fn print_let(&mut self, pats: &[P<ast::Pat>], scrutinee: &ast::Expr) {
+        self.s.word("let ");
+
+        self.print_pats(pats);
+        self.s.space();
+
+        self.word_space("=");
+        self.print_expr_cond_paren(
+            scrutinee,
+            Self::cond_needs_par(scrutinee)
+            || parser::needs_par_as_let_scrutinee(scrutinee.precedence().order())
+        )
+    }
+
+    fn print_else(&mut self, els: Option<&ast::Expr>) {
         match els {
             Some(_else) => {
                 match _else.node {
-                    // "another else-if"
+                    // Another `else if` block.
                     ast::ExprKind::If(ref i, ref then, ref e) => {
-                        self.cbox(INDENT_UNIT - 1)?;
-                        self.ibox(0)?;
-                        self.s.word(" else if ")?;
-                        self.print_expr_as_cond(i)?;
-                        self.s.space()?;
-                        self.print_block(then)?;
-                        self.print_else(e.as_ref().map(|e| &**e))
-                    }
-                    // "another else-if-let"
-                    ast::ExprKind::IfLet(ref pats, ref expr, ref then, ref e) => {
-                        self.cbox(INDENT_UNIT - 1)?;
-                        self.ibox(0)?;
-                        self.s.word(" else if let ")?;
-                        self.print_pats(pats)?;
-                        self.s.space()?;
-                        self.word_space("=")?;
-                        self.print_expr_as_cond(expr)?;
-                        self.s.space()?;
-                        self.print_block(then)?;
+                        self.cbox(INDENT_UNIT - 1);
+                        self.ibox(0);
+                        self.s.word(" else if ");
+                        self.print_expr_as_cond(i);
+                        self.s.space();
+                        self.print_block(then);
                         self.print_else(e.as_ref().map(|e| &**e))
                     }
-                    // "final else"
+                    // Final `else` block.
                     ast::ExprKind::Block(ref b, _) => {
-                        self.cbox(INDENT_UNIT - 1)?;
-                        self.ibox(0)?;
-                        self.s.word(" else ")?;
+                        self.cbox(INDENT_UNIT - 1);
+                        self.ibox(0);
+                        self.s.word(" else ");
                         self.print_block(b)
                     }
-                    // BLEAH, constraints would be great here
+                    // Constraints would be great here!
                     _ => {
                         panic!("print_if saw if with weird alternative");
                     }
                 }
             }
-            _ => Ok(())
+            _ => {}
         }
     }
 
-    pub fn print_if(&mut self, test: &ast::Expr, blk: &ast::Block,
-                    elseopt: Option<&ast::Expr>) -> io::Result<()> {
-        self.head("if")?;
-        self.print_expr_as_cond(test)?;
-        self.s.space()?;
-        self.print_block(blk)?;
-        self.print_else(elseopt)
-    }
+    crate fn print_if(&mut self, test: &ast::Expr, blk: &ast::Block,
+                    elseopt: Option<&ast::Expr>) {
+        self.head("if");
+
+        self.print_expr_as_cond(test);
+        self.s.space();
 
-    pub fn print_if_let(&mut self, pats: &[P<ast::Pat>], expr: &ast::Expr, blk: &ast::Block,
-                        elseopt: Option<&ast::Expr>) -> io::Result<()> {
-        self.head("if let")?;
-        self.print_pats(pats)?;
-        self.s.space()?;
-        self.word_space("=")?;
-        self.print_expr_as_cond(expr)?;
-        self.s.space()?;
-        self.print_block(blk)?;
+        self.print_block(blk);
         self.print_else(elseopt)
     }
 
-    pub fn print_mac(&mut self, m: &ast::Mac) -> io::Result<()> {
-        self.print_path(&m.node.path, false, 0)?;
-        self.s.word("!")?;
-        match m.node.delim {
-            MacDelimiter::Parenthesis => self.popen()?,
-            MacDelimiter::Bracket => self.s.word("[")?,
-            MacDelimiter::Brace => {
-                self.head("")?;
-                self.bopen()?;
-            }
-        }
-        self.print_tts(m.node.stream())?;
-        match m.node.delim {
-            MacDelimiter::Parenthesis => self.pclose(),
-            MacDelimiter::Bracket => self.s.word("]"),
-            MacDelimiter::Brace => self.bclose(m.span),
-        }
+    crate fn print_mac(&mut self, m: &ast::Mac) {
+        self.print_mac_common(
+            Some(MacHeader::Path(&m.path)),
+            true,
+            None,
+            m.delim.to_token(),
+            m.stream(),
+            true,
+            m.span,
+        );
     }
 
-
-    fn print_call_post(&mut self, args: &[P<ast::Expr>]) -> io::Result<()> {
-        self.popen()?;
-        self.commasep_exprs(Inconsistent, args)?;
+    fn print_call_post(&mut self, args: &[P<ast::Expr>]) {
+        self.popen();
+        self.commasep_exprs(Inconsistent, args);
         self.pclose()
     }
 
-    pub fn print_expr_maybe_paren(&mut self, expr: &ast::Expr, prec: i8) -> io::Result<()> {
-        let needs_par = expr.precedence().order() < prec;
-        if needs_par {
-            self.popen()?;
-        }
-        self.print_expr(expr)?;
-        if needs_par {
-            self.pclose()?;
-        }
-        Ok(())
+    crate fn print_expr_maybe_paren(&mut self, expr: &ast::Expr, prec: i8) {
+        self.print_expr_cond_paren(expr, expr.precedence().order() < prec)
     }
 
     /// Print an expr using syntax that's acceptable in a condition position, such as the `cond` in
     /// `if cond { ... }`.
-    pub fn print_expr_as_cond(&mut self, expr: &ast::Expr) -> io::Result<()> {
-        let needs_par = match expr.node {
+    crate fn print_expr_as_cond(&mut self, expr: &ast::Expr) {
+        self.print_expr_cond_paren(expr, Self::cond_needs_par(expr))
+    }
+
+    /// Does `expr` need parenthesis when printed in a condition position?
+    fn cond_needs_par(expr: &ast::Expr) -> bool {
+        match expr.node {
             // These cases need parens due to the parse error observed in #26461: `if return {}`
             // parses as the erroneous construct `if (return {})`, not `if (return) {}`.
             ast::ExprKind::Closure(..) |
@@ -1824,115 +1797,116 @@ impl<'a> State<'a> {
             ast::ExprKind::Break(..) => true,
 
             _ => parser::contains_exterior_struct_lit(expr),
-        };
+        }
+    }
 
+    /// Print `expr` or `(expr)` when `needs_par` holds.
+    fn print_expr_cond_paren(&mut self, expr: &ast::Expr, needs_par: bool) {
         if needs_par {
-            self.popen()?;
+            self.popen();
         }
-        self.print_expr(expr)?;
+        self.print_expr(expr);
         if needs_par {
-            self.pclose()?;
+            self.pclose();
         }
-        Ok(())
     }
 
     fn print_expr_vec(&mut self, exprs: &[P<ast::Expr>],
-                      attrs: &[Attribute]) -> io::Result<()> {
-        self.ibox(INDENT_UNIT)?;
-        self.s.word("[")?;
-        self.print_inner_attributes_inline(attrs)?;
-        self.commasep_exprs(Inconsistent, &exprs[..])?;
-        self.s.word("]")?;
-        self.end()
+                      attrs: &[Attribute]) {
+        self.ibox(INDENT_UNIT);
+        self.s.word("[");
+        self.print_inner_attributes_inline(attrs);
+        self.commasep_exprs(Inconsistent, &exprs[..]);
+        self.s.word("]");
+        self.end();
     }
 
     fn print_expr_repeat(&mut self,
                          element: &ast::Expr,
                          count: &ast::AnonConst,
-                         attrs: &[Attribute]) -> io::Result<()> {
-        self.ibox(INDENT_UNIT)?;
-        self.s.word("[")?;
-        self.print_inner_attributes_inline(attrs)?;
-        self.print_expr(element)?;
-        self.word_space(";")?;
-        self.print_expr(&count.value)?;
-        self.s.word("]")?;
-        self.end()
+                         attrs: &[Attribute]) {
+        self.ibox(INDENT_UNIT);
+        self.s.word("[");
+        self.print_inner_attributes_inline(attrs);
+        self.print_expr(element);
+        self.word_space(";");
+        self.print_expr(&count.value);
+        self.s.word("]");
+        self.end();
     }
 
     fn print_expr_struct(&mut self,
                          path: &ast::Path,
                          fields: &[ast::Field],
                          wth: &Option<P<ast::Expr>>,
-                         attrs: &[Attribute]) -> io::Result<()> {
-        self.print_path(path, true, 0)?;
-        self.s.word("{")?;
-        self.print_inner_attributes_inline(attrs)?;
+                         attrs: &[Attribute]) {
+        self.print_path(path, true, 0);
+        self.s.word("{");
+        self.print_inner_attributes_inline(attrs);
         self.commasep_cmnt(
             Consistent,
             &fields[..],
             |s, field| {
-                s.ibox(INDENT_UNIT)?;
+                s.ibox(INDENT_UNIT);
                 if !field.is_shorthand {
-                    s.print_ident(field.ident)?;
-                    s.word_space(":")?;
+                    s.print_ident(field.ident);
+                    s.word_space(":");
                 }
-                s.print_expr(&field.expr)?;
-                s.end()
+                s.print_expr(&field.expr);
+                s.end();
             },
-            |f| f.span)?;
+            |f| f.span);
         match *wth {
             Some(ref expr) => {
-                self.ibox(INDENT_UNIT)?;
+                self.ibox(INDENT_UNIT);
                 if !fields.is_empty() {
-                    self.s.word(",")?;
-                    self.s.space()?;
+                    self.s.word(",");
+                    self.s.space();
                 }
-                self.s.word("..")?;
-                self.print_expr(expr)?;
-                self.end()?;
+                self.s.word("..");
+                self.print_expr(expr);
+                self.end();
             }
             _ => if !fields.is_empty() {
-                self.s.word(",")?
+                self.s.word(",")
             }
         }
-        self.s.word("}")?;
-        Ok(())
+        self.s.word("}");
     }
 
     fn print_expr_tup(&mut self, exprs: &[P<ast::Expr>],
-                      attrs: &[Attribute]) -> io::Result<()> {
-        self.popen()?;
-        self.print_inner_attributes_inline(attrs)?;
-        self.commasep_exprs(Inconsistent, &exprs[..])?;
+                      attrs: &[Attribute]) {
+        self.popen();
+        self.print_inner_attributes_inline(attrs);
+        self.commasep_exprs(Inconsistent, &exprs[..]);
         if exprs.len() == 1 {
-            self.s.word(",")?;
+            self.s.word(",");
         }
         self.pclose()
     }
 
     fn print_expr_call(&mut self,
                        func: &ast::Expr,
-                       args: &[P<ast::Expr>]) -> io::Result<()> {
+                       args: &[P<ast::Expr>]) {
         let prec =
             match func.node {
                 ast::ExprKind::Field(..) => parser::PREC_FORCE_PAREN,
                 _ => parser::PREC_POSTFIX,
             };
 
-        self.print_expr_maybe_paren(func, prec)?;
+        self.print_expr_maybe_paren(func, prec);
         self.print_call_post(args)
     }
 
     fn print_expr_method_call(&mut self,
                               segment: &ast::PathSegment,
-                              args: &[P<ast::Expr>]) -> io::Result<()> {
+                              args: &[P<ast::Expr>]) {
         let base_args = &args[1..];
-        self.print_expr_maybe_paren(&args[0], parser::PREC_POSTFIX)?;
-        self.s.word(".")?;
-        self.print_ident(segment.ident)?;
+        self.print_expr_maybe_paren(&args[0], parser::PREC_POSTFIX);
+        self.s.word(".");
+        self.print_ident(segment.ident);
         if let Some(ref args) = segment.args {
-            self.print_generic_args(args, true)?;
+            self.print_generic_args(args, true);
         }
         self.print_call_post(base_args)
     }
@@ -1940,7 +1914,7 @@ impl<'a> State<'a> {
     fn print_expr_binary(&mut self,
                          op: ast::BinOp,
                          lhs: &ast::Expr,
-                         rhs: &ast::Expr) -> io::Result<()> {
+                         rhs: &ast::Expr) {
         let assoc_op = AssocOp::from_ast_binop(op.node);
         let prec = assoc_op.precedence() as i8;
         let fixity = assoc_op.fixity();
@@ -1957,240 +1931,223 @@ impl<'a> State<'a> {
             // of `(x as i32) < ...`. We need to convince it _not_ to do that.
             (&ast::ExprKind::Cast { .. }, ast::BinOpKind::Lt) |
             (&ast::ExprKind::Cast { .. }, ast::BinOpKind::Shl) => parser::PREC_FORCE_PAREN,
+            // We are given `(let _ = a) OP b`.
+            //
+            // - When `OP <= LAnd` we should print `let _ = a OP b` to avoid redundant parens
+            //   as the parser will interpret this as `(let _ = a) OP b`.
+            //
+            // - Otherwise, e.g. when we have `(let a = b) < c` in AST,
+            //   parens are required since the parser would interpret `let a = b < c` as
+            //   `let a = (b < c)`. To achieve this, we force parens.
+            (&ast::ExprKind::Let { .. }, _) if !parser::needs_par_as_let_scrutinee(prec) => {
+                parser::PREC_FORCE_PAREN
+            }
             _ => left_prec,
         };
 
-        self.print_expr_maybe_paren(lhs, left_prec)?;
-        self.s.space()?;
-        self.word_space(op.node.to_string())?;
+        self.print_expr_maybe_paren(lhs, left_prec);
+        self.s.space();
+        self.word_space(op.node.to_string());
         self.print_expr_maybe_paren(rhs, right_prec)
     }
 
     fn print_expr_unary(&mut self,
                         op: ast::UnOp,
-                        expr: &ast::Expr) -> io::Result<()> {
-        self.s.word(ast::UnOp::to_string(op))?;
+                        expr: &ast::Expr) {
+        self.s.word(ast::UnOp::to_string(op));
         self.print_expr_maybe_paren(expr, parser::PREC_PREFIX)
     }
 
     fn print_expr_addr_of(&mut self,
                           mutability: ast::Mutability,
-                          expr: &ast::Expr) -> io::Result<()> {
-        self.s.word("&")?;
-        self.print_mutability(mutability)?;
+                          expr: &ast::Expr) {
+        self.s.word("&");
+        self.print_mutability(mutability);
         self.print_expr_maybe_paren(expr, parser::PREC_PREFIX)
     }
 
-    pub fn print_expr(&mut self, expr: &ast::Expr) -> io::Result<()> {
+    crate fn print_expr(&mut self, expr: &ast::Expr) {
         self.print_expr_outer_attr_style(expr, true)
     }
 
     fn print_expr_outer_attr_style(&mut self,
                                   expr: &ast::Expr,
-                                  is_inline: bool) -> io::Result<()> {
-        self.maybe_print_comment(expr.span.lo())?;
+                                  is_inline: bool) {
+        self.maybe_print_comment(expr.span.lo());
 
         let attrs = &expr.attrs;
         if is_inline {
-            self.print_outer_attributes_inline(attrs)?;
+            self.print_outer_attributes_inline(attrs);
         } else {
-            self.print_outer_attributes(attrs)?;
+            self.print_outer_attributes(attrs);
         }
 
-        self.ibox(INDENT_UNIT)?;
-        self.ann.pre(self, AnnNode::Expr(expr))?;
+        self.ibox(INDENT_UNIT);
+        self.ann.pre(self, AnnNode::Expr(expr));
         match expr.node {
             ast::ExprKind::Box(ref expr) => {
-                self.word_space("box")?;
-                self.print_expr_maybe_paren(expr, parser::PREC_PREFIX)?;
-            }
-            ast::ExprKind::ObsoleteInPlace(ref place, ref expr) => {
-                let prec = AssocOp::ObsoleteInPlace.precedence() as i8;
-                self.print_expr_maybe_paren(place, prec + 1)?;
-                self.s.space()?;
-                self.word_space("<-")?;
-                self.print_expr_maybe_paren(expr, prec)?;
+                self.word_space("box");
+                self.print_expr_maybe_paren(expr, parser::PREC_PREFIX);
             }
             ast::ExprKind::Array(ref exprs) => {
-                self.print_expr_vec(&exprs[..], attrs)?;
+                self.print_expr_vec(&exprs[..], attrs);
             }
             ast::ExprKind::Repeat(ref element, ref count) => {
-                self.print_expr_repeat(element, count, attrs)?;
+                self.print_expr_repeat(element, count, attrs);
             }
             ast::ExprKind::Struct(ref path, ref fields, ref wth) => {
-                self.print_expr_struct(path, &fields[..], wth, attrs)?;
+                self.print_expr_struct(path, &fields[..], wth, attrs);
             }
             ast::ExprKind::Tup(ref exprs) => {
-                self.print_expr_tup(&exprs[..], attrs)?;
+                self.print_expr_tup(&exprs[..], attrs);
             }
             ast::ExprKind::Call(ref func, ref args) => {
-                self.print_expr_call(func, &args[..])?;
+                self.print_expr_call(func, &args[..]);
             }
             ast::ExprKind::MethodCall(ref segment, ref args) => {
-                self.print_expr_method_call(segment, &args[..])?;
+                self.print_expr_method_call(segment, &args[..]);
             }
             ast::ExprKind::Binary(op, ref lhs, ref rhs) => {
-                self.print_expr_binary(op, lhs, rhs)?;
+                self.print_expr_binary(op, lhs, rhs);
             }
             ast::ExprKind::Unary(op, ref expr) => {
-                self.print_expr_unary(op, expr)?;
+                self.print_expr_unary(op, expr);
             }
             ast::ExprKind::AddrOf(m, ref expr) => {
-                self.print_expr_addr_of(m, expr)?;
+                self.print_expr_addr_of(m, expr);
             }
             ast::ExprKind::Lit(ref lit) => {
-                self.print_literal(lit)?;
+                self.print_literal(lit);
             }
             ast::ExprKind::Cast(ref expr, ref ty) => {
                 let prec = AssocOp::As.precedence() as i8;
-                self.print_expr_maybe_paren(expr, prec)?;
-                self.s.space()?;
-                self.word_space("as")?;
-                self.print_type(ty)?;
+                self.print_expr_maybe_paren(expr, prec);
+                self.s.space();
+                self.word_space("as");
+                self.print_type(ty);
             }
             ast::ExprKind::Type(ref expr, ref ty) => {
                 let prec = AssocOp::Colon.precedence() as i8;
-                self.print_expr_maybe_paren(expr, prec)?;
-                self.word_space(":")?;
-                self.print_type(ty)?;
+                self.print_expr_maybe_paren(expr, prec);
+                self.word_space(":");
+                self.print_type(ty);
             }
-            ast::ExprKind::If(ref test, ref blk, ref elseopt) => {
-                self.print_if(test, blk, elseopt.as_ref().map(|e| &**e))?;
+            ast::ExprKind::Let(ref pats, ref scrutinee) => {
+                self.print_let(pats, scrutinee);
             }
-            ast::ExprKind::IfLet(ref pats, ref expr, ref blk, ref elseopt) => {
-                self.print_if_let(pats, expr, blk, elseopt.as_ref().map(|e| &**e))?;
+            ast::ExprKind::If(ref test, ref blk, ref elseopt) => {
+                self.print_if(test, blk, elseopt.as_ref().map(|e| &**e));
             }
             ast::ExprKind::While(ref test, ref blk, opt_label) => {
                 if let Some(label) = opt_label {
-                    self.print_ident(label.ident)?;
-                    self.word_space(":")?;
+                    self.print_ident(label.ident);
+                    self.word_space(":");
                 }
-                self.head("while")?;
-                self.print_expr_as_cond(test)?;
-                self.s.space()?;
-                self.print_block_with_attrs(blk, attrs)?;
-            }
-            ast::ExprKind::WhileLet(ref pats, ref expr, ref blk, opt_label) => {
-                if let Some(label) = opt_label {
-                    self.print_ident(label.ident)?;
-                    self.word_space(":")?;
-                }
-                self.head("while let")?;
-                self.print_pats(pats)?;
-                self.s.space()?;
-                self.word_space("=")?;
-                self.print_expr_as_cond(expr)?;
-                self.s.space()?;
-                self.print_block_with_attrs(blk, attrs)?;
+                self.head("while");
+                self.print_expr_as_cond(test);
+                self.s.space();
+                self.print_block_with_attrs(blk, attrs);
             }
             ast::ExprKind::ForLoop(ref pat, ref iter, ref blk, opt_label) => {
                 if let Some(label) = opt_label {
-                    self.print_ident(label.ident)?;
-                    self.word_space(":")?;
+                    self.print_ident(label.ident);
+                    self.word_space(":");
                 }
-                self.head("for")?;
-                self.print_pat(pat)?;
-                self.s.space()?;
-                self.word_space("in")?;
-                self.print_expr_as_cond(iter)?;
-                self.s.space()?;
-                self.print_block_with_attrs(blk, attrs)?;
+                self.head("for");
+                self.print_pat(pat);
+                self.s.space();
+                self.word_space("in");
+                self.print_expr_as_cond(iter);
+                self.s.space();
+                self.print_block_with_attrs(blk, attrs);
             }
             ast::ExprKind::Loop(ref blk, opt_label) => {
                 if let Some(label) = opt_label {
-                    self.print_ident(label.ident)?;
-                    self.word_space(":")?;
+                    self.print_ident(label.ident);
+                    self.word_space(":");
                 }
-                self.head("loop")?;
-                self.s.space()?;
-                self.print_block_with_attrs(blk, attrs)?;
+                self.head("loop");
+                self.s.space();
+                self.print_block_with_attrs(blk, attrs);
             }
             ast::ExprKind::Match(ref expr, ref arms) => {
-                self.cbox(INDENT_UNIT)?;
-                self.ibox(4)?;
-                self.word_nbsp("match")?;
-                self.print_expr_as_cond(expr)?;
-                self.s.space()?;
-                self.bopen()?;
-                self.print_inner_attributes_no_trailing_hardbreak(attrs)?;
+                self.cbox(INDENT_UNIT);
+                self.ibox(INDENT_UNIT);
+                self.word_nbsp("match");
+                self.print_expr_as_cond(expr);
+                self.s.space();
+                self.bopen();
+                self.print_inner_attributes_no_trailing_hardbreak(attrs);
                 for arm in arms {
-                    self.print_arm(arm)?;
+                    self.print_arm(arm);
                 }
-                self.bclose_(expr.span, INDENT_UNIT)?;
+                self.bclose(expr.span);
             }
             ast::ExprKind::Closure(
-                capture_clause, ref asyncness, movability, ref decl, ref body, _) => {
-                self.print_movability(movability)?;
-                self.print_asyncness(asyncness)?;
-                self.print_capture_clause(capture_clause)?;
+                capture_clause, asyncness, movability, ref decl, ref body, _) => {
+                self.print_movability(movability);
+                self.print_asyncness(asyncness);
+                self.print_capture_clause(capture_clause);
 
-                self.print_fn_block_args(decl)?;
-                self.s.space()?;
-                self.print_expr(body)?;
-                self.end()?; // need to close a box
+                self.print_fn_block_args(decl);
+                self.s.space();
+                self.print_expr(body);
+                self.end(); // need to close a box
 
                 // a box will be closed by print_expr, but we didn't want an overall
                 // wrapper so we closed the corresponding opening. so create an
                 // empty box to satisfy the close.
-                self.ibox(0)?;
+                self.ibox(0);
             }
             ast::ExprKind::Block(ref blk, opt_label) => {
                 if let Some(label) = opt_label {
-                    self.print_ident(label.ident)?;
-                    self.word_space(":")?;
+                    self.print_ident(label.ident);
+                    self.word_space(":");
                 }
                 // containing cbox, will be closed by print-block at }
-                self.cbox(INDENT_UNIT)?;
+                self.cbox(INDENT_UNIT);
                 // head-box, will be closed by print-block after {
-                self.ibox(0)?;
-                self.print_block_with_attrs(blk, attrs)?;
+                self.ibox(0);
+                self.print_block_with_attrs(blk, attrs);
             }
             ast::ExprKind::Async(capture_clause, _, ref blk) => {
-                self.word_nbsp("async")?;
-                self.print_capture_clause(capture_clause)?;
-                self.s.space()?;
+                self.word_nbsp("async");
+                self.print_capture_clause(capture_clause);
+                self.s.space();
                 // cbox/ibox in analogy to the `ExprKind::Block` arm above
-                self.cbox(INDENT_UNIT)?;
-                self.ibox(0)?;
-                self.print_block_with_attrs(blk, attrs)?;
-            }
-            ast::ExprKind::Await(origin, ref expr) => {
-                match origin {
-                    ast::AwaitOrigin::MacroLike => {
-                        self.s.word("await!")?;
-                        self.print_expr_maybe_paren(expr, parser::PREC_FORCE_PAREN)?;
-                    }
-                    ast::AwaitOrigin::FieldLike => {
-                        self.print_expr_maybe_paren(expr, parser::PREC_POSTFIX)?;
-                        self.s.word(".await")?;
-                    }
-                }
+                self.cbox(INDENT_UNIT);
+                self.ibox(0);
+                self.print_block_with_attrs(blk, attrs);
+            }
+            ast::ExprKind::Await(ref expr) => {
+                self.print_expr_maybe_paren(expr, parser::PREC_POSTFIX);
+                self.s.word(".await");
             }
             ast::ExprKind::Assign(ref lhs, ref rhs) => {
                 let prec = AssocOp::Assign.precedence() as i8;
-                self.print_expr_maybe_paren(lhs, prec + 1)?;
-                self.s.space()?;
-                self.word_space("=")?;
-                self.print_expr_maybe_paren(rhs, prec)?;
+                self.print_expr_maybe_paren(lhs, prec + 1);
+                self.s.space();
+                self.word_space("=");
+                self.print_expr_maybe_paren(rhs, prec);
             }
             ast::ExprKind::AssignOp(op, ref lhs, ref rhs) => {
                 let prec = AssocOp::Assign.precedence() as i8;
-                self.print_expr_maybe_paren(lhs, prec + 1)?;
-                self.s.space()?;
-                self.s.word(op.node.to_string())?;
-                self.word_space("=")?;
-                self.print_expr_maybe_paren(rhs, prec)?;
+                self.print_expr_maybe_paren(lhs, prec + 1);
+                self.s.space();
+                self.s.word(op.node.to_string());
+                self.word_space("=");
+                self.print_expr_maybe_paren(rhs, prec);
             }
             ast::ExprKind::Field(ref expr, ident) => {
-                self.print_expr_maybe_paren(expr, parser::PREC_POSTFIX)?;
-                self.s.word(".")?;
-                self.print_ident(ident)?;
+                self.print_expr_maybe_paren(expr, parser::PREC_POSTFIX);
+                self.s.word(".");
+                self.print_ident(ident);
             }
             ast::ExprKind::Index(ref expr, ref index) => {
-                self.print_expr_maybe_paren(expr, parser::PREC_POSTFIX)?;
-                self.s.word("[")?;
-                self.print_expr(index)?;
-                self.s.word("]")?;
+                self.print_expr_maybe_paren(expr, parser::PREC_POSTFIX);
+                self.s.word("[");
+                self.print_expr(index);
+                self.s.word("]");
             }
             ast::ExprKind::Range(ref start, ref end, limits) => {
                 // Special case for `Range`.  `AssocOp` claims that `Range` has higher precedence
@@ -2199,55 +2156,55 @@ impl<'a> State<'a> {
                 // a "normal" binop gets parenthesized.  (`LOr` is the lowest-precedence binop.)
                 let fake_prec = AssocOp::LOr.precedence() as i8;
                 if let Some(ref e) = *start {
-                    self.print_expr_maybe_paren(e, fake_prec)?;
+                    self.print_expr_maybe_paren(e, fake_prec);
                 }
                 if limits == ast::RangeLimits::HalfOpen {
-                    self.s.word("..")?;
+                    self.s.word("..");
                 } else {
-                    self.s.word("..=")?;
+                    self.s.word("..=");
                 }
                 if let Some(ref e) = *end {
-                    self.print_expr_maybe_paren(e, fake_prec)?;
+                    self.print_expr_maybe_paren(e, fake_prec);
                 }
             }
             ast::ExprKind::Path(None, ref path) => {
-                self.print_path(path, true, 0)?
+                self.print_path(path, true, 0)
             }
             ast::ExprKind::Path(Some(ref qself), ref path) => {
-                self.print_qpath(path, qself, true)?
+                self.print_qpath(path, qself, true)
             }
             ast::ExprKind::Break(opt_label, ref opt_expr) => {
-                self.s.word("break")?;
-                self.s.space()?;
+                self.s.word("break");
+                self.s.space();
                 if let Some(label) = opt_label {
-                    self.print_ident(label.ident)?;
-                    self.s.space()?;
+                    self.print_ident(label.ident);
+                    self.s.space();
                 }
                 if let Some(ref expr) = *opt_expr {
-                    self.print_expr_maybe_paren(expr, parser::PREC_JUMP)?;
-                    self.s.space()?;
+                    self.print_expr_maybe_paren(expr, parser::PREC_JUMP);
+                    self.s.space();
                 }
             }
             ast::ExprKind::Continue(opt_label) => {
-                self.s.word("continue")?;
-                self.s.space()?;
+                self.s.word("continue");
+                self.s.space();
                 if let Some(label) = opt_label {
-                    self.print_ident(label.ident)?;
-                    self.s.space()?
+                    self.print_ident(label.ident);
+                    self.s.space()
                 }
             }
             ast::ExprKind::Ret(ref result) => {
-                self.s.word("return")?;
+                self.s.word("return");
                 if let Some(ref expr) = *result {
-                    self.s.word(" ")?;
-                    self.print_expr_maybe_paren(expr, parser::PREC_JUMP)?;
+                    self.s.word(" ");
+                    self.print_expr_maybe_paren(expr, parser::PREC_JUMP);
                 }
             }
             ast::ExprKind::InlineAsm(ref a) => {
-                self.s.word("asm!")?;
-                self.popen()?;
-                self.print_string(&a.asm.as_str(), a.asm_str_style)?;
-                self.word_space(":")?;
+                self.s.word("asm!");
+                self.popen();
+                self.print_string(&a.asm.as_str(), a.asm_str_style);
+                self.word_space(":");
 
                 self.commasep(Inconsistent, &a.outputs, |s, out| {
                     let constraint = out.constraint.as_str();
@@ -2255,33 +2212,30 @@ impl<'a> State<'a> {
                     match ch.next() {
                         Some('=') if out.is_rw => {
                             s.print_string(&format!("+{}", ch.as_str()),
-                                           ast::StrStyle::Cooked)?
+                                           ast::StrStyle::Cooked)
                         }
-                        _ => s.print_string(&constraint, ast::StrStyle::Cooked)?
+                        _ => s.print_string(&constraint, ast::StrStyle::Cooked)
                     }
-                    s.popen()?;
-                    s.print_expr(&out.expr)?;
-                    s.pclose()?;
-                    Ok(())
-                })?;
-                self.s.space()?;
-                self.word_space(":")?;
+                    s.popen();
+                    s.print_expr(&out.expr);
+                    s.pclose();
+                });
+                self.s.space();
+                self.word_space(":");
 
                 self.commasep(Inconsistent, &a.inputs, |s, &(co, ref o)| {
-                    s.print_string(&co.as_str(), ast::StrStyle::Cooked)?;
-                    s.popen()?;
-                    s.print_expr(o)?;
-                    s.pclose()?;
-                    Ok(())
-                })?;
-                self.s.space()?;
-                self.word_space(":")?;
+                    s.print_string(&co.as_str(), ast::StrStyle::Cooked);
+                    s.popen();
+                    s.print_expr(o);
+                    s.pclose();
+                });
+                self.s.space();
+                self.word_space(":");
 
                 self.commasep(Inconsistent, &a.clobbers,
                                    |s, co| {
-                    s.print_string(&co.as_str(), ast::StrStyle::Cooked)?;
-                    Ok(())
-                })?;
+                    s.print_string(&co.as_str(), ast::StrStyle::Cooked);
+                });
 
                 let mut options = vec![];
                 if a.volatile {
@@ -2295,607 +2249,430 @@ impl<'a> State<'a> {
                 }
 
                 if !options.is_empty() {
-                    self.s.space()?;
-                    self.word_space(":")?;
+                    self.s.space();
+                    self.word_space(":");
                     self.commasep(Inconsistent, &options,
                                   |s, &co| {
-                                      s.print_string(co, ast::StrStyle::Cooked)?;
-                                      Ok(())
-                                  })?;
+                                      s.print_string(co, ast::StrStyle::Cooked);
+                                  });
                 }
 
-                self.pclose()?;
+                self.pclose();
             }
-            ast::ExprKind::Mac(ref m) => self.print_mac(m)?,
+            ast::ExprKind::Mac(ref m) => self.print_mac(m),
             ast::ExprKind::Paren(ref e) => {
-                self.popen()?;
-                self.print_inner_attributes_inline(attrs)?;
-                self.print_expr(e)?;
-                self.pclose()?;
+                self.popen();
+                self.print_inner_attributes_inline(attrs);
+                self.print_expr(e);
+                self.pclose();
             },
             ast::ExprKind::Yield(ref e) => {
-                self.s.word("yield")?;
+                self.s.word("yield");
                 match *e {
                     Some(ref expr) => {
-                        self.s.space()?;
-                        self.print_expr_maybe_paren(expr, parser::PREC_JUMP)?;
+                        self.s.space();
+                        self.print_expr_maybe_paren(expr, parser::PREC_JUMP);
                     }
                     _ => ()
                 }
             }
             ast::ExprKind::Try(ref e) => {
-                self.print_expr_maybe_paren(e, parser::PREC_POSTFIX)?;
-                self.s.word("?")?
+                self.print_expr_maybe_paren(e, parser::PREC_POSTFIX);
+                self.s.word("?")
             }
             ast::ExprKind::TryBlock(ref blk) => {
-                self.head("try")?;
-                self.s.space()?;
-                self.print_block_with_attrs(blk, attrs)?
+                self.head("try");
+                self.s.space();
+                self.print_block_with_attrs(blk, attrs)
             }
             ast::ExprKind::Err => {
-                self.popen()?;
-                self.s.word("/*ERROR*/")?;
-                self.pclose()?
+                self.popen();
+                self.s.word("/*ERROR*/");
+                self.pclose()
             }
         }
-        self.ann.post(self, AnnNode::Expr(expr))?;
-        self.end()
+        self.ann.post(self, AnnNode::Expr(expr));
+        self.end();
     }
 
-    pub fn print_local_decl(&mut self, loc: &ast::Local) -> io::Result<()> {
-        self.print_pat(&loc.pat)?;
+    crate fn print_local_decl(&mut self, loc: &ast::Local) {
+        self.print_pat(&loc.pat);
         if let Some(ref ty) = loc.ty {
-            self.word_space(":")?;
-            self.print_type(ty)?;
+            self.word_space(":");
+            self.print_type(ty);
         }
-        Ok(())
-    }
-
-    pub fn print_ident(&mut self, ident: ast::Ident) -> io::Result<()> {
-        if ident.is_raw_guess() {
-            self.s.word(format!("r#{}", ident))?;
-        } else {
-            self.s.word(ident.as_str().to_string())?;
-        }
-        self.ann.post(self, AnnNode::Ident(&ident))
     }
 
-    pub fn print_usize(&mut self, i: usize) -> io::Result<()> {
+    crate fn print_usize(&mut self, i: usize) {
         self.s.word(i.to_string())
     }
 
-    pub fn print_name(&mut self, name: ast::Name) -> io::Result<()> {
-        self.s.word(name.as_str().to_string())?;
+    crate fn print_name(&mut self, name: ast::Name) {
+        self.s.word(name.as_str().to_string());
         self.ann.post(self, AnnNode::Name(&name))
     }
 
-    pub fn print_for_decl(&mut self, loc: &ast::Local,
-                          coll: &ast::Expr) -> io::Result<()> {
-        self.print_local_decl(loc)?;
-        self.s.space()?;
-        self.word_space("in")?;
-        self.print_expr(coll)
-    }
-
-    fn print_path(&mut self,
-                  path: &ast::Path,
-                  colons_before_params: bool,
-                  depth: usize)
-                  -> io::Result<()>
-    {
-        self.maybe_print_comment(path.span.lo())?;
-
-        for (i, segment) in path.segments[..path.segments.len() - depth].iter().enumerate() {
-            if i > 0 {
-                self.s.word("::")?
-            }
-            self.print_path_segment(segment, colons_before_params)?;
-        }
-
-        Ok(())
-    }
-
-    fn print_path_segment(&mut self,
-                          segment: &ast::PathSegment,
-                          colons_before_params: bool)
-                          -> io::Result<()>
-    {
-        if segment.ident.name != keywords::PathRoot.name() {
-            if segment.ident.name == keywords::DollarCrate.name() {
-                self.print_dollar_crate(segment.ident)?;
-            } else {
-                self.print_ident(segment.ident)?;
-            }
-            if let Some(ref args) = segment.args {
-                self.print_generic_args(args, colons_before_params)?;
-            }
-        }
-        Ok(())
-    }
-
     fn print_qpath(&mut self,
                    path: &ast::Path,
                    qself: &ast::QSelf,
                    colons_before_params: bool)
-                   -> io::Result<()>
     {
-        self.s.word("<")?;
-        self.print_type(&qself.ty)?;
+        self.s.word("<");
+        self.print_type(&qself.ty);
         if qself.position > 0 {
-            self.s.space()?;
-            self.word_space("as")?;
+            self.s.space();
+            self.word_space("as");
             let depth = path.segments.len() - qself.position;
-            self.print_path(path, false, depth)?;
+            self.print_path(path, false, depth);
         }
-        self.s.word(">")?;
-        self.s.word("::")?;
+        self.s.word(">");
+        self.s.word("::");
         let item_segment = path.segments.last().unwrap();
-        self.print_ident(item_segment.ident)?;
+        self.print_ident(item_segment.ident);
         match item_segment.args {
             Some(ref args) => self.print_generic_args(args, colons_before_params),
-            None => Ok(()),
-        }
-    }
-
-    fn print_generic_args(&mut self,
-                          args: &ast::GenericArgs,
-                          colons_before_params: bool)
-                          -> io::Result<()>
-    {
-        if colons_before_params {
-            self.s.word("::")?
-        }
-
-        match *args {
-            ast::GenericArgs::AngleBracketed(ref data) => {
-                self.s.word("<")?;
-
-                self.commasep(Inconsistent, &data.args, |s, generic_arg| {
-                    s.print_generic_arg(generic_arg)
-                })?;
-
-                let mut comma = data.args.len() != 0;
-
-                for binding in data.bindings.iter() {
-                    if comma {
-                        self.word_space(",")?
-                    }
-                    self.print_ident(binding.ident)?;
-                    self.s.space()?;
-                    self.word_space("=")?;
-                    self.print_type(&binding.ty)?;
-                    comma = true;
-                }
-
-                self.s.word(">")?
-            }
-
-            ast::GenericArgs::Parenthesized(ref data) => {
-                self.s.word("(")?;
-                self.commasep(
-                    Inconsistent,
-                    &data.inputs,
-                    |s, ty| s.print_type(ty))?;
-                self.s.word(")")?;
-
-                if let Some(ref ty) = data.output {
-                    self.space_if_not_bol()?;
-                    self.word_space("->")?;
-                    self.print_type(ty)?;
-                }
-            }
+            None => {},
         }
-
-        Ok(())
     }
 
-    pub fn print_pat(&mut self, pat: &ast::Pat) -> io::Result<()> {
-        self.maybe_print_comment(pat.span.lo())?;
-        self.ann.pre(self, AnnNode::Pat(pat))?;
+    crate fn print_pat(&mut self, pat: &ast::Pat) {
+        self.maybe_print_comment(pat.span.lo());
+        self.ann.pre(self, AnnNode::Pat(pat));
         /* Pat isn't normalized, but the beauty of it
          is that it doesn't matter */
         match pat.node {
-            PatKind::Wild => self.s.word("_")?,
+            PatKind::Wild => self.s.word("_"),
             PatKind::Ident(binding_mode, ident, ref sub) => {
                 match binding_mode {
                     ast::BindingMode::ByRef(mutbl) => {
-                        self.word_nbsp("ref")?;
-                        self.print_mutability(mutbl)?;
+                        self.word_nbsp("ref");
+                        self.print_mutability(mutbl);
                     }
                     ast::BindingMode::ByValue(ast::Mutability::Immutable) => {}
                     ast::BindingMode::ByValue(ast::Mutability::Mutable) => {
-                        self.word_nbsp("mut")?;
+                        self.word_nbsp("mut");
                     }
                 }
-                self.print_ident(ident)?;
+                self.print_ident(ident);
                 if let Some(ref p) = *sub {
-                    self.s.word("@")?;
-                    self.print_pat(p)?;
+                    self.s.word("@");
+                    self.print_pat(p);
                 }
             }
-            PatKind::TupleStruct(ref path, ref elts, ddpos) => {
-                self.print_path(path, true, 0)?;
-                self.popen()?;
-                if let Some(ddpos) = ddpos {
-                    self.commasep(Inconsistent, &elts[..ddpos], |s, p| s.print_pat(p))?;
-                    if ddpos != 0 {
-                        self.word_space(",")?;
-                    }
-                    self.s.word("..")?;
-                    if ddpos != elts.len() {
-                        self.s.word(",")?;
-                        self.commasep(Inconsistent, &elts[ddpos..], |s, p| s.print_pat(p))?;
-                    }
-                } else {
-                    self.commasep(Inconsistent, &elts[..], |s, p| s.print_pat(p))?;
-                }
-                self.pclose()?;
+            PatKind::TupleStruct(ref path, ref elts) => {
+                self.print_path(path, true, 0);
+                self.popen();
+                self.commasep(Inconsistent, &elts[..], |s, p| s.print_pat(p));
+                self.pclose();
+            }
+            PatKind::Or(ref pats) => {
+                self.strsep("|", true, Inconsistent, &pats[..], |s, p| s.print_pat(p));
             }
             PatKind::Path(None, ref path) => {
-                self.print_path(path, true, 0)?;
+                self.print_path(path, true, 0);
             }
             PatKind::Path(Some(ref qself), ref path) => {
-                self.print_qpath(path, qself, false)?;
+                self.print_qpath(path, qself, false);
             }
             PatKind::Struct(ref path, ref fields, etc) => {
-                self.print_path(path, true, 0)?;
-                self.nbsp()?;
-                self.word_space("{")?;
+                self.print_path(path, true, 0);
+                self.nbsp();
+                self.word_space("{");
                 self.commasep_cmnt(
                     Consistent, &fields[..],
                     |s, f| {
-                        s.cbox(INDENT_UNIT)?;
-                        if !f.node.is_shorthand {
-                            s.print_ident(f.node.ident)?;
-                            s.word_nbsp(":")?;
+                        s.cbox(INDENT_UNIT);
+                        if !f.is_shorthand {
+                            s.print_ident(f.ident);
+                            s.word_nbsp(":");
                         }
-                        s.print_pat(&f.node.pat)?;
-                        s.end()
+                        s.print_pat(&f.pat);
+                        s.end();
                     },
-                    |f| f.node.pat.span)?;
+                    |f| f.pat.span);
                 if etc {
-                    if !fields.is_empty() { self.word_space(",")?; }
-                    self.s.word("..")?;
-                }
-                self.s.space()?;
-                self.s.word("}")?;
-            }
-            PatKind::Tuple(ref elts, ddpos) => {
-                self.popen()?;
-                if let Some(ddpos) = ddpos {
-                    self.commasep(Inconsistent, &elts[..ddpos], |s, p| s.print_pat(p))?;
-                    if ddpos != 0 {
-                        self.word_space(",")?;
-                    }
-                    self.s.word("..")?;
-                    if ddpos != elts.len() {
-                        self.s.word(",")?;
-                        self.commasep(Inconsistent, &elts[ddpos..], |s, p| s.print_pat(p))?;
-                    }
-                } else {
-                    self.commasep(Inconsistent, &elts[..], |s, p| s.print_pat(p))?;
-                    if elts.len() == 1 {
-                        self.s.word(",")?;
-                    }
+                    if !fields.is_empty() { self.word_space(","); }
+                    self.s.word("..");
                 }
-                self.pclose()?;
+                self.s.space();
+                self.s.word("}");
+            }
+            PatKind::Tuple(ref elts) => {
+                self.popen();
+                self.commasep(Inconsistent, &elts[..], |s, p| s.print_pat(p));
+                if elts.len() == 1 {
+                    self.s.word(",");
+                }
+                self.pclose();
             }
             PatKind::Box(ref inner) => {
-                self.s.word("box ")?;
-                self.print_pat(inner)?;
+                self.s.word("box ");
+                self.print_pat(inner);
             }
             PatKind::Ref(ref inner, mutbl) => {
-                self.s.word("&")?;
+                self.s.word("&");
                 if mutbl == ast::Mutability::Mutable {
-                    self.s.word("mut ")?;
+                    self.s.word("mut ");
                 }
-                self.print_pat(inner)?;
+                self.print_pat(inner);
             }
-            PatKind::Lit(ref e) => self.print_expr(&**e)?,
+            PatKind::Lit(ref e) => self.print_expr(&**e),
             PatKind::Range(ref begin, ref end, Spanned { node: ref end_kind, .. }) => {
-                self.print_expr(begin)?;
-                self.s.space()?;
+                self.print_expr(begin);
+                self.s.space();
                 match *end_kind {
-                    RangeEnd::Included(RangeSyntax::DotDotDot) => self.s.word("...")?,
-                    RangeEnd::Included(RangeSyntax::DotDotEq) => self.s.word("..=")?,
-                    RangeEnd::Excluded => self.s.word("..")?,
-                }
-                self.print_expr(end)?;
-            }
-            PatKind::Slice(ref before, ref slice, ref after) => {
-                self.s.word("[")?;
-                self.commasep(Inconsistent,
-                                   &before[..],
-                                   |s, p| s.print_pat(p))?;
-                if let Some(ref p) = *slice {
-                    if !before.is_empty() { self.word_space(",")?; }
-                    if let PatKind::Wild = p.node {
-                        // Print nothing
-                    } else {
-                        self.print_pat(p)?;
-                    }
-                    self.s.word("..")?;
-                    if !after.is_empty() { self.word_space(",")?; }
+                    RangeEnd::Included(RangeSyntax::DotDotDot) => self.s.word("..."),
+                    RangeEnd::Included(RangeSyntax::DotDotEq) => self.s.word("..="),
+                    RangeEnd::Excluded => self.s.word(".."),
                 }
-                self.commasep(Inconsistent,
-                                   &after[..],
-                                   |s, p| s.print_pat(p))?;
-                self.s.word("]")?;
+                self.print_expr(end);
+            }
+            PatKind::Slice(ref elts) => {
+                self.s.word("[");
+                self.commasep(Inconsistent, &elts[..], |s, p| s.print_pat(p));
+                self.s.word("]");
             }
+            PatKind::Rest => self.s.word(".."),
             PatKind::Paren(ref inner) => {
-                self.popen()?;
-                self.print_pat(inner)?;
-                self.pclose()?;
+                self.popen();
+                self.print_pat(inner);
+                self.pclose();
             }
-            PatKind::Mac(ref m) => self.print_mac(m)?,
+            PatKind::Mac(ref m) => self.print_mac(m),
         }
         self.ann.post(self, AnnNode::Pat(pat))
     }
 
-    fn print_pats(&mut self, pats: &[P<ast::Pat>]) -> io::Result<()> {
-        let mut first = true;
-        for p in pats {
-            if first {
-                first = false;
-            } else {
-                self.s.space()?;
-                self.word_space("|")?;
-            }
-            self.print_pat(p)?;
-        }
-        Ok(())
+    fn print_pats(&mut self, pats: &[P<ast::Pat>]) {
+        self.strsep("|", true, Inconsistent, pats, |s, p| s.print_pat(p));
     }
 
-    fn print_arm(&mut self, arm: &ast::Arm) -> io::Result<()> {
+    fn print_arm(&mut self, arm: &ast::Arm) {
         // I have no idea why this check is necessary, but here it
         // is :(
         if arm.attrs.is_empty() {
-            self.s.space()?;
+            self.s.space();
         }
-        self.cbox(INDENT_UNIT)?;
-        self.ibox(0)?;
-        self.maybe_print_comment(arm.pats[0].span.lo())?;
-        self.print_outer_attributes(&arm.attrs)?;
-        self.print_pats(&arm.pats)?;
-        self.s.space()?;
-        if let Some(ref g) = arm.guard {
-            match g {
-                ast::Guard::If(ref e) => {
-                    self.word_space("if")?;
-                    self.print_expr(e)?;
-                    self.s.space()?;
-                }
-            }
+        self.cbox(INDENT_UNIT);
+        self.ibox(0);
+        self.maybe_print_comment(arm.pats[0].span.lo());
+        self.print_outer_attributes(&arm.attrs);
+        self.print_pats(&arm.pats);
+        self.s.space();
+        if let Some(ref e) = arm.guard {
+            self.word_space("if");
+            self.print_expr(e);
+            self.s.space();
         }
-        self.word_space("=>")?;
+        self.word_space("=>");
 
         match arm.body.node {
             ast::ExprKind::Block(ref blk, opt_label) => {
                 if let Some(label) = opt_label {
-                    self.print_ident(label.ident)?;
-                    self.word_space(":")?;
+                    self.print_ident(label.ident);
+                    self.word_space(":");
                 }
 
                 // the block will close the pattern's ibox
-                self.print_block_unclosed_indent(blk, INDENT_UNIT)?;
+                self.print_block_unclosed_indent(blk);
 
                 // If it is a user-provided unsafe block, print a comma after it
                 if let BlockCheckMode::Unsafe(ast::UserProvided) = blk.rules {
-                    self.s.word(",")?;
+                    self.s.word(",");
                 }
             }
             _ => {
-                self.end()?; // close the ibox for the pattern
-                self.print_expr(&arm.body)?;
-                self.s.word(",")?;
+                self.end(); // close the ibox for the pattern
+                self.print_expr(&arm.body);
+                self.s.word(",");
             }
         }
-        self.end() // close enclosing cbox
+        self.end(); // close enclosing cbox
     }
 
-    fn print_explicit_self(&mut self, explicit_self: &ast::ExplicitSelf) -> io::Result<()> {
+    fn print_explicit_self(&mut self, explicit_self: &ast::ExplicitSelf) {
         match explicit_self.node {
             SelfKind::Value(m) => {
-                self.print_mutability(m)?;
+                self.print_mutability(m);
                 self.s.word("self")
             }
             SelfKind::Region(ref lt, m) => {
-                self.s.word("&")?;
-                self.print_opt_lifetime(lt)?;
-                self.print_mutability(m)?;
+                self.s.word("&");
+                self.print_opt_lifetime(lt);
+                self.print_mutability(m);
                 self.s.word("self")
             }
             SelfKind::Explicit(ref typ, m) => {
-                self.print_mutability(m)?;
-                self.s.word("self")?;
-                self.word_space(":")?;
+                self.print_mutability(m);
+                self.s.word("self");
+                self.word_space(":");
                 self.print_type(typ)
             }
         }
     }
 
-    pub fn print_fn(&mut self,
+    crate fn print_fn(&mut self,
                     decl: &ast::FnDecl,
-                    header: &ast::FnHeader,
+                    header: ast::FnHeader,
                     name: Option<ast::Ident>,
                     generics: &ast::Generics,
-                    vis: &ast::Visibility) -> io::Result<()> {
-        self.print_fn_header_info(header, vis)?;
+                    vis: &ast::Visibility) {
+        self.print_fn_header_info(header, vis);
 
         if let Some(name) = name {
-            self.nbsp()?;
-            self.print_ident(name)?;
+            self.nbsp();
+            self.print_ident(name);
         }
-        self.print_generic_params(&generics.params)?;
-        self.print_fn_args_and_ret(decl)?;
+        self.print_generic_params(&generics.params);
+        self.print_fn_args_and_ret(decl);
         self.print_where_clause(&generics.where_clause)
     }
 
-    pub fn print_fn_args_and_ret(&mut self, decl: &ast::FnDecl)
-        -> io::Result<()> {
-        self.popen()?;
-        self.commasep(Inconsistent, &decl.inputs, |s, arg| s.print_arg(arg, false))?;
-        self.pclose()?;
+    crate fn print_fn_args_and_ret(&mut self, decl: &ast::FnDecl) {
+        self.popen();
+        self.commasep(Inconsistent, &decl.inputs, |s, arg| s.print_arg(arg, false));
+        self.pclose();
 
         self.print_fn_output(decl)
     }
 
-    pub fn print_fn_block_args(
-            &mut self,
-            decl: &ast::FnDecl)
-            -> io::Result<()> {
-        self.s.word("|")?;
-        self.commasep(Inconsistent, &decl.inputs, |s, arg| s.print_arg(arg, true))?;
-        self.s.word("|")?;
+    crate fn print_fn_block_args(&mut self, decl: &ast::FnDecl) {
+        self.s.word("|");
+        self.commasep(Inconsistent, &decl.inputs, |s, arg| s.print_arg(arg, true));
+        self.s.word("|");
 
         if let ast::FunctionRetTy::Default(..) = decl.output {
-            return Ok(());
+            return;
         }
 
-        self.space_if_not_bol()?;
-        self.word_space("->")?;
+        self.space_if_not_bol();
+        self.word_space("->");
         match decl.output {
             ast::FunctionRetTy::Ty(ref ty) => {
-                self.print_type(ty)?;
+                self.print_type(ty);
                 self.maybe_print_comment(ty.span.lo())
             }
             ast::FunctionRetTy::Default(..) => unreachable!(),
         }
     }
 
-    pub fn print_movability(&mut self, movability: ast::Movability)
-                                -> io::Result<()> {
+    crate fn print_movability(&mut self, movability: ast::Movability) {
         match movability {
             ast::Movability::Static => self.word_space("static"),
-            ast::Movability::Movable => Ok(()),
+            ast::Movability::Movable => {},
         }
     }
 
-    pub fn print_asyncness(&mut self, asyncness: &ast::IsAsync) -> io::Result<()> {
+    crate fn print_asyncness(&mut self, asyncness: ast::IsAsync) {
         if asyncness.is_async() {
-            self.word_nbsp("async")?;
+            self.word_nbsp("async");
         }
-        Ok(())
     }
 
-    pub fn print_capture_clause(&mut self, capture_clause: ast::CaptureBy)
-                                -> io::Result<()> {
+    crate fn print_capture_clause(&mut self, capture_clause: ast::CaptureBy) {
         match capture_clause {
             ast::CaptureBy::Value => self.word_space("move"),
-            ast::CaptureBy::Ref => Ok(()),
+            ast::CaptureBy::Ref => {},
         }
     }
 
-    pub fn print_type_bounds(&mut self, prefix: &'static str, bounds: &[ast::GenericBound])
-                             -> io::Result<()> {
+    crate fn print_type_bounds(&mut self, prefix: &'static str, bounds: &[ast::GenericBound]) {
         if !bounds.is_empty() {
-            self.s.word(prefix)?;
+            self.s.word(prefix);
             let mut first = true;
             for bound in bounds {
                 if !(first && prefix.is_empty()) {
-                    self.nbsp()?;
+                    self.nbsp();
                 }
                 if first {
                     first = false;
                 } else {
-                    self.word_space("+")?;
+                    self.word_space("+");
                 }
 
                 match bound {
                     GenericBound::Trait(tref, modifier) => {
                         if modifier == &TraitBoundModifier::Maybe {
-                            self.s.word("?")?;
+                            self.s.word("?");
                         }
-                        self.print_poly_trait_ref(tref)?;
+                        self.print_poly_trait_ref(tref);
                     }
-                    GenericBound::Outlives(lt) => self.print_lifetime(*lt)?,
+                    GenericBound::Outlives(lt) => self.print_lifetime(*lt),
                 }
             }
         }
-        Ok(())
     }
 
-    pub fn print_lifetime(&mut self, lifetime: ast::Lifetime) -> io::Result<()> {
+    crate fn print_lifetime(&mut self, lifetime: ast::Lifetime) {
         self.print_name(lifetime.ident.name)
     }
 
-    pub fn print_lifetime_bounds(&mut self, lifetime: ast::Lifetime, bounds: &ast::GenericBounds)
-        -> io::Result<()>
-    {
-        self.print_lifetime(lifetime)?;
+    crate fn print_lifetime_bounds(
+        &mut self, lifetime: ast::Lifetime, bounds: &ast::GenericBounds) {
+        self.print_lifetime(lifetime);
         if !bounds.is_empty() {
-            self.s.word(": ")?;
+            self.s.word(": ");
             for (i, bound) in bounds.iter().enumerate() {
                 if i != 0 {
-                    self.s.word(" + ")?;
+                    self.s.word(" + ");
                 }
                 match bound {
-                    ast::GenericBound::Outlives(lt) => self.print_lifetime(*lt)?,
+                    ast::GenericBound::Outlives(lt) => self.print_lifetime(*lt),
                     _ => panic!(),
                 }
             }
         }
-        Ok(())
     }
 
-    pub fn print_generic_params(
-        &mut self,
-        generic_params: &[ast::GenericParam]
-    ) -> io::Result<()> {
+    crate fn print_generic_params(&mut self, generic_params: &[ast::GenericParam]) {
         if generic_params.is_empty() {
-            return Ok(());
+            return;
         }
 
-        self.s.word("<")?;
+        self.s.word("<");
 
         self.commasep(Inconsistent, &generic_params, |s, param| {
+            s.print_outer_attributes_inline(&param.attrs);
+
             match param.kind {
                 ast::GenericParamKind::Lifetime => {
-                    s.print_outer_attributes_inline(&param.attrs)?;
                     let lt = ast::Lifetime { id: param.id, ident: param.ident };
                     s.print_lifetime_bounds(lt, &param.bounds)
                 }
                 ast::GenericParamKind::Type { ref default } => {
-                    s.print_outer_attributes_inline(&param.attrs)?;
-                    s.print_ident(param.ident)?;
-                    s.print_type_bounds(":", &param.bounds)?;
-                    match default {
-                        Some(ref default) => {
-                            s.s.space()?;
-                            s.word_space("=")?;
-                            s.print_type(default)
-                        }
-                        _ => Ok(())
+                    s.print_ident(param.ident);
+                    s.print_type_bounds(":", &param.bounds);
+                    if let Some(ref default) = default {
+                        s.s.space();
+                        s.word_space("=");
+                        s.print_type(default)
                     }
                 }
                 ast::GenericParamKind::Const { ref ty } => {
-                    s.print_outer_attributes_inline(&param.attrs)?;
-                    s.word_space("const")?;
-                    s.print_ident(param.ident)?;
-                    s.s.space()?;
-                    s.word_space(":")?;
-                    s.print_type(ty)?;
+                    s.word_space("const");
+                    s.print_ident(param.ident);
+                    s.s.space();
+                    s.word_space(":");
+                    s.print_type(ty);
                     s.print_type_bounds(":", &param.bounds)
                 }
             }
-        })?;
+        });
 
-        self.s.word(">")?;
-        Ok(())
+        self.s.word(">");
     }
 
-    pub fn print_where_clause(&mut self, where_clause: &ast::WhereClause)
-                              -> io::Result<()> {
+    crate fn print_where_clause(&mut self, where_clause: &ast::WhereClause) {
         if where_clause.predicates.is_empty() {
-            return Ok(())
+            return;
         }
 
-        self.s.space()?;
-        self.word_space("where")?;
+        self.s.space();
+        self.word_space("where");
 
         for (i, predicate) in where_clause.predicates.iter().enumerate() {
             if i != 0 {
-                self.word_space(",")?;
+                self.word_space(",");
             }
 
             match *predicate {
@@ -2905,295 +2682,201 @@ impl<'a> State<'a> {
                     ref bounds,
                     ..
                 }) => {
-                    self.print_formal_generic_params(bound_generic_params)?;
-                    self.print_type(bounded_ty)?;
-                    self.print_type_bounds(":", bounds)?;
+                    self.print_formal_generic_params(bound_generic_params);
+                    self.print_type(bounded_ty);
+                    self.print_type_bounds(":", bounds);
                 }
                 ast::WherePredicate::RegionPredicate(ast::WhereRegionPredicate{ref lifetime,
                                                                                ref bounds,
                                                                                ..}) => {
-                    self.print_lifetime_bounds(*lifetime, bounds)?;
+                    self.print_lifetime_bounds(*lifetime, bounds);
                 }
                 ast::WherePredicate::EqPredicate(ast::WhereEqPredicate{ref lhs_ty,
                                                                        ref rhs_ty,
                                                                        ..}) => {
-                    self.print_type(lhs_ty)?;
-                    self.s.space()?;
-                    self.word_space("=")?;
-                    self.print_type(rhs_ty)?;
+                    self.print_type(lhs_ty);
+                    self.s.space();
+                    self.word_space("=");
+                    self.print_type(rhs_ty);
                 }
             }
         }
-
-        Ok(())
     }
 
-    pub fn print_use_tree(&mut self, tree: &ast::UseTree) -> io::Result<()> {
+    crate fn print_use_tree(&mut self, tree: &ast::UseTree) {
         match tree.kind {
             ast::UseTreeKind::Simple(rename, ..) => {
-                self.print_path(&tree.prefix, false, 0)?;
+                self.print_path(&tree.prefix, false, 0);
                 if let Some(rename) = rename {
-                    self.s.space()?;
-                    self.word_space("as")?;
-                    self.print_ident(rename)?;
+                    self.s.space();
+                    self.word_space("as");
+                    self.print_ident(rename);
                 }
             }
             ast::UseTreeKind::Glob => {
                 if !tree.prefix.segments.is_empty() {
-                    self.print_path(&tree.prefix, false, 0)?;
-                    self.s.word("::")?;
+                    self.print_path(&tree.prefix, false, 0);
+                    self.s.word("::");
                 }
-                self.s.word("*")?;
+                self.s.word("*");
             }
             ast::UseTreeKind::Nested(ref items) => {
                 if tree.prefix.segments.is_empty() {
-                    self.s.word("{")?;
+                    self.s.word("{");
                 } else {
-                    self.print_path(&tree.prefix, false, 0)?;
-                    self.s.word("::{")?;
+                    self.print_path(&tree.prefix, false, 0);
+                    self.s.word("::{");
                 }
                 self.commasep(Inconsistent, &items[..], |this, &(ref tree, _)| {
                     this.print_use_tree(tree)
-                })?;
-                self.s.word("}")?;
+                });
+                self.s.word("}");
             }
         }
-
-        Ok(())
     }
 
-    pub fn print_mutability(&mut self,
-                            mutbl: ast::Mutability) -> io::Result<()> {
+    crate fn print_mutability(&mut self, mutbl: ast::Mutability) {
         match mutbl {
             ast::Mutability::Mutable => self.word_nbsp("mut"),
-            ast::Mutability::Immutable => Ok(()),
+            ast::Mutability::Immutable => {},
         }
     }
 
-    pub fn print_mt(&mut self, mt: &ast::MutTy) -> io::Result<()> {
-        self.print_mutability(mt.mutbl)?;
+    crate fn print_mt(&mut self, mt: &ast::MutTy) {
+        self.print_mutability(mt.mutbl);
         self.print_type(&mt.ty)
     }
 
-    pub fn print_arg(&mut self, input: &ast::Arg, is_closure: bool) -> io::Result<()> {
-        self.ibox(INDENT_UNIT)?;
+    crate fn print_arg(&mut self, input: &ast::Arg, is_closure: bool) {
+        self.ibox(INDENT_UNIT);
+
+        self.print_outer_attributes_inline(&input.attrs);
+
         match input.ty.node {
-            ast::TyKind::Infer if is_closure => self.print_pat(&input.pat)?,
+            ast::TyKind::Infer if is_closure => self.print_pat(&input.pat),
             _ => {
                 if let Some(eself) = input.to_self() {
-                    self.print_explicit_self(&eself)?;
+                    self.print_explicit_self(&eself);
                 } else {
                     let invalid = if let PatKind::Ident(_, ident, _) = input.pat.node {
-                        ident.name == keywords::Invalid.name()
+                        ident.name == kw::Invalid
                     } else {
                         false
                     };
                     if !invalid {
-                        self.print_pat(&input.pat)?;
-                        self.s.word(":")?;
-                        self.s.space()?;
+                        self.print_pat(&input.pat);
+                        self.s.word(":");
+                        self.s.space();
                     }
-                    self.print_type(&input.ty)?;
+                    self.print_type(&input.ty);
                 }
             }
         }
-        self.end()
+        self.end();
     }
 
-    pub fn print_fn_output(&mut self, decl: &ast::FnDecl) -> io::Result<()> {
+    crate fn print_fn_output(&mut self, decl: &ast::FnDecl) {
         if let ast::FunctionRetTy::Default(..) = decl.output {
-            return Ok(());
+            return;
         }
 
-        self.space_if_not_bol()?;
-        self.ibox(INDENT_UNIT)?;
-        self.word_space("->")?;
+        self.space_if_not_bol();
+        self.ibox(INDENT_UNIT);
+        self.word_space("->");
         match decl.output {
             ast::FunctionRetTy::Default(..) => unreachable!(),
             ast::FunctionRetTy::Ty(ref ty) =>
-                self.print_type(ty)?
+                self.print_type(ty),
         }
-        self.end()?;
+        self.end();
 
         match decl.output {
             ast::FunctionRetTy::Ty(ref output) => self.maybe_print_comment(output.span.lo()),
-            _ => Ok(())
+            _ => {}
         }
     }
 
-    pub fn print_ty_fn(&mut self,
+    crate fn print_ty_fn(&mut self,
                        abi: abi::Abi,
                        unsafety: ast::Unsafety,
                        decl: &ast::FnDecl,
                        name: Option<ast::Ident>,
                        generic_params: &[ast::GenericParam])
-                       -> io::Result<()> {
-        self.ibox(INDENT_UNIT)?;
+                       {
+        self.ibox(INDENT_UNIT);
         if !generic_params.is_empty() {
-            self.s.word("for")?;
-            self.print_generic_params(generic_params)?;
+            self.s.word("for");
+            self.print_generic_params(generic_params);
         }
         let generics = ast::Generics {
             params: Vec::new(),
             where_clause: ast::WhereClause {
-                id: ast::DUMMY_NODE_ID,
                 predicates: Vec::new(),
                 span: syntax_pos::DUMMY_SP,
             },
             span: syntax_pos::DUMMY_SP,
         };
         self.print_fn(decl,
-                      &ast::FnHeader { unsafety, abi, ..ast::FnHeader::default() },
+                      ast::FnHeader { unsafety, abi, ..ast::FnHeader::default() },
                       name,
                       &generics,
-                      &source_map::dummy_spanned(ast::VisibilityKind::Inherited))?;
-        self.end()
+                      &source_map::dummy_spanned(ast::VisibilityKind::Inherited));
+        self.end();
     }
 
-    pub fn maybe_print_trailing_comment(&mut self, span: syntax_pos::Span,
+    crate fn maybe_print_trailing_comment(&mut self, span: syntax_pos::Span,
                                         next_pos: Option<BytePos>)
-        -> io::Result<()> {
-        let cm = match self.cm {
-            Some(cm) => cm,
-            _ => return Ok(())
-        };
-        if let Some(ref cmnt) = self.next_comment() {
-            if cmnt.style != comments::Trailing { return Ok(()) }
-            let span_line = cm.lookup_char_pos(span.hi());
-            let comment_line = cm.lookup_char_pos(cmnt.pos);
-            let next = next_pos.unwrap_or_else(|| cmnt.pos + BytePos(1));
-            if span.hi() < cmnt.pos && cmnt.pos < next && span_line.line == comment_line.line {
-                self.print_comment(cmnt)?;
+    {
+        if let Some(cmnts) = self.comments() {
+            if let Some(cmnt) = cmnts.trailing_comment(span, next_pos) {
+                self.print_comment(&cmnt);
             }
         }
-        Ok(())
     }
 
-    pub fn print_remaining_comments(&mut self) -> io::Result<()> {
+    crate fn print_remaining_comments(&mut self) {
         // If there aren't any remaining comments, then we need to manually
         // make sure there is a line break at the end.
         if self.next_comment().is_none() {
-            self.s.hardbreak()?;
+            self.s.hardbreak();
         }
         while let Some(ref cmnt) = self.next_comment() {
-            self.print_comment(cmnt)?;
+            self.print_comment(cmnt);
         }
-        Ok(())
     }
 
-    pub fn print_opt_abi_and_extern_if_nondefault(&mut self,
-                                                  opt_abi: Option<Abi>)
-        -> io::Result<()> {
-        match opt_abi {
-            Some(Abi::Rust) => Ok(()),
-            Some(abi) => {
-                self.word_nbsp("extern")?;
-                self.word_nbsp(abi.to_string())
-            }
-            None => Ok(())
-        }
-    }
-
-    pub fn print_extern_opt_abi(&mut self,
-                                opt_abi: Option<Abi>) -> io::Result<()> {
-        match opt_abi {
-            Some(abi) => {
-                self.word_nbsp("extern")?;
-                self.word_nbsp(abi.to_string())
-            }
-            None => Ok(())
-        }
-    }
-
-    pub fn print_fn_header_info(&mut self,
-                                header: &ast::FnHeader,
-                                vis: &ast::Visibility) -> io::Result<()> {
-        self.s.word(visibility_qualified(vis, ""))?;
+    crate fn print_fn_header_info(&mut self,
+                                header: ast::FnHeader,
+                                vis: &ast::Visibility) {
+        self.s.word(visibility_qualified(vis, ""));
 
         match header.constness.node {
             ast::Constness::NotConst => {}
-            ast::Constness::Const => self.word_nbsp("const")?
+            ast::Constness::Const => self.word_nbsp("const")
         }
 
-        self.print_asyncness(&header.asyncness.node)?;
-        self.print_unsafety(header.unsafety)?;
+        self.print_asyncness(header.asyncness.node);
+        self.print_unsafety(header.unsafety);
 
         if header.abi != Abi::Rust {
-            self.word_nbsp("extern")?;
-            self.word_nbsp(header.abi.to_string())?;
+            self.word_nbsp("extern");
+            self.word_nbsp(header.abi.to_string());
         }
 
         self.s.word("fn")
     }
 
-    pub fn print_unsafety(&mut self, s: ast::Unsafety) -> io::Result<()> {
+    crate fn print_unsafety(&mut self, s: ast::Unsafety) {
         match s {
-            ast::Unsafety::Normal => Ok(()),
+            ast::Unsafety::Normal => {},
             ast::Unsafety::Unsafe => self.word_nbsp("unsafe"),
         }
     }
 
