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<T>`, where `X`
53 /// is a type parameter `X` with the given id `def_id` and T
54 /// matches `assoc_name`. This is a subset of the full set of
57 /// This is used for one specific purpose: resolving "short-hand"
58 /// associated type references like `T::Item`. In principle, we
59 /// would do that by first getting the full set of predicates in
60 /// scope and then filtering down to find those that apply to `T`,
61 /// but this can lead to cycle errors. The problem is that we have
62 /// to do this resolution *in order to create the predicates in
63 /// the first place*. Hence, we have this "special pass".
64 fn get_type_parameter_bounds(
69 ) -> ty::GenericPredicates<'tcx>;
71 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
72 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
73 -> Option<ty::Region<'tcx>>;
75 /// Returns the type to use when a type is omitted.
76 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
78 /// Returns `true` if `_` is allowed in type signatures in the current context.
79 fn allow_ty_infer(&self) -> bool;
81 /// Returns the const to use when a const is omitted.
85 param: Option<&ty::GenericParamDef>,
87 ) -> &'tcx Const<'tcx>;
89 /// Projecting an associated type from a (potentially)
90 /// higher-ranked trait reference is more complicated, because of
91 /// the possibility of late-bound regions appearing in the
92 /// associated type binding. This is not legal in function
93 /// signatures for that reason. In a function body, we can always
94 /// handle it because we can use inference variables to remove the
95 /// late-bound regions.
96 fn projected_ty_from_poly_trait_ref(
100 item_segment: &hir::PathSegment<'_>,
101 poly_trait_ref: ty::PolyTraitRef<'tcx>,
104 /// Normalize an associated type coming from the user.
105 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
107 /// Invoked when we encounter an error from some prior pass
108 /// (e.g., resolve) that is translated into a ty-error. This is
109 /// used to help suppress derived errors typeck might otherwise
111 fn set_tainted_by_errors(&self);
113 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
116 pub enum SizedByDefault {
122 struct ConvertedBinding<'a, 'tcx> {
124 kind: ConvertedBindingKind<'a, 'tcx>,
125 gen_args: &'a GenericArgs<'a>,
130 enum ConvertedBindingKind<'a, 'tcx> {
132 Constraint(&'a [hir::GenericBound<'a>]),
135 /// New-typed boolean indicating whether explicit late-bound lifetimes
136 /// are present in a set of generic arguments.
138 /// For example if we have some method `fn f<'a>(&'a self)` implemented
139 /// for some type `T`, although `f` is generic in the lifetime `'a`, `'a`
140 /// is late-bound so should not be provided explicitly. Thus, if `f` is
141 /// instantiated with some generic arguments providing `'a` explicitly,
142 /// we taint those arguments with `ExplicitLateBound::Yes` so that we
143 /// can provide an appropriate diagnostic later.
144 #[derive(Copy, Clone, PartialEq)]
145 pub enum ExplicitLateBound {
150 #[derive(Copy, Clone, PartialEq)]
151 pub enum IsMethodCall {
156 /// Denotes the "position" of a generic argument, indicating if it is a generic type,
157 /// generic function or generic method call.
158 #[derive(Copy, Clone, PartialEq)]
159 pub(crate) enum GenericArgPosition {
161 Value, // e.g., functions
165 /// A marker denoting that the generic arguments that were
166 /// provided did not match the respective generic parameters.
167 #[derive(Clone, Default)]
168 pub struct GenericArgCountMismatch {
169 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
170 pub reported: Option<ErrorReported>,
171 /// A list of spans of arguments provided that were not valid.
172 pub invalid_args: Vec<Span>,
175 /// Decorates the result of a generic argument count mismatch
176 /// check with whether explicit late bounds were provided.
178 pub struct GenericArgCountResult {
179 pub explicit_late_bound: ExplicitLateBound,
180 pub correct: Result<(), GenericArgCountMismatch>,
183 pub trait CreateSubstsForGenericArgsCtxt<'a, 'tcx> {
184 fn args_for_def_id(&mut self, def_id: DefId) -> (Option<&'a GenericArgs<'a>>, bool);
188 param: &ty::GenericParamDef,
189 arg: &GenericArg<'_>,
190 ) -> subst::GenericArg<'tcx>;
194 substs: Option<&[subst::GenericArg<'tcx>]>,
195 param: &ty::GenericParamDef,
197 ) -> subst::GenericArg<'tcx>;
200 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
201 pub fn ast_region_to_region(
203 lifetime: &hir::Lifetime,
204 def: Option<&ty::GenericParamDef>,
205 ) -> ty::Region<'tcx> {
206 let tcx = self.tcx();
207 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
209 let r = match tcx.named_region(lifetime.hir_id) {
210 Some(rl::Region::Static) => tcx.lifetimes.re_static,
212 Some(rl::Region::LateBound(debruijn, id, _)) => {
213 let name = lifetime_name(id.expect_local());
214 let br = ty::BoundRegion { kind: ty::BrNamed(id, name) };
215 tcx.mk_region(ty::ReLateBound(debruijn, br))
218 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
219 let br = ty::BoundRegion { kind: ty::BrAnon(index) };
220 tcx.mk_region(ty::ReLateBound(debruijn, br))
223 Some(rl::Region::EarlyBound(index, id, _)) => {
224 let name = lifetime_name(id.expect_local());
225 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
228 Some(rl::Region::Free(scope, id)) => {
229 let name = lifetime_name(id.expect_local());
230 tcx.mk_region(ty::ReFree(ty::FreeRegion {
232 bound_region: ty::BrNamed(id, name),
235 // (*) -- not late-bound, won't change
239 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
240 // This indicates an illegal lifetime
241 // elision. `resolve_lifetime` should have
242 // reported an error in this case -- but if
243 // not, let's error out.
244 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
246 // Supply some dummy value. We don't have an
247 // `re_error`, annoyingly, so use `'static`.
248 tcx.lifetimes.re_static
253 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
258 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
259 /// returns an appropriate set of substitutions for this particular reference to `I`.
260 pub fn ast_path_substs_for_ty(
264 item_segment: &hir::PathSegment<'_>,
265 ) -> SubstsRef<'tcx> {
266 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
272 item_segment.infer_args,
276 if let Some(b) = assoc_bindings.first() {
277 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
283 /// Given the type/lifetime/const arguments provided to some path (along with
284 /// an implicit `Self`, if this is a trait reference), returns the complete
285 /// set of substitutions. This may involve applying defaulted type parameters.
286 /// Also returns back constraints on associated types.
291 /// T: std::ops::Index<usize, Output = u32>
292 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
295 /// 1. The `self_ty` here would refer to the type `T`.
296 /// 2. The path in question is the path to the trait `std::ops::Index`,
297 /// which will have been resolved to a `def_id`
298 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
299 /// parameters are returned in the `SubstsRef`, the associated type bindings like
300 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
302 /// Note that the type listing given here is *exactly* what the user provided.
304 /// For (generic) associated types
307 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
310 /// We have the parent substs are the substs for the parent trait:
311 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
312 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
313 /// lists: `[Vec<u8>, u8, 'a]`.
314 fn create_substs_for_ast_path<'a>(
318 parent_substs: &[subst::GenericArg<'tcx>],
319 seg: &hir::PathSegment<'_>,
320 generic_args: &'a hir::GenericArgs<'_>,
322 self_ty: Option<Ty<'tcx>>,
323 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
324 // If the type is parameterized by this region, then replace this
325 // region with the current anon region binding (in other words,
326 // whatever & would get replaced with).
328 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
330 def_id, self_ty, generic_args
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.len() == 0 {
367 return (tcx.intern_substs(&[]), vec![], 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().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(<, Some(param)).into()
422 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
424 tcx.check_optional_stability(
429 // Default generic parameters may not be marked
430 // with stability attributes, i.e. when the
431 // default parameter was defined at the same time
432 // as the rest of the type. As such, we ignore missing
433 // stability attributes.
437 if let (hir::TyKind::Infer, false) =
438 (&ty.kind, self.astconv.allow_ty_infer())
440 self.inferred_params.push(ty.span);
441 tcx.ty_error().into()
443 self.astconv.ast_ty_to_ty(&ty).into()
446 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
447 ty::Const::from_opt_const_arg_anon_const(
449 ty::WithOptConstParam {
450 did: tcx.hir().local_def_id(ct.value.hir_id),
451 const_param_did: Some(param.def_id),
462 substs: Option<&[subst::GenericArg<'tcx>]>,
463 param: &ty::GenericParamDef,
465 ) -> subst::GenericArg<'tcx> {
466 let tcx = self.astconv.tcx();
468 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
469 GenericParamDefKind::Type { has_default, .. } => {
470 if !infer_args && has_default {
471 // No type parameter provided, but a default exists.
473 // If we are converting an object type, then the
474 // `Self` parameter is unknown. However, some of the
475 // other type parameters may reference `Self` in their
476 // defaults. This will lead to an ICE if we are not
478 if self.default_needs_object_self(param) {
479 self.missing_type_params.push(param.name.to_string());
480 tcx.ty_error().into()
482 // This is a default type parameter.
486 tcx.at(self.span).type_of(param.def_id).subst_spanned(
494 } else if infer_args {
495 // No type parameters were provided, we can infer all.
496 let param = if !self.default_needs_object_self(param) {
501 self.astconv.ty_infer(param, self.span).into()
503 // We've already errored above about the mismatch.
504 tcx.ty_error().into()
507 GenericParamDefKind::Const => {
508 let ty = tcx.at(self.span).type_of(param.def_id);
509 // FIXME(const_generics_defaults)
511 // No const parameters were provided, we can infer all.
512 self.astconv.ct_infer(ty, Some(param), self.span).into()
514 // We've already errored above about the mismatch.
515 tcx.const_error(ty).into()
522 let mut substs_ctx = SubstsForAstPathCtxt {
527 missing_type_params: vec![],
528 inferred_params: vec![],
532 let substs = Self::create_substs_for_generic_args(
542 self.complain_about_missing_type_params(
543 substs_ctx.missing_type_params,
546 generic_args.args.is_empty(),
549 // Convert associated-type bindings or constraints into a separate vector.
550 // Example: Given this:
552 // T: Iterator<Item = u32>
554 // The `T` is passed in as a self-type; the `Item = u32` is
555 // not a "type parameter" of the `Iterator` trait, but rather
556 // a restriction on `<T as Iterator>::Item`, so it is passed
558 let assoc_bindings = generic_args
562 let kind = match binding.kind {
563 hir::TypeBindingKind::Equality { ref ty } => {
564 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
566 hir::TypeBindingKind::Constraint { ref bounds } => {
567 ConvertedBindingKind::Constraint(bounds)
571 item_name: binding.ident,
573 gen_args: binding.gen_args,
580 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
581 generics, self_ty, substs
584 (substs, assoc_bindings, arg_count)
587 crate fn create_substs_for_associated_item(
592 item_segment: &hir::PathSegment<'_>,
593 parent_substs: SubstsRef<'tcx>,
594 ) -> SubstsRef<'tcx> {
595 if tcx.generics_of(item_def_id).params.is_empty() {
596 self.prohibit_generics(slice::from_ref(item_segment));
600 self.create_substs_for_ast_path(
606 item_segment.infer_args,
613 /// Instantiates the path for the given trait reference, assuming that it's
614 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
615 /// The type _cannot_ be a type other than a trait type.
617 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
618 /// are disallowed. Otherwise, they are pushed onto the vector given.
619 pub fn instantiate_mono_trait_ref(
621 trait_ref: &hir::TraitRef<'_>,
623 ) -> ty::TraitRef<'tcx> {
624 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
626 self.ast_path_to_mono_trait_ref(
628 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
630 trait_ref.path.segments.last().unwrap(),
634 /// The given trait-ref must actually be a trait.
635 pub(super) fn instantiate_poly_trait_ref_inner(
637 trait_ref: &hir::TraitRef<'_>,
639 constness: Constness,
641 bounds: &mut Bounds<'tcx>,
643 ) -> GenericArgCountResult {
644 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
646 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
648 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
650 let (substs, assoc_bindings, arg_count) = self.create_substs_for_ast_trait_ref(
654 trait_ref.path.segments.last().unwrap(),
656 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
658 bounds.trait_bounds.push((poly_trait_ref, span, constness));
660 let mut dup_bindings = FxHashMap::default();
661 for binding in &assoc_bindings {
662 // Specify type to assert that error was already reported in `Err` case.
663 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
664 trait_ref.hir_ref_id,
672 // Okay to ignore `Err` because of `ErrorReported` (see above).
676 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
677 trait_ref, bounds, poly_trait_ref
683 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
684 /// a full trait reference. The resulting trait reference is returned. This may also generate
685 /// auxiliary bounds, which are added to `bounds`.
