vendor/rustc-ap-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, TreeAndSpacing};
  21 use rustc_ast::DUMMY_NODE_ID;
  22 use rustc_ast::{self as ast, AnonConst, AttrStyle, AttrVec, Const, CrateSugar, Extern, HasTokens};
  23 use rustc_ast::{Async, Expr, ExprKind, MacArgs, MacDelimiter, Mutability, StrLit, Unsafe};
  24 use rustc_ast::{Visibility, VisibilityKind};
  25 use rustc_ast_pretty::pprust;
  26 use rustc_data_structures::sync::Lrc;
  27 use rustc_errors::PResult;
  28 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, FatalError};
  29 use rustc_session::parse::ParseSess;
  30 use rustc_span::source_map::{Span, DUMMY_SP};
  31 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  32 use tracing::debug;
  33
  34 use std::{cmp, mem, slice};
  35
  36 bitflags::bitflags! {
  37     struct Restrictions: u8 {
  38         const STMT_EXPR         = 1 << 0;
  39         const NO_STRUCT_LITERAL = 1 << 1;
  40         const CONST_EXPR        = 1 << 2;
  41     }
  42 }
  43
  44 #[derive(Clone, Copy, PartialEq, Debug)]
  45 enum SemiColonMode {
  46     Break,
  47     Ignore,
  48     Comma,
  49 }
  50
  51 #[derive(Clone, Copy, PartialEq, Debug)]
  52 enum BlockMode {
  53     Break,
  54     Ignore,
  55 }
  56
  57 /// Whether or not we should force collection of tokens for an AST node,
  58 /// regardless of whether or not it has attributes
  59 pub enum ForceCollect {
  60     Yes,
  61     No,
  62 }
  63
  64 pub enum TrailingToken {
  65     None,
  66     Semi,
  67 }
  68
  69 /// Like `maybe_whole_expr`, but for things other than expressions.
  70 #[macro_export]
  71 macro_rules! maybe_whole {
  72     ($p:expr, $constructor:ident, |$x:ident| $e:expr) => {
  73         if let token::Interpolated(nt) = &$p.token.kind {
  74             if let token::$constructor(x) = &**nt {
  75                 let $x = x.clone();
  76                 $p.bump();
  77                 return Ok($e);
  78             }
  79         }
  80     };
  81 }
  82
  83 /// If the next tokens are ill-formed `$ty::` recover them as `<$ty>::`.
  84 #[macro_export]
  85 macro_rules! maybe_recover_from_interpolated_ty_qpath {
  86     ($self: expr, $allow_qpath_recovery: expr) => {
  87         if $allow_qpath_recovery && $self.look_ahead(1, |t| t == &token::ModSep) {
  88             if let token::Interpolated(nt) = &$self.token.kind {
  89                 if let token::NtTy(ty) = &**nt {
  90                     let ty = ty.clone();
  91                     $self.bump();
  92                     return $self.maybe_recover_from_bad_qpath_stage_2($self.prev_token.span, ty);
  93                 }
  94             }
  95         }
  96     };
  97 }
  98
  99 #[derive(Clone)]
 100 pub struct Parser<'a> {
 101     pub sess: &'a ParseSess,
 102     /// The current token.
 103     pub token: Token,
 104     /// The spacing for the current token
 105     pub token_spacing: Spacing,
 106     /// The previous token.
 107     pub prev_token: Token,
 108     restrictions: Restrictions,
 109     expected_tokens: Vec<TokenType>,
 110     // Important: This must only be advanced from `next_tok`
 111     // to ensure that `token_cursor.num_next_calls` is updated properly
 112     token_cursor: TokenCursor,
 113     desugar_doc_comments: bool,
 114     /// This field is used to keep track of how many left angle brackets we have seen. This is
 115     /// required in order to detect extra leading left angle brackets (`<` characters) and error
 116     /// appropriately.
 117     ///
 118     /// See the comments in the `parse_path_segment` function for more details.
 119     unmatched_angle_bracket_count: u32,
 120     max_angle_bracket_count: u32,
 121     /// A list of all unclosed delimiters found by the lexer. If an entry is used for error recovery
 122     /// it gets removed from here. Every entry left at the end gets emitted as an independent
 123     /// error.
 124     pub(super) unclosed_delims: Vec<UnmatchedBrace>,
 125     last_unexpected_token_span: Option<Span>,
 126     /// Span pointing at the `:` for the last type ascription the parser has seen, and whether it
 127     /// looked like it could have been a mistyped path or literal `Option:Some(42)`).
 128     pub last_type_ascription: Option<(Span, bool /* likely path typo */)>,
 129     /// If present, this `Parser` is not parsing Rust code but rather a macro call.
 130     subparser_name: Option<&'static str>,
 131 }
 132
 133 impl<'a> Drop for Parser<'a> {
 134     fn drop(&mut self) {
 135         emit_unclosed_delims(&mut self.unclosed_delims, &self.sess);
 136     }
 137 }
 138
 139 #[derive(Clone)]
 140 struct TokenCursor {
 141     frame: TokenCursorFrame,
 142     stack: Vec<TokenCursorFrame>,
 143     desugar_doc_comments: bool,
 144     // Counts the number of calls to `next` or `next_desugared`,
 145     // depending on whether `desugar_doc_comments` is set.
 146     num_next_calls: usize,
 147     // During parsing, we may sometimes need to 'unglue' a
 148     // glued token into two component tokens
 149     // (e.g. '>>' into '>' and '>), so that the parser
 150     // can consume them one at a time. This process
 151     // bypasses the normal capturing mechanism
 152     // (e.g. `num_next_calls` will not be incremented),
 153     // since the 'unglued' tokens due not exist in
 154     // the original `TokenStream`.
 155     //
 156     // If we end up consuming both unglued tokens,
 157     // then this is not an issue - we'll end up
 158     // capturing the single 'glued' token.
 159     //
 160     // However, in certain circumstances, we may
 161     // want to capture just the first 'unglued' token.
 162     // For example, capturing the `Vec<u8>`
 163     // in `Option<Vec<u8>>` requires us to unglue
 164     // the trailing `>>` token. The `append_unglued_token`
 165     // field is used to track this token - it gets
 166     // appended to the captured stream when
 167     // we evaluate a `LazyTokenStream`
 168     append_unglued_token: Option<TreeAndSpacing>,
 169 }
 170
 171 #[derive(Clone)]
 172 struct TokenCursorFrame {
 173     delim: token::DelimToken,
 174     span: DelimSpan,
 175     open_delim: bool,
 176     tree_cursor: tokenstream::Cursor,
 177     close_delim: bool,
 178 }
 179
 180 impl TokenCursorFrame {
 181     fn new(span: DelimSpan, delim: DelimToken, tts: TokenStream) -> Self {
 182         TokenCursorFrame {
 183             delim,
 184             span,
 185             open_delim: delim == token::NoDelim,
 186             tree_cursor: tts.into_trees(),
 187             close_delim: delim == token::NoDelim,
 188         }
 189     }
 190 }
 191
 192 impl TokenCursor {
 193     fn next(&mut self) -> (Token, Spacing) {
 194         loop {
 195             let (tree, spacing) = if !self.frame.open_delim {
 196                 self.frame.open_delim = true;
 197                 TokenTree::open_tt(self.frame.span, self.frame.delim).into()
 198             } else if let Some(tree) = self.frame.tree_cursor.next_with_spacing() {
 199                 tree
 200             } else if !self.frame.close_delim {
 201                 self.frame.close_delim = true;
 202                 TokenTree::close_tt(self.frame.span, self.frame.delim).into()
 203             } else if let Some(frame) = self.stack.pop() {
 204                 self.frame = frame;
 205                 continue;
 206             } else {
 207                 (TokenTree::Token(Token::new(token::Eof, DUMMY_SP)), Spacing::Alone)
 208             };
 209
 210             match tree {
 211                 TokenTree::Token(token) => {
 212                     return (token, spacing);
 213                 }
 214                 TokenTree::Delimited(sp, delim, tts) => {
 215                     let frame = TokenCursorFrame::new(sp, delim, tts);
 216                     self.stack.push(mem::replace(&mut self.frame, frame));
 217                 }
 218             }
 219         }
 220     }
 221
 222     fn next_desugared(&mut self) -> (Token, Spacing) {
 223         let (data, attr_style, sp) = match self.next() {
 224             (Token { kind: token::DocComment(_, attr_style, data), span }, _) => {
 225                 (data, attr_style, span)
 226             }
 227             tok => return tok,
 228         };
 229
 230         // Searches for the occurrences of `"#*` and returns the minimum number of `#`s
 231         // required to wrap the text.
 232         let mut num_of_hashes = 0;
 233         let mut count = 0;
 234         for ch in data.as_str().chars() {
 235             count = match ch {
 236                 '"' => 1,
 237                 '#' if count > 0 => count + 1,
 238                 _ => 0,
 239             };
 240             num_of_hashes = cmp::max(num_of_hashes, count);
 241         }
 242
 243         let delim_span = DelimSpan::from_single(sp);
 244         let body = TokenTree::Delimited(
 245             delim_span,
 246             token::Bracket,
 247             [
 248                 TokenTree::token(token::Ident(sym::doc, false), sp),
 249                 TokenTree::token(token::Eq, sp),
 250                 TokenTree::token(TokenKind::lit(token::StrRaw(num_of_hashes), data, None), sp),
 251             ]
 252             .iter()
 253             .cloned()
 254             .collect::<TokenStream>(),
 255         );
 256
 257         self.stack.push(mem::replace(
 258             &mut self.frame,
 259             TokenCursorFrame::new(
 260                 delim_span,
 261                 token::NoDelim,
 262                 if attr_style == AttrStyle::Inner {
 263                     [TokenTree::token(token::Pound, sp), TokenTree::token(token::Not, sp), body]
 264                         .iter()
 265                         .cloned()
 266                         .collect::<TokenStream>()
 267                 } else {
 268                     [TokenTree::token(token::Pound, sp), body]
 269                         .iter()
 270                         .cloned()
 271                         .collect::<TokenStream>()
 272                 },
 273             ),
 274         ));
 275
 276         self.next()
 277     }
 278 }
 279
 280 #[derive(Debug, Clone, PartialEq)]
 281 enum TokenType {
 282     Token(TokenKind),
 283     Keyword(Symbol),
 284     Operator,
 285     Lifetime,
 286     Ident,
 287     Path,
 288     Type,
 289     Const,
 290 }
 291
 292 impl TokenType {
 293     fn to_string(&self) -> String {
 294         match *self {
 295             TokenType::Token(ref t) => format!("`{}`", pprust::token_kind_to_string(t)),
 296             TokenType::Keyword(kw) => format!("`{}`", kw),
 297             TokenType::Operator => "an operator".to_string(),
 298             TokenType::Lifetime => "lifetime".to_string(),
 299             TokenType::Ident => "identifier".to_string(),
 300             TokenType::Path => "path".to_string(),
 301             TokenType::Type => "type".to_string(),
 302             TokenType::Const => "a const expression".to_string(),
 303         }
 304     }
 305 }
 306
 307 #[derive(Copy, Clone, Debug)]
 308 enum TokenExpectType {
 309     Expect,
 310     NoExpect,
 311 }
 312
 313 /// A sequence separator.
 314 struct SeqSep {
 315     /// The separator token.
 316     sep: Option<TokenKind>,
 317     /// `true` if a trailing separator is allowed.
 318     trailing_sep_allowed: bool,
 319 }
 320
 321 impl SeqSep {
 322     fn trailing_allowed(t: TokenKind) -> SeqSep {
 323         SeqSep { sep: Some(t), trailing_sep_allowed: true }
 324     }
 325
 326     fn none() -> SeqSep {
 327         SeqSep { sep: None, trailing_sep_allowed: false }
 328     }
 329 }
 330
 331 pub enum FollowedByType {
 332     Yes,
 333     No,
 334 }
 335
 336 fn token_descr_opt(token: &Token) -> Option<&'static str> {
 337     Some(match token.kind {
 338         _ if token.is_special_ident() => "reserved identifier",
 339         _ if token.is_used_keyword() => "keyword",
 340         _ if token.is_unused_keyword() => "reserved keyword",
 341         token::DocComment(..) => "doc comment",
 342         _ => return None,
 343     })
 344 }
 345
 346 pub(super) fn token_descr(token: &Token) -> String {
 347     let token_str = pprust::token_to_string(token);
 348     match token_descr_opt(token) {
 349         Some(prefix) => format!("{} `{}`", prefix, token_str),
 350         _ => format!("`{}`", token_str),
 351     }
 352 }
 353
 354 impl<'a> Parser<'a> {
 355     pub fn new(
 356         sess: &'a ParseSess,
 357         tokens: TokenStream,
 358         desugar_doc_comments: bool,
 359         subparser_name: Option<&'static str>,
 360     ) -> Self {
 361         let mut parser = Parser {
 362             sess,
 363             token: Token::dummy(),
 364             token_spacing: Spacing::Alone,
 365             prev_token: Token::dummy(),
 366             restrictions: Restrictions::empty(),
 367             expected_tokens: Vec::new(),
 368             token_cursor: TokenCursor {
 369                 frame: TokenCursorFrame::new(DelimSpan::dummy(), token::NoDelim, tokens),
 370                 stack: Vec::new(),
 371                 num_next_calls: 0,
 372                 desugar_doc_comments,
 373                 append_unglued_token: None,
 374             },
 375             desugar_doc_comments,
 376             unmatched_angle_bracket_count: 0,
 377             max_angle_bracket_count: 0,
 378             unclosed_delims: Vec::new(),
 379             last_unexpected_token_span: None,
 380             last_type_ascription: None,
 381             subparser_name,
 382         };
 383
 384         // Make parser point to the first token.
 385         parser.bump();
 386
 387         parser
 388     }
 389
 390     fn next_tok(&mut self, fallback_span: Span) -> (Token, Spacing) {
 391         let (mut next, spacing) = if self.desugar_doc_comments {
 392             self.token_cursor.next_desugared()
 393         } else {
 394             self.token_cursor.next()
 395         };
 396         self.token_cursor.num_next_calls += 1;
 397         // We've retrieved an token from the underlying
 398         // cursor, so we no longer need to worry about
 399         // an unglued token. See `break_and_eat` for more details
 400         self.token_cursor.append_unglued_token = None;
 401         if next.span.is_dummy() {
 402             // Tweak the location for better diagnostics, but keep syntactic context intact.
 403             next.span = fallback_span.with_ctxt(next.span.ctxt());
 404         }
 405         (next, spacing)
 406     }
 407
 408     pub fn unexpected<T>(&mut self) -> PResult<'a, T> {
 409         match self.expect_one_of(&[], &[]) {
 410             Err(e) => Err(e),
 411             // We can get `Ok(true)` from `recover_closing_delimiter`
 412             // which is called in `expected_one_of_not_found`.
 413             Ok(_) => FatalError.raise(),
 414         }
 415     }
 416
 417     /// Expects and consumes the token `t`. Signals an error if the next token is not `t`.
 418     pub fn expect(&mut self, t: &TokenKind) -> PResult<'a, bool /* recovered */> {
 419         if self.expected_tokens.is_empty() {
 420             if self.token == *t {
 421                 self.bump();
 422                 Ok(false)
 423             } else {
 424                 self.unexpected_try_recover(t)
 425             }
 426         } else {
 427             self.expect_one_of(slice::from_ref(t), &[])
 428         }
 429     }
 430
 431     /// Expect next token to be edible or inedible token.  If edible,
 432     /// then consume it; if inedible, then return without consuming
 433     /// anything.  Signal a fatal error if next token is unexpected.
 434     pub fn expect_one_of(
 435         &mut self,
 436         edible: &[TokenKind],
 437         inedible: &[TokenKind],
 438     ) -> PResult<'a, bool /* recovered */> {
 439         if edible.contains(&self.token.kind) {
 440             self.bump();
 441             Ok(false)
 442         } else if inedible.contains(&self.token.kind) {
 443             // leave it in the input
 444             Ok(false)
 445         } else if self.last_unexpected_token_span == Some(self.token.span) {
 446             FatalError.raise();
 447         } else {
 448             self.expected_one_of_not_found(edible, inedible)
 449         }
 450     }
 451
 452     // Public for rustfmt usage.
 453     pub fn parse_ident(&mut self) -> PResult<'a, Ident> {
 454         self.parse_ident_common(true)
 455     }
 456
 457     fn parse_ident_common(&mut self, recover: bool) -> PResult<'a, Ident> {
 458         match self.token.ident() {
 459             Some((ident, is_raw)) => {
 460                 if !is_raw && ident.is_reserved() {
 461                     let mut err = self.expected_ident_found();
 462                     if recover {
 463                         err.emit();
 464                     } else {
 465                         return Err(err);
 466                     }
 467                 }
 468                 self.bump();
 469                 Ok(ident)
 470             }
 471             _ => Err(match self.prev_token.kind {
 472                 TokenKind::DocComment(..) => {
 473                     self.span_fatal_err(self.prev_token.span, Error::UselessDocComment)
 474                 }
 475                 _ => self.expected_ident_found(),
 476             }),
 477         }
 478     }
 479
 480     /// Checks if the next token is `tok`, and returns `true` if so.
 481     ///
 482     /// This method will automatically add `tok` to `expected_tokens` if `tok` is not
 483     /// encountered.
 484     fn check(&mut self, tok: &TokenKind) -> bool {
 485         let is_present = self.token == *tok;
 486         if !is_present {
 487             self.expected_tokens.push(TokenType::Token(tok.clone()));
 488         }
 489         is_present
 490     }
 491
 492     /// Consumes a token 'tok' if it exists. Returns whether the given token was present.
 493     pub fn eat(&mut self, tok: &TokenKind) -> bool {
 494         let is_present = self.check(tok);
 495         if is_present {
 496             self.bump()
 497         }
 498         is_present
 499     }
 500
 501     /// If the next token is the given keyword, returns `true` without eating it.
 502     /// An expectation is also added for diagnostics purposes.
 503     fn check_keyword(&mut self, kw: Symbol) -> bool {
 504         self.expected_tokens.push(TokenType::Keyword(kw));
 505         self.token.is_keyword(kw)
 506     }
 507
 508     /// If the next token is the given keyword, eats it and returns `true`.
 509     /// Otherwise, returns `false`. An expectation is also added for diagnostics purposes.
 510     // Public for rustfmt usage.
 511     pub fn eat_keyword(&mut self, kw: Symbol) -> bool {
 512         if self.check_keyword(kw) {
 513             self.bump();
 514             true
 515         } else {
 516             false
 517         }
 518     }
 519
 520     fn eat_keyword_noexpect(&mut self, kw: Symbol) -> bool {
 521         if self.token.is_keyword(kw) {
 522             self.bump();
 523             true
 524         } else {
 525             false
 526         }
 527     }
 528
 529     /// If the given word is not a keyword, signals an error.
 530     /// If the next token is not the given word, signals an error.
 531     /// Otherwise, eats it.
 532     fn expect_keyword(&mut self, kw: Symbol) -> PResult<'a, ()> {
 533         if !self.eat_keyword(kw) { self.unexpected() } else { Ok(()) }
 534     }
 535
 536     /// Is the given keyword `kw` followed by a non-reserved identifier?
 537     fn is_kw_followed_by_ident(&self, kw: Symbol) -> bool {
 538         self.token.is_keyword(kw) && self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident())
 539     }
 540
 541     fn check_or_expected(&mut self, ok: bool, typ: TokenType) -> bool {
 542         if ok {
 543             true
 544         } else {
 545             self.expected_tokens.push(typ);
 546             false
 547         }
 548     }
 549
 550     fn check_ident(&mut self) -> bool {
 551         self.check_or_expected(self.token.is_ident(), TokenType::Ident)
 552     }
 553
 554     fn check_path(&mut self) -> bool {
 555         self.check_or_expected(self.token.is_path_start(), TokenType::Path)
 556     }
 557
 558     fn check_type(&mut self) -> bool {
 559         self.check_or_expected(self.token.can_begin_type(), TokenType::Type)
 560     }
 561
 562     fn check_const_arg(&mut self) -> bool {
 563         self.check_or_expected(self.token.can_begin_const_arg(), TokenType::Const)
 564     }
 565
 566     fn check_inline_const(&self, dist: usize) -> bool {
 567         self.is_keyword_ahead(dist, &[kw::Const])
 568             && self.look_ahead(dist + 1, |t| match t.kind {
 569                 token::Interpolated(ref nt) => matches!(**nt, token::NtBlock(..)),
 570                 token::OpenDelim(DelimToken::Brace) => true,
 571                 _ => false,
 572             })
 573     }
 574
 575     /// Checks to see if the next token is either `+` or `+=`.
 576     /// Otherwise returns `false`.
 577     fn check_plus(&mut self) -> bool {
 578         self.check_or_expected(
 579             self.token.is_like_plus(),
 580             TokenType::Token(token::BinOp(token::Plus)),
 581         )
 582     }
 583
 584     /// Eats the expected token if it's present possibly breaking
 585     /// compound tokens like multi-character operators in process.
 586     /// Returns `true` if the token was eaten.
 587     fn break_and_eat(&mut self, expected: TokenKind) -> bool {
 588         if self.token.kind == expected {
 589             self.bump();
 590             return true;
 591         }
 592         match self.token.kind.break_two_token_op() {
 593             Some((first, second)) if first == expected => {
 594                 let first_span = self.sess.source_map().start_point(self.token.span);
 595                 let second_span = self.token.span.with_lo(first_span.hi());
 596                 self.token = Token::new(first, first_span);
 597                 // Keep track of this token - if we end token capturing now,
 598                 // we'll want to append this token to the captured stream.
 599                 //
 600                 // If we consume any additional tokens, then this token
 601                 // is not needed (we'll capture the entire 'glued' token),
 602                 // and `next_tok` will set this field to `None`
 603                 self.token_cursor.append_unglued_token =
 604                     Some((TokenTree::Token(self.token.clone()), Spacing::Alone));
 605                 // Use the spacing of the glued token as the spacing
 606                 // of the unglued second token.
 607                 self.bump_with((Token::new(second, second_span), self.token_spacing));
 608                 true
 609             }
 610             _ => {
 611                 self.expected_tokens.push(TokenType::Token(expected));
 612                 false
 613             }
 614         }
 615     }
 616
 617     /// Eats `+` possibly breaking tokens like `+=` in process.
 618     fn eat_plus(&mut self) -> bool {
 619         self.break_and_eat(token::BinOp(token::Plus))
 620     }
 621
 622     /// Eats `&` possibly breaking tokens like `&&` in process.
 623     /// Signals an error if `&` is not eaten.
 624     fn expect_and(&mut self) -> PResult<'a, ()> {
 625         if self.break_and_eat(token::BinOp(token::And)) { Ok(()) } else { self.unexpected() }
 626     }
 627
 628     /// Eats `|` possibly breaking tokens like `||` in process.
 629     /// Signals an error if `|` was not eaten.
 630     fn expect_or(&mut self) -> PResult<'a, ()> {
 631         if self.break_and_eat(token::BinOp(token::Or)) { Ok(()) } else { self.unexpected() }
 632     }
 633
 634     /// Eats `<` possibly breaking tokens like `<<` in process.
 635     fn eat_lt(&mut self) -> bool {
 636         let ate = self.break_and_eat(token::Lt);
 637         if ate {
 638             // See doc comment for `unmatched_angle_bracket_count`.
 639             self.unmatched_angle_bracket_count += 1;
 640             self.max_angle_bracket_count += 1;
 641             debug!("eat_lt: (increment) count={:?}", self.unmatched_angle_bracket_count);
 642         }
 643         ate
 644     }
 645
 646     /// Eats `<` possibly breaking tokens like `<<` in process.
 647     /// Signals an error if `<` was not eaten.
 648     fn expect_lt(&mut self) -> PResult<'a, ()> {
 649         if self.eat_lt() { Ok(()) } else { self.unexpected() }
 650     }
 651
 652     /// Eats `>` possibly breaking tokens like `>>` in process.
 653     /// Signals an error if `>` was not eaten.
 654     fn expect_gt(&mut self) -> PResult<'a, ()> {
 655         if self.break_and_eat(token::Gt) {
 656             // See doc comment for `unmatched_angle_bracket_count`.
 657             if self.unmatched_angle_bracket_count > 0 {
 658                 self.unmatched_angle_bracket_count -= 1;
 659                 debug!("expect_gt: (decrement) count={:?}", self.unmatched_angle_bracket_count);
 660             }
 661             Ok(())
 662         } else {
 663             self.unexpected()
 664         }
 665     }
 666
 667     fn expect_any_with_type(&mut self, kets: &[&TokenKind], expect: TokenExpectType) -> bool {
 668         kets.iter().any(|k| match expect {
 669             TokenExpectType::Expect => self.check(k),
 670             TokenExpectType::NoExpect => self.token == **k,
 671         })
 672     }
 673
 674     fn parse_seq_to_before_tokens<T>(
 675         &mut self,
 676         kets: &[&TokenKind],
 677         sep: SeqSep,
 678         expect: TokenExpectType,
 679         mut f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 680     ) -> PResult<'a, (Vec<T>, bool /* trailing */, bool /* recovered */)> {
 681         let mut first = true;
 682         let mut recovered = false;
 683         let mut trailing = false;
 684         let mut v = vec![];
 685         while !self.expect_any_with_type(kets, expect) {
 686             if let token::CloseDelim(..) | token::Eof = self.token.kind {
 687                 break;
 688             }
 689             if let Some(ref t) = sep.sep {
 690                 if first {
 691                     first = false;
 692                 } else {
 693                     match self.expect(t) {
 694                         Ok(false) => {}
 695                         Ok(true) => {
 696                             recovered = true;
 697                             break;
 698                         }
 699                         Err(mut expect_err) => {
 700                             let sp = self.prev_token.span.shrink_to_hi();
 701                             let token_str = pprust::token_kind_to_string(t);
 702
 703                             // Attempt to keep parsing if it was a similar separator.
 704                             if let Some(ref tokens) = t.similar_tokens() {
 705                                 if tokens.contains(&self.token.kind) {
 706                                     self.bump();
 707                                 }
 708                             }
 709
 710                             // If this was a missing `@` in a binding pattern
 711                             // bail with a suggestion
 712                             // https://github.com/rust-lang/rust/issues/72373
 713                             if self.prev_token.is_ident() && self.token.kind == token::DotDot {
 714                                 let msg = format!(
 715                                     "if you meant to bind the contents of \
 716                                     the rest of the array pattern into `{}`, use `@`",
 717                                     pprust::token_to_string(&self.prev_token)
 718                                 );
 719                                 expect_err
 720                                     .span_suggestion_verbose(
 721                                         self.prev_token.span.shrink_to_hi().until(self.token.span),
 722                                         &msg,
 723                                         " @ ".to_string(),
 724                                         Applicability::MaybeIncorrect,
 725                                     )
 726                                     .emit();
 727                                 break;
 728                             }
 729
 730                             // Attempt to keep parsing if it was an omitted separator.
 731                             match f(self) {
 732                                 Ok(t) => {
 733                                     // Parsed successfully, therefore most probably the code only
 734                                     // misses a separator.
 735                                     expect_err
 736                                         .span_suggestion_short(
 737                                             sp,
 738                                             &format!("missing `{}`", token_str),
 739                                             token_str,
 740                                             Applicability::MaybeIncorrect,
 741                                         )
 742                                         .emit();
 743
 744                                     v.push(t);
 745                                     continue;
 746                                 }
 747                                 Err(mut e) => {
 748                                     // Parsing failed, therefore it must be something more serious
 749                                     // than just a missing separator.
 750                                     expect_err.emit();
 751
 752                                     e.cancel();
 753                                     break;
 754                                 }
 755                             }
 756                         }
 757                     }
 758                 }
 759             }
 760             if sep.trailing_sep_allowed && self.expect_any_with_type(kets, expect) {
 761                 trailing = true;
 762                 break;
 763             }
 764
 765             let t = f(self)?;
 766             v.push(t);
 767         }
 768
 769         Ok((v, trailing, recovered))
 770     }
 771
 772     /// Parses a sequence, not including the closing delimiter. The function
 773     /// `f` must consume tokens until reaching the next separator or
 774     /// closing bracket.
 775     fn parse_seq_to_before_end<T>(
 776         &mut self,
 777         ket: &TokenKind,
 778         sep: SeqSep,
 779         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 780     ) -> PResult<'a, (Vec<T>, bool, bool)> {
 781         self.parse_seq_to_before_tokens(&[ket], sep, TokenExpectType::Expect, f)
 782     }
 783
 784     /// Parses a sequence, including the closing delimiter. The function
 785     /// `f` must consume tokens until reaching the next separator or
 786     /// closing bracket.
 787     fn parse_seq_to_end<T>(
 788         &mut self,
 789         ket: &TokenKind,
 790         sep: SeqSep,
 791         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 792     ) -> PResult<'a, (Vec<T>, bool /* trailing */)> {
 793         let (val, trailing, recovered) = self.parse_seq_to_before_end(ket, sep, f)?;
 794         if !recovered {
 795             self.eat(ket);
 796         }
 797         Ok((val, trailing))
 798     }
 799
 800     /// Parses a sequence, including the closing delimiter. The function
 801     /// `f` must consume tokens until reaching the next separator or
 802     /// closing bracket.
 803     fn parse_unspanned_seq<T>(
 804         &mut self,
 805         bra: &TokenKind,
 806         ket: &TokenKind,
 807         sep: SeqSep,
 808         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 809     ) -> PResult<'a, (Vec<T>, bool)> {
 810         self.expect(bra)?;
 811         self.parse_seq_to_end(ket, sep, f)
 812     }
 813
 814     fn parse_delim_comma_seq<T>(
 815         &mut self,
 816         delim: DelimToken,
 817         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 818     ) -> PResult<'a, (Vec<T>, bool)> {
 819         self.parse_unspanned_seq(
 820             &token::OpenDelim(delim),
 821             &token::CloseDelim(delim),
 822             SeqSep::trailing_allowed(token::Comma),
 823             f,
 824         )
 825     }
 826
 827     fn parse_paren_comma_seq<T>(
 828         &mut self,
 829         f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 830     ) -> PResult<'a, (Vec<T>, bool)> {
 831         self.parse_delim_comma_seq(token::Paren, f)
 832     }
 833
 834     /// Advance the parser by one token using provided token as the next one.
 835     fn bump_with(&mut self, (next_token, next_spacing): (Token, Spacing)) {
 836         // Bumping after EOF is a bad sign, usually an infinite loop.
 837         if self.prev_token.kind == TokenKind::Eof {
 838             let msg = "attempted to bump the parser past EOF (may be stuck in a loop)";
 839             self.span_bug(self.token.span, msg);
 840         }
 841
 842         // Update the current and previous tokens.
 843         self.prev_token = mem::replace(&mut self.token, next_token);
 844         self.token_spacing = next_spacing;
 845
 846         // Diagnostics.
 847         self.expected_tokens.clear();
 848     }
 849
 850     /// Advance the parser by one token.
 851     pub fn bump(&mut self) {
 852         let next_token = self.next_tok(self.token.span);
 853         self.bump_with(next_token);
 854     }
 855
 856     /// Look-ahead `dist` tokens of `self.token` and get access to that token there.
 857     /// When `dist == 0` then the current token is looked at.
 858     pub fn look_ahead<R>(&self, dist: usize, looker: impl FnOnce(&Token) -> R) -> R {
 859         if dist == 0 {
 860             return looker(&self.token);
 861         }
 862
 863         let frame = &self.token_cursor.frame;
 864         match frame.tree_cursor.look_ahead(dist - 1) {
 865             Some(tree) => match tree {
 866                 TokenTree::Token(token) => looker(token),
 867                 TokenTree::Delimited(dspan, delim, _) => {
 868                     looker(&Token::new(token::OpenDelim(*delim), dspan.open))
 869                 }
 870             },
 871             None => looker(&Token::new(token::CloseDelim(frame.delim), frame.span.close)),
 872         }
 873     }
 874
 875     /// Returns whether any of the given keywords are `dist` tokens ahead of the current one.
 876     fn is_keyword_ahead(&self, dist: usize, kws: &[Symbol]) -> bool {
 877         self.look_ahead(dist, |t| kws.iter().any(|&kw| t.is_keyword(kw)))
 878     }
 879
 880     /// Parses asyncness: `async` or nothing.
 881     fn parse_asyncness(&mut self) -> Async {
 882         if self.eat_keyword(kw::Async) {
 883             let span = self.prev_token.uninterpolated_span();
 884             Async::Yes { span, closure_id: DUMMY_NODE_ID, return_impl_trait_id: DUMMY_NODE_ID }
 885         } else {
 886             Async::No
 887         }
 888     }
 889
 890     /// Parses unsafety: `unsafe` or nothing.
 891     fn parse_unsafety(&mut self) -> Unsafe {
 892         if self.eat_keyword(kw::Unsafe) {
 893             Unsafe::Yes(self.prev_token.uninterpolated_span())
 894         } else {
 895             Unsafe::No
 896         }
 897     }
 898
 899     /// Parses constness: `const` or nothing.
 900     fn parse_constness(&mut self) -> Const {
 901         // Avoid const blocks to be parsed as const items
 902         if self.look_ahead(1, |t| t != &token::OpenDelim(DelimToken::Brace))
 903             && self.eat_keyword(kw::Const)
 904         {
 905             Const::Yes(self.prev_token.uninterpolated_span())
 906         } else {
 907             Const::No
 908         }
 909     }
 910
 911     /// Parses inline const expressions.
 912     fn parse_const_block(&mut self, span: Span) -> PResult<'a, P<Expr>> {
 913         self.sess.gated_spans.gate(sym::inline_const, span);
 914         self.eat_keyword(kw::Const);
 915         let blk = self.parse_block()?;
 916         let anon_const = AnonConst {
 917             id: DUMMY_NODE_ID,
 918             value: self.mk_expr(blk.span, ExprKind::Block(blk, None), AttrVec::new()),
 919         };
 920         let blk_span = anon_const.value.span;
 921         Ok(self.mk_expr(span.to(blk_span), ExprKind::ConstBlock(anon_const), AttrVec::new()))
 922     }
 923
 924     /// Parses mutability (`mut` or nothing).
 925     fn parse_mutability(&mut self) -> Mutability {
 926         if self.eat_keyword(kw::Mut) { Mutability::Mut } else { Mutability::Not }
 927     }
 928
 929     /// Possibly parses mutability (`const` or `mut`).
 930     fn parse_const_or_mut(&mut self) -> Option<Mutability> {
 931         if self.eat_keyword(kw::Mut) {
 932             Some(Mutability::Mut)
 933         } else if self.eat_keyword(kw::Const) {
 934             Some(Mutability::Not)
 935         } else {
 936             None
 937         }
 938     }
 939
 940     fn parse_field_name(&mut self) -> PResult<'a, Ident> {
 941         if let token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) = self.token.kind
 942         {
 943             self.expect_no_suffix(self.token.span, "a tuple index", suffix);
 944             self.bump();
 945             Ok(Ident::new(symbol, self.prev_token.span))
 946         } else {
 947             self.parse_ident_common(false)
 948         }
 949     }
 950
 951     fn parse_mac_args(&mut self) -> PResult<'a, P<MacArgs>> {
 952         self.parse_mac_args_common(true).map(P)
 953     }
 954
 955     fn parse_attr_args(&mut self) -> PResult<'a, MacArgs> {
 956         self.parse_mac_args_common(false)
 957     }
 958
 959     fn parse_mac_args_common(&mut self, delimited_only: bool) -> PResult<'a, MacArgs> {
 960         Ok(
 961             if self.check(&token::OpenDelim(DelimToken::Paren))
 962                 || self.check(&token::OpenDelim(DelimToken::Bracket))
 963                 || self.check(&token::OpenDelim(DelimToken::Brace))
 964             {
 965                 match self.parse_token_tree() {
 966                     TokenTree::Delimited(dspan, delim, tokens) =>
 967                     // We've confirmed above that there is a delimiter so unwrapping is OK.
 968                     {
 969                         MacArgs::Delimited(dspan, MacDelimiter::from_token(delim).unwrap(), tokens)
 970                     }
 971                     _ => unreachable!(),
 972                 }
 973             } else if !delimited_only {
 974                 if self.eat(&token::Eq) {
 975                     let eq_span = self.prev_token.span;
 976                     let mut is_interpolated_expr = false;
 977                     if let token::Interpolated(nt) = &self.token.kind {
 978                         if let token::NtExpr(..) = **nt {
 979                             is_interpolated_expr = true;
 980                         }
 981                     }
 982
 983                     // Collect tokens because they are used during lowering to HIR.
 984                     let expr = self.collect_tokens(|this| this.parse_expr())?;
 985                     let span = expr.span;
 986
 987                     match &expr.kind {
 988                         // Not gated to supporte things like `doc = $expr` that work on stable.
 989                         _ if is_interpolated_expr => {}
 990                         ExprKind::Lit(lit) if lit.kind.is_unsuffixed() => {}
 991                         _ => self.sess.gated_spans.gate(sym::extended_key_value_attributes, span),
 992                     }
 993
 994                     let token_kind = token::Interpolated(Lrc::new(token::NtExpr(expr)));
 995                     MacArgs::Eq(eq_span, Token::new(token_kind, span))
 996                 } else {
 997                     MacArgs::Empty
 998                 }
 999             } else {
1000                 return self.unexpected();
1001             },
1002         )
1003     }
1004
1005     fn parse_or_use_outer_attributes(
1006         &mut self,
1007         already_parsed_attrs: Option<AttrVec>,
1008     ) -> PResult<'a, AttrVec> {
1009         if let Some(attrs) = already_parsed_attrs {
1010             Ok(attrs)
1011         } else {
1012             self.parse_outer_attributes().map(|a| a.into())
1013         }
1014     }
1015
1016     /// Parses a single token tree from the input.
1017     pub(crate) fn parse_token_tree(&mut self) -> TokenTree {
1018         match self.token.kind {
1019             token::OpenDelim(..) => {
1020                 let depth = self.token_cursor.stack.len();
1021
1022                 // We keep advancing the token cursor until we hit
1023                 // the matching `CloseDelim` token.
1024                 while !(depth == self.token_cursor.stack.len()
1025                     && matches!(self.token.kind, token::CloseDelim(_)))
1026                 {
1027                     // Advance one token at a time, so `TokenCursor::next()`
1028                     // can capture these tokens if necessary.
1029                     self.bump();
1030                 }
1031                 // We are still inside the frame corresponding
1032                 // to the delimited stream we captured, so grab
1033                 // the tokens from this frame.
1034                 let frame = &self.token_cursor.frame;
1035                 let stream = frame.tree_cursor.stream.clone();
1036                 let span = frame.span;
1037                 let delim = frame.delim;
1038                 // Consume close delimiter
1039                 self.bump();
1040                 TokenTree::Delimited(span, delim, stream)
1041             }
1042             token::CloseDelim(_) | token::Eof => unreachable!(),
1043             _ => {
1044                 self.bump();
1045                 TokenTree::Token(self.prev_token.clone())
1046             }
1047         }
1048     }
1049
1050     /// Parses a stream of tokens into a list of `TokenTree`s, up to EOF.
1051     pub fn parse_all_token_trees(&mut self) -> PResult<'a, Vec<TokenTree>> {
1052         let mut tts = Vec::new();
1053         while self.token != token::Eof {
1054             tts.push(self.parse_token_tree());
1055         }
1056         Ok(tts)
1057     }
1058
1059     pub fn parse_tokens(&mut self) -> TokenStream {
1060         let mut result = Vec::new();
1061         loop {
1062             match self.token.kind {
1063                 token::Eof | token::CloseDelim(..) => break,
1064                 _ => result.push(self.parse_token_tree().into()),
1065             }
1066         }
1067         TokenStream::new(result)
1068     }
1069
1070     /// Evaluates the closure with restrictions in place.
1071     ///
1072     /// Afters the closure is evaluated, restrictions are reset.
1073     fn with_res<T>(&mut self, res: Restrictions, f: impl FnOnce(&mut Self) -> T) -> T {
1074         let old = self.restrictions;
1075         self.restrictions = res;
1076         let res = f(self);
1077         self.restrictions = old;
1078         res
1079     }
1080
1081     fn is_crate_vis(&self) -> bool {
1082         self.token.is_keyword(kw::Crate) && self.look_ahead(1, |t| t != &token::ModSep)
1083     }
1084
1085     /// Parses `pub`, `pub(crate)` and `pub(in path)` plus shortcuts `crate` for `pub(crate)`,
1086     /// `pub(self)` for `pub(in self)` and `pub(super)` for `pub(in super)`.
1087     /// If the following element can't be a tuple (i.e., it's a function definition), then
1088     /// it's not a tuple struct field), and the contents within the parentheses isn't valid,
1089     /// so emit a proper diagnostic.
1090     // Public for rustfmt usage.
1091     pub fn parse_visibility(&mut self, fbt: FollowedByType) -> PResult<'a, Visibility> {
1092         maybe_whole!(self, NtVis, |x| x);
1093
1094         self.expected_tokens.push(TokenType::Keyword(kw::Crate));
1095         if self.is_crate_vis() {
1096             self.bump(); // `crate`
1097             self.sess.gated_spans.gate(sym::crate_visibility_modifier, self.prev_token.span);
1098             return Ok(Visibility {
1099                 span: self.prev_token.span,
1100                 kind: VisibilityKind::Crate(CrateSugar::JustCrate),
1101                 tokens: None,
1102             });
1103         }
1104
1105         if !self.eat_keyword(kw::Pub) {
1106             // We need a span for our `Spanned<VisibilityKind>`, but there's inherently no
1107             // keyword to grab a span from for inherited visibility; an empty span at the
1108             // beginning of the current token would seem to be the "Schelling span".
1109             return Ok(Visibility {
1110                 span: self.token.span.shrink_to_lo(),
1111                 kind: VisibilityKind::Inherited,
1112                 tokens: None,
1113             });
1114         }
1115         let lo = self.prev_token.span;
1116
1117         if self.check(&token::OpenDelim(token::Paren)) {
1118             // We don't `self.bump()` the `(` yet because this might be a struct definition where
1119             // `()` or a tuple might be allowed. For example, `struct Struct(pub (), pub (usize));`.
1120             // Because of this, we only `bump` the `(` if we're assured it is appropriate to do so
1121             // by the following tokens.
1122             if self.is_keyword_ahead(1, &[kw::Crate]) && self.look_ahead(2, |t| t != &token::ModSep)
1123             // account for `pub(crate::foo)`
1124             {
1125                 // Parse `pub(crate)`.
1126                 self.bump(); // `(`
1127                 self.bump(); // `crate`
1128                 self.expect(&token::CloseDelim(token::Paren))?; // `)`
1129                 let vis = VisibilityKind::Crate(CrateSugar::PubCrate);
1130                 return Ok(Visibility {
1131                     span: lo.to(self.prev_token.span),
1132                     kind: vis,
1133                     tokens: None,
1134                 });
1135             } else if self.is_keyword_ahead(1, &[kw::In]) {
1136                 // Parse `pub(in path)`.
1137                 self.bump(); // `(`
1138                 self.bump(); // `in`
1139                 let path = self.parse_path(PathStyle::Mod)?; // `path`
1140                 self.expect(&token::CloseDelim(token::Paren))?; // `)`
1141                 let vis = VisibilityKind::Restricted { path: P(path), id: ast::DUMMY_NODE_ID };
1142                 return Ok(Visibility {
1143                     span: lo.to(self.prev_token.span),
1144                     kind: vis,
1145                     tokens: None,
1146                 });
1147             } else if self.look_ahead(2, |t| t == &token::CloseDelim(token::Paren))
1148                 && self.is_keyword_ahead(1, &[kw::Super, kw::SelfLower])
1149             {
1150                 // Parse `pub(self)` or `pub(super)`.
1151                 self.bump(); // `(`
1152                 let path = self.parse_path(PathStyle::Mod)?; // `super`/`self`
1153                 self.expect(&token::CloseDelim(token::Paren))?; // `)`
1154                 let vis = VisibilityKind::Restricted { path: P(path), id: ast::DUMMY_NODE_ID };
1155                 return Ok(Visibility {
1156                     span: lo.to(self.prev_token.span),
1157                     kind: vis,
1158                     tokens: None,
1159                 });
1160             } else if let FollowedByType::No = fbt {
1161                 // Provide this diagnostic if a type cannot follow;
1162                 // in particular, if this is not a tuple struct.
1163                 self.recover_incorrect_vis_restriction()?;
1164                 // Emit diagnostic, but continue with public visibility.
1165             }
1166         }
1167
1168         Ok(Visibility { span: lo, kind: VisibilityKind::Public, tokens: None })
1169     }
1170
1171     /// Recovery for e.g. `pub(something) fn ...` or `struct X { pub(something) y: Z }`
1172     fn recover_incorrect_vis_restriction(&mut self) -> PResult<'a, ()> {
1173         self.bump(); // `(`
1174         let path = self.parse_path(PathStyle::Mod)?;
1175         self.expect(&token::CloseDelim(token::Paren))?; // `)`
1176
1177         let msg = "incorrect visibility restriction";
1178         let suggestion = r##"some possible visibility restrictions are:
1179 `pub(crate)`: visible only on the current crate
1180 `pub(super)`: visible only in the current module's parent
1181 `pub(in path::to::module)`: visible only on the specified path"##;
1182
1183         let path_str = pprust::path_to_string(&path);
1184
1185         struct_span_err!(self.sess.span_diagnostic, path.span, E0704, "{}", msg)
1186             .help(suggestion)
1187             .span_suggestion(
1188                 path.span,
1189                 &format!("make this visible only to module `{}` with `in`", path_str),
1190                 format!("in {}", path_str),
1191                 Applicability::MachineApplicable,
1192             )
1193             .emit();
1194
1195         Ok(())
1196     }
1197
1198     /// Parses `extern string_literal?`.
1199     fn parse_extern(&mut self) -> PResult<'a, Extern> {
1200         Ok(if self.eat_keyword(kw::Extern) {
1201             Extern::from_abi(self.parse_abi())
1202         } else {
1203             Extern::None
1204         })
1205     }
1206
1207     /// Parses a string literal as an ABI spec.
1208     fn parse_abi(&mut self) -> Option<StrLit> {
1209         match self.parse_str_lit() {
1210             Ok(str_lit) => Some(str_lit),
1211             Err(Some(lit)) => match lit.kind {
1212                 ast::LitKind::Err(_) => None,
1213                 _ => {
1214                     self.struct_span_err(lit.span, "non-string ABI literal")
1215                         .span_suggestion(
1216                             lit.span,
1217                             "specify the ABI with a string literal",
1218                             "\"C\"".to_string(),
1219                             Applicability::MaybeIncorrect,
1220                         )
1221                         .emit();
1222                     None
1223                 }
1224             },
1225             Err(None) => None,
1226         }
1227     }
1228
1229     pub fn collect_tokens<R: HasTokens>(
1230         &mut self,
1231         f: impl FnOnce(&mut Self) -> PResult<'a, R>,
1232     ) -> PResult<'a, R> {
1233         self.collect_tokens_trailing_token(|this| Ok((f(this)?, TrailingToken::None)))
1234     }
1235
1236     /// Records all tokens consumed by the provided callback,
1237     /// including the current token. These tokens are collected
1238     /// into a `LazyTokenStream`, and returned along with the result
1239     /// of the callback.
1240     ///
1241     /// Note: If your callback consumes an opening delimiter
1242     /// (including the case where you call `collect_tokens`
1243     /// when the current token is an opening delimeter),
1244     /// you must also consume the corresponding closing delimiter.
1245     ///
1246     /// That is, you can consume
1247     /// `something ([{ }])` or `([{}])`, but not `([{}]`
1248     ///
1249     /// This restriction shouldn't be an issue in practice,
1250     /// since this function is used to record the tokens for
1251     /// a parsed AST item, which always has matching delimiters.
1252     pub fn collect_tokens_trailing_token<R: HasTokens>(
1253         &mut self,
1254         f: impl FnOnce(&mut Self) -> PResult<'a, (R, TrailingToken)>,
1255     ) -> PResult<'a, R> {
1256         let start_token = (self.token.clone(), self.token_spacing);
1257         let cursor_snapshot = self.token_cursor.clone();
1258
1259         let (mut ret, trailing_token) = f(self)?;
1260
1261         // Produces a `TokenStream` on-demand. Using `cursor_snapshot`
1262         // and `num_calls`, we can reconstruct the `TokenStream` seen
1263         // by the callback. This allows us to avoid producing a `TokenStream`
1264         // if it is never needed - for example, a captured `macro_rules!`
1265         // argument that is never passed to a proc macro.
1266         // In practice token stream creation happens rarely compared to
1267         // calls to `collect_tokens` (see some statistics in #78736),
1268         // so we are doing as little up-front work as possible.
1269         //
1270         // This also makes `Parser` very cheap to clone, since
1271         // there is no intermediate collection buffer to clone.
1272         #[derive(Clone)]
1273         struct LazyTokenStreamImpl {
1274             start_token: (Token, Spacing),
1275             cursor_snapshot: TokenCursor,
1276             num_calls: usize,
1277             desugar_doc_comments: bool,
1278             append_unglued_token: Option<TreeAndSpacing>,
1279         }
1280         impl CreateTokenStream for LazyTokenStreamImpl {
1281             fn create_token_stream(&self) -> TokenStream {
1282                 // The token produced by the final call to `next` or `next_desugared`
1283                 // was not actually consumed by the callback. The combination
1284                 // of chaining the initial token and using `take` produces the desired
1285                 // result - we produce an empty `TokenStream` if no calls were made,
1286                 // and omit the final token otherwise.
1287                 let mut cursor_snapshot = self.cursor_snapshot.clone();
1288                 let tokens = std::iter::once(self.start_token.clone())
1289                     .chain((0..self.num_calls).map(|_| {
1290                         if self.desugar_doc_comments {
1291                             cursor_snapshot.next_desugared()
1292                         } else {
1293                             cursor_snapshot.next()
1294                         }
1295                     }))
1296                     .take(self.num_calls);
1297
1298                 make_token_stream(tokens, self.append_unglued_token.clone())
1299             }
1300         }
1301
1302         let mut num_calls = self.token_cursor.num_next_calls - cursor_snapshot.num_next_calls;
1303         match trailing_token {
1304             TrailingToken::None => {}
1305             TrailingToken::Semi => {
1306                 assert_eq!(self.token.kind, token::Semi);
1307                 num_calls += 1;
1308             }
1309         }
1310
1311         let lazy_impl = LazyTokenStreamImpl {
1312             start_token,
1313             num_calls,
1314             cursor_snapshot,
1315             desugar_doc_comments: self.desugar_doc_comments,
1316             append_unglued_token: self.token_cursor.append_unglued_token.clone(),
1317         };
1318         ret.finalize_tokens(LazyTokenStream::new(lazy_impl));
1319         Ok(ret)
1320     }
1321
1322     /// `::{` or `::*`
1323     fn is_import_coupler(&mut self) -> bool {
1324         self.check(&token::ModSep)
1325             && self.look_ahead(1, |t| {
1326                 *t == token::OpenDelim(token::Brace) || *t == token::BinOp(token::Star)
1327             })
1328     }
1329
1330     pub fn clear_expected_tokens(&mut self) {
1331         self.expected_tokens.clear();
1332     }
1333 }
1334
1335 crate fn make_unclosed_delims_error(
1336     unmatched: UnmatchedBrace,
1337     sess: &ParseSess,
1338 ) -> Option<DiagnosticBuilder<'_>> {
1339     // `None` here means an `Eof` was found. We already emit those errors elsewhere, we add them to
1340     // `unmatched_braces` only for error recovery in the `Parser`.
1341     let found_delim = unmatched.found_delim?;
1342     let mut err = sess.span_diagnostic.struct_span_err(
1343         unmatched.found_span,
1344         &format!(
1345             "mismatched closing delimiter: `{}`",
1346             pprust::token_kind_to_string(&token::CloseDelim(found_delim)),
1347         ),
1348     );
1349     err.span_label(unmatched.found_span, "mismatched closing delimiter");
1350     if let Some(sp) = unmatched.candidate_span {
1351         err.span_label(sp, "closing delimiter possibly meant for this");
1352     }
1353     if let Some(sp) = unmatched.unclosed_span {
1354         err.span_label(sp, "unclosed delimiter");
1355     }
1356     Some(err)
1357 }
1358
1359 pub fn emit_unclosed_delims(unclosed_delims: &mut Vec<UnmatchedBrace>, sess: &ParseSess) {
1360     *sess.reached_eof.borrow_mut() |=
1361         unclosed_delims.iter().any(|unmatched_delim| unmatched_delim.found_delim.is_none());
1362     for unmatched in unclosed_delims.drain(..) {
1363         if let Some(mut e) = make_unclosed_delims_error(unmatched, sess) {
1364             e.emit();
1365         }
1366     }
1367 }
1368
1369 /// Converts a flattened iterator of tokens (including open and close delimiter tokens)
1370 /// into a `TokenStream`, creating a `TokenTree::Delimited` for each matching pair
1371 /// of open and close delims.
1372 fn make_token_stream(
1373     tokens: impl Iterator<Item = (Token, Spacing)>,
1374     append_unglued_token: Option<TreeAndSpacing>,
1375 ) -> TokenStream {
1376     #[derive(Debug)]
1377     struct FrameData {
1378         open: Span,
1379         inner: Vec<(TokenTree, Spacing)>,
1380     }
1381     let mut stack = vec![FrameData { open: DUMMY_SP, inner: vec![] }];
1382     for (token, spacing) in tokens {
1383         match token {
1384             Token { kind: TokenKind::OpenDelim(_), span } => {
1385                 stack.push(FrameData { open: span, inner: vec![] });
1386             }
1387             Token { kind: TokenKind::CloseDelim(delim), span } => {
1388                 let frame_data = stack.pop().expect("Token stack was empty!");
1389                 let dspan = DelimSpan::from_pair(frame_data.open, span);
1390                 let stream = TokenStream::new(frame_data.inner);
1391                 let delimited = TokenTree::Delimited(dspan, delim, stream);
1392                 stack
1393                     .last_mut()
1394                     .unwrap_or_else(|| panic!("Bottom token frame is missing for tokens!"))
1395                     .inner
1396                     .push((delimited, Spacing::Alone));
1397             }
1398             token => {
1399                 stack
1400                     .last_mut()
1401                     .expect("Bottom token frame is missing!")
1402                     .inner
1403                     .push((TokenTree::Token(token), spacing));
1404             }
1405         }
1406     }
1407     let mut final_buf = stack.pop().expect("Missing final buf!");
1408     final_buf.inner.extend(append_unglued_token);
1409     assert!(stack.is_empty(), "Stack should be empty: final_buf={:?} stack={:?}", final_buf, stack);
1410     TokenStream::new(final_buf.inner)
1411 }
1412
1413 #[macro_export]
1414 macro_rules! maybe_collect_tokens {
1415     ($self:ident, $force_collect:expr, $attrs:expr, $f:expr) => {
1416         if matches!($force_collect, ForceCollect::Yes)
1417             || $crate::parser::attr::maybe_needs_tokens($attrs)
1418         {
1419             $self.collect_tokens_trailing_token($f)
1420         } else {
1421             Ok($f($self)?.0)
1422         }
1423     };
1424 }