-    pub fn print_is_auto(&mut self, s: ast::IsAuto) -> io::Result<()> {
+    crate fn print_is_auto(&mut self, s: ast::IsAuto) {
         match s {
             ast::IsAuto::Yes => self.word_nbsp("auto"),
-            ast::IsAuto::No => Ok(()),
+            ast::IsAuto::No => {}
         }
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    use crate::ast;
-    use crate::source_map;
-    use crate::with_globals;
-    use syntax_pos;
-
-    #[test]
-    fn test_fun_to_string() {
-        with_globals(|| {
-            let abba_ident = ast::Ident::from_str("abba");
-
-            let decl = ast::FnDecl {
-                inputs: Vec::new(),
-                output: ast::FunctionRetTy::Default(syntax_pos::DUMMY_SP),
-                c_variadic: false
-            };
-            let generics = ast::Generics::default();
-            assert_eq!(
-                fun_to_string(
-                    &decl,
-                    &ast::FnHeader {
-                        unsafety: ast::Unsafety::Normal,
-                        constness: source_map::dummy_spanned(ast::Constness::NotConst),
-                        asyncness: source_map::dummy_spanned(ast::IsAsync::NotAsync),
-                        abi: Abi::Rust,
-                    },
-                    abba_ident,
-                    &generics
-                ),
-                "fn abba()"
-            );
-        })
-    }
-
-    #[test]
-    fn test_variant_to_string() {
-        with_globals(|| {
-            let ident = ast::Ident::from_str("principal_skinner");
-
-            let var = source_map::respan(syntax_pos::DUMMY_SP, ast::Variant_ {
-                ident,
-                attrs: Vec::new(),
-                id: ast::DUMMY_NODE_ID,
-                // making this up as I go.... ?
-                data: ast::VariantData::Unit(ast::DUMMY_NODE_ID),
-                disr_expr: None,
-            });
-
-            let varstr = variant_to_string(&var);
-            assert_eq!(varstr, "principal_skinner");
-        })
-    }
-}
diff --git a/src/libsyntax/print/pprust/tests.rs b/src/libsyntax/print/pprust/tests.rs
new file mode 100644
index 00000000000..25214673e69
--- /dev/null
+++ b/src/libsyntax/print/pprust/tests.rs
@@ -0,0 +1,70 @@
+use super::*;
+
+use crate::ast;
+use crate::source_map;
+use crate::with_default_globals;
+use syntax_pos;
+
+fn fun_to_string(
+    decl: &ast::FnDecl, header: ast::FnHeader, name: ast::Ident, generics: &ast::Generics
+) -> String {
+    to_string(|s| {
+        s.head("");
+        s.print_fn(decl, header, Some(name),
+                   generics, &source_map::dummy_spanned(ast::VisibilityKind::Inherited));
+        s.end(); // Close the head box
+        s.end(); // Close the outer box
+    })
+}
+
+fn variant_to_string(var: &ast::Variant) -> String {
+    to_string(|s| s.print_variant(var))
+}
+
+#[test]
+fn test_fun_to_string() {
+    with_default_globals(|| {
+        let abba_ident = ast::Ident::from_str("abba");
+
+        let decl = ast::FnDecl {
+            inputs: Vec::new(),
+            output: ast::FunctionRetTy::Default(syntax_pos::DUMMY_SP),
+            c_variadic: false
+        };
+        let generics = ast::Generics::default();
+        assert_eq!(
+            fun_to_string(
+                &decl,
+                ast::FnHeader {
+                    unsafety: ast::Unsafety::Normal,
+                    constness: source_map::dummy_spanned(ast::Constness::NotConst),
+                    asyncness: source_map::dummy_spanned(ast::IsAsync::NotAsync),
+                    abi: Abi::Rust,
+                },
+                abba_ident,
+                &generics
+            ),
+            "fn abba()"
+        );
+    })
+}
+
+#[test]
+fn test_variant_to_string() {
+    with_default_globals(|| {
+        let ident = ast::Ident::from_str("principal_skinner");
+
+        let var = ast::Variant {
+            ident,
+            attrs: Vec::new(),
+            id: ast::DUMMY_NODE_ID,
+            // making this up as I go.... ?
+            data: ast::VariantData::Unit(ast::DUMMY_NODE_ID),
+            disr_expr: None,
+            span: syntax_pos::DUMMY_SP,
+        };
+
+        let varstr = variant_to_string(&var);
+        assert_eq!(varstr, "principal_skinner");
+    })
+}
diff --git a/src/libsyntax/ptr.rs b/src/libsyntax/ptr.rs
index 9afcb7c4621..b5eb8ca94c0 100644
--- a/src/libsyntax/ptr.rs
+++ b/src/libsyntax/ptr.rs
@@ -31,7 +31,7 @@ use std::iter::FromIterator;
 use std::ops::{Deref, DerefMut};
 use std::{slice, vec};
 
-use serialize::{Encodable, Decodable, Encoder, Decoder};
+use rustc_serialize::{Encodable, Decodable, Encoder, Decoder};
 
 use rustc_data_structures::stable_hasher::{StableHasher, StableHasherResult,
                                            HashStable};
@@ -41,11 +41,11 @@ pub struct P<T: ?Sized> {
     ptr: Box<T>
 }
 
-#[allow(non_snake_case)]
 /// Construct a `P<T>` from a `T` value.
+#[allow(non_snake_case)]
 pub fn P<T: 'static>(value: T) -> P<T> {
     P {
-        ptr: Box::new(value)
+        ptr: box value
     }
 }
 
@@ -57,7 +57,8 @@ impl<T: 'static> P<T> {
     {
         f(*self.ptr)
     }
-    /// Equivalent to and_then(|x| x)
+
+    /// Equivalent to `and_then(|x| x)`.
     pub fn into_inner(self) -> T {
         *self.ptr
     }
@@ -132,8 +133,15 @@ impl<T: Encodable> Encodable for P<T> {
 }
 
 impl<T> P<[T]> {
-    pub fn new() -> P<[T]> {
-        P { ptr: Default::default() }
+    pub const fn new() -> P<[T]> {
+        // HACK(eddyb) bypass the lack of a `const fn` to create an empty `Box<[T]>`
+        // (as trait methods, `default` in this case, can't be `const fn` yet).
+        P {
+            ptr: unsafe {
+                use std::ptr::NonNull;
+                std::mem::transmute(NonNull::<[T; 0]>::dangling() as NonNull<[T]>)
+            },
+        }
     }
 
     #[inline(never)]
diff --git a/src/libsyntax/source_map.rs b/src/libsyntax/source_map.rs
index 215618bd09c..7190cfd72a9 100644
--- a/src/libsyntax/source_map.rs
+++ b/src/libsyntax/source_map.rs
@@ -7,10 +7,8 @@
 //! within the SourceMap, which upon request can be converted to line and column
 //! information, source code snippets, etc.
 
-
 pub use syntax_pos::*;
-pub use syntax_pos::hygiene::{ExpnFormat, ExpnInfo};
-pub use ExpnFormat::*;
+pub use syntax_pos::hygiene::{ExpnKind, ExpnData};
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::stable_hasher::StableHasher;
@@ -26,16 +24,20 @@ use log::debug;
 
 use errors::SourceMapper;
 
+#[cfg(test)]
+mod tests;
+
 /// Returns the span itself if it doesn't come from a macro expansion,
 /// otherwise return the call site span up to the `enclosing_sp` by
-/// following the `expn_info` chain.
+/// following the `expn_data` chain.
 pub fn original_sp(sp: Span, enclosing_sp: Span) -> Span {
-    let call_site1 = sp.ctxt().outer().expn_info().map(|ei| ei.call_site);
-    let call_site2 = enclosing_sp.ctxt().outer().expn_info().map(|ei| ei.call_site);
-    match (call_site1, call_site2) {
-        (None, _) => sp,
-        (Some(call_site1), Some(call_site2)) if call_site1 == call_site2 => sp,
-        (Some(call_site1), _) => original_sp(call_site1, enclosing_sp),
+    let expn_data1 = sp.ctxt().outer_expn_data();
+    let expn_data2 = enclosing_sp.ctxt().outer_expn_data();
+    if expn_data1.is_root() ||
+       !expn_data2.is_root() && expn_data1.call_site == expn_data2.call_site {
+        sp
+    } else {
+        original_sp(expn_data1.call_site, enclosing_sp)
     }
 }
 
@@ -124,12 +126,12 @@ impl StableSourceFileId {
 
 #[derive(Default)]
 pub(super) struct SourceMapFiles {
-    pub(super) source_files: Vec<Lrc<SourceFile>>,
+    source_files: Vec<Lrc<SourceFile>>,
     stable_id_to_source_file: FxHashMap<StableSourceFileId, Lrc<SourceFile>>
 }
 
 pub struct SourceMap {
-    pub(super) files: Lock<SourceMapFiles>,
+    files: Lock<SourceMapFiles>,
     file_loader: Box<dyn FileLoader + Sync + Send>,
     // This is used to apply the file path remapping as specified via
     // --remap-path-prefix to all SourceFiles allocated within this SourceMap.
@@ -150,7 +152,7 @@ impl SourceMap {
                             -> SourceMap {
         SourceMap {
             files: Default::default(),
-            file_loader: file_loader,
+            file_loader,
             path_mapping,
         }
     }
@@ -169,6 +171,26 @@ impl SourceMap {
         Ok(self.new_source_file(filename, src))
     }
 
+    /// Loads source file as a binary blob.
+    ///
+    /// Unlike `load_file`, guarantees that no normalization like BOM-removal
+    /// takes place.
+    pub fn load_binary_file(&self, path: &Path) -> io::Result<Vec<u8>> {
+        // Ideally, this should use `self.file_loader`, but it can't
+        // deal with binary files yet.
+        let bytes = fs::read(path)?;
+
+        // We need to add file to the `SourceMap`, so that it is present
+        // in dep-info. There's also an edge case that file might be both
+        // loaded as a binary via `include_bytes!` and as proper `SourceFile`
+        // via `mod`, so we try to use real file contents and not just an
+        // empty string.
+        let text = std::str::from_utf8(&bytes).unwrap_or("")
+            .to_string();
+        self.new_source_file(path.to_owned().into(), text);
+        Ok(bytes)
+    }
+
     pub fn files(&self) -> MappedLockGuard<'_, Vec<Lrc<SourceFile>>> {
         LockGuard::map(self.files.borrow(), |files| &mut files.source_files)
     }
@@ -191,6 +213,18 @@ impl SourceMap {
     /// If a file already exists in the source_map with the same id, that file is returned
     /// unmodified
     pub fn new_source_file(&self, filename: FileName, src: String) -> Lrc<SourceFile> {
+        self.try_new_source_file(filename, src)
+            .unwrap_or_else(|OffsetOverflowError| {
+                eprintln!("fatal error: rustc does not support files larger than 4GB");
+                errors::FatalError.raise()
+            })
+    }
+
+    fn try_new_source_file(
+        &self,
+        filename: FileName,
+        src: String
+    ) -> Result<Lrc<SourceFile>, OffsetOverflowError> {
         let start_pos = self.next_start_pos();
 
         // The path is used to determine the directory for loading submodules and
@@ -212,7 +246,7 @@ impl SourceMap {
                                                        was_remapped,
                                                        Some(&unmapped_path));
 
-        return match self.source_file_by_stable_id(file_id) {
+        let lrc_sf = match self.source_file_by_stable_id(file_id) {
             Some(lrc_sf) => lrc_sf,
             None => {
                 let source_file = Lrc::new(SourceFile::new(
@@ -221,7 +255,7 @@ impl SourceMap {
                     unmapped_path,
                     src,
                     Pos::from_usize(start_pos),
-                ));
+                )?);
 
                 let mut files = self.files.borrow_mut();
 
@@ -230,7 +264,8 @@ impl SourceMap {
 
                 source_file
             }
-        }
+        };
+        Ok(lrc_sf)
     }
 
     /// Allocates a new SourceFile representing a source file from an external
@@ -383,7 +418,7 @@ impl SourceMap {
         let f = (*self.files.borrow().source_files)[idx].clone();
 
         match f.lookup_line(pos) {
-            Some(line) => Ok(SourceFileAndLine { sf: f, line: line }),
+            Some(line) => Ok(SourceFileAndLine { sf: f, line }),
             None => Err(f)
         }
     }
@@ -498,14 +533,14 @@ impl SourceMap {
                               start_col,
                               end_col: hi.col });
 
-        Ok(FileLines {file: lo.file, lines: lines})
+        Ok(FileLines {file: lo.file, lines})
     }
 
     /// Extracts the source surrounding the given `Span` using the `extract_source` function. The
     /// extract function takes three arguments: a string slice containing the source, an index in
     /// the slice for the beginning of the span and an index in the slice for the end of the span.
     fn span_to_source<F>(&self, sp: Span, extract_source: F) -> Result<String, SpanSnippetError>
-        where F: Fn(&str, usize, usize) -> String
+        where F: Fn(&str, usize, usize) -> Result<String, SpanSnippetError>
     {
         if sp.lo() > sp.hi() {
             return Err(SpanSnippetError::IllFormedSpan(sp));
@@ -540,9 +575,9 @@ impl SourceMap {
             }
 
             if let Some(ref src) = local_begin.sf.src {
-                return Ok(extract_source(src, start_index, end_index));
+                return extract_source(src, start_index, end_index);
             } else if let Some(src) = local_begin.sf.external_src.borrow().get_source() {
-                return Ok(extract_source(src, start_index, end_index));
+                return extract_source(src, start_index, end_index);
             } else {
                 return Err(SpanSnippetError::SourceNotAvailable {
                     filename: local_begin.sf.name.clone()
@@ -553,8 +588,9 @@ impl SourceMap {
 
     /// Returns the source snippet as `String` corresponding to the given `Span`
     pub fn span_to_snippet(&self, sp: Span) -> Result<String, SpanSnippetError> {
-        self.span_to_source(sp, |src, start_index, end_index| src[start_index..end_index]
-                                                                .to_string())
+        self.span_to_source(sp, |src, start_index, end_index| src.get(start_index..end_index)
+            .map(|s| s.to_string())
+            .ok_or_else(|| SpanSnippetError::IllFormedSpan(sp)))
     }
 
     pub fn span_to_margin(&self, sp: Span) -> Option<usize> {
@@ -568,7 +604,9 @@ impl SourceMap {
 
     /// Returns the source snippet as `String` before the given `Span`
     pub fn span_to_prev_source(&self, sp: Span) -> Result<String, SpanSnippetError> {
-        self.span_to_source(sp, |src, start_index, _| src[..start_index].to_string())
+        self.span_to_source(sp, |src, start_index, _| src.get(..start_index)
+            .map(|s| s.to_string())
+            .ok_or_else(|| SpanSnippetError::IllFormedSpan(sp)))
     }
 
     /// Extend the given `Span` to just after the previous occurrence of `c`. Return the same span
@@ -727,6 +765,11 @@ impl SourceMap {
         debug!("find_width_of_character_at_span: local_begin=`{:?}`, local_end=`{:?}`",
                local_begin, local_end);
 
+        if local_begin.sf.start_pos != local_end.sf.start_pos {
+            debug!("find_width_of_character_at_span: begin and end are in different files");
+            return 1;
+        }
+
         let start_index = local_begin.pos.to_usize();
         let end_index = local_end.pos.to_usize();
         debug!("find_width_of_character_at_span: start_index=`{:?}`, end_index=`{:?}`",
@@ -802,7 +845,7 @@ impl SourceMap {
         let idx = self.lookup_source_file_idx(bpos);
         let sf = (*self.files.borrow().source_files)[idx].clone();
         let offset = bpos - sf.start_pos;
-        SourceFileAndBytePos {sf: sf, pos: offset}
+        SourceFileAndBytePos {sf, pos: offset}
     }
 
     /// Converts an absolute BytePos to a CharPos relative to the source_file.
@@ -930,27 +973,6 @@ impl SourceMap {
 
         None
     }
-
-    /// Reuses the span but adds information like the kind of the desugaring and features that are
-    /// allowed inside this span.
-    pub fn mark_span_with_reason(
-        &self,
-        reason: hygiene::CompilerDesugaringKind,
-        span: Span,
-        allow_internal_unstable: Option<Lrc<[symbol::Symbol]>>,
-    ) -> Span {
-        let mark = Mark::fresh(Mark::root());
-        mark.set_expn_info(ExpnInfo {
-            call_site: span,
-            def_site: Some(span),
-            format: CompilerDesugaring(reason),
-            allow_internal_unstable,
-            allow_internal_unsafe: false,
-            local_inner_macros: false,
-            edition: hygiene::default_edition(),
-        });
-        span.with_ctxt(SyntaxContext::empty().apply_mark(mark))
-    }
 }
 
