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 ty = self.mk_ty(span, kind);
317 // Try to recover from use of `+` with incorrect priority.
318 self.maybe_report_ambiguous_plus(allow_plus, impl_dyn_multi, &ty);
319 self.maybe_recover_from_bad_type_plus(allow_plus, &ty)?;
320 let ty = self.maybe_recover_from_question_mark(ty, recover_question_mark);
321 self.maybe_recover_from_bad_qpath(ty, allow_qpath_recovery)
325 /// - `(TYPE)`, a parenthesized type.
326 /// - `(TYPE,)`, a tuple with a single field of type TYPE.
327 fn parse_ty_tuple_or_parens(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
328 let mut trailing_plus = false;
329 let (ts, trailing) = self.parse_paren_comma_seq(|p| {
330 let ty = p.parse_ty()?;
331 trailing_plus = p.prev_token.kind == TokenKind::BinOp(token::Plus);
335 if ts.len() == 1 && !trailing {
336 let ty = ts.into_iter().next().unwrap().into_inner();
337 let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
339 // `(TY_BOUND_NOPAREN) + BOUND + ...`.
340 TyKind::Path(None, path) if maybe_bounds => {
341 self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
343 TyKind::TraitObject(bounds, TraitObjectSyntax::None)
344 if maybe_bounds && bounds.len() == 1 && !trailing_plus =>
346 self.parse_remaining_bounds(bounds, true)
349 _ => Ok(TyKind::Paren(P(ty))),
356 fn parse_bare_trait_object(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
357 let lt_no_plus = self.check_lifetime() && !self.look_ahead(1, |t| t.is_like_plus());
358 let bounds = self.parse_generic_bounds_common(allow_plus, None)?;
360 self.struct_span_err(lo, "lifetime in trait object type must be followed by `+`")
363 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
366 fn parse_remaining_bounds_path(
368 generic_params: Vec<GenericParam>,
372 ) -> PResult<'a, TyKind> {
373 let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_token.span));
374 let bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
375 self.parse_remaining_bounds(bounds, parse_plus)
378 /// Parse the remainder of a bare trait object type given an already parsed list.
379 fn parse_remaining_bounds(
381 mut bounds: GenericBounds,
383 ) -> PResult<'a, TyKind> {
385 self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
386 bounds.append(&mut self.parse_generic_bounds(Some(self.prev_token.span))?);
388 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
391 /// Parses a raw pointer type: `*[const | mut] $type`.
392 fn parse_ty_ptr(&mut self) -> PResult<'a, TyKind> {
393 let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
394 let span = self.prev_token.span;
395 let msg = "expected mut or const in raw pointer type";
396 self.struct_span_err(span, msg)
397 .span_label(span, msg)
398 .help("use `*mut T` or `*const T` as appropriate")
402 let ty = self.parse_ty_no_plus()?;
403 Ok(TyKind::Ptr(MutTy { ty, mutbl }))
406 /// Parses an array (`[TYPE; EXPR]`) or slice (`[TYPE]`) type.
407 /// The opening `[` bracket is already eaten.
408 fn parse_array_or_slice_ty(&mut self) -> PResult<'a, TyKind> {
409 let elt_ty = match self.parse_ty() {
412 if self.look_ahead(1, |t| t.kind == token::CloseDelim(Delimiter::Bracket))
413 | self.look_ahead(1, |t| t.kind == token::Semi) =>
415 // Recover from `[LIT; EXPR]` and `[LIT]`
418 self.mk_ty(self.prev_token.span, TyKind::Err)
420 Err(err) => return Err(err),
423 let ty = if self.eat(&token::Semi) {
424 let mut length = self.parse_anon_const_expr()?;
425 if let Err(e) = self.expect(&token::CloseDelim(Delimiter::Bracket)) {
426 // Try to recover from `X<Y, ...>` when `X::<Y, ...>` works
427 self.check_mistyped_turbofish_with_multiple_type_params(e, &mut length.value)?;
428 self.expect(&token::CloseDelim(Delimiter::Bracket))?;
430 TyKind::Array(elt_ty, length)
432 self.expect(&token::CloseDelim(Delimiter::Bracket))?;
433 TyKind::Slice(elt_ty)
439 fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
440 let and_span = self.prev_token.span;
441 let mut opt_lifetime =
442 if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
443 let mut mutbl = self.parse_mutability();
444 if self.token.is_lifetime() && mutbl == Mutability::Mut && opt_lifetime.is_none() {
445 // A lifetime is invalid here: it would be part of a bare trait bound, which requires
446 // it to be followed by a plus, but we disallow plus in the pointee type.
447 // So we can handle this case as an error here, and suggest `'a mut`.
448 // If there *is* a plus next though, handling the error later provides better suggestions
449 // (like adding parentheses)
450 if !self.look_ahead(1, |t| t.is_like_plus()) {
451 let lifetime_span = self.token.span;
452 let span = and_span.to(lifetime_span);
454 let mut err = self.struct_span_err(span, "lifetime must precede `mut`");
455 if let Ok(lifetime_src) = self.span_to_snippet(lifetime_span) {
458 "place the lifetime before `mut`",
459 format!("&{} mut", lifetime_src),
460 Applicability::MaybeIncorrect,
465 opt_lifetime = Some(self.expect_lifetime());
467 } else if self.token.is_keyword(kw::Dyn)
468 && mutbl == Mutability::Not
469 && self.look_ahead(1, |t| t.is_keyword(kw::Mut))
471 // We have `&dyn mut ...`, which is invalid and should be `&mut dyn ...`.
472 let span = and_span.to(self.look_ahead(1, |t| t.span));
473 let mut err = self.struct_span_err(span, "`mut` must precede `dyn`");
476 "place `mut` before `dyn`",
477 "&mut dyn".to_string(),
478 Applicability::MachineApplicable,
483 mutbl = Mutability::Mut;
484 let (dyn_tok, dyn_tok_sp) = (self.token.clone(), self.token_spacing);
486 self.bump_with((dyn_tok, dyn_tok_sp));
488 let ty = self.parse_ty_no_plus()?;
489 Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }))
492 // Parses the `typeof(EXPR)`.
493 // To avoid ambiguity, the type is surrounded by parentheses.
494 fn parse_typeof_ty(&mut self) -> PResult<'a, TyKind> {
495 self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
496 let expr = self.parse_anon_const_expr()?;
497 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
498 Ok(TyKind::Typeof(expr))
501 /// Parses a function pointer type (`TyKind::BareFn`).
503 /// [unsafe] [extern "ABI"] fn (S) -> T
504 /// ^~~~~^ ^~~~^ ^~^ ^
506 /// | | | Return type
507 /// Function Style ABI Parameter types
509 /// We actually parse `FnHeader FnDecl`, but we error on `const` and `async` qualifiers.
513 params: Vec<GenericParam>,
514 recover_return_sign: RecoverReturnSign,
515 ) -> PResult<'a, TyKind> {
516 let inherited_vis = rustc_ast::Visibility {
517 span: rustc_span::DUMMY_SP,
518 kind: rustc_ast::VisibilityKind::Inherited,
521 let ast::FnHeader { ext, unsafety, constness, asyncness } =
522 self.parse_fn_front_matter(&inherited_vis)?;
523 let decl = self.parse_fn_decl(|_| false, AllowPlus::No, recover_return_sign)?;
524 let whole_span = lo.to(self.prev_token.span);
525 if let ast::Const::Yes(span) = constness {
526 // If we ever start to allow `const fn()`, then update
527 // feature gating for `#![feature(const_extern_fn)]` to
529 self.error_fn_ptr_bad_qualifier(whole_span, span, "const");
531 if let ast::Async::Yes { span, .. } = asyncness {
532 self.error_fn_ptr_bad_qualifier(whole_span, span, "async");
534 Ok(TyKind::BareFn(P(BareFnTy { ext, unsafety, generic_params: params, decl })))
537 /// Emit an error for the given bad function pointer qualifier.
538 fn error_fn_ptr_bad_qualifier(&self, span: Span, qual_span: Span, qual: &str) {
539 self.struct_span_err(span, &format!("an `fn` pointer type cannot be `{}`", qual))
540 .span_label(qual_span, format!("`{}` because of this", qual))
541 .span_suggestion_short(
543 &format!("remove the `{}` qualifier", qual),
545 Applicability::MaybeIncorrect,
550 /// Parses an `impl B0 + ... + Bn` type.
551 fn parse_impl_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
552 // Always parse bounds greedily for better error recovery.
553 let bounds = self.parse_generic_bounds(None)?;
554 *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
555 Ok(TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds))
558 /// Is a `dyn B0 + ... + Bn` type allowed here?
559 fn is_explicit_dyn_type(&mut self) -> bool {
560 self.check_keyword(kw::Dyn)
561 && (!self.token.uninterpolated_span().rust_2015()
562 || self.look_ahead(1, |t| {
563 t.can_begin_bound() && !can_continue_type_after_non_fn_ident(t)
567 /// Parses a `dyn B0 + ... + Bn` type.
569 /// Note that this does *not* parse bare trait objects.
570 fn parse_dyn_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
571 self.bump(); // `dyn`
572 // Always parse bounds greedily for better error recovery.
573 let bounds = self.parse_generic_bounds(None)?;
574 *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
575 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn))
578 /// Parses a type starting with a path.
581 /// 1. a type macro, `mac!(...)`,
582 /// 2. a bare trait object, `B0 + ... + Bn`,
583 /// 3. or a path, `path::to::MyType`.
584 fn parse_path_start_ty(
587 allow_plus: AllowPlus,
588 ty_generics: Option<&Generics>,
589 ) -> PResult<'a, TyKind> {
591 let path = self.parse_path_inner(PathStyle::Type, ty_generics)?;
592 if self.eat(&token::Not) {
593 // Macro invocation in type position
594 Ok(TyKind::MacCall(MacCall {
596 args: self.parse_mac_args()?,
597 prior_type_ascription: self.last_type_ascription,
599 } else if allow_plus == AllowPlus::Yes && self.check_plus() {
600 // `Trait1 + Trait2 + 'a`
601 self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
604 Ok(TyKind::Path(None, path))
608 fn error_illegal_c_varadic_ty(&self, lo: Span) {
610 self.sess.span_diagnostic,
611 lo.to(self.prev_token.span),
613 "C-variadic type `...` may not be nested inside another type",
618 pub(super) fn parse_generic_bounds(
620 colon_span: Option<Span>,
621 ) -> PResult<'a, GenericBounds> {
622 self.parse_generic_bounds_common(AllowPlus::Yes, colon_span)
625 /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
627 /// See `parse_generic_bound` for the `BOUND` grammar.
628 fn parse_generic_bounds_common(
630 allow_plus: AllowPlus,
631 colon_span: Option<Span>,
632 ) -> PResult<'a, GenericBounds> {
633 let mut bounds = Vec::new();
634 let mut negative_bounds = Vec::new();
636 while self.can_begin_bound() || self.token.is_keyword(kw::Dyn) {
637 if self.token.is_keyword(kw::Dyn) {
638 // Account for `&dyn Trait + dyn Other`.
639 self.struct_span_err(self.token.span, "invalid `dyn` keyword")
640 .help("`dyn` is only needed at the start of a trait `+`-separated list")
643 "remove this keyword",
645 Applicability::MachineApplicable,
650 match self.parse_generic_bound()? {
651 Ok(bound) => bounds.push(bound),
652 Err(neg_sp) => negative_bounds.push(neg_sp),
654 if allow_plus == AllowPlus::No || !self.eat_plus() {
659 if !negative_bounds.is_empty() {
660 self.error_negative_bounds(colon_span, &bounds, negative_bounds);
666 /// Can the current token begin a bound?
667 fn can_begin_bound(&mut self) -> bool {
668 // This needs to be synchronized with `TokenKind::can_begin_bound`.
670 || self.check_lifetime()
671 || self.check(&token::Not) // Used for error reporting only.
672 || self.check(&token::Question)
673 || self.check(&token::Tilde)
674 || self.check_keyword(kw::For)
675 || self.check(&token::OpenDelim(Delimiter::Parenthesis))
678 fn error_negative_bounds(
680 colon_span: Option<Span>,
681 bounds: &[GenericBound],
682 negative_bounds: Vec<Span>,
684 let negative_bounds_len = negative_bounds.len();
685 let last_span = *negative_bounds.last().expect("no negative bounds, but still error?");
686 let mut err = self.struct_span_err(negative_bounds, "negative bounds are not supported");
687 err.span_label(last_span, "negative bounds are not supported");
688 if let Some(bound_list) = colon_span {
689 let bound_list = bound_list.to(self.prev_token.span);
690 let mut new_bound_list = String::new();
691 if !bounds.is_empty() {
692 let mut snippets = bounds.iter().map(|bound| self.span_to_snippet(bound.span()));
693 while let Some(Ok(snippet)) = snippets.next() {
694 new_bound_list.push_str(" + ");
695 new_bound_list.push_str(&snippet);
697 new_bound_list = new_bound_list.replacen(" +", ":", 1);
699 err.tool_only_span_suggestion(
701 &format!("remove the bound{}", pluralize!(negative_bounds_len)),
703 Applicability::MachineApplicable,
709 /// Parses a bound according to the grammar:
711 /// BOUND = TY_BOUND | LT_BOUND
713 fn parse_generic_bound(&mut self) -> PResult<'a, Result<GenericBound, Span>> {
714 let anchor_lo = self.prev_token.span;
715 let lo = self.token.span;
716 let has_parens = self.eat(&token::OpenDelim(Delimiter::Parenthesis));
717 let inner_lo = self.token.span;
718 let is_negative = self.eat(&token::Not);
720 let modifiers = self.parse_ty_bound_modifiers()?;
721 let bound = if self.token.is_lifetime() {
722 self.error_lt_bound_with_modifiers(modifiers);
723 self.parse_generic_lt_bound(lo, inner_lo, has_parens)?
725 self.parse_generic_ty_bound(lo, has_parens, modifiers)?
