Rollup merge of #38171 - jseyfried:cleanup, r=nrc

Miscellaneous cleanup/refactoring in `resolve` and `syntax::ext`

r? @nrc

15 files changed, 145 insertions, 344 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 2a911aceb9d..fdd82225b97 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -47,10 +47,14 @@ impl Ident {
         Ident { name: name, ctxt: SyntaxContext::empty() }
     }
 
-   /// Maps a string to an identifier with an empty syntax context.
-   pub fn from_str(s: &str) -> Ident {
-       Ident::with_empty_ctxt(Symbol::intern(s))
-   }
+    /// Maps a string to an identifier with an empty syntax context.
+    pub fn from_str(s: &str) -> Ident {
+        Ident::with_empty_ctxt(Symbol::intern(s))
+    }
+
+    pub fn unhygienize(&self) -> Ident {
+        Ident { name: self.name, ctxt: SyntaxContext::empty() }
+    }
 }
 
 impl fmt::Debug for Ident {
@@ -133,12 +137,7 @@ impl Path {
         Path {
             span: s,
             global: false,
-            segments: vec![
-                PathSegment {
-                    identifier: identifier,
-                    parameters: PathParameters::none()
-                }
-            ],
+            segments: vec![identifier.into()],
         }
     }
 }
@@ -156,7 +155,15 @@ pub struct PathSegment {
     /// this is more than just simple syntactic sugar; the use of
     /// parens affects the region binding rules, so we preserve the
     /// distinction.
-    pub parameters: PathParameters,
+    /// The `Option<P<..>>` wrapper is purely a size optimization;
+    /// `None` is used to represent both `Path` and `Path<>`.
+    pub parameters: Option<P<PathParameters>>,
+}
+
+impl From<Ident> for PathSegment {
+    fn from(id: Ident) -> Self {
+        PathSegment { identifier: id, parameters: None }
+    }
 }
 
 /// Parameters of a path segment.
@@ -170,79 +177,8 @@ pub enum PathParameters {
     Parenthesized(ParenthesizedParameterData),
 }
 
-impl PathParameters {
-    pub fn none() -> PathParameters {
-        PathParameters::AngleBracketed(AngleBracketedParameterData {
-            lifetimes: Vec::new(),
-            types: P::new(),
-            bindings: P::new(),
-        })
-    }
-
-    pub fn is_empty(&self) -> bool {
-        match *self {
-            PathParameters::AngleBracketed(ref data) => data.is_empty(),
-
-            // Even if the user supplied no types, something like
-            // `X()` is equivalent to `X<(),()>`.
-            PathParameters::Parenthesized(..) => false,
-        }
-    }
-
-    pub fn has_lifetimes(&self) -> bool {
-        match *self {
-            PathParameters::AngleBracketed(ref data) => !data.lifetimes.is_empty(),
-            PathParameters::Parenthesized(_) => false,
-        }
-    }
-
-    pub fn has_types(&self) -> bool {
-        match *self {
-            PathParameters::AngleBracketed(ref data) => !data.types.is_empty(),
-            PathParameters::Parenthesized(..) => true,
-        }
-    }
-
-    /// Returns the types that the user wrote. Note that these do not necessarily map to the type
-    /// parameters in the parenthesized case.
-    pub fn types(&self) -> Vec<&P<Ty>> {
-        match *self {
-            PathParameters::AngleBracketed(ref data) => {
-                data.types.iter().collect()
-            }
-            PathParameters::Parenthesized(ref data) => {
-                data.inputs.iter()
-                    .chain(data.output.iter())
-                    .collect()
-            }
-        }
-    }
-
-    pub fn lifetimes(&self) -> Vec<&Lifetime> {
-        match *self {
-            PathParameters::AngleBracketed(ref data) => {
-                data.lifetimes.iter().collect()
-            }
-            PathParameters::Parenthesized(_) => {
-                Vec::new()
-            }
-        }
-    }
-
-    pub fn bindings(&self) -> Vec<&TypeBinding> {
-        match *self {
-            PathParameters::AngleBracketed(ref data) => {
-                data.bindings.iter().collect()
-            }
-            PathParameters::Parenthesized(_) => {
-                Vec::new()
-            }
-        }
-    }
-}
-
 /// A path like `Foo<'a, T>`
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Default)]
 pub struct AngleBracketedParameterData {
     /// The lifetime parameters for this path segment.
     pub lifetimes: Vec<Lifetime>,
@@ -254,9 +190,10 @@ pub struct AngleBracketedParameterData {
     pub bindings: P<[TypeBinding]>,
 }
 
-impl AngleBracketedParameterData {
-    fn is_empty(&self) -> bool {
-        self.lifetimes.is_empty() && self.types.is_empty() && self.bindings.is_empty()
+impl Into<Option<P<PathParameters>>> for AngleBracketedParameterData {
+    fn into(self) -> Option<P<PathParameters>> {
+        let empty = self.lifetimes.is_empty() && self.types.is_empty() && self.bindings.is_empty();
+        if empty { None } else { Some(P(PathParameters::AngleBracketed(self))) }
     }
 }
 