690 /// poly_trait_ref = Iterator<Item = u32>
694 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
696 /// **A note on binders:** against our usual convention, there is an implied bounder around
697 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
698 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
699 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
700 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
702 pub fn instantiate_poly_trait_ref(
704 poly_trait_ref: &hir::PolyTraitRef<'_>,
705 constness: Constness,
707 bounds: &mut Bounds<'tcx>,
708 ) -> GenericArgCountResult {
709 self.instantiate_poly_trait_ref_inner(
710 &poly_trait_ref.trait_ref,
719 pub fn instantiate_lang_item_trait_ref(
721 lang_item: hir::LangItem,
724 args: &GenericArgs<'_>,
726 bounds: &mut Bounds<'tcx>,
728 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
730 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
734 &hir::PathSegment::invalid(),
739 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
740 bounds.trait_bounds.push((poly_trait_ref, span, Constness::NotConst));
742 let mut dup_bindings = FxHashMap::default();
743 for binding in assoc_bindings {
744 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
756 fn ast_path_to_mono_trait_ref(
761 trait_segment: &hir::PathSegment<'_>,
762 ) -> ty::TraitRef<'tcx> {
763 let (substs, assoc_bindings, _) =
764 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
765 if let Some(b) = assoc_bindings.first() {
766 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
768 ty::TraitRef::new(trait_def_id, substs)
771 fn create_substs_for_ast_trait_ref<'a>(
776 trait_segment: &'a hir::PathSegment<'a>,
777 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
778 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
780 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
782 self.create_substs_for_ast_path(
787 trait_segment.args(),
788 trait_segment.infer_args,
793 fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
795 .associated_items(trait_def_id)
796 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
800 // Returns `true` if a bounds list includes `?Sized`.
801 pub fn is_unsized(&self, ast_bounds: &[&hir::GenericBound<'_>], span: Span) -> bool {
802 let tcx = self.tcx();
804 // Try to find an unbound in bounds.
805 let mut unbound = None;
806 for ab in ast_bounds {
807 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
808 if unbound.is_none() {
809 unbound = Some(&ptr.trait_ref);
811 tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
816 let kind_id = tcx.lang_items().require(LangItem::Sized);
819 // FIXME(#8559) currently requires the unbound to be built-in.
820 if let Ok(kind_id) = kind_id {
821 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
824 "default bound relaxed for a type parameter, but \
825 this does nothing because the given bound is not \
826 a default; only `?Sized` is supported",
831 _ if kind_id.is_ok() => {
834 // No lang item for `Sized`, so we can't add it as a bound.
841 /// This helper takes a *converted* parameter type (`param_ty`)
842 /// and an *unconverted* list of bounds:
846 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
848 /// `param_ty`, in ty form
851 /// It adds these `ast_bounds` into the `bounds` structure.
853 /// **A note on binders:** there is an implied binder around
854 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
855 /// for more details.
859 ast_bounds: &[&hir::GenericBound<'_>],
860 bounds: &mut Bounds<'tcx>,
862 let constness = self.default_constness_for_trait_bounds();
863 for ast_bound in ast_bounds {
865 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
866 self.instantiate_poly_trait_ref(b, constness, param_ty, bounds);
868 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
869 self.instantiate_poly_trait_ref(b, Constness::NotConst, param_ty, bounds);
871 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
872 hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => self
873 .instantiate_lang_item_trait_ref(
874 *lang_item, *span, *hir_id, args, param_ty, bounds,
876 hir::GenericBound::Outlives(ref l) => bounds
878 .push((ty::Binder::bind(self.ast_region_to_region(l, None)), l.span)),
883 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
884 /// The self-type for the bounds is given by `param_ty`.
889 /// fn foo<T: Bar + Baz>() { }
890 /// ^ ^^^^^^^^^ ast_bounds
894 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
895 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
896 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
898 /// `span` should be the declaration size of the parameter.
899 pub fn compute_bounds(
902 ast_bounds: &[hir::GenericBound<'_>],
903 sized_by_default: SizedByDefault,
906 let ast_bounds: Vec<_> = ast_bounds.iter().collect();
907 self.compute_bounds_inner(param_ty, &ast_bounds, sized_by_default, span)
910 /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
911 /// named `assoc_name` into ty::Bounds. Ignore the rest.
912 pub fn compute_bounds_that_match_assoc_type(
915 ast_bounds: &[hir::GenericBound<'_>],
916 sized_by_default: SizedByDefault,
920 let mut result = Vec::new();
922 for ast_bound in ast_bounds {
923 if let Some(trait_ref) = ast_bound.trait_ref() {
924 if let Some(trait_did) = trait_ref.trait_def_id() {
925 if self.tcx().trait_may_define_assoc_type(trait_did, assoc_name) {
926 result.push(ast_bound);
932 self.compute_bounds_inner(param_ty, &result, sized_by_default, span)
935 fn compute_bounds_inner(
938 ast_bounds: &[&hir::GenericBound<'_>],
939 sized_by_default: SizedByDefault,
942 let mut bounds = Bounds::default();
944 self.add_bounds(param_ty, ast_bounds, &mut bounds);
946 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
947 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
955 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
958 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
959 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
960 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
961 fn add_predicates_for_ast_type_binding(
963 hir_ref_id: hir::HirId,
964 trait_ref: ty::PolyTraitRef<'tcx>,
965 binding: &ConvertedBinding<'_, 'tcx>,
966 bounds: &mut Bounds<'tcx>,
968 dup_bindings: &mut FxHashMap<DefId, Span>,
970 ) -> Result<(), ErrorReported> {
971 // Given something like `U: SomeTrait<T = X>`, we want to produce a
972 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
973 // subtle in the event that `T` is defined in a supertrait of
974 // `SomeTrait`, because in that case we need to upcast.
976 // That is, consider this case:
979 // trait SubTrait: SuperTrait<i32> { }
980 // trait SuperTrait<A> { type T; }
982 // ... B: SubTrait<T = foo> ...
985 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
987 debug!(?hir_ref_id, ?trait_ref, ?binding, ?bounds, "add_predicates_for_ast_type_binding",);
988 let tcx = self.tcx();
991 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
992 // Simple case: X is defined in the current trait.
995 // Otherwise, we have to walk through the supertraits to find
997 self.one_bound_for_assoc_type(
998 || traits::supertraits(tcx, trait_ref),
999 || trait_ref.print_only_trait_path().to_string(),
1002 || match binding.kind {
1003 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1009 let (assoc_ident, def_scope) =
1010 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1012 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1013 // of calling `filter_by_name_and_kind`.
1015 .associated_items(candidate.def_id())
1016 .filter_by_name_unhygienic(assoc_ident.name)
1018 i.kind == ty::AssocKind::Type && i.ident.normalize_to_macros_2_0() == assoc_ident
1020 .expect("missing associated type");
1022 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1026 &format!("associated type `{}` is private", binding.item_name),
1028 .span_label(binding.span, "private associated type")
1031 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1035 .entry(assoc_ty.def_id)
1036 .and_modify(|prev_span| {
1037 self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
1039 prev_span: *prev_span,
1040 item_name: binding.item_name,
1041 def_path: tcx.def_path_str(assoc_ty.container.id()),
1044 .or_insert(binding.span);
1047 // Include substitutions for generic parameters of associated types
1048 let projection_ty = candidate.map_bound(|trait_ref| {
1049 let item_segment = hir::PathSegment {
1050 ident: assoc_ty.ident,
1053 args: Some(binding.gen_args),
1057 let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
1066 "add_predicates_for_ast_type_binding: substs for trait-ref and assoc_item: {:?}",
1067 substs_trait_ref_and_assoc_item
1071 item_def_id: assoc_ty.def_id,
1072 substs: substs_trait_ref_and_assoc_item,
1077 // Find any late-bound regions declared in `ty` that are not
1078 // declared in the trait-ref or assoc_ty. These are not well-formed.
1082 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1083 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1084 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1085 let late_bound_in_trait_ref =
1086 tcx.collect_constrained_late_bound_regions(&projection_ty);
1087 let late_bound_in_ty =
1088 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1089 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1090 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1092 // FIXME: point at the type params that don't have appropriate lifetimes:
1093 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1094 // ---- ---- ^^^^^^^
1095 self.validate_late_bound_regions(
1096 late_bound_in_trait_ref,
1103 "binding for associated type `{}` references {}, \
1104 which does not appear in the trait input types",
1113 match binding.kind {
1114 ConvertedBindingKind::Equality(ref ty) => {
1115 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1116 // the "projection predicate" for:
1118 // `<T as Iterator>::Item = u32`
1119 bounds.projection_bounds.push((
1120 projection_ty.map_bound(|projection_ty| {
1122 "add_predicates_for_ast_type_binding: projection_ty {:?}, substs: {:?}",
1123 projection_ty, projection_ty.substs
1125 ty::ProjectionPredicate { projection_ty, ty }
1130 ConvertedBindingKind::Constraint(ast_bounds) => {
1131 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1133 // `<T as Iterator>::Item: Debug`
1135 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1136 // parameter to have a skipped binder.
1138 tcx.mk_projection(assoc_ty.def_id, projection_ty.skip_binder().substs);
1139 let ast_bounds: Vec<_> = ast_bounds.iter().collect();
1140 self.add_bounds(param_ty, &ast_bounds, bounds);
1150 item_segment: &hir::PathSegment<'_>,
1152 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1153 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1156 fn conv_object_ty_poly_trait_ref(
1159 trait_bounds: &[hir::PolyTraitRef<'_>],
1160 lifetime: &hir::Lifetime,
1163 let tcx = self.tcx();
1165 let mut bounds = Bounds::default();
1166 let mut potential_assoc_types = Vec::new();
1167 let dummy_self = self.tcx().types.trait_object_dummy_self;
1168 for trait_bound in trait_bounds.iter().rev() {
1169 if let GenericArgCountResult {
1171 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1173 } = self.instantiate_poly_trait_ref(
1175 Constness::NotConst,
1179 potential_assoc_types.extend(cur_potential_assoc_types);
1183 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1184 // is used and no 'maybe' bounds are used.
1185 let expanded_traits =
1186 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1187 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1188 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1189 if regular_traits.len() > 1 {
1190 let first_trait = ®ular_traits[0];
1191 let additional_trait = ®ular_traits[1];
1192 let mut err = struct_span_err!(
1194 additional_trait.bottom().1,
1196 "only auto traits can be used as additional traits in a trait object"
1198 additional_trait.label_with_exp_info(
1200 "additional non-auto trait",
1203 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1205 "consider creating a new trait with all of these as super-traits and using that \
1206 trait here instead: `trait NewTrait: {} {{}}`",
1209 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1210 .collect::<Vec<_>>()
1214 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1215 for more information on them, visit \
1216 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1221 if regular_traits.is_empty() && auto_traits.is_empty() {
1222 tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span });
1223 return tcx.ty_error();
1226 // Check that there are no gross object safety violations;
1227 // most importantly, that the supertraits don't contain `Self`,
1229 for item in ®ular_traits {
1230 let object_safety_violations =
1231 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1232 if !object_safety_violations.is_empty() {
1233 report_object_safety_error(
1236 item.trait_ref().def_id(),
1237 &object_safety_violations[..],
1240 return tcx.ty_error();
1244 // Use a `BTreeSet` to keep output in a more consistent order.
1245 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1247 let regular_traits_refs_spans = bounds
1250 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1252 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1253 assert_eq!(constness, Constness::NotConst);
1255 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1257 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1258 obligation.predicate
1261 let bound_predicate = obligation.predicate.kind();
1262 match bound_predicate.skip_binder() {
1263 ty::PredicateKind::Trait(pred, _) => {
1264 let pred = bound_predicate.rebind(pred);
1265 associated_types.entry(span).or_default().extend(
1266 tcx.associated_items(pred.def_id())
1267 .in_definition_order()
1268 .filter(|item| item.kind == ty::AssocKind::Type)
1269 .map(|item| item.def_id),
1272 ty::PredicateKind::Projection(pred) => {
1273 let pred = bound_predicate.rebind(pred);
1274 // A `Self` within the original bound will be substituted with a
1275 // `trait_object_dummy_self`, so check for that.
1276 let references_self =
1277 pred.skip_binder().ty.walk().any(|arg| arg == dummy_self.into());
1279 // If the projection output contains `Self`, force the user to
1280 // elaborate it explicitly to avoid a lot of complexity.
1282 // The "classicaly useful" case is the following:
1284 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1289 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1290 // but actually supporting that would "expand" to an infinitely-long type
1291 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1293 // Instead, we force the user to write
1294 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1295 // the discussion in #56288 for alternatives.
1296 if !references_self {
1297 // Include projections defined on supertraits.
1298 bounds.projection_bounds.push((pred, span));
1306 for (projection_bound, _) in &bounds.projection_bounds {
1307 for def_ids in associated_types.values_mut() {
1308 def_ids.remove(&projection_bound.projection_def_id());
1312 self.complain_about_missing_associated_types(
1314 potential_assoc_types,
1318 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1319 // `dyn Trait + Send`.
