compiler/rustc_parse/src/parser/ty.rs

   1 use super::{Parser, PathStyle, TokenType};
   2
   3 use crate::errors::{
   4     DynAfterMut, ExpectedFnPathFoundFnKeyword, ExpectedMutOrConstInRawPointerType,
   5     FnPointerCannotBeAsync, FnPointerCannotBeConst, FnPtrWithGenerics, FnPtrWithGenericsSugg,
   6     InvalidDynKeyword, LifetimeAfterMut, NeedPlusAfterTraitObjectLifetime,
   7     NegativeBoundsNotSupported, NegativeBoundsNotSupportedSugg, NestedCVariadicType,
   8     ReturnTypesUseThinArrow,
   9 };
  10 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
  11
  12 use ast::DUMMY_NODE_ID;
  13 use rustc_ast::ptr::P;
  14 use rustc_ast::token::{self, Delimiter, Token, TokenKind};
  15 use rustc_ast::util::case::Case;
  16 use rustc_ast::{
  17     self as ast, BareFnTy, FnRetTy, GenericBound, GenericBounds, GenericParam, Generics, Lifetime,
  18     MacCall, MutTy, Mutability, PolyTraitRef, TraitBoundModifier, TraitObjectSyntax, Ty, TyKind,
  19 };
  20 use rustc_errors::{Applicability, PResult};
  21 use rustc_span::source_map::Span;
  22 use rustc_span::symbol::{kw, sym, Ident};
  23 use rustc_span::Symbol;
  24 use thin_vec::thin_vec;
  25
  26 /// Any `?` or `~const` modifiers that appear at the start of a bound.
  27 struct BoundModifiers {
  28     /// `?Trait`.
  29     maybe: Option<Span>,
  30
  31     /// `~const Trait`.
  32     maybe_const: Option<Span>,
  33 }
  34
  35 impl BoundModifiers {
  36     fn to_trait_bound_modifier(&self) -> TraitBoundModifier {
  37         match (self.maybe, self.maybe_const) {
  38             (None, None) => TraitBoundModifier::None,
  39             (Some(_), None) => TraitBoundModifier::Maybe,
  40             (None, Some(_)) => TraitBoundModifier::MaybeConst,
  41             (Some(_), Some(_)) => TraitBoundModifier::MaybeConstMaybe,
  42         }
  43     }
  44 }
  45
  46 #[derive(Copy, Clone, PartialEq)]
  47 pub(super) enum AllowPlus {
  48     Yes,
  49     No,
  50 }
  51
  52 #[derive(PartialEq)]
  53 pub(super) enum RecoverQPath {
  54     Yes,
  55     No,
  56 }
  57
  58 pub(super) enum RecoverQuestionMark {
  59     Yes,
  60     No,
  61 }
  62
  63 /// Signals whether parsing a type should recover `->`.
  64 ///
  65 /// More specifically, when parsing a function like:
  66 /// ```compile_fail
  67 /// fn foo() => u8 { 0 }
  68 /// fn bar(): u8 { 0 }
  69 /// ```
  70 /// The compiler will try to recover interpreting `foo() => u8` as `foo() -> u8` when calling
  71 /// `parse_ty` with anything except `RecoverReturnSign::No`, and it will try to recover `bar(): u8`
  72 /// as `bar() -> u8` when passing `RecoverReturnSign::Yes` to `parse_ty`
  73 #[derive(Copy, Clone, PartialEq)]
  74 pub(super) enum RecoverReturnSign {
  75     Yes,
  76     OnlyFatArrow,
  77     No,
  78 }
  79
  80 impl RecoverReturnSign {
  81     /// [RecoverReturnSign::Yes] allows for recovering `fn foo() => u8` and `fn foo(): u8`,
  82     /// [RecoverReturnSign::OnlyFatArrow] allows for recovering only `fn foo() => u8` (recovering
  83     /// colons can cause problems when parsing where clauses), and
  84     /// [RecoverReturnSign::No] doesn't allow for any recovery of the return type arrow
  85     fn can_recover(self, token: &TokenKind) -> bool {
  86         match self {
  87             Self::Yes => matches!(token, token::FatArrow | token::Colon),
  88             Self::OnlyFatArrow => matches!(token, token::FatArrow),
  89             Self::No => false,
  90         }
  91     }
  92 }
  93
  94 // Is `...` (`CVarArgs`) legal at this level of type parsing?
  95 #[derive(PartialEq)]
  96 enum AllowCVariadic {
  97     Yes,
  98     No,
  99 }
 100
 101 /// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
 102 /// `IDENT<<u8 as Trait>::AssocTy>`.
 103 ///
 104 /// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
 105 /// that `IDENT` is not the ident of a fn trait.
 106 fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
 107     t == &token::ModSep || t == &token::Lt || t == &token::BinOp(token::Shl)
 108 }
 109
 110 impl<'a> Parser<'a> {
 111     /// Parses a type.
 112     pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
 113         self.parse_ty_common(
 114             AllowPlus::Yes,
 115             AllowCVariadic::No,
 116             RecoverQPath::Yes,
 117             RecoverReturnSign::Yes,
 118             None,
 119             RecoverQuestionMark::Yes,
 120         )
 121     }
 122
 123     pub(super) fn parse_ty_with_generics_recovery(
 124         &mut self,
 125         ty_params: &Generics,
 126     ) -> PResult<'a, P<Ty>> {
 127         self.parse_ty_common(
 128             AllowPlus::Yes,
 129             AllowCVariadic::No,
 130             RecoverQPath::Yes,
 131             RecoverReturnSign::Yes,
 132             Some(ty_params),
 133             RecoverQuestionMark::Yes,
 134         )
 135     }
 136
 137     /// Parse a type suitable for a function or function pointer parameter.
 138     /// The difference from `parse_ty` is that this version allows `...`
 139     /// (`CVarArgs`) at the top level of the type.
 140     pub(super) fn parse_ty_for_param(&mut self) -> PResult<'a, P<Ty>> {
 141         self.parse_ty_common(
 142             AllowPlus::Yes,
 143             AllowCVariadic::Yes,
 144             RecoverQPath::Yes,
 145             RecoverReturnSign::Yes,
 146             None,
 147             RecoverQuestionMark::Yes,
 148         )
 149     }
 150
 151     /// Parses a type in restricted contexts where `+` is not permitted.
 152     ///
 153     /// Example 1: `&'a TYPE`
 154     ///     `+` is prohibited to maintain operator priority (P(+) < P(&)).
 155     /// Example 2: `value1 as TYPE + value2`
 156     ///     `+` is prohibited to avoid interactions with expression grammar.
 157     pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
 158         self.parse_ty_common(
 159             AllowPlus::No,
 160             AllowCVariadic::No,
 161             RecoverQPath::Yes,
 162             RecoverReturnSign::Yes,
 163             None,
 164             RecoverQuestionMark::Yes,
 165         )
 166     }
 167
 168     /// Parses a type following an `as` cast. Similar to `parse_ty_no_plus`, but signaling origin
 169     /// for better diagnostics involving `?`.
 170     pub(super) fn parse_as_cast_ty(&mut self) -> PResult<'a, P<Ty>> {
 171         self.parse_ty_common(
 172             AllowPlus::No,
 173             AllowCVariadic::No,
 174             RecoverQPath::Yes,
 175             RecoverReturnSign::Yes,
 176             None,
 177             RecoverQuestionMark::No,
 178         )
 179     }
 180
 181     pub(super) fn parse_no_question_mark_recover(&mut self) -> PResult<'a, P<Ty>> {
 182         self.parse_ty_common(
 183             AllowPlus::Yes,
 184             AllowCVariadic::No,
 185             RecoverQPath::Yes,
 186             RecoverReturnSign::Yes,
 187             None,
 188             RecoverQuestionMark::No,
 189         )
 190     }
 191
 192     /// Parse a type without recovering `:` as `->` to avoid breaking code such as `where fn() : for<'a>`
 193     pub(super) fn parse_ty_for_where_clause(&mut self) -> PResult<'a, P<Ty>> {
 194         self.parse_ty_common(
 195             AllowPlus::Yes,
 196             AllowCVariadic::Yes,
 197             RecoverQPath::Yes,
 198             RecoverReturnSign::OnlyFatArrow,
 199             None,
 200             RecoverQuestionMark::Yes,
 201         )
 202     }
 203
 204     /// Parses an optional return type `[ -> TY ]` in a function declaration.
 205     pub(super) fn parse_ret_ty(
 206         &mut self,
 207         allow_plus: AllowPlus,
 208         recover_qpath: RecoverQPath,
 209         recover_return_sign: RecoverReturnSign,
 210     ) -> PResult<'a, FnRetTy> {
 211         Ok(if self.eat(&token::RArrow) {
 212             // FIXME(Centril): Can we unconditionally `allow_plus`?
 213             let ty = self.parse_ty_common(
 214                 allow_plus,
 215                 AllowCVariadic::No,
 216                 recover_qpath,
 217                 recover_return_sign,
 218                 None,
 219                 RecoverQuestionMark::Yes,
 220             )?;
 221             FnRetTy::Ty(ty)
 222         } else if recover_return_sign.can_recover(&self.token.kind) {
 223             // Don't `eat` to prevent `=>` from being added as an expected token which isn't
 224             // actually expected and could only confuse users
 225             self.bump();
 226             self.sess.emit_err(ReturnTypesUseThinArrow { span: self.prev_token.span });
 227             let ty = self.parse_ty_common(
 228                 allow_plus,
 229                 AllowCVariadic::No,
 230                 recover_qpath,
 231                 recover_return_sign,
 232                 None,
 233                 RecoverQuestionMark::Yes,
 234             )?;
 235             FnRetTy::Ty(ty)
 236         } else {
 237             FnRetTy::Default(self.token.span.shrink_to_lo())
 238         })
 239     }
 240
 241     fn parse_ty_common(
 242         &mut self,
 243         allow_plus: AllowPlus,
 244         allow_c_variadic: AllowCVariadic,
 245         recover_qpath: RecoverQPath,
 246         recover_return_sign: RecoverReturnSign,
 247         ty_generics: Option<&Generics>,
 248         recover_question_mark: RecoverQuestionMark,
 249     ) -> PResult<'a, P<Ty>> {
 250         let allow_qpath_recovery = recover_qpath == RecoverQPath::Yes;
 251         maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
 252         maybe_whole!(self, NtTy, |x| x);
 253
 254         let lo = self.token.span;
 255         let mut impl_dyn_multi = false;
 256         let kind = if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
 257             self.parse_ty_tuple_or_parens(lo, allow_plus)?
 258         } else if self.eat(&token::Not) {
 259             // Never type `!`
 260             TyKind::Never
 261         } else if self.eat(&token::BinOp(token::Star)) {
 262             self.parse_ty_ptr()?
 263         } else if self.eat(&token::OpenDelim(Delimiter::Bracket)) {
 264             self.parse_array_or_slice_ty()?
 265         } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
 266             // Reference
 267             self.expect_and()?;
 268             self.parse_borrowed_pointee()?
 269         } else if self.eat_keyword_noexpect(kw::Typeof) {
 270             self.parse_typeof_ty()?
 271         } else if self.eat_keyword(kw::Underscore) {
 272             // A type to be inferred `_`
 273             TyKind::Infer
 274         } else if self.check_fn_front_matter(false, Case::Sensitive) {
 275             // Function pointer type
 276             self.parse_ty_bare_fn(lo, Vec::new(), None, recover_return_sign)?
 277         } else if self.check_keyword(kw::For) {
 278             // Function pointer type or bound list (trait object type) starting with a poly-trait.
