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, SubstsRef};
30 use rustc_middle::ty::DynKind;
31 use rustc_middle::ty::GenericParamDefKind;
32 use rustc_middle::ty::{
33 self, Const, DefIdTree, EarlyBinder, IsSuggestable, Ty, TyCtxt, TypeVisitable,
35 use rustc_session::lint::builtin::{AMBIGUOUS_ASSOCIATED_ITEMS, BARE_TRAIT_OBJECTS};
36 use rustc_span::edition::Edition;
37 use rustc_span::lev_distance::find_best_match_for_name;
38 use rustc_span::symbol::{kw, Ident, Symbol};
40 use rustc_target::spec::abi;
41 use rustc_trait_selection::traits;
42 use rustc_trait_selection::traits::astconv_object_safety_violations;
43 use rustc_trait_selection::traits::error_reporting::{
44 report_object_safety_error, suggestions::NextTypeParamName,
46 use rustc_trait_selection::traits::wf::object_region_bounds;
48 use smallvec::{smallvec, SmallVec};
49 use std::collections::BTreeSet;
53 pub struct PathSeg(pub DefId, pub usize);
55 pub trait AstConv<'tcx> {
56 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
58 fn item_def_id(&self) -> Option<DefId>;
60 /// Returns predicates in scope of the form `X: Foo<T>`, where `X`
61 /// is a type parameter `X` with the given id `def_id` and T
62 /// matches `assoc_name`. This is a subset of the full set of
65 /// This is used for one specific purpose: resolving "short-hand"
66 /// associated type references like `T::Item`. In principle, we
67 /// would do that by first getting the full set of predicates in
68 /// scope and then filtering down to find those that apply to `T`,
69 /// but this can lead to cycle errors. The problem is that we have
70 /// to do this resolution *in order to create the predicates in
71 /// the first place*. Hence, we have this "special pass".
72 fn get_type_parameter_bounds(
77 ) -> ty::GenericPredicates<'tcx>;
79 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
80 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
81 -> Option<ty::Region<'tcx>>;
83 /// Returns the type to use when a type is omitted.
84 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
86 /// Returns `true` if `_` is allowed in type signatures in the current context.
87 fn allow_ty_infer(&self) -> bool;
89 /// Returns the const to use when a const is omitted.
93 param: Option<&ty::GenericParamDef>,
97 /// Projecting an associated type from a (potentially)
98 /// higher-ranked trait reference is more complicated, because of
99 /// the possibility of late-bound regions appearing in the
100 /// associated type binding. This is not legal in function
101 /// signatures for that reason. In a function body, we can always
102 /// handle it because we can use inference variables to remove the
103 /// late-bound regions.
104 fn projected_ty_from_poly_trait_ref(
108 item_segment: &hir::PathSegment<'_>,
109 poly_trait_ref: ty::PolyTraitRef<'tcx>,
112 /// Normalize an associated type coming from the user.
113 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
115 /// Invoked when we encounter an error from some prior pass
116 /// (e.g., resolve) that is translated into a ty-error. This is
117 /// used to help suppress derived errors typeck might otherwise
119 fn set_tainted_by_errors(&self);
121 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
125 struct ConvertedBinding<'a, 'tcx> {
128 kind: ConvertedBindingKind<'a, 'tcx>,
129 gen_args: &'a GenericArgs<'a>,
134 enum ConvertedBindingKind<'a, 'tcx> {
135 Equality(ty::Term<'tcx>),
136 Constraint(&'a [hir::GenericBound<'a>]),
139 /// New-typed boolean indicating whether explicit late-bound lifetimes
140 /// are present in a set of generic arguments.
142 /// For example if we have some method `fn f<'a>(&'a self)` implemented
143 /// for some type `T`, although `f` is generic in the lifetime `'a`, `'a`
144 /// is late-bound so should not be provided explicitly. Thus, if `f` is
145 /// instantiated with some generic arguments providing `'a` explicitly,
146 /// we taint those arguments with `ExplicitLateBound::Yes` so that we
147 /// can provide an appropriate diagnostic later.
148 #[derive(Copy, Clone, PartialEq, Debug)]
149 pub enum ExplicitLateBound {
154 #[derive(Copy, Clone, PartialEq)]
155 pub enum IsMethodCall {
160 /// Denotes the "position" of a generic argument, indicating if it is a generic type,
161 /// generic function or generic method call.
162 #[derive(Copy, Clone, PartialEq)]
163 pub(crate) enum GenericArgPosition {
165 Value, // e.g., functions
169 /// A marker denoting that the generic arguments that were
170 /// provided did not match the respective generic parameters.
171 #[derive(Clone, Default, Debug)]
172 pub struct GenericArgCountMismatch {
173 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
174 pub reported: Option<ErrorGuaranteed>,
175 /// A list of spans of arguments provided that were not valid.
176 pub invalid_args: Vec<Span>,
179 /// Decorates the result of a generic argument count mismatch
180 /// check with whether explicit late bounds were provided.
181 #[derive(Clone, Debug)]
182 pub struct GenericArgCountResult {
183 pub explicit_late_bound: ExplicitLateBound,
184 pub correct: Result<(), GenericArgCountMismatch>,
187 pub trait CreateSubstsForGenericArgsCtxt<'a, 'tcx> {
188 fn args_for_def_id(&mut self, def_id: DefId) -> (Option<&'a GenericArgs<'a>>, bool);
192 param: &ty::GenericParamDef,
193 arg: &GenericArg<'_>,
194 ) -> subst::GenericArg<'tcx>;
198 substs: Option<&[subst::GenericArg<'tcx>]>,
199 param: &ty::GenericParamDef,
201 ) -> subst::GenericArg<'tcx>;
204 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
205 #[instrument(level = "debug", skip(self), ret)]
206 pub fn ast_region_to_region(
208 lifetime: &hir::Lifetime,
209 def: Option<&ty::GenericParamDef>,
210 ) -> ty::Region<'tcx> {
211 let tcx = self.tcx();
212 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
214 match tcx.named_region(lifetime.hir_id) {
215 Some(rl::Region::Static) => tcx.lifetimes.re_static,
217 Some(rl::Region::LateBound(debruijn, index, def_id)) => {
218 let name = lifetime_name(def_id.expect_local());
219 let br = ty::BoundRegion {
220 var: ty::BoundVar::from_u32(index),
221 kind: ty::BrNamed(def_id, name),
223 tcx.mk_region(ty::ReLateBound(debruijn, br))
226 Some(rl::Region::EarlyBound(def_id)) => {
227 let name = tcx.hir().ty_param_name(def_id.expect_local());
228 let item_def_id = tcx.hir().ty_param_owner(def_id.expect_local());
229 let generics = tcx.generics_of(item_def_id);
230 let index = generics.param_def_id_to_index[&def_id];
231 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, index, name }))
234 Some(rl::Region::Free(scope, id)) => {
235 let name = lifetime_name(id.expect_local());
236 tcx.mk_region(ty::ReFree(ty::FreeRegion {
238 bound_region: ty::BrNamed(id, name),
241 // (*) -- not late-bound, won't change
245 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
246 debug!(?lifetime, "unelided lifetime in signature");
248 // This indicates an illegal lifetime
249 // elision. `resolve_lifetime` should have
250 // reported an error in this case -- but if
251 // not, let's error out.
252 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
254 // Supply some dummy value. We don't have an
255 // `re_error`, annoyingly, so use `'static`.
256 tcx.lifetimes.re_static
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 #[instrument(level = "debug", skip(self, span), ret)]
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(
542 fn create_assoc_bindings_for_generic_args<'a>(
544 generic_args: &'a hir::GenericArgs<'_>,
545 ) -> Vec<ConvertedBinding<'a, 'tcx>> {
546 // Convert associated-type bindings or constraints into a separate vector.
547 // Example: Given this:
549 // T: Iterator<Item = u32>
551 // The `T` is passed in as a self-type; the `Item = u32` is
552 // not a "type parameter" of the `Iterator` trait, but rather
553 // a restriction on `<T as Iterator>::Item`, so it is passed
555 let assoc_bindings = generic_args
559 let kind = match binding.kind {
560 hir::TypeBindingKind::Equality { ref term } => match term {
561 hir::Term::Ty(ref ty) => {
562 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty).into())
564 hir::Term::Const(ref c) => {
565 let local_did = self.tcx().hir().local_def_id(c.hir_id);
566 let c = Const::from_anon_const(self.tcx(), local_did);
567 ConvertedBindingKind::Equality(c.into())
570 hir::TypeBindingKind::Constraint { ref bounds } => {
571 ConvertedBindingKind::Constraint(bounds)
575 hir_id: binding.hir_id,
576 item_name: binding.ident,
578 gen_args: binding.gen_args,
587 pub(crate) fn create_substs_for_associated_item(
592 item_segment: &hir::PathSegment<'_>,
593 parent_substs: SubstsRef<'tcx>,
594 ) -> SubstsRef<'tcx> {
596 "create_substs_for_associated_item(span: {:?}, item_def_id: {:?}, item_segment: {:?}",
597 span, item_def_id, item_segment
599 if tcx.generics_of(item_def_id).params.is_empty() {
600 self.prohibit_generics(slice::from_ref(item_segment).iter(), |_| {});
604 self.create_substs_for_ast_path(
610 item_segment.infer_args,
617 /// Instantiates the path for the given trait reference, assuming that it's
618 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
619 /// The type _cannot_ be a type other than a trait type.
621 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
622 /// are disallowed. Otherwise, they are pushed onto the vector given.
623 pub fn instantiate_mono_trait_ref(
625 trait_ref: &hir::TraitRef<'_>,
627 ) -> ty::TraitRef<'tcx> {
628 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
630 self.ast_path_to_mono_trait_ref(
632 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
634 trait_ref.path.segments.last().unwrap(),
639 fn instantiate_poly_trait_ref_inner(
643 binding_span: Option<Span>,
644 constness: ty::BoundConstness,
645 bounds: &mut Bounds<'tcx>,
647 trait_ref_span: Span,
649 trait_segment: &hir::PathSegment<'_>,
650 args: &GenericArgs<'_>,
653 ) -> GenericArgCountResult {
654 let (substs, arg_count) = self.create_substs_for_ast_path(
664 let tcx = self.tcx();
665 let bound_vars = tcx.late_bound_vars(hir_id);
668 let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
671 ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
673 debug!(?poly_trait_ref, ?assoc_bindings);
674 bounds.trait_bounds.push((poly_trait_ref, span, constness));
676 let mut dup_bindings = FxHashMap::default();
677 for binding in &assoc_bindings {
678 // Specify type to assert that error was already reported in `Err` case.
679 let _: Result<_, ErrorGuaranteed> = self.add_predicates_for_ast_type_binding(
686 binding_span.unwrap_or(binding.span),
688 // Okay to ignore `Err` because of `ErrorGuaranteed` (see above).
694 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
695 /// a full trait reference. The resulting trait reference is returned. This may also generate
696 /// auxiliary bounds, which are added to `bounds`.
700 /// ```ignore (illustrative)
701 /// poly_trait_ref = Iterator<Item = u32>
705 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
707 /// **A note on binders:** against our usual convention, there is an implied bounder around
708 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
709 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
710 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
711 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
713 #[instrument(level = "debug", skip(self, span, constness, bounds, speculative))]
714 pub(crate) fn instantiate_poly_trait_ref(
716 trait_ref: &hir::TraitRef<'_>,
718 constness: ty::BoundConstness,
720 bounds: &mut Bounds<'tcx>,
722 ) -> GenericArgCountResult {
723 let hir_id = trait_ref.hir_ref_id;
724 let binding_span = None;
725 let trait_ref_span = trait_ref.path.span;
726 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
727 let trait_segment = trait_ref.path.segments.last().unwrap();
728 let args = trait_segment.args();
729 let infer_args = trait_segment.infer_args;
731 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
732 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, false);
734 self.instantiate_poly_trait_ref_inner(
750 pub(crate) fn instantiate_lang_item_trait_ref(
752 lang_item: hir::LangItem,
755 args: &GenericArgs<'_>,
757 bounds: &mut Bounds<'tcx>,
759 let binding_span = Some(span);
760 let constness = ty::BoundConstness::NotConst;
761 let speculative = false;
762 let trait_ref_span = span;
763 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
764 let trait_segment = &hir::PathSegment::invalid();
765 let infer_args = false;
767 self.instantiate_poly_trait_ref_inner(
783 fn ast_path_to_mono_trait_ref(
788 trait_segment: &hir::PathSegment<'_>,
790 ) -> ty::TraitRef<'tcx> {
791 let (substs, _) = self.create_substs_for_ast_trait_ref(
798 let assoc_bindings = self.create_assoc_bindings_for_generic_args(trait_segment.args());
799 if let Some(b) = assoc_bindings.first() {
800 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
802 ty::TraitRef::new(trait_def_id, substs)
805 #[instrument(level = "debug", skip(self, span))]
806 fn create_substs_for_ast_trait_ref<'a>(
811 trait_segment: &'a hir::PathSegment<'a>,
813 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
814 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
816 self.create_substs_for_ast_path(
821 trait_segment.args(),
822 trait_segment.infer_args,
827 fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
829 .associated_items(trait_def_id)
830 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
833 fn trait_defines_associated_const_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
835 .associated_items(trait_def_id)
836 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Const, trait_def_id)
840 // Sets `implicitly_sized` to true on `Bounds` if necessary
841 pub(crate) fn add_implicitly_sized<'hir>(
843 bounds: &mut Bounds<'hir>,
844 ast_bounds: &'hir [hir::GenericBound<'hir>],
845 self_ty_where_predicates: Option<(hir::HirId, &'hir [hir::WherePredicate<'hir>])>,
848 let tcx = self.tcx();
850 // Try to find an unbound in bounds.
851 let mut unbound = None;
852 let mut search_bounds = |ast_bounds: &'hir [hir::GenericBound<'hir>]| {
853 for ab in ast_bounds {
854 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
855 if unbound.is_none() {
856 unbound = Some(&ptr.trait_ref);
858 tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
863 search_bounds(ast_bounds);
864 if let Some((self_ty, where_clause)) = self_ty_where_predicates {
865 let self_ty_def_id = tcx.hir().local_def_id(self_ty).to_def_id();
866 for clause in where_clause {
867 if let hir::WherePredicate::BoundPredicate(pred) = clause {
868 if pred.is_param_bound(self_ty_def_id) {
869 search_bounds(pred.bounds);
875 let sized_def_id = tcx.lang_items().require(LangItem::Sized);
876 match (&sized_def_id, unbound) {
877 (Ok(sized_def_id), Some(tpb))
878 if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) =>
880 // There was in fact a `?Sized` bound, return without doing anything
884 // There was a `?Trait` bound, but it was not `?Sized`; warn.
887 "default bound relaxed for a type parameter, but \
888 this does nothing because the given bound is not \
889 a default; only `?Sized` is supported",
891 // Otherwise, add implicitly sized if `Sized` is available.
894 // There was no `?Sized` bound; add implicitly sized if `Sized` is available.
897 if sized_def_id.is_err() {
898 // No lang item for `Sized`, so we can't add it as a bound.
901 bounds.implicitly_sized = Some(span);
904 /// This helper takes a *converted* parameter type (`param_ty`)
905 /// and an *unconverted* list of bounds:
909 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
911 /// `param_ty`, in ty form
914 /// It adds these `ast_bounds` into the `bounds` structure.
916 /// **A note on binders:** there is an implied binder around
917 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
918 /// for more details.
919 #[instrument(level = "debug", skip(self, ast_bounds, bounds))]
920 pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>(
924 bounds: &mut Bounds<'tcx>,
925 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
927 for ast_bound in ast_bounds {
929 hir::GenericBound::Trait(poly_trait_ref, modifier) => {
930 let constness = match modifier {
931 hir::TraitBoundModifier::MaybeConst => ty::BoundConstness::ConstIfConst,
932 hir::TraitBoundModifier::None => ty::BoundConstness::NotConst,
933 hir::TraitBoundModifier::Maybe => continue,
936 let _ = self.instantiate_poly_trait_ref(
937 &poly_trait_ref.trait_ref,
945 &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
946 self.instantiate_lang_item_trait_ref(
947 lang_item, span, hir_id, args, param_ty, bounds,
950 hir::GenericBound::Outlives(lifetime) => {
951 let region = self.ast_region_to_region(lifetime, None);
954 .push((ty::Binder::bind_with_vars(region, bound_vars), lifetime.span));
960 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
961 /// The self-type for the bounds is given by `param_ty`.
965 /// ```ignore (illustrative)
966 /// fn foo<T: Bar + Baz>() { }
967 /// // ^ ^^^^^^^^^ ast_bounds
971 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
972 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
973 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
975 /// `span` should be the declaration size of the parameter.
976 pub(crate) fn compute_bounds(
979 ast_bounds: &[hir::GenericBound<'_>],
981 self.compute_bounds_inner(param_ty, ast_bounds)
984 /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
985 /// named `assoc_name` into ty::Bounds. Ignore the rest.
986 pub(crate) fn compute_bounds_that_match_assoc_type(
989 ast_bounds: &[hir::GenericBound<'_>],
992 let mut result = Vec::new();
994 for ast_bound in ast_bounds {
995 if let Some(trait_ref) = ast_bound.trait_ref()
996 && let Some(trait_did) = trait_ref.trait_def_id()
997 && self.tcx().trait_may_define_assoc_type(trait_did, assoc_name)
999 result.push(ast_bound.clone());
1003 self.compute_bounds_inner(param_ty, &result)
1006 fn compute_bounds_inner(
1009 ast_bounds: &[hir::GenericBound<'_>],
1011 let mut bounds = Bounds::default();
1013 self.add_bounds(param_ty, ast_bounds.iter(), &mut bounds, ty::List::empty());
1019 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1022 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1023 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1024 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1025 #[instrument(level = "debug", skip(self, bounds, speculative, dup_bindings, path_span))]
1026 fn add_predicates_for_ast_type_binding(
1028 hir_ref_id: hir::HirId,
1029 trait_ref: ty::PolyTraitRef<'tcx>,
1030 binding: &ConvertedBinding<'_, 'tcx>,
1031 bounds: &mut Bounds<'tcx>,
1033 dup_bindings: &mut FxHashMap<DefId, Span>,
1035 ) -> Result<(), ErrorGuaranteed> {
1036 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1037 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1038 // subtle in the event that `T` is defined in a supertrait of
1039 // `SomeTrait`, because in that case we need to upcast.
1041 // That is, consider this case:
1044 // trait SubTrait: SuperTrait<i32> { }
1045 // trait SuperTrait<A> { type T; }
1047 // ... B: SubTrait<T = foo> ...
1050 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
1052 let tcx = self.tcx();
1055 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1056 // Simple case: X is defined in the current trait.
1059 // Otherwise, we have to walk through the supertraits to find
1061 self.one_bound_for_assoc_type(
1062 || traits::supertraits(tcx, trait_ref),
1063 || trait_ref.print_only_trait_path().to_string(),
1066 || match binding.kind {
1067 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1073 let (assoc_ident, def_scope) =
1074 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1076 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1077 // of calling `filter_by_name_and_kind`.
1078 let find_item_of_kind = |kind| {
1079 tcx.associated_items(candidate.def_id())
1080 .filter_by_name_unhygienic(assoc_ident.name)
1081 .find(|i| i.kind == kind && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident)
1083 let assoc_item = find_item_of_kind(ty::AssocKind::Type)
1084 .or_else(|| find_item_of_kind(ty::AssocKind::Const))
1085 .expect("missing associated type");
1087 if !assoc_item.visibility(tcx).is_accessible_from(def_scope, tcx) {
1091 &format!("{} `{}` is private", assoc_item.kind, binding.item_name),
1093 .span_label(binding.span, &format!("private {}", assoc_item.kind))
1096 tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None);
1100 .entry(assoc_item.def_id)
1101 .and_modify(|prev_span| {
1102 self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
1104 prev_span: *prev_span,
1105 item_name: binding.item_name,
1106 def_path: tcx.def_path_str(assoc_item.container_id(tcx)),
1109 .or_insert(binding.span);
1112 // Include substitutions for generic parameters of associated types
1113 let projection_ty = candidate.map_bound(|trait_ref| {
1114 let ident = Ident::new(assoc_item.name, binding.item_name.span);
1115 let item_segment = hir::PathSegment {
1117 hir_id: binding.hir_id,
1119 args: Some(binding.gen_args),
1123 let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
1132 "add_predicates_for_ast_type_binding: substs for trait-ref and assoc_item: {:?}",
1133 substs_trait_ref_and_assoc_item
1137 item_def_id: assoc_item.def_id,
1138 substs: substs_trait_ref_and_assoc_item,
1143 // Find any late-bound regions declared in `ty` that are not
1144 // declared in the trait-ref or assoc_item. These are not well-formed.
1148 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1149 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1150 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1151 let late_bound_in_trait_ref =
1152 tcx.collect_constrained_late_bound_regions(&projection_ty);
1153 let late_bound_in_ty =
1154 tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty));
1155 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1156 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1158 // FIXME: point at the type params that don't have appropriate lifetimes:
1159 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1160 // ---- ---- ^^^^^^^
1161 self.validate_late_bound_regions(
1162 late_bound_in_trait_ref,
1169 "binding for associated type `{}` references {}, \
1170 which does not appear in the trait input types",
1179 match binding.kind {
1180 ConvertedBindingKind::Equality(mut term) => {
1181 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1182 // the "projection predicate" for:
1184 // `<T as Iterator>::Item = u32`
1185 let assoc_item_def_id = projection_ty.skip_binder().item_def_id;
1186 let def_kind = tcx.def_kind(assoc_item_def_id);
1187 match (def_kind, term.unpack()) {
1188 (hir::def::DefKind::AssocTy, ty::TermKind::Ty(_))
1189 | (hir::def::DefKind::AssocConst, ty::TermKind::Const(_)) => (),
1191 let got = if let Some(_) = term.ty() { "type" } else { "constant" };
1192 let expected = def_kind.descr(assoc_item_def_id);
1196 &format!("expected {expected} bound, found {got}"),
1199 tcx.def_span(assoc_item_def_id),
1200 &format!("{expected} defined here"),
1203 term = match def_kind {
1204 hir::def::DefKind::AssocTy => tcx.ty_error().into(),
1205 hir::def::DefKind::AssocConst => tcx
1207 tcx.bound_type_of(assoc_item_def_id)
1208 .subst(tcx, projection_ty.skip_binder().substs),
1211 _ => unreachable!(),
1215 bounds.projection_bounds.push((
1216 projection_ty.map_bound(|projection_ty| ty::ProjectionPredicate {
1223 ConvertedBindingKind::Constraint(ast_bounds) => {
1224 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1226 // `<T as Iterator>::Item: Debug`
1228 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1229 // parameter to have a skipped binder.
1230 let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
1231 self.add_bounds(param_ty, ast_bounds.iter(), bounds, candidate.bound_vars());
1241 item_segment: &hir::PathSegment<'_>,
1243 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1246 EarlyBinder(self.tcx().at(span).type_of(did)).subst(self.tcx(), substs),
1250 fn conv_object_ty_poly_trait_ref(
1253 trait_bounds: &[hir::PolyTraitRef<'_>],
1254 lifetime: &hir::Lifetime,
1256 representation: DynKind,
1258 let tcx = self.tcx();
1260 let mut bounds = Bounds::default();
1261 let mut potential_assoc_types = Vec::new();
1262 let dummy_self = self.tcx().types.trait_object_dummy_self;
1263 for trait_bound in trait_bounds.iter().rev() {
1264 if let GenericArgCountResult {
1266 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1268 } = self.instantiate_poly_trait_ref(
1269 &trait_bound.trait_ref,
1271 ty::BoundConstness::NotConst,
1276 potential_assoc_types.extend(cur_potential_assoc_types);
1280 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1281 // is used and no 'maybe' bounds are used.
1282 let expanded_traits =
1283 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1284 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) = expanded_traits
1285 .filter(|i| i.trait_ref().self_ty().skip_binder() == dummy_self)
1286 .partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1287 if regular_traits.len() > 1 {
1288 let first_trait = ®ular_traits[0];
1289 let additional_trait = ®ular_traits[1];
1290 let mut err = struct_span_err!(
1292 additional_trait.bottom().1,
1294 "only auto traits can be used as additional traits in a trait object"
1296 additional_trait.label_with_exp_info(
1298 "additional non-auto trait",
1301 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1303 "consider creating a new trait with all of these as supertraits and using that \
1304 trait here instead: `trait NewTrait: {} {{}}`",
1307 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1308 .collect::<Vec<_>>()
1312 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1313 for more information on them, visit \
1314 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1319 if regular_traits.is_empty() && auto_traits.is_empty() {
1320 let trait_alias_span = bounds
1323 .map(|&(trait_ref, _, _)| trait_ref.def_id())
1324 .find(|&trait_ref| tcx.is_trait_alias(trait_ref))
1325 .map(|trait_ref| tcx.def_span(trait_ref));
1326 tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span, trait_alias_span });
1327 return tcx.ty_error();
1330 // Check that there are no gross object safety violations;
1331 // most importantly, that the supertraits don't contain `Self`,
1333 for item in ®ular_traits {
1334 let object_safety_violations =
1335 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1336 if !object_safety_violations.is_empty() {
1337 report_object_safety_error(
1340 item.trait_ref().def_id(),
1341 &object_safety_violations,
1344 return tcx.ty_error();
1348 // Use a `BTreeSet` to keep output in a more consistent order.
1349 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1351 let regular_traits_refs_spans = bounds
1354 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1356 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1357 assert_eq!(constness, ty::BoundConstness::NotConst);
1359 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1361 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1362 obligation.predicate
1365 let bound_predicate = obligation.predicate.kind();
1366 match bound_predicate.skip_binder() {
1367 ty::PredicateKind::Trait(pred) => {
1368 let pred = bound_predicate.rebind(pred);
1369 associated_types.entry(span).or_default().extend(
1370 tcx.associated_items(pred.def_id())
1371 .in_definition_order()
1372 .filter(|item| item.kind == ty::AssocKind::Type)
1373 .map(|item| item.def_id),
1376 ty::PredicateKind::Projection(pred) => {
1377 let pred = bound_predicate.rebind(pred);
1378 // A `Self` within the original bound will be substituted with a
1379 // `trait_object_dummy_self`, so check for that.
1380 let references_self = match pred.skip_binder().term.unpack() {
1381 ty::TermKind::Ty(ty) => ty.walk().any(|arg| arg == dummy_self.into()),
1382 ty::TermKind::Const(c) => {
1383 c.ty().walk().any(|arg| arg == dummy_self.into())
1387 // If the projection output contains `Self`, force the user to
1388 // elaborate it explicitly to avoid a lot of complexity.
1390 // The "classically useful" case is the following:
1392 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1397 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1398 // but actually supporting that would "expand" to an infinitely-long type
1399 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1401 // Instead, we force the user to write
1402 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1403 // the discussion in #56288 for alternatives.
1404 if !references_self {
1405 // Include projections defined on supertraits.
1406 bounds.projection_bounds.push((pred, span));
1414 for (projection_bound, _) in &bounds.projection_bounds {
1415 for def_ids in associated_types.values_mut() {
1416 def_ids.remove(&projection_bound.projection_def_id());
1420 self.complain_about_missing_associated_types(
1422 potential_assoc_types,
1426 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1427 // `dyn Trait + Send`.
1428 // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
1430 let mut duplicates = FxHashSet::default();
1431 auto_traits.retain(|i| duplicates.insert(i.trait_ref().def_id()));
1432 debug!("regular_traits: {:?}", regular_traits);
1433 debug!("auto_traits: {:?}", auto_traits);
1435 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1436 let existential_trait_refs = regular_traits.iter().map(|i| {
1437 i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
1438 assert_eq!(trait_ref.self_ty(), dummy_self);
1440 // Verify that `dummy_self` did not leak inside default type parameters. This
1441 // could not be done at path creation, since we need to see through trait aliases.
1442 let mut missing_type_params = vec![];
1443 let mut references_self = false;
1444 let generics = tcx.generics_of(trait_ref.def_id);
1445 let substs: Vec<_> = trait_ref
1449 .skip(1) // Remove `Self` for `ExistentialPredicate`.
1450 .map(|(index, arg)| {
1451 if arg == dummy_self.into() {
1452 let param = &generics.params[index];
1453 missing_type_params.push(param.name);
1454 return tcx.ty_error().into();
1455 } else if arg.walk().any(|arg| arg == dummy_self.into()) {
1456 references_self = true;
1457 return tcx.ty_error().into();
1462 let substs = tcx.intern_substs(&substs[..]);
1464 let span = i.bottom().1;
1465 let empty_generic_args = trait_bounds.iter().any(|hir_bound| {
1466 hir_bound.trait_ref.path.res == Res::Def(DefKind::Trait, trait_ref.def_id)
1467 && hir_bound.span.contains(span)
1469 self.complain_about_missing_type_params(
1470 missing_type_params,
1476 if references_self {
1477 let def_id = i.bottom().0.def_id();
1478 let mut err = struct_span_err!(
1482 "the {} `{}` cannot be made into an object",
1483 tcx.def_kind(def_id).descr(def_id),
1484 tcx.item_name(def_id),
1487 rustc_middle::traits::ObjectSafetyViolation::SupertraitSelf(smallvec![])
1493 ty::ExistentialTraitRef { def_id: trait_ref.def_id, substs }
1497 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1498 bound.map_bound(|mut b| {
1499 assert_eq!(b.projection_ty.self_ty(), dummy_self);
1501 // Like for trait refs, verify that `dummy_self` did not leak inside default type
1503 let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
1504 if arg.walk().any(|arg| arg == dummy_self.into()) {
1509 if references_self {
1511 .delay_span_bug(span, "trait object projection bounds reference `Self`");
1512 let substs: Vec<_> = b
1517 if arg.walk().any(|arg| arg == dummy_self.into()) {
1518 return tcx.ty_error().into();
1523 b.projection_ty.substs = tcx.intern_substs(&substs[..]);
1526 ty::ExistentialProjection::erase_self_ty(tcx, b)
1530 let regular_trait_predicates = existential_trait_refs
1531 .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));
1532 let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
1533 ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
1535 // N.b. principal, projections, auto traits
1536 // FIXME: This is actually wrong with multiple principals in regards to symbol mangling
1537 let mut v = regular_trait_predicates
1539 existential_projections.map(|x| x.map_bound(ty::ExistentialPredicate::Projection)),
1541 .chain(auto_trait_predicates)
1542 .collect::<SmallVec<[_; 8]>>();
1543 v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
1545 let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
1547 // Use explicitly-specified region bound.
1548 let region_bound = if !lifetime.is_elided() {
1549 self.ast_region_to_region(lifetime, None)
1551 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1552 if tcx.named_region(lifetime.hir_id).is_some() {
1553 self.ast_region_to_region(lifetime, None)
1555 self.re_infer(None, span).unwrap_or_else(|| {
1556 let mut err = struct_span_err!(
1560 "the lifetime bound for this object type cannot be deduced \
1561 from context; please supply an explicit bound"
1564 // We will have already emitted an error E0106 complaining about a
1565 // missing named lifetime in `&dyn Trait`, so we elide this one.
1570 tcx.lifetimes.re_static
1575 debug!("region_bound: {:?}", region_bound);
1577 let ty = tcx.mk_dynamic(existential_predicates, region_bound, representation);
1578 debug!("trait_object_type: {:?}", ty);
1582 fn report_ambiguous_associated_type(
1588 ) -> ErrorGuaranteed {
1589 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1593 .confused_type_with_std_module
1595 .any(|full_span| full_span.contains(span))
1597 err.span_suggestion(
1598 span.shrink_to_lo(),
1599 "you are looking for the module in `std`, not the primitive type",
1601 Applicability::MachineApplicable,
1604 err.span_suggestion(
1606 "use fully-qualified syntax",
1607 format!("<{} as {}>::{}", type_str, trait_str, name),
1608 Applicability::HasPlaceholders,
1614 // Search for a bound on a type parameter which includes the associated item
1615 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1616 // This function will fail if there are no suitable bounds or there is
1618 fn find_bound_for_assoc_item(
1620 ty_param_def_id: LocalDefId,
1623 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed> {
1624 let tcx = self.tcx();
1627 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1628 ty_param_def_id, assoc_name, span,
1631 let predicates = &self
1632 .get_type_parameter_bounds(span, ty_param_def_id.to_def_id(), assoc_name)
1635 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1637 let param_name = tcx.hir().ty_param_name(ty_param_def_id);
1638 self.one_bound_for_assoc_type(
1640 traits::transitive_bounds_that_define_assoc_type(
1642 predicates.iter().filter_map(|(p, _)| {
1643 Some(p.to_opt_poly_trait_pred()?.map_bound(|t| t.trait_ref))
1648 || param_name.to_string(),
1655 // Checks that `bounds` contains exactly one element and reports appropriate
1656 // errors otherwise.
1657 fn one_bound_for_assoc_type<I>(
1659 all_candidates: impl Fn() -> I,
1660 ty_param_name: impl Fn() -> String,
1663 is_equality: impl Fn() -> Option<String>,
1664 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed>
1666 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1668 let mut matching_candidates = all_candidates()
1669 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1670 let mut const_candidates = all_candidates()
1671 .filter(|r| self.trait_defines_associated_const_named(r.def_id(), assoc_name));
1673 let (bound, next_cand) = match (matching_candidates.next(), const_candidates.next()) {
1674 (Some(bound), _) => (bound, matching_candidates.next()),
1675 (None, Some(bound)) => (bound, const_candidates.next()),
1677 let reported = self.complain_about_assoc_type_not_found(
1683 return Err(reported);
1686 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1688 if let Some(bound2) = next_cand {
1689 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1691 let is_equality = is_equality();
1692 let bounds = IntoIterator::into_iter([bound, bound2]).chain(matching_candidates);
1693 let mut err = if is_equality.is_some() {
1694 // More specific Error Index entry.
1699 "ambiguous associated type `{}` in bounds of `{}`",
1708 "ambiguous associated type `{}` in bounds of `{}`",
1713 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1715 let mut where_bounds = vec![];
1716 for bound in bounds {
1717 let bound_id = bound.def_id();
1718 let bound_span = self
1720 .associated_items(bound_id)
1721 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1722 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1724 if let Some(bound_span) = bound_span {
1728 "ambiguous `{}` from `{}`",
1730 bound.print_only_trait_path(),
1733 if let Some(constraint) = &is_equality {
1734 where_bounds.push(format!(
1735 " T: {trait}::{assoc} = {constraint}",
1736 trait=bound.print_only_trait_path(),
1738 constraint=constraint,
1741 err.span_suggestion_verbose(
1742 span.with_hi(assoc_name.span.lo()),
1743 "use fully qualified syntax to disambiguate",
1747 bound.print_only_trait_path(),
1749 Applicability::MaybeIncorrect,
1754 "associated type `{}` could derive from `{}`",
1756 bound.print_only_trait_path(),
1760 if !where_bounds.is_empty() {
1762 "consider introducing a new type parameter `T` and adding `where` constraints:\
1763 \n where\n T: {},\n{}",
1765 where_bounds.join(",\n"),
1768 let reported = err.emit();
1769 if !where_bounds.is_empty() {
1770 return Err(reported);
1777 // Create a type from a path to an associated type.
1778 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1779 // and item_segment is the path segment for `D`. We return a type and a def for
1781 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1782 // parameter or `Self`.
1783 // NOTE: When this function starts resolving `Trait::AssocTy` successfully
1784 // it should also start reporting the `BARE_TRAIT_OBJECTS` lint.
1785 pub fn associated_path_to_ty(
1787 hir_ref_id: hir::HirId,
1790 qself: &hir::Ty<'_>,
1791 assoc_segment: &hir::PathSegment<'_>,
1792 permit_variants: bool,
1793 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
1794 let tcx = self.tcx();
1795 let assoc_ident = assoc_segment.ident;
1796 let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
1802 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1804 // Check if we have an enum variant.
1805 let mut variant_resolution = None;
1806 if let ty::Adt(adt_def, _) = qself_ty.kind() {
1807 if adt_def.is_enum() {
1808 let variant_def = adt_def
1811 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident(tcx), adt_def.did()));
1812 if let Some(variant_def) = variant_def {
1813 if permit_variants {
1814 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span, None);
1815 self.prohibit_generics(slice::from_ref(assoc_segment).iter(), |err| {
1816 err.note("enum variants can't have type parameters");
1817 let type_name = tcx.item_name(adt_def.did());
1819 "you might have meant to specity type parameters on enum \
1822 let Some(args) = assoc_segment.args else { return; };
1823 // Get the span of the generics args *including* the leading `::`.
1824 let args_span = assoc_segment.ident.span.shrink_to_hi().to(args.span_ext);
1825 if tcx.generics_of(adt_def.did()).count() == 0 {
1826 // FIXME(estebank): we could also verify that the arguments being
1827 // work for the `enum`, instead of just looking if it takes *any*.
1828 err.span_suggestion_verbose(
1830 &format!("{type_name} doesn't have generic parameters"),
1832 Applicability::MachineApplicable,
1836 let Ok(snippet) = tcx.sess.source_map().span_to_snippet(args_span) else {
1840 let (qself_sugg_span, is_self) = if let hir::TyKind::Path(
1841 hir::QPath::Resolved(_, ref path)
1843 // If the path segment already has type params, we want to overwrite
1845 match &path.segments[..] {
1846 // `segment` is the previous to last element on the path,
1847 // which would normally be the `enum` itself, while the last
1848 // `_` `PathSegment` corresponds to the variant.
1849 [.., hir::PathSegment {
1852 res: Res::Def(DefKind::Enum, _),
1855 // We need to include the `::` in `Type::Variant::<Args>`
1856 // to point the span to `::<Args>`, not just `<Args>`.
1857 ident.span.shrink_to_hi().to(args.map_or(
1858 ident.span.shrink_to_hi(),
1863 // We need to include the `::` in `Type::Variant::<Args>`
1864 // to point the span to `::<Args>`, not just `<Args>`.
1865 segment.ident.span.shrink_to_hi().to(segment.args.map_or(
1866 segment.ident.span.shrink_to_hi(),
1868 kw::SelfUpper == segment.ident.name,
1879 let suggestion = vec![
1881 // Account for people writing `Self::Variant::<Args>`, where
1882 // `Self` is the enum, and suggest replacing `Self` with the
1883 // appropriate type: `Type::<Args>::Variant`.
1884 (qself.span, format!("{type_name}{snippet}"))
1886 (qself_sugg_span, snippet)
1888 (args_span, String::new()),
1890 err.multipart_suggestion_verbose(
1893 Applicability::MaybeIncorrect,
1896 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1898 variant_resolution = Some(variant_def.def_id);
1904 // Find the type of the associated item, and the trait where the associated
1905 // item is declared.
1906 let bound = match (&qself_ty.kind(), qself_res) {
1907 (_, Res::SelfTy { trait_: Some(_), alias_to: Some((impl_def_id, _)) }) => {
1908 // `Self` in an impl of a trait -- we have a concrete self type and a
1910 let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) else {
1911 // A cycle error occurred, most likely.
1912 let guar = tcx.sess.delay_span_bug(span, "expected cycle error");
1916 self.one_bound_for_assoc_type(
1917 || traits::supertraits(tcx, ty::Binder::dummy(trait_ref)),
1918 || "Self".to_string(),
1926 Res::SelfTy { trait_: Some(param_did), alias_to: None }
1927 | Res::Def(DefKind::TyParam, param_did),
1928 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
1930 let reported = if variant_resolution.is_some() {
1931 // Variant in type position
1932 let msg = format!("expected type, found variant `{}`", assoc_ident);
1933 tcx.sess.span_err(span, &msg)
1934 } else if qself_ty.is_enum() {
1935 let mut err = struct_span_err!(
1939 "no variant named `{}` found for enum `{}`",
1944 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1945 if let Some(suggested_name) = find_best_match_for_name(
1949 .map(|variant| variant.name)
1950 .collect::<Vec<Symbol>>(),
1954 err.span_suggestion(
1956 "there is a variant with a similar name",
1958 Applicability::MaybeIncorrect,
1963 format!("variant not found in `{}`", qself_ty),
1967 if let Some(sp) = tcx.hir().span_if_local(adt_def.did()) {
1968 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1972 } else if let Some(reported) = qself_ty.error_reported() {
1975 // Don't print `TyErr` to the user.
1976 self.report_ambiguous_associated_type(
1978 &qself_ty.to_string(),
1983 return Err(reported);
1987 let trait_did = bound.def_id();
1988 let (assoc_ident, def_scope) =
1989 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1991 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1992 // of calling `filter_by_name_and_kind`.
1993 let item = tcx.associated_items(trait_did).in_definition_order().find(|i| {
1994 i.kind.namespace() == Namespace::TypeNS
1995 && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident
1997 // Assume that if it's not matched, there must be a const defined with the same name
1998 // but it was used in a type position.
1999 let Some(item) = item else {
2000 let msg = format!("found associated const `{assoc_ident}` when type was expected");
2001 let guar = tcx.sess.struct_span_err(span, &msg).emit();
2005 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2006 let ty = self.normalize_ty(span, ty);
2008 let kind = DefKind::AssocTy;
2009 if !item.visibility(tcx).is_accessible_from(def_scope, tcx) {
2010 let kind = kind.descr(item.def_id);
2011 let msg = format!("{} `{}` is private", kind, assoc_ident);
2013 .struct_span_err(span, &msg)
2014 .span_label(span, &format!("private {}", kind))
2017 tcx.check_stability(item.def_id, Some(hir_ref_id), span, None);
2019 if let Some(variant_def_id) = variant_resolution {
2020 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2021 let mut err = lint.build("ambiguous associated item");
2022 let mut could_refer_to = |kind: DefKind, def_id, also| {
2023 let note_msg = format!(
2024 "`{}` could{} refer to the {} defined here",
2029 err.span_note(tcx.def_span(def_id), ¬e_msg);
2032 could_refer_to(DefKind::Variant, variant_def_id, "");
2033 could_refer_to(kind, item.def_id, " also");
2035 err.span_suggestion(
2037 "use fully-qualified syntax",
2038 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2039 Applicability::MachineApplicable,
2045 Ok((ty, kind, item.def_id))
2051 opt_self_ty: Option<Ty<'tcx>>,
2053 trait_segment: &hir::PathSegment<'_>,
2054 item_segment: &hir::PathSegment<'_>,
2056 let tcx = self.tcx();
2058 let trait_def_id = tcx.parent(item_def_id);
2060 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2062 let Some(self_ty) = opt_self_ty else {
2063 let path_str = tcx.def_path_str(trait_def_id);
2065 let def_id = self.item_def_id();
2067 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2069 let parent_def_id = def_id
2070 .and_then(|def_id| {
2071 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
2073 .map(|hir_id| tcx.hir().get_parent_item(hir_id).to_def_id());
2075 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2077 // If the trait in segment is the same as the trait defining the item,
2078 // use the `<Self as ..>` syntax in the error.
2079 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2080 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2082 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2088 self.report_ambiguous_associated_type(
2092 item_segment.ident.name,
2094 return tcx.ty_error();
2097 debug!("qpath_to_ty: self_type={:?}", self_ty);
2100 self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment, false);
2102 let item_substs = self.create_substs_for_associated_item(
2110 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2112 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2115 pub fn prohibit_generics<'a>(
2117 segments: impl Iterator<Item = &'a hir::PathSegment<'a>> + Clone,
2118 extend: impl Fn(&mut Diagnostic),
2120 let args = segments.clone().flat_map(|segment| segment.args().args);
2122 let (lt, ty, ct, inf) =
2123 args.clone().fold((false, false, false, false), |(lt, ty, ct, inf), arg| match arg {
2124 hir::GenericArg::Lifetime(_) => (true, ty, ct, inf),
2125 hir::GenericArg::Type(_) => (lt, true, ct, inf),
2126 hir::GenericArg::Const(_) => (lt, ty, true, inf),
2127 hir::GenericArg::Infer(_) => (lt, ty, ct, true),
2129 let mut emitted = false;
2130 if lt || ty || ct || inf {
2131 let types_and_spans: Vec<_> = segments
2133 .flat_map(|segment| {
2134 if segment.args().args.is_empty() {
2139 Res::PrimTy(ty) => format!("{} `{}`", segment.res.descr(), ty.name()),
2141 if let Some(name) = self.tcx().opt_item_name(def_id) => {
2142 format!("{} `{name}`", segment.res.descr())
2144 Res::Err => "this type".to_string(),
2145 _ => segment.res.descr().to_string(),
2152 let this_type = match &types_and_spans[..] {
2153 [.., _, (last, _)] => format!(
2155 types_and_spans[..types_and_spans.len() - 1]
2157 .map(|(x, _)| x.as_str())
2159 .collect::<String>()
2161 [(only, _)] => only.to_string(),
2162 [] => "this type".to_string(),
2165 let arg_spans: Vec<Span> = args.map(|arg| arg.span()).collect();
2167 let mut kinds = Vec::with_capacity(4);
2169 kinds.push("lifetime");
2175 kinds.push("const");
2178 kinds.push("generic");
2180 let (kind, s) = match kinds[..] {
2184 kinds[..kinds.len() - 1]
2188 .collect::<String>()
2192 [only] => (format!("{only}"), ""),
2193 [] => unreachable!(),
2195 let last_span = *arg_spans.last().unwrap();
2196 let span: MultiSpan = arg_spans.into();
2197 let mut err = struct_span_err!(
2201 "{kind} arguments are not allowed on {this_type}",
2203 err.span_label(last_span, format!("{kind} argument{s} not allowed"));
2204 for (what, span) in types_and_spans {
2205 err.span_label(span, format!("not allowed on {what}"));
2212 for segment in segments {
2213 // Only emit the first error to avoid overloading the user with error messages.
2214 if let [binding, ..] = segment.args().bindings {
2215 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2222 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2223 pub fn def_ids_for_value_path_segments(
2225 segments: &[hir::PathSegment<'_>],
2226 self_ty: Option<Ty<'tcx>>,
2230 // We need to extract the type parameters supplied by the user in
2231 // the path `path`. Due to the current setup, this is a bit of a
2232 // tricky-process; the problem is that resolve only tells us the
2233 // end-point of the path resolution, and not the intermediate steps.
2234 // Luckily, we can (at least for now) deduce the intermediate steps
2235 // just from the end-point.
2237 // There are basically five cases to consider:
2239 // 1. Reference to a constructor of a struct:
2241 // struct Foo<T>(...)
2243 // In this case, the parameters are declared in the type space.
2245 // 2. Reference to a constructor of an enum variant:
2247 // enum E<T> { Foo(...) }
2249 // In this case, the parameters are defined in the type space,
2250 // but may be specified either on the type or the variant.
2252 // 3. Reference to a fn item or a free constant:
2256 // In this case, the path will again always have the form
2257 // `a::b::foo::<T>` where only the final segment should have
2258 // type parameters. However, in this case, those parameters are
2259 // declared on a value, and hence are in the `FnSpace`.
2261 // 4. Reference to a method or an associated constant:
2263 // impl<A> SomeStruct<A> {
2267 // Here we can have a path like
2268 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2269 // may appear in two places. The penultimate segment,
2270 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2271 // final segment, `foo::<B>` contains parameters in fn space.
2273 // The first step then is to categorize the segments appropriately.
2275 let tcx = self.tcx();
2277 assert!(!segments.is_empty());
2278 let last = segments.len() - 1;
2280 let mut path_segs = vec![];
2283 // Case 1. Reference to a struct constructor.
2284 DefKind::Ctor(CtorOf::Struct, ..) => {
2285 // Everything but the final segment should have no
2286 // parameters at all.
2287 let generics = tcx.generics_of(def_id);
2288 // Variant and struct constructors use the
2289 // generics of their parent type definition.
2290 let generics_def_id = generics.parent.unwrap_or(def_id);
2291 path_segs.push(PathSeg(generics_def_id, last));
2294 // Case 2. Reference to a variant constructor.
2295 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2296 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2297 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2298 debug_assert!(adt_def.is_enum());
2299 (adt_def.did(), last)
2300 } else if last >= 1 && segments[last - 1].args.is_some() {
2301 // Everything but the penultimate segment should have no
2302 // parameters at all.
2303 let mut def_id = def_id;
2305 // `DefKind::Ctor` -> `DefKind::Variant`
2306 if let DefKind::Ctor(..) = kind {
2307 def_id = tcx.parent(def_id);
2310 // `DefKind::Variant` -> `DefKind::Enum`
2311 let enum_def_id = tcx.parent(def_id);
2312 (enum_def_id, last - 1)
2314 // FIXME: lint here recommending `Enum::<...>::Variant` form
2315 // instead of `Enum::Variant::<...>` form.
2317 // Everything but the final segment should have no
2318 // parameters at all.
2319 let generics = tcx.generics_of(def_id);
2320 // Variant and struct constructors use the
2321 // generics of their parent type definition.
2322 (generics.parent.unwrap_or(def_id), last)
2324 path_segs.push(PathSeg(generics_def_id, index));
2327 // Case 3. Reference to a top-level value.
2328 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static(_) => {
2329 path_segs.push(PathSeg(def_id, last));
2332 // Case 4. Reference to a method or associated const.
2333 DefKind::AssocFn | DefKind::AssocConst => {
2334 if segments.len() >= 2 {
2335 let generics = tcx.generics_of(def_id);
2336 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2338 path_segs.push(PathSeg(def_id, last));
2341 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2344 debug!("path_segs = {:?}", path_segs);
2349 // Check a type `Path` and convert it to a `Ty`.
2352 opt_self_ty: Option<Ty<'tcx>>,
2353 path: &hir::Path<'_>,
2354 permit_variants: bool,
2356 let tcx = self.tcx();
2359 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2360 path.res, opt_self_ty, path.segments
2363 let span = path.span;
2365 Res::Def(DefKind::OpaqueTy | DefKind::ImplTraitPlaceholder, did) => {
2366 // Check for desugared `impl Trait`.
2367 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2368 let item_segment = path.segments.split_last().unwrap();
2369 self.prohibit_generics(item_segment.1.iter(), |err| {
2370 err.note("`impl Trait` types can't have type parameters");
2372 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2373 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2380 | DefKind::ForeignTy,
2383 assert_eq!(opt_self_ty, None);
2384 self.prohibit_generics(path.segments.split_last().unwrap().1.iter(), |_| {});
2385 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2387 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2388 // Convert "variant type" as if it were a real type.
2389 // The resulting `Ty` is type of the variant's enum for now.
2390 assert_eq!(opt_self_ty, None);
2393 self.def_ids_for_value_path_segments(path.segments, None, kind, def_id);
2394 let generic_segs: FxHashSet<_> =
2395 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2396 self.prohibit_generics(
2397 path.segments.iter().enumerate().filter_map(|(index, seg)| {
2398 if !generic_segs.contains(&index) { Some(seg) } else { None }
2401 err.note("enum variants can't have type parameters");
2405 let PathSeg(def_id, index) = path_segs.last().unwrap();
2406 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2408 Res::Def(DefKind::TyParam, def_id) => {
2409 assert_eq!(opt_self_ty, None);
2410 self.prohibit_generics(path.segments.iter(), |err| {
2411 if let Some(span) = tcx.def_ident_span(def_id) {
2412 let name = tcx.item_name(def_id);
2413 err.span_note(span, &format!("type parameter `{name}` defined here"));
2417 let def_id = def_id.expect_local();
2418 let item_def_id = tcx.hir().ty_param_owner(def_id);
2419 let generics = tcx.generics_of(item_def_id);
2420 let index = generics.param_def_id_to_index[&def_id.to_def_id()];
2421 tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id))
2423 Res::SelfTy { trait_: Some(_), alias_to: None } => {
2424 // `Self` in trait or type alias.
2425 assert_eq!(opt_self_ty, None);
2426 self.prohibit_generics(path.segments.iter(), |err| {
2427 if let [hir::PathSegment { args: Some(args), ident, .. }] = &path.segments[..] {
2428 err.span_suggestion_verbose(
2429 ident.span.shrink_to_hi().to(args.span_ext),
2430 "the `Self` type doesn't accept type parameters",
2432 Applicability::MaybeIncorrect,
2436 tcx.types.self_param
2438 Res::SelfTy { trait_: _, alias_to: Some((def_id, forbid_generic)) } => {
2439 // `Self` in impl (we know the concrete type).
2440 assert_eq!(opt_self_ty, None);
2441 // Try to evaluate any array length constants.
2442 let ty = tcx.at(span).type_of(def_id);
2443 let span_of_impl = tcx.span_of_impl(def_id);
2444 self.prohibit_generics(path.segments.iter(), |err| {
2445 let def_id = match *ty.kind() {
2446 ty::Adt(self_def, _) => self_def.did(),
2450 let type_name = tcx.item_name(def_id);
2451 let span_of_ty = tcx.def_ident_span(def_id);
2452 let generics = tcx.generics_of(def_id).count();
2454 let msg = format!("`Self` is of type `{ty}`");
2455 if let (Ok(i_sp), Some(t_sp)) = (span_of_impl, span_of_ty) {
2456 let mut span: MultiSpan = vec![t_sp].into();
2457 span.push_span_label(
2459 &format!("`Self` is on type `{type_name}` in this `impl`"),
2461 let mut postfix = "";
2463 postfix = ", which doesn't have generic parameters";
2465 span.push_span_label(
2467 &format!("`Self` corresponds to this type{postfix}"),
2469 err.span_note(span, &msg);
2473 for segment in path.segments {
2474 if let Some(args) = segment.args && segment.ident.name == kw::SelfUpper {
2476 // FIXME(estebank): we could also verify that the arguments being
2477 // work for the `enum`, instead of just looking if it takes *any*.
2478 err.span_suggestion_verbose(
2479 segment.ident.span.shrink_to_hi().to(args.span_ext),
2480 "the `Self` type doesn't accept type parameters",
2482 Applicability::MachineApplicable,
2486 err.span_suggestion_verbose(
2489 "the `Self` type doesn't accept type parameters, use the \
2490 concrete type's name `{type_name}` instead if you want to \
2491 specify its type parameters"
2494 Applicability::MaybeIncorrect,
2500 // HACK(min_const_generics): Forbid generic `Self` types
2501 // here as we can't easily do that during nameres.
2503 // We do this before normalization as we otherwise allow
2505 // trait AlwaysApplicable { type Assoc; }
2506 // impl<T: ?Sized> AlwaysApplicable for T { type Assoc = usize; }
2508 // trait BindsParam<T> {
2511 // impl<T> BindsParam<T> for <T as AlwaysApplicable>::Assoc {
2512 // type ArrayTy = [u8; Self::MAX];
2515 // Note that the normalization happens in the param env of
2516 // the anon const, which is empty. This is why the
2517 // `AlwaysApplicable` impl needs a `T: ?Sized` bound for
2518 // this to compile if we were to normalize here.
2519 if forbid_generic && ty.needs_subst() {
2520 let mut err = tcx.sess.struct_span_err(
2522 "generic `Self` types are currently not permitted in anonymous constants",
2524 if let Some(hir::Node::Item(&hir::Item {
2525 kind: hir::ItemKind::Impl(ref impl_),
2527 })) = tcx.hir().get_if_local(def_id)
2529 err.span_note(impl_.self_ty.span, "not a concrete type");
2534 self.normalize_ty(span, ty)
2537 Res::Def(DefKind::AssocTy, def_id) => {
2538 debug_assert!(path.segments.len() >= 2);
2539 self.prohibit_generics(path.segments[..path.segments.len() - 2].iter(), |_| {});
2544 &path.segments[path.segments.len() - 2],
2545 path.segments.last().unwrap(),
2548 Res::PrimTy(prim_ty) => {
2549 assert_eq!(opt_self_ty, None);
2550 self.prohibit_generics(path.segments.iter(), |err| {
2551 let name = prim_ty.name_str();
2552 for segment in path.segments {
2553 if let Some(args) = segment.args {
2554 err.span_suggestion_verbose(
2555 segment.ident.span.shrink_to_hi().to(args.span_ext),
2556 &format!("primitive type `{name}` doesn't have generic parameters"),
2558 Applicability::MaybeIncorrect,
2564 hir::PrimTy::Bool => tcx.types.bool,
2565 hir::PrimTy::Char => tcx.types.char,
2566 hir::PrimTy::Int(it) => tcx.mk_mach_int(ty::int_ty(it)),
2567 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(ty::uint_ty(uit)),
2568 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ty::float_ty(ft)),
2569 hir::PrimTy::Str => tcx.types.str_,
2573 self.set_tainted_by_errors();
2574 self.tcx().ty_error()
2576 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2580 /// Parses the programmer's textual representation of a type into our
2581 /// internal notion of a type.
2582 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2583 self.ast_ty_to_ty_inner(ast_ty, false, false)
2586 /// Parses the programmer's textual representation of a type into our
2587 /// internal notion of a type. This is meant to be used within a path.
2588 pub fn ast_ty_to_ty_in_path(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2589 self.ast_ty_to_ty_inner(ast_ty, false, true)
2592 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2593 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2594 #[instrument(level = "debug", skip(self), ret)]
2595 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool, in_path: bool) -> Ty<'tcx> {
2596 let tcx = self.tcx();
2598 let result_ty = match ast_ty.kind {
2599 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
2600 hir::TyKind::Ptr(ref mt) => {
2601 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
2603 hir::TyKind::Rptr(ref region, ref mt) => {
2604 let r = self.ast_region_to_region(region, None);
2606 let t = self.ast_ty_to_ty_inner(mt.ty, true, false);
2607 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2609 hir::TyKind::Never => tcx.types.never,
2610 hir::TyKind::Tup(fields) => tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(t))),
2611 hir::TyKind::BareFn(bf) => {
2612 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
2614 tcx.mk_fn_ptr(self.ty_of_fn(
2623 hir::TyKind::TraitObject(bounds, ref lifetime, repr) => {
2624 self.maybe_lint_bare_trait(ast_ty, in_path);
2625 let repr = match repr {
2626 TraitObjectSyntax::Dyn | TraitObjectSyntax::None => ty::Dyn,
2627 TraitObjectSyntax::DynStar => ty::DynStar,
2629 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed, repr)
2631 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2632 debug!(?maybe_qself, ?path);
2633 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2634 self.res_to_ty(opt_self_ty, path, false)
2636 hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
2637 let opaque_ty = tcx.hir().item(item_id);
2638 let def_id = item_id.def_id.to_def_id();
2640 match opaque_ty.kind {
2641 hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
2642 self.impl_trait_ty_to_ty(def_id, lifetimes, origin, in_trait)
2644 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2647 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2648 debug!(?qself, ?segment);
2649 let ty = self.ast_ty_to_ty_inner(qself, false, true);
2650 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, qself, segment, false)
2651 .map(|(ty, _, _)| ty)
2652 .unwrap_or_else(|_| tcx.ty_error())
2654 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
2655 let def_id = tcx.require_lang_item(lang_item, Some(span));
2656 let (substs, _) = self.create_substs_for_ast_path(
2660 &hir::PathSegment::invalid(),
2661 &GenericArgs::none(),
2665 EarlyBinder(self.normalize_ty(span, tcx.at(span).type_of(def_id)))
2668 hir::TyKind::Array(ref ty, ref length) => {
2669 let length = match length {
2670 &hir::ArrayLen::Infer(_, span) => self.ct_infer(tcx.types.usize, None, span),
2671 hir::ArrayLen::Body(constant) => {
2672 let length_def_id = tcx.hir().local_def_id(constant.hir_id);
2673 ty::Const::from_anon_const(tcx, length_def_id)
2677 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(ty), length));
2678 self.normalize_ty(ast_ty.span, array_ty)
2680 hir::TyKind::Typeof(ref e) => {
2681 let ty_erased = tcx.type_of(tcx.hir().local_def_id(e.hir_id));
2682 let ty = tcx.fold_regions(ty_erased, |r, _| {
2683 if r.is_erased() { tcx.lifetimes.re_static } else { r }
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(),
2705 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2709 #[instrument(level = "debug", skip(self), ret)]
2710 fn impl_trait_ty_to_ty(
2713 lifetimes: &[hir::GenericArg<'_>],
2714 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 if in_trait { tcx.mk_projection(def_id, substs) } else { tcx.mk_opaque(def_id, substs) }
2762 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2764 hir::TyKind::Infer if expected_ty.is_some() => {
2765 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2766 expected_ty.unwrap()
2768 _ => self.ast_ty_to_ty(ty),
2775 unsafety: hir::Unsafety,
2777 decl: &hir::FnDecl<'_>,
2778 generics: Option<&hir::Generics<'_>>,
2779 hir_ty: Option<&hir::Ty<'_>>,
2780 ) -> ty::PolyFnSig<'tcx> {
2783 let tcx = self.tcx();
2784 let bound_vars = tcx.late_bound_vars(hir_id);
2785 debug!(?bound_vars);
2787 // We proactively collect all the inferred type params to emit a single error per fn def.
2788 let mut visitor = HirPlaceholderCollector::default();
2789 let mut infer_replacements = vec![];
2791 if let Some(generics) = generics {
2792 walk_generics(&mut visitor, generics);
2795 let input_tys: Vec<_> = decl
2800 if let hir::TyKind::Infer = a.kind && !self.allow_ty_infer() {
2801 if let Some(suggested_ty) =
2802 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, Some(i))
2804 infer_replacements.push((a.span, suggested_ty.to_string()));
2805 return suggested_ty;
2809 // Only visit the type looking for `_` if we didn't fix the type above
2810 visitor.visit_ty(a);
2811 self.ty_of_arg(a, None)
2815 let output_ty = match decl.output {
2816 hir::FnRetTy::Return(output) => {
2817 if let hir::TyKind::Infer = output.kind
2818 && !self.allow_ty_infer()
2819 && let Some(suggested_ty) =
2820 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, None)
2822 infer_replacements.push((output.span, suggested_ty.to_string()));
2825 visitor.visit_ty(output);
2826 self.ast_ty_to_ty(output)
2829 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2832 debug!("ty_of_fn: output_ty={:?}", output_ty);
2834 let fn_ty = tcx.mk_fn_sig(input_tys.into_iter(), output_ty, decl.c_variadic, unsafety, abi);
2835 let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
2837 if !self.allow_ty_infer() && !(visitor.0.is_empty() && infer_replacements.is_empty()) {
2838 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2839 // only want to emit an error complaining about them if infer types (`_`) are not
2840 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2841 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2843 let mut diag = crate::collect::placeholder_type_error_diag(
2847 infer_replacements.iter().map(|(s, _)| *s).collect(),
2853 if !infer_replacements.is_empty() {
2854 diag.multipart_suggestion(
2856 "try replacing `_` with the type{} in the corresponding trait method signature",
2857 rustc_errors::pluralize!(infer_replacements.len()),
2860 Applicability::MachineApplicable,
2867 // Find any late-bound regions declared in return type that do
2868 // not appear in the arguments. These are not well-formed.
2871 // for<'a> fn() -> &'a str <-- 'a is bad
2872 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2873 let inputs = bare_fn_ty.inputs();
2874 let late_bound_in_args =
2875 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2876 let output = bare_fn_ty.output();
2877 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2879 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
2884 "return type references {}, which is not constrained by the fn input types",
2892 /// Given a fn_hir_id for a impl function, suggest the type that is found on the
2893 /// corresponding function in the trait that the impl implements, if it exists.
2894 /// If arg_idx is Some, then it corresponds to an input type index, otherwise it
2895 /// corresponds to the return type.
2896 fn suggest_trait_fn_ty_for_impl_fn_infer(
2898 fn_hir_id: hir::HirId,
2899 arg_idx: Option<usize>,
2900 ) -> Option<Ty<'tcx>> {
2901 let tcx = self.tcx();
2902 let hir = tcx.hir();
2904 let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), ident, .. }) =
2905 hir.get(fn_hir_id) else { return None };
2906 let hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(i), .. }) =
2907 hir.get(hir.get_parent_node(fn_hir_id)) else { bug!("ImplItem should have Impl parent") };
2910 self.instantiate_mono_trait_ref(i.of_trait.as_ref()?, self.ast_ty_to_ty(i.self_ty));
2912 let assoc = tcx.associated_items(trait_ref.def_id).find_by_name_and_kind(
2919 let fn_sig = tcx.bound_fn_sig(assoc.def_id).subst(
2921 trait_ref.substs.extend_to(tcx, assoc.def_id, |param, _| tcx.mk_param_from_def(param)),
2924 let ty = if let Some(arg_idx) = arg_idx { fn_sig.input(arg_idx) } else { fn_sig.output() };
2926 Some(tcx.liberate_late_bound_regions(fn_hir_id.expect_owner().to_def_id(), ty))
2929 fn validate_late_bound_regions(
2931 constrained_regions: FxHashSet<ty::BoundRegionKind>,
2932 referenced_regions: FxHashSet<ty::BoundRegionKind>,
2933 generate_err: impl Fn(&str) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
2935 for br in referenced_regions.difference(&constrained_regions) {
2936 let br_name = match *br {
2937 ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) | ty::BrEnv => {
2938 "an anonymous lifetime".to_string()
2940 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
2943 let mut err = generate_err(&br_name);
2945 if let ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) = *br {
2946 // The only way for an anonymous lifetime to wind up
2947 // in the return type but **also** be unconstrained is
2948 // if it only appears in "associated types" in the
2949 // input. See #47511 and #62200 for examples. In this case,
2950 // though we can easily give a hint that ought to be
2953 "lifetimes appearing in an associated or opaque type are not considered constrained",
2955 err.note("consider introducing a named lifetime parameter");
2962 /// Given the bounds on an object, determines what single region bound (if any) we can
2963 /// use to summarize this type. The basic idea is that we will use the bound the user
2964 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2965 /// for region bounds. It may be that we can derive no bound at all, in which case
2966 /// we return `None`.
2967 fn compute_object_lifetime_bound(
2970 existential_predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
2971 ) -> Option<ty::Region<'tcx>> // if None, use the default
2973 let tcx = self.tcx();
2975 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2977 // No explicit region bound specified. Therefore, examine trait
2978 // bounds and see if we can derive region bounds from those.
2979 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2981 // If there are no derived region bounds, then report back that we
2982 // can find no region bound. The caller will use the default.
2983 if derived_region_bounds.is_empty() {
2987 // If any of the derived region bounds are 'static, that is always
2989 if derived_region_bounds.iter().any(|r| r.is_static()) {
2990 return Some(tcx.lifetimes.re_static);
2993 // Determine whether there is exactly one unique region in the set
2994 // of derived region bounds. If so, use that. Otherwise, report an
2996 let r = derived_region_bounds[0];
2997 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2998 tcx.sess.emit_err(AmbiguousLifetimeBound { span });
3003 /// Make sure that we are in the condition to suggest the blanket implementation.
3004 fn maybe_lint_blanket_trait_impl(&self, self_ty: &hir::Ty<'_>, diag: &mut Diagnostic) {
3005 let tcx = self.tcx();
3006 let parent_id = tcx.hir().get_parent_item(self_ty.hir_id);
3007 if let hir::Node::Item(hir::Item {
3009 hir::ItemKind::Impl(hir::Impl {
3010 self_ty: impl_self_ty, of_trait: Some(of_trait_ref), generics, ..
3013 }) = tcx.hir().get_by_def_id(parent_id) && self_ty.hir_id == impl_self_ty.hir_id
3015 if !of_trait_ref.trait_def_id().map_or(false, |def_id| def_id.is_local()) {
3018 let of_trait_span = of_trait_ref.path.span;
3019 // make sure that we are not calling unwrap to abort during the compilation
3020 let Ok(impl_trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else { return; };
3021 let Ok(of_trait_name) = tcx.sess.source_map().span_to_snippet(of_trait_span) else { return; };
3022 // check if the trait has generics, to make a correct suggestion
3023 let param_name = generics.params.next_type_param_name(None);
3025 let add_generic_sugg = if let Some(span) = generics.span_for_param_suggestion() {
3026 (span, format!(", {}: {}", param_name, impl_trait_name))
3028 (generics.span, format!("<{}: {}>", param_name, impl_trait_name))
3030 diag.multipart_suggestion(
3031 format!("alternatively use a blanket \
3032 implementation to implement `{of_trait_name}` for \
3033 all types that also implement `{impl_trait_name}`"),
3035 (self_ty.span, param_name),
3038 Applicability::MaybeIncorrect,
3043 fn maybe_lint_bare_trait(&self, self_ty: &hir::Ty<'_>, in_path: bool) {
3044 let tcx = self.tcx();
3045 if let hir::TyKind::TraitObject([poly_trait_ref, ..], _, TraitObjectSyntax::None) =
3048 let needs_bracket = in_path
3052 .span_to_prev_source(self_ty.span)
3054 .map_or(false, |s| s.trim_end().ends_with('<'));
3056 let is_global = poly_trait_ref.trait_ref.path.is_global();
3057 let sugg = Vec::from_iter([
3059 self_ty.span.shrink_to_lo(),
3062 if needs_bracket { "<" } else { "" },
3063 if is_global { "(" } else { "" },
3067 self_ty.span.shrink_to_hi(),
3070 if is_global { ")" } else { "" },
3071 if needs_bracket { ">" } else { "" },
3075 if self_ty.span.edition() >= Edition::Edition2021 {
3076 let msg = "trait objects must include the `dyn` keyword";
3077 let label = "add `dyn` keyword before this trait";
3079 rustc_errors::struct_span_err!(tcx.sess, self_ty.span, E0782, "{}", msg);
3080 diag.multipart_suggestion_verbose(label, sugg, Applicability::MachineApplicable);
3081 // check if the impl trait that we are considering is a impl of a local trait
3082 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);
3085 let msg = "trait objects without an explicit `dyn` are deprecated";
3086 tcx.struct_span_lint_hir(
3091 let mut diag = lint.build(msg);
3092 diag.multipart_suggestion_verbose(
3095 Applicability::MachineApplicable,
3097 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);