compiler/rustc_parse/src/parser/diagnostics.rs

   1 use super::pat::Expected;
   2 use super::{
   3     BlockMode, CommaRecoveryMode, Parser, PathStyle, Restrictions, SemiColonMode, SeqSep,
   4     TokenExpectType, TokenType,
   5 };
   6
   7 use crate::lexer::UnmatchedBrace;
   8 use rustc_ast as ast;
   9 use rustc_ast::ptr::P;
  10 use rustc_ast::token::{self, Delimiter, Lit, LitKind, TokenKind};
  11 use rustc_ast::util::parser::AssocOp;
  12 use rustc_ast::{
  13     AngleBracketedArg, AngleBracketedArgs, AnonConst, AttrVec, BinOpKind, BindingMode, Block,
  14     BlockCheckMode, Expr, ExprKind, GenericArg, Generics, Item, ItemKind, Mutability, Param, Pat,
  15     PatKind, Path, PathSegment, QSelf, Ty, TyKind,
  16 };
  17 use rustc_ast_pretty::pprust;
  18 use rustc_data_structures::fx::FxHashSet;
  19 use rustc_errors::{
  20     fluent, Applicability, DiagnosticBuilder, DiagnosticMessage, Handler, MultiSpan, PResult,
  21 };
  22 use rustc_errors::{pluralize, struct_span_err, Diagnostic, EmissionGuarantee, ErrorGuaranteed};
  23 use rustc_macros::{SessionDiagnostic, SessionSubdiagnostic};
  24 use rustc_span::source_map::Spanned;
  25 use rustc_span::symbol::{kw, Ident};
  26 use rustc_span::{Span, SpanSnippetError, DUMMY_SP};
  27 use std::ops::{Deref, DerefMut};
  28
  29 use std::mem::take;
  30
  31 use crate::parser;
  32 use tracing::{debug, trace};
  33
  34 const TURBOFISH_SUGGESTION_STR: &str =
  35     "use `::<...>` instead of `<...>` to specify lifetime, type, or const arguments";
  36
  37 /// Creates a placeholder argument.
  38 pub(super) fn dummy_arg(ident: Ident) -> Param {
  39     let pat = P(Pat {
  40         id: ast::DUMMY_NODE_ID,
  41         kind: PatKind::Ident(BindingMode::ByValue(Mutability::Not), ident, None),
  42         span: ident.span,
  43         tokens: None,
  44     });
  45     let ty = Ty { kind: TyKind::Err, span: ident.span, id: ast::DUMMY_NODE_ID, tokens: None };
  46     Param {
  47         attrs: AttrVec::default(),
  48         id: ast::DUMMY_NODE_ID,
  49         pat,
  50         span: ident.span,
  51         ty: P(ty),
  52         is_placeholder: false,
  53     }
  54 }
  55
  56 pub enum Error {
  57     UselessDocComment,
  58 }
  59
  60 impl Error {
  61     fn span_err(
  62         self,
  63         sp: impl Into<MultiSpan>,
  64         handler: &Handler,
  65     ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
  66         match self {
  67             Error::UselessDocComment => {
  68                 let mut err = struct_span_err!(
  69                     handler,
  70                     sp,
  71                     E0585,
  72                     "found a documentation comment that doesn't document anything",
  73                 );
  74                 err.help(
  75                     "doc comments must come before what they document, maybe a comment was \
  76                           intended with `//`?",
  77                 );
  78                 err
  79             }
  80         }
  81     }
  82 }
  83
  84 pub(super) trait RecoverQPath: Sized + 'static {
  85     const PATH_STYLE: PathStyle = PathStyle::Expr;
  86     fn to_ty(&self) -> Option<P<Ty>>;
  87     fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self;
  88 }
  89
  90 impl RecoverQPath for Ty {
  91     const PATH_STYLE: PathStyle = PathStyle::Type;
  92     fn to_ty(&self) -> Option<P<Ty>> {
  93         Some(P(self.clone()))
  94     }
  95     fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
  96         Self {
  97             span: path.span,
  98             kind: TyKind::Path(qself, path),
  99             id: ast::DUMMY_NODE_ID,
 100             tokens: None,
 101         }
 102     }
 103 }
 104
 105 impl RecoverQPath for Pat {
 106     fn to_ty(&self) -> Option<P<Ty>> {
 107         self.to_ty()
 108     }
 109     fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
 110         Self {
 111             span: path.span,
 112             kind: PatKind::Path(qself, path),
 113             id: ast::DUMMY_NODE_ID,
 114             tokens: None,
 115         }
 116     }
 117 }
 118
 119 impl RecoverQPath for Expr {
 120     fn to_ty(&self) -> Option<P<Ty>> {
 121         self.to_ty()
 122     }
 123     fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
 124         Self {
 125             span: path.span,
 126             kind: ExprKind::Path(qself, path),
 127             attrs: AttrVec::new(),
 128             id: ast::DUMMY_NODE_ID,
 129             tokens: None,
 130         }
 131     }
 132 }
 133
 134 /// Control whether the closing delimiter should be consumed when calling `Parser::consume_block`.
 135 pub(crate) enum ConsumeClosingDelim {
 136     Yes,
 137     No,
 138 }
 139
 140 #[derive(Clone, Copy)]
 141 pub enum AttemptLocalParseRecovery {
 142     Yes,
 143     No,
 144 }
 145
 146 impl AttemptLocalParseRecovery {
 147     pub fn yes(&self) -> bool {
 148         match self {
 149             AttemptLocalParseRecovery::Yes => true,
 150             AttemptLocalParseRecovery::No => false,
 151         }
 152     }
 153
 154     pub fn no(&self) -> bool {
 155         match self {
 156             AttemptLocalParseRecovery::Yes => false,
 157             AttemptLocalParseRecovery::No => true,
 158         }
 159     }
 160 }
 161
 162 /// Information for emitting suggestions and recovering from
 163 /// C-style `i++`, `--i`, etc.
 164 #[derive(Debug, Copy, Clone)]
 165 struct IncDecRecovery {
 166     /// Is this increment/decrement its own statement?
 167     standalone: IsStandalone,
 168     /// Is this an increment or decrement?
 169     op: IncOrDec,
 170     /// Is this pre- or postfix?
 171     fixity: UnaryFixity,
 172 }
 173
 174 /// Is an increment or decrement expression its own statement?
 175 #[derive(Debug, Copy, Clone)]
 176 enum IsStandalone {
 177     /// It's standalone, i.e., its own statement.
 178     Standalone,
 179     /// It's a subexpression, i.e., *not* standalone.
 180     Subexpr,
 181     /// It's maybe standalone; we're not sure.
 182     Maybe,
 183 }
 184
 185 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 186 enum IncOrDec {
 187     Inc,
 188     // FIXME: `i--` recovery isn't implemented yet
 189     #[allow(dead_code)]
 190     Dec,
 191 }
 192
 193 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 194 enum UnaryFixity {
 195     Pre,
 196     Post,
 197 }
 198
 199 impl IncOrDec {
 200     fn chr(&self) -> char {
 201         match self {
 202             Self::Inc => '+',
 203             Self::Dec => '-',
 204         }
 205     }
 206
 207     fn name(&self) -> &'static str {
 208         match self {
 209             Self::Inc => "increment",
 210             Self::Dec => "decrement",
 211         }
 212     }
 213 }
 214
 215 impl std::fmt::Display for UnaryFixity {
 216     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
 217         match self {
 218             Self::Pre => write!(f, "prefix"),
 219             Self::Post => write!(f, "postfix"),
 220         }
 221     }
 222 }
 223
 224 struct MultiSugg {
 225     msg: String,
 226     patches: Vec<(Span, String)>,
 227     applicability: Applicability,
 228 }
 229
 230 impl MultiSugg {
 231     fn emit<G: EmissionGuarantee>(self, err: &mut DiagnosticBuilder<'_, G>) {
 232         err.multipart_suggestion(&self.msg, self.patches, self.applicability);
 233     }
 234
 235     /// Overrides individual messages and applicabilities.
 236     fn emit_many<G: EmissionGuarantee>(
 237         err: &mut DiagnosticBuilder<'_, G>,
 238         msg: &str,
 239         applicability: Applicability,
 240         suggestions: impl Iterator<Item = Self>,
 241     ) {
 242         err.multipart_suggestions(msg, suggestions.map(|s| s.patches), applicability);
 243     }
 244 }
 245
 246 #[derive(SessionDiagnostic)]
 247 #[error(parser::maybe_report_ambiguous_plus)]
 248 struct AmbiguousPlus {
 249     pub sum_ty: String,
 250     #[primary_span]
 251     #[suggestion(code = "({sum_ty})")]
 252     pub span: Span,
 253 }
 254
 255 #[derive(SessionDiagnostic)]
 256 #[error(parser::maybe_recover_from_bad_type_plus, code = "E0178")]
 257 struct BadTypePlus {
 258     pub ty: String,
 259     #[primary_span]
 260     pub span: Span,
 261     #[subdiagnostic]
 262     pub sub: BadTypePlusSub,
 263 }
 264
 265 #[derive(SessionSubdiagnostic)]
 266 pub enum BadTypePlusSub {
 267     #[suggestion(
 268         parser::add_paren,
 269         code = "{sum_with_parens}",
 270         applicability = "machine-applicable"
 271     )]
 272     AddParen {
 273         sum_with_parens: String,
 274         #[primary_span]
 275         span: Span,
 276     },
 277     #[label(parser::forgot_paren)]
 278     ForgotParen {
 279         #[primary_span]
 280         span: Span,
 281     },
 282     #[label(parser::expect_path)]
 283     ExpectPath {
 284         #[primary_span]
 285         span: Span,
 286     },
 287 }
 288
 289 #[derive(SessionDiagnostic)]
 290 #[error(parser::maybe_recover_from_bad_qpath_stage_2)]
 291 struct BadQPathStage2 {
 292     #[primary_span]
 293     #[suggestion(applicability = "maybe-incorrect")]
 294     span: Span,
 295     ty: String,
 296 }
 297
 298 #[derive(SessionDiagnostic)]
 299 #[error(parser::incorrect_semicolon)]
 300 struct IncorrectSemicolon<'a> {
 301     #[primary_span]
 302     #[suggestion_short(applicability = "machine-applicable")]
 303     span: Span,
 304     #[help]
 305     opt_help: Option<()>,
 306     name: &'a str,
 307 }
 308
 309 #[derive(SessionDiagnostic)]
 310 #[error(parser::incorrect_use_of_await)]
 311 struct IncorrectUseOfAwait {
 312     #[primary_span]
 313     #[suggestion(parser::parentheses_suggestion, applicability = "machine-applicable")]
 314     span: Span,
 315 }
 316
 317 #[derive(SessionDiagnostic)]
 318 #[error(parser::incorrect_use_of_await)]
 319 struct IncorrectAwait {
 320     #[primary_span]
 321     span: Span,
 322     #[suggestion(parser::postfix_suggestion, code = "{expr}.await{question_mark}")]
 323     sugg_span: (Span, Applicability),
 324     expr: String,
 325     question_mark: &'static str,
 326 }
 327
 328 #[derive(SessionDiagnostic)]
 329 #[error(parser::in_in_typo)]
 330 struct InInTypo {
 331     #[primary_span]
 332     span: Span,
 333     #[suggestion(applicability = "machine-applicable")]
 334     sugg_span: Span,
 335 }
 336
 337 // SnapshotParser is used to create a snapshot of the parser
 338 // without causing duplicate errors being emitted when the `Parser`
 339 // is dropped.
 340 pub struct SnapshotParser<'a> {
 341     parser: Parser<'a>,
 342     unclosed_delims: Vec<UnmatchedBrace>,
 343 }
 344
 345 impl<'a> Deref for SnapshotParser<'a> {
 346     type Target = Parser<'a>;
 347
 348     fn deref(&self) -> &Self::Target {
 349         &self.parser
 350     }
 351 }
 352
 353 impl<'a> DerefMut for SnapshotParser<'a> {
 354     fn deref_mut(&mut self) -> &mut Self::Target {
 355         &mut self.parser
 356     }
 357 }
 358
 359 impl<'a> Parser<'a> {
 360     pub(super) fn span_err<S: Into<MultiSpan>>(
 361         &self,
 362         sp: S,
 363         err: Error,
 364     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 365         err.span_err(sp, self.diagnostic())
 366     }
 367
 368     pub fn struct_span_err<S: Into<MultiSpan>>(
 369         &self,
 370         sp: S,
 371         m: impl Into<DiagnosticMessage>,
 372     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 373         self.sess.span_diagnostic.struct_span_err(sp, m)
 374     }
 375
 376     pub fn span_bug<S: Into<MultiSpan>>(&self, sp: S, m: impl Into<DiagnosticMessage>) -> ! {
 377         self.sess.span_diagnostic.span_bug(sp, m)
 378     }
 379
 380     pub(super) fn diagnostic(&self) -> &'a Handler {
 381         &self.sess.span_diagnostic
 382     }
 383
 384     /// Replace `self` with `snapshot.parser` and extend `unclosed_delims` with `snapshot.unclosed_delims`.
 385     /// This is to avoid losing unclosed delims errors `create_snapshot_for_diagnostic` clears.
 386     pub(super) fn restore_snapshot(&mut self, snapshot: SnapshotParser<'a>) {
 387         *self = snapshot.parser;
 388         self.unclosed_delims.extend(snapshot.unclosed_delims.clone());
 389     }
 390
 391     pub fn unclosed_delims(&self) -> &[UnmatchedBrace] {
 392         &self.unclosed_delims
 393     }
 394
 395     /// Create a snapshot of the `Parser`.
