1 use super::ty::AllowPlus;
2 use super::{BlockMode, Parser, PathStyle, SemiColonMode, SeqSep, TokenExpectType, TokenType};
4 use rustc_ast_pretty::pprust;
5 use rustc_data_structures::fx::FxHashSet;
6 use rustc_errors::{pluralize, struct_span_err};
7 use rustc_errors::{Applicability, DiagnosticBuilder, Handler, PResult};
8 use rustc_span::source_map::Spanned;
9 use rustc_span::symbol::kw;
10 use rustc_span::{MultiSpan, Span, SpanSnippetError, DUMMY_SP};
12 self, BinOpKind, BindingMode, BlockCheckMode, Expr, ExprKind, Ident, Item, Param,
14 use syntax::ast::{AttrVec, ItemKind, Mutability, Pat, PatKind, PathSegment, QSelf, Ty, TyKind};
16 use syntax::token::{self, token_can_begin_expr, TokenKind};
17 use syntax::util::parser::AssocOp;
19 use log::{debug, trace};
22 const TURBOFISH: &'static str = "use `::<...>` instead of `<...>` to specify type arguments";
24 /// Creates a placeholder argument.
25 pub(super) fn dummy_arg(ident: Ident) -> Param {
27 id: ast::DUMMY_NODE_ID,
28 kind: PatKind::Ident(BindingMode::ByValue(Mutability::Not), ident, None),
31 let ty = Ty { kind: TyKind::Err, span: ident.span, id: ast::DUMMY_NODE_ID };
33 attrs: AttrVec::default(),
34 id: ast::DUMMY_NODE_ID,
38 is_placeholder: false,
43 FileNotFoundForModule {
46 secondary_path: String,
52 secondary_path: String,
58 fn span_err(self, sp: impl Into<MultiSpan>, handler: &Handler) -> DiagnosticBuilder<'_> {
60 Error::FileNotFoundForModule {
66 let mut err = struct_span_err!(
70 "file not found for module `{}`",
74 "name the file either {} or {} inside the directory \"{}\"",
75 default_path, secondary_path, dir_path,
79 Error::DuplicatePaths { ref mod_name, ref default_path, ref secondary_path } => {
80 let mut err = struct_span_err!(
84 "file for module `{}` found at both {} and {}",
89 err.help("delete or rename one of them to remove the ambiguity");
92 Error::UselessDocComment => {
93 let mut err = struct_span_err!(
97 "found a documentation comment that doesn't document anything",
100 "doc comments must come before what they document, maybe a comment was \
101 intended with `//`?",
109 pub(super) trait RecoverQPath: Sized + 'static {
110 const PATH_STYLE: PathStyle = PathStyle::Expr;
111 fn to_ty(&self) -> Option<P<Ty>>;
112 fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self;
115 impl RecoverQPath for Ty {
116 const PATH_STYLE: PathStyle = PathStyle::Type;
117 fn to_ty(&self) -> Option<P<Ty>> {
118 Some(P(self.clone()))
120 fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
121 Self { span: path.span, kind: TyKind::Path(qself, path), id: ast::DUMMY_NODE_ID }
125 impl RecoverQPath for Pat {
126 fn to_ty(&self) -> Option<P<Ty>> {
129 fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
130 Self { span: path.span, kind: PatKind::Path(qself, path), id: ast::DUMMY_NODE_ID }
134 impl RecoverQPath for Expr {
135 fn to_ty(&self) -> Option<P<Ty>> {
138 fn recovered(qself: Option<QSelf>, path: ast::Path) -> Self {
141 kind: ExprKind::Path(qself, path),
142 attrs: AttrVec::new(),
143 id: ast::DUMMY_NODE_ID,
148 /// Control whether the closing delimiter should be consumed when calling `Parser::consume_block`.
149 crate enum ConsumeClosingDelim {
154 impl<'a> Parser<'a> {
155 pub(super) fn span_fatal_err<S: Into<MultiSpan>>(
159 ) -> DiagnosticBuilder<'a> {
160 err.span_err(sp, self.diagnostic())
163 pub fn struct_span_err<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> DiagnosticBuilder<'a> {
164 self.sess.span_diagnostic.struct_span_err(sp, m)
167 pub fn span_bug<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> ! {
168 self.sess.span_diagnostic.span_bug(sp, m)
171 pub(super) fn diagnostic(&self) -> &'a Handler {
172 &self.sess.span_diagnostic
175 pub(super) fn span_to_snippet(&self, span: Span) -> Result<String, SpanSnippetError> {
176 self.sess.source_map().span_to_snippet(span)
179 pub(super) fn expected_ident_found(&self) -> DiagnosticBuilder<'a> {
180 let mut err = self.struct_span_err(
182 &format!("expected identifier, found {}", super::token_descr(&self.token)),
184 let valid_follow = &[
190 TokenKind::OpenDelim(token::DelimToken::Brace),
191 TokenKind::OpenDelim(token::DelimToken::Paren),
192 TokenKind::CloseDelim(token::DelimToken::Brace),
193 TokenKind::CloseDelim(token::DelimToken::Paren),
195 if let token::Ident(name, false) = self.token.kind {
196 if Ident::new(name, self.token.span).is_raw_guess()
197 && self.look_ahead(1, |t| valid_follow.contains(&t.kind))
201 "you can escape reserved keywords to use them as identifiers",
202 format!("r#{}", name),
203 Applicability::MaybeIncorrect,
207 if let Some(token_descr) = super::token_descr_opt(&self.token) {
208 err.span_label(self.token.span, format!("expected identifier, found {}", token_descr));
210 err.span_label(self.token.span, "expected identifier");
211 if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
216 Applicability::MachineApplicable,
223 pub(super) fn expected_one_of_not_found(
225 edible: &[TokenKind],
226 inedible: &[TokenKind],
227 ) -> PResult<'a, bool /* recovered */> {
228 fn tokens_to_string(tokens: &[TokenType]) -> String {
229 let mut i = tokens.iter();
230 // This might be a sign we need a connect method on `Iterator`.
231 let b = i.next().map_or(String::new(), |t| t.to_string());
232 i.enumerate().fold(b, |mut b, (i, a)| {
233 if tokens.len() > 2 && i == tokens.len() - 2 {
235 } else if tokens.len() == 2 && i == tokens.len() - 2 {
240 b.push_str(&a.to_string());
245 let mut expected = edible
247 .map(|x| TokenType::Token(x.clone()))
248 .chain(inedible.iter().map(|x| TokenType::Token(x.clone())))
249 .chain(self.expected_tokens.iter().cloned())
250 .collect::<Vec<_>>();
251 expected.sort_by_cached_key(|x| x.to_string());
253 let expect = tokens_to_string(&expected[..]);
254 let actual = super::token_descr(&self.token);
255 let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
256 let short_expect = if expected.len() > 6 {
257 format!("{} possible tokens", expected.len())
262 format!("expected one of {}, found {}", expect, actual),
263 (self.prev_span.shrink_to_hi(), format!("expected one of {}", short_expect)),
265 } else if expected.is_empty() {
267 format!("unexpected token: {}", actual),
268 (self.prev_span, "unexpected token after this".to_string()),
272 format!("expected {}, found {}", expect, actual),
273 (self.prev_span.shrink_to_hi(), format!("expected {}", expect)),
276 self.last_unexpected_token_span = Some(self.token.span);
277 let mut err = self.struct_span_err(self.token.span, &msg_exp);
278 let sp = if self.token == token::Eof {
279 // This is EOF; don't want to point at the following char, but rather the last token.
284 match self.recover_closing_delimiter(
287 .filter_map(|tt| match tt {
288 TokenType::Token(t) => Some(t.clone()),
291 .collect::<Vec<_>>(),
296 return Ok(recovered);
300 let sm = self.sess.source_map();
301 if self.prev_span == DUMMY_SP {
302 // Account for macro context where the previous span might not be
303 // available to avoid incorrect output (#54841).
304 err.span_label(self.token.span, label_exp);
305 } else if !sm.is_multiline(self.token.span.shrink_to_hi().until(sp.shrink_to_lo())) {
306 // When the spans are in the same line, it means that the only content between
307 // them is whitespace, point at the found token in that case:
309 // X | () => { syntax error };
310 // | ^^^^^ expected one of 8 possible tokens here
312 // instead of having:
314 // X | () => { syntax error };
315 // | -^^^^^ unexpected token
317 // | expected one of 8 possible tokens here
318 err.span_label(self.token.span, label_exp);
320 err.span_label(sp, label_exp);
321 err.span_label(self.token.span, "unexpected token");
323 self.maybe_annotate_with_ascription(&mut err, false);
327 pub fn maybe_annotate_with_ascription(
329 err: &mut DiagnosticBuilder<'_>,
330 maybe_expected_semicolon: bool,
332 if let Some((sp, likely_path)) = self.last_type_ascription.take() {
333 let sm = self.sess.source_map();
334 let next_pos = sm.lookup_char_pos(self.token.span.lo());
335 let op_pos = sm.lookup_char_pos(sp.hi());
337 let allow_unstable = self.sess.unstable_features.is_nightly_build();
342 "maybe write a path separator here",
345 Applicability::MaybeIncorrect
347 Applicability::MachineApplicable
350 } else if op_pos.line != next_pos.line && maybe_expected_semicolon {
353 "try using a semicolon",
355 Applicability::MaybeIncorrect,
357 } else if allow_unstable {
358 err.span_label(sp, "tried to parse a type due to this type ascription");
360 err.span_label(sp, "tried to parse a type due to this");
363 // Give extra information about type ascription only if it's a nightly compiler.
365 "`#![feature(type_ascription)]` lets you annotate an expression with a \
366 type: `<expr>: <type>`",
369 "for more information, see \
370 https://github.com/rust-lang/rust/issues/23416",
376 /// Eats and discards tokens until one of `kets` is encountered. Respects token trees,
377 /// passes through any errors encountered. Used for error recovery.
378 pub(super) fn eat_to_tokens(&mut self, kets: &[&TokenKind]) {
379 if let Err(ref mut err) =
380 self.parse_seq_to_before_tokens(kets, SeqSep::none(), TokenExpectType::Expect, |p| {
381 Ok(p.parse_token_tree())
388 /// This function checks if there are trailing angle brackets and produces
389 /// a diagnostic to suggest removing them.
391 /// ```ignore (diagnostic)
392 /// let _ = vec![1, 2, 3].into_iter().collect::<Vec<usize>>>>();
393 /// ^^ help: remove extra angle brackets
395 pub(super) fn check_trailing_angle_brackets(&mut self, segment: &PathSegment, end: TokenKind) {
396 // This function is intended to be invoked after parsing a path segment where there are two
399 // 1. A specific token is expected after the path segment.
400 // eg. `x.foo(`, `x.foo::<u32>(` (parenthesis - method call),
401 // `Foo::`, or `Foo::<Bar>::` (mod sep - continued path).
402 // 2. No specific token is expected after the path segment.
403 // eg. `x.foo` (field access)
405 // This function is called after parsing `.foo` and before parsing the token `end` (if
406 // present). This includes any angle bracket arguments, such as `.foo::<u32>` or
409 // We only care about trailing angle brackets if we previously parsed angle bracket
410 // arguments. This helps stop us incorrectly suggesting that extra angle brackets be
411 // removed in this case:
413 // `x.foo >> (3)` (where `x.foo` is a `u32` for example)
415 // This case is particularly tricky as we won't notice it just looking at the tokens -
416 // it will appear the same (in terms of upcoming tokens) as below (since the `::<u32>` will
417 // have already been parsed):
419 // `x.foo::<u32>>>(3)`
420 let parsed_angle_bracket_args =
421 segment.args.as_ref().map(|args| args.is_angle_bracketed()).unwrap_or(false);
424 "check_trailing_angle_brackets: parsed_angle_bracket_args={:?}",
425 parsed_angle_bracket_args,
427 if !parsed_angle_bracket_args {
431 // Keep the span at the start so we can highlight the sequence of `>` characters to be
433 let lo = self.token.span;
435 // We need to look-ahead to see if we have `>` characters without moving the cursor forward
436 // (since we might have the field access case and the characters we're eating are
437 // actual operators and not trailing characters - ie `x.foo >> 3`).
438 let mut position = 0;
440 // We can encounter `>` or `>>` tokens in any order, so we need to keep track of how
441 // many of each (so we can correctly pluralize our error messages) and continue to
443 let mut number_of_shr = 0;
444 let mut number_of_gt = 0;
445 while self.look_ahead(position, |t| {
446 trace!("check_trailing_angle_brackets: t={:?}", t);
447 if *t == token::BinOp(token::BinOpToken::Shr) {
450 } else if *t == token::Gt {
460 // If we didn't find any trailing `>` characters, then we have nothing to error about.
462 "check_trailing_angle_brackets: number_of_gt={:?} number_of_shr={:?}",
463 number_of_gt, number_of_shr,
465 if number_of_gt < 1 && number_of_shr < 1 {
469 // Finally, double check that we have our end token as otherwise this is the
471 if self.look_ahead(position, |t| {
472 trace!("check_trailing_angle_brackets: t={:?}", t);
475 // Eat from where we started until the end token so that parsing can continue
476 // as if we didn't have those extra angle brackets.
477 self.eat_to_tokens(&[&end]);
478 let span = lo.until(self.token.span);
480 let total_num_of_gt = number_of_gt + number_of_shr * 2;
481 self.struct_span_err(
483 &format!("unmatched angle bracket{}", pluralize!(total_num_of_gt)),
487 &format!("remove extra angle bracket{}", pluralize!(total_num_of_gt)),
489 Applicability::MachineApplicable,
495 /// Check to see if a pair of chained operators looks like an attempt at chained comparison,
496 /// e.g. `1 < x <= 3`. If so, suggest either splitting the comparison into two, or
497 /// parenthesising the leftmost comparison.
498 fn attempt_chained_comparison_suggestion(
500 err: &mut DiagnosticBuilder<'_>,
502 outer_op: &Spanned<AssocOp>,
504 if let ExprKind::Binary(op, ref l1, ref r1) = inner_op.kind {
505 match (op.node, &outer_op.node) {
506 // `x < y < z` and friends.
507 (BinOpKind::Lt, AssocOp::Less) | (BinOpKind::Lt, AssocOp::LessEqual) |
508 (BinOpKind::Le, AssocOp::LessEqual) | (BinOpKind::Le, AssocOp::Less) |
509 // `x > y > z` and friends.
510 (BinOpKind::Gt, AssocOp::Greater) | (BinOpKind::Gt, AssocOp::GreaterEqual) |
511 (BinOpKind::Ge, AssocOp::GreaterEqual) | (BinOpKind::Ge, AssocOp::Greater) => {
512 let expr_to_str = |e: &Expr| {
513 self.span_to_snippet(e.span)
514 .unwrap_or_else(|_| pprust::expr_to_string(&e))
517 inner_op.span.to(outer_op.span),
518 "split the comparison into two...",
525 outer_op.node.to_ast_binop().unwrap().to_string(),
527 Applicability::MaybeIncorrect,
530 inner_op.span.to(outer_op.span),
531 "...or parenthesize one of the comparisons",
537 outer_op.node.to_ast_binop().unwrap().to_string(),
539 Applicability::MaybeIncorrect,
547 /// Produces an error if comparison operators are chained (RFC #558).
548 /// We only need to check the LHS, not the RHS, because all comparison ops have same
549 /// precedence (see `fn precedence`) and are left-associative (see `fn fixity`).
551 /// This can also be hit if someone incorrectly writes `foo<bar>()` when they should have used
552 /// the turbofish (`foo::<bar>()`) syntax. We attempt some heuristic recovery if that is the
555 /// Keep in mind that given that `outer_op.is_comparison()` holds and comparison ops are left
556 /// associative we can infer that we have:
563 pub(super) fn check_no_chained_comparison(
566 outer_op: &Spanned<AssocOp>,
567 ) -> PResult<'a, Option<P<Expr>>> {
569 outer_op.node.is_comparison(),
570 "check_no_chained_comparison: {:?} is not comparison",
575 |this: &Self, span| Ok(Some(this.mk_expr(span, ExprKind::Err, AttrVec::new())));
577 match inner_op.kind {
578 ExprKind::Binary(op, _, _) if op.node.is_comparison() => {
579 // Respan to include both operators.
580 let op_span = op.span.to(self.prev_span);
582 self.struct_span_err(op_span, "comparison operators cannot be chained");
584 // If it looks like a genuine attempt to chain operators (as opposed to a
585 // misformatted turbofish, for instance), suggest a correct form.
586 self.attempt_chained_comparison_suggestion(&mut err, inner_op, outer_op);
588 let suggest = |err: &mut DiagnosticBuilder<'_>| {
589 err.span_suggestion_verbose(
590 op_span.shrink_to_lo(),
593 Applicability::MaybeIncorrect,
597 if op.node == BinOpKind::Lt &&
598 outer_op.node == AssocOp::Less || // Include `<` to provide this recommendation
599 outer_op.node == AssocOp::Greater
600 // even in a case like the following:
602 // Foo<Bar<Baz<Qux, ()>>>
603 if outer_op.node == AssocOp::Less {
604 let snapshot = self.clone();
606 // So far we have parsed `foo<bar<`, consume the rest of the type args.
608 [(token::Lt, 1), (token::Gt, -1), (token::BinOp(token::Shr), -2)];
609 self.consume_tts(1, &modifiers[..]);
611 if !&[token::OpenDelim(token::Paren), token::ModSep]
612 .contains(&self.token.kind)
614 // We don't have `foo< bar >(` or `foo< bar >::`, so we rewind the
615 // parser and bail out.
616 mem::replace(self, snapshot.clone());
619 return if token::ModSep == self.token.kind {
620 // We have some certainty that this was a bad turbofish at this point.
624 let snapshot = self.clone();
627 // Consume the rest of the likely `foo<bar>::new()` or return at `foo<bar>`.
628 match self.parse_expr() {
630 // 99% certain that the suggestion is correct, continue parsing.
632 // FIXME: actually check that the two expressions in the binop are
633 // paths and resynthesize new fn call expression instead of using
634 // `ExprKind::Err` placeholder.
635 mk_err_expr(self, inner_op.span.to(self.prev_span))
637 Err(mut expr_err) => {
639 // Not entirely sure now, but we bubble the error up with the
641 mem::replace(self, snapshot);
645 } else if token::OpenDelim(token::Paren) == self.token.kind {
646 // We have high certainty that this was a bad turbofish at this point.
649 // Consume the fn call arguments.
650 match self.consume_fn_args() {
654 // FIXME: actually check that the two expressions in the binop are
655 // paths and resynthesize new fn call expression instead of using
656 // `ExprKind::Err` placeholder.
657 mk_err_expr(self, inner_op.span.to(self.prev_span))
661 // All we know is that this is `foo < bar >` and *nothing* else. Try to
662 // be helpful, but don't attempt to recover.
664 err.help("or use `(...)` if you meant to specify fn arguments");
665 // These cases cause too many knock-down errors, bail out (#61329).
676 fn consume_fn_args(&mut self) -> Result<(), ()> {
677 let snapshot = self.clone();
680 // Consume the fn call arguments.
682 [(token::OpenDelim(token::Paren), 1), (token::CloseDelim(token::Paren), -1)];
683 self.consume_tts(1, &modifiers[..]);
685 if self.token.kind == token::Eof {
686 // Not entirely sure that what we consumed were fn arguments, rollback.
687 mem::replace(self, snapshot);
690 // 99% certain that the suggestion is correct, continue parsing.
695 pub(super) fn maybe_report_ambiguous_plus(
697 allow_plus: AllowPlus,
698 impl_dyn_multi: bool,
701 if matches!(allow_plus, AllowPlus::No) && impl_dyn_multi {
702 let sum_with_parens = format!("({})", pprust::ty_to_string(&ty));
703 self.struct_span_err(ty.span, "ambiguous `+` in a type")
706 "use parentheses to disambiguate",
708 Applicability::MachineApplicable,
714 pub(super) fn maybe_recover_from_bad_type_plus(
716 allow_plus: AllowPlus,
718 ) -> PResult<'a, ()> {
719 // Do not add `+` to expected tokens.
720 if matches!(allow_plus, AllowPlus::No) || !self.token.is_like_plus() {
725 let bounds = self.parse_generic_bounds(None)?;
726 let sum_span = ty.span.to(self.prev_span);
728 let mut err = struct_span_err!(
729 self.sess.span_diagnostic,
732 "expected a path on the left-hand side of `+`, not `{}`",
733 pprust::ty_to_string(ty)
737 TyKind::Rptr(ref lifetime, ref mut_ty) => {
738 let sum_with_parens = pprust::to_string(|s| {
740 s.print_opt_lifetime(lifetime);
741 s.print_mutability(mut_ty.mutbl, false);
743 s.print_type(&mut_ty.ty);
744 s.print_type_bounds(" +", &bounds);
749 "try adding parentheses",
751 Applicability::MachineApplicable,
754 TyKind::Ptr(..) | TyKind::BareFn(..) => {
755 err.span_label(sum_span, "perhaps you forgot parentheses?");
758 err.span_label(sum_span, "expected a path");
765 /// Tries to recover from associated item paths like `[T]::AssocItem` / `(T, U)::AssocItem`.
766 /// Attempts to convert the base expression/pattern/type into a type, parses the `::AssocItem`
767 /// tail, and combines them into a `<Ty>::AssocItem` expression/pattern/type.
768 pub(super) fn maybe_recover_from_bad_qpath<T: RecoverQPath>(
771 allow_recovery: bool,
772 ) -> PResult<'a, P<T>> {
773 // Do not add `::` to expected tokens.
774 if allow_recovery && self.token == token::ModSep {
775 if let Some(ty) = base.to_ty() {
776 return self.maybe_recover_from_bad_qpath_stage_2(ty.span, ty);
782 /// Given an already parsed `Ty`, parses the `::AssocItem` tail and
783 /// combines them into a `<Ty>::AssocItem` expression/pattern/type.
784 pub(super) fn maybe_recover_from_bad_qpath_stage_2<T: RecoverQPath>(
788 ) -> PResult<'a, P<T>> {
789 self.expect(&token::ModSep)?;
791 let mut path = ast::Path { segments: Vec::new(), span: DUMMY_SP };
792 self.parse_path_segments(&mut path.segments, T::PATH_STYLE)?;
793 path.span = ty_span.to(self.prev_span);
795 let ty_str = self.span_to_snippet(ty_span).unwrap_or_else(|_| pprust::ty_to_string(&ty));
796 self.struct_span_err(path.span, "missing angle brackets in associated item path")
798 // This is a best-effort recovery.
801 format!("<{}>::{}", ty_str, pprust::path_to_string(&path)),
802 Applicability::MaybeIncorrect,
806 let path_span = ty_span.shrink_to_hi(); // Use an empty path since `position == 0`.
807 Ok(P(T::recovered(Some(QSelf { ty, path_span, position: 0 }), path)))
810 pub(super) fn maybe_consume_incorrect_semicolon(&mut self, items: &[P<Item>]) -> bool {
811 if self.eat(&token::Semi) {
812 let mut err = self.struct_span_err(self.prev_span, "expected item, found `;`");
813 err.span_suggestion_short(
815 "remove this semicolon",
817 Applicability::MachineApplicable,
819 if !items.is_empty() {
820 let previous_item = &items[items.len() - 1];
821 let previous_item_kind_name = match previous_item.kind {
822 // Say "braced struct" because tuple-structs and
823 // braceless-empty-struct declarations do take a semicolon.
824 ItemKind::Struct(..) => Some("braced struct"),
825 ItemKind::Enum(..) => Some("enum"),
826 ItemKind::Trait(..) => Some("trait"),
827 ItemKind::Union(..) => Some("union"),
830 if let Some(name) = previous_item_kind_name {
831 err.help(&format!("{} declarations are not followed by a semicolon", name));
841 /// Creates a `DiagnosticBuilder` for an unexpected token `t` and tries to recover if it is a
842 /// closing delimiter.
843 pub(super) fn unexpected_try_recover(
846 ) -> PResult<'a, bool /* recovered */> {
847 let token_str = pprust::token_kind_to_string(t);
848 let this_token_str = super::token_descr(&self.token);
849 let (prev_sp, sp) = match (&self.token.kind, self.subparser_name) {
850 // Point at the end of the macro call when reaching end of macro arguments.
851 (token::Eof, Some(_)) => {
852 let sp = self.sess.source_map().next_point(self.token.span);
855 // We don't want to point at the following span after DUMMY_SP.
856 // This happens when the parser finds an empty TokenStream.
857 _ if self.prev_span == DUMMY_SP => (self.token.span, self.token.span),
858 // EOF, don't want to point at the following char, but rather the last token.
859 (token::Eof, None) => (self.prev_span, self.token.span),
860 _ => (self.prev_span.shrink_to_hi(), self.token.span),
863 "expected `{}`, found {}",
865 match (&self.token.kind, self.subparser_name) {
866 (token::Eof, Some(origin)) => format!("end of {}", origin),
870 let mut err = self.struct_span_err(sp, &msg);
871 let label_exp = format!("expected `{}`", token_str);
872 match self.recover_closing_delimiter(&[t.clone()], err) {
875 return Ok(recovered);
878 let sm = self.sess.source_map();
879 if !sm.is_multiline(prev_sp.until(sp)) {
880 // When the spans are in the same line, it means that the only content
881 // between them is whitespace, point only at the found token.
882 err.span_label(sp, label_exp);
884 err.span_label(prev_sp, label_exp);
885 err.span_label(sp, "unexpected token");
890 pub(super) fn expect_semi(&mut self) -> PResult<'a, ()> {
891 if self.eat(&token::Semi) {
894 let sm = self.sess.source_map();
895 let msg = format!("expected `;`, found `{}`", super::token_descr(&self.token));
896 let appl = Applicability::MachineApplicable;
897 if self.token.span == DUMMY_SP || self.prev_span == DUMMY_SP {
898 // Likely inside a macro, can't provide meaninful suggestions.
899 return self.expect(&token::Semi).map(drop);
900 } else if !sm.is_multiline(self.prev_span.until(self.token.span)) {
901 // The current token is in the same line as the prior token, not recoverable.
902 } else if self.look_ahead(1, |t| {
903 t == &token::CloseDelim(token::Brace)
904 || token_can_begin_expr(t) && t.kind != token::Colon
905 }) && [token::Comma, token::Colon].contains(&self.token.kind)
907 // Likely typo: `,` → `;` or `:` → `;`. This is triggered if the current token is
908 // either `,` or `:`, and the next token could either start a new statement or is a
909 // block close. For example:
914 let sp = self.prev_span;
915 self.struct_span_err(sp, &msg)
916 .span_suggestion(sp, "change this to `;`", ";".to_string(), appl)
919 } else if self.look_ahead(0, |t| {
920 t == &token::CloseDelim(token::Brace)
922 token_can_begin_expr(t) && t != &token::Semi && t != &token::Pound
923 // Avoid triggering with too many trailing `#` in raw string.
926 // Missing semicolon typo. This is triggered if the next token could either start a
927 // new statement or is a block close. For example:
931 let sp = self.prev_span.shrink_to_hi();
932 self.struct_span_err(sp, &msg)
933 .span_label(self.token.span, "unexpected token")
934 .span_suggestion_short(sp, "add `;` here", ";".to_string(), appl)
938 self.expect(&token::Semi).map(drop) // Error unconditionally
941 /// Consumes alternative await syntaxes like `await!(<expr>)`, `await <expr>`,
942 /// `await? <expr>`, `await(<expr>)`, and `await { <expr> }`.
943 pub(super) fn recover_incorrect_await_syntax(
948 ) -> PResult<'a, P<Expr>> {
949 let (hi, expr, is_question) = if self.token == token::Not {
950 // Handle `await!(<expr>)`.
951 self.recover_await_macro()?
953 self.recover_await_prefix(await_sp)?
955 let sp = self.error_on_incorrect_await(lo, hi, &expr, is_question);
956 let expr = self.mk_expr(lo.to(sp), ExprKind::Await(expr), attrs);
957 self.maybe_recover_from_bad_qpath(expr, true)
960 fn recover_await_macro(&mut self) -> PResult<'a, (Span, P<Expr>, bool)> {
961 self.expect(&token::Not)?;
962 self.expect(&token::OpenDelim(token::Paren))?;
963 let expr = self.parse_expr()?;
964 self.expect(&token::CloseDelim(token::Paren))?;
965 Ok((self.prev_span, expr, false))
968 fn recover_await_prefix(&mut self, await_sp: Span) -> PResult<'a, (Span, P<Expr>, bool)> {
969 let is_question = self.eat(&token::Question); // Handle `await? <expr>`.
970 let expr = if self.token == token::OpenDelim(token::Brace) {
971 // Handle `await { <expr> }`.
972 // This needs to be handled separatedly from the next arm to avoid
973 // interpreting `await { <expr> }?` as `<expr>?.await`.
974 self.parse_block_expr(None, self.token.span, BlockCheckMode::Default, AttrVec::new())
979 err.span_label(await_sp, "while parsing this incorrect await expression");
982 Ok((expr.span, expr, is_question))
985 fn error_on_incorrect_await(&self, lo: Span, hi: Span, expr: &Expr, is_question: bool) -> Span {
987 self.span_to_snippet(expr.span).unwrap_or_else(|_| pprust::expr_to_string(&expr));
988 let suggestion = format!("{}.await{}", expr_str, if is_question { "?" } else { "" });
990 let app = match expr.kind {
991 ExprKind::Try(_) => Applicability::MaybeIncorrect, // `await <expr>?`
992 _ => Applicability::MachineApplicable,
994 self.struct_span_err(sp, "incorrect use of `await`")
995 .span_suggestion(sp, "`await` is a postfix operation", suggestion, app)
1000 /// If encountering `future.await()`, consumes and emits an error.
1001 pub(super) fn recover_from_await_method_call(&mut self) {
1002 if self.token == token::OpenDelim(token::Paren)
1003 && self.look_ahead(1, |t| t == &token::CloseDelim(token::Paren))
1006 let lo = self.token.span;
1008 let sp = lo.to(self.token.span);
1010 self.struct_span_err(sp, "incorrect use of `await`")
1013 "`await` is not a method call, remove the parentheses",
1015 Applicability::MachineApplicable,
1021 /// Recovers a situation like `for ( $pat in $expr )`
1022 /// and suggest writing `for $pat in $expr` instead.
1024 /// This should be called before parsing the `$block`.
1025 pub(super) fn recover_parens_around_for_head(
1029 begin_paren: Option<Span>,
1031 match (&self.token.kind, begin_paren) {
1032 (token::CloseDelim(token::Paren), Some(begin_par_sp)) => {
1036 // Remove the `(` from the span of the pattern:
1037 .span_to_snippet(pat.span.trim_start(begin_par_sp).unwrap())
1038 .unwrap_or_else(|_| pprust::pat_to_string(&pat));
1040 self.struct_span_err(self.prev_span, "unexpected closing `)`")
1041 .span_label(begin_par_sp, "opening `(`")
1043 begin_par_sp.to(self.prev_span),
1044 "remove parenthesis in `for` loop",
1045 format!("{} in {}", pat_str, pprust::expr_to_string(&expr)),
1046 // With e.g. `for (x) in y)` this would replace `(x) in y)`
1047 // with `x) in y)` which is syntactically invalid.
1048 // However, this is prevented before we get here.
1049 Applicability::MachineApplicable,
1053 // Unwrap `(pat)` into `pat` to avoid the `unused_parens` lint.
1054 pat.and_then(|pat| match pat.kind {
1055 PatKind::Paren(pat) => pat,
1063 pub(super) fn could_ascription_be_path(&self, node: &ast::ExprKind) -> bool {
1064 (self.token == token::Lt && // `foo:<bar`, likely a typoed turbofish.
1065 self.look_ahead(1, |t| t.is_ident() && !t.is_reserved_ident()))
1066 || self.token.is_ident() &&
1068 // `foo::` → `foo:` or `foo.bar::` → `foo.bar:`
1069 ast::ExprKind::Path(..) | ast::ExprKind::Field(..) => true,
1072 !self.token.is_reserved_ident() && // v `foo:bar(baz)`
1073 self.look_ahead(1, |t| t == &token::OpenDelim(token::Paren))
1074 || self.look_ahead(1, |t| t == &token::Lt) && // `foo:bar<baz`
1075 self.look_ahead(2, |t| t.is_ident())
1076 || self.look_ahead(1, |t| t == &token::Colon) && // `foo:bar:baz`
1077 self.look_ahead(2, |t| t.is_ident())
1078 || self.look_ahead(1, |t| t == &token::ModSep)
1079 && (self.look_ahead(2, |t| t.is_ident()) || // `foo:bar::baz`
1080 self.look_ahead(2, |t| t == &token::Lt)) // `foo:bar::<baz>`
1083 pub(super) fn recover_seq_parse_error(
1085 delim: token::DelimToken,
1087 result: PResult<'a, P<Expr>>,
1093 // Recover from parse error, callers expect the closing delim to be consumed.
1094 self.consume_block(delim, ConsumeClosingDelim::Yes);
1095 self.mk_expr(lo.to(self.prev_span), ExprKind::Err, AttrVec::new())
1100 pub(super) fn recover_closing_delimiter(
1102 tokens: &[TokenKind],
1103 mut err: DiagnosticBuilder<'a>,
1104 ) -> PResult<'a, bool> {
1106 // We want to use the last closing delim that would apply.
1107 for (i, unmatched) in self.unclosed_delims.iter().enumerate().rev() {
1108 if tokens.contains(&token::CloseDelim(unmatched.expected_delim))
1109 && Some(self.token.span) > unmatched.unclosed_span
1116 // Recover and assume that the detected unclosed delimiter was meant for
1117 // this location. Emit the diagnostic and act as if the delimiter was
1118 // present for the parser's sake.
1120 // Don't attempt to recover from this unclosed delimiter more than once.
1121 let unmatched = self.unclosed_delims.remove(pos);
1122 let delim = TokenType::Token(token::CloseDelim(unmatched.expected_delim));
1123 if unmatched.found_delim.is_none() {
1124 // We encountered `Eof`, set this fact here to avoid complaining about missing
1125 // `fn main()` when we found place to suggest the closing brace.
1126 *self.sess.reached_eof.borrow_mut() = true;
1129 // We want to suggest the inclusion of the closing delimiter where it makes
1130 // the most sense, which is immediately after the last token:
1135 // | help: `)` may belong here
1137 // unclosed delimiter
1138 if let Some(sp) = unmatched.unclosed_span {
1139 err.span_label(sp, "unclosed delimiter");
1141 err.span_suggestion_short(
1142 self.prev_span.shrink_to_hi(),
1143 &format!("{} may belong here", delim.to_string()),
1145 Applicability::MaybeIncorrect,
1147 if unmatched.found_delim.is_none() {
1148 // Encountered `Eof` when lexing blocks. Do not recover here to avoid knockdown
1149 // errors which would be emitted elsewhere in the parser and let other error
1150 // recovery consume the rest of the file.
1154 self.expected_tokens.clear(); // Reduce the number of errors.
1162 /// Eats tokens until we can be relatively sure we reached the end of the
1163 /// statement. This is something of a best-effort heuristic.
1165 /// We terminate when we find an unmatched `}` (without consuming it).
1166 pub(super) fn recover_stmt(&mut self) {
1167 self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore)
1170 /// If `break_on_semi` is `Break`, then we will stop consuming tokens after
1171 /// finding (and consuming) a `;` outside of `{}` or `[]` (note that this is
1172 /// approximate -- it can mean we break too early due to macros, but that
1173 /// should only lead to sub-optimal recovery, not inaccurate parsing).
1175 /// If `break_on_block` is `Break`, then we will stop consuming tokens
1176 /// after finding (and consuming) a brace-delimited block.
1177 pub(super) fn recover_stmt_(
1179 break_on_semi: SemiColonMode,
1180 break_on_block: BlockMode,
1182 let mut brace_depth = 0;
1183 let mut bracket_depth = 0;
1184 let mut in_block = false;
1185 debug!("recover_stmt_ enter loop (semi={:?}, block={:?})", break_on_semi, break_on_block);
1187 debug!("recover_stmt_ loop {:?}", self.token);
1188 match self.token.kind {
1189 token::OpenDelim(token::DelimToken::Brace) => {
1192 if break_on_block == BlockMode::Break && brace_depth == 1 && bracket_depth == 0
1197 token::OpenDelim(token::DelimToken::Bracket) => {
1201 token::CloseDelim(token::DelimToken::Brace) => {
1202 if brace_depth == 0 {
1203 debug!("recover_stmt_ return - close delim {:?}", self.token);
1208 if in_block && bracket_depth == 0 && brace_depth == 0 {
1209 debug!("recover_stmt_ return - block end {:?}", self.token);
1213 token::CloseDelim(token::DelimToken::Bracket) => {
1215 if bracket_depth < 0 {
1221 debug!("recover_stmt_ return - Eof");
1226 if break_on_semi == SemiColonMode::Break
1228 && bracket_depth == 0
1230 debug!("recover_stmt_ return - Semi");
1235 if break_on_semi == SemiColonMode::Comma
1237 && bracket_depth == 0 =>
1239 debug!("recover_stmt_ return - Semi");
1247 pub(super) fn check_for_for_in_in_typo(&mut self, in_span: Span) {
1248 if self.eat_keyword(kw::In) {
1249 // a common typo: `for _ in in bar {}`
1250 self.struct_span_err(self.prev_span, "expected iterable, found keyword `in`")
1251 .span_suggestion_short(
1252 in_span.until(self.prev_span),
1253 "remove the duplicated `in`",
1255 Applicability::MachineApplicable,
1261 pub(super) fn expected_semi_or_open_brace<T>(&mut self) -> PResult<'a, T> {
1262 let token_str = super::token_descr(&self.token);
1263 let msg = &format!("expected `;` or `{{`, found {}", token_str);
1264 let mut err = self.struct_span_err(self.token.span, msg);
1265 err.span_label(self.token.span, "expected `;` or `{`");
1269 pub(super) fn eat_incorrect_doc_comment_for_param_type(&mut self) {
1270 if let token::DocComment(_) = self.token.kind {
1271 self.struct_span_err(
1273 "documentation comments cannot be applied to a function parameter's type",
1275 .span_label(self.token.span, "doc comments are not allowed here")
1278 } else if self.token == token::Pound
1279 && self.look_ahead(1, |t| *t == token::OpenDelim(token::Bracket))
1281 let lo = self.token.span;
1282 // Skip every token until next possible arg.
1283 while self.token != token::CloseDelim(token::Bracket) {
1286 let sp = lo.to(self.token.span);
1288 self.struct_span_err(sp, "attributes cannot be applied to a function parameter's type")
1289 .span_label(sp, "attributes are not allowed here")
1294 pub(super) fn parameter_without_type(
1296 err: &mut DiagnosticBuilder<'_>,
1300 ) -> Option<Ident> {
1301 // If we find a pattern followed by an identifier, it could be an (incorrect)
1302 // C-style parameter declaration.
1303 if self.check_ident()
1304 && self.look_ahead(1, |t| *t == token::Comma || *t == token::CloseDelim(token::Paren))
1306 // `fn foo(String s) {}`
1307 let ident = self.parse_ident().unwrap();
1308 let span = pat.span.with_hi(ident.span.hi());
1310 err.span_suggestion(
1312 "declare the type after the parameter binding",
1313 String::from("<identifier>: <type>"),
1314 Applicability::HasPlaceholders,
1317 } else if let PatKind::Ident(_, ident, _) = pat.kind {
1319 && (self.token == token::Comma
1320 || self.token == token::Lt
1321 || self.token == token::CloseDelim(token::Paren))
1323 // `fn foo(a, b) {}`, `fn foo(a<x>, b<y>) {}` or `fn foo(usize, usize) {}`
1325 err.span_suggestion(
1327 "if this is a `self` type, give it a parameter name",
1328 format!("self: {}", ident),
1329 Applicability::MaybeIncorrect,
1332 // Avoid suggesting that `fn foo(HashMap<u32>)` is fixed with a change to
1333 // `fn foo(HashMap: TypeName<u32>)`.
1334 if self.token != token::Lt {
1335 err.span_suggestion(
1337 "if this was a parameter name, give it a type",
1338 format!("{}: TypeName", ident),
1339 Applicability::HasPlaceholders,
1342 err.span_suggestion(
1344 "if this is a type, explicitly ignore the parameter name",
1345 format!("_: {}", ident),
1346 Applicability::MachineApplicable,
1348 err.note("anonymous parameters are removed in the 2018 edition (see RFC 1685)");
1350 // Don't attempt to recover by using the `X` in `X<Y>` as the parameter name.
1351 return if self.token == token::Lt { None } else { Some(ident) };
1357 pub(super) fn recover_arg_parse(&mut self) -> PResult<'a, (P<ast::Pat>, P<ast::Ty>)> {
1358 let pat = self.parse_pat(Some("argument name"))?;
1359 self.expect(&token::Colon)?;
1360 let ty = self.parse_ty()?;
1366 "patterns aren't allowed in methods without bodies",
1368 .span_suggestion_short(
1370 "give this argument a name or use an underscore to ignore it",
1372 Applicability::MachineApplicable,
1376 // Pretend the pattern is `_`, to avoid duplicate errors from AST validation.
1377 let pat = P(Pat { kind: PatKind::Wild, span: pat.span, id: ast::DUMMY_NODE_ID });
1381 pub(super) fn recover_bad_self_param(&mut self, mut param: Param) -> PResult<'a, Param> {
1382 let sp = param.pat.span;
1383 param.ty.kind = TyKind::Err;
1384 self.struct_span_err(sp, "unexpected `self` parameter in function")
1385 .span_label(sp, "must be the first parameter of an associated function")
1390 pub(super) fn consume_block(
1392 delim: token::DelimToken,
1393 consume_close: ConsumeClosingDelim,
1395 let mut brace_depth = 0;
1397 if self.eat(&token::OpenDelim(delim)) {
1399 } else if self.check(&token::CloseDelim(delim)) {
1400 if brace_depth == 0 {
1401 if let ConsumeClosingDelim::Yes = consume_close {
1402 // Some of the callers of this method expect to be able to parse the
1403 // closing delimiter themselves, so we leave it alone. Otherwise we advance
1413 } else if self.token == token::Eof || self.eat(&token::CloseDelim(token::NoDelim)) {
1421 pub(super) fn expected_expression_found(&self) -> DiagnosticBuilder<'a> {
1422 let (span, msg) = match (&self.token.kind, self.subparser_name) {
1423 (&token::Eof, Some(origin)) => {
1424 let sp = self.sess.source_map().next_point(self.token.span);
1425 (sp, format!("expected expression, found end of {}", origin))
1429 format!("expected expression, found {}", super::token_descr(&self.token),),
1432 let mut err = self.struct_span_err(span, &msg);
1433 let sp = self.sess.source_map().start_point(self.token.span);
1434 if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
1435 self.sess.expr_parentheses_needed(&mut err, *sp, None);
1437 err.span_label(span, "expected expression");
1443 mut acc: i64, // `i64` because malformed code can have more closing delims than opening.
1444 // Not using `FxHashMap` due to `token::TokenKind: !Eq + !Hash`.
1445 modifier: &[(token::TokenKind, i64)],
1448 if let Some((_, val)) = modifier.iter().find(|(t, _)| *t == self.token.kind) {
1451 if self.token.kind == token::Eof {
1458 /// Replace duplicated recovered parameters with `_` pattern to avoid unnecessary errors.
1460 /// This is necessary because at this point we don't know whether we parsed a function with
1461 /// anonymous parameters or a function with names but no types. In order to minimize
1462 /// unnecessary errors, we assume the parameters are in the shape of `fn foo(a, b, c)` where
1463 /// the parameters are *names* (so we don't emit errors about not being able to find `b` in
1464 /// the local scope), but if we find the same name multiple times, like in `fn foo(i8, i8)`,
1465 /// we deduplicate them to not complain about duplicated parameter names.
1466 pub(super) fn deduplicate_recovered_params_names(&self, fn_inputs: &mut Vec<Param>) {
1467 let mut seen_inputs = FxHashSet::default();
1468 for input in fn_inputs.iter_mut() {
1469 let opt_ident = if let (PatKind::Ident(_, ident, _), TyKind::Err) =
1470 (&input.pat.kind, &input.ty.kind)
1476 if let Some(ident) = opt_ident {
1477 if seen_inputs.contains(&ident) {
1478 input.pat.kind = PatKind::Wild;
1480 seen_inputs.insert(ident);