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::{Constness, GenericArg, GenericArgs};
24 use rustc_middle::ty::subst::{self, 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 fn default_constness_for_trait_bounds(&self) -> Constness;
52 /// Returns predicates in scope of the form `X: Foo`, where `X` is
53 /// a type parameter `X` with the given id `def_id`. This is a
54 /// subset of the full set of predicates.
56 /// This is used for one specific purpose: resolving "short-hand"
57 /// associated type references like `T::Item`. In principle, we
58 /// would do that by first getting the full set of predicates in
59 /// scope and then filtering down to find those that apply to `T`,
60 /// but this can lead to cycle errors. The problem is that we have
61 /// to do this resolution *in order to create the predicates in
62 /// the first place*. Hence, we have this "special pass".
63 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx>;
65 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
66 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
67 -> Option<ty::Region<'tcx>>;
69 /// Returns the type to use when a type is omitted.
70 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
72 /// Returns `true` if `_` is allowed in type signatures in the current context.
73 fn allow_ty_infer(&self) -> bool;
75 /// Returns the const to use when a const is omitted.
79 param: Option<&ty::GenericParamDef>,
81 ) -> &'tcx Const<'tcx>;
83 /// Projecting an associated type from a (potentially)
84 /// higher-ranked trait reference is more complicated, because of
85 /// the possibility of late-bound regions appearing in the
86 /// associated type binding. This is not legal in function
87 /// signatures for that reason. In a function body, we can always
88 /// handle it because we can use inference variables to remove the
89 /// late-bound regions.
90 fn projected_ty_from_poly_trait_ref(
94 item_segment: &hir::PathSegment<'_>,
95 poly_trait_ref: ty::PolyTraitRef<'tcx>,
98 /// Normalize an associated type coming from the user.
99 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
101 /// Invoked when we encounter an error from some prior pass
102 /// (e.g., resolve) that is translated into a ty-error. This is
103 /// used to help suppress derived errors typeck might otherwise
105 fn set_tainted_by_errors(&self);
107 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
110 pub enum SizedByDefault {
115 struct ConvertedBinding<'a, 'tcx> {
117 kind: ConvertedBindingKind<'a, 'tcx>,
121 enum ConvertedBindingKind<'a, 'tcx> {
123 Constraint(&'a [hir::GenericBound<'a>]),
126 /// New-typed boolean indicating whether explicit late-bound lifetimes
127 /// are present in a set of generic arguments.
129 /// For example if we have some method `fn f<'a>(&'a self)` implemented
130 /// for some type `T`, although `f` is generic in the lifetime `'a`, `'a`
131 /// is late-bound so should not be provided explicitly. Thus, if `f` is
132 /// instantiated with some generic arguments providing `'a` explicitly,
133 /// we taint those arguments with `ExplicitLateBound::Yes` so that we
134 /// can provide an appropriate diagnostic later.
135 #[derive(Copy, Clone, PartialEq)]
136 pub enum ExplicitLateBound {
141 /// Denotes the "position" of a generic argument, indicating if it is a generic type,
142 /// generic function or generic method call.
143 #[derive(Copy, Clone, PartialEq)]
144 pub(crate) enum GenericArgPosition {
146 Value, // e.g., functions
150 /// A marker denoting that the generic arguments that were
151 /// provided did not match the respective generic parameters.
152 #[derive(Clone, Default)]
153 pub struct GenericArgCountMismatch {
154 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
155 pub reported: Option<ErrorReported>,
156 /// A list of spans of arguments provided that were not valid.
157 pub invalid_args: Vec<Span>,
160 /// Decorates the result of a generic argument count mismatch
161 /// check with whether explicit late bounds were provided.
163 pub struct GenericArgCountResult {
164 pub explicit_late_bound: ExplicitLateBound,
165 pub correct: Result<(), GenericArgCountMismatch>,
168 pub trait CreateSubstsForGenericArgsCtxt<'a, 'tcx> {
169 fn args_for_def_id(&mut self, def_id: DefId) -> (Option<&'a GenericArgs<'a>>, bool);
173 param: &ty::GenericParamDef,
174 arg: &GenericArg<'_>,
175 ) -> subst::GenericArg<'tcx>;
179 substs: Option<&[subst::GenericArg<'tcx>]>,
180 param: &ty::GenericParamDef,
182 ) -> subst::GenericArg<'tcx>;
185 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
186 pub fn ast_region_to_region(
188 lifetime: &hir::Lifetime,
189 def: Option<&ty::GenericParamDef>,
190 ) -> ty::Region<'tcx> {
191 let tcx = self.tcx();
192 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
194 let r = match tcx.named_region(lifetime.hir_id) {
195 Some(rl::Region::Static) => tcx.lifetimes.re_static,
197 Some(rl::Region::LateBound(debruijn, id, _)) => {
198 let name = lifetime_name(id.expect_local());
199 let br = ty::BoundRegion { kind: ty::BrNamed(id, name) };
200 tcx.mk_region(ty::ReLateBound(debruijn, br))
203 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
204 let br = ty::BoundRegion { kind: ty::BrAnon(index) };
205 tcx.mk_region(ty::ReLateBound(debruijn, br))
208 Some(rl::Region::EarlyBound(index, id, _)) => {
209 let name = lifetime_name(id.expect_local());
210 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
213 Some(rl::Region::Free(scope, id)) => {
214 let name = lifetime_name(id.expect_local());
215 tcx.mk_region(ty::ReFree(ty::FreeRegion {
217 bound_region: ty::BrNamed(id, name),
220 // (*) -- not late-bound, won't change
224 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
225 // This indicates an illegal lifetime
226 // elision. `resolve_lifetime` should have
227 // reported an error in this case -- but if
228 // not, let's error out.
229 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
231 // Supply some dummy value. We don't have an
232 // `re_error`, annoyingly, so use `'static`.
233 tcx.lifetimes.re_static
238 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
243 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
244 /// returns an appropriate set of substitutions for this particular reference to `I`.
245 pub fn ast_path_substs_for_ty(
249 item_segment: &hir::PathSegment<'_>,
250 ) -> SubstsRef<'tcx> {
251 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
255 item_segment.generic_args(),
256 item_segment.infer_args,
260 if let Some(b) = assoc_bindings.first() {
261 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
267 /// Given the type/lifetime/const arguments provided to some path (along with
268 /// an implicit `Self`, if this is a trait reference), returns the complete
269 /// set of substitutions. This may involve applying defaulted type parameters.
270 /// Also returns back constraints on associated types.
275 /// T: std::ops::Index<usize, Output = u32>
276 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
279 /// 1. The `self_ty` here would refer to the type `T`.
280 /// 2. The path in question is the path to the trait `std::ops::Index`,
281 /// which will have been resolved to a `def_id`
282 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
283 /// parameters are returned in the `SubstsRef`, the associated type bindings like
284 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
286 /// Note that the type listing given here is *exactly* what the user provided.
288 /// For (generic) associated types
291 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
294 /// We have the parent substs are the substs for the parent trait:
295 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
296 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
297 /// lists: `[Vec<u8>, u8, 'a]`.
298 fn create_substs_for_ast_path<'a>(
302 parent_substs: &[subst::GenericArg<'tcx>],
303 generic_args: &'a hir::GenericArgs<'_>,
305 self_ty: Option<Ty<'tcx>>,
306 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
307 // If the type is parameterized by this region, then replace this
308 // region with the current anon region binding (in other words,
309 // whatever & would get replaced with).
311 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
313 def_id, self_ty, generic_args
316 let tcx = self.tcx();
317 let generic_params = tcx.generics_of(def_id);
319 if generic_params.has_self {
320 if generic_params.parent.is_some() {
321 // The parent is a trait so it should have at least one subst
322 // for the `Self` type.
323 assert!(!parent_substs.is_empty())
325 // This item (presumably a trait) needs a self-type.
326 assert!(self_ty.is_some());
329 assert!(self_ty.is_none() && parent_substs.is_empty());
332 let arg_count = Self::check_generic_arg_count(
337 GenericArgPosition::Type,
342 // Skip processing if type has no generic parameters.
343 // Traits always have `Self` as a generic parameter, which means they will not return early
344 // here and so associated type bindings will be handled regardless of whether there are any
345 // non-`Self` generic parameters.
346 if generic_params.params.len() == 0 {
347 return (tcx.intern_substs(&[]), vec![], arg_count);
350 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
352 struct SubstsForAstPathCtxt<'a, 'tcx> {
353 astconv: &'a (dyn AstConv<'tcx> + 'a),
355 generic_args: &'a GenericArgs<'a>,
357 missing_type_params: Vec<String>,
358 inferred_params: Vec<Span>,
363 impl<'tcx, 'a> SubstsForAstPathCtxt<'tcx, 'a> {
364 fn default_needs_object_self(&mut self, param: &ty::GenericParamDef) -> bool {
365 let tcx = self.astconv.tcx();
366 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
367 if self.is_object && has_default {
368 let default_ty = tcx.at(self.span).type_of(param.def_id);
369 let self_param = tcx.types.self_param;
370 if default_ty.walk().any(|arg| arg == self_param.into()) {
371 // There is no suitable inference default for a type parameter
372 // that references self, in an object type.
382 impl<'a, 'tcx> CreateSubstsForGenericArgsCtxt<'a, 'tcx> for SubstsForAstPathCtxt<'a, 'tcx> {
383 fn args_for_def_id(&mut self, did: DefId) -> (Option<&'a GenericArgs<'a>>, bool) {
384 if did == self.def_id {
385 (Some(self.generic_args), self.infer_args)
387 // The last component of this tuple is unimportant.
394 param: &ty::GenericParamDef,
395 arg: &GenericArg<'_>,
396 ) -> subst::GenericArg<'tcx> {
397 let tcx = self.astconv.tcx();
398 match (¶m.kind, arg) {
399 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
400 self.astconv.ast_region_to_region(<, Some(param)).into()
402 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
404 tcx.check_optional_stability(
409 // Default generic parameters may not be marked
410 // with stability attributes, i.e. when the
411 // default parameter was defined at the same time
412 // as the rest of the type. As such, we ignore missing
413 // stability attributes.
417 if let (hir::TyKind::Infer, false) =
418 (&ty.kind, self.astconv.allow_ty_infer())
420 self.inferred_params.push(ty.span);
421 tcx.ty_error().into()
423 self.astconv.ast_ty_to_ty(&ty).into()
426 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
427 ty::Const::from_opt_const_arg_anon_const(
429 ty::WithOptConstParam {
430 did: tcx.hir().local_def_id(ct.value.hir_id),
431 const_param_did: Some(param.def_id),
442 substs: Option<&[subst::GenericArg<'tcx>]>,
443 param: &ty::GenericParamDef,
445 ) -> subst::GenericArg<'tcx> {
446 let tcx = self.astconv.tcx();
448 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
449 GenericParamDefKind::Type { has_default, .. } => {
450 if !infer_args && has_default {
451 // No type parameter provided, but a default exists.
453 // If we are converting an object type, then the
454 // `Self` parameter is unknown. However, some of the
455 // other type parameters may reference `Self` in their
456 // defaults. This will lead to an ICE if we are not
458 if self.default_needs_object_self(param) {
459 self.missing_type_params.push(param.name.to_string());
460 tcx.ty_error().into()
462 // This is a default type parameter.
466 tcx.at(self.span).type_of(param.def_id).subst_spanned(
474 } else if infer_args {
475 // No type parameters were provided, we can infer all.
476 let param = if !self.default_needs_object_self(param) {
481 self.astconv.ty_infer(param, self.span).into()
483 // We've already errored above about the mismatch.
484 tcx.ty_error().into()
487 GenericParamDefKind::Const => {
488 let ty = tcx.at(self.span).type_of(param.def_id);
489 // FIXME(const_generics:defaults)
491 // No const parameters were provided, we can infer all.
492 self.astconv.ct_infer(ty, Some(param), self.span).into()
494 // We've already errored above about the mismatch.
495 tcx.const_error(ty).into()
502 let mut substs_ctx = SubstsForAstPathCtxt {
507 missing_type_params: vec![],
508 inferred_params: vec![],
512 let substs = Self::create_substs_for_generic_args(
522 self.complain_about_missing_type_params(
523 substs_ctx.missing_type_params,
526 generic_args.args.is_empty(),
529 // Convert associated-type bindings or constraints into a separate vector.
530 // Example: Given this:
532 // T: Iterator<Item = u32>
534 // The `T` is passed in as a self-type; the `Item = u32` is
535 // not a "type parameter" of the `Iterator` trait, but rather
536 // a restriction on `<T as Iterator>::Item`, so it is passed
538 let assoc_bindings = generic_args
542 let kind = match binding.kind {
543 hir::TypeBindingKind::Equality { ref ty } => {
544 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
546 hir::TypeBindingKind::Constraint { ref bounds } => {
547 ConvertedBindingKind::Constraint(bounds)
550 ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
555 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
556 generic_params, self_ty, substs
559 (substs, assoc_bindings, arg_count)
562 crate fn create_substs_for_associated_item(
567 item_segment: &hir::PathSegment<'_>,
568 parent_substs: SubstsRef<'tcx>,
569 ) -> SubstsRef<'tcx> {
570 if tcx.generics_of(item_def_id).params.is_empty() {
571 self.prohibit_generics(slice::from_ref(item_segment));
575 self.create_substs_for_ast_path(
579 item_segment.generic_args(),
580 item_segment.infer_args,
587 /// Instantiates the path for the given trait reference, assuming that it's
588 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
589 /// The type _cannot_ be a type other than a trait type.