 impl SourceMapper for SourceMap {
@@ -1025,223 +1047,3 @@ impl FilePathMapping {
         (path, false)
     }
 }
-
-// _____________________________________________________________________________
-// Tests
-//
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use rustc_data_structures::sync::Lrc;
-
-    fn init_source_map() -> SourceMap {
-        let sm = SourceMap::new(FilePathMapping::empty());
-        sm.new_source_file(PathBuf::from("blork.rs").into(),
-                       "first line.\nsecond line".to_string());
-        sm.new_source_file(PathBuf::from("empty.rs").into(),
-                       String::new());
-        sm.new_source_file(PathBuf::from("blork2.rs").into(),
-                       "first line.\nsecond line".to_string());
-        sm
-    }
-
-    #[test]
-    fn t3() {
-        // Test lookup_byte_offset
-        let sm = init_source_map();
-
-        let srcfbp1 = sm.lookup_byte_offset(BytePos(23));
-        assert_eq!(srcfbp1.sf.name, PathBuf::from("blork.rs").into());
-        assert_eq!(srcfbp1.pos, BytePos(23));
-
-        let srcfbp1 = sm.lookup_byte_offset(BytePos(24));
-        assert_eq!(srcfbp1.sf.name, PathBuf::from("empty.rs").into());
-        assert_eq!(srcfbp1.pos, BytePos(0));
-
-        let srcfbp2 = sm.lookup_byte_offset(BytePos(25));
-        assert_eq!(srcfbp2.sf.name, PathBuf::from("blork2.rs").into());
-        assert_eq!(srcfbp2.pos, BytePos(0));
-    }
-
-    #[test]
-    fn t4() {
-        // Test bytepos_to_file_charpos
-        let sm = init_source_map();
-
-        let cp1 = sm.bytepos_to_file_charpos(BytePos(22));
-        assert_eq!(cp1, CharPos(22));
-
-        let cp2 = sm.bytepos_to_file_charpos(BytePos(25));
-        assert_eq!(cp2, CharPos(0));
-    }
-
-    #[test]
-    fn t5() {
-        // Test zero-length source_files.
-        let sm = init_source_map();
-
-        let loc1 = sm.lookup_char_pos(BytePos(22));
-        assert_eq!(loc1.file.name, PathBuf::from("blork.rs").into());
-        assert_eq!(loc1.line, 2);
-        assert_eq!(loc1.col, CharPos(10));
-
-        let loc2 = sm.lookup_char_pos(BytePos(25));
-        assert_eq!(loc2.file.name, PathBuf::from("blork2.rs").into());
-        assert_eq!(loc2.line, 1);
-        assert_eq!(loc2.col, CharPos(0));
-    }
-
-    fn init_source_map_mbc() -> SourceMap {
-        let sm = SourceMap::new(FilePathMapping::empty());
-        // € is a three byte utf8 char.
-        sm.new_source_file(PathBuf::from("blork.rs").into(),
-                       "fir€st €€€€ line.\nsecond line".to_string());
-        sm.new_source_file(PathBuf::from("blork2.rs").into(),
-                       "first line€€.\n€ second line".to_string());
-        sm
-    }
-
-    #[test]
-    fn t6() {
-        // Test bytepos_to_file_charpos in the presence of multi-byte chars
-        let sm = init_source_map_mbc();
-
-        let cp1 = sm.bytepos_to_file_charpos(BytePos(3));
-        assert_eq!(cp1, CharPos(3));
-
-        let cp2 = sm.bytepos_to_file_charpos(BytePos(6));
-        assert_eq!(cp2, CharPos(4));
-
-        let cp3 = sm.bytepos_to_file_charpos(BytePos(56));
-        assert_eq!(cp3, CharPos(12));
-
-        let cp4 = sm.bytepos_to_file_charpos(BytePos(61));
-        assert_eq!(cp4, CharPos(15));
-    }
-
-    #[test]
-    fn t7() {
-        // Test span_to_lines for a span ending at the end of source_file
-        let sm = init_source_map();
-        let span = Span::new(BytePos(12), BytePos(23), NO_EXPANSION);
-        let file_lines = sm.span_to_lines(span).unwrap();
-
-        assert_eq!(file_lines.file.name, PathBuf::from("blork.rs").into());
-        assert_eq!(file_lines.lines.len(), 1);
-        assert_eq!(file_lines.lines[0].line_index, 1);
-    }
-
-    /// Given a string like " ~~~~~~~~~~~~ ", produces a span
-    /// converting that range. The idea is that the string has the same
-    /// length as the input, and we uncover the byte positions. Note
-    /// that this can span lines and so on.
-    fn span_from_selection(input: &str, selection: &str) -> Span {
-        assert_eq!(input.len(), selection.len());
-        let left_index = selection.find('~').unwrap() as u32;
-        let right_index = selection.rfind('~').map(|x|x as u32).unwrap_or(left_index);
-        Span::new(BytePos(left_index), BytePos(right_index + 1), NO_EXPANSION)
-    }
-
-    /// Tests span_to_snippet and span_to_lines for a span converting 3
-    /// lines in the middle of a file.
-    #[test]
-    fn span_to_snippet_and_lines_spanning_multiple_lines() {
-        let sm = SourceMap::new(FilePathMapping::empty());
-        let inputtext = "aaaaa\nbbbbBB\nCCC\nDDDDDddddd\neee\n";
-        let selection = "     \n    ~~\n~~~\n~~~~~     \n   \n";
-        sm.new_source_file(Path::new("blork.rs").to_owned().into(), inputtext.to_string());
-        let span = span_from_selection(inputtext, selection);
-
-        // check that we are extracting the text we thought we were extracting
-        assert_eq!(&sm.span_to_snippet(span).unwrap(), "BB\nCCC\nDDDDD");
-
-        // check that span_to_lines gives us the complete result with the lines/cols we expected
-        let lines = sm.span_to_lines(span).unwrap();
-        let expected = vec![
-            LineInfo { line_index: 1, start_col: CharPos(4), end_col: CharPos(6) },
-            LineInfo { line_index: 2, start_col: CharPos(0), end_col: CharPos(3) },
-            LineInfo { line_index: 3, start_col: CharPos(0), end_col: CharPos(5) }
-            ];
-        assert_eq!(lines.lines, expected);
-    }
-
-    #[test]
-    fn t8() {
-        // Test span_to_snippet for a span ending at the end of source_file
-        let sm = init_source_map();
-        let span = Span::new(BytePos(12), BytePos(23), NO_EXPANSION);
-        let snippet = sm.span_to_snippet(span);
-
-        assert_eq!(snippet, Ok("second line".to_string()));
-    }
-
-    #[test]
-    fn t9() {
-        // Test span_to_str for a span ending at the end of source_file
-        let sm = init_source_map();
-        let span = Span::new(BytePos(12), BytePos(23), NO_EXPANSION);
-        let sstr =  sm.span_to_string(span);
-
-        assert_eq!(sstr, "blork.rs:2:1: 2:12");
-    }
-
-    /// Tests failing to merge two spans on different lines
-    #[test]
-    fn span_merging_fail() {
-        let sm = SourceMap::new(FilePathMapping::empty());
-        let inputtext  = "bbbb BB\ncc CCC\n";
-        let selection1 = "     ~~\n      \n";
-        let selection2 = "       \n   ~~~\n";
-        sm.new_source_file(Path::new("blork.rs").to_owned().into(), inputtext.to_owned());
-        let span1 = span_from_selection(inputtext, selection1);
-        let span2 = span_from_selection(inputtext, selection2);
-
-        assert!(sm.merge_spans(span1, span2).is_none());
-    }
-
-    /// Returns the span corresponding to the `n`th occurrence of
-    /// `substring` in `source_text`.
-    trait SourceMapExtension {
-        fn span_substr(&self,
-                    file: &Lrc<SourceFile>,
-                    source_text: &str,
-                    substring: &str,
-                    n: usize)
-                    -> Span;
-    }
-
-    impl SourceMapExtension for SourceMap {
-        fn span_substr(&self,
-                    file: &Lrc<SourceFile>,
-                    source_text: &str,
-                    substring: &str,
-                    n: usize)
-                    -> Span
-        {
-            println!("span_substr(file={:?}/{:?}, substring={:?}, n={})",
-                    file.name, file.start_pos, substring, n);
-            let mut i = 0;
-            let mut hi = 0;
-            loop {
-                let offset = source_text[hi..].find(substring).unwrap_or_else(|| {
-                    panic!("source_text `{}` does not have {} occurrences of `{}`, only {}",
-                        source_text, n, substring, i);
-                });
-                let lo = hi + offset;
-                hi = lo + substring.len();
-                if i == n {
-                    let span = Span::new(
-                        BytePos(lo as u32 + file.start_pos.0),
-                        BytePos(hi as u32 + file.start_pos.0),
-                        NO_EXPANSION,
-                    );
-                    assert_eq!(&self.span_to_snippet(span).unwrap()[..],
-                            substring);
-                    return span;
-                }
-                i += 1;
-            }
-        }
-    }
-}
diff --git a/src/libsyntax/source_map/tests.rs b/src/libsyntax/source_map/tests.rs
new file mode 100644
index 00000000000..c7b8332c53e
--- /dev/null
+++ b/src/libsyntax/source_map/tests.rs
@@ -0,0 +1,212 @@
+use super::*;
+
+use rustc_data_structures::sync::Lrc;
+
+fn init_source_map() -> SourceMap {
+    let sm = SourceMap::new(FilePathMapping::empty());
+    sm.new_source_file(PathBuf::from("blork.rs").into(),
+                    "first line.\nsecond line".to_string());
+    sm.new_source_file(PathBuf::from("empty.rs").into(),
+                    String::new());
+    sm.new_source_file(PathBuf::from("blork2.rs").into(),
+                    "first line.\nsecond line".to_string());
+    sm
+}
+
+#[test]
+fn t3() {
+    // Test lookup_byte_offset
+    let sm = init_source_map();
+
+    let srcfbp1 = sm.lookup_byte_offset(BytePos(23));
+    assert_eq!(srcfbp1.sf.name, PathBuf::from("blork.rs").into());
+    assert_eq!(srcfbp1.pos, BytePos(23));
+
+    let srcfbp1 = sm.lookup_byte_offset(BytePos(24));
+    assert_eq!(srcfbp1.sf.name, PathBuf::from("empty.rs").into());
+    assert_eq!(srcfbp1.pos, BytePos(0));
+
+    let srcfbp2 = sm.lookup_byte_offset(BytePos(25));
+    assert_eq!(srcfbp2.sf.name, PathBuf::from("blork2.rs").into());
+    assert_eq!(srcfbp2.pos, BytePos(0));
+}
+
+#[test]
+fn t4() {
+    // Test bytepos_to_file_charpos
+    let sm = init_source_map();
+
+    let cp1 = sm.bytepos_to_file_charpos(BytePos(22));
+    assert_eq!(cp1, CharPos(22));
+
+    let cp2 = sm.bytepos_to_file_charpos(BytePos(25));
+    assert_eq!(cp2, CharPos(0));
+}
+
+#[test]
+fn t5() {
+    // Test zero-length source_files.
+    let sm = init_source_map();
+
+    let loc1 = sm.lookup_char_pos(BytePos(22));
+    assert_eq!(loc1.file.name, PathBuf::from("blork.rs").into());
+    assert_eq!(loc1.line, 2);
+    assert_eq!(loc1.col, CharPos(10));
+
+    let loc2 = sm.lookup_char_pos(BytePos(25));
+    assert_eq!(loc2.file.name, PathBuf::from("blork2.rs").into());
+    assert_eq!(loc2.line, 1);
+    assert_eq!(loc2.col, CharPos(0));
+}
+
+fn init_source_map_mbc() -> SourceMap {
+    let sm = SourceMap::new(FilePathMapping::empty());
+    // € is a three byte utf8 char.
+    sm.new_source_file(PathBuf::from("blork.rs").into(),
+                    "fir€st €€€€ line.\nsecond line".to_string());
+    sm.new_source_file(PathBuf::from("blork2.rs").into(),
+                    "first line€€.\n€ second line".to_string());
+    sm
+}
+
+#[test]
+fn t6() {
+    // Test bytepos_to_file_charpos in the presence of multi-byte chars
+    let sm = init_source_map_mbc();
+
+    let cp1 = sm.bytepos_to_file_charpos(BytePos(3));
+    assert_eq!(cp1, CharPos(3));
+
+    let cp2 = sm.bytepos_to_file_charpos(BytePos(6));
+    assert_eq!(cp2, CharPos(4));
+
+    let cp3 = sm.bytepos_to_file_charpos(BytePos(56));
+    assert_eq!(cp3, CharPos(12));
+
+    let cp4 = sm.bytepos_to_file_charpos(BytePos(61));
+    assert_eq!(cp4, CharPos(15));
+}
+
+#[test]
+fn t7() {
+    // Test span_to_lines for a span ending at the end of source_file
+    let sm = init_source_map();
+    let span = Span::with_root_ctxt(BytePos(12), BytePos(23));
+    let file_lines = sm.span_to_lines(span).unwrap();
+
+    assert_eq!(file_lines.file.name, PathBuf::from("blork.rs").into());
+    assert_eq!(file_lines.lines.len(), 1);
+    assert_eq!(file_lines.lines[0].line_index, 1);
+}
+
+/// Given a string like " ~~~~~~~~~~~~ ", produces a span
+/// converting that range. The idea is that the string has the same
+/// length as the input, and we uncover the byte positions. Note
+/// that this can span lines and so on.
+fn span_from_selection(input: &str, selection: &str) -> Span {
+    assert_eq!(input.len(), selection.len());
+    let left_index = selection.find('~').unwrap() as u32;
+    let right_index = selection.rfind('~').map(|x|x as u32).unwrap_or(left_index);
+    Span::with_root_ctxt(BytePos(left_index), BytePos(right_index + 1))
+}
+
+/// Tests span_to_snippet and span_to_lines for a span converting 3
+/// lines in the middle of a file.
+#[test]
+fn span_to_snippet_and_lines_spanning_multiple_lines() {
+    let sm = SourceMap::new(FilePathMapping::empty());
+    let inputtext = "aaaaa\nbbbbBB\nCCC\nDDDDDddddd\neee\n";
+    let selection = "     \n    ~~\n~~~\n~~~~~     \n   \n";
+    sm.new_source_file(Path::new("blork.rs").to_owned().into(), inputtext.to_string());
+    let span = span_from_selection(inputtext, selection);
+
+    // check that we are extracting the text we thought we were extracting
+    assert_eq!(&sm.span_to_snippet(span).unwrap(), "BB\nCCC\nDDDDD");
+
+    // check that span_to_lines gives us the complete result with the lines/cols we expected
+    let lines = sm.span_to_lines(span).unwrap();
+    let expected = vec![
+        LineInfo { line_index: 1, start_col: CharPos(4), end_col: CharPos(6) },
+        LineInfo { line_index: 2, start_col: CharPos(0), end_col: CharPos(3) },
+        LineInfo { line_index: 3, start_col: CharPos(0), end_col: CharPos(5) }
+        ];
+    assert_eq!(lines.lines, expected);
+}
+
+#[test]
+fn t8() {
+    // Test span_to_snippet for a span ending at the end of source_file
+    let sm = init_source_map();
+    let span = Span::with_root_ctxt(BytePos(12), BytePos(23));
+    let snippet = sm.span_to_snippet(span);
+
+    assert_eq!(snippet, Ok("second line".to_string()));
+}
+
+#[test]
+fn t9() {
+    // Test span_to_str for a span ending at the end of source_file
+    let sm = init_source_map();
+    let span = Span::with_root_ctxt(BytePos(12), BytePos(23));
+    let sstr =  sm.span_to_string(span);
+
+    assert_eq!(sstr, "blork.rs:2:1: 2:12");
+}
+
+/// Tests failing to merge two spans on different lines
+#[test]
+fn span_merging_fail() {
+    let sm = SourceMap::new(FilePathMapping::empty());
+    let inputtext  = "bbbb BB\ncc CCC\n";
+    let selection1 = "     ~~\n      \n";
+    let selection2 = "       \n   ~~~\n";
+    sm.new_source_file(Path::new("blork.rs").to_owned().into(), inputtext.to_owned());
+    let span1 = span_from_selection(inputtext, selection1);
+    let span2 = span_from_selection(inputtext, selection2);
+
+    assert!(sm.merge_spans(span1, span2).is_none());
+}
+
+/// Returns the span corresponding to the `n`th occurrence of
+/// `substring` in `source_text`.
+trait SourceMapExtension {
+    fn span_substr(&self,
+                file: &Lrc<SourceFile>,
+                source_text: &str,
+                substring: &str,
+                n: usize)
+                -> Span;
+}
+
+impl SourceMapExtension for SourceMap {
+    fn span_substr(&self,
+                file: &Lrc<SourceFile>,
+                source_text: &str,
+                substring: &str,
+                n: usize)
+                -> Span
+    {
+        println!("span_substr(file={:?}/{:?}, substring={:?}, n={})",
+                file.name, file.start_pos, substring, n);
+        let mut i = 0;
+        let mut hi = 0;
+        loop {
+            let offset = source_text[hi..].find(substring).unwrap_or_else(|| {
+                panic!("source_text `{}` does not have {} occurrences of `{}`, only {}",
+                    source_text, n, substring, i);
+            });
+            let lo = hi + offset;
+            hi = lo + substring.len();
+            if i == n {
+                let span = Span::with_root_ctxt(
+                    BytePos(lo as u32 + file.start_pos.0),
+                    BytePos(hi as u32 + file.start_pos.0),
+                );
+                assert_eq!(&self.span_to_snippet(span).unwrap()[..],
+                        substring);
+                return span;
+            }
+            i += 1;
+        }
+    }
+}
diff --git a/src/libsyntax/std_inject.rs b/src/libsyntax/std_inject.rs
deleted file mode 100644
index 6784a2abe55..00000000000
--- a/src/libsyntax/std_inject.rs
+++ /dev/null
@@ -1,130 +0,0 @@
-use crate::ast;
-use crate::attr;
-use crate::edition::Edition;
-use crate::ext::hygiene::{Mark, SyntaxContext};
-use crate::symbol::{Symbol, keywords, sym};
-use crate::source_map::{ExpnInfo, MacroAttribute, dummy_spanned, hygiene, respan};
-use crate::ptr::P;
-use crate::tokenstream::TokenStream;
-
-use std::cell::Cell;
-use std::iter;
-use syntax_pos::{DUMMY_SP, Span};
-
-/// Craft a span that will be ignored by the stability lint's
-/// call to source_map's `is_internal` check.
-/// The expanded code uses the unstable `#[prelude_import]` attribute.
-fn ignored_span(sp: Span) -> Span {
-    let mark = Mark::fresh(Mark::root());
-    mark.set_expn_info(ExpnInfo {
-        call_site: DUMMY_SP,
-        def_site: None,
-        format: MacroAttribute(Symbol::intern("std_inject")),
-        allow_internal_unstable: Some(vec![
-            Symbol::intern("prelude_import"),
-        ].into()),
-        allow_internal_unsafe: false,
-        local_inner_macros: false,
-        edition: hygiene::default_edition(),
-    });
-    sp.with_ctxt(SyntaxContext::empty().apply_mark(mark))
-}
-
-pub fn injected_crate_name() -> Option<&'static str> {
-    INJECTED_CRATE_NAME.with(|name| name.get())
-}
-
-thread_local! {
-    // A `Symbol` might make more sense here, but it doesn't work, probably for
-    // reasons relating to the use of thread-local storage for the Symbol
-    // interner.
-    static INJECTED_CRATE_NAME: Cell<Option<&'static str>> = Cell::new(None);
-}
-
-pub fn maybe_inject_crates_ref(
-    mut krate: ast::Crate,
-    alt_std_name: Option<&str>,
-    edition: Edition,
-) -> ast::Crate {
-    let rust_2018 = edition >= Edition::Edition2018;
-
-    // the first name in this list is the crate name of the crate with the prelude
-    let names: &[&str] = if attr::contains_name(&krate.attrs, sym::no_core) {
-        return krate;
-    } else if attr::contains_name(&krate.attrs, sym::no_std) {
-        if attr::contains_name(&krate.attrs, sym::compiler_builtins) {
-            &["core"]
-        } else {
-            &["core", "compiler_builtins"]
-        }
-    } else {
-        &["std"]
-    };
-
-    // .rev() to preserve ordering above in combination with insert(0, ...)
-    let alt_std_name = alt_std_name.map(Symbol::intern);
-    for orig_name in names.iter().rev() {
-        let orig_name = Symbol::intern(orig_name);
-        let mut rename = orig_name;
-        // HACK(eddyb) gensym the injected crates on the Rust 2018 edition,
-        // so they don't accidentally interfere with the new import paths.
-        if rust_2018 {
-            rename = orig_name.gensymed();
-        }
-        let orig_name = if rename != orig_name {
-            Some(orig_name)
-        } else {
-            None
-        };
-        krate.module.items.insert(0, P(ast::Item {
-            attrs: vec![attr::mk_attr_outer(
-                DUMMY_SP,
-                attr::mk_attr_id(),
-                attr::mk_word_item(ast::Ident::with_empty_ctxt(sym::macro_use))
-            )],
-            vis: dummy_spanned(ast::VisibilityKind::Inherited),
-            node: ast::ItemKind::ExternCrate(alt_std_name.or(orig_name)),
-            ident: ast::Ident::with_empty_ctxt(rename),
-            id: ast::DUMMY_NODE_ID,
-            span: DUMMY_SP,
-            tokens: None,
-        }));
-    }
-
-    // the crates have been injected, the assumption is that the first one is the one with
-    // the prelude.
-    let name = names[0];
-
-    INJECTED_CRATE_NAME.with(|opt_name| opt_name.set(Some(name)));
-
-    let span = ignored_span(DUMMY_SP);
-    krate.module.items.insert(0, P(ast::Item {
-        attrs: vec![ast::Attribute {
-            style: ast::AttrStyle::Outer,
-            path: ast::Path::from_ident(ast::Ident::new(Symbol::intern("prelude_import"), span)),
-            tokens: TokenStream::empty(),
-            id: attr::mk_attr_id(),
-            is_sugared_doc: false,
-            span,
-        }],
-        vis: respan(span.shrink_to_lo(), ast::VisibilityKind::Inherited),
-        node: ast::ItemKind::Use(P(ast::UseTree {
-            prefix: ast::Path {
-                segments: iter::once(keywords::PathRoot.ident())
-                    .chain(
-                        [name, "prelude", "v1"].iter().cloned()
-                            .map(ast::Ident::from_str)
-                    ).map(ast::PathSegment::from_ident).collect(),
-                span,
-            },
-            kind: ast::UseTreeKind::Glob,
-            span,
-        })),
-        id: ast::DUMMY_NODE_ID,
-        ident: keywords::Invalid.ident(),
-        span,
-        tokens: None,
-    }));
-
-    krate
-}
diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
deleted file mode 100644
index 3fd0790161c..00000000000
--- a/src/libsyntax/test.rs
+++ /dev/null
@@ -1,446 +0,0 @@
-// Code that generates a test runner to run all the tests in a crate
-
-#![allow(dead_code)]
-#![allow(unused_imports)]
-
-use HasTestSignature::*;
-
-use std::iter;
-use std::slice;
-use std::mem;
-use std::vec;
-
-use log::debug;
-use smallvec::{smallvec, SmallVec};
-use syntax_pos::{DUMMY_SP, NO_EXPANSION, Span, SourceFile, BytePos};
-
-use crate::attr::{self, HasAttrs};
-use crate::source_map::{self, SourceMap, ExpnInfo, MacroAttribute, dummy_spanned, respan};
-use crate::config;
-use crate::entry::{self, EntryPointType};
-use crate::ext::base::{ExtCtxt, Resolver};
-use crate::ext::build::AstBuilder;
-use crate::ext::expand::ExpansionConfig;
-use crate::ext::hygiene::{self, Mark, SyntaxContext};
-use crate::mut_visit::{*, ExpectOne};
-use crate::feature_gate::Features;
-use crate::util::map_in_place::MapInPlace;
-use crate::parse::{token, ParseSess};
-use crate::print::pprust;
-use crate::ast::{self, Ident};
-use crate::ptr::P;
-use crate::symbol::{self, Symbol, keywords, sym};
-use crate::ThinVec;
-
-struct Test {
-    span: Span,
-    path: Vec<Ident>,
-}
-
-struct TestCtxt<'a> {
-    span_diagnostic: &'a errors::Handler,
-    path: Vec<Ident>,
-    ext_cx: ExtCtxt<'a>,
-    test_cases: Vec<Test>,
-    reexport_test_harness_main: Option<Symbol>,
-    is_libtest: bool,
-    ctxt: SyntaxContext,
-    features: &'a Features,
-    test_runner: Option<ast::Path>,
-
-    // top-level re-export submodule, filled out after folding is finished
-    toplevel_reexport: Option<Ident>,
-}
-
-// Traverse the crate, collecting all the test functions, eliding any
-// existing main functions, and synthesizing a main test harness
-pub fn modify_for_testing(sess: &ParseSess,
-                          resolver: &mut dyn Resolver,
-                          should_test: bool,
-                          krate: &mut ast::Crate,
-                          span_diagnostic: &errors::Handler,
-                          features: &Features) {
-    // Check for #[reexport_test_harness_main = "some_name"] which
-    // creates a `use __test::main as some_name;`. This needs to be
-    // unconditional, so that the attribute is still marked as used in
-    // non-test builds.
-    let reexport_test_harness_main =
-        attr::first_attr_value_str_by_name(&krate.attrs, sym::reexport_test_harness_main);
-
-    // Do this here so that the test_runner crate attribute gets marked as used
-    // even in non-test builds
-    let test_runner = get_test_runner(span_diagnostic, &krate);
-
-    if should_test {
-        generate_test_harness(sess, resolver, reexport_test_harness_main,
-                              krate, span_diagnostic, features, test_runner)
-    }
-}
-
-struct TestHarnessGenerator<'a> {
-    cx: TestCtxt<'a>,
-    tests: Vec<Ident>,
-
-    // submodule name, gensym'd identifier for re-exports
-    tested_submods: Vec<(Ident, Ident)>,
-}
-
-impl<'a> MutVisitor for TestHarnessGenerator<'a> {
-    fn visit_crate(&mut self, c: &mut ast::Crate) {
-        noop_visit_crate(c, self);
-
-        // Create a main function to run our tests
-        let test_main = {
-            let unresolved = mk_main(&mut self.cx);
-            self.cx.ext_cx.monotonic_expander().flat_map_item(unresolved).pop().unwrap()
-        };
-
-        c.module.items.push(test_main);
-    }
-
-    fn flat_map_item(&mut self, i: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
-        let ident = i.ident;
-        if ident.name != keywords::Invalid.name() {
-            self.cx.path.push(ident);
-        }
-        debug!("current path: {}", path_name_i(&self.cx.path));
-
-        let mut item = i.into_inner();
-        if is_test_case(&item) {
-            debug!("this is a test item");
-
-            let test = Test {
-                span: item.span,
-                path: self.cx.path.clone(),
-            };
-            self.cx.test_cases.push(test);
-            self.tests.push(item.ident);
-        }
-
-        // We don't want to recurse into anything other than mods, since
-        // mods or tests inside of functions will break things
-        if let ast::ItemKind::Mod(mut module) = item.node {
-            let tests = mem::replace(&mut self.tests, Vec::new());
-            let tested_submods = mem::replace(&mut self.tested_submods, Vec::new());
-            noop_visit_mod(&mut module, self);
-            let tests = mem::replace(&mut self.tests, tests);
-            let tested_submods = mem::replace(&mut self.tested_submods, tested_submods);
-
-            if !tests.is_empty() || !tested_submods.is_empty() {
-                let (it, sym) = mk_reexport_mod(&mut self.cx, item.id, tests, tested_submods);
-                module.items.push(it);
-
-                if !self.cx.path.is_empty() {
-                    self.tested_submods.push((self.cx.path[self.cx.path.len()-1], sym));
-                } else {
-                    debug!("pushing nothing, sym: {:?}", sym);
-                    self.cx.toplevel_reexport = Some(sym);
-                }
-            }
-            item.node = ast::ItemKind::Mod(module);
-        }
-        if ident.name != keywords::Invalid.name() {
-            self.cx.path.pop();
-        }
-        smallvec![P(item)]
-    }
-
-    fn visit_mac(&mut self, _mac: &mut ast::Mac) {
-        // Do nothing.
-    }
-}
-
-/// A folder used to remove any entry points (like fn main) because the harness
-/// generator will provide its own
-struct EntryPointCleaner {
-    // Current depth in the ast
-    depth: usize,
-}
-
-impl MutVisitor for EntryPointCleaner {
-    fn flat_map_item(&mut self, i: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
-        self.depth += 1;
-        let item = noop_flat_map_item(i, self).expect_one("noop did something");
-        self.depth -= 1;
-
-        // Remove any #[main] or #[start] from the AST so it doesn't
-        // clash with the one we're going to add, but mark it as
-        // #[allow(dead_code)] to avoid printing warnings.
-        let item = match entry::entry_point_type(&item, self.depth) {
-            EntryPointType::MainNamed |
-            EntryPointType::MainAttr |
-            EntryPointType::Start =>
-                item.map(|ast::Item {id, ident, attrs, node, vis, span, tokens}| {
-                    let allow_ident = Ident::with_empty_ctxt(sym::allow);
-                    let dc_nested = attr::mk_nested_word_item(Ident::from_str("dead_code"));
-                    let allow_dead_code_item = attr::mk_list_item(DUMMY_SP, allow_ident,
-                                                                  vec![dc_nested]);
-                    let allow_dead_code = attr::mk_attr_outer(DUMMY_SP,
-                                                              attr::mk_attr_id(),
-                                                              allow_dead_code_item);
-
-                    ast::Item {
-                        id,
-                        ident,
-                        attrs: attrs.into_iter()
-                            .filter(|attr| {
-                                !attr.check_name(sym::main) && !attr.check_name(sym::start)
-                            })
-                            .chain(iter::once(allow_dead_code))
-                            .collect(),
-                        node,
-                        vis,
-                        span,
-                        tokens,
-                    }
-                }),
-            EntryPointType::None |
-            EntryPointType::OtherMain => item,
-        };
-
-        smallvec![item]
-    }
-
-    fn visit_mac(&mut self, _mac: &mut ast::Mac) {
-        // Do nothing.
-    }
-}
-
-/// Creates an item (specifically a module) that "pub use"s the tests passed in.
-/// Each tested submodule will contain a similar reexport module that we will export
-/// under the name of the original module. That is, `submod::__test_reexports` is
-/// reexported like so `pub use submod::__test_reexports as submod`.
-fn mk_reexport_mod(cx: &mut TestCtxt<'_>,
-                   parent: ast::NodeId,
-                   tests: Vec<Ident>,
-                   tested_submods: Vec<(Ident, Ident)>)
-                   -> (P<ast::Item>, Ident) {
-    let super_ = Ident::with_empty_ctxt(keywords::Super.name());
-
-    let items = tests.into_iter().map(|r| {
-        cx.ext_cx.item_use_simple(DUMMY_SP, dummy_spanned(ast::VisibilityKind::Public),
-                                  cx.ext_cx.path(DUMMY_SP, vec![super_, r]))
-    }).chain(tested_submods.into_iter().map(|(r, sym)| {
-        let path = cx.ext_cx.path(DUMMY_SP, vec![super_, r, sym]);
-        cx.ext_cx.item_use_simple_(DUMMY_SP, dummy_spanned(ast::VisibilityKind::Public),
-                                   Some(r), path)
-    })).collect();
-
-    let reexport_mod = ast::Mod {
-        inline: true,
-        inner: DUMMY_SP,
-        items,
-    };
-
-    let sym = Ident::with_empty_ctxt(Symbol::gensym("__test_reexports"));
-    let parent = if parent == ast::DUMMY_NODE_ID { ast::CRATE_NODE_ID } else { parent };
-    cx.ext_cx.current_expansion.mark = cx.ext_cx.resolver.get_module_scope(parent);
-    let it = cx.ext_cx.monotonic_expander().flat_map_item(P(ast::Item {
-        ident: sym,
-        attrs: Vec::new(),
-        id: ast::DUMMY_NODE_ID,
-        node: ast::ItemKind::Mod(reexport_mod),
-        vis: dummy_spanned(ast::VisibilityKind::Public),
-        span: DUMMY_SP,
-        tokens: None,
-    })).pop().unwrap();
-
-    (it, sym)
-}
-
-/// Crawl over the crate, inserting test reexports and the test main function
-fn generate_test_harness(sess: &ParseSess,
-                         resolver: &mut dyn Resolver,
-                         reexport_test_harness_main: Option<Symbol>,
-                         krate: &mut ast::Crate,
-                         sd: &errors::Handler,
-                         features: &Features,
-                         test_runner: Option<ast::Path>) {
-    // Remove the entry points
-    let mut cleaner = EntryPointCleaner { depth: 0 };
-    cleaner.visit_crate(krate);
-
-    let mark = Mark::fresh(Mark::root());
-
-    let mut econfig = ExpansionConfig::default("test".to_string());
-    econfig.features = Some(features);
-
-    let cx = TestCtxt {
-        span_diagnostic: sd,
-        ext_cx: ExtCtxt::new(sess, econfig, resolver),
-        path: Vec::new(),
-        test_cases: Vec::new(),
-        reexport_test_harness_main,
-        // N.B., doesn't consider the value of `--crate-name` passed on the command line.
-        is_libtest: attr::find_crate_name(&krate.attrs)
-            .map(|s| s == sym::test).unwrap_or(false),
-        toplevel_reexport: None,
-        ctxt: SyntaxContext::empty().apply_mark(mark),
-        features,
-        test_runner
-    };
-
-    mark.set_expn_info(ExpnInfo {
-        call_site: DUMMY_SP,
-        def_site: None,
-        format: MacroAttribute(Symbol::intern("test_case")),
-        allow_internal_unstable: Some(vec![
-            Symbol::intern("main"),
-            Symbol::intern("test"),
-            Symbol::intern("rustc_attrs"),
-        ].into()),
-        allow_internal_unsafe: false,
-        local_inner_macros: false,
-        edition: hygiene::default_edition(),
-    });
-
-    TestHarnessGenerator {
-        cx,
-        tests: Vec::new(),
-        tested_submods: Vec::new(),
-    }.visit_crate(krate);
-}
-
-/// Craft a span that will be ignored by the stability lint's
-/// call to source_map's `is_internal` check.
-/// The expanded code calls some unstable functions in the test crate.
-fn ignored_span(cx: &TestCtxt<'_>, sp: Span) -> Span {
-    sp.with_ctxt(cx.ctxt)
-}
-
-enum HasTestSignature {
-    Yes,
-    No(BadTestSignature),
-}
-
-#[derive(PartialEq)]
-enum BadTestSignature {
-    NotEvenAFunction,
-    WrongTypeSignature,
-    NoArgumentsAllowed,
-    ShouldPanicOnlyWithNoArgs,
-}
-
-/// Creates a function item for use as the main function of a test build.
-/// This function will call the `test_runner` as specified by the crate attribute
-fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
-    // Writing this out by hand with 'ignored_span':
-    //        pub fn main() {
-    //            #![main]
-    //            test::test_main_static(&[..tests]);
-    //        }
-    let sp = ignored_span(cx, DUMMY_SP);
-    let ecx = &cx.ext_cx;
-    let test_id = ecx.ident_of("test").gensym();
-
-    // test::test_main_static(...)
-    let mut test_runner = cx.test_runner.clone().unwrap_or(
-        ecx.path(sp, vec![
-            test_id, ecx.ident_of("test_main_static")
-        ]));
-
-    test_runner.span = sp;
-
-    let test_main_path_expr = ecx.expr_path(test_runner);
-    let call_test_main = ecx.expr_call(sp, test_main_path_expr,
-                                       vec![mk_tests_slice(cx)]);
-    let call_test_main = ecx.stmt_expr(call_test_main);
-
-    // #![main]
-    let main_meta = ecx.meta_word(sp, Symbol::intern("main"));
-    let main_attr = ecx.attribute(sp, main_meta);
-
-    // extern crate test as test_gensym
-    let test_extern_stmt = ecx.stmt_item(sp, ecx.item(sp,
-        test_id,
-        vec![],
-        ast::ItemKind::ExternCrate(Some(Symbol::intern("test")))
-    ));
-
-    // pub fn main() { ... }
-    let main_ret_ty = ecx.ty(sp, ast::TyKind::Tup(vec![]));
-
-    // If no test runner is provided we need to import the test crate
-    let main_body = if cx.test_runner.is_none() {
-        ecx.block(sp, vec![test_extern_stmt, call_test_main])
-    } else {
-        ecx.block(sp, vec![call_test_main])
-    };
-
-    let main = ast::ItemKind::Fn(ecx.fn_decl(vec![], ast::FunctionRetTy::Ty(main_ret_ty)),
-                           ast::FnHeader::default(),
-                           ast::Generics::default(),
-                           main_body);
-
-    // Honor the reexport_test_harness_main attribute
-    let main_id = Ident::new(
-        cx.reexport_test_harness_main.unwrap_or(Symbol::gensym("main")),
-        sp);
-
-    P(ast::Item {
-        ident: main_id,
-        attrs: vec![main_attr],
-        id: ast::DUMMY_NODE_ID,
-        node: main,
-        vis: dummy_spanned(ast::VisibilityKind::Public),
-        span: sp,
-        tokens: None,
-    })
-
-}
-
-fn path_name_i(idents: &[Ident]) -> String {
-    let mut path_name = "".to_string();
-    let mut idents_iter = idents.iter().peekable();
-    while let Some(ident) = idents_iter.next() {
-        path_name.push_str(&ident.as_str());
-        if idents_iter.peek().is_some() {
-            path_name.push_str("::")
-        }
-    }
-    path_name
-}
-
-/// Creates a slice containing every test like so:
-/// &[path::to::test1, path::to::test2]
-fn mk_tests_slice(cx: &TestCtxt<'_>) -> P<ast::Expr> {
-    debug!("building test vector from {} tests", cx.test_cases.len());
-    let ref ecx = cx.ext_cx;
-
-    ecx.expr_vec_slice(DUMMY_SP,
-        cx.test_cases.iter().map(|test| {
-            ecx.expr_addr_of(test.span,
-                ecx.expr_path(ecx.path(test.span, visible_path(cx, &test.path))))
-        }).collect())
-}
-
-/// Creates a path from the top-level __test module to the test via __test_reexports
-fn visible_path(cx: &TestCtxt<'_>, path: &[Ident]) -> Vec<Ident>{
-    let mut visible_path = vec![];
-    match cx.toplevel_reexport {
-        Some(id) => visible_path.push(id),
-        None => {
-            cx.span_diagnostic.bug("expected to find top-level re-export name, but found None");
-        }
-    }
-    visible_path.extend_from_slice(path);
-    visible_path
-}
-
-fn is_test_case(i: &ast::Item) -> bool {
-    attr::contains_name(&i.attrs, sym::rustc_test_marker)
-}
-
-fn get_test_runner(sd: &errors::Handler, krate: &ast::Crate) -> Option<ast::Path> {
-    let test_attr = attr::find_by_name(&krate.attrs, sym::test_runner)?;
-    test_attr.meta_item_list().map(|meta_list| {
-        if meta_list.len() != 1 {
-            sd.span_fatal(test_attr.span,
-                "#![test_runner(..)] accepts exactly 1 argument").raise()
-        }
-        match meta_list[0].meta_item() {
-            Some(meta_item) if meta_item.is_word() => meta_item.path.clone(),
-            _ => sd.span_fatal(test_attr.span, "`test_runner` argument must be a path").raise()
-        }
-    })
-}
diff --git a/src/libsyntax/test_snippet.rs b/src/libsyntax/tests.rs
index 3cf6699538d..4c0e1e3704d 100644
--- a/src/libsyntax/test_snippet.rs
+++ b/src/libsyntax/tests.rs
@@ -1,16 +1,106 @@
+use crate::{ast, panictry};
+use crate::parse::{ParseSess, PResult, source_file_to_stream};
+use crate::parse::new_parser_from_source_str;
+use crate::parse::parser::Parser;
 use crate::source_map::{SourceMap, FilePathMapping};
-use crate::with_globals;
+use crate::tokenstream::TokenStream;
+use crate::with_default_globals;
 
-use errors::Handler;
 use errors::emitter::EmitterWriter;
+use errors::Handler;
+use rustc_data_structures::sync::Lrc;
+use syntax_pos::{BytePos, Span, MultiSpan};
 
 use std::io;
 use std::io::prelude::*;
-use rustc_data_structures::sync::Lrc;
+use std::iter::Peekable;
+use std::path::{Path, PathBuf};
 use std::str;
 use std::sync::{Arc, Mutex};
-use std::path::Path;
-use syntax_pos::{BytePos, NO_EXPANSION, Span, MultiSpan};
+
+/// Map string to parser (via tts)
+fn string_to_parser(ps: &ParseSess, source_str: String) -> Parser<'_> {
+    new_parser_from_source_str(ps, PathBuf::from("bogofile").into(), source_str)
+}
+
+crate fn with_error_checking_parse<'a, T, F>(s: String, ps: &'a ParseSess, f: F) -> T where
+    F: FnOnce(&mut Parser<'a>) -> PResult<'a, T>,
+{
+    let mut p = string_to_parser(&ps, s);
+    let x = panictry!(f(&mut p));
+    p.sess.span_diagnostic.abort_if_errors();
+    x
+}
+
+/// Map a string to tts, using a made-up filename:
+crate fn string_to_stream(source_str: String) -> TokenStream {
+    let ps = ParseSess::new(FilePathMapping::empty());
+    source_file_to_stream(
+        &ps,
+        ps.source_map().new_source_file(PathBuf::from("bogofile").into(),
+        source_str,
+    ), None).0
+}
+
+/// Parse a string, return a crate.
+crate fn string_to_crate(source_str : String) -> ast::Crate {
+    let ps = ParseSess::new(FilePathMapping::empty());
+    with_error_checking_parse(source_str, &ps, |p| {
+        p.parse_crate_mod()
+    })
+}
+
+/// Does the given string match the pattern? whitespace in the first string
+/// may be deleted or replaced with other whitespace to match the pattern.
+/// This function is relatively Unicode-ignorant; fortunately, the careful design
+/// of UTF-8 mitigates this ignorance. It doesn't do NKF-normalization(?).
+crate fn matches_codepattern(a : &str, b : &str) -> bool {
+    let mut a_iter = a.chars().peekable();
+    let mut b_iter = b.chars().peekable();
+
+    loop {
+        let (a, b) = match (a_iter.peek(), b_iter.peek()) {
+            (None, None) => return true,
+            (None, _) => return false,
+            (Some(&a), None) => {
+                if is_pattern_whitespace(a) {
+                    break // trailing whitespace check is out of loop for borrowck
+                } else {
+                    return false
+                }
+            }
+            (Some(&a), Some(&b)) => (a, b)
+        };
+
+        if is_pattern_whitespace(a) && is_pattern_whitespace(b) {
+            // skip whitespace for a and b
+            scan_for_non_ws_or_end(&mut a_iter);
+            scan_for_non_ws_or_end(&mut b_iter);
+        } else if is_pattern_whitespace(a) {
+            // skip whitespace for a
+            scan_for_non_ws_or_end(&mut a_iter);
+        } else if a == b {
+            a_iter.next();
+            b_iter.next();
+        } else {
+            return false
+        }
+    }
+
+    // check if a has *only* trailing whitespace
+    a_iter.all(is_pattern_whitespace)
+}
+
+/// Advances the given peekable `Iterator` until it reaches a non-whitespace character
+fn scan_for_non_ws_or_end<I: Iterator<Item = char>>(iter: &mut Peekable<I>) {
+    while iter.peek().copied().map(|c| is_pattern_whitespace(c)) == Some(true) {
+        iter.next();
+    }
+}
+
+fn is_pattern_whitespace(c: char) -> bool {
+    rustc_lexer::character_properties::is_whitespace(c)
+}
 
 /// Identify a position in the text by the Nth occurrence of a string.
 struct Position {
@@ -39,7 +129,7 @@ impl<T: Write> Write for Shared<T> {
 }
 
 fn test_harness(file_text: &str, span_labels: Vec<SpanLabel>, expected_output: &str) {
-    with_globals(|| {
+    with_default_globals(|| {
         let output = Arc::new(Mutex::new(Vec::new()));
 
         let source_map = Lrc::new(SourceMap::new(FilePathMapping::empty()));
@@ -79,7 +169,7 @@ fn make_span(file_text: &str, start: &Position, end: &Position) -> Span {
     let start = make_pos(file_text, start);
     let end = make_pos(file_text, end) + end.string.len(); // just after matching thing ends
     assert!(start <= end);
-    Span::new(BytePos(start as u32), BytePos(end as u32), NO_EXPANSION)
+    Span::with_root_ctxt(BytePos(start as u32), BytePos(end as u32))
 }
 
 fn make_pos(file_text: &str, pos: &Position) -> usize {
diff --git a/src/libsyntax/tokenstream.rs b/src/libsyntax/tokenstream.rs
index 93b5ecadd14..6ff8898fe21 100644
--- a/src/libsyntax/tokenstream.rs
+++ b/src/libsyntax/tokenstream.rs
@@ -16,19 +16,22 @@
 use crate::ext::base;
 use crate::ext::tt::{macro_parser, quoted};
 use crate::parse::Directory;
-use crate::parse::token::{self, DelimToken, Token};
+use crate::parse::token::{self, DelimToken, Token, TokenKind};
 use crate::print::pprust;
 
-use syntax_pos::{BytePos, Mark, Span, DUMMY_SP};
+use syntax_pos::{BytePos, ExpnId, Span, DUMMY_SP};
 #[cfg(target_arch = "x86_64")]
-use rustc_data_structures::static_assert;
+use rustc_data_structures::static_assert_size;
 use rustc_data_structures::sync::Lrc;
-use serialize::{Decoder, Decodable, Encoder, Encodable};
+use rustc_serialize::{Decoder, Decodable, Encoder, Encodable};
 use smallvec::{SmallVec, smallvec};
 
 use std::borrow::Cow;
 use std::{fmt, iter, mem};
 
+#[cfg(test)]
+mod tests;
+
 /// When the main rust parser encounters a syntax-extension invocation, it
 /// parses the arguments to the invocation as a token-tree. This is a very
 /// loose structure, such that all sorts of different AST-fragments can
@@ -44,11 +47,21 @@ use std::{fmt, iter, mem};
 #[derive(Debug, Clone, PartialEq, RustcEncodable, RustcDecodable)]
 pub enum TokenTree {
     /// A single token
-    Token(Span, token::Token),
+    Token(Token),
     /// A delimited sequence of token trees
     Delimited(DelimSpan, DelimToken, TokenStream),
 }
 
+// Ensure all fields of `TokenTree` is `Send` and `Sync`.
+#[cfg(parallel_compiler)]
+fn _dummy()
+where
+    Token: Send + Sync,
+    DelimSpan: Send + Sync,
+    DelimToken: Send + Sync,
+    TokenStream: Send + Sync,
+{}
+
 impl TokenTree {
     /// Use this token tree as a matcher to parse given tts.
     pub fn parse(cx: &base::ExtCtxt<'_>, mtch: &[quoted::TokenTree], tts: TokenStream)
@@ -64,12 +77,11 @@ impl TokenTree {
     /// Checks if this TokenTree is equal to the other, regardless of span information.
     pub fn eq_unspanned(&self, other: &TokenTree) -> bool {
         match (self, other) {
-            (&TokenTree::Token(_, ref tk), &TokenTree::Token(_, ref tk2)) => tk == tk2,
-            (&TokenTree::Delimited(_, delim, ref tts),
-             &TokenTree::Delimited(_, delim2, ref tts2)) => {
+            (TokenTree::Token(token), TokenTree::Token(token2)) => token.kind == token2.kind,
+            (TokenTree::Delimited(_, delim, tts), TokenTree::Delimited(_, delim2, tts2)) => {
                 delim == delim2 && tts.eq_unspanned(&tts2)
             }
-            (_, _) => false,
+            _ => false,
         }
     }
 
@@ -80,38 +92,29 @@ impl TokenTree {
     // different method.
     pub fn probably_equal_for_proc_macro(&self, other: &TokenTree) -> bool {
         match (self, other) {
-            (&TokenTree::Token(_, ref tk), &TokenTree::Token(_, ref tk2)) => {
-                tk.probably_equal_for_proc_macro(tk2)
+            (TokenTree::Token(token), TokenTree::Token(token2)) => {
+                token.probably_equal_for_proc_macro(token2)
             }
-            (&TokenTree::Delimited(_, delim, ref tts),
-             &TokenTree::Delimited(_, delim2, ref tts2)) => {
+            (TokenTree::Delimited(_, delim, tts), TokenTree::Delimited(_, delim2, tts2)) => {
                 delim == delim2 && tts.probably_equal_for_proc_macro(&tts2)
             }
-            (_, _) => false,
+            _ => false,
         }
     }
 
     /// Retrieves the TokenTree's span.
     pub fn span(&self) -> Span {
-        match *self {
-            TokenTree::Token(sp, _) => sp,
+        match self {
+            TokenTree::Token(token) => token.span,
             TokenTree::Delimited(sp, ..) => sp.entire(),
         }
     }
 
     /// Modify the `TokenTree`'s span in-place.
     pub fn set_span(&mut self, span: Span) {
-        match *self {
-            TokenTree::Token(ref mut sp, _) => *sp = span,
-            TokenTree::Delimited(ref mut sp, ..) => *sp = DelimSpan::from_single(span),
-        }
-    }
-
-    /// Indicates if the stream is a token that is equal to the provided token.
-    pub fn eq_token(&self, t: Token) -> bool {
-        match *self {
-            TokenTree::Token(_, ref tk) => *tk == t,
-            _ => false,
+        match self {
+            TokenTree::Token(token) => token.span = span,
+            TokenTree::Delimited(dspan, ..) => *dspan = DelimSpan::from_single(span),
         }
     }
 
@@ -119,6 +122,10 @@ impl TokenTree {
         TokenStream::new(vec![(self, Joint)])
     }
 
+    pub fn token(kind: TokenKind, span: Span) -> TokenTree {
+        TokenTree::Token(Token::new(kind, span))
+    }
+
     /// Returns the opening delimiter as a token tree.
     pub fn open_tt(span: Span, delim: DelimToken) -> TokenTree {
         let open_span = if span.is_dummy() {
@@ -126,7 +133,7 @@ impl TokenTree {
         } else {
             span.with_hi(span.lo() + BytePos(delim.len() as u32))
         };
-        TokenTree::Token(open_span, token::OpenDelim(delim))
+        TokenTree::token(token::OpenDelim(delim), open_span)
     }
 
     /// Returns the closing delimiter as a token tree.
@@ -136,7 +143,7 @@ impl TokenTree {
         } else {
             span.with_lo(span.hi() - BytePos(delim.len() as u32))
         };
-        TokenTree::Token(close_span, token::CloseDelim(delim))
+        TokenTree::token(token::CloseDelim(delim), close_span)
     }
 }
 
@@ -145,7 +152,7 @@ impl TokenTree {
 /// A `TokenStream` is an abstract sequence of tokens, organized into `TokenTree`s.
 /// The goal is for procedural macros to work with `TokenStream`s and `TokenTree`s
 /// instead of a representation of the abstract syntax tree.
-/// Today's `TokenTree`s can still contain AST via `Token::Interpolated` for back-compat.
+/// Today's `TokenTree`s can still contain AST via `token::Interpolated` for back-compat.
 ///
 /// The use of `Option` is an optimization that avoids the need for an
 /// allocation when the stream is empty. However, it is not guaranteed that an
@@ -158,7 +165,7 @@ pub type TreeAndJoint = (TokenTree, IsJoint);
 
 // `TokenStream` is used a lot. Make sure it doesn't unintentionally get bigger.
 #[cfg(target_arch = "x86_64")]
-static_assert!(MEM_SIZE_OF_TOKEN_STREAM: mem::size_of::<TokenStream>() == 8);
+static_assert_size!(TokenStream, 8);
 
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub enum IsJoint {
@@ -179,18 +186,18 @@ impl TokenStream {
             while let Some((pos, ts)) = iter.next() {
                 if let Some((_, next)) = iter.peek() {
                     let sp = match (&ts, &next) {
-                        (_, (TokenTree::Token(_, token::Token::Comma), _)) => continue,
-                        ((TokenTree::Token(sp, token_left), NonJoint),
-                         (TokenTree::Token(_, token_right), _))
+                        (_, (TokenTree::Token(Token { kind: token::Comma, .. }), _)) => continue,
+                        ((TokenTree::Token(token_left), NonJoint),
+                         (TokenTree::Token(token_right), _))
                         if ((token_left.is_ident() && !token_left.is_reserved_ident())
                             || token_left.is_lit()) &&
                             ((token_right.is_ident() && !token_right.is_reserved_ident())
-                            || token_right.is_lit()) => *sp,
+                            || token_right.is_lit()) => token_left.span,
                         ((TokenTree::Delimited(sp, ..), NonJoint), _) => sp.entire(),
                         _ => continue,
                     };
                     let sp = sp.shrink_to_hi();
-                    let comma = (TokenTree::Token(sp, token::Comma), NonJoint);
+                    let comma = (TokenTree::token(token::Comma, sp), NonJoint);
                     suggestion = Some((pos, comma, sp));
                 }
             }
@@ -219,12 +226,6 @@ impl From<TokenTree> for TreeAndJoint {
     }
 }
 
