1 use super::{Parser, PathStyle, TokenType};
3 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
6 use rustc_ast::token::{self, Token, TokenKind};
7 use rustc_ast::{self as ast, BareFnTy, FnRetTy, GenericParam, Lifetime, MutTy, Ty, TyKind};
8 use rustc_ast::{GenericBound, GenericBounds, MacCall, Mutability};
9 use rustc_ast::{PolyTraitRef, TraitBoundModifier, TraitObjectSyntax};
10 use rustc_errors::{pluralize, struct_span_err, Applicability, PResult};
11 use rustc_span::source_map::Span;
12 use rustc_span::symbol::{kw, sym};
14 /// Any `?` or `~const` modifiers that appear at the start of a bound.
15 struct BoundModifiers {
20 maybe_const: Option<Span>,
24 fn to_trait_bound_modifier(&self) -> TraitBoundModifier {
25 match (self.maybe, self.maybe_const) {
26 (None, None) => TraitBoundModifier::None,
27 (Some(_), None) => TraitBoundModifier::Maybe,
28 (None, Some(_)) => TraitBoundModifier::MaybeConst,
29 (Some(_), Some(_)) => TraitBoundModifier::MaybeConstMaybe,
34 #[derive(Copy, Clone, PartialEq)]
35 pub(super) enum AllowPlus {
41 pub(super) enum RecoverQPath {
46 /// Signals whether parsing a type should recover `->`.
48 /// More specifically, when parsing a function like:
50 /// fn foo() => u8 { 0 }
51 /// fn bar(): u8 { 0 }
53 /// The compiler will try to recover interpreting `foo() => u8` as `foo() -> u8` when calling
54 /// `parse_ty` with anything except `RecoverReturnSign::No`, and it will try to recover `bar(): u8`
55 /// as `bar() -> u8` when passing `RecoverReturnSign::Yes` to `parse_ty`
56 #[derive(Copy, Clone, PartialEq)]
57 pub(super) enum RecoverReturnSign {
63 impl RecoverReturnSign {
64 /// [RecoverReturnSign::Yes] allows for recovering `fn foo() => u8` and `fn foo(): u8`,
65 /// [RecoverReturnSign::OnlyFatArrow] allows for recovering only `fn foo() => u8` (recovering
66 /// colons can cause problems when parsing where clauses), and
67 /// [RecoverReturnSign::No] doesn't allow for any recovery of the return type arrow
68 fn can_recover(self, token: &TokenKind) -> bool {
70 Self::Yes => matches!(token, token::FatArrow | token::Colon),
71 Self::OnlyFatArrow => matches!(token, token::FatArrow),
77 // Is `...` (`CVarArgs`) legal at this level of type parsing?
84 /// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
85 /// `IDENT<<u8 as Trait>::AssocTy>`.
87 /// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
88 /// that `IDENT` is not the ident of a fn trait.
89 fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
90 t == &token::ModSep || t == &token::Lt || t == &token::BinOp(token::Shl)
95 pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
100 RecoverReturnSign::Yes,
104 /// Parse a type suitable for a function or function pointer parameter.
105 /// The difference from `parse_ty` is that this version allows `...`
106 /// (`CVarArgs`) at the top level of the type.
107 pub(super) fn parse_ty_for_param(&mut self) -> PResult<'a, P<Ty>> {
108 self.parse_ty_common(
112 RecoverReturnSign::Yes,
116 /// Parses a type in restricted contexts where `+` is not permitted.
118 /// Example 1: `&'a TYPE`
119 /// `+` is prohibited to maintain operator priority (P(+) < P(&)).
120 /// Example 2: `value1 as TYPE + value2`
121 /// `+` is prohibited to avoid interactions with expression grammar.
122 pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
123 self.parse_ty_common(
127 RecoverReturnSign::Yes,
131 /// Parse a type without recovering `:` as `->` to avoid breaking code such as `where fn() : for<'a>`
132 pub(super) fn parse_ty_for_where_clause(&mut self) -> PResult<'a, P<Ty>> {
133 self.parse_ty_common(
137 RecoverReturnSign::OnlyFatArrow,
141 /// Parses an optional return type `[ -> TY ]` in a function declaration.
142 pub(super) fn parse_ret_ty(
144 allow_plus: AllowPlus,
145 recover_qpath: RecoverQPath,
146 recover_return_sign: RecoverReturnSign,
147 ) -> PResult<'a, FnRetTy> {
148 Ok(if self.eat(&token::RArrow) {
149 // FIXME(Centril): Can we unconditionally `allow_plus`?
150 let ty = self.parse_ty_common(
157 } else if recover_return_sign.can_recover(&self.token.kind) {
158 // Don't `eat` to prevent `=>` from being added as an expected token which isn't
159 // actually expected and could only confuse users
161 self.struct_span_err(self.prev_token.span, "return types are denoted using `->`")
162 .span_suggestion_short(
163 self.prev_token.span,
166 Applicability::MachineApplicable,
169 let ty = self.parse_ty_common(
177 FnRetTy::Default(self.token.span.shrink_to_lo())
183 allow_plus: AllowPlus,
184 allow_c_variadic: AllowCVariadic,
185 recover_qpath: RecoverQPath,
186 recover_return_sign: RecoverReturnSign,
187 ) -> PResult<'a, P<Ty>> {
188 let allow_qpath_recovery = recover_qpath == RecoverQPath::Yes;
189 maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
190 maybe_whole!(self, NtTy, |x| x);
192 let lo = self.token.span;
193 let mut impl_dyn_multi = false;
194 let kind = if self.check(&token::OpenDelim(token::Paren)) {
195 self.parse_ty_tuple_or_parens(lo, allow_plus)?
196 } else if self.eat(&token::Not) {
199 } else if self.eat(&token::BinOp(token::Star)) {
201 } else if self.eat(&token::OpenDelim(token::Bracket)) {
202 self.parse_array_or_slice_ty()?
203 } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
206 self.parse_borrowed_pointee()?
207 } else if self.eat_keyword_noexpect(kw::Typeof) {
208 self.parse_typeof_ty()?
209 } else if self.eat_keyword(kw::Underscore) {
210 // A type to be inferred `_`
212 } else if self.check_fn_front_matter(false) {
213 // Function pointer type
214 self.parse_ty_bare_fn(lo, Vec::new(), recover_return_sign)?
215 } else if self.check_keyword(kw::For) {
216 // Function pointer type or bound list (trait object type) starting with a poly-trait.
217 // `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
218 // `for<'lt> Trait1<'lt> + Trait2 + 'a`
219 let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
220 if self.check_fn_front_matter(false) {
221 self.parse_ty_bare_fn(lo, lifetime_defs, recover_return_sign)?
223 let path = self.parse_path(PathStyle::Type)?;
224 let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
225 self.parse_remaining_bounds_path(lifetime_defs, path, lo, parse_plus)?
227 } else if self.eat_keyword(kw::Impl) {
228 self.parse_impl_ty(&mut impl_dyn_multi)?
229 } else if self.is_explicit_dyn_type() {
230 self.parse_dyn_ty(&mut impl_dyn_multi)?
231 } else if self.eat_lt() {
233 let (qself, path) = self.parse_qpath(PathStyle::Type)?;
234 TyKind::Path(Some(qself), path)
235 } else if self.check_path() {
236 self.parse_path_start_ty(lo, allow_plus)?
237 } else if self.can_begin_bound() {
238 self.parse_bare_trait_object(lo, allow_plus)?
239 } else if self.eat(&token::DotDotDot) {
240 if allow_c_variadic == AllowCVariadic::Yes {
243 // FIXME(Centril): Should we just allow `...` syntactically
244 // anywhere in a type and use semantic restrictions instead?
245 self.error_illegal_c_varadic_ty(lo);
249 let msg = format!("expected type, found {}", super::token_descr(&self.token));
250 let mut err = self.struct_span_err(self.token.span, &msg);
251 err.span_label(self.token.span, "expected type");
252 self.maybe_annotate_with_ascription(&mut err, true);
256 let span = lo.to(self.prev_token.span);
257 let ty = self.mk_ty(span, kind);
259 // Try to recover from use of `+` with incorrect priority.
260 self.maybe_report_ambiguous_plus(allow_plus, impl_dyn_multi, &ty);
261 self.maybe_recover_from_bad_type_plus(allow_plus, &ty)?;
262 self.maybe_recover_from_bad_qpath(ty, allow_qpath_recovery)
266 /// - `(TYPE)`, a parenthesized type.
267 /// - `(TYPE,)`, a tuple with a single field of type TYPE.
268 fn parse_ty_tuple_or_parens(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
269 let mut trailing_plus = false;
270 let (ts, trailing) = self.parse_paren_comma_seq(|p| {
271 let ty = p.parse_ty()?;
272 trailing_plus = p.prev_token.kind == TokenKind::BinOp(token::Plus);
276 if ts.len() == 1 && !trailing {
277 let ty = ts.into_iter().next().unwrap().into_inner();
278 let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
280 // `(TY_BOUND_NOPAREN) + BOUND + ...`.
