1 //! Conversion from AST representation of types to the `ty.rs` representation.
2 //! The main routine here is `ast_ty_to_ty()`; each use is parameterized by an
3 //! instance of `AstConv`.
8 use crate::bounds::Bounds;
9 use crate::collect::PlaceholderHirTyCollector;
11 AmbiguousLifetimeBound, MultipleRelaxedDefaultBounds, TraitObjectDeclaredWithNoTraits,
12 TypeofReservedKeywordUsed, ValueOfAssociatedStructAlreadySpecified,
14 use crate::middle::resolve_lifetime as rl;
15 use crate::require_c_abi_if_c_variadic;
16 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
17 use rustc_errors::{struct_span_err, Applicability, ErrorReported, FatalError};
19 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
20 use rustc_hir::def_id::{DefId, LocalDefId};
21 use rustc_hir::intravisit::{walk_generics, Visitor as _};
22 use rustc_hir::lang_items::LangItem;
23 use rustc_hir::{GenericArg, GenericArgs};
24 use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, Subst, SubstsRef};
25 use rustc_middle::ty::GenericParamDefKind;
26 use rustc_middle::ty::{self, Const, DefIdTree, Ty, TyCtxt, TypeFoldable};
27 use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
28 use rustc_span::lev_distance::find_best_match_for_name;
29 use rustc_span::symbol::{Ident, Symbol};
30 use rustc_span::{Span, DUMMY_SP};
31 use rustc_target::spec::abi;
32 use rustc_trait_selection::traits;
33 use rustc_trait_selection::traits::astconv_object_safety_violations;
34 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
35 use rustc_trait_selection::traits::wf::object_region_bounds;
37 use smallvec::SmallVec;
38 use std::collections::BTreeSet;
42 pub struct PathSeg(pub DefId, pub usize);
44 pub trait AstConv<'tcx> {
45 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
47 fn item_def_id(&self) -> Option<DefId>;
49 /// Returns predicates in scope of the form `X: Foo<T>`, where `X`
50 /// is a type parameter `X` with the given id `def_id` and T
51 /// matches `assoc_name`. This is a subset of the full set of
54 /// This is used for one specific purpose: resolving "short-hand"
55 /// associated type references like `T::Item`. In principle, we
56 /// would do that by first getting the full set of predicates in
57 /// scope and then filtering down to find those that apply to `T`,
58 /// but this can lead to cycle errors. The problem is that we have
59 /// to do this resolution *in order to create the predicates in
60 /// the first place*. Hence, we have this "special pass".
61 fn get_type_parameter_bounds(
66 ) -> ty::GenericPredicates<'tcx>;
68 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
69 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
70 -> Option<ty::Region<'tcx>>;
72 /// Returns the type to use when a type is omitted.
73 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
75 /// Returns `true` if `_` is allowed in type signatures in the current context.
76 fn allow_ty_infer(&self) -> bool;
78 /// Returns the const to use when a const is omitted.
82 param: Option<&ty::GenericParamDef>,
84 ) -> &'tcx Const<'tcx>;
86 /// Projecting an associated type from a (potentially)
87 /// higher-ranked trait reference is more complicated, because of
88 /// the possibility of late-bound regions appearing in the
89 /// associated type binding. This is not legal in function
90 /// signatures for that reason. In a function body, we can always
91 /// handle it because we can use inference variables to remove the
92 /// late-bound regions.
93 fn projected_ty_from_poly_trait_ref(
97 item_segment: &hir::PathSegment<'_>,
98 poly_trait_ref: ty::PolyTraitRef<'tcx>,
101 /// Normalize an associated type coming from the user.
102 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
104 /// Invoked when we encounter an error from some prior pass
105 /// (e.g., resolve) that is translated into a ty-error. This is
106 /// used to help suppress derived errors typeck might otherwise
108 fn set_tainted_by_errors(&self);
110 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
114 struct ConvertedBinding<'a, 'tcx> {
117 kind: ConvertedBindingKind<'a, 'tcx>,
118 gen_args: &'a GenericArgs<'a>,
123 enum ConvertedBindingKind<'a, 'tcx> {
125 Constraint(&'a [hir::GenericBound<'a>]),
128 /// New-typed boolean indicating whether explicit late-bound lifetimes
129 /// are present in a set of generic arguments.
131 /// For example if we have some method `fn f<'a>(&'a self)` implemented
132 /// for some type `T`, although `f` is generic in the lifetime `'a`, `'a`
133 /// is late-bound so should not be provided explicitly. Thus, if `f` is
134 /// instantiated with some generic arguments providing `'a` explicitly,
135 /// we taint those arguments with `ExplicitLateBound::Yes` so that we
136 /// can provide an appropriate diagnostic later.
137 #[derive(Copy, Clone, PartialEq)]
138 pub enum ExplicitLateBound {
143 #[derive(Copy, Clone, PartialEq)]
144 pub enum IsMethodCall {
149 /// Denotes the "position" of a generic argument, indicating if it is a generic type,
150 /// generic function or generic method call.
151 #[derive(Copy, Clone, PartialEq)]
152 pub(crate) enum GenericArgPosition {
154 Value, // e.g., functions
158 /// A marker denoting that the generic arguments that were
159 /// provided did not match the respective generic parameters.
160 #[derive(Clone, Default)]
161 pub struct GenericArgCountMismatch {
162 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
163 pub reported: Option<ErrorReported>,
164 /// A list of spans of arguments provided that were not valid.
165 pub invalid_args: Vec<Span>,
168 /// Decorates the result of a generic argument count mismatch
169 /// check with whether explicit late bounds were provided.
171 pub struct GenericArgCountResult {
172 pub explicit_late_bound: ExplicitLateBound,
173 pub correct: Result<(), GenericArgCountMismatch>,
176 pub trait CreateSubstsForGenericArgsCtxt<'a, 'tcx> {
177 fn args_for_def_id(&mut self, def_id: DefId) -> (Option<&'a GenericArgs<'a>>, bool);
181 param: &ty::GenericParamDef,
182 arg: &GenericArg<'_>,
183 ) -> subst::GenericArg<'tcx>;
187 substs: Option<&[subst::GenericArg<'tcx>]>,
188 param: &ty::GenericParamDef,
190 ) -> subst::GenericArg<'tcx>;
193 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
194 #[tracing::instrument(level = "debug", skip(self))]
195 pub fn ast_region_to_region(
197 lifetime: &hir::Lifetime,
198 def: Option<&ty::GenericParamDef>,
199 ) -> ty::Region<'tcx> {
200 let tcx = self.tcx();
201 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
203 let r = match tcx.named_region(lifetime.hir_id) {
204 Some(rl::Region::Static) => tcx.lifetimes.re_static,
206 Some(rl::Region::LateBound(debruijn, index, def_id, _)) => {
207 let name = lifetime_name(def_id.expect_local());
208 let br = ty::BoundRegion {
209 var: ty::BoundVar::from_u32(index),
210 kind: ty::BrNamed(def_id, name),
212 tcx.mk_region(ty::ReLateBound(debruijn, br))
215 Some(rl::Region::LateBoundAnon(debruijn, index, anon_index)) => {
216 let br = ty::BoundRegion {
217 var: ty::BoundVar::from_u32(index),
218 kind: ty::BrAnon(anon_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 debug!(?lifetime, "unelided lifetime in signature");
242 // This indicates an illegal lifetime
243 // elision. `resolve_lifetime` should have
244 // reported an error in this case -- but if
245 // not, let's error out.
246 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
248 // Supply some dummy value. We don't have an
249 // `re_error`, annoyingly, so use `'static`.
250 tcx.lifetimes.re_static
255 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
260 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
261 /// returns an appropriate set of substitutions for this particular reference to `I`.
262 pub fn ast_path_substs_for_ty(
266 item_segment: &hir::PathSegment<'_>,
267 ) -> SubstsRef<'tcx> {
268 let (substs, _) = self.create_substs_for_ast_path(
274 item_segment.infer_args,
277 let assoc_bindings = self.create_assoc_bindings_for_generic_args(item_segment.args());
279 if let Some(b) = assoc_bindings.first() {
280 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
286 /// Given the type/lifetime/const arguments provided to some path (along with
287 /// an implicit `Self`, if this is a trait reference), returns the complete
288 /// set of substitutions. This may involve applying defaulted type parameters.
289 /// Also returns back constraints on associated types.
294 /// T: std::ops::Index<usize, Output = u32>
295 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
298 /// 1. The `self_ty` here would refer to the type `T`.
299 /// 2. The path in question is the path to the trait `std::ops::Index`,
300 /// which will have been resolved to a `def_id`
301 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
302 /// parameters are returned in the `SubstsRef`, the associated type bindings like
303 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
305 /// Note that the type listing given here is *exactly* what the user provided.
307 /// For (generic) associated types
310 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
313 /// We have the parent substs are the substs for the parent trait:
314 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
315 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
316 /// lists: `[Vec<u8>, u8, 'a]`.
317 #[tracing::instrument(level = "debug", skip(self, span))]
318 fn create_substs_for_ast_path<'a>(
322 parent_substs: &[subst::GenericArg<'tcx>],
323 seg: &hir::PathSegment<'_>,
324 generic_args: &'a hir::GenericArgs<'_>,
326 self_ty: Option<Ty<'tcx>>,
327 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
328 // If the type is parameterized by this region, then replace this
329 // region with the current anon region binding (in other words,
330 // whatever & would get replaced with).
332 let tcx = self.tcx();
333 let generics = tcx.generics_of(def_id);
334 debug!("generics: {:?}", generics);
336 if generics.has_self {
337 if generics.parent.is_some() {
338 // The parent is a trait so it should have at least one subst
339 // for the `Self` type.
340 assert!(!parent_substs.is_empty())
342 // This item (presumably a trait) needs a self-type.
343 assert!(self_ty.is_some());
346 assert!(self_ty.is_none() && parent_substs.is_empty());
349 let arg_count = Self::check_generic_arg_count(
356 GenericArgPosition::Type,
361 // Skip processing if type has no generic parameters.
362 // Traits always have `Self` as a generic parameter, which means they will not return early
363 // here and so associated type bindings will be handled regardless of whether there are any
364 // non-`Self` generic parameters.
365 if generics.params.is_empty() {
366 return (tcx.intern_substs(&[]), arg_count);
369 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
371 struct SubstsForAstPathCtxt<'a, 'tcx> {
372 astconv: &'a (dyn AstConv<'tcx> + 'a),
374 generic_args: &'a GenericArgs<'a>,
376 missing_type_params: Vec<String>,
377 inferred_params: Vec<Span>,
382 impl<'tcx, 'a> SubstsForAstPathCtxt<'tcx, 'a> {
383 fn default_needs_object_self(&mut self, param: &ty::GenericParamDef) -> bool {
384 let tcx = self.astconv.tcx();
385 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
386 if self.is_object && has_default {
387 let default_ty = tcx.at(self.span).type_of(param.def_id);
388 let self_param = tcx.types.self_param;
389 if default_ty.walk(tcx).any(|arg| arg == self_param.into()) {
390 // There is no suitable inference default for a type parameter
391 // that references self, in an object type.
401 impl<'a, 'tcx> CreateSubstsForGenericArgsCtxt<'a, 'tcx> for SubstsForAstPathCtxt<'a, 'tcx> {
402 fn args_for_def_id(&mut self, did: DefId) -> (Option<&'a GenericArgs<'a>>, bool) {
403 if did == self.def_id {
404 (Some(self.generic_args), self.infer_args)
406 // The last component of this tuple is unimportant.
413 param: &ty::GenericParamDef,
414 arg: &GenericArg<'_>,
415 ) -> subst::GenericArg<'tcx> {
416 let tcx = self.astconv.tcx();
418 let mut handle_ty_args = |has_default, ty: &hir::Ty<'_>| {
420 tcx.check_optional_stability(
426 // Default generic parameters may not be marked
427 // with stability attributes, i.e. when the
428 // default parameter was defined at the same time
429 // as the rest of the type. As such, we ignore missing
430 // stability attributes.
434 if let (hir::TyKind::Infer, false) = (&ty.kind, self.astconv.allow_ty_infer()) {
435 self.inferred_params.push(ty.span);
436 tcx.ty_error().into()
438 self.astconv.ast_ty_to_ty(ty).into()
442 match (¶m.kind, arg) {
443 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
444 self.astconv.ast_region_to_region(lt, Some(param)).into()
446 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
447 handle_ty_args(has_default, ty)
449 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Infer(inf)) => {
450 handle_ty_args(has_default, &inf.to_ty())
452 (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
453 ty::Const::from_opt_const_arg_anon_const(
455 ty::WithOptConstParam {
456 did: tcx.hir().local_def_id(ct.value.hir_id),
457 const_param_did: Some(param.def_id),
462 (&GenericParamDefKind::Const { .. }, hir::GenericArg::Infer(inf)) => {
463 let ty = tcx.at(self.span).type_of(param.def_id);
464 if self.astconv.allow_ty_infer() {
465 self.astconv.ct_infer(ty, Some(param), inf.span).into()
467 self.inferred_params.push(inf.span);
468 tcx.const_error(ty).into()
477 substs: Option<&[subst::GenericArg<'tcx>]>,
478 param: &ty::GenericParamDef,
480 ) -> subst::GenericArg<'tcx> {
481 let tcx = self.astconv.tcx();
483 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
484 GenericParamDefKind::Type { has_default, .. } => {
485 if !infer_args && has_default {
486 // No type parameter provided, but a default exists.
488 // If we are converting an object type, then the
489 // `Self` parameter is unknown. However, some of the
490 // other type parameters may reference `Self` in their
491 // defaults. This will lead to an ICE if we are not
493 if self.default_needs_object_self(param) {
494 self.missing_type_params.push(param.name.to_string());
495 tcx.ty_error().into()
497 // This is a default type parameter.
498 let substs = substs.unwrap();
499 if substs.iter().any(|arg| match arg.unpack() {
500 GenericArgKind::Type(ty) => ty.references_error(),
503 // Avoid ICE #86756 when type error recovery goes awry.
504 return tcx.ty_error().into();
509 tcx.at(self.span).type_of(param.def_id).subst_spanned(
517 } else if infer_args {
518 // No type parameters were provided, we can infer all.
519 let param = if !self.default_needs_object_self(param) {
524 self.astconv.ty_infer(param, self.span).into()
526 // We've already errored above about the mismatch.
527 tcx.ty_error().into()
530 GenericParamDefKind::Const { has_default } => {
531 let ty = tcx.at(self.span).type_of(param.def_id);
532 if !infer_args && has_default {
533 tcx.const_param_default(param.def_id)
534 .subst_spanned(tcx, substs.unwrap(), Some(self.span))
538 self.astconv.ct_infer(ty, Some(param), self.span).into()
540 // We've already errored above about the mismatch.
541 tcx.const_error(ty).into()
549 let mut substs_ctx = SubstsForAstPathCtxt {
554 missing_type_params: vec![],
555 inferred_params: vec![],
559 let substs = Self::create_substs_for_generic_args(
569 self.complain_about_missing_type_params(
570 substs_ctx.missing_type_params,
573 generic_args.args.is_empty(),
577 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
578 generics, self_ty, substs
584 fn create_assoc_bindings_for_generic_args<'a>(
586 generic_args: &'a hir::GenericArgs<'_>,
587 ) -> Vec<ConvertedBinding<'a, 'tcx>> {
588 // Convert associated-type bindings or constraints into a separate vector.
589 // Example: Given this:
591 // T: Iterator<Item = u32>
593 // The `T` is passed in as a self-type; the `Item = u32` is
594 // not a "type parameter" of the `Iterator` trait, but rather
595 // a restriction on `<T as Iterator>::Item`, so it is passed
597 let assoc_bindings = generic_args
601 let kind = match binding.kind {
602 hir::TypeBindingKind::Equality { ty } => {
603 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
605 hir::TypeBindingKind::Constraint { bounds } => {
606 ConvertedBindingKind::Constraint(bounds)
610 hir_id: binding.hir_id,
611 item_name: binding.ident,
613 gen_args: binding.gen_args,
622 crate fn create_substs_for_associated_item(
627 item_segment: &hir::PathSegment<'_>,
628 parent_substs: SubstsRef<'tcx>,
629 ) -> SubstsRef<'tcx> {
631 "create_substs_for_associated_item(span: {:?}, item_def_id: {:?}, item_segment: {:?}",
632 span, item_def_id, item_segment
634 if tcx.generics_of(item_def_id).params.is_empty() {
635 self.prohibit_generics(slice::from_ref(item_segment));
639 self.create_substs_for_ast_path(
645 item_segment.infer_args,
652 /// Instantiates the path for the given trait reference, assuming that it's
653 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
654 /// The type _cannot_ be a type other than a trait type.
656 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
657 /// are disallowed. Otherwise, they are pushed onto the vector given.
658 pub fn instantiate_mono_trait_ref(
660 trait_ref: &hir::TraitRef<'_>,
662 ) -> ty::TraitRef<'tcx> {
663 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
665 self.ast_path_to_mono_trait_ref(
667 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
669 trait_ref.path.segments.last().unwrap(),
673 fn instantiate_poly_trait_ref_inner(
677 binding_span: Option<Span>,
678 constness: ty::BoundConstness,
679 bounds: &mut Bounds<'tcx>,
681 trait_ref_span: Span,
683 trait_segment: &hir::PathSegment<'_>,
684 args: &GenericArgs<'_>,
687 ) -> GenericArgCountResult {
688 let (substs, arg_count) = self.create_substs_for_ast_path(
698 let tcx = self.tcx();
699 let bound_vars = tcx.late_bound_vars(hir_id);
702 let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
705 ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
707 debug!(?poly_trait_ref, ?assoc_bindings);
708 bounds.trait_bounds.push((poly_trait_ref, span, constness));
710 let mut dup_bindings = FxHashMap::default();
711 for binding in &assoc_bindings {
712 // Specify type to assert that error was already reported in `Err` case.
713 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
720 binding_span.unwrap_or(binding.span),
722 // Okay to ignore `Err` because of `ErrorReported` (see above).
728 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
729 /// a full trait reference. The resulting trait reference is returned. This may also generate
730 /// auxiliary bounds, which are added to `bounds`.
735 /// poly_trait_ref = Iterator<Item = u32>
739 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
741 /// **A note on binders:** against our usual convention, there is an implied bounder around
742 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
743 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
744 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
745 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
747 #[tracing::instrument(level = "debug", skip(self, span, constness, bounds, speculative))]
748 pub(crate) fn instantiate_poly_trait_ref(
750 trait_ref: &hir::TraitRef<'_>,
752 constness: ty::BoundConstness,
754 bounds: &mut Bounds<'tcx>,
756 ) -> GenericArgCountResult {
757 let hir_id = trait_ref.hir_ref_id;
758 let binding_span = None;
759 let trait_ref_span = trait_ref.path.span;
760 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
761 let trait_segment = trait_ref.path.segments.last().unwrap();
762 let args = trait_segment.args();
763 let infer_args = trait_segment.infer_args;
765 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
766 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
768 self.instantiate_poly_trait_ref_inner(
784 pub(crate) fn instantiate_lang_item_trait_ref(
786 lang_item: hir::LangItem,
789 args: &GenericArgs<'_>,
791 bounds: &mut Bounds<'tcx>,
793 let binding_span = Some(span);
794 let constness = ty::BoundConstness::NotConst;
795 let speculative = false;
796 let trait_ref_span = span;
797 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
798 let trait_segment = &hir::PathSegment::invalid();
799 let infer_args = false;
801 self.instantiate_poly_trait_ref_inner(
817 fn ast_path_to_mono_trait_ref(
822 trait_segment: &hir::PathSegment<'_>,
823 ) -> ty::TraitRef<'tcx> {
825 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
826 let assoc_bindings = self.create_assoc_bindings_for_generic_args(trait_segment.args());
827 if let Some(b) = assoc_bindings.first() {
828 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
830 ty::TraitRef::new(trait_def_id, substs)
833 #[tracing::instrument(level = "debug", skip(self, span))]
834 fn create_substs_for_ast_trait_ref<'a>(
839 trait_segment: &'a hir::PathSegment<'a>,
840 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
841 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
843 self.create_substs_for_ast_path(
848 trait_segment.args(),
849 trait_segment.infer_args,
854 fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
856 .associated_items(trait_def_id)
857 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
861 // Sets `implicitly_sized` to true on `Bounds` if necessary
862 pub(crate) fn add_implicitly_sized<'hir>(
864 bounds: &mut Bounds<'hir>,
865 ast_bounds: &'hir [hir::GenericBound<'hir>],
866 self_ty_where_predicates: Option<(hir::HirId, &'hir [hir::WherePredicate<'hir>])>,
869 let tcx = self.tcx();
871 // Try to find an unbound in bounds.
872 let mut unbound = None;
873 let mut search_bounds = |ast_bounds: &'hir [hir::GenericBound<'hir>]| {
874 for ab in ast_bounds {
875 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
876 if unbound.is_none() {
877 unbound = Some(&ptr.trait_ref);
879 tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
884 search_bounds(ast_bounds);
885 if let Some((self_ty, where_clause)) = self_ty_where_predicates {
886 let self_ty_def_id = tcx.hir().local_def_id(self_ty).to_def_id();
887 for clause in where_clause {
888 if let hir::WherePredicate::BoundPredicate(pred) = clause {
889 match pred.bounded_ty.kind {
890 hir::TyKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
891 Res::Def(DefKind::TyParam, def_id) if def_id == self_ty_def_id => {}
896 search_bounds(pred.bounds);
901 let sized_def_id = tcx.lang_items().require(LangItem::Sized);
902 match (&sized_def_id, unbound) {
903 (Ok(sized_def_id), Some(tpb))
904 if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) =>
906 // There was in fact a `?Sized` bound, return without doing anything
910 // There was a `?Trait` bound, but it was not `?Sized`; warn.
913 "default bound relaxed for a type parameter, but \
914 this does nothing because the given bound is not \
915 a default; only `?Sized` is supported",
917 // Otherwise, add implicitly sized if `Sized` is available.
920 // There was no `?Sized` bound; add implicitly sized if `Sized` is available.
923 if sized_def_id.is_err() {
924 // No lang item for `Sized`, so we can't add it as a bound.
927 bounds.implicitly_sized = Some(span);
930 /// This helper takes a *converted* parameter type (`param_ty`)
931 /// and an *unconverted* list of bounds:
935 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
937 /// `param_ty`, in ty form
940 /// It adds these `ast_bounds` into the `bounds` structure.
942 /// **A note on binders:** there is an implied binder around
943 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
944 /// for more details.
945 #[tracing::instrument(level = "debug", skip(self, ast_bounds, bounds))]
946 pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>(
950 bounds: &mut Bounds<'tcx>,
951 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
953 for ast_bound in ast_bounds {
955 hir::GenericBound::Trait(poly_trait_ref, modifier) => {
956 let constness = match modifier {
957 hir::TraitBoundModifier::MaybeConst => ty::BoundConstness::ConstIfConst,
958 hir::TraitBoundModifier::None => ty::BoundConstness::NotConst,
959 hir::TraitBoundModifier::Maybe => continue,
962 let _ = self.instantiate_poly_trait_ref(
963 &poly_trait_ref.trait_ref,
971 &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
972 self.instantiate_lang_item_trait_ref(
973 lang_item, span, hir_id, args, param_ty, bounds,
976 hir::GenericBound::Outlives(lifetime) => {
977 let region = self.ast_region_to_region(lifetime, None);
980 .push((ty::Binder::bind_with_vars(region, bound_vars), lifetime.span));
986 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
987 /// The self-type for the bounds is given by `param_ty`.
992 /// fn foo<T: Bar + Baz>() { }
993 /// ^ ^^^^^^^^^ ast_bounds
997 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
998 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
999 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1001 /// `span` should be the declaration size of the parameter.
1002 pub(crate) fn compute_bounds(
1005 ast_bounds: &[hir::GenericBound<'_>],
1007 self.compute_bounds_inner(param_ty, ast_bounds)
1010 /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
1011 /// named `assoc_name` into ty::Bounds. Ignore the rest.
1012 pub(crate) fn compute_bounds_that_match_assoc_type(
1015 ast_bounds: &[hir::GenericBound<'_>],
1018 let mut result = Vec::new();
1020 for ast_bound in ast_bounds {
1021 if let Some(trait_ref) = ast_bound.trait_ref() {
1022 if let Some(trait_did) = trait_ref.trait_def_id() {
1023 if self.tcx().trait_may_define_assoc_type(trait_did, assoc_name) {
1024 result.push(ast_bound.clone());
1030 self.compute_bounds_inner(param_ty, &result)
1033 fn compute_bounds_inner(
1036 ast_bounds: &[hir::GenericBound<'_>],
1038 let mut bounds = Bounds::default();
1040 self.add_bounds(param_ty, ast_bounds.iter(), &mut bounds, ty::List::empty());
1045 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1048 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1049 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1050 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1051 #[tracing::instrument(
1053 skip(self, bounds, speculative, dup_bindings, path_span)
1055 fn add_predicates_for_ast_type_binding(
1057 hir_ref_id: hir::HirId,
1058 trait_ref: ty::PolyTraitRef<'tcx>,
1059 binding: &ConvertedBinding<'_, 'tcx>,
1060 bounds: &mut Bounds<'tcx>,
1062 dup_bindings: &mut FxHashMap<DefId, Span>,
1064 ) -> Result<(), ErrorReported> {
1065 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1066 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1067 // subtle in the event that `T` is defined in a supertrait of
1068 // `SomeTrait`, because in that case we need to upcast.
1070 // That is, consider this case:
1073 // trait SubTrait: SuperTrait<i32> { }
1074 // trait SuperTrait<A> { type T; }
1076 // ... B: SubTrait<T = foo> ...
1079 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
1081 let tcx = self.tcx();
1084 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1085 // Simple case: X is defined in the current trait.
1088 // Otherwise, we have to walk through the supertraits to find
1090 self.one_bound_for_assoc_type(
1091 || traits::supertraits(tcx, trait_ref),
1092 || trait_ref.print_only_trait_path().to_string(),
1095 || match binding.kind {
1096 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1102 let (assoc_ident, def_scope) =
1103 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1105 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1106 // of calling `filter_by_name_and_kind`.
1108 .associated_items(candidate.def_id())
1109 .filter_by_name_unhygienic(assoc_ident.name)
1111 i.kind == ty::AssocKind::Type && i.ident.normalize_to_macros_2_0() == assoc_ident
1113 .expect("missing associated type");
1115 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1119 &format!("associated type `{}` is private", binding.item_name),
1121 .span_label(binding.span, "private associated type")
1124 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span, None);
1128 .entry(assoc_ty.def_id)
1129 .and_modify(|prev_span| {
1130 self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
1132 prev_span: *prev_span,
1133 item_name: binding.item_name,
1134 def_path: tcx.def_path_str(assoc_ty.container.id()),
1137 .or_insert(binding.span);
1140 // Include substitutions for generic parameters of associated types
1141 let projection_ty = candidate.map_bound(|trait_ref| {
1142 let ident = Ident::new(assoc_ty.ident.name, binding.item_name.span);
1143 let item_segment = hir::PathSegment {
1145 hir_id: Some(binding.hir_id),
1147 args: Some(binding.gen_args),
1151 let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
1160 "add_predicates_for_ast_type_binding: substs for trait-ref and assoc_item: {:?}",
1161 substs_trait_ref_and_assoc_item
1165 item_def_id: assoc_ty.def_id,
1166 substs: substs_trait_ref_and_assoc_item,
1171 // Find any late-bound regions declared in `ty` that are not
1172 // declared in the trait-ref or assoc_ty. These are not well-formed.
1176 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1177 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1178 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1179 let late_bound_in_trait_ref =
1180 tcx.collect_constrained_late_bound_regions(&projection_ty);
1181 let late_bound_in_ty =
1182 tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty));
1183 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1184 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1186 // FIXME: point at the type params that don't have appropriate lifetimes:
1187 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1188 // ---- ---- ^^^^^^^
1189 self.validate_late_bound_regions(
1190 late_bound_in_trait_ref,
1197 "binding for associated type `{}` references {}, \
1198 which does not appear in the trait input types",
1207 match binding.kind {
1208 ConvertedBindingKind::Equality(ty) => {
1209 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1210 // the "projection predicate" for:
1212 // `<T as Iterator>::Item = u32`
1213 bounds.projection_bounds.push((
1214 projection_ty.map_bound(|projection_ty| {
1216 "add_predicates_for_ast_type_binding: projection_ty {:?}, substs: {:?}",
1217 projection_ty, projection_ty.substs
1219 ty::ProjectionPredicate { projection_ty, ty }
1224 ConvertedBindingKind::Constraint(ast_bounds) => {
1225 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1227 // `<T as Iterator>::Item: Debug`
1229 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1230 // parameter to have a skipped binder.
1231 let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
1232 self.add_bounds(param_ty, ast_bounds.iter(), bounds, candidate.bound_vars());
1242 item_segment: &hir::PathSegment<'_>,
1244 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1245 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1248 fn conv_object_ty_poly_trait_ref(
1251 trait_bounds: &[hir::PolyTraitRef<'_>],
1252 lifetime: &hir::Lifetime,
1255 let tcx = self.tcx();
1257 let mut bounds = Bounds::default();
1258 let mut potential_assoc_types = Vec::new();
1259 let dummy_self = self.tcx().types.trait_object_dummy_self;
1260 for trait_bound in trait_bounds.iter().rev() {
1261 if let GenericArgCountResult {
1263 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1265 } = self.instantiate_poly_trait_ref(
1266 &trait_bound.trait_ref,
1268 ty::BoundConstness::NotConst,
1273 potential_assoc_types.extend(cur_potential_assoc_types);
1277 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1278 // is used and no 'maybe' bounds are used.
1279 let expanded_traits =
1280 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1281 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1282 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1283 if regular_traits.len() > 1 {
1284 let first_trait = ®ular_traits[0];
1285 let additional_trait = ®ular_traits[1];
1286 let mut err = struct_span_err!(
1288 additional_trait.bottom().1,
1290 "only auto traits can be used as additional traits in a trait object"
1292 additional_trait.label_with_exp_info(
1294 "additional non-auto trait",
1297 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1299 "consider creating a new trait with all of these as supertraits and using that \
1300 trait here instead: `trait NewTrait: {} {{}}`",
1303 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1304 .collect::<Vec<_>>()
1308 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1309 for more information on them, visit \
1310 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1315 if regular_traits.is_empty() && auto_traits.is_empty() {
1316 tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span });
1317 return tcx.ty_error();
1320 // Check that there are no gross object safety violations;
1321 // most importantly, that the supertraits don't contain `Self`,
1323 for item in ®ular_traits {
1324 let object_safety_violations =
1325 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1326 if !object_safety_violations.is_empty() {
1327 report_object_safety_error(
1330 item.trait_ref().def_id(),
1331 &object_safety_violations,
1334 return tcx.ty_error();
1338 // Use a `BTreeSet` to keep output in a more consistent order.
1339 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1341 let regular_traits_refs_spans = bounds
1344 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1346 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1347 assert_eq!(constness, ty::BoundConstness::NotConst);
1349 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1351 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1352 obligation.predicate
1355 let bound_predicate = obligation.predicate.kind();
1356 match bound_predicate.skip_binder() {
1357 ty::PredicateKind::Trait(pred) => {
1358 let pred = bound_predicate.rebind(pred);
1359 associated_types.entry(span).or_default().extend(
1360 tcx.associated_items(pred.def_id())
1361 .in_definition_order()
1362 .filter(|item| item.kind == ty::AssocKind::Type)
1363 .map(|item| item.def_id),
1366 ty::PredicateKind::Projection(pred) => {
1367 let pred = bound_predicate.rebind(pred);
1368 // A `Self` within the original bound will be substituted with a
1369 // `trait_object_dummy_self`, so check for that.
1370 let references_self =
1371 pred.skip_binder().ty.walk(tcx).any(|arg| arg == dummy_self.into());
1373 // If the projection output contains `Self`, force the user to
1374 // elaborate it explicitly to avoid a lot of complexity.
1376 // The "classicaly useful" case is the following:
1378 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1383 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1384 // but actually supporting that would "expand" to an infinitely-long type
1385 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1387 // Instead, we force the user to write
1388 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1389 // the discussion in #56288 for alternatives.
1390 if !references_self {
1391 // Include projections defined on supertraits.
1392 bounds.projection_bounds.push((pred, span));
1400 for (projection_bound, _) in &bounds.projection_bounds {
1401 for def_ids in associated_types.values_mut() {
1402 def_ids.remove(&projection_bound.projection_def_id());
1406 self.complain_about_missing_associated_types(
1408 potential_assoc_types,
1412 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1413 // `dyn Trait + Send`.
1414 // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
1416 let mut duplicates = FxHashSet::default();
1417 auto_traits.retain(|i| duplicates.insert(i.trait_ref().def_id()));
1418 debug!("regular_traits: {:?}", regular_traits);
1419 debug!("auto_traits: {:?}", auto_traits);
1421 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1422 let existential_trait_refs = regular_traits.iter().map(|i| {
1423 i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
1424 if trait_ref.self_ty() != dummy_self {
1425 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1426 // which picks up non-supertraits where clauses - but also, the object safety
1427 // completely ignores trait aliases, which could be object safety hazards. We
1428 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1429 // disabled. (#66420)
1430 tcx.sess.delay_span_bug(
1433 "trait_ref_to_existential called on {:?} with non-dummy Self",
1438 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1441 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1442 bound.map_bound(|b| {
1443 if b.projection_ty.self_ty() != dummy_self {
1444 tcx.sess.delay_span_bug(
1446 &format!("trait_ref_to_existential called on {:?} with non-dummy Self", b),
1449 ty::ExistentialProjection::erase_self_ty(tcx, b)
1453 let regular_trait_predicates = existential_trait_refs
1454 .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));
1455 let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
1456 ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
1458 // N.b. principal, projections, auto traits
1459 // FIXME: This is actually wrong with multiple principals in regards to symbol mangling
1460 let mut v = regular_trait_predicates
1462 existential_projections.map(|x| x.map_bound(ty::ExistentialPredicate::Projection)),
1464 .chain(auto_trait_predicates)
1465 .collect::<SmallVec<[_; 8]>>();
1466 v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
1468 let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
1470 // Use explicitly-specified region bound.
1471 let region_bound = if !lifetime.is_elided() {
1472 self.ast_region_to_region(lifetime, None)
1474 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1475 if tcx.named_region(lifetime.hir_id).is_some() {
1476 self.ast_region_to_region(lifetime, None)
1478 self.re_infer(None, span).unwrap_or_else(|| {
1479 let mut err = struct_span_err!(
1483 "the lifetime bound for this object type cannot be deduced \
1484 from context; please supply an explicit bound"
1487 // We will have already emitted an error E0106 complaining about a
1488 // missing named lifetime in `&dyn Trait`, so we elide this one.
1493 tcx.lifetimes.re_static
1498 debug!("region_bound: {:?}", region_bound);
1500 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1501 debug!("trait_object_type: {:?}", ty);
1505 fn report_ambiguous_associated_type(
1512 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1513 if let (true, Ok(snippet)) = (
1516 .confused_type_with_std_module
1518 .any(|full_span| full_span.contains(span)),
1519 self.tcx().sess.source_map().span_to_snippet(span),
1521 err.span_suggestion(
1523 "you are looking for the module in `std`, not the primitive type",
1524 format!("std::{}", snippet),
1525 Applicability::MachineApplicable,
1528 err.span_suggestion(
1530 "use fully-qualified syntax",
1531 format!("<{} as {}>::{}", type_str, trait_str, name),
1532 Applicability::HasPlaceholders,
1538 // Search for a bound on a type parameter which includes the associated item
1539 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1540 // This function will fail if there are no suitable bounds or there is
1542 fn find_bound_for_assoc_item(
1544 ty_param_def_id: LocalDefId,
1547 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1548 let tcx = self.tcx();
1551 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1552 ty_param_def_id, assoc_name, span,
1555 let predicates = &self
1556 .get_type_parameter_bounds(span, ty_param_def_id.to_def_id(), assoc_name)
1559 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1561 let param_hir_id = tcx.hir().local_def_id_to_hir_id(ty_param_def_id);
1562 let param_name = tcx.hir().ty_param_name(param_hir_id);
1563 self.one_bound_for_assoc_type(
1565 traits::transitive_bounds_that_define_assoc_type(
1567 predicates.iter().filter_map(|(p, _)| {
1568 Some(p.to_opt_poly_trait_pred()?.map_bound(|t| t.trait_ref))
1573 || param_name.to_string(),
1580 // Checks that `bounds` contains exactly one element and reports appropriate
1581 // errors otherwise.
1582 fn one_bound_for_assoc_type<I>(
1584 all_candidates: impl Fn() -> I,
1585 ty_param_name: impl Fn() -> String,
1588 is_equality: impl Fn() -> Option<String>,
1589 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1591 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1593 let mut matching_candidates = all_candidates()
1594 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1596 let bound = match matching_candidates.next() {
1597 Some(bound) => bound,
1599 self.complain_about_assoc_type_not_found(
1605 return Err(ErrorReported);
1609 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1611 if let Some(bound2) = matching_candidates.next() {
1612 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1614 let is_equality = is_equality();
1615 let bounds = IntoIterator::into_iter([bound, bound2]).chain(matching_candidates);
1616 let mut err = if is_equality.is_some() {
1617 // More specific Error Index entry.
1622 "ambiguous associated type `{}` in bounds of `{}`",
1631 "ambiguous associated type `{}` in bounds of `{}`",
1636 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1638 let mut where_bounds = vec![];
1639 for bound in bounds {
1640 let bound_id = bound.def_id();
1641 let bound_span = self
1643 .associated_items(bound_id)
1644 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1645 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1647 if let Some(bound_span) = bound_span {
1651 "ambiguous `{}` from `{}`",
1653 bound.print_only_trait_path(),
1656 if let Some(constraint) = &is_equality {
1657 where_bounds.push(format!(
1658 " T: {trait}::{assoc} = {constraint}",
1659 trait=bound.print_only_trait_path(),
1661 constraint=constraint,
1664 err.span_suggestion_verbose(
1665 span.with_hi(assoc_name.span.lo()),
1666 "use fully qualified syntax to disambiguate",
1670 bound.print_only_trait_path(),
1672 Applicability::MaybeIncorrect,
1677 "associated type `{}` could derive from `{}`",
1679 bound.print_only_trait_path(),
1683 if !where_bounds.is_empty() {
1685 "consider introducing a new type parameter `T` and adding `where` constraints:\
1686 \n where\n T: {},\n{}",
1688 where_bounds.join(",\n"),
1692 if !where_bounds.is_empty() {
1693 return Err(ErrorReported);
1699 // Create a type from a path to an associated type.
1700 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1701 // and item_segment is the path segment for `D`. We return a type and a def for
1703 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1704 // parameter or `Self`.
1705 // NOTE: When this function starts resolving `Trait::AssocTy` successfully
1706 // it should also start reportint the `BARE_TRAIT_OBJECTS` lint.
1707 pub fn associated_path_to_ty(
1709 hir_ref_id: hir::HirId,
1713 assoc_segment: &hir::PathSegment<'_>,
1714 permit_variants: bool,
1715 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
1716 let tcx = self.tcx();
1717 let assoc_ident = assoc_segment.ident;
1719 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1721 // Check if we have an enum variant.
1722 let mut variant_resolution = None;
1723 if let ty::Adt(adt_def, _) = qself_ty.kind() {
1724 if adt_def.is_enum() {
1725 let variant_def = adt_def
1728 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
1729 if let Some(variant_def) = variant_def {
1730 if permit_variants {
1731 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span, None);
1732 self.prohibit_generics(slice::from_ref(assoc_segment));
1733 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1735 variant_resolution = Some(variant_def.def_id);
1741 // Find the type of the associated item, and the trait where the associated
1742 // item is declared.
1743 let bound = match (&qself_ty.kind(), qself_res) {
1744 (_, Res::SelfTy(Some(_), Some((impl_def_id, _)))) => {
1745 // `Self` in an impl of a trait -- we have a concrete self type and a
1747 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1748 Some(trait_ref) => trait_ref,
1750 // A cycle error occurred, most likely.
1751 return Err(ErrorReported);
1755 self.one_bound_for_assoc_type(
1756 || traits::supertraits(tcx, ty::Binder::dummy(trait_ref)),
1757 || "Self".to_string(),
1765 Res::SelfTy(Some(param_did), None) | Res::Def(DefKind::TyParam, param_did),
1766 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
1768 if variant_resolution.is_some() {
1769 // Variant in type position
1770 let msg = format!("expected type, found variant `{}`", assoc_ident);
1771 tcx.sess.span_err(span, &msg);
1772 } else if qself_ty.is_enum() {
1773 let mut err = struct_span_err!(
1777 "no variant named `{}` found for enum `{}`",
1782 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1783 if let Some(suggested_name) = find_best_match_for_name(
1787 .map(|variant| variant.ident.name)
1788 .collect::<Vec<Symbol>>(),
1792 err.span_suggestion(
1794 "there is a variant with a similar name",
1795 suggested_name.to_string(),
1796 Applicability::MaybeIncorrect,
1801 format!("variant not found in `{}`", qself_ty),
1805 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
1806 let sp = tcx.sess.source_map().guess_head_span(sp);
1807 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1811 } else if !qself_ty.references_error() {
1812 // Don't print `TyErr` to the user.
1813 self.report_ambiguous_associated_type(
1815 &qself_ty.to_string(),
1820 return Err(ErrorReported);
1824 let trait_did = bound.def_id();
1825 let (assoc_ident, def_scope) =
1826 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1828 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1829 // of calling `filter_by_name_and_kind`.
1831 .associated_items(trait_did)
1832 .in_definition_order()
1834 i.kind.namespace() == Namespace::TypeNS
1835 && i.ident.normalize_to_macros_2_0() == assoc_ident
1837 .expect("missing associated type");
1839 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
1840 let ty = self.normalize_ty(span, ty);
1842 let kind = DefKind::AssocTy;
1843 if !item.vis.is_accessible_from(def_scope, tcx) {
1844 let kind = kind.descr(item.def_id);
1845 let msg = format!("{} `{}` is private", kind, assoc_ident);
1847 .struct_span_err(span, &msg)
1848 .span_label(span, &format!("private {}", kind))
1851 tcx.check_stability(item.def_id, Some(hir_ref_id), span, None);
1853 if let Some(variant_def_id) = variant_resolution {
1854 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
1855 let mut err = lint.build("ambiguous associated item");
1856 let mut could_refer_to = |kind: DefKind, def_id, also| {
1857 let note_msg = format!(
1858 "`{}` could{} refer to the {} defined here",
1863 err.span_note(tcx.def_span(def_id), ¬e_msg);
1866 could_refer_to(DefKind::Variant, variant_def_id, "");
1867 could_refer_to(kind, item.def_id, " also");
1869 err.span_suggestion(
1871 "use fully-qualified syntax",
1872 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
1873 Applicability::MachineApplicable,
1879 Ok((ty, kind, item.def_id))
1885 opt_self_ty: Option<Ty<'tcx>>,
1887 trait_segment: &hir::PathSegment<'_>,
1888 item_segment: &hir::PathSegment<'_>,
1890 let tcx = self.tcx();
1892 let trait_def_id = tcx.parent(item_def_id).unwrap();
1894 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
1896 let Some(self_ty) = opt_self_ty else {
1897 let path_str = tcx.def_path_str(trait_def_id);
1899 let def_id = self.item_def_id();
1901 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
1903 let parent_def_id = def_id
1904 .and_then(|def_id| {
1905 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
1907 .map(|hir_id| tcx.hir().get_parent_did(hir_id).to_def_id());
1909 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
1911 // If the trait in segment is the same as the trait defining the item,
1912 // use the `<Self as ..>` syntax in the error.
1913 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
1914 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
1916 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
1922 self.report_ambiguous_associated_type(
1926 item_segment.ident.name,
1928 return tcx.ty_error();
1931 debug!("qpath_to_ty: self_type={:?}", self_ty);
1933 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
1935 let item_substs = self.create_substs_for_associated_item(
1943 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1945 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
1948 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
1952 let mut has_err = false;
1953 for segment in segments {
1954 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1955 for arg in segment.args().args {
1956 let (span, kind) = match arg {
1957 hir::GenericArg::Lifetime(lt) => {
1963 (lt.span, "lifetime")
1965 hir::GenericArg::Type(ty) => {
1973 hir::GenericArg::Const(ct) => {
1981 hir::GenericArg::Infer(inf) => {
1987 (inf.span, "generic")
1990 let mut err = struct_span_err!(
1994 "{} arguments are not allowed for this type",
1997 err.span_label(span, format!("{} argument not allowed", kind));
1999 if err_for_lt && err_for_ty && err_for_ct {
2004 // Only emit the first error to avoid overloading the user with error messages.
2005 if let [binding, ..] = segment.args().bindings {
2007 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2013 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2014 pub fn def_ids_for_value_path_segments(
2016 segments: &[hir::PathSegment<'_>],
2017 self_ty: Option<Ty<'tcx>>,
2021 // We need to extract the type parameters supplied by the user in
2022 // the path `path`. Due to the current setup, this is a bit of a
2023 // tricky-process; the problem is that resolve only tells us the
2024 // end-point of the path resolution, and not the intermediate steps.
2025 // Luckily, we can (at least for now) deduce the intermediate steps
2026 // just from the end-point.
2028 // There are basically five cases to consider:
2030 // 1. Reference to a constructor of a struct:
2032 // struct Foo<T>(...)
2034 // In this case, the parameters are declared in the type space.
2036 // 2. Reference to a constructor of an enum variant:
2038 // enum E<T> { Foo(...) }
2040 // In this case, the parameters are defined in the type space,
2041 // but may be specified either on the type or the variant.
2043 // 3. Reference to a fn item or a free constant:
2047 // In this case, the path will again always have the form
2048 // `a::b::foo::<T>` where only the final segment should have
2049 // type parameters. However, in this case, those parameters are
2050 // declared on a value, and hence are in the `FnSpace`.
2052 // 4. Reference to a method or an associated constant:
2054 // impl<A> SomeStruct<A> {
2058 // Here we can have a path like
2059 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2060 // may appear in two places. The penultimate segment,
2061 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2062 // final segment, `foo::<B>` contains parameters in fn space.
2064 // The first step then is to categorize the segments appropriately.
2066 let tcx = self.tcx();
2068 assert!(!segments.is_empty());
2069 let last = segments.len() - 1;
2071 let mut path_segs = vec![];
2074 // Case 1. Reference to a struct constructor.
2075 DefKind::Ctor(CtorOf::Struct, ..) => {
2076 // Everything but the final segment should have no
2077 // parameters at all.
2078 let generics = tcx.generics_of(def_id);
2079 // Variant and struct constructors use the
2080 // generics of their parent type definition.
2081 let generics_def_id = generics.parent.unwrap_or(def_id);
2082 path_segs.push(PathSeg(generics_def_id, last));
2085 // Case 2. Reference to a variant constructor.
2086 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2087 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2088 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2089 debug_assert!(adt_def.is_enum());
2091 } else if last >= 1 && segments[last - 1].args.is_some() {
2092 // Everything but the penultimate segment should have no
2093 // parameters at all.
2094 let mut def_id = def_id;
2096 // `DefKind::Ctor` -> `DefKind::Variant`
2097 if let DefKind::Ctor(..) = kind {
2098 def_id = tcx.parent(def_id).unwrap()
2101 // `DefKind::Variant` -> `DefKind::Enum`
2102 let enum_def_id = tcx.parent(def_id).unwrap();
2103 (enum_def_id, last - 1)
2105 // FIXME: lint here recommending `Enum::<...>::Variant` form
2106 // instead of `Enum::Variant::<...>` form.
2108 // Everything but the final segment should have no
2109 // parameters at all.
2110 let generics = tcx.generics_of(def_id);
2111 // Variant and struct constructors use the
2112 // generics of their parent type definition.
2113 (generics.parent.unwrap_or(def_id), last)
2115 path_segs.push(PathSeg(generics_def_id, index));
2118 // Case 3. Reference to a top-level value.
2119 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2120 path_segs.push(PathSeg(def_id, last));
2123 // Case 4. Reference to a method or associated const.
2124 DefKind::AssocFn | DefKind::AssocConst => {
2125 if segments.len() >= 2 {
2126 let generics = tcx.generics_of(def_id);
2127 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2129 path_segs.push(PathSeg(def_id, last));
2132 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2135 debug!("path_segs = {:?}", path_segs);
2140 // Check a type `Path` and convert it to a `Ty`.
2143 opt_self_ty: Option<Ty<'tcx>>,
2144 path: &hir::Path<'_>,
2145 permit_variants: bool,
2147 let tcx = self.tcx();
2150 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2151 path.res, opt_self_ty, path.segments
2154 let span = path.span;
2156 Res::Def(DefKind::OpaqueTy, did) => {
2157 // Check for desugared `impl Trait`.
2158 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2159 let item_segment = path.segments.split_last().unwrap();
2160 self.prohibit_generics(item_segment.1);
2161 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2162 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2169 | DefKind::ForeignTy,
2172 assert_eq!(opt_self_ty, None);
2173 self.prohibit_generics(path.segments.split_last().unwrap().1);
2174 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2176 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2177 // Convert "variant type" as if it were a real type.
2178 // The resulting `Ty` is type of the variant's enum for now.
2179 assert_eq!(opt_self_ty, None);
2182 self.def_ids_for_value_path_segments(path.segments, None, kind, def_id);
2183 let generic_segs: FxHashSet<_> =
2184 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2185 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2187 if !generic_segs.contains(&index) { Some(seg) } else { None }
2191 let PathSeg(def_id, index) = path_segs.last().unwrap();
2192 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2194 Res::Def(DefKind::TyParam, def_id) => {
2195 assert_eq!(opt_self_ty, None);
2196 self.prohibit_generics(path.segments);
2198 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2199 let item_id = tcx.hir().get_parent_node(hir_id);
2200 let item_def_id = tcx.hir().local_def_id(item_id);
2201 let generics = tcx.generics_of(item_def_id);
2202 let index = generics.param_def_id_to_index[&def_id];
2203 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2205 Res::SelfTy(Some(_), None) => {
2206 // `Self` in trait or type alias.
2207 assert_eq!(opt_self_ty, None);
2208 self.prohibit_generics(path.segments);
2209 tcx.types.self_param
2211 Res::SelfTy(_, Some((def_id, forbid_generic))) => {
2212 // `Self` in impl (we know the concrete type).
2213 assert_eq!(opt_self_ty, None);
2214 self.prohibit_generics(path.segments);
2215 // Try to evaluate any array length constants.
2216 let normalized_ty = self.normalize_ty(span, tcx.at(span).type_of(def_id));
2217 if forbid_generic && normalized_ty.definitely_needs_subst(tcx) {
2218 let mut err = tcx.sess.struct_span_err(
2220 "generic `Self` types are currently not permitted in anonymous constants",
2222 if let Some(hir::Node::Item(&hir::Item {
2223 kind: hir::ItemKind::Impl(ref impl_),
2225 })) = tcx.hir().get_if_local(def_id)
2227 err.span_note(impl_.self_ty.span, "not a concrete type");
2235 Res::Def(DefKind::AssocTy, def_id) => {
2236 debug_assert!(path.segments.len() >= 2);
2237 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2242 &path.segments[path.segments.len() - 2],
2243 path.segments.last().unwrap(),
2246 Res::PrimTy(prim_ty) => {
2247 assert_eq!(opt_self_ty, None);
2248 self.prohibit_generics(path.segments);
2250 hir::PrimTy::Bool => tcx.types.bool,
2251 hir::PrimTy::Char => tcx.types.char,
2252 hir::PrimTy::Int(it) => tcx.mk_mach_int(ty::int_ty(it)),
2253 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(ty::uint_ty(uit)),
2254 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ty::float_ty(ft)),
2255 hir::PrimTy::Str => tcx.types.str_,
2259 self.set_tainted_by_errors();
2260 self.tcx().ty_error()
2262 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2266 /// Parses the programmer's textual representation of a type into our
2267 /// internal notion of a type.
2268 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2269 self.ast_ty_to_ty_inner(ast_ty, false)
2272 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2273 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2274 #[tracing::instrument(level = "debug", skip(self))]
2275 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool) -> Ty<'tcx> {
2276 let tcx = self.tcx();
2278 let result_ty = match ast_ty.kind {
2279 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
2280 hir::TyKind::Ptr(ref mt) => {
2281 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
2283 hir::TyKind::Rptr(ref region, ref mt) => {
2284 let r = self.ast_region_to_region(region, None);
2286 let t = self.ast_ty_to_ty_inner(mt.ty, true);
2287 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2289 hir::TyKind::Never => tcx.types.never,
2290 hir::TyKind::Tup(fields) => tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(t))),
2291 hir::TyKind::BareFn(bf) => {
2292 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
2294 tcx.mk_fn_ptr(self.ty_of_fn(
2299 &hir::Generics::empty(),
2304 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
2305 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed)
2307 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2308 debug!(?maybe_qself, ?path);
2309 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2310 self.res_to_ty(opt_self_ty, path, false)
2312 hir::TyKind::OpaqueDef(item_id, lifetimes) => {
2313 let opaque_ty = tcx.hir().item(item_id);
2314 let def_id = item_id.def_id.to_def_id();
2316 match opaque_ty.kind {
2317 hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => self
2318 .impl_trait_ty_to_ty(
2323 hir::OpaqueTyOrigin::FnReturn(..)
2324 | hir::OpaqueTyOrigin::AsyncFn(..)
2327 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2330 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2331 debug!(?qself, ?segment);
2332 let ty = self.ast_ty_to_ty(qself);
2334 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, path)) = qself.kind {
2339 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2340 .map(|(ty, _, _)| ty)
2341 .unwrap_or_else(|_| tcx.ty_error())
2343 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
2344 let def_id = tcx.require_lang_item(lang_item, Some(span));
2345 let (substs, _) = self.create_substs_for_ast_path(
2349 &hir::PathSegment::invalid(),
2350 &GenericArgs::none(),
2354 self.normalize_ty(span, tcx.at(span).type_of(def_id).subst(tcx, substs))
2356 hir::TyKind::Array(ref ty, ref length) => {
2357 let length_def_id = tcx.hir().local_def_id(length.hir_id);
2358 let length = ty::Const::from_anon_const(tcx, length_def_id);
2359 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(ty), length));
2360 self.normalize_ty(ast_ty.span, array_ty)
2362 hir::TyKind::Typeof(ref e) => {
2363 tcx.sess.emit_err(TypeofReservedKeywordUsed { span: ast_ty.span });
2364 tcx.type_of(tcx.hir().local_def_id(e.hir_id))
2366 hir::TyKind::Infer => {
2367 // Infer also appears as the type of arguments or return
2368 // values in an ExprKind::Closure, or as
2369 // the type of local variables. Both of these cases are
2370 // handled specially and will not descend into this routine.
2371 self.ty_infer(None, ast_ty.span)
2373 hir::TyKind::Err => tcx.ty_error(),
2378 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2382 fn impl_trait_ty_to_ty(
2385 lifetimes: &[hir::GenericArg<'_>],
2386 replace_parent_lifetimes: bool,
2388 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2389 let tcx = self.tcx();
2391 let generics = tcx.generics_of(def_id);
2393 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2394 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2395 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2396 // Our own parameters are the resolved lifetimes.
2397 if let GenericParamDefKind::Lifetime = param.kind {
2398 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2399 self.ast_region_to_region(lifetime, None).into()
2408 // For RPIT (return position impl trait), only lifetimes
2409 // mentioned in the impl Trait predicate are captured by
2410 // the opaque type, so the lifetime parameters from the
2411 // parent item need to be replaced with `'static`.
2413 // For `impl Trait` in the types of statics, constants,
2414 // locals and type aliases. These capture all parent
2415 // lifetimes, so they can use their identity subst.
2416 GenericParamDefKind::Lifetime if replace_parent_lifetimes => {
2417 tcx.lifetimes.re_static.into()
2419 _ => tcx.mk_param_from_def(param),
2423 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2425 let ty = tcx.mk_opaque(def_id, substs);
2426 debug!("impl_trait_ty_to_ty: {}", ty);
2430 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2432 hir::TyKind::Infer if expected_ty.is_some() => {
2433 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2434 expected_ty.unwrap()
2436 _ => self.ast_ty_to_ty(ty),
2443 unsafety: hir::Unsafety,
2445 decl: &hir::FnDecl<'_>,
2446 generics: &hir::Generics<'_>,
2447 ident_span: Option<Span>,
2448 hir_ty: Option<&hir::Ty<'_>>,
2449 ) -> ty::PolyFnSig<'tcx> {
2452 let tcx = self.tcx();
2453 let bound_vars = tcx.late_bound_vars(hir_id);
2454 debug!(?bound_vars);
2456 // We proactively collect all the inferred type params to emit a single error per fn def.
2457 let mut visitor = PlaceholderHirTyCollector::default();
2458 for ty in decl.inputs {
2459 visitor.visit_ty(ty);
2461 walk_generics(&mut visitor, generics);
2463 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2464 let output_ty = match decl.output {
2465 hir::FnRetTy::Return(output) => {
2466 visitor.visit_ty(output);
2467 self.ast_ty_to_ty(output)
2469 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2472 debug!("ty_of_fn: output_ty={:?}", output_ty);
2474 let fn_ty = tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi);
2475 let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
2477 if !self.allow_ty_infer() {
2478 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2479 // only want to emit an error complaining about them if infer types (`_`) are not
2480 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2481 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2483 crate::collect::placeholder_type_error(
2485 ident_span.map(|sp| sp.shrink_to_hi()),
2494 // Find any late-bound regions declared in return type that do
2495 // not appear in the arguments. These are not well-formed.
2498 // for<'a> fn() -> &'a str <-- 'a is bad
2499 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2500 let inputs = bare_fn_ty.inputs();
2501 let late_bound_in_args =
2502 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2503 let output = bare_fn_ty.output();
2504 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2506 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
2511 "return type references {}, which is not constrained by the fn input types",
2519 fn validate_late_bound_regions(
2521 constrained_regions: FxHashSet<ty::BoundRegionKind>,
2522 referenced_regions: FxHashSet<ty::BoundRegionKind>,
2523 generate_err: impl Fn(&str) -> rustc_errors::DiagnosticBuilder<'tcx>,
2525 for br in referenced_regions.difference(&constrained_regions) {
2526 let br_name = match *br {
2527 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
2528 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2531 let mut err = generate_err(&br_name);
2533 if let ty::BrAnon(_) = *br {
2534 // The only way for an anonymous lifetime to wind up
2535 // in the return type but **also** be unconstrained is
2536 // if it only appears in "associated types" in the
2537 // input. See #47511 and #62200 for examples. In this case,
2538 // though we can easily give a hint that ought to be
2541 "lifetimes appearing in an associated type are not considered constrained",
2549 /// Given the bounds on an object, determines what single region bound (if any) we can
2550 /// use to summarize this type. The basic idea is that we will use the bound the user
2551 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2552 /// for region bounds. It may be that we can derive no bound at all, in which case
2553 /// we return `None`.
2554 fn compute_object_lifetime_bound(
2557 existential_predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
2558 ) -> Option<ty::Region<'tcx>> // if None, use the default
2560 let tcx = self.tcx();
2562 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2564 // No explicit region bound specified. Therefore, examine trait
2565 // bounds and see if we can derive region bounds from those.
2566 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2568 // If there are no derived region bounds, then report back that we
2569 // can find no region bound. The caller will use the default.
2570 if derived_region_bounds.is_empty() {
2574 // If any of the derived region bounds are 'static, that is always
2576 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2577 return Some(tcx.lifetimes.re_static);
2580 // Determine whether there is exactly one unique region in the set
2581 // of derived region bounds. If so, use that. Otherwise, report an
2583 let r = derived_region_bounds[0];
2584 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2585 tcx.sess.emit_err(AmbiguousLifetimeBound { span });