-impl From<Token> for TokenStream {
-    fn from(token: Token) -> TokenStream {
-        TokenTree::Token(DUMMY_SP, token).into()
-    }
-}
-
 impl<T: Into<TokenStream>> iter::FromIterator<T> for TokenStream {
     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
         TokenStream::from_streams(iter.into_iter().map(Into::into).collect::<SmallVec<_>>())
@@ -327,22 +328,25 @@ impl TokenStream {
         // streams, making a comparison between a token stream generated from an
         // AST and a token stream which was parsed into an AST more reliable.
         fn semantic_tree(tree: &TokenTree) -> bool {
-            match tree {
-                // The pretty printer tends to add trailing commas to
-                // everything, and in particular, after struct fields.
-                | TokenTree::Token(_, Token::Comma)
-                // The pretty printer emits `NoDelim` as whitespace.
-                | TokenTree::Token(_, Token::OpenDelim(DelimToken::NoDelim))
-                | TokenTree::Token(_, Token::CloseDelim(DelimToken::NoDelim))
-                // The pretty printer collapses many semicolons into one.
-                | TokenTree::Token(_, Token::Semi)
-                // The pretty printer collapses whitespace arbitrarily and can
-                // introduce whitespace from `NoDelim`.
-                | TokenTree::Token(_, Token::Whitespace)
-                // The pretty printer can turn `$crate` into `::crate_name`
-                | TokenTree::Token(_, Token::ModSep) => false,
-                _ => true
+            if let TokenTree::Token(token) = tree {
+                if let
+                    // The pretty printer tends to add trailing commas to
+                    // everything, and in particular, after struct fields.
+                    | token::Comma
+                    // The pretty printer emits `NoDelim` as whitespace.
+                    | token::OpenDelim(DelimToken::NoDelim)
+                    | token::CloseDelim(DelimToken::NoDelim)
+                    // The pretty printer collapses many semicolons into one.
+                    | token::Semi
+                    // The pretty printer collapses whitespace arbitrarily and can
+                    // introduce whitespace from `NoDelim`.
+                    | token::Whitespace
+                    // The pretty printer can turn `$crate` into `::crate_name`
+                    | token::ModSep = token.kind {
+                    return false;
+                }
             }
+            true
         }
 
         let mut t1 = self.trees().filter(semantic_tree);
@@ -408,13 +412,12 @@ impl TokenStreamBuilder {
     pub fn push<T: Into<TokenStream>>(&mut self, stream: T) {
         let stream = stream.into();
         let last_tree_if_joint = self.0.last().and_then(TokenStream::last_tree_if_joint);
-        if let Some(TokenTree::Token(last_span, last_tok)) = last_tree_if_joint {
-            if let Some((TokenTree::Token(span, tok), is_joint)) = stream.first_tree_and_joint() {
-                if let Some(glued_tok) = last_tok.glue(tok) {
+        if let Some(TokenTree::Token(last_token)) = last_tree_if_joint {
+            if let Some((TokenTree::Token(token), is_joint)) = stream.first_tree_and_joint() {
+                if let Some(glued_tok) = last_token.glue(token) {
                     let last_stream = self.0.pop().unwrap();
                     self.push_all_but_last_tree(&last_stream);
-                    let glued_span = last_span.to(span);
-                    let glued_tt = TokenTree::Token(glued_span, glued_tok);
+                    let glued_tt = TokenTree::Token(glued_tok);
                     let glued_tokenstream = TokenStream::new(vec![(glued_tt, is_joint)]);
                     self.0.push(glued_tokenstream);
                     self.push_all_but_first_tree(&stream);
@@ -545,120 +548,10 @@ impl DelimSpan {
         self.open.with_hi(self.close.hi())
     }
 
-    pub fn apply_mark(self, mark: Mark) -> Self {
+    pub fn apply_mark(self, expn_id: ExpnId) -> Self {
         DelimSpan {
-            open: self.open.apply_mark(mark),
-            close: self.close.apply_mark(mark),
+            open: self.open.apply_mark(expn_id),
+            close: self.close.apply_mark(expn_id),
         }
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::syntax::ast::Ident;
-    use crate::with_globals;
-    use crate::parse::token::Token;
-    use crate::util::parser_testing::string_to_stream;
-    use syntax_pos::{Span, BytePos, NO_EXPANSION};
-
-    fn string_to_ts(string: &str) -> TokenStream {
-        string_to_stream(string.to_owned())
-    }
-
-    fn sp(a: u32, b: u32) -> Span {
-        Span::new(BytePos(a), BytePos(b), NO_EXPANSION)
-    }
-
-    #[test]
-    fn test_concat() {
-        with_globals(|| {
-            let test_res = string_to_ts("foo::bar::baz");
-            let test_fst = string_to_ts("foo::bar");
-            let test_snd = string_to_ts("::baz");
-            let eq_res = TokenStream::from_streams(smallvec![test_fst, test_snd]);
-            assert_eq!(test_res.trees().count(), 5);
-            assert_eq!(eq_res.trees().count(), 5);
-            assert_eq!(test_res.eq_unspanned(&eq_res), true);
-        })
-    }
-
-    #[test]
-    fn test_to_from_bijection() {
-        with_globals(|| {
-            let test_start = string_to_ts("foo::bar(baz)");
-            let test_end = test_start.trees().collect();
-            assert_eq!(test_start, test_end)
-        })
-    }
-
-    #[test]
-    fn test_eq_0() {
-        with_globals(|| {
-            let test_res = string_to_ts("foo");
-            let test_eqs = string_to_ts("foo");
-            assert_eq!(test_res, test_eqs)
-        })
-    }
-
-    #[test]
-    fn test_eq_1() {
-        with_globals(|| {
-            let test_res = string_to_ts("::bar::baz");
-            let test_eqs = string_to_ts("::bar::baz");
-            assert_eq!(test_res, test_eqs)
-        })
-    }
-
-    #[test]
-    fn test_eq_3() {
-        with_globals(|| {
-            let test_res = string_to_ts("");
-            let test_eqs = string_to_ts("");
-            assert_eq!(test_res, test_eqs)
-        })
-    }
-
-    #[test]
-    fn test_diseq_0() {
-        with_globals(|| {
-            let test_res = string_to_ts("::bar::baz");
-            let test_eqs = string_to_ts("bar::baz");
-            assert_eq!(test_res == test_eqs, false)
-        })
-    }
-
-    #[test]
-    fn test_diseq_1() {
-        with_globals(|| {
-            let test_res = string_to_ts("(bar,baz)");
-            let test_eqs = string_to_ts("bar,baz");
-            assert_eq!(test_res == test_eqs, false)
-        })
-    }
-
-    #[test]
-    fn test_is_empty() {
-        with_globals(|| {
-            let test0: TokenStream = Vec::<TokenTree>::new().into_iter().collect();
-            let test1: TokenStream =
-                TokenTree::Token(sp(0, 1), Token::Ident(Ident::from_str("a"), false)).into();
-            let test2 = string_to_ts("foo(bar::baz)");
-
-            assert_eq!(test0.is_empty(), true);
-            assert_eq!(test1.is_empty(), false);
-            assert_eq!(test2.is_empty(), false);
-        })
-    }
-
-    #[test]
-    fn test_dotdotdot() {
-        let mut builder = TokenStreamBuilder::new();
-        builder.push(TokenTree::Token(sp(0, 1), Token::Dot).joint());
-        builder.push(TokenTree::Token(sp(1, 2), Token::Dot).joint());
-        builder.push(TokenTree::Token(sp(2, 3), Token::Dot));
-        let stream = builder.build();
-        assert!(stream.eq_unspanned(&string_to_ts("...")));
-        assert_eq!(stream.trees().count(), 1);
-    }
-}
diff --git a/src/libsyntax/tokenstream/tests.rs b/src/libsyntax/tokenstream/tests.rs
new file mode 100644
index 00000000000..5017e5f5424
--- /dev/null
+++ b/src/libsyntax/tokenstream/tests.rs
@@ -0,0 +1,108 @@
+use super::*;
+
+use crate::ast::Name;
+use crate::with_default_globals;
+use crate::tests::string_to_stream;
+use syntax_pos::{Span, BytePos};
+
+fn string_to_ts(string: &str) -> TokenStream {
+    string_to_stream(string.to_owned())
+}
+
+fn sp(a: u32, b: u32) -> Span {
+    Span::with_root_ctxt(BytePos(a), BytePos(b))
+}
+
+#[test]
+fn test_concat() {
+    with_default_globals(|| {
+        let test_res = string_to_ts("foo::bar::baz");
+        let test_fst = string_to_ts("foo::bar");
+        let test_snd = string_to_ts("::baz");
+        let eq_res = TokenStream::from_streams(smallvec![test_fst, test_snd]);
+        assert_eq!(test_res.trees().count(), 5);
+        assert_eq!(eq_res.trees().count(), 5);
+        assert_eq!(test_res.eq_unspanned(&eq_res), true);
+    })
+}
+
+#[test]
+fn test_to_from_bijection() {
+    with_default_globals(|| {
+        let test_start = string_to_ts("foo::bar(baz)");
+        let test_end = test_start.trees().collect();
+        assert_eq!(test_start, test_end)
+    })
+}
+
+#[test]
+fn test_eq_0() {
+    with_default_globals(|| {
+        let test_res = string_to_ts("foo");
+        let test_eqs = string_to_ts("foo");
+        assert_eq!(test_res, test_eqs)
+    })
+}
+
+#[test]
+fn test_eq_1() {
+    with_default_globals(|| {
+        let test_res = string_to_ts("::bar::baz");
+        let test_eqs = string_to_ts("::bar::baz");
+        assert_eq!(test_res, test_eqs)
+    })
+}
+
+#[test]
+fn test_eq_3() {
+    with_default_globals(|| {
+        let test_res = string_to_ts("");
+        let test_eqs = string_to_ts("");
+        assert_eq!(test_res, test_eqs)
+    })
+}
+
+#[test]
+fn test_diseq_0() {
+    with_default_globals(|| {
+        let test_res = string_to_ts("::bar::baz");
+        let test_eqs = string_to_ts("bar::baz");
+        assert_eq!(test_res == test_eqs, false)
+    })
+}
+
+#[test]
+fn test_diseq_1() {
+    with_default_globals(|| {
+        let test_res = string_to_ts("(bar,baz)");
+        let test_eqs = string_to_ts("bar,baz");
+        assert_eq!(test_res == test_eqs, false)
+    })
+}
+
+#[test]
+fn test_is_empty() {
+    with_default_globals(|| {
+        let test0: TokenStream = Vec::<TokenTree>::new().into_iter().collect();
+        let test1: TokenStream =
+            TokenTree::token(token::Ident(Name::intern("a"), false), sp(0, 1)).into();
+        let test2 = string_to_ts("foo(bar::baz)");
+
+        assert_eq!(test0.is_empty(), true);
+        assert_eq!(test1.is_empty(), false);
+        assert_eq!(test2.is_empty(), false);
+    })
+}
+
+#[test]
+fn test_dotdotdot() {
+    with_default_globals(|| {
+        let mut builder = TokenStreamBuilder::new();
+        builder.push(TokenTree::token(token::Dot, sp(0, 1)).joint());
+        builder.push(TokenTree::token(token::Dot, sp(1, 2)).joint());
+        builder.push(TokenTree::token(token::Dot, sp(2, 3)));
+        let stream = builder.build();
+        assert!(stream.eq_unspanned(&string_to_ts("...")));
+        assert_eq!(stream.trees().count(), 1);
+    })
+}
diff --git a/src/libsyntax/util/lev_distance.rs b/src/libsyntax/util/lev_distance.rs
index 2f150d22159..4127a8c7fce 100644
--- a/src/libsyntax/util/lev_distance.rs
+++ b/src/libsyntax/util/lev_distance.rs
@@ -1,6 +1,9 @@
 use std::cmp;
 use crate::symbol::Symbol;
 
+#[cfg(test)]
+mod tests;
+
 /// Finds the Levenshtein distance between two strings
 pub fn lev_distance(a: &str, b: &str) -> usize {
     // cases which don't require further computation
@@ -77,60 +80,3 @@ pub fn find_best_match_for_name<'a, T>(iter_names: T,
         if let Some((candidate, _)) = levenstein_match { Some(candidate) } else { None }
     }
 }
-
-#[test]
-fn test_lev_distance() {
-    use std::char::{from_u32, MAX};
-    // Test bytelength agnosticity
-    for c in (0..MAX as u32)
-             .filter_map(|i| from_u32(i))
-             .map(|i| i.to_string()) {
-        assert_eq!(lev_distance(&c[..], &c[..]), 0);
-    }
-
-    let a = "\nMäry häd ä little lämb\n\nLittle lämb\n";
-    let b = "\nMary häd ä little lämb\n\nLittle lämb\n";
-    let c = "Mary häd ä little lämb\n\nLittle lämb\n";
-    assert_eq!(lev_distance(a, b), 1);
-    assert_eq!(lev_distance(b, a), 1);
-    assert_eq!(lev_distance(a, c), 2);
-    assert_eq!(lev_distance(c, a), 2);
-    assert_eq!(lev_distance(b, c), 1);
-    assert_eq!(lev_distance(c, b), 1);
-}
-
-#[test]
-fn test_find_best_match_for_name() {
-    use crate::with_globals;
-    with_globals(|| {
-        let input = vec![Symbol::intern("aaab"), Symbol::intern("aaabc")];
-        assert_eq!(
-            find_best_match_for_name(input.iter(), "aaaa", None),
-            Some(Symbol::intern("aaab"))
-        );
-
-        assert_eq!(
-            find_best_match_for_name(input.iter(), "1111111111", None),
-            None
-        );
-
-        let input = vec![Symbol::intern("aAAA")];
-        assert_eq!(
-            find_best_match_for_name(input.iter(), "AAAA", None),
-            Some(Symbol::intern("aAAA"))
-        );
-
-        let input = vec![Symbol::intern("AAAA")];
-        // Returns None because `lev_distance > max_dist / 3`
-        assert_eq!(
-            find_best_match_for_name(input.iter(), "aaaa", None),
-            None
-        );
-
-        let input = vec![Symbol::intern("AAAA")];
-        assert_eq!(
-            find_best_match_for_name(input.iter(), "aaaa", Some(4)),
-            Some(Symbol::intern("AAAA"))
-        );
-    })
-}
diff --git a/src/libsyntax/util/lev_distance/tests.rs b/src/libsyntax/util/lev_distance/tests.rs
new file mode 100644
index 00000000000..1a746a67ec0
--- /dev/null
+++ b/src/libsyntax/util/lev_distance/tests.rs
@@ -0,0 +1,58 @@
+use super::*;
+
+#[test]
+fn test_lev_distance() {
+    use std::char::{from_u32, MAX};
+    // Test bytelength agnosticity
+    for c in (0..MAX as u32)
+             .filter_map(|i| from_u32(i))
+             .map(|i| i.to_string()) {
+        assert_eq!(lev_distance(&c[..], &c[..]), 0);
+    }
+
+    let a = "\nMäry häd ä little lämb\n\nLittle lämb\n";
+    let b = "\nMary häd ä little lämb\n\nLittle lämb\n";
+    let c = "Mary häd ä little lämb\n\nLittle lämb\n";
+    assert_eq!(lev_distance(a, b), 1);
+    assert_eq!(lev_distance(b, a), 1);
+    assert_eq!(lev_distance(a, c), 2);
+    assert_eq!(lev_distance(c, a), 2);
+    assert_eq!(lev_distance(b, c), 1);
+    assert_eq!(lev_distance(c, b), 1);
+}
+
+#[test]
+fn test_find_best_match_for_name() {
+    use crate::with_default_globals;
+    with_default_globals(|| {
+        let input = vec![Symbol::intern("aaab"), Symbol::intern("aaabc")];
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "aaaa", None),
+            Some(Symbol::intern("aaab"))
+        );
+
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "1111111111", None),
+            None
+        );
+
+        let input = vec![Symbol::intern("aAAA")];
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "AAAA", None),
+            Some(Symbol::intern("aAAA"))
+        );
+
+        let input = vec![Symbol::intern("AAAA")];
+        // Returns None because `lev_distance > max_dist / 3`
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "aaaa", None),
+            None
+        );
+
+        let input = vec![Symbol::intern("AAAA")];
+        assert_eq!(
+            find_best_match_for_name(input.iter(), "aaaa", Some(4)),
+            Some(Symbol::intern("AAAA"))
+        );
+    })
+}
diff --git a/src/libsyntax/util/node_count.rs b/src/libsyntax/util/node_count.rs
index 521edac8f5f..f17eb3b3943 100644
--- a/src/libsyntax/util/node_count.rs
+++ b/src/libsyntax/util/node_count.rs
@@ -131,9 +131,9 @@ impl<'ast> Visitor<'ast> for NodeCounter {
         self.count += 1;
         walk_generic_args(self, path_span, generic_args)
     }
-    fn visit_assoc_type_binding(&mut self, type_binding: &TypeBinding) {
+    fn visit_assoc_ty_constraint(&mut self, constraint: &AssocTyConstraint) {
         self.count += 1;
-        walk_assoc_type_binding(self, type_binding)
+        walk_assoc_ty_constraint(self, constraint)
     }
     fn visit_attribute(&mut self, _attr: &Attribute) {
         self.count += 1;
diff --git a/src/libsyntax/util/parser.rs b/src/libsyntax/util/parser.rs
index 86e89945afe..a501541c959 100644
--- a/src/libsyntax/util/parser.rs
+++ b/src/libsyntax/util/parser.rs
@@ -1,5 +1,5 @@
-use crate::parse::token::{Token, BinOpToken};
-use crate::symbol::keywords;
+use crate::parse::token::{self, Token, BinOpToken};
+use crate::symbol::kw;
 use crate::ast::{self, BinOpKind};
 
 /// Associative operator with precedence.
@@ -45,8 +45,6 @@ pub enum AssocOp {
     GreaterEqual,
     /// `=`
     Assign,
-    /// `<-`
-    ObsoleteInPlace,
     /// `?=` where ? is one of the BinOpToken
     AssignOp(BinOpToken),
     /// `as`
@@ -73,34 +71,35 @@ impl AssocOp {
     /// Creates a new AssocOP from a token
     pub fn from_token(t: &Token) -> Option<AssocOp> {
         use AssocOp::*;
-        match *t {
-            Token::BinOpEq(k) => Some(AssignOp(k)),
-            Token::LArrow => Some(ObsoleteInPlace),
-            Token::Eq => Some(Assign),
-            Token::BinOp(BinOpToken::Star) => Some(Multiply),
-            Token::BinOp(BinOpToken::Slash) => Some(Divide),
-            Token::BinOp(BinOpToken::Percent) => Some(Modulus),
-            Token::BinOp(BinOpToken::Plus) => Some(Add),
-            Token::BinOp(BinOpToken::Minus) => Some(Subtract),
-            Token::BinOp(BinOpToken::Shl) => Some(ShiftLeft),
-            Token::BinOp(BinOpToken::Shr) => Some(ShiftRight),
-            Token::BinOp(BinOpToken::And) => Some(BitAnd),
-            Token::BinOp(BinOpToken::Caret) => Some(BitXor),
-            Token::BinOp(BinOpToken::Or) => Some(BitOr),
-            Token::Lt => Some(Less),
-            Token::Le => Some(LessEqual),
-            Token::Ge => Some(GreaterEqual),
-            Token::Gt => Some(Greater),
-            Token::EqEq => Some(Equal),
-            Token::Ne => Some(NotEqual),
-            Token::AndAnd => Some(LAnd),
-            Token::OrOr => Some(LOr),
-            Token::DotDot => Some(DotDot),
-            Token::DotDotEq => Some(DotDotEq),
+        match t.kind {
+            token::BinOpEq(k) => Some(AssignOp(k)),
+            token::Eq => Some(Assign),
+            token::BinOp(BinOpToken::Star) => Some(Multiply),
+            token::BinOp(BinOpToken::Slash) => Some(Divide),
+            token::BinOp(BinOpToken::Percent) => Some(Modulus),
+            token::BinOp(BinOpToken::Plus) => Some(Add),
+            token::BinOp(BinOpToken::Minus) => Some(Subtract),
+            token::BinOp(BinOpToken::Shl) => Some(ShiftLeft),
+            token::BinOp(BinOpToken::Shr) => Some(ShiftRight),
+            token::BinOp(BinOpToken::And) => Some(BitAnd),
+            token::BinOp(BinOpToken::Caret) => Some(BitXor),
+            token::BinOp(BinOpToken::Or) => Some(BitOr),
+            token::Lt => Some(Less),
+            token::Le => Some(LessEqual),
+            token::Ge => Some(GreaterEqual),
+            token::Gt => Some(Greater),
+            token::EqEq => Some(Equal),
+            token::Ne => Some(NotEqual),
+            token::AndAnd => Some(LAnd),
+            token::OrOr => Some(LOr),
+            token::DotDot => Some(DotDot),
+            token::DotDotEq => Some(DotDotEq),
             // DotDotDot is no longer supported, but we need some way to display the error
-            Token::DotDotDot => Some(DotDotEq),
-            Token::Colon => Some(Colon),
-            _ if t.is_keyword(keywords::As) => Some(As),
+            token::DotDotDot => Some(DotDotEq),
+            token::Colon => Some(Colon),
+            // `<-` should probably be `< -`
+            token::LArrow => Some(Less),
+            _ if t.is_keyword(kw::As) => Some(As),
             _ => None
         }
     }
@@ -145,7 +144,6 @@ impl AssocOp {
             LAnd => 6,
             LOr => 5,
             DotDot | DotDotEq => 4,
-            ObsoleteInPlace => 3,
             Assign | AssignOp(_) => 2,
         }
     }
@@ -155,7 +153,7 @@ impl AssocOp {
         use AssocOp::*;
         // NOTE: it is a bug to have an operators that has same precedence but different fixities!
         match *self {
-            ObsoleteInPlace | Assign | AssignOp(_) => Fixity::Right,
+            Assign | AssignOp(_) => Fixity::Right,
             As | Multiply | Divide | Modulus | Add | Subtract | ShiftLeft | ShiftRight | BitAnd |
             BitXor | BitOr | Less | Greater | LessEqual | GreaterEqual | Equal | NotEqual |
             LAnd | LOr | Colon => Fixity::Left,
@@ -167,7 +165,7 @@ impl AssocOp {
         use AssocOp::*;
         match *self {
             Less | Greater | LessEqual | GreaterEqual | Equal | NotEqual => true,
-            ObsoleteInPlace | Assign | AssignOp(_) | As | Multiply | Divide | Modulus | Add |
+            Assign | AssignOp(_) | As | Multiply | Divide | Modulus | Add |
             Subtract | ShiftLeft | ShiftRight | BitAnd | BitXor | BitOr | LAnd | LOr |
             DotDot | DotDotEq | Colon => false
         }
@@ -176,7 +174,7 @@ impl AssocOp {
     pub fn is_assign_like(&self) -> bool {
         use AssocOp::*;
         match *self {
-            Assign | AssignOp(_) | ObsoleteInPlace => true,
+            Assign | AssignOp(_) => true,
             Less | Greater | LessEqual | GreaterEqual | Equal | NotEqual | As | Multiply | Divide |
             Modulus | Add | Subtract | ShiftLeft | ShiftRight | BitAnd | BitXor | BitOr | LAnd |
             LOr | DotDot | DotDotEq | Colon => false
@@ -204,7 +202,7 @@ impl AssocOp {
             BitOr => Some(BinOpKind::BitOr),
             LAnd => Some(BinOpKind::And),
             LOr => Some(BinOpKind::Or),
-            ObsoleteInPlace | Assign | AssignOp(_) | As | DotDot | DotDotEq | Colon => None
+            Assign | AssignOp(_) | As | DotDot | DotDotEq | Colon => None
         }
     }
 
@@ -238,7 +236,7 @@ pub const PREC_RESET: i8 = -100;
 pub const PREC_CLOSURE: i8 = -40;
 pub const PREC_JUMP: i8 = -30;
 pub const PREC_RANGE: i8 = -10;
-// The range 2 ... 14 is reserved for AssocOp binary operator precedences.
+// The range 2..=14 is reserved for AssocOp binary operator precedences.
 pub const PREC_PREFIX: i8 = 50;
 pub const PREC_POSTFIX: i8 = 60;
 pub const PREC_PAREN: i8 = 99;
@@ -256,7 +254,6 @@ pub enum ExprPrecedence {
 
     Binary(BinOpKind),
 
-    ObsoleteInPlace,
     Cast,
     Type,
 
@@ -265,6 +262,7 @@ pub enum ExprPrecedence {
 
     Box,
     AddrOf,
+    Let,
     Unary,
 
     Call,
@@ -282,9 +280,7 @@ pub enum ExprPrecedence {
     Path,
     Paren,
     If,
-    IfLet,
     While,
-    WhileLet,
     ForLoop,
     Loop,
     Match,
@@ -314,7 +310,6 @@ impl ExprPrecedence {
 
             // Binop-like expr kinds, handled by `AssocOp`.
             ExprPrecedence::Binary(op) => AssocOp::from_ast_binop(op).precedence() as i8,
-            ExprPrecedence::ObsoleteInPlace => AssocOp::ObsoleteInPlace.precedence() as i8,
             ExprPrecedence::Cast => AssocOp::As.precedence() as i8,
             ExprPrecedence::Type => AssocOp::Colon.precedence() as i8,
 
@@ -324,6 +319,11 @@ impl ExprPrecedence {
             // Unary, prefix
             ExprPrecedence::Box |
             ExprPrecedence::AddrOf |
+            // Here `let pats = expr` has `let pats =` as a "unary" prefix of `expr`.
+            // However, this is not exactly right. When `let _ = a` is the LHS of a binop we
+            // need parens sometimes. E.g. we can print `(let _ = a) && b` as `let _ = a && b`
+            // but we need to print `(let _ = a) < b` as-is with parens.
+            ExprPrecedence::Let |
             ExprPrecedence::Unary => PREC_PREFIX,
 
             // Unary, postfix
@@ -344,9 +344,7 @@ impl ExprPrecedence {
             ExprPrecedence::Path |
             ExprPrecedence::Paren |
             ExprPrecedence::If |
-            ExprPrecedence::IfLet |
             ExprPrecedence::While |
-            ExprPrecedence::WhileLet |
             ExprPrecedence::ForLoop |
             ExprPrecedence::Loop |
             ExprPrecedence::Match |
@@ -359,6 +357,19 @@ impl ExprPrecedence {
     }
 }
 
+/// In `let p = e`, operators with precedence `<=` this one requires parenthesis in `e`.
+crate fn prec_let_scrutinee_needs_par() -> usize {
+    AssocOp::LAnd.precedence()
+}
+
+/// Suppose we have `let _ = e` and the `order` of `e`.
+/// Is the `order` such that `e` in `let _ = e` needs parenthesis when it is on the RHS?
+///
+/// Conversely, suppose that we have `(let _ = a) OP b` and `order` is that of `OP`.
+/// Can we print this as `let _ = a OP b`?
+crate fn needs_par_as_let_scrutinee(order: i8) -> bool {
+    order <= prec_let_scrutinee_needs_par() as i8
+}
 
 /// Expressions that syntactically contain an "exterior" struct literal i.e., not surrounded by any
 /// parens or other delimiters, e.g., `X { y: 1 }`, `X { y: 1 }.method()`, `foo == X { y: 1 }` and
@@ -373,7 +384,7 @@ pub fn contains_exterior_struct_lit(value: &ast::Expr) -> bool {
             // X { y: 1 } + X { y: 2 }
             contains_exterior_struct_lit(&lhs) || contains_exterior_struct_lit(&rhs)
         }
-        ast::ExprKind::Await(_, ref x) |
+        ast::ExprKind::Await(ref x) |
         ast::ExprKind::Unary(_, ref x) |
         ast::ExprKind::Cast(ref x, _) |
         ast::ExprKind::Type(ref x, _) |
diff --git a/src/libsyntax/util/parser_testing.rs b/src/libsyntax/util/parser_testing.rs
deleted file mode 100644
index 733c4f83e37..00000000000
--- a/src/libsyntax/util/parser_testing.rs
+++ /dev/null
@@ -1,160 +0,0 @@
-use crate::ast::{self, Ident};
-use crate::source_map::FilePathMapping;
-use crate::parse::{ParseSess, PResult, source_file_to_stream};
-use crate::parse::{lexer, new_parser_from_source_str};
-use crate::parse::parser::Parser;
-use crate::ptr::P;
-use crate::tokenstream::TokenStream;
-
-use std::iter::Peekable;
-use std::path::PathBuf;
-
-/// Map a string to tts, using a made-up filename:
-pub fn string_to_stream(source_str: String) -> TokenStream {
-    let ps = ParseSess::new(FilePathMapping::empty());
-    source_file_to_stream(
-        &ps,
-        ps.source_map().new_source_file(PathBuf::from("bogofile").into(),
-        source_str,
-    ), None).0
-}
-
-/// Map string to parser (via tts)
-pub fn string_to_parser<'a>(ps: &'a ParseSess, source_str: String) -> Parser<'a> {
-    new_parser_from_source_str(ps, PathBuf::from("bogofile").into(), source_str)
-}
-
-fn with_error_checking_parse<'a, T, F>(s: String, ps: &'a ParseSess, f: F) -> T where
-    F: FnOnce(&mut Parser<'a>) -> PResult<'a, T>,
-{
-    let mut p = string_to_parser(&ps, s);
-    let x = panictry!(f(&mut p));
-    p.sess.span_diagnostic.abort_if_errors();
-    x
-}
-
-/// Parse a string, return a crate.
-pub fn string_to_crate (source_str : String) -> ast::Crate {
-    let ps = ParseSess::new(FilePathMapping::empty());
-    with_error_checking_parse(source_str, &ps, |p| {
-        p.parse_crate_mod()
-    })
-}
-
-/// Parse a string, return an expr
-pub fn string_to_expr (source_str : String) -> P<ast::Expr> {
-    let ps = ParseSess::new(FilePathMapping::empty());
-    with_error_checking_parse(source_str, &ps, |p| {
-        p.parse_expr()
-    })
-}
-
-/// Parse a string, return an item
-pub fn string_to_item (source_str : String) -> Option<P<ast::Item>> {
-    let ps = ParseSess::new(FilePathMapping::empty());
-    with_error_checking_parse(source_str, &ps, |p| {
-        p.parse_item()
-    })
-}
-
-/// Parse a string, return a pat. Uses "irrefutable"... which doesn't
-/// (currently) affect parsing.
-pub fn string_to_pat(source_str: String) -> P<ast::Pat> {
-    let ps = ParseSess::new(FilePathMapping::empty());
-    with_error_checking_parse(source_str, &ps, |p| {
-        p.parse_pat(None)
-    })
-}
-
-/// Converts a vector of strings to a vector of Ident's
-pub fn strs_to_idents(ids: Vec<&str> ) -> Vec<Ident> {
-    ids.iter().map(|u| Ident::from_str(*u)).collect()
-}
-
-/// Does the given string match the pattern? whitespace in the first string
-/// may be deleted or replaced with other whitespace to match the pattern.
-/// This function is relatively Unicode-ignorant; fortunately, the careful design
-/// of UTF-8 mitigates this ignorance. It doesn't do NKF-normalization(?).
-pub fn matches_codepattern(a : &str, b : &str) -> bool {
-    let mut a_iter = a.chars().peekable();
-    let mut b_iter = b.chars().peekable();
-
-    loop {
-        let (a, b) = match (a_iter.peek(), b_iter.peek()) {
-            (None, None) => return true,
-            (None, _) => return false,
-            (Some(&a), None) => {
-                if is_pattern_whitespace(a) {
-                    break // trailing whitespace check is out of loop for borrowck
-                } else {
-                    return false
-                }
-            }
-            (Some(&a), Some(&b)) => (a, b)
-        };
-
-        if is_pattern_whitespace(a) && is_pattern_whitespace(b) {
-            // skip whitespace for a and b
-            scan_for_non_ws_or_end(&mut a_iter);
-            scan_for_non_ws_or_end(&mut b_iter);
-        } else if is_pattern_whitespace(a) {
-            // skip whitespace for a
-            scan_for_non_ws_or_end(&mut a_iter);
-        } else if a == b {
-            a_iter.next();
-            b_iter.next();
-        } else {
-            return false
-        }
-    }
-
-    // check if a has *only* trailing whitespace
-    a_iter.all(is_pattern_whitespace)
-}
-
-/// Advances the given peekable `Iterator` until it reaches a non-whitespace character
-fn scan_for_non_ws_or_end<I: Iterator<Item= char>>(iter: &mut Peekable<I>) {
-    while lexer::is_pattern_whitespace(iter.peek().cloned()) {
-        iter.next();
-    }
-}
-
-pub fn is_pattern_whitespace(c: char) -> bool {
-    lexer::is_pattern_whitespace(Some(c))
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn eqmodws() {
-        assert_eq!(matches_codepattern("",""),true);
-        assert_eq!(matches_codepattern("","a"),false);
-        assert_eq!(matches_codepattern("a",""),false);
-        assert_eq!(matches_codepattern("a","a"),true);
-        assert_eq!(matches_codepattern("a b","a   \n\t\r  b"),true);
-        assert_eq!(matches_codepattern("a b ","a   \n\t\r  b"),true);
-        assert_eq!(matches_codepattern("a b","a   \n\t\r  b "),false);
-        assert_eq!(matches_codepattern("a   b","a b"),true);
-        assert_eq!(matches_codepattern("ab","a b"),false);
-        assert_eq!(matches_codepattern("a   b","ab"),true);
-        assert_eq!(matches_codepattern(" a   b","ab"),true);
-    }
-
-    #[test]
-    fn pattern_whitespace() {
-        assert_eq!(matches_codepattern("","\x0C"), false);
-        assert_eq!(matches_codepattern("a b ","a   \u{0085}\n\t\r  b"),true);
-        assert_eq!(matches_codepattern("a b","a   \u{0085}\n\t\r  b "),false);
-    }
-
-    #[test]
-    fn non_pattern_whitespace() {
-        // These have the property 'White_Space' but not 'Pattern_White_Space'
-        assert_eq!(matches_codepattern("a b","a\u{2002}b"), false);
-        assert_eq!(matches_codepattern("a   b","a\u{2002}b"), false);
-        assert_eq!(matches_codepattern("\u{205F}a   b","ab"), false);
-        assert_eq!(matches_codepattern("a  \u{3000}b","ab"), false);
-    }
-}
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 0503e5644db..91b92d84a81 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -66,6 +66,7 @@ pub trait Visitor<'ast>: Sized {
     fn visit_local(&mut self, l: &'ast Local) { walk_local(self, l) }
     fn visit_block(&mut self, b: &'ast Block) { walk_block(self, b) }
     fn visit_stmt(&mut self, s: &'ast Stmt) { walk_stmt(self, s) }
+    fn visit_arg(&mut self, arg: &'ast Arg) { walk_arg(self, arg) }
     fn visit_arm(&mut self, a: &'ast Arm) { walk_arm(self, a) }
     fn visit_pat(&mut self, p: &'ast Pat) { walk_pat(self, p) }
     fn visit_anon_const(&mut self, c: &'ast AnonConst) { walk_anon_const(self, c) }
@@ -139,8 +140,8 @@ pub trait Visitor<'ast>: Sized {
             GenericArg::Const(ct) => self.visit_anon_const(ct),
         }
     }
-    fn visit_assoc_type_binding(&mut self, type_binding: &'ast TypeBinding) {
-        walk_assoc_type_binding(self, type_binding)
+    fn visit_assoc_ty_constraint(&mut self, constraint: &'ast AssocTyConstraint) {
+        walk_assoc_ty_constraint(self, constraint)
     }
     fn visit_attribute(&mut self, attr: &'ast Attribute) {
         walk_attribute(self, attr)
@@ -254,11 +255,11 @@ pub fn walk_item<'a, V: Visitor<'a>>(visitor: &mut V, item: &'a Item) {
             walk_list!(visitor, visit_foreign_item, &foreign_module.items);
         }
         ItemKind::GlobalAsm(ref ga) => visitor.visit_global_asm(ga),
-        ItemKind::Ty(ref typ, ref generics) => {
+        ItemKind::TyAlias(ref typ, ref generics) => {
             visitor.visit_ty(typ);
             visitor.visit_generics(generics)
         }
-        ItemKind::Existential(ref bounds, ref generics) => {
+        ItemKind::OpaqueTy(ref bounds, ref generics) => {
             walk_list!(visitor, visit_param_bound, bounds);
             visitor.visit_generics(generics)
         }
@@ -310,11 +311,11 @@ pub fn walk_variant<'a, V>(visitor: &mut V,
                            item_id: NodeId)
     where V: Visitor<'a>,
 {
-    visitor.visit_ident(variant.node.ident);
-    visitor.visit_variant_data(&variant.node.data, variant.node.ident,
+    visitor.visit_ident(variant.ident);
+    visitor.visit_variant_data(&variant.data, variant.ident,
                              generics, item_id, variant.span);
-    walk_list!(visitor, visit_anon_const, &variant.node.disr_expr);
-    walk_list!(visitor, visit_attribute, &variant.node.attrs);
+    walk_list!(visitor, visit_anon_const, &variant.disr_expr);
+    walk_list!(visitor, visit_attribute, &variant.attrs);
 }
 
 pub fn walk_ty<'a, V: Visitor<'a>>(visitor: &mut V, typ: &'a Ty) {
@@ -404,7 +405,7 @@ pub fn walk_generic_args<'a, V>(visitor: &mut V,
     match *generic_args {
         GenericArgs::AngleBracketed(ref data) => {
             walk_list!(visitor, visit_generic_arg, &data.args);
-            walk_list!(visitor, visit_assoc_type_binding, &data.bindings);
+            walk_list!(visitor, visit_assoc_ty_constraint, &data.constraints);
         }
         GenericArgs::Parenthesized(ref data) => {
             walk_list!(visitor, visit_ty, &data.inputs);
@@ -413,17 +414,24 @@ pub fn walk_generic_args<'a, V>(visitor: &mut V,
     }
 }
 
-pub fn walk_assoc_type_binding<'a, V: Visitor<'a>>(visitor: &mut V,
-                                                   type_binding: &'a TypeBinding) {
-    visitor.visit_ident(type_binding.ident);
-    visitor.visit_ty(&type_binding.ty);
+pub fn walk_assoc_ty_constraint<'a, V: Visitor<'a>>(visitor: &mut V,
+                                                    constraint: &'a AssocTyConstraint) {
+    visitor.visit_ident(constraint.ident);
+    match constraint.kind {
+        AssocTyConstraintKind::Equality { ref ty } => {
+            visitor.visit_ty(ty);
+        }
+        AssocTyConstraintKind::Bound { ref bounds } => {
+            walk_list!(visitor, visit_param_bound, bounds);
+        }
+    }
 }
 
 pub fn walk_pat<'a, V: Visitor<'a>>(visitor: &mut V, pattern: &'a Pat) {
     match pattern.node {
-        PatKind::TupleStruct(ref path, ref children, _) => {
+        PatKind::TupleStruct(ref path, ref elems) => {
             visitor.visit_path(path, pattern.id);
-            walk_list!(visitor, visit_pat, children);
+            walk_list!(visitor, visit_pat, elems);
         }
         PatKind::Path(ref opt_qself, ref path) => {
             if let Some(ref qself) = *opt_qself {
@@ -434,14 +442,11 @@ pub fn walk_pat<'a, V: Visitor<'a>>(visitor: &mut V, pattern: &'a Pat) {
         PatKind::Struct(ref path, ref fields, _) => {
             visitor.visit_path(path, pattern.id);
             for field in fields {
-                walk_list!(visitor, visit_attribute, field.node.attrs.iter());
-                visitor.visit_ident(field.node.ident);
-                visitor.visit_pat(&field.node.pat)
+                walk_list!(visitor, visit_attribute, field.attrs.iter());
+                visitor.visit_ident(field.ident);
+                visitor.visit_pat(&field.pat)
             }
         }
-        PatKind::Tuple(ref tuple_elements, _) => {
-            walk_list!(visitor, visit_pat, tuple_elements);
-        }
         PatKind::Box(ref subpattern) |
         PatKind::Ref(ref subpattern, _) |
         PatKind::Paren(ref subpattern) => {
@@ -456,11 +461,11 @@ pub fn walk_pat<'a, V: Visitor<'a>>(visitor: &mut V, pattern: &'a Pat) {
             visitor.visit_expr(lower_bound);
             visitor.visit_expr(upper_bound);
         }
-        PatKind::Wild => (),
-        PatKind::Slice(ref prepatterns, ref slice_pattern, ref postpatterns) => {
-            walk_list!(visitor, visit_pat, prepatterns);
-            walk_list!(visitor, visit_pat, slice_pattern);
-            walk_list!(visitor, visit_pat, postpatterns);
+        PatKind::Wild | PatKind::Rest => {},
+        PatKind::Tuple(ref elems)
+        | PatKind::Slice(ref elems)
+        | PatKind::Or(ref elems) => {
+            walk_list!(visitor, visit_pat, elems);
         }
         PatKind::Mac(ref mac) => visitor.visit_mac(mac),
     }
@@ -499,7 +504,7 @@ pub fn walk_generic_param<'a, V: Visitor<'a>>(visitor: &mut V, param: &'a Generi
     walk_list!(visitor, visit_attribute, param.attrs.iter());
     walk_list!(visitor, visit_param_bound, &param.bounds);
     match param.kind {
-        GenericParamKind::Lifetime => {}
+        GenericParamKind::Lifetime => (),
         GenericParamKind::Type { ref default } => walk_list!(visitor, visit_ty, default),
         GenericParamKind::Const { ref ty, .. } => visitor.visit_ty(ty),
     }
@@ -542,14 +547,10 @@ pub fn walk_fn_ret_ty<'a, V: Visitor<'a>>(visitor: &mut V, ret_ty: &'a FunctionR
 }
 
 pub fn walk_fn_decl<'a, V: Visitor<'a>>(visitor: &mut V, function_declaration: &'a FnDecl) {
-    for argument in &function_declaration.inputs {
-        visitor.visit_pat(&argument.pat);
-        if let ArgSource::AsyncFn(pat) = &argument.source {
-            visitor.visit_pat(pat);
-        }
-        visitor.visit_ty(&argument.ty)
+    for arg in &function_declaration.inputs {
+        visitor.visit_arg(arg);
     }
-    visitor.visit_fn_ret_ty(&function_declaration.output)
+    visitor.visit_fn_ret_ty(&function_declaration.output);
 }
 
 pub fn walk_fn<'a, V>(visitor: &mut V, kind: FnKind<'a>, declaration: &'a FnDecl, _span: Span)
@@ -614,10 +615,10 @@ pub fn walk_impl_item<'a, V: Visitor<'a>>(visitor: &mut V, impl_item: &'a ImplIt
             visitor.visit_fn(FnKind::Method(impl_item.ident, sig, Some(&impl_item.vis), body),
                              &sig.decl, impl_item.span, impl_item.id);
         }
-        ImplItemKind::Type(ref ty) => {
+        ImplItemKind::TyAlias(ref ty) => {
             visitor.visit_ty(ty);
         }
-        ImplItemKind::Existential(ref bounds) => {
+        ImplItemKind::OpaqueTy(ref bounds) => {
             walk_list!(visitor, visit_param_bound, bounds);
         }
         ImplItemKind::Macro(ref mac) => {
@@ -661,7 +662,7 @@ pub fn walk_stmt<'a, V: Visitor<'a>>(visitor: &mut V, statement: &'a Stmt) {
 }
 
 pub fn walk_mac<'a, V: Visitor<'a>>(visitor: &mut V, mac: &'a Mac) {
-    visitor.visit_path(&mac.node.path, DUMMY_NODE_ID);
+    visitor.visit_path(&mac.path, DUMMY_NODE_ID);
 }
 
 pub fn walk_anon_const<'a, V: Visitor<'a>>(visitor: &mut V, constant: &'a AnonConst) {
@@ -676,10 +677,6 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         ExprKind::Box(ref subexpression) => {
             visitor.visit_expr(subexpression)
         }
-        ExprKind::ObsoleteInPlace(ref place, ref subexpression) => {
-            visitor.visit_expr(place);
-            visitor.visit_expr(subexpression)
-        }
         ExprKind::Array(ref subexpressions) => {
             walk_list!(visitor, visit_expr, subexpressions);
         }
@@ -714,11 +711,14 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         ExprKind::AddrOf(_, ref subexpression) | ExprKind::Unary(_, ref subexpression) => {
             visitor.visit_expr(subexpression)
         }
-        ExprKind::Lit(_) => {}
         ExprKind::Cast(ref subexpression, ref typ) | ExprKind::Type(ref subexpression, ref typ) => {
             visitor.visit_expr(subexpression);
             visitor.visit_ty(typ)
         }
+        ExprKind::Let(ref pats, ref scrutinee) => {
+            walk_list!(visitor, visit_pat, pats);
+            visitor.visit_expr(scrutinee);
+        }
         ExprKind::If(ref head_expression, ref if_block, ref optional_else) => {
             visitor.visit_expr(head_expression);
             visitor.visit_block(if_block);
@@ -729,18 +729,6 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
             visitor.visit_expr(subexpression);
             visitor.visit_block(block);
         }
-        ExprKind::IfLet(ref pats, ref subexpression, ref if_block, ref optional_else) => {
-            walk_list!(visitor, visit_pat, pats);
-            visitor.visit_expr(subexpression);
-            visitor.visit_block(if_block);
-            walk_list!(visitor, visit_expr, optional_else);
-        }
-        ExprKind::WhileLet(ref pats, ref subexpression, ref block, ref opt_label) => {
-            walk_list!(visitor, visit_label, opt_label);
-            walk_list!(visitor, visit_pat, pats);
-            visitor.visit_expr(subexpression);
-            visitor.visit_block(block);
-        }
         ExprKind::ForLoop(ref pattern, ref subexpression, ref block, ref opt_label) => {
             walk_list!(visitor, visit_label, opt_label);
             visitor.visit_pat(pattern);
@@ -768,7 +756,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         ExprKind::Async(_, _, ref body) => {
             visitor.visit_block(body);
         }
-        ExprKind::Await(_, ref expr) => visitor.visit_expr(expr),
+        ExprKind::Await(ref expr) => visitor.visit_expr(expr),
         ExprKind::Assign(ref left_hand_expression, ref right_hand_expression) => {
             visitor.visit_expr(left_hand_expression);
             visitor.visit_expr(right_hand_expression);
@@ -826,18 +814,22 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
         ExprKind::TryBlock(ref body) => {
             visitor.visit_block(body)
         }
-        ExprKind::Err => {}
+        ExprKind::Lit(_) | ExprKind::Err => {}
     }
 
     visitor.visit_expr_post(expression)
 }
 
+pub fn walk_arg<'a, V: Visitor<'a>>(visitor: &mut V, arg: &'a Arg) {
+    walk_list!(visitor, visit_attribute, arg.attrs.iter());
+    visitor.visit_pat(&arg.pat);
+    visitor.visit_ty(&arg.ty);
+}
+
 pub fn walk_arm<'a, V: Visitor<'a>>(visitor: &mut V, arm: &'a Arm) {
     walk_list!(visitor, visit_pat, &arm.pats);
-    if let Some(ref g) = &arm.guard {
-        match g {
-            Guard::If(ref e) => visitor.visit_expr(e),
-        }
+    if let Some(ref e) = &arm.guard {
+        visitor.visit_expr(e);
     }
     visitor.visit_expr(&arm.body);
     walk_list!(visitor, visit_attribute, &arm.attrs);
@@ -855,7 +847,7 @@ pub fn walk_attribute<'a, V: Visitor<'a>>(visitor: &mut V, attr: &'a Attribute)
 
 pub fn walk_tt<'a, V: Visitor<'a>>(visitor: &mut V, tt: TokenTree) {
     match tt {
-        TokenTree::Token(_, tok) => visitor.visit_token(tok),
+        TokenTree::Token(token) => visitor.visit_token(token),
         TokenTree::Delimited(_, _, tts) => visitor.visit_tts(tts),
     }
 }