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::HirPlaceholderCollector;
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_ast::TraitObjectSyntax;
17 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
19 struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, FatalError,
23 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
24 use rustc_hir::def_id::{DefId, LocalDefId};
25 use rustc_hir::intravisit::{walk_generics, Visitor as _};
26 use rustc_hir::lang_items::LangItem;
27 use rustc_hir::{GenericArg, GenericArgs, OpaqueTyOrigin};
28 use rustc_middle::middle::stability::AllowUnstable;
29 use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, Subst, SubstsRef};
30 use rustc_middle::ty::GenericParamDefKind;
31 use rustc_middle::ty::{
32 self, Const, DefIdTree, EarlyBinder, IsSuggestable, Ty, TyCtxt, TypeVisitable,
34 use rustc_session::lint::builtin::{AMBIGUOUS_ASSOCIATED_ITEMS, BARE_TRAIT_OBJECTS};
35 use rustc_span::edition::Edition;
36 use rustc_span::lev_distance::find_best_match_for_name;
37 use rustc_span::symbol::{kw, Ident, Symbol};
39 use rustc_target::spec::abi;
40 use rustc_trait_selection::traits;
41 use rustc_trait_selection::traits::astconv_object_safety_violations;
42 use rustc_trait_selection::traits::error_reporting::{
43 report_object_safety_error, suggestions::NextTypeParamName,
45 use rustc_trait_selection::traits::wf::object_region_bounds;
47 use smallvec::{smallvec, SmallVec};
48 use std::collections::BTreeSet;
52 pub struct PathSeg(pub DefId, pub usize);
54 pub trait AstConv<'tcx> {
55 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
57 fn item_def_id(&self) -> Option<DefId>;
59 /// Returns predicates in scope of the form `X: Foo<T>`, where `X`
60 /// is a type parameter `X` with the given id `def_id` and T
61 /// matches `assoc_name`. This is a subset of the full set of
64 /// This is used for one specific purpose: resolving "short-hand"
65 /// associated type references like `T::Item`. In principle, we
66 /// would do that by first getting the full set of predicates in
67 /// scope and then filtering down to find those that apply to `T`,
68 /// but this can lead to cycle errors. The problem is that we have
69 /// to do this resolution *in order to create the predicates in
70 /// the first place*. Hence, we have this "special pass".
71 fn get_type_parameter_bounds(
76 ) -> ty::GenericPredicates<'tcx>;
78 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
79 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
80 -> Option<ty::Region<'tcx>>;
82 /// Returns the type to use when a type is omitted.
83 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
85 /// Returns `true` if `_` is allowed in type signatures in the current context.
86 fn allow_ty_infer(&self) -> bool;
88 /// Returns the const to use when a const is omitted.
92 param: Option<&ty::GenericParamDef>,
96 /// Projecting an associated type from a (potentially)
97 /// higher-ranked trait reference is more complicated, because of
98 /// the possibility of late-bound regions appearing in the
99 /// associated type binding. This is not legal in function
100 /// signatures for that reason. In a function body, we can always
101 /// handle it because we can use inference variables to remove the
102 /// late-bound regions.
103 fn projected_ty_from_poly_trait_ref(
107 item_segment: &hir::PathSegment<'_>,
108 poly_trait_ref: ty::PolyTraitRef<'tcx>,
111 /// Normalize an associated type coming from the user.
112 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
114 /// Invoked when we encounter an error from some prior pass
115 /// (e.g., resolve) that is translated into a ty-error. This is
116 /// used to help suppress derived errors typeck might otherwise
118 fn set_tainted_by_errors(&self);
120 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
124 struct ConvertedBinding<'a, 'tcx> {
127 kind: ConvertedBindingKind<'a, 'tcx>,
128 gen_args: &'a GenericArgs<'a>,
133 enum ConvertedBindingKind<'a, 'tcx> {
134 Equality(ty::Term<'tcx>),
135 Constraint(&'a [hir::GenericBound<'a>]),
138 /// New-typed boolean indicating whether explicit late-bound lifetimes
139 /// are present in a set of generic arguments.
141 /// For example if we have some method `fn f<'a>(&'a self)` implemented
142 /// for some type `T`, although `f` is generic in the lifetime `'a`, `'a`
143 /// is late-bound so should not be provided explicitly. Thus, if `f` is
144 /// instantiated with some generic arguments providing `'a` explicitly,
145 /// we taint those arguments with `ExplicitLateBound::Yes` so that we
146 /// can provide an appropriate diagnostic later.
147 #[derive(Copy, Clone, PartialEq, Debug)]
148 pub enum ExplicitLateBound {
153 #[derive(Copy, Clone, PartialEq)]
154 pub enum IsMethodCall {
159 /// Denotes the "position" of a generic argument, indicating if it is a generic type,
160 /// generic function or generic method call.
161 #[derive(Copy, Clone, PartialEq)]
162 pub(crate) enum GenericArgPosition {
164 Value, // e.g., functions
168 /// A marker denoting that the generic arguments that were
169 /// provided did not match the respective generic parameters.
170 #[derive(Clone, Default, Debug)]
171 pub struct GenericArgCountMismatch {
172 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
173 pub reported: Option<ErrorGuaranteed>,
174 /// A list of spans of arguments provided that were not valid.
175 pub invalid_args: Vec<Span>,
178 /// Decorates the result of a generic argument count mismatch
179 /// check with whether explicit late bounds were provided.
180 #[derive(Clone, Debug)]
181 pub struct GenericArgCountResult {
182 pub explicit_late_bound: ExplicitLateBound,
183 pub correct: Result<(), GenericArgCountMismatch>,
186 pub trait CreateSubstsForGenericArgsCtxt<'a, 'tcx> {
187 fn args_for_def_id(&mut self, def_id: DefId) -> (Option<&'a GenericArgs<'a>>, bool);
191 param: &ty::GenericParamDef,
192 arg: &GenericArg<'_>,
193 ) -> subst::GenericArg<'tcx>;
197 substs: Option<&[subst::GenericArg<'tcx>]>,
198 param: &ty::GenericParamDef,
200 ) -> subst::GenericArg<'tcx>;
203 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
204 #[instrument(level = "debug", skip(self), ret)]
205 pub fn ast_region_to_region(
207 lifetime: &hir::Lifetime,
208 def: Option<&ty::GenericParamDef>,
209 ) -> ty::Region<'tcx> {
210 let tcx = self.tcx();
211 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
213 match tcx.named_region(lifetime.hir_id) {
214 Some(rl::Region::Static) => tcx.lifetimes.re_static,
216 Some(rl::Region::LateBound(debruijn, index, def_id)) => {
217 let name = lifetime_name(def_id.expect_local());
218 let br = ty::BoundRegion {
219 var: ty::BoundVar::from_u32(index),
220 kind: ty::BrNamed(def_id, name),
222 tcx.mk_region(ty::ReLateBound(debruijn, br))
225 Some(rl::Region::EarlyBound(def_id)) => {
226 let name = tcx.hir().ty_param_name(def_id.expect_local());
227 let item_def_id = tcx.hir().ty_param_owner(def_id.expect_local());
228 let generics = tcx.generics_of(item_def_id);
229 let index = generics.param_def_id_to_index[&def_id];
230 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, index, name }))
233 Some(rl::Region::Free(scope, id)) => {
234 let name = lifetime_name(id.expect_local());
235 tcx.mk_region(ty::ReFree(ty::FreeRegion {
237 bound_region: ty::BrNamed(id, name),
240 // (*) -- not late-bound, won't change
244 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
245 debug!(?lifetime, "unelided lifetime in signature");
247 // This indicates an illegal lifetime
248 // elision. `resolve_lifetime` should have
249 // reported an error in this case -- but if
250 // not, let's error out.
251 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
253 // Supply some dummy value. We don't have an
254 // `re_error`, annoyingly, so use `'static`.
255 tcx.lifetimes.re_static
261 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
262 /// returns an appropriate set of substitutions for this particular reference to `I`.
263 pub fn ast_path_substs_for_ty(
267 item_segment: &hir::PathSegment<'_>,
268 ) -> SubstsRef<'tcx> {
269 let (substs, _) = self.create_substs_for_ast_path(
275 item_segment.infer_args,
278 let assoc_bindings = self.create_assoc_bindings_for_generic_args(item_segment.args());
280 if let Some(b) = assoc_bindings.first() {
281 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
287 /// Given the type/lifetime/const arguments provided to some path (along with
288 /// an implicit `Self`, if this is a trait reference), returns the complete
289 /// set of substitutions. This may involve applying defaulted type parameters.
290 /// Constraints on associated types are created from `create_assoc_bindings_for_generic_args`.
294 /// ```ignore (illustrative)
295 /// T: std::ops::Index<usize, Output = u32>
296 /// // ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
299 /// 1. The `self_ty` here would refer to the type `T`.
300 /// 2. The path in question is the path to the trait `std::ops::Index`,
301 /// which will have been resolved to a `def_id`
302 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
303 /// parameters are returned in the `SubstsRef`, the associated type bindings like
304 /// `Output = u32` are returned from `create_assoc_bindings_for_generic_args`.
306 /// Note that the type listing given here is *exactly* what the user provided.
308 /// For (generic) associated types
310 /// ```ignore (illustrative)
311 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
314 /// We have the parent substs are the substs for the parent trait:
315 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
316 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
317 /// lists: `[Vec<u8>, u8, 'a]`.
318 #[instrument(level = "debug", skip(self, span), ret)]
319 fn create_substs_for_ast_path<'a>(
323 parent_substs: &[subst::GenericArg<'tcx>],
324 seg: &hir::PathSegment<'_>,
325 generic_args: &'a hir::GenericArgs<'_>,
327 self_ty: Option<Ty<'tcx>>,
328 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
329 // If the type is parameterized by this region, then replace this
330 // region with the current anon region binding (in other words,
331 // whatever & would get replaced with).
333 let tcx = self.tcx();
334 let generics = tcx.generics_of(def_id);
335 debug!("generics: {:?}", generics);
337 if generics.has_self {
338 if generics.parent.is_some() {
339 // The parent is a trait so it should have at least one subst
340 // for the `Self` type.
341 assert!(!parent_substs.is_empty())
343 // This item (presumably a trait) needs a self-type.
344 assert!(self_ty.is_some());
347 assert!(self_ty.is_none() && parent_substs.is_empty());
350 let arg_count = Self::check_generic_arg_count(
357 GenericArgPosition::Type,
362 // Skip processing if type has no generic parameters.
363 // Traits always have `Self` as a generic parameter, which means they will not return early
364 // here and so associated type bindings will be handled regardless of whether there are any
365 // non-`Self` generic parameters.
366 if generics.params.is_empty() {
367 return (tcx.intern_substs(&[]), arg_count);
370 struct SubstsForAstPathCtxt<'a, 'tcx> {
371 astconv: &'a (dyn AstConv<'tcx> + 'a),
373 generic_args: &'a GenericArgs<'a>,
375 inferred_params: Vec<Span>,
379 impl<'a, 'tcx> CreateSubstsForGenericArgsCtxt<'a, 'tcx> for SubstsForAstPathCtxt<'a, 'tcx> {
380 fn args_for_def_id(&mut self, did: DefId) -> (Option<&'a GenericArgs<'a>>, bool) {
381 if did == self.def_id {
382 (Some(self.generic_args), self.infer_args)
384 // The last component of this tuple is unimportant.
391 param: &ty::GenericParamDef,
392 arg: &GenericArg<'_>,
393 ) -> subst::GenericArg<'tcx> {
394 let tcx = self.astconv.tcx();
396 let mut handle_ty_args = |has_default, ty: &hir::Ty<'_>| {
398 tcx.check_optional_stability(
405 // Default generic parameters may not be marked
406 // with stability attributes, i.e. when the
407 // default parameter was defined at the same time
408 // as the rest of the type. As such, we ignore missing
409 // stability attributes.
413 if let (hir::TyKind::Infer, false) = (&ty.kind, self.astconv.allow_ty_infer()) {
414 self.inferred_params.push(ty.span);
415 tcx.ty_error().into()
417 self.astconv.ast_ty_to_ty(ty).into()
421 match (¶m.kind, arg) {
422 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
423 self.astconv.ast_region_to_region(lt, Some(param)).into()
425 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
426 handle_ty_args(has_default, ty)
428 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Infer(inf)) => {
429 handle_ty_args(has_default, &inf.to_ty())
431 (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
432 ty::Const::from_opt_const_arg_anon_const(
434 ty::WithOptConstParam {
435 did: tcx.hir().local_def_id(ct.value.hir_id),
436 const_param_did: Some(param.def_id),
441 (&GenericParamDefKind::Const { .. }, hir::GenericArg::Infer(inf)) => {
442 let ty = tcx.at(self.span).type_of(param.def_id);
443 if self.astconv.allow_ty_infer() {
444 self.astconv.ct_infer(ty, Some(param), inf.span).into()
446 self.inferred_params.push(inf.span);
447 tcx.const_error(ty).into()
456 substs: Option<&[subst::GenericArg<'tcx>]>,
457 param: &ty::GenericParamDef,
459 ) -> subst::GenericArg<'tcx> {
460 let tcx = self.astconv.tcx();
462 GenericParamDefKind::Lifetime => self
464 .re_infer(Some(param), self.span)
466 debug!(?param, "unelided lifetime in signature");
468 // This indicates an illegal lifetime in a non-assoc-trait position
469 tcx.sess.delay_span_bug(self.span, "unelided lifetime in signature");
471 // Supply some dummy value. We don't have an
472 // `re_error`, annoyingly, so use `'static`.
473 tcx.lifetimes.re_static
476 GenericParamDefKind::Type { has_default, .. } => {
477 if !infer_args && has_default {
478 // No type parameter provided, but a default exists.
479 let substs = substs.unwrap();
480 if substs.iter().any(|arg| match arg.unpack() {
481 GenericArgKind::Type(ty) => ty.references_error(),
484 // Avoid ICE #86756 when type error recovery goes awry.
485 return tcx.ty_error().into();
490 EarlyBinder(tcx.at(self.span).type_of(param.def_id))
494 } else if infer_args {
495 self.astconv.ty_infer(Some(param), self.span).into()
497 // We've already errored above about the mismatch.
498 tcx.ty_error().into()
501 GenericParamDefKind::Const { has_default } => {
502 let ty = tcx.at(self.span).type_of(param.def_id);
503 if !infer_args && has_default {
504 tcx.bound_const_param_default(param.def_id)
505 .subst(tcx, substs.unwrap())
509 self.astconv.ct_infer(ty, Some(param), self.span).into()
511 // We've already errored above about the mismatch.
512 tcx.const_error(ty).into()
520 let mut substs_ctx = SubstsForAstPathCtxt {
525 inferred_params: vec![],
528 let substs = Self::create_substs_for_generic_args(
541 fn create_assoc_bindings_for_generic_args<'a>(
543 generic_args: &'a hir::GenericArgs<'_>,
544 ) -> Vec<ConvertedBinding<'a, 'tcx>> {
545 // Convert associated-type bindings or constraints into a separate vector.
546 // Example: Given this:
548 // T: Iterator<Item = u32>
550 // The `T` is passed in as a self-type; the `Item = u32` is
551 // not a "type parameter" of the `Iterator` trait, but rather
552 // a restriction on `<T as Iterator>::Item`, so it is passed
554 let assoc_bindings = generic_args
558 let kind = match binding.kind {
559 hir::TypeBindingKind::Equality { ref term } => match term {
560 hir::Term::Ty(ref ty) => {
561 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty).into())
563 hir::Term::Const(ref c) => {
564 let local_did = self.tcx().hir().local_def_id(c.hir_id);
565 let c = Const::from_anon_const(self.tcx(), local_did);
566 ConvertedBindingKind::Equality(c.into())
569 hir::TypeBindingKind::Constraint { ref bounds } => {
570 ConvertedBindingKind::Constraint(bounds)
574 hir_id: binding.hir_id,
575 item_name: binding.ident,
577 gen_args: binding.gen_args,
586 pub(crate) fn create_substs_for_associated_item(
591 item_segment: &hir::PathSegment<'_>,
592 parent_substs: SubstsRef<'tcx>,
593 ) -> SubstsRef<'tcx> {
595 "create_substs_for_associated_item(span: {:?}, item_def_id: {:?}, item_segment: {:?}",
596 span, item_def_id, item_segment
598 if tcx.generics_of(item_def_id).params.is_empty() {
599 self.prohibit_generics(slice::from_ref(item_segment).iter(), |_| {});
603 self.create_substs_for_ast_path(
609 item_segment.infer_args,
616 /// Instantiates the path for the given trait reference, assuming that it's
617 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
618 /// The type _cannot_ be a type other than a trait type.
620 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
621 /// are disallowed. Otherwise, they are pushed onto the vector given.
622 pub fn instantiate_mono_trait_ref(
624 trait_ref: &hir::TraitRef<'_>,
626 ) -> ty::TraitRef<'tcx> {
627 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
629 self.ast_path_to_mono_trait_ref(
631 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
633 trait_ref.path.segments.last().unwrap(),
638 fn instantiate_poly_trait_ref_inner(
642 binding_span: Option<Span>,
643 constness: ty::BoundConstness,
644 bounds: &mut Bounds<'tcx>,
646 trait_ref_span: Span,
648 trait_segment: &hir::PathSegment<'_>,
649 args: &GenericArgs<'_>,
652 ) -> GenericArgCountResult {
653 let (substs, arg_count) = self.create_substs_for_ast_path(
663 let tcx = self.tcx();
664 let bound_vars = tcx.late_bound_vars(hir_id);
667 let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
670 ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
672 debug!(?poly_trait_ref, ?assoc_bindings);
673 bounds.trait_bounds.push((poly_trait_ref, span, constness));
675 let mut dup_bindings = FxHashMap::default();
676 for binding in &assoc_bindings {
677 // Specify type to assert that error was already reported in `Err` case.
678 let _: Result<_, ErrorGuaranteed> = self.add_predicates_for_ast_type_binding(
685 binding_span.unwrap_or(binding.span),
687 // Okay to ignore `Err` because of `ErrorGuaranteed` (see above).
693 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
694 /// a full trait reference. The resulting trait reference is returned. This may also generate
695 /// auxiliary bounds, which are added to `bounds`.
699 /// ```ignore (illustrative)
700 /// poly_trait_ref = Iterator<Item = u32>
704 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
706 /// **A note on binders:** against our usual convention, there is an implied bounder around
707 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
708 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
709 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
710 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
712 #[instrument(level = "debug", skip(self, span, constness, bounds, speculative))]
713 pub(crate) fn instantiate_poly_trait_ref(
715 trait_ref: &hir::TraitRef<'_>,
717 constness: ty::BoundConstness,
719 bounds: &mut Bounds<'tcx>,
721 ) -> GenericArgCountResult {
722 let hir_id = trait_ref.hir_ref_id;
723 let binding_span = None;
724 let trait_ref_span = trait_ref.path.span;
725 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
726 let trait_segment = trait_ref.path.segments.last().unwrap();
727 let args = trait_segment.args();
728 let infer_args = trait_segment.infer_args;
730 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
731 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, false);
733 self.instantiate_poly_trait_ref_inner(
749 pub(crate) fn instantiate_lang_item_trait_ref(
751 lang_item: hir::LangItem,
754 args: &GenericArgs<'_>,
756 bounds: &mut Bounds<'tcx>,
758 let binding_span = Some(span);
759 let constness = ty::BoundConstness::NotConst;
760 let speculative = false;
761 let trait_ref_span = span;
762 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
763 let trait_segment = &hir::PathSegment::invalid();
764 let infer_args = false;
766 self.instantiate_poly_trait_ref_inner(
782 fn ast_path_to_mono_trait_ref(
787 trait_segment: &hir::PathSegment<'_>,
789 ) -> ty::TraitRef<'tcx> {
790 let (substs, _) = self.create_substs_for_ast_trait_ref(
797 let assoc_bindings = self.create_assoc_bindings_for_generic_args(trait_segment.args());
798 if let Some(b) = assoc_bindings.first() {
799 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
801 ty::TraitRef::new(trait_def_id, substs)
804 #[instrument(level = "debug", skip(self, span))]
805 fn create_substs_for_ast_trait_ref<'a>(
810 trait_segment: &'a hir::PathSegment<'a>,
812 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
813 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
815 self.create_substs_for_ast_path(
820 trait_segment.args(),
821 trait_segment.infer_args,
826 fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
828 .associated_items(trait_def_id)
829 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
832 fn trait_defines_associated_const_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
834 .associated_items(trait_def_id)
835 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Const, trait_def_id)
839 // Sets `implicitly_sized` to true on `Bounds` if necessary
840 pub(crate) fn add_implicitly_sized<'hir>(
842 bounds: &mut Bounds<'hir>,
843 ast_bounds: &'hir [hir::GenericBound<'hir>],
844 self_ty_where_predicates: Option<(hir::HirId, &'hir [hir::WherePredicate<'hir>])>,
847 let tcx = self.tcx();
849 // Try to find an unbound in bounds.
850 let mut unbound = None;
851 let mut search_bounds = |ast_bounds: &'hir [hir::GenericBound<'hir>]| {
852 for ab in ast_bounds {
853 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
854 if unbound.is_none() {
855 unbound = Some(&ptr.trait_ref);
857 tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
862 search_bounds(ast_bounds);
863 if let Some((self_ty, where_clause)) = self_ty_where_predicates {
864 let self_ty_def_id = tcx.hir().local_def_id(self_ty).to_def_id();
865 for clause in where_clause {
866 if let hir::WherePredicate::BoundPredicate(pred) = clause {
867 if pred.is_param_bound(self_ty_def_id) {
868 search_bounds(pred.bounds);
874 let sized_def_id = tcx.lang_items().require(LangItem::Sized);
875 match (&sized_def_id, unbound) {
876 (Ok(sized_def_id), Some(tpb))
877 if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) =>
879 // There was in fact a `?Sized` bound, return without doing anything
883 // There was a `?Trait` bound, but it was not `?Sized`; warn.
886 "default bound relaxed for a type parameter, but \
887 this does nothing because the given bound is not \
888 a default; only `?Sized` is supported",
890 // Otherwise, add implicitly sized if `Sized` is available.
893 // There was no `?Sized` bound; add implicitly sized if `Sized` is available.
896 if sized_def_id.is_err() {
897 // No lang item for `Sized`, so we can't add it as a bound.
900 bounds.implicitly_sized = Some(span);
903 /// This helper takes a *converted* parameter type (`param_ty`)
904 /// and an *unconverted* list of bounds:
908 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
910 /// `param_ty`, in ty form
913 /// It adds these `ast_bounds` into the `bounds` structure.
915 /// **A note on binders:** there is an implied binder around
916 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
917 /// for more details.
918 #[instrument(level = "debug", skip(self, ast_bounds, bounds))]
919 pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>(
923 bounds: &mut Bounds<'tcx>,
924 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
926 for ast_bound in ast_bounds {
928 hir::GenericBound::Trait(poly_trait_ref, modifier) => {
929 let constness = match modifier {
930 hir::TraitBoundModifier::MaybeConst => ty::BoundConstness::ConstIfConst,
931 hir::TraitBoundModifier::None => ty::BoundConstness::NotConst,
932 hir::TraitBoundModifier::Maybe => continue,
935 let _ = self.instantiate_poly_trait_ref(
936 &poly_trait_ref.trait_ref,
944 &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
945 self.instantiate_lang_item_trait_ref(
946 lang_item, span, hir_id, args, param_ty, bounds,
949 hir::GenericBound::Outlives(lifetime) => {
950 let region = self.ast_region_to_region(lifetime, None);
953 .push((ty::Binder::bind_with_vars(region, bound_vars), lifetime.span));
959 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
960 /// The self-type for the bounds is given by `param_ty`.
964 /// ```ignore (illustrative)
965 /// fn foo<T: Bar + Baz>() { }
966 /// // ^ ^^^^^^^^^ ast_bounds
970 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
971 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
972 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
974 /// `span` should be the declaration size of the parameter.
975 pub(crate) fn compute_bounds(
978 ast_bounds: &[hir::GenericBound<'_>],
980 self.compute_bounds_inner(param_ty, ast_bounds)
983 /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
984 /// named `assoc_name` into ty::Bounds. Ignore the rest.
985 pub(crate) fn compute_bounds_that_match_assoc_type(
988 ast_bounds: &[hir::GenericBound<'_>],
991 let mut result = Vec::new();
993 for ast_bound in ast_bounds {
994 if let Some(trait_ref) = ast_bound.trait_ref()
995 && let Some(trait_did) = trait_ref.trait_def_id()
996 && self.tcx().trait_may_define_assoc_type(trait_did, assoc_name)
998 result.push(ast_bound.clone());
1002 self.compute_bounds_inner(param_ty, &result)
1005 fn compute_bounds_inner(
1008 ast_bounds: &[hir::GenericBound<'_>],
1010 let mut bounds = Bounds::default();
1012 self.add_bounds(param_ty, ast_bounds.iter(), &mut bounds, ty::List::empty());
1018 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1021 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1022 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1023 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1024 #[instrument(level = "debug", skip(self, bounds, speculative, dup_bindings, path_span))]
1025 fn add_predicates_for_ast_type_binding(
1027 hir_ref_id: hir::HirId,
1028 trait_ref: ty::PolyTraitRef<'tcx>,
1029 binding: &ConvertedBinding<'_, 'tcx>,
1030 bounds: &mut Bounds<'tcx>,
1032 dup_bindings: &mut FxHashMap<DefId, Span>,
1034 ) -> Result<(), ErrorGuaranteed> {
1035 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1036 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1037 // subtle in the event that `T` is defined in a supertrait of
1038 // `SomeTrait`, because in that case we need to upcast.
1040 // That is, consider this case:
1043 // trait SubTrait: SuperTrait<i32> { }
1044 // trait SuperTrait<A> { type T; }
1046 // ... B: SubTrait<T = foo> ...
1049 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
1051 let tcx = self.tcx();
1054 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1055 // Simple case: X is defined in the current trait.
1058 // Otherwise, we have to walk through the supertraits to find
1060 self.one_bound_for_assoc_type(
1061 || traits::supertraits(tcx, trait_ref),
1062 || trait_ref.print_only_trait_path().to_string(),
1065 || match binding.kind {
1066 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1072 let (assoc_ident, def_scope) =
1073 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1075 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1076 // of calling `filter_by_name_and_kind`.
1077 let find_item_of_kind = |kind| {
1078 tcx.associated_items(candidate.def_id())
1079 .filter_by_name_unhygienic(assoc_ident.name)
1080 .find(|i| i.kind == kind && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident)
1082 let assoc_item = find_item_of_kind(ty::AssocKind::Type)
1083 .or_else(|| find_item_of_kind(ty::AssocKind::Const))
1084 .expect("missing associated type");
1086 if !assoc_item.visibility(tcx).is_accessible_from(def_scope, tcx) {
1090 &format!("{} `{}` is private", assoc_item.kind, binding.item_name),
1092 .span_label(binding.span, &format!("private {}", assoc_item.kind))
1095 tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None);
1099 .entry(assoc_item.def_id)
1100 .and_modify(|prev_span| {
1101 self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
1103 prev_span: *prev_span,
1104 item_name: binding.item_name,
1105 def_path: tcx.def_path_str(assoc_item.container_id(tcx)),
1108 .or_insert(binding.span);
1111 // Include substitutions for generic parameters of associated types
1112 let projection_ty = candidate.map_bound(|trait_ref| {
1113 let ident = Ident::new(assoc_item.name, binding.item_name.span);
1114 let item_segment = hir::PathSegment {
1116 hir_id: binding.hir_id,
1118 args: Some(binding.gen_args),
1122 let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
1131 "add_predicates_for_ast_type_binding: substs for trait-ref and assoc_item: {:?}",
1132 substs_trait_ref_and_assoc_item
1136 item_def_id: assoc_item.def_id,
1137 substs: substs_trait_ref_and_assoc_item,
1142 // Find any late-bound regions declared in `ty` that are not
1143 // declared in the trait-ref or assoc_item. These are not well-formed.
1147 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1148 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1149 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1150 let late_bound_in_trait_ref =
1151 tcx.collect_constrained_late_bound_regions(&projection_ty);
1152 let late_bound_in_ty =
1153 tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty));
1154 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1155 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1157 // FIXME: point at the type params that don't have appropriate lifetimes:
1158 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1159 // ---- ---- ^^^^^^^
1160 self.validate_late_bound_regions(
1161 late_bound_in_trait_ref,
1168 "binding for associated type `{}` references {}, \
1169 which does not appear in the trait input types",
1178 match binding.kind {
1179 ConvertedBindingKind::Equality(mut term) => {
1180 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1181 // the "projection predicate" for:
1183 // `<T as Iterator>::Item = u32`
1184 let assoc_item_def_id = projection_ty.skip_binder().item_def_id;
1185 let def_kind = tcx.def_kind(assoc_item_def_id);
1186 match (def_kind, term.unpack()) {
1187 (hir::def::DefKind::AssocTy, ty::TermKind::Ty(_))
1188 | (hir::def::DefKind::AssocConst, ty::TermKind::Const(_)) => (),
1190 let got = if let Some(_) = term.ty() { "type" } else { "constant" };
1191 let expected = def_kind.descr(assoc_item_def_id);
1195 &format!("expected {expected} bound, found {got}"),
1198 tcx.def_span(assoc_item_def_id),
1199 &format!("{expected} defined here"),
1202 term = match def_kind {
1203 hir::def::DefKind::AssocTy => tcx.ty_error().into(),
1204 hir::def::DefKind::AssocConst => tcx
1206 tcx.bound_type_of(assoc_item_def_id)
1207 .subst(tcx, projection_ty.skip_binder().substs),
1210 _ => unreachable!(),
1214 bounds.projection_bounds.push((
1215 projection_ty.map_bound(|projection_ty| ty::ProjectionPredicate {
1222 ConvertedBindingKind::Constraint(ast_bounds) => {
1223 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1225 // `<T as Iterator>::Item: Debug`
1227 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1228 // parameter to have a skipped binder.
1229 let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
1230 self.add_bounds(param_ty, ast_bounds.iter(), bounds, candidate.bound_vars());
1240 item_segment: &hir::PathSegment<'_>,
1242 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1245 EarlyBinder(self.tcx().at(span).type_of(did)).subst(self.tcx(), substs),
1249 fn conv_object_ty_poly_trait_ref(
1252 trait_bounds: &[hir::PolyTraitRef<'_>],
1253 lifetime: &hir::Lifetime,
1256 let tcx = self.tcx();
1258 let mut bounds = Bounds::default();
1259 let mut potential_assoc_types = Vec::new();
1260 let dummy_self = self.tcx().types.trait_object_dummy_self;
1261 for trait_bound in trait_bounds.iter().rev() {
1262 if let GenericArgCountResult {
1264 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1266 } = self.instantiate_poly_trait_ref(
1267 &trait_bound.trait_ref,
1269 ty::BoundConstness::NotConst,
1274 potential_assoc_types.extend(cur_potential_assoc_types);
1278 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1279 // is used and no 'maybe' bounds are used.
1280 let expanded_traits =
1281 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1282 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) = expanded_traits
1283 .filter(|i| i.trait_ref().self_ty().skip_binder() == dummy_self)
1284 .partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1285 if regular_traits.len() > 1 {
1286 let first_trait = ®ular_traits[0];
1287 let additional_trait = ®ular_traits[1];
1288 let mut err = struct_span_err!(
1290 additional_trait.bottom().1,
1292 "only auto traits can be used as additional traits in a trait object"
1294 additional_trait.label_with_exp_info(
1296 "additional non-auto trait",
1299 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1301 "consider creating a new trait with all of these as supertraits and using that \
1302 trait here instead: `trait NewTrait: {} {{}}`",
1305 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1306 .collect::<Vec<_>>()
1310 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1311 for more information on them, visit \
1312 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1317 if regular_traits.is_empty() && auto_traits.is_empty() {
1318 let trait_alias_span = bounds
1321 .map(|&(trait_ref, _, _)| trait_ref.def_id())
1322 .find(|&trait_ref| tcx.is_trait_alias(trait_ref))
1323 .map(|trait_ref| tcx.def_span(trait_ref));
1324 tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span, trait_alias_span });
1325 return tcx.ty_error();
1328 // Check that there are no gross object safety violations;
1329 // most importantly, that the supertraits don't contain `Self`,
1331 for item in ®ular_traits {
1332 let object_safety_violations =
1333 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1334 if !object_safety_violations.is_empty() {
1335 report_object_safety_error(
1338 item.trait_ref().def_id(),
1339 &object_safety_violations,
1342 return tcx.ty_error();
1346 // Use a `BTreeSet` to keep output in a more consistent order.
1347 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1349 let regular_traits_refs_spans = bounds
1352 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1354 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1355 assert_eq!(constness, ty::BoundConstness::NotConst);
1357 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1359 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1360 obligation.predicate
1363 let bound_predicate = obligation.predicate.kind();
1364 match bound_predicate.skip_binder() {
1365 ty::PredicateKind::Trait(pred) => {
1366 let pred = bound_predicate.rebind(pred);
1367 associated_types.entry(span).or_default().extend(
1368 tcx.associated_items(pred.def_id())
1369 .in_definition_order()
1370 .filter(|item| item.kind == ty::AssocKind::Type)
1371 .map(|item| item.def_id),
1374 ty::PredicateKind::Projection(pred) => {
1375 let pred = bound_predicate.rebind(pred);
1376 // A `Self` within the original bound will be substituted with a
1377 // `trait_object_dummy_self`, so check for that.
1378 let references_self = match pred.skip_binder().term.unpack() {
1379 ty::TermKind::Ty(ty) => ty.walk().any(|arg| arg == dummy_self.into()),
1380 ty::TermKind::Const(c) => {
1381 c.ty().walk().any(|arg| arg == dummy_self.into())
1385 // If the projection output contains `Self`, force the user to
1386 // elaborate it explicitly to avoid a lot of complexity.
1388 // The "classically useful" case is the following:
1390 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1395 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1396 // but actually supporting that would "expand" to an infinitely-long type
1397 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1399 // Instead, we force the user to write
1400 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1401 // the discussion in #56288 for alternatives.
1402 if !references_self {
1403 // Include projections defined on supertraits.
1404 bounds.projection_bounds.push((pred, span));
1412 for (projection_bound, _) in &bounds.projection_bounds {
1413 for def_ids in associated_types.values_mut() {
1414 def_ids.remove(&projection_bound.projection_def_id());
1418 self.complain_about_missing_associated_types(
1420 potential_assoc_types,
1424 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1425 // `dyn Trait + Send`.
1426 // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
1428 let mut duplicates = FxHashSet::default();
1429 auto_traits.retain(|i| duplicates.insert(i.trait_ref().def_id()));
1430 debug!("regular_traits: {:?}", regular_traits);
1431 debug!("auto_traits: {:?}", auto_traits);
1433 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1434 let existential_trait_refs = regular_traits.iter().map(|i| {
1435 i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
1436 assert_eq!(trait_ref.self_ty(), dummy_self);
1438 // Verify that `dummy_self` did not leak inside default type parameters. This
1439 // could not be done at path creation, since we need to see through trait aliases.
1440 let mut missing_type_params = vec![];
1441 let mut references_self = false;
1442 let generics = tcx.generics_of(trait_ref.def_id);
1443 let substs: Vec<_> = trait_ref
1447 .skip(1) // Remove `Self` for `ExistentialPredicate`.
1448 .map(|(index, arg)| {
1449 if arg == dummy_self.into() {
1450 let param = &generics.params[index];
1451 missing_type_params.push(param.name);
1452 return tcx.ty_error().into();
1453 } else if arg.walk().any(|arg| arg == dummy_self.into()) {
1454 references_self = true;
1455 return tcx.ty_error().into();
1460 let substs = tcx.intern_substs(&substs[..]);
1462 let span = i.bottom().1;
1463 let empty_generic_args = trait_bounds.iter().any(|hir_bound| {
1464 hir_bound.trait_ref.path.res == Res::Def(DefKind::Trait, trait_ref.def_id)
1465 && hir_bound.span.contains(span)
1467 self.complain_about_missing_type_params(
1468 missing_type_params,
1474 if references_self {
1475 let def_id = i.bottom().0.def_id();
1476 let mut err = struct_span_err!(
1480 "the {} `{}` cannot be made into an object",
1481 tcx.def_kind(def_id).descr(def_id),
1482 tcx.item_name(def_id),
1485 rustc_middle::traits::ObjectSafetyViolation::SupertraitSelf(smallvec![])
1491 ty::ExistentialTraitRef { def_id: trait_ref.def_id, substs }
1495 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1496 bound.map_bound(|mut b| {
1497 assert_eq!(b.projection_ty.self_ty(), dummy_self);
1499 // Like for trait refs, verify that `dummy_self` did not leak inside default type
1501 let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
1502 if arg.walk().any(|arg| arg == dummy_self.into()) {
1507 if references_self {
1509 .delay_span_bug(span, "trait object projection bounds reference `Self`");
1510 let substs: Vec<_> = b
1515 if arg.walk().any(|arg| arg == dummy_self.into()) {
1516 return tcx.ty_error().into();
1521 b.projection_ty.substs = tcx.intern_substs(&substs[..]);
1524 ty::ExistentialProjection::erase_self_ty(tcx, b)
1528 let regular_trait_predicates = existential_trait_refs
1529 .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));
1530 let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
1531 ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
1533 // N.b. principal, projections, auto traits
1534 // FIXME: This is actually wrong with multiple principals in regards to symbol mangling
1535 let mut v = regular_trait_predicates
1537 existential_projections.map(|x| x.map_bound(ty::ExistentialPredicate::Projection)),
1539 .chain(auto_trait_predicates)
1540 .collect::<SmallVec<[_; 8]>>();
1541 v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
1543 let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
1545 // Use explicitly-specified region bound.
1546 let region_bound = if !lifetime.is_elided() {
1547 self.ast_region_to_region(lifetime, None)
1549 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1550 if tcx.named_region(lifetime.hir_id).is_some() {
1551 self.ast_region_to_region(lifetime, None)
1553 self.re_infer(None, span).unwrap_or_else(|| {
1554 let mut err = struct_span_err!(
1558 "the lifetime bound for this object type cannot be deduced \
1559 from context; please supply an explicit bound"
1562 // We will have already emitted an error E0106 complaining about a
1563 // missing named lifetime in `&dyn Trait`, so we elide this one.
1568 tcx.lifetimes.re_static
1573 debug!("region_bound: {:?}", region_bound);
1575 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1576 debug!("trait_object_type: {:?}", ty);
1580 fn report_ambiguous_associated_type(
1586 ) -> ErrorGuaranteed {
1587 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1591 .confused_type_with_std_module
1593 .any(|full_span| full_span.contains(span))
1595 err.span_suggestion(
1596 span.shrink_to_lo(),
1597 "you are looking for the module in `std`, not the primitive type",
1599 Applicability::MachineApplicable,
1602 err.span_suggestion(
1604 "use fully-qualified syntax",
1605 format!("<{} as {}>::{}", type_str, trait_str, name),
1606 Applicability::HasPlaceholders,
1612 // Search for a bound on a type parameter which includes the associated item
1613 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1614 // This function will fail if there are no suitable bounds or there is
1616 fn find_bound_for_assoc_item(
1618 ty_param_def_id: LocalDefId,
1621 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed> {
1622 let tcx = self.tcx();
1625 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1626 ty_param_def_id, assoc_name, span,
1629 let predicates = &self
1630 .get_type_parameter_bounds(span, ty_param_def_id.to_def_id(), assoc_name)
1633 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1635 let param_name = tcx.hir().ty_param_name(ty_param_def_id);
1636 self.one_bound_for_assoc_type(
1638 traits::transitive_bounds_that_define_assoc_type(
1640 predicates.iter().filter_map(|(p, _)| {
1641 Some(p.to_opt_poly_trait_pred()?.map_bound(|t| t.trait_ref))
1646 || param_name.to_string(),
1653 // Checks that `bounds` contains exactly one element and reports appropriate
1654 // errors otherwise.
1655 fn one_bound_for_assoc_type<I>(
1657 all_candidates: impl Fn() -> I,
1658 ty_param_name: impl Fn() -> String,
1661 is_equality: impl Fn() -> Option<String>,
1662 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed>
1664 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1666 let mut matching_candidates = all_candidates()
1667 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1668 let mut const_candidates = all_candidates()
1669 .filter(|r| self.trait_defines_associated_const_named(r.def_id(), assoc_name));
1671 let (bound, next_cand) = match (matching_candidates.next(), const_candidates.next()) {
1672 (Some(bound), _) => (bound, matching_candidates.next()),
1673 (None, Some(bound)) => (bound, const_candidates.next()),
1675 let reported = self.complain_about_assoc_type_not_found(
1681 return Err(reported);
1684 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1686 if let Some(bound2) = next_cand {
1687 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1689 let is_equality = is_equality();
1690 let bounds = IntoIterator::into_iter([bound, bound2]).chain(matching_candidates);
1691 let mut err = if is_equality.is_some() {
1692 // More specific Error Index entry.
1697 "ambiguous associated type `{}` in bounds of `{}`",
1706 "ambiguous associated type `{}` in bounds of `{}`",
1711 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1713 let mut where_bounds = vec![];
1714 for bound in bounds {
1715 let bound_id = bound.def_id();
1716 let bound_span = self
1718 .associated_items(bound_id)
1719 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1720 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1722 if let Some(bound_span) = bound_span {
1726 "ambiguous `{}` from `{}`",
1728 bound.print_only_trait_path(),
1731 if let Some(constraint) = &is_equality {
1732 where_bounds.push(format!(
1733 " T: {trait}::{assoc} = {constraint}",
1734 trait=bound.print_only_trait_path(),
1736 constraint=constraint,
1739 err.span_suggestion_verbose(
1740 span.with_hi(assoc_name.span.lo()),
1741 "use fully qualified syntax to disambiguate",
1745 bound.print_only_trait_path(),
1747 Applicability::MaybeIncorrect,
1752 "associated type `{}` could derive from `{}`",
1754 bound.print_only_trait_path(),
1758 if !where_bounds.is_empty() {
1760 "consider introducing a new type parameter `T` and adding `where` constraints:\
1761 \n where\n T: {},\n{}",
1763 where_bounds.join(",\n"),
1766 let reported = err.emit();
1767 if !where_bounds.is_empty() {
1768 return Err(reported);
1775 // Create a type from a path to an associated type.
1776 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1777 // and item_segment is the path segment for `D`. We return a type and a def for
1779 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1780 // parameter or `Self`.
1781 // NOTE: When this function starts resolving `Trait::AssocTy` successfully
1782 // it should also start reporting the `BARE_TRAIT_OBJECTS` lint.
1783 pub fn associated_path_to_ty(
1785 hir_ref_id: hir::HirId,
1788 qself: &hir::Ty<'_>,
1789 assoc_segment: &hir::PathSegment<'_>,
1790 permit_variants: bool,
1791 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
1792 let tcx = self.tcx();
1793 let assoc_ident = assoc_segment.ident;
1794 let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
1800 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1802 // Check if we have an enum variant.
1803 let mut variant_resolution = None;
1804 if let ty::Adt(adt_def, _) = qself_ty.kind() {
1805 if adt_def.is_enum() {
1806 let variant_def = adt_def
1809 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident(tcx), adt_def.did()));
1810 if let Some(variant_def) = variant_def {
1811 if permit_variants {
1812 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span, None);
1813 self.prohibit_generics(slice::from_ref(assoc_segment).iter(), |err| {
1814 err.note("enum variants can't have type parameters");
1815 let type_name = tcx.item_name(adt_def.did());
1817 "you might have meant to specity type parameters on enum \
1820 let Some(args) = assoc_segment.args else { return; };
1821 // Get the span of the generics args *including* the leading `::`.
1822 let args_span = assoc_segment.ident.span.shrink_to_hi().to(args.span_ext);
1823 if tcx.generics_of(adt_def.did()).count() == 0 {
1824 // FIXME(estebank): we could also verify that the arguments being
1825 // work for the `enum`, instead of just looking if it takes *any*.
1826 err.span_suggestion_verbose(
1828 &format!("{type_name} doesn't have generic parameters"),
1830 Applicability::MachineApplicable,
1834 let Ok(snippet) = tcx.sess.source_map().span_to_snippet(args_span) else {
1838 let (qself_sugg_span, is_self) = if let hir::TyKind::Path(
1839 hir::QPath::Resolved(_, ref path)
1841 // If the path segment already has type params, we want to overwrite
1843 match &path.segments[..] {
1844 // `segment` is the previous to last element on the path,
1845 // which would normally be the `enum` itself, while the last
1846 // `_` `PathSegment` corresponds to the variant.
1847 [.., hir::PathSegment {
1850 res: Res::Def(DefKind::Enum, _),
1853 // We need to include the `::` in `Type::Variant::<Args>`
1854 // to point the span to `::<Args>`, not just `<Args>`.
1855 ident.span.shrink_to_hi().to(args.map_or(
1856 ident.span.shrink_to_hi(),
1861 // We need to include the `::` in `Type::Variant::<Args>`
1862 // to point the span to `::<Args>`, not just `<Args>`.
1863 segment.ident.span.shrink_to_hi().to(segment.args.map_or(
1864 segment.ident.span.shrink_to_hi(),
1866 kw::SelfUpper == segment.ident.name,
1877 let suggestion = vec![
1879 // Account for people writing `Self::Variant::<Args>`, where
1880 // `Self` is the enum, and suggest replacing `Self` with the
1881 // appropriate type: `Type::<Args>::Variant`.
1882 (qself.span, format!("{type_name}{snippet}"))
1884 (qself_sugg_span, snippet)
1886 (args_span, String::new()),
1888 err.multipart_suggestion_verbose(
1891 Applicability::MaybeIncorrect,
1894 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1896 variant_resolution = Some(variant_def.def_id);
1902 // Find the type of the associated item, and the trait where the associated
1903 // item is declared.
1904 let bound = match (&qself_ty.kind(), qself_res) {
1905 (_, Res::SelfTy { trait_: Some(_), alias_to: Some((impl_def_id, _)) }) => {
1906 // `Self` in an impl of a trait -- we have a concrete self type and a
1908 let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) else {
1909 // A cycle error occurred, most likely.
1910 let guar = tcx.sess.delay_span_bug(span, "expected cycle error");
1914 self.one_bound_for_assoc_type(
1915 || traits::supertraits(tcx, ty::Binder::dummy(trait_ref)),
1916 || "Self".to_string(),
1924 Res::SelfTy { trait_: Some(param_did), alias_to: None }
1925 | Res::Def(DefKind::TyParam, param_did),
1926 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
1928 let reported = if variant_resolution.is_some() {
1929 // Variant in type position
1930 let msg = format!("expected type, found variant `{}`", assoc_ident);
1931 tcx.sess.span_err(span, &msg)
1932 } else if qself_ty.is_enum() {
1933 let mut err = struct_span_err!(
1937 "no variant named `{}` found for enum `{}`",
1942 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1943 if let Some(suggested_name) = find_best_match_for_name(
1947 .map(|variant| variant.name)
1948 .collect::<Vec<Symbol>>(),
1952 err.span_suggestion(
1954 "there is a variant with a similar name",
1956 Applicability::MaybeIncorrect,
1961 format!("variant not found in `{}`", qself_ty),
1965 if let Some(sp) = tcx.hir().span_if_local(adt_def.did()) {
1966 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1970 } else if let Some(reported) = qself_ty.error_reported() {
1973 // Don't print `TyErr` to the user.
1974 self.report_ambiguous_associated_type(
1976 &qself_ty.to_string(),
1981 return Err(reported);
1985 let trait_did = bound.def_id();
1986 let (assoc_ident, def_scope) =
1987 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1989 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1990 // of calling `filter_by_name_and_kind`.
1991 let item = tcx.associated_items(trait_did).in_definition_order().find(|i| {
1992 i.kind.namespace() == Namespace::TypeNS
1993 && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident
1995 // Assume that if it's not matched, there must be a const defined with the same name
1996 // but it was used in a type position.
1997 let Some(item) = item else {
1998 let msg = format!("found associated const `{assoc_ident}` when type was expected");
1999 let guar = tcx.sess.struct_span_err(span, &msg).emit();
2003 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2004 let ty = self.normalize_ty(span, ty);
2006 let kind = DefKind::AssocTy;
2007 if !item.visibility(tcx).is_accessible_from(def_scope, tcx) {
2008 let kind = kind.descr(item.def_id);
2009 let msg = format!("{} `{}` is private", kind, assoc_ident);
2011 .struct_span_err(span, &msg)
2012 .span_label(span, &format!("private {}", kind))
2015 tcx.check_stability(item.def_id, Some(hir_ref_id), span, None);
2017 if let Some(variant_def_id) = variant_resolution {
2018 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2019 let mut err = lint.build("ambiguous associated item");
2020 let mut could_refer_to = |kind: DefKind, def_id, also| {
2021 let note_msg = format!(
2022 "`{}` could{} refer to the {} defined here",
2027 err.span_note(tcx.def_span(def_id), ¬e_msg);
2030 could_refer_to(DefKind::Variant, variant_def_id, "");
2031 could_refer_to(kind, item.def_id, " also");
2033 err.span_suggestion(
2035 "use fully-qualified syntax",
2036 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2037 Applicability::MachineApplicable,
2043 Ok((ty, kind, item.def_id))
2049 opt_self_ty: Option<Ty<'tcx>>,
2051 trait_segment: &hir::PathSegment<'_>,
2052 item_segment: &hir::PathSegment<'_>,
2054 let tcx = self.tcx();
2056 let trait_def_id = tcx.parent(item_def_id);
2058 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2060 let Some(self_ty) = opt_self_ty else {
2061 let path_str = tcx.def_path_str(trait_def_id);
2063 let def_id = self.item_def_id();
2065 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2067 let parent_def_id = def_id
2068 .and_then(|def_id| {
2069 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
2071 .map(|hir_id| tcx.hir().get_parent_item(hir_id).to_def_id());
2073 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2075 // If the trait in segment is the same as the trait defining the item,
2076 // use the `<Self as ..>` syntax in the error.
2077 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2078 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2080 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2086 self.report_ambiguous_associated_type(
2090 item_segment.ident.name,
2092 return tcx.ty_error();
2095 debug!("qpath_to_ty: self_type={:?}", self_ty);
2098 self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment, false);
2100 let item_substs = self.create_substs_for_associated_item(
2108 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2110 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2113 pub fn prohibit_generics<'a>(
2115 segments: impl Iterator<Item = &'a hir::PathSegment<'a>> + Clone,
2116 extend: impl Fn(&mut Diagnostic),
2118 let args = segments.clone().flat_map(|segment| segment.args().args);
2120 let (lt, ty, ct, inf) =
2121 args.clone().fold((false, false, false, false), |(lt, ty, ct, inf), arg| match arg {
2122 hir::GenericArg::Lifetime(_) => (true, ty, ct, inf),
2123 hir::GenericArg::Type(_) => (lt, true, ct, inf),
2124 hir::GenericArg::Const(_) => (lt, ty, true, inf),
2125 hir::GenericArg::Infer(_) => (lt, ty, ct, true),
2127 let mut emitted = false;
2128 if lt || ty || ct || inf {
2129 let types_and_spans: Vec<_> = segments
2131 .flat_map(|segment| {
2132 if segment.args().args.is_empty() {
2137 Res::PrimTy(ty) => format!("{} `{}`", segment.res.descr(), ty.name()),
2139 if let Some(name) = self.tcx().opt_item_name(def_id) => {
2140 format!("{} `{name}`", segment.res.descr())
2142 Res::Err => "this type".to_string(),
2143 _ => segment.res.descr().to_string(),
2150 let this_type = match &types_and_spans[..] {
2151 [.., _, (last, _)] => format!(
2153 types_and_spans[..types_and_spans.len() - 1]
2155 .map(|(x, _)| x.as_str())
2157 .collect::<String>()
2159 [(only, _)] => only.to_string(),
2160 [] => "this type".to_string(),
2163 let arg_spans: Vec<Span> = args.map(|arg| arg.span()).collect();
2165 let mut kinds = Vec::with_capacity(4);
2167 kinds.push("lifetime");
2173 kinds.push("const");
2176 kinds.push("generic");
2178 let (kind, s) = match kinds[..] {
2182 kinds[..kinds.len() - 1]
2186 .collect::<String>()
2190 [only] => (format!("{only}"), ""),
2191 [] => unreachable!(),
2193 let last_span = *arg_spans.last().unwrap();
2194 let span: MultiSpan = arg_spans.into();
2195 let mut err = struct_span_err!(
2199 "{kind} arguments are not allowed on {this_type}",
2201 err.span_label(last_span, format!("{kind} argument{s} not allowed"));
2202 for (what, span) in types_and_spans {
2203 err.span_label(span, format!("not allowed on {what}"));
2210 for segment in segments {
2211 // Only emit the first error to avoid overloading the user with error messages.
2212 if let [binding, ..] = segment.args().bindings {
2213 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2220 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2221 pub fn def_ids_for_value_path_segments(
2223 segments: &[hir::PathSegment<'_>],
2224 self_ty: Option<Ty<'tcx>>,
2228 // We need to extract the type parameters supplied by the user in
2229 // the path `path`. Due to the current setup, this is a bit of a
2230 // tricky-process; the problem is that resolve only tells us the
2231 // end-point of the path resolution, and not the intermediate steps.
2232 // Luckily, we can (at least for now) deduce the intermediate steps
2233 // just from the end-point.
2235 // There are basically five cases to consider:
2237 // 1. Reference to a constructor of a struct:
2239 // struct Foo<T>(...)
2241 // In this case, the parameters are declared in the type space.
2243 // 2. Reference to a constructor of an enum variant:
2245 // enum E<T> { Foo(...) }
2247 // In this case, the parameters are defined in the type space,
2248 // but may be specified either on the type or the variant.
2250 // 3. Reference to a fn item or a free constant:
2254 // In this case, the path will again always have the form
2255 // `a::b::foo::<T>` where only the final segment should have
2256 // type parameters. However, in this case, those parameters are
2257 // declared on a value, and hence are in the `FnSpace`.
2259 // 4. Reference to a method or an associated constant:
2261 // impl<A> SomeStruct<A> {
2265 // Here we can have a path like
2266 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2267 // may appear in two places. The penultimate segment,
2268 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2269 // final segment, `foo::<B>` contains parameters in fn space.
2271 // The first step then is to categorize the segments appropriately.
2273 let tcx = self.tcx();
2275 assert!(!segments.is_empty());
2276 let last = segments.len() - 1;
2278 let mut path_segs = vec![];
2281 // Case 1. Reference to a struct constructor.
2282 DefKind::Ctor(CtorOf::Struct, ..) => {
2283 // Everything but the final segment should have no
2284 // parameters at all.
2285 let generics = tcx.generics_of(def_id);
2286 // Variant and struct constructors use the
2287 // generics of their parent type definition.
2288 let generics_def_id = generics.parent.unwrap_or(def_id);
2289 path_segs.push(PathSeg(generics_def_id, last));
2292 // Case 2. Reference to a variant constructor.
2293 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2294 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2295 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2296 debug_assert!(adt_def.is_enum());
2297 (adt_def.did(), last)
2298 } else if last >= 1 && segments[last - 1].args.is_some() {
2299 // Everything but the penultimate segment should have no
2300 // parameters at all.
2301 let mut def_id = def_id;
2303 // `DefKind::Ctor` -> `DefKind::Variant`
2304 if let DefKind::Ctor(..) = kind {
2305 def_id = tcx.parent(def_id);
2308 // `DefKind::Variant` -> `DefKind::Enum`
2309 let enum_def_id = tcx.parent(def_id);
2310 (enum_def_id, last - 1)
2312 // FIXME: lint here recommending `Enum::<...>::Variant` form
2313 // instead of `Enum::Variant::<...>` form.
2315 // Everything but the final segment should have no
2316 // parameters at all.
2317 let generics = tcx.generics_of(def_id);
2318 // Variant and struct constructors use the
2319 // generics of their parent type definition.
2320 (generics.parent.unwrap_or(def_id), last)
2322 path_segs.push(PathSeg(generics_def_id, index));
2325 // Case 3. Reference to a top-level value.
2326 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static(_) => {
2327 path_segs.push(PathSeg(def_id, last));
2330 // Case 4. Reference to a method or associated const.
2331 DefKind::AssocFn | DefKind::AssocConst => {
2332 if segments.len() >= 2 {
2333 let generics = tcx.generics_of(def_id);
2334 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2336 path_segs.push(PathSeg(def_id, last));
2339 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2342 debug!("path_segs = {:?}", path_segs);
2347 // Check a type `Path` and convert it to a `Ty`.
2350 opt_self_ty: Option<Ty<'tcx>>,
2351 path: &hir::Path<'_>,
2352 permit_variants: bool,
2354 let tcx = self.tcx();
2357 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2358 path.res, opt_self_ty, path.segments
2361 let span = path.span;
2363 Res::Def(DefKind::OpaqueTy | DefKind::ImplTraitPlaceholder, did) => {
2364 // Check for desugared `impl Trait`.
2365 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2366 let item_segment = path.segments.split_last().unwrap();
2367 self.prohibit_generics(item_segment.1.iter(), |err| {
2368 err.note("`impl Trait` types can't have type parameters");
2370 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2371 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2378 | DefKind::ForeignTy,
2381 assert_eq!(opt_self_ty, None);
2382 self.prohibit_generics(path.segments.split_last().unwrap().1.iter(), |_| {});
2383 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2385 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2386 // Convert "variant type" as if it were a real type.
2387 // The resulting `Ty` is type of the variant's enum for now.
2388 assert_eq!(opt_self_ty, None);
2391 self.def_ids_for_value_path_segments(path.segments, None, kind, def_id);
2392 let generic_segs: FxHashSet<_> =
2393 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2394 self.prohibit_generics(
2395 path.segments.iter().enumerate().filter_map(|(index, seg)| {
2396 if !generic_segs.contains(&index) { Some(seg) } else { None }
2399 err.note("enum variants can't have type parameters");
2403 let PathSeg(def_id, index) = path_segs.last().unwrap();
2404 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2406 Res::Def(DefKind::TyParam, def_id) => {
2407 assert_eq!(opt_self_ty, None);
2408 self.prohibit_generics(path.segments.iter(), |err| {
2409 if let Some(span) = tcx.def_ident_span(def_id) {
2410 let name = tcx.item_name(def_id);
2411 err.span_note(span, &format!("type parameter `{name}` defined here"));
2415 let def_id = def_id.expect_local();
2416 let item_def_id = tcx.hir().ty_param_owner(def_id);
2417 let generics = tcx.generics_of(item_def_id);
2418 let index = generics.param_def_id_to_index[&def_id.to_def_id()];
2419 tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id))
2421 Res::SelfTy { trait_: Some(_), alias_to: None } => {
2422 // `Self` in trait or type alias.
2423 assert_eq!(opt_self_ty, None);
2424 self.prohibit_generics(path.segments.iter(), |err| {
2425 if let [hir::PathSegment { args: Some(args), ident, .. }] = &path.segments[..] {
2426 err.span_suggestion_verbose(
2427 ident.span.shrink_to_hi().to(args.span_ext),
2428 "the `Self` type doesn't accept type parameters",
2430 Applicability::MaybeIncorrect,
2434 tcx.types.self_param
2436 Res::SelfTy { trait_: _, alias_to: Some((def_id, forbid_generic)) } => {
2437 // `Self` in impl (we know the concrete type).
2438 assert_eq!(opt_self_ty, None);
2439 // Try to evaluate any array length constants.
2440 let ty = tcx.at(span).type_of(def_id);
2441 let span_of_impl = tcx.span_of_impl(def_id);
2442 self.prohibit_generics(path.segments.iter(), |err| {
2443 let def_id = match *ty.kind() {
2444 ty::Adt(self_def, _) => self_def.did(),
2448 let type_name = tcx.item_name(def_id);
2449 let span_of_ty = tcx.def_ident_span(def_id);
2450 let generics = tcx.generics_of(def_id).count();
2452 let msg = format!("`Self` is of type `{ty}`");
2453 if let (Ok(i_sp), Some(t_sp)) = (span_of_impl, span_of_ty) {
2454 let mut span: MultiSpan = vec![t_sp].into();
2455 span.push_span_label(
2457 &format!("`Self` is on type `{type_name}` in this `impl`"),
2459 let mut postfix = "";
2461 postfix = ", which doesn't have generic parameters";
2463 span.push_span_label(
2465 &format!("`Self` corresponds to this type{postfix}"),
2467 err.span_note(span, &msg);
2471 for segment in path.segments {
2472 if let Some(args) = segment.args && segment.ident.name == kw::SelfUpper {
2474 // FIXME(estebank): we could also verify that the arguments being
2475 // work for the `enum`, instead of just looking if it takes *any*.
2476 err.span_suggestion_verbose(
2477 segment.ident.span.shrink_to_hi().to(args.span_ext),
2478 "the `Self` type doesn't accept type parameters",
2480 Applicability::MachineApplicable,
2484 err.span_suggestion_verbose(
2487 "the `Self` type doesn't accept type parameters, use the \
2488 concrete type's name `{type_name}` instead if you want to \
2489 specify its type parameters"
2492 Applicability::MaybeIncorrect,
2498 // HACK(min_const_generics): Forbid generic `Self` types
2499 // here as we can't easily do that during nameres.
2501 // We do this before normalization as we otherwise allow
2503 // trait AlwaysApplicable { type Assoc; }
2504 // impl<T: ?Sized> AlwaysApplicable for T { type Assoc = usize; }
2506 // trait BindsParam<T> {
2509 // impl<T> BindsParam<T> for <T as AlwaysApplicable>::Assoc {
2510 // type ArrayTy = [u8; Self::MAX];
2513 // Note that the normalization happens in the param env of
2514 // the anon const, which is empty. This is why the
2515 // `AlwaysApplicable` impl needs a `T: ?Sized` bound for
2516 // this to compile if we were to normalize here.
2517 if forbid_generic && ty.needs_subst() {
2518 let mut err = tcx.sess.struct_span_err(
2520 "generic `Self` types are currently not permitted in anonymous constants",
2522 if let Some(hir::Node::Item(&hir::Item {
2523 kind: hir::ItemKind::Impl(ref impl_),
2525 })) = tcx.hir().get_if_local(def_id)
2527 err.span_note(impl_.self_ty.span, "not a concrete type");
2532 self.normalize_ty(span, ty)
2535 Res::Def(DefKind::AssocTy, def_id) => {
2536 debug_assert!(path.segments.len() >= 2);
2537 self.prohibit_generics(path.segments[..path.segments.len() - 2].iter(), |_| {});
2542 &path.segments[path.segments.len() - 2],
2543 path.segments.last().unwrap(),
2546 Res::PrimTy(prim_ty) => {
2547 assert_eq!(opt_self_ty, None);
2548 self.prohibit_generics(path.segments.iter(), |err| {
2549 let name = prim_ty.name_str();
2550 for segment in path.segments {
2551 if let Some(args) = segment.args {
2552 err.span_suggestion_verbose(
2553 segment.ident.span.shrink_to_hi().to(args.span_ext),
2554 &format!("primitive type `{name}` doesn't have generic parameters"),
2556 Applicability::MaybeIncorrect,
2562 hir::PrimTy::Bool => tcx.types.bool,
2563 hir::PrimTy::Char => tcx.types.char,
2564 hir::PrimTy::Int(it) => tcx.mk_mach_int(ty::int_ty(it)),
2565 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(ty::uint_ty(uit)),
2566 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ty::float_ty(ft)),
2567 hir::PrimTy::Str => tcx.types.str_,
2571 self.set_tainted_by_errors();
2572 self.tcx().ty_error()
2574 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2578 /// Parses the programmer's textual representation of a type into our
2579 /// internal notion of a type.
2580 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2581 self.ast_ty_to_ty_inner(ast_ty, false, false)
2584 /// Parses the programmer's textual representation of a type into our
2585 /// internal notion of a type. This is meant to be used within a path.
2586 pub fn ast_ty_to_ty_in_path(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2587 self.ast_ty_to_ty_inner(ast_ty, false, true)
2590 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2591 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2592 #[instrument(level = "debug", skip(self), ret)]
2593 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool, in_path: bool) -> Ty<'tcx> {
2594 let tcx = self.tcx();
2596 let result_ty = match ast_ty.kind {
2597 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
2598 hir::TyKind::Ptr(ref mt) => {
2599 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
2601 hir::TyKind::Rptr(ref region, ref mt) => {
2602 let r = self.ast_region_to_region(region, None);
2604 let t = self.ast_ty_to_ty_inner(mt.ty, true, false);
2605 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2607 hir::TyKind::Never => tcx.types.never,
2608 hir::TyKind::Tup(fields) => tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(t))),
2609 hir::TyKind::BareFn(bf) => {
2610 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
2612 tcx.mk_fn_ptr(self.ty_of_fn(
2621 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
2622 self.maybe_lint_bare_trait(ast_ty, in_path);
2623 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed)
2625 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2626 debug!(?maybe_qself, ?path);
2627 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2628 self.res_to_ty(opt_self_ty, path, false)
2630 hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
2631 let opaque_ty = tcx.hir().item(item_id);
2632 let def_id = item_id.def_id.to_def_id();
2634 match opaque_ty.kind {
2635 hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
2636 self.impl_trait_ty_to_ty(def_id, lifetimes, origin, in_trait)
2638 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2641 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2642 debug!(?qself, ?segment);
2643 let ty = self.ast_ty_to_ty_inner(qself, false, true);
2644 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, qself, segment, false)
2645 .map(|(ty, _, _)| ty)
2646 .unwrap_or_else(|_| tcx.ty_error())
2648 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
2649 let def_id = tcx.require_lang_item(lang_item, Some(span));
2650 let (substs, _) = self.create_substs_for_ast_path(
2654 &hir::PathSegment::invalid(),
2655 &GenericArgs::none(),
2659 EarlyBinder(self.normalize_ty(span, tcx.at(span).type_of(def_id)))
2662 hir::TyKind::Array(ref ty, ref length) => {
2663 let length = match length {
2664 &hir::ArrayLen::Infer(_, span) => self.ct_infer(tcx.types.usize, None, span),
2665 hir::ArrayLen::Body(constant) => {
2666 let length_def_id = tcx.hir().local_def_id(constant.hir_id);
2667 ty::Const::from_anon_const(tcx, length_def_id)
2671 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(ty), length));
2672 self.normalize_ty(ast_ty.span, array_ty)
2674 hir::TyKind::Typeof(ref e) => {
2675 let ty = tcx.type_of(tcx.hir().local_def_id(e.hir_id));
2676 let span = ast_ty.span;
2677 tcx.sess.emit_err(TypeofReservedKeywordUsed {
2680 opt_sugg: Some((span, Applicability::MachineApplicable))
2681 .filter(|_| ty.is_suggestable(tcx, false)),
2686 hir::TyKind::Infer => {
2687 // Infer also appears as the type of arguments or return
2688 // values in an ExprKind::Closure, or as
2689 // the type of local variables. Both of these cases are
2690 // handled specially and will not descend into this routine.
2691 self.ty_infer(None, ast_ty.span)
2693 hir::TyKind::Err => tcx.ty_error(),
2696 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2700 #[instrument(level = "debug", skip(self), ret)]
2701 fn impl_trait_ty_to_ty(
2704 lifetimes: &[hir::GenericArg<'_>],
2705 origin: OpaqueTyOrigin,
2708 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2709 let tcx = self.tcx();
2711 let generics = tcx.generics_of(def_id);
2713 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2714 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2715 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2716 // Our own parameters are the resolved lifetimes.
2717 if let GenericParamDefKind::Lifetime = param.kind {
2718 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2719 self.ast_region_to_region(lifetime, None).into()
2728 // For RPIT (return position impl trait), only lifetimes
2729 // mentioned in the impl Trait predicate are captured by
2730 // the opaque type, so the lifetime parameters from the
2731 // parent item need to be replaced with `'static`.
2733 // For `impl Trait` in the types of statics, constants,
2734 // locals and type aliases. These capture all parent
2735 // lifetimes, so they can use their identity subst.
2736 GenericParamDefKind::Lifetime
2739 hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..)
2742 tcx.lifetimes.re_static.into()
2744 _ => tcx.mk_param_from_def(param),
2748 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2750 if in_trait { tcx.mk_projection(def_id, substs) } else { tcx.mk_opaque(def_id, substs) }
2753 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2755 hir::TyKind::Infer if expected_ty.is_some() => {
2756 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2757 expected_ty.unwrap()
2759 _ => self.ast_ty_to_ty(ty),
2766 unsafety: hir::Unsafety,
2768 decl: &hir::FnDecl<'_>,
2769 generics: Option<&hir::Generics<'_>>,
2770 hir_ty: Option<&hir::Ty<'_>>,
2771 ) -> ty::PolyFnSig<'tcx> {
2774 let tcx = self.tcx();
2775 let bound_vars = tcx.late_bound_vars(hir_id);
2776 debug!(?bound_vars);
2778 // We proactively collect all the inferred type params to emit a single error per fn def.
2779 let mut visitor = HirPlaceholderCollector::default();
2780 let mut infer_replacements = vec![];
2782 if let Some(generics) = generics {
2783 walk_generics(&mut visitor, generics);
2786 let input_tys: Vec<_> = decl
2791 if let hir::TyKind::Infer = a.kind && !self.allow_ty_infer() {
2792 if let Some(suggested_ty) =
2793 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, Some(i))
2795 infer_replacements.push((a.span, suggested_ty.to_string()));
2796 return suggested_ty;
2800 // Only visit the type looking for `_` if we didn't fix the type above
2801 visitor.visit_ty(a);
2802 self.ty_of_arg(a, None)
2806 let output_ty = match decl.output {
2807 hir::FnRetTy::Return(output) => {
2808 if let hir::TyKind::Infer = output.kind
2809 && !self.allow_ty_infer()
2810 && let Some(suggested_ty) =
2811 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, None)
2813 infer_replacements.push((output.span, suggested_ty.to_string()));
2816 visitor.visit_ty(output);
2817 self.ast_ty_to_ty(output)
2820 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2823 debug!("ty_of_fn: output_ty={:?}", output_ty);
2825 let fn_ty = tcx.mk_fn_sig(input_tys.into_iter(), output_ty, decl.c_variadic, unsafety, abi);
2826 let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
2828 if !self.allow_ty_infer() && !(visitor.0.is_empty() && infer_replacements.is_empty()) {
2829 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2830 // only want to emit an error complaining about them if infer types (`_`) are not
2831 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2832 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2834 let mut diag = crate::collect::placeholder_type_error_diag(
2838 infer_replacements.iter().map(|(s, _)| *s).collect(),
2844 if !infer_replacements.is_empty() {
2845 diag.multipart_suggestion(
2847 "try replacing `_` with the type{} in the corresponding trait method signature",
2848 rustc_errors::pluralize!(infer_replacements.len()),
2851 Applicability::MachineApplicable,
2858 // Find any late-bound regions declared in return type that do
2859 // not appear in the arguments. These are not well-formed.
2862 // for<'a> fn() -> &'a str <-- 'a is bad
2863 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2864 let inputs = bare_fn_ty.inputs();
2865 let late_bound_in_args =
2866 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2867 let output = bare_fn_ty.output();
2868 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2870 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
2875 "return type references {}, which is not constrained by the fn input types",
2883 /// Given a fn_hir_id for a impl function, suggest the type that is found on the
2884 /// corresponding function in the trait that the impl implements, if it exists.
2885 /// If arg_idx is Some, then it corresponds to an input type index, otherwise it
2886 /// corresponds to the return type.
2887 fn suggest_trait_fn_ty_for_impl_fn_infer(
2889 fn_hir_id: hir::HirId,
2890 arg_idx: Option<usize>,
2891 ) -> Option<Ty<'tcx>> {
2892 let tcx = self.tcx();
2893 let hir = tcx.hir();
2895 let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), ident, .. }) =
2896 hir.get(fn_hir_id) else { return None };
2897 let hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(i), .. }) =
2898 hir.get(hir.get_parent_node(fn_hir_id)) else { bug!("ImplItem should have Impl parent") };
2901 self.instantiate_mono_trait_ref(i.of_trait.as_ref()?, self.ast_ty_to_ty(i.self_ty));
2903 let assoc = tcx.associated_items(trait_ref.def_id).find_by_name_and_kind(
2910 let fn_sig = tcx.bound_fn_sig(assoc.def_id).subst(
2912 trait_ref.substs.extend_to(tcx, assoc.def_id, |param, _| tcx.mk_param_from_def(param)),
2915 let ty = if let Some(arg_idx) = arg_idx { fn_sig.input(arg_idx) } else { fn_sig.output() };
2917 Some(tcx.liberate_late_bound_regions(fn_hir_id.expect_owner().to_def_id(), ty))
2920 fn validate_late_bound_regions(
2922 constrained_regions: FxHashSet<ty::BoundRegionKind>,
2923 referenced_regions: FxHashSet<ty::BoundRegionKind>,
2924 generate_err: impl Fn(&str) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
2926 for br in referenced_regions.difference(&constrained_regions) {
2927 let br_name = match *br {
2928 ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) | ty::BrEnv => {
2929 "an anonymous lifetime".to_string()
2931 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
2934 let mut err = generate_err(&br_name);
2936 if let ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) = *br {
2937 // The only way for an anonymous lifetime to wind up
2938 // in the return type but **also** be unconstrained is
2939 // if it only appears in "associated types" in the
2940 // input. See #47511 and #62200 for examples. In this case,
2941 // though we can easily give a hint that ought to be
2944 "lifetimes appearing in an associated or opaque type are not considered constrained",
2946 err.note("consider introducing a named lifetime parameter");
2953 /// Given the bounds on an object, determines what single region bound (if any) we can
2954 /// use to summarize this type. The basic idea is that we will use the bound the user
2955 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2956 /// for region bounds. It may be that we can derive no bound at all, in which case
2957 /// we return `None`.
2958 fn compute_object_lifetime_bound(
2961 existential_predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
2962 ) -> Option<ty::Region<'tcx>> // if None, use the default
2964 let tcx = self.tcx();
2966 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2968 // No explicit region bound specified. Therefore, examine trait
2969 // bounds and see if we can derive region bounds from those.
2970 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2972 // If there are no derived region bounds, then report back that we
2973 // can find no region bound. The caller will use the default.
2974 if derived_region_bounds.is_empty() {
2978 // If any of the derived region bounds are 'static, that is always
2980 if derived_region_bounds.iter().any(|r| r.is_static()) {
2981 return Some(tcx.lifetimes.re_static);
2984 // Determine whether there is exactly one unique region in the set
2985 // of derived region bounds. If so, use that. Otherwise, report an
2987 let r = derived_region_bounds[0];
2988 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2989 tcx.sess.emit_err(AmbiguousLifetimeBound { span });
2994 /// Make sure that we are in the condition to suggest the blanket implementation.
2995 fn maybe_lint_blanket_trait_impl(&self, self_ty: &hir::Ty<'_>, diag: &mut Diagnostic) {
2996 let tcx = self.tcx();
2997 let parent_id = tcx.hir().get_parent_item(self_ty.hir_id);
2998 if let hir::Node::Item(hir::Item {
3000 hir::ItemKind::Impl(hir::Impl {
3001 self_ty: impl_self_ty, of_trait: Some(of_trait_ref), generics, ..
3004 }) = tcx.hir().get_by_def_id(parent_id) && self_ty.hir_id == impl_self_ty.hir_id
3006 if !of_trait_ref.trait_def_id().map_or(false, |def_id| def_id.is_local()) {
3009 let of_trait_span = of_trait_ref.path.span;
3010 // make sure that we are not calling unwrap to abort during the compilation
3011 let Ok(impl_trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else { return; };
3012 let Ok(of_trait_name) = tcx.sess.source_map().span_to_snippet(of_trait_span) else { return; };
3013 // check if the trait has generics, to make a correct suggestion
3014 let param_name = generics.params.next_type_param_name(None);
3016 let add_generic_sugg = if let Some(span) = generics.span_for_param_suggestion() {
3017 (span, format!(", {}: {}", param_name, impl_trait_name))
3019 (generics.span, format!("<{}: {}>", param_name, impl_trait_name))
3021 diag.multipart_suggestion(
3022 format!("alternatively use a blanket \
3023 implementation to implement `{of_trait_name}` for \
3024 all types that also implement `{impl_trait_name}`"),
3026 (self_ty.span, param_name),
3029 Applicability::MaybeIncorrect,
3034 fn maybe_lint_bare_trait(&self, self_ty: &hir::Ty<'_>, in_path: bool) {
3035 let tcx = self.tcx();
3036 if let hir::TyKind::TraitObject([poly_trait_ref, ..], _, TraitObjectSyntax::None) =
3039 let needs_bracket = in_path
3043 .span_to_prev_source(self_ty.span)
3045 .map_or(false, |s| s.trim_end().ends_with('<'));
3047 let is_global = poly_trait_ref.trait_ref.path.is_global();
3048 let sugg = Vec::from_iter([
3050 self_ty.span.shrink_to_lo(),
3053 if needs_bracket { "<" } else { "" },
3054 if is_global { "(" } else { "" },
3058 self_ty.span.shrink_to_hi(),
3061 if is_global { ")" } else { "" },
3062 if needs_bracket { ">" } else { "" },
3066 if self_ty.span.edition() >= Edition::Edition2021 {
3067 let msg = "trait objects must include the `dyn` keyword";
3068 let label = "add `dyn` keyword before this trait";
3070 rustc_errors::struct_span_err!(tcx.sess, self_ty.span, E0782, "{}", msg);
3071 diag.multipart_suggestion_verbose(label, sugg, Applicability::MachineApplicable);
3072 // check if the impl trait that we are considering is a impl of a local trait
3073 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);
3076 let msg = "trait objects without an explicit `dyn` are deprecated";
3077 tcx.struct_span_lint_hir(
3082 let mut diag = lint.build(msg);
3083 diag.multipart_suggestion_verbose(
3086 Applicability::MachineApplicable,
3088 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);