591 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
592 /// are disallowed. Otherwise, they are pushed onto the vector given.
593 pub fn instantiate_mono_trait_ref(
595 trait_ref: &hir::TraitRef<'_>,
597 ) -> ty::TraitRef<'tcx> {
598 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
600 self.ast_path_to_mono_trait_ref(
602 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
604 trait_ref.path.segments.last().unwrap(),
608 /// The given trait-ref must actually be a trait.
609 pub(super) fn instantiate_poly_trait_ref_inner(
611 trait_ref: &hir::TraitRef<'_>,
613 constness: Constness,
615 bounds: &mut Bounds<'tcx>,
617 ) -> GenericArgCountResult {
618 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
620 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
622 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
624 let (substs, assoc_bindings, arg_count) = self.create_substs_for_ast_trait_ref(
628 trait_ref.path.segments.last().unwrap(),
630 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
632 bounds.trait_bounds.push((poly_trait_ref, span, constness));
634 let mut dup_bindings = FxHashMap::default();
635 for binding in &assoc_bindings {
636 // Specify type to assert that error was already reported in `Err` case.
637 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
638 trait_ref.hir_ref_id,
646 // Okay to ignore `Err` because of `ErrorReported` (see above).
650 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
651 trait_ref, bounds, poly_trait_ref
657 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
658 /// a full trait reference. The resulting trait reference is returned. This may also generate
659 /// auxiliary bounds, which are added to `bounds`.
664 /// poly_trait_ref = Iterator<Item = u32>
668 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
670 /// **A note on binders:** against our usual convention, there is an implied bounder around
671 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
672 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
673 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
674 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
676 pub fn instantiate_poly_trait_ref(
678 poly_trait_ref: &hir::PolyTraitRef<'_>,
679 constness: Constness,
681 bounds: &mut Bounds<'tcx>,
682 ) -> GenericArgCountResult {
683 self.instantiate_poly_trait_ref_inner(
684 &poly_trait_ref.trait_ref,
693 pub fn instantiate_lang_item_trait_ref(
695 lang_item: hir::LangItem,
698 args: &GenericArgs<'_>,
700 bounds: &mut Bounds<'tcx>,
702 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
704 let (substs, assoc_bindings, _) =
705 self.create_substs_for_ast_path(span, trait_def_id, &[], args, false, Some(self_ty));
706 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
707 bounds.trait_bounds.push((poly_trait_ref, span, Constness::NotConst));
709 let mut dup_bindings = FxHashMap::default();
710 for binding in assoc_bindings {
711 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
723 fn ast_path_to_mono_trait_ref(
728 trait_segment: &hir::PathSegment<'_>,
729 ) -> ty::TraitRef<'tcx> {
730 let (substs, assoc_bindings, _) =
731 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
732 if let Some(b) = assoc_bindings.first() {
733 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
735 ty::TraitRef::new(trait_def_id, substs)
738 fn create_substs_for_ast_trait_ref<'a>(
743 trait_segment: &'a hir::PathSegment<'a>,
744 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
745 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
747 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
749 self.create_substs_for_ast_path(
753 trait_segment.generic_args(),
754 trait_segment.infer_args,
759 fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
761 .associated_items(trait_def_id)
762 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
766 // Returns `true` if a bounds list includes `?Sized`.
767 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
768 let tcx = self.tcx();
770 // Try to find an unbound in bounds.
771 let mut unbound = None;
772 for ab in ast_bounds {
773 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
774 if unbound.is_none() {
775 unbound = Some(&ptr.trait_ref);
777 tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
782 let kind_id = tcx.lang_items().require(LangItem::Sized);
785 // FIXME(#8559) currently requires the unbound to be built-in.
786 if let Ok(kind_id) = kind_id {
787 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
790 "default bound relaxed for a type parameter, but \
791 this does nothing because the given bound is not \
792 a default; only `?Sized` is supported",
797 _ if kind_id.is_ok() => {
800 // No lang item for `Sized`, so we can't add it as a bound.
807 /// This helper takes a *converted* parameter type (`param_ty`)
808 /// and an *unconverted* list of bounds:
812 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
814 /// `param_ty`, in ty form
817 /// It adds these `ast_bounds` into the `bounds` structure.
819 /// **A note on binders:** there is an implied binder around
820 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
821 /// for more details.
825 ast_bounds: &[hir::GenericBound<'_>],
826 bounds: &mut Bounds<'tcx>,
828 let constness = self.default_constness_for_trait_bounds();
829 for ast_bound in ast_bounds {
831 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
832 self.instantiate_poly_trait_ref(b, constness, param_ty, bounds);
834 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
835 self.instantiate_poly_trait_ref(b, Constness::NotConst, param_ty, bounds);
837 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
838 hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => self
839 .instantiate_lang_item_trait_ref(
840 lang_item, span, hir_id, args, param_ty, bounds,
842 hir::GenericBound::Outlives(ref l) => bounds
844 .push((ty::Binder::bind(self.ast_region_to_region(l, None)), l.span)),
849 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
850 /// The self-type for the bounds is given by `param_ty`.
855 /// fn foo<T: Bar + Baz>() { }
856 /// ^ ^^^^^^^^^ ast_bounds
860 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
861 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
862 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
864 /// `span` should be the declaration size of the parameter.
865 pub fn compute_bounds(
868 ast_bounds: &[hir::GenericBound<'_>],
869 sized_by_default: SizedByDefault,
872 let mut bounds = Bounds::default();
874 self.add_bounds(param_ty, ast_bounds, &mut bounds);
875 bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
877 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
878 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
886 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
889 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
890 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
891 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
892 fn add_predicates_for_ast_type_binding(
894 hir_ref_id: hir::HirId,
895 trait_ref: ty::PolyTraitRef<'tcx>,
896 binding: &ConvertedBinding<'_, 'tcx>,
897 bounds: &mut Bounds<'tcx>,
899 dup_bindings: &mut FxHashMap<DefId, Span>,
901 ) -> Result<(), ErrorReported> {
902 let tcx = self.tcx();
905 // Given something like `U: SomeTrait<T = X>`, we want to produce a
906 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
907 // subtle in the event that `T` is defined in a supertrait of
908 // `SomeTrait`, because in that case we need to upcast.
910 // That is, consider this case:
913 // trait SubTrait: SuperTrait<i32> { }
914 // trait SuperTrait<A> { type T; }
916 // ... B: SubTrait<T = foo> ...
919 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
921 // Find any late-bound regions declared in `ty` that are not
922 // declared in the trait-ref. These are not well-formed.
926 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
927 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
928 if let ConvertedBindingKind::Equality(ty) = binding.kind {
929 let late_bound_in_trait_ref =
930 tcx.collect_constrained_late_bound_regions(&trait_ref);
931 let late_bound_in_ty =
932 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
933 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
934 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
936 // FIXME: point at the type params that don't have appropriate lifetimes:
937 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
939 self.validate_late_bound_regions(
940 late_bound_in_trait_ref,
947 "binding for associated type `{}` references {}, \
948 which does not appear in the trait input types",
958 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
959 // Simple case: X is defined in the current trait.
962 // Otherwise, we have to walk through the supertraits to find
964 self.one_bound_for_assoc_type(
965 || traits::supertraits(tcx, trait_ref),
966 || trait_ref.print_only_trait_path().to_string(),
969 || match binding.kind {
970 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
976 let (assoc_ident, def_scope) =
977 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
979 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
980 // of calling `filter_by_name_and_kind`.
982 .associated_items(candidate.def_id())
983 .filter_by_name_unhygienic(assoc_ident.name)
985 i.kind == ty::AssocKind::Type && i.ident.normalize_to_macros_2_0() == assoc_ident
987 .expect("missing associated type");
989 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
993 &format!("associated type `{}` is private", binding.item_name),
995 .span_label(binding.span, "private associated type")
998 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1002 .entry(assoc_ty.def_id)
1003 .and_modify(|prev_span| {
1004 self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
1006 prev_span: *prev_span,
1007 item_name: binding.item_name,
1008 def_path: tcx.def_path_str(assoc_ty.container.id()),
1011 .or_insert(binding.span);
1014 match binding.kind {
1015 ConvertedBindingKind::Equality(ref ty) => {
1016 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1017 // the "projection predicate" for:
1019 // `<T as Iterator>::Item = u32`
1020 bounds.projection_bounds.push((
1021 candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
1022 projection_ty: ty::ProjectionTy::from_ref_and_name(
1032 ConvertedBindingKind::Constraint(ast_bounds) => {
1033 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1035 // `<T as Iterator>::Item: Debug`
1037 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1038 // parameter to have a skipped binder.
1039 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1040 self.add_bounds(param_ty, ast_bounds, bounds);
1050 item_segment: &hir::PathSegment<'_>,
1052 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1053 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1056 fn conv_object_ty_poly_trait_ref(
1059 trait_bounds: &[hir::PolyTraitRef<'_>],
1060 lifetime: &hir::Lifetime,
1063 let tcx = self.tcx();
1065 let mut bounds = Bounds::default();
1066 let mut potential_assoc_types = Vec::new();
1067 let dummy_self = self.tcx().types.trait_object_dummy_self;
1068 for trait_bound in trait_bounds.iter().rev() {
1069 if let GenericArgCountResult {
1071 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1073 } = self.instantiate_poly_trait_ref(
1075 Constness::NotConst,
1079 potential_assoc_types.extend(cur_potential_assoc_types.into_iter());
1083 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1084 // is used and no 'maybe' bounds are used.
1085 let expanded_traits =
1086 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1087 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1088 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1089 if regular_traits.len() > 1 {
1090 let first_trait = ®ular_traits[0];
1091 let additional_trait = ®ular_traits[1];
1092 let mut err = struct_span_err!(
1094 additional_trait.bottom().1,
1096 "only auto traits can be used as additional traits in a trait object"
1098 additional_trait.label_with_exp_info(
1100 "additional non-auto trait",
1103 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1105 "consider creating a new trait with all of these as super-traits and using that \
1106 trait here instead: `trait NewTrait: {} {{}}`",
1109 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1110 .collect::<Vec<_>>()
1114 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1115 for more information on them, visit \
1116 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1121 if regular_traits.is_empty() && auto_traits.is_empty() {
1122 tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span });
1123 return tcx.ty_error();
1126 // Check that there are no gross object safety violations;
1127 // most importantly, that the supertraits don't contain `Self`,
1129 for item in ®ular_traits {
1130 let object_safety_violations =
1131 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1132 if !object_safety_violations.is_empty() {
1133 report_object_safety_error(
1136 item.trait_ref().def_id(),
1137 &object_safety_violations[..],
1140 return tcx.ty_error();
1144 // Use a `BTreeSet` to keep output in a more consistent order.
1145 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1147 let regular_traits_refs_spans = bounds
1150 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1152 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1153 assert_eq!(constness, Constness::NotConst);
1155 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1157 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1158 obligation.predicate
1161 let bound_predicate = obligation.predicate.bound_atom();
1162 match bound_predicate.skip_binder() {
1163 ty::PredicateAtom::Trait(pred, _) => {
1164 let pred = bound_predicate.rebind(pred);
1165 associated_types.entry(span).or_default().extend(
1166 tcx.associated_items(pred.def_id())
1167 .in_definition_order()
1168 .filter(|item| item.kind == ty::AssocKind::Type)
1169 .map(|item| item.def_id),
1172 ty::PredicateAtom::Projection(pred) => {
1173 let pred = bound_predicate.rebind(pred);
1174 // A `Self` within the original bound will be substituted with a
1175 // `trait_object_dummy_self`, so check for that.
1176 let references_self =
1177 pred.skip_binder().ty.walk().any(|arg| arg == dummy_self.into());
1179 // If the projection output contains `Self`, force the user to
1180 // elaborate it explicitly to avoid a lot of complexity.
1182 // The "classicaly useful" case is the following:
1184 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1189 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1190 // but actually supporting that would "expand" to an infinitely-long type
1191 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1193 // Instead, we force the user to write
1194 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1195 // the discussion in #56288 for alternatives.
1196 if !references_self {
1197 // Include projections defined on supertraits.
1198 bounds.projection_bounds.push((pred, span));
1206 for (projection_bound, _) in &bounds.projection_bounds {
1207 for def_ids in associated_types.values_mut() {
1208 def_ids.remove(&projection_bound.projection_def_id());
1212 self.complain_about_missing_associated_types(
1214 potential_assoc_types,
1218 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1219 // `dyn Trait + Send`.
1220 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1221 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1222 debug!("regular_traits: {:?}", regular_traits);
1223 debug!("auto_traits: {:?}", auto_traits);
1225 // Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1226 // removing the dummy `Self` type (`trait_object_dummy_self`).
1227 let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
1228 if trait_ref.self_ty() != dummy_self {
1229 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1230 // which picks up non-supertraits where clauses - but also, the object safety
1231 // completely ignores trait aliases, which could be object safety hazards. We
1232 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1233 // disabled. (#66420)
1234 tcx.sess.delay_span_bug(
1237 "trait_ref_to_existential called on {:?} with non-dummy Self",
1242 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1245 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1246 let existential_trait_refs =
1247 regular_traits.iter().map(|i| i.trait_ref().map_bound(trait_ref_to_existential));
1248 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1249 bound.map_bound(|b| {
1250 let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1251 ty::ExistentialProjection {
1253 item_def_id: b.projection_ty.item_def_id,
1254 substs: trait_ref.substs,
1259 let regular_trait_predicates = existential_trait_refs.map(|trait_ref| {
1260 trait_ref.map_bound(|trait_ref| ty::ExistentialPredicate::Trait(trait_ref))
1262 let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
1263 ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
1265 let mut v = regular_trait_predicates
1266 .chain(auto_trait_predicates)
1268 existential_projections
1269 .map(|x| x.map_bound(|x| ty::ExistentialPredicate::Projection(x))),
1271 .collect::<SmallVec<[_; 8]>>();
1272 v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
1274 let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
1276 // Use explicitly-specified region bound.
1277 let region_bound = if !lifetime.is_elided() {
1278 self.ast_region_to_region(lifetime, None)
1280 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1281 if tcx.named_region(lifetime.hir_id).is_some() {
1282 self.ast_region_to_region(lifetime, None)
1284 self.re_infer(None, span).unwrap_or_else(|| {
1285 let mut err = struct_span_err!(
1289 "the lifetime bound for this object type cannot be deduced \
1290 from context; please supply an explicit bound"
1293 // We will have already emitted an error E0106 complaining about a
1294 // missing named lifetime in `&dyn Trait`, so we elide this one.
1299 tcx.lifetimes.re_static
1304 debug!("region_bound: {:?}", region_bound);
1306 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1307 debug!("trait_object_type: {:?}", ty);
1311 fn report_ambiguous_associated_type(
1318 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1319 if let (Some(_), Ok(snippet)) = (
1320 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1321 self.tcx().sess.source_map().span_to_snippet(span),
1323 err.span_suggestion(
1325 "you are looking for the module in `std`, not the primitive type",
1326 format!("std::{}", snippet),
1327 Applicability::MachineApplicable,
1330 err.span_suggestion(
1332 "use fully-qualified syntax",
1333 format!("<{} as {}>::{}", type_str, trait_str, name),
1334 Applicability::HasPlaceholders,
1340 // Search for a bound on a type parameter which includes the associated item
1341 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1342 // This function will fail if there are no suitable bounds or there is
1344 fn find_bound_for_assoc_item(
1346 ty_param_def_id: LocalDefId,
1349 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1350 let tcx = self.tcx();
1353 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1354 ty_param_def_id, assoc_name, span,
1358 &self.get_type_parameter_bounds(span, ty_param_def_id.to_def_id()).predicates;
1360 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1362 let param_hir_id = tcx.hir().local_def_id_to_hir_id(ty_param_def_id);
1363 let param_name = tcx.hir().ty_param_name(param_hir_id);
1364 self.one_bound_for_assoc_type(
1366 traits::transitive_bounds(
1368 predicates.iter().filter_map(|(p, _)| {
1369 p.to_opt_poly_trait_ref().map(|trait_ref| trait_ref.value)
1373 || param_name.to_string(),
1380 // Checks that `bounds` contains exactly one element and reports appropriate
1381 // errors otherwise.
1382 fn one_bound_for_assoc_type<I>(
1384 all_candidates: impl Fn() -> I,
1385 ty_param_name: impl Fn() -> String,
1388 is_equality: impl Fn() -> Option<String>,
1389 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1391 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1393 let mut matching_candidates = all_candidates()
1394 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1396 let bound = match matching_candidates.next() {
1397 Some(bound) => bound,
1399 self.complain_about_assoc_type_not_found(
1405 return Err(ErrorReported);
1409 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1411 if let Some(bound2) = matching_candidates.next() {
1412 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1414 let is_equality = is_equality();
1415 let bounds = array::IntoIter::new([bound, bound2]).chain(matching_candidates);
1416 let mut err = if is_equality.is_some() {
1417 // More specific Error Index entry.
1422 "ambiguous associated type `{}` in bounds of `{}`",
1431 "ambiguous associated type `{}` in bounds of `{}`",
1436 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1438 let mut where_bounds = vec![];
1439 for bound in bounds {
1440 let bound_id = bound.def_id();
1441 let bound_span = self
1443 .associated_items(bound_id)
1444 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1445 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1447 if let Some(bound_span) = bound_span {
1451 "ambiguous `{}` from `{}`",
1453 bound.print_only_trait_path(),
1456 if let Some(constraint) = &is_equality {
1457 where_bounds.push(format!(
1458 " T: {trait}::{assoc} = {constraint}",
1459 trait=bound.print_only_trait_path(),
1461 constraint=constraint,
1464 err.span_suggestion(
1466 "use fully qualified syntax to disambiguate",
1470 bound.print_only_trait_path(),
1473 Applicability::MaybeIncorrect,
1478 "associated type `{}` could derive from `{}`",
1480 bound.print_only_trait_path(),
1484 if !where_bounds.is_empty() {
1486 "consider introducing a new type parameter `T` and adding `where` constraints:\
1487 \n where\n T: {},\n{}",
1489 where_bounds.join(",\n"),
1493 if !where_bounds.is_empty() {
1494 return Err(ErrorReported);
1500 // Create a type from a path to an associated type.
1501 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1502 // and item_segment is the path segment for `D`. We return a type and a def for
1504 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1505 // parameter or `Self`.
1506 pub fn associated_path_to_ty(
1508 hir_ref_id: hir::HirId,
1512 assoc_segment: &hir::PathSegment<'_>,
1513 permit_variants: bool,
1514 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
1515 let tcx = self.tcx();
1516 let assoc_ident = assoc_segment.ident;
1518 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1520 // Check if we have an enum variant.
1521 let mut variant_resolution = None;
1522 if let ty::Adt(adt_def, _) = qself_ty.kind() {
1523 if adt_def.is_enum() {
1524 let variant_def = adt_def
1527 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
1528 if let Some(variant_def) = variant_def {
1529 if permit_variants {
1530 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
1531 self.prohibit_generics(slice::from_ref(assoc_segment));
1532 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1534 variant_resolution = Some(variant_def.def_id);
1540 // Find the type of the associated item, and the trait where the associated
1541 // item is declared.
1542 let bound = match (&qself_ty.kind(), qself_res) {
1543 (_, Res::SelfTy(Some(_), Some((impl_def_id, _)))) => {
1544 // `Self` in an impl of a trait -- we have a concrete self type and a
1546 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1547 Some(trait_ref) => trait_ref,
1549 // A cycle error occurred, most likely.
1550 return Err(ErrorReported);
1554 self.one_bound_for_assoc_type(
1555 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
1556 || "Self".to_string(),
1564 Res::SelfTy(Some(param_did), None) | Res::Def(DefKind::TyParam, param_did),
1565 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
1567 if variant_resolution.is_some() {
1568 // Variant in type position
1569 let msg = format!("expected type, found variant `{}`", assoc_ident);
1570 tcx.sess.span_err(span, &msg);
1571 } else if qself_ty.is_enum() {
1572 let mut err = struct_span_err!(
1576 "no variant named `{}` found for enum `{}`",
1581 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1582 if let Some(suggested_name) = find_best_match_for_name(
1586 .map(|variant| variant.ident.name)
1587 .collect::<Vec<Symbol>>(),
1591 err.span_suggestion(
1593 "there is a variant with a similar name",
1594 suggested_name.to_string(),
1595 Applicability::MaybeIncorrect,
1600 format!("variant not found in `{}`", qself_ty),
1604 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
1605 let sp = tcx.sess.source_map().guess_head_span(sp);
1606 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1610 } else if !qself_ty.references_error() {
1611 // Don't print `TyErr` to the user.
1612 self.report_ambiguous_associated_type(
1614 &qself_ty.to_string(),
1619 return Err(ErrorReported);
1623 let trait_did = bound.def_id();
1624 let (assoc_ident, def_scope) =
1625 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1627 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1628 // of calling `filter_by_name_and_kind`.
1630 .associated_items(trait_did)
1631 .in_definition_order()
1633 i.kind.namespace() == Namespace::TypeNS
1634 && i.ident.normalize_to_macros_2_0() == assoc_ident
1636 .expect("missing associated type");
1638 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
1639 let ty = self.normalize_ty(span, ty);
1641 let kind = DefKind::AssocTy;
1642 if !item.vis.is_accessible_from(def_scope, tcx) {
1643 let kind = kind.descr(item.def_id);
1644 let msg = format!("{} `{}` is private", kind, assoc_ident);
1646 .struct_span_err(span, &msg)
1647 .span_label(span, &format!("private {}", kind))
1650 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
1652 if let Some(variant_def_id) = variant_resolution {
1653 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
1654 let mut err = lint.build("ambiguous associated item");
1655 let mut could_refer_to = |kind: DefKind, def_id, also| {
1656 let note_msg = format!(
1657 "`{}` could{} refer to the {} defined here",
1662 err.span_note(tcx.def_span(def_id), ¬e_msg);
1665 could_refer_to(DefKind::Variant, variant_def_id, "");
1666 could_refer_to(kind, item.def_id, " also");
1668 err.span_suggestion(
1670 "use fully-qualified syntax",
1671 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
1672 Applicability::MachineApplicable,
1678 Ok((ty, kind, item.def_id))
1684 opt_self_ty: Option<Ty<'tcx>>,
1686 trait_segment: &hir::PathSegment<'_>,
1687 item_segment: &hir::PathSegment<'_>,
1689 let tcx = self.tcx();
1691 let trait_def_id = tcx.parent(item_def_id).unwrap();
1693 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
1695 let self_ty = if let Some(ty) = opt_self_ty {
1698 let path_str = tcx.def_path_str(trait_def_id);
1700 let def_id = self.item_def_id();
1702 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
1704 let parent_def_id = def_id
1705 .and_then(|def_id| {
1706 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
1708 .map(|hir_id| tcx.hir().get_parent_did(hir_id).to_def_id());
1710 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
1712 // If the trait in segment is the same as the trait defining the item,
1713 // use the `<Self as ..>` syntax in the error.
1714 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
1715 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
1717 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
1723 self.report_ambiguous_associated_type(
1727 item_segment.ident.name,
1729 return tcx.ty_error();
1732 debug!("qpath_to_ty: self_type={:?}", self_ty);
1734 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
1736 let item_substs = self.create_substs_for_associated_item(
1744 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1746 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
1749 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
1753 let mut has_err = false;
1754 for segment in segments {
1755 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1756 for arg in segment.generic_args().args {
1757 let (span, kind) = match arg {
1758 hir::GenericArg::Lifetime(lt) => {
1764 (lt.span, "lifetime")
1766 hir::GenericArg::Type(ty) => {
1774 hir::GenericArg::Const(ct) => {
1783 let mut err = struct_span_err!(
1787 "{} arguments are not allowed for this type",
1790 err.span_label(span, format!("{} argument not allowed", kind));
1792 if err_for_lt && err_for_ty && err_for_ct {
1797 // Only emit the first error to avoid overloading the user with error messages.
1798 if let [binding, ..] = segment.generic_args().bindings {
1800 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
1806 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
1807 pub fn def_ids_for_value_path_segments(
1809 segments: &[hir::PathSegment<'_>],
1810 self_ty: Option<Ty<'tcx>>,
1814 // We need to extract the type parameters supplied by the user in
1815 // the path `path`. Due to the current setup, this is a bit of a
1816 // tricky-process; the problem is that resolve only tells us the
1817 // end-point of the path resolution, and not the intermediate steps.
1818 // Luckily, we can (at least for now) deduce the intermediate steps
1819 // just from the end-point.
1821 // There are basically five cases to consider:
1823 // 1. Reference to a constructor of a struct:
1825 // struct Foo<T>(...)
1827 // In this case, the parameters are declared in the type space.
1829 // 2. Reference to a constructor of an enum variant:
1831 // enum E<T> { Foo(...) }
1833 // In this case, the parameters are defined in the type space,
1834 // but may be specified either on the type or the variant.
1836 // 3. Reference to a fn item or a free constant:
1840 // In this case, the path will again always have the form
1841 // `a::b::foo::<T>` where only the final segment should have
1842 // type parameters. However, in this case, those parameters are
1843 // declared on a value, and hence are in the `FnSpace`.
1845 // 4. Reference to a method or an associated constant:
1847 // impl<A> SomeStruct<A> {
1851 // Here we can have a path like
1852 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
1853 // may appear in two places. The penultimate segment,
1854 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
1855 // final segment, `foo::<B>` contains parameters in fn space.
1857 // The first step then is to categorize the segments appropriately.
1859 let tcx = self.tcx();
1861 assert!(!segments.is_empty());
1862 let last = segments.len() - 1;
1864 let mut path_segs = vec![];
1867 // Case 1. Reference to a struct constructor.
1868 DefKind::Ctor(CtorOf::Struct, ..) => {
1869 // Everything but the final segment should have no
1870 // parameters at all.
1871 let generics = tcx.generics_of(def_id);
1872 // Variant and struct constructors use the
1873 // generics of their parent type definition.
1874 let generics_def_id = generics.parent.unwrap_or(def_id);
1875 path_segs.push(PathSeg(generics_def_id, last));
1878 // Case 2. Reference to a variant constructor.
1879 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
1880 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
1881 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
1882 debug_assert!(adt_def.is_enum());
1884 } else if last >= 1 && segments[last - 1].args.is_some() {
1885 // Everything but the penultimate segment should have no
1886 // parameters at all.
1887 let mut def_id = def_id;
1889 // `DefKind::Ctor` -> `DefKind::Variant`
1890 if let DefKind::Ctor(..) = kind {
1891 def_id = tcx.parent(def_id).unwrap()
1894 // `DefKind::Variant` -> `DefKind::Enum`
1895 let enum_def_id = tcx.parent(def_id).unwrap();
1896 (enum_def_id, last - 1)
1898 // FIXME: lint here recommending `Enum::<...>::Variant` form
1899 // instead of `Enum::Variant::<...>` form.
1901 // Everything but the final segment should have no
1902 // parameters at all.
1903 let generics = tcx.generics_of(def_id);
1904 // Variant and struct constructors use the
1905 // generics of their parent type definition.
1906 (generics.parent.unwrap_or(def_id), last)
1908 path_segs.push(PathSeg(generics_def_id, index));
1911 // Case 3. Reference to a top-level value.
1912 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
1913 path_segs.push(PathSeg(def_id, last));
1916 // Case 4. Reference to a method or associated const.
1917 DefKind::AssocFn | DefKind::AssocConst => {
1918 if segments.len() >= 2 {
1919 let generics = tcx.generics_of(def_id);
1920 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
1922 path_segs.push(PathSeg(def_id, last));
1925 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
1928 debug!("path_segs = {:?}", path_segs);
1933 // Check a type `Path` and convert it to a `Ty`.
1936 opt_self_ty: Option<Ty<'tcx>>,
1937 path: &hir::Path<'_>,
1938 permit_variants: bool,
1940 let tcx = self.tcx();
1943 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
1944 path.res, opt_self_ty, path.segments
1947 let span = path.span;
1949 Res::Def(DefKind::OpaqueTy, did) => {
1950 // Check for desugared `impl Trait`.
1951 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
1952 let item_segment = path.segments.split_last().unwrap();
1953 self.prohibit_generics(item_segment.1);
1954 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
1955 self.normalize_ty(span, tcx.mk_opaque(did, substs))
1962 | DefKind::ForeignTy,
1965 assert_eq!(opt_self_ty, None);
1966 self.prohibit_generics(path.segments.split_last().unwrap().1);
1967 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
1969 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
1970 // Convert "variant type" as if it were a real type.
1971 // The resulting `Ty` is type of the variant's enum for now.
1972 assert_eq!(opt_self_ty, None);
1975 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
1976 let generic_segs: FxHashSet<_> =
1977 path_segs.iter().map(|PathSeg(_, index)| index).collect();
1978 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
1980 if !generic_segs.contains(&index) { Some(seg) } else { None }
1984 let PathSeg(def_id, index) = path_segs.last().unwrap();
1985 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
1987 Res::Def(DefKind::TyParam, def_id) => {
1988 assert_eq!(opt_self_ty, None);
1989 self.prohibit_generics(path.segments);
1991 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
1992 let item_id = tcx.hir().get_parent_node(hir_id);
1993 let item_def_id = tcx.hir().local_def_id(item_id);
1994 let generics = tcx.generics_of(item_def_id);
1995 let index = generics.param_def_id_to_index[&def_id];
1996 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
1998 Res::SelfTy(Some(_), None) => {
1999 // `Self` in trait or type alias.
2000 assert_eq!(opt_self_ty, None);
2001 self.prohibit_generics(path.segments);
2002 tcx.types.self_param
2004 Res::SelfTy(_, Some((def_id, forbid_generic))) => {
2005 // `Self` in impl (we know the concrete type).
2006 assert_eq!(opt_self_ty, None);
2007 self.prohibit_generics(path.segments);
2008 // Try to evaluate any array length constants.
2009 let normalized_ty = self.normalize_ty(span, tcx.at(span).type_of(def_id));
2010 if forbid_generic && normalized_ty.needs_subst() {
2011 let mut err = tcx.sess.struct_span_err(
2013 "generic `Self` types are currently not permitted in anonymous constants",
2015 if let Some(hir::Node::Item(&hir::Item {
2016 kind: hir::ItemKind::Impl { self_ty, .. },
2018 })) = tcx.hir().get_if_local(def_id)
2020 err.span_note(self_ty.span, "not a concrete type");
2028 Res::Def(DefKind::AssocTy, def_id) => {
2029 debug_assert!(path.segments.len() >= 2);
2030 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2035 &path.segments[path.segments.len() - 2],
2036 path.segments.last().unwrap(),
2039 Res::PrimTy(prim_ty) => {
2040 assert_eq!(opt_self_ty, None);
2041 self.prohibit_generics(path.segments);
2043 hir::PrimTy::Bool => tcx.types.bool,
2044 hir::PrimTy::Char => tcx.types.char,
2045 hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
2046 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
2047 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
2048 hir::PrimTy::Str => tcx.types.str_,
2052 self.set_tainted_by_errors();
2053 self.tcx().ty_error()
2055 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2059 /// Parses the programmer's textual representation of a type into our
2060 /// internal notion of a type.
2061 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2062 self.ast_ty_to_ty_inner(ast_ty, false)
2065 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2066 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2067 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool) -> Ty<'tcx> {
2068 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2070 let tcx = self.tcx();
2072 let result_ty = match ast_ty.kind {
2073 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2074 hir::TyKind::Ptr(ref mt) => {
2075 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2077 hir::TyKind::Rptr(ref region, ref mt) => {
2078 let r = self.ast_region_to_region(region, None);
2079 debug!("ast_ty_to_ty: r={:?}", r);
2080 let t = self.ast_ty_to_ty_inner(&mt.ty, true);
2081 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2083 hir::TyKind::Never => tcx.types.never,
2084 hir::TyKind::Tup(ref fields) => {
2085 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2087 hir::TyKind::BareFn(ref bf) => {
2088 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2089 tcx.mk_fn_ptr(self.ty_of_fn(
2093 &hir::Generics::empty(),
2097 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2098 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed)
2100 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2101 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2102 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2103 self.res_to_ty(opt_self_ty, path, false)
2105 hir::TyKind::OpaqueDef(item_id, ref lifetimes) => {
2106 let opaque_ty = tcx.hir().expect_item(item_id.id);
2107 let def_id = tcx.hir().local_def_id(item_id.id).to_def_id();
2109 match opaque_ty.kind {
2110 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn, .. }) => {
2111 self.impl_trait_ty_to_ty(def_id, lifetimes, impl_trait_fn.is_some())
2113 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2116 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2117 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2118 let ty = self.ast_ty_to_ty(qself);
2120 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2125 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2126 .map(|(ty, _, _)| ty)
2127 .unwrap_or_else(|_| tcx.ty_error())
2129 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span)) => {
2130 let def_id = tcx.require_lang_item(lang_item, Some(span));
2131 let (substs, _, _) = self.create_substs_for_ast_path(
2135 &GenericArgs::none(),
2139 self.normalize_ty(span, tcx.at(span).type_of(def_id).subst(tcx, substs))
2141 hir::TyKind::Array(ref ty, ref length) => {
2142 let length_def_id = tcx.hir().local_def_id(length.hir_id);
2143 let length = ty::Const::from_anon_const(tcx, length_def_id);
2144 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2145 self.normalize_ty(ast_ty.span, array_ty)
2147 hir::TyKind::Typeof(ref _e) => {
2148 tcx.sess.emit_err(TypeofReservedKeywordUsed { span: ast_ty.span });
2151 hir::TyKind::Infer => {
2152 // Infer also appears as the type of arguments or return
2153 // values in a ExprKind::Closure, or as
2154 // the type of local variables. Both of these cases are
2155 // handled specially and will not descend into this routine.
2156 self.ty_infer(None, ast_ty.span)
2158 hir::TyKind::Err => tcx.ty_error(),
2161 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2163 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2167 pub fn impl_trait_ty_to_ty(
2170 lifetimes: &[hir::GenericArg<'_>],
2171 replace_parent_lifetimes: bool,
2173 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2174 let tcx = self.tcx();
2176 let generics = tcx.generics_of(def_id);
2178 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2179 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2180 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2181 // Our own parameters are the resolved lifetimes.
2183 GenericParamDefKind::Lifetime => {
2184 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2185 self.ast_region_to_region(lifetime, None).into()
2194 // For RPIT (return position impl trait), only lifetimes
2195 // mentioned in the impl Trait predicate are captured by
2196 // the opaque type, so the lifetime parameters from the
2197 // parent item need to be replaced with `'static`.
2199 // For `impl Trait` in the types of statics, constants,
2200 // locals and type aliases. These capture all parent
2201 // lifetimes, so they can use their identity subst.
2202 GenericParamDefKind::Lifetime if replace_parent_lifetimes => {
2203 tcx.lifetimes.re_static.into()
2205 _ => tcx.mk_param_from_def(param),
2209 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2211 let ty = tcx.mk_opaque(def_id, substs);
2212 debug!("impl_trait_ty_to_ty: {}", ty);
2216 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2218 hir::TyKind::Infer if expected_ty.is_some() => {
2219 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2220 expected_ty.unwrap()
2222 _ => self.ast_ty_to_ty(ty),
2228 unsafety: hir::Unsafety,
2230 decl: &hir::FnDecl<'_>,
2231 generics: &hir::Generics<'_>,
2232 ident_span: Option<Span>,
2233 ) -> ty::PolyFnSig<'tcx> {
2236 let tcx = self.tcx();
2238 // We proactively collect all the inferred type params to emit a single error per fn def.
2239 let mut visitor = PlaceholderHirTyCollector::default();
2240 for ty in decl.inputs {
2241 visitor.visit_ty(ty);
2243 walk_generics(&mut visitor, generics);
2245 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2246 let output_ty = match decl.output {
2247 hir::FnRetTy::Return(ref output) => {
2248 visitor.visit_ty(output);
2249 self.ast_ty_to_ty(output)
2251 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2254 debug!("ty_of_fn: output_ty={:?}", output_ty);
2257 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
2259 if !self.allow_ty_infer() {
2260 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2261 // only want to emit an error complaining about them if infer types (`_`) are not
2262 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2263 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2264 crate::collect::placeholder_type_error(
2266 ident_span.map(|sp| sp.shrink_to_hi()),
2267 &generics.params[..],
2273 // Find any late-bound regions declared in return type that do
2274 // not appear in the arguments. These are not well-formed.
2277 // for<'a> fn() -> &'a str <-- 'a is bad
2278 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2279 let inputs = bare_fn_ty.inputs();
2280 let late_bound_in_args =
2281 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2282 let output = bare_fn_ty.output();
2283 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2285 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
2290 "return type references {}, which is not constrained by the fn input types",
2298 fn validate_late_bound_regions(
2300 constrained_regions: FxHashSet<ty::BoundRegionKind>,
2301 referenced_regions: FxHashSet<ty::BoundRegionKind>,
2302 generate_err: impl Fn(&str) -> rustc_errors::DiagnosticBuilder<'tcx>,
2304 for br in referenced_regions.difference(&constrained_regions) {
2305 let br_name = match *br {
2306 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
2307 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2310 let mut err = generate_err(&br_name);
2312 if let ty::BrAnon(_) = *br {
2313 // The only way for an anonymous lifetime to wind up
2314 // in the return type but **also** be unconstrained is
2315 // if it only appears in "associated types" in the
2316 // input. See #47511 and #62200 for examples. In this case,
2317 // though we can easily give a hint that ought to be
2320 "lifetimes appearing in an associated type are not considered constrained",
2328 /// Given the bounds on an object, determines what single region bound (if any) we can
2329 /// use to summarize this type. The basic idea is that we will use the bound the user
2330 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2331 /// for region bounds. It may be that we can derive no bound at all, in which case
2332 /// we return `None`.
2333 fn compute_object_lifetime_bound(
2336 existential_predicates: &'tcx ty::List<ty::Binder<ty::ExistentialPredicate<'tcx>>>,
2337 ) -> Option<ty::Region<'tcx>> // if None, use the default
2339 let tcx = self.tcx();
2341 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2343 // No explicit region bound specified. Therefore, examine trait
2344 // bounds and see if we can derive region bounds from those.
2345 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2347 // If there are no derived region bounds, then report back that we
2348 // can find no region bound. The caller will use the default.
2349 if derived_region_bounds.is_empty() {
2353 // If any of the derived region bounds are 'static, that is always
2355 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2356 return Some(tcx.lifetimes.re_static);
2359 // Determine whether there is exactly one unique region in the set
2360 // of derived region bounds. If so, use that. Otherwise, report an
2362 let r = derived_region_bounds[0];
2363 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2364 tcx.sess.emit_err(AmbiguousLifetimeBound { span });