 396     pub fn create_snapshot_for_diagnostic(&self) -> SnapshotParser<'a> {
 397         let mut snapshot = self.clone();
 398         let unclosed_delims = self.unclosed_delims.clone();
 399         // Clear `unclosed_delims` in snapshot to avoid
 400         // duplicate errors being emitted when the `Parser`
 401         // is dropped (which may or may not happen, depending
 402         // if the parsing the snapshot is created for is successful)
 403         snapshot.unclosed_delims.clear();
 404         SnapshotParser { parser: snapshot, unclosed_delims }
 405     }
 406
 407     pub(super) fn span_to_snippet(&self, span: Span) -> Result<String, SpanSnippetError> {
 408         self.sess.source_map().span_to_snippet(span)
 409     }
 410
 411     pub(super) fn expected_ident_found(&self) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
 412         let mut err = self.struct_span_err(
 413             self.token.span,
 414             &format!("expected identifier, found {}", super::token_descr(&self.token)),
 415         );
 416         let valid_follow = &[
 417             TokenKind::Eq,
 418             TokenKind::Colon,
 419             TokenKind::Comma,
 420             TokenKind::Semi,
 421             TokenKind::ModSep,
 422             TokenKind::OpenDelim(Delimiter::Brace),
 423             TokenKind::OpenDelim(Delimiter::Parenthesis),
 424             TokenKind::CloseDelim(Delimiter::Brace),
 425             TokenKind::CloseDelim(Delimiter::Parenthesis),
 426         ];
 427         match self.token.ident() {
 428             Some((ident, false))
 429                 if ident.is_raw_guess()
 430                     && self.look_ahead(1, |t| valid_follow.contains(&t.kind)) =>
 431             {
 432                 err.span_suggestion_verbose(
 433                     ident.span.shrink_to_lo(),
 434                     &format!("escape `{}` to use it as an identifier", ident.name),
 435                     "r#",
 436                     Applicability::MaybeIncorrect,
 437                 );
 438             }
 439             _ => {}
 440         }
 441         if let Some(token_descr) = super::token_descr_opt(&self.token) {
 442             err.span_label(self.token.span, format!("expected identifier, found {}", token_descr));
 443         } else {
 444             err.span_label(self.token.span, "expected identifier");
 445             if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
 446                 err.span_suggestion(
 447                     self.token.span,
 448                     "remove this comma",
 449                     "",
 450                     Applicability::MachineApplicable,
 451                 );
 452             }
 453         }
 454         err
 455     }
 456
 457     pub(super) fn expected_one_of_not_found(
 458         &mut self,
 459         edible: &[TokenKind],
 460         inedible: &[TokenKind],
 461     ) -> PResult<'a, bool /* recovered */> {
 462         debug!("expected_one_of_not_found(edible: {:?}, inedible: {:?})", edible, inedible);
 463         fn tokens_to_string(tokens: &[TokenType]) -> String {
 464             let mut i = tokens.iter();
 465             // This might be a sign we need a connect method on `Iterator`.
 466             let b = i.next().map_or_else(String::new, |t| t.to_string());
 467             i.enumerate().fold(b, |mut b, (i, a)| {
 468                 if tokens.len() > 2 && i == tokens.len() - 2 {
 469                     b.push_str(", or ");
 470                 } else if tokens.len() == 2 && i == tokens.len() - 2 {
 471                     b.push_str(" or ");
 472                 } else {
 473                     b.push_str(", ");
 474                 }
 475                 b.push_str(&a.to_string());
 476                 b
 477             })
 478         }
 479
 480         let mut expected = edible
 481             .iter()
 482             .map(|x| TokenType::Token(x.clone()))
 483             .chain(inedible.iter().map(|x| TokenType::Token(x.clone())))
 484             .chain(self.expected_tokens.iter().cloned())
 485             .filter_map(|token| {
 486                 // filter out suggestions which suggest the same token which was found and deemed incorrect
 487                 fn is_ident_eq_keyword(found: &TokenKind, expected: &TokenType) -> bool {
 488                     if let TokenKind::Ident(current_sym, _) = found {
 489                         if let TokenType::Keyword(suggested_sym) = expected {
 490                             return current_sym == suggested_sym;
 491                         }
 492                     }
 493                     false
 494                 }
 495                 if token != parser::TokenType::Token(self.token.kind.clone()) {
 496                     let eq = is_ident_eq_keyword(&self.token.kind, &token);
 497                     // if the suggestion is a keyword and the found token is an ident,
 498                     // the content of which are equal to the suggestion's content,
 499                     // we can remove that suggestion (see the return None statement below)
 500
 501                     // if this isn't the case however, and the suggestion is a token the
 502                     // content of which is the same as the found token's, we remove it as well
 503                     if !eq {
 504                         if let TokenType::Token(kind) = &token {
 505                             if kind == &self.token.kind {
 506                                 return None;
 507                             }
 508                         }
 509                         return Some(token);
 510                     }
 511                 }
 512                 return None;
 513             })
 514             .collect::<Vec<_>>();
 515         expected.sort_by_cached_key(|x| x.to_string());
 516         expected.dedup();
 517
 518         let sm = self.sess.source_map();
 519         let msg = format!("expected `;`, found {}", super::token_descr(&self.token));
 520         let appl = Applicability::MachineApplicable;
 521         if expected.contains(&TokenType::Token(token::Semi)) {
 522             if self.token.span == DUMMY_SP || self.prev_token.span == DUMMY_SP {
 523                 // Likely inside a macro, can't provide meaningful suggestions.
 524             } else if !sm.is_multiline(self.prev_token.span.until(self.token.span)) {
 525                 // The current token is in the same line as the prior token, not recoverable.
 526             } else if [token::Comma, token::Colon].contains(&self.token.kind)
 527                 && self.prev_token.kind == token::CloseDelim(Delimiter::Parenthesis)
 528             {
 529                 // Likely typo: The current token is on a new line and is expected to be
 530                 // `.`, `;`, `?`, or an operator after a close delimiter token.
 531                 //
 532                 // let a = std::process::Command::new("echo")
 533                 //         .arg("1")
 534                 //         ,arg("2")
 535                 //         ^
 536                 // https://github.com/rust-lang/rust/issues/72253
 537             } else if self.look_ahead(1, |t| {
 538                 t == &token::CloseDelim(Delimiter::Brace)
 539                     || t.can_begin_expr() && t.kind != token::Colon
 540             }) && [token::Comma, token::Colon].contains(&self.token.kind)
 541             {
 542                 // Likely typo: `,` → `;` or `:` → `;`. This is triggered if the current token is
 543                 // either `,` or `:`, and the next token could either start a new statement or is a
 544                 // block close. For example:
 545                 //
 546                 //   let x = 32:
 547                 //   let y = 42;
 548                 self.bump();
 549                 let sp = self.prev_token.span;
 550                 self.struct_span_err(sp, &msg)
 551                     .span_suggestion_short(sp, "change this to `;`", ";", appl)
 552                     .emit();
 553                 return Ok(true);
 554             } else if self.look_ahead(0, |t| {
 555                 t == &token::CloseDelim(Delimiter::Brace)
 556                     || (t.can_begin_expr() && t != &token::Semi && t != &token::Pound)
 557                     // Avoid triggering with too many trailing `#` in raw string.
 558                     || (sm.is_multiline(
 559                         self.prev_token.span.shrink_to_hi().until(self.token.span.shrink_to_lo())
 560                     ) && t == &token::Pound)
 561             }) {
 562                 // Missing semicolon typo. This is triggered if the next token could either start a
 563                 // new statement or is a block close. For example:
 564                 //
 565                 //   let x = 32
 566                 //   let y = 42;
 567                 let sp = self.prev_token.span.shrink_to_hi();
 568                 self.struct_span_err(sp, &msg)
 569                     .span_label(self.token.span, "unexpected token")
 570                     .span_suggestion_short(sp, "add `;` here", ";", appl)
 571                     .emit();
 572                 return Ok(true);
 573             }
 574         }
 575
 576         let expect = tokens_to_string(&expected);
 577         let actual = super::token_descr(&self.token);
 578         let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
 579             let short_expect = if expected.len() > 6 {
 580                 format!("{} possible tokens", expected.len())
 581             } else {
 582                 expect.clone()
 583             };
 584             (
 585                 format!("expected one of {expect}, found {actual}"),
 586                 (self.prev_token.span.shrink_to_hi(), format!("expected one of {short_expect}")),
 587             )
 588         } else if expected.is_empty() {
 589             (
 590                 format!("unexpected token: {}", actual),
 591                 (self.prev_token.span, "unexpected token after this".to_string()),
 592             )
 593         } else {
 594             (
 595                 format!("expected {expect}, found {actual}"),
 596                 (self.prev_token.span.shrink_to_hi(), format!("expected {expect}")),
 597             )
 598         };
 599         self.last_unexpected_token_span = Some(self.token.span);
 600         let mut err = self.struct_span_err(self.token.span, &msg_exp);
 601
 602         // Add suggestion for a missing closing angle bracket if '>' is included in expected_tokens
 603         // there are unclosed angle brackets
 604         if self.unmatched_angle_bracket_count > 0
 605             && self.token.kind == TokenKind::Eq
 606             && expected.iter().any(|tok| matches!(tok, TokenType::Token(TokenKind::Gt)))
 607         {
 608             err.span_label(self.prev_token.span, "maybe try to close unmatched angle bracket");
 609         }
 610
 611         let sp = if self.token == token::Eof {
 612             // This is EOF; don't want to point at the following char, but rather the last token.
 613             self.prev_token.span
 614         } else {
 615             label_sp
 616         };
 617         match self.recover_closing_delimiter(
 618             &expected
 619                 .iter()
 620                 .filter_map(|tt| match tt {
 621                     TokenType::Token(t) => Some(t.clone()),
 622                     _ => None,
 623                 })
 624                 .collect::<Vec<_>>(),
 625             err,
 626         ) {
 627             Err(e) => err = e,
 628             Ok(recovered) => {
 629                 return Ok(recovered);
 630             }
 631         }
 632
 633         if self.check_too_many_raw_str_terminators(&mut err) {
 634             if expected.contains(&TokenType::Token(token::Semi)) && self.eat(&token::Semi) {
 635                 err.emit();
 636                 return Ok(true);
 637             } else {
 638                 return Err(err);
 639             }
 640         }
 641
 642         if self.prev_token.span == DUMMY_SP {
 643             // Account for macro context where the previous span might not be
 644             // available to avoid incorrect output (#54841).
 645             err.span_label(self.token.span, label_exp);
 646         } else if !sm.is_multiline(self.token.span.shrink_to_hi().until(sp.shrink_to_lo())) {
 647             // When the spans are in the same line, it means that the only content between
 648             // them is whitespace, point at the found token in that case:
 649             //
 650             // X |     () => { syntax error };
 651             //   |                    ^^^^^ expected one of 8 possible tokens here
 652             //
 653             // instead of having:
 654             //
 655             // X |     () => { syntax error };
 656             //   |                   -^^^^^ unexpected token
 657             //   |                   |
 658             //   |                   expected one of 8 possible tokens here
 659             err.span_label(self.token.span, label_exp);
 660         } else {
 661             err.span_label(sp, label_exp);
 662             err.span_label(self.token.span, "unexpected token");
 663         }
 664         self.maybe_annotate_with_ascription(&mut err, false);
 665         Err(err)
 666     }
 667
 668     fn check_too_many_raw_str_terminators(&mut self, err: &mut Diagnostic) -> bool {
 669         let sm = self.sess.source_map();
 670         match (&self.prev_token.kind, &self.token.kind) {
 671             (
 672                 TokenKind::Literal(Lit {
 673                     kind: LitKind::StrRaw(n_hashes) | LitKind::ByteStrRaw(n_hashes),
 674                     ..
 675                 }),
 676                 TokenKind::Pound,
 677             ) if !sm.is_multiline(
 678                 self.prev_token.span.shrink_to_hi().until(self.token.span.shrink_to_lo()),
 679             ) =>
 680             {
 681                 let n_hashes: u8 = *n_hashes;
 682                 err.set_primary_message("too many `#` when terminating raw string");
 683                 let str_span = self.prev_token.span;
 684                 let mut span = self.token.span;
 685                 let mut count = 0;
 686                 while self.token.kind == TokenKind::Pound
 687                     && !sm.is_multiline(span.shrink_to_hi().until(self.token.span.shrink_to_lo()))
 688                 {
 689                     span = span.with_hi(self.token.span.hi());
 690                     self.bump();
 691                     count += 1;
 692                 }
 693                 err.set_span(span);
 694                 err.span_suggestion(
 695                     span,
 696                     &format!("remove the extra `#`{}", pluralize!(count)),
 697                     "",
 698                     Applicability::MachineApplicable,
 699                 );
 700                 err.span_label(
 701                     str_span,
 702                     &format!("this raw string started with {n_hashes} `#`{}", pluralize!(n_hashes)),
 703                 );
 704                 true
 705             }
 706             _ => false,
 707         }
 708     }
 709
 710     pub fn maybe_suggest_struct_literal(
 711         &mut self,
 712         lo: Span,
 713         s: BlockCheckMode,
 714     ) -> Option<PResult<'a, P<Block>>> {
 715         if self.token.is_ident() && self.look_ahead(1, |t| t == &token::Colon) {
 716             // We might be having a struct literal where people forgot to include the path:
 717             // fn foo() -> Foo {
 718             //     field: value,
 719             // }
 720             let mut snapshot = self.create_snapshot_for_diagnostic();
 721             let path =
 722                 Path { segments: vec![], span: self.prev_token.span.shrink_to_lo(), tokens: None };
 723             let struct_expr = snapshot.parse_struct_expr(None, path, AttrVec::new(), false);
 724             let block_tail = self.parse_block_tail(lo, s, AttemptLocalParseRecovery::No);
 725             return Some(match (struct_expr, block_tail) {
 726                 (Ok(expr), Err(mut err)) => {
 727                     // We have encountered the following:
 728                     // fn foo() -> Foo {
 729                     //     field: value,
 730                     // }
 731                     // Suggest:
 732                     // fn foo() -> Foo { Path {
 733                     //     field: value,
 734                     // } }
 735                     err.delay_as_bug();
 736                     self.struct_span_err(
 737                         expr.span,
 738                         fluent::parser::struct_literal_body_without_path,
 739                     )
 740                     .multipart_suggestion(
 741                         fluent::parser::suggestion,
 742                         vec![
 743                             (expr.span.shrink_to_lo(), "{ SomeStruct ".to_string()),
 744                             (expr.span.shrink_to_hi(), " }".to_string()),
 745                         ],
 746                         Applicability::MaybeIncorrect,
 747                     )
 748                     .emit();
 749                     self.restore_snapshot(snapshot);
 750                     let mut tail = self.mk_block(
 751                         vec![self.mk_stmt_err(expr.span)],
 752                         s,
 753                         lo.to(self.prev_token.span),
 754                     );
 755                     tail.could_be_bare_literal = true;
 756                     Ok(tail)
 757                 }
 758                 (Err(err), Ok(tail)) => {
 759                     // We have a block tail that contains a somehow valid type ascription expr.
