1 use super::{Parser, PathStyle, TokenType};
3 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
6 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
8 self as ast, BareFnTy, FnRetTy, GenericBound, GenericBounds, GenericParam, Generics, Lifetime,
9 MacCall, MutTy, Mutability, PolyTraitRef, TraitBoundModifier, TraitObjectSyntax, Ty, TyKind,
11 use rustc_errors::{pluralize, struct_span_err, Applicability, PResult};
12 use rustc_span::source_map::Span;
13 use rustc_span::symbol::{kw, sym};
15 /// Any `?` or `~const` modifiers that appear at the start of a bound.
16 struct BoundModifiers {
21 maybe_const: Option<Span>,
25 fn to_trait_bound_modifier(&self) -> TraitBoundModifier {
26 match (self.maybe, self.maybe_const) {
27 (None, None) => TraitBoundModifier::None,
28 (Some(_), None) => TraitBoundModifier::Maybe,
29 (None, Some(_)) => TraitBoundModifier::MaybeConst,
30 (Some(_), Some(_)) => TraitBoundModifier::MaybeConstMaybe,
35 #[derive(Copy, Clone, PartialEq)]
36 pub(super) enum AllowPlus {
42 pub(super) enum RecoverQPath {
47 pub(super) enum RecoverQuestionMark {
52 /// Signals whether parsing a type should recover `->`.
54 /// More specifically, when parsing a function like:
56 /// fn foo() => u8 { 0 }
57 /// fn bar(): u8 { 0 }
59 /// The compiler will try to recover interpreting `foo() => u8` as `foo() -> u8` when calling
60 /// `parse_ty` with anything except `RecoverReturnSign::No`, and it will try to recover `bar(): u8`
61 /// as `bar() -> u8` when passing `RecoverReturnSign::Yes` to `parse_ty`
62 #[derive(Copy, Clone, PartialEq)]
63 pub(super) enum RecoverReturnSign {
69 impl RecoverReturnSign {
70 /// [RecoverReturnSign::Yes] allows for recovering `fn foo() => u8` and `fn foo(): u8`,
71 /// [RecoverReturnSign::OnlyFatArrow] allows for recovering only `fn foo() => u8` (recovering
72 /// colons can cause problems when parsing where clauses), and
73 /// [RecoverReturnSign::No] doesn't allow for any recovery of the return type arrow
74 fn can_recover(self, token: &TokenKind) -> bool {
76 Self::Yes => matches!(token, token::FatArrow | token::Colon),
77 Self::OnlyFatArrow => matches!(token, token::FatArrow),
83 // Is `...` (`CVarArgs`) legal at this level of type parsing?
90 /// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
91 /// `IDENT<<u8 as Trait>::AssocTy>`.
93 /// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
94 /// that `IDENT` is not the ident of a fn trait.
95 fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
96 t == &token::ModSep || t == &token::Lt || t == &token::BinOp(token::Shl)
101 pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
102 self.parse_ty_common(
106 RecoverReturnSign::Yes,
108 RecoverQuestionMark::Yes,
112 pub(super) fn parse_ty_with_generics_recovery(
114 ty_params: &Generics,
115 ) -> PResult<'a, P<Ty>> {
116 self.parse_ty_common(
120 RecoverReturnSign::Yes,
122 RecoverQuestionMark::Yes,
126 /// Parse a type suitable for a function or function pointer parameter.
127 /// The difference from `parse_ty` is that this version allows `...`
128 /// (`CVarArgs`) at the top level of the type.
129 pub(super) fn parse_ty_for_param(&mut self) -> PResult<'a, P<Ty>> {
130 self.parse_ty_common(
134 RecoverReturnSign::Yes,
136 RecoverQuestionMark::Yes,
140 /// Parses a type in restricted contexts where `+` is not permitted.
142 /// Example 1: `&'a TYPE`
143 /// `+` is prohibited to maintain operator priority (P(+) < P(&)).
144 /// Example 2: `value1 as TYPE + value2`
145 /// `+` is prohibited to avoid interactions with expression grammar.
146 pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
147 self.parse_ty_common(
151 RecoverReturnSign::Yes,
153 RecoverQuestionMark::Yes,
157 /// Parses a type following an `as` cast. Similar to `parse_ty_no_plus`, but signaling origin
158 /// for better diagnostics involving `?`.