281 TyKind::Path(None, path) if maybe_bounds => {
282 self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
284 TyKind::TraitObject(bounds, TraitObjectSyntax::None)
285 if maybe_bounds && bounds.len() == 1 && !trailing_plus =>
287 self.parse_remaining_bounds(bounds, true)
290 _ => Ok(TyKind::Paren(P(ty))),
297 fn parse_bare_trait_object(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
298 let lt_no_plus = self.check_lifetime() && !self.look_ahead(1, |t| t.is_like_plus());
299 let bounds = self.parse_generic_bounds_common(allow_plus, None)?;
301 self.struct_span_err(lo, "lifetime in trait object type must be followed by `+`").emit()
303 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
306 fn parse_remaining_bounds_path(
308 generic_params: Vec<GenericParam>,
312 ) -> PResult<'a, TyKind> {
313 let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_token.span));
314 let bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
315 self.parse_remaining_bounds(bounds, parse_plus)
318 /// Parse the remainder of a bare trait object type given an already parsed list.
319 fn parse_remaining_bounds(
321 mut bounds: GenericBounds,
323 ) -> PResult<'a, TyKind> {
325 self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
326 bounds.append(&mut self.parse_generic_bounds(Some(self.prev_token.span))?);
328 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
331 /// Parses a raw pointer type: `*[const | mut] $type`.
332 fn parse_ty_ptr(&mut self) -> PResult<'a, TyKind> {
333 let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
334 let span = self.prev_token.span;
335 let msg = "expected mut or const in raw pointer type";
336 self.struct_span_err(span, msg)
337 .span_label(span, msg)
338 .help("use `*mut T` or `*const T` as appropriate")
342 let ty = self.parse_ty_no_plus()?;
343 Ok(TyKind::Ptr(MutTy { ty, mutbl }))
346 /// Parses an array (`[TYPE; EXPR]`) or slice (`[TYPE]`) type.
347 /// The opening `[` bracket is already eaten.
348 fn parse_array_or_slice_ty(&mut self) -> PResult<'a, TyKind> {
349 let elt_ty = match self.parse_ty() {
352 if self.look_ahead(1, |t| t.kind == token::CloseDelim(token::Bracket))
353 | self.look_ahead(1, |t| t.kind == token::Semi) =>
355 // Recover from `[LIT; EXPR]` and `[LIT]`
358 self.mk_ty(self.prev_token.span, TyKind::Err)
360 Err(err) => return Err(err),
363 let ty = if self.eat(&token::Semi) {
364 let mut length = self.parse_anon_const_expr()?;
365 if let Err(e) = self.expect(&token::CloseDelim(token::Bracket)) {
366 // Try to recover from `X<Y, ...>` when `X::<Y, ...>` works
367 self.check_mistyped_turbofish_with_multiple_type_params(e, &mut length.value)?;
368 self.expect(&token::CloseDelim(token::Bracket))?;
370 TyKind::Array(elt_ty, length)
372 self.expect(&token::CloseDelim(token::Bracket))?;
373 TyKind::Slice(elt_ty)
379 fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
380 let and_span = self.prev_token.span;
381 let mut opt_lifetime =
382 if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
383 let mut mutbl = self.parse_mutability();
384 if self.token.is_lifetime() && mutbl == Mutability::Mut && opt_lifetime.is_none() {
385 // A lifetime is invalid here: it would be part of a bare trait bound, which requires
386 // it to be followed by a plus, but we disallow plus in the pointee type.
387 // So we can handle this case as an error here, and suggest `'a mut`.
388 // If there *is* a plus next though, handling the error later provides better suggestions
389 // (like adding parentheses)
390 if !self.look_ahead(1, |t| t.is_like_plus()) {
391 let lifetime_span = self.token.span;
392 let span = and_span.to(lifetime_span);
394 let mut err = self.struct_span_err(span, "lifetime must precede `mut`");
395 if let Ok(lifetime_src) = self.span_to_snippet(lifetime_span) {
398 "place the lifetime before `mut`",
399 format!("&{} mut", lifetime_src),
400 Applicability::MaybeIncorrect,
405 opt_lifetime = Some(self.expect_lifetime());
407 } else if self.token.is_keyword(kw::Dyn)
408 && mutbl == Mutability::Not
409 && self.look_ahead(1, |t| t.is_keyword(kw::Mut))
411 // We have `&dyn mut ...`, which is invalid and should be `&mut dyn ...`.
412 let span = and_span.to(self.look_ahead(1, |t| t.span));
413 let mut err = self.struct_span_err(span, "`mut` must precede `dyn`");
416 "place `mut` before `dyn`",
417 "&mut dyn".to_string(),
418 Applicability::MachineApplicable,
423 mutbl = Mutability::Mut;
424 let (dyn_tok, dyn_tok_sp) = (self.token.clone(), self.token_spacing);
426 self.bump_with((dyn_tok, dyn_tok_sp));
428 let ty = self.parse_ty_no_plus()?;
429 Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }))
432 // Parses the `typeof(EXPR)`.
433 // To avoid ambiguity, the type is surrounded by parenthesis.
434 fn parse_typeof_ty(&mut self) -> PResult<'a, TyKind> {
435 self.expect(&token::OpenDelim(token::Paren))?;
436 let expr = self.parse_anon_const_expr()?;
437 self.expect(&token::CloseDelim(token::Paren))?;
438 Ok(TyKind::Typeof(expr))
441 /// Parses a function pointer type (`TyKind::BareFn`).
443 /// [unsafe] [extern "ABI"] fn (S) -> T
444 /// ^~~~~^ ^~~~^ ^~^ ^
446 /// | | | Return type
447 /// Function Style ABI Parameter types
449 /// We actually parse `FnHeader FnDecl`, but we error on `const` and `async` qualifiers.
453 params: Vec<GenericParam>,
454 recover_return_sign: RecoverReturnSign,
455 ) -> PResult<'a, TyKind> {
456 let ast::FnHeader { ext, unsafety, constness, asyncness } = self.parse_fn_front_matter()?;
457 let decl = self.parse_fn_decl(|_| false, AllowPlus::No, recover_return_sign)?;
458 let whole_span = lo.to(self.prev_token.span);
459 if let ast::Const::Yes(span) = constness {
460 self.error_fn_ptr_bad_qualifier(whole_span, span, "const");
462 if let ast::Async::Yes { span, .. } = asyncness {
463 self.error_fn_ptr_bad_qualifier(whole_span, span, "async");
465 Ok(TyKind::BareFn(P(BareFnTy { ext, unsafety, generic_params: params, decl })))
468 /// Emit an error for the given bad function pointer qualifier.
469 fn error_fn_ptr_bad_qualifier(&self, span: Span, qual_span: Span, qual: &str) {
470 self.struct_span_err(span, &format!("an `fn` pointer type cannot be `{}`", qual))
471 .span_label(qual_span, format!("`{}` because of this", qual))
472 .span_suggestion_short(
474 &format!("remove the `{}` qualifier", qual),
476 Applicability::MaybeIncorrect,
481 /// Parses an `impl B0 + ... + Bn` type.
482 fn parse_impl_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
483 // Always parse bounds greedily for better error recovery.
484 let bounds = self.parse_generic_bounds(None)?;
485 *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
486 Ok(TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds))
489 /// Is a `dyn B0 + ... + Bn` type allowed here?
490 fn is_explicit_dyn_type(&mut self) -> bool {
491 self.check_keyword(kw::Dyn)
492 && (!self.token.uninterpolated_span().rust_2015()
493 || self.look_ahead(1, |t| {
494 t.can_begin_bound() && !can_continue_type_after_non_fn_ident(t)
498 /// Parses a `dyn B0 + ... + Bn` type.
500 /// Note that this does *not* parse bare trait objects.
501 fn parse_dyn_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
502 self.bump(); // `dyn`
503 // Always parse bounds greedily for better error recovery.
504 let bounds = self.parse_generic_bounds(None)?;
505 *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
506 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn))
509 /// Parses a type starting with a path.
512 /// 1. a type macro, `mac!(...)`,
513 /// 2. a bare trait object, `B0 + ... + Bn`,
514 /// 3. or a path, `path::to::MyType`.
515 fn parse_path_start_ty(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
517 let path = self.parse_path(PathStyle::Type)?;
518 if self.eat(&token::Not) {
519 // Macro invocation in type position
520 Ok(TyKind::MacCall(MacCall {
522 args: self.parse_mac_args()?,
523 prior_type_ascription: self.last_type_ascription,
525 } else if allow_plus == AllowPlus::Yes && self.check_plus() {
526 // `Trait1 + Trait2 + 'a`
527 self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
530 Ok(TyKind::Path(None, path))
534 fn error_illegal_c_varadic_ty(&self, lo: Span) {
536 self.sess.span_diagnostic,
537 lo.to(self.prev_token.span),
539 "C-variadic type `...` may not be nested inside another type",
544 pub(super) fn parse_generic_bounds(
546 colon_span: Option<Span>,
547 ) -> PResult<'a, GenericBounds> {
548 self.parse_generic_bounds_common(AllowPlus::Yes, colon_span)
551 /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
553 /// See `parse_generic_bound` for the `BOUND` grammar.
554 fn parse_generic_bounds_common(
556 allow_plus: AllowPlus,
557 colon_span: Option<Span>,
558 ) -> PResult<'a, GenericBounds> {
559 let mut bounds = Vec::new();
560 let mut negative_bounds = Vec::new();
562 while self.can_begin_bound() || self.token.is_keyword(kw::Dyn) {
563 if self.token.is_keyword(kw::Dyn) {
564 // Account for `&dyn Trait + dyn Other`.
565 self.struct_span_err(self.token.span, "invalid `dyn` keyword")
566 .help("`dyn` is only needed at the start of a trait `+`-separated list")
569 "remove this keyword",
571 Applicability::MachineApplicable,
576 match self.parse_generic_bound()? {
577 Ok(bound) => bounds.push(bound),
578 Err(neg_sp) => negative_bounds.push(neg_sp),
580 if allow_plus == AllowPlus::No || !self.eat_plus() {
585 if !negative_bounds.is_empty() {
586 self.error_negative_bounds(colon_span, &bounds, negative_bounds);
592 /// Can the current token begin a bound?
593 fn can_begin_bound(&mut self) -> bool {
594 // This needs to be synchronized with `TokenKind::can_begin_bound`.
596 || self.check_lifetime()
597 || self.check(&token::Not) // Used for error reporting only.
598 || self.check(&token::Question)
599 || self.check(&token::Tilde)
600 || self.check_keyword(kw::For)
601 || self.check(&token::OpenDelim(token::Paren))
604 fn error_negative_bounds(
606 colon_span: Option<Span>,
607 bounds: &[GenericBound],
608 negative_bounds: Vec<Span>,
610 let negative_bounds_len = negative_bounds.len();
611 let last_span = *negative_bounds.last().expect("no negative bounds, but still error?");
612 let mut err = self.struct_span_err(negative_bounds, "negative bounds are not supported");
613 err.span_label(last_span, "negative bounds are not supported");
614 if let Some(bound_list) = colon_span {
615 let bound_list = bound_list.to(self.prev_token.span);
616 let mut new_bound_list = String::new();
617 if !bounds.is_empty() {
618 let mut snippets = bounds.iter().map(|bound| self.span_to_snippet(bound.span()));
619 while let Some(Ok(snippet)) = snippets.next() {
620 new_bound_list.push_str(" + ");
621 new_bound_list.push_str(&snippet);
623 new_bound_list = new_bound_list.replacen(" +", ":", 1);
625 err.tool_only_span_suggestion(
627 &format!("remove the bound{}", pluralize!(negative_bounds_len)),
629 Applicability::MachineApplicable,
635 /// Parses a bound according to the grammar:
637 /// BOUND = TY_BOUND | LT_BOUND
639 fn parse_generic_bound(&mut self) -> PResult<'a, Result<GenericBound, Span>> {
640 let anchor_lo = self.prev_token.span;
641 let lo = self.token.span;
642 let has_parens = self.eat(&token::OpenDelim(token::Paren));
643 let inner_lo = self.token.span;
644 let is_negative = self.eat(&token::Not);
646 let modifiers = self.parse_ty_bound_modifiers()?;
647 let bound = if self.token.is_lifetime() {
648 self.error_lt_bound_with_modifiers(modifiers);
649 self.parse_generic_lt_bound(lo, inner_lo, has_parens)?
651 self.parse_generic_ty_bound(lo, has_parens, modifiers)?
654 Ok(if is_negative { Err(anchor_lo.to(self.prev_token.span)) } else { Ok(bound) })
657 /// Parses a lifetime ("outlives") bound, e.g. `'a`, according to:
659 /// LT_BOUND = LIFETIME
661 fn parse_generic_lt_bound(
666 ) -> PResult<'a, GenericBound> {
667 let bound = GenericBound::Outlives(self.expect_lifetime());
669 // FIXME(Centril): Consider not erroring here and accepting `('lt)` instead,
670 // possibly introducing `GenericBound::Paren(P<GenericBound>)`?
