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::{GenericArg, GenericArgs, OpaqueTyOrigin};
27 use rustc_middle::middle::stability::AllowUnstable;
28 use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, SubstsRef};
29 use rustc_middle::ty::DynKind;
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};
38 use rustc_span::{sym, Span};
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) -> 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,
279 if let Some(b) = item_segment.args().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 /// Constraints on associated types are created from `create_assoc_bindings_for_generic_args`.
293 /// ```ignore (illustrative)
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 from `create_assoc_bindings_for_generic_args`.
305 /// Note that the type listing given here is *exactly* what the user provided.
307 /// For (generic) associated types
309 /// ```ignore (illustrative)
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 #[instrument(level = "debug", skip(self, span), ret)]
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 constness: Option<ty::BoundConstness>,
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(parent_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 ty.references_error() {
504 return tcx.const_error(ty).into();
506 if !infer_args && has_default {
507 tcx.bound_const_param_default(param.def_id)
508 .subst(tcx, substs.unwrap())
512 self.astconv.ct_infer(ty, Some(param), self.span).into()
514 // We've already errored above about the mismatch.
515 tcx.const_error(ty).into()
523 let mut substs_ctx = SubstsForAstPathCtxt {
528 inferred_params: vec![],
531 let substs = Self::create_substs_for_generic_args(
541 if let Some(ty::BoundConstness::ConstIfConst) = constness
542 && generics.has_self && !tcx.has_attr(def_id, sym::const_trait)
544 tcx.sess.emit_err(crate::errors::ConstBoundForNonConstTrait { span } );
550 fn create_assoc_bindings_for_generic_args<'a>(
552 generic_args: &'a hir::GenericArgs<'_>,
553 ) -> Vec<ConvertedBinding<'a, 'tcx>> {
554 // Convert associated-type bindings or constraints into a separate vector.
555 // Example: Given this:
557 // T: Iterator<Item = u32>
559 // The `T` is passed in as a self-type; the `Item = u32` is
560 // not a "type parameter" of the `Iterator` trait, but rather
561 // a restriction on `<T as Iterator>::Item`, so it is passed
563 let assoc_bindings = generic_args
567 let kind = match binding.kind {
568 hir::TypeBindingKind::Equality { ref term } => match term {
569 hir::Term::Ty(ref ty) => {
570 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty).into())
572 hir::Term::Const(ref c) => {
573 let local_did = self.tcx().hir().local_def_id(c.hir_id);
574 let c = Const::from_anon_const(self.tcx(), local_did);
575 ConvertedBindingKind::Equality(c.into())
578 hir::TypeBindingKind::Constraint { ref bounds } => {
579 ConvertedBindingKind::Constraint(bounds)
583 hir_id: binding.hir_id,
584 item_name: binding.ident,
586 gen_args: binding.gen_args,
595 pub fn create_substs_for_associated_item(
599 item_segment: &hir::PathSegment<'_>,
600 parent_substs: SubstsRef<'tcx>,
601 ) -> SubstsRef<'tcx> {
603 "create_substs_for_associated_item(span: {:?}, item_def_id: {:?}, item_segment: {:?}",
604 span, item_def_id, item_segment
606 let (args, _) = self.create_substs_for_ast_path(
612 item_segment.infer_args,
617 if let Some(b) = item_segment.args().bindings.first() {
618 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
624 /// Instantiates the path for the given trait reference, assuming that it's
625 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
626 /// The type _cannot_ be a type other than a trait type.
628 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
629 /// are disallowed. Otherwise, they are pushed onto the vector given.
630 pub fn instantiate_mono_trait_ref(
632 trait_ref: &hir::TraitRef<'_>,
634 constness: ty::BoundConstness,
635 ) -> ty::TraitRef<'tcx> {
636 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
638 self.ast_path_to_mono_trait_ref(
640 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
642 trait_ref.path.segments.last().unwrap(),
648 fn instantiate_poly_trait_ref_inner(
652 binding_span: Option<Span>,
653 constness: ty::BoundConstness,
654 bounds: &mut Bounds<'tcx>,
656 trait_ref_span: Span,
658 trait_segment: &hir::PathSegment<'_>,
659 args: &GenericArgs<'_>,
662 ) -> GenericArgCountResult {
663 let (substs, arg_count) = self.create_substs_for_ast_path(
674 let tcx = self.tcx();
675 let bound_vars = tcx.late_bound_vars(hir_id);
678 let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
681 ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
683 debug!(?poly_trait_ref, ?assoc_bindings);
684 bounds.trait_bounds.push((poly_trait_ref, span, constness));
686 let mut dup_bindings = FxHashMap::default();
687 for binding in &assoc_bindings {
688 // Specify type to assert that error was already reported in `Err` case.
689 let _: Result<_, ErrorGuaranteed> = self.add_predicates_for_ast_type_binding(
696 binding_span.unwrap_or(binding.span),
699 // Okay to ignore `Err` because of `ErrorGuaranteed` (see above).
705 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
706 /// a full trait reference. The resulting trait reference is returned. This may also generate
707 /// auxiliary bounds, which are added to `bounds`.
711 /// ```ignore (illustrative)
712 /// poly_trait_ref = Iterator<Item = u32>
716 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
718 /// **A note on binders:** against our usual convention, there is an implied bounder around
719 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
720 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
721 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
722 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
724 #[instrument(level = "debug", skip(self, span, constness, bounds, speculative))]
725 pub(crate) fn instantiate_poly_trait_ref(
727 trait_ref: &hir::TraitRef<'_>,
729 constness: ty::BoundConstness,
731 bounds: &mut Bounds<'tcx>,
733 ) -> GenericArgCountResult {
734 let hir_id = trait_ref.hir_ref_id;
735 let binding_span = None;
736 let trait_ref_span = trait_ref.path.span;
737 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
738 let trait_segment = trait_ref.path.segments.last().unwrap();
739 let args = trait_segment.args();
740 let infer_args = trait_segment.infer_args;
742 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
743 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, false);
745 self.instantiate_poly_trait_ref_inner(
761 pub(crate) fn instantiate_lang_item_trait_ref(
763 lang_item: hir::LangItem,
766 args: &GenericArgs<'_>,
768 bounds: &mut Bounds<'tcx>,
770 let binding_span = Some(span);
771 let constness = ty::BoundConstness::NotConst;
772 let speculative = false;
773 let trait_ref_span = span;
774 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
775 let trait_segment = &hir::PathSegment::invalid();
776 let infer_args = false;
778 self.instantiate_poly_trait_ref_inner(
794 fn ast_path_to_mono_trait_ref(
799 trait_segment: &hir::PathSegment<'_>,
801 constness: Option<ty::BoundConstness>,
802 ) -> ty::TraitRef<'tcx> {
803 let (substs, _) = self.create_substs_for_ast_trait_ref(
811 if let Some(b) = trait_segment.args().bindings.first() {
812 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
814 ty::TraitRef::new(trait_def_id, substs)
817 #[instrument(level = "debug", skip(self, span))]
818 fn create_substs_for_ast_trait_ref<'a>(
823 trait_segment: &'a hir::PathSegment<'a>,
825 constness: Option<ty::BoundConstness>,
826 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
827 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
829 self.create_substs_for_ast_path(
834 trait_segment.args(),
835 trait_segment.infer_args,
841 fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
843 .associated_items(trait_def_id)
844 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
847 fn trait_defines_associated_const_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
849 .associated_items(trait_def_id)
850 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Const, trait_def_id)
854 // Sets `implicitly_sized` to true on `Bounds` if necessary
855 pub(crate) fn add_implicitly_sized<'hir>(
857 bounds: &mut Bounds<'hir>,
858 ast_bounds: &'hir [hir::GenericBound<'hir>],
859 self_ty_where_predicates: Option<(hir::HirId, &'hir [hir::WherePredicate<'hir>])>,
862 let tcx = self.tcx();
864 // Try to find an unbound in bounds.
865 let mut unbound = None;
866 let mut search_bounds = |ast_bounds: &'hir [hir::GenericBound<'hir>]| {
867 for ab in ast_bounds {
868 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
869 if unbound.is_none() {
870 unbound = Some(&ptr.trait_ref);
872 tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
877 search_bounds(ast_bounds);
878 if let Some((self_ty, where_clause)) = self_ty_where_predicates {
879 let self_ty_def_id = tcx.hir().local_def_id(self_ty).to_def_id();
880 for clause in where_clause {
881 if let hir::WherePredicate::BoundPredicate(pred) = clause {
882 if pred.is_param_bound(self_ty_def_id) {
883 search_bounds(pred.bounds);
889 let sized_def_id = tcx.lang_items().sized_trait();
890 match (&sized_def_id, unbound) {
891 (Some(sized_def_id), Some(tpb))
892 if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) =>
894 // There was in fact a `?Sized` bound, return without doing anything
898 // There was a `?Trait` bound, but it was not `?Sized`; warn.
901 "default bound relaxed for a type parameter, but \
902 this does nothing because the given bound is not \
903 a default; only `?Sized` is supported",
905 // Otherwise, add implicitly sized if `Sized` is available.
908 // There was no `?Sized` bound; add implicitly sized if `Sized` is available.
911 if sized_def_id.is_none() {
912 // No lang item for `Sized`, so we can't add it as a bound.
915 bounds.implicitly_sized = Some(span);
918 /// This helper takes a *converted* parameter type (`param_ty`)
919 /// and an *unconverted* list of bounds:
923 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
925 /// `param_ty`, in ty form
928 /// It adds these `ast_bounds` into the `bounds` structure.
930 /// **A note on binders:** there is an implied binder around
931 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
932 /// for more details.
933 #[instrument(level = "debug", skip(self, ast_bounds, bounds))]
934 pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>(
938 bounds: &mut Bounds<'tcx>,
939 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
941 for ast_bound in ast_bounds {
943 hir::GenericBound::Trait(poly_trait_ref, modifier) => {
944 let constness = match modifier {
945 hir::TraitBoundModifier::MaybeConst => ty::BoundConstness::ConstIfConst,
946 hir::TraitBoundModifier::None => ty::BoundConstness::NotConst,
947 hir::TraitBoundModifier::Maybe => continue,
950 let _ = self.instantiate_poly_trait_ref(
951 &poly_trait_ref.trait_ref,
959 &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
960 self.instantiate_lang_item_trait_ref(
961 lang_item, span, hir_id, args, param_ty, bounds,
964 hir::GenericBound::Outlives(lifetime) => {
965 let region = self.ast_region_to_region(lifetime, None);
968 .push((ty::Binder::bind_with_vars(region, bound_vars), lifetime.span));
974 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
975 /// The self-type for the bounds is given by `param_ty`.
979 /// ```ignore (illustrative)
980 /// fn foo<T: Bar + Baz>() { }
981 /// // ^ ^^^^^^^^^ ast_bounds
985 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
986 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
987 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
989 /// `span` should be the declaration size of the parameter.
990 pub(crate) fn compute_bounds(
993 ast_bounds: &[hir::GenericBound<'_>],
995 self.compute_bounds_inner(param_ty, ast_bounds)
998 /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
999 /// named `assoc_name` into ty::Bounds. Ignore the rest.
1000 pub(crate) fn compute_bounds_that_match_assoc_type(
1003 ast_bounds: &[hir::GenericBound<'_>],
1006 let mut result = Vec::new();
1008 for ast_bound in ast_bounds {
1009 if let Some(trait_ref) = ast_bound.trait_ref()
1010 && let Some(trait_did) = trait_ref.trait_def_id()
1011 && self.tcx().trait_may_define_assoc_type(trait_did, assoc_name)
1013 result.push(ast_bound.clone());
1017 self.compute_bounds_inner(param_ty, &result)
1020 fn compute_bounds_inner(
1023 ast_bounds: &[hir::GenericBound<'_>],
1025 let mut bounds = Bounds::default();
1027 self.add_bounds(param_ty, ast_bounds.iter(), &mut bounds, ty::List::empty());
1033 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1036 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1037 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1038 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1039 #[instrument(level = "debug", skip(self, bounds, speculative, dup_bindings, path_span))]
1040 fn add_predicates_for_ast_type_binding(
1042 hir_ref_id: hir::HirId,
1043 trait_ref: ty::PolyTraitRef<'tcx>,
1044 binding: &ConvertedBinding<'_, 'tcx>,
1045 bounds: &mut Bounds<'tcx>,
1047 dup_bindings: &mut FxHashMap<DefId, Span>,
1049 constness: ty::BoundConstness,
1050 ) -> Result<(), ErrorGuaranteed> {
1051 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1052 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1053 // subtle in the event that `T` is defined in a supertrait of
1054 // `SomeTrait`, because in that case we need to upcast.
1056 // That is, consider this case:
1059 // trait SubTrait: SuperTrait<i32> { }
1060 // trait SuperTrait<A> { type T; }
1062 // ... B: SubTrait<T = foo> ...
1065 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
1067 let tcx = self.tcx();
1070 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1071 // Simple case: X is defined in the current trait.
1074 // Otherwise, we have to walk through the supertraits to find
1076 self.one_bound_for_assoc_type(
1077 || traits::supertraits(tcx, trait_ref),
1078 || trait_ref.print_only_trait_path().to_string(),
1081 || match binding.kind {
1082 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1088 let (assoc_ident, def_scope) =
1089 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1091 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1092 // of calling `filter_by_name_and_kind`.
1093 let find_item_of_kind = |kind| {
1094 tcx.associated_items(candidate.def_id())
1095 .filter_by_name_unhygienic(assoc_ident.name)
1096 .find(|i| i.kind == kind && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident)
1098 let assoc_item = find_item_of_kind(ty::AssocKind::Type)
1099 .or_else(|| find_item_of_kind(ty::AssocKind::Const))
1100 .expect("missing associated type");
1102 if !assoc_item.visibility(tcx).is_accessible_from(def_scope, tcx) {
1106 &format!("{} `{}` is private", assoc_item.kind, binding.item_name),
1108 .span_label(binding.span, &format!("private {}", assoc_item.kind))
1111 tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None);
1115 .entry(assoc_item.def_id)
1116 .and_modify(|prev_span| {
1117 self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
1119 prev_span: *prev_span,
1120 item_name: binding.item_name,
1121 def_path: tcx.def_path_str(assoc_item.container_id(tcx)),
1124 .or_insert(binding.span);
1127 // Include substitutions for generic parameters of associated types
1128 let projection_ty = candidate.map_bound(|trait_ref| {
1129 let ident = Ident::new(assoc_item.name, binding.item_name.span);
1130 let item_segment = hir::PathSegment {
1132 hir_id: binding.hir_id,
1134 args: Some(binding.gen_args),
1138 let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
1145 debug!(?substs_trait_ref_and_assoc_item);
1148 item_def_id: assoc_item.def_id,
1149 substs: substs_trait_ref_and_assoc_item,
1154 // Find any late-bound regions declared in `ty` that are not
1155 // declared in the trait-ref or assoc_item. These are not well-formed.
1159 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1160 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1161 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1162 let late_bound_in_trait_ref =
1163 tcx.collect_constrained_late_bound_regions(&projection_ty);
1164 let late_bound_in_ty =
1165 tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty));
1166 debug!(?late_bound_in_trait_ref);
1167 debug!(?late_bound_in_ty);
1169 // FIXME: point at the type params that don't have appropriate lifetimes:
1170 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1171 // ---- ---- ^^^^^^^
1172 self.validate_late_bound_regions(
1173 late_bound_in_trait_ref,
1180 "binding for associated type `{}` references {}, \
1181 which does not appear in the trait input types",
1190 match binding.kind {
1191 ConvertedBindingKind::Equality(mut term) => {
1192 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1193 // the "projection predicate" for:
1195 // `<T as Iterator>::Item = u32`
1196 let assoc_item_def_id = projection_ty.skip_binder().item_def_id;
1197 let def_kind = tcx.def_kind(assoc_item_def_id);
1198 match (def_kind, term.unpack()) {
1199 (hir::def::DefKind::AssocTy, ty::TermKind::Ty(_))
1200 | (hir::def::DefKind::AssocConst, ty::TermKind::Const(_)) => (),
1202 let got = if let Some(_) = term.ty() { "type" } else { "constant" };
1203 let expected = def_kind.descr(assoc_item_def_id);
1207 &format!("expected {expected} bound, found {got}"),
1210 tcx.def_span(assoc_item_def_id),
1211 &format!("{expected} defined here"),
1214 term = match def_kind {
1215 hir::def::DefKind::AssocTy => tcx.ty_error().into(),
1216 hir::def::DefKind::AssocConst => tcx
1218 tcx.bound_type_of(assoc_item_def_id)
1219 .subst(tcx, projection_ty.skip_binder().substs),
1222 _ => unreachable!(),
1226 bounds.projection_bounds.push((
1227 projection_ty.map_bound(|projection_ty| ty::ProjectionPredicate {
1234 ConvertedBindingKind::Constraint(ast_bounds) => {
1235 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1237 // `<T as Iterator>::Item: Debug`
1239 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1240 // parameter to have a skipped binder.
1241 let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
1242 self.add_bounds(param_ty, ast_bounds.iter(), bounds, candidate.bound_vars());
1252 item_segment: &hir::PathSegment<'_>,
1254 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1257 EarlyBinder(self.tcx().at(span).type_of(did)).subst(self.tcx(), substs),
1261 fn conv_object_ty_poly_trait_ref(
1264 trait_bounds: &[hir::PolyTraitRef<'_>],
1265 lifetime: &hir::Lifetime,
1267 representation: DynKind,
1269 let tcx = self.tcx();
1271 let mut bounds = Bounds::default();
1272 let mut potential_assoc_types = Vec::new();
1273 let dummy_self = self.tcx().types.trait_object_dummy_self;
1274 for trait_bound in trait_bounds.iter().rev() {
1275 if let GenericArgCountResult {
1277 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1279 } = self.instantiate_poly_trait_ref(
1280 &trait_bound.trait_ref,
1282 ty::BoundConstness::NotConst,
1287 potential_assoc_types.extend(cur_potential_assoc_types);
1291 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1292 // is used and no 'maybe' bounds are used.
1293 let expanded_traits =
1294 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1295 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) = expanded_traits
1296 .filter(|i| i.trait_ref().self_ty().skip_binder() == dummy_self)
1297 .partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1298 if regular_traits.len() > 1 {
1299 let first_trait = ®ular_traits[0];
1300 let additional_trait = ®ular_traits[1];
1301 let mut err = struct_span_err!(
1303 additional_trait.bottom().1,
1305 "only auto traits can be used as additional traits in a trait object"
1307 additional_trait.label_with_exp_info(
1309 "additional non-auto trait",
1312 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1314 "consider creating a new trait with all of these as supertraits and using that \
1315 trait here instead: `trait NewTrait: {} {{}}`",
1318 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1319 .collect::<Vec<_>>()
1323 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1324 for more information on them, visit \
1325 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1330 if regular_traits.is_empty() && auto_traits.is_empty() {
1331 let trait_alias_span = bounds
1334 .map(|&(trait_ref, _, _)| trait_ref.def_id())
1335 .find(|&trait_ref| tcx.is_trait_alias(trait_ref))
1336 .map(|trait_ref| tcx.def_span(trait_ref));
1337 tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span, trait_alias_span });
1338 return tcx.ty_error();
1341 // Check that there are no gross object safety violations;
1342 // most importantly, that the supertraits don't contain `Self`,
1344 for item in ®ular_traits {
1345 let object_safety_violations =
1346 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1347 if !object_safety_violations.is_empty() {
1348 report_object_safety_error(
1351 item.trait_ref().def_id(),
1352 &object_safety_violations,
1355 return tcx.ty_error();
1359 // Use a `BTreeSet` to keep output in a more consistent order.
1360 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1362 let regular_traits_refs_spans = bounds
1365 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1367 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1368 assert_eq!(constness, ty::BoundConstness::NotConst);
1370 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1372 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1373 obligation.predicate
1376 let bound_predicate = obligation.predicate.kind();
1377 match bound_predicate.skip_binder() {
1378 ty::PredicateKind::Trait(pred) => {
1379 let pred = bound_predicate.rebind(pred);
1380 associated_types.entry(span).or_default().extend(
1381 tcx.associated_items(pred.def_id())
1382 .in_definition_order()
1383 .filter(|item| item.kind == ty::AssocKind::Type)
1384 .map(|item| item.def_id),
1387 ty::PredicateKind::Projection(pred) => {
1388 let pred = bound_predicate.rebind(pred);
1389 // A `Self` within the original bound will be substituted with a
1390 // `trait_object_dummy_self`, so check for that.
1391 let references_self = match pred.skip_binder().term.unpack() {
1392 ty::TermKind::Ty(ty) => ty.walk().any(|arg| arg == dummy_self.into()),
1393 ty::TermKind::Const(c) => {
1394 c.ty().walk().any(|arg| arg == dummy_self.into())
1398 // If the projection output contains `Self`, force the user to
1399 // elaborate it explicitly to avoid a lot of complexity.
1401 // The "classically useful" case is the following:
1403 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1408 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1409 // but actually supporting that would "expand" to an infinitely-long type
1410 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1412 // Instead, we force the user to write
1413 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1414 // the discussion in #56288 for alternatives.
1415 if !references_self {
1416 // Include projections defined on supertraits.
1417 bounds.projection_bounds.push((pred, span));
1425 for (projection_bound, _) in &bounds.projection_bounds {
1426 for def_ids in associated_types.values_mut() {
1427 def_ids.remove(&projection_bound.projection_def_id());
1431 self.complain_about_missing_associated_types(
1433 potential_assoc_types,
1437 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1438 // `dyn Trait + Send`.
1439 // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
1441 let mut duplicates = FxHashSet::default();
1442 auto_traits.retain(|i| duplicates.insert(i.trait_ref().def_id()));
1443 debug!("regular_traits: {:?}", regular_traits);
1444 debug!("auto_traits: {:?}", auto_traits);
1446 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1447 let existential_trait_refs = regular_traits.iter().map(|i| {
1448 i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
1449 assert_eq!(trait_ref.self_ty(), dummy_self);
1451 // Verify that `dummy_self` did not leak inside default type parameters. This
1452 // could not be done at path creation, since we need to see through trait aliases.
1453 let mut missing_type_params = vec![];
1454 let mut references_self = false;
1455 let generics = tcx.generics_of(trait_ref.def_id);
1456 let substs: Vec<_> = trait_ref
1460 .skip(1) // Remove `Self` for `ExistentialPredicate`.
1461 .map(|(index, arg)| {
1462 if arg == dummy_self.into() {
1463 let param = &generics.params[index];
1464 missing_type_params.push(param.name);
1465 return tcx.ty_error().into();
1466 } else if arg.walk().any(|arg| arg == dummy_self.into()) {
1467 references_self = true;
1468 return tcx.ty_error().into();
1473 let substs = tcx.intern_substs(&substs[..]);
1475 let span = i.bottom().1;
1476 let empty_generic_args = trait_bounds.iter().any(|hir_bound| {
1477 hir_bound.trait_ref.path.res == Res::Def(DefKind::Trait, trait_ref.def_id)
1478 && hir_bound.span.contains(span)
1480 self.complain_about_missing_type_params(
1481 missing_type_params,
1487 if references_self {
1488 let def_id = i.bottom().0.def_id();
1489 let mut err = struct_span_err!(
1493 "the {} `{}` cannot be made into an object",
1494 tcx.def_kind(def_id).descr(def_id),
1495 tcx.item_name(def_id),
1498 rustc_middle::traits::ObjectSafetyViolation::SupertraitSelf(smallvec![])
1504 ty::ExistentialTraitRef { def_id: trait_ref.def_id, substs }
1508 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1509 bound.map_bound(|mut b| {
1510 assert_eq!(b.projection_ty.self_ty(), dummy_self);
1512 // Like for trait refs, verify that `dummy_self` did not leak inside default type
1514 let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
1515 if arg.walk().any(|arg| arg == dummy_self.into()) {
1520 if references_self {
1522 .delay_span_bug(span, "trait object projection bounds reference `Self`");
1523 let substs: Vec<_> = b
1528 if arg.walk().any(|arg| arg == dummy_self.into()) {
1529 return tcx.ty_error().into();
1534 b.projection_ty.substs = tcx.intern_substs(&substs[..]);
1537 ty::ExistentialProjection::erase_self_ty(tcx, b)
1541 let regular_trait_predicates = existential_trait_refs
1542 .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));
1543 let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
1544 ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
1546 // N.b. principal, projections, auto traits
1547 // FIXME: This is actually wrong with multiple principals in regards to symbol mangling
1548 let mut v = regular_trait_predicates
1550 existential_projections.map(|x| x.map_bound(ty::ExistentialPredicate::Projection)),
1552 .chain(auto_trait_predicates)
1553 .collect::<SmallVec<[_; 8]>>();
1554 v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
1556 let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
1558 // Use explicitly-specified region bound.
1559 let region_bound = if !lifetime.is_elided() {
1560 self.ast_region_to_region(lifetime, None)
1562 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1563 if tcx.named_region(lifetime.hir_id).is_some() {
1564 self.ast_region_to_region(lifetime, None)
1566 self.re_infer(None, span).unwrap_or_else(|| {
1567 let mut err = struct_span_err!(
1571 "the lifetime bound for this object type cannot be deduced \
1572 from context; please supply an explicit bound"
1575 // We will have already emitted an error E0106 complaining about a
1576 // missing named lifetime in `&dyn Trait`, so we elide this one.
1581 tcx.lifetimes.re_static
1586 debug!("region_bound: {:?}", region_bound);
1588 let ty = tcx.mk_dynamic(existential_predicates, region_bound, representation);
1589 debug!("trait_object_type: {:?}", ty);
1593 fn report_ambiguous_associated_type(
1599 ) -> ErrorGuaranteed {
1600 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1604 .confused_type_with_std_module
1606 .any(|full_span| full_span.contains(span))
1608 err.span_suggestion(
1609 span.shrink_to_lo(),
1610 "you are looking for the module in `std`, not the primitive type",
1612 Applicability::MachineApplicable,
1615 err.span_suggestion(
1617 "use fully-qualified syntax",
1618 format!("<{} as {}>::{}", type_str, trait_str, name),
1619 Applicability::HasPlaceholders,
1625 // Search for a bound on a type parameter which includes the associated item
1626 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1627 // This function will fail if there are no suitable bounds or there is
1629 fn find_bound_for_assoc_item(
1631 ty_param_def_id: LocalDefId,
1634 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed> {
1635 let tcx = self.tcx();
1638 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1639 ty_param_def_id, assoc_name, span,
1642 let predicates = &self
1643 .get_type_parameter_bounds(span, ty_param_def_id.to_def_id(), assoc_name)
1646 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1648 let param_name = tcx.hir().ty_param_name(ty_param_def_id);
1649 self.one_bound_for_assoc_type(
1651 traits::transitive_bounds_that_define_assoc_type(
1653 predicates.iter().filter_map(|(p, _)| {
1654 Some(p.to_opt_poly_trait_pred()?.map_bound(|t| t.trait_ref))
1659 || param_name.to_string(),
1666 // Checks that `bounds` contains exactly one element and reports appropriate
1667 // errors otherwise.
1668 #[instrument(level = "debug", skip(self, all_candidates, ty_param_name, is_equality), ret)]
1669 fn one_bound_for_assoc_type<I>(
1671 all_candidates: impl Fn() -> I,
1672 ty_param_name: impl Fn() -> String,
1675 is_equality: impl Fn() -> Option<String>,
1676 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed>
1678 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1680 let mut matching_candidates = all_candidates()
1681 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1682 let mut const_candidates = all_candidates()
1683 .filter(|r| self.trait_defines_associated_const_named(r.def_id(), assoc_name));
1685 let (bound, next_cand) = match (matching_candidates.next(), const_candidates.next()) {
1686 (Some(bound), _) => (bound, matching_candidates.next()),
1687 (None, Some(bound)) => (bound, const_candidates.next()),
1689 let reported = self.complain_about_assoc_type_not_found(
1695 return Err(reported);
1700 if let Some(bound2) = next_cand {
1703 let is_equality = is_equality();
1704 let bounds = IntoIterator::into_iter([bound, bound2]).chain(matching_candidates);
1705 let mut err = if is_equality.is_some() {
1706 // More specific Error Index entry.
1711 "ambiguous associated type `{}` in bounds of `{}`",
1720 "ambiguous associated type `{}` in bounds of `{}`",
1725 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1727 let mut where_bounds = vec![];
1728 for bound in bounds {
1729 let bound_id = bound.def_id();
1730 let bound_span = self
1732 .associated_items(bound_id)
1733 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1734 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1736 if let Some(bound_span) = bound_span {
1740 "ambiguous `{}` from `{}`",
1742 bound.print_only_trait_path(),
1745 if let Some(constraint) = &is_equality {
1746 where_bounds.push(format!(
1747 " T: {trait}::{assoc} = {constraint}",
1748 trait=bound.print_only_trait_path(),
1750 constraint=constraint,
1753 err.span_suggestion_verbose(
1754 span.with_hi(assoc_name.span.lo()),
1755 "use fully qualified syntax to disambiguate",
1759 bound.print_only_trait_path(),
1761 Applicability::MaybeIncorrect,
1766 "associated type `{}` could derive from `{}`",
1768 bound.print_only_trait_path(),
1772 if !where_bounds.is_empty() {
1774 "consider introducing a new type parameter `T` and adding `where` constraints:\
1775 \n where\n T: {},\n{}",
1777 where_bounds.join(",\n"),
1780 let reported = err.emit();
1781 if !where_bounds.is_empty() {
1782 return Err(reported);
1789 // Create a type from a path to an associated type.
1790 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1791 // and item_segment is the path segment for `D`. We return a type and a def for
1793 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1794 // parameter or `Self`.
1795 // NOTE: When this function starts resolving `Trait::AssocTy` successfully
1796 // it should also start reporting the `BARE_TRAIT_OBJECTS` lint.
1797 #[instrument(level = "debug", skip(self, hir_ref_id, span, qself, assoc_segment), fields(assoc_ident=?assoc_segment.ident), ret)]
1798 pub fn associated_path_to_ty(
1800 hir_ref_id: hir::HirId,
1803 qself: &hir::Ty<'_>,
1804 assoc_segment: &hir::PathSegment<'_>,
1805 permit_variants: bool,
1806 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
1807 let tcx = self.tcx();
1808 let assoc_ident = assoc_segment.ident;
1809 let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
1815 // Check if we have an enum variant.
1816 let mut variant_resolution = None;
1817 if let ty::Adt(adt_def, _) = qself_ty.kind() {
1818 if adt_def.is_enum() {
1819 let variant_def = adt_def
1822 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident(tcx), adt_def.did()));
1823 if let Some(variant_def) = variant_def {
1824 if permit_variants {
1825 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span, None);
1826 self.prohibit_generics(slice::from_ref(assoc_segment).iter(), |err| {
1827 err.note("enum variants can't have type parameters");
1828 let type_name = tcx.item_name(adt_def.did());
1830 "you might have meant to specity type parameters on enum \
1833 let Some(args) = assoc_segment.args else { return; };
1834 // Get the span of the generics args *including* the leading `::`.
1835 let args_span = assoc_segment.ident.span.shrink_to_hi().to(args.span_ext);
1836 if tcx.generics_of(adt_def.did()).count() == 0 {
1837 // FIXME(estebank): we could also verify that the arguments being
1838 // work for the `enum`, instead of just looking if it takes *any*.
1839 err.span_suggestion_verbose(
1841 &format!("{type_name} doesn't have generic parameters"),
1843 Applicability::MachineApplicable,
1847 let Ok(snippet) = tcx.sess.source_map().span_to_snippet(args_span) else {
1851 let (qself_sugg_span, is_self) = if let hir::TyKind::Path(
1852 hir::QPath::Resolved(_, ref path)
1854 // If the path segment already has type params, we want to overwrite
1856 match &path.segments[..] {
1857 // `segment` is the previous to last element on the path,
1858 // which would normally be the `enum` itself, while the last
1859 // `_` `PathSegment` corresponds to the variant.
1860 [.., hir::PathSegment {
1863 res: Res::Def(DefKind::Enum, _),
1866 // We need to include the `::` in `Type::Variant::<Args>`
1867 // to point the span to `::<Args>`, not just `<Args>`.
1868 ident.span.shrink_to_hi().to(args.map_or(
1869 ident.span.shrink_to_hi(),
1874 // We need to include the `::` in `Type::Variant::<Args>`
1875 // to point the span to `::<Args>`, not just `<Args>`.
1876 segment.ident.span.shrink_to_hi().to(segment.args.map_or(
1877 segment.ident.span.shrink_to_hi(),
1879 kw::SelfUpper == segment.ident.name,
1890 let suggestion = vec![
1892 // Account for people writing `Self::Variant::<Args>`, where
1893 // `Self` is the enum, and suggest replacing `Self` with the
1894 // appropriate type: `Type::<Args>::Variant`.
1895 (qself.span, format!("{type_name}{snippet}"))
1897 (qself_sugg_span, snippet)
1899 (args_span, String::new()),
1901 err.multipart_suggestion_verbose(
1904 Applicability::MaybeIncorrect,
1907 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1909 variant_resolution = Some(variant_def.def_id);
1915 // Find the type of the associated item, and the trait where the associated
1916 // item is declared.
1917 let bound = match (&qself_ty.kind(), qself_res) {
1918 (_, Res::SelfTyAlias { alias_to: impl_def_id, is_trait_impl: true, .. }) => {
1919 // `Self` in an impl of a trait -- we have a concrete self type and a
1921 let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) else {
1922 // A cycle error occurred, most likely.
1923 let guar = tcx.sess.delay_span_bug(span, "expected cycle error");
1927 self.one_bound_for_assoc_type(
1928 || traits::supertraits(tcx, ty::Binder::dummy(trait_ref)),
1929 || "Self".to_string(),
1937 Res::SelfTyParam { trait_: param_did } | Res::Def(DefKind::TyParam, param_did),
1938 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
1940 let reported = if variant_resolution.is_some() {
1941 // Variant in type position
1942 let msg = format!("expected type, found variant `{}`", assoc_ident);
1943 tcx.sess.span_err(span, &msg)
1944 } else if qself_ty.is_enum() {
1945 let mut err = struct_span_err!(
1949 "no variant named `{}` found for enum `{}`",
1954 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1955 if let Some(suggested_name) = find_best_match_for_name(
1959 .map(|variant| variant.name)
1960 .collect::<Vec<Symbol>>(),
1964 err.span_suggestion(
1966 "there is a variant with a similar name",
1968 Applicability::MaybeIncorrect,
1973 format!("variant not found in `{}`", qself_ty),
1977 if let Some(sp) = tcx.hir().span_if_local(adt_def.did()) {
1978 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1982 } else if let Some(reported) = qself_ty.error_reported() {
1985 // Don't print `TyErr` to the user.
1986 self.report_ambiguous_associated_type(
1988 &qself_ty.to_string(),
1993 return Err(reported);
1997 let trait_did = bound.def_id();
1998 let (assoc_ident, def_scope) =
1999 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
2001 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
2002 // of calling `filter_by_name_and_kind`.
2003 let item = tcx.associated_items(trait_did).in_definition_order().find(|i| {
2004 i.kind.namespace() == Namespace::TypeNS
2005 && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident
2007 // Assume that if it's not matched, there must be a const defined with the same name
2008 // but it was used in a type position.
2009 let Some(item) = item else {
2010 let msg = format!("found associated const `{assoc_ident}` when type was expected");
2011 let guar = tcx.sess.struct_span_err(span, &msg).emit();
2015 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2016 let ty = self.normalize_ty(span, ty);
2018 let kind = DefKind::AssocTy;
2019 if !item.visibility(tcx).is_accessible_from(def_scope, tcx) {
2020 let kind = kind.descr(item.def_id);
2021 let msg = format!("{} `{}` is private", kind, assoc_ident);
2023 .struct_span_err(span, &msg)
2024 .span_label(span, &format!("private {}", kind))
2027 tcx.check_stability(item.def_id, Some(hir_ref_id), span, None);
2029 if let Some(variant_def_id) = variant_resolution {
2030 tcx.struct_span_lint_hir(
2031 AMBIGUOUS_ASSOCIATED_ITEMS,
2034 "ambiguous associated item",
2036 let mut could_refer_to = |kind: DefKind, def_id, also| {
2037 let note_msg = format!(
2038 "`{}` could{} refer to the {} defined here",
2043 lint.span_note(tcx.def_span(def_id), ¬e_msg);
2046 could_refer_to(DefKind::Variant, variant_def_id, "");
2047 could_refer_to(kind, item.def_id, " also");
2049 lint.span_suggestion(
2051 "use fully-qualified syntax",
2052 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2053 Applicability::MachineApplicable,
2060 Ok((ty, kind, item.def_id))
2066 opt_self_ty: Option<Ty<'tcx>>,
2068 trait_segment: &hir::PathSegment<'_>,
2069 item_segment: &hir::PathSegment<'_>,
2070 constness: ty::BoundConstness,
2072 let tcx = self.tcx();
2074 let trait_def_id = tcx.parent(item_def_id);
2076 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2078 let Some(self_ty) = opt_self_ty else {
2079 let path_str = tcx.def_path_str(trait_def_id);
2081 let def_id = self.item_def_id();
2083 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2085 let parent_def_id = def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
2086 .map(|hir_id| tcx.hir().get_parent_item(hir_id).to_def_id());
2088 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2090 // If the trait in segment is the same as the trait defining the item,
2091 // use the `<Self as ..>` syntax in the error.
2092 let is_part_of_self_trait_constraints = def_id == trait_def_id;
2093 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2095 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2101 self.report_ambiguous_associated_type(
2105 item_segment.ident.name,
2107 return tcx.ty_error();
2110 debug!("qpath_to_ty: self_type={:?}", self_ty);
2112 let trait_ref = self.ast_path_to_mono_trait_ref(
2121 let item_substs = self.create_substs_for_associated_item(
2128 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2130 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2133 pub fn prohibit_generics<'a>(
2135 segments: impl Iterator<Item = &'a hir::PathSegment<'a>> + Clone,
2136 extend: impl Fn(&mut Diagnostic),
2138 let args = segments.clone().flat_map(|segment| segment.args().args);
2140 let (lt, ty, ct, inf) =
2141 args.clone().fold((false, false, false, false), |(lt, ty, ct, inf), arg| match arg {
2142 hir::GenericArg::Lifetime(_) => (true, ty, ct, inf),
2143 hir::GenericArg::Type(_) => (lt, true, ct, inf),
2144 hir::GenericArg::Const(_) => (lt, ty, true, inf),
2145 hir::GenericArg::Infer(_) => (lt, ty, ct, true),
2147 let mut emitted = false;
2148 if lt || ty || ct || inf {
2149 let types_and_spans: Vec<_> = segments
2151 .flat_map(|segment| {
2152 if segment.args().args.is_empty() {
2157 Res::PrimTy(ty) => format!("{} `{}`", segment.res.descr(), ty.name()),
2159 if let Some(name) = self.tcx().opt_item_name(def_id) => {
2160 format!("{} `{name}`", segment.res.descr())
2162 Res::Err => "this type".to_string(),
2163 _ => segment.res.descr().to_string(),
2170 let this_type = match &types_and_spans[..] {
2171 [.., _, (last, _)] => format!(
2173 types_and_spans[..types_and_spans.len() - 1]
2175 .map(|(x, _)| x.as_str())
2177 .collect::<String>()
2179 [(only, _)] => only.to_string(),
2180 [] => "this type".to_string(),
2183 let arg_spans: Vec<Span> = args.map(|arg| arg.span()).collect();
2185 let mut kinds = Vec::with_capacity(4);
2187 kinds.push("lifetime");
2193 kinds.push("const");
2196 kinds.push("generic");
2198 let (kind, s) = match kinds[..] {
2202 kinds[..kinds.len() - 1]
2206 .collect::<String>()
2210 [only] => (format!("{only}"), ""),
2211 [] => unreachable!(),
2213 let last_span = *arg_spans.last().unwrap();
2214 let span: MultiSpan = arg_spans.into();
2215 let mut err = struct_span_err!(
2219 "{kind} arguments are not allowed on {this_type}",
2221 err.span_label(last_span, format!("{kind} argument{s} not allowed"));
2222 for (what, span) in types_and_spans {
2223 err.span_label(span, format!("not allowed on {what}"));
2230 for segment in segments {
2231 // Only emit the first error to avoid overloading the user with error messages.
2232 if let Some(b) = segment.args().bindings.first() {
2233 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
2240 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2241 pub fn def_ids_for_value_path_segments(
2243 segments: &[hir::PathSegment<'_>],
2244 self_ty: Option<Ty<'tcx>>,
2248 // We need to extract the type parameters supplied by the user in
2249 // the path `path`. Due to the current setup, this is a bit of a
2250 // tricky-process; the problem is that resolve only tells us the
2251 // end-point of the path resolution, and not the intermediate steps.
2252 // Luckily, we can (at least for now) deduce the intermediate steps
2253 // just from the end-point.
2255 // There are basically five cases to consider:
2257 // 1. Reference to a constructor of a struct:
2259 // struct Foo<T>(...)
2261 // In this case, the parameters are declared in the type space.
2263 // 2. Reference to a constructor of an enum variant:
2265 // enum E<T> { Foo(...) }
2267 // In this case, the parameters are defined in the type space,
2268 // but may be specified either on the type or the variant.
2270 // 3. Reference to a fn item or a free constant:
2274 // In this case, the path will again always have the form
2275 // `a::b::foo::<T>` where only the final segment should have
2276 // type parameters. However, in this case, those parameters are
2277 // declared on a value, and hence are in the `FnSpace`.
2279 // 4. Reference to a method or an associated constant:
2281 // impl<A> SomeStruct<A> {
2285 // Here we can have a path like
2286 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2287 // may appear in two places. The penultimate segment,
2288 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2289 // final segment, `foo::<B>` contains parameters in fn space.
2291 // The first step then is to categorize the segments appropriately.
2293 let tcx = self.tcx();
2295 assert!(!segments.is_empty());
2296 let last = segments.len() - 1;
2298 let mut path_segs = vec![];
2301 // Case 1. Reference to a struct constructor.
2302 DefKind::Ctor(CtorOf::Struct, ..) => {
2303 // Everything but the final segment should have no
2304 // parameters at all.
2305 let generics = tcx.generics_of(def_id);
2306 // Variant and struct constructors use the
2307 // generics of their parent type definition.
2308 let generics_def_id = generics.parent.unwrap_or(def_id);
2309 path_segs.push(PathSeg(generics_def_id, last));
2312 // Case 2. Reference to a variant constructor.
2313 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2314 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2315 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2316 debug_assert!(adt_def.is_enum());
2317 (adt_def.did(), last)
2318 } else if last >= 1 && segments[last - 1].args.is_some() {
2319 // Everything but the penultimate segment should have no
2320 // parameters at all.
2321 let mut def_id = def_id;
2323 // `DefKind::Ctor` -> `DefKind::Variant`
2324 if let DefKind::Ctor(..) = kind {
2325 def_id = tcx.parent(def_id);
2328 // `DefKind::Variant` -> `DefKind::Enum`
2329 let enum_def_id = tcx.parent(def_id);
2330 (enum_def_id, last - 1)
2332 // FIXME: lint here recommending `Enum::<...>::Variant` form
2333 // instead of `Enum::Variant::<...>` form.
2335 // Everything but the final segment should have no
2336 // parameters at all.
2337 let generics = tcx.generics_of(def_id);
2338 // Variant and struct constructors use the
2339 // generics of their parent type definition.
2340 (generics.parent.unwrap_or(def_id), last)
2342 path_segs.push(PathSeg(generics_def_id, index));
2345 // Case 3. Reference to a top-level value.
2346 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static(_) => {
2347 path_segs.push(PathSeg(def_id, last));
2350 // Case 4. Reference to a method or associated const.
2351 DefKind::AssocFn | DefKind::AssocConst => {
2352 if segments.len() >= 2 {
2353 let generics = tcx.generics_of(def_id);
2354 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2356 path_segs.push(PathSeg(def_id, last));
2359 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2362 debug!("path_segs = {:?}", path_segs);
2367 // Check a type `Path` and convert it to a `Ty`.
2370 opt_self_ty: Option<Ty<'tcx>>,
2371 path: &hir::Path<'_>,
2372 permit_variants: bool,
2374 let tcx = self.tcx();
2377 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2378 path.res, opt_self_ty, path.segments
2381 let span = path.span;
2383 Res::Def(DefKind::OpaqueTy | DefKind::ImplTraitPlaceholder, did) => {
2384 // Check for desugared `impl Trait`.
2385 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2386 let item_segment = path.segments.split_last().unwrap();
2387 self.prohibit_generics(item_segment.1.iter(), |err| {
2388 err.note("`impl Trait` types can't have type parameters");
2390 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2391 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2398 | DefKind::ForeignTy,
2401 assert_eq!(opt_self_ty, None);
2402 self.prohibit_generics(path.segments.split_last().unwrap().1.iter(), |_| {});
2403 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2405 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2406 // Convert "variant type" as if it were a real type.
2407 // The resulting `Ty` is type of the variant's enum for now.
2408 assert_eq!(opt_self_ty, None);
2411 self.def_ids_for_value_path_segments(path.segments, None, kind, def_id);
2412 let generic_segs: FxHashSet<_> =
2413 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2414 self.prohibit_generics(
2415 path.segments.iter().enumerate().filter_map(|(index, seg)| {
2416 if !generic_segs.contains(&index) { Some(seg) } else { None }
2419 err.note("enum variants can't have type parameters");
2423 let PathSeg(def_id, index) = path_segs.last().unwrap();
2424 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2426 Res::Def(DefKind::TyParam, def_id) => {
2427 assert_eq!(opt_self_ty, None);
2428 self.prohibit_generics(path.segments.iter(), |err| {
2429 if let Some(span) = tcx.def_ident_span(def_id) {
2430 let name = tcx.item_name(def_id);
2431 err.span_note(span, &format!("type parameter `{name}` defined here"));
2435 let def_id = def_id.expect_local();
2436 let item_def_id = tcx.hir().ty_param_owner(def_id);
2437 let generics = tcx.generics_of(item_def_id);
2438 let index = generics.param_def_id_to_index[&def_id.to_def_id()];
2439 tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id))
2441 Res::SelfTyParam { .. } => {
2442 // `Self` in trait or type alias.
2443 assert_eq!(opt_self_ty, None);
2444 self.prohibit_generics(path.segments.iter(), |err| {
2445 if let [hir::PathSegment { args: Some(args), ident, .. }] = &path.segments[..] {
2446 err.span_suggestion_verbose(
2447 ident.span.shrink_to_hi().to(args.span_ext),
2448 "the `Self` type doesn't accept type parameters",
2450 Applicability::MaybeIncorrect,
2454 tcx.types.self_param
2456 Res::SelfTyAlias { alias_to: def_id, forbid_generic, .. } => {
2457 // `Self` in impl (we know the concrete type).
2458 assert_eq!(opt_self_ty, None);
2459 // Try to evaluate any array length constants.
2460 let ty = tcx.at(span).type_of(def_id);
2461 let span_of_impl = tcx.span_of_impl(def_id);
2462 self.prohibit_generics(path.segments.iter(), |err| {
2463 let def_id = match *ty.kind() {
2464 ty::Adt(self_def, _) => self_def.did(),
2468 let type_name = tcx.item_name(def_id);
2469 let span_of_ty = tcx.def_ident_span(def_id);
2470 let generics = tcx.generics_of(def_id).count();
2472 let msg = format!("`Self` is of type `{ty}`");
2473 if let (Ok(i_sp), Some(t_sp)) = (span_of_impl, span_of_ty) {
2474 let mut span: MultiSpan = vec![t_sp].into();
2475 span.push_span_label(
2477 &format!("`Self` is on type `{type_name}` in this `impl`"),
2479 let mut postfix = "";
2481 postfix = ", which doesn't have generic parameters";
2483 span.push_span_label(
2485 &format!("`Self` corresponds to this type{postfix}"),
2487 err.span_note(span, &msg);
2491 for segment in path.segments {
2492 if let Some(args) = segment.args && segment.ident.name == kw::SelfUpper {
2494 // FIXME(estebank): we could also verify that the arguments being
2495 // work for the `enum`, instead of just looking if it takes *any*.
2496 err.span_suggestion_verbose(
2497 segment.ident.span.shrink_to_hi().to(args.span_ext),
2498 "the `Self` type doesn't accept type parameters",
2500 Applicability::MachineApplicable,
2504 err.span_suggestion_verbose(
2507 "the `Self` type doesn't accept type parameters, use the \
2508 concrete type's name `{type_name}` instead if you want to \
2509 specify its type parameters"
2512 Applicability::MaybeIncorrect,
2518 // HACK(min_const_generics): Forbid generic `Self` types
2519 // here as we can't easily do that during nameres.
2521 // We do this before normalization as we otherwise allow
2523 // trait AlwaysApplicable { type Assoc; }
2524 // impl<T: ?Sized> AlwaysApplicable for T { type Assoc = usize; }
2526 // trait BindsParam<T> {
2529 // impl<T> BindsParam<T> for <T as AlwaysApplicable>::Assoc {
2530 // type ArrayTy = [u8; Self::MAX];
2533 // Note that the normalization happens in the param env of
2534 // the anon const, which is empty. This is why the
2535 // `AlwaysApplicable` impl needs a `T: ?Sized` bound for
2536 // this to compile if we were to normalize here.
2537 if forbid_generic && ty.needs_subst() {
2538 let mut err = tcx.sess.struct_span_err(
2540 "generic `Self` types are currently not permitted in anonymous constants",
2542 if let Some(hir::Node::Item(&hir::Item {
2543 kind: hir::ItemKind::Impl(ref impl_),
2545 })) = tcx.hir().get_if_local(def_id)
2547 err.span_note(impl_.self_ty.span, "not a concrete type");
2552 self.normalize_ty(span, ty)
2555 Res::Def(DefKind::AssocTy, def_id) => {
2556 debug_assert!(path.segments.len() >= 2);
2557 self.prohibit_generics(path.segments[..path.segments.len() - 2].iter(), |_| {});
2558 // HACK: until we support `<Type as ~const Trait>`, assume all of them are.
2559 let constness = if tcx.has_attr(tcx.parent(def_id), sym::const_trait) {
2560 ty::BoundConstness::ConstIfConst
2562 ty::BoundConstness::NotConst
2568 &path.segments[path.segments.len() - 2],
2569 path.segments.last().unwrap(),
2573 Res::PrimTy(prim_ty) => {
2574 assert_eq!(opt_self_ty, None);
2575 self.prohibit_generics(path.segments.iter(), |err| {
2576 let name = prim_ty.name_str();
2577 for segment in path.segments {
2578 if let Some(args) = segment.args {
2579 err.span_suggestion_verbose(
2580 segment.ident.span.shrink_to_hi().to(args.span_ext),
2581 &format!("primitive type `{name}` doesn't have generic parameters"),
2583 Applicability::MaybeIncorrect,
2589 hir::PrimTy::Bool => tcx.types.bool,
2590 hir::PrimTy::Char => tcx.types.char,
2591 hir::PrimTy::Int(it) => tcx.mk_mach_int(ty::int_ty(it)),
2592 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(ty::uint_ty(uit)),
2593 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ty::float_ty(ft)),
2594 hir::PrimTy::Str => tcx.types.str_,
2598 self.set_tainted_by_errors();
2599 self.tcx().ty_error()
2601 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2605 /// Parses the programmer's textual representation of a type into our
2606 /// internal notion of a type.
2607 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2608 self.ast_ty_to_ty_inner(ast_ty, false, false)
2611 /// Parses the programmer's textual representation of a type into our
2612 /// internal notion of a type. This is meant to be used within a path.
2613 pub fn ast_ty_to_ty_in_path(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2614 self.ast_ty_to_ty_inner(ast_ty, false, true)
2617 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2618 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2619 #[instrument(level = "debug", skip(self), ret)]
2620 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool, in_path: bool) -> Ty<'tcx> {
2621 let tcx = self.tcx();
2623 let result_ty = match ast_ty.kind {
2624 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
2625 hir::TyKind::Ptr(ref mt) => {
2626 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
2628 hir::TyKind::Rptr(ref region, ref mt) => {
2629 let r = self.ast_region_to_region(region, None);
2631 let t = self.ast_ty_to_ty_inner(mt.ty, true, false);
2632 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2634 hir::TyKind::Never => tcx.types.never,
2635 hir::TyKind::Tup(fields) => tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(t))),
2636 hir::TyKind::BareFn(bf) => {
2637 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
2639 tcx.mk_fn_ptr(self.ty_of_fn(
2648 hir::TyKind::TraitObject(bounds, ref lifetime, repr) => {
2649 self.maybe_lint_bare_trait(ast_ty, in_path);
2650 let repr = match repr {
2651 TraitObjectSyntax::Dyn | TraitObjectSyntax::None => ty::Dyn,
2652 TraitObjectSyntax::DynStar => ty::DynStar,
2654 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed, repr)
2656 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2657 debug!(?maybe_qself, ?path);
2658 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2659 self.res_to_ty(opt_self_ty, path, false)
2661 hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
2662 let opaque_ty = tcx.hir().item(item_id);
2663 let def_id = item_id.owner_id.to_def_id();
2665 match opaque_ty.kind {
2666 hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
2667 self.impl_trait_ty_to_ty(def_id, lifetimes, origin, in_trait)
2669 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2672 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2673 debug!(?qself, ?segment);
2674 let ty = self.ast_ty_to_ty_inner(qself, false, true);
2675 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, qself, segment, false)
2676 .map(|(ty, _, _)| ty)
2677 .unwrap_or_else(|_| tcx.ty_error())
2679 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
2680 let def_id = tcx.require_lang_item(lang_item, Some(span));
2681 let (substs, _) = self.create_substs_for_ast_path(
2685 &hir::PathSegment::invalid(),
2686 &GenericArgs::none(),
2691 EarlyBinder(self.normalize_ty(span, tcx.at(span).type_of(def_id)))
2694 hir::TyKind::Array(ref ty, ref length) => {
2695 let length = match length {
2696 &hir::ArrayLen::Infer(_, span) => self.ct_infer(tcx.types.usize, None, span),
2697 hir::ArrayLen::Body(constant) => {
2698 let length_def_id = tcx.hir().local_def_id(constant.hir_id);
2699 ty::Const::from_anon_const(tcx, length_def_id)
2703 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(ty), length));
2704 self.normalize_ty(ast_ty.span, array_ty)
2706 hir::TyKind::Typeof(ref e) => {
2707 let ty_erased = tcx.type_of(tcx.hir().local_def_id(e.hir_id));
2708 let ty = tcx.fold_regions(ty_erased, |r, _| {
2709 if r.is_erased() { tcx.lifetimes.re_static } else { r }
2711 let span = ast_ty.span;
2712 tcx.sess.emit_err(TypeofReservedKeywordUsed {
2715 opt_sugg: Some((span, Applicability::MachineApplicable))
2716 .filter(|_| ty.is_suggestable(tcx, false)),
2721 hir::TyKind::Infer => {
2722 // Infer also appears as the type of arguments or return
2723 // values in an ExprKind::Closure, or as
2724 // the type of local variables. Both of these cases are
2725 // handled specially and will not descend into this routine.
2726 self.ty_infer(None, ast_ty.span)
2728 hir::TyKind::Err => tcx.ty_error(),
2731 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2735 #[instrument(level = "debug", skip(self), ret)]
2736 fn impl_trait_ty_to_ty(
2739 lifetimes: &[hir::GenericArg<'_>],
2740 origin: OpaqueTyOrigin,
2743 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2744 let tcx = self.tcx();
2746 let generics = tcx.generics_of(def_id);
2748 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2749 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2750 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2751 // Our own parameters are the resolved lifetimes.
2752 if let GenericParamDefKind::Lifetime = param.kind {
2753 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2754 self.ast_region_to_region(lifetime, None).into()
2763 // For RPIT (return position impl trait), only lifetimes
2764 // mentioned in the impl Trait predicate are captured by
2765 // the opaque type, so the lifetime parameters from the
2766 // parent item need to be replaced with `'static`.
2768 // For `impl Trait` in the types of statics, constants,
2769 // locals and type aliases. These capture all parent
2770 // lifetimes, so they can use their identity subst.
2771 GenericParamDefKind::Lifetime
2774 hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..)
2777 tcx.lifetimes.re_static.into()
2779 _ => tcx.mk_param_from_def(param),
2783 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2785 if in_trait { tcx.mk_projection(def_id, substs) } else { tcx.mk_opaque(def_id, substs) }
2788 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2790 hir::TyKind::Infer if expected_ty.is_some() => {
2791 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2792 expected_ty.unwrap()
2794 _ => self.ast_ty_to_ty(ty),
2798 #[instrument(level = "debug", skip(self, hir_id, unsafety, abi, decl, generics, hir_ty), ret)]
2802 unsafety: hir::Unsafety,
2804 decl: &hir::FnDecl<'_>,
2805 generics: Option<&hir::Generics<'_>>,
2806 hir_ty: Option<&hir::Ty<'_>>,
2807 ) -> ty::PolyFnSig<'tcx> {
2808 let tcx = self.tcx();
2809 let bound_vars = tcx.late_bound_vars(hir_id);
2810 debug!(?bound_vars);
2812 // We proactively collect all the inferred type params to emit a single error per fn def.
2813 let mut visitor = HirPlaceholderCollector::default();
2814 let mut infer_replacements = vec![];
2816 if let Some(generics) = generics {
2817 walk_generics(&mut visitor, generics);
2820 let input_tys: Vec<_> = decl
2825 if let hir::TyKind::Infer = a.kind && !self.allow_ty_infer() {
2826 if let Some(suggested_ty) =
2827 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, Some(i))
2829 infer_replacements.push((a.span, suggested_ty.to_string()));
2830 return suggested_ty;
2834 // Only visit the type looking for `_` if we didn't fix the type above
2835 visitor.visit_ty(a);
2836 self.ty_of_arg(a, None)
2840 let output_ty = match decl.output {
2841 hir::FnRetTy::Return(output) => {
2842 if let hir::TyKind::Infer = output.kind
2843 && !self.allow_ty_infer()
2844 && let Some(suggested_ty) =
2845 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, None)
2847 infer_replacements.push((output.span, suggested_ty.to_string()));
2850 visitor.visit_ty(output);
2851 self.ast_ty_to_ty(output)
2854 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2859 let fn_ty = tcx.mk_fn_sig(input_tys.into_iter(), output_ty, decl.c_variadic, unsafety, abi);
2860 let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
2862 if !self.allow_ty_infer() && !(visitor.0.is_empty() && infer_replacements.is_empty()) {
2863 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2864 // only want to emit an error complaining about them if infer types (`_`) are not
2865 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2866 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2868 let mut diag = crate::collect::placeholder_type_error_diag(
2872 infer_replacements.iter().map(|(s, _)| *s).collect(),
2878 if !infer_replacements.is_empty() {
2879 diag.multipart_suggestion(
2881 "try replacing `_` with the type{} in the corresponding trait method signature",
2882 rustc_errors::pluralize!(infer_replacements.len()),
2885 Applicability::MachineApplicable,
2892 // Find any late-bound regions declared in return type that do
2893 // not appear in the arguments. These are not well-formed.
2896 // for<'a> fn() -> &'a str <-- 'a is bad
2897 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2898 let inputs = bare_fn_ty.inputs();
2899 let late_bound_in_args =
2900 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2901 let output = bare_fn_ty.output();
2902 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2904 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
2909 "return type references {}, which is not constrained by the fn input types",
2917 /// Given a fn_hir_id for a impl function, suggest the type that is found on the
2918 /// corresponding function in the trait that the impl implements, if it exists.
2919 /// If arg_idx is Some, then it corresponds to an input type index, otherwise it
2920 /// corresponds to the return type.
2921 fn suggest_trait_fn_ty_for_impl_fn_infer(
2923 fn_hir_id: hir::HirId,
2924 arg_idx: Option<usize>,
2925 ) -> Option<Ty<'tcx>> {
2926 let tcx = self.tcx();
2927 let hir = tcx.hir();
2929 let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), ident, .. }) =
2930 hir.get(fn_hir_id) else { return None };
2931 let hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(i), .. }) =
2932 hir.get(hir.get_parent_node(fn_hir_id)) else { bug!("ImplItem should have Impl parent") };
2934 let trait_ref = self.instantiate_mono_trait_ref(
2935 i.of_trait.as_ref()?,
2936 self.ast_ty_to_ty(i.self_ty),
2937 ty::BoundConstness::NotConst,
2940 let assoc = tcx.associated_items(trait_ref.def_id).find_by_name_and_kind(
2947 let fn_sig = tcx.bound_fn_sig(assoc.def_id).subst(
2949 trait_ref.substs.extend_to(tcx, assoc.def_id, |param, _| tcx.mk_param_from_def(param)),
2952 let ty = if let Some(arg_idx) = arg_idx { fn_sig.input(arg_idx) } else { fn_sig.output() };
2954 Some(tcx.liberate_late_bound_regions(fn_hir_id.expect_owner().to_def_id(), ty))
2957 fn validate_late_bound_regions(
2959 constrained_regions: FxHashSet<ty::BoundRegionKind>,
2960 referenced_regions: FxHashSet<ty::BoundRegionKind>,
2961 generate_err: impl Fn(&str) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
2963 for br in referenced_regions.difference(&constrained_regions) {
2964 let br_name = match *br {
2965 ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) | ty::BrEnv => {
2966 "an anonymous lifetime".to_string()
2968 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
2971 let mut err = generate_err(&br_name);
2973 if let ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) = *br {
2974 // The only way for an anonymous lifetime to wind up
2975 // in the return type but **also** be unconstrained is
2976 // if it only appears in "associated types" in the
2977 // input. See #47511 and #62200 for examples. In this case,
2978 // though we can easily give a hint that ought to be
2981 "lifetimes appearing in an associated or opaque type are not considered constrained",
2983 err.note("consider introducing a named lifetime parameter");
2990 /// Given the bounds on an object, determines what single region bound (if any) we can
2991 /// use to summarize this type. The basic idea is that we will use the bound the user
2992 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2993 /// for region bounds. It may be that we can derive no bound at all, in which case
2994 /// we return `None`.
2995 fn compute_object_lifetime_bound(
2998 existential_predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
2999 ) -> Option<ty::Region<'tcx>> // if None, use the default
3001 let tcx = self.tcx();
3003 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
3005 // No explicit region bound specified. Therefore, examine trait
3006 // bounds and see if we can derive region bounds from those.
3007 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
3009 // If there are no derived region bounds, then report back that we
3010 // can find no region bound. The caller will use the default.
3011 if derived_region_bounds.is_empty() {
3015 // If any of the derived region bounds are 'static, that is always
3017 if derived_region_bounds.iter().any(|r| r.is_static()) {
3018 return Some(tcx.lifetimes.re_static);
3021 // Determine whether there is exactly one unique region in the set
3022 // of derived region bounds. If so, use that. Otherwise, report an
3024 let r = derived_region_bounds[0];
3025 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
3026 tcx.sess.emit_err(AmbiguousLifetimeBound { span });
3031 /// Make sure that we are in the condition to suggest the blanket implementation.
3032 fn maybe_lint_blanket_trait_impl(&self, self_ty: &hir::Ty<'_>, diag: &mut Diagnostic) {
3033 let tcx = self.tcx();
3034 let parent_id = tcx.hir().get_parent_item(self_ty.hir_id).def_id;
3035 if let hir::Node::Item(hir::Item {
3037 hir::ItemKind::Impl(hir::Impl {
3038 self_ty: impl_self_ty, of_trait: Some(of_trait_ref), generics, ..
3041 }) = tcx.hir().get_by_def_id(parent_id) && self_ty.hir_id == impl_self_ty.hir_id
3043 if !of_trait_ref.trait_def_id().map_or(false, |def_id| def_id.is_local()) {
3046 let of_trait_span = of_trait_ref.path.span;
3047 // make sure that we are not calling unwrap to abort during the compilation
3048 let Ok(impl_trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else { return; };
3049 let Ok(of_trait_name) = tcx.sess.source_map().span_to_snippet(of_trait_span) else { return; };
3050 // check if the trait has generics, to make a correct suggestion
3051 let param_name = generics.params.next_type_param_name(None);
3053 let add_generic_sugg = if let Some(span) = generics.span_for_param_suggestion() {
3054 (span, format!(", {}: {}", param_name, impl_trait_name))
3056 (generics.span, format!("<{}: {}>", param_name, impl_trait_name))
3058 diag.multipart_suggestion(
3059 format!("alternatively use a blanket \
3060 implementation to implement `{of_trait_name}` for \
3061 all types that also implement `{impl_trait_name}`"),
3063 (self_ty.span, param_name),
3066 Applicability::MaybeIncorrect,
3071 fn maybe_lint_bare_trait(&self, self_ty: &hir::Ty<'_>, in_path: bool) {
3072 let tcx = self.tcx();
3073 if let hir::TyKind::TraitObject([poly_trait_ref, ..], _, TraitObjectSyntax::None) =
3076 let needs_bracket = in_path
3080 .span_to_prev_source(self_ty.span)
3082 .map_or(false, |s| s.trim_end().ends_with('<'));
3084 let is_global = poly_trait_ref.trait_ref.path.is_global();
3086 let mut sugg = Vec::from_iter([(
3087 self_ty.span.shrink_to_lo(),
3090 if needs_bracket { "<" } else { "" },
3091 if is_global { "(" } else { "" },
3095 if is_global || needs_bracket {
3097 self_ty.span.shrink_to_hi(),
3100 if is_global { ")" } else { "" },
3101 if needs_bracket { ">" } else { "" },
3106 if self_ty.span.edition() >= Edition::Edition2021 {
3107 let msg = "trait objects must include the `dyn` keyword";
3108 let label = "add `dyn` keyword before this trait";
3110 rustc_errors::struct_span_err!(tcx.sess, self_ty.span, E0782, "{}", msg);
3111 diag.multipart_suggestion_verbose(label, sugg, Applicability::MachineApplicable);
3112 // check if the impl trait that we are considering is a impl of a local trait
3113 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);
3116 let msg = "trait objects without an explicit `dyn` are deprecated";
3117 tcx.struct_span_lint_hir(
3123 lint.multipart_suggestion_verbose(
3126 Applicability::MachineApplicable,
3128 self.maybe_lint_blanket_trait_impl(&self_ty, lint);