Auto merge of #74862 - mark-i-m:mv-compiler, r=petrochenkov

Move almost all compiler crates to compiler/

This PR implements https://github.com/rust-lang/compiler-team/issues/336 and moves all `rustc_*` crates from `src` to the new `compiler` directory.

`librustc_foo` directories are renamed to `rustc_foo`.
`src` directories are introduced inside `rustc_*` directories to mirror the scheme already use for `library` crates.

1 files changed, 1270 insertions, 0 deletions

diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
new file mode 100644
index 00000000000..d67ed74bc99
--- /dev/null
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -0,0 +1,1270 @@
+pub mod attr;
+mod diagnostics;
+mod expr;
+mod generics;
+mod item;
+mod nonterminal;
+mod pat;
+mod path;
+mod stmt;
+mod ty;
+
+use crate::lexer::UnmatchedBrace;
+use diagnostics::Error;
+pub use path::PathStyle;
+
+use rustc_ast::ptr::P;
+use rustc_ast::token::{self, DelimToken, Token, TokenKind};
+use rustc_ast::tokenstream::{self, DelimSpan, TokenStream, TokenTree, TreeAndJoint};
+use rustc_ast::DUMMY_NODE_ID;
+use rustc_ast::{self as ast, AttrStyle, AttrVec, Const, CrateSugar, Extern, Unsafe};
+use rustc_ast::{Async, MacArgs, MacDelimiter, Mutability, StrLit, Visibility, VisibilityKind};
+use rustc_ast_pretty::pprust;
+use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, FatalError, PResult};
+use rustc_session::parse::ParseSess;
+use rustc_span::source_map::{respan, Span, DUMMY_SP};
+use rustc_span::symbol::{kw, sym, Ident, Symbol};
+use tracing::debug;
+
+use std::{cmp, mem, slice};
+
+bitflags::bitflags! {
+    struct Restrictions: u8 {
+        const STMT_EXPR         = 1 << 0;
+        const NO_STRUCT_LITERAL = 1 << 1;
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Debug)]
+enum SemiColonMode {
+    Break,
+    Ignore,
+    Comma,
+}
+
+#[derive(Clone, Copy, PartialEq, Debug)]
+enum BlockMode {
+    Break,
+    Ignore,
+}
+
+/// Like `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.kind {
+            if let token::$constructor(x) = &**nt {
+                let $x = x.clone();
+                $p.bump();
+                return Ok($e);
+            }
+        }
+    };
+}
+
+/// 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.kind {
+                if let token::NtTy(ty) = &**nt {
+                    let ty = ty.clone();
+                    $self.bump();
+                    return $self.maybe_recover_from_bad_qpath_stage_2($self.prev_token.span, ty);
+                }
+            }
+        }
+    };
+}
+
+#[derive(Clone)]
+pub struct Parser<'a> {
+    pub sess: &'a ParseSess,
+    /// The current token.
+    pub token: Token,
+    /// The previous token.
+    pub prev_token: Token,
+    restrictions: Restrictions,
+    expected_tokens: Vec<TokenType>,
+    token_cursor: TokenCursor,
+    desugar_doc_comments: 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
+    /// appropriately.
+    ///
+    /// See the comments in the `parse_path_segment` function for more details.
+    unmatched_angle_bracket_count: u32,
+    max_angle_bracket_count: u32,
+    /// A list of all unclosed delimiters found by the lexer. If an entry is used for error recovery
+    /// it gets removed from here. Every entry left at the end gets emitted as an independent
+    /// error.
+    pub(super) unclosed_delims: Vec<UnmatchedBrace>,
+    last_unexpected_token_span: Option<Span>,
+    /// Span pointing at the `:` for the last type ascription the parser has seen, and whether it
+    /// looked like it could have been a mistyped path or literal `Option:Some(42)`).
+    pub last_type_ascription: Option<(Span, bool /* likely path typo */)>,
+    /// If present, this `Parser` is not parsing Rust code but rather a macro call.
+    subparser_name: Option<&'static str>,
+}
+
+impl<'a> Drop for Parser<'a> {
+    fn drop(&mut self) {
+        emit_unclosed_delims(&mut self.unclosed_delims, &self.sess);
+    }
+}
+
+#[derive(Clone)]
+struct TokenCursor {
+    frame: TokenCursorFrame,
+    stack: Vec<TokenCursorFrame>,
+    cur_token: Option<TreeAndJoint>,
+    collecting: Option<Collecting>,
+}
+
+#[derive(Clone)]
+struct TokenCursorFrame {
+    delim: token::DelimToken,
+    span: DelimSpan,
+    open_delim: bool,
+    tree_cursor: tokenstream::Cursor,
+    close_delim: bool,
+}
+
+/// Used to track additional state needed by `collect_tokens`
+#[derive(Clone, Debug)]
+struct Collecting {
+    /// Holds the current tokens captured during the most
+    /// recent call to `collect_tokens`
+    buf: Vec<TreeAndJoint>,
+    /// The depth of the `TokenCursor` stack at the time
+    /// collection was started. When we encounter a `TokenTree::Delimited`,
+    /// we want to record the `TokenTree::Delimited` itself,
+    /// but *not* any of the inner tokens while we are inside
+    /// the new frame (this would cause us to record duplicate tokens).
+    ///
+    /// This `depth` fields tracks stack depth we are recording tokens.
+    /// Only tokens encountered at this depth will be recorded. See
+    /// `TokenCursor::next` for more details.
+    depth: usize,
+}
+
+impl TokenCursorFrame {
+    fn new(span: DelimSpan, delim: DelimToken, tts: &TokenStream) -> Self {
+        TokenCursorFrame {
+            delim,
+            span,
+            open_delim: delim == token::NoDelim,
+            tree_cursor: tts.clone().into_trees(),
+            close_delim: delim == token::NoDelim,
+        }
+    }
+}
+
+impl TokenCursor {
+    fn next(&mut self) -> Token {
+        loop {
+            let tree = if !self.frame.open_delim {
+                self.frame.open_delim = true;
+                TokenTree::open_tt(self.frame.span, self.frame.delim).into()
+            } else if let Some(tree) = self.frame.tree_cursor.next_with_joint() {
+                tree
+            } else if !self.frame.close_delim {
+                self.frame.close_delim = true;
+                TokenTree::close_tt(self.frame.span, self.frame.delim).into()
+            } else if let Some(frame) = self.stack.pop() {
+                self.frame = frame;
+                continue;
+            } else {
+                return Token::new(token::Eof, DUMMY_SP);
+            };
+
+            // Don't set an open delimiter as our current token - we want
+            // to leave it as the full `TokenTree::Delimited` from the previous
+            // iteration of this loop
+            if !matches!(tree.0, TokenTree::Token(Token { kind: TokenKind::OpenDelim(_), .. })) {
+                self.cur_token = Some(tree.clone());
+            }
+
+            if let Some(collecting) = &mut self.collecting {
+                if collecting.depth == self.stack.len() {
+                    debug!(
+                        "TokenCursor::next():  collected {:?} at depth {:?}",
+                        tree,
+                        self.stack.len()
+                    );
+                    collecting.buf.push(tree.clone())
+                }
+            }
+
+            match tree.0 {
+                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));
+                }
+            }
+        }
+    }
+
+    fn next_desugared(&mut self) -> Token {
+        let (data, attr_style, sp) = match self.next() {
+            Token { kind: token::DocComment(_, attr_style, data), span } => {
+                (data, attr_style, span)
+            }
+            tok => return tok,
+        };
+
+        // Searches for the occurrences of `"#*` and returns the minimum number of `#`s
+        // required to wrap the text.
+        let mut num_of_hashes = 0;
+        let mut count = 0;
+        for ch in data.as_str().chars() {
+            count = match ch {
+                '"' => 1,
+                '#' if count > 0 => count + 1,
+                _ => 0,
+            };
+            num_of_hashes = cmp::max(num_of_hashes, count);
+        }
+
+        let delim_span = DelimSpan::from_single(sp);
+        let body = TokenTree::Delimited(
+            delim_span,
+            token::Bracket,
+            [
+                TokenTree::token(token::Ident(sym::doc, false), sp),
+                TokenTree::token(token::Eq, sp),
+                TokenTree::token(TokenKind::lit(token::StrRaw(num_of_hashes), data, None), sp),
+            ]
+            .iter()
+            .cloned()
+            .collect::<TokenStream>(),
+        );
+
+        self.stack.push(mem::replace(
+            &mut self.frame,
+            TokenCursorFrame::new(
+                delim_span,
+                token::NoDelim,
+                &if attr_style == AttrStyle::Inner {
+                    [TokenTree::token(token::Pound, sp), TokenTree::token(token::Not, sp), body]
+                        .iter()
+                        .cloned()
+                        .collect::<TokenStream>()
+                } else {
+                    [TokenTree::token(token::Pound, sp), body]
+                        .iter()
+                        .cloned()
+                        .collect::<TokenStream>()
+                },
+            ),
+        ));
+
+        self.next()
+    }
+}
+
+#[derive(Clone, PartialEq)]
+enum TokenType {
+    Token(TokenKind),
+    Keyword(Symbol),
+    Operator,
+    Lifetime,
+    Ident,
+    Path,
+    Type,
+    Const,
+}
+
+impl TokenType {
+    fn to_string(&self) -> String {
+        match *self {
+            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(),
+            TokenType::Path => "path".to_string(),
+            TokenType::Type => "type".to_string(),
+            TokenType::Const => "const".to_string(),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+enum TokenExpectType {
+    Expect,
+    NoExpect,
+}
+
+/// A sequence separator.
+struct SeqSep {
+    /// The separator token.
+    sep: Option<TokenKind>,
+    /// `true` if a trailing separator is allowed.
+    trailing_sep_allowed: bool,
+}
+
+impl SeqSep {
+    fn trailing_allowed(t: TokenKind) -> SeqSep {
+        SeqSep { sep: Some(t), trailing_sep_allowed: true }
+    }
+
+    fn none() -> SeqSep {
+        SeqSep { sep: None, trailing_sep_allowed: false }
+    }
+}
+
+pub enum FollowedByType {
+    Yes,
+    No,
+}
+
+fn token_descr_opt(token: &Token) -> Option<&'static str> {
+    Some(match token.kind {
+        _ if token.is_special_ident() => "reserved identifier",
+        _ if token.is_used_keyword() => "keyword",
+        _ if token.is_unused_keyword() => "reserved keyword",
+        token::DocComment(..) => "doc comment",
+        _ => return None,
+    })
+}
+
+pub(super) fn token_descr(token: &Token) -> String {
+    let token_str = pprust::token_to_string(token);
+    match token_descr_opt(token) {
+        Some(prefix) => format!("{} `{}`", prefix, token_str),
+        _ => format!("`{}`", token_str),
+    }
+}
+
+impl<'a> Parser<'a> {
+    pub fn new(
+        sess: &'a ParseSess,
+        tokens: TokenStream,
+        desugar_doc_comments: bool,
+        subparser_name: Option<&'static str>,
+    ) -> Self {
+        let mut parser = Parser {
+            sess,
+            token: Token::dummy(),
+            prev_token: Token::dummy(),
+            restrictions: Restrictions::empty(),
+            expected_tokens: Vec::new(),
+            token_cursor: TokenCursor {
+                frame: TokenCursorFrame::new(DelimSpan::dummy(), token::NoDelim, &tokens),
+                stack: Vec::new(),
+                cur_token: None,
+                collecting: None,
+            },
+            desugar_doc_comments,
+            unmatched_angle_bracket_count: 0,
+            max_angle_bracket_count: 0,
+            unclosed_delims: Vec::new(),
+            last_unexpected_token_span: None,
+            last_type_ascription: None,
+            subparser_name,
+        };
+
+        // Make parser point to the first token.
+        parser.bump();
+
+        parser
+    }
+
+    fn next_tok(&mut self, fallback_span: Span) -> Token {
+        let mut next = if self.desugar_doc_comments {
+            self.token_cursor.next_desugared()
+        } else {
+            self.token_cursor.next()
+        };
+        if next.span.is_dummy() {
+            // Tweak the location for better diagnostics, but keep syntactic context intact.
+            next.span = fallback_span.with_ctxt(next.span.ctxt());
+        }
+        next
+    }
+
+    crate fn unexpected<T>(&mut self) -> PResult<'a, T> {
+        match self.expect_one_of(&[], &[]) {
+            Err(e) => Err(e),
+            // We can get `Ok(true)` from `recover_closing_delimiter`
+            // which is called in `expected_one_of_not_found`.
+            Ok(_) => FatalError.raise(),
+        }
+    }
+
+    /// Expects and consumes the token `t`. Signals an error if the next token is not `t`.
+    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 {
+                self.unexpected_try_recover(t)
+            }
+        } else {
+            self.expect_one_of(slice::from_ref(t), &[])
+        }
+    }
+
+    /// Expect next token to be edible or inedible token.  If edible,
+    /// then consume it; if inedible, then return without consuming
+    /// anything.  Signal a fatal error if next token is unexpected.
+    pub fn expect_one_of(
+        &mut self,
+        edible: &[TokenKind],
+        inedible: &[TokenKind],
+    ) -> PResult<'a, bool /* recovered */> {
+        if edible.contains(&self.token.kind) {
+            self.bump();
+            Ok(false)
+        } else if inedible.contains(&self.token.kind) {
+            // leave it in the input
+            Ok(false)
+        } else if self.last_unexpected_token_span == Some(self.token.span) {
+            FatalError.raise();
+        } else {
+            self.expected_one_of_not_found(edible, inedible)
+        }
+    }
+
+    // Public for rustfmt usage.
+    pub fn parse_ident(&mut self) -> PResult<'a, Ident> {
+        self.parse_ident_common(true)
+    }
+
+    fn parse_ident_common(&mut self, recover: bool) -> PResult<'a, Ident> {
+        match self.token.ident() {
+            Some((ident, is_raw)) => {
+                if !is_raw && ident.is_reserved() {
+                    let mut err = self.expected_ident_found();
+                    if recover {
+                        err.emit();
+                    } else {
+                        return Err(err);
+                    }
+                }
+                self.bump();
+                Ok(ident)
+            }
+            _ => Err(match self.prev_token.kind {
+                TokenKind::DocComment(..) => {
+                    self.span_fatal_err(self.prev_token.span, Error::UselessDocComment)
+                }
+                _ => self.expected_ident_found(),
+            }),
+        }
+    }
+
+    /// Checks if the next token is `tok`, and returns `true` if so.
+    ///
+    /// This method will automatically add `tok` to `expected_tokens` if `tok` is not
+    /// encountered.
+    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: &TokenKind) -> bool {
+        let is_present = self.check(tok);
+        if is_present {
+            self.bump()
+        }
+        is_present
+    }
+
+    /// If the next token is the given keyword, returns `true` without eating it.
+    /// An expectation is also added for diagnostics purposes.
+    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`. An expectation is also added for diagnostics purposes.
+    // Public for rustfmt usage.
+    pub fn eat_keyword(&mut self, kw: Symbol) -> bool {
+        if self.check_keyword(kw) {
+            self.bump();
+            true
+        } else {
+            false
+        }
+    }
+
+    fn eat_keyword_noexpect(&mut self, kw: Symbol) -> bool {
+        if self.token.is_keyword(kw) {
+            self.bump();
+            true
+        } else {
+            false
+        }
+    }
+
+    /// 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: Symbol) -> PResult<'a, ()> {
+        if !self.eat_keyword(kw) { self.unexpected() } else { Ok(()) }
+    }
+
+    /// Is the given keyword `kw` followed by a non-reserved identifier?
+    fn is_kw_followed_by_ident(&self, kw: Symbol) -> bool {
+        self.token.is_keyword(kw) && self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident())
+    }
+
+    fn check_or_expected(&mut self, ok: bool, typ: TokenType) -> bool {
+        if ok {
+            true
+        } else {
+            self.expected_tokens.push(typ);
+            false
+        }
+    }
+
+    fn check_ident(&mut self) -> bool {
+        self.check_or_expected(self.token.is_ident(), TokenType::Ident)
+    }
+
+    fn check_path(&mut self) -> bool {
+        self.check_or_expected(self.token.is_path_start(), TokenType::Path)
+    }
+
+    fn check_type(&mut self) -> bool {
+        self.check_or_expected(self.token.can_begin_type(), TokenType::Type)
+    }
+
+    fn check_const_arg(&mut self) -> bool {
+        self.check_or_expected(self.token.can_begin_const_arg(), TokenType::Const)
+    }
+
+    /// Checks to see if the next token is either `+` or `+=`.
+    /// Otherwise returns `false`.
+    fn check_plus(&mut self) -> bool {
+        self.check_or_expected(
+            self.token.is_like_plus(),
+            TokenType::Token(token::BinOp(token::Plus)),
+        )
+    }
+
+    /// Eats the expected token if it's present possibly breaking
+    /// compound tokens like multi-character operators in process.
+    /// Returns `true` if the token was eaten.
+    fn break_and_eat(&mut self, expected: TokenKind) -> bool {
+        if self.token.kind == expected {
+            self.bump();
+            return true;
+        }
+        match self.token.kind.break_two_token_op() {
+            Some((first, second)) if first == expected => {
+                let first_span = self.sess.source_map().start_point(self.token.span);
+                let second_span = self.token.span.with_lo(first_span.hi());
+                self.token = Token::new(first, first_span);
+                self.bump_with(Token::new(second, second_span));
+                true
+            }
+            _ => {
+                self.expected_tokens.push(TokenType::Token(expected));
+                false
+            }
+        }
+    }
+
+    /// Eats `+` possibly breaking tokens like `+=` in process.
+    fn eat_plus(&mut self) -> bool {
+        self.break_and_eat(token::BinOp(token::Plus))
+    }
+
+    /// Eats `&` possibly breaking tokens like `&&` in process.
+    /// Signals an error if `&` is not eaten.
+    fn expect_and(&mut self) -> PResult<'a, ()> {
+        if self.break_and_eat(token::BinOp(token::And)) { Ok(()) } else { self.unexpected() }
+    }
+
+    /// Eats `|` possibly breaking tokens like `||` in process.
+    /// Signals an error if `|` was not eaten.
+    fn expect_or(&mut self) -> PResult<'a, ()> {
+        if self.break_and_eat(token::BinOp(token::Or)) { Ok(()) } else { self.unexpected() }
+    }
+
+    /// Eats `<` possibly breaking tokens like `<<` in process.
+    fn eat_lt(&mut self) -> bool {
+        let ate = self.break_and_eat(token::Lt);
+        if ate {
+            // See doc comment for `unmatched_angle_bracket_count`.
+            self.unmatched_angle_bracket_count += 1;
+            self.max_angle_bracket_count += 1;
+            debug!("eat_lt: (increment) count={:?}", self.unmatched_angle_bracket_count);
+        }
+        ate
+    }
+
+    /// Eats `<` possibly breaking tokens like `<<` in process.
+    /// Signals an error if `<` was not eaten.
+    fn expect_lt(&mut self) -> PResult<'a, ()> {
+        if self.eat_lt() { Ok(()) } else { self.unexpected() }
+    }
+
+    /// Eats `>` possibly breaking tokens like `>>` in process.
+    /// Signals an error if `>` was not eaten.
+    fn expect_gt(&mut self) -> PResult<'a, ()> {
+        if self.break_and_eat(token::Gt) {
+            // See doc comment for `unmatched_angle_bracket_count`.
+            if self.unmatched_angle_bracket_count > 0 {
+                self.unmatched_angle_bracket_count -= 1;
+                debug!("expect_gt: (decrement) count={:?}", self.unmatched_angle_bracket_count);
+            }
+            Ok(())
+        } else {
+            self.unexpected()
+        }
+    }
+
+    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,
+        })
+    }
+
+    fn parse_seq_to_before_tokens<T>(
+        &mut self,
+        kets: &[&TokenKind],
+        sep: SeqSep,
+        expect: TokenExpectType,
+        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 !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;
+                } else {
+                    match self.expect(t) {
+                        Ok(false) => {}
+                        Ok(true) => {
+                            recovered = true;
+                            break;
+                        }
+                        Err(mut expect_err) => {
+                            let sp = self.prev_token.span.shrink_to_hi();
+                            let token_str = pprust::token_kind_to_string(t);
+
+                            // Attempt to keep parsing if it was a similar separator.
+                            if let Some(ref tokens) = t.similar_tokens() {
+                                if tokens.contains(&self.token.kind) {
+                                    self.bump();
+                                }
+                            }
+
+                            // If this was a missing `@` in a binding pattern
+                            // bail with a suggestion
+                            // https://github.com/rust-lang/rust/issues/72373
+                            if self.prev_token.is_ident() && self.token.kind == token::DotDot {
+                                let msg = format!(
+                                    "if you meant to bind the contents of \
+                                    the rest of the array pattern into `{}`, use `@`",
+                                    pprust::token_to_string(&self.prev_token)
+                                );
+                                expect_err
+                                    .span_suggestion_verbose(
+                                        self.prev_token.span.shrink_to_hi().until(self.token.span),
+                                        &msg,
+                                        " @ ".to_string(),
+                                        Applicability::MaybeIncorrect,
+                                    )
+                                    .emit();
+                                break;
+                            }
+
+                            // Attempt to keep parsing if it was an omitted separator.
+                            match f(self) {
+                                Ok(t) => {
+                                    // Parsed successfully, therefore most probably the code only
+                                    // misses a separator.
+                                    expect_err
+                                        .span_suggestion_short(
+                                            self.sess.source_map().next_point(sp),
+                                            &format!("missing `{}`", token_str),
+                                            token_str,
+                                            Applicability::MaybeIncorrect,
+                                        )
+                                        .emit();
+
+                                    v.push(t);
+                                    continue;
+                                }
+                                Err(mut e) => {
+                                    // Parsing failed, therefore it must be something more serious
+                                    // than just a missing separator.
+                                    expect_err.emit();
+
+                                    e.cancel();
+                                    break;
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+            if sep.trailing_sep_allowed && self.expect_any_with_type(kets, expect) {
+                trailing = true;
+                break;
+            }
+
+            let t = f(self)?;
+            v.push(t);
+        }
+
+        Ok((v, trailing, recovered))
+    }
+
+    /// Parses a sequence, not including the closing delimiter. The function
+    /// `f` must consume tokens until reaching the next separator or
+    /// closing bracket.
+    fn parse_seq_to_before_end<T>(
+        &mut self,
+        ket: &TokenKind,
+        sep: SeqSep,
+        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)
+    }
+
+    /// Parses a sequence, including the closing delimiter. The function
+    /// `f` must consume tokens until reaching the next separator or
+    /// closing bracket.
+    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>, bool /* trailing */)> {
+        let (val, trailing, recovered) = self.parse_seq_to_before_end(ket, sep, f)?;
+        if !recovered {
+            self.eat(ket);
+        }
+        Ok((val, trailing))
+    }
+
+    /// 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>(
+        &mut self,
+        bra: &TokenKind,
+        ket: &TokenKind,
+        sep: SeqSep,
+        f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
+    ) -> PResult<'a, (Vec<T>, bool)> {
+        self.expect(bra)?;
+        self.parse_seq_to_end(ket, sep, f)
+    }
+
+    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 using provided token as the next one.
+    fn bump_with(&mut self, next_token: Token) {
+        // Bumping after EOF is a bad sign, usually an infinite loop.
+        if self.prev_token.kind == TokenKind::Eof {
+            let msg = "attempted to bump the parser past EOF (may be stuck in a loop)";
+            self.span_bug(self.token.span, msg);
+        }
+
+        // Update the current and previous tokens.
+        self.prev_token = mem::replace(&mut self.token, next_token);
+
+        // Diagnostics.
+        self.expected_tokens.clear();
+    }
+
+    /// Advance the parser by one token.
+    pub fn bump(&mut self) {
+        let next_token = self.next_tok(self.token.span);
+        self.bump_with(next_token);
+    }
+
+    /// Look-ahead `dist` tokens of `self.token` and get access to that token there.
+    /// When `dist == 0` then the current token is looked at.
+    pub fn look_ahead<R>(&self, dist: usize, looker: impl FnOnce(&Token) -> R) -> R {
+        if dist == 0 {
+            return looker(&self.token);
+        }
+
+        let frame = &self.token_cursor.frame;
+        looker(&match frame.tree_cursor.look_ahead(dist - 1) {
+            Some(tree) => match tree {
+                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),
+        })
+    }
+
+    /// 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) -> Async {
+        if self.eat_keyword(kw::Async) {
+            let span = self.prev_token.uninterpolated_span();
+            Async::Yes { span, closure_id: DUMMY_NODE_ID, return_impl_trait_id: DUMMY_NODE_ID }
+        } else {
+            Async::No
+        }
+    }
+
+    /// Parses unsafety: `unsafe` or nothing.
+    fn parse_unsafety(&mut self) -> Unsafe {
+        if self.eat_keyword(kw::Unsafe) {
+            Unsafe::Yes(self.prev_token.uninterpolated_span())
+        } else {
+            Unsafe::No
+        }
+    }
+
+    /// Parses constness: `const` or nothing.
+    fn parse_constness(&mut self) -> Const {
+        if self.eat_keyword(kw::Const) {
+            Const::Yes(self.prev_token.uninterpolated_span())
+        } else {
+            Const::No
+        }
+    }
+
+    /// Parses mutability (`mut` or nothing).
+    fn parse_mutability(&mut self) -> Mutability {
+        if self.eat_keyword(kw::Mut) { Mutability::Mut } else { Mutability::Not }
+    }
+
+    /// Possibly parses mutability (`const` or `mut`).
+    fn parse_const_or_mut(&mut self) -> Option<Mutability> {
+        if self.eat_keyword(kw::Mut) {
+            Some(Mutability::Mut)
+        } else if self.eat_keyword(kw::Const) {
+            Some(Mutability::Not)
+        } else {
+            None
+        }
+    }
+
+    fn parse_field_name(&mut self) -> PResult<'a, Ident> {
+        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(symbol, self.prev_token.span))
+        } else {
+            self.parse_ident_common(false)
+        }
+    }
+
+    fn parse_mac_args(&mut self) -> PResult<'a, P<MacArgs>> {
+        self.parse_mac_args_common(true).map(P)
+    }
+
+    fn parse_attr_args(&mut self) -> PResult<'a, MacArgs> {
+        self.parse_mac_args_common(false)
+    }
+
+    fn parse_mac_args_common(&mut self, delimited_only: bool) -> PResult<'a, MacArgs> {
+        Ok(
+            if self.check(&token::OpenDelim(DelimToken::Paren))
+                || self.check(&token::OpenDelim(DelimToken::Bracket))
+                || self.check(&token::OpenDelim(DelimToken::Brace))
+            {
+                match self.parse_token_tree() {
+                    TokenTree::Delimited(dspan, delim, tokens) =>
+                    // We've confirmed above that there is a delimiter so unwrapping is OK.
+                    {
+                        MacArgs::Delimited(dspan, MacDelimiter::from_token(delim).unwrap(), tokens)
+                    }
+                    _ => unreachable!(),
+                }
+            } else if !delimited_only {
+                if self.eat(&token::Eq) {
+                    let eq_span = self.prev_token.span;
+                    let mut is_interpolated_expr = false;
+                    if let token::Interpolated(nt) = &self.token.kind {
+                        if let token::NtExpr(..) = **nt {
+                            is_interpolated_expr = true;
+                        }
+                    }
+                    let token_tree = if is_interpolated_expr {
+                        // We need to accept arbitrary interpolated expressions to continue
+                        // supporting things like `doc = $expr` that work on stable.
+                        // Non-literal interpolated expressions are rejected after expansion.
+                        self.parse_token_tree()
+                    } else {
+                        self.parse_unsuffixed_lit()?.token_tree()
+                    };
+
+                    MacArgs::Eq(eq_span, token_tree.into())
+                } else {
+                    MacArgs::Empty
+                }
+            } else {
+                return self.unexpected();
+            },
+        )
+    }
+
+    fn parse_or_use_outer_attributes(
+        &mut self,
+        already_parsed_attrs: Option<AttrVec>,
+    ) -> PResult<'a, AttrVec> {
+        if let Some(attrs) = already_parsed_attrs {
+            Ok(attrs)
+        } else {
+            self.parse_outer_attributes().map(|a| a.into())
+        }
+    }
+
+    /// Parses a single token tree from the input.
+    pub(crate) fn parse_token_tree(&mut self) -> TokenTree {
+        match self.token.kind {
+            token::OpenDelim(..) => {
+                let frame = mem::replace(
+                    &mut self.token_cursor.frame,
+                    self.token_cursor.stack.pop().unwrap(),
+                );
+                self.token = Token::new(TokenKind::CloseDelim(frame.delim), frame.span.close);
+                self.bump();
+                TokenTree::Delimited(frame.span, frame.delim, frame.tree_cursor.stream)
+            }
+            token::CloseDelim(_) | token::Eof => unreachable!(),
+            _ => {
+                self.bump();
+                TokenTree::Token(self.prev_token.clone())
+            }
+        }
+    }
+
+    /// 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 {
+            tts.push(self.parse_token_tree());
+        }
+        Ok(tts)
+    }
+
+    pub fn parse_tokens(&mut self) -> TokenStream {
+        let mut result = Vec::new();
+        loop {
+            match self.token.kind {
+                token::Eof | token::CloseDelim(..) => break,
+                _ => result.push(self.parse_token_tree().into()),
+            }
+        }
+        TokenStream::new(result)
+    }
+
+    /// Evaluates the closure with restrictions in place.
+    ///
+    /// Afters the closure is evaluated, restrictions are reset.
+    fn with_res<T>(&mut self, res: Restrictions, f: impl FnOnce(&mut Self) -> T) -> T {
+        let old = self.restrictions;
+        self.restrictions = res;
+        let res = f(self);
+        self.restrictions = old;
+        res
+    }
+
+    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)`,
+    /// `pub(self)` for `pub(in self)` and `pub(super)` for `pub(in super)`.
+    /// If the following element can't be a tuple (i.e., it's a function definition), then
+    /// it's not a tuple struct field), and the contents within the parentheses isn't valid,
+    /// so emit a proper diagnostic.
+    pub(crate) fn parse_visibility(&mut self, fbt: FollowedByType) -> PResult<'a, Visibility> {
+        maybe_whole!(self, NtVis, |x| x);
+
+        self.expected_tokens.push(TokenType::Keyword(kw::Crate));
+        if self.is_crate_vis() {
+            self.bump(); // `crate`
+            self.sess.gated_spans.gate(sym::crate_visibility_modifier, self.prev_token.span);
+            return Ok(respan(self.prev_token.span, VisibilityKind::Crate(CrateSugar::JustCrate)));
+        }
+
+        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.token.span.shrink_to_lo(), VisibilityKind::Inherited));
+        }
+        let lo = self.prev_token.span;
+
+        if self.check(&token::OpenDelim(token::Paren)) {
+            // We don't `self.bump()` the `(` yet because this might be a struct definition where
+            // `()` 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.is_keyword_ahead(1, &[kw::Crate]) && self.look_ahead(2, |t| t != &token::ModSep)
+            // account for `pub(crate::foo)`
+            {
+                // Parse `pub(crate)`.
+                self.bump(); // `(`
+                self.bump(); // `crate`
+                self.expect(&token::CloseDelim(token::Paren))?; // `)`
+                let vis = VisibilityKind::Crate(CrateSugar::PubCrate);
+                return Ok(respan(lo.to(self.prev_token.span), vis));
+            } else if self.is_keyword_ahead(1, &[kw::In]) {
+                // Parse `pub(in path)`.
+                self.bump(); // `(`
+                self.bump(); // `in`
+                let path = self.parse_path(PathStyle::Mod)?; // `path`
+                self.expect(&token::CloseDelim(token::Paren))?; // `)`
+                let vis = VisibilityKind::Restricted { path: P(path), id: ast::DUMMY_NODE_ID };
+                return Ok(respan(lo.to(self.prev_token.span), vis));
+            } else if self.look_ahead(2, |t| t == &token::CloseDelim(token::Paren))
+                && self.is_keyword_ahead(1, &[kw::Super, kw::SelfLower])
+            {
+                // Parse `pub(self)` or `pub(super)`.
+                self.bump(); // `(`
+                let path = self.parse_path(PathStyle::Mod)?; // `super`/`self`
+                self.expect(&token::CloseDelim(token::Paren))?; // `)`
+                let vis = VisibilityKind::Restricted { path: P(path), id: ast::DUMMY_NODE_ID };
+                return Ok(respan(lo.to(self.prev_token.span), vis));
+            } else if let FollowedByType::No = fbt {
+                // Provide this diagnostic if a type cannot follow;
+                // in particular, if this is not a tuple struct.
+                self.recover_incorrect_vis_restriction()?;
+                // Emit diagnostic, but continue with public visibility.
+            }
+        }
+
+        Ok(respan(lo, VisibilityKind::Public))
+    }
+
+    /// Recovery for e.g. `pub(something) fn ...` or `struct X { pub(something) y: Z }`
+    fn recover_incorrect_vis_restriction(&mut self) -> PResult<'a, ()> {
+        self.bump(); // `(`
+        let path = self.parse_path(PathStyle::Mod)?;
+        self.expect(&token::CloseDelim(token::Paren))?; // `)`
+
+        let msg = "incorrect visibility restriction";
+        let suggestion = r##"some possible visibility restrictions are:
+`pub(crate)`: visible only on the current crate
+`pub(super)`: visible only in the current module's parent
+`pub(in path::to::module)`: visible only on the specified path"##;
+
+        let path_str = pprust::path_to_string(&path);
+
+        struct_span_err!(self.sess.span_diagnostic, path.span, E0704, "{}", msg)
+            .help(suggestion)
+            .span_suggestion(
+                path.span,
+                &format!("make this visible only to module `{}` with `in`", path_str),
+                format!("in {}", path_str),
+                Applicability::MachineApplicable,
+            )
+            .emit();
+
+        Ok(())
+    }
+
+    /// Parses `extern string_literal?`.
+    fn parse_extern(&mut self) -> PResult<'a, Extern> {
+        Ok(if self.eat_keyword(kw::Extern) {
+            Extern::from_abi(self.parse_abi())
+        } else {
+            Extern::None
+        })
+    }
+
+    /// Parses a string literal as an ABI spec.
+    fn parse_abi(&mut self) -> Option<StrLit> {
+        match self.parse_str_lit() {
+            Ok(str_lit) => Some(str_lit),
+            Err(Some(lit)) => match lit.kind {
+                ast::LitKind::Err(_) => None,
+                _ => {
+                    self.struct_span_err(lit.span, "non-string ABI literal")
+                        .span_suggestion(
+                            lit.span,
+                            "specify the ABI with a string literal",
+                            "\"C\"".to_string(),
+                            Applicability::MaybeIncorrect,
+                        )
+                        .emit();
+                    None
+                }
+            },
+            Err(None) => None,
+        }
+    }
+
+    /// Records all tokens consumed by the provided callback,
+    /// including the current token. These tokens are collected
+    /// into a `TokenStream`, and returned along with the result
+    /// of the callback.
+    ///
+    /// Note: If your callback consumes an opening delimiter
+    /// (including the case where you call `collect_tokens`
+    /// when the current token is an opening delimeter),
+    /// you must also consume the corresponding closing delimiter.
+    ///
+    /// That is, you can consume
+    /// `something ([{ }])` or `([{}])`, but not `([{}]`
+    ///
+    /// This restriction shouldn't be an issue in practice,
+    /// since this function is used to record the tokens for
+    /// a parsed AST item, which always has matching delimiters.
+    pub fn collect_tokens<R>(
+        &mut self,
+        f: impl FnOnce(&mut Self) -> PResult<'a, R>,
+    ) -> PResult<'a, (R, TokenStream)> {
+        // Record all tokens we parse when parsing this item.
+        let tokens: Vec<TreeAndJoint> = self.token_cursor.cur_token.clone().into_iter().collect();
+        debug!("collect_tokens: starting with {:?}", tokens);
+
+        // We need special handling for the case where `collect_tokens` is called
+        // on an opening delimeter (e.g. '('). At this point, we have already pushed
+        // a new frame - however, we want to record the original `TokenTree::Delimited`,
+        // for consistency with the case where we start recording one token earlier.
+        // See `TokenCursor::next` to see how `cur_token` is set up.
+        let prev_depth =
+            if matches!(self.token_cursor.cur_token, Some((TokenTree::Delimited(..), _))) {
+                if self.token_cursor.stack.is_empty() {
+                    // There is nothing below us in the stack that
+                    // the function could consume, so the only thing it can legally
+                    // capture is the entire contents of the current frame.
+                    return Ok((f(self)?, TokenStream::new(tokens)));
+                }
+                // We have already recorded the full `TokenTree::Delimited` when we created
+                // our `tokens` vector at the start of this function. We are now inside
+                // a new frame corresponding to the `TokenTree::Delimited` we already recoreded.
+                // We don't want to record any of the tokens inside this frame, since they
+                // will be duplicates of the tokens nested inside the `TokenTree::Delimited`.
+                // Therefore, we set our recording depth to the *previous* frame. This allows
+                // us to record a sequence like: `(foo).bar()`: the `(foo)` will be recored
+                // as our initial `cur_token`, while the `.bar()` will be recored after we
+                // pop the `(foo)` frame.
+                self.token_cursor.stack.len() - 1
+            } else {
+                self.token_cursor.stack.len()
+            };
+        let prev_collecting =
+            self.token_cursor.collecting.replace(Collecting { buf: tokens, depth: prev_depth });
+
+        let ret = f(self);
+
+        let mut collected_tokens = if let Some(collecting) = self.token_cursor.collecting.take() {
+            collecting.buf
+        } else {
+            let msg = "our vector went away?";
+            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::default()));
+        };
+
+        debug!("collect_tokens: got raw tokens {:?}", collected_tokens);
+
+        // If we're not at EOF our current token wasn't actually consumed by
+        // `f`, but it'll still be in our list that we pulled out. In that case
+        // put it back.
+        let extra_token = if self.token != token::Eof { collected_tokens.pop() } else { None };
+
+        if let Some(mut collecting) = prev_collecting {
+            // If we were previously collecting at the same depth,
+            // then the previous call to `collect_tokens` needs to see
+            // the tokens we just recorded.
+            //
+            // If we were previously recording at an lower `depth`,
+            // then the previous `collect_tokens` call already recorded
+            // this entire frame in the form of a `TokenTree::Delimited`,
+            // so there is nothing else for us to do.
+            if collecting.depth == prev_depth {
+                collecting.buf.extend(collected_tokens.iter().cloned());
+                collecting.buf.extend(extra_token);
+                debug!("collect_tokens: updating previous buf to {:?}", collecting);
+            }
+            self.token_cursor.collecting = Some(collecting)
+        }
+
+        Ok((ret?, TokenStream::new(collected_tokens)))
+    }
+
+    /// `::{` or `::*`
+    fn is_import_coupler(&mut self) -> bool {
+        self.check(&token::ModSep)
+            && self.look_ahead(1, |t| {
+                *t == token::OpenDelim(token::Brace) || *t == token::BinOp(token::Star)
+            })
+    }
+}
+
+crate fn make_unclosed_delims_error(
+    unmatched: UnmatchedBrace,
+    sess: &ParseSess,
+) -> Option<DiagnosticBuilder<'_>> {
+    // `None` here means an `Eof` was found. We already emit those errors elsewhere, we add them to
+    // `unmatched_braces` only for error recovery in the `Parser`.
+    let found_delim = unmatched.found_delim?;
+    let mut err = sess.span_diagnostic.struct_span_err(
+        unmatched.found_span,
+        &format!(
+            "mismatched closing delimiter: `{}`",
+            pprust::token_kind_to_string(&token::CloseDelim(found_delim)),
+        ),
+    );
+    err.span_label(unmatched.found_span, "mismatched closing delimiter");
+    if let Some(sp) = unmatched.candidate_span {
+        err.span_label(sp, "closing delimiter possibly meant for this");
+    }
+    if let Some(sp) = unmatched.unclosed_span {
+        err.span_label(sp, "unclosed delimiter");
+    }
+    Some(err)
+}
+
+pub fn emit_unclosed_delims(unclosed_delims: &mut Vec<UnmatchedBrace>, sess: &ParseSess) {
+    *sess.reached_eof.borrow_mut() |=
+        unclosed_delims.iter().any(|unmatched_delim| unmatched_delim.found_delim.is_none());
+    for unmatched in unclosed_delims.drain(..) {
+        if let Some(mut e) = make_unclosed_delims_error(unmatched, sess) {
+            e.emit();
+        }
+    }
+}