compiler/rustc_parse/src/parser/mod.rs

   1 pub mod attr;
   2 mod diagnostics;
   3 mod expr;
   4 mod generics;
   5 mod item;
   6 mod nonterminal;
   7 mod pat;
   8 mod path;
   9 mod stmt;
  10 mod ty;
  11
  12 use crate::lexer::UnmatchedBrace;
  13 pub use diagnostics::AttemptLocalParseRecovery;
  14 use diagnostics::Error;
  15 pub use path::PathStyle;
  16
  17 use rustc_ast::ptr::P;
  18 use rustc_ast::token::{self, DelimToken, Token, TokenKind};
  19 use rustc_ast::tokenstream::{self, DelimSpan, LazyTokenStream, Spacing};
  20 use rustc_ast::tokenstream::{CreateTokenStream, TokenStream, TokenTree};
  21 use rustc_ast::DUMMY_NODE_ID;
  22 use rustc_ast::{self as ast, AnonConst, AttrStyle, AttrVec, Const, CrateSugar, Extern, Unsafe};
  23 use rustc_ast::{Async, Expr, ExprKind, MacArgs, MacDelimiter, Mutability, StrLit};
  24 use rustc_ast::{Visibility, VisibilityKind};
  25 use rustc_ast_pretty::pprust;
  26 use rustc_errors::PResult;
  27 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, FatalError};
  28 use rustc_session::parse::ParseSess;
  29 use rustc_span::source_map::{Span, DUMMY_SP};
  30 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  31 use tracing::debug;
  32
  33 use std::{cmp, mem, slice};
  34
  35 bitflags::bitflags! {
  36     struct Restrictions: u8 {
  37         const STMT_EXPR         = 1 << 0;
  38         const NO_STRUCT_LITERAL = 1 << 1;
  39         const CONST_EXPR        = 1 << 2;
  40     }
  41 }
  42
  43 #[derive(Clone, Copy, PartialEq, Debug)]
  44 enum SemiColonMode {
  45     Break,
  46     Ignore,
  47     Comma,
  48 }
  49
  50 #[derive(Clone, Copy, PartialEq, Debug)]
  51 enum BlockMode {
  52     Break,
  53     Ignore,
  54 }
  55
  56 /// Like `maybe_whole_expr`, but for things other than expressions.
  57 #[macro_export]
  58 macro_rules! maybe_whole {
  59     ($p:expr, $constructor:ident, |$x:ident| $e:expr) => {
  60         if let token::Interpolated(nt) = &$p.token.kind {
  61             if let token::$constructor(x) = &**nt {
  62                 let $x = x.clone();
  63                 $p.bump();
  64                 return Ok($e);
  65             }
  66         }
  67     };
  68 }
  69
  70 /// If the next tokens are ill-formed `$ty::` recover them as `<$ty>::`.
  71 #[macro_export]
  72 macro_rules! maybe_recover_from_interpolated_ty_qpath {
  73     ($self: expr, $allow_qpath_recovery: expr) => {
  74         if $allow_qpath_recovery && $self.look_ahead(1, |t| t == &token::ModSep) {
  75             if let token::Interpolated(nt) = &$self.token.kind {
  76                 if let token::NtTy(ty) = &**nt {
  77                     let ty = ty.clone();
  78                     $self.bump();
  79                     return $self.maybe_recover_from_bad_qpath_stage_2($self.prev_token.span, ty);
  80                 }
  81             }
  82         }
  83     };
  84 }
  85
  86 #[derive(Clone)]
  87 pub struct Parser<'a> {
  88     pub sess: &'a ParseSess,
  89     /// The current token.
  90     pub token: Token,
  91     /// The spacing for the current token
  92     pub token_spacing: Spacing,
  93     /// The previous token.
  94     pub prev_token: Token,
  95     restrictions: Restrictions,
  96     expected_tokens: Vec<TokenType>,
  97     // Important: This must only be advanced from `next_tok`
  98     // to ensure that `token_cursor.num_next_calls` is updated properly
  99     token_cursor: TokenCursor,
 100     desugar_doc_comments: bool,
 101     /// This field is used to keep track of how many left angle brackets we have seen. This is
 102     /// required in order to detect extra leading left angle brackets (`<` characters) and error
 103     /// appropriately.
 104     ///
 105     /// See the comments in the `parse_path_segment` function for more details.
 106     unmatched_angle_bracket_count: u32,
 107     max_angle_bracket_count: u32,
 108     /// A list of all unclosed delimiters found by the lexer. If an entry is used for error recovery
 109     /// it gets removed from here. Every entry left at the end gets emitted as an independent
 110     /// error.
 111     pub(super) unclosed_delims: Vec<UnmatchedBrace>,
 112     last_unexpected_token_span: Option<Span>,
 113     /// Span pointing at the `:` for the last type ascription the parser has seen, and whether it
 114     /// looked like it could have been a mistyped path or literal `Option:Some(42)`).
 115     pub last_type_ascription: Option<(Span, bool /* likely path typo */)>,
 116     /// If present, this `Parser` is not parsing Rust code but rather a macro call.
 117     subparser_name: Option<&'static str>,
 118 }
 119
 120 impl<'a> Drop for Parser<'a> {
 121     fn drop(&mut self) {
 122         emit_unclosed_delims(&mut self.unclosed_delims, &self.sess);
 123     }
 124 }
 125
 126 #[derive(Clone)]
 127 struct TokenCursor {
 128     frame: TokenCursorFrame,
 129     stack: Vec<TokenCursorFrame>,
 130     desugar_doc_comments: bool,
 131     // Counts the number of calls to `next` or `next_desugared`,
 132     // depending on whether `desugar_doc_comments` is set.
 133     num_next_calls: usize,
 134 }
 135
 136 #[derive(Clone)]
 137 struct TokenCursorFrame {
 138     delim: token::DelimToken,
 139     span: DelimSpan,
 140     open_delim: bool,
 141     tree_cursor: tokenstream::Cursor,
 142     close_delim: bool,
 143 }
 144
 145 impl TokenCursorFrame {
 146     fn new(span: DelimSpan, delim: DelimToken, tts: TokenStream) -> Self {
 147         TokenCursorFrame {
 148             delim,
 149             span,
 150             open_delim: delim == token::NoDelim,
 151             tree_cursor: tts.into_trees(),
 152             close_delim: delim == token::NoDelim,
 153         }
 154     }
 155 }
 156
 157 impl TokenCursor {
 158     fn next(&mut self) -> (Token, Spacing) {
 159         loop {
 160             let (tree, spacing) = if !self.frame.open_delim {
 161                 self.frame.open_delim = true;
 162                 TokenTree::open_tt(self.frame.span, self.frame.delim).into()
 163             } else if let Some(tree) = self.frame.tree_cursor.next_with_spacing() {
 164                 tree
 165             } else if !self.frame.close_delim {
 166                 self.frame.close_delim = true;
 167                 TokenTree::close_tt(self.frame.span, self.frame.delim).into()
 168             } else if let Some(frame) = self.stack.pop() {
 169                 self.frame = frame;
 170                 continue;
 171             } else {
 172                 (TokenTree::Token(Token::new(token::Eof, DUMMY_SP)), Spacing::Alone)
 173             };
 174
 175             match tree {
 176                 TokenTree::Token(token) => {
 177                     return (token, spacing);
 178                 }
 179                 TokenTree::Delimited(sp, delim, tts) => {
 180                     let frame = TokenCursorFrame::new(sp, delim, tts);
 181                     self.stack.push(mem::replace(&mut self.frame, frame));
 182                 }
 183             }
 184         }
 185     }
 186
 187     fn next_desugared(&mut self) -> (Token, Spacing) {
 188         let (data, attr_style, sp) = match self.next() {
 189             (Token { kind: token::DocComment(_, attr_style, data), span }, _) => {
 190                 (data, attr_style, span)
 191             }
 192             tok => return tok,
 193         };
 194
 195         // Searches for the occurrences of `"#*` and returns the minimum number of `#`s
 196         // required to wrap the text.
 197         let mut num_of_hashes = 0;
 198         let mut count = 0;
 199         for ch in data.as_str().chars() {
 200             count = match ch {
 201                 '"' => 1,
 202                 '#' if count > 0 => count + 1,
 203                 _ => 0,
 204             };
 205             num_of_hashes = cmp::max(num_of_hashes, count);
 206         }
 207
 208         let delim_span = DelimSpan::from_single(sp);
 209         let body = TokenTree::Delimited(
 210             delim_span,
 211             token::Bracket,
 212             [
 213                 TokenTree::token(token::Ident(sym::doc, false), sp),
 214                 TokenTree::token(token::Eq, sp),
 215                 TokenTree::token(TokenKind::lit(token::StrRaw(num_of_hashes), data, None), sp),
 216             ]
 217             .iter()
 218             .cloned()
 219             .collect::<TokenStream>(),
 220         );
 221
 222         self.stack.push(mem::replace(
 223             &mut self.frame,
 224             TokenCursorFrame::new(
 225                 delim_span,
 226                 token::NoDelim,
 227                 if attr_style == AttrStyle::Inner {
 228                     [TokenTree::token(token::Pound, sp), TokenTree::token(token::Not, sp), body]
 229                         .iter()
 230                         .cloned()
 231                         .collect::<TokenStream>()
 232                 } else {
 233                     [TokenTree::token(token::Pound, sp), body]
 234                         .iter()
 235                         .cloned()
 236                         .collect::<TokenStream>()
 237                 },
 238             ),
 239         ));
 240
 241         self.next()
 242     }
 243 }
 244
 245 #[derive(Clone, PartialEq)]
 246 enum TokenType {
 247     Token(TokenKind),
 248     Keyword(Symbol),
 249     Operator,
 250     Lifetime,
 251     Ident,
 252     Path,
 253     Type,
 254     Const,
 255 }
 256
 257 impl TokenType {
 258     fn to_string(&self) -> String {
 259         match *self {
 260             TokenType::Token(ref t) => format!("`{}`", pprust::token_kind_to_string(t)),
 261             TokenType::Keyword(kw) => format!("`{}`", kw),
 262             TokenType::Operator => "an operator".to_string(),
 263             TokenType::Lifetime => "lifetime".to_string(),
 264             TokenType::Ident => "identifier".to_string(),
 265             TokenType::Path => "path".to_string(),
 266             TokenType::Type => "type".to_string(),
 267             TokenType::Const => "const".to_string(),
 268         }
 269     }
 270 }
 271
 272 #[derive(Copy, Clone, Debug)]
 273 enum TokenExpectType {
 274     Expect,
 275     NoExpect,
 276 }
 277
 278 /// A sequence separator.
 279 struct SeqSep {
 280     /// The separator token.
 281     sep: Option<TokenKind>,
 282     /// `true` if a trailing separator is allowed.
 283     trailing_sep_allowed: bool,
 284 }
 285
 286 impl SeqSep {
 287     fn trailing_allowed(t: TokenKind) -> SeqSep {
 288         SeqSep { sep: Some(t), trailing_sep_allowed: true }
 289     }
 290
 291     fn none() -> SeqSep {
 292         SeqSep { sep: None, trailing_sep_allowed: false }
 293     }
 294 }
 295
 296 pub enum FollowedByType {
 297     Yes,
 298     No,
 299 }
 300
 301 fn token_descr_opt(token: &Token) -> Option<&'static str> {
 302     Some(match token.kind {
 303         _ if token.is_special_ident() => "reserved identifier",
 304         _ if token.is_used_keyword() => "keyword",
 305         _ if token.is_unused_keyword() => "reserved keyword",
 306         token::DocComment(..) => "doc comment",
 307         _ => return None,
 308     })
 309 }
 310
 311 pub(super) fn token_descr(token: &Token) -> String {
 312     let token_str = pprust::token_to_string(token);
 313     match token_descr_opt(token) {
 314         Some(prefix) => format!("{} `{}`", prefix, token_str),
 315         _ => format!("`{}`", token_str),
 316     }
 317 }
 318
 319 impl<'a> Parser<'a> {
 320     pub fn new(
 321         sess: &'a ParseSess,
 322         tokens: TokenStream,
 323         desugar_doc_comments: bool,
 324         subparser_name: Option<&'static str>,
 325     ) -> Self {
 326         let mut parser = Parser {
 327             sess,
 328             token: Token::dummy(),
 329             token_spacing: Spacing::Alone,
 330             prev_token: Token::dummy(),
 331             restrictions: Restrictions::empty(),
 332             expected_tokens: Vec::new(),
 333             token_cursor: TokenCursor {
 334                 frame: TokenCursorFrame::new(DelimSpan::dummy(), token::NoDelim, tokens),
 335                 stack: Vec::new(),
 336                 num_next_calls: 0,
 337                 desugar_doc_comments,
 338             },
 339             desugar_doc_comments,
 340             unmatched_angle_bracket_count: 0,
 341             max_angle_bracket_count: 0,
 342             unclosed_delims: Vec::new(),
 343             last_unexpected_token_span: None,
 344             last_type_ascription: None,
 345             subparser_name,
 346         };
 347
 348         // Make parser point to the first token.
 349         parser.bump();
 350
 351         parser
 352     }
 353
 354     fn next_tok(&mut self, fallback_span: Span) -> (Token, Spacing) {
 355         let (mut next, spacing) = if self.desugar_doc_comments {
 356             self.token_cursor.next_desugared()
 357         } else {
 358             self.token_cursor.next()
 359         };
 360         self.token_cursor.num_next_calls += 1;
 361         if next.span.is_dummy() {
 362             // Tweak the location for better diagnostics, but keep syntactic context intact.
 363             next.span = fallback_span.with_ctxt(next.span.ctxt());
 364         }
 365         (next, spacing)
 366     }
 367
 368     pub fn unexpected<T>(&mut self) -> PResult<'a, T> {
 369         match self.expect_one_of(&[], &[]) {
 370             Err(e) => Err(e),
 371             // We can get `Ok(true)` from `recover_closing_delimiter`
 372             // which is called in `expected_one_of_not_found`.
 373             Ok(_) => FatalError.raise(),
 374         }
 375     }
 376
 377     /// Expects and consumes the token `t`. Signals an error if the next token is not `t`.
 378     pub fn expect(&mut self, t: &TokenKind) -> PResult<'a, bool /* recovered */> {
 379         if self.expected_tokens.is_empty() {
 380             if self.token == *t {
 381                 self.bump();
 382                 Ok(false)
 383             } else {
 384                 self.unexpected_try_recover(t)
 385             }
 386         } else {
 387             self.expect_one_of(slice::from_ref(t), &[])
 388         }
 389     }
 390
 391     /// Expect next token to be edible or inedible token.  If edible,
 392     /// then consume it; if inedible, then return without consuming
 393     /// anything.  Signal a fatal error if next token is unexpected.
 394     pub fn expect_one_of(
 395         &mut self,
 396         edible: &[TokenKind],
 397         inedible: &[TokenKind],
 398     ) -> PResult<'a, bool /* recovered */> {
 399         if edible.contains(&self.token.kind) {
 400             self.bump();
 401             Ok(false)
 402         } else if inedible.contains(&self.token.kind) {
 403             // leave it in the input
 404             Ok(false)
 405         } else if self.last_unexpected_token_span == Some(self.token.span) {
 406             FatalError.raise();
 407         } else {
 408             self.expected_one_of_not_found(edible, inedible)
 409         }
 410     }
 411
 412     // Public for rustfmt usage.
 413     pub fn parse_ident(&mut self) -> PResult<'a, Ident> {
 414         self.parse_ident_common(true)
 415     }
 416
 417     fn parse_ident_common(&mut self, recover: bool) -> PResult<'a, Ident> {
 418         match self.token.ident() {
 419             Some((ident, is_raw)) => {
 420                 if !is_raw && ident.is_reserved() {
 421                     let mut err = self.expected_ident_found();
 422                     if recover {
 423                         err.emit();
 424                     } else {
 425                         return Err(err);
 426                     }
 427                 }
 428                 self.bump();
 429                 Ok(ident)
 430             }
 431             _ => Err(match self.prev_token.kind {
 432                 TokenKind::DocComment(..) => {
 433                     self.span_fatal_err(self.prev_token.span, Error::UselessDocComment)
 434                 }
 435                 _ => self.expected_ident_found(),
 436             }),
 437         }
 438     }
 439
 440     /// Checks if the next token is `tok`, and returns `true` if so.
 441     ///
 442     /// This method will automatically add `tok` to `expected_tokens` if `tok` is not
 443     /// encountered.
 444     fn check(&mut self, tok: &TokenKind) -> bool {
 445         let is_present = self.token == *tok;
 446         if !is_present {
 447             self.expected_tokens.push(TokenType::Token(tok.clone()));
 448         }
 449         is_present
 450     }
 451
 452     /// Consumes a token 'tok' if it exists. Returns whether the given token was present.
 453     pub fn eat(&mut self, tok: &TokenKind) -> bool {
 454         let is_present = self.check(tok);
 455         if is_present {
 456             self.bump()
 457         }
 458         is_present
 459     }
 460
 461     /// If the next token is the given keyword, returns `true` without eating it.
 462     /// An expectation is also added for diagnostics purposes.
 463     fn check_keyword(&mut self, kw: Symbol) -> bool {
 464         self.expected_tokens.push(TokenType::Keyword(kw));
 465         self.token.is_keyword(kw)
 466     }
 467
 468     /// If the next token is the given keyword, eats it and returns `true`.
 469     /// Otherwise, returns `false`. An expectation is also added for diagnostics purposes.
 470     // Public for rustfmt usage.
 471     pub fn eat_keyword(&mut self, kw: Symbol) -> bool {
 472         if self.check_keyword(kw) {
 473             self.bump();
 474             true
 475         } else {
 476             false
 477         }
 478     }
 479
 480     fn eat_keyword_noexpect(&mut self, kw: Symbol) -> bool {
 481         if self.token.is_keyword(kw) {
 482             self.bump();
 483             true
 484         } else {
 485             false
 486         }
 487     }
 488
 489     /// If the given word is not a keyword, signals an error.
 490     /// If the next token is not the given word, signals an error.
 491     /// Otherwise, eats it.
 492     fn expect_keyword(&mut self, kw: Symbol) -> PResult<'a, ()> {
 493         if !self.eat_keyword(kw) { self.unexpected() } else { Ok(()) }
 494     }
 495
 496     /// Is the given keyword `kw` followed by a non-reserved identifier?
 497     fn is_kw_followed_by_ident(&self, kw: Symbol) -> bool {
 498         self.token.is_keyword(kw) && self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident())
 499     }
 500
 501     fn check_or_expected(&mut self, ok: bool, typ: TokenType) -> bool {
 502         if ok {
 503             true
 504         } else {
 505             self.expected_tokens.push(typ);
 506             false
 507         }
 508     }
 509
 510     fn check_ident(&mut self) -> bool {
 511         self.check_or_expected(self.token.is_ident(), TokenType::Ident)
 512     }
 513
 514     fn check_path(&mut self) -> bool {
 515         self.check_or_expected(self.token.is_path_start(), TokenType::Path)
 516     }
 517
 518     fn check_type(&mut self) -> bool {
 519         self.check_or_expected(self.token.can_begin_type(), TokenType::Type)
 520     }
 521
 522     fn check_const_arg(&mut self) -> bool {
 523         self.check_or_expected(self.token.can_begin_const_arg(), TokenType::Const)
 524     }
 525
 526     fn check_inline_const(&self, dist: usize) -> bool {
 527         self.is_keyword_ahead(dist, &[kw::Const])
 528             && self.look_ahead(dist + 1, |t| match t.kind {
 529                 token::Interpolated(ref nt) => matches!(**nt, token::NtBlock(..)),
 530                 token::OpenDelim(DelimToken::Brace) => true,
 531                 _ => false,
 532             })
 533     }
 534
 535     /// Checks to see if the next token is either `+` or `+=`.
 536     /// Otherwise returns `false`.
 537     fn check_plus(&mut self) -> bool {
 538         self.check_or_expected(
 539             self.token.is_like_plus(),
 540             TokenType::Token(token::BinOp(token::Plus)),
 541         )
 542     }
 543
 544     /// Eats the expected token if it's present possibly breaking
 545     /// compound tokens like multi-character operators in process.
 546     /// Returns `true` if the token was eaten.
 547     fn break_and_eat(&mut self, expected: TokenKind) -> bool {
 548         if self.token.kind == expected {
 549             self.bump();
 550             return true;
 551         }
 552         match self.token.kind.break_two_token_op() {
 553             Some((first, second)) if first == expected => {
 554                 let first_span = self.sess.source_map().start_point(self.token.span);
 555                 let second_span = self.token.span.with_lo(first_span.hi());
 556                 self.token = Token::new(first, first_span);
 557                 // Use the spacing of the glued token as the spacing
 558                 // of the unglued second token.
 559                 self.bump_with((Token::new(second, second_span), self.token_spacing));
 560                 true
 561             }
 562             _ => {
 563                 self.expected_tokens.push(TokenType::Token(expected));
 564                 false
 565             }
 566         }
 567     }
 568
 569     /// Eats `+` possibly breaking tokens like `+=` in process.
 570     fn eat_plus(&mut self) -> bool {
 571         self.break_and_eat(token::BinOp(token::Plus))
 572     }
 573
 574     /// Eats `&` possibly breaking tokens like `&&` in process.
 575     /// Signals an error if `&` is not eaten.
 576     fn expect_and(&mut self) -> PResult<'a, ()> {
 577         if self.break_and_eat(token::BinOp(token::And)) { Ok(()) } else { self.unexpected() }
 578     }
 579
 580     /// Eats `|` possibly breaking tokens like `||` in process.
 581     /// Signals an error if `|` was not eaten.
 582     fn expect_or(&mut self) -> PResult<'a, ()> {
 583         if self.break_and_eat(token::BinOp(token::Or)) { Ok(()) } else { self.unexpected() }
 584     }
 585
 586     /// Eats `<` possibly breaking tokens like `<<` in process.
 587     fn eat_lt(&mut self) -> bool {
 588         let ate = self.break_and_eat(token::Lt);
 589         if ate {
 590             // See doc comment for `unmatched_angle_bracket_count`.
 591             self.unmatched_angle_bracket_count += 1;
 592             self.max_angle_bracket_count += 1;
 593             debug!("eat_lt: (increment) count={:?}", self.unmatched_angle_bracket_count);
 594         }
 595         ate
 596     }
 597
 598     /// Eats `<` possibly breaking tokens like `<<` in process.
 599     /// Signals an error if `<` was not eaten.
 600     fn expect_lt(&mut self) -> PResult<'a, ()> {
 601         if self.eat_lt() { Ok(()) } else { self.unexpected() }
 602     }
 603
 604     /// Eats `>` possibly breaking tokens like `>>` in process.
 605     /// Signals an error if `>` was not eaten.
 606     fn expect_gt(&mut self) -> PResult<'a, ()> {
 607         if self.break_and_eat(token::Gt) {
 608             // See doc comment for `unmatched_angle_bracket_count`.
 609             if self.unmatched_angle_bracket_count > 0 {
 610                 self.unmatched_angle_bracket_count -= 1;
 611                 debug!("expect_gt: (decrement) count={:?}", self.unmatched_angle_bracket_count);
 612             }
 613             Ok(())
 614         } else {
 615             self.unexpected()
 616         }
 617     }
 618
 619     fn expect_any_with_type(&mut self, kets: &[&TokenKind], expect: TokenExpectType) -> bool {
 620         kets.iter().any(|k| match expect {
 621             TokenExpectType::Expect => self.check(k),
 622             TokenExpectType::NoExpect => self.token == **k,
 623         })
 624     }
 625
 626     fn parse_seq_to_before_tokens<T>(
 627         &mut self,
 628         kets: &[&TokenKind],
 629         sep: SeqSep,
 630         expect: TokenExpectType,
 631         mut f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 632     ) -> PResult<'a, (Vec<T>, bool /* trailing */, bool /* recovered */)> {
 633         let mut first = true;
 634         let mut recovered = false;
 635         let mut trailing = false;
 636         let mut v = vec![];
 637         while !self.expect_any_with_type(kets, expect) {
 638             if let token::CloseDelim(..) | token::Eof = self.token.kind {
 639                 break;
 640             }
 641             if let Some(ref t) = sep.sep {
 642                 if first {
 643                     first = false;
 644                 } else {
 645                     match self.expect(t) {
 646                         Ok(false) => {}
 647                         Ok(true) => {
 648                             recovered = true;
 649                             break;
 650                         }
 651                         Err(mut expect_err) => {
 652                             let sp = self.prev_token.span.shrink_to_hi();
 653                             let token_str = pprust::token_kind_to_string(t);
 654
 655                             // Attempt to keep parsing if it was a similar separator.
 656                             if let Some(ref tokens) = t.similar_tokens() {
 657                                 if tokens.contains(&self.token.kind) {
 658                                     self.bump();
 659                                 }
 660                             }
 661
 662                             // If this was a missing `@` in a binding pattern
 663                             // bail with a suggestion
 664                             // https://github.com/rust-lang/rust/issues/72373
 665                             if self.prev_token.is_ident() && self.token.kind == token::DotDot {
 666                                 let msg = format!(
 667                                     "if you meant to bind the contents of \
 668                                     the rest of the array pattern into `{}`, use `@`",
 669                                     pprust::token_to_string(&self.prev_token)
 670                                 );
 671                                 expect_err
 672                                     .span_suggestion_verbose(
 673                                         self.prev_token.span.shrink_to_hi().until(self.token.span),
 674                                         &msg,
 675                                         " @ ".to_string(),
 676                                         Applicability::MaybeIncorrect,
 677                                     )
 678                                     .emit();
 679                                 break;
 680                             }
 681
 682                             // Attempt to keep parsing if it was an omitted separator.
 683                             match f(self) {
 684                                 Ok(t) => {
 685                                     // Parsed successfully, therefore most probably the code only
 686                                     // misses a separator.
 687                                     let mut exp_span = self.sess.source_map().next_point(sp);
 688                                     if self.sess.source_map().is_multiline(exp_span) {
 689                                         exp_span = sp;
 690                                     }
 691                                     expect_err
 692                                         .span_suggestion_short(
 693                                             exp_span,
 694                                             &format!("missing `{}`", token_str),
 695                                             token_str,
 696                                             Applicability::MaybeIncorrect,
 697                                         )
 698                                         .emit();
 699
 700                                     v.push(t);
 701                                     continue;
 702                                 }
 703                                 Err(mut e) => {
 704                                     // Parsing failed, therefore it must be something more serious
 705                                     // than just a missing separator.
 706                                     expect_err.emit();
 707
 708                                     e.cancel();
 709                                     break;
 710                                 }
 711                             }
 712                         }
 713                     }
 714                 }
 715             }
 716             if sep.trailing_sep_allowed && self.expect_any_with_type(kets, expect) {
 717                 trailing = true;
 718                 break;
 719             }
 720
 721             let t = f(self)?;
 722             v.push(t);
 723         }
 724
 725         Ok((v, trailing, recovered))
 726     }
 727
 728     /// Parses a sequence, not including the closing delimiter. The function
 729     /// `f` must consume tokens until reaching the next separator or
 730     /// closing bracket.
 731     fn parse_seq_to_before_end<T>(
 732         &mut self,
 733         ket: &TokenKind,
 734         sep: SeqSep,
 735         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 736     ) -> PResult<'a, (Vec<T>, bool, bool)> {
 737         self.parse_seq_to_before_tokens(&[ket], sep, TokenExpectType::Expect, f)
 738     }
 739
 740     /// Parses a sequence, including the closing delimiter. The function
 741     /// `f` must consume tokens until reaching the next separator or
 742     /// closing bracket.
 743     fn parse_seq_to_end<T>(
 744         &mut self,
 745         ket: &TokenKind,
 746         sep: SeqSep,
 747         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 748     ) -> PResult<'a, (Vec<T>, bool /* trailing */)> {
 749         let (val, trailing, recovered) = self.parse_seq_to_before_end(ket, sep, f)?;
 750         if !recovered {
 751             self.eat(ket);
 752         }
 753         Ok((val, trailing))
 754     }
 755
 756     /// Parses a sequence, including the closing delimiter. The function
 757     /// `f` must consume tokens until reaching the next separator or
 758     /// closing bracket.
 759     fn parse_unspanned_seq<T>(
 760         &mut self,
 761         bra: &TokenKind,
 762         ket: &TokenKind,
 763         sep: SeqSep,
 764         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 765     ) -> PResult<'a, (Vec<T>, bool)> {
 766         self.expect(bra)?;
 767         self.parse_seq_to_end(ket, sep, f)
 768     }
 769
 770     fn parse_delim_comma_seq<T>(
 771         &mut self,
 772         delim: DelimToken,
 773         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 774     ) -> PResult<'a, (Vec<T>, bool)> {
 775         self.parse_unspanned_seq(
 776             &token::OpenDelim(delim),
 777             &token::CloseDelim(delim),
 778             SeqSep::trailing_allowed(token::Comma),
 779             f,
 780         )
 781     }
 782
 783     fn parse_paren_comma_seq<T>(
 784         &mut self,
 785         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 786     ) -> PResult<'a, (Vec<T>, bool)> {
 787         self.parse_delim_comma_seq(token::Paren, f)
 788     }
 789
 790     /// Advance the parser by one token using provided token as the next one.
 791     fn bump_with(&mut self, (next_token, next_spacing): (Token, Spacing)) {
 792         // Bumping after EOF is a bad sign, usually an infinite loop.
 793         if self.prev_token.kind == TokenKind::Eof {
 794             let msg = "attempted to bump the parser past EOF (may be stuck in a loop)";
 795             self.span_bug(self.token.span, msg);
 796         }
 797
 798         // Update the current and previous tokens.
 799         self.prev_token = mem::replace(&mut self.token, next_token);
 800         self.token_spacing = next_spacing;
 801
 802         // Diagnostics.
 803         self.expected_tokens.clear();
 804     }
 805
 806     /// Advance the parser by one token.
 807     pub fn bump(&mut self) {
 808         let next_token = self.next_tok(self.token.span);
 809         self.bump_with(next_token);
 810     }
 811
 812     /// Look-ahead `dist` tokens of `self.token` and get access to that token there.
 813     /// When `dist == 0` then the current token is looked at.
 814     pub fn look_ahead<R>(&self, dist: usize, looker: impl FnOnce(&Token) -> R) -> R {
 815         if dist == 0 {
 816             return looker(&self.token);
 817         }
 818
 819         let frame = &self.token_cursor.frame;
 820         match frame.tree_cursor.look_ahead(dist - 1) {
 821             Some(tree) => match tree {
 822                 TokenTree::Token(token) => looker(token),
 823                 TokenTree::Delimited(dspan, delim, _) => {
 824                     looker(&Token::new(token::OpenDelim(*delim), dspan.open))
 825                 }
 826             },
 827             None => looker(&Token::new(token::CloseDelim(frame.delim), frame.span.close)),
 828         }
 829     }
 830
 831     /// Returns whether any of the given keywords are `dist` tokens ahead of the current one.
 832     fn is_keyword_ahead(&self, dist: usize, kws: &[Symbol]) -> bool {
 833         self.look_ahead(dist, |t| kws.iter().any(|&kw| t.is_keyword(kw)))
 834     }
 835
 836     /// Parses asyncness: `async` or nothing.
 837     fn parse_asyncness(&mut self) -> Async {
 838         if self.eat_keyword(kw::Async) {
 839             let span = self.prev_token.uninterpolated_span();
 840             Async::Yes { span, closure_id: DUMMY_NODE_ID, return_impl_trait_id: DUMMY_NODE_ID }
 841         } else {
 842             Async::No
 843         }
 844     }
 845
 846     /// Parses unsafety: `unsafe` or nothing.
 847     fn parse_unsafety(&mut self) -> Unsafe {
 848         if self.eat_keyword(kw::Unsafe) {
 849             Unsafe::Yes(self.prev_token.uninterpolated_span())
 850         } else {
 851             Unsafe::No
 852         }
 853     }
 854
 855     /// Parses constness: `const` or nothing.
 856     fn parse_constness(&mut self) -> Const {
 857         // Avoid const blocks to be parsed as const items
 858         if self.look_ahead(1, |t| t != &token::OpenDelim(DelimToken::Brace))
 859             && self.eat_keyword(kw::Const)
 860         {
 861             Const::Yes(self.prev_token.uninterpolated_span())
 862         } else {
 863             Const::No
 864         }
 865     }
 866
 867     /// Parses inline const expressions.
 868     fn parse_const_block(&mut self, span: Span) -> PResult<'a, P<Expr>> {
 869         self.sess.gated_spans.gate(sym::inline_const, span);
 870         self.eat_keyword(kw::Const);
 871         let blk = self.parse_block()?;
 872         let anon_const = AnonConst {
 873             id: DUMMY_NODE_ID,
 874             value: self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new()),
 875         };
 876         Ok(self.mk_expr(span, ExprKind::ConstBlock(anon_const), AttrVec::new()))
 877     }
 878
 879     /// Parses mutability (`mut` or nothing).
 880     fn parse_mutability(&mut self) -> Mutability {
 881         if self.eat_keyword(kw::Mut) { Mutability::Mut } else { Mutability::Not }
 882     }
 883
 884     /// Possibly parses mutability (`const` or `mut`).
 885     fn parse_const_or_mut(&mut self) -> Option<Mutability> {
 886         if self.eat_keyword(kw::Mut) {
 887             Some(Mutability::Mut)
 888         } else if self.eat_keyword(kw::Const) {
 889             Some(Mutability::Not)
 890         } else {
 891             None
 892         }
 893     }
 894
 895     fn parse_field_name(&mut self) -> PResult<'a, Ident> {
 896         if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) = self.token.kind
 897         {
 898             self.expect_no_suffix(self.token.span, "a tuple index", suffix);
 899             self.bump();
 900             Ok(Ident::new(symbol, self.prev_token.span))
 901         } else {
 902             self.parse_ident_common(false)
 903         }
 904     }
 905
 906     fn parse_mac_args(&mut self) -> PResult<'a, P<MacArgs>> {
 907         self.parse_mac_args_common(true).map(P)
 908     }
 909
 910     fn parse_attr_args(&mut self) -> PResult<'a, MacArgs> {
 911         self.parse_mac_args_common(false)
 912     }
 913
 914     fn parse_mac_args_common(&mut self, delimited_only: bool) -> PResult<'a, MacArgs> {
 915         Ok(
 916             if self.check(&token::OpenDelim(DelimToken::Paren))
 917                 || self.check(&token::OpenDelim(DelimToken::Bracket))
 918                 || self.check(&token::OpenDelim(DelimToken::Brace))
 919             {
 920                 match self.parse_token_tree() {
 921                     TokenTree::Delimited(dspan, delim, tokens) =>
 922                     // We've confirmed above that there is a delimiter so unwrapping is OK.
 923                     {
 924                         MacArgs::Delimited(dspan, MacDelimiter::from_token(delim).unwrap(), tokens)
 925                     }
 926                     _ => unreachable!(),
 927                 }
 928             } else if !delimited_only {
 929                 if self.eat(&token::Eq) {
 930                     let eq_span = self.prev_token.span;
 931                     let mut is_interpolated_expr = false;
 932                     if let token::Interpolated(nt) = &self.token.kind {
 933                         if let token::NtExpr(..) = **nt {
 934                             is_interpolated_expr = true;
 935                         }
 936                     }
 937                     let token_tree = if is_interpolated_expr {
 938                         // We need to accept arbitrary interpolated expressions to continue
 939                         // supporting things like `doc = $expr` that work on stable.
 940                         // Non-literal interpolated expressions are rejected after expansion.
 941                         self.parse_token_tree()
 942                     } else {
 943                         self.parse_unsuffixed_lit()?.token_tree()
 944                     };
 945
 946                     MacArgs::Eq(eq_span, token_tree.into())
 947                 } else {
 948                     MacArgs::Empty
 949                 }
 950             } else {
 951                 return self.unexpected();
 952             },
 953         )
 954     }
 955
 956     fn parse_or_use_outer_attributes(
 957         &mut self,
 958         already_parsed_attrs: Option<AttrVec>,
 959     ) -> PResult<'a, AttrVec> {
 960         if let Some(attrs) = already_parsed_attrs {
 961             Ok(attrs)
 962         } else {
 963             self.parse_outer_attributes().map(|a| a.into())
 964         }
 965     }
 966
 967     /// Parses a single token tree from the input.
 968     pub(crate) fn parse_token_tree(&mut self) -> TokenTree {
 969         match self.token.kind {
 970             token::OpenDelim(..) => {
 971                 let depth = self.token_cursor.stack.len();
 972
 973                 // We keep advancing the token cursor until we hit
 974                 // the matching `CloseDelim` token.
 975                 while !(depth == self.token_cursor.stack.len()
 976                     && matches!(self.token.kind, token::CloseDelim(_)))
 977                 {
 978                     // Advance one token at a time, so `TokenCursor::next()`
 979                     // can capture these tokens if necessary.
 980                     self.bump();
 981                 }
 982                 // We are still inside the frame corresponding
 983                 // to the delimited stream we captured, so grab
 984                 // the tokens from this frame.
 985                 let frame = &self.token_cursor.frame;
 986                 let stream = frame.tree_cursor.stream.clone();
 987                 let span = frame.span;
 988                 let delim = frame.delim;
 989                 // Consume close delimiter
 990                 self.bump();
 991                 TokenTree::Delimited(span, delim, stream)
 992             }
 993             token::CloseDelim(_) | token::Eof => unreachable!(),
 994             _ => {
 995                 self.bump();
 996                 TokenTree::Token(self.prev_token.clone())
 997             }
 998         }
 999     }
1000
1001     /// Parses a stream of tokens into a list of `TokenTree`s, up to EOF.
1002     pub fn parse_all_token_trees(&mut self) -> PResult<'a, Vec<TokenTree>> {
1003         let mut tts = Vec::new();
1004         while self.token != token::Eof {
1005             tts.push(self.parse_token_tree());
1006         }
1007         Ok(tts)
1008     }
1009
1010     pub fn parse_tokens(&mut self) -> TokenStream {
1011         let mut result = Vec::new();
1012         loop {
1013             match self.token.kind {
1014                 token::Eof | token::CloseDelim(..) => break,
1015                 _ => result.push(self.parse_token_tree().into()),
1016             }
1017         }
1018         TokenStream::new(result)
1019     }
1020
1021     /// Evaluates the closure with restrictions in place.
1022     ///
1023     /// Afters the closure is evaluated, restrictions are reset.
1024     fn with_res<T>(&mut self, res: Restrictions, f: impl FnOnce(&mut Self) -> T) -> T {
1025         let old = self.restrictions;
1026         self.restrictions = res;
1027         let res = f(self);
1028         self.restrictions = old;
1029         res
1030     }
1031
1032     fn is_crate_vis(&self) -> bool {
1033         self.token.is_keyword(kw::Crate) && self.look_ahead(1, |t| t != &token::ModSep)
1034     }
1035
1036     /// Parses `pub`, `pub(crate)` and `pub(in path)` plus shortcuts `crate` for `pub(crate)`,
1037     /// `pub(self)` for `pub(in self)` and `pub(super)` for `pub(in super)`.
1038     /// If the following element can't be a tuple (i.e., it's a function definition), then
1039     /// it's not a tuple struct field), and the contents within the parentheses isn't valid,
1040     /// so emit a proper diagnostic.
1041     // Public for rustfmt usage.
1042     pub fn parse_visibility(&mut self, fbt: FollowedByType) -> PResult<'a, Visibility> {
1043         maybe_whole!(self, NtVis, |x| x);
1044
1045         self.expected_tokens.push(TokenType::Keyword(kw::Crate));
1046         if self.is_crate_vis() {
1047             self.bump(); // `crate`
1048             self.sess.gated_spans.gate(sym::crate_visibility_modifier, self.prev_token.span);
1049             return Ok(Visibility {
1050                 span: self.prev_token.span,
1051                 kind: VisibilityKind::Crate(CrateSugar::JustCrate),
1052                 tokens: None,
1053             });
1054         }
1055
1056         if !self.eat_keyword(kw::Pub) {
1057             // We need a span for our `Spanned<VisibilityKind>`, but there's inherently no
1058             // keyword to grab a span from for inherited visibility; an empty span at the
1059             // beginning of the current token would seem to be the "Schelling span".
1060             return Ok(Visibility {
1061                 span: self.token.span.shrink_to_lo(),
1062                 kind: VisibilityKind::Inherited,
1063                 tokens: None,
1064             });
1065         }
1066         let lo = self.prev_token.span;
1067
1068         if self.check(&token::OpenDelim(token::Paren)) {
1069             // We don't `self.bump()` the `(` yet because this might be a struct definition where
1070             // `()` or a tuple might be allowed. For example, `struct Struct(pub (), pub (usize));`.
1071             // Because of this, we only `bump` the `(` if we're assured it is appropriate to do so
1072             // by the following tokens.
1073             if self.is_keyword_ahead(1, &[kw::Crate]) && self.look_ahead(2, |t| t != &token::ModSep)
1074             // account for `pub(crate::foo)`
1075             {
1076                 // Parse `pub(crate)`.
1077                 self.bump(); // `(`
1078                 self.bump(); // `crate`
1079                 self.expect(&token::CloseDelim(token::Paren))?; // `)`
1080                 let vis = VisibilityKind::Crate(CrateSugar::PubCrate);
1081                 return Ok(Visibility {
1082                     span: lo.to(self.prev_token.span),
1083                     kind: vis,
1084                     tokens: None,
1085                 });
1086             } else if self.is_keyword_ahead(1, &[kw::In]) {
1087                 // Parse `pub(in path)`.
1088                 self.bump(); // `(`
1089                 self.bump(); // `in`
1090                 let path = self.parse_path(PathStyle::Mod)?; // `path`
1091                 self.expect(&token::CloseDelim(token::Paren))?; // `)`
1092                 let vis = VisibilityKind::Restricted { path: P(path), id: ast::DUMMY_NODE_ID };
1093                 return Ok(Visibility {
1094                     span: lo.to(self.prev_token.span),
1095                     kind: vis,
1096                     tokens: None,
1097                 });
1098             } else if self.look_ahead(2, |t| t == &token::CloseDelim(token::Paren))
1099                 && self.is_keyword_ahead(1, &[kw::Super, kw::SelfLower])
1100             {
1101                 // Parse `pub(self)` or `pub(super)`.
1102                 self.bump(); // `(`
1103                 let path = self.parse_path(PathStyle::Mod)?; // `super`/`self`
1104                 self.expect(&token::CloseDelim(token::Paren))?; // `)`
1105                 let vis = VisibilityKind::Restricted { path: P(path), id: ast::DUMMY_NODE_ID };
1106                 return Ok(Visibility {
1107                     span: lo.to(self.prev_token.span),
1108                     kind: vis,
1109                     tokens: None,
1110                 });
1111             } else if let FollowedByType::No = fbt {
1112                 // Provide this diagnostic if a type cannot follow;
1113                 // in particular, if this is not a tuple struct.
1114                 self.recover_incorrect_vis_restriction()?;
1115                 // Emit diagnostic, but continue with public visibility.
1116             }
1117         }
1118
1119         Ok(Visibility { span: lo, kind: VisibilityKind::Public, tokens: None })
1120     }
1121
1122     /// Recovery for e.g. `pub(something) fn ...` or `struct X { pub(something) y: Z }`
1123     fn recover_incorrect_vis_restriction(&mut self) -> PResult<'a, ()> {
1124         self.bump(); // `(`
1125         let path = self.parse_path(PathStyle::Mod)?;
1126         self.expect(&token::CloseDelim(token::Paren))?; // `)`
1127
1128         let msg = "incorrect visibility restriction";
1129         let suggestion = r##"some possible visibility restrictions are:
1130 `pub(crate)`: visible only on the current crate
1131 `pub(super)`: visible only in the current module's parent
1132 `pub(in path::to::module)`: visible only on the specified path"##;
1133
1134         let path_str = pprust::path_to_string(&path);
1135
1136         struct_span_err!(self.sess.span_diagnostic, path.span, E0704, "{}", msg)
1137             .help(suggestion)
1138             .span_suggestion(
1139                 path.span,
1140                 &format!("make this visible only to module `{}` with `in`", path_str),
1141                 format!("in {}", path_str),
1142                 Applicability::MachineApplicable,
1143             )
1144             .emit();
1145
1146         Ok(())
1147     }
1148
1149     /// Parses `extern string_literal?`.
1150     fn parse_extern(&mut self) -> PResult<'a, Extern> {
1151         Ok(if self.eat_keyword(kw::Extern) {
1152             Extern::from_abi(self.parse_abi())
1153         } else {
1154             Extern::None
1155         })
1156     }
1157
1158     /// Parses a string literal as an ABI spec.
1159     fn parse_abi(&mut self) -> Option<StrLit> {
1160         match self.parse_str_lit() {
1161             Ok(str_lit) => Some(str_lit),
1162             Err(Some(lit)) => match lit.kind {
1163                 ast::LitKind::Err(_) => None,
1164                 _ => {
1165                     self.struct_span_err(lit.span, "non-string ABI literal")
1166                         .span_suggestion(
1167                             lit.span,
1168                             "specify the ABI with a string literal",
1169                             "\"C\"".to_string(),
1170                             Applicability::MaybeIncorrect,
1171                         )
1172                         .emit();
1173                     None
1174                 }
1175             },
1176             Err(None) => None,
1177         }
1178     }
1179
1180     /// Records all tokens consumed by the provided callback,
1181     /// including the current token. These tokens are collected
1182     /// into a `LazyTokenStream`, and returned along with the result
1183     /// of the callback. The returned `LazyTokenStream` will be `None`
1184     /// if not tokens were captured.
1185     ///
1186     /// Note: If your callback consumes an opening delimiter
1187     /// (including the case where you call `collect_tokens`
1188     /// when the current token is an opening delimeter),
1189     /// you must also consume the corresponding closing delimiter.
1190     ///
1191     /// That is, you can consume
1192     /// `something ([{ }])` or `([{}])`, but not `([{}]`
1193     ///
1194     /// This restriction shouldn't be an issue in practice,
1195     /// since this function is used to record the tokens for
1196     /// a parsed AST item, which always has matching delimiters.
1197     pub fn collect_tokens<R>(
1198         &mut self,
1199         f: impl FnOnce(&mut Self) -> PResult<'a, R>,
1200     ) -> PResult<'a, (R, Option<LazyTokenStream>)> {
1201         let start_token = (self.token.clone(), self.token_spacing);
1202         let cursor_snapshot = self.token_cursor.clone();
1203
1204         let ret = f(self)?;
1205
1206         // We didn't capture any tokens
1207         let num_calls = self.token_cursor.num_next_calls - cursor_snapshot.num_next_calls;
1208         if num_calls == 0 {
1209             return Ok((ret, None));
1210         }
1211
1212         // Produces a `TokenStream` on-demand. Using `cursor_snapshot`
1213         // and `num_calls`, we can reconstruct the `TokenStream` seen
1214         // by the callback. This allows us to avoid producing a `TokenStream`
1215         // if it is never needed - for example, a captured `macro_rules!`
1216         // argument that is never passed to a proc macro.
1217         //
1218         // This also makes `Parser` very cheap to clone, since
1219         // there is no intermediate collection buffer to clone.
1220         struct LazyTokenStreamImpl {
1221             start_token: (Token, Spacing),
1222             cursor_snapshot: TokenCursor,
1223             num_calls: usize,
1224             desugar_doc_comments: bool,
1225         }
1226         impl CreateTokenStream for LazyTokenStreamImpl {
1227             fn create_token_stream(&self) -> TokenStream {
1228                 // The token produced by the final call to `next` or `next_desugared`
1229                 // was not actually consumed by the callback. The combination
1230                 // of chaining the initial token and using `take` produces the desired
1231                 // result - we produce an empty `TokenStream` if no calls were made,
1232                 // and omit the final token otherwise.
1233                 let mut cursor_snapshot = self.cursor_snapshot.clone();
1234                 let tokens = std::iter::once(self.start_token.clone())
1235                     .chain((0..self.num_calls).map(|_| {
1236                         if self.desugar_doc_comments {
1237                             cursor_snapshot.next_desugared()
1238                         } else {
1239                             cursor_snapshot.next()
1240                         }
1241                     }))
1242                     .take(self.num_calls);
1243
1244                 make_token_stream(tokens)
1245             }
1246         }
1247
1248         let lazy_impl = LazyTokenStreamImpl {
1249             start_token,
1250             cursor_snapshot,
1251             num_calls,
1252             desugar_doc_comments: self.desugar_doc_comments,
1253         };
1254         Ok((ret, Some(LazyTokenStream::new(lazy_impl))))
1255     }
1256
1257     /// `::{` or `::*`
1258     fn is_import_coupler(&mut self) -> bool {
1259         self.check(&token::ModSep)
1260             && self.look_ahead(1, |t| {
1261                 *t == token::OpenDelim(token::Brace) || *t == token::BinOp(token::Star)
1262             })
1263     }
1264
1265     pub fn clear_expected_tokens(&mut self) {
1266         self.expected_tokens.clear();
1267     }
1268 }
1269
1270 crate fn make_unclosed_delims_error(
1271     unmatched: UnmatchedBrace,
1272     sess: &ParseSess,
1273 ) -> Option<DiagnosticBuilder<'_>> {
1274     // `None` here means an `Eof` was found. We already emit those errors elsewhere, we add them to
1275     // `unmatched_braces` only for error recovery in the `Parser`.
1276     let found_delim = unmatched.found_delim?;
1277     let mut err = sess.span_diagnostic.struct_span_err(
1278         unmatched.found_span,
1279         &format!(
1280             "mismatched closing delimiter: `{}`",
1281             pprust::token_kind_to_string(&token::CloseDelim(found_delim)),
1282         ),
1283     );
1284     err.span_label(unmatched.found_span, "mismatched closing delimiter");
1285     if let Some(sp) = unmatched.candidate_span {
1286         err.span_label(sp, "closing delimiter possibly meant for this");
1287     }
1288     if let Some(sp) = unmatched.unclosed_span {
1289         err.span_label(sp, "unclosed delimiter");
1290     }
1291     Some(err)
1292 }
1293
1294 pub fn emit_unclosed_delims(unclosed_delims: &mut Vec<UnmatchedBrace>, sess: &ParseSess) {
1295     *sess.reached_eof.borrow_mut() |=
1296         unclosed_delims.iter().any(|unmatched_delim| unmatched_delim.found_delim.is_none());
1297     for unmatched in unclosed_delims.drain(..) {
1298         if let Some(mut e) = make_unclosed_delims_error(unmatched, sess) {
1299             e.emit();
1300         }
1301     }
1302 }
1303
1304 /// Converts a flattened iterator of tokens (including open and close delimiter tokens)
1305 /// into a `TokenStream`, creating a `TokenTree::Delimited` for each matching pair
1306 /// of open and close delims.
1307 fn make_token_stream(tokens: impl Iterator<Item = (Token, Spacing)>) -> TokenStream {
1308     #[derive(Debug)]
1309     struct FrameData {
1310         open: Span,
1311         inner: Vec<(TokenTree, Spacing)>,
1312     }
1313     let mut stack = vec![FrameData { open: DUMMY_SP, inner: vec![] }];
1314     for (token, spacing) in tokens {
1315         match token {
1316             Token { kind: TokenKind::OpenDelim(_), span } => {
1317                 stack.push(FrameData { open: span, inner: vec![] });
1318             }
1319             Token { kind: TokenKind::CloseDelim(delim), span } => {
1320                 let frame_data = stack.pop().expect("Token stack was empty!");
1321                 let dspan = DelimSpan::from_pair(frame_data.open, span);
1322                 let stream = TokenStream::new(frame_data.inner);
1323                 let delimited = TokenTree::Delimited(dspan, delim, stream);
1324                 stack
1325                     .last_mut()
1326                     .unwrap_or_else(|| panic!("Bottom token frame is missing for tokens!"))
1327                     .inner
1328                     .push((delimited, Spacing::Alone));
1329             }
1330             token => stack
1331                 .last_mut()
1332                 .expect("Bottom token frame is missing!")
1333                 .inner
1334                 .push((TokenTree::Token(token), spacing)),
1335         }
1336     }
1337     let final_buf = stack.pop().expect("Missing final buf!");
1338     assert!(stack.is_empty(), "Stack should be empty: final_buf={:?} stack={:?}", final_buf, stack);
1339     TokenStream::new(final_buf.inner)
1340 }