1320 // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
1322 let mut duplicates = FxHashSet::default();
1323 auto_traits.retain(|i| duplicates.insert(i.trait_ref().def_id()));
1324 debug!("regular_traits: {:?}", regular_traits);
1325 debug!("auto_traits: {:?}", auto_traits);
1327 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1328 let existential_trait_refs = regular_traits.iter().map(|i| {
1329 i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
1330 if trait_ref.self_ty() != dummy_self {
1331 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1332 // which picks up non-supertraits where clauses - but also, the object safety
1333 // completely ignores trait aliases, which could be object safety hazards. We
1334 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1335 // disabled. (#66420)
1336 tcx.sess.delay_span_bug(
1339 "trait_ref_to_existential called on {:?} with non-dummy Self",
1344 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1347 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1348 bound.map_bound(|b| {
1349 if b.projection_ty.self_ty() != dummy_self {
1350 tcx.sess.delay_span_bug(
1352 &format!("trait_ref_to_existential called on {:?} with non-dummy Self", b),
1355 ty::ExistentialProjection::erase_self_ty(tcx, b)
1359 let regular_trait_predicates = existential_trait_refs
1360 .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));
1361 let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
1362 ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
1364 let mut v = regular_trait_predicates
1365 .chain(auto_trait_predicates)
1367 existential_projections.map(|x| x.map_bound(ty::ExistentialPredicate::Projection)),
1369 .collect::<SmallVec<[_; 8]>>();
1370 v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
1372 let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
1374 // Use explicitly-specified region bound.
1375 let region_bound = if !lifetime.is_elided() {
1376 self.ast_region_to_region(lifetime, None)
1378 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1379 if tcx.named_region(lifetime.hir_id).is_some() {
1380 self.ast_region_to_region(lifetime, None)
1382 self.re_infer(None, span).unwrap_or_else(|| {
1383 let mut err = struct_span_err!(
1387 "the lifetime bound for this object type cannot be deduced \
1388 from context; please supply an explicit bound"
1391 // We will have already emitted an error E0106 complaining about a
1392 // missing named lifetime in `&dyn Trait`, so we elide this one.
1397 tcx.lifetimes.re_static
1402 debug!("region_bound: {:?}", region_bound);
1404 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1405 debug!("trait_object_type: {:?}", ty);
1409 fn report_ambiguous_associated_type(
1416 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1417 if let (Some(_), Ok(snippet)) = (
1418 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1419 self.tcx().sess.source_map().span_to_snippet(span),
1421 err.span_suggestion(
1423 "you are looking for the module in `std`, not the primitive type",
1424 format!("std::{}", snippet),
1425 Applicability::MachineApplicable,
1428 err.span_suggestion(
1430 "use fully-qualified syntax",
1431 format!("<{} as {}>::{}", type_str, trait_str, name),
1432 Applicability::HasPlaceholders,
1438 // Search for a bound on a type parameter which includes the associated item
1439 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1440 // This function will fail if there are no suitable bounds or there is
1442 fn find_bound_for_assoc_item(
1444 ty_param_def_id: LocalDefId,
1447 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1448 let tcx = self.tcx();
1451 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1452 ty_param_def_id, assoc_name, span,
1455 let predicates = &self
1456 .get_type_parameter_bounds(span, ty_param_def_id.to_def_id(), assoc_name)
1459 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1461 let param_hir_id = tcx.hir().local_def_id_to_hir_id(ty_param_def_id);
1462 let param_name = tcx.hir().ty_param_name(param_hir_id);
1463 self.one_bound_for_assoc_type(
1465 traits::transitive_bounds_that_define_assoc_type(
1467 predicates.iter().filter_map(|(p, _)| {
1468 p.to_opt_poly_trait_ref().map(|trait_ref| trait_ref.value)
1473 || param_name.to_string(),
1480 // Checks that `bounds` contains exactly one element and reports appropriate
1481 // errors otherwise.
1482 fn one_bound_for_assoc_type<I>(
1484 all_candidates: impl Fn() -> I,
1485 ty_param_name: impl Fn() -> String,
1488 is_equality: impl Fn() -> Option<String>,
1489 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1491 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1493 let mut matching_candidates = all_candidates()
1494 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1496 let bound = match matching_candidates.next() {
1497 Some(bound) => bound,
1499 self.complain_about_assoc_type_not_found(
1505 return Err(ErrorReported);
1509 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1511 if let Some(bound2) = matching_candidates.next() {
1512 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1514 let is_equality = is_equality();
1515 let bounds = array::IntoIter::new([bound, bound2]).chain(matching_candidates);
1516 let mut err = if is_equality.is_some() {
1517 // More specific Error Index entry.
1522 "ambiguous associated type `{}` in bounds of `{}`",
1531 "ambiguous associated type `{}` in bounds of `{}`",
1536 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1538 let mut where_bounds = vec![];
1539 for bound in bounds {
1540 let bound_id = bound.def_id();
1541 let bound_span = self
1543 .associated_items(bound_id)
1544 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1545 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1547 if let Some(bound_span) = bound_span {
1551 "ambiguous `{}` from `{}`",
1553 bound.print_only_trait_path(),
1556 if let Some(constraint) = &is_equality {
1557 where_bounds.push(format!(
1558 " T: {trait}::{assoc} = {constraint}",
1559 trait=bound.print_only_trait_path(),
1561 constraint=constraint,
1564 err.span_suggestion(
1566 "use fully qualified syntax to disambiguate",
1570 bound.print_only_trait_path(),
1573 Applicability::MaybeIncorrect,
1578 "associated type `{}` could derive from `{}`",
1580 bound.print_only_trait_path(),
1584 if !where_bounds.is_empty() {
1586 "consider introducing a new type parameter `T` and adding `where` constraints:\
1587 \n where\n T: {},\n{}",
1589 where_bounds.join(",\n"),
1593 if !where_bounds.is_empty() {
1594 return Err(ErrorReported);
1600 // Create a type from a path to an associated type.
1601 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1602 // and item_segment is the path segment for `D`. We return a type and a def for
1604 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1605 // parameter or `Self`.
1606 pub fn associated_path_to_ty(
1608 hir_ref_id: hir::HirId,
1612 assoc_segment: &hir::PathSegment<'_>,
1613 permit_variants: bool,
1614 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
1615 let tcx = self.tcx();
1616 let assoc_ident = assoc_segment.ident;
1618 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1620 // Check if we have an enum variant.
1621 let mut variant_resolution = None;
1622 if let ty::Adt(adt_def, _) = qself_ty.kind() {
1623 if adt_def.is_enum() {
1624 let variant_def = adt_def
1627 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
1628 if let Some(variant_def) = variant_def {
1629 if permit_variants {
1630 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
1631 self.prohibit_generics(slice::from_ref(assoc_segment));
1632 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1634 variant_resolution = Some(variant_def.def_id);
1640 // Find the type of the associated item, and the trait where the associated
1641 // item is declared.
1642 let bound = match (&qself_ty.kind(), qself_res) {
1643 (_, Res::SelfTy(Some(_), Some((impl_def_id, _)))) => {
1644 // `Self` in an impl of a trait -- we have a concrete self type and a
1646 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1647 Some(trait_ref) => trait_ref,
1649 // A cycle error occurred, most likely.
1650 return Err(ErrorReported);
1654 self.one_bound_for_assoc_type(
1655 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
1656 || "Self".to_string(),
1664 Res::SelfTy(Some(param_did), None) | Res::Def(DefKind::TyParam, param_did),
1665 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
1667 if variant_resolution.is_some() {
1668 // Variant in type position
1669 let msg = format!("expected type, found variant `{}`", assoc_ident);
1670 tcx.sess.span_err(span, &msg);
1671 } else if qself_ty.is_enum() {
1672 let mut err = struct_span_err!(
1676 "no variant named `{}` found for enum `{}`",
1681 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1682 if let Some(suggested_name) = find_best_match_for_name(
1686 .map(|variant| variant.ident.name)
1687 .collect::<Vec<Symbol>>(),
1691 err.span_suggestion(
1693 "there is a variant with a similar name",
1694 suggested_name.to_string(),
1695 Applicability::MaybeIncorrect,
1700 format!("variant not found in `{}`", qself_ty),
1704 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
1705 let sp = tcx.sess.source_map().guess_head_span(sp);
1706 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1710 } else if !qself_ty.references_error() {
1711 // Don't print `TyErr` to the user.
1712 self.report_ambiguous_associated_type(
1714 &qself_ty.to_string(),
1719 return Err(ErrorReported);
1723 let trait_did = bound.def_id();
1724 let (assoc_ident, def_scope) =
1725 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1727 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1728 // of calling `filter_by_name_and_kind`.
1730 .associated_items(trait_did)
1731 .in_definition_order()
1733 i.kind.namespace() == Namespace::TypeNS
1734 && i.ident.normalize_to_macros_2_0() == assoc_ident
1736 .expect("missing associated type");
1738 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
1739 let ty = self.normalize_ty(span, ty);
1741 let kind = DefKind::AssocTy;
1742 if !item.vis.is_accessible_from(def_scope, tcx) {
1743 let kind = kind.descr(item.def_id);
1744 let msg = format!("{} `{}` is private", kind, assoc_ident);
1746 .struct_span_err(span, &msg)
1747 .span_label(span, &format!("private {}", kind))
1750 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
1752 if let Some(variant_def_id) = variant_resolution {
1753 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
1754 let mut err = lint.build("ambiguous associated item");
1755 let mut could_refer_to = |kind: DefKind, def_id, also| {
1756 let note_msg = format!(
1757 "`{}` could{} refer to the {} defined here",
1762 err.span_note(tcx.def_span(def_id), ¬e_msg);
1765 could_refer_to(DefKind::Variant, variant_def_id, "");
1766 could_refer_to(kind, item.def_id, " also");
1768 err.span_suggestion(
1770 "use fully-qualified syntax",
1771 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
1772 Applicability::MachineApplicable,
1778 Ok((ty, kind, item.def_id))
1784 opt_self_ty: Option<Ty<'tcx>>,
1786 trait_segment: &hir::PathSegment<'_>,
1787 item_segment: &hir::PathSegment<'_>,
1789 let tcx = self.tcx();
1791 let trait_def_id = tcx.parent(item_def_id).unwrap();
1793 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
1795 let self_ty = if let Some(ty) = opt_self_ty {
1798 let path_str = tcx.def_path_str(trait_def_id);
1800 let def_id = self.item_def_id();
1802 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
1804 let parent_def_id = def_id
1805 .and_then(|def_id| {
1806 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
1808 .map(|hir_id| tcx.hir().get_parent_did(hir_id).to_def_id());
1810 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
1812 // If the trait in segment is the same as the trait defining the item,
1813 // use the `<Self as ..>` syntax in the error.
1814 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
1815 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
1817 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
1823 self.report_ambiguous_associated_type(
1827 item_segment.ident.name,
1829 return tcx.ty_error();
1832 debug!("qpath_to_ty: self_type={:?}", self_ty);
1834 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
1836 let item_substs = self.create_substs_for_associated_item(
1844 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1846 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
1849 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
1853 let mut has_err = false;
1854 for segment in segments {
1855 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1856 for arg in segment.args().args {
1857 let (span, kind) = match arg {
1858 hir::GenericArg::Lifetime(lt) => {
1864 (lt.span, "lifetime")
1866 hir::GenericArg::Type(ty) => {
1874 hir::GenericArg::Const(ct) => {
1883 let mut err = struct_span_err!(
1887 "{} arguments are not allowed for this type",
1890 err.span_label(span, format!("{} argument not allowed", kind));
1892 if err_for_lt && err_for_ty && err_for_ct {
1897 // Only emit the first error to avoid overloading the user with error messages.
1898 if let [binding, ..] = segment.args().bindings {
1900 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
1906 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
1907 pub fn def_ids_for_value_path_segments(
1909 segments: &[hir::PathSegment<'_>],
1910 self_ty: Option<Ty<'tcx>>,
1914 // We need to extract the type parameters supplied by the user in
1915 // the path `path`. Due to the current setup, this is a bit of a
1916 // tricky-process; the problem is that resolve only tells us the
1917 // end-point of the path resolution, and not the intermediate steps.
1918 // Luckily, we can (at least for now) deduce the intermediate steps
1919 // just from the end-point.
1921 // There are basically five cases to consider:
1923 // 1. Reference to a constructor of a struct:
1925 // struct Foo<T>(...)
1927 // In this case, the parameters are declared in the type space.
1929 // 2. Reference to a constructor of an enum variant:
1931 // enum E<T> { Foo(...) }
1933 // In this case, the parameters are defined in the type space,
1934 // but may be specified either on the type or the variant.
1936 // 3. Reference to a fn item or a free constant:
1940 // In this case, the path will again always have the form
1941 // `a::b::foo::<T>` where only the final segment should have
1942 // type parameters. However, in this case, those parameters are
1943 // declared on a value, and hence are in the `FnSpace`.
1945 // 4. Reference to a method or an associated constant:
1947 // impl<A> SomeStruct<A> {
1951 // Here we can have a path like
1952 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
1953 // may appear in two places. The penultimate segment,
1954 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
1955 // final segment, `foo::<B>` contains parameters in fn space.
1957 // The first step then is to categorize the segments appropriately.
1959 let tcx = self.tcx();
1961 assert!(!segments.is_empty());
1962 let last = segments.len() - 1;
1964 let mut path_segs = vec![];
1967 // Case 1. Reference to a struct constructor.
1968 DefKind::Ctor(CtorOf::Struct, ..) => {
1969 // Everything but the final segment should have no
1970 // parameters at all.
1971 let generics = tcx.generics_of(def_id);
1972 // Variant and struct constructors use the
1973 // generics of their parent type definition.
1974 let generics_def_id = generics.parent.unwrap_or(def_id);
1975 path_segs.push(PathSeg(generics_def_id, last));
1978 // Case 2. Reference to a variant constructor.
1979 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
1980 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
1981 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
1982 debug_assert!(adt_def.is_enum());
1984 } else if last >= 1 && segments[last - 1].args.is_some() {
1985 // Everything but the penultimate segment should have no
1986 // parameters at all.
1987 let mut def_id = def_id;
1989 // `DefKind::Ctor` -> `DefKind::Variant`
1990 if let DefKind::Ctor(..) = kind {
1991 def_id = tcx.parent(def_id).unwrap()
1994 // `DefKind::Variant` -> `DefKind::Enum`
1995 let enum_def_id = tcx.parent(def_id).unwrap();
1996 (enum_def_id, last - 1)
1998 // FIXME: lint here recommending `Enum::<...>::Variant` form
1999 // instead of `Enum::Variant::<...>` form.
2001 // Everything but the final segment should have no
2002 // parameters at all.
2003 let generics = tcx.generics_of(def_id);
2004 // Variant and struct constructors use the
2005 // generics of their parent type definition.
2006 (generics.parent.unwrap_or(def_id), last)
2008 path_segs.push(PathSeg(generics_def_id, index));
2011 // Case 3. Reference to a top-level value.
2012 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2013 path_segs.push(PathSeg(def_id, last));
2016 // Case 4. Reference to a method or associated const.
2017 DefKind::AssocFn | DefKind::AssocConst => {
2018 if segments.len() >= 2 {
2019 let generics = tcx.generics_of(def_id);
2020 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2022 path_segs.push(PathSeg(def_id, last));
2025 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2028 debug!("path_segs = {:?}", path_segs);
2033 // Check a type `Path` and convert it to a `Ty`.
2036 opt_self_ty: Option<Ty<'tcx>>,
2037 path: &hir::Path<'_>,
2038 permit_variants: bool,
2040 let tcx = self.tcx();
2043 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2044 path.res, opt_self_ty, path.segments
2047 let span = path.span;
2049 Res::Def(DefKind::OpaqueTy, did) => {
2050 // Check for desugared `impl Trait`.
2051 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2052 let item_segment = path.segments.split_last().unwrap();
2053 self.prohibit_generics(item_segment.1);
2054 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2055 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2062 | DefKind::ForeignTy,
2065 assert_eq!(opt_self_ty, None);
2066 self.prohibit_generics(path.segments.split_last().unwrap().1);
2067 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2069 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2070 // Convert "variant type" as if it were a real type.
2071 // The resulting `Ty` is type of the variant's enum for now.
2072 assert_eq!(opt_self_ty, None);
2075 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2076 let generic_segs: FxHashSet<_> =
2077 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2078 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2080 if !generic_segs.contains(&index) { Some(seg) } else { None }
2084 let PathSeg(def_id, index) = path_segs.last().unwrap();
2085 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2087 Res::Def(DefKind::TyParam, def_id) => {
2088 assert_eq!(opt_self_ty, None);
2089 self.prohibit_generics(path.segments);
2091 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2092 let item_id = tcx.hir().get_parent_node(hir_id);
2093 let item_def_id = tcx.hir().local_def_id(item_id);
2094 let generics = tcx.generics_of(item_def_id);
2095 let index = generics.param_def_id_to_index[&def_id];
2096 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2098 Res::SelfTy(Some(_), None) => {
2099 // `Self` in trait or type alias.
2100 assert_eq!(opt_self_ty, None);
2101 self.prohibit_generics(path.segments);
2102 tcx.types.self_param
2104 Res::SelfTy(_, Some((def_id, forbid_generic))) => {
2105 // `Self` in impl (we know the concrete type).
2106 assert_eq!(opt_self_ty, None);
2107 self.prohibit_generics(path.segments);
2108 // Try to evaluate any array length constants.
2109 let normalized_ty = self.normalize_ty(span, tcx.at(span).type_of(def_id));
2110 if forbid_generic && normalized_ty.needs_subst() {
2111 let mut err = tcx.sess.struct_span_err(
2113 "generic `Self` types are currently not permitted in anonymous constants",
2115 if let Some(hir::Node::Item(&hir::Item {
2116 kind: hir::ItemKind::Impl(ref impl_),
2118 })) = tcx.hir().get_if_local(def_id)
2120 err.span_note(impl_.self_ty.span, "not a concrete type");
2128 Res::Def(DefKind::AssocTy, def_id) => {
2129 debug_assert!(path.segments.len() >= 2);
2130 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2135 &path.segments[path.segments.len() - 2],
2136 path.segments.last().unwrap(),
2139 Res::PrimTy(prim_ty) => {
2140 assert_eq!(opt_self_ty, None);
2141 self.prohibit_generics(path.segments);
2143 hir::PrimTy::Bool => tcx.types.bool,
2144 hir::PrimTy::Char => tcx.types.char,
2145 hir::PrimTy::Int(it) => tcx.mk_mach_int(ty::int_ty(it)),
2146 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(ty::uint_ty(uit)),
2147 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ty::float_ty(ft)),
2148 hir::PrimTy::Str => tcx.types.str_,
2152 self.set_tainted_by_errors();
2153 self.tcx().ty_error()
2155 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2159 /// Parses the programmer's textual representation of a type into our
2160 /// internal notion of a type.
2161 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2162 self.ast_ty_to_ty_inner(ast_ty, false)
2165 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2166 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2167 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool) -> Ty<'tcx> {
2168 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2170 let tcx = self.tcx();
2172 let result_ty = match ast_ty.kind {
2173 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2174 hir::TyKind::Ptr(ref mt) => {
2175 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2177 hir::TyKind::Rptr(ref region, ref mt) => {
2178 let r = self.ast_region_to_region(region, None);
2179 debug!("ast_ty_to_ty: r={:?}", r);
2180 let t = self.ast_ty_to_ty_inner(&mt.ty, true);
2181 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2183 hir::TyKind::Never => tcx.types.never,
2184 hir::TyKind::Tup(ref fields) => {
2185 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2187 hir::TyKind::BareFn(ref bf) => {
2188 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2190 tcx.mk_fn_ptr(self.ty_of_fn(
2194 &hir::Generics::empty(),
2199 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2200 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed)
2202 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2203 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2204 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2205 self.res_to_ty(opt_self_ty, path, false)
2207 hir::TyKind::OpaqueDef(item_id, ref lifetimes) => {
2208 let opaque_ty = tcx.hir().item(item_id);
2209 let def_id = item_id.def_id.to_def_id();
2211 match opaque_ty.kind {
2212 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn, .. }) => {
2213 self.impl_trait_ty_to_ty(def_id, lifetimes, impl_trait_fn.is_some())
2215 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2218 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2219 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2220 let ty = self.ast_ty_to_ty(qself);
2222 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2227 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2228 .map(|(ty, _, _)| ty)
2229 .unwrap_or_else(|_| tcx.ty_error())
2231 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span)) => {
2232 let def_id = tcx.require_lang_item(lang_item, Some(span));
2233 let (substs, _, _) = self.create_substs_for_ast_path(
2237 &hir::PathSegment::invalid(),
2238 &GenericArgs::none(),
2242 self.normalize_ty(span, tcx.at(span).type_of(def_id).subst(tcx, substs))
2244 hir::TyKind::Array(ref ty, ref length) => {
2245 let length_def_id = tcx.hir().local_def_id(length.hir_id);
2246 let length = ty::Const::from_anon_const(tcx, length_def_id);
2247 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2248 self.normalize_ty(ast_ty.span, array_ty)
2250 hir::TyKind::Typeof(ref _e) => {
2251 tcx.sess.emit_err(TypeofReservedKeywordUsed { span: ast_ty.span });
2254 hir::TyKind::Infer => {
2255 // Infer also appears as the type of arguments or return
2256 // values in a ExprKind::Closure, or as
2257 // the type of local variables. Both of these cases are
2258 // handled specially and will not descend into this routine.
2259 self.ty_infer(None, ast_ty.span)
2261 hir::TyKind::Err => tcx.ty_error(),
2264 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2266 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2270 pub fn impl_trait_ty_to_ty(
2273 lifetimes: &[hir::GenericArg<'_>],
2274 replace_parent_lifetimes: bool,
2276 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2277 let tcx = self.tcx();
2279 let generics = tcx.generics_of(def_id);
2281 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2282 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2283 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2284 // Our own parameters are the resolved lifetimes.
2286 GenericParamDefKind::Lifetime => {
2287 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2288 self.ast_region_to_region(lifetime, None).into()
2297 // For RPIT (return position impl trait), only lifetimes
2298 // mentioned in the impl Trait predicate are captured by
2299 // the opaque type, so the lifetime parameters from the
2300 // parent item need to be replaced with `'static`.
2302 // For `impl Trait` in the types of statics, constants,
2303 // locals and type aliases. These capture all parent
2304 // lifetimes, so they can use their identity subst.
2305 GenericParamDefKind::Lifetime if replace_parent_lifetimes => {
2306 tcx.lifetimes.re_static.into()
2308 _ => tcx.mk_param_from_def(param),
2312 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2314 let ty = tcx.mk_opaque(def_id, substs);
2315 debug!("impl_trait_ty_to_ty: {}", ty);
2319 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2321 hir::TyKind::Infer if expected_ty.is_some() => {
2322 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2323 expected_ty.unwrap()
2325 _ => self.ast_ty_to_ty(ty),
2331 unsafety: hir::Unsafety,
2333 decl: &hir::FnDecl<'_>,
2334 generics: &hir::Generics<'_>,
2335 ident_span: Option<Span>,
2336 hir_ty: Option<&hir::Ty<'_>>,
2337 ) -> ty::PolyFnSig<'tcx> {
2340 let tcx = self.tcx();
2342 // We proactively collect all the inferred type params to emit a single error per fn def.
2343 let mut visitor = PlaceholderHirTyCollector::default();
2344 for ty in decl.inputs {
2345 visitor.visit_ty(ty);
2347 walk_generics(&mut visitor, generics);
2349 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2350 let output_ty = match decl.output {
2351 hir::FnRetTy::Return(ref output) => {
2352 visitor.visit_ty(output);
2353 self.ast_ty_to_ty(output)
2355 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2358 debug!("ty_of_fn: output_ty={:?}", output_ty);
2361 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
2363 if !self.allow_ty_infer() {
2364 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2365 // only want to emit an error complaining about them if infer types (`_`) are not
2366 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2367 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2369 crate::collect::placeholder_type_error(
2371 ident_span.map(|sp| sp.shrink_to_hi()),
2379 // Find any late-bound regions declared in return type that do
2380 // not appear in the arguments. These are not well-formed.
2383 // for<'a> fn() -> &'a str <-- 'a is bad
2384 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2385 let inputs = bare_fn_ty.inputs();
2386 let late_bound_in_args =
2387 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2388 let output = bare_fn_ty.output();
2389 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2391 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
2396 "return type references {}, which is not constrained by the fn input types",
2404 fn validate_late_bound_regions(
2406 constrained_regions: FxHashSet<ty::BoundRegionKind>,
2407 referenced_regions: FxHashSet<ty::BoundRegionKind>,
2408 generate_err: impl Fn(&str) -> rustc_errors::DiagnosticBuilder<'tcx>,
2410 for br in referenced_regions.difference(&constrained_regions) {
2411 let br_name = match *br {
2412 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
2413 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2416 let mut err = generate_err(&br_name);
2418 if let ty::BrAnon(_) = *br {
2419 // The only way for an anonymous lifetime to wind up
2420 // in the return type but **also** be unconstrained is
2421 // if it only appears in "associated types" in the
2422 // input. See #47511 and #62200 for examples. In this case,
2423 // though we can easily give a hint that ought to be
2426 "lifetimes appearing in an associated type are not considered constrained",
2434 /// Given the bounds on an object, determines what single region bound (if any) we can
2435 /// use to summarize this type. The basic idea is that we will use the bound the user
2436 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2437 /// for region bounds. It may be that we can derive no bound at all, in which case
2438 /// we return `None`.
2439 fn compute_object_lifetime_bound(
2442 existential_predicates: &'tcx ty::List<ty::Binder<ty::ExistentialPredicate<'tcx>>>,
2443 ) -> Option<ty::Region<'tcx>> // if None, use the default
2445 let tcx = self.tcx();
2447 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2449 // No explicit region bound specified. Therefore, examine trait
2450 // bounds and see if we can derive region bounds from those.
2451 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2453 // If there are no derived region bounds, then report back that we
2454 // can find no region bound. The caller will use the default.
2455 if derived_region_bounds.is_empty() {
2459 // If any of the derived region bounds are 'static, that is always
2461 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2462 return Some(tcx.lifetimes.re_static);
2465 // Determine whether there is exactly one unique region in the set
2466 // of derived region bounds. If so, use that. Otherwise, report an
2468 let r = derived_region_bounds[0];
2469 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2470 tcx.sess.emit_err(AmbiguousLifetimeBound { span });