1 //! Conversion from AST representation of types to the `ty.rs` representation.
2 //! The main routine here is `ast_ty_to_ty()`; each use is parameterized by an
3 //! instance of `AstConv`.
8 use crate::bounds::Bounds;
9 use crate::collect::PlaceholderHirTyCollector;
11 AmbiguousLifetimeBound, MultipleRelaxedDefaultBounds, TraitObjectDeclaredWithNoTraits,
12 TypeofReservedKeywordUsed, ValueOfAssociatedStructAlreadySpecified,
14 use crate::middle::resolve_lifetime as rl;
15 use crate::require_c_abi_if_c_variadic;
16 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
17 use rustc_errors::{struct_span_err, Applicability, ErrorReported, FatalError};
19 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
20 use rustc_hir::def_id::{DefId, LocalDefId};
21 use rustc_hir::intravisit::{walk_generics, Visitor as _};
22 use rustc_hir::lang_items::LangItem;
23 use rustc_hir::{GenericArg, GenericArgs};
24 use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, Subst, SubstsRef};
25 use rustc_middle::ty::GenericParamDefKind;
26 use rustc_middle::ty::{self, Const, DefIdTree, Ty, TyCtxt, TypeFoldable};
27 use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
28 use rustc_span::lev_distance::find_best_match_for_name;
29 use rustc_span::symbol::{Ident, Symbol};
30 use rustc_span::{Span, DUMMY_SP};
31 use rustc_target::spec::abi;
32 use rustc_trait_selection::traits;
33 use rustc_trait_selection::traits::astconv_object_safety_violations;
34 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
35 use rustc_trait_selection::traits::wf::object_region_bounds;
37 use smallvec::SmallVec;
39 use std::collections::BTreeSet;
43 pub struct PathSeg(pub DefId, pub usize);
45 pub trait AstConv<'tcx> {
46 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
48 fn item_def_id(&self) -> Option<DefId>;
50 /// Returns predicates in scope of the form `X: Foo<T>`, where `X`
51 /// is a type parameter `X` with the given id `def_id` and T
52 /// matches `assoc_name`. This is a subset of the full set of
55 /// This is used for one specific purpose: resolving "short-hand"
56 /// associated type references like `T::Item`. In principle, we
57 /// would do that by first getting the full set of predicates in
58 /// scope and then filtering down to find those that apply to `T`,
59 /// but this can lead to cycle errors. The problem is that we have
60 /// to do this resolution *in order to create the predicates in
61 /// the first place*. Hence, we have this "special pass".
62 fn get_type_parameter_bounds(
67 ) -> ty::GenericPredicates<'tcx>;
69 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
70 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
71 -> Option<ty::Region<'tcx>>;
73 /// Returns the type to use when a type is omitted.
74 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
76 /// Returns `true` if `_` is allowed in type signatures in the current context.
77 fn allow_ty_infer(&self) -> bool;
79 /// Returns the const to use when a const is omitted.
83 param: Option<&ty::GenericParamDef>,
85 ) -> &'tcx Const<'tcx>;
87 /// Projecting an associated type from a (potentially)
88 /// higher-ranked trait reference is more complicated, because of
89 /// the possibility of late-bound regions appearing in the
90 /// associated type binding. This is not legal in function
91 /// signatures for that reason. In a function body, we can always
92 /// handle it because we can use inference variables to remove the
93 /// late-bound regions.
94 fn projected_ty_from_poly_trait_ref(
98 item_segment: &hir::PathSegment<'_>,
99 poly_trait_ref: ty::PolyTraitRef<'tcx>,
102 /// Normalize an associated type coming from the user.
103 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
105 /// Invoked when we encounter an error from some prior pass
106 /// (e.g., resolve) that is translated into a ty-error. This is
107 /// used to help suppress derived errors typeck might otherwise
109 fn set_tainted_by_errors(&self);
111 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
115 struct ConvertedBinding<'a, 'tcx> {
118 kind: ConvertedBindingKind<'a, 'tcx>,
119 gen_args: &'a GenericArgs<'a>,
124 enum ConvertedBindingKind<'a, 'tcx> {
126 Constraint(&'a [hir::GenericBound<'a>]),
129 /// New-typed boolean indicating whether explicit late-bound lifetimes
130 /// are present in a set of generic arguments.
132 /// For example if we have some method `fn f<'a>(&'a self)` implemented
133 /// for some type `T`, although `f` is generic in the lifetime `'a`, `'a`
134 /// is late-bound so should not be provided explicitly. Thus, if `f` is
135 /// instantiated with some generic arguments providing `'a` explicitly,
136 /// we taint those arguments with `ExplicitLateBound::Yes` so that we
137 /// can provide an appropriate diagnostic later.
138 #[derive(Copy, Clone, PartialEq)]
139 pub enum ExplicitLateBound {
144 #[derive(Copy, Clone, PartialEq)]
145 pub enum IsMethodCall {
150 /// Denotes the "position" of a generic argument, indicating if it is a generic type,
151 /// generic function or generic method call.
152 #[derive(Copy, Clone, PartialEq)]
153 pub(crate) enum GenericArgPosition {
155 Value, // e.g., functions
159 /// A marker denoting that the generic arguments that were
160 /// provided did not match the respective generic parameters.
161 #[derive(Clone, Default)]
162 pub struct GenericArgCountMismatch {
163 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
164 pub reported: Option<ErrorReported>,
165 /// A list of spans of arguments provided that were not valid.
166 pub invalid_args: Vec<Span>,
169 /// Decorates the result of a generic argument count mismatch
170 /// check with whether explicit late bounds were provided.
172 pub struct GenericArgCountResult {
173 pub explicit_late_bound: ExplicitLateBound,
174 pub correct: Result<(), GenericArgCountMismatch>,
177 pub trait CreateSubstsForGenericArgsCtxt<'a, 'tcx> {
178 fn args_for_def_id(&mut self, def_id: DefId) -> (Option<&'a GenericArgs<'a>>, bool);
182 param: &ty::GenericParamDef,
183 arg: &GenericArg<'_>,
184 ) -> subst::GenericArg<'tcx>;
188 substs: Option<&[subst::GenericArg<'tcx>]>,
189 param: &ty::GenericParamDef,
191 ) -> subst::GenericArg<'tcx>;
194 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
195 #[tracing::instrument(level = "debug", skip(self))]
196 pub fn ast_region_to_region(
198 lifetime: &hir::Lifetime,
199 def: Option<&ty::GenericParamDef>,
200 ) -> ty::Region<'tcx> {
201 let tcx = self.tcx();
202 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
204 let r = match tcx.named_region(lifetime.hir_id) {
205 Some(rl::Region::Static) => tcx.lifetimes.re_static,
207 Some(rl::Region::LateBound(debruijn, index, def_id, _)) => {
208 let name = lifetime_name(def_id.expect_local());
209 let br = ty::BoundRegion {
210 var: ty::BoundVar::from_u32(index),
211 kind: ty::BrNamed(def_id, name),
213 tcx.mk_region(ty::ReLateBound(debruijn, br))
216 Some(rl::Region::LateBoundAnon(debruijn, index, anon_index)) => {
217 let br = ty::BoundRegion {
218 var: ty::BoundVar::from_u32(index),
219 kind: ty::BrAnon(anon_index),
221 tcx.mk_region(ty::ReLateBound(debruijn, br))
224 Some(rl::Region::EarlyBound(index, id, _)) => {
225 let name = lifetime_name(id.expect_local());
226 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
229 Some(rl::Region::Free(scope, id)) => {
230 let name = lifetime_name(id.expect_local());
231 tcx.mk_region(ty::ReFree(ty::FreeRegion {
233 bound_region: ty::BrNamed(id, name),
236 // (*) -- not late-bound, won't change
240 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
241 debug!(?lifetime, "unelided lifetime in signature");
243 // This indicates an illegal lifetime
244 // elision. `resolve_lifetime` should have
245 // reported an error in this case -- but if
246 // not, let's error out.
247 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
249 // Supply some dummy value. We don't have an
250 // `re_error`, annoyingly, so use `'static`.
251 tcx.lifetimes.re_static
256 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
261 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
262 /// returns an appropriate set of substitutions for this particular reference to `I`.
263 pub fn ast_path_substs_for_ty(
267 item_segment: &hir::PathSegment<'_>,
268 ) -> SubstsRef<'tcx> {
269 let (substs, _) = self.create_substs_for_ast_path(
275 item_segment.infer_args,
278 let assoc_bindings = self.create_assoc_bindings_for_generic_args(item_segment.args());
280 if let Some(b) = assoc_bindings.first() {
281 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
287 /// Given the type/lifetime/const arguments provided to some path (along with
288 /// an implicit `Self`, if this is a trait reference), returns the complete
289 /// set of substitutions. This may involve applying defaulted type parameters.
290 /// Also returns back constraints on associated types.
295 /// T: std::ops::Index<usize, Output = u32>
296 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
299 /// 1. The `self_ty` here would refer to the type `T`.
300 /// 2. The path in question is the path to the trait `std::ops::Index`,
301 /// which will have been resolved to a `def_id`
302 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
303 /// parameters are returned in the `SubstsRef`, the associated type bindings like
304 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
306 /// Note that the type listing given here is *exactly* what the user provided.
308 /// For (generic) associated types
311 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
314 /// We have the parent substs are the substs for the parent trait:
315 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
316 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
317 /// lists: `[Vec<u8>, u8, 'a]`.
318 #[tracing::instrument(level = "debug", skip(self, span))]
319 fn create_substs_for_ast_path<'a>(
323 parent_substs: &[subst::GenericArg<'tcx>],
324 seg: &hir::PathSegment<'_>,
325 generic_args: &'a hir::GenericArgs<'_>,
327 self_ty: Option<Ty<'tcx>>,
328 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
329 // If the type is parameterized by this region, then replace this
330 // region with the current anon region binding (in other words,
331 // whatever & would get replaced with).
333 let tcx = self.tcx();
334 let generics = tcx.generics_of(def_id);
335 debug!("generics: {:?}", generics);
337 if generics.has_self {
338 if generics.parent.is_some() {
339 // The parent is a trait so it should have at least one subst
340 // for the `Self` type.
341 assert!(!parent_substs.is_empty())
343 // This item (presumably a trait) needs a self-type.
344 assert!(self_ty.is_some());
347 assert!(self_ty.is_none() && parent_substs.is_empty());
350 let arg_count = Self::check_generic_arg_count(
357 GenericArgPosition::Type,
362 // Skip processing if type has no generic parameters.
363 // Traits always have `Self` as a generic parameter, which means they will not return early
364 // here and so associated type bindings will be handled regardless of whether there are any
365 // non-`Self` generic parameters.
366 if generics.params.is_empty() {
367 return (tcx.intern_substs(&[]), arg_count);
370 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
372 struct SubstsForAstPathCtxt<'a, 'tcx> {
373 astconv: &'a (dyn AstConv<'tcx> + 'a),
375 generic_args: &'a GenericArgs<'a>,
377 missing_type_params: Vec<String>,
378 inferred_params: Vec<Span>,
383 impl<'tcx, 'a> SubstsForAstPathCtxt<'tcx, 'a> {
384 fn default_needs_object_self(&mut self, param: &ty::GenericParamDef) -> bool {
385 let tcx = self.astconv.tcx();
386 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
387 if self.is_object && has_default {
388 let default_ty = tcx.at(self.span).type_of(param.def_id);
389 let self_param = tcx.types.self_param;
390 if default_ty.walk(tcx).any(|arg| arg == self_param.into()) {
391 // There is no suitable inference default for a type parameter
392 // that references self, in an object type.
402 impl<'a, 'tcx> CreateSubstsForGenericArgsCtxt<'a, 'tcx> for SubstsForAstPathCtxt<'a, 'tcx> {
403 fn args_for_def_id(&mut self, did: DefId) -> (Option<&'a GenericArgs<'a>>, bool) {
404 if did == self.def_id {
405 (Some(self.generic_args), self.infer_args)
407 // The last component of this tuple is unimportant.
414 param: &ty::GenericParamDef,
415 arg: &GenericArg<'_>,
416 ) -> subst::GenericArg<'tcx> {
417 let tcx = self.astconv.tcx();
418 match (¶m.kind, arg) {
419 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
420 self.astconv.ast_region_to_region(lt, Some(param)).into()
422 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
424 tcx.check_optional_stability(
430 // Default generic parameters may not be marked
431 // with stability attributes, i.e. when the
432 // default parameter was defined at the same time
433 // as the rest of the type. As such, we ignore missing
434 // stability attributes.
438 if let (hir::TyKind::Infer, false) =
439 (&ty.kind, self.astconv.allow_ty_infer())
441 self.inferred_params.push(ty.span);
442 tcx.ty_error().into()
444 self.astconv.ast_ty_to_ty(ty).into()
447 (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
448 ty::Const::from_opt_const_arg_anon_const(
450 ty::WithOptConstParam {
451 did: tcx.hir().local_def_id(ct.value.hir_id),
452 const_param_did: Some(param.def_id),
457 (&GenericParamDefKind::Const { has_default }, hir::GenericArg::Infer(inf)) => {
459 tcx.const_param_default(param.def_id).into()
460 } else if self.astconv.allow_ty_infer() {
461 // FIXME(const_generics): Actually infer parameter here?
464 self.inferred_params.push(inf.span);
465 tcx.ty_error().into()
469 &GenericParamDefKind::Type { has_default, .. },
470 hir::GenericArg::Infer(inf),
473 tcx.check_optional_stability(
479 // Default generic parameters may not be marked
480 // with stability attributes, i.e. when the
481 // default parameter was defined at the same time
482 // as the rest of the type. As such, we ignore missing
483 // stability attributes.
487 if self.astconv.allow_ty_infer() {
488 self.astconv.ast_ty_to_ty(&inf.to_ty()).into()
490 self.inferred_params.push(inf.span);
491 tcx.ty_error().into()
500 substs: Option<&[subst::GenericArg<'tcx>]>,
501 param: &ty::GenericParamDef,
503 ) -> subst::GenericArg<'tcx> {
504 let tcx = self.astconv.tcx();
506 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
507 GenericParamDefKind::Type { has_default, .. } => {
508 if !infer_args && has_default {
509 // No type parameter provided, but a default exists.
511 // If we are converting an object type, then the
512 // `Self` parameter is unknown. However, some of the
513 // other type parameters may reference `Self` in their
514 // defaults. This will lead to an ICE if we are not
516 if self.default_needs_object_self(param) {
517 self.missing_type_params.push(param.name.to_string());
518 tcx.ty_error().into()
520 // This is a default type parameter.
521 let substs = substs.unwrap();
522 if substs.iter().any(|arg| match arg.unpack() {
523 GenericArgKind::Type(ty) => ty.references_error(),
526 // Avoid ICE #86756 when type error recovery goes awry.
527 return tcx.ty_error().into();
532 tcx.at(self.span).type_of(param.def_id).subst_spanned(
540 } else if infer_args {
541 // No type parameters were provided, we can infer all.
542 let param = if !self.default_needs_object_self(param) {
547 self.astconv.ty_infer(param, self.span).into()
549 // We've already errored above about the mismatch.
550 tcx.ty_error().into()
553 GenericParamDefKind::Const { has_default } => {
554 let ty = tcx.at(self.span).type_of(param.def_id);
555 if !infer_args && has_default {
556 tcx.const_param_default(param.def_id)
557 .subst_spanned(tcx, substs.unwrap(), Some(self.span))
561 self.astconv.ct_infer(ty, Some(param), self.span).into()
563 // We've already errored above about the mismatch.
564 tcx.const_error(ty).into()
572 let mut substs_ctx = SubstsForAstPathCtxt {
577 missing_type_params: vec![],
578 inferred_params: vec![],
582 let substs = Self::create_substs_for_generic_args(
592 self.complain_about_missing_type_params(
593 substs_ctx.missing_type_params,
596 generic_args.args.is_empty(),
600 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
601 generics, self_ty, substs
607 fn create_assoc_bindings_for_generic_args<'a>(
609 generic_args: &'a hir::GenericArgs<'_>,
610 ) -> Vec<ConvertedBinding<'a, 'tcx>> {
611 // Convert associated-type bindings or constraints into a separate vector.
612 // Example: Given this:
614 // T: Iterator<Item = u32>
616 // The `T` is passed in as a self-type; the `Item = u32` is
617 // not a "type parameter" of the `Iterator` trait, but rather
618 // a restriction on `<T as Iterator>::Item`, so it is passed
620 let assoc_bindings = generic_args
624 let kind = match binding.kind {
625 hir::TypeBindingKind::Equality { ty } => {
626 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
628 hir::TypeBindingKind::Constraint { bounds } => {
629 ConvertedBindingKind::Constraint(bounds)
633 hir_id: binding.hir_id,
634 item_name: binding.ident,
636 gen_args: binding.gen_args,
645 crate fn create_substs_for_associated_item(
650 item_segment: &hir::PathSegment<'_>,
651 parent_substs: SubstsRef<'tcx>,
652 ) -> SubstsRef<'tcx> {
654 "create_substs_for_associated_item(span: {:?}, item_def_id: {:?}, item_segment: {:?}",
655 span, item_def_id, item_segment
657 if tcx.generics_of(item_def_id).params.is_empty() {
658 self.prohibit_generics(slice::from_ref(item_segment));
662 self.create_substs_for_ast_path(
668 item_segment.infer_args,
675 /// Instantiates the path for the given trait reference, assuming that it's
676 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
677 /// The type _cannot_ be a type other than a trait type.
679 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
680 /// are disallowed. Otherwise, they are pushed onto the vector given.
681 pub fn instantiate_mono_trait_ref(
683 trait_ref: &hir::TraitRef<'_>,
685 ) -> ty::TraitRef<'tcx> {
686 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
688 self.ast_path_to_mono_trait_ref(
690 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
692 trait_ref.path.segments.last().unwrap(),
696 fn instantiate_poly_trait_ref_inner(
700 binding_span: Option<Span>,
701 constness: ty::BoundConstness,
702 bounds: &mut Bounds<'tcx>,
704 trait_ref_span: Span,
706 trait_segment: &hir::PathSegment<'_>,
707 args: &GenericArgs<'_>,
710 ) -> GenericArgCountResult {
711 let (substs, arg_count) = self.create_substs_for_ast_path(
721 let tcx = self.tcx();
722 let bound_vars = tcx.late_bound_vars(hir_id);
725 let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
728 ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
730 debug!(?poly_trait_ref, ?assoc_bindings);
731 bounds.trait_bounds.push((poly_trait_ref, span, constness));
733 let mut dup_bindings = FxHashMap::default();
734 for binding in &assoc_bindings {
735 // Specify type to assert that error was already reported in `Err` case.
736 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
743 binding_span.unwrap_or(binding.span),
745 // Okay to ignore `Err` because of `ErrorReported` (see above).
751 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
752 /// a full trait reference. The resulting trait reference is returned. This may also generate
753 /// auxiliary bounds, which are added to `bounds`.
758 /// poly_trait_ref = Iterator<Item = u32>
762 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
764 /// **A note on binders:** against our usual convention, there is an implied bounder around
765 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
766 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
767 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
768 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
770 #[tracing::instrument(level = "debug", skip(self, span, constness, bounds, speculative))]
771 pub(crate) fn instantiate_poly_trait_ref(
773 trait_ref: &hir::TraitRef<'_>,
775 constness: ty::BoundConstness,
777 bounds: &mut Bounds<'tcx>,
779 ) -> GenericArgCountResult {
780 let hir_id = trait_ref.hir_ref_id;
781 let binding_span = None;
782 let trait_ref_span = trait_ref.path.span;
783 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
784 let trait_segment = trait_ref.path.segments.last().unwrap();
785 let args = trait_segment.args();
786 let infer_args = trait_segment.infer_args;
788 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
789 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
791 self.instantiate_poly_trait_ref_inner(
807 pub(crate) fn instantiate_lang_item_trait_ref(
809 lang_item: hir::LangItem,
812 args: &GenericArgs<'_>,
814 bounds: &mut Bounds<'tcx>,
816 let binding_span = Some(span);
817 let constness = ty::BoundConstness::NotConst;
818 let speculative = false;
819 let trait_ref_span = span;
820 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
821 let trait_segment = &hir::PathSegment::invalid();
822 let infer_args = false;
824 self.instantiate_poly_trait_ref_inner(
840 fn ast_path_to_mono_trait_ref(
845 trait_segment: &hir::PathSegment<'_>,
846 ) -> ty::TraitRef<'tcx> {
848 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
849 let assoc_bindings = self.create_assoc_bindings_for_generic_args(trait_segment.args());
850 if let Some(b) = assoc_bindings.first() {
851 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
853 ty::TraitRef::new(trait_def_id, substs)
856 #[tracing::instrument(level = "debug", skip(self, span))]
857 fn create_substs_for_ast_trait_ref<'a>(
862 trait_segment: &'a hir::PathSegment<'a>,
863 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
864 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
866 self.create_substs_for_ast_path(
871 trait_segment.args(),
872 trait_segment.infer_args,
877 fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
879 .associated_items(trait_def_id)
880 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
884 // Sets `implicitly_sized` to true on `Bounds` if necessary
885 pub(crate) fn add_implicitly_sized<'hir>(
887 bounds: &mut Bounds<'hir>,
888 ast_bounds: &'hir [hir::GenericBound<'hir>],
889 self_ty_where_predicates: Option<(hir::HirId, &'hir [hir::WherePredicate<'hir>])>,
892 let tcx = self.tcx();
894 // Try to find an unbound in bounds.
895 let mut unbound = None;
896 let mut search_bounds = |ast_bounds: &'hir [hir::GenericBound<'hir>]| {
897 for ab in ast_bounds {
898 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
899 if unbound.is_none() {
900 unbound = Some(&ptr.trait_ref);
902 tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
907 search_bounds(ast_bounds);
908 if let Some((self_ty, where_clause)) = self_ty_where_predicates {
909 let self_ty_def_id = tcx.hir().local_def_id(self_ty).to_def_id();
910 for clause in where_clause {
911 if let hir::WherePredicate::BoundPredicate(pred) = clause {
912 match pred.bounded_ty.kind {
913 hir::TyKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
914 Res::Def(DefKind::TyParam, def_id) if def_id == self_ty_def_id => {}
919 search_bounds(pred.bounds);
924 let sized_def_id = tcx.lang_items().require(LangItem::Sized);
925 match (&sized_def_id, unbound) {
926 (Ok(sized_def_id), Some(tpb))
927 if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) =>
929 // There was in fact a `?Sized` bound, return without doing anything
933 // There was a `?Trait` bound, but it was not `?Sized`; warn.
936 "default bound relaxed for a type parameter, but \
937 this does nothing because the given bound is not \
938 a default; only `?Sized` is supported",
940 // Otherwise, add implicitly sized if `Sized` is available.
943 // There was no `?Sized` bound; add implicitly sized if `Sized` is available.
946 if sized_def_id.is_err() {
947 // No lang item for `Sized`, so we can't add it as a bound.
950 bounds.implicitly_sized = Some(span);
953 /// This helper takes a *converted* parameter type (`param_ty`)
954 /// and an *unconverted* list of bounds:
958 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
960 /// `param_ty`, in ty form
963 /// It adds these `ast_bounds` into the `bounds` structure.
965 /// **A note on binders:** there is an implied binder around
966 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
967 /// for more details.
968 #[tracing::instrument(level = "debug", skip(self, ast_bounds, bounds))]
969 pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>(
973 bounds: &mut Bounds<'tcx>,
974 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
976 for ast_bound in ast_bounds {
978 hir::GenericBound::Trait(poly_trait_ref, modifier) => {
979 let constness = match modifier {
980 hir::TraitBoundModifier::MaybeConst => ty::BoundConstness::ConstIfConst,
981 hir::TraitBoundModifier::None => ty::BoundConstness::NotConst,
982 hir::TraitBoundModifier::Maybe => continue,
985 let _ = self.instantiate_poly_trait_ref(
986 &poly_trait_ref.trait_ref,
994 &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
995 self.instantiate_lang_item_trait_ref(
996 lang_item, span, hir_id, args, param_ty, bounds,
999 hir::GenericBound::Outlives(lifetime) => {
1000 let region = self.ast_region_to_region(lifetime, None);
1003 .push((ty::Binder::bind_with_vars(region, bound_vars), lifetime.span));
1009 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1010 /// The self-type for the bounds is given by `param_ty`.
1015 /// fn foo<T: Bar + Baz>() { }
1016 /// ^ ^^^^^^^^^ ast_bounds
1020 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1021 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1022 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1024 /// `span` should be the declaration size of the parameter.
1025 pub(crate) fn compute_bounds(
1028 ast_bounds: &[hir::GenericBound<'_>],
1030 self.compute_bounds_inner(param_ty, ast_bounds)
1033 /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
1034 /// named `assoc_name` into ty::Bounds. Ignore the rest.
1035 pub(crate) fn compute_bounds_that_match_assoc_type(
1038 ast_bounds: &[hir::GenericBound<'_>],
1041 let mut result = Vec::new();
1043 for ast_bound in ast_bounds {
1044 if let Some(trait_ref) = ast_bound.trait_ref() {
1045 if let Some(trait_did) = trait_ref.trait_def_id() {
1046 if self.tcx().trait_may_define_assoc_type(trait_did, assoc_name) {
1047 result.push(ast_bound.clone());
1053 self.compute_bounds_inner(param_ty, &result)
1056 fn compute_bounds_inner(
1059 ast_bounds: &[hir::GenericBound<'_>],
1061 let mut bounds = Bounds::default();
1063 self.add_bounds(param_ty, ast_bounds.iter(), &mut bounds, ty::List::empty());
1068 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1071 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1072 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1073 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1074 #[tracing::instrument(
1076 skip(self, bounds, speculative, dup_bindings, path_span)
1078 fn add_predicates_for_ast_type_binding(
1080 hir_ref_id: hir::HirId,
1081 trait_ref: ty::PolyTraitRef<'tcx>,
1082 binding: &ConvertedBinding<'_, 'tcx>,
1083 bounds: &mut Bounds<'tcx>,
1085 dup_bindings: &mut FxHashMap<DefId, Span>,
1087 ) -> Result<(), ErrorReported> {
1088 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1089 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1090 // subtle in the event that `T` is defined in a supertrait of
1091 // `SomeTrait`, because in that case we need to upcast.
1093 // That is, consider this case:
1096 // trait SubTrait: SuperTrait<i32> { }
1097 // trait SuperTrait<A> { type T; }
1099 // ... B: SubTrait<T = foo> ...
1102 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
1104 let tcx = self.tcx();
1107 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1108 // Simple case: X is defined in the current trait.
1111 // Otherwise, we have to walk through the supertraits to find
1113 self.one_bound_for_assoc_type(
1114 || traits::supertraits(tcx, trait_ref),
1115 || trait_ref.print_only_trait_path().to_string(),
1118 || match binding.kind {
1119 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1125 let (assoc_ident, def_scope) =
1126 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1128 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1129 // of calling `filter_by_name_and_kind`.
1131 .associated_items(candidate.def_id())
1132 .filter_by_name_unhygienic(assoc_ident.name)
1134 i.kind == ty::AssocKind::Type && i.ident.normalize_to_macros_2_0() == assoc_ident
1136 .expect("missing associated type");
1138 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1142 &format!("associated type `{}` is private", binding.item_name),
1144 .span_label(binding.span, "private associated type")
1147 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span, None);
1151 .entry(assoc_ty.def_id)
1152 .and_modify(|prev_span| {
1153 self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
1155 prev_span: *prev_span,
1156 item_name: binding.item_name,
1157 def_path: tcx.def_path_str(assoc_ty.container.id()),
1160 .or_insert(binding.span);
1163 // Include substitutions for generic parameters of associated types
1164 let projection_ty = candidate.map_bound(|trait_ref| {
1165 let ident = Ident::new(assoc_ty.ident.name, binding.item_name.span);
1166 let item_segment = hir::PathSegment {
1168 hir_id: Some(binding.hir_id),
1170 args: Some(binding.gen_args),
1174 let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
1183 "add_predicates_for_ast_type_binding: substs for trait-ref and assoc_item: {:?}",
1184 substs_trait_ref_and_assoc_item
1188 item_def_id: assoc_ty.def_id,
1189 substs: substs_trait_ref_and_assoc_item,
1194 // Find any late-bound regions declared in `ty` that are not
1195 // declared in the trait-ref or assoc_ty. These are not well-formed.
1199 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1200 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1201 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1202 let late_bound_in_trait_ref =
1203 tcx.collect_constrained_late_bound_regions(&projection_ty);
1204 let late_bound_in_ty =
1205 tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty));
1206 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1207 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1209 // FIXME: point at the type params that don't have appropriate lifetimes:
1210 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1211 // ---- ---- ^^^^^^^
1212 self.validate_late_bound_regions(
1213 late_bound_in_trait_ref,
1220 "binding for associated type `{}` references {}, \
1221 which does not appear in the trait input types",
1230 match binding.kind {
1231 ConvertedBindingKind::Equality(ty) => {
1232 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1233 // the "projection predicate" for:
1235 // `<T as Iterator>::Item = u32`
1236 bounds.projection_bounds.push((
1237 projection_ty.map_bound(|projection_ty| {
1239 "add_predicates_for_ast_type_binding: projection_ty {:?}, substs: {:?}",
1240 projection_ty, projection_ty.substs
1242 ty::ProjectionPredicate { projection_ty, ty }
1247 ConvertedBindingKind::Constraint(ast_bounds) => {
1248 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1250 // `<T as Iterator>::Item: Debug`
1252 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1253 // parameter to have a skipped binder.
1254 let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
1255 self.add_bounds(param_ty, ast_bounds.iter(), bounds, candidate.bound_vars());
1265 item_segment: &hir::PathSegment<'_>,
1267 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1268 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1271 fn conv_object_ty_poly_trait_ref(
1274 trait_bounds: &[hir::PolyTraitRef<'_>],
1275 lifetime: &hir::Lifetime,
1278 let tcx = self.tcx();
1280 let mut bounds = Bounds::default();
1281 let mut potential_assoc_types = Vec::new();
1282 let dummy_self = self.tcx().types.trait_object_dummy_self;
1283 for trait_bound in trait_bounds.iter().rev() {
1284 if let GenericArgCountResult {
1286 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1288 } = self.instantiate_poly_trait_ref(
1289 &trait_bound.trait_ref,
1291 ty::BoundConstness::NotConst,
1296 potential_assoc_types.extend(cur_potential_assoc_types);
1300 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1301 // is used and no 'maybe' bounds are used.
1302 let expanded_traits =
1303 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1304 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1305 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1306 if regular_traits.len() > 1 {
1307 let first_trait = ®ular_traits[0];
1308 let additional_trait = ®ular_traits[1];
1309 let mut err = struct_span_err!(
1311 additional_trait.bottom().1,
1313 "only auto traits can be used as additional traits in a trait object"
1315 additional_trait.label_with_exp_info(
1317 "additional non-auto trait",
1320 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1322 "consider creating a new trait with all of these as supertraits and using that \
1323 trait here instead: `trait NewTrait: {} {{}}`",
1326 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1327 .collect::<Vec<_>>()
1331 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1332 for more information on them, visit \
1333 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1338 if regular_traits.is_empty() && auto_traits.is_empty() {
1339 tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span });
1340 return tcx.ty_error();
1343 // Check that there are no gross object safety violations;
1344 // most importantly, that the supertraits don't contain `Self`,
1346 for item in ®ular_traits {
1347 let object_safety_violations =
1348 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1349 if !object_safety_violations.is_empty() {
1350 report_object_safety_error(
1353 item.trait_ref().def_id(),
1354 &object_safety_violations[..],
1357 return tcx.ty_error();
1361 // Use a `BTreeSet` to keep output in a more consistent order.
1362 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1364 let regular_traits_refs_spans = bounds
1367 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1369 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1370 assert_eq!(constness, ty::BoundConstness::NotConst);
1372 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1374 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1375 obligation.predicate
1378 let bound_predicate = obligation.predicate.kind();
1379 match bound_predicate.skip_binder() {
1380 ty::PredicateKind::Trait(pred) => {
1381 let pred = bound_predicate.rebind(pred);
1382 associated_types.entry(span).or_default().extend(
1383 tcx.associated_items(pred.def_id())
1384 .in_definition_order()
1385 .filter(|item| item.kind == ty::AssocKind::Type)
1386 .map(|item| item.def_id),
1389 ty::PredicateKind::Projection(pred) => {
1390 let pred = bound_predicate.rebind(pred);
1391 // A `Self` within the original bound will be substituted with a
1392 // `trait_object_dummy_self`, so check for that.
1393 let references_self =
1394 pred.skip_binder().ty.walk(tcx).any(|arg| arg == dummy_self.into());
1396 // If the projection output contains `Self`, force the user to
1397 // elaborate it explicitly to avoid a lot of complexity.
1399 // The "classicaly useful" case is the following:
1401 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1406 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1407 // but actually supporting that would "expand" to an infinitely-long type
1408 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1410 // Instead, we force the user to write
1411 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1412 // the discussion in #56288 for alternatives.
1413 if !references_self {
1414 // Include projections defined on supertraits.
1415 bounds.projection_bounds.push((pred, span));
1423 for (projection_bound, _) in &bounds.projection_bounds {
1424 for def_ids in associated_types.values_mut() {
1425 def_ids.remove(&projection_bound.projection_def_id());
1429 self.complain_about_missing_associated_types(
1431 potential_assoc_types,
1435 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1436 // `dyn Trait + Send`.
1437 // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
1439 let mut duplicates = FxHashSet::default();
1440 auto_traits.retain(|i| duplicates.insert(i.trait_ref().def_id()));
1441 debug!("regular_traits: {:?}", regular_traits);
1442 debug!("auto_traits: {:?}", auto_traits);
1444 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1445 let existential_trait_refs = regular_traits.iter().map(|i| {
1446 i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
1447 if trait_ref.self_ty() != dummy_self {
1448 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1449 // which picks up non-supertraits where clauses - but also, the object safety
1450 // completely ignores trait aliases, which could be object safety hazards. We
1451 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1452 // disabled. (#66420)
1453 tcx.sess.delay_span_bug(
1456 "trait_ref_to_existential called on {:?} with non-dummy Self",
1461 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1464 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1465 bound.map_bound(|b| {
1466 if b.projection_ty.self_ty() != dummy_self {
1467 tcx.sess.delay_span_bug(
1469 &format!("trait_ref_to_existential called on {:?} with non-dummy Self", b),
1472 ty::ExistentialProjection::erase_self_ty(tcx, b)
1476 let regular_trait_predicates = existential_trait_refs
1477 .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));
1478 let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
1479 ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
1481 // N.b. principal, projections, auto traits
1482 // FIXME: This is actually wrong with multiple principals in regards to symbol mangling
1483 let mut v = regular_trait_predicates
1485 existential_projections.map(|x| x.map_bound(ty::ExistentialPredicate::Projection)),
1487 .chain(auto_trait_predicates)
1488 .collect::<SmallVec<[_; 8]>>();
1489 v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
1491 let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
1493 // Use explicitly-specified region bound.
1494 let region_bound = if !lifetime.is_elided() {
1495 self.ast_region_to_region(lifetime, None)
1497 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1498 if tcx.named_region(lifetime.hir_id).is_some() {
1499 self.ast_region_to_region(lifetime, None)
1501 self.re_infer(None, span).unwrap_or_else(|| {
1502 let mut err = struct_span_err!(
1506 "the lifetime bound for this object type cannot be deduced \
1507 from context; please supply an explicit bound"
1510 // We will have already emitted an error E0106 complaining about a
1511 // missing named lifetime in `&dyn Trait`, so we elide this one.
1516 tcx.lifetimes.re_static
1521 debug!("region_bound: {:?}", region_bound);
1523 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1524 debug!("trait_object_type: {:?}", ty);
1528 fn report_ambiguous_associated_type(
1535 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1536 if let (true, Ok(snippet)) = (
1539 .confused_type_with_std_module
1541 .any(|full_span| full_span.contains(span)),
1542 self.tcx().sess.source_map().span_to_snippet(span),
1544 err.span_suggestion(
1546 "you are looking for the module in `std`, not the primitive type",
1547 format!("std::{}", snippet),
1548 Applicability::MachineApplicable,
1551 err.span_suggestion(
1553 "use fully-qualified syntax",
1554 format!("<{} as {}>::{}", type_str, trait_str, name),
1555 Applicability::HasPlaceholders,
1561 // Search for a bound on a type parameter which includes the associated item
1562 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1563 // This function will fail if there are no suitable bounds or there is
1565 fn find_bound_for_assoc_item(
1567 ty_param_def_id: LocalDefId,
1570 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1571 let tcx = self.tcx();
1574 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1575 ty_param_def_id, assoc_name, span,
1578 let predicates = &self
1579 .get_type_parameter_bounds(span, ty_param_def_id.to_def_id(), assoc_name)
1582 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1584 let param_hir_id = tcx.hir().local_def_id_to_hir_id(ty_param_def_id);
1585 let param_name = tcx.hir().ty_param_name(param_hir_id);
1586 self.one_bound_for_assoc_type(
1588 traits::transitive_bounds_that_define_assoc_type(
1590 predicates.iter().filter_map(|(p, _)| {
1591 p.to_opt_poly_trait_ref().map(|trait_ref| trait_ref.value)
1596 || param_name.to_string(),
1603 // Checks that `bounds` contains exactly one element and reports appropriate
1604 // errors otherwise.
1605 fn one_bound_for_assoc_type<I>(
1607 all_candidates: impl Fn() -> I,
1608 ty_param_name: impl Fn() -> String,
1611 is_equality: impl Fn() -> Option<String>,
1612 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1614 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1616 let mut matching_candidates = all_candidates()
1617 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1619 let bound = match matching_candidates.next() {
1620 Some(bound) => bound,
1622 self.complain_about_assoc_type_not_found(
1628 return Err(ErrorReported);
1632 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1634 if let Some(bound2) = matching_candidates.next() {
1635 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1637 let is_equality = is_equality();
1638 let bounds = array::IntoIter::new([bound, bound2]).chain(matching_candidates);
1639 let mut err = if is_equality.is_some() {
1640 // More specific Error Index entry.
1645 "ambiguous associated type `{}` in bounds of `{}`",
1654 "ambiguous associated type `{}` in bounds of `{}`",
1659 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1661 let mut where_bounds = vec![];
1662 for bound in bounds {
1663 let bound_id = bound.def_id();
1664 let bound_span = self
1666 .associated_items(bound_id)
1667 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1668 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1670 if let Some(bound_span) = bound_span {
1674 "ambiguous `{}` from `{}`",
1676 bound.print_only_trait_path(),
1679 if let Some(constraint) = &is_equality {
1680 where_bounds.push(format!(
1681 " T: {trait}::{assoc} = {constraint}",
1682 trait=bound.print_only_trait_path(),
1684 constraint=constraint,
1687 err.span_suggestion_verbose(
1688 span.with_hi(assoc_name.span.lo()),
1689 "use fully qualified syntax to disambiguate",
1693 bound.print_only_trait_path(),
1695 Applicability::MaybeIncorrect,
1700 "associated type `{}` could derive from `{}`",
1702 bound.print_only_trait_path(),
1706 if !where_bounds.is_empty() {
1708 "consider introducing a new type parameter `T` and adding `where` constraints:\
1709 \n where\n T: {},\n{}",
1711 where_bounds.join(",\n"),
1715 if !where_bounds.is_empty() {
1716 return Err(ErrorReported);
1722 // Create a type from a path to an associated type.
1723 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1724 // and item_segment is the path segment for `D`. We return a type and a def for
1726 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1727 // parameter or `Self`.
1728 // NOTE: When this function starts resolving `Trait::AssocTy` successfully
1729 // it should also start reportint the `BARE_TRAIT_OBJECTS` lint.
1730 pub fn associated_path_to_ty(
1732 hir_ref_id: hir::HirId,
1736 assoc_segment: &hir::PathSegment<'_>,
1737 permit_variants: bool,
1738 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
1739 let tcx = self.tcx();
1740 let assoc_ident = assoc_segment.ident;
1742 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1744 // Check if we have an enum variant.
1745 let mut variant_resolution = None;
1746 if let ty::Adt(adt_def, _) = qself_ty.kind() {
1747 if adt_def.is_enum() {
1748 let variant_def = adt_def
1751 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
1752 if let Some(variant_def) = variant_def {
1753 if permit_variants {
1754 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span, None);
1755 self.prohibit_generics(slice::from_ref(assoc_segment));
1756 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1758 variant_resolution = Some(variant_def.def_id);
1764 // Find the type of the associated item, and the trait where the associated
1765 // item is declared.
1766 let bound = match (&qself_ty.kind(), qself_res) {
1767 (_, Res::SelfTy(Some(_), Some((impl_def_id, _)))) => {
1768 // `Self` in an impl of a trait -- we have a concrete self type and a
1770 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1771 Some(trait_ref) => trait_ref,
1773 // A cycle error occurred, most likely.
1774 return Err(ErrorReported);
1778 self.one_bound_for_assoc_type(
1779 || traits::supertraits(tcx, ty::Binder::dummy(trait_ref)),
1780 || "Self".to_string(),
1788 Res::SelfTy(Some(param_did), None) | Res::Def(DefKind::TyParam, param_did),
1789 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
1791 if variant_resolution.is_some() {
1792 // Variant in type position
1793 let msg = format!("expected type, found variant `{}`", assoc_ident);
1794 tcx.sess.span_err(span, &msg);
1795 } else if qself_ty.is_enum() {
1796 let mut err = struct_span_err!(
1800 "no variant named `{}` found for enum `{}`",
1805 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1806 if let Some(suggested_name) = find_best_match_for_name(
1810 .map(|variant| variant.ident.name)
1811 .collect::<Vec<Symbol>>(),
1815 err.span_suggestion(
1817 "there is a variant with a similar name",
1818 suggested_name.to_string(),
1819 Applicability::MaybeIncorrect,
1824 format!("variant not found in `{}`", qself_ty),
1828 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
1829 let sp = tcx.sess.source_map().guess_head_span(sp);
1830 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1834 } else if !qself_ty.references_error() {
1835 // Don't print `TyErr` to the user.
1836 self.report_ambiguous_associated_type(
1838 &qself_ty.to_string(),
1843 return Err(ErrorReported);
1847 let trait_did = bound.def_id();
1848 let (assoc_ident, def_scope) =
1849 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1851 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1852 // of calling `filter_by_name_and_kind`.
1854 .associated_items(trait_did)
1855 .in_definition_order()
1857 i.kind.namespace() == Namespace::TypeNS
1858 && i.ident.normalize_to_macros_2_0() == assoc_ident
1860 .expect("missing associated type");
1862 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
1863 let ty = self.normalize_ty(span, ty);
1865 let kind = DefKind::AssocTy;
1866 if !item.vis.is_accessible_from(def_scope, tcx) {
1867 let kind = kind.descr(item.def_id);
1868 let msg = format!("{} `{}` is private", kind, assoc_ident);
1870 .struct_span_err(span, &msg)
1871 .span_label(span, &format!("private {}", kind))
1874 tcx.check_stability(item.def_id, Some(hir_ref_id), span, None);
1876 if let Some(variant_def_id) = variant_resolution {
1877 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
1878 let mut err = lint.build("ambiguous associated item");
1879 let mut could_refer_to = |kind: DefKind, def_id, also| {
1880 let note_msg = format!(
1881 "`{}` could{} refer to the {} defined here",
1886 err.span_note(tcx.def_span(def_id), ¬e_msg);
1889 could_refer_to(DefKind::Variant, variant_def_id, "");
1890 could_refer_to(kind, item.def_id, " also");
1892 err.span_suggestion(
1894 "use fully-qualified syntax",
1895 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
1896 Applicability::MachineApplicable,
1902 Ok((ty, kind, item.def_id))
1908 opt_self_ty: Option<Ty<'tcx>>,
1910 trait_segment: &hir::PathSegment<'_>,
1911 item_segment: &hir::PathSegment<'_>,
1913 let tcx = self.tcx();
1915 let trait_def_id = tcx.parent(item_def_id).unwrap();
1917 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
1919 let self_ty = if let Some(ty) = opt_self_ty {
1922 let path_str = tcx.def_path_str(trait_def_id);
1924 let def_id = self.item_def_id();
1926 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
1928 let parent_def_id = def_id
1929 .and_then(|def_id| {
1930 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
1932 .map(|hir_id| tcx.hir().get_parent_did(hir_id).to_def_id());
1934 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
1936 // If the trait in segment is the same as the trait defining the item,
1937 // use the `<Self as ..>` syntax in the error.
1938 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
1939 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
1941 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
1947 self.report_ambiguous_associated_type(
1951 item_segment.ident.name,
1953 return tcx.ty_error();
1956 debug!("qpath_to_ty: self_type={:?}", self_ty);
1958 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
1960 let item_substs = self.create_substs_for_associated_item(
1968 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1970 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
1973 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
1977 let mut has_err = false;
1978 for segment in segments {
1979 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1980 for arg in segment.args().args {
1981 let (span, kind) = match arg {
1982 hir::GenericArg::Lifetime(lt) => {
1988 (lt.span, "lifetime")
1990 hir::GenericArg::Type(ty) => {
1998 hir::GenericArg::Const(ct) => {
2006 hir::GenericArg::Infer(inf) => {
2012 (inf.span, "generic")
2015 let mut err = struct_span_err!(
2019 "{} arguments are not allowed for this type",
2022 err.span_label(span, format!("{} argument not allowed", kind));
2024 if err_for_lt && err_for_ty && err_for_ct {
2029 // Only emit the first error to avoid overloading the user with error messages.
2030 if let [binding, ..] = segment.args().bindings {
2032 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2038 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2039 pub fn def_ids_for_value_path_segments(
2041 segments: &[hir::PathSegment<'_>],
2042 self_ty: Option<Ty<'tcx>>,
2046 // We need to extract the type parameters supplied by the user in
2047 // the path `path`. Due to the current setup, this is a bit of a
2048 // tricky-process; the problem is that resolve only tells us the
2049 // end-point of the path resolution, and not the intermediate steps.
2050 // Luckily, we can (at least for now) deduce the intermediate steps
2051 // just from the end-point.
2053 // There are basically five cases to consider:
2055 // 1. Reference to a constructor of a struct:
2057 // struct Foo<T>(...)
2059 // In this case, the parameters are declared in the type space.
2061 // 2. Reference to a constructor of an enum variant:
2063 // enum E<T> { Foo(...) }
2065 // In this case, the parameters are defined in the type space,
2066 // but may be specified either on the type or the variant.
2068 // 3. Reference to a fn item or a free constant:
2072 // In this case, the path will again always have the form
2073 // `a::b::foo::<T>` where only the final segment should have
2074 // type parameters. However, in this case, those parameters are
2075 // declared on a value, and hence are in the `FnSpace`.
2077 // 4. Reference to a method or an associated constant:
2079 // impl<A> SomeStruct<A> {
2083 // Here we can have a path like
2084 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2085 // may appear in two places. The penultimate segment,
2086 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2087 // final segment, `foo::<B>` contains parameters in fn space.
2089 // The first step then is to categorize the segments appropriately.
2091 let tcx = self.tcx();
2093 assert!(!segments.is_empty());
2094 let last = segments.len() - 1;
2096 let mut path_segs = vec![];
2099 // Case 1. Reference to a struct constructor.
2100 DefKind::Ctor(CtorOf::Struct, ..) => {
2101 // Everything but the final segment should have no
2102 // parameters at all.
2103 let generics = tcx.generics_of(def_id);
2104 // Variant and struct constructors use the
2105 // generics of their parent type definition.
2106 let generics_def_id = generics.parent.unwrap_or(def_id);
2107 path_segs.push(PathSeg(generics_def_id, last));
2110 // Case 2. Reference to a variant constructor.
2111 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2112 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2113 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2114 debug_assert!(adt_def.is_enum());
2116 } else if last >= 1 && segments[last - 1].args.is_some() {
2117 // Everything but the penultimate segment should have no
2118 // parameters at all.
2119 let mut def_id = def_id;
2121 // `DefKind::Ctor` -> `DefKind::Variant`
2122 if let DefKind::Ctor(..) = kind {
2123 def_id = tcx.parent(def_id).unwrap()
2126 // `DefKind::Variant` -> `DefKind::Enum`
2127 let enum_def_id = tcx.parent(def_id).unwrap();
2128 (enum_def_id, last - 1)
2130 // FIXME: lint here recommending `Enum::<...>::Variant` form
2131 // instead of `Enum::Variant::<...>` form.
2133 // Everything but the final segment should have no
2134 // parameters at all.
2135 let generics = tcx.generics_of(def_id);
2136 // Variant and struct constructors use the
2137 // generics of their parent type definition.
2138 (generics.parent.unwrap_or(def_id), last)
2140 path_segs.push(PathSeg(generics_def_id, index));
2143 // Case 3. Reference to a top-level value.
2144 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2145 path_segs.push(PathSeg(def_id, last));
2148 // Case 4. Reference to a method or associated const.
2149 DefKind::AssocFn | DefKind::AssocConst => {
2150 if segments.len() >= 2 {
2151 let generics = tcx.generics_of(def_id);
2152 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2154 path_segs.push(PathSeg(def_id, last));
2157 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2160 debug!("path_segs = {:?}", path_segs);
2165 // Check a type `Path` and convert it to a `Ty`.
2168 opt_self_ty: Option<Ty<'tcx>>,
2169 path: &hir::Path<'_>,
2170 permit_variants: bool,
2172 let tcx = self.tcx();
2175 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2176 path.res, opt_self_ty, path.segments
2179 let span = path.span;
2181 Res::Def(DefKind::OpaqueTy, did) => {
2182 // Check for desugared `impl Trait`.
2183 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2184 let item_segment = path.segments.split_last().unwrap();
2185 self.prohibit_generics(item_segment.1);
2186 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2187 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2194 | DefKind::ForeignTy,
2197 assert_eq!(opt_self_ty, None);
2198 self.prohibit_generics(path.segments.split_last().unwrap().1);
2199 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2201 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2202 // Convert "variant type" as if it were a real type.
2203 // The resulting `Ty` is type of the variant's enum for now.
2204 assert_eq!(opt_self_ty, None);
2207 self.def_ids_for_value_path_segments(path.segments, None, kind, def_id);
2208 let generic_segs: FxHashSet<_> =
2209 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2210 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2212 if !generic_segs.contains(&index) { Some(seg) } else { None }
2216 let PathSeg(def_id, index) = path_segs.last().unwrap();
2217 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2219 Res::Def(DefKind::TyParam, def_id) => {
2220 assert_eq!(opt_self_ty, None);
2221 self.prohibit_generics(path.segments);
2223 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2224 let item_id = tcx.hir().get_parent_node(hir_id);
2225 let item_def_id = tcx.hir().local_def_id(item_id);
2226 let generics = tcx.generics_of(item_def_id);
2227 let index = generics.param_def_id_to_index[&def_id];
2228 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2230 Res::SelfTy(Some(_), None) => {
2231 // `Self` in trait or type alias.
2232 assert_eq!(opt_self_ty, None);
2233 self.prohibit_generics(path.segments);
2234 tcx.types.self_param
2236 Res::SelfTy(_, Some((def_id, forbid_generic))) => {
2237 // `Self` in impl (we know the concrete type).
2238 assert_eq!(opt_self_ty, None);
2239 self.prohibit_generics(path.segments);
2240 // Try to evaluate any array length constants.
2241 let normalized_ty = self.normalize_ty(span, tcx.at(span).type_of(def_id));
2242 if forbid_generic && normalized_ty.definitely_needs_subst(tcx) {
2243 let mut err = tcx.sess.struct_span_err(
2245 "generic `Self` types are currently not permitted in anonymous constants",
2247 if let Some(hir::Node::Item(&hir::Item {
2248 kind: hir::ItemKind::Impl(ref impl_),
2250 })) = tcx.hir().get_if_local(def_id)
2252 err.span_note(impl_.self_ty.span, "not a concrete type");
2260 Res::Def(DefKind::AssocTy, def_id) => {
2261 debug_assert!(path.segments.len() >= 2);
2262 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2267 &path.segments[path.segments.len() - 2],
2268 path.segments.last().unwrap(),
2271 Res::PrimTy(prim_ty) => {
2272 assert_eq!(opt_self_ty, None);
2273 self.prohibit_generics(path.segments);
2275 hir::PrimTy::Bool => tcx.types.bool,
2276 hir::PrimTy::Char => tcx.types.char,
2277 hir::PrimTy::Int(it) => tcx.mk_mach_int(ty::int_ty(it)),
2278 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(ty::uint_ty(uit)),
2279 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ty::float_ty(ft)),
2280 hir::PrimTy::Str => tcx.types.str_,
2284 self.set_tainted_by_errors();
2285 self.tcx().ty_error()
2287 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2291 /// Parses the programmer's textual representation of a type into our
2292 /// internal notion of a type.
2293 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2294 self.ast_ty_to_ty_inner(ast_ty, false)
2297 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2298 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2299 #[tracing::instrument(level = "debug", skip(self))]
2300 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool) -> Ty<'tcx> {
2301 let tcx = self.tcx();
2303 let result_ty = match ast_ty.kind {
2304 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
2305 hir::TyKind::Ptr(ref mt) => {
2306 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
2308 hir::TyKind::Rptr(ref region, ref mt) => {
2309 let r = self.ast_region_to_region(region, None);
2311 let t = self.ast_ty_to_ty_inner(mt.ty, true);
2312 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2314 hir::TyKind::Never => tcx.types.never,
2315 hir::TyKind::Tup(fields) => tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(t))),
2316 hir::TyKind::BareFn(bf) => {
2317 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
2319 tcx.mk_fn_ptr(self.ty_of_fn(
2324 &hir::Generics::empty(),
2329 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
2330 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed)
2332 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2333 debug!(?maybe_qself, ?path);
2334 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2335 self.res_to_ty(opt_self_ty, path, false)
2337 hir::TyKind::OpaqueDef(item_id, lifetimes) => {
2338 let opaque_ty = tcx.hir().item(item_id);
2339 let def_id = item_id.def_id.to_def_id();
2341 match opaque_ty.kind {
2342 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn, .. }) => {
2343 self.impl_trait_ty_to_ty(def_id, lifetimes, impl_trait_fn.is_some())
2345 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2348 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2349 debug!(?qself, ?segment);
2350 let ty = self.ast_ty_to_ty(qself);
2352 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, path)) = qself.kind {
2357 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2358 .map(|(ty, _, _)| ty)
2359 .unwrap_or_else(|_| tcx.ty_error())
2361 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span)) => {
2362 let def_id = tcx.require_lang_item(lang_item, Some(span));
2363 let (substs, _) = self.create_substs_for_ast_path(
2367 &hir::PathSegment::invalid(),
2368 &GenericArgs::none(),
2372 self.normalize_ty(span, tcx.at(span).type_of(def_id).subst(tcx, substs))
2374 hir::TyKind::Array(ref ty, ref length) => {
2375 let length_def_id = tcx.hir().local_def_id(length.hir_id);
2376 let length = ty::Const::from_anon_const(tcx, length_def_id);
2377 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(ty), length));
2378 self.normalize_ty(ast_ty.span, array_ty)
2380 hir::TyKind::Typeof(ref e) => {
2381 tcx.sess.emit_err(TypeofReservedKeywordUsed { span: ast_ty.span });
2382 tcx.type_of(tcx.hir().local_def_id(e.hir_id))
2384 hir::TyKind::Infer => {
2385 // Infer also appears as the type of arguments or return
2386 // values in an ExprKind::Closure, or as
2387 // the type of local variables. Both of these cases are
2388 // handled specially and will not descend into this routine.
2389 self.ty_infer(None, ast_ty.span)
2391 hir::TyKind::Err => tcx.ty_error(),
2396 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2400 fn impl_trait_ty_to_ty(
2403 lifetimes: &[hir::GenericArg<'_>],
2404 replace_parent_lifetimes: bool,
2406 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2407 let tcx = self.tcx();
2409 let generics = tcx.generics_of(def_id);
2411 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2412 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2413 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2414 // Our own parameters are the resolved lifetimes.
2415 if let GenericParamDefKind::Lifetime = param.kind {
2416 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2417 self.ast_region_to_region(lifetime, None).into()
2426 // For RPIT (return position impl trait), only lifetimes
2427 // mentioned in the impl Trait predicate are captured by
2428 // the opaque type, so the lifetime parameters from the
2429 // parent item need to be replaced with `'static`.
2431 // For `impl Trait` in the types of statics, constants,
2432 // locals and type aliases. These capture all parent
2433 // lifetimes, so they can use their identity subst.
2434 GenericParamDefKind::Lifetime if replace_parent_lifetimes => {
2435 tcx.lifetimes.re_static.into()
2437 _ => tcx.mk_param_from_def(param),
2441 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2443 let ty = tcx.mk_opaque(def_id, substs);
2444 debug!("impl_trait_ty_to_ty: {}", ty);
2448 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2450 hir::TyKind::Infer if expected_ty.is_some() => {
2451 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2452 expected_ty.unwrap()
2454 _ => self.ast_ty_to_ty(ty),
2461 unsafety: hir::Unsafety,
2463 decl: &hir::FnDecl<'_>,
2464 generics: &hir::Generics<'_>,
2465 ident_span: Option<Span>,
2466 hir_ty: Option<&hir::Ty<'_>>,
2467 ) -> ty::PolyFnSig<'tcx> {
2470 let tcx = self.tcx();
2471 let bound_vars = tcx.late_bound_vars(hir_id);
2472 debug!(?bound_vars);
2474 // We proactively collect all the inferred type params to emit a single error per fn def.
2475 let mut visitor = PlaceholderHirTyCollector::default();
2476 for ty in decl.inputs {
2477 visitor.visit_ty(ty);
2479 walk_generics(&mut visitor, generics);
2481 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2482 let output_ty = match decl.output {
2483 hir::FnRetTy::Return(output) => {
2484 visitor.visit_ty(output);
2485 self.ast_ty_to_ty(output)
2487 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2490 debug!("ty_of_fn: output_ty={:?}", output_ty);
2492 let fn_ty = tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi);
2493 let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
2495 if !self.allow_ty_infer() {
2496 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2497 // only want to emit an error complaining about them if infer types (`_`) are not
2498 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2499 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2501 crate::collect::placeholder_type_error(
2503 ident_span.map(|sp| sp.shrink_to_hi()),
2512 // Find any late-bound regions declared in return type that do
2513 // not appear in the arguments. These are not well-formed.
2516 // for<'a> fn() -> &'a str <-- 'a is bad
2517 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2518 let inputs = bare_fn_ty.inputs();
2519 let late_bound_in_args =
2520 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2521 let output = bare_fn_ty.output();
2522 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2524 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
2529 "return type references {}, which is not constrained by the fn input types",
2537 fn validate_late_bound_regions(
2539 constrained_regions: FxHashSet<ty::BoundRegionKind>,
2540 referenced_regions: FxHashSet<ty::BoundRegionKind>,
2541 generate_err: impl Fn(&str) -> rustc_errors::DiagnosticBuilder<'tcx>,
2543 for br in referenced_regions.difference(&constrained_regions) {
2544 let br_name = match *br {
2545 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
2546 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2549 let mut err = generate_err(&br_name);
2551 if let ty::BrAnon(_) = *br {
2552 // The only way for an anonymous lifetime to wind up
2553 // in the return type but **also** be unconstrained is
2554 // if it only appears in "associated types" in the
2555 // input. See #47511 and #62200 for examples. In this case,
2556 // though we can easily give a hint that ought to be
2559 "lifetimes appearing in an associated type are not considered constrained",
2567 /// Given the bounds on an object, determines what single region bound (if any) we can
2568 /// use to summarize this type. The basic idea is that we will use the bound the user
2569 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2570 /// for region bounds. It may be that we can derive no bound at all, in which case
2571 /// we return `None`.
2572 fn compute_object_lifetime_bound(
2575 existential_predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
2576 ) -> Option<ty::Region<'tcx>> // if None, use the default
2578 let tcx = self.tcx();
2580 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2582 // No explicit region bound specified. Therefore, examine trait
2583 // bounds and see if we can derive region bounds from those.
2584 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2586 // If there are no derived region bounds, then report back that we
2587 // can find no region bound. The caller will use the default.
2588 if derived_region_bounds.is_empty() {
2592 // If any of the derived region bounds are 'static, that is always
2594 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2595 return Some(tcx.lifetimes.re_static);
2598 // Determine whether there is exactly one unique region in the set
2599 // of derived region bounds. If so, use that. Otherwise, report an
2601 let r = derived_region_bounds[0];
2602 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2603 tcx.sess.emit_err(AmbiguousLifetimeBound { span });