159 pub(super) fn parse_as_cast_ty(&mut self) -> PResult<'a, P<Ty>> {
160 self.parse_ty_common(
164 RecoverReturnSign::Yes,
166 RecoverQuestionMark::No,
170 pub(super) fn parse_no_question_mark_recover(&mut self) -> PResult<'a, P<Ty>> {
171 self.parse_ty_common(
175 RecoverReturnSign::Yes,
177 RecoverQuestionMark::No,
181 /// Parse a type without recovering `:` as `->` to avoid breaking code such as `where fn() : for<'a>`
182 pub(super) fn parse_ty_for_where_clause(&mut self) -> PResult<'a, P<Ty>> {
183 self.parse_ty_common(
187 RecoverReturnSign::OnlyFatArrow,
189 RecoverQuestionMark::Yes,
193 /// Parses an optional return type `[ -> TY ]` in a function declaration.
194 pub(super) fn parse_ret_ty(
196 allow_plus: AllowPlus,
197 recover_qpath: RecoverQPath,
198 recover_return_sign: RecoverReturnSign,
199 ) -> PResult<'a, FnRetTy> {
200 Ok(if self.eat(&token::RArrow) {
201 // FIXME(Centril): Can we unconditionally `allow_plus`?
202 let ty = self.parse_ty_common(
208 RecoverQuestionMark::Yes,
211 } else if recover_return_sign.can_recover(&self.token.kind) {
212 // Don't `eat` to prevent `=>` from being added as an expected token which isn't
213 // actually expected and could only confuse users
215 self.struct_span_err(self.prev_token.span, "return types are denoted using `->`")
216 .span_suggestion_short(
217 self.prev_token.span,
220 Applicability::MachineApplicable,
223 let ty = self.parse_ty_common(
229 RecoverQuestionMark::Yes,
233 FnRetTy::Default(self.token.span.shrink_to_lo())
239 allow_plus: AllowPlus,
240 allow_c_variadic: AllowCVariadic,
241 recover_qpath: RecoverQPath,
242 recover_return_sign: RecoverReturnSign,
243 ty_generics: Option<&Generics>,
244 recover_question_mark: RecoverQuestionMark,
245 ) -> PResult<'a, P<Ty>> {
246 let allow_qpath_recovery = recover_qpath == RecoverQPath::Yes;
247 maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
248 maybe_whole!(self, NtTy, |x| x);
250 let lo = self.token.span;
251 let mut impl_dyn_multi = false;
252 let kind = if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
253 self.parse_ty_tuple_or_parens(lo, allow_plus)?
254 } else if self.eat(&token::Not) {
257 } else if self.eat(&token::BinOp(token::Star)) {
259 } else if self.eat(&token::OpenDelim(Delimiter::Bracket)) {
260 self.parse_array_or_slice_ty()?
261 } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
264 self.parse_borrowed_pointee()?
265 } else if self.eat_keyword_noexpect(kw::Typeof) {
266 self.parse_typeof_ty()?
267 } else if self.eat_keyword(kw::Underscore) {
268 // A type to be inferred `_`
270 } else if self.check_fn_front_matter(false) {
271 // Function pointer type
272 self.parse_ty_bare_fn(lo, Vec::new(), recover_return_sign)?
273 } else if self.check_keyword(kw::For) {
274 // Function pointer type or bound list (trait object type) starting with a poly-trait.
275 // `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
276 // `for<'lt> Trait1<'lt> + Trait2 + 'a`
277 let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
278 if self.check_fn_front_matter(false) {
279 self.parse_ty_bare_fn(lo, lifetime_defs, recover_return_sign)?
281 let path = self.parse_path(PathStyle::Type)?;
282 let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
283 self.parse_remaining_bounds_path(lifetime_defs, path, lo, parse_plus)?
285 } else if self.eat_keyword(kw::Impl) {
286 self.parse_impl_ty(&mut impl_dyn_multi)?
287 } else if self.is_explicit_dyn_type() {
288 self.parse_dyn_ty(&mut impl_dyn_multi)?
289 } else if self.eat_lt() {
291 let (qself, path) = self.parse_qpath(PathStyle::Type)?;
292 TyKind::Path(Some(qself), path)
293 } else if self.check_path() {
294 self.parse_path_start_ty(lo, allow_plus, ty_generics)?
295 } else if self.can_begin_bound() {
296 self.parse_bare_trait_object(lo, allow_plus)?
297 } else if self.eat(&token::DotDotDot) {
298 if allow_c_variadic == AllowCVariadic::Yes {
301 // FIXME(Centril): Should we just allow `...` syntactically
302 // anywhere in a type and use semantic restrictions instead?
303 self.error_illegal_c_varadic_ty(lo);
307 let msg = format!("expected type, found {}", super::token_descr(&self.token));
308 let mut err = self.struct_span_err(self.token.span, &msg);
309 err.span_label(self.token.span, "expected type");
310 self.maybe_annotate_with_ascription(&mut err, true);
314 let span = lo.to(self.prev_token.span);
315 let mut ty = self.mk_ty(span, kind);
317 // Try to recover from use of `+` with incorrect priority.
318 if matches!(allow_plus, AllowPlus::Yes) {
319 self.maybe_recover_from_bad_type_plus(&ty)?;
321 self.maybe_report_ambiguous_plus(impl_dyn_multi, &ty);
323 if let RecoverQuestionMark::Yes = recover_question_mark {
324 ty = self.maybe_recover_from_question_mark(ty);
326 if allow_qpath_recovery { self.maybe_recover_from_bad_qpath(ty) } else { Ok(ty) }
330 /// - `(TYPE)`, a parenthesized type.
331 /// - `(TYPE,)`, a tuple with a single field of type TYPE.
332 fn parse_ty_tuple_or_parens(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
333 let mut trailing_plus = false;
334 let (ts, trailing) = self.parse_paren_comma_seq(|p| {
335 let ty = p.parse_ty()?;
336 trailing_plus = p.prev_token.kind == TokenKind::BinOp(token::Plus);
340 if ts.len() == 1 && !trailing {
341 let ty = ts.into_iter().next().unwrap().into_inner();
342 let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
344 // `(TY_BOUND_NOPAREN) + BOUND + ...`.
345 TyKind::Path(None, path) if maybe_bounds => {
346 self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
348 TyKind::TraitObject(bounds, TraitObjectSyntax::None)
349 if maybe_bounds && bounds.len() == 1 && !trailing_plus =>
351 self.parse_remaining_bounds(bounds, true)
354 _ => Ok(TyKind::Paren(P(ty))),
361 fn parse_bare_trait_object(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
362 let lt_no_plus = self.check_lifetime() && !self.look_ahead(1, |t| t.is_like_plus());
363 let bounds = self.parse_generic_bounds_common(allow_plus, None)?;
365 self.struct_span_err(lo, "lifetime in trait object type must be followed by `+`")
368 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
371 fn parse_remaining_bounds_path(
373 generic_params: Vec<GenericParam>,
377 ) -> PResult<'a, TyKind> {
378 let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_token.span));
379 let bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
380 self.parse_remaining_bounds(bounds, parse_plus)
383 /// Parse the remainder of a bare trait object type given an already parsed list.
384 fn parse_remaining_bounds(
386 mut bounds: GenericBounds,
388 ) -> PResult<'a, TyKind> {
390 self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
391 bounds.append(&mut self.parse_generic_bounds(Some(self.prev_token.span))?);
393 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
396 /// Parses a raw pointer type: `*[const | mut] $type`.
397 fn parse_ty_ptr(&mut self) -> PResult<'a, TyKind> {
398 let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
399 let span = self.prev_token.span;
400 self.struct_span_err(span, "expected `mut` or `const` keyword in raw pointer type")
403 "add `mut` or `const` here",
404 ["mut ".to_string(), "const ".to_string()],
405 Applicability::HasPlaceholders,
410 let ty = self.parse_ty_no_plus()?;
411 Ok(TyKind::Ptr(MutTy { ty, mutbl }))
414 /// Parses an array (`[TYPE; EXPR]`) or slice (`[TYPE]`) type.
415 /// The opening `[` bracket is already eaten.
416 fn parse_array_or_slice_ty(&mut self) -> PResult<'a, TyKind> {
417 let elt_ty = match self.parse_ty() {
420 if self.look_ahead(1, |t| t.kind == token::CloseDelim(Delimiter::Bracket))
421 | self.look_ahead(1, |t| t.kind == token::Semi) =>
423 // Recover from `[LIT; EXPR]` and `[LIT]`
426 self.mk_ty(self.prev_token.span, TyKind::Err)
428 Err(err) => return Err(err),
431 let ty = if self.eat(&token::Semi) {
432 let mut length = self.parse_anon_const_expr()?;
433 if let Err(e) = self.expect(&token::CloseDelim(Delimiter::Bracket)) {
434 // Try to recover from `X<Y, ...>` when `X::<Y, ...>` works
435 self.check_mistyped_turbofish_with_multiple_type_params(e, &mut length.value)?;
436 self.expect(&token::CloseDelim(Delimiter::Bracket))?;
438 TyKind::Array(elt_ty, length)
440 self.expect(&token::CloseDelim(Delimiter::Bracket))?;
441 TyKind::Slice(elt_ty)
447 fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
448 let and_span = self.prev_token.span;
449 let mut opt_lifetime =
450 if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
451 let mut mutbl = self.parse_mutability();
452 if self.token.is_lifetime() && mutbl == Mutability::Mut && opt_lifetime.is_none() {
453 // A lifetime is invalid here: it would be part of a bare trait bound, which requires
454 // it to be followed by a plus, but we disallow plus in the pointee type.
455 // So we can handle this case as an error here, and suggest `'a mut`.
456 // If there *is* a plus next though, handling the error later provides better suggestions
457 // (like adding parentheses)
458 if !self.look_ahead(1, |t| t.is_like_plus()) {
459 let lifetime_span = self.token.span;
460 let span = and_span.to(lifetime_span);
462 let mut err = self.struct_span_err(span, "lifetime must precede `mut`");
463 if let Ok(lifetime_src) = self.span_to_snippet(lifetime_span) {
466 "place the lifetime before `mut`",
467 format!("&{} mut", lifetime_src),
468 Applicability::MaybeIncorrect,
473 opt_lifetime = Some(self.expect_lifetime());
475 } else if self.token.is_keyword(kw::Dyn)
476 && mutbl == Mutability::Not
477 && self.look_ahead(1, |t| t.is_keyword(kw::Mut))
479 // We have `&dyn mut ...`, which is invalid and should be `&mut dyn ...`.
480 let span = and_span.to(self.look_ahead(1, |t| t.span));
481 let mut err = self.struct_span_err(span, "`mut` must precede `dyn`");
484 "place `mut` before `dyn`",
486 Applicability::MachineApplicable,
491 mutbl = Mutability::Mut;
492 let (dyn_tok, dyn_tok_sp) = (self.token.clone(), self.token_spacing);
494 self.bump_with((dyn_tok, dyn_tok_sp));
496 let ty = self.parse_ty_no_plus()?;
497 Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }))
500 // Parses the `typeof(EXPR)`.
501 // To avoid ambiguity, the type is surrounded by parentheses.
502 fn parse_typeof_ty(&mut self) -> PResult<'a, TyKind> {
503 self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
504 let expr = self.parse_anon_const_expr()?;
505 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
506 Ok(TyKind::Typeof(expr))
509 /// Parses a function pointer type (`TyKind::BareFn`).
510 /// ```ignore (illustrative)
511 /// [unsafe] [extern "ABI"] fn (S) -> T
512 /// // ^~~~~^ ^~~~^ ^~^ ^
514 /// // | | | Return type
515 /// // Function Style ABI Parameter types
517 /// We actually parse `FnHeader FnDecl`, but we error on `const` and `async` qualifiers.
521 params: Vec<GenericParam>,
522 recover_return_sign: RecoverReturnSign,
523 ) -> PResult<'a, TyKind> {
524 let inherited_vis = rustc_ast::Visibility {
525 span: rustc_span::DUMMY_SP,
526 kind: rustc_ast::VisibilityKind::Inherited,
529 let span_start = self.token.span;
530 let ast::FnHeader { ext, unsafety, constness, asyncness } =
531 self.parse_fn_front_matter(&inherited_vis)?;
532 let decl = self.parse_fn_decl(|_| false, AllowPlus::No, recover_return_sign)?;
533 let whole_span = lo.to(self.prev_token.span);
534 if let ast::Const::Yes(span) = constness {
535 // If we ever start to allow `const fn()`, then update
536 // feature gating for `#![feature(const_extern_fn)]` to
538 self.error_fn_ptr_bad_qualifier(whole_span, span, "const");
540 if let ast::Async::Yes { span, .. } = asyncness {
541 self.error_fn_ptr_bad_qualifier(whole_span, span, "async");
543 let decl_span = span_start.to(self.token.span);
544 Ok(TyKind::BareFn(P(BareFnTy { ext, unsafety, generic_params: params, decl, decl_span })))
547 /// Emit an error for the given bad function pointer qualifier.
548 fn error_fn_ptr_bad_qualifier(&self, span: Span, qual_span: Span, qual: &str) {
549 self.struct_span_err(span, &format!("an `fn` pointer type cannot be `{}`", qual))
550 .span_label(qual_span, format!("`{}` because of this", qual))
551 .span_suggestion_short(
553 &format!("remove the `{}` qualifier", qual),
555 Applicability::MaybeIncorrect,
560 /// Parses an `impl B0 + ... + Bn` type.
561 fn parse_impl_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
562 // Always parse bounds greedily for better error recovery.
563 let bounds = self.parse_generic_bounds(None)?;
564 *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
565 Ok(TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds))
568 /// Is a `dyn B0 + ... + Bn` type allowed here?
569 fn is_explicit_dyn_type(&mut self) -> bool {
570 self.check_keyword(kw::Dyn)
571 && (!self.token.uninterpolated_span().rust_2015()
572 || self.look_ahead(1, |t| {
573 (t.can_begin_bound() || t.kind == TokenKind::BinOp(token::Star))
574 && !can_continue_type_after_non_fn_ident(t)
578 /// Parses a `dyn B0 + ... + Bn` type.
580 /// Note that this does *not* parse bare trait objects.
581 fn parse_dyn_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
582 self.bump(); // `dyn`
585 let syntax = if self.eat(&TokenKind::BinOp(token::Star)) {
586 TraitObjectSyntax::DynStar
588 TraitObjectSyntax::Dyn
591 // Always parse bounds greedily for better error recovery.
592 let bounds = self.parse_generic_bounds(None)?;
593 *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
594 Ok(TyKind::TraitObject(bounds, syntax))
597 /// Parses a type starting with a path.
600 /// 1. a type macro, `mac!(...)`,
601 /// 2. a bare trait object, `B0 + ... + Bn`,
602 /// 3. or a path, `path::to::MyType`.
603 fn parse_path_start_ty(
606 allow_plus: AllowPlus,
607 ty_generics: Option<&Generics>,
608 ) -> PResult<'a, TyKind> {
610 let path = self.parse_path_inner(PathStyle::Type, ty_generics)?;
611 if self.eat(&token::Not) {
612 // Macro invocation in type position
613 Ok(TyKind::MacCall(P(MacCall {
615 args: self.parse_mac_args()?,
616 prior_type_ascription: self.last_type_ascription,
618 } else if allow_plus == AllowPlus::Yes && self.check_plus() {
619 // `Trait1 + Trait2 + 'a`
620 self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
623 Ok(TyKind::Path(None, path))
627 fn error_illegal_c_varadic_ty(&self, lo: Span) {
629 self.sess.span_diagnostic,
630 lo.to(self.prev_token.span),
632 "C-variadic type `...` may not be nested inside another type",
637 pub(super) fn parse_generic_bounds(
639 colon_span: Option<Span>,
640 ) -> PResult<'a, GenericBounds> {
641 self.parse_generic_bounds_common(AllowPlus::Yes, colon_span)
644 /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
646 /// See `parse_generic_bound` for the `BOUND` grammar.
647 fn parse_generic_bounds_common(
649 allow_plus: AllowPlus,
650 colon_span: Option<Span>,
651 ) -> PResult<'a, GenericBounds> {
652 let mut bounds = Vec::new();
653 let mut negative_bounds = Vec::new();
655 while self.can_begin_bound()
656 // Continue even if we find a keyword.
657 // This is necessary for error recover on, for example, `impl fn()`.
659 // The only keyword that can go after generic bounds is `where`, so stop if it's it.
660 || (self.token.is_reserved_ident() && !self.token.is_keyword(kw::Where))
662 if self.token.is_keyword(kw::Dyn) {
663 // Account for `&dyn Trait + dyn Other`.
664 self.struct_span_err(self.token.span, "invalid `dyn` keyword")
665 .help("`dyn` is only needed at the start of a trait `+`-separated list")
668 "remove this keyword",
670 Applicability::MachineApplicable,
675 match self.parse_generic_bound()? {
676 Ok(bound) => bounds.push(bound),
677 Err(neg_sp) => negative_bounds.push(neg_sp),
679 if allow_plus == AllowPlus::No || !self.eat_plus() {
684 if !negative_bounds.is_empty() {
685 self.error_negative_bounds(colon_span, &bounds, negative_bounds);
691 /// Can the current token begin a bound?
692 fn can_begin_bound(&mut self) -> bool {
693 // This needs to be synchronized with `TokenKind::can_begin_bound`.
695 || self.check_lifetime()
696 || self.check(&token::Not) // Used for error reporting only.
697 || self.check(&token::Question)
698 || self.check(&token::Tilde)
699 || self.check_keyword(kw::For)
700 || self.check(&token::OpenDelim(Delimiter::Parenthesis))
703 fn error_negative_bounds(
705 colon_span: Option<Span>,
706 bounds: &[GenericBound],
707 negative_bounds: Vec<Span>,
709 let negative_bounds_len = negative_bounds.len();
710 let last_span = *negative_bounds.last().expect("no negative bounds, but still error?");
711 let mut err = self.struct_span_err(negative_bounds, "negative bounds are not supported");
712 err.span_label(last_span, "negative bounds are not supported");
713 if let Some(bound_list) = colon_span {
714 let bound_list = bound_list.to(self.prev_token.span);
715 let mut new_bound_list = String::new();
716 if !bounds.is_empty() {
717 let mut snippets = bounds.iter().map(|bound| self.span_to_snippet(bound.span()));
718 while let Some(Ok(snippet)) = snippets.next() {
719 new_bound_list.push_str(" + ");
720 new_bound_list.push_str(&snippet);
722 new_bound_list = new_bound_list.replacen(" +", ":", 1);
724 err.tool_only_span_suggestion(
726 &format!("remove the bound{}", pluralize!(negative_bounds_len)),
728 Applicability::MachineApplicable,
734 /// Parses a bound according to the grammar:
736 /// BOUND = TY_BOUND | LT_BOUND
738 fn parse_generic_bound(&mut self) -> PResult<'a, Result<GenericBound, Span>> {
739 let anchor_lo = self.prev_token.span;
740 let lo = self.token.span;
741 let has_parens = self.eat(&token::OpenDelim(Delimiter::Parenthesis));
742 let inner_lo = self.token.span;
743 let is_negative = self.eat(&token::Not);
745 let modifiers = self.parse_ty_bound_modifiers()?;
746 let bound = if self.token.is_lifetime() {
747 self.error_lt_bound_with_modifiers(modifiers);
748 self.parse_generic_lt_bound(lo, inner_lo, has_parens)?
750 self.parse_generic_ty_bound(lo, has_parens, modifiers)?
753 Ok(if is_negative { Err(anchor_lo.to(self.prev_token.span)) } else { Ok(bound) })
756 /// Parses a lifetime ("outlives") bound, e.g. `'a`, according to:
758 /// LT_BOUND = LIFETIME
760 fn parse_generic_lt_bound(
765 ) -> PResult<'a, GenericBound> {
766 let bound = GenericBound::Outlives(self.expect_lifetime());
768 // FIXME(Centril): Consider not erroring here and accepting `('lt)` instead,
769 // possibly introducing `GenericBound::Paren(P<GenericBound>)`?
770 self.recover_paren_lifetime(lo, inner_lo)?;
775 /// Emits an error if any trait bound modifiers were present.
776 fn error_lt_bound_with_modifiers(&self, modifiers: BoundModifiers) {
777 if let Some(span) = modifiers.maybe_const {
778 self.struct_span_err(
780 "`~const` may only modify trait bounds, not lifetime bounds",
785 if let Some(span) = modifiers.maybe {
786 self.struct_span_err(span, "`?` may only modify trait bounds, not lifetime bounds")
791 /// Recover on `('lifetime)` with `(` already eaten.
792 fn recover_paren_lifetime(&mut self, lo: Span, inner_lo: Span) -> PResult<'a, ()> {
793 let inner_span = inner_lo.to(self.prev_token.span);
794 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
795 let mut err = self.struct_span_err(
796 lo.to(self.prev_token.span),
797 "parenthesized lifetime bounds are not supported",
799 if let Ok(snippet) = self.span_to_snippet(inner_span) {
800 err.span_suggestion_short(
801 lo.to(self.prev_token.span),
802 "remove the parentheses",
804 Applicability::MachineApplicable,
811 /// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `~const Trait`.
813 /// If no modifiers are present, this does not consume any tokens.
816 /// TY_BOUND_MODIFIERS = ["~const"] ["?"]
818 fn parse_ty_bound_modifiers(&mut self) -> PResult<'a, BoundModifiers> {
819 let maybe_const = if self.eat(&token::Tilde) {
820 let tilde = self.prev_token.span;
821 self.expect_keyword(kw::Const)?;
822 let span = tilde.to(self.prev_token.span);
823 self.sess.gated_spans.gate(sym::const_trait_impl, span);
825 } else if self.eat_keyword(kw::Const) {
826 let span = self.prev_token.span;
827 self.sess.gated_spans.gate(sym::const_trait_impl, span);
829 self.struct_span_err(span, "const bounds must start with `~`")
834 Applicability::MachineApplicable,
843 let maybe = if self.eat(&token::Question) { Some(self.prev_token.span) } else { None };
845 Ok(BoundModifiers { maybe, maybe_const })
848 /// Parses a type bound according to:
850 /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
851 /// TY_BOUND_NOPAREN = [TY_BOUND_MODIFIERS] [for<LT_PARAM_DEFS>] SIMPLE_PATH
854 /// For example, this grammar accepts `~const ?for<'a: 'b> m::Trait<'a>`.
855 fn parse_generic_ty_bound(
859 modifiers: BoundModifiers,
860 ) -> PResult<'a, GenericBound> {
861 let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
862 let path = self.parse_path(PathStyle::Type)?;
864 if self.token.is_like_plus() {
865 // Someone has written something like `&dyn (Trait + Other)`. The correct code
866 // would be `&(dyn Trait + Other)`, but we don't have access to the appropriate
867 // span to suggest that. When written as `&dyn Trait + Other`, an appropriate
868 // suggestion is given.
870 self.parse_remaining_bounds(bounds, true)?;
871 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
872 let sp = vec![lo, self.prev_token.span];
873 let sugg: Vec<_> = sp.iter().map(|sp| (*sp, String::new())).collect();
874 self.struct_span_err(sp, "incorrect braces around trait bounds")
875 .multipart_suggestion(
876 "remove the parentheses",
878 Applicability::MachineApplicable,
882 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
886 let modifier = modifiers.to_trait_bound_modifier();
887 let poly_trait = PolyTraitRef::new(lifetime_defs, path, lo.to(self.prev_token.span));
888 Ok(GenericBound::Trait(poly_trait, modifier))
891 /// Optionally parses `for<$generic_params>`.
892 pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
893 if self.eat_keyword(kw::For) {
895 let params = self.parse_generic_params()?;
897 // We rely on AST validation to rule out invalid cases: There must not be type
898 // parameters, and the lifetime parameters must not have bounds.
905 pub(super) fn check_lifetime(&mut self) -> bool {
906 self.expected_tokens.push(TokenType::Lifetime);
907 self.token.is_lifetime()
910 /// Parses a single lifetime `'a` or panics.
911 pub(super) fn expect_lifetime(&mut self) -> Lifetime {
912 if let Some(ident) = self.token.lifetime() {
914 Lifetime { ident, id: ast::DUMMY_NODE_ID }
916 self.span_bug(self.token.span, "not a lifetime")
920 pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
921 P(Ty { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })