1 use super::item::ParamCfg;
2 use super::{Parser, PathStyle, TokenType};
4 use crate::{maybe_recover_from_interpolated_ty_qpath, maybe_whole};
6 use rustc_errors::{pluralize, struct_span_err, Applicability, PResult};
7 use rustc_span::source_map::Span;
8 use rustc_span::symbol::{kw, sym};
10 self, BareFnTy, FunctionRetTy, GenericParam, Ident, Lifetime, MutTy, Ty, TyKind,
13 GenericBound, GenericBounds, PolyTraitRef, TraitBoundModifier, TraitObjectSyntax,
15 use syntax::ast::{Mac, Mutability};
17 use syntax::token::{self, Token, TokenKind};
19 /// Any `?` or `?const` modifiers that appear at the start of a bound.
20 struct BoundModifiers {
25 maybe_const: Option<Span>,
29 fn to_trait_bound_modifier(&self) -> TraitBoundModifier {
30 match (self.maybe, self.maybe_const) {
31 (None, None) => TraitBoundModifier::None,
32 (Some(_), None) => TraitBoundModifier::Maybe,
33 (None, Some(_)) => TraitBoundModifier::MaybeConst,
34 (Some(_), Some(_)) => TraitBoundModifier::MaybeConstMaybe,
39 #[derive(Copy, Clone, PartialEq)]
40 pub(super) enum AllowPlus {
46 pub(super) enum RecoverQPath {
51 // Is `...` (`CVarArgs`) legal at this level of type parsing?
58 /// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
59 /// `IDENT<<u8 as Trait>::AssocTy>`.
61 /// Types can also be of the form `IDENT(u8, u8) -> u8`, however this assumes
62 /// that `IDENT` is not the ident of a fn trait.
63 fn can_continue_type_after_non_fn_ident(t: &Token) -> bool {
64 t == &token::ModSep || t == &token::Lt || t == &token::BinOp(token::Shl)
69 pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
70 self.parse_ty_common(AllowPlus::Yes, RecoverQPath::Yes, AllowCVariadic::No)
73 /// Parse a type suitable for a function or function pointer parameter.
74 /// The difference from `parse_ty` is that this version allows `...`
75 /// (`CVarArgs`) at the top level of the the type.
76 pub(super) fn parse_ty_for_param(&mut self) -> PResult<'a, P<Ty>> {
77 self.parse_ty_common(AllowPlus::Yes, RecoverQPath::Yes, AllowCVariadic::Yes)
80 /// Parses a type in restricted contexts where `+` is not permitted.
82 /// Example 1: `&'a TYPE`
83 /// `+` is prohibited to maintain operator priority (P(+) < P(&)).
84 /// Example 2: `value1 as TYPE + value2`
85 /// `+` is prohibited to avoid interactions with expression grammar.
86 pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
87 self.parse_ty_common(AllowPlus::No, RecoverQPath::Yes, AllowCVariadic::No)
90 /// Parses an optional return type `[ -> TY ]` in a function declaration.
91 pub(super) fn parse_ret_ty(
93 allow_plus: AllowPlus,
94 recover_qpath: RecoverQPath,
95 ) -> PResult<'a, FunctionRetTy> {
96 Ok(if self.eat(&token::RArrow) {
97 // FIXME(Centril): Can we unconditionally `allow_plus`?
98 let ty = self.parse_ty_common(allow_plus, recover_qpath, AllowCVariadic::No)?;
101 FunctionRetTy::Default(self.token.span.shrink_to_lo())
107 allow_plus: AllowPlus,
108 recover_qpath: RecoverQPath,
109 allow_c_variadic: AllowCVariadic,
110 ) -> PResult<'a, P<Ty>> {
111 let allow_qpath_recovery = recover_qpath == RecoverQPath::Yes;
112 maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
113 maybe_whole!(self, NtTy, |x| x);
115 let lo = self.token.span;
116 let mut impl_dyn_multi = false;
117 let kind = if self.check(&token::OpenDelim(token::Paren)) {
118 self.parse_ty_tuple_or_parens(lo, allow_plus)?
119 } else if self.eat(&token::Not) {
122 } else if self.eat(&token::BinOp(token::Star)) {
124 } else if self.eat(&token::OpenDelim(token::Bracket)) {
125 self.parse_array_or_slice_ty()?
126 } else if self.check(&token::BinOp(token::And)) || self.check(&token::AndAnd) {
129 self.parse_borrowed_pointee()?
130 } else if self.eat_keyword_noexpect(kw::Typeof) {
131 self.parse_typeof_ty()?
132 } else if self.eat_keyword(kw::Underscore) {
133 // A type to be inferred `_`
135 } else if self.token_is_bare_fn_keyword() {
136 // Function pointer type
137 self.parse_ty_bare_fn(Vec::new())?
138 } else if self.check_keyword(kw::For) {
139 // Function pointer type or bound list (trait object type) starting with a poly-trait.
140 // `for<'lt> [unsafe] [extern "ABI"] fn (&'lt S) -> T`
141 // `for<'lt> Trait1<'lt> + Trait2 + 'a`
142 let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
143 if self.token_is_bare_fn_keyword() {
144 self.parse_ty_bare_fn(lifetime_defs)?
146 let path = self.parse_path(PathStyle::Type)?;
147 let parse_plus = allow_plus == AllowPlus::Yes && self.check_plus();
148 self.parse_remaining_bounds(lifetime_defs, path, lo, parse_plus)?
150 } else if self.eat_keyword(kw::Impl) {
151 self.parse_impl_ty(&mut impl_dyn_multi)?
152 } else if self.is_explicit_dyn_type() {
153 self.parse_dyn_ty(&mut impl_dyn_multi)?
154 } else if self.check(&token::Question)
155 || self.check_lifetime() && self.look_ahead(1, |t| t.is_like_plus())
157 // Bound list (trait object type)
158 let bounds = self.parse_generic_bounds_common(allow_plus, None)?;
159 TyKind::TraitObject(bounds, TraitObjectSyntax::None)
160 } else if self.eat_lt() {
162 let (qself, path) = self.parse_qpath(PathStyle::Type)?;
163 TyKind::Path(Some(qself), path)
164 } else if self.token.is_path_start() {
165 self.parse_path_start_ty(lo, allow_plus)?
166 } else if self.eat(&token::DotDotDot) {
167 if allow_c_variadic == AllowCVariadic::Yes {
170 // FIXME(Centril): Should we just allow `...` syntactically
171 // anywhere in a type and use semantic restrictions instead?
172 self.error_illegal_c_varadic_ty(lo);
176 let msg = format!("expected type, found {}", super::token_descr(&self.token));
177 let mut err = self.struct_span_err(self.token.span, &msg);
178 err.span_label(self.token.span, "expected type");
179 self.maybe_annotate_with_ascription(&mut err, true);
183 let span = lo.to(self.prev_span);
184 let ty = self.mk_ty(span, kind);
186 // Try to recover from use of `+` with incorrect priority.
187 self.maybe_report_ambiguous_plus(allow_plus, impl_dyn_multi, &ty);
188 self.maybe_recover_from_bad_type_plus(allow_plus, &ty)?;
189 self.maybe_recover_from_bad_qpath(ty, allow_qpath_recovery)
193 /// - `(TYPE)`, a parenthesized type.
194 /// - `(TYPE,)`, a tuple with a single field of type TYPE.
195 fn parse_ty_tuple_or_parens(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
196 let mut trailing_plus = false;
197 let (ts, trailing) = self.parse_paren_comma_seq(|p| {
198 let ty = p.parse_ty()?;
199 trailing_plus = p.prev_token.kind == TokenKind::BinOp(token::Plus);
203 if ts.len() == 1 && !trailing {
204 let ty = ts.into_iter().nth(0).unwrap().into_inner();
205 let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
207 // `(TY_BOUND_NOPAREN) + BOUND + ...`.
208 TyKind::Path(None, path) if maybe_bounds => {
209 self.parse_remaining_bounds(Vec::new(), path, lo, true)
211 TyKind::TraitObject(mut bounds, TraitObjectSyntax::None)
212 if maybe_bounds && bounds.len() == 1 && !trailing_plus =>
214 let path = match bounds.remove(0) {
215 GenericBound::Trait(pt, ..) => pt.trait_ref.path,
216 GenericBound::Outlives(..) => {
217 return Err(self.struct_span_err(
219 "expected trait bound, not lifetime bound",
223 self.parse_remaining_bounds(Vec::new(), path, lo, true)
226 _ => Ok(TyKind::Paren(P(ty))),
233 fn parse_remaining_bounds(
235 generic_params: Vec<GenericParam>,
239 ) -> PResult<'a, TyKind> {
240 assert_ne!(self.token, token::Question);
242 let poly_trait_ref = PolyTraitRef::new(generic_params, path, lo.to(self.prev_span));
243 let mut bounds = vec![GenericBound::Trait(poly_trait_ref, TraitBoundModifier::None)];
245 self.eat_plus(); // `+`, or `+=` gets split and `+` is discarded
246 bounds.append(&mut self.parse_generic_bounds(Some(self.prev_span))?);
248 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::None))
251 /// Parses a raw pointer type: `*[const | mut] $type`.
252 fn parse_ty_ptr(&mut self) -> PResult<'a, TyKind> {
253 let mutbl = self.parse_const_or_mut().unwrap_or_else(|| {
254 let span = self.prev_span;
255 let msg = "expected mut or const in raw pointer type";
256 self.struct_span_err(span, msg)
257 .span_label(span, msg)
258 .help("use `*mut T` or `*const T` as appropriate")
262 let ty = self.parse_ty_no_plus()?;
263 Ok(TyKind::Ptr(MutTy { ty, mutbl }))
266 /// Parses an array (`[TYPE; EXPR]`) or slice (`[TYPE]`) type.
267 /// The opening `[` bracket is already eaten.
268 fn parse_array_or_slice_ty(&mut self) -> PResult<'a, TyKind> {
269 let elt_ty = self.parse_ty()?;
270 let ty = if self.eat(&token::Semi) {
271 TyKind::Array(elt_ty, self.parse_anon_const_expr()?)
273 TyKind::Slice(elt_ty)
275 self.expect(&token::CloseDelim(token::Bracket))?;
279 fn parse_borrowed_pointee(&mut self) -> PResult<'a, TyKind> {
280 let opt_lifetime = if self.check_lifetime() { Some(self.expect_lifetime()) } else { None };
281 let mutbl = self.parse_mutability();
282 let ty = self.parse_ty_no_plus()?;
283 Ok(TyKind::Rptr(opt_lifetime, MutTy { ty, mutbl }))
286 // Parses the `typeof(EXPR)`.
287 // To avoid ambiguity, the type is surrounded by parenthesis.
288 fn parse_typeof_ty(&mut self) -> PResult<'a, TyKind> {
289 self.expect(&token::OpenDelim(token::Paren))?;
290 let expr = self.parse_anon_const_expr()?;
291 self.expect(&token::CloseDelim(token::Paren))?;
292 Ok(TyKind::Typeof(expr))
295 /// Is the current token one of the keywords that signals a bare function type?
296 fn token_is_bare_fn_keyword(&mut self) -> bool {
297 self.check_keyword(kw::Fn)
298 || self.check_keyword(kw::Unsafe)
299 || self.check_keyword(kw::Extern)
302 /// Parses a function pointer type (`TyKind::BareFn`).
304 /// [unsafe] [extern "ABI"] fn (S) -> T
305 /// ^~~~~^ ^~~~^ ^~^ ^
307 /// | | | Return type
308 /// Function Style ABI Parameter types
310 fn parse_ty_bare_fn(&mut self, generic_params: Vec<GenericParam>) -> PResult<'a, TyKind> {
311 let unsafety = self.parse_unsafety();
312 let ext = self.parse_extern()?;
313 self.expect_keyword(kw::Fn)?;
314 let cfg = ParamCfg { is_name_required: |_| false };
315 let decl = self.parse_fn_decl(&cfg, AllowPlus::No)?;
316 Ok(TyKind::BareFn(P(BareFnTy { ext, unsafety, generic_params, decl })))
319 /// Parses an `impl B0 + ... + Bn` type.
320 fn parse_impl_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
321 // Always parse bounds greedily for better error recovery.
322 let bounds = self.parse_generic_bounds(None)?;
323 *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
324 Ok(TyKind::ImplTrait(ast::DUMMY_NODE_ID, bounds))
327 /// Is a `dyn B0 + ... + Bn` type allowed here?
328 fn is_explicit_dyn_type(&mut self) -> bool {
329 self.check_keyword(kw::Dyn)
330 && (self.token.span.rust_2018()
331 || self.look_ahead(1, |t| {
332 t.can_begin_bound() && !can_continue_type_after_non_fn_ident(t)
336 /// Parses a `dyn B0 + ... + Bn` type.
338 /// Note that this does *not* parse bare trait objects.
339 fn parse_dyn_ty(&mut self, impl_dyn_multi: &mut bool) -> PResult<'a, TyKind> {
340 self.bump(); // `dyn`
341 // Always parse bounds greedily for better error recovery.
342 let bounds = self.parse_generic_bounds(None)?;
343 *impl_dyn_multi = bounds.len() > 1 || self.prev_token.kind == TokenKind::BinOp(token::Plus);
344 Ok(TyKind::TraitObject(bounds, TraitObjectSyntax::Dyn))
347 /// Parses a type starting with a path.
350 /// 1. a type macro, `mac!(...)`,
351 /// 2. a bare trait object, `B0 + ... + Bn`,
352 /// 3. or a path, `path::to::MyType`.
353 fn parse_path_start_ty(&mut self, lo: Span, allow_plus: AllowPlus) -> PResult<'a, TyKind> {
355 let path = self.parse_path(PathStyle::Type)?;
356 if self.eat(&token::Not) {
357 // Macro invocation in type position
360 args: self.parse_mac_args()?,
361 prior_type_ascription: self.last_type_ascription,
363 } else if allow_plus == AllowPlus::Yes && self.check_plus() {
364 // `Trait1 + Trait2 + 'a`
365 self.parse_remaining_bounds(Vec::new(), path, lo, true)
368 Ok(TyKind::Path(None, path))
372 fn error_illegal_c_varadic_ty(&self, lo: Span) {
374 self.sess.span_diagnostic,
375 lo.to(self.prev_span),
377 "C-variadic type `...` may not be nested inside another type",
382 pub(super) fn parse_generic_bounds(
384 colon_span: Option<Span>,
385 ) -> PResult<'a, GenericBounds> {
386 self.parse_generic_bounds_common(AllowPlus::Yes, colon_span)
389 /// Parses bounds of a type parameter `BOUND + BOUND + ...`, possibly with trailing `+`.
391 /// See `parse_generic_bound` for the `BOUND` grammar.
392 fn parse_generic_bounds_common(
394 allow_plus: AllowPlus,
395 colon_span: Option<Span>,
396 ) -> PResult<'a, GenericBounds> {
397 let mut bounds = Vec::new();
398 let mut negative_bounds = Vec::new();
399 while self.can_begin_bound() {
400 match self.parse_generic_bound()? {
401 Ok(bound) => bounds.push(bound),
402 Err(neg_sp) => negative_bounds.push(neg_sp),
404 if allow_plus == AllowPlus::No || !self.eat_plus() {
409 if !negative_bounds.is_empty() {
410 self.error_negative_bounds(colon_span, &bounds, negative_bounds);
416 /// Can the current token begin a bound?
417 fn can_begin_bound(&mut self) -> bool {
418 // This needs to be synchronized with `TokenKind::can_begin_bound`.
420 || self.check_lifetime()
421 || self.check(&token::Not) // Used for error reporting only.
422 || self.check(&token::Question)
423 || self.check_keyword(kw::For)
424 || self.check(&token::OpenDelim(token::Paren))
427 fn error_negative_bounds(
429 colon_span: Option<Span>,
430 bounds: &[GenericBound],
431 negative_bounds: Vec<Span>,
433 let negative_bounds_len = negative_bounds.len();
434 let last_span = *negative_bounds.last().expect("no negative bounds, but still error?");
435 let mut err = self.struct_span_err(negative_bounds, "negative bounds are not supported");
436 err.span_label(last_span, "negative bounds are not supported");
437 if let Some(bound_list) = colon_span {
438 let bound_list = bound_list.to(self.prev_span);
439 let mut new_bound_list = String::new();
440 if !bounds.is_empty() {
441 let mut snippets = bounds.iter().map(|bound| self.span_to_snippet(bound.span()));
442 while let Some(Ok(snippet)) = snippets.next() {
443 new_bound_list.push_str(" + ");
444 new_bound_list.push_str(&snippet);
446 new_bound_list = new_bound_list.replacen(" +", ":", 1);
448 err.tool_only_span_suggestion(
450 &format!("remove the bound{}", pluralize!(negative_bounds_len)),
452 Applicability::MachineApplicable,
458 /// Parses a bound according to the grammar:
460 /// BOUND = TY_BOUND | LT_BOUND
462 fn parse_generic_bound(&mut self) -> PResult<'a, Result<GenericBound, Span>> {
463 let anchor_lo = self.prev_span;
464 let lo = self.token.span;
465 let has_parens = self.eat(&token::OpenDelim(token::Paren));
466 let inner_lo = self.token.span;
467 let is_negative = self.eat(&token::Not);
469 let modifiers = self.parse_ty_bound_modifiers();
470 let bound = if self.token.is_lifetime() {
471 self.error_lt_bound_with_modifiers(modifiers);
472 self.parse_generic_lt_bound(lo, inner_lo, has_parens)?
474 self.parse_generic_ty_bound(lo, has_parens, modifiers)?
477 Ok(if is_negative { Err(anchor_lo.to(self.prev_span)) } else { Ok(bound) })
480 /// Parses a lifetime ("outlives") bound, e.g. `'a`, according to:
482 /// LT_BOUND = LIFETIME
484 fn parse_generic_lt_bound(
489 ) -> PResult<'a, GenericBound> {
490 let bound = GenericBound::Outlives(self.expect_lifetime());
492 // FIXME(Centril): Consider not erroring here and accepting `('lt)` instead,
493 // possibly introducing `GenericBound::Paren(P<GenericBound>)`?
494 self.recover_paren_lifetime(lo, inner_lo)?;
499 /// Emits an error if any trait bound modifiers were present.
500 fn error_lt_bound_with_modifiers(&self, modifiers: BoundModifiers) {
501 if let Some(span) = modifiers.maybe_const {
502 self.struct_span_err(
504 "`?const` may only modify trait bounds, not lifetime bounds",
509 if let Some(span) = modifiers.maybe {
510 self.struct_span_err(span, "`?` may only modify trait bounds, not lifetime bounds")
515 /// Recover on `('lifetime)` with `(` already eaten.
516 fn recover_paren_lifetime(&mut self, lo: Span, inner_lo: Span) -> PResult<'a, ()> {
517 let inner_span = inner_lo.to(self.prev_span);
518 self.expect(&token::CloseDelim(token::Paren))?;
519 let mut err = self.struct_span_err(
520 lo.to(self.prev_span),
521 "parenthesized lifetime bounds are not supported",
523 if let Ok(snippet) = self.span_to_snippet(inner_span) {
524 err.span_suggestion_short(
525 lo.to(self.prev_span),
526 "remove the parentheses",
528 Applicability::MachineApplicable,
535 /// Parses the modifiers that may precede a trait in a bound, e.g. `?Trait` or `?const Trait`.
537 /// If no modifiers are present, this does not consume any tokens.
540 /// TY_BOUND_MODIFIERS = "?" ["const" ["?"]]
542 fn parse_ty_bound_modifiers(&mut self) -> BoundModifiers {
543 if !self.eat(&token::Question) {
544 return BoundModifiers { maybe: None, maybe_const: None };
548 let first_question = self.prev_span;
549 if !self.eat_keyword(kw::Const) {
550 return BoundModifiers { maybe: Some(first_question), maybe_const: None };
554 let maybe_const = first_question.to(self.prev_span);
555 self.sess.gated_spans.gate(sym::const_trait_bound_opt_out, maybe_const);
556 if !self.eat(&token::Question) {
557 return BoundModifiers { maybe: None, maybe_const: Some(maybe_const) };
561 let second_question = self.prev_span;
562 BoundModifiers { maybe: Some(second_question), maybe_const: Some(maybe_const) }
565 /// Parses a type bound according to:
567 /// TY_BOUND = TY_BOUND_NOPAREN | (TY_BOUND_NOPAREN)
568 /// TY_BOUND_NOPAREN = [TY_BOUND_MODIFIERS] [for<LT_PARAM_DEFS>] SIMPLE_PATH
571 /// For example, this grammar accepts `?const ?for<'a: 'b> m::Trait<'a>`.
572 fn parse_generic_ty_bound(
576 modifiers: BoundModifiers,
577 ) -> PResult<'a, GenericBound> {
578 let lifetime_defs = self.parse_late_bound_lifetime_defs()?;
579 let path = self.parse_path(PathStyle::Type)?;
581 self.expect(&token::CloseDelim(token::Paren))?;
584 let modifier = modifiers.to_trait_bound_modifier();
585 let poly_trait = PolyTraitRef::new(lifetime_defs, path, lo.to(self.prev_span));
586 Ok(GenericBound::Trait(poly_trait, modifier))
589 /// Optionally parses `for<$generic_params>`.
590 pub(super) fn parse_late_bound_lifetime_defs(&mut self) -> PResult<'a, Vec<GenericParam>> {
591 if self.eat_keyword(kw::For) {
593 let params = self.parse_generic_params()?;
595 // We rely on AST validation to rule out invalid cases: There must not be type
596 // parameters, and the lifetime parameters must not have bounds.
603 pub fn check_lifetime(&mut self) -> bool {
604 self.expected_tokens.push(TokenType::Lifetime);
605 self.token.is_lifetime()
608 /// Parses a single lifetime `'a` or panics.
609 pub fn expect_lifetime(&mut self) -> Lifetime {
610 if let Some(ident) = self.token.lifetime() {
611 let span = self.token.span;
613 Lifetime { ident: Ident::new(ident.name, span), id: ast::DUMMY_NODE_ID }
615 self.span_bug(self.token.span, "not a lifetime")
619 pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
620 P(Ty { kind, span, id: ast::DUMMY_NODE_ID })