 279             //   `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
 280             //   `for<'lt> Trait1<'lt> + Trait2 + 'a`
 281             let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
 282             if self.check_fn_front_matter(false, Case::Sensitive) {
 283                 self.parse_ty_bare_fn(
 284                     lo,
 285                     lifetime_defs,
 286                     Some(self.prev_token.span.shrink_to_lo()),
 287                     recover_return_sign,
 288                 )?
 289             } else {
 290                 let path = self.parse_path(PathStyle::Type)?;
 291                 let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
 292                 self.parse_remaining_bounds_path(lifetime_defs, path, lo, parse_plus)?
 293             }
 294         } else if self.eat_keyword(kw::Impl) {
 295             self.parse_impl_ty(&mut impl_dyn_multi)?
 296         } else if self.is_explicit_dyn_type() {
 297             self.parse_dyn_ty(&mut impl_dyn_multi)?
 298         } else if self.eat_lt() {
 299             // Qualified path
 300             let (qself, path) = self.parse_qpath(PathStyle::Type)?;
 301             TyKind::Path(Some(qself), path)
 302         } else if self.check_path() {
 303             self.parse_path_start_ty(lo, allow_plus, ty_generics)?
 304         } else if self.can_begin_bound() {
 305             self.parse_bare_trait_object(lo, allow_plus)?
 306         } else if self.eat(&token::DotDotDot) {
 307             match allow_c_variadic {
 308                 AllowCVariadic::Yes => TyKind::CVarArgs,
 309                 AllowCVariadic::No => {
 310                     // FIXME(Centril): Should we just allow `...` syntactically
 311                     // anywhere in a type and use semantic restrictions instead?
 312                     self.sess.emit_err(NestedCVariadicType { span: lo.to(self.prev_token.span) });
 313                     TyKind::Err
 314                 }
 315             }
 316         } else {
 317             let msg = format!("expected type, found {}", super::token_descr(&self.token));
 318             let mut err = self.struct_span_err(self.token.span, &msg);
 319             err.span_label(self.token.span, "expected type");
 320             self.maybe_annotate_with_ascription(&mut err, true);
 321             return Err(err);
 322         };
 323
 324         let span = lo.to(self.prev_token.span);
 325         let mut ty = self.mk_ty(span, kind);
 326
 327         // Try to recover from use of `+` with incorrect priority.
 328         match allow_plus {
 329             AllowPlus::Yes => self.maybe_recover_from_bad_type_plus(&ty)?,
 330             AllowPlus::No => self.maybe_report_ambiguous_plus(impl_dyn_multi, &ty),
 331         }
 332         if let RecoverQuestionMark::Yes = recover_question_mark {
 333             ty = self.maybe_recover_from_question_mark(ty);
 334         }
 335         if allow_qpath_recovery { self.maybe_recover_from_bad_qpath(ty) } else { Ok(ty) }
 336     }
 337
 338     /// Parses either:
 339     /// - `(TYPE)`, a parenthesized type.
 340     /// - `(TYPE,)`, a tuple with a single field of type TYPE.
 341     fn parse_ty_tuple_or_parens(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
 342         let mut trailing_plus = false;
 343         let (ts, trailing) = self.parse_paren_comma_seq(|p| {
 344             let ty = p.parse_ty()?;
 345             trailing_plus = p.prev_token.kind == TokenKind::BinOp(token::Plus);
 346             Ok(ty)
 347         })?;
 348
 349         if ts.len() == 1 && !trailing {
 350             let ty = ts.into_iter().next().unwrap().into_inner();
 351             let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
 352             match ty.kind {
 353                 // `(TY_BOUND_NOPAREN) + BOUND + ...`.
 354                 TyKind::Path(None, path) if maybe_bounds => {
 355                     self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
 356                 }
 357                 TyKind::TraitObject(bounds, TraitObjectSyntax::None)
 358                     if maybe_bounds && bounds.len() == 1 && !trailing_plus =>
 359                 {
 360                     self.parse_remaining_bounds(bounds, true)
 361                 }
 362                 // `(TYPE)`
 363                 _ => Ok(TyKind::Paren(P(ty))),
 364             }
 365         } else {
 366             Ok(TyKind::Tup(ts))
 367         }
 368     }
 369
 370     fn parse_bare_trait_object(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
 371         let lt_no_plus = self.check_lifetime() && !self.look_ahead(1, |t| t.is_like_plus());
 372         let bounds = self.parse_generic_bounds_common(allow_plus, None)?;
 373         if lt_no_plus {
 374             self.sess.emit_err(NeedPlusAfterTraitObjectLifetime { span: lo });
 375         }
 376         Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
 377     }
 378
 379     fn parse_remaining_bounds_path(
 380         &mut self,
 381         generic_params: Vec<GenericParam>,
 382         path: ast::Path,
 383         lo: Span,
 384         parse_plus: bool,
 385     ) -> PResult<'a, TyKind> {
 386         let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_token.span));
 387         let bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
 388         self.parse_remaining_bounds(bounds, parse_plus)
 389     }
 390
 391     /// Parse the remainder of a bare trait object type given an already parsed list.
 392     fn parse_remaining_bounds(
 393         &mut self,
 394         mut bounds: GenericBounds,
 395         plus: bool,
 396     ) -> PResult<'a, TyKind> {
 397         if plus {
 398             self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
 399             bounds.append(&mut self.parse_generic_bounds(Some(self.prev_token.span))?);
 400         }
 401         Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
 402     }
 403
 404     /// Parses a raw pointer type: `*[const | mut] $type`.
 405     fn parse_ty_ptr(&mut self) -> PResult<'a, TyKind> {
 406         let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
 407             let span = self.prev_token.span;
 408             self.sess.emit_err(ExpectedMutOrConstInRawPointerType {
 409                 span,
 410                 after_asterisk: span.shrink_to_hi(),
 411             });
 412             Mutability::Not
 413         });
 414         let ty = self.parse_ty_no_plus()?;
 415         Ok(TyKind::Ptr(MutTy { ty, mutbl }))
 416     }
 417
 418     /// Parses an array (`[TYPE; EXPR]`) or slice (`[TYPE]`) type.
 419     /// The opening `[` bracket is already eaten.
 420     fn parse_array_or_slice_ty(&mut self) -> PResult<'a, TyKind> {
 421         let elt_ty = match self.parse_ty() {
 422             Ok(ty) => ty,
 423             Err(mut err)
 424                 if self.look_ahead(1, |t| t.kind == token::CloseDelim(Delimiter::Bracket))
 425                     | self.look_ahead(1, |t| t.kind == token::Semi) =>
 426             {
 427                 // Recover from `[LIT; EXPR]` and `[LIT]`
 428                 self.bump();
 429                 err.emit();
 430                 self.mk_ty(self.prev_token.span, TyKind::Err)
 431             }
 432             Err(err) => return Err(err),
 433         };
 434
 435         let ty = if self.eat(&token::Semi) {
 436             let mut length = self.parse_anon_const_expr()?;
 437             if let Err(e) = self.expect(&token::CloseDelim(Delimiter::Bracket)) {
 438                 // Try to recover from `X<Y, ...>` when `X::<Y, ...>` works
 439                 self.check_mistyped_turbofish_with_multiple_type_params(e, &mut length.value)?;
 440                 self.expect(&token::CloseDelim(Delimiter::Bracket))?;
 441             }
 442             TyKind::Array(elt_ty, length)
 443         } else {
 444             self.expect(&token::CloseDelim(Delimiter::Bracket))?;
 445             TyKind::Slice(elt_ty)
 446         };
 447
 448         Ok(ty)
 449     }
 450
 451     fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
 452         let and_span = self.prev_token.span;
 453         let mut opt_lifetime =
 454             if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
 455         let mut mutbl = self.parse_mutability();
 456         if self.token.is_lifetime() && mutbl == Mutability::Mut && opt_lifetime.is_none() {
 457             // A lifetime is invalid here: it would be part of a bare trait bound, which requires
 458             // it to be followed by a plus, but we disallow plus in the pointee type.
 459             // So we can handle this case as an error here, and suggest `'a mut`.
 460             // If there *is* a plus next though, handling the error later provides better suggestions
 461             // (like adding parentheses)
 462             if !self.look_ahead(1, |t| t.is_like_plus()) {
 463                 let lifetime_span = self.token.span;
 464                 let span = and_span.to(lifetime_span);
 465
 466                 let (suggest_lifetime, snippet) =
 467                     if let Ok(lifetime_src) = self.span_to_snippet(lifetime_span) {
 468                         (Some(span), lifetime_src)
 469                     } else {
 470                         (None, String::new())
 471                     };
 472                 self.sess.emit_err(LifetimeAfterMut { span, suggest_lifetime, snippet });
 473
 474                 opt_lifetime = Some(self.expect_lifetime());
 475             }
 476         } else if self.token.is_keyword(kw::Dyn)
 477             && mutbl == Mutability::Not
 478             && self.look_ahead(1, |t| t.is_keyword(kw::Mut))
 479         {
 480             // We have `&dyn mut ...`, which is invalid and should be `&mut dyn ...`.
 481             let span = and_span.to(self.look_ahead(1, |t| t.span));
 482             self.sess.emit_err(DynAfterMut { span });
 483
 484             // Recovery
 485             mutbl = Mutability::Mut;
 486             let (dyn_tok, dyn_tok_sp) = (self.token.clone(), self.token_spacing);
 487             self.bump();
 488             self.bump_with((dyn_tok, dyn_tok_sp));
 489         }
 490         let ty = self.parse_ty_no_plus()?;
 491         Ok(TyKind::Ref(opt_lifetime, MutTy { ty, mutbl }))
 492     }
 493
 494     // Parses the `typeof(EXPR)`.
 495     // To avoid ambiguity, the type is surrounded by parentheses.
 496     fn parse_typeof_ty(&mut self) -> PResult<'a, TyKind> {
 497         self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
 498         let expr = self.parse_anon_const_expr()?;
 499         self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
 500         Ok(TyKind::Typeof(expr))
 501     }
 502
 503     /// Parses a function pointer type (`TyKind::BareFn`).
 504     /// ```ignore (illustrative)
 505     ///    [unsafe] [extern "ABI"] fn (S) -> T
 506     /// //  ^~~~~^          ^~~~^     ^~^    ^
 507     /// //    |               |        |     |
 508     /// //    |               |        |   Return type
 509     /// // Function Style    ABI  Parameter types
 510     /// ```
 511     /// We actually parse `FnHeader FnDecl`, but we error on `const` and `async` qualifiers.
 512     fn parse_ty_bare_fn(
 513         &mut self,
 514         lo: Span,
 515         mut params: Vec<GenericParam>,
 516         param_insertion_point: Option<Span>,
 517         recover_return_sign: RecoverReturnSign,
 518     ) -> PResult<'a, TyKind> {
 519         let inherited_vis = rustc_ast::Visibility {
 520             span: rustc_span::DUMMY_SP,
 521             kind: rustc_ast::VisibilityKind::Inherited,
 522             tokens: None,
 523         };
 524         let span_start = self.token.span;
 525         let ast::FnHeader { ext, unsafety, constness, asyncness } =
 526             self.parse_fn_front_matter(&inherited_vis, Case::Sensitive)?;
 527         if self.may_recover() && self.token.kind == TokenKind::Lt {
 528             self.recover_fn_ptr_with_generics(lo, &mut params, param_insertion_point)?;
 529         }
 530         let decl = self.parse_fn_decl(|_| false, AllowPlus::No, recover_return_sign)?;
 531         let whole_span = lo.to(self.prev_token.span);
 532         if let ast::Const::Yes(span) = constness {
 533             // If we ever start to allow `const fn()`, then update
 534             // feature gating for `#![feature(const_extern_fn)]` to
 535             // cover it.
 536             self.sess.emit_err(FnPointerCannotBeConst { span: whole_span, qualifier: span });
 537         }
 538         if let ast::Async::Yes { span, .. } = asyncness {
 539             self.sess.emit_err(FnPointerCannotBeAsync { span: whole_span, qualifier: span });
 540         }
 541         let decl_span = span_start.to(self.token.span);
 542         Ok(TyKind::BareFn(P(BareFnTy { ext, unsafety, generic_params: params, decl, decl_span })))
 543     }
 544
 545     /// Recover from function pointer types with a generic parameter list (e.g. `fn<'a>(&'a str)`).
 546     fn recover_fn_ptr_with_generics(
 547         &mut self,
 548         lo: Span,
 549         params: &mut Vec<GenericParam>,
 550         param_insertion_point: Option<Span>,
 551     ) -> PResult<'a, ()> {
 552         let generics = self.parse_generics()?;
 553         let arity = generics.params.len();
 554
 555         let mut lifetimes: Vec<_> = generics
 556             .params
 557             .into_iter()
 558             .filter(|param| matches!(param.kind, ast::GenericParamKind::Lifetime))
 559             .collect();
 560
 561         let sugg = if !lifetimes.is_empty() {
 562             let snippet =
 563                 lifetimes.iter().map(|param| param.ident.as_str()).intersperse(", ").collect();
 564
 565             let (left, snippet) = if let Some(span) = param_insertion_point {
 566                 (span, if params.is_empty() { snippet } else { format!(", {snippet}") })
 567             } else {
 568                 (lo.shrink_to_lo(), format!("for<{snippet}> "))
 569             };
 570
 571             Some(FnPtrWithGenericsSugg {
 572                 left,
 573                 snippet,
 574                 right: generics.span,
 575                 arity,
 576                 for_param_list_exists: param_insertion_point.is_some(),
 577             })
 578         } else {
 579             None
 580         };
 581
 582         self.sess.emit_err(FnPtrWithGenerics { span: generics.span, sugg });
 583         params.append(&mut lifetimes);
 584         Ok(())
 585     }
 586
 587     /// Parses an `impl B0 + ... + Bn` type.
 588     fn parse_impl_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
 589         // Always parse bounds greedily for better error recovery.
 590         if self.token.is_lifetime() {
 591             self.look_ahead(1, |t| {
 592                 if let token::Ident(symname, _) = t.kind {
 593                     // parse pattern with "'a Sized" we're supposed to give suggestion like
 594                     // "'a + Sized"
 595                     self.struct_span_err(
 596                         self.token.span,
 597                         &format!("expected `+` between lifetime and {}", symname),
 598                     )
 599                     .span_suggestion_verbose(
 600                         self.token.span.shrink_to_hi(),
 601                         "add `+`",
 602                         " +",
 603                         Applicability::MaybeIncorrect,
 604                     )
 605                     .emit();
 606                 }
 607             })
 608         }
 609         let bounds = self.parse_generic_bounds(None)?;
 610         *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
 611         Ok(TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds))
 612     }
 613
 614     /// Is a `dyn B0 + ... + Bn` type allowed here?
 615     fn is_explicit_dyn_type(&mut self) -> bool {
 616         self.check_keyword(kw::Dyn)
 617             && (self.token.uninterpolated_span().rust_2018()
 618                 || self.look_ahead(1, |t| {
 619                     (t.can_begin_bound() || t.kind == TokenKind::BinOp(token::Star))
 620                         && !can_continue_type_after_non_fn_ident(t)
 621                 }))
 622     }
 623
 624     /// Parses a `dyn B0 + ... + Bn` type.
 625     ///
 626     /// Note that this does *not* parse bare trait objects.
 627     fn parse_dyn_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
 628         self.bump(); // `dyn`
 629
 630         // parse dyn* types
 631         let syntax = if self.eat(&TokenKind::BinOp(token::Star)) {
 632             TraitObjectSyntax::DynStar
 633         } else {
 634             TraitObjectSyntax::Dyn
 635         };
 636
 637         // Always parse bounds greedily for better error recovery.
 638         let bounds = self.parse_generic_bounds(None)?;
 639         *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
 640         Ok(TyKind::TraitObject(bounds, syntax))
 641     }
 642
 643     /// Parses a type starting with a path.
 644     ///
 645     /// This can be:
 646     /// 1. a type macro, `mac!(...)`,
 647     /// 2. a bare trait object, `B0 + ... + Bn`,
 648     /// 3. or a path, `path::to::MyType`.
 649     fn parse_path_start_ty(
 650         &mut self,
 651         lo: Span,
 652         allow_plus: AllowPlus,
 653         ty_generics: Option<&Generics>,
 654     ) -> PResult<'a, TyKind> {
 655         // Simple path
 656         let path = self.parse_path_inner(PathStyle::Type, ty_generics)?;
 657         if self.eat(&token::Not) {
 658             // Macro invocation in type position
 659             Ok(TyKind::MacCall(P(MacCall {
 660                 path,
 661                 args: self.parse_delim_args()?,
 662                 prior_type_ascription: self.last_type_ascription,
 663             })))
 664         } else if allow_plus == AllowPlus::Yes && self.check_plus() {
 665             // `Trait1 + Trait2 + 'a`
 666             self.parse_remaining_bounds_path(Vec::new(), path, lo, true)
 667         } else {
 668             // Just a type path.
 669             Ok(TyKind::Path(None, path))
 670         }
 671     }
 672
 673     pub(super) fn parse_generic_bounds(
 674         &mut self,
 675         colon_span: Option<Span>,
 676     ) -> PResult<'a, GenericBounds> {
 677         self.parse_generic_bounds_common(AllowPlus::Yes, colon_span)
 678     }
 679
 680     /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
 681     ///
 682     /// See `parse_generic_bound` for the `BOUND` grammar.
 683     fn parse_generic_bounds_common(
 684         &mut self,
 685         allow_plus: AllowPlus,
 686         colon_span: Option<Span>,
 687     ) -> PResult<'a, GenericBounds> {
 688         let mut bounds = Vec::new();
 689         let mut negative_bounds = Vec::new();
 690
 691         // In addition to looping while we find generic bounds:
 692         // We continue even if we find a keyword. This is necessary for error recovery on,
 693         // for example, `impl fn()`. The only keyword that can go after generic bounds is
 694         // `where`, so stop if it's it.
 695         // We also continue if we find types (not traits), again for error recovery.
 696         while self.can_begin_bound()
 697             || (self.may_recover()
 698                 && (self.token.can_begin_type()
 699                     || (self.token.is_reserved_ident() && !self.token.is_keyword(kw::Where))))
 700         {
 701             if self.token.is_keyword(kw::Dyn) {
 702                 // Account for `&dyn Trait + dyn Other`.
 703                 self.sess.emit_err(InvalidDynKeyword { span: self.token.span });
 704                 self.bump();
 705             }
 706             match self.parse_generic_bound()? {
 707                 Ok(bound) => bounds.push(bound),
 708                 Err(neg_sp) => negative_bounds.push(neg_sp),
 709             }
 710             if allow_plus == AllowPlus::No || !self.eat_plus() {
 711                 break;
 712             }
 713         }
 714
 715         if !negative_bounds.is_empty() {
 716             self.error_negative_bounds(colon_span, &bounds, negative_bounds);
 717         }
 718
 719         Ok(bounds)
 720     }
 721
 722     /// Can the current token begin a bound?
 723     fn can_begin_bound(&mut self) -> bool {
 724         // This needs to be synchronized with `TokenKind::can_begin_bound`.
 725         self.check_path()
 726         || self.check_lifetime()
 727         || self.check(&token::Not) // Used for error reporting only.
 728         || self.check(&token::Question)
 729         || self.check(&token::Tilde)
 730         || self.check_keyword(kw::For)
 731         || self.check(&token::OpenDelim(Delimiter::Parenthesis))
 732     }
 733
 734     fn error_negative_bounds(
 735         &self,
 736         colon_span: Option<Span>,
 737         bounds: &[GenericBound],
 738         negative_bounds: Vec<Span>,
 739     ) {
 740         let sub = if let Some(bound_list) = colon_span {
 741             let bound_list = bound_list.to(self.prev_token.span);
 742             let mut new_bound_list = String::new();
 743             if !bounds.is_empty() {
 744                 let mut snippets = bounds.iter().map(|bound| self.span_to_snippet(bound.span()));
 745                 while let Some(Ok(snippet)) = snippets.next() {
 746                     new_bound_list.push_str(" + ");
 747                     new_bound_list.push_str(&snippet);
 748                 }
 749                 new_bound_list = new_bound_list.replacen(" +", ":", 1);
 750             }
 751
 752             Some(NegativeBoundsNotSupportedSugg {
 753                 bound_list,
 754                 num_bounds: negative_bounds.len(),
 755                 fixed: new_bound_list,
 756             })
 757         } else {
 758             None
 759         };
 760
 761         let last_span = *negative_bounds.last().expect("no negative bounds, but still error?");
 762         self.sess.emit_err(NegativeBoundsNotSupported { negative_bounds, last_span, sub });
 763     }
 764
 765     /// Parses a bound according to the grammar:
 766     /// ```ebnf
 767     /// BOUND = TY_BOUND | LT_BOUND
 768     /// ```
 769     fn parse_generic_bound(&mut self) -> PResult<'a, Result<GenericBound, Span>> {
 770         let anchor_lo = self.prev_token.span;
 771         let lo = self.token.span;
 772         let has_parens = self.eat(&token::OpenDelim(Delimiter::Parenthesis));
 773         let inner_lo = self.token.span;
 774         let is_negative = self.eat(&token::Not);
 775
 776         let modifiers = self.parse_ty_bound_modifiers()?;
 777         let bound = if self.token.is_lifetime() {
 778             self.error_lt_bound_with_modifiers(modifiers);
 779             self.parse_generic_lt_bound(lo, inner_lo, has_parens)?
 780         } else {
 781             self.parse_generic_ty_bound(lo, has_parens, modifiers)?
 782         };
 783
 784         Ok(if is_negative { Err(anchor_lo.to(self.prev_token.span)) } else { Ok(bound) })
 785     }
 786
 787     /// Parses a lifetime ("outlives") bound, e.g. `'a`, according to:
 788     /// ```ebnf
 789     /// LT_BOUND = LIFETIME
 790     /// ```
 791     fn parse_generic_lt_bound(
 792         &mut self,
 793         lo: Span,
 794         inner_lo: Span,
 795         has_parens: bool,
 796     ) -> PResult<'a, GenericBound> {
 797         let bound = GenericBound::Outlives(self.expect_lifetime());
 798         if has_parens {
 799             // FIXME(Centril): Consider not erroring here and accepting `('lt)` instead,
 800             // possibly introducing `GenericBound::Paren(P<GenericBound>)`?
 801             self.recover_paren_lifetime(lo, inner_lo)?;
 802         }
 803         Ok(bound)
 804     }
 805
 806     /// Emits an error if any trait bound modifiers were present.
 807     fn error_lt_bound_with_modifiers(&self, modifiers: BoundModifiers) {
 808         if let Some(span) = modifiers.maybe_const {
 809             self.struct_span_err(
 810                 span,
 811                 "`~const` may only modify trait bounds, not lifetime bounds",
 812             )
 813             .emit();
 814         }
 815
 816         if let Some(span) = modifiers.maybe {
 817             self.struct_span_err(span, "`?` may only modify trait bounds, not lifetime bounds")
 818                 .emit();
 819         }
 820     }
 821
 822     /// Recover on `('lifetime)` with `(` already eaten.
 823     fn recover_paren_lifetime(&mut self, lo: Span, inner_lo: Span) -> PResult<'a, ()> {
 824         let inner_span = inner_lo.to(self.prev_token.span);
 825         self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
 826         let mut err = self.struct_span_err(
 827             lo.to(self.prev_token.span),
 828             "parenthesized lifetime bounds are not supported",
 829         );
 830         if let Ok(snippet) = self.span_to_snippet(inner_span) {
 831             err.span_suggestion_short(
 832                 lo.to(self.prev_token.span),
 833                 "remove the parentheses",
 834                 snippet,
 835                 Applicability::MachineApplicable,
 836             );
 837         }
 838         err.emit();
 839         Ok(())
 840     }
 841
 842     /// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `~const Trait`.
 843     ///
 844     /// If no modifiers are present, this does not consume any tokens.
 845     ///
 846     /// ```ebnf
 847     /// TY_BOUND_MODIFIERS = ["~const"] ["?"]
 848     /// ```
 849     fn parse_ty_bound_modifiers(&mut self) -> PResult<'a, BoundModifiers> {
 850         let maybe_const = if self.eat(&token::Tilde) {
 851             let tilde = self.prev_token.span;
 852             self.expect_keyword(kw::Const)?;
 853             let span = tilde.to(self.prev_token.span);
 854             self.sess.gated_spans.gate(sym::const_trait_impl, span);
 855             Some(span)
 856         } else if self.eat_keyword(kw::Const) {
 857             let span = self.prev_token.span;
 858             self.sess.gated_spans.gate(sym::const_trait_impl, span);
 859
 860             self.struct_span_err(span, "const bounds must start with `~`")
 861                 .span_suggestion(
 862                     span.shrink_to_lo(),
 863                     "add `~`",
 864                     "~",
 865                     Applicability::MachineApplicable,
 866                 )
 867                 .emit();
 868
 869             Some(span)
 870         } else {
 871             None
 872         };
 873
 874         let maybe = if self.eat(&token::Question) { Some(self.prev_token.span) } else { None };
 875
 876         Ok(BoundModifiers { maybe, maybe_const })
 877     }
 878
 879     /// Parses a type bound according to:
 880     /// ```ebnf
 881     /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
 882     /// TY_BOUND_NOPAREN = [TY_BOUND_MODIFIERS] [for<LT_PARAM_DEFS>] SIMPLE_PATH
 883     /// ```
 884     ///
 885     /// For example, this grammar accepts `~const ?for<'a: 'b> m::Trait<'a>`.
 886     fn parse_generic_ty_bound(
 887         &mut self,
 888         lo: Span,
 889         has_parens: bool,
 890         modifiers: BoundModifiers,
 891     ) -> PResult<'a, GenericBound> {
 892         let mut lifetime_defs = self.parse_late_bound_lifetime_defs()?;
 893         let mut path = if self.token.is_keyword(kw::Fn)
 894             && self.look_ahead(1, |tok| tok.kind == TokenKind::OpenDelim(Delimiter::Parenthesis))
 895             && let Some(path) = self.recover_path_from_fn()
 896         {
 897             path
 898         } else if !self.token.is_path_start() && self.token.can_begin_type() {
 899             let ty = self.parse_ty_no_plus()?;
 900             // Instead of finding a path (a trait), we found a type.
 901             let mut err = self.struct_span_err(ty.span, "expected a trait, found type");
 902
 903             // If we can recover, try to extract a path from the type. Note
 904             // that we do not use the try operator when parsing the type because
 905             // if it fails then we get a parser error which we don't want (we're trying
 906             // to recover from errors, not make more).
 907             let path = if self.may_recover()
 908                 && matches!(ty.kind, TyKind::Ptr(..) | TyKind::Ref(..))
 909                 && let TyKind::Path(_, path) = &ty.peel_refs().kind {
 910                 // Just get the indirection part of the type.
 911                 let span = ty.span.until(path.span);
 912
 913                 err.span_suggestion_verbose(
 914                     span,
 915                     "consider removing the indirection",
 916                     "",
 917                     Applicability::MaybeIncorrect,
 918                 );
 919
 920                 path.clone()
 921             } else {
 922                 return Err(err);
 923             };
 924
 925             err.emit();
 926
 927             path
 928         } else {
 929             self.parse_path(PathStyle::Type)?
 930         };
 931
 932         if self.may_recover() && self.token == TokenKind::OpenDelim(Delimiter::Parenthesis) {
 933             self.recover_fn_trait_with_lifetime_params(&mut path, &mut lifetime_defs)?;
 934         }
 935
 936         if has_parens {
 937             if self.token.is_like_plus() {
 938                 // Someone has written something like `&dyn (Trait + Other)`. The correct code
 939                 // would be `&(dyn Trait + Other)`, but we don't have access to the appropriate
 940                 // span to suggest that. When written as `&dyn Trait + Other`, an appropriate
 941                 // suggestion is given.
 942                 let bounds = vec![];
 943                 self.parse_remaining_bounds(bounds, true)?;
 944                 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
 945                 let sp = vec![lo, self.prev_token.span];
 946                 let sugg = vec![(lo, String::from(" ")), (self.prev_token.span, String::new())];
 947                 self.struct_span_err(sp, "incorrect braces around trait bounds")
 948                     .multipart_suggestion(
 949                         "remove the parentheses",
 950                         sugg,
 951                         Applicability::MachineApplicable,
 952                     )
 953                     .emit();
 954             } else {
 955                 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
 956             }
 957         }
 958
 959         let modifier = modifiers.to_trait_bound_modifier();
 960         let poly_trait = PolyTraitRef::new(lifetime_defs, path, lo.to(self.prev_token.span));
 961         Ok(GenericBound::Trait(poly_trait, modifier))
 962     }
 963
 964     // recovers a `Fn(..)` parenthesized-style path from `fn(..)`
 965     fn recover_path_from_fn(&mut self) -> Option<ast::Path> {
 966         let fn_token_span = self.token.span;
 967         self.bump();
 968         let args_lo = self.token.span;
 969         let snapshot = self.create_snapshot_for_diagnostic();
 970         match self.parse_fn_decl(|_| false, AllowPlus::No, RecoverReturnSign::OnlyFatArrow) {
 971             Ok(decl) => {
 972                 self.sess.emit_err(ExpectedFnPathFoundFnKeyword { fn_token_span });
 973                 Some(ast::Path {
 974                     span: fn_token_span.to(self.prev_token.span),
 975                     segments: thin_vec![ast::PathSegment {
 976                         ident: Ident::new(Symbol::intern("Fn"), fn_token_span),
 977                         id: DUMMY_NODE_ID,
 978                         args: Some(P(ast::GenericArgs::Parenthesized(ast::ParenthesizedArgs {
 979                             span: args_lo.to(self.prev_token.span),
 980                             inputs: decl.inputs.iter().map(|a| a.ty.clone()).collect(),
 981                             inputs_span: args_lo.until(decl.output.span()),
 982                             output: decl.output.clone(),
 983                         }))),
 984                     }],
 985                     tokens: None,
 986                 })
 987             }
 988             Err(diag) => {
 989                 diag.cancel();
 990                 self.restore_snapshot(snapshot);
 991                 None
 992             }
 993         }
 994     }
 995
 996     /// Optionally parses `for<$generic_params>`.
 997     pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
 998         if self.eat_keyword(kw::For) {
 999             self.expect_lt()?;
1000             let params = self.parse_generic_params()?;
1001             self.expect_gt()?;
1002             // We rely on AST validation to rule out invalid cases: There must not be type
1003             // parameters, and the lifetime parameters must not have bounds.
1004             Ok(params)
1005         } else {
1006             Ok(Vec::new())
1007         }
1008     }
1009
1010     /// Recover from `Fn`-family traits (Fn, FnMut, FnOnce) with lifetime arguments
1011     /// (e.g. `FnOnce<'a>(&'a str) -> bool`). Up to generic arguments have already
1012     /// been eaten.
1013     fn recover_fn_trait_with_lifetime_params(
1014         &mut self,
1015         fn_path: &mut ast::Path,
1016         lifetime_defs: &mut Vec<GenericParam>,
1017     ) -> PResult<'a, ()> {
1018         let fn_path_segment = fn_path.segments.last_mut().unwrap();
1019         let generic_args = if let Some(p_args) = &fn_path_segment.args {
1020             p_args.clone().into_inner()
1021         } else {
1022             // Normally it wouldn't come here because the upstream should have parsed
1023             // generic parameters (otherwise it's impossible to call this function).
1024             return Ok(());
1025         };
1026         let lifetimes =
1027             if let ast::GenericArgs::AngleBracketed(ast::AngleBracketedArgs { span: _, args }) =
1028                 &generic_args
1029             {
1030                 args.into_iter()
1031                     .filter_map(|arg| {
1032                         if let ast::AngleBracketedArg::Arg(generic_arg) = arg
1033                             && let ast::GenericArg::Lifetime(lifetime) = generic_arg {
1034                             Some(lifetime)
1035                         } else {
1036                             None
1037                         }
1038                     })
1039                     .collect()
1040             } else {
1041                 Vec::new()
1042             };
1043         // Only try to recover if the trait has lifetime params.
1044         if lifetimes.is_empty() {
1045             return Ok(());
1046         }
1047
1048         // Parse `(T, U) -> R`.
1049         let inputs_lo = self.token.span;
1050         let inputs: Vec<_> =
1051             self.parse_fn_params(|_| false)?.into_iter().map(|input| input.ty).collect();
1052         let inputs_span = inputs_lo.to(self.prev_token.span);
1053         let output = self.parse_ret_ty(AllowPlus::No, RecoverQPath::No, RecoverReturnSign::No)?;
1054         let args = ast::ParenthesizedArgs {
1055             span: fn_path_segment.span().to(self.prev_token.span),
1056             inputs,
1057             inputs_span,
1058             output,
1059         }
1060         .into();
1061         *fn_path_segment =
1062             ast::PathSegment { ident: fn_path_segment.ident, args, id: ast::DUMMY_NODE_ID };
1063
1064         // Convert parsed `<'a>` in `Fn<'a>` into `for<'a>`.
1065         let mut generic_params = lifetimes
1066             .iter()
1067             .map(|lt| GenericParam {
1068                 id: lt.id,
1069                 ident: lt.ident,
1070                 attrs: ast::AttrVec::new(),
1071                 bounds: Vec::new(),
1072                 is_placeholder: false,
1073                 kind: ast::GenericParamKind::Lifetime,
1074                 colon_span: None,
1075             })
1076             .collect::<Vec<GenericParam>>();
1077         lifetime_defs.append(&mut generic_params);
1078
1079         let generic_args_span = generic_args.span();
1080         let mut err =
1081             self.struct_span_err(generic_args_span, "`Fn` traits cannot take lifetime parameters");
1082         let snippet = format!(
1083             "for<{}> ",
1084             lifetimes.iter().map(|lt| lt.ident.as_str()).intersperse(", ").collect::<String>(),
1085         );
1086         let before_fn_path = fn_path.span.shrink_to_lo();
1087         err.multipart_suggestion(
1088             "consider using a higher-ranked trait bound instead",
1089             vec![(generic_args_span, "".to_owned()), (before_fn_path, snippet)],
1090             Applicability::MaybeIncorrect,
1091         )
1092         .emit();
1093         Ok(())
1094     }
1095
1096     pub(super) fn check_lifetime(&mut self) -> bool {
1097         self.expected_tokens.push(TokenType::Lifetime);
1098         self.token.is_lifetime()
1099     }
1100
1101     /// Parses a single lifetime `'a` or panics.
1102     pub(super) fn expect_lifetime(&mut self) -> Lifetime {
1103         if let Some(ident) = self.token.lifetime() {
1104             self.bump();
1105             Lifetime { ident, id: ast::DUMMY_NODE_ID }
1106         } else {
1107             self.span_bug(self.token.span, "not a lifetime")
1108         }
1109     }
1110
1111     pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
1112         P(Ty { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })
1113     }
1114 }