@@ -1968,8 +1905,6 @@ pub struct MacroDef {
     pub attrs: Vec<Attribute>,
     pub id: NodeId,
     pub span: Span,
-    pub imported_from: Option<Ident>,
-    pub allow_internal_unstable: bool,
     pub body: Vec<TokenTree>,
 }
 
diff --git a/src/libsyntax/attr.rs b/src/libsyntax/attr.rs
index 45c120e0b95..c31bcfbd869 100644
--- a/src/libsyntax/attr.rs
+++ b/src/libsyntax/attr.rs
@@ -29,7 +29,6 @@ use symbol::Symbol;
 use util::ThinVec;
 
 use std::cell::{RefCell, Cell};
-use std::collections::HashSet;
 
 thread_local! {
     static USED_ATTRS: RefCell<Vec<u64>> = RefCell::new(Vec::new());
@@ -372,16 +371,6 @@ pub fn mk_spanned_attr_outer(sp: Span, id: AttrId, item: MetaItem) -> Attribute
     }
 }
 
-pub fn mk_doc_attr_outer(id: AttrId, item: MetaItem, is_sugared_doc: bool) -> Attribute {
-    Attribute {
-        id: id,
-        style: ast::AttrStyle::Outer,
-        value: item,
-        is_sugared_doc: is_sugared_doc,
-        span: DUMMY_SP,
-    }
-}
-
 pub fn mk_sugared_doc_attr(id: AttrId, text: Symbol, lo: BytePos, hi: BytePos)
                            -> Attribute {
     let style = doc_comment_style(&text.as_str());
@@ -421,13 +410,6 @@ pub fn first_attr_value_str_by_name(attrs: &[Attribute], name: &str) -> Option<S
         .and_then(|at| at.value_str())
 }
 
-pub fn last_meta_item_value_str_by_name(items: &[MetaItem], name: &str) -> Option<Symbol> {
-    items.iter()
-         .rev()
-         .find(|mi| mi.check_name(name))
-         .and_then(|i| i.value_str())
-}
-
 /* Higher-level applications */
 
 pub fn find_crate_name(attrs: &[Attribute]) -> Option<Symbol> {
@@ -856,18 +838,6 @@ pub fn find_deprecation(diagnostic: &Handler, attrs: &[Attribute],
     find_deprecation_generic(diagnostic, attrs.iter(), item_sp)
 }
 
-pub fn require_unique_names(diagnostic: &Handler, metas: &[MetaItem]) {
-    let mut set = HashSet::new();
-    for meta in metas {
-        let name = meta.name();
-
-        if !set.insert(name.clone()) {
-            panic!(diagnostic.span_fatal(meta.span,
-                                         &format!("duplicate meta item `{}`", name)));
-        }
-    }
-}
-
 
 /// Parse #[repr(...)] forms.
 ///
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index ddbca47429d..8e63f73fdaa 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -217,8 +217,7 @@ pub trait IdentMacroExpander {
                    cx: &'cx mut ExtCtxt,
                    sp: Span,
                    ident: ast::Ident,
-                   token_tree: Vec<tokenstream::TokenTree>,
-                   attrs: Vec<ast::Attribute>)
+                   token_tree: Vec<tokenstream::TokenTree>)
                    -> Box<MacResult+'cx>;
 }
 
@@ -234,8 +233,7 @@ impl<F> IdentMacroExpander for F
                    cx: &'cx mut ExtCtxt,
                    sp: Span,
                    ident: ast::Ident,
-                   token_tree: Vec<tokenstream::TokenTree>,
-                   _attrs: Vec<ast::Attribute>)
+                   token_tree: Vec<tokenstream::TokenTree>)
                    -> Box<MacResult+'cx>
     {
         (*self)(cx, sp, ident, token_tree)
@@ -520,7 +518,6 @@ pub trait Resolver {
     fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item>;
 
     fn visit_expansion(&mut self, mark: Mark, expansion: &Expansion);
-    fn add_macro(&mut self, scope: Mark, def: ast::MacroDef, export: bool);
     fn add_ext(&mut self, ident: ast::Ident, ext: Rc<SyntaxExtension>);
     fn add_expansions_at_stmt(&mut self, id: ast::NodeId, macros: Vec<Mark>);
 
@@ -544,7 +541,6 @@ impl Resolver for DummyResolver {
     fn eliminate_crate_var(&mut self, item: P<ast::Item>) -> P<ast::Item> { item }
 
     fn visit_expansion(&mut self, _invoc: Mark, _expansion: &Expansion) {}
-    fn add_macro(&mut self, _scope: Mark, _def: ast::MacroDef, _export: bool) {}
     fn add_ext(&mut self, _ident: ast::Ident, _ext: Rc<SyntaxExtension>) {}
     fn add_expansions_at_stmt(&mut self, _id: ast::NodeId, _macros: Vec<Mark>) {}
 
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 6c0d40b69d3..c3dc64f9124 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -322,21 +322,17 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                 bindings: Vec<ast::TypeBinding> )
                 -> ast::Path {
         let last_identifier = idents.pop().unwrap();
-        let mut segments: Vec<ast::PathSegment> = idents.into_iter()
-                                                      .map(|ident| {
-            ast::PathSegment {
-                identifier: ident,
-                parameters: ast::PathParameters::none(),
-            }
-        }).collect();
-        segments.push(ast::PathSegment {
-            identifier: last_identifier,
-            parameters: ast::PathParameters::AngleBracketed(ast::AngleBracketedParameterData {
+        let mut segments: Vec<ast::PathSegment> = idents.into_iter().map(Into::into).collect();
+        let parameters = if lifetimes.is_empty() && types.is_empty() && bindings.is_empty() {
+            None
+        } else {
+            Some(P(ast::PathParameters::AngleBracketed(ast::AngleBracketedParameterData {
                 lifetimes: lifetimes,
                 types: P::from_vec(types),
                 bindings: P::from_vec(bindings),
-            })
-        });
+            })))
+        };
+        segments.push(ast::PathSegment { identifier: last_identifier, parameters: parameters });
         ast::Path {
             span: sp,
             global: global,
@@ -367,13 +363,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                  bindings: Vec<ast::TypeBinding>)
                  -> (ast::QSelf, ast::Path) {
         let mut path = trait_path;
+        let parameters = ast::AngleBracketedParameterData {
+            lifetimes: lifetimes,
+            types: P::from_vec(types),
+            bindings: P::from_vec(bindings),
+        };
         path.segments.push(ast::PathSegment {
             identifier: ident,
-            parameters: ast::PathParameters::AngleBracketed(ast::AngleBracketedParameterData {
-                lifetimes: lifetimes,
-                types: P::from_vec(types),
-                bindings: P::from_vec(bindings),
-            })
+            parameters: Some(P(ast::PathParameters::AngleBracketed(parameters))),
         });
 
         (ast::QSelf {
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 19545e2e642..5d62175fbf2 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -158,7 +158,6 @@ pub struct Invocation {
 
 pub enum InvocationKind {
     Bang {
-        attrs: Vec<ast::Attribute>,
         mac: ast::Mac,
         ident: Option<Ident>,
         span: Span,
@@ -276,7 +275,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             if expansions.len() < depth {
                 expansions.push(Vec::new());
             }
-            expansions[depth - 1].push((mark.as_u32(), expansion));
+            expansions[depth - 1].push((mark, expansion));
             if !self.cx.ecfg.single_step {
                 invocations.extend(new_invocations.into_iter().rev());
             }
@@ -287,7 +286,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         let mut placeholder_expander = PlaceholderExpander::new(self.cx, self.monotonic);
         while let Some(expansions) = expansions.pop() {
             for (mark, expansion) in expansions.into_iter().rev() {
-                placeholder_expander.add(ast::NodeId::from_u32(mark), expansion);
+                placeholder_expander.add(mark.as_placeholder_id(), expansion);
             }
         }
 
@@ -386,20 +385,12 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
     /// Expand a macro invocation. Returns the result of expansion.
     fn expand_bang_invoc(&mut self, invoc: Invocation, ext: Rc<SyntaxExtension>) -> Expansion {
         let (mark, kind) = (invoc.expansion_data.mark, invoc.expansion_kind);
-        let (attrs, mac, ident, span) = match invoc.kind {
-            InvocationKind::Bang { attrs, mac, ident, span } => (attrs, mac, ident, span),
+        let (mac, ident, span) = match invoc.kind {
+            InvocationKind::Bang { mac, ident, span } => (mac, ident, span),
             _ => unreachable!(),
         };
         let Mac_ { path, tts, .. } = mac.node;
 
-        // Detect use of feature-gated or invalid attributes on macro invoations
-        // since they will not be detected after macro expansion.
-        for attr in attrs.iter() {
-            feature_gate::check_attribute(&attr, &self.cx.parse_sess,
-                                          &self.cx.parse_sess.codemap(),
-                                          &self.cx.ecfg.features.unwrap());
-        }
-
         let extname = path.segments.last().unwrap().identifier.name;
         let ident = ident.unwrap_or(keywords::Invalid.ident());
         let marked_tts = mark_tts(&tts, mark);
@@ -440,7 +431,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     }
                 });
 
-                kind.make_from(expander.expand(self.cx, span, ident, marked_tts, attrs))
+                kind.make_from(expander.expand(self.cx, span, ident, marked_tts))
             }
 
             MultiDecorator(..) | MultiModifier(..) | SyntaxExtension::AttrProcMacro(..) => {
@@ -595,13 +586,11 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                 ..self.cx.current_expansion.clone()
             },
         });
-        placeholder(expansion_kind, ast::NodeId::from_u32(mark.as_u32()))
+        placeholder(expansion_kind, mark.as_placeholder_id())
     }
 
-    fn collect_bang(
-        &mut self, mac: ast::Mac, attrs: Vec<ast::Attribute>, span: Span, kind: ExpansionKind,
-    ) -> Expansion {
-        self.collect(kind, InvocationKind::Bang { attrs: attrs, mac: mac, ident: None, span: span })
+    fn collect_bang(&mut self, mac: ast::Mac, span: Span, kind: ExpansionKind) -> Expansion {
+        self.collect(kind, InvocationKind::Bang { mac: mac, ident: None, span: span })
     }
 
     fn collect_attr(&mut self, attr: ast::Attribute, item: Annotatable, kind: ExpansionKind)
@@ -622,6 +611,16 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
     fn configure<T: HasAttrs>(&mut self, node: T) -> Option<T> {
         self.cfg.configure(node)
     }
+
+    // Detect use of feature-gated or invalid attributes on macro invocations
+    // since they will not be detected after macro expansion.
+    fn check_attributes(&mut self, attrs: &[ast::Attribute]) {
+        let codemap = &self.cx.parse_sess.codemap();
+        let features = self.cx.ecfg.features.unwrap();
+        for attr in attrs.iter() {
+            feature_gate::check_attribute(&attr, &self.cx.parse_sess, codemap, features);
+        }
+    }
 }
 
 // These are pretty nasty. Ideally, we would keep the tokens around, linked from
@@ -660,7 +659,8 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
         expr.node = self.cfg.configure_expr_kind(expr.node);
 
         if let ast::ExprKind::Mac(mac) = expr.node {
-            self.collect_bang(mac, expr.attrs.into(), expr.span, ExpansionKind::Expr).make_expr()
+            self.check_attributes(&expr.attrs);
+            self.collect_bang(mac, expr.span, ExpansionKind::Expr).make_expr()
         } else {
             P(noop_fold_expr(expr, self))
         }
@@ -671,8 +671,8 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
         expr.node = self.cfg.configure_expr_kind(expr.node);
 
         if let ast::ExprKind::Mac(mac) = expr.node {
-            self.collect_bang(mac, expr.attrs.into(), expr.span, ExpansionKind::OptExpr)
-                .make_opt_expr()
+            self.check_attributes(&expr.attrs);
+            self.collect_bang(mac, expr.span, ExpansionKind::OptExpr).make_opt_expr()
         } else {
             Some(P(noop_fold_expr(expr, self)))
         }
@@ -685,8 +685,7 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
         }
 
         pat.and_then(|pat| match pat.node {
-            PatKind::Mac(mac) =>
-                self.collect_bang(mac, Vec::new(), pat.span, ExpansionKind::Pat).make_pat(),
+            PatKind::Mac(mac) => self.collect_bang(mac, pat.span, ExpansionKind::Pat).make_pat(),
             _ => unreachable!(),
         })
     }
@@ -707,8 +706,8 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
             }).collect()
         };
 
-        let mut placeholder =
-            self.collect_bang(mac, attrs.into(), stmt.span, ExpansionKind::Stmts).make_stmts();
+        self.check_attributes(&attrs);
+        let mut placeholder = self.collect_bang(mac, stmt.span, ExpansionKind::Stmts).make_stmts();
 
         // If this is a macro invocation with a semicolon, then apply that
         // semicolon to the final statement produced by expansion.
@@ -740,18 +739,21 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
 
         match item.node {
             ast::ItemKind::Mac(..) => {
-                if match item.node {
-                    ItemKind::Mac(ref mac) => mac.node.path.segments.is_empty(),
-                    _ => unreachable!(),
-                } {
-                    return SmallVector::one(item);
-                }
+                self.check_attributes(&item.attrs);
+                let is_macro_def = if let ItemKind::Mac(ref mac) = item.node {
+                    mac.node.path.segments[0].identifier.name == "macro_rules"
+                } else {
+                    unreachable!()
+                };
 
-                item.and_then(|item| match item.node {
+                item.and_then(|mut item| match item.node {
+                    ItemKind::Mac(_) if is_macro_def => {
+                        item.id = Mark::fresh().as_placeholder_id();
+                        SmallVector::one(P(item))
+                    }
                     ItemKind::Mac(mac) => {
                         self.collect(ExpansionKind::Items, InvocationKind::Bang {
                             mac: mac,
-                            attrs: item.attrs,
                             ident: Some(item.ident),
                             span: item.span,
                         }).make_items()
@@ -823,7 +825,8 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
         match item.node {
             ast::TraitItemKind::Macro(mac) => {
                 let ast::TraitItem { attrs, span, .. } = item;
-                self.collect_bang(mac, attrs, span, ExpansionKind::TraitItems).make_trait_items()
+                self.check_attributes(&attrs);
+                self.collect_bang(mac, span, ExpansionKind::TraitItems).make_trait_items()
             }
             _ => fold::noop_fold_trait_item(item, self),
         }
@@ -841,7 +844,8 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
         match item.node {
             ast::ImplItemKind::Macro(mac) => {
                 let ast::ImplItem { attrs, span, .. } = item;
-                self.collect_bang(mac, attrs, span, ExpansionKind::ImplItems).make_impl_items()
+                self.check_attributes(&attrs);
+                self.collect_bang(mac, span, ExpansionKind::ImplItems).make_impl_items()
             }
             _ => fold::noop_fold_impl_item(item, self),
         }
@@ -854,8 +858,7 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
         };
 
         match ty.node {
-            ast::TyKind::Mac(mac) =>
-                self.collect_bang(mac, Vec::new(), ty.span, ExpansionKind::Ty).make_ty(),
+            ast::TyKind::Mac(mac) => self.collect_bang(mac, ty.span, ExpansionKind::Ty).make_ty(),
             _ => unreachable!(),
         }
     }
diff --git a/src/libsyntax/ext/hygiene.rs b/src/libsyntax/ext/hygiene.rs
index 0fd72277cca..2af5c2ea999 100644
--- a/src/libsyntax/ext/hygiene.rs
+++ b/src/libsyntax/ext/hygiene.rs
@@ -51,7 +51,11 @@ impl Mark {
         Mark(id.as_u32())
     }
 
-    pub fn as_u32(&self) -> u32 {
+    pub fn as_placeholder_id(self) -> NodeId {
+        NodeId::from_u32(self.0)
+    }
+
+    pub fn as_u32(self) -> u32 {
         self.0
     }
 }
@@ -115,12 +119,12 @@ impl SyntaxContext {
         })
     }
 
-   /// If `ident` is macro expanded, return the source ident from the macro definition
-   /// and the mark of the expansion that created the macro definition.
-   pub fn source(self) -> (Self /* source context */, Mark /* source macro */) {
-        let macro_def_ctxt = self.data().prev_ctxt.data();
-        (macro_def_ctxt.prev_ctxt, macro_def_ctxt.outer_mark)
-   }
+    /// If `ident` is macro expanded, return the source ident from the macro definition
+    /// and the mark of the expansion that created the macro definition.
+    pub fn source(self) -> (Self /* source context */, Mark /* source macro */) {
+         let macro_def_ctxt = self.data().prev_ctxt.data();
+         (macro_def_ctxt.prev_ctxt, macro_def_ctxt.outer_mark)
+    }
 }
 
 impl fmt::Debug for SyntaxContext {
diff --git a/src/libsyntax/ext/placeholders.rs b/src/libsyntax/ext/placeholders.rs
index 4fe57a8345e..eb4b6144c8d 100644
--- a/src/libsyntax/ext/placeholders.rs
+++ b/src/libsyntax/ext/placeholders.rs
@@ -12,9 +12,10 @@ use ast;
 use codemap::{DUMMY_SP, dummy_spanned};
 use ext::base::ExtCtxt;
 use ext::expand::{Expansion, ExpansionKind};
+use ext::hygiene::Mark;
 use fold::*;
 use ptr::P;
-use symbol::{Symbol, keywords};
+use symbol::keywords;
 use util::move_map::MoveMap;
 use util::small_vector::SmallVector;
 
@@ -68,10 +69,6 @@ pub fn placeholder(kind: ExpansionKind, id: ast::NodeId) -> Expansion {
     }
 }
 
-pub fn macro_scope_placeholder() -> Expansion {
-    placeholder(ExpansionKind::Items, ast::DUMMY_NODE_ID)
-}
-
 pub struct PlaceholderExpander<'a, 'b: 'a> {
     expansions: HashMap<ast::NodeId, Expansion>,
     cx: &'a mut ExtCtxt<'b>,
@@ -100,11 +97,12 @@ impl<'a, 'b> PlaceholderExpander<'a, 'b> {
 impl<'a, 'b> Folder for PlaceholderExpander<'a, 'b> {
     fn fold_item(&mut self, item: P<ast::Item>) -> SmallVector<P<ast::Item>> {
         match item.node {
-            // Scope placeholder
-            ast::ItemKind::Mac(_) if item.id == ast::DUMMY_NODE_ID => SmallVector::one(item),
-            ast::ItemKind::Mac(_) => self.remove(item.id).make_items(),
-            _ => noop_fold_item(item, self),
+            ast::ItemKind::Mac(ref mac) if !mac.node.path.segments.is_empty() => {}
+            ast::ItemKind::Mac(_) => return self.remove(item.id).make_items(),
+            _ => {}
         }
+
+        noop_fold_item(item, self)
     }
 
     fn fold_trait_item(&mut self, item: ast::TraitItem) -> SmallVector<ast::TraitItem> {
@@ -172,10 +170,10 @@ impl<'a, 'b> Folder for PlaceholderExpander<'a, 'b> {
             block.stmts = block.stmts.move_flat_map(|mut stmt| {
                 remaining_stmts -= 1;
 
-                // Scope placeholder
+                // `macro_rules!` macro definition
                 if let ast::StmtKind::Item(ref item) = stmt.node {
-                    if let ast::ItemKind::Mac(..) = item.node {
-                        macros.push(item.ident.ctxt.data().outer_mark);
+                    if let ast::ItemKind::Mac(_) = item.node {
+                        macros.push(Mark::from_placeholder_id(item.id));
                         return None;
                     }
                 }
@@ -208,33 +206,13 @@ impl<'a, 'b> Folder for PlaceholderExpander<'a, 'b> {
     fn fold_mod(&mut self, module: ast::Mod) -> ast::Mod {
         let mut module = noop_fold_mod(module, self);
         module.items = module.items.move_flat_map(|item| match item.node {
-            ast::ItemKind::Mac(_) => None, // remove scope placeholders from modules
+            ast::ItemKind::Mac(_) if !self.cx.ecfg.keep_macs => None, // remove macro definitions
             _ => Some(item),
         });
         module
     }
-}
 
-pub fn reconstructed_macro_rules(def: &ast::MacroDef) -> Expansion {
-    Expansion::Items(SmallVector::one(P(ast::Item {
-        ident: def.ident,
-        attrs: def.attrs.clone(),
-        id: ast::DUMMY_NODE_ID,
-        node: ast::ItemKind::Mac(ast::Mac {
-            span: def.span,
-            node: ast::Mac_ {
-                path: ast::Path {
-                    span: DUMMY_SP,
-                    global: false,
-                    segments: vec![ast::PathSegment {
-                        identifier: ast::Ident::with_empty_ctxt(Symbol::intern("macro_rules")),
-                        parameters: ast::PathParameters::none(),
-                    }],
-                },
-                tts: def.body.clone(),
-            }
-        }),
-        vis: ast::Visibility::Inherited,
-        span: def.span,
-    })))
+    fn fold_mac(&mut self, mac: ast::Mac) -> ast::Mac {
+        mac
+    }
 }
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index ca18e580ecd..3abd24b50ba 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -10,10 +10,9 @@
 
 use {ast, attr};
 use syntax_pos::{Span, DUMMY_SP};
-use ext::base::{DummyResult, ExtCtxt, MacEager, MacResult, SyntaxExtension};
-use ext::base::{IdentMacroExpander, NormalTT, TTMacroExpander};
+use ext::base::{DummyResult, ExtCtxt, MacResult, SyntaxExtension};
+use ext::base::{NormalTT, TTMacroExpander};
 use ext::expand::{Expansion, ExpansionKind};
-use ext::placeholders;
 use ext::tt::macro_parser::{Success, Error, Failure};
 use ext::tt::macro_parser::{MatchedSeq, MatchedNonterminal};
 use ext::tt::macro_parser::{parse, parse_failure_msg};
@@ -151,38 +150,6 @@ fn generic_extension<'cx>(cx: &'cx ExtCtxt,
     cx.span_fatal(best_fail_spot.substitute_dummy(sp), &best_fail_msg);
 }
 
-pub struct MacroRulesExpander;
-impl IdentMacroExpander for MacroRulesExpander {
-    fn expand(&self,
-              cx: &mut ExtCtxt,
-              span: Span,
-              ident: ast::Ident,
-              tts: Vec<tokenstream::TokenTree>,
-              attrs: Vec<ast::Attribute>)
-              -> Box<MacResult> {
-        let export = attr::contains_name(&attrs, "macro_export");
-        let def = ast::MacroDef {
-            ident: ident,
-            id: ast::DUMMY_NODE_ID,
-            span: span,
-            imported_from: None,
-            body: tts,
-            allow_internal_unstable: attr::contains_name(&attrs, "allow_internal_unstable"),
-            attrs: attrs,
-        };
-
-        // If keep_macs is true, expands to a MacEager::items instead.
-        let result = if cx.ecfg.keep_macs {
-            MacEager::items(placeholders::reconstructed_macro_rules(&def).make_items())
-        } else {
-            MacEager::items(placeholders::macro_scope_placeholder().make_items())
-        };
-
-        cx.resolver.add_macro(cx.current_expansion.mark, def, export);
-        result
-    }
-}
-
 // Note that macro-by-example's input is also matched against a token tree:
 //                   $( $lhs:tt => $rhs:tt );+
 //
@@ -282,7 +249,7 @@ pub fn compile(sess: &ParseSess, def: &ast::MacroDef) -> SyntaxExtension {
         valid: valid,
     });
 
-    NormalTT(exp, Some(def.span), def.allow_internal_unstable)
+    NormalTT(exp, Some(def.span), attr::contains_name(&def.attrs, "allow_internal_unstable"))
 }
 
 fn check_lhs_nt_follows(sess: &ParseSess, lhs: &TokenTree) -> bool {
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index 6af8efb2a19..b3753e3e977 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -438,7 +438,7 @@ pub fn noop_fold_path<T: Folder>(Path {global, segments, span}: Path, fld: &mut
         global: global,
         segments: segments.move_map(|PathSegment {identifier, parameters}| PathSegment {
             identifier: fld.fold_ident(identifier),
-            parameters: fld.fold_path_parameters(parameters),
+            parameters: parameters.map(|ps| ps.map(|ps| fld.fold_path_parameters(ps))),
         }),
         span: fld.new_span(span)
     }
diff --git a/src/libsyntax/parse/mod.rs b/src/libsyntax/parse/mod.rs
index c982205f0ec..b9e6605639e 100644
--- a/src/libsyntax/parse/mod.rs
+++ b/src/libsyntax/parse/mod.rs
@@ -634,12 +634,7 @@ mod tests {
                     node: ast::ExprKind::Path(None, ast::Path {
                         span: sp(0, 1),
                         global: false,
-                        segments: vec![
-                            ast::PathSegment {
-                                identifier: Ident::from_str("a"),
-                                parameters: ast::PathParameters::none(),
-                            }
-                        ],
+                        segments: vec![Ident::from_str("a").into()],
                     }),
                     span: sp(0, 1),
                     attrs: ThinVec::new(),
@@ -651,19 +646,10 @@ mod tests {
                    P(ast::Expr {
                     id: ast::DUMMY_NODE_ID,
                     node: ast::ExprKind::Path(None, ast::Path {
-                            span: sp(0, 6),
-                            global: true,
-                            segments: vec![
-                                ast::PathSegment {
-                                    identifier: Ident::from_str("a"),
-                                    parameters: ast::PathParameters::none(),
-                                },
-                                ast::PathSegment {
-                                    identifier: Ident::from_str("b"),
-                                    parameters: ast::PathParameters::none(),
-                                }
-                            ]
-                        }),
+                        span: sp(0, 6),
+                        global: true,
+                        segments: vec![Ident::from_str("a").into(), Ident::from_str("b").into()],
+                    }),
                     span: sp(0, 6),
                     attrs: ThinVec::new(),
                    }))
@@ -772,12 +758,7 @@ mod tests {
                         node:ast::ExprKind::Path(None, ast::Path{
                             span: sp(7, 8),
                             global: false,
-                            segments: vec![
-                                ast::PathSegment {
-                                    identifier: Ident::from_str("d"),
-                                    parameters: ast::PathParameters::none(),
-                                }
-                            ],
+                            segments: vec![Ident::from_str("d").into()],
                         }),
                         span:sp(7,8),
                         attrs: ThinVec::new(),
@@ -795,12 +776,7 @@ mod tests {
                            node: ast::ExprKind::Path(None, ast::Path {
                                span:sp(0,1),
                                global:false,
-                               segments: vec![
-                                ast::PathSegment {
-                                    identifier: Ident::from_str("b"),
-                                    parameters: ast::PathParameters::none(),
-                                }
-                               ],
+                               segments: vec![Ident::from_str("b").into()],
                             }),
                            span: sp(0,1),
                            attrs: ThinVec::new()})),
@@ -842,12 +818,7 @@ mod tests {
                                                   node: ast::TyKind::Path(None, ast::Path{
                                         span:sp(10,13),
                                         global:false,
-                                        segments: vec![
-                                            ast::PathSegment {
-                                                identifier: Ident::from_str("i32"),
-                                                parameters: ast::PathParameters::none(),
-                                            }
-                                        ],
+                                        segments: vec![Ident::from_str("i32").into()],
                                         }),
                                         span:sp(10,13)
                                     }),
@@ -890,13 +861,7 @@ mod tests {
                                                       ast::Path{
                                                         span:sp(17,18),
                                                         global:false,
-                                                        segments: vec![
-                                                            ast::PathSegment {
-                                                                identifier: Ident::from_str("b"),
-                                                                parameters:
-                                                                ast::PathParameters::none(),
-                                                            }
-                                                        ],
+                                                        segments: vec![Ident::from_str("b").into()],
                                                       }),
                                                 span: sp(17,18),
                                                 attrs: ThinVec::new()})),
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index a1d4ad9d629..72462b74e68 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -1705,12 +1705,11 @@ impl<'a> Parser<'a> {
             // Parse types, optionally.
             let parameters = if self.eat_lt() {
                 let (lifetimes, types, bindings) = self.parse_generic_values_after_lt()?;
-
-                ast::PathParameters::AngleBracketed(ast::AngleBracketedParameterData {
+                ast::AngleBracketedParameterData {
                     lifetimes: lifetimes,
                     types: P::from_vec(types),
                     bindings: P::from_vec(bindings),
-                })
+                }.into()
             } else if self.eat(&token::OpenDelim(token::Paren)) {
                 let lo = self.prev_span.lo;
 
@@ -1727,18 +1726,17 @@ impl<'a> Parser<'a> {
 
                 let hi = self.prev_span.hi;
 
-                ast::PathParameters::Parenthesized(ast::ParenthesizedParameterData {
+                Some(P(ast::PathParameters::Parenthesized(ast::ParenthesizedParameterData {
                     span: mk_sp(lo, hi),
                     inputs: inputs,
                     output: output_ty,
-                })
+                })))
             } else {
-                ast::PathParameters::none()
+                None
             };
 
             // Assemble and push the result.
-            segments.push(ast::PathSegment { identifier: identifier,
-                                             parameters: parameters });
+            segments.push(ast::PathSegment { identifier: identifier, parameters: parameters });
 
             // Continue only if we see a `::`
             if !self.eat(&token::ModSep) {
@@ -1757,10 +1755,7 @@ impl<'a> Parser<'a> {
 
             // If we do not see a `::`, stop.
             if !self.eat(&token::ModSep) {
-                segments.push(ast::PathSegment {
-                    identifier: identifier,
-                    parameters: ast::PathParameters::none()
-                });
+                segments.push(identifier.into());
                 return Ok(segments);
             }
 
@@ -1768,14 +1763,13 @@ impl<'a> Parser<'a> {
             if self.eat_lt() {
                 // Consumed `a::b::<`, go look for types
                 let (lifetimes, types, bindings) = self.parse_generic_values_after_lt()?;
-                let parameters = ast::AngleBracketedParameterData {
-                    lifetimes: lifetimes,
-                    types: P::from_vec(types),
-                    bindings: P::from_vec(bindings),
-                };
                 segments.push(ast::PathSegment {
                     identifier: identifier,
-                    parameters: ast::PathParameters::AngleBracketed(parameters),
+                    parameters: ast::AngleBracketedParameterData {
+                        lifetimes: lifetimes,
+                        types: P::from_vec(types),
+                        bindings: P::from_vec(bindings),
+                    }.into(),
                 });
 
                 // Consumed `a::b::<T,U>`, check for `::` before proceeding
@@ -1784,10 +1778,7 @@ impl<'a> Parser<'a> {
                 }
             } else {
                 // Consumed `a::`, go look for `b`
-                segments.push(ast::PathSegment {
-                    identifier: identifier,
-                    parameters: ast::PathParameters::none(),
-                });
+                segments.push(identifier.into());
             }
         }
     }
@@ -1802,10 +1793,7 @@ impl<'a> Parser<'a> {
             let identifier = self.parse_path_segment_ident()?;
 
             // Assemble and push the result.
-            segments.push(ast::PathSegment {
-                identifier: identifier,
-                parameters: ast::PathParameters::none()
-            });
+            segments.push(identifier.into());
 
             // If we do not see a `::` or see `::{`/`::*`, stop.
             if !self.check(&token::ModSep) || self.is_import_coupler() {
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index c28b9d00501..22e8391de93 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -2349,7 +2349,9 @@ impl<'a> State<'a> {
 
             try!(self.print_ident(segment.identifier));
 
-            try!(self.print_path_parameters(&segment.parameters, colons_before_params));
+            if let Some(ref parameters) = segment.parameters {
+                try!(self.print_path_parameters(parameters, colons_before_params))
+            }
         }
 
         Ok(())
@@ -2373,7 +2375,10 @@ impl<'a> State<'a> {
         try!(word(&mut self.s, "::"));
         let item_segment = path.segments.last().unwrap();
         try!(self.print_ident(item_segment.identifier));
-        self.print_path_parameters(&item_segment.parameters, colons_before_params)
+        match item_segment.parameters {
+            Some(ref parameters) => self.print_path_parameters(parameters, colons_before_params),
+            None => Ok(()),
+        }
     }
 
     fn print_path_parameters(&mut self,
@@ -2381,10 +2386,6 @@ impl<'a> State<'a> {
                              colons_before_params: bool)
                              -> io::Result<()>
     {
-        if parameters.is_empty() {
-            return Ok(());
-        }
-
         if colons_before_params {
             try!(word(&mut self.s, "::"))
         }
diff --git a/src/libsyntax/std_inject.rs b/src/libsyntax/std_inject.rs
index 6a291ad9c40..4ad760a3caf 100644
--- a/src/libsyntax/std_inject.rs
+++ b/src/libsyntax/std_inject.rs
@@ -81,9 +81,8 @@ pub fn maybe_inject_crates_ref(sess: &ParseSess,
         vis: ast::Visibility::Inherited,
         node: ast::ItemKind::Use(P(codemap::dummy_spanned(ast::ViewPathGlob(ast::Path {
             global: false,
-            segments: vec![name, "prelude", "v1"].into_iter().map(|name| ast::PathSegment {
-                identifier: ast::Ident::from_str(name),
-                parameters: ast::PathParameters::none(),
+            segments: vec![name, "prelude", "v1"].into_iter().map(|name| {
+                ast::Ident::from_str(name).into()
             }).collect(),
             span: span,
         })))),
diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
index fca89e265e4..7709d3bd1cf 100644
--- a/src/libsyntax/test.rs
+++ b/src/libsyntax/test.rs
@@ -580,10 +580,7 @@ fn path_node(ids: Vec<Ident>) -> ast::Path {
     ast::Path {
         span: DUMMY_SP,
         global: false,
-        segments: ids.into_iter().map(|identifier| ast::PathSegment {
-            identifier: identifier,
-            parameters: ast::PathParameters::none(),
-        }).collect()
+        segments: ids.into_iter().map(Into::into).collect(),
     }
 }
 
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 3e0353d532d..ad29cb50a84 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -178,7 +178,6 @@ pub fn walk_crate<'a, V: Visitor<'a>>(visitor: &mut V, krate: &'a Crate) {
 
 pub fn walk_macro_def<'a, V: Visitor<'a>>(visitor: &mut V, macro_def: &'a MacroDef) {
     visitor.visit_ident(macro_def.span, macro_def.ident);
-    walk_opt_ident(visitor, macro_def.span, macro_def.imported_from);
     walk_list!(visitor, visit_attribute, &macro_def.attrs);
 }
 
@@ -384,7 +383,9 @@ pub fn walk_path_segment<'a, V: Visitor<'a>>(visitor: &mut V,
                                              path_span: Span,
                                              segment: &'a PathSegment) {
     visitor.visit_ident(path_span, segment.identifier);
-    visitor.visit_path_parameters(path_span, &segment.parameters);
+    if let Some(ref parameters) = segment.parameters {
+        visitor.visit_path_parameters(path_span, parameters);
+    }
 }
 
 pub fn walk_path_parameters<'a, V>(visitor: &mut V,