compiler/rustc_parse/src/parser/diagnostics.rs

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