728 Ok(if is_negative { Err(anchor_lo.to(self.prev_token.span)) } else { Ok(bound) })
731 /// Parses a lifetime ("outlives") bound, e.g. `'a`, according to:
733 /// LT_BOUND = LIFETIME
735 fn parse_generic_lt_bound(
740 ) -> PResult<'a, GenericBound> {
741 let bound = GenericBound::Outlives(self.expect_lifetime());
743 // FIXME(Centril): Consider not erroring here and accepting `('lt)` instead,
744 // possibly introducing `GenericBound::Paren(P<GenericBound>)`?
745 self.recover_paren_lifetime(lo, inner_lo)?;
750 /// Emits an error if any trait bound modifiers were present.
751 fn error_lt_bound_with_modifiers(&self, modifiers: BoundModifiers) {
752 if let Some(span) = modifiers.maybe_const {
753 self.struct_span_err(
755 "`~const` may only modify trait bounds, not lifetime bounds",
760 if let Some(span) = modifiers.maybe {
761 self.struct_span_err(span, "`?` may only modify trait bounds, not lifetime bounds")
766 /// Recover on `('lifetime)` with `(` already eaten.
767 fn recover_paren_lifetime(&mut self, lo: Span, inner_lo: Span) -> PResult<'a, ()> {
768 let inner_span = inner_lo.to(self.prev_token.span);
769 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
770 let mut err = self.struct_span_err(
771 lo.to(self.prev_token.span),
772 "parenthesized lifetime bounds are not supported",
774 if let Ok(snippet) = self.span_to_snippet(inner_span) {
775 err.span_suggestion_short(
776 lo.to(self.prev_token.span),
777 "remove the parentheses",
779 Applicability::MachineApplicable,
786 /// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `~const Trait`.
788 /// If no modifiers are present, this does not consume any tokens.
791 /// TY_BOUND_MODIFIERS = ["~const"] ["?"]
793 fn parse_ty_bound_modifiers(&mut self) -> PResult<'a, BoundModifiers> {
794 let maybe_const = if self.eat(&token::Tilde) {
795 let tilde = self.prev_token.span;
796 self.expect_keyword(kw::Const)?;
797 let span = tilde.to(self.prev_token.span);
798 self.sess.gated_spans.gate(sym::const_trait_impl, span);
804 let maybe = if self.eat(&token::Question) { Some(self.prev_token.span) } else { None };
806 Ok(BoundModifiers { maybe, maybe_const })
809 /// Parses a type bound according to:
811 /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
812 /// TY_BOUND_NOPAREN = [TY_BOUND_MODIFIERS] [for<LT_PARAM_DEFS>] SIMPLE_PATH
815 /// For example, this grammar accepts `~const ?for<'a: 'b> m::Trait<'a>`.
816 fn parse_generic_ty_bound(
820 modifiers: BoundModifiers,
821 ) -> PResult<'a, GenericBound> {
822 let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
823 let path = self.parse_path(PathStyle::Type)?;
825 if self.token.is_like_plus() {
826 // Someone has written something like `&dyn (Trait + Other)`. The correct code
827 // would be `&(dyn Trait + Other)`, but we don't have access to the appropriate
828 // span to suggest that. When written as `&dyn Trait + Other`, an appropriate
829 // suggestion is given.
831 self.parse_remaining_bounds(bounds, true)?;
832 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
833 let sp = vec![lo, self.prev_token.span];
834 let sugg: Vec<_> = sp.iter().map(|sp| (*sp, String::new())).collect();
835 self.struct_span_err(sp, "incorrect braces around trait bounds")
836 .multipart_suggestion(
837 "remove the parentheses",
839 Applicability::MachineApplicable,
843 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
847 let modifier = modifiers.to_trait_bound_modifier();
848 let poly_trait = PolyTraitRef::new(lifetime_defs, path, lo.to(self.prev_token.span));
849 Ok(GenericBound::Trait(poly_trait, modifier))
852 /// Optionally parses `for<$generic_params>`.
853 pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
854 if self.eat_keyword(kw::For) {
856 let params = self.parse_generic_params()?;
858 // We rely on AST validation to rule out invalid cases: There must not be type
859 // parameters, and the lifetime parameters must not have bounds.
866 pub(super) fn check_lifetime(&mut self) -> bool {
867 self.expected_tokens.push(TokenType::Lifetime);
868 self.token.is_lifetime()
871 /// Parses a single lifetime `'a` or panics.
872 pub(super) fn expect_lifetime(&mut self) -> Lifetime {
873 if let Some(ident) = self.token.lifetime() {
875 Lifetime { ident, id: ast::DUMMY_NODE_ID }
877 self.span_bug(self.token.span, "not a lifetime")
881 pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
882 P(Ty { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })