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)]
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)]
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.
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 #[tracing::instrument(level = "debug", skip(self))]
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 let r = 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(index, id)) => {
226 let name = lifetime_name(id.expect_local());
227 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
230 Some(rl::Region::Free(scope, id)) => {
231 let name = lifetime_name(id.expect_local());
232 tcx.mk_region(ty::ReFree(ty::FreeRegion {
234 bound_region: ty::BrNamed(id, name),
237 // (*) -- not late-bound, won't change
241 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
242 debug!(?lifetime, "unelided lifetime in signature");
244 // This indicates an illegal lifetime
245 // elision. `resolve_lifetime` should have
246 // reported an error in this case -- but if
247 // not, let's error out.
248 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
250 // Supply some dummy value. We don't have an
251 // `re_error`, annoyingly, so use `'static`.
252 tcx.lifetimes.re_static
257 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
262 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
263 /// returns an appropriate set of substitutions for this particular reference to `I`.
264 pub fn ast_path_substs_for_ty(
268 item_segment: &hir::PathSegment<'_>,
269 ) -> SubstsRef<'tcx> {
270 let (substs, _) = self.create_substs_for_ast_path(
276 item_segment.infer_args,
279 let assoc_bindings = self.create_assoc_bindings_for_generic_args(item_segment.args());
281 if let Some(b) = assoc_bindings.first() {
282 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
288 /// Given the type/lifetime/const arguments provided to some path (along with
289 /// an implicit `Self`, if this is a trait reference), returns the complete
290 /// set of substitutions. This may involve applying defaulted type parameters.
291 /// Constraints on associated types are created from `create_assoc_bindings_for_generic_args`.
295 /// ```ignore (illustrative)
296 /// T: std::ops::Index<usize, Output = u32>
297 /// // ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
300 /// 1. The `self_ty` here would refer to the type `T`.
301 /// 2. The path in question is the path to the trait `std::ops::Index`,
302 /// which will have been resolved to a `def_id`
303 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
304 /// parameters are returned in the `SubstsRef`, the associated type bindings like
305 /// `Output = u32` are returned from `create_assoc_bindings_for_generic_args`.
307 /// Note that the type listing given here is *exactly* what the user provided.
309 /// For (generic) associated types
311 /// ```ignore (illustrative)
312 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
315 /// We have the parent substs are the substs for the parent trait:
316 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
317 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
318 /// lists: `[Vec<u8>, u8, 'a]`.
319 #[tracing::instrument(level = "debug", skip(self, span))]
320 fn create_substs_for_ast_path<'a>(
324 parent_substs: &[subst::GenericArg<'tcx>],
325 seg: &hir::PathSegment<'_>,
326 generic_args: &'a hir::GenericArgs<'_>,
328 self_ty: Option<Ty<'tcx>>,
329 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
330 // If the type is parameterized by this region, then replace this
331 // region with the current anon region binding (in other words,
332 // whatever & would get replaced with).
334 let tcx = self.tcx();
335 let generics = tcx.generics_of(def_id);
336 debug!("generics: {:?}", generics);
338 if generics.has_self {
339 if generics.parent.is_some() {
340 // The parent is a trait so it should have at least one subst
341 // for the `Self` type.
342 assert!(!parent_substs.is_empty())
344 // This item (presumably a trait) needs a self-type.
345 assert!(self_ty.is_some());
348 assert!(self_ty.is_none() && parent_substs.is_empty());
351 let arg_count = Self::check_generic_arg_count(
358 GenericArgPosition::Type,
363 // Skip processing if type has no generic parameters.
364 // Traits always have `Self` as a generic parameter, which means they will not return early
365 // here and so associated type bindings will be handled regardless of whether there are any
366 // non-`Self` generic parameters.
367 if generics.params.is_empty() {
368 return (tcx.intern_substs(&[]), arg_count);
371 struct SubstsForAstPathCtxt<'a, 'tcx> {
372 astconv: &'a (dyn AstConv<'tcx> + 'a),
374 generic_args: &'a GenericArgs<'a>,
376 inferred_params: Vec<Span>,
380 impl<'a, 'tcx> CreateSubstsForGenericArgsCtxt<'a, 'tcx> for SubstsForAstPathCtxt<'a, 'tcx> {
381 fn args_for_def_id(&mut self, did: DefId) -> (Option<&'a GenericArgs<'a>>, bool) {
382 if did == self.def_id {
383 (Some(self.generic_args), self.infer_args)
385 // The last component of this tuple is unimportant.
392 param: &ty::GenericParamDef,
393 arg: &GenericArg<'_>,
394 ) -> subst::GenericArg<'tcx> {
395 let tcx = self.astconv.tcx();
397 let mut handle_ty_args = |has_default, ty: &hir::Ty<'_>| {
399 tcx.check_optional_stability(
406 // Default generic parameters may not be marked
407 // with stability attributes, i.e. when the
408 // default parameter was defined at the same time
409 // as the rest of the type. As such, we ignore missing
410 // stability attributes.
414 if let (hir::TyKind::Infer, false) = (&ty.kind, self.astconv.allow_ty_infer()) {
415 self.inferred_params.push(ty.span);
416 tcx.ty_error().into()
418 self.astconv.ast_ty_to_ty(ty).into()
422 match (¶m.kind, arg) {
423 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
424 self.astconv.ast_region_to_region(lt, Some(param)).into()
426 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
427 handle_ty_args(has_default, ty)
429 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Infer(inf)) => {
430 handle_ty_args(has_default, &inf.to_ty())
432 (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
433 ty::Const::from_opt_const_arg_anon_const(
435 ty::WithOptConstParam {
436 did: tcx.hir().local_def_id(ct.value.hir_id),
437 const_param_did: Some(param.def_id),
442 (&GenericParamDefKind::Const { .. }, hir::GenericArg::Infer(inf)) => {
443 let ty = tcx.at(self.span).type_of(param.def_id);
444 if self.astconv.allow_ty_infer() {
445 self.astconv.ct_infer(ty, Some(param), inf.span).into()
447 self.inferred_params.push(inf.span);
448 tcx.const_error(ty).into()
457 substs: Option<&[subst::GenericArg<'tcx>]>,
458 param: &ty::GenericParamDef,
460 ) -> subst::GenericArg<'tcx> {
461 let tcx = self.astconv.tcx();
463 GenericParamDefKind::Lifetime => self
465 .re_infer(Some(param), self.span)
467 debug!(?param, "unelided lifetime in signature");
469 // This indicates an illegal lifetime in a non-assoc-trait position
470 tcx.sess.delay_span_bug(self.span, "unelided lifetime in signature");
472 // Supply some dummy value. We don't have an
473 // `re_error`, annoyingly, so use `'static`.
474 tcx.lifetimes.re_static
477 GenericParamDefKind::Type { has_default, .. } => {
478 if !infer_args && has_default {
479 // No type parameter provided, but a default exists.
480 let substs = substs.unwrap();
481 if substs.iter().any(|arg| match arg.unpack() {
482 GenericArgKind::Type(ty) => ty.references_error(),
485 // Avoid ICE #86756 when type error recovery goes awry.
486 return tcx.ty_error().into();
491 EarlyBinder(tcx.at(self.span).type_of(param.def_id))
495 } else if infer_args {
496 self.astconv.ty_infer(Some(param), self.span).into()
498 // We've already errored above about the mismatch.
499 tcx.ty_error().into()
502 GenericParamDefKind::Const { has_default } => {
503 let ty = tcx.at(self.span).type_of(param.def_id);
504 if !infer_args && has_default {
505 tcx.bound_const_param_default(param.def_id)
506 .subst(tcx, substs.unwrap())
510 self.astconv.ct_infer(ty, Some(param), self.span).into()
512 // We've already errored above about the mismatch.
513 tcx.const_error(ty).into()
521 let mut substs_ctx = SubstsForAstPathCtxt {
526 inferred_params: vec![],
529 let substs = Self::create_substs_for_generic_args(
540 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
541 generics, self_ty, substs
547 fn create_assoc_bindings_for_generic_args<'a>(
549 generic_args: &'a hir::GenericArgs<'_>,
550 ) -> Vec<ConvertedBinding<'a, 'tcx>> {
551 // Convert associated-type bindings or constraints into a separate vector.
552 // Example: Given this:
554 // T: Iterator<Item = u32>
556 // The `T` is passed in as a self-type; the `Item = u32` is
557 // not a "type parameter" of the `Iterator` trait, but rather
558 // a restriction on `<T as Iterator>::Item`, so it is passed
560 let assoc_bindings = generic_args
564 let kind = match binding.kind {
565 hir::TypeBindingKind::Equality { ref term } => match term {
566 hir::Term::Ty(ref ty) => {
567 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty).into())
569 hir::Term::Const(ref c) => {
570 let local_did = self.tcx().hir().local_def_id(c.hir_id);
571 let c = Const::from_anon_const(self.tcx(), local_did);
572 ConvertedBindingKind::Equality(c.into())
575 hir::TypeBindingKind::Constraint { ref bounds } => {
576 ConvertedBindingKind::Constraint(bounds)
580 hir_id: binding.hir_id,
581 item_name: binding.ident,
583 gen_args: binding.gen_args,
592 pub(crate) fn create_substs_for_associated_item(
597 item_segment: &hir::PathSegment<'_>,
598 parent_substs: SubstsRef<'tcx>,
599 ) -> SubstsRef<'tcx> {
601 "create_substs_for_associated_item(span: {:?}, item_def_id: {:?}, item_segment: {:?}",
602 span, item_def_id, item_segment
604 if tcx.generics_of(item_def_id).params.is_empty() {
605 self.prohibit_generics(slice::from_ref(item_segment).iter(), |_| {});
609 self.create_substs_for_ast_path(
615 item_segment.infer_args,
622 /// Instantiates the path for the given trait reference, assuming that it's
623 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
624 /// The type _cannot_ be a type other than a trait type.
626 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
627 /// are disallowed. Otherwise, they are pushed onto the vector given.
628 pub fn instantiate_mono_trait_ref(
630 trait_ref: &hir::TraitRef<'_>,
632 ) -> ty::TraitRef<'tcx> {
633 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
635 self.ast_path_to_mono_trait_ref(
637 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
639 trait_ref.path.segments.last().unwrap(),
644 fn instantiate_poly_trait_ref_inner(
648 binding_span: Option<Span>,
649 constness: ty::BoundConstness,
650 bounds: &mut Bounds<'tcx>,
652 trait_ref_span: Span,
654 trait_segment: &hir::PathSegment<'_>,
655 args: &GenericArgs<'_>,
658 ) -> GenericArgCountResult {
659 let (substs, arg_count) = self.create_substs_for_ast_path(
669 let tcx = self.tcx();
670 let bound_vars = tcx.late_bound_vars(hir_id);
673 let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
676 ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
678 debug!(?poly_trait_ref, ?assoc_bindings);
679 bounds.trait_bounds.push((poly_trait_ref, span, constness));
681 let mut dup_bindings = FxHashMap::default();
682 for binding in &assoc_bindings {
683 // Specify type to assert that error was already reported in `Err` case.
684 let _: Result<_, ErrorGuaranteed> = self.add_predicates_for_ast_type_binding(
691 binding_span.unwrap_or(binding.span),
693 // Okay to ignore `Err` because of `ErrorGuaranteed` (see above).
699 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
700 /// a full trait reference. The resulting trait reference is returned. This may also generate
701 /// auxiliary bounds, which are added to `bounds`.
705 /// ```ignore (illustrative)
706 /// poly_trait_ref = Iterator<Item = u32>
710 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
712 /// **A note on binders:** against our usual convention, there is an implied bounder around
713 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
714 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
715 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
716 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
718 #[tracing::instrument(level = "debug", skip(self, span, constness, bounds, speculative))]
719 pub(crate) fn instantiate_poly_trait_ref(
721 trait_ref: &hir::TraitRef<'_>,
723 constness: ty::BoundConstness,
725 bounds: &mut Bounds<'tcx>,
727 ) -> GenericArgCountResult {
728 let hir_id = trait_ref.hir_ref_id;
729 let binding_span = None;
730 let trait_ref_span = trait_ref.path.span;
731 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
732 let trait_segment = trait_ref.path.segments.last().unwrap();
733 let args = trait_segment.args();
734 let infer_args = trait_segment.infer_args;
736 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
737 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, false);
739 self.instantiate_poly_trait_ref_inner(
755 pub(crate) fn instantiate_lang_item_trait_ref(
757 lang_item: hir::LangItem,
760 args: &GenericArgs<'_>,
762 bounds: &mut Bounds<'tcx>,
764 let binding_span = Some(span);
765 let constness = ty::BoundConstness::NotConst;
766 let speculative = false;
767 let trait_ref_span = span;
768 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
769 let trait_segment = &hir::PathSegment::invalid();
770 let infer_args = false;
772 self.instantiate_poly_trait_ref_inner(
788 fn ast_path_to_mono_trait_ref(
793 trait_segment: &hir::PathSegment<'_>,
795 ) -> ty::TraitRef<'tcx> {
796 let (substs, _) = self.create_substs_for_ast_trait_ref(
803 let assoc_bindings = self.create_assoc_bindings_for_generic_args(trait_segment.args());
804 if let Some(b) = assoc_bindings.first() {
805 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
807 ty::TraitRef::new(trait_def_id, substs)
810 #[tracing::instrument(level = "debug", skip(self, span))]
811 fn create_substs_for_ast_trait_ref<'a>(
816 trait_segment: &'a hir::PathSegment<'a>,
818 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
819 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
821 self.create_substs_for_ast_path(
826 trait_segment.args(),
827 trait_segment.infer_args,
832 fn trait_defines_associated_type_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::Type, trait_def_id)
838 fn trait_defines_associated_const_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
840 .associated_items(trait_def_id)
841 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Const, trait_def_id)
845 // Sets `implicitly_sized` to true on `Bounds` if necessary
846 pub(crate) fn add_implicitly_sized<'hir>(
848 bounds: &mut Bounds<'hir>,
849 ast_bounds: &'hir [hir::GenericBound<'hir>],
850 self_ty_where_predicates: Option<(hir::HirId, &'hir [hir::WherePredicate<'hir>])>,
853 let tcx = self.tcx();
855 // Try to find an unbound in bounds.
856 let mut unbound = None;
857 let mut search_bounds = |ast_bounds: &'hir [hir::GenericBound<'hir>]| {
858 for ab in ast_bounds {
859 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
860 if unbound.is_none() {
861 unbound = Some(&ptr.trait_ref);
863 tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
868 search_bounds(ast_bounds);
869 if let Some((self_ty, where_clause)) = self_ty_where_predicates {
870 let self_ty_def_id = tcx.hir().local_def_id(self_ty).to_def_id();
871 for clause in where_clause {
872 if let hir::WherePredicate::BoundPredicate(pred) = clause {
873 if pred.is_param_bound(self_ty_def_id) {
874 search_bounds(pred.bounds);
880 let sized_def_id = tcx.lang_items().require(LangItem::Sized);
881 match (&sized_def_id, unbound) {
882 (Ok(sized_def_id), Some(tpb))
883 if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) =>
885 // There was in fact a `?Sized` bound, return without doing anything
889 // There was a `?Trait` bound, but it was not `?Sized`; warn.
892 "default bound relaxed for a type parameter, but \
893 this does nothing because the given bound is not \
894 a default; only `?Sized` is supported",
896 // Otherwise, add implicitly sized if `Sized` is available.
899 // There was no `?Sized` bound; add implicitly sized if `Sized` is available.
902 if sized_def_id.is_err() {
903 // No lang item for `Sized`, so we can't add it as a bound.
906 bounds.implicitly_sized = Some(span);
909 /// This helper takes a *converted* parameter type (`param_ty`)
910 /// and an *unconverted* list of bounds:
914 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
916 /// `param_ty`, in ty form
919 /// It adds these `ast_bounds` into the `bounds` structure.
921 /// **A note on binders:** there is an implied binder around
922 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
923 /// for more details.
924 #[tracing::instrument(level = "debug", skip(self, ast_bounds, bounds))]
925 pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>(
929 bounds: &mut Bounds<'tcx>,
930 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
932 for ast_bound in ast_bounds {
934 hir::GenericBound::Trait(poly_trait_ref, modifier) => {
935 let constness = match modifier {
936 hir::TraitBoundModifier::MaybeConst => ty::BoundConstness::ConstIfConst,
937 hir::TraitBoundModifier::None => ty::BoundConstness::NotConst,
938 hir::TraitBoundModifier::Maybe => continue,
941 let _ = self.instantiate_poly_trait_ref(
942 &poly_trait_ref.trait_ref,
950 &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
951 self.instantiate_lang_item_trait_ref(
952 lang_item, span, hir_id, args, param_ty, bounds,
955 hir::GenericBound::Outlives(lifetime) => {
956 let region = self.ast_region_to_region(lifetime, None);
959 .push((ty::Binder::bind_with_vars(region, bound_vars), lifetime.span));
965 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
966 /// The self-type for the bounds is given by `param_ty`.
970 /// ```ignore (illustrative)
971 /// fn foo<T: Bar + Baz>() { }
972 /// // ^ ^^^^^^^^^ ast_bounds
976 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
977 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
978 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
980 /// `span` should be the declaration size of the parameter.
981 pub(crate) fn compute_bounds(
984 ast_bounds: &[hir::GenericBound<'_>],
986 self.compute_bounds_inner(param_ty, ast_bounds)
989 /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
990 /// named `assoc_name` into ty::Bounds. Ignore the rest.
991 pub(crate) fn compute_bounds_that_match_assoc_type(
994 ast_bounds: &[hir::GenericBound<'_>],
997 let mut result = Vec::new();
999 for ast_bound in ast_bounds {
1000 if let Some(trait_ref) = ast_bound.trait_ref()
1001 && let Some(trait_did) = trait_ref.trait_def_id()
1002 && self.tcx().trait_may_define_assoc_type(trait_did, assoc_name)
1004 result.push(ast_bound.clone());
1008 self.compute_bounds_inner(param_ty, &result)
1011 fn compute_bounds_inner(
1014 ast_bounds: &[hir::GenericBound<'_>],
1016 let mut bounds = Bounds::default();
1018 self.add_bounds(param_ty, ast_bounds.iter(), &mut bounds, ty::List::empty());
1024 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1027 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1028 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1029 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1030 #[tracing::instrument(
1032 skip(self, bounds, speculative, dup_bindings, path_span)
1034 fn add_predicates_for_ast_type_binding(
1036 hir_ref_id: hir::HirId,
1037 trait_ref: ty::PolyTraitRef<'tcx>,
1038 binding: &ConvertedBinding<'_, 'tcx>,
1039 bounds: &mut Bounds<'tcx>,
1041 dup_bindings: &mut FxHashMap<DefId, Span>,
1043 ) -> Result<(), ErrorGuaranteed> {
1044 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1045 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1046 // subtle in the event that `T` is defined in a supertrait of
1047 // `SomeTrait`, because in that case we need to upcast.
1049 // That is, consider this case:
1052 // trait SubTrait: SuperTrait<i32> { }
1053 // trait SuperTrait<A> { type T; }
1055 // ... B: SubTrait<T = foo> ...
1058 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
1060 let tcx = self.tcx();
1063 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1064 // Simple case: X is defined in the current trait.
1067 // Otherwise, we have to walk through the supertraits to find
1069 self.one_bound_for_assoc_type(
1070 || traits::supertraits(tcx, trait_ref),
1071 || trait_ref.print_only_trait_path().to_string(),
1074 || match binding.kind {
1075 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1081 let (assoc_ident, def_scope) =
1082 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1084 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1085 // of calling `filter_by_name_and_kind`.
1086 let find_item_of_kind = |kind| {
1087 tcx.associated_items(candidate.def_id())
1088 .filter_by_name_unhygienic(assoc_ident.name)
1089 .find(|i| i.kind == kind && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident)
1091 let assoc_item = find_item_of_kind(ty::AssocKind::Type)
1092 .or_else(|| find_item_of_kind(ty::AssocKind::Const))
1093 .expect("missing associated type");
1095 if !assoc_item.visibility(tcx).is_accessible_from(def_scope, tcx) {
1099 &format!("{} `{}` is private", assoc_item.kind, binding.item_name),
1101 .span_label(binding.span, &format!("private {}", assoc_item.kind))
1104 tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None);
1108 .entry(assoc_item.def_id)
1109 .and_modify(|prev_span| {
1110 self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
1112 prev_span: *prev_span,
1113 item_name: binding.item_name,
1114 def_path: tcx.def_path_str(assoc_item.container_id(tcx)),
1117 .or_insert(binding.span);
1120 // Include substitutions for generic parameters of associated types
1121 let projection_ty = candidate.map_bound(|trait_ref| {
1122 let ident = Ident::new(assoc_item.name, binding.item_name.span);
1123 let item_segment = hir::PathSegment {
1125 hir_id: Some(binding.hir_id),
1127 args: Some(binding.gen_args),
1131 let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
1140 "add_predicates_for_ast_type_binding: substs for trait-ref and assoc_item: {:?}",
1141 substs_trait_ref_and_assoc_item
1145 item_def_id: assoc_item.def_id,
1146 substs: substs_trait_ref_and_assoc_item,
1151 // Find any late-bound regions declared in `ty` that are not
1152 // declared in the trait-ref or assoc_item. These are not well-formed.
1156 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1157 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1158 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1159 let late_bound_in_trait_ref =
1160 tcx.collect_constrained_late_bound_regions(&projection_ty);
1161 let late_bound_in_ty =
1162 tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty));
1163 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1164 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1166 // FIXME: point at the type params that don't have appropriate lifetimes:
1167 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1168 // ---- ---- ^^^^^^^
1169 self.validate_late_bound_regions(
1170 late_bound_in_trait_ref,
1177 "binding for associated type `{}` references {}, \
1178 which does not appear in the trait input types",
1187 match binding.kind {
1188 ConvertedBindingKind::Equality(mut term) => {
1189 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1190 // the "projection predicate" for:
1192 // `<T as Iterator>::Item = u32`
1193 let assoc_item_def_id = projection_ty.skip_binder().item_def_id;
1194 let def_kind = tcx.def_kind(assoc_item_def_id);
1195 match (def_kind, term) {
1196 (hir::def::DefKind::AssocTy, ty::Term::Ty(_))
1197 | (hir::def::DefKind::AssocConst, ty::Term::Const(_)) => (),
1199 let got = if let ty::Term::Ty(_) = term { "type" } else { "constant" };
1200 let expected = def_kind.descr(assoc_item_def_id);
1204 &format!("expected {expected} bound, found {got}"),
1207 tcx.def_span(assoc_item_def_id),
1208 &format!("{expected} defined here"),
1211 term = match def_kind {
1212 hir::def::DefKind::AssocTy => tcx.ty_error().into(),
1213 hir::def::DefKind::AssocConst => tcx
1215 tcx.bound_type_of(assoc_item_def_id)
1216 .subst(tcx, projection_ty.skip_binder().substs),
1219 _ => unreachable!(),
1223 bounds.projection_bounds.push((
1224 projection_ty.map_bound(|projection_ty| ty::ProjectionPredicate {
1231 ConvertedBindingKind::Constraint(ast_bounds) => {
1232 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1234 // `<T as Iterator>::Item: Debug`
1236 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1237 // parameter to have a skipped binder.
1238 let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
1239 self.add_bounds(param_ty, ast_bounds.iter(), bounds, candidate.bound_vars());
1249 item_segment: &hir::PathSegment<'_>,
1251 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1254 EarlyBinder(self.tcx().at(span).type_of(did)).subst(self.tcx(), substs),
1258 fn conv_object_ty_poly_trait_ref(
1261 trait_bounds: &[hir::PolyTraitRef<'_>],
1262 lifetime: &hir::Lifetime,
1265 let tcx = self.tcx();
1267 let mut bounds = Bounds::default();
1268 let mut potential_assoc_types = Vec::new();
1269 let dummy_self = self.tcx().types.trait_object_dummy_self;
1270 for trait_bound in trait_bounds.iter().rev() {
1271 if let GenericArgCountResult {
1273 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1275 } = self.instantiate_poly_trait_ref(
1276 &trait_bound.trait_ref,
1278 ty::BoundConstness::NotConst,
1283 potential_assoc_types.extend(cur_potential_assoc_types);
1287 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1288 // is used and no 'maybe' bounds are used.
1289 let expanded_traits =
1290 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1291 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) = expanded_traits
1292 .filter(|i| i.trait_ref().self_ty().skip_binder() == dummy_self)
1293 .partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1294 if regular_traits.len() > 1 {
1295 let first_trait = ®ular_traits[0];
1296 let additional_trait = ®ular_traits[1];
1297 let mut err = struct_span_err!(
1299 additional_trait.bottom().1,
1301 "only auto traits can be used as additional traits in a trait object"
1303 additional_trait.label_with_exp_info(
1305 "additional non-auto trait",
1308 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1310 "consider creating a new trait with all of these as supertraits and using that \
1311 trait here instead: `trait NewTrait: {} {{}}`",
1314 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1315 .collect::<Vec<_>>()
1319 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1320 for more information on them, visit \
1321 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1326 if regular_traits.is_empty() && auto_traits.is_empty() {
1327 let trait_alias_span = bounds
1330 .map(|&(trait_ref, _, _)| trait_ref.def_id())
1331 .find(|&trait_ref| tcx.is_trait_alias(trait_ref))
1332 .map(|trait_ref| tcx.def_span(trait_ref));
1333 tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span, trait_alias_span });
1334 return tcx.ty_error();
1337 // Check that there are no gross object safety violations;
1338 // most importantly, that the supertraits don't contain `Self`,
1340 for item in ®ular_traits {
1341 let object_safety_violations =
1342 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1343 if !object_safety_violations.is_empty() {
1344 report_object_safety_error(
1347 item.trait_ref().def_id(),
1348 &object_safety_violations,
1351 return tcx.ty_error();
1355 // Use a `BTreeSet` to keep output in a more consistent order.
1356 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1358 let regular_traits_refs_spans = bounds
1361 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1363 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1364 assert_eq!(constness, ty::BoundConstness::NotConst);
1366 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1368 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1369 obligation.predicate
1372 let bound_predicate = obligation.predicate.kind();
1373 match bound_predicate.skip_binder() {
1374 ty::PredicateKind::Trait(pred) => {
1375 let pred = bound_predicate.rebind(pred);
1376 associated_types.entry(span).or_default().extend(
1377 tcx.associated_items(pred.def_id())
1378 .in_definition_order()
1379 .filter(|item| item.kind == ty::AssocKind::Type)
1380 .map(|item| item.def_id),
1383 ty::PredicateKind::Projection(pred) => {
1384 let pred = bound_predicate.rebind(pred);
1385 // A `Self` within the original bound will be substituted with a
1386 // `trait_object_dummy_self`, so check for that.
1387 let references_self = match pred.skip_binder().term {
1388 ty::Term::Ty(ty) => ty.walk().any(|arg| arg == dummy_self.into()),
1389 ty::Term::Const(c) => c.ty().walk().any(|arg| arg == dummy_self.into()),
1392 // If the projection output contains `Self`, force the user to
1393 // elaborate it explicitly to avoid a lot of complexity.
1395 // The "classically useful" case is the following:
1397 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1402 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1403 // but actually supporting that would "expand" to an infinitely-long type
1404 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1406 // Instead, we force the user to write
1407 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1408 // the discussion in #56288 for alternatives.
1409 if !references_self {
1410 // Include projections defined on supertraits.
1411 bounds.projection_bounds.push((pred, span));
1419 for (projection_bound, _) in &bounds.projection_bounds {
1420 for def_ids in associated_types.values_mut() {
1421 def_ids.remove(&projection_bound.projection_def_id());
1425 self.complain_about_missing_associated_types(
1427 potential_assoc_types,
1431 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1432 // `dyn Trait + Send`.
1433 // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
1435 let mut duplicates = FxHashSet::default();
1436 auto_traits.retain(|i| duplicates.insert(i.trait_ref().def_id()));
1437 debug!("regular_traits: {:?}", regular_traits);
1438 debug!("auto_traits: {:?}", auto_traits);
1440 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1441 let existential_trait_refs = regular_traits.iter().map(|i| {
1442 i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
1443 assert_eq!(trait_ref.self_ty(), dummy_self);
1445 // Verify that `dummy_self` did not leak inside default type parameters. This
1446 // could not be done at path creation, since we need to see through trait aliases.
1447 let mut missing_type_params = vec![];
1448 let mut references_self = false;
1449 let generics = tcx.generics_of(trait_ref.def_id);
1450 let substs: Vec<_> = trait_ref
1454 .skip(1) // Remove `Self` for `ExistentialPredicate`.
1455 .map(|(index, arg)| {
1456 if arg == dummy_self.into() {
1457 let param = &generics.params[index];
1458 missing_type_params.push(param.name);
1459 return tcx.ty_error().into();
1460 } else if arg.walk().any(|arg| arg == dummy_self.into()) {
1461 references_self = true;
1462 return tcx.ty_error().into();
1467 let substs = tcx.intern_substs(&substs[..]);
1469 let span = i.bottom().1;
1470 let empty_generic_args = trait_bounds.iter().any(|hir_bound| {
1471 hir_bound.trait_ref.path.res == Res::Def(DefKind::Trait, trait_ref.def_id)
1472 && hir_bound.span.contains(span)
1474 self.complain_about_missing_type_params(
1475 missing_type_params,
1481 if references_self {
1482 let def_id = i.bottom().0.def_id();
1483 let mut err = struct_span_err!(
1487 "the {} `{}` cannot be made into an object",
1488 tcx.def_kind(def_id).descr(def_id),
1489 tcx.item_name(def_id),
1492 rustc_middle::traits::ObjectSafetyViolation::SupertraitSelf(smallvec![])
1498 ty::ExistentialTraitRef { def_id: trait_ref.def_id, substs }
1502 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1503 bound.map_bound(|mut b| {
1504 assert_eq!(b.projection_ty.self_ty(), dummy_self);
1506 // Like for trait refs, verify that `dummy_self` did not leak inside default type
1508 let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
1509 if arg.walk().any(|arg| arg == dummy_self.into()) {
1514 if references_self {
1516 .delay_span_bug(span, "trait object projection bounds reference `Self`");
1517 let substs: Vec<_> = b
1522 if arg.walk().any(|arg| arg == dummy_self.into()) {
1523 return tcx.ty_error().into();
1528 b.projection_ty.substs = tcx.intern_substs(&substs[..]);
1531 ty::ExistentialProjection::erase_self_ty(tcx, b)
1535 let regular_trait_predicates = existential_trait_refs
1536 .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));
1537 let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
1538 ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
1540 // N.b. principal, projections, auto traits
1541 // FIXME: This is actually wrong with multiple principals in regards to symbol mangling
1542 let mut v = regular_trait_predicates
1544 existential_projections.map(|x| x.map_bound(ty::ExistentialPredicate::Projection)),
1546 .chain(auto_trait_predicates)
1547 .collect::<SmallVec<[_; 8]>>();
1548 v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
1550 let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
1552 // Use explicitly-specified region bound.
1553 let region_bound = if !lifetime.is_elided() {
1554 self.ast_region_to_region(lifetime, None)
1556 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1557 if tcx.named_region(lifetime.hir_id).is_some() {
1558 self.ast_region_to_region(lifetime, None)
1560 self.re_infer(None, span).unwrap_or_else(|| {
1561 let mut err = struct_span_err!(
1565 "the lifetime bound for this object type cannot be deduced \
1566 from context; please supply an explicit bound"
1569 // We will have already emitted an error E0106 complaining about a
1570 // missing named lifetime in `&dyn Trait`, so we elide this one.
1575 tcx.lifetimes.re_static
1580 debug!("region_bound: {:?}", region_bound);
1582 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1583 debug!("trait_object_type: {:?}", ty);
1587 fn report_ambiguous_associated_type(
1593 ) -> ErrorGuaranteed {
1594 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1598 .confused_type_with_std_module
1600 .any(|full_span| full_span.contains(span))
1602 err.span_suggestion(
1603 span.shrink_to_lo(),
1604 "you are looking for the module in `std`, not the primitive type",
1606 Applicability::MachineApplicable,
1609 err.span_suggestion(
1611 "use fully-qualified syntax",
1612 format!("<{} as {}>::{}", type_str, trait_str, name),
1613 Applicability::HasPlaceholders,
1619 // Search for a bound on a type parameter which includes the associated item
1620 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1621 // This function will fail if there are no suitable bounds or there is
1623 fn find_bound_for_assoc_item(
1625 ty_param_def_id: LocalDefId,
1628 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed> {
1629 let tcx = self.tcx();
1632 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1633 ty_param_def_id, assoc_name, span,
1636 let predicates = &self
1637 .get_type_parameter_bounds(span, ty_param_def_id.to_def_id(), assoc_name)
1640 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1642 let param_name = tcx.hir().ty_param_name(ty_param_def_id);
1643 self.one_bound_for_assoc_type(
1645 traits::transitive_bounds_that_define_assoc_type(
1647 predicates.iter().filter_map(|(p, _)| {
1648 Some(p.to_opt_poly_trait_pred()?.map_bound(|t| t.trait_ref))
1653 || param_name.to_string(),
1660 // Checks that `bounds` contains exactly one element and reports appropriate
1661 // errors otherwise.
1662 fn one_bound_for_assoc_type<I>(
1664 all_candidates: impl Fn() -> I,
1665 ty_param_name: impl Fn() -> String,
1668 is_equality: impl Fn() -> Option<String>,
1669 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed>
1671 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1673 let mut matching_candidates = all_candidates()
1674 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1675 let mut const_candidates = all_candidates()
1676 .filter(|r| self.trait_defines_associated_const_named(r.def_id(), assoc_name));
1678 let (bound, next_cand) = match (matching_candidates.next(), const_candidates.next()) {
1679 (Some(bound), _) => (bound, matching_candidates.next()),
1680 (None, Some(bound)) => (bound, const_candidates.next()),
1682 let reported = self.complain_about_assoc_type_not_found(
1688 return Err(reported);
1691 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1693 if let Some(bound2) = next_cand {
1694 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1696 let is_equality = is_equality();
1697 let bounds = IntoIterator::into_iter([bound, bound2]).chain(matching_candidates);
1698 let mut err = if is_equality.is_some() {
1699 // More specific Error Index entry.
1704 "ambiguous associated type `{}` in bounds of `{}`",
1713 "ambiguous associated type `{}` in bounds of `{}`",
1718 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1720 let mut where_bounds = vec![];
1721 for bound in bounds {
1722 let bound_id = bound.def_id();
1723 let bound_span = self
1725 .associated_items(bound_id)
1726 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1727 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1729 if let Some(bound_span) = bound_span {
1733 "ambiguous `{}` from `{}`",
1735 bound.print_only_trait_path(),
1738 if let Some(constraint) = &is_equality {
1739 where_bounds.push(format!(
1740 " T: {trait}::{assoc} = {constraint}",
1741 trait=bound.print_only_trait_path(),
1743 constraint=constraint,
1746 err.span_suggestion_verbose(
1747 span.with_hi(assoc_name.span.lo()),
1748 "use fully qualified syntax to disambiguate",
1752 bound.print_only_trait_path(),
1754 Applicability::MaybeIncorrect,
1759 "associated type `{}` could derive from `{}`",
1761 bound.print_only_trait_path(),
1765 if !where_bounds.is_empty() {
1767 "consider introducing a new type parameter `T` and adding `where` constraints:\
1768 \n where\n T: {},\n{}",
1770 where_bounds.join(",\n"),
1773 let reported = err.emit();
1774 if !where_bounds.is_empty() {
1775 return Err(reported);
1782 // Create a type from a path to an associated type.
1783 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1784 // and item_segment is the path segment for `D`. We return a type and a def for
1786 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1787 // parameter or `Self`.
1788 // NOTE: When this function starts resolving `Trait::AssocTy` successfully
1789 // it should also start reporting the `BARE_TRAIT_OBJECTS` lint.
1790 pub fn associated_path_to_ty(
1792 hir_ref_id: hir::HirId,
1795 qself: &hir::Ty<'_>,
1796 assoc_segment: &hir::PathSegment<'_>,
1797 permit_variants: bool,
1798 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
1799 let tcx = self.tcx();
1800 let assoc_ident = assoc_segment.ident;
1801 let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
1807 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1809 // Check if we have an enum variant.
1810 let mut variant_resolution = None;
1811 if let ty::Adt(adt_def, _) = qself_ty.kind() {
1812 if adt_def.is_enum() {
1813 let variant_def = adt_def
1816 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident(tcx), adt_def.did()));
1817 if let Some(variant_def) = variant_def {
1818 if permit_variants {
1819 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span, None);
1820 self.prohibit_generics(slice::from_ref(assoc_segment).iter(), |err| {
1821 err.note("enum variants can't have type parameters");
1822 let type_name = tcx.item_name(adt_def.did());
1824 "you might have meant to specity type parameters on enum \
1827 let Some(args) = assoc_segment.args else { return; };
1828 // Get the span of the generics args *including* the leading `::`.
1829 let args_span = assoc_segment.ident.span.shrink_to_hi().to(args.span_ext);
1830 if tcx.generics_of(adt_def.did()).count() == 0 {
1831 // FIXME(estebank): we could also verify that the arguments being
1832 // work for the `enum`, instead of just looking if it takes *any*.
1833 err.span_suggestion_verbose(
1835 &format!("{type_name} doesn't have generic parameters"),
1837 Applicability::MachineApplicable,
1841 let Ok(snippet) = tcx.sess.source_map().span_to_snippet(args_span) else {
1845 let (qself_sugg_span, is_self) = if let hir::TyKind::Path(
1846 hir::QPath::Resolved(_, ref path)
1848 // If the path segment already has type params, we want to overwrite
1850 match &path.segments[..] {
1851 // `segment` is the previous to last element on the path,
1852 // which would normally be the `enum` itself, while the last
1853 // `_` `PathSegment` corresponds to the variant.
1854 [.., hir::PathSegment {
1857 res: Some(Res::Def(DefKind::Enum, _)),
1860 // We need to include the `::` in `Type::Variant::<Args>`
1861 // to point the span to `::<Args>`, not just `<Args>`.
1862 ident.span.shrink_to_hi().to(args.map_or(
1863 ident.span.shrink_to_hi(),
1868 // We need to include the `::` in `Type::Variant::<Args>`
1869 // to point the span to `::<Args>`, not just `<Args>`.
1870 segment.ident.span.shrink_to_hi().to(segment.args.map_or(
1871 segment.ident.span.shrink_to_hi(),
1873 kw::SelfUpper == segment.ident.name,
1884 let suggestion = vec![
1886 // Account for people writing `Self::Variant::<Args>`, where
1887 // `Self` is the enum, and suggest replacing `Self` with the
1888 // appropriate type: `Type::<Args>::Variant`.
1889 (qself.span, format!("{type_name}{snippet}"))
1891 (qself_sugg_span, snippet)
1893 (args_span, String::new()),
1895 err.multipart_suggestion_verbose(
1898 Applicability::MaybeIncorrect,
1901 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1903 variant_resolution = Some(variant_def.def_id);
1909 // Find the type of the associated item, and the trait where the associated
1910 // item is declared.
1911 let bound = match (&qself_ty.kind(), qself_res) {
1912 (_, Res::SelfTy { trait_: Some(_), alias_to: Some((impl_def_id, _)) }) => {
1913 // `Self` in an impl of a trait -- we have a concrete self type and a
1915 let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) else {
1916 // A cycle error occurred, most likely.
1917 let guar = tcx.sess.delay_span_bug(span, "expected cycle error");
1921 self.one_bound_for_assoc_type(
1922 || traits::supertraits(tcx, ty::Binder::dummy(trait_ref)),
1923 || "Self".to_string(),
1931 Res::SelfTy { trait_: Some(param_did), alias_to: None }
1932 | Res::Def(DefKind::TyParam, param_did),
1933 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
1935 let reported = if variant_resolution.is_some() {
1936 // Variant in type position
1937 let msg = format!("expected type, found variant `{}`", assoc_ident);
1938 tcx.sess.span_err(span, &msg)
1939 } else if qself_ty.is_enum() {
1940 let mut err = struct_span_err!(
1944 "no variant named `{}` found for enum `{}`",
1949 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1950 if let Some(suggested_name) = find_best_match_for_name(
1954 .map(|variant| variant.name)
1955 .collect::<Vec<Symbol>>(),
1959 err.span_suggestion(
1961 "there is a variant with a similar name",
1963 Applicability::MaybeIncorrect,
1968 format!("variant not found in `{}`", qself_ty),
1972 if let Some(sp) = tcx.hir().span_if_local(adt_def.did()) {
1973 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1977 } else if let Some(reported) = qself_ty.error_reported() {
1980 // Don't print `TyErr` to the user.
1981 self.report_ambiguous_associated_type(
1983 &qself_ty.to_string(),
1988 return Err(reported);
1992 let trait_did = bound.def_id();
1993 let (assoc_ident, def_scope) =
1994 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1996 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1997 // of calling `filter_by_name_and_kind`.
1998 let item = tcx.associated_items(trait_did).in_definition_order().find(|i| {
1999 i.kind.namespace() == Namespace::TypeNS
2000 && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident
2002 // Assume that if it's not matched, there must be a const defined with the same name
2003 // but it was used in a type position.
2004 let Some(item) = item else {
2005 let msg = format!("found associated const `{assoc_ident}` when type was expected");
2006 let guar = tcx.sess.struct_span_err(span, &msg).emit();
2010 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2011 let ty = self.normalize_ty(span, ty);
2013 let kind = DefKind::AssocTy;
2014 if !item.visibility(tcx).is_accessible_from(def_scope, tcx) {
2015 let kind = kind.descr(item.def_id);
2016 let msg = format!("{} `{}` is private", kind, assoc_ident);
2018 .struct_span_err(span, &msg)
2019 .span_label(span, &format!("private {}", kind))
2022 tcx.check_stability(item.def_id, Some(hir_ref_id), span, None);
2024 if let Some(variant_def_id) = variant_resolution {
2025 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2026 let mut err = lint.build("ambiguous associated item");
2027 let mut could_refer_to = |kind: DefKind, def_id, also| {
2028 let note_msg = format!(
2029 "`{}` could{} refer to the {} defined here",
2034 err.span_note(tcx.def_span(def_id), ¬e_msg);
2037 could_refer_to(DefKind::Variant, variant_def_id, "");
2038 could_refer_to(kind, item.def_id, " also");
2040 err.span_suggestion(
2042 "use fully-qualified syntax",
2043 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2044 Applicability::MachineApplicable,
2050 Ok((ty, kind, item.def_id))
2056 opt_self_ty: Option<Ty<'tcx>>,
2058 trait_segment: &hir::PathSegment<'_>,
2059 item_segment: &hir::PathSegment<'_>,
2061 let tcx = self.tcx();
2063 let trait_def_id = tcx.parent(item_def_id);
2065 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2067 let Some(self_ty) = opt_self_ty else {
2068 let path_str = tcx.def_path_str(trait_def_id);
2070 let def_id = self.item_def_id();
2072 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2074 let parent_def_id = def_id
2075 .and_then(|def_id| {
2076 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
2078 .map(|hir_id| tcx.hir().get_parent_item(hir_id).to_def_id());
2080 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2082 // If the trait in segment is the same as the trait defining the item,
2083 // use the `<Self as ..>` syntax in the error.
2084 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2085 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2087 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2093 self.report_ambiguous_associated_type(
2097 item_segment.ident.name,
2099 return tcx.ty_error();
2102 debug!("qpath_to_ty: self_type={:?}", self_ty);
2105 self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment, false);
2107 let item_substs = self.create_substs_for_associated_item(
2115 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2117 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2120 pub fn prohibit_generics<'a>(
2122 segments: impl Iterator<Item = &'a hir::PathSegment<'a>> + Clone,
2123 extend: impl Fn(&mut Diagnostic),
2125 let args = segments.clone().flat_map(|segment| segment.args().args);
2127 let (lt, ty, ct, inf) =
2128 args.clone().fold((false, false, false, false), |(lt, ty, ct, inf), arg| match arg {
2129 hir::GenericArg::Lifetime(_) => (true, ty, ct, inf),
2130 hir::GenericArg::Type(_) => (lt, true, ct, inf),
2131 hir::GenericArg::Const(_) => (lt, ty, true, inf),
2132 hir::GenericArg::Infer(_) => (lt, ty, ct, true),
2134 let mut emitted = false;
2135 if lt || ty || ct || inf {
2136 let types_and_spans: Vec<_> = segments
2138 .flat_map(|segment| {
2139 segment.res.and_then(|res| {
2140 if segment.args().args.is_empty() {
2145 Res::PrimTy(ty) => format!("{} `{}`", res.descr(), ty.name()),
2147 if let Some(name) = self.tcx().opt_item_name(def_id) => {
2148 format!("{} `{name}`", res.descr())
2150 Res::Err => "this type".to_string(),
2151 _ => res.descr().to_string(),
2159 let this_type = match &types_and_spans[..] {
2160 [.., _, (last, _)] => format!(
2162 types_and_spans[..types_and_spans.len() - 1]
2164 .map(|(x, _)| x.as_str())
2166 .collect::<String>()
2168 [(only, _)] => only.to_string(),
2169 [] => "this type".to_string(),
2172 let arg_spans: Vec<Span> = args.map(|arg| arg.span()).collect();
2174 let mut kinds = Vec::with_capacity(4);
2176 kinds.push("lifetime");
2182 kinds.push("const");
2185 kinds.push("generic");
2187 let (kind, s) = match kinds[..] {
2191 kinds[..kinds.len() - 1]
2195 .collect::<String>()
2199 [only] => (format!("{only}"), ""),
2200 [] => unreachable!(),
2202 let last_span = *arg_spans.last().unwrap();
2203 let span: MultiSpan = arg_spans.into();
2204 let mut err = struct_span_err!(
2208 "{kind} arguments are not allowed on {this_type}",
2210 err.span_label(last_span, format!("{kind} argument{s} not allowed"));
2211 for (what, span) in types_and_spans {
2212 err.span_label(span, format!("not allowed on {what}"));
2219 for segment in segments {
2220 // Only emit the first error to avoid overloading the user with error messages.
2221 if let [binding, ..] = segment.args().bindings {
2222 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2229 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2230 pub fn def_ids_for_value_path_segments(
2232 segments: &[hir::PathSegment<'_>],
2233 self_ty: Option<Ty<'tcx>>,
2237 // We need to extract the type parameters supplied by the user in
2238 // the path `path`. Due to the current setup, this is a bit of a
2239 // tricky-process; the problem is that resolve only tells us the
2240 // end-point of the path resolution, and not the intermediate steps.
2241 // Luckily, we can (at least for now) deduce the intermediate steps
2242 // just from the end-point.
2244 // There are basically five cases to consider:
2246 // 1. Reference to a constructor of a struct:
2248 // struct Foo<T>(...)
2250 // In this case, the parameters are declared in the type space.
2252 // 2. Reference to a constructor of an enum variant:
2254 // enum E<T> { Foo(...) }
2256 // In this case, the parameters are defined in the type space,
2257 // but may be specified either on the type or the variant.
2259 // 3. Reference to a fn item or a free constant:
2263 // In this case, the path will again always have the form
2264 // `a::b::foo::<T>` where only the final segment should have
2265 // type parameters. However, in this case, those parameters are
2266 // declared on a value, and hence are in the `FnSpace`.
2268 // 4. Reference to a method or an associated constant:
2270 // impl<A> SomeStruct<A> {
2274 // Here we can have a path like
2275 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2276 // may appear in two places. The penultimate segment,
2277 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2278 // final segment, `foo::<B>` contains parameters in fn space.
2280 // The first step then is to categorize the segments appropriately.
2282 let tcx = self.tcx();
2284 assert!(!segments.is_empty());
2285 let last = segments.len() - 1;
2287 let mut path_segs = vec![];
2290 // Case 1. Reference to a struct constructor.
2291 DefKind::Ctor(CtorOf::Struct, ..) => {
2292 // Everything but the final segment should have no
2293 // parameters at all.
2294 let generics = tcx.generics_of(def_id);
2295 // Variant and struct constructors use the
2296 // generics of their parent type definition.
2297 let generics_def_id = generics.parent.unwrap_or(def_id);
2298 path_segs.push(PathSeg(generics_def_id, last));
2301 // Case 2. Reference to a variant constructor.
2302 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2303 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2304 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2305 debug_assert!(adt_def.is_enum());
2306 (adt_def.did(), last)
2307 } else if last >= 1 && segments[last - 1].args.is_some() {
2308 // Everything but the penultimate segment should have no
2309 // parameters at all.
2310 let mut def_id = def_id;
2312 // `DefKind::Ctor` -> `DefKind::Variant`
2313 if let DefKind::Ctor(..) = kind {
2314 def_id = tcx.parent(def_id);
2317 // `DefKind::Variant` -> `DefKind::Enum`
2318 let enum_def_id = tcx.parent(def_id);
2319 (enum_def_id, last - 1)
2321 // FIXME: lint here recommending `Enum::<...>::Variant` form
2322 // instead of `Enum::Variant::<...>` form.
2324 // Everything but the final segment should have no
2325 // parameters at all.
2326 let generics = tcx.generics_of(def_id);
2327 // Variant and struct constructors use the
2328 // generics of their parent type definition.
2329 (generics.parent.unwrap_or(def_id), last)
2331 path_segs.push(PathSeg(generics_def_id, index));
2334 // Case 3. Reference to a top-level value.
2335 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static(_) => {
2336 path_segs.push(PathSeg(def_id, last));
2339 // Case 4. Reference to a method or associated const.
2340 DefKind::AssocFn | DefKind::AssocConst => {
2341 if segments.len() >= 2 {
2342 let generics = tcx.generics_of(def_id);
2343 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2345 path_segs.push(PathSeg(def_id, last));
2348 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2351 debug!("path_segs = {:?}", path_segs);
2356 // Check a type `Path` and convert it to a `Ty`.
2359 opt_self_ty: Option<Ty<'tcx>>,
2360 path: &hir::Path<'_>,
2361 permit_variants: bool,
2363 let tcx = self.tcx();
2366 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2367 path.res, opt_self_ty, path.segments
2370 let span = path.span;
2372 Res::Def(DefKind::OpaqueTy, did) => {
2373 // Check for desugared `impl Trait`.
2374 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2375 let item_segment = path.segments.split_last().unwrap();
2376 self.prohibit_generics(item_segment.1.iter(), |err| {
2377 err.note("`impl Trait` types can't have type parameters");
2379 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2380 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2387 | DefKind::ForeignTy,
2390 assert_eq!(opt_self_ty, None);
2391 self.prohibit_generics(path.segments.split_last().unwrap().1.iter(), |_| {});
2392 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2394 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2395 // Convert "variant type" as if it were a real type.
2396 // The resulting `Ty` is type of the variant's enum for now.
2397 assert_eq!(opt_self_ty, None);
2400 self.def_ids_for_value_path_segments(path.segments, None, kind, def_id);
2401 let generic_segs: FxHashSet<_> =
2402 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2403 self.prohibit_generics(
2404 path.segments.iter().enumerate().filter_map(|(index, seg)| {
2405 if !generic_segs.contains(&index) { Some(seg) } else { None }
2408 err.note("enum variants can't have type parameters");
2412 let PathSeg(def_id, index) = path_segs.last().unwrap();
2413 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2415 Res::Def(DefKind::TyParam, def_id) => {
2416 assert_eq!(opt_self_ty, None);
2417 self.prohibit_generics(path.segments.iter(), |err| {
2418 if let Some(span) = tcx.def_ident_span(def_id) {
2419 let name = tcx.item_name(def_id);
2420 err.span_note(span, &format!("type parameter `{name}` defined here"));
2424 let def_id = def_id.expect_local();
2425 let item_def_id = tcx.hir().ty_param_owner(def_id);
2426 let generics = tcx.generics_of(item_def_id);
2427 let index = generics.param_def_id_to_index[&def_id.to_def_id()];
2428 tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id))
2430 Res::SelfTy { trait_: Some(_), alias_to: None } => {
2431 // `Self` in trait or type alias.
2432 assert_eq!(opt_self_ty, None);
2433 self.prohibit_generics(path.segments.iter(), |err| {
2434 if let [hir::PathSegment { args: Some(args), ident, .. }] = &path.segments[..] {
2435 err.span_suggestion_verbose(
2436 ident.span.shrink_to_hi().to(args.span_ext),
2437 "the `Self` type doesn't accept type parameters",
2439 Applicability::MaybeIncorrect,
2443 tcx.types.self_param
2445 Res::SelfTy { trait_: _, alias_to: Some((def_id, forbid_generic)) } => {
2446 // `Self` in impl (we know the concrete type).
2447 assert_eq!(opt_self_ty, None);
2448 // Try to evaluate any array length constants.
2449 let ty = tcx.at(span).type_of(def_id);
2450 let span_of_impl = tcx.span_of_impl(def_id);
2451 self.prohibit_generics(path.segments.iter(), |err| {
2452 let def_id = match *ty.kind() {
2453 ty::Adt(self_def, _) => self_def.did(),
2457 let type_name = tcx.item_name(def_id);
2458 let span_of_ty = tcx.def_ident_span(def_id);
2459 let generics = tcx.generics_of(def_id).count();
2461 let msg = format!("`Self` is of type `{ty}`");
2462 if let (Ok(i_sp), Some(t_sp)) = (span_of_impl, span_of_ty) {
2463 let mut span: MultiSpan = vec![t_sp].into();
2464 span.push_span_label(
2466 &format!("`Self` is on type `{type_name}` in this `impl`"),
2468 let mut postfix = "";
2470 postfix = ", which doesn't have generic parameters";
2472 span.push_span_label(
2474 &format!("`Self` corresponds to this type{postfix}"),
2476 err.span_note(span, &msg);
2480 for segment in path.segments {
2481 if let Some(args) = segment.args && segment.ident.name == kw::SelfUpper {
2483 // FIXME(estebank): we could also verify that the arguments being
2484 // work for the `enum`, instead of just looking if it takes *any*.
2485 err.span_suggestion_verbose(
2486 segment.ident.span.shrink_to_hi().to(args.span_ext),
2487 "the `Self` type doesn't accept type parameters",
2489 Applicability::MachineApplicable,
2493 err.span_suggestion_verbose(
2496 "the `Self` type doesn't accept type parameters, use the \
2497 concrete type's name `{type_name}` instead if you want to \
2498 specify its type parameters"
2501 Applicability::MaybeIncorrect,
2507 // HACK(min_const_generics): Forbid generic `Self` types
2508 // here as we can't easily do that during nameres.
2510 // We do this before normalization as we otherwise allow
2512 // trait AlwaysApplicable { type Assoc; }
2513 // impl<T: ?Sized> AlwaysApplicable for T { type Assoc = usize; }
2515 // trait BindsParam<T> {
2518 // impl<T> BindsParam<T> for <T as AlwaysApplicable>::Assoc {
2519 // type ArrayTy = [u8; Self::MAX];
2522 // Note that the normalization happens in the param env of
2523 // the anon const, which is empty. This is why the
2524 // `AlwaysApplicable` impl needs a `T: ?Sized` bound for
2525 // this to compile if we were to normalize here.
2526 if forbid_generic && ty.needs_subst() {
2527 let mut err = tcx.sess.struct_span_err(
2529 "generic `Self` types are currently not permitted in anonymous constants",
2531 if let Some(hir::Node::Item(&hir::Item {
2532 kind: hir::ItemKind::Impl(ref impl_),
2534 })) = tcx.hir().get_if_local(def_id)
2536 err.span_note(impl_.self_ty.span, "not a concrete type");
2541 self.normalize_ty(span, ty)
2544 Res::Def(DefKind::AssocTy, def_id) => {
2545 debug_assert!(path.segments.len() >= 2);
2546 self.prohibit_generics(path.segments[..path.segments.len() - 2].iter(), |_| {});
2551 &path.segments[path.segments.len() - 2],
2552 path.segments.last().unwrap(),
2555 Res::PrimTy(prim_ty) => {
2556 assert_eq!(opt_self_ty, None);
2557 self.prohibit_generics(path.segments.iter(), |err| {
2558 let name = prim_ty.name_str();
2559 for segment in path.segments {
2560 if let Some(args) = segment.args {
2561 err.span_suggestion_verbose(
2562 segment.ident.span.shrink_to_hi().to(args.span_ext),
2563 &format!("primitive type `{name}` doesn't have generic parameters"),
2565 Applicability::MaybeIncorrect,
2571 hir::PrimTy::Bool => tcx.types.bool,
2572 hir::PrimTy::Char => tcx.types.char,
2573 hir::PrimTy::Int(it) => tcx.mk_mach_int(ty::int_ty(it)),
2574 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(ty::uint_ty(uit)),
2575 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ty::float_ty(ft)),
2576 hir::PrimTy::Str => tcx.types.str_,
2580 self.set_tainted_by_errors();
2581 self.tcx().ty_error()
2583 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2587 /// Parses the programmer's textual representation of a type into our
2588 /// internal notion of a type.
2589 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2590 self.ast_ty_to_ty_inner(ast_ty, false, false)
2593 /// Parses the programmer's textual representation of a type into our
2594 /// internal notion of a type. This is meant to be used within a path.
2595 pub fn ast_ty_to_ty_in_path(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2596 self.ast_ty_to_ty_inner(ast_ty, false, true)
2599 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2600 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2601 #[tracing::instrument(level = "debug", skip(self))]
2602 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool, in_path: bool) -> Ty<'tcx> {
2603 let tcx = self.tcx();
2605 let result_ty = match ast_ty.kind {
2606 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
2607 hir::TyKind::Ptr(ref mt) => {
2608 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
2610 hir::TyKind::Rptr(ref region, ref mt) => {
2611 let r = self.ast_region_to_region(region, None);
2613 let t = self.ast_ty_to_ty_inner(mt.ty, true, false);
2614 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2616 hir::TyKind::Never => tcx.types.never,
2617 hir::TyKind::Tup(fields) => tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(t))),
2618 hir::TyKind::BareFn(bf) => {
2619 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
2621 tcx.mk_fn_ptr(self.ty_of_fn(
2630 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
2631 self.maybe_lint_bare_trait(ast_ty, in_path);
2632 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed)
2634 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2635 debug!(?maybe_qself, ?path);
2636 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2637 self.res_to_ty(opt_self_ty, path, false)
2639 hir::TyKind::OpaqueDef(item_id, lifetimes) => {
2640 let opaque_ty = tcx.hir().item(item_id);
2641 let def_id = item_id.def_id.to_def_id();
2643 match opaque_ty.kind {
2644 hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
2645 self.impl_trait_ty_to_ty(def_id, lifetimes, origin)
2647 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2650 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2651 debug!(?qself, ?segment);
2652 let ty = self.ast_ty_to_ty_inner(qself, false, true);
2653 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, qself, segment, false)
2654 .map(|(ty, _, _)| ty)
2655 .unwrap_or_else(|_| tcx.ty_error())
2657 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
2658 let def_id = tcx.require_lang_item(lang_item, Some(span));
2659 let (substs, _) = self.create_substs_for_ast_path(
2663 &hir::PathSegment::invalid(),
2664 &GenericArgs::none(),
2668 EarlyBinder(self.normalize_ty(span, tcx.at(span).type_of(def_id)))
2671 hir::TyKind::Array(ref ty, ref length) => {
2672 let length = match length {
2673 &hir::ArrayLen::Infer(_, span) => self.ct_infer(tcx.types.usize, None, span),
2674 hir::ArrayLen::Body(constant) => {
2675 let length_def_id = tcx.hir().local_def_id(constant.hir_id);
2676 ty::Const::from_anon_const(tcx, length_def_id)
2680 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(ty), length));
2681 self.normalize_ty(ast_ty.span, array_ty)
2683 hir::TyKind::Typeof(ref e) => {
2684 let ty = tcx.type_of(tcx.hir().local_def_id(e.hir_id));
2685 let span = ast_ty.span;
2686 tcx.sess.emit_err(TypeofReservedKeywordUsed {
2689 opt_sugg: Some((span, Applicability::MachineApplicable))
2690 .filter(|_| ty.is_suggestable(tcx, false)),
2695 hir::TyKind::Infer => {
2696 // Infer also appears as the type of arguments or return
2697 // values in an ExprKind::Closure, or as
2698 // the type of local variables. Both of these cases are
2699 // handled specially and will not descend into this routine.
2700 self.ty_infer(None, ast_ty.span)
2702 hir::TyKind::Err => tcx.ty_error(),
2707 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2711 fn impl_trait_ty_to_ty(
2714 lifetimes: &[hir::GenericArg<'_>],
2715 origin: OpaqueTyOrigin,
2717 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2718 let tcx = self.tcx();
2720 let generics = tcx.generics_of(def_id);
2722 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2723 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2724 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2725 // Our own parameters are the resolved lifetimes.
2726 if let GenericParamDefKind::Lifetime = param.kind {
2727 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2728 self.ast_region_to_region(lifetime, None).into()
2737 // For RPIT (return position impl trait), only lifetimes
2738 // mentioned in the impl Trait predicate are captured by
2739 // the opaque type, so the lifetime parameters from the
2740 // parent item need to be replaced with `'static`.
2742 // For `impl Trait` in the types of statics, constants,
2743 // locals and type aliases. These capture all parent
2744 // lifetimes, so they can use their identity subst.
2745 GenericParamDefKind::Lifetime
2748 hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..)
2751 tcx.lifetimes.re_static.into()
2753 _ => tcx.mk_param_from_def(param),
2757 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2759 let ty = tcx.mk_opaque(def_id, substs);
2760 debug!("impl_trait_ty_to_ty: {}", ty);
2764 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2766 hir::TyKind::Infer if expected_ty.is_some() => {
2767 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2768 expected_ty.unwrap()
2770 _ => self.ast_ty_to_ty(ty),
2777 unsafety: hir::Unsafety,
2779 decl: &hir::FnDecl<'_>,
2780 generics: Option<&hir::Generics<'_>>,
2781 hir_ty: Option<&hir::Ty<'_>>,
2782 ) -> ty::PolyFnSig<'tcx> {
2785 let tcx = self.tcx();
2786 let bound_vars = tcx.late_bound_vars(hir_id);
2787 debug!(?bound_vars);
2789 // We proactively collect all the inferred type params to emit a single error per fn def.
2790 let mut visitor = HirPlaceholderCollector::default();
2791 let mut infer_replacements = vec![];
2793 if let Some(generics) = generics {
2794 walk_generics(&mut visitor, generics);
2797 let input_tys: Vec<_> = decl
2802 if let hir::TyKind::Infer = a.kind && !self.allow_ty_infer() {
2803 if let Some(suggested_ty) =
2804 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, Some(i))
2806 infer_replacements.push((a.span, suggested_ty.to_string()));
2807 return suggested_ty;
2811 // Only visit the type looking for `_` if we didn't fix the type above
2812 visitor.visit_ty(a);
2813 self.ty_of_arg(a, None)
2817 let output_ty = match decl.output {
2818 hir::FnRetTy::Return(output) => {
2819 if let hir::TyKind::Infer = output.kind
2820 && !self.allow_ty_infer()
2821 && let Some(suggested_ty) =
2822 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, None)
2824 infer_replacements.push((output.span, suggested_ty.to_string()));
2827 visitor.visit_ty(output);
2828 self.ast_ty_to_ty(output)
2831 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2834 debug!("ty_of_fn: output_ty={:?}", output_ty);
2836 let fn_ty = tcx.mk_fn_sig(input_tys.into_iter(), output_ty, decl.c_variadic, unsafety, abi);
2837 let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
2839 if !self.allow_ty_infer() && !(visitor.0.is_empty() && infer_replacements.is_empty()) {
2840 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2841 // only want to emit an error complaining about them if infer types (`_`) are not
2842 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2843 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2845 let mut diag = crate::collect::placeholder_type_error_diag(
2849 infer_replacements.iter().map(|(s, _)| *s).collect(),
2855 if !infer_replacements.is_empty() {
2856 diag.multipart_suggestion(&format!(
2857 "try replacing `_` with the type{} in the corresponding trait method signature",
2858 rustc_errors::pluralize!(infer_replacements.len()),
2859 ), infer_replacements, Applicability::MachineApplicable);
2865 // Find any late-bound regions declared in return type that do
2866 // not appear in the arguments. These are not well-formed.
2869 // for<'a> fn() -> &'a str <-- 'a is bad
2870 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2871 let inputs = bare_fn_ty.inputs();
2872 let late_bound_in_args =
2873 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2874 let output = bare_fn_ty.output();
2875 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2877 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
2882 "return type references {}, which is not constrained by the fn input types",
2890 /// Given a fn_hir_id for a impl function, suggest the type that is found on the
2891 /// corresponding function in the trait that the impl implements, if it exists.
2892 /// If arg_idx is Some, then it corresponds to an input type index, otherwise it
2893 /// corresponds to the return type.
2894 fn suggest_trait_fn_ty_for_impl_fn_infer(
2896 fn_hir_id: hir::HirId,
2897 arg_idx: Option<usize>,
2898 ) -> Option<Ty<'tcx>> {
2899 let tcx = self.tcx();
2900 let hir = tcx.hir();
2902 let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), ident, .. }) =
2903 hir.get(fn_hir_id) else { return None };
2904 let hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(i), .. }) =
2905 hir.get(hir.get_parent_node(fn_hir_id)) else { bug!("ImplItem should have Impl parent") };
2908 self.instantiate_mono_trait_ref(i.of_trait.as_ref()?, self.ast_ty_to_ty(i.self_ty));
2910 let assoc = tcx.associated_items(trait_ref.def_id).find_by_name_and_kind(
2917 let fn_sig = tcx.bound_fn_sig(assoc.def_id).subst(
2919 trait_ref.substs.extend_to(tcx, assoc.def_id, |param, _| tcx.mk_param_from_def(param)),
2922 let ty = if let Some(arg_idx) = arg_idx { fn_sig.input(arg_idx) } else { fn_sig.output() };
2924 Some(tcx.liberate_late_bound_regions(fn_hir_id.expect_owner().to_def_id(), ty))
2927 fn validate_late_bound_regions(
2929 constrained_regions: FxHashSet<ty::BoundRegionKind>,
2930 referenced_regions: FxHashSet<ty::BoundRegionKind>,
2931 generate_err: impl Fn(&str) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
2933 for br in referenced_regions.difference(&constrained_regions) {
2934 let br_name = match *br {
2935 ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) | ty::BrEnv => {
2936 "an anonymous lifetime".to_string()
2938 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
2941 let mut err = generate_err(&br_name);
2943 if let ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) = *br {
2944 // The only way for an anonymous lifetime to wind up
2945 // in the return type but **also** be unconstrained is
2946 // if it only appears in "associated types" in the
2947 // input. See #47511 and #62200 for examples. In this case,
2948 // though we can easily give a hint that ought to be
2951 "lifetimes appearing in an associated type are not considered constrained",
2959 /// Given the bounds on an object, determines what single region bound (if any) we can
2960 /// use to summarize this type. The basic idea is that we will use the bound the user
2961 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2962 /// for region bounds. It may be that we can derive no bound at all, in which case
2963 /// we return `None`.
2964 fn compute_object_lifetime_bound(
2967 existential_predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
2968 ) -> Option<ty::Region<'tcx>> // if None, use the default
2970 let tcx = self.tcx();
2972 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2974 // No explicit region bound specified. Therefore, examine trait
2975 // bounds and see if we can derive region bounds from those.
2976 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2978 // If there are no derived region bounds, then report back that we
2979 // can find no region bound. The caller will use the default.
2980 if derived_region_bounds.is_empty() {
2984 // If any of the derived region bounds are 'static, that is always
2986 if derived_region_bounds.iter().any(|r| r.is_static()) {
2987 return Some(tcx.lifetimes.re_static);
2990 // Determine whether there is exactly one unique region in the set
2991 // of derived region bounds. If so, use that. Otherwise, report an
2993 let r = derived_region_bounds[0];
2994 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2995 tcx.sess.emit_err(AmbiguousLifetimeBound { span });
3000 /// Make sure that we are in the condition to suggest the blanket implementation.
3001 fn maybe_lint_blanket_trait_impl(&self, self_ty: &hir::Ty<'_>, diag: &mut Diagnostic) {
3002 let tcx = self.tcx();
3003 let parent_id = tcx.hir().get_parent_item(self_ty.hir_id);
3004 if let hir::Node::Item(hir::Item {
3006 hir::ItemKind::Impl(hir::Impl {
3007 self_ty: impl_self_ty, of_trait: Some(of_trait_ref), generics, ..
3010 }) = tcx.hir().get_by_def_id(parent_id) && self_ty.hir_id == impl_self_ty.hir_id
3012 if !of_trait_ref.trait_def_id().map_or(false, |def_id| def_id.is_local()) {
3015 let of_trait_span = of_trait_ref.path.span;
3016 // make sure that we are not calling unwrap to abort during the compilation
3017 let Ok(impl_trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else { return; };
3018 let Ok(of_trait_name) = tcx.sess.source_map().span_to_snippet(of_trait_span) else { return; };
3019 // check if the trait has generics, to make a correct suggestion
3020 let param_name = generics.params.next_type_param_name(None);
3022 let add_generic_sugg = if let Some(span) = generics.span_for_param_suggestion() {
3023 (span, format!(", {}: {}", param_name, impl_trait_name))
3025 (generics.span, format!("<{}: {}>", param_name, impl_trait_name))
3027 diag.multipart_suggestion(
3028 format!("alternatively use a blanket \
3029 implementation to implement `{of_trait_name}` for \
3030 all types that also implement `{impl_trait_name}`"),
3032 (self_ty.span, param_name),
3035 Applicability::MaybeIncorrect,
3040 fn maybe_lint_bare_trait(&self, self_ty: &hir::Ty<'_>, in_path: bool) {
3041 let tcx = self.tcx();
3042 if let hir::TyKind::TraitObject([poly_trait_ref, ..], _, TraitObjectSyntax::None) =
3045 let needs_bracket = in_path
3049 .span_to_prev_source(self_ty.span)
3051 .map_or(false, |s| s.trim_end().ends_with('<'));
3053 let is_global = poly_trait_ref.trait_ref.path.is_global();
3054 let sugg = Vec::from_iter([
3056 self_ty.span.shrink_to_lo(),
3059 if needs_bracket { "<" } else { "" },
3060 if is_global { "(" } else { "" },
3064 self_ty.span.shrink_to_hi(),
3067 if is_global { ")" } else { "" },
3068 if needs_bracket { ">" } else { "" },
3072 if self_ty.span.edition() >= Edition::Edition2021 {
3073 let msg = "trait objects must include the `dyn` keyword";
3074 let label = "add `dyn` keyword before this trait";
3076 rustc_errors::struct_span_err!(tcx.sess, self_ty.span, E0782, "{}", msg);
3077 diag.multipart_suggestion_verbose(label, sugg, Applicability::MachineApplicable);
3078 // check if the impl trait that we are considering is a impl of a local trait
3079 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);
3082 let msg = "trait objects without an explicit `dyn` are deprecated";
3083 tcx.struct_span_lint_hir(
3088 let mut diag = lint.build(msg);
3089 diag.multipart_suggestion_verbose(
3092 Applicability::MachineApplicable,
3094 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);