671 self.recover_paren_lifetime(lo, inner_lo)?;
676 /// Emits an error if any trait bound modifiers were present.
677 fn error_lt_bound_with_modifiers(&self, modifiers: BoundModifiers) {
678 if let Some(span) = modifiers.maybe_const {
679 self.struct_span_err(
681 "`~const` may only modify trait bounds, not lifetime bounds",
686 if let Some(span) = modifiers.maybe {
687 self.struct_span_err(span, "`?` may only modify trait bounds, not lifetime bounds")
692 /// Recover on `('lifetime)` with `(` already eaten.
693 fn recover_paren_lifetime(&mut self, lo: Span, inner_lo: Span) -> PResult<'a, ()> {
694 let inner_span = inner_lo.to(self.prev_token.span);
695 self.expect(&token::CloseDelim(token::Paren))?;
696 let mut err = self.struct_span_err(
697 lo.to(self.prev_token.span),
698 "parenthesized lifetime bounds are not supported",
700 if let Ok(snippet) = self.span_to_snippet(inner_span) {
701 err.span_suggestion_short(
702 lo.to(self.prev_token.span),
703 "remove the parentheses",
705 Applicability::MachineApplicable,
712 /// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `~const Trait`.
714 /// If no modifiers are present, this does not consume any tokens.
717 /// TY_BOUND_MODIFIERS = ["~const"] ["?"]
719 fn parse_ty_bound_modifiers(&mut self) -> PResult<'a, BoundModifiers> {
720 let maybe_const = if self.eat(&token::Tilde) {
721 let tilde = self.prev_token.span;
722 self.expect_keyword(kw::Const)?;
723 let span = tilde.to(self.prev_token.span);
724 self.sess.gated_spans.gate(sym::const_trait_impl, span);
730 let maybe = if self.eat(&token::Question) { Some(self.prev_token.span) } else { None };
732 Ok(BoundModifiers { maybe, maybe_const })
735 /// Parses a type bound according to:
737 /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
738 /// TY_BOUND_NOPAREN = [TY_BOUND_MODIFIERS] [for<LT_PARAM_DEFS>] SIMPLE_PATH
741 /// For example, this grammar accepts `~const ?for<'a: 'b> m::Trait<'a>`.
742 fn parse_generic_ty_bound(
746 modifiers: BoundModifiers,
747 ) -> PResult<'a, GenericBound> {
748 let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
749 let path = self.parse_path(PathStyle::Type)?;
751 if self.token.is_like_plus() {
752 // Someone has written something like `&dyn (Trait + Other)`. The correct code
753 // would be `&(dyn Trait + Other)`, but we don't have access to the appropriate
754 // span to suggest that. When written as `&dyn Trait + Other`, an appropriate
755 // suggestion is given.
757 self.parse_remaining_bounds(bounds, true)?;
758 self.expect(&token::CloseDelim(token::Paren))?;
759 let sp = vec![lo, self.prev_token.span];
760 let sugg: Vec<_> = sp.iter().map(|sp| (*sp, String::new())).collect();
761 self.struct_span_err(sp, "incorrect braces around trait bounds")
762 .multipart_suggestion(
763 "remove the parentheses",
765 Applicability::MachineApplicable,
769 self.expect(&token::CloseDelim(token::Paren))?;
773 let modifier = modifiers.to_trait_bound_modifier();
774 let poly_trait = PolyTraitRef::new(lifetime_defs, path, lo.to(self.prev_token.span));
775 Ok(GenericBound::Trait(poly_trait, modifier))
778 /// Optionally parses `for<$generic_params>`.
779 pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
780 if self.eat_keyword(kw::For) {
782 let params = self.parse_generic_params()?;
784 // We rely on AST validation to rule out invalid cases: There must not be type
785 // parameters, and the lifetime parameters must not have bounds.
792 pub(super) fn check_lifetime(&mut self) -> bool {
793 self.expected_tokens.push(TokenType::Lifetime);
794 self.token.is_lifetime()
797 /// Parses a single lifetime `'a` or panics.
798 pub(super) fn expect_lifetime(&mut self) -> Lifetime {
799 if let Some(ident) = self.token.lifetime() {
801 Lifetime { ident, id: ast::DUMMY_NODE_ID }
803 self.span_bug(self.token.span, "not a lifetime")
807 pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
808 P(Ty { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })