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, DiagnosticBuilder, ErrorGuaranteed, FatalError, MultiSpan,
22 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
23 use rustc_hir::def_id::{DefId, LocalDefId};
24 use rustc_hir::intravisit::{walk_generics, Visitor as _};
25 use rustc_hir::lang_items::LangItem;
26 use rustc_hir::{GenericArg, GenericArgs, OpaqueTyOrigin};
27 use rustc_middle::middle::stability::AllowUnstable;
28 use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, Subst, SubstsRef};
29 use rustc_middle::ty::GenericParamDefKind;
30 use rustc_middle::ty::{
31 self, Const, DefIdTree, EarlyBinder, IsSuggestable, Ty, TyCtxt, TypeVisitable,
33 use rustc_session::lint::builtin::{AMBIGUOUS_ASSOCIATED_ITEMS, BARE_TRAIT_OBJECTS};
34 use rustc_span::edition::Edition;
35 use rustc_span::lev_distance::find_best_match_for_name;
36 use rustc_span::symbol::{kw, Ident, Symbol};
37 use rustc_span::{Span, DUMMY_SP};
38 use rustc_target::spec::abi;
39 use rustc_trait_selection::traits;
40 use rustc_trait_selection::traits::astconv_object_safety_violations;
41 use rustc_trait_selection::traits::error_reporting::{
42 report_object_safety_error, suggestions::NextTypeParamName,
44 use rustc_trait_selection::traits::wf::object_region_bounds;
46 use smallvec::SmallVec;
47 use std::collections::BTreeSet;
51 pub struct PathSeg(pub DefId, pub usize);
53 pub trait AstConv<'tcx> {
54 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
56 fn item_def_id(&self) -> Option<DefId>;
58 /// Returns predicates in scope of the form `X: Foo<T>`, where `X`
59 /// is a type parameter `X` with the given id `def_id` and T
60 /// matches `assoc_name`. This is a subset of the full set of
63 /// This is used for one specific purpose: resolving "short-hand"
64 /// associated type references like `T::Item`. In principle, we
65 /// would do that by first getting the full set of predicates in
66 /// scope and then filtering down to find those that apply to `T`,
67 /// but this can lead to cycle errors. The problem is that we have
68 /// to do this resolution *in order to create the predicates in
69 /// the first place*. Hence, we have this "special pass".
70 fn get_type_parameter_bounds(
75 ) -> ty::GenericPredicates<'tcx>;
77 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
78 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
79 -> Option<ty::Region<'tcx>>;
81 /// Returns the type to use when a type is omitted.
82 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
84 /// Returns `true` if `_` is allowed in type signatures in the current context.
85 fn allow_ty_infer(&self) -> bool;
87 /// Returns the const to use when a const is omitted.
91 param: Option<&ty::GenericParamDef>,
95 /// Projecting an associated type from a (potentially)
96 /// higher-ranked trait reference is more complicated, because of
97 /// the possibility of late-bound regions appearing in the
98 /// associated type binding. This is not legal in function
99 /// signatures for that reason. In a function body, we can always
100 /// handle it because we can use inference variables to remove the
101 /// late-bound regions.
102 fn projected_ty_from_poly_trait_ref(
106 item_segment: &hir::PathSegment<'_>,
107 poly_trait_ref: ty::PolyTraitRef<'tcx>,
110 /// Normalize an associated type coming from the user.
111 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
113 /// Invoked when we encounter an error from some prior pass
114 /// (e.g., resolve) that is translated into a ty-error. This is
115 /// used to help suppress derived errors typeck might otherwise
117 fn set_tainted_by_errors(&self);
119 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
123 struct ConvertedBinding<'a, 'tcx> {
126 kind: ConvertedBindingKind<'a, 'tcx>,
127 gen_args: &'a GenericArgs<'a>,
132 enum ConvertedBindingKind<'a, 'tcx> {
133 Equality(ty::Term<'tcx>),
134 Constraint(&'a [hir::GenericBound<'a>]),
137 /// New-typed boolean indicating whether explicit late-bound lifetimes
138 /// are present in a set of generic arguments.
140 /// For example if we have some method `fn f<'a>(&'a self)` implemented
141 /// for some type `T`, although `f` is generic in the lifetime `'a`, `'a`
142 /// is late-bound so should not be provided explicitly. Thus, if `f` is
143 /// instantiated with some generic arguments providing `'a` explicitly,
144 /// we taint those arguments with `ExplicitLateBound::Yes` so that we
145 /// can provide an appropriate diagnostic later.
146 #[derive(Copy, Clone, PartialEq)]
147 pub enum ExplicitLateBound {
152 #[derive(Copy, Clone, PartialEq)]
153 pub enum IsMethodCall {
158 /// Denotes the "position" of a generic argument, indicating if it is a generic type,
159 /// generic function or generic method call.
160 #[derive(Copy, Clone, PartialEq)]
161 pub(crate) enum GenericArgPosition {
163 Value, // e.g., functions
167 /// A marker denoting that the generic arguments that were
168 /// provided did not match the respective generic parameters.
169 #[derive(Clone, Default)]
170 pub struct GenericArgCountMismatch {
171 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
172 pub reported: Option<ErrorGuaranteed>,
173 /// A list of spans of arguments provided that were not valid.
174 pub invalid_args: Vec<Span>,
177 /// Decorates the result of a generic argument count mismatch
178 /// check with whether explicit late bounds were provided.
180 pub struct GenericArgCountResult {
181 pub explicit_late_bound: ExplicitLateBound,
182 pub correct: Result<(), GenericArgCountMismatch>,
185 pub trait CreateSubstsForGenericArgsCtxt<'a, 'tcx> {
186 fn args_for_def_id(&mut self, def_id: DefId) -> (Option<&'a GenericArgs<'a>>, bool);
190 param: &ty::GenericParamDef,
191 arg: &GenericArg<'_>,
192 ) -> subst::GenericArg<'tcx>;
196 substs: Option<&[subst::GenericArg<'tcx>]>,
197 param: &ty::GenericParamDef,
199 ) -> subst::GenericArg<'tcx>;
202 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
203 #[tracing::instrument(level = "debug", skip(self))]
204 pub fn ast_region_to_region(
206 lifetime: &hir::Lifetime,
207 def: Option<&ty::GenericParamDef>,
208 ) -> ty::Region<'tcx> {
209 let tcx = self.tcx();
210 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
212 let r = match tcx.named_region(lifetime.hir_id) {
213 Some(rl::Region::Static) => tcx.lifetimes.re_static,
215 Some(rl::Region::LateBound(debruijn, index, def_id)) => {
216 let name = lifetime_name(def_id.expect_local());
217 let br = ty::BoundRegion {
218 var: ty::BoundVar::from_u32(index),
219 kind: ty::BrNamed(def_id, name),
221 tcx.mk_region(ty::ReLateBound(debruijn, br))
224 Some(rl::Region::LateBoundAnon(debruijn, index, anon_index)) => {
225 let br = ty::BoundRegion {
226 var: ty::BoundVar::from_u32(index),
227 kind: ty::BrAnon(anon_index),
229 tcx.mk_region(ty::ReLateBound(debruijn, br))
232 Some(rl::Region::EarlyBound(index, id)) => {
233 let name = lifetime_name(id.expect_local());
234 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
237 Some(rl::Region::Free(scope, id)) => {
238 let name = lifetime_name(id.expect_local());
239 tcx.mk_region(ty::ReFree(ty::FreeRegion {
241 bound_region: ty::BrNamed(id, name),
244 // (*) -- not late-bound, won't change
248 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
249 debug!(?lifetime, "unelided lifetime in signature");
251 // This indicates an illegal lifetime
252 // elision. `resolve_lifetime` should have
253 // reported an error in this case -- but if
254 // not, let's error out.
255 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
257 // Supply some dummy value. We don't have an
258 // `re_error`, annoyingly, so use `'static`.
259 tcx.lifetimes.re_static
264 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
269 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
270 /// returns an appropriate set of substitutions for this particular reference to `I`.
271 pub fn ast_path_substs_for_ty(
275 item_segment: &hir::PathSegment<'_>,
276 ) -> SubstsRef<'tcx> {
277 let (substs, _) = self.create_substs_for_ast_path(
283 item_segment.infer_args,
286 let assoc_bindings = self.create_assoc_bindings_for_generic_args(item_segment.args());
288 if let Some(b) = assoc_bindings.first() {
289 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
295 /// Given the type/lifetime/const arguments provided to some path (along with
296 /// an implicit `Self`, if this is a trait reference), returns the complete
297 /// set of substitutions. This may involve applying defaulted type parameters.
298 /// Constraints on associated types are created from `create_assoc_bindings_for_generic_args`.
302 /// ```ignore (illustrative)
303 /// T: std::ops::Index<usize, Output = u32>
304 /// // ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
307 /// 1. The `self_ty` here would refer to the type `T`.
308 /// 2. The path in question is the path to the trait `std::ops::Index`,
309 /// which will have been resolved to a `def_id`
310 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
311 /// parameters are returned in the `SubstsRef`, the associated type bindings like
312 /// `Output = u32` are returned from `create_assoc_bindings_for_generic_args`.
314 /// Note that the type listing given here is *exactly* what the user provided.
316 /// For (generic) associated types
318 /// ```ignore (illustrative)
319 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
322 /// We have the parent substs are the substs for the parent trait:
323 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
324 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
325 /// lists: `[Vec<u8>, u8, 'a]`.
326 #[tracing::instrument(level = "debug", skip(self, span))]
327 fn create_substs_for_ast_path<'a>(
331 parent_substs: &[subst::GenericArg<'tcx>],
332 seg: &hir::PathSegment<'_>,
333 generic_args: &'a hir::GenericArgs<'_>,
335 self_ty: Option<Ty<'tcx>>,
336 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
337 // If the type is parameterized by this region, then replace this
338 // region with the current anon region binding (in other words,
339 // whatever & would get replaced with).
341 let tcx = self.tcx();
342 let generics = tcx.generics_of(def_id);
343 debug!("generics: {:?}", generics);
345 if generics.has_self {
346 if generics.parent.is_some() {
347 // The parent is a trait so it should have at least one subst
348 // for the `Self` type.
349 assert!(!parent_substs.is_empty())
351 // This item (presumably a trait) needs a self-type.
352 assert!(self_ty.is_some());
355 assert!(self_ty.is_none() && parent_substs.is_empty());
358 let arg_count = Self::check_generic_arg_count(
365 GenericArgPosition::Type,
370 // Skip processing if type has no generic parameters.
371 // Traits always have `Self` as a generic parameter, which means they will not return early
372 // here and so associated type bindings will be handled regardless of whether there are any
373 // non-`Self` generic parameters.
374 if generics.params.is_empty() {
375 return (tcx.intern_substs(&[]), arg_count);
378 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
380 struct SubstsForAstPathCtxt<'a, 'tcx> {
381 astconv: &'a (dyn AstConv<'tcx> + 'a),
383 generic_args: &'a GenericArgs<'a>,
385 missing_type_params: Vec<String>,
386 inferred_params: Vec<Span>,
391 impl<'tcx, 'a> SubstsForAstPathCtxt<'tcx, 'a> {
392 fn default_needs_object_self(&mut self, param: &ty::GenericParamDef) -> bool {
393 let tcx = self.astconv.tcx();
394 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
395 if self.is_object && has_default {
396 let default_ty = tcx.at(self.span).type_of(param.def_id);
397 let self_param = tcx.types.self_param;
398 if default_ty.walk().any(|arg| arg == self_param.into()) {
399 // There is no suitable inference default for a type parameter
400 // that references self, in an object type.
410 impl<'a, 'tcx> CreateSubstsForGenericArgsCtxt<'a, 'tcx> for SubstsForAstPathCtxt<'a, 'tcx> {
411 fn args_for_def_id(&mut self, did: DefId) -> (Option<&'a GenericArgs<'a>>, bool) {
412 if did == self.def_id {
413 (Some(self.generic_args), self.infer_args)
415 // The last component of this tuple is unimportant.
422 param: &ty::GenericParamDef,
423 arg: &GenericArg<'_>,
424 ) -> subst::GenericArg<'tcx> {
425 let tcx = self.astconv.tcx();
427 let mut handle_ty_args = |has_default, ty: &hir::Ty<'_>| {
429 tcx.check_optional_stability(
436 // Default generic parameters may not be marked
437 // with stability attributes, i.e. when the
438 // default parameter was defined at the same time
439 // as the rest of the type. As such, we ignore missing
440 // stability attributes.
444 if let (hir::TyKind::Infer, false) = (&ty.kind, self.astconv.allow_ty_infer()) {
445 self.inferred_params.push(ty.span);
446 tcx.ty_error().into()
448 self.astconv.ast_ty_to_ty(ty).into()
452 match (¶m.kind, arg) {
453 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
454 self.astconv.ast_region_to_region(lt, Some(param)).into()
456 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Type(ty)) => {
457 handle_ty_args(has_default, ty)
459 (&GenericParamDefKind::Type { has_default, .. }, GenericArg::Infer(inf)) => {
460 handle_ty_args(has_default, &inf.to_ty())
462 (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => {
463 ty::Const::from_opt_const_arg_anon_const(
465 ty::WithOptConstParam {
466 did: tcx.hir().local_def_id(ct.value.hir_id),
467 const_param_did: Some(param.def_id),
472 (&GenericParamDefKind::Const { .. }, hir::GenericArg::Infer(inf)) => {
473 let ty = tcx.at(self.span).type_of(param.def_id);
474 if self.astconv.allow_ty_infer() {
475 self.astconv.ct_infer(ty, Some(param), inf.span).into()
477 self.inferred_params.push(inf.span);
478 tcx.const_error(ty).into()
487 substs: Option<&[subst::GenericArg<'tcx>]>,
488 param: &ty::GenericParamDef,
490 ) -> subst::GenericArg<'tcx> {
491 let tcx = self.astconv.tcx();
493 GenericParamDefKind::Lifetime => self
495 .re_infer(Some(param), self.span)
497 debug!(?param, "unelided lifetime in signature");
499 // This indicates an illegal lifetime in a non-assoc-trait position
500 tcx.sess.delay_span_bug(self.span, "unelided lifetime in signature");
502 // Supply some dummy value. We don't have an
503 // `re_error`, annoyingly, so use `'static`.
504 tcx.lifetimes.re_static
507 GenericParamDefKind::Type { has_default, .. } => {
508 if !infer_args && has_default {
509 // No type parameter provided, but a default exists.
511 // If we are converting an object type, then the
512 // `Self` parameter is unknown. However, some of the
513 // other type parameters may reference `Self` in their
514 // defaults. This will lead to an ICE if we are not
516 if self.default_needs_object_self(param) {
517 self.missing_type_params.push(param.name.to_string());
518 tcx.ty_error().into()
520 // This is a default type parameter.
521 let substs = substs.unwrap();
522 if substs.iter().any(|arg| match arg.unpack() {
523 GenericArgKind::Type(ty) => ty.references_error(),
526 // Avoid ICE #86756 when type error recovery goes awry.
527 return tcx.ty_error().into();
532 EarlyBinder(tcx.at(self.span).type_of(param.def_id))
537 } else if infer_args {
538 // No type parameters were provided, we can infer all.
539 let param = if !self.default_needs_object_self(param) {
544 self.astconv.ty_infer(param, self.span).into()
546 // We've already errored above about the mismatch.
547 tcx.ty_error().into()
550 GenericParamDefKind::Const { has_default } => {
551 let ty = tcx.at(self.span).type_of(param.def_id);
552 if !infer_args && has_default {
553 tcx.bound_const_param_default(param.def_id)
554 .subst(tcx, substs.unwrap())
558 self.astconv.ct_infer(ty, Some(param), self.span).into()
560 // We've already errored above about the mismatch.
561 tcx.const_error(ty).into()
569 let mut substs_ctx = SubstsForAstPathCtxt {
574 missing_type_params: vec![],
575 inferred_params: vec![],
579 let substs = Self::create_substs_for_generic_args(
589 self.complain_about_missing_type_params(
590 substs_ctx.missing_type_params,
593 generic_args.args.is_empty(),
597 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
598 generics, self_ty, substs
604 fn create_assoc_bindings_for_generic_args<'a>(
606 generic_args: &'a hir::GenericArgs<'_>,
607 ) -> Vec<ConvertedBinding<'a, 'tcx>> {
608 // Convert associated-type bindings or constraints into a separate vector.
609 // Example: Given this:
611 // T: Iterator<Item = u32>
613 // The `T` is passed in as a self-type; the `Item = u32` is
614 // not a "type parameter" of the `Iterator` trait, but rather
615 // a restriction on `<T as Iterator>::Item`, so it is passed
617 let assoc_bindings = generic_args
621 let kind = match binding.kind {
622 hir::TypeBindingKind::Equality { ref term } => match term {
623 hir::Term::Ty(ref ty) => {
624 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty).into())
626 hir::Term::Const(ref c) => {
627 let local_did = self.tcx().hir().local_def_id(c.hir_id);
628 let c = Const::from_anon_const(self.tcx(), local_did);
629 ConvertedBindingKind::Equality(c.into())
632 hir::TypeBindingKind::Constraint { ref bounds } => {
633 ConvertedBindingKind::Constraint(bounds)
637 hir_id: binding.hir_id,
638 item_name: binding.ident,
640 gen_args: binding.gen_args,
649 pub(crate) fn create_substs_for_associated_item(
654 item_segment: &hir::PathSegment<'_>,
655 parent_substs: SubstsRef<'tcx>,
656 ) -> SubstsRef<'tcx> {
658 "create_substs_for_associated_item(span: {:?}, item_def_id: {:?}, item_segment: {:?}",
659 span, item_def_id, item_segment
661 if tcx.generics_of(item_def_id).params.is_empty() {
662 self.prohibit_generics(slice::from_ref(item_segment).iter(), |_| {});
666 self.create_substs_for_ast_path(
672 item_segment.infer_args,
679 /// Instantiates the path for the given trait reference, assuming that it's
680 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
681 /// The type _cannot_ be a type other than a trait type.
683 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
684 /// are disallowed. Otherwise, they are pushed onto the vector given.
685 pub fn instantiate_mono_trait_ref(
687 trait_ref: &hir::TraitRef<'_>,
689 ) -> ty::TraitRef<'tcx> {
690 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
692 self.ast_path_to_mono_trait_ref(
694 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
696 trait_ref.path.segments.last().unwrap(),
701 fn instantiate_poly_trait_ref_inner(
705 binding_span: Option<Span>,
706 constness: ty::BoundConstness,
707 bounds: &mut Bounds<'tcx>,
709 trait_ref_span: Span,
711 trait_segment: &hir::PathSegment<'_>,
712 args: &GenericArgs<'_>,
715 ) -> GenericArgCountResult {
716 let (substs, arg_count) = self.create_substs_for_ast_path(
726 let tcx = self.tcx();
727 let bound_vars = tcx.late_bound_vars(hir_id);
730 let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
733 ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
735 debug!(?poly_trait_ref, ?assoc_bindings);
736 bounds.trait_bounds.push((poly_trait_ref, span, constness));
738 let mut dup_bindings = FxHashMap::default();
739 for binding in &assoc_bindings {
740 // Specify type to assert that error was already reported in `Err` case.
741 let _: Result<_, ErrorGuaranteed> = self.add_predicates_for_ast_type_binding(
748 binding_span.unwrap_or(binding.span),
750 // Okay to ignore `Err` because of `ErrorGuaranteed` (see above).
756 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
757 /// a full trait reference. The resulting trait reference is returned. This may also generate
758 /// auxiliary bounds, which are added to `bounds`.
762 /// ```ignore (illustrative)
763 /// poly_trait_ref = Iterator<Item = u32>
767 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
769 /// **A note on binders:** against our usual convention, there is an implied bounder around
770 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
771 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
772 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
773 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
775 #[tracing::instrument(level = "debug", skip(self, span, constness, bounds, speculative))]
776 pub(crate) fn instantiate_poly_trait_ref(
778 trait_ref: &hir::TraitRef<'_>,
780 constness: ty::BoundConstness,
782 bounds: &mut Bounds<'tcx>,
784 ) -> GenericArgCountResult {
785 let hir_id = trait_ref.hir_ref_id;
786 let binding_span = None;
787 let trait_ref_span = trait_ref.path.span;
788 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
789 let trait_segment = trait_ref.path.segments.last().unwrap();
790 let args = trait_segment.args();
791 let infer_args = trait_segment.infer_args;
793 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
794 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, false);
796 self.instantiate_poly_trait_ref_inner(
812 pub(crate) fn instantiate_lang_item_trait_ref(
814 lang_item: hir::LangItem,
817 args: &GenericArgs<'_>,
819 bounds: &mut Bounds<'tcx>,
821 let binding_span = Some(span);
822 let constness = ty::BoundConstness::NotConst;
823 let speculative = false;
824 let trait_ref_span = span;
825 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
826 let trait_segment = &hir::PathSegment::invalid();
827 let infer_args = false;
829 self.instantiate_poly_trait_ref_inner(
845 fn ast_path_to_mono_trait_ref(
850 trait_segment: &hir::PathSegment<'_>,
852 ) -> ty::TraitRef<'tcx> {
853 let (substs, _) = self.create_substs_for_ast_trait_ref(
860 let assoc_bindings = self.create_assoc_bindings_for_generic_args(trait_segment.args());
861 if let Some(b) = assoc_bindings.first() {
862 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
864 ty::TraitRef::new(trait_def_id, substs)
867 #[tracing::instrument(level = "debug", skip(self, span))]
868 fn create_substs_for_ast_trait_ref<'a>(
873 trait_segment: &'a hir::PathSegment<'a>,
875 ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
876 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
878 self.create_substs_for_ast_path(
883 trait_segment.args(),
884 trait_segment.infer_args,
889 fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
891 .associated_items(trait_def_id)
892 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
895 fn trait_defines_associated_const_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
897 .associated_items(trait_def_id)
898 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Const, trait_def_id)
902 // Sets `implicitly_sized` to true on `Bounds` if necessary
903 pub(crate) fn add_implicitly_sized<'hir>(
905 bounds: &mut Bounds<'hir>,
906 ast_bounds: &'hir [hir::GenericBound<'hir>],
907 self_ty_where_predicates: Option<(hir::HirId, &'hir [hir::WherePredicate<'hir>])>,
910 let tcx = self.tcx();
912 // Try to find an unbound in bounds.
913 let mut unbound = None;
914 let mut search_bounds = |ast_bounds: &'hir [hir::GenericBound<'hir>]| {
915 for ab in ast_bounds {
916 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
917 if unbound.is_none() {
918 unbound = Some(&ptr.trait_ref);
920 tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
925 search_bounds(ast_bounds);
926 if let Some((self_ty, where_clause)) = self_ty_where_predicates {
927 let self_ty_def_id = tcx.hir().local_def_id(self_ty).to_def_id();
928 for clause in where_clause {
929 if let hir::WherePredicate::BoundPredicate(pred) = clause {
930 if pred.is_param_bound(self_ty_def_id) {
931 search_bounds(pred.bounds);
937 let sized_def_id = tcx.lang_items().require(LangItem::Sized);
938 match (&sized_def_id, unbound) {
939 (Ok(sized_def_id), Some(tpb))
940 if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) =>
942 // There was in fact a `?Sized` bound, return without doing anything
946 // There was a `?Trait` bound, but it was not `?Sized`; warn.
949 "default bound relaxed for a type parameter, but \
950 this does nothing because the given bound is not \
951 a default; only `?Sized` is supported",
953 // Otherwise, add implicitly sized if `Sized` is available.
956 // There was no `?Sized` bound; add implicitly sized if `Sized` is available.
959 if sized_def_id.is_err() {
960 // No lang item for `Sized`, so we can't add it as a bound.
963 bounds.implicitly_sized = Some(span);
966 /// This helper takes a *converted* parameter type (`param_ty`)
967 /// and an *unconverted* list of bounds:
971 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
973 /// `param_ty`, in ty form
976 /// It adds these `ast_bounds` into the `bounds` structure.
978 /// **A note on binders:** there is an implied binder around
979 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
980 /// for more details.
981 #[tracing::instrument(level = "debug", skip(self, ast_bounds, bounds))]
982 pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>(
986 bounds: &mut Bounds<'tcx>,
987 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
989 for ast_bound in ast_bounds {
991 hir::GenericBound::Trait(poly_trait_ref, modifier) => {
992 let constness = match modifier {
993 hir::TraitBoundModifier::MaybeConst => ty::BoundConstness::ConstIfConst,
994 hir::TraitBoundModifier::None => ty::BoundConstness::NotConst,
995 hir::TraitBoundModifier::Maybe => continue,
998 let _ = self.instantiate_poly_trait_ref(
999 &poly_trait_ref.trait_ref,
1000 poly_trait_ref.span,
1007 &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
1008 self.instantiate_lang_item_trait_ref(
1009 lang_item, span, hir_id, args, param_ty, bounds,
1012 hir::GenericBound::Outlives(lifetime) => {
1013 let region = self.ast_region_to_region(lifetime, None);
1016 .push((ty::Binder::bind_with_vars(region, bound_vars), lifetime.span));
1022 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1023 /// The self-type for the bounds is given by `param_ty`.
1027 /// ```ignore (illustrative)
1028 /// fn foo<T: Bar + Baz>() { }
1029 /// // ^ ^^^^^^^^^ ast_bounds
1033 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1034 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1035 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1037 /// `span` should be the declaration size of the parameter.
1038 pub(crate) fn compute_bounds(
1041 ast_bounds: &[hir::GenericBound<'_>],
1043 self.compute_bounds_inner(param_ty, ast_bounds)
1046 /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
1047 /// named `assoc_name` into ty::Bounds. Ignore the rest.
1048 pub(crate) fn compute_bounds_that_match_assoc_type(
1051 ast_bounds: &[hir::GenericBound<'_>],
1054 let mut result = Vec::new();
1056 for ast_bound in ast_bounds {
1057 if let Some(trait_ref) = ast_bound.trait_ref()
1058 && let Some(trait_did) = trait_ref.trait_def_id()
1059 && self.tcx().trait_may_define_assoc_type(trait_did, assoc_name)
1061 result.push(ast_bound.clone());
1065 self.compute_bounds_inner(param_ty, &result)
1068 fn compute_bounds_inner(
1071 ast_bounds: &[hir::GenericBound<'_>],
1073 let mut bounds = Bounds::default();
1075 self.add_bounds(param_ty, ast_bounds.iter(), &mut bounds, ty::List::empty());
1081 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1084 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1085 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1086 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1087 #[tracing::instrument(
1089 skip(self, bounds, speculative, dup_bindings, path_span)
1091 fn add_predicates_for_ast_type_binding(
1093 hir_ref_id: hir::HirId,
1094 trait_ref: ty::PolyTraitRef<'tcx>,
1095 binding: &ConvertedBinding<'_, 'tcx>,
1096 bounds: &mut Bounds<'tcx>,
1098 dup_bindings: &mut FxHashMap<DefId, Span>,
1100 ) -> Result<(), ErrorGuaranteed> {
1101 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1102 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1103 // subtle in the event that `T` is defined in a supertrait of
1104 // `SomeTrait`, because in that case we need to upcast.
1106 // That is, consider this case:
1109 // trait SubTrait: SuperTrait<i32> { }
1110 // trait SuperTrait<A> { type T; }
1112 // ... B: SubTrait<T = foo> ...
1115 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
1117 let tcx = self.tcx();
1120 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1121 // Simple case: X is defined in the current trait.
1124 // Otherwise, we have to walk through the supertraits to find
1126 self.one_bound_for_assoc_type(
1127 || traits::supertraits(tcx, trait_ref),
1128 || trait_ref.print_only_trait_path().to_string(),
1131 || match binding.kind {
1132 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1138 let (assoc_ident, def_scope) =
1139 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1141 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1142 // of calling `filter_by_name_and_kind`.
1143 let find_item_of_kind = |kind| {
1144 tcx.associated_items(candidate.def_id())
1145 .filter_by_name_unhygienic(assoc_ident.name)
1146 .find(|i| i.kind == kind && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident)
1148 let assoc_item = find_item_of_kind(ty::AssocKind::Type)
1149 .or_else(|| find_item_of_kind(ty::AssocKind::Const))
1150 .expect("missing associated type");
1152 if !assoc_item.vis.is_accessible_from(def_scope, tcx) {
1153 let kind = match assoc_item.kind {
1154 ty::AssocKind::Type => "type",
1155 ty::AssocKind::Const => "const",
1156 _ => unreachable!(),
1161 &format!("associated {kind} `{}` is private", binding.item_name),
1163 .span_label(binding.span, &format!("private associated {kind}"))
1166 tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None);
1170 .entry(assoc_item.def_id)
1171 .and_modify(|prev_span| {
1172 self.tcx().sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
1174 prev_span: *prev_span,
1175 item_name: binding.item_name,
1176 def_path: tcx.def_path_str(assoc_item.container.id()),
1179 .or_insert(binding.span);
1182 // Include substitutions for generic parameters of associated types
1183 let projection_ty = candidate.map_bound(|trait_ref| {
1184 let ident = Ident::new(assoc_item.name, binding.item_name.span);
1185 let item_segment = hir::PathSegment {
1187 hir_id: Some(binding.hir_id),
1189 args: Some(binding.gen_args),
1193 let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
1202 "add_predicates_for_ast_type_binding: substs for trait-ref and assoc_item: {:?}",
1203 substs_trait_ref_and_assoc_item
1207 item_def_id: assoc_item.def_id,
1208 substs: substs_trait_ref_and_assoc_item,
1213 // Find any late-bound regions declared in `ty` that are not
1214 // declared in the trait-ref or assoc_item. These are not well-formed.
1218 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1219 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1220 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1221 let late_bound_in_trait_ref =
1222 tcx.collect_constrained_late_bound_regions(&projection_ty);
1223 let late_bound_in_ty =
1224 tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty));
1225 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1226 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1228 // FIXME: point at the type params that don't have appropriate lifetimes:
1229 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1230 // ---- ---- ^^^^^^^
1231 self.validate_late_bound_regions(
1232 late_bound_in_trait_ref,
1239 "binding for associated type `{}` references {}, \
1240 which does not appear in the trait input types",
1249 match binding.kind {
1250 ConvertedBindingKind::Equality(term) => {
1251 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1252 // the "projection predicate" for:
1254 // `<T as Iterator>::Item = u32`
1255 let assoc_item_def_id = projection_ty.skip_binder().item_def_id;
1256 let def_kind = tcx.def_kind(assoc_item_def_id);
1257 match (def_kind, term) {
1258 (hir::def::DefKind::AssocTy, ty::Term::Ty(_))
1259 | (hir::def::DefKind::AssocConst, ty::Term::Const(_)) => (),
1261 let got = if let ty::Term::Ty(_) = term { "type" } else { "const" };
1262 let expected = def_kind.descr(assoc_item_def_id);
1266 &format!("mismatch in bind of {expected}, got {got}"),
1269 tcx.def_span(assoc_item_def_id),
1270 &format!("{expected} defined here does not match {got}"),
1275 bounds.projection_bounds.push((
1276 projection_ty.map_bound(|projection_ty| ty::ProjectionPredicate {
1283 ConvertedBindingKind::Constraint(ast_bounds) => {
1284 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1286 // `<T as Iterator>::Item: Debug`
1288 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1289 // parameter to have a skipped binder.
1290 let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
1291 self.add_bounds(param_ty, ast_bounds.iter(), bounds, candidate.bound_vars());
1301 item_segment: &hir::PathSegment<'_>,
1303 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1306 EarlyBinder(self.tcx().at(span).type_of(did)).subst(self.tcx(), substs),
1310 fn conv_object_ty_poly_trait_ref(
1313 trait_bounds: &[hir::PolyTraitRef<'_>],
1314 lifetime: &hir::Lifetime,
1317 let tcx = self.tcx();
1319 let mut bounds = Bounds::default();
1320 let mut potential_assoc_types = Vec::new();
1321 let dummy_self = self.tcx().types.trait_object_dummy_self;
1322 for trait_bound in trait_bounds.iter().rev() {
1323 if let GenericArgCountResult {
1325 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1327 } = self.instantiate_poly_trait_ref(
1328 &trait_bound.trait_ref,
1330 ty::BoundConstness::NotConst,
1335 potential_assoc_types.extend(cur_potential_assoc_types);
1339 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1340 // is used and no 'maybe' bounds are used.
1341 let expanded_traits =
1342 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1343 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) = expanded_traits
1344 .filter(|i| i.trait_ref().self_ty().skip_binder() == dummy_self)
1345 .partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1346 if regular_traits.len() > 1 {
1347 let first_trait = ®ular_traits[0];
1348 let additional_trait = ®ular_traits[1];
1349 let mut err = struct_span_err!(
1351 additional_trait.bottom().1,
1353 "only auto traits can be used as additional traits in a trait object"
1355 additional_trait.label_with_exp_info(
1357 "additional non-auto trait",
1360 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1362 "consider creating a new trait with all of these as supertraits and using that \
1363 trait here instead: `trait NewTrait: {} {{}}`",
1366 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1367 .collect::<Vec<_>>()
1371 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1372 for more information on them, visit \
1373 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1378 if regular_traits.is_empty() && auto_traits.is_empty() {
1379 let trait_alias_span = bounds
1382 .map(|&(trait_ref, _, _)| trait_ref.def_id())
1383 .find(|&trait_ref| tcx.is_trait_alias(trait_ref))
1384 .map(|trait_ref| tcx.def_span(trait_ref));
1385 tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span, trait_alias_span });
1386 return tcx.ty_error();
1389 // Check that there are no gross object safety violations;
1390 // most importantly, that the supertraits don't contain `Self`,
1392 for item in ®ular_traits {
1393 let object_safety_violations =
1394 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1395 if !object_safety_violations.is_empty() {
1396 report_object_safety_error(
1399 item.trait_ref().def_id(),
1400 &object_safety_violations,
1403 return tcx.ty_error();
1407 // Use a `BTreeSet` to keep output in a more consistent order.
1408 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1410 let regular_traits_refs_spans = bounds
1413 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1415 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1416 assert_eq!(constness, ty::BoundConstness::NotConst);
1418 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1420 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1421 obligation.predicate
1424 let bound_predicate = obligation.predicate.kind();
1425 match bound_predicate.skip_binder() {
1426 ty::PredicateKind::Trait(pred) => {
1427 let pred = bound_predicate.rebind(pred);
1428 associated_types.entry(span).or_default().extend(
1429 tcx.associated_items(pred.def_id())
1430 .in_definition_order()
1431 .filter(|item| item.kind == ty::AssocKind::Type)
1432 .map(|item| item.def_id),
1435 ty::PredicateKind::Projection(pred) => {
1436 let pred = bound_predicate.rebind(pred);
1437 // A `Self` within the original bound will be substituted with a
1438 // `trait_object_dummy_self`, so check for that.
1439 let references_self = match pred.skip_binder().term {
1440 ty::Term::Ty(ty) => ty.walk().any(|arg| arg == dummy_self.into()),
1441 ty::Term::Const(c) => c.ty().walk().any(|arg| arg == dummy_self.into()),
1444 // If the projection output contains `Self`, force the user to
1445 // elaborate it explicitly to avoid a lot of complexity.
1447 // The "classically useful" case is the following:
1449 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1454 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1455 // but actually supporting that would "expand" to an infinitely-long type
1456 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1458 // Instead, we force the user to write
1459 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1460 // the discussion in #56288 for alternatives.
1461 if !references_self {
1462 // Include projections defined on supertraits.
1463 bounds.projection_bounds.push((pred, span));
1471 for (projection_bound, _) in &bounds.projection_bounds {
1472 for def_ids in associated_types.values_mut() {
1473 def_ids.remove(&projection_bound.projection_def_id());
1477 self.complain_about_missing_associated_types(
1479 potential_assoc_types,
1483 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1484 // `dyn Trait + Send`.
1485 // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
1487 let mut duplicates = FxHashSet::default();
1488 auto_traits.retain(|i| duplicates.insert(i.trait_ref().def_id()));
1489 debug!("regular_traits: {:?}", regular_traits);
1490 debug!("auto_traits: {:?}", auto_traits);
1492 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1493 let existential_trait_refs = regular_traits.iter().map(|i| {
1494 i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
1495 if trait_ref.self_ty() != dummy_self {
1496 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1497 // which picks up non-supertraits where clauses - but also, the object safety
1498 // completely ignores trait aliases, which could be object safety hazards. We
1499 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1500 // disabled. (#66420)
1501 tcx.sess.delay_span_bug(
1504 "trait_ref_to_existential called on {:?} with non-dummy Self",
1509 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1512 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1513 bound.map_bound(|b| {
1514 if b.projection_ty.self_ty() != dummy_self {
1515 tcx.sess.delay_span_bug(
1517 &format!("trait_ref_to_existential called on {:?} with non-dummy Self", b),
1520 ty::ExistentialProjection::erase_self_ty(tcx, b)
1524 let regular_trait_predicates = existential_trait_refs
1525 .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));
1526 let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
1527 ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
1529 // N.b. principal, projections, auto traits
1530 // FIXME: This is actually wrong with multiple principals in regards to symbol mangling
1531 let mut v = regular_trait_predicates
1533 existential_projections.map(|x| x.map_bound(ty::ExistentialPredicate::Projection)),
1535 .chain(auto_trait_predicates)
1536 .collect::<SmallVec<[_; 8]>>();
1537 v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
1539 let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
1541 // Use explicitly-specified region bound.
1542 let region_bound = if !lifetime.is_elided() {
1543 self.ast_region_to_region(lifetime, None)
1545 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1546 if tcx.named_region(lifetime.hir_id).is_some() {
1547 self.ast_region_to_region(lifetime, None)
1549 self.re_infer(None, span).unwrap_or_else(|| {
1550 let mut err = struct_span_err!(
1554 "the lifetime bound for this object type cannot be deduced \
1555 from context; please supply an explicit bound"
1558 // We will have already emitted an error E0106 complaining about a
1559 // missing named lifetime in `&dyn Trait`, so we elide this one.
1564 tcx.lifetimes.re_static
1569 debug!("region_bound: {:?}", region_bound);
1571 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1572 debug!("trait_object_type: {:?}", ty);
1576 fn report_ambiguous_associated_type(
1582 ) -> ErrorGuaranteed {
1583 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1587 .confused_type_with_std_module
1589 .any(|full_span| full_span.contains(span))
1591 err.span_suggestion(
1592 span.shrink_to_lo(),
1593 "you are looking for the module in `std`, not the primitive type",
1595 Applicability::MachineApplicable,
1598 err.span_suggestion(
1600 "use fully-qualified syntax",
1601 format!("<{} as {}>::{}", type_str, trait_str, name),
1602 Applicability::HasPlaceholders,
1608 // Search for a bound on a type parameter which includes the associated item
1609 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1610 // This function will fail if there are no suitable bounds or there is
1612 fn find_bound_for_assoc_item(
1614 ty_param_def_id: LocalDefId,
1617 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed> {
1618 let tcx = self.tcx();
1621 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1622 ty_param_def_id, assoc_name, span,
1625 let predicates = &self
1626 .get_type_parameter_bounds(span, ty_param_def_id.to_def_id(), assoc_name)
1629 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1631 let param_name = tcx.hir().ty_param_name(ty_param_def_id);
1632 self.one_bound_for_assoc_type(
1634 traits::transitive_bounds_that_define_assoc_type(
1636 predicates.iter().filter_map(|(p, _)| {
1637 Some(p.to_opt_poly_trait_pred()?.map_bound(|t| t.trait_ref))
1642 || param_name.to_string(),
1649 // Checks that `bounds` contains exactly one element and reports appropriate
1650 // errors otherwise.
1651 fn one_bound_for_assoc_type<I>(
1653 all_candidates: impl Fn() -> I,
1654 ty_param_name: impl Fn() -> String,
1657 is_equality: impl Fn() -> Option<String>,
1658 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorGuaranteed>
1660 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1662 let mut matching_candidates = all_candidates()
1663 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1664 let mut const_candidates = all_candidates()
1665 .filter(|r| self.trait_defines_associated_const_named(r.def_id(), assoc_name));
1667 let (bound, next_cand) = match (matching_candidates.next(), const_candidates.next()) {
1668 (Some(bound), _) => (bound, matching_candidates.next()),
1669 (None, Some(bound)) => (bound, const_candidates.next()),
1671 let reported = self.complain_about_assoc_type_not_found(
1677 return Err(reported);
1680 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1682 if let Some(bound2) = next_cand {
1683 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1685 let is_equality = is_equality();
1686 let bounds = IntoIterator::into_iter([bound, bound2]).chain(matching_candidates);
1687 let mut err = if is_equality.is_some() {
1688 // More specific Error Index entry.
1693 "ambiguous associated type `{}` in bounds of `{}`",
1702 "ambiguous associated type `{}` in bounds of `{}`",
1707 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1709 let mut where_bounds = vec![];
1710 for bound in bounds {
1711 let bound_id = bound.def_id();
1712 let bound_span = self
1714 .associated_items(bound_id)
1715 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1716 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1718 if let Some(bound_span) = bound_span {
1722 "ambiguous `{}` from `{}`",
1724 bound.print_only_trait_path(),
1727 if let Some(constraint) = &is_equality {
1728 where_bounds.push(format!(
1729 " T: {trait}::{assoc} = {constraint}",
1730 trait=bound.print_only_trait_path(),
1732 constraint=constraint,
1735 err.span_suggestion_verbose(
1736 span.with_hi(assoc_name.span.lo()),
1737 "use fully qualified syntax to disambiguate",
1741 bound.print_only_trait_path(),
1743 Applicability::MaybeIncorrect,
1748 "associated type `{}` could derive from `{}`",
1750 bound.print_only_trait_path(),
1754 if !where_bounds.is_empty() {
1756 "consider introducing a new type parameter `T` and adding `where` constraints:\
1757 \n where\n T: {},\n{}",
1759 where_bounds.join(",\n"),
1762 let reported = err.emit();
1763 if !where_bounds.is_empty() {
1764 return Err(reported);
1771 // Create a type from a path to an associated type.
1772 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1773 // and item_segment is the path segment for `D`. We return a type and a def for
1775 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1776 // parameter or `Self`.
1777 // NOTE: When this function starts resolving `Trait::AssocTy` successfully
1778 // it should also start reporting the `BARE_TRAIT_OBJECTS` lint.
1779 pub fn associated_path_to_ty(
1781 hir_ref_id: hir::HirId,
1784 qself: &hir::Ty<'_>,
1785 assoc_segment: &hir::PathSegment<'_>,
1786 permit_variants: bool,
1787 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
1788 let tcx = self.tcx();
1789 let assoc_ident = assoc_segment.ident;
1790 let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
1796 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1798 // Check if we have an enum variant.
1799 let mut variant_resolution = None;
1800 if let ty::Adt(adt_def, _) = qself_ty.kind() {
1801 if adt_def.is_enum() {
1802 let variant_def = adt_def
1805 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident(tcx), adt_def.did()));
1806 if let Some(variant_def) = variant_def {
1807 if permit_variants {
1808 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span, None);
1809 self.prohibit_generics(slice::from_ref(assoc_segment).iter(), |err| {
1810 err.note("enum variants can't have type parameters");
1811 let type_name = tcx.item_name(adt_def.did());
1813 "you might have meant to specity type parameters on enum \
1816 let Some(args) = assoc_segment.args else { return; };
1817 // Get the span of the generics args *including* the leading `::`.
1818 let args_span = assoc_segment.ident.span.shrink_to_hi().to(args.span_ext);
1819 if tcx.generics_of(adt_def.did()).count() == 0 {
1820 // FIXME(estebank): we could also verify that the arguments being
1821 // work for the `enum`, instead of just looking if it takes *any*.
1822 err.span_suggestion_verbose(
1824 &format!("{type_name} doesn't have generic parameters"),
1826 Applicability::MachineApplicable,
1830 let Ok(snippet) = tcx.sess.source_map().span_to_snippet(args_span) else {
1834 let (qself_sugg_span, is_self) = if let hir::TyKind::Path(
1835 hir::QPath::Resolved(_, ref path)
1837 // If the path segment already has type params, we want to overwrite
1839 match &path.segments[..] {
1840 // `segment` is the previous to last element on the path,
1841 // which would normally be the `enum` itself, while the last
1842 // `_` `PathSegment` corresponds to the variant.
1843 [.., hir::PathSegment {
1846 res: Some(Res::Def(DefKind::Enum, _)),
1849 // We need to include the `::` in `Type::Variant::<Args>`
1850 // to point the span to `::<Args>`, not just `<Args>`.
1851 ident.span.shrink_to_hi().to(args.map_or(
1852 ident.span.shrink_to_hi(),
1857 // We need to include the `::` in `Type::Variant::<Args>`
1858 // to point the span to `::<Args>`, not just `<Args>`.
1859 segment.ident.span.shrink_to_hi().to(segment.args.map_or(
1860 segment.ident.span.shrink_to_hi(),
1862 kw::SelfUpper == segment.ident.name,
1873 let suggestion = vec![
1875 // Account for people writing `Self::Variant::<Args>`, where
1876 // `Self` is the enum, and suggest replacing `Self` with the
1877 // appropriate type: `Type::<Args>::Variant`.
1878 (qself.span, format!("{type_name}{snippet}"))
1880 (qself_sugg_span, snippet)
1882 (args_span, String::new()),
1884 err.multipart_suggestion_verbose(
1887 Applicability::MaybeIncorrect,
1890 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1892 variant_resolution = Some(variant_def.def_id);
1898 // Find the type of the associated item, and the trait where the associated
1899 // item is declared.
1900 let bound = match (&qself_ty.kind(), qself_res) {
1901 (_, Res::SelfTy { trait_: Some(_), alias_to: Some((impl_def_id, _)) }) => {
1902 // `Self` in an impl of a trait -- we have a concrete self type and a
1904 let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) else {
1905 // A cycle error occurred, most likely.
1906 let guar = tcx.sess.delay_span_bug(span, "expected cycle error");
1910 self.one_bound_for_assoc_type(
1911 || traits::supertraits(tcx, ty::Binder::dummy(trait_ref)),
1912 || "Self".to_string(),
1920 Res::SelfTy { trait_: Some(param_did), alias_to: None }
1921 | Res::Def(DefKind::TyParam, param_did),
1922 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
1924 let reported = if variant_resolution.is_some() {
1925 // Variant in type position
1926 let msg = format!("expected type, found variant `{}`", assoc_ident);
1927 tcx.sess.span_err(span, &msg)
1928 } else if qself_ty.is_enum() {
1929 let mut err = struct_span_err!(
1933 "no variant named `{}` found for enum `{}`",
1938 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1939 if let Some(suggested_name) = find_best_match_for_name(
1943 .map(|variant| variant.name)
1944 .collect::<Vec<Symbol>>(),
1948 err.span_suggestion(
1950 "there is a variant with a similar name",
1952 Applicability::MaybeIncorrect,
1957 format!("variant not found in `{}`", qself_ty),
1961 if let Some(sp) = tcx.hir().span_if_local(adt_def.did()) {
1962 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1966 } else if let Some(reported) = qself_ty.error_reported() {
1969 // Don't print `TyErr` to the user.
1970 self.report_ambiguous_associated_type(
1972 &qself_ty.to_string(),
1977 return Err(reported);
1981 let trait_did = bound.def_id();
1982 let (assoc_ident, def_scope) =
1983 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1985 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1986 // of calling `filter_by_name_and_kind`.
1987 let item = tcx.associated_items(trait_did).in_definition_order().find(|i| {
1988 i.kind.namespace() == Namespace::TypeNS
1989 && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident
1991 // Assume that if it's not matched, there must be a const defined with the same name
1992 // but it was used in a type position.
1993 let Some(item) = item else {
1994 let msg = format!("found associated const `{assoc_ident}` when type was expected");
1995 let guar = tcx.sess.struct_span_err(span, &msg).emit();
1999 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2000 let ty = self.normalize_ty(span, ty);
2002 let kind = DefKind::AssocTy;
2003 if !item.vis.is_accessible_from(def_scope, tcx) {
2004 let kind = kind.descr(item.def_id);
2005 let msg = format!("{} `{}` is private", kind, assoc_ident);
2007 .struct_span_err(span, &msg)
2008 .span_label(span, &format!("private {}", kind))
2011 tcx.check_stability(item.def_id, Some(hir_ref_id), span, None);
2013 if let Some(variant_def_id) = variant_resolution {
2014 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2015 let mut err = lint.build("ambiguous associated item");
2016 let mut could_refer_to = |kind: DefKind, def_id, also| {
2017 let note_msg = format!(
2018 "`{}` could{} refer to the {} defined here",
2023 err.span_note(tcx.def_span(def_id), ¬e_msg);
2026 could_refer_to(DefKind::Variant, variant_def_id, "");
2027 could_refer_to(kind, item.def_id, " also");
2029 err.span_suggestion(
2031 "use fully-qualified syntax",
2032 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2033 Applicability::MachineApplicable,
2039 Ok((ty, kind, item.def_id))
2045 opt_self_ty: Option<Ty<'tcx>>,
2047 trait_segment: &hir::PathSegment<'_>,
2048 item_segment: &hir::PathSegment<'_>,
2050 let tcx = self.tcx();
2052 let trait_def_id = tcx.parent(item_def_id);
2054 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2056 let Some(self_ty) = opt_self_ty else {
2057 let path_str = tcx.def_path_str(trait_def_id);
2059 let def_id = self.item_def_id();
2061 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2063 let parent_def_id = def_id
2064 .and_then(|def_id| {
2065 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
2067 .map(|hir_id| tcx.hir().get_parent_item(hir_id).to_def_id());
2069 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2071 // If the trait in segment is the same as the trait defining the item,
2072 // use the `<Self as ..>` syntax in the error.
2073 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2074 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2076 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2082 self.report_ambiguous_associated_type(
2086 item_segment.ident.name,
2088 return tcx.ty_error();
2091 debug!("qpath_to_ty: self_type={:?}", self_ty);
2094 self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment, false);
2096 let item_substs = self.create_substs_for_associated_item(
2104 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2106 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2109 pub fn prohibit_generics<'a>(
2111 segments: impl Iterator<Item = &'a hir::PathSegment<'a>> + Clone,
2112 extend: impl Fn(&mut DiagnosticBuilder<'tcx, ErrorGuaranteed>),
2114 let args = segments.clone().flat_map(|segment| segment.args().args);
2116 let (lt, ty, ct, inf) =
2117 args.clone().fold((false, false, false, false), |(lt, ty, ct, inf), arg| match arg {
2118 hir::GenericArg::Lifetime(_) => (true, ty, ct, inf),
2119 hir::GenericArg::Type(_) => (lt, true, ct, inf),
2120 hir::GenericArg::Const(_) => (lt, ty, true, inf),
2121 hir::GenericArg::Infer(_) => (lt, ty, ct, true),
2123 let mut emitted = false;
2124 if lt || ty || ct || inf {
2125 let types_and_spans: Vec<_> = segments
2127 .flat_map(|segment| {
2128 segment.res.and_then(|res| {
2129 if segment.args().args.is_empty() {
2134 Res::PrimTy(ty) => format!("{} `{}`", res.descr(), ty.name()),
2136 if let Some(name) = self.tcx().opt_item_name(def_id) => {
2137 format!("{} `{name}`", res.descr())
2139 Res::Err => "this type".to_string(),
2140 _ => res.descr().to_string(),
2148 let this_type = match &types_and_spans[..] {
2149 [.., _, (last, _)] => format!(
2151 types_and_spans[..types_and_spans.len() - 1]
2153 .map(|(x, _)| x.as_str())
2155 .collect::<String>()
2157 [(only, _)] => only.to_string(),
2158 [] => "this type".to_string(),
2161 let arg_spans: Vec<Span> = args.map(|arg| arg.span()).collect();
2163 let mut kinds = Vec::with_capacity(4);
2165 kinds.push("lifetime");
2171 kinds.push("const");
2174 kinds.push("generic");
2176 let (kind, s) = match kinds[..] {
2180 kinds[..kinds.len() - 1]
2184 .collect::<String>()
2188 [only] => (format!("{only}"), ""),
2189 [] => unreachable!(),
2191 let last_span = *arg_spans.last().unwrap();
2192 let span: MultiSpan = arg_spans.into();
2193 let mut err = struct_span_err!(
2197 "{kind} arguments are not allowed on {this_type}",
2199 err.span_label(last_span, format!("{kind} argument{s} not allowed"));
2200 for (what, span) in types_and_spans {
2201 err.span_label(span, format!("not allowed on {what}"));
2208 for segment in segments {
2209 // Only emit the first error to avoid overloading the user with error messages.
2210 if let [binding, ..] = segment.args().bindings {
2211 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2218 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2219 pub fn def_ids_for_value_path_segments(
2221 segments: &[hir::PathSegment<'_>],
2222 self_ty: Option<Ty<'tcx>>,
2226 // We need to extract the type parameters supplied by the user in
2227 // the path `path`. Due to the current setup, this is a bit of a
2228 // tricky-process; the problem is that resolve only tells us the
2229 // end-point of the path resolution, and not the intermediate steps.
2230 // Luckily, we can (at least for now) deduce the intermediate steps
2231 // just from the end-point.
2233 // There are basically five cases to consider:
2235 // 1. Reference to a constructor of a struct:
2237 // struct Foo<T>(...)
2239 // In this case, the parameters are declared in the type space.
2241 // 2. Reference to a constructor of an enum variant:
2243 // enum E<T> { Foo(...) }
2245 // In this case, the parameters are defined in the type space,
2246 // but may be specified either on the type or the variant.
2248 // 3. Reference to a fn item or a free constant:
2252 // In this case, the path will again always have the form
2253 // `a::b::foo::<T>` where only the final segment should have
2254 // type parameters. However, in this case, those parameters are
2255 // declared on a value, and hence are in the `FnSpace`.
2257 // 4. Reference to a method or an associated constant:
2259 // impl<A> SomeStruct<A> {
2263 // Here we can have a path like
2264 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2265 // may appear in two places. The penultimate segment,
2266 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2267 // final segment, `foo::<B>` contains parameters in fn space.
2269 // The first step then is to categorize the segments appropriately.
2271 let tcx = self.tcx();
2273 assert!(!segments.is_empty());
2274 let last = segments.len() - 1;
2276 let mut path_segs = vec![];
2279 // Case 1. Reference to a struct constructor.
2280 DefKind::Ctor(CtorOf::Struct, ..) => {
2281 // Everything but the final segment should have no
2282 // parameters at all.
2283 let generics = tcx.generics_of(def_id);
2284 // Variant and struct constructors use the
2285 // generics of their parent type definition.
2286 let generics_def_id = generics.parent.unwrap_or(def_id);
2287 path_segs.push(PathSeg(generics_def_id, last));
2290 // Case 2. Reference to a variant constructor.
2291 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2292 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2293 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2294 debug_assert!(adt_def.is_enum());
2295 (adt_def.did(), last)
2296 } else if last >= 1 && segments[last - 1].args.is_some() {
2297 // Everything but the penultimate segment should have no
2298 // parameters at all.
2299 let mut def_id = def_id;
2301 // `DefKind::Ctor` -> `DefKind::Variant`
2302 if let DefKind::Ctor(..) = kind {
2303 def_id = tcx.parent(def_id);
2306 // `DefKind::Variant` -> `DefKind::Enum`
2307 let enum_def_id = tcx.parent(def_id);
2308 (enum_def_id, last - 1)
2310 // FIXME: lint here recommending `Enum::<...>::Variant` form
2311 // instead of `Enum::Variant::<...>` form.
2313 // Everything but the final segment should have no
2314 // parameters at all.
2315 let generics = tcx.generics_of(def_id);
2316 // Variant and struct constructors use the
2317 // generics of their parent type definition.
2318 (generics.parent.unwrap_or(def_id), last)
2320 path_segs.push(PathSeg(generics_def_id, index));
2323 // Case 3. Reference to a top-level value.
2324 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static(_) => {
2325 path_segs.push(PathSeg(def_id, last));
2328 // Case 4. Reference to a method or associated const.
2329 DefKind::AssocFn | DefKind::AssocConst => {
2330 if segments.len() >= 2 {
2331 let generics = tcx.generics_of(def_id);
2332 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2334 path_segs.push(PathSeg(def_id, last));
2337 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2340 debug!("path_segs = {:?}", path_segs);
2345 // Check a type `Path` and convert it to a `Ty`.
2348 opt_self_ty: Option<Ty<'tcx>>,
2349 path: &hir::Path<'_>,
2350 permit_variants: bool,
2352 let tcx = self.tcx();
2355 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2356 path.res, opt_self_ty, path.segments
2359 let span = path.span;
2361 Res::Def(DefKind::OpaqueTy, did) => {
2362 // Check for desugared `impl Trait`.
2363 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2364 let item_segment = path.segments.split_last().unwrap();
2365 self.prohibit_generics(item_segment.1.iter(), |err| {
2366 err.note("`impl Trait` types can't have type parameters");
2368 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2369 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2376 | DefKind::ForeignTy,
2379 assert_eq!(opt_self_ty, None);
2380 self.prohibit_generics(path.segments.split_last().unwrap().1.iter(), |_| {});
2381 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2383 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2384 // Convert "variant type" as if it were a real type.
2385 // The resulting `Ty` is type of the variant's enum for now.
2386 assert_eq!(opt_self_ty, None);
2389 self.def_ids_for_value_path_segments(path.segments, None, kind, def_id);
2390 let generic_segs: FxHashSet<_> =
2391 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2392 self.prohibit_generics(
2393 path.segments.iter().enumerate().filter_map(|(index, seg)| {
2394 if !generic_segs.contains(&index) { Some(seg) } else { None }
2397 err.note("enum variants can't have type parameters");
2401 let PathSeg(def_id, index) = path_segs.last().unwrap();
2402 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2404 Res::Def(DefKind::TyParam, def_id) => {
2405 assert_eq!(opt_self_ty, None);
2406 self.prohibit_generics(path.segments.iter(), |err| {
2407 if let Some(span) = tcx.def_ident_span(def_id) {
2408 let name = tcx.item_name(def_id);
2409 err.span_note(span, &format!("type parameter `{name}` defined here"));
2413 let def_id = def_id.expect_local();
2414 let item_def_id = tcx.hir().ty_param_owner(def_id);
2415 let generics = tcx.generics_of(item_def_id);
2416 let index = generics.param_def_id_to_index[&def_id.to_def_id()];
2417 tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id))
2419 Res::SelfTy { trait_: Some(_), alias_to: None } => {
2420 // `Self` in trait or type alias.
2421 assert_eq!(opt_self_ty, None);
2422 self.prohibit_generics(path.segments.iter(), |err| {
2423 if let [hir::PathSegment { args: Some(args), ident, .. }] = &path.segments[..] {
2424 err.span_suggestion_verbose(
2425 ident.span.shrink_to_hi().to(args.span_ext),
2426 "the `Self` type doesn't accept type parameters",
2428 Applicability::MaybeIncorrect,
2432 tcx.types.self_param
2434 Res::SelfTy { trait_: _, alias_to: Some((def_id, forbid_generic)) } => {
2435 // `Self` in impl (we know the concrete type).
2436 assert_eq!(opt_self_ty, None);
2437 // Try to evaluate any array length constants.
2438 let ty = tcx.at(span).type_of(def_id);
2439 let span_of_impl = tcx.span_of_impl(def_id);
2440 self.prohibit_generics(path.segments.iter(), |err| {
2441 let def_id = match *ty.kind() {
2442 ty::Adt(self_def, _) => self_def.did(),
2446 let type_name = tcx.item_name(def_id);
2447 let span_of_ty = tcx.def_ident_span(def_id);
2448 let generics = tcx.generics_of(def_id).count();
2450 let msg = format!("`Self` is of type `{ty}`");
2451 if let (Ok(i_sp), Some(t_sp)) = (span_of_impl, span_of_ty) {
2452 let mut span: MultiSpan = vec![t_sp].into();
2453 span.push_span_label(
2455 &format!("`Self` is on type `{type_name}` in this `impl`"),
2457 let mut postfix = "";
2459 postfix = ", which doesn't have generic parameters";
2461 span.push_span_label(
2463 &format!("`Self` corresponds to this type{postfix}"),
2465 err.span_note(span, &msg);
2469 for segment in path.segments {
2470 if let Some(args) = segment.args && segment.ident.name == kw::SelfUpper {
2472 // FIXME(estebank): we could also verify that the arguments being
2473 // work for the `enum`, instead of just looking if it takes *any*.
2474 err.span_suggestion_verbose(
2475 segment.ident.span.shrink_to_hi().to(args.span_ext),
2476 "the `Self` type doesn't accept type parameters",
2478 Applicability::MachineApplicable,
2482 err.span_suggestion_verbose(
2485 "the `Self` type doesn't accept type parameters, use the \
2486 concrete type's name `{type_name}` instead if you want to \
2487 specify its type parameters"
2490 Applicability::MaybeIncorrect,
2496 // HACK(min_const_generics): Forbid generic `Self` types
2497 // here as we can't easily do that during nameres.
2499 // We do this before normalization as we otherwise allow
2501 // trait AlwaysApplicable { type Assoc; }
2502 // impl<T: ?Sized> AlwaysApplicable for T { type Assoc = usize; }
2504 // trait BindsParam<T> {
2507 // impl<T> BindsParam<T> for <T as AlwaysApplicable>::Assoc {
2508 // type ArrayTy = [u8; Self::MAX];
2511 // Note that the normalization happens in the param env of
2512 // the anon const, which is empty. This is why the
2513 // `AlwaysApplicable` impl needs a `T: ?Sized` bound for
2514 // this to compile if we were to normalize here.
2515 if forbid_generic && ty.needs_subst() {
2516 let mut err = tcx.sess.struct_span_err(
2518 "generic `Self` types are currently not permitted in anonymous constants",
2520 if let Some(hir::Node::Item(&hir::Item {
2521 kind: hir::ItemKind::Impl(ref impl_),
2523 })) = tcx.hir().get_if_local(def_id)
2525 err.span_note(impl_.self_ty.span, "not a concrete type");
2530 self.normalize_ty(span, ty)
2533 Res::Def(DefKind::AssocTy, def_id) => {
2534 debug_assert!(path.segments.len() >= 2);
2535 self.prohibit_generics(path.segments[..path.segments.len() - 2].iter(), |_| {});
2540 &path.segments[path.segments.len() - 2],
2541 path.segments.last().unwrap(),
2544 Res::PrimTy(prim_ty) => {
2545 assert_eq!(opt_self_ty, None);
2546 self.prohibit_generics(path.segments.iter(), |err| {
2547 let name = prim_ty.name_str();
2548 for segment in path.segments {
2549 if let Some(args) = segment.args {
2550 err.span_suggestion_verbose(
2551 segment.ident.span.shrink_to_hi().to(args.span_ext),
2552 &format!("primitive type `{name}` doesn't have generic parameters"),
2554 Applicability::MaybeIncorrect,
2560 hir::PrimTy::Bool => tcx.types.bool,
2561 hir::PrimTy::Char => tcx.types.char,
2562 hir::PrimTy::Int(it) => tcx.mk_mach_int(ty::int_ty(it)),
2563 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(ty::uint_ty(uit)),
2564 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ty::float_ty(ft)),
2565 hir::PrimTy::Str => tcx.types.str_,
2569 self.set_tainted_by_errors();
2570 self.tcx().ty_error()
2572 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2576 /// Parses the programmer's textual representation of a type into our
2577 /// internal notion of a type.
2578 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2579 self.ast_ty_to_ty_inner(ast_ty, false, false)
2582 /// Parses the programmer's textual representation of a type into our
2583 /// internal notion of a type. This is meant to be used within a path.
2584 pub fn ast_ty_to_ty_in_path(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2585 self.ast_ty_to_ty_inner(ast_ty, false, true)
2588 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2589 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2590 #[tracing::instrument(level = "debug", skip(self))]
2591 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool, in_path: bool) -> Ty<'tcx> {
2592 let tcx = self.tcx();
2594 let result_ty = match ast_ty.kind {
2595 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
2596 hir::TyKind::Ptr(ref mt) => {
2597 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
2599 hir::TyKind::Rptr(ref region, ref mt) => {
2600 let r = self.ast_region_to_region(region, None);
2602 let t = self.ast_ty_to_ty_inner(mt.ty, true, false);
2603 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2605 hir::TyKind::Never => tcx.types.never,
2606 hir::TyKind::Tup(fields) => tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(t))),
2607 hir::TyKind::BareFn(bf) => {
2608 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
2610 tcx.mk_fn_ptr(self.ty_of_fn(
2619 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
2620 self.maybe_lint_bare_trait(ast_ty, in_path);
2621 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed)
2623 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2624 debug!(?maybe_qself, ?path);
2625 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2626 self.res_to_ty(opt_self_ty, path, false)
2628 hir::TyKind::OpaqueDef(item_id, lifetimes) => {
2629 let opaque_ty = tcx.hir().item(item_id);
2630 let def_id = item_id.def_id.to_def_id();
2632 match opaque_ty.kind {
2633 hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
2634 self.impl_trait_ty_to_ty(def_id, lifetimes, origin)
2636 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2639 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2640 debug!(?qself, ?segment);
2641 let ty = self.ast_ty_to_ty_inner(qself, false, true);
2642 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, qself, segment, false)
2643 .map(|(ty, _, _)| ty)
2644 .unwrap_or_else(|_| tcx.ty_error())
2646 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
2647 let def_id = tcx.require_lang_item(lang_item, Some(span));
2648 let (substs, _) = self.create_substs_for_ast_path(
2652 &hir::PathSegment::invalid(),
2653 &GenericArgs::none(),
2657 EarlyBinder(self.normalize_ty(span, tcx.at(span).type_of(def_id)))
2660 hir::TyKind::Array(ref ty, ref length) => {
2661 let length = match length {
2662 &hir::ArrayLen::Infer(_, span) => self.ct_infer(tcx.types.usize, None, span),
2663 hir::ArrayLen::Body(constant) => {
2664 let length_def_id = tcx.hir().local_def_id(constant.hir_id);
2665 ty::Const::from_anon_const(tcx, length_def_id)
2669 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(ty), length));
2670 self.normalize_ty(ast_ty.span, array_ty)
2672 hir::TyKind::Typeof(ref e) => {
2673 let ty = tcx.type_of(tcx.hir().local_def_id(e.hir_id));
2674 let span = ast_ty.span;
2675 tcx.sess.emit_err(TypeofReservedKeywordUsed {
2678 opt_sugg: Some((span, Applicability::MachineApplicable))
2679 .filter(|_| ty.is_suggestable(tcx)),
2684 hir::TyKind::Infer => {
2685 // Infer also appears as the type of arguments or return
2686 // values in an ExprKind::Closure, or as
2687 // the type of local variables. Both of these cases are
2688 // handled specially and will not descend into this routine.
2689 self.ty_infer(None, ast_ty.span)
2691 hir::TyKind::Err => tcx.ty_error(),
2696 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2700 fn impl_trait_ty_to_ty(
2703 lifetimes: &[hir::GenericArg<'_>],
2704 origin: OpaqueTyOrigin,
2706 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2707 let tcx = self.tcx();
2709 let generics = tcx.generics_of(def_id);
2711 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2712 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2713 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2714 // Our own parameters are the resolved lifetimes.
2715 if let GenericParamDefKind::Lifetime = param.kind {
2716 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2717 self.ast_region_to_region(lifetime, None).into()
2726 // For RPIT (return position impl trait), only lifetimes
2727 // mentioned in the impl Trait predicate are captured by
2728 // the opaque type, so the lifetime parameters from the
2729 // parent item need to be replaced with `'static`.
2731 // For `impl Trait` in the types of statics, constants,
2732 // locals and type aliases. These capture all parent
2733 // lifetimes, so they can use their identity subst.
2734 GenericParamDefKind::Lifetime
2737 hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..)
2740 tcx.lifetimes.re_static.into()
2742 _ => tcx.mk_param_from_def(param),
2746 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2748 let ty = tcx.mk_opaque(def_id, substs);
2749 debug!("impl_trait_ty_to_ty: {}", ty);
2753 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2755 hir::TyKind::Infer if expected_ty.is_some() => {
2756 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2757 expected_ty.unwrap()
2759 _ => self.ast_ty_to_ty(ty),
2766 unsafety: hir::Unsafety,
2768 decl: &hir::FnDecl<'_>,
2769 generics: Option<&hir::Generics<'_>>,
2770 hir_ty: Option<&hir::Ty<'_>>,
2771 ) -> ty::PolyFnSig<'tcx> {
2774 let tcx = self.tcx();
2775 let bound_vars = tcx.late_bound_vars(hir_id);
2776 debug!(?bound_vars);
2778 // We proactively collect all the inferred type params to emit a single error per fn def.
2779 let mut visitor = HirPlaceholderCollector::default();
2780 let mut infer_replacements = vec![];
2782 if let Some(generics) = generics {
2783 walk_generics(&mut visitor, generics);
2786 let input_tys: Vec<_> = decl
2791 if let hir::TyKind::Infer = a.kind && !self.allow_ty_infer() {
2792 if let Some(suggested_ty) =
2793 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, Some(i))
2795 infer_replacements.push((a.span, suggested_ty.to_string()));
2796 return suggested_ty;
2800 // Only visit the type looking for `_` if we didn't fix the type above
2801 visitor.visit_ty(a);
2802 self.ty_of_arg(a, None)
2806 let output_ty = match decl.output {
2807 hir::FnRetTy::Return(output) => {
2808 if let hir::TyKind::Infer = output.kind
2809 && !self.allow_ty_infer()
2810 && let Some(suggested_ty) =
2811 self.suggest_trait_fn_ty_for_impl_fn_infer(hir_id, None)
2813 infer_replacements.push((output.span, suggested_ty.to_string()));
2816 visitor.visit_ty(output);
2817 self.ast_ty_to_ty(output)
2820 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2823 debug!("ty_of_fn: output_ty={:?}", output_ty);
2825 let fn_ty = tcx.mk_fn_sig(input_tys.into_iter(), output_ty, decl.c_variadic, unsafety, abi);
2826 let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
2828 if !self.allow_ty_infer() && !(visitor.0.is_empty() && infer_replacements.is_empty()) {
2829 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2830 // only want to emit an error complaining about them if infer types (`_`) are not
2831 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2832 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2834 let mut diag = crate::collect::placeholder_type_error_diag(
2838 infer_replacements.iter().map(|(s, _)| *s).collect(),
2844 if !infer_replacements.is_empty() {
2845 diag.multipart_suggestion(&format!(
2846 "try replacing `_` with the type{} in the corresponding trait method signature",
2847 rustc_errors::pluralize!(infer_replacements.len()),
2848 ), infer_replacements, Applicability::MachineApplicable);
2854 // Find any late-bound regions declared in return type that do
2855 // not appear in the arguments. These are not well-formed.
2858 // for<'a> fn() -> &'a str <-- 'a is bad
2859 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2860 let inputs = bare_fn_ty.inputs();
2861 let late_bound_in_args =
2862 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2863 let output = bare_fn_ty.output();
2864 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2866 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
2871 "return type references {}, which is not constrained by the fn input types",
2879 /// Given a fn_hir_id for a impl function, suggest the type that is found on the
2880 /// corresponding function in the trait that the impl implements, if it exists.
2881 /// If arg_idx is Some, then it corresponds to an input type index, otherwise it
2882 /// corresponds to the return type.
2883 fn suggest_trait_fn_ty_for_impl_fn_infer(
2885 fn_hir_id: hir::HirId,
2886 arg_idx: Option<usize>,
2887 ) -> Option<Ty<'tcx>> {
2888 let tcx = self.tcx();
2889 let hir = tcx.hir();
2891 let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), ident, .. }) =
2892 hir.get(fn_hir_id) else { return None };
2893 let hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(i), .. }) =
2894 hir.get(hir.get_parent_node(fn_hir_id)) else { bug!("ImplItem should have Impl parent") };
2897 self.instantiate_mono_trait_ref(i.of_trait.as_ref()?, self.ast_ty_to_ty(i.self_ty));
2899 let assoc = tcx.associated_items(trait_ref.def_id).find_by_name_and_kind(
2906 let fn_sig = tcx.bound_fn_sig(assoc.def_id).subst(
2908 trait_ref.substs.extend_to(tcx, assoc.def_id, |param, _| tcx.mk_param_from_def(param)),
2911 let ty = if let Some(arg_idx) = arg_idx { fn_sig.input(arg_idx) } else { fn_sig.output() };
2913 Some(tcx.liberate_late_bound_regions(fn_hir_id.expect_owner().to_def_id(), ty))
2916 fn validate_late_bound_regions(
2918 constrained_regions: FxHashSet<ty::BoundRegionKind>,
2919 referenced_regions: FxHashSet<ty::BoundRegionKind>,
2920 generate_err: impl Fn(&str) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>,
2922 for br in referenced_regions.difference(&constrained_regions) {
2923 let br_name = match *br {
2924 ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) | ty::BrEnv => {
2925 "an anonymous lifetime".to_string()
2927 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
2930 let mut err = generate_err(&br_name);
2932 if let ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(_) = *br {
2933 // The only way for an anonymous lifetime to wind up
2934 // in the return type but **also** be unconstrained is
2935 // if it only appears in "associated types" in the
2936 // input. See #47511 and #62200 for examples. In this case,
2937 // though we can easily give a hint that ought to be
2940 "lifetimes appearing in an associated type are not considered constrained",
2948 /// Given the bounds on an object, determines what single region bound (if any) we can
2949 /// use to summarize this type. The basic idea is that we will use the bound the user
2950 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2951 /// for region bounds. It may be that we can derive no bound at all, in which case
2952 /// we return `None`.
2953 fn compute_object_lifetime_bound(
2956 existential_predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
2957 ) -> Option<ty::Region<'tcx>> // if None, use the default
2959 let tcx = self.tcx();
2961 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2963 // No explicit region bound specified. Therefore, examine trait
2964 // bounds and see if we can derive region bounds from those.
2965 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2967 // If there are no derived region bounds, then report back that we
2968 // can find no region bound. The caller will use the default.
2969 if derived_region_bounds.is_empty() {
2973 // If any of the derived region bounds are 'static, that is always
2975 if derived_region_bounds.iter().any(|r| r.is_static()) {
2976 return Some(tcx.lifetimes.re_static);
2979 // Determine whether there is exactly one unique region in the set
2980 // of derived region bounds. If so, use that. Otherwise, report an
2982 let r = derived_region_bounds[0];
2983 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2984 tcx.sess.emit_err(AmbiguousLifetimeBound { span });
2989 /// Make sure that we are in the condition to suggest the blanket implementation.
2990 fn maybe_lint_blanket_trait_impl<T: rustc_errors::EmissionGuarantee>(
2992 self_ty: &hir::Ty<'_>,
2993 diag: &mut DiagnosticBuilder<'_, T>,
2995 let tcx = self.tcx();
2996 let parent_id = tcx.hir().get_parent_item(self_ty.hir_id);
2997 if let hir::Node::Item(hir::Item {
2999 hir::ItemKind::Impl(hir::Impl {
3000 self_ty: impl_self_ty, of_trait: Some(of_trait_ref), generics, ..
3003 }) = tcx.hir().get_by_def_id(parent_id) && self_ty.hir_id == impl_self_ty.hir_id
3005 if !of_trait_ref.trait_def_id().map_or(false, |def_id| def_id.is_local()) {
3008 let of_trait_span = of_trait_ref.path.span;
3009 // make sure that we are not calling unwrap to abort during the compilation
3010 let Ok(impl_trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else { return; };
3011 let Ok(of_trait_name) = tcx.sess.source_map().span_to_snippet(of_trait_span) else { return; };
3012 // check if the trait has generics, to make a correct suggestion
3013 let param_name = generics.params.next_type_param_name(None);
3015 let add_generic_sugg = if let Some(span) = generics.span_for_param_suggestion() {
3016 (span, format!(", {}: {}", param_name, impl_trait_name))
3018 (generics.span, format!("<{}: {}>", param_name, impl_trait_name))
3020 diag.multipart_suggestion(
3021 format!("alternatively use a blanket \
3022 implementation to implement `{of_trait_name}` for \
3023 all types that also implement `{impl_trait_name}`"),
3025 (self_ty.span, param_name),
3028 Applicability::MaybeIncorrect,
3033 fn maybe_lint_bare_trait(&self, self_ty: &hir::Ty<'_>, in_path: bool) {
3034 let tcx = self.tcx();
3035 if let hir::TyKind::TraitObject([poly_trait_ref, ..], _, TraitObjectSyntax::None) =
3038 let needs_bracket = in_path
3042 .span_to_prev_source(self_ty.span)
3044 .map_or(false, |s| s.trim_end().ends_with('<'));
3046 let is_global = poly_trait_ref.trait_ref.path.is_global();
3047 let sugg = Vec::from_iter([
3049 self_ty.span.shrink_to_lo(),
3052 if needs_bracket { "<" } else { "" },
3053 if is_global { "(" } else { "" },
3057 self_ty.span.shrink_to_hi(),
3060 if is_global { ")" } else { "" },
3061 if needs_bracket { ">" } else { "" },
3065 if self_ty.span.edition() >= Edition::Edition2021 {
3066 let msg = "trait objects must include the `dyn` keyword";
3067 let label = "add `dyn` keyword before this trait";
3069 rustc_errors::struct_span_err!(tcx.sess, self_ty.span, E0782, "{}", msg);
3070 diag.multipart_suggestion_verbose(label, sugg, Applicability::MachineApplicable);
3071 // check if the impl trait that we are considering is a impl of a local trait
3072 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);
3075 let msg = "trait objects without an explicit `dyn` are deprecated";
3076 tcx.struct_span_lint_hir(
3081 let mut diag = lint.build(msg);
3082 diag.multipart_suggestion_verbose(
3085 Applicability::MachineApplicable,
3087 self.maybe_lint_blanket_trait_impl::<()>(&self_ty, &mut diag);