 760                     err.cancel();
 761                     Ok(tail)
 762                 }
 763                 (Err(snapshot_err), Err(err)) => {
 764                     // We don't know what went wrong, emit the normal error.
 765                     snapshot_err.cancel();
 766                     self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
 767                     Err(err)
 768                 }
 769                 (Ok(_), Ok(mut tail)) => {
 770                     tail.could_be_bare_literal = true;
 771                     Ok(tail)
 772                 }
 773             });
 774         }
 775         None
 776     }
 777
 778     pub fn maybe_annotate_with_ascription(
 779         &mut self,
 780         err: &mut Diagnostic,
 781         maybe_expected_semicolon: bool,
 782     ) {
 783         if let Some((sp, likely_path)) = self.last_type_ascription.take() {
 784             let sm = self.sess.source_map();
 785             let next_pos = sm.lookup_char_pos(self.token.span.lo());
 786             let op_pos = sm.lookup_char_pos(sp.hi());
 787
 788             let allow_unstable = self.sess.unstable_features.is_nightly_build();
 789
 790             if likely_path {
 791                 err.span_suggestion(
 792                     sp,
 793                     "maybe write a path separator here",
 794                     "::",
 795                     if allow_unstable {
 796                         Applicability::MaybeIncorrect
 797                     } else {
 798                         Applicability::MachineApplicable
 799                     },
 800                 );
 801                 self.sess.type_ascription_path_suggestions.borrow_mut().insert(sp);
 802             } else if op_pos.line != next_pos.line && maybe_expected_semicolon {
 803                 err.span_suggestion(
 804                     sp,
 805                     "try using a semicolon",
 806                     ";",
 807                     Applicability::MaybeIncorrect,
 808                 );
 809             } else if allow_unstable {
 810                 err.span_label(sp, "tried to parse a type due to this type ascription");
 811             } else {
 812                 err.span_label(sp, "tried to parse a type due to this");
 813             }
 814             if allow_unstable {
 815                 // Give extra information about type ascription only if it's a nightly compiler.
 816                 err.note(
 817                     "`#![feature(type_ascription)]` lets you annotate an expression with a type: \
 818                      `<expr>: <type>`",
 819                 );
 820                 if !likely_path {
 821                     // Avoid giving too much info when it was likely an unrelated typo.
 822                     err.note(
 823                         "see issue #23416 <https://github.com/rust-lang/rust/issues/23416> \
 824                         for more information",
 825                     );
 826                 }
 827             }
 828         }
 829     }
 830
 831     /// Eats and discards tokens until one of `kets` is encountered. Respects token trees,
 832     /// passes through any errors encountered. Used for error recovery.
 833     pub(super) fn eat_to_tokens(&mut self, kets: &[&TokenKind]) {
 834         if let Err(err) =
 835             self.parse_seq_to_before_tokens(kets, SeqSep::none(), TokenExpectType::Expect, |p| {
 836                 Ok(p.parse_token_tree())
 837             })
 838         {
 839             err.cancel();
 840         }
 841     }
 842
 843     /// This function checks if there are trailing angle brackets and produces
 844     /// a diagnostic to suggest removing them.
 845     ///
 846     /// ```ignore (diagnostic)
 847     /// let _ = [1, 2, 3].into_iter().collect::<Vec<usize>>>>();
 848     ///                                                    ^^ help: remove extra angle brackets
 849     /// ```
 850     ///
 851     /// If `true` is returned, then trailing brackets were recovered, tokens were consumed
 852     /// up until one of the tokens in 'end' was encountered, and an error was emitted.
 853     pub(super) fn check_trailing_angle_brackets(
 854         &mut self,
 855         segment: &PathSegment,
 856         end: &[&TokenKind],
 857     ) -> bool {
 858         // This function is intended to be invoked after parsing a path segment where there are two
 859         // cases:
 860         //
 861         // 1. A specific token is expected after the path segment.
 862         //    eg. `x.foo(`, `x.foo::<u32>(` (parenthesis - method call),
 863         //        `Foo::`, or `Foo::<Bar>::` (mod sep - continued path).
 864         // 2. No specific token is expected after the path segment.
 865         //    eg. `x.foo` (field access)
 866         //
 867         // This function is called after parsing `.foo` and before parsing the token `end` (if
 868         // present). This includes any angle bracket arguments, such as `.foo::<u32>` or
 869         // `Foo::<Bar>`.
 870
 871         // We only care about trailing angle brackets if we previously parsed angle bracket
 872         // arguments. This helps stop us incorrectly suggesting that extra angle brackets be
 873         // removed in this case:
 874         //
 875         // `x.foo >> (3)` (where `x.foo` is a `u32` for example)
 876         //
 877         // This case is particularly tricky as we won't notice it just looking at the tokens -
 878         // it will appear the same (in terms of upcoming tokens) as below (since the `::<u32>` will
 879         // have already been parsed):
 880         //
 881         // `x.foo::<u32>>>(3)`
 882         let parsed_angle_bracket_args =
 883             segment.args.as_ref().map_or(false, |args| args.is_angle_bracketed());
 884
 885         debug!(
 886             "check_trailing_angle_brackets: parsed_angle_bracket_args={:?}",
 887             parsed_angle_bracket_args,
 888         );
 889         if !parsed_angle_bracket_args {
 890             return false;
 891         }
 892
 893         // Keep the span at the start so we can highlight the sequence of `>` characters to be
 894         // removed.
 895         let lo = self.token.span;
 896
 897         // We need to look-ahead to see if we have `>` characters without moving the cursor forward
 898         // (since we might have the field access case and the characters we're eating are
 899         // actual operators and not trailing characters - ie `x.foo >> 3`).
 900         let mut position = 0;
 901
 902         // We can encounter `>` or `>>` tokens in any order, so we need to keep track of how
 903         // many of each (so we can correctly pluralize our error messages) and continue to
 904         // advance.
 905         let mut number_of_shr = 0;
 906         let mut number_of_gt = 0;
 907         while self.look_ahead(position, |t| {
 908             trace!("check_trailing_angle_brackets: t={:?}", t);
 909             if *t == token::BinOp(token::BinOpToken::Shr) {
 910                 number_of_shr += 1;
 911                 true
 912             } else if *t == token::Gt {
 913                 number_of_gt += 1;
 914                 true
 915             } else {
 916                 false
 917             }
 918         }) {
 919             position += 1;
 920         }
 921
 922         // If we didn't find any trailing `>` characters, then we have nothing to error about.
 923         debug!(
 924             "check_trailing_angle_brackets: number_of_gt={:?} number_of_shr={:?}",
 925             number_of_gt, number_of_shr,
 926         );
 927         if number_of_gt < 1 && number_of_shr < 1 {
 928             return false;
 929         }
 930
 931         // Finally, double check that we have our end token as otherwise this is the
 932         // second case.
 933         if self.look_ahead(position, |t| {
 934             trace!("check_trailing_angle_brackets: t={:?}", t);
 935             end.contains(&&t.kind)
 936         }) {
 937             // Eat from where we started until the end token so that parsing can continue
 938             // as if we didn't have those extra angle brackets.
 939             self.eat_to_tokens(end);
 940             let span = lo.until(self.token.span);
 941
 942             let total_num_of_gt = number_of_gt + number_of_shr * 2;
 943             self.struct_span_err(
 944                 span,
 945                 &format!("unmatched angle bracket{}", pluralize!(total_num_of_gt)),
 946             )
 947             .span_suggestion(
 948                 span,
 949                 &format!("remove extra angle bracket{}", pluralize!(total_num_of_gt)),
 950                 "",
 951                 Applicability::MachineApplicable,
 952             )
 953             .emit();
 954             return true;
 955         }
 956         false
 957     }
 958
 959     /// Check if a method call with an intended turbofish has been written without surrounding
 960     /// angle brackets.
 961     pub(super) fn check_turbofish_missing_angle_brackets(&mut self, segment: &mut PathSegment) {
 962         if token::ModSep == self.token.kind && segment.args.is_none() {
 963             let snapshot = self.create_snapshot_for_diagnostic();
 964             self.bump();
 965             let lo = self.token.span;
 966             match self.parse_angle_args(None) {
 967                 Ok(args) => {
 968                     let span = lo.to(self.prev_token.span);
 969                     // Detect trailing `>` like in `x.collect::Vec<_>>()`.
 970                     let mut trailing_span = self.prev_token.span.shrink_to_hi();
 971                     while self.token.kind == token::BinOp(token::Shr)
 972                         || self.token.kind == token::Gt
 973                     {
 974                         trailing_span = trailing_span.to(self.token.span);
 975                         self.bump();
 976                     }
 977                     if self.token.kind == token::OpenDelim(Delimiter::Parenthesis) {
 978                         // Recover from bad turbofish: `foo.collect::Vec<_>()`.
 979                         let args = AngleBracketedArgs { args, span }.into();
 980                         segment.args = args;
 981
 982                         self.struct_span_err(
 983                             span,
 984                             "generic parameters without surrounding angle brackets",
 985                         )
 986                         .multipart_suggestion(
 987                             "surround the type parameters with angle brackets",
 988                             vec![
 989                                 (span.shrink_to_lo(), "<".to_string()),
 990                                 (trailing_span, ">".to_string()),
 991                             ],
 992                             Applicability::MachineApplicable,
 993                         )
 994                         .emit();
 995                     } else {
 996                         // This doesn't look like an invalid turbofish, can't recover parse state.
 997                         self.restore_snapshot(snapshot);
 998                     }
 999                 }
1000                 Err(err) => {
1001                     // We couldn't parse generic parameters, unlikely to be a turbofish. Rely on
1002                     // generic parse error instead.
1003                     err.cancel();
1004                     self.restore_snapshot(snapshot);
1005                 }
1006             }
1007         }
1008     }
1009
1010     /// When writing a turbofish with multiple type parameters missing the leading `::`, we will
1011     /// encounter a parse error when encountering the first `,`.
1012     pub(super) fn check_mistyped_turbofish_with_multiple_type_params(
1013         &mut self,
1014         mut e: DiagnosticBuilder<'a, ErrorGuaranteed>,
1015         expr: &mut P<Expr>,
1016     ) -> PResult<'a, ()> {
1017         if let ExprKind::Binary(binop, _, _) = &expr.kind
1018             && let ast::BinOpKind::Lt = binop.node
1019             && self.eat(&token::Comma)
1020         {
1021             let x = self.parse_seq_to_before_end(
1022                 &token::Gt,
1023                 SeqSep::trailing_allowed(token::Comma),
1024                 |p| p.parse_generic_arg(None),
1025             );
1026             match x {
1027                 Ok((_, _, false)) => {
1028                     if self.eat(&token::Gt) {
1029                         e.span_suggestion_verbose(
1030                             binop.span.shrink_to_lo(),
1031                             TURBOFISH_SUGGESTION_STR,
1032                             "::",
1033                             Applicability::MaybeIncorrect,
1034                         )
1035                         .emit();
1036                         match self.parse_expr() {
1037                             Ok(_) => {
1038                                 *expr =
1039                                     self.mk_expr_err(expr.span.to(self.prev_token.span));
1040                                 return Ok(());
1041                             }
1042                             Err(err) => {
1043                                 *expr = self.mk_expr_err(expr.span);
1044                                 err.cancel();
1045                             }
1046                         }
1047                     }
1048                 }
1049                 Err(err) => {
1050                     err.cancel();
1051                 }
1052                 _ => {}
1053             }
1054         }
1055         Err(e)
1056     }
1057
1058     /// Check to see if a pair of chained operators looks like an attempt at chained comparison,
1059     /// e.g. `1 < x <= 3`. If so, suggest either splitting the comparison into two, or
1060     /// parenthesising the leftmost comparison.
1061     fn attempt_chained_comparison_suggestion(
1062         &mut self,
1063         err: &mut Diagnostic,
1064         inner_op: &Expr,
1065         outer_op: &Spanned<AssocOp>,
1066     ) -> bool /* advanced the cursor */ {
1067         if let ExprKind::Binary(op, ref l1, ref r1) = inner_op.kind {
1068             if let ExprKind::Field(_, ident) = l1.kind
1069                 && ident.as_str().parse::<i32>().is_err()
1070                 && !matches!(r1.kind, ExprKind::Lit(_))
1071             {
1072                 // The parser has encountered `foo.bar<baz`, the likelihood of the turbofish
1073                 // suggestion being the only one to apply is high.
1074                 return false;
1075             }
1076             let mut enclose = |left: Span, right: Span| {
1077                 err.multipart_suggestion(
1078                     "parenthesize the comparison",
1079                     vec![
1080                         (left.shrink_to_lo(), "(".to_string()),
1081                         (right.shrink_to_hi(), ")".to_string()),
1082                     ],
1083                     Applicability::MaybeIncorrect,
1084                 );
1085             };
1086             return match (op.node, &outer_op.node) {
1087                 // `x == y == z`
1088                 (BinOpKind::Eq, AssocOp::Equal) |
1089                 // `x < y < z` and friends.
1090                 (BinOpKind::Lt, AssocOp::Less | AssocOp::LessEqual) |
1091                 (BinOpKind::Le, AssocOp::LessEqual | AssocOp::Less) |
1092                 // `x > y > z` and friends.
1093                 (BinOpKind::Gt, AssocOp::Greater | AssocOp::GreaterEqual) |
1094                 (BinOpKind::Ge, AssocOp::GreaterEqual | AssocOp::Greater) => {
1095                     let expr_to_str = |e: &Expr| {
1096                         self.span_to_snippet(e.span)
1097                             .unwrap_or_else(|_| pprust::expr_to_string(&e))
1098                     };
1099                     err.span_suggestion_verbose(
1100                         inner_op.span.shrink_to_hi(),
1101                         "split the comparison into two",
1102                         format!(" && {}", expr_to_str(&r1)),
1103                         Applicability::MaybeIncorrect,
1104                     );
1105                     false // Keep the current parse behavior, where the AST is `(x < y) < z`.
1106                 }
1107                 // `x == y < z`
1108                 (BinOpKind::Eq, AssocOp::Less | AssocOp::LessEqual | AssocOp::Greater | AssocOp::GreaterEqual) => {
1109                     // Consume `z`/outer-op-rhs.
1110                     let snapshot = self.create_snapshot_for_diagnostic();
1111                     match self.parse_expr() {
1112                         Ok(r2) => {
1113                             // We are sure that outer-op-rhs could be consumed, the suggestion is
1114                             // likely correct.
1115                             enclose(r1.span, r2.span);
1116                             true
1117                         }
1118                         Err(expr_err) => {
1119                             expr_err.cancel();
1120                             self.restore_snapshot(snapshot);
1121                             false
1122                         }
1123                     }
1124                 }
1125                 // `x > y == z`
1126                 (BinOpKind::Lt | BinOpKind::Le | BinOpKind::Gt | BinOpKind::Ge, AssocOp::Equal) => {
1127                     let snapshot = self.create_snapshot_for_diagnostic();
1128                     // At this point it is always valid to enclose the lhs in parentheses, no
1129                     // further checks are necessary.
1130                     match self.parse_expr() {
1131                         Ok(_) => {
1132                             enclose(l1.span, r1.span);
1133                             true
1134                         }
1135                         Err(expr_err) => {
1136                             expr_err.cancel();
1137                             self.restore_snapshot(snapshot);
1138                             false
1139                         }
1140                     }
1141                 }
1142                 _ => false,
1143             };
1144         }
1145         false
1146     }
1147
1148     /// Produces an error if comparison operators are chained (RFC #558).
1149     /// We only need to check the LHS, not the RHS, because all comparison ops have same
1150     /// precedence (see `fn precedence`) and are left-associative (see `fn fixity`).
1151     ///
1152     /// This can also be hit if someone incorrectly writes `foo<bar>()` when they should have used
1153     /// the turbofish (`foo::<bar>()`) syntax. We attempt some heuristic recovery if that is the
1154     /// case.
1155     ///
1156     /// Keep in mind that given that `outer_op.is_comparison()` holds and comparison ops are left
1157     /// associative we can infer that we have:
1158     ///
1159     /// ```text
1160     ///           outer_op
1161     ///           /   \
1162     ///     inner_op   r2
1163     ///        /  \
1164     ///      l1    r1
1165     /// ```
1166     pub(super) fn check_no_chained_comparison(
1167         &mut self,
1168         inner_op: &Expr,
1169         outer_op: &Spanned<AssocOp>,
1170     ) -> PResult<'a, Option<P<Expr>>> {
1171         debug_assert!(
1172             outer_op.node.is_comparison(),
1173             "check_no_chained_comparison: {:?} is not comparison",
1174             outer_op.node,
1175         );
1176
1177         let mk_err_expr =
1178             |this: &Self, span| Ok(Some(this.mk_expr(span, ExprKind::Err, AttrVec::new())));
1179
1180         match inner_op.kind {
1181             ExprKind::Binary(op, ref l1, ref r1) if op.node.is_comparison() => {
1182                 let mut err = self.struct_span_err(
1183                     vec![op.span, self.prev_token.span],
1184                     "comparison operators cannot be chained",
1185                 );
1186
1187                 let suggest = |err: &mut Diagnostic| {
1188                     err.span_suggestion_verbose(
1189                         op.span.shrink_to_lo(),
1190                         TURBOFISH_SUGGESTION_STR,
1191                         "::",
1192                         Applicability::MaybeIncorrect,
1193                     );
1194                 };
1195
1196                 // Include `<` to provide this recommendation even in a case like
1197                 // `Foo<Bar<Baz<Qux, ()>>>`
1198                 if op.node == BinOpKind::Lt && outer_op.node == AssocOp::Less
1199                     || outer_op.node == AssocOp::Greater
1200                 {
1201                     if outer_op.node == AssocOp::Less {
1202                         let snapshot = self.create_snapshot_for_diagnostic();
1203                         self.bump();
1204                         // So far we have parsed `foo<bar<`, consume the rest of the type args.
1205                         let modifiers =
1206                             [(token::Lt, 1), (token::Gt, -1), (token::BinOp(token::Shr), -2)];
1207                         self.consume_tts(1, &modifiers);
1208
1209                         if !&[token::OpenDelim(Delimiter::Parenthesis), token::ModSep]
1210                             .contains(&self.token.kind)
1211                         {
1212                             // We don't have `foo< bar >(` or `foo< bar >::`, so we rewind the
1213                             // parser and bail out.
1214                             self.restore_snapshot(snapshot);
1215                         }
1216                     }
1217                     return if token::ModSep == self.token.kind {
1218                         // We have some certainty that this was a bad turbofish at this point.
1219                         // `foo< bar >::`
1220                         suggest(&mut err);
1221
1222                         let snapshot = self.create_snapshot_for_diagnostic();
1223                         self.bump(); // `::`
1224
1225                         // Consume the rest of the likely `foo<bar>::new()` or return at `foo<bar>`.
1226                         match self.parse_expr() {
1227                             Ok(_) => {
1228                                 // 99% certain that the suggestion is correct, continue parsing.
1229                                 err.emit();
1230                                 // FIXME: actually check that the two expressions in the binop are
1231                                 // paths and resynthesize new fn call expression instead of using
1232                                 // `ExprKind::Err` placeholder.
1233                                 mk_err_expr(self, inner_op.span.to(self.prev_token.span))
1234                             }
1235                             Err(expr_err) => {
1236                                 expr_err.cancel();
1237                                 // Not entirely sure now, but we bubble the error up with the
1238                                 // suggestion.
1239                                 self.restore_snapshot(snapshot);
1240                                 Err(err)
1241                             }
1242                         }
1243                     } else if token::OpenDelim(Delimiter::Parenthesis) == self.token.kind {
1244                         // We have high certainty that this was a bad turbofish at this point.
1245                         // `foo< bar >(`
1246                         suggest(&mut err);
1247                         // Consume the fn call arguments.
1248                         match self.consume_fn_args() {
1249                             Err(()) => Err(err),
1250                             Ok(()) => {
1251                                 err.emit();
1252                                 // FIXME: actually check that the two expressions in the binop are
1253                                 // paths and resynthesize new fn call expression instead of using
1254                                 // `ExprKind::Err` placeholder.
1255                                 mk_err_expr(self, inner_op.span.to(self.prev_token.span))
1256                             }
1257                         }
1258                     } else {
1259                         if !matches!(l1.kind, ExprKind::Lit(_))
1260                             && !matches!(r1.kind, ExprKind::Lit(_))
1261                         {
1262                             // All we know is that this is `foo < bar >` and *nothing* else. Try to
1263                             // be helpful, but don't attempt to recover.
1264                             err.help(TURBOFISH_SUGGESTION_STR);
1265                             err.help("or use `(...)` if you meant to specify fn arguments");
1266                         }
1267
1268                         // If it looks like a genuine attempt to chain operators (as opposed to a
1269                         // misformatted turbofish, for instance), suggest a correct form.
1270                         if self.attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op)
1271                         {
1272                             err.emit();
1273                             mk_err_expr(self, inner_op.span.to(self.prev_token.span))
1274                         } else {
1275                             // These cases cause too many knock-down errors, bail out (#61329).
1276                             Err(err)
1277                         }
1278                     };
1279                 }
1280                 let recover =
1281                     self.attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op);
1282                 err.emit();
1283                 if recover {
1284                     return mk_err_expr(self, inner_op.span.to(self.prev_token.span));
1285                 }
1286             }
1287             _ => {}
1288         }
1289         Ok(None)
1290     }
1291
1292     fn consume_fn_args(&mut self) -> Result<(), ()> {
1293         let snapshot = self.create_snapshot_for_diagnostic();
1294         self.bump(); // `(`
1295
1296         // Consume the fn call arguments.
1297         let modifiers = [
1298             (token::OpenDelim(Delimiter::Parenthesis), 1),
1299             (token::CloseDelim(Delimiter::Parenthesis), -1),
1300         ];
1301         self.consume_tts(1, &modifiers);
1302
1303         if self.token.kind == token::Eof {
1304             // Not entirely sure that what we consumed were fn arguments, rollback.
1305             self.restore_snapshot(snapshot);
1306             Err(())
1307         } else {
1308             // 99% certain that the suggestion is correct, continue parsing.
1309             Ok(())
1310         }
1311     }
1312
1313     pub(super) fn maybe_report_ambiguous_plus(&mut self, impl_dyn_multi: bool, ty: &Ty) {
1314         if impl_dyn_multi {
1315             self.sess.emit_err(AmbiguousPlus { sum_ty: pprust::ty_to_string(&ty), span: ty.span });
1316         }
1317     }
1318
1319     /// Swift lets users write `Ty?` to mean `Option<Ty>`. Parse the construct and recover from it.
1320     pub(super) fn maybe_recover_from_question_mark(&mut self, ty: P<Ty>) -> P<Ty> {
1321         if self.token == token::Question {
1322             self.bump();
1323             self.struct_span_err(self.prev_token.span, "invalid `?` in type")
1324                 .span_label(self.prev_token.span, "`?` is only allowed on expressions, not types")
1325                 .multipart_suggestion(
1326                     "if you meant to express that the type might not contain a value, use the `Option` wrapper type",
1327                     vec![
1328                         (ty.span.shrink_to_lo(), "Option<".to_string()),
1329                         (self.prev_token.span, ">".to_string()),
1330                     ],
1331                     Applicability::MachineApplicable,
1332                 )
1333                 .emit();
1334             self.mk_ty(ty.span.to(self.prev_token.span), TyKind::Err)
1335         } else {
1336             ty
1337         }
1338     }
1339
1340     pub(super) fn maybe_recover_from_bad_type_plus(&mut self, ty: &Ty) -> PResult<'a, ()> {
1341         // Do not add `+` to expected tokens.
1342         if !self.token.is_like_plus() {
1343             return Ok(());
1344         }
1345
1346         self.bump(); // `+`
1347         let bounds = self.parse_generic_bounds(None)?;
1348         let sum_span = ty.span.to(self.prev_token.span);
1349
1350         let sub = match ty.kind {
1351             TyKind::Rptr(ref lifetime, ref mut_ty) => {
1352                 let sum_with_parens = pprust::to_string(|s| {
1353                     s.s.word("&");
1354                     s.print_opt_lifetime(lifetime);
1355                     s.print_mutability(mut_ty.mutbl, false);
1356                     s.popen();
1357                     s.print_type(&mut_ty.ty);
1358                     if !bounds.is_empty() {
1359                         s.word(" + ");
1360                         s.print_type_bounds(&bounds);
1361                     }
1362                     s.pclose()
1363                 });
1364
1365                 BadTypePlusSub::AddParen { sum_with_parens, span: sum_span }
1366             }
1367             TyKind::Ptr(..) | TyKind::BareFn(..) => BadTypePlusSub::ForgotParen { span: sum_span },
1368             _ => BadTypePlusSub::ExpectPath { span: sum_span },
1369         };
1370
1371         self.sess.emit_err(BadTypePlus { ty: pprust::ty_to_string(ty), span: sum_span, sub });
1372
1373         Ok(())
1374     }
1375
1376     pub(super) fn recover_from_prefix_increment(
1377         &mut self,
1378         operand_expr: P<Expr>,
1379         op_span: Span,
1380         prev_is_semi: bool,
1381     ) -> PResult<'a, P<Expr>> {
1382         let standalone =
1383             if prev_is_semi { IsStandalone::Standalone } else { IsStandalone::Subexpr };
1384         let kind = IncDecRecovery { standalone, op: IncOrDec::Inc, fixity: UnaryFixity::Pre };
1385
1386         self.recover_from_inc_dec(operand_expr, kind, op_span)
1387     }
1388
1389     pub(super) fn recover_from_postfix_increment(
1390         &mut self,
1391         operand_expr: P<Expr>,
1392         op_span: Span,
1393     ) -> PResult<'a, P<Expr>> {
1394         let kind = IncDecRecovery {
1395             standalone: IsStandalone::Maybe,
1396             op: IncOrDec::Inc,
1397             fixity: UnaryFixity::Post,
1398         };
1399
1400         self.recover_from_inc_dec(operand_expr, kind, op_span)
1401     }
1402
1403     fn recover_from_inc_dec(
1404         &mut self,
1405         base: P<Expr>,
1406         kind: IncDecRecovery,
1407         op_span: Span,
1408     ) -> PResult<'a, P<Expr>> {
1409         let mut err = self.struct_span_err(
1410             op_span,
1411             &format!("Rust has no {} {} operator", kind.fixity, kind.op.name()),
1412         );
1413         err.span_label(op_span, &format!("not a valid {} operator", kind.fixity));
1414
1415         let help_base_case = |mut err: DiagnosticBuilder<'_, _>, base| {
1416             err.help(&format!("use `{}= 1` instead", kind.op.chr()));
1417             err.emit();
1418             Ok(base)
1419         };
1420
1421         // (pre, post)
1422         let spans = match kind.fixity {
1423             UnaryFixity::Pre => (op_span, base.span.shrink_to_hi()),
1424             UnaryFixity::Post => (base.span.shrink_to_lo(), op_span),
1425         };
1426
1427         match kind.standalone {
1428             IsStandalone::Standalone => self.inc_dec_standalone_suggest(kind, spans).emit(&mut err),
1429             IsStandalone::Subexpr => {
1430                 let Ok(base_src) = self.span_to_snippet(base.span)
1431                     else { return help_base_case(err, base) };
1432                 match kind.fixity {
1433                     UnaryFixity::Pre => {
1434                         self.prefix_inc_dec_suggest(base_src, kind, spans).emit(&mut err)
1435                     }
1436                     UnaryFixity::Post => {
1437                         self.postfix_inc_dec_suggest(base_src, kind, spans).emit(&mut err)
1438                     }
1439                 }
1440             }
1441             IsStandalone::Maybe => {
1442                 let Ok(base_src) = self.span_to_snippet(base.span)
1443                     else { return help_base_case(err, base) };
1444                 let sugg1 = match kind.fixity {
1445                     UnaryFixity::Pre => self.prefix_inc_dec_suggest(base_src, kind, spans),
1446                     UnaryFixity::Post => self.postfix_inc_dec_suggest(base_src, kind, spans),
1447                 };
1448                 let sugg2 = self.inc_dec_standalone_suggest(kind, spans);
1449                 MultiSugg::emit_many(
1450                     &mut err,
1451                     "use `+= 1` instead",
1452                     Applicability::Unspecified,
1453                     [sugg1, sugg2].into_iter(),
1454                 )
1455             }
1456         }
1457         Err(err)
1458     }
1459
1460     fn prefix_inc_dec_suggest(
1461         &mut self,
1462         base_src: String,
1463         kind: IncDecRecovery,
1464         (pre_span, post_span): (Span, Span),
1465     ) -> MultiSugg {
1466         MultiSugg {
1467             msg: format!("use `{}= 1` instead", kind.op.chr()),
1468             patches: vec![
1469                 (pre_span, "{ ".to_string()),
1470                 (post_span, format!(" {}= 1; {} }}", kind.op.chr(), base_src)),
1471             ],
1472             applicability: Applicability::MachineApplicable,
1473         }
1474     }
1475
1476     fn postfix_inc_dec_suggest(
1477         &mut self,
1478         base_src: String,
1479         kind: IncDecRecovery,
1480         (pre_span, post_span): (Span, Span),
1481     ) -> MultiSugg {
1482         let tmp_var = if base_src.trim() == "tmp" { "tmp_" } else { "tmp" };
1483         MultiSugg {
1484             msg: format!("use `{}= 1` instead", kind.op.chr()),
1485             patches: vec![
1486                 (pre_span, format!("{{ let {} = ", tmp_var)),
1487                 (post_span, format!("; {} {}= 1; {} }}", base_src, kind.op.chr(), tmp_var)),
1488             ],
1489             applicability: Applicability::HasPlaceholders,
1490         }
1491     }
1492
1493     fn inc_dec_standalone_suggest(
1494         &mut self,
1495         kind: IncDecRecovery,
1496         (pre_span, post_span): (Span, Span),
1497     ) -> MultiSugg {
1498         MultiSugg {
1499             msg: format!("use `{}= 1` instead", kind.op.chr()),
1500             patches: vec![(pre_span, String::new()), (post_span, format!(" {}= 1", kind.op.chr()))],
1501             applicability: Applicability::MachineApplicable,
1502         }
1503     }
1504
1505     /// Tries to recover from associated item paths like `[T]::AssocItem` / `(T, U)::AssocItem`.
1506     /// Attempts to convert the base expression/pattern/type into a type, parses the `::AssocItem`
1507     /// tail, and combines them into a `<Ty>::AssocItem` expression/pattern/type.
1508     pub(super) fn maybe_recover_from_bad_qpath<T: RecoverQPath>(
1509         &mut self,
1510         base: P<T>,
1511     ) -> PResult<'a, P<T>> {
1512         // Do not add `::` to expected tokens.
1513         if self.token == token::ModSep {
1514             if let Some(ty) = base.to_ty() {
1515                 return self.maybe_recover_from_bad_qpath_stage_2(ty.span, ty);
1516             }
1517         }
1518         Ok(base)
1519     }
1520
1521     /// Given an already parsed `Ty`, parses the `::AssocItem` tail and
1522     /// combines them into a `<Ty>::AssocItem` expression/pattern/type.
1523     pub(super) fn maybe_recover_from_bad_qpath_stage_2<T: RecoverQPath>(
1524         &mut self,
1525         ty_span: Span,
1526         ty: P<Ty>,
1527     ) -> PResult<'a, P<T>> {
1528         self.expect(&token::ModSep)?;
1529
1530         let mut path = ast::Path { segments: Vec::new(), span: DUMMY_SP, tokens: None };
1531         self.parse_path_segments(&mut path.segments, T::PATH_STYLE, None)?;
1532         path.span = ty_span.to(self.prev_token.span);
1533
1534         let ty_str = self.span_to_snippet(ty_span).unwrap_or_else(|_| pprust::ty_to_string(&ty));
1535         self.sess.emit_err(BadQPathStage2 {
1536             span: path.span,
1537             ty: format!("<{}>::{}", ty_str, pprust::path_to_string(&path)),
1538         });
1539
1540         let path_span = ty_span.shrink_to_hi(); // Use an empty path since `position == 0`.
1541         Ok(P(T::recovered(Some(QSelf { ty, path_span, position: 0 }), path)))
1542     }
1543
1544     pub fn maybe_consume_incorrect_semicolon(&mut self, items: &[P<Item>]) -> bool {
1545         if self.token.kind == TokenKind::Semi {
1546             self.bump();
1547
1548             let mut err =
1549                 IncorrectSemicolon { span: self.prev_token.span, opt_help: None, name: "" };
1550
1551             if !items.is_empty() {
1552                 let previous_item = &items[items.len() - 1];
1553                 let previous_item_kind_name = match previous_item.kind {
1554                     // Say "braced struct" because tuple-structs and
1555                     // braceless-empty-struct declarations do take a semicolon.
1556                     ItemKind::Struct(..) => Some("braced struct"),
1557                     ItemKind::Enum(..) => Some("enum"),
1558                     ItemKind::Trait(..) => Some("trait"),
1559                     ItemKind::Union(..) => Some("union"),
1560                     _ => None,
1561                 };
1562                 if let Some(name) = previous_item_kind_name {
1563                     err.opt_help = Some(());
1564                     err.name = name;
1565                 }
1566             }
1567             self.sess.emit_err(err);
1568             true
1569         } else {
1570             false
1571         }
1572     }
1573
1574     /// Creates a `DiagnosticBuilder` for an unexpected token `t` and tries to recover if it is a
1575     /// closing delimiter.
1576     pub(super) fn unexpected_try_recover(
1577         &mut self,
1578         t: &TokenKind,
1579     ) -> PResult<'a, bool /* recovered */> {
1580         let token_str = pprust::token_kind_to_string(t);
1581         let this_token_str = super::token_descr(&self.token);
1582         let (prev_sp, sp) = match (&self.token.kind, self.subparser_name) {
1583             // Point at the end of the macro call when reaching end of macro arguments.
1584             (token::Eof, Some(_)) => {
1585                 let sp = self.sess.source_map().next_point(self.prev_token.span);
1586                 (sp, sp)
1587             }
1588             // We don't want to point at the following span after DUMMY_SP.
1589             // This happens when the parser finds an empty TokenStream.
1590             _ if self.prev_token.span == DUMMY_SP => (self.token.span, self.token.span),
1591             // EOF, don't want to point at the following char, but rather the last token.
1592             (token::Eof, None) => (self.prev_token.span, self.token.span),
1593             _ => (self.prev_token.span.shrink_to_hi(), self.token.span),
1594         };
1595         let msg = format!(
1596             "expected `{}`, found {}",
1597             token_str,
1598             match (&self.token.kind, self.subparser_name) {
1599                 (token::Eof, Some(origin)) => format!("end of {origin}"),
1600                 _ => this_token_str,
1601             },
1602         );
1603         let mut err = self.struct_span_err(sp, &msg);
1604         let label_exp = format!("expected `{token_str}`");
1605         match self.recover_closing_delimiter(&[t.clone()], err) {
1606             Err(e) => err = e,
1607             Ok(recovered) => {
1608                 return Ok(recovered);
1609             }
1610         }
1611         let sm = self.sess.source_map();
1612         if !sm.is_multiline(prev_sp.until(sp)) {
1613             // When the spans are in the same line, it means that the only content
1614             // between them is whitespace, point only at the found token.
1615             err.span_label(sp, label_exp);
1616         } else {
1617             err.span_label(prev_sp, label_exp);
1618             err.span_label(sp, "unexpected token");
1619         }
1620         Err(err)
1621     }
1622
1623     pub(super) fn expect_semi(&mut self) -> PResult<'a, ()> {
1624         if self.eat(&token::Semi) {
1625             return Ok(());
1626         }
1627         self.expect(&token::Semi).map(drop) // Error unconditionally
1628     }
1629
1630     /// Consumes alternative await syntaxes like `await!(<expr>)`, `await <expr>`,
1631     /// `await? <expr>`, `await(<expr>)`, and `await { <expr> }`.
1632     pub(super) fn recover_incorrect_await_syntax(
1633         &mut self,
1634         lo: Span,
1635         await_sp: Span,
1636         attrs: AttrVec,
1637     ) -> PResult<'a, P<Expr>> {
1638         let (hi, expr, is_question) = if self.token == token::Not {
1639             // Handle `await!(<expr>)`.
1640             self.recover_await_macro()?
1641         } else {
1642             self.recover_await_prefix(await_sp)?
1643         };
1644         let sp = self.error_on_incorrect_await(lo, hi, &expr, is_question);
1645         let kind = match expr.kind {
1646             // Avoid knock-down errors as we don't know whether to interpret this as `foo().await?`
1647             // or `foo()?.await` (the very reason we went with postfix syntax 😅).
1648             ExprKind::Try(_) => ExprKind::Err,
1649             _ => ExprKind::Await(expr),
1650         };
1651         let expr = self.mk_expr(lo.to(sp), kind, attrs);
1652         self.maybe_recover_from_bad_qpath(expr)
1653     }
1654
1655     fn recover_await_macro(&mut self) -> PResult<'a, (Span, P<Expr>, bool)> {
1656         self.expect(&token::Not)?;
1657         self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
1658         let expr = self.parse_expr()?;
1659         self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
1660         Ok((self.prev_token.span, expr, false))
1661     }
1662
1663     fn recover_await_prefix(&mut self, await_sp: Span) -> PResult<'a, (Span, P<Expr>, bool)> {
1664         let is_question = self.eat(&token::Question); // Handle `await? <expr>`.
1665         let expr = if self.token == token::OpenDelim(Delimiter::Brace) {
1666             // Handle `await { <expr> }`.
1667             // This needs to be handled separately from the next arm to avoid
1668             // interpreting `await { <expr> }?` as `<expr>?.await`.
1669             self.parse_block_expr(None, self.token.span, BlockCheckMode::Default, AttrVec::new())
1670         } else {
1671             self.parse_expr()
1672         }
1673         .map_err(|mut err| {
1674             err.span_label(await_sp, "while parsing this incorrect await expression");
1675             err
1676         })?;
1677         Ok((expr.span, expr, is_question))
1678     }
1679
1680     fn error_on_incorrect_await(&self, lo: Span, hi: Span, expr: &Expr, is_question: bool) -> Span {
1681         let span = lo.to(hi);
1682         let applicability = match expr.kind {
1683             ExprKind::Try(_) => Applicability::MaybeIncorrect, // `await <expr>?`
1684             _ => Applicability::MachineApplicable,
1685         };
1686
1687         self.sess.emit_err(IncorrectAwait {
1688             span,
1689             sugg_span: (span, applicability),
1690             expr: self.span_to_snippet(expr.span).unwrap_or_else(|_| pprust::expr_to_string(&expr)),
1691             question_mark: if is_question { "?" } else { "" },
1692         });
1693
1694         span
1695     }
1696
1697     /// If encountering `future.await()`, consumes and emits an error.
1698     pub(super) fn recover_from_await_method_call(&mut self) {
1699         if self.token == token::OpenDelim(Delimiter::Parenthesis)
1700             && self.look_ahead(1, |t| t == &token::CloseDelim(Delimiter::Parenthesis))
1701         {
1702             // future.await()
1703             let lo = self.token.span;
1704             self.bump(); // (
1705             let span = lo.to(self.token.span);
1706             self.bump(); // )
1707
1708             self.sess.emit_err(IncorrectUseOfAwait { span });
1709         }
1710     }
1711
1712     pub(super) fn try_macro_suggestion(&mut self) -> PResult<'a, P<Expr>> {
1713         let is_try = self.token.is_keyword(kw::Try);
1714         let is_questionmark = self.look_ahead(1, |t| t == &token::Not); //check for !
1715         let is_open = self.look_ahead(2, |t| t == &token::OpenDelim(Delimiter::Parenthesis)); //check for (
1716
1717         if is_try && is_questionmark && is_open {
1718             let lo = self.token.span;
1719             self.bump(); //remove try
1720             self.bump(); //remove !
1721             let try_span = lo.to(self.token.span); //we take the try!( span
1722             self.bump(); //remove (
1723             let is_empty = self.token == token::CloseDelim(Delimiter::Parenthesis); //check if the block is empty
1724             self.consume_block(Delimiter::Parenthesis, ConsumeClosingDelim::No); //eat the block
1725             let hi = self.token.span;
1726             self.bump(); //remove )
1727             let mut err = self.struct_span_err(lo.to(hi), "use of deprecated `try` macro");
1728             err.note("in the 2018 edition `try` is a reserved keyword, and the `try!()` macro is deprecated");
1729             let prefix = if is_empty { "" } else { "alternatively, " };
1730             if !is_empty {
1731                 err.multipart_suggestion(
1732                     "you can use the `?` operator instead",
1733                     vec![(try_span, "".to_owned()), (hi, "?".to_owned())],
1734                     Applicability::MachineApplicable,
1735                 );
1736             }
1737             err.span_suggestion(lo.shrink_to_lo(), &format!("{prefix}you can still access the deprecated `try!()` macro using the \"raw identifier\" syntax"), "r#", Applicability::MachineApplicable);
1738             err.emit();
1739             Ok(self.mk_expr_err(lo.to(hi)))
1740         } else {
1741             Err(self.expected_expression_found()) // The user isn't trying to invoke the try! macro
1742         }
1743     }
1744
1745     /// Recovers a situation like `for ( $pat in $expr )`
1746     /// and suggest writing `for $pat in $expr` instead.
1747     ///
1748     /// This should be called before parsing the `$block`.
1749     pub(super) fn recover_parens_around_for_head(
1750         &mut self,
1751         pat: P<Pat>,
1752         begin_paren: Option<Span>,
1753     ) -> P<Pat> {
1754         match (&self.token.kind, begin_paren) {
1755             (token::CloseDelim(Delimiter::Parenthesis), Some(begin_par_sp)) => {
1756                 self.bump();
1757
1758                 self.struct_span_err(
1759                     MultiSpan::from_spans(vec![begin_par_sp, self.prev_token.span]),
1760                     "unexpected parentheses surrounding `for` loop head",
1761                 )
1762                 .multipart_suggestion(
1763                     "remove parentheses in `for` loop",
1764                     vec![(begin_par_sp, String::new()), (self.prev_token.span, String::new())],
1765                     // With e.g. `for (x) in y)` this would replace `(x) in y)`
1766                     // with `x) in y)` which is syntactically invalid.
1767                     // However, this is prevented before we get here.
1768                     Applicability::MachineApplicable,
1769                 )
1770                 .emit();
1771
1772                 // Unwrap `(pat)` into `pat` to avoid the `unused_parens` lint.
1773                 pat.and_then(|pat| match pat.kind {
1774                     PatKind::Paren(pat) => pat,
1775                     _ => P(pat),
1776                 })
1777             }
1778             _ => pat,
1779         }
1780     }
1781
1782     pub(super) fn could_ascription_be_path(&self, node: &ast::ExprKind) -> bool {
1783         (self.token == token::Lt && // `foo:<bar`, likely a typoed turbofish.
1784             self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident()))
1785             || self.token.is_ident() &&
1786             matches!(node, ast::ExprKind::Path(..) | ast::ExprKind::Field(..)) &&
1787             !self.token.is_reserved_ident() &&           // v `foo:bar(baz)`
1788             self.look_ahead(1, |t| t == &token::OpenDelim(Delimiter::Parenthesis))
1789             || self.look_ahead(1, |t| t == &token::OpenDelim(Delimiter::Brace)) // `foo:bar {`
1790             || self.look_ahead(1, |t| t == &token::Colon) &&     // `foo:bar::<baz`
1791             self.look_ahead(2, |t| t == &token::Lt) &&
1792             self.look_ahead(3, |t| t.is_ident())
1793             || self.look_ahead(1, |t| t == &token::Colon) &&  // `foo:bar:baz`
1794             self.look_ahead(2, |t| t.is_ident())
1795             || self.look_ahead(1, |t| t == &token::ModSep)
1796                 && (self.look_ahead(2, |t| t.is_ident()) ||   // `foo:bar::baz`
1797             self.look_ahead(2, |t| t == &token::Lt)) // `foo:bar::<baz>`
1798     }
1799
1800     pub(super) fn recover_seq_parse_error(
1801         &mut self,
1802         delim: Delimiter,
1803         lo: Span,
1804         result: PResult<'a, P<Expr>>,
1805     ) -> P<Expr> {
1806         match result {
1807             Ok(x) => x,
1808             Err(mut err) => {
1809                 err.emit();
1810                 // Recover from parse error, callers expect the closing delim to be consumed.
1811                 self.consume_block(delim, ConsumeClosingDelim::Yes);
1812                 self.mk_expr(lo.to(self.prev_token.span), ExprKind::Err, AttrVec::new())
1813             }
1814         }
1815     }
1816
1817     pub(super) fn recover_closing_delimiter(
1818         &mut self,
1819         tokens: &[TokenKind],
1820         mut err: DiagnosticBuilder<'a, ErrorGuaranteed>,
1821     ) -> PResult<'a, bool> {
1822         let mut pos = None;
1823         // We want to use the last closing delim that would apply.
1824         for (i, unmatched) in self.unclosed_delims.iter().enumerate().rev() {
1825             if tokens.contains(&token::CloseDelim(unmatched.expected_delim))
1826                 && Some(self.token.span) > unmatched.unclosed_span
1827             {
1828                 pos = Some(i);
1829             }
1830         }
1831         match pos {
1832             Some(pos) => {
1833                 // Recover and assume that the detected unclosed delimiter was meant for
1834                 // this location. Emit the diagnostic and act as if the delimiter was
1835                 // present for the parser's sake.
1836
1837                 // Don't attempt to recover from this unclosed delimiter more than once.
1838                 let unmatched = self.unclosed_delims.remove(pos);
1839                 let delim = TokenType::Token(token::CloseDelim(unmatched.expected_delim));
1840                 if unmatched.found_delim.is_none() {
1841                     // We encountered `Eof`, set this fact here to avoid complaining about missing
1842                     // `fn main()` when we found place to suggest the closing brace.
1843                     *self.sess.reached_eof.borrow_mut() = true;
1844                 }
1845
1846                 // We want to suggest the inclusion of the closing delimiter where it makes
1847                 // the most sense, which is immediately after the last token:
1848                 //
1849                 //  {foo(bar {}}
1850                 //      ^      ^
1851                 //      |      |
1852                 //      |      help: `)` may belong here
1853                 //      |
1854                 //      unclosed delimiter
1855                 if let Some(sp) = unmatched.unclosed_span {
1856                     let mut primary_span: Vec<Span> =
1857                         err.span.primary_spans().iter().cloned().collect();
1858                     primary_span.push(sp);
1859                     let mut primary_span: MultiSpan = primary_span.into();
1860                     for span_label in err.span.span_labels() {
1861                         if let Some(label) = span_label.label {
1862                             primary_span.push_span_label(span_label.span, label);
1863                         }
1864                     }
1865                     err.set_span(primary_span);
1866                     err.span_label(sp, "unclosed delimiter");
1867                 }
1868                 // Backticks should be removed to apply suggestions.
1869                 let mut delim = delim.to_string();
1870                 delim.retain(|c| c != '`');
1871                 err.span_suggestion_short(
1872                     self.prev_token.span.shrink_to_hi(),
1873                     &format!("`{delim}` may belong here"),
1874                     delim,
1875                     Applicability::MaybeIncorrect,
1876                 );
1877                 if unmatched.found_delim.is_none() {
1878                     // Encountered `Eof` when lexing blocks. Do not recover here to avoid knockdown
1879                     // errors which would be emitted elsewhere in the parser and let other error
1880                     // recovery consume the rest of the file.
1881                     Err(err)
1882                 } else {
1883                     err.emit();
1884                     self.expected_tokens.clear(); // Reduce the number of errors.
1885                     Ok(true)
1886                 }
1887             }
1888             _ => Err(err),
1889         }
1890     }
1891
1892     /// Eats tokens until we can be relatively sure we reached the end of the
1893     /// statement. This is something of a best-effort heuristic.
1894     ///
1895     /// We terminate when we find an unmatched `}` (without consuming it).
1896     pub(super) fn recover_stmt(&mut self) {
1897         self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore)
1898     }
1899
1900     /// If `break_on_semi` is `Break`, then we will stop consuming tokens after
1901     /// finding (and consuming) a `;` outside of `{}` or `[]` (note that this is
1902     /// approximate -- it can mean we break too early due to macros, but that
1903     /// should only lead to sub-optimal recovery, not inaccurate parsing).
1904     ///
1905     /// If `break_on_block` is `Break`, then we will stop consuming tokens
1906     /// after finding (and consuming) a brace-delimited block.
1907     pub(super) fn recover_stmt_(
1908         &mut self,
1909         break_on_semi: SemiColonMode,
1910         break_on_block: BlockMode,
1911     ) {
1912         let mut brace_depth = 0;
1913         let mut bracket_depth = 0;
1914         let mut in_block = false;
1915         debug!("recover_stmt_ enter loop (semi={:?}, block={:?})", break_on_semi, break_on_block);
1916         loop {
1917             debug!("recover_stmt_ loop {:?}", self.token);
1918             match self.token.kind {
1919                 token::OpenDelim(Delimiter::Brace) => {
1920                     brace_depth += 1;
1921                     self.bump();
1922                     if break_on_block == BlockMode::Break && brace_depth == 1 && bracket_depth == 0
1923                     {
1924                         in_block = true;
1925                     }
1926                 }
1927                 token::OpenDelim(Delimiter::Bracket) => {
1928                     bracket_depth += 1;
1929                     self.bump();
1930                 }
1931                 token::CloseDelim(Delimiter::Brace) => {
1932                     if brace_depth == 0 {
1933                         debug!("recover_stmt_ return - close delim {:?}", self.token);
1934                         break;
1935                     }
1936                     brace_depth -= 1;
1937                     self.bump();
1938                     if in_block && bracket_depth == 0 && brace_depth == 0 {
1939                         debug!("recover_stmt_ return - block end {:?}", self.token);
1940                         break;
1941                     }
1942                 }
1943                 token::CloseDelim(Delimiter::Bracket) => {
1944                     bracket_depth -= 1;
1945                     if bracket_depth < 0 {
1946                         bracket_depth = 0;
1947                     }
1948                     self.bump();
1949                 }
1950                 token::Eof => {
1951                     debug!("recover_stmt_ return - Eof");
1952                     break;
1953                 }
1954                 token::Semi => {
1955                     self.bump();
1956                     if break_on_semi == SemiColonMode::Break
1957                         && brace_depth == 0
1958                         && bracket_depth == 0
1959                     {
1960                         debug!("recover_stmt_ return - Semi");
1961                         break;
1962                     }
1963                 }
1964                 token::Comma
1965                     if break_on_semi == SemiColonMode::Comma
1966                         && brace_depth == 0
1967                         && bracket_depth == 0 =>
1968                 {
1969                     debug!("recover_stmt_ return - Semi");
1970                     break;
1971                 }
1972                 _ => self.bump(),
1973             }
1974         }
1975     }
1976
1977     pub(super) fn check_for_for_in_in_typo(&mut self, in_span: Span) {
1978         if self.eat_keyword(kw::In) {
1979             // a common typo: `for _ in in bar {}`
1980             self.sess.emit_err(InInTypo {
1981                 span: self.prev_token.span,
1982                 sugg_span: in_span.until(self.prev_token.span),
1983             });
1984         }
1985     }
1986
1987     pub(super) fn eat_incorrect_doc_comment_for_param_type(&mut self) {
1988         if let token::DocComment(..) = self.token.kind {
1989             self.struct_span_err(
1990                 self.token.span,
1991                 "documentation comments cannot be applied to a function parameter's type",
1992             )
1993             .span_label(self.token.span, "doc comments are not allowed here")
1994             .emit();
1995             self.bump();
1996         } else if self.token == token::Pound
1997             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Bracket))
1998         {
1999             let lo = self.token.span;
2000             // Skip every token until next possible arg.
2001             while self.token != token::CloseDelim(Delimiter::Bracket) {
2002                 self.bump();
2003             }
2004             let sp = lo.to(self.token.span);
2005             self.bump();
2006             self.struct_span_err(sp, "attributes cannot be applied to a function parameter's type")
2007                 .span_label(sp, "attributes are not allowed here")
2008                 .emit();
2009         }
2010     }
2011
2012     pub(super) fn parameter_without_type(
2013         &mut self,
2014         err: &mut Diagnostic,
2015         pat: P<ast::Pat>,
2016         require_name: bool,
2017         first_param: bool,
2018     ) -> Option<Ident> {
2019         // If we find a pattern followed by an identifier, it could be an (incorrect)
2020         // C-style parameter declaration.
2021         if self.check_ident()
2022             && self.look_ahead(1, |t| {
2023                 *t == token::Comma || *t == token::CloseDelim(Delimiter::Parenthesis)
2024             })
2025         {
2026             // `fn foo(String s) {}`
2027             let ident = self.parse_ident().unwrap();
2028             let span = pat.span.with_hi(ident.span.hi());
2029
2030             err.span_suggestion(
2031                 span,
2032                 "declare the type after the parameter binding",
2033                 "<identifier>: <type>",
2034                 Applicability::HasPlaceholders,
2035             );
2036             return Some(ident);
2037         } else if require_name
2038             && (self.token == token::Comma
2039                 || self.token == token::Lt
2040                 || self.token == token::CloseDelim(Delimiter::Parenthesis))
2041         {
2042             let rfc_note = "anonymous parameters are removed in the 2018 edition (see RFC 1685)";
2043
2044             let (ident, self_sugg, param_sugg, type_sugg, self_span, param_span, type_span) =
2045                 match pat.kind {
2046                     PatKind::Ident(_, ident, _) => (
2047                         ident,
2048                         "self: ",
2049                         ": TypeName".to_string(),
2050                         "_: ",
2051                         pat.span.shrink_to_lo(),
2052                         pat.span.shrink_to_hi(),
2053                         pat.span.shrink_to_lo(),
2054                     ),
2055                     // Also catches `fn foo(&a)`.
2056                     PatKind::Ref(ref inner_pat, mutab)
2057                         if matches!(inner_pat.clone().into_inner().kind, PatKind::Ident(..)) =>
2058                     {
2059                         match inner_pat.clone().into_inner().kind {
2060                             PatKind::Ident(_, ident, _) => {
2061                                 let mutab = mutab.prefix_str();
2062                                 (
2063                                     ident,
2064                                     "self: ",
2065                                     format!("{ident}: &{mutab}TypeName"),
2066                                     "_: ",
2067                                     pat.span.shrink_to_lo(),
2068                                     pat.span,
2069                                     pat.span.shrink_to_lo(),
2070                                 )
2071                             }
2072                             _ => unreachable!(),
2073                         }
2074                     }
2075                     _ => {
2076                         // Otherwise, try to get a type and emit a suggestion.
2077                         if let Some(ty) = pat.to_ty() {
2078                             err.span_suggestion_verbose(
2079                                 pat.span,
2080                                 "explicitly ignore the parameter name",
2081                                 format!("_: {}", pprust::ty_to_string(&ty)),
2082                                 Applicability::MachineApplicable,
2083                             );
2084                             err.note(rfc_note);
2085                         }
2086
2087                         return None;
2088                     }
2089                 };
2090
2091             // `fn foo(a, b) {}`, `fn foo(a<x>, b<y>) {}` or `fn foo(usize, usize) {}`
2092             if first_param {
2093                 err.span_suggestion(
2094                     self_span,
2095                     "if this is a `self` type, give it a parameter name",
2096                     self_sugg,
2097                     Applicability::MaybeIncorrect,
2098                 );
2099             }
2100             // Avoid suggesting that `fn foo(HashMap<u32>)` is fixed with a change to
2101             // `fn foo(HashMap: TypeName<u32>)`.
2102             if self.token != token::Lt {
2103                 err.span_suggestion(
2104                     param_span,
2105                     "if this is a parameter name, give it a type",
2106                     param_sugg,
2107                     Applicability::HasPlaceholders,
2108                 );
2109             }
2110             err.span_suggestion(
2111                 type_span,
2112                 "if this is a type, explicitly ignore the parameter name",
2113                 type_sugg,
2114                 Applicability::MachineApplicable,
2115             );
2116             err.note(rfc_note);
2117
2118             // Don't attempt to recover by using the `X` in `X<Y>` as the parameter name.
2119             return if self.token == token::Lt { None } else { Some(ident) };
2120         }
2121         None
2122     }
2123
2124     pub(super) fn recover_arg_parse(&mut self) -> PResult<'a, (P<ast::Pat>, P<ast::Ty>)> {
2125         let pat = self.parse_pat_no_top_alt(Some("argument name"))?;
2126         self.expect(&token::Colon)?;
2127         let ty = self.parse_ty()?;
2128
2129         struct_span_err!(
2130             self.diagnostic(),
2131             pat.span,
2132             E0642,
2133             "patterns aren't allowed in methods without bodies",
2134         )
2135         .span_suggestion_short(
2136             pat.span,
2137             "give this argument a name or use an underscore to ignore it",
2138             "_",
2139             Applicability::MachineApplicable,
2140         )
2141         .emit();
2142
2143         // Pretend the pattern is `_`, to avoid duplicate errors from AST validation.
2144         let pat =
2145             P(Pat { kind: PatKind::Wild, span: pat.span, id: ast::DUMMY_NODE_ID, tokens: None });
2146         Ok((pat, ty))
2147     }
2148
2149     pub(super) fn recover_bad_self_param(&mut self, mut param: Param) -> PResult<'a, Param> {
2150         let sp = param.pat.span;
2151         param.ty.kind = TyKind::Err;
2152         self.struct_span_err(sp, "unexpected `self` parameter in function")
2153             .span_label(sp, "must be the first parameter of an associated function")
2154             .emit();
2155         Ok(param)
2156     }
2157
2158     pub(super) fn consume_block(&mut self, delim: Delimiter, consume_close: ConsumeClosingDelim) {
2159         let mut brace_depth = 0;
2160         loop {
2161             if self.eat(&token::OpenDelim(delim)) {
2162                 brace_depth += 1;
2163             } else if self.check(&token::CloseDelim(delim)) {
2164                 if brace_depth == 0 {
2165                     if let ConsumeClosingDelim::Yes = consume_close {
2166                         // Some of the callers of this method expect to be able to parse the
2167                         // closing delimiter themselves, so we leave it alone. Otherwise we advance
2168                         // the parser.
2169                         self.bump();
2170                     }
2171                     return;
2172                 } else {
2173                     self.bump();
2174                     brace_depth -= 1;
2175                     continue;
2176                 }
2177             } else if self.token == token::Eof {
2178                 return;
2179             } else {
2180                 self.bump();
2181             }
2182         }
2183     }
2184
2185     pub(super) fn expected_expression_found(&self) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2186         let (span, msg) = match (&self.token.kind, self.subparser_name) {
2187             (&token::Eof, Some(origin)) => {
2188                 let sp = self.sess.source_map().next_point(self.prev_token.span);
2189                 (sp, format!("expected expression, found end of {origin}"))
2190             }
2191             _ => (
2192                 self.token.span,
2193                 format!("expected expression, found {}", super::token_descr(&self.token),),
2194             ),
2195         };
2196         let mut err = self.struct_span_err(span, &msg);
2197         let sp = self.sess.source_map().start_point(self.token.span);
2198         if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
2199             self.sess.expr_parentheses_needed(&mut err, *sp);
2200         }
2201         err.span_label(span, "expected expression");
2202         err
2203     }
2204
2205     fn consume_tts(
2206         &mut self,
2207         mut acc: i64, // `i64` because malformed code can have more closing delims than opening.
2208         // Not using `FxHashMap` due to `token::TokenKind: !Eq + !Hash`.
2209         modifier: &[(token::TokenKind, i64)],
2210     ) {
2211         while acc > 0 {
2212             if let Some((_, val)) = modifier.iter().find(|(t, _)| *t == self.token.kind) {
2213                 acc += *val;
2214             }
2215             if self.token.kind == token::Eof {
2216                 break;
2217             }
2218             self.bump();
2219         }
2220     }
2221
2222     /// Replace duplicated recovered parameters with `_` pattern to avoid unnecessary errors.
2223     ///
2224     /// This is necessary because at this point we don't know whether we parsed a function with
2225     /// anonymous parameters or a function with names but no types. In order to minimize
2226     /// unnecessary errors, we assume the parameters are in the shape of `fn foo(a, b, c)` where
2227     /// the parameters are *names* (so we don't emit errors about not being able to find `b` in
2228     /// the local scope), but if we find the same name multiple times, like in `fn foo(i8, i8)`,
2229     /// we deduplicate them to not complain about duplicated parameter names.
2230     pub(super) fn deduplicate_recovered_params_names(&self, fn_inputs: &mut Vec<Param>) {
2231         let mut seen_inputs = FxHashSet::default();
2232         for input in fn_inputs.iter_mut() {
2233             let opt_ident = if let (PatKind::Ident(_, ident, _), TyKind::Err) =
2234                 (&input.pat.kind, &input.ty.kind)
2235             {
2236                 Some(*ident)
2237             } else {
2238                 None
2239             };
2240             if let Some(ident) = opt_ident {
2241                 if seen_inputs.contains(&ident) {
2242                     input.pat.kind = PatKind::Wild;
2243                 }
2244                 seen_inputs.insert(ident);
2245             }
2246         }
2247     }
2248
2249     /// Handle encountering a symbol in a generic argument list that is not a `,` or `>`. In this
2250     /// case, we emit an error and try to suggest enclosing a const argument in braces if it looks
2251     /// like the user has forgotten them.
2252     pub fn handle_ambiguous_unbraced_const_arg(
2253         &mut self,
2254         args: &mut Vec<AngleBracketedArg>,
2255     ) -> PResult<'a, bool> {
2256         // If we haven't encountered a closing `>`, then the argument is malformed.
2257         // It's likely that the user has written a const expression without enclosing it
2258         // in braces, so we try to recover here.
2259         let arg = args.pop().unwrap();
2260         // FIXME: for some reason using `unexpected` or `expected_one_of_not_found` has
2261         // adverse side-effects to subsequent errors and seems to advance the parser.
2262         // We are causing this error here exclusively in case that a `const` expression
2263         // could be recovered from the current parser state, even if followed by more
2264         // arguments after a comma.
2265         let mut err = self.struct_span_err(
2266             self.token.span,
2267             &format!("expected one of `,` or `>`, found {}", super::token_descr(&self.token)),
2268         );
2269         err.span_label(self.token.span, "expected one of `,` or `>`");
2270         match self.recover_const_arg(arg.span(), err) {
2271             Ok(arg) => {
2272                 args.push(AngleBracketedArg::Arg(arg));
2273                 if self.eat(&token::Comma) {
2274                     return Ok(true); // Continue
2275                 }
2276             }
2277             Err(mut err) => {
2278                 args.push(arg);
2279                 // We will emit a more generic error later.
2280                 err.delay_as_bug();
2281             }
2282         }
2283         return Ok(false); // Don't continue.
2284     }
2285
2286     /// Attempt to parse a generic const argument that has not been enclosed in braces.
2287     /// There are a limited number of expressions that are permitted without being encoded
2288     /// in braces:
2289     /// - Literals.
2290     /// - Single-segment paths (i.e. standalone generic const parameters).
2291     /// All other expressions that can be parsed will emit an error suggesting the expression be
2292     /// wrapped in braces.
2293     pub fn handle_unambiguous_unbraced_const_arg(&mut self) -> PResult<'a, P<Expr>> {
2294         let start = self.token.span;
2295         let expr = self.parse_expr_res(Restrictions::CONST_EXPR, None).map_err(|mut err| {
2296             err.span_label(
2297                 start.shrink_to_lo(),
2298                 "while parsing a const generic argument starting here",
2299             );
2300             err
2301         })?;
2302         if !self.expr_is_valid_const_arg(&expr) {
2303             self.struct_span_err(
2304                 expr.span,
2305                 "expressions must be enclosed in braces to be used as const generic \
2306                     arguments",
2307             )
2308             .multipart_suggestion(
2309                 "enclose the `const` expression in braces",
2310                 vec![
2311                     (expr.span.shrink_to_lo(), "{ ".to_string()),
2312                     (expr.span.shrink_to_hi(), " }".to_string()),
2313                 ],
2314                 Applicability::MachineApplicable,
2315             )
2316             .emit();
2317         }
2318         Ok(expr)
2319     }
2320
2321     fn recover_const_param_decl(&mut self, ty_generics: Option<&Generics>) -> Option<GenericArg> {
2322         let snapshot = self.create_snapshot_for_diagnostic();
2323         let param = match self.parse_const_param(vec![]) {
2324             Ok(param) => param,
2325             Err(err) => {
2326                 err.cancel();
2327                 self.restore_snapshot(snapshot);
2328                 return None;
2329             }
2330         };
2331         let mut err =
2332             self.struct_span_err(param.span(), "unexpected `const` parameter declaration");
2333         err.span_label(param.span(), "expected a `const` expression, not a parameter declaration");
2334         if let (Some(generics), Ok(snippet)) =
2335             (ty_generics, self.sess.source_map().span_to_snippet(param.span()))
2336         {
2337             let (span, sugg) = match &generics.params[..] {
2338                 [] => (generics.span, format!("<{snippet}>")),
2339                 [.., generic] => (generic.span().shrink_to_hi(), format!(", {snippet}")),
2340             };
2341             err.multipart_suggestion(
2342                 "`const` parameters must be declared for the `impl`",
2343                 vec![(span, sugg), (param.span(), param.ident.to_string())],
2344                 Applicability::MachineApplicable,
2345             );
2346         }
2347         let value = self.mk_expr_err(param.span());
2348         err.emit();
2349         Some(GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value }))
2350     }
2351
2352     pub fn recover_const_param_declaration(
2353         &mut self,
2354         ty_generics: Option<&Generics>,
2355     ) -> PResult<'a, Option<GenericArg>> {
2356         // We have to check for a few different cases.
2357         if let Some(arg) = self.recover_const_param_decl(ty_generics) {
2358             return Ok(Some(arg));
2359         }
2360
2361         // We haven't consumed `const` yet.
2362         let start = self.token.span;
2363         self.bump(); // `const`
2364
2365         // Detect and recover from the old, pre-RFC2000 syntax for const generics.
2366         let mut err = self
2367             .struct_span_err(start, "expected lifetime, type, or constant, found keyword `const`");
2368         if self.check_const_arg() {
2369             err.span_suggestion_verbose(
2370                 start.until(self.token.span),
2371                 "the `const` keyword is only needed in the definition of the type",
2372                 "",
2373                 Applicability::MaybeIncorrect,
2374             );
2375             err.emit();
2376             Ok(Some(GenericArg::Const(self.parse_const_arg()?)))
2377         } else {
2378             let after_kw_const = self.token.span;
2379             self.recover_const_arg(after_kw_const, err).map(Some)
2380         }
2381     }
2382
2383     /// Try to recover from possible generic const argument without `{` and `}`.
2384     ///
2385     /// When encountering code like `foo::< bar + 3 >` or `foo::< bar - baz >` we suggest
2386     /// `foo::<{ bar + 3 }>` and `foo::<{ bar - baz }>`, respectively. We only provide a suggestion
2387     /// if we think that that the resulting expression would be well formed.
2388     pub fn recover_const_arg(
2389         &mut self,
2390         start: Span,
2391         mut err: DiagnosticBuilder<'a, ErrorGuaranteed>,
2392     ) -> PResult<'a, GenericArg> {
2393         let is_op_or_dot = AssocOp::from_token(&self.token)
2394             .and_then(|op| {
2395                 if let AssocOp::Greater
2396                 | AssocOp::Less
2397                 | AssocOp::ShiftRight
2398                 | AssocOp::GreaterEqual
2399                 // Don't recover from `foo::<bar = baz>`, because this could be an attempt to
2400                 // assign a value to a defaulted generic parameter.
2401                 | AssocOp::Assign
2402                 | AssocOp::AssignOp(_) = op
2403                 {
2404                     None
2405                 } else {
2406                     Some(op)
2407                 }
2408             })
2409             .is_some()
2410             || self.token.kind == TokenKind::Dot;
2411         // This will be true when a trait object type `Foo +` or a path which was a `const fn` with
2412         // type params has been parsed.
2413         let was_op =
2414             matches!(self.prev_token.kind, token::BinOp(token::Plus | token::Shr) | token::Gt);
2415         if !is_op_or_dot && !was_op {
2416             // We perform these checks and early return to avoid taking a snapshot unnecessarily.
2417             return Err(err);
2418         }
2419         let snapshot = self.create_snapshot_for_diagnostic();
2420         if is_op_or_dot {
2421             self.bump();
2422         }
2423         match self.parse_expr_res(Restrictions::CONST_EXPR, None) {
2424             Ok(expr) => {
2425                 // Find a mistake like `MyTrait<Assoc == S::Assoc>`.
2426                 if token::EqEq == snapshot.token.kind {
2427                     err.span_suggestion(
2428                         snapshot.token.span,
2429                         "if you meant to use an associated type binding, replace `==` with `=`",
2430                         "=",
2431                         Applicability::MaybeIncorrect,
2432                     );
2433                     let value = self.mk_expr_err(start.to(expr.span));
2434                     err.emit();
2435                     return Ok(GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value }));
2436                 } else if token::Colon == snapshot.token.kind
2437                     && expr.span.lo() == snapshot.token.span.hi()
2438                     && matches!(expr.kind, ExprKind::Path(..))
2439                 {
2440                     // Find a mistake like "foo::var:A".
2441                     err.span_suggestion(
2442                         snapshot.token.span,
2443                         "write a path separator here",
2444                         "::",
2445                         Applicability::MaybeIncorrect,
2446                     );
2447                     err.emit();
2448                     return Ok(GenericArg::Type(self.mk_ty(start.to(expr.span), TyKind::Err)));
2449                 } else if token::Comma == self.token.kind || self.token.kind.should_end_const_arg()
2450                 {
2451                     // Avoid the following output by checking that we consumed a full const arg:
2452                     // help: expressions must be enclosed in braces to be used as const generic
2453                     //       arguments
2454                     //    |
2455                     // LL |     let sr: Vec<{ (u32, _, _) = vec![] };
2456                     //    |                 ^                      ^
2457                     return Ok(self.dummy_const_arg_needs_braces(err, start.to(expr.span)));
2458                 }
2459             }
2460             Err(err) => {
2461                 err.cancel();
2462             }
2463         }
2464         self.restore_snapshot(snapshot);
2465         Err(err)
2466     }
2467
2468     /// Creates a dummy const argument, and reports that the expression must be enclosed in braces
2469     pub fn dummy_const_arg_needs_braces(
2470         &self,
2471         mut err: DiagnosticBuilder<'a, ErrorGuaranteed>,
2472         span: Span,
2473     ) -> GenericArg {
2474         err.multipart_suggestion(
2475             "expressions must be enclosed in braces to be used as const generic \
2476              arguments",
2477             vec![(span.shrink_to_lo(), "{ ".to_string()), (span.shrink_to_hi(), " }".to_string())],
2478             Applicability::MaybeIncorrect,
2479         );
2480         let value = self.mk_expr_err(span);
2481         err.emit();
2482         GenericArg::Const(AnonConst { id: ast::DUMMY_NODE_ID, value })
2483     }
2484
2485     /// Get the diagnostics for the cases where `move async` is found.
2486     ///
2487     /// `move_async_span` starts at the 'm' of the move keyword and ends with the 'c' of the async keyword
2488     pub(super) fn incorrect_move_async_order_found(
2489         &self,
2490         move_async_span: Span,
2491     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
2492         let mut err =
2493             self.struct_span_err(move_async_span, "the order of `move` and `async` is incorrect");
2494         err.span_suggestion_verbose(
2495             move_async_span,
2496             "try switching the order",
2497             "async move",
2498             Applicability::MaybeIncorrect,
2499         );
2500         err
2501     }
2502
2503     /// Some special error handling for the "top-level" patterns in a match arm,
2504     /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
2505     pub(crate) fn maybe_recover_colon_colon_in_pat_typo(
2506         &mut self,
2507         mut first_pat: P<Pat>,
2508         expected: Expected,
2509     ) -> P<Pat> {
2510         if token::Colon != self.token.kind {
2511             return first_pat;
2512         }
2513         if !matches!(first_pat.kind, PatKind::Ident(_, _, None) | PatKind::Path(..))
2514             || !self.look_ahead(1, |token| token.is_ident() && !token.is_reserved_ident())
2515         {
2516             return first_pat;
2517         }
2518         // The pattern looks like it might be a path with a `::` -> `:` typo:
2519         // `match foo { bar:baz => {} }`
2520         let span = self.token.span;
2521         // We only emit "unexpected `:`" error here if we can successfully parse the
2522         // whole pattern correctly in that case.
2523         let snapshot = self.create_snapshot_for_diagnostic();
2524
2525         // Create error for "unexpected `:`".
2526         match self.expected_one_of_not_found(&[], &[]) {
2527             Err(mut err) => {
2528                 self.bump(); // Skip the `:`.
2529                 match self.parse_pat_no_top_alt(expected) {
2530                     Err(inner_err) => {
2531                         // Carry on as if we had not done anything, callers will emit a
2532                         // reasonable error.
2533                         inner_err.cancel();
2534                         err.cancel();
2535                         self.restore_snapshot(snapshot);
2536                     }
2537                     Ok(mut pat) => {
2538                         // We've parsed the rest of the pattern.
2539                         let new_span = first_pat.span.to(pat.span);
2540                         let mut show_sugg = false;
2541                         // Try to construct a recovered pattern.
2542                         match &mut pat.kind {
2543                             PatKind::Struct(qself @ None, path, ..)
2544                             | PatKind::TupleStruct(qself @ None, path, _)
2545                             | PatKind::Path(qself @ None, path) => match &first_pat.kind {
2546                                 PatKind::Ident(_, ident, _) => {
2547                                     path.segments.insert(0, PathSegment::from_ident(*ident));
2548                                     path.span = new_span;
2549                                     show_sugg = true;
2550                                     first_pat = pat;
2551                                 }
2552                                 PatKind::Path(old_qself, old_path) => {
2553                                     path.segments = old_path
2554                                         .segments
2555                                         .iter()
2556                                         .cloned()
2557                                         .chain(take(&mut path.segments))
2558                                         .collect();
2559                                     path.span = new_span;
2560                                     *qself = old_qself.clone();
2561                                     first_pat = pat;
2562                                     show_sugg = true;
2563                                 }
2564                                 _ => {}
2565                             },
2566                             PatKind::Ident(BindingMode::ByValue(Mutability::Not), ident, None) => {
2567                                 match &first_pat.kind {
2568                                     PatKind::Ident(_, old_ident, _) => {
2569                                         let path = PatKind::Path(
2570                                             None,
2571                                             Path {
2572                                                 span: new_span,
2573                                                 segments: vec![
2574                                                     PathSegment::from_ident(*old_ident),
2575                                                     PathSegment::from_ident(*ident),
2576                                                 ],
2577                                                 tokens: None,
2578                                             },
2579                                         );
2580                                         first_pat = self.mk_pat(new_span, path);
2581                                         show_sugg = true;
2582                                     }
2583                                     PatKind::Path(old_qself, old_path) => {
2584                                         let mut segments = old_path.segments.clone();
2585                                         segments.push(PathSegment::from_ident(*ident));
2586                                         let path = PatKind::Path(
2587                                             old_qself.clone(),
2588                                             Path { span: new_span, segments, tokens: None },
2589                                         );
2590                                         first_pat = self.mk_pat(new_span, path);
2591                                         show_sugg = true;
2592                                     }
2593                                     _ => {}
2594                                 }
2595                             }
2596                             _ => {}
2597                         }
2598                         if show_sugg {
2599                             err.span_suggestion(
2600                                 span,
2601                                 "maybe write a path separator here",
2602                                 "::",
2603                                 Applicability::MaybeIncorrect,
2604                             );
2605                         } else {
2606                             first_pat = self.mk_pat(new_span, PatKind::Wild);
2607                         }
2608                         err.emit();
2609                     }
2610                 }
2611             }
2612             _ => {
2613                 // Carry on as if we had not done anything. This should be unreachable.
2614                 self.restore_snapshot(snapshot);
2615             }
2616         };
2617         first_pat
2618     }
2619
2620     pub(crate) fn maybe_recover_unexpected_block_label(&mut self) -> bool {
2621         let Some(label) = self.eat_label().filter(|_| {
2622             self.eat(&token::Colon) && self.token.kind == token::OpenDelim(Delimiter::Brace)
2623         }) else {
2624             return false;
2625         };
2626         let span = label.ident.span.to(self.prev_token.span);
2627         let mut err = self.struct_span_err(span, "block label not supported here");
2628         err.span_label(span, "not supported here");
2629         err.tool_only_span_suggestion(
2630             label.ident.span.until(self.token.span),
2631             "remove this block label",
2632             "",
2633             Applicability::MachineApplicable,
2634         );
2635         err.emit();
2636         true
2637     }
2638
2639     /// Some special error handling for the "top-level" patterns in a match arm,
2640     /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
2641     pub(crate) fn maybe_recover_unexpected_comma(
2642         &mut self,
2643         lo: Span,
2644         rt: CommaRecoveryMode,
2645     ) -> PResult<'a, ()> {
2646         if self.token != token::Comma {
2647             return Ok(());
2648         }
2649
2650         // An unexpected comma after a top-level pattern is a clue that the
2651         // user (perhaps more accustomed to some other language) forgot the
2652         // parentheses in what should have been a tuple pattern; return a
2653         // suggestion-enhanced error here rather than choking on the comma later.
2654         let comma_span = self.token.span;
2655         self.bump();
2656         if let Err(err) = self.skip_pat_list() {
2657             // We didn't expect this to work anyway; we just wanted to advance to the
2658             // end of the comma-sequence so we know the span to suggest parenthesizing.
2659             err.cancel();
2660         }
2661         let seq_span = lo.to(self.prev_token.span);
2662         let mut err = self.struct_span_err(comma_span, "unexpected `,` in pattern");
2663         if let Ok(seq_snippet) = self.span_to_snippet(seq_span) {
2664             err.multipart_suggestion(
2665                 &format!(
2666                     "try adding parentheses to match on a tuple{}",
2667                     if let CommaRecoveryMode::LikelyTuple = rt { "" } else { "..." },
2668                 ),
2669                 vec![
2670                     (seq_span.shrink_to_lo(), "(".to_string()),
2671                     (seq_span.shrink_to_hi(), ")".to_string()),
2672                 ],
2673                 Applicability::MachineApplicable,
2674             );
2675             if let CommaRecoveryMode::EitherTupleOrPipe = rt {
2676                 err.span_suggestion(
2677                     seq_span,
2678                     "...or a vertical bar to match on multiple alternatives",
2679                     seq_snippet.replace(',', " |"),
2680                     Applicability::MachineApplicable,
2681                 );
2682             }
2683         }
2684         Err(err)
2685     }
2686
2687     pub(crate) fn maybe_recover_bounds_doubled_colon(&mut self, ty: &Ty) -> PResult<'a, ()> {
2688         let TyKind::Path(qself, path) = &ty.kind else { return Ok(()) };
2689         let qself_position = qself.as_ref().map(|qself| qself.position);
2690         for (i, segments) in path.segments.windows(2).enumerate() {
2691             if qself_position.map(|pos| i < pos).unwrap_or(false) {
2692                 continue;
2693             }
2694             if let [a, b] = segments {
2695                 let (a_span, b_span) = (a.span(), b.span());
2696                 let between_span = a_span.shrink_to_hi().to(b_span.shrink_to_lo());
2697                 if self.span_to_snippet(between_span).as_ref().map(|a| &a[..]) == Ok(":: ") {
2698                     let mut err = self.struct_span_err(
2699                         path.span.shrink_to_hi(),
2700                         "expected `:` followed by trait or lifetime",
2701                     );
2702                     err.span_suggestion(
2703                         between_span,
2704                         "use single colon",
2705                         ": ",
2706                         Applicability::MachineApplicable,
2707                     );
2708                     return Err(err);
2709                 }
2710             }
2711         }
2712         Ok(())
2713     }
2714
2715     /// Parse and throw away a parenthesized comma separated
2716     /// sequence of patterns until `)` is reached.
2717     fn skip_pat_list(&mut self) -> PResult<'a, ()> {
2718         while !self.check(&token::CloseDelim(Delimiter::Parenthesis)) {
2719             self.parse_pat_no_top_alt(None)?;
2720             if !self.eat(&token::Comma) {
2721                 return Ok(());
2722             }
2723         }
2724         Ok(())
2725     }
2726 }