1 use super::potentially_plural_count;
2 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
3 use hir::def_id::DefId;
4 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
5 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed};
7 use rustc_hir::def::{DefKind, Res};
8 use rustc_hir::intravisit;
9 use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind};
10 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
11 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
12 use rustc_infer::infer::{self, TyCtxtInferExt};
13 use rustc_infer::traits::util;
14 use rustc_middle::ty::error::{ExpectedFound, TypeError};
15 use rustc_middle::ty::util::ExplicitSelf;
16 use rustc_middle::ty::InternalSubsts;
17 use rustc_middle::ty::{
18 self, AssocItem, DefIdTree, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable,
20 use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
22 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
23 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
24 use rustc_trait_selection::traits::{
25 self, ObligationCause, ObligationCauseCode, ObligationCtxt, Reveal,
29 /// Checks that a method from an impl conforms to the signature of
30 /// the same method as declared in the trait.
34 /// - `impl_m`: type of the method we are checking
35 /// - `impl_m_span`: span to use for reporting errors
36 /// - `trait_m`: the method in the trait
37 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
38 pub(crate) fn compare_impl_method<'tcx>(
40 impl_m: &ty::AssocItem,
41 trait_m: &ty::AssocItem,
42 impl_trait_ref: ty::TraitRef<'tcx>,
43 trait_item_span: Option<Span>,
45 debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
47 let impl_m_span = tcx.def_span(impl_m.def_id);
49 if let Err(_) = compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref) {
53 if let Err(_) = compare_number_of_generics(tcx, impl_m, impl_m_span, trait_m, trait_item_span) {
57 if let Err(_) = compare_generic_param_kinds(tcx, impl_m, trait_m) {
62 compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
67 if let Err(_) = compare_synthetic_generics(tcx, impl_m, trait_m) {
71 if let Err(_) = compare_predicate_entailment(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
77 /// This function is best explained by example. Consider a trait:
79 /// trait Trait<'t, T> {
81 /// fn method<'a, M>(t: &'t T, m: &'a M) -> Self;
86 /// impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
88 /// fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo;
91 /// We wish to decide if those two method types are compatible.
92 /// For this we have to show that, assuming the bounds of the impl hold, the
93 /// bounds of `trait_m` imply the bounds of `impl_m`.
95 /// We start out with `trait_to_impl_substs`, that maps the trait
96 /// type parameters to impl type parameters. This is taken from the
97 /// impl trait reference:
99 /// trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
101 /// We create a mapping `dummy_substs` that maps from the impl type
102 /// parameters to fresh types and regions. For type parameters,
103 /// this is the identity transform, but we could as well use any
104 /// placeholder types. For regions, we convert from bound to free
105 /// regions (Note: but only early-bound regions, i.e., those
106 /// declared on the impl or used in type parameter bounds).
108 /// impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 }
110 /// Now we can apply `placeholder_substs` to the type of the impl method
111 /// to yield a new function type in terms of our fresh, placeholder
114 /// <'b> fn(t: &'i0 U0, m: &'b) -> Foo
116 /// We now want to extract and substitute the type of the *trait*
117 /// method and compare it. To do so, we must create a compound
118 /// substitution by combining `trait_to_impl_substs` and
119 /// `impl_to_placeholder_substs`, and also adding a mapping for the method
120 /// type parameters. We extend the mapping to also include
121 /// the method parameters.
123 /// trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 }
125 /// Applying this to the trait method type yields:
127 /// <'a> fn(t: &'i0 U0, m: &'a) -> Foo
129 /// This type is also the same but the name of the bound region (`'a`
130 /// vs `'b`). However, the normal subtyping rules on fn types handle
131 /// this kind of equivalency just fine.
133 /// We now use these substitutions to ensure that all declared bounds are
134 /// satisfied by the implementation's method.
136 /// We do this by creating a parameter environment which contains a
137 /// substitution corresponding to `impl_to_placeholder_substs`. We then build
138 /// `trait_to_placeholder_substs` and use it to convert the predicates contained
139 /// in the `trait_m` generics to the placeholder form.
141 /// Finally we register each of these predicates as an obligation and check that
143 #[instrument(level = "debug", skip(tcx, impl_m_span, impl_trait_ref))]
144 fn compare_predicate_entailment<'tcx>(
149 impl_trait_ref: ty::TraitRef<'tcx>,
150 ) -> Result<(), ErrorGuaranteed> {
151 let trait_to_impl_substs = impl_trait_ref.substs;
153 // This node-id should be used for the `body_id` field on each
154 // `ObligationCause` (and the `FnCtxt`).
156 // FIXME(@lcnr): remove that after removing `cause.body_id` from
158 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
159 // We sometimes modify the span further down.
160 let mut cause = ObligationCause::new(
163 ObligationCauseCode::CompareImplItemObligation {
164 impl_item_def_id: impl_m.def_id.expect_local(),
165 trait_item_def_id: trait_m.def_id,
170 // Create mapping from impl to placeholder.
171 let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
173 // Create mapping from trait to placeholder.
174 let trait_to_placeholder_substs =
175 impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs);
176 debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs);
178 let impl_m_generics = tcx.generics_of(impl_m.def_id);
179 let trait_m_generics = tcx.generics_of(trait_m.def_id);
180 let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
181 let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
183 // Check region bounds.
184 check_region_bounds_on_impl_item(tcx, impl_m, trait_m, &trait_m_generics, &impl_m_generics)?;
186 // Create obligations for each predicate declared by the impl
187 // definition in the context of the trait's parameter
188 // environment. We can't just use `impl_env.caller_bounds`,
189 // however, because we want to replace all late-bound regions with
191 let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
192 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
194 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
196 // This is the only tricky bit of the new way we check implementation methods
197 // We need to build a set of predicates where only the method-level bounds
198 // are from the trait and we assume all other bounds from the implementation
199 // to be previously satisfied.
201 // We then register the obligations from the impl_m and check to see
202 // if all constraints hold.
205 .extend(trait_m_predicates.instantiate_own(tcx, trait_to_placeholder_substs).predicates);
207 // Construct trait parameter environment and then shift it into the placeholder viewpoint.
208 // The key step here is to update the caller_bounds's predicates to be
209 // the new hybrid bounds we computed.
210 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
211 let param_env = ty::ParamEnv::new(
212 tcx.intern_predicates(&hybrid_preds.predicates),
214 hir::Constness::NotConst,
216 let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
218 tcx.infer_ctxt().enter(|ref infcx| {
219 let ocx = ObligationCtxt::new(infcx);
221 debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds());
223 let mut selcx = traits::SelectionContext::new(&infcx);
224 let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs);
225 for (predicate, span) in iter::zip(impl_m_own_bounds.predicates, impl_m_own_bounds.spans) {
226 let normalize_cause = traits::ObligationCause::misc(span, impl_m_hir_id);
227 let traits::Normalized { value: predicate, obligations } =
228 traits::normalize(&mut selcx, param_env, normalize_cause, predicate);
230 ocx.register_obligations(obligations);
231 let cause = ObligationCause::new(
234 ObligationCauseCode::CompareImplItemObligation {
235 impl_item_def_id: impl_m.def_id.expect_local(),
236 trait_item_def_id: trait_m.def_id,
240 ocx.register_obligation(traits::Obligation::new(cause, param_env, predicate));
243 // We now need to check that the signature of the impl method is
244 // compatible with that of the trait method. We do this by
245 // checking that `impl_fty <: trait_fty`.
247 // FIXME. Unfortunately, this doesn't quite work right now because
248 // associated type normalization is not integrated into subtype
249 // checks. For the comparison to be valid, we need to
250 // normalize the associated types in the impl/trait methods
251 // first. However, because function types bind regions, just
252 // calling `normalize_associated_types_in` would have no effect on
253 // any associated types appearing in the fn arguments or return
256 // Compute placeholder form of impl and trait method tys.
259 let mut wf_tys = FxHashSet::default();
261 let impl_sig = infcx.replace_bound_vars_with_fresh_vars(
263 infer::HigherRankedType,
264 tcx.fn_sig(impl_m.def_id),
267 let norm_cause = ObligationCause::misc(impl_m_span, impl_m_hir_id);
268 let impl_sig = ocx.normalize(norm_cause.clone(), param_env, impl_sig);
269 let impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(impl_sig));
270 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
272 let trait_sig = tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs);
273 let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_sig);
275 // Next, add all inputs and output as well-formed tys. Importantly,
276 // we have to do this before normalization, since the normalized ty may
277 // not contain the input parameters. See issue #87748.
278 wf_tys.extend(trait_sig.inputs_and_output.iter());
279 let trait_sig = ocx.normalize(norm_cause, param_env, trait_sig);
280 // We also have to add the normalized trait signature
281 // as we don't normalize during implied bounds computation.
282 wf_tys.extend(trait_sig.inputs_and_output.iter());
283 let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig));
285 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
287 // FIXME: We'd want to keep more accurate spans than "the method signature" when
288 // processing the comparison between the trait and impl fn, but we sadly lose them
289 // and point at the whole signature when a trait bound or specific input or output
290 // type would be more appropriate. In other places we have a `Vec<Span>`
291 // corresponding to their `Vec<Predicate>`, but we don't have that here.
292 // Fixing this would improve the output of test `issue-83765.rs`.
293 let mut result = infcx
294 .at(&cause, param_env)
295 .sup(trait_fty, impl_fty)
296 .map(|infer_ok| ocx.register_infer_ok_obligations(infer_ok));
298 // HACK(RPITIT): #101614. When we are trying to infer the hidden types for
299 // RPITITs, we need to equate the output tys instead of just subtyping. If
300 // we just use `sup` above, we'll end up `&'static str <: _#1t`, which causes
301 // us to infer `_#1t = #'_#2r str`, where `'_#2r` is unconstrained, which gets
302 // fixed up to `ReEmpty`, and which is certainly not what we want.
303 if trait_fty.has_infer_types() {
304 result = result.and_then(|()| {
306 .at(&cause, param_env)
307 .eq(trait_sig.output(), impl_sig.output())
308 .map(|infer_ok| ocx.register_infer_ok_obligations(infer_ok))
312 if let Err(terr) = result {
313 debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
315 let (impl_err_span, trait_err_span) =
316 extract_spans_for_error_reporting(&infcx, terr, &cause, impl_m, trait_m);
318 cause.span = impl_err_span;
320 let mut diag = struct_span_err!(
324 "method `{}` has an incompatible type for trait",
328 TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0)
329 if trait_m.fn_has_self_parameter =>
331 let ty = trait_sig.inputs()[0];
332 let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty())
334 ExplicitSelf::ByValue => "self".to_owned(),
335 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
336 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => {
337 "&mut self".to_owned()
339 _ => format!("self: {ty}"),
342 // When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
343 // span points only at the type `Box<Self`>, but we want to cover the whole
344 // argument pattern and type.
345 let span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
346 ImplItemKind::Fn(ref sig, body) => tcx
348 .body_param_names(body)
349 .zip(sig.decl.inputs.iter())
350 .map(|(param, ty)| param.span.to(ty.span))
352 .unwrap_or(impl_err_span),
353 _ => bug!("{:?} is not a method", impl_m),
356 diag.span_suggestion(
358 "change the self-receiver type to match the trait",
360 Applicability::MachineApplicable,
363 TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => {
364 if trait_sig.inputs().len() == *i {
365 // Suggestion to change output type. We do not suggest in `async` functions
366 // to avoid complex logic or incorrect output.
367 match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
368 ImplItemKind::Fn(ref sig, _)
369 if sig.header.asyncness == hir::IsAsync::NotAsync =>
371 let msg = "change the output type to match the trait";
372 let ap = Applicability::MachineApplicable;
373 match sig.decl.output {
374 hir::FnRetTy::DefaultReturn(sp) => {
375 let sugg = format!("-> {} ", trait_sig.output());
376 diag.span_suggestion_verbose(sp, msg, sugg, ap);
378 hir::FnRetTy::Return(hir_ty) => {
379 let sugg = trait_sig.output();
380 diag.span_suggestion(hir_ty.span, msg, sugg, ap);
386 } else if let Some(trait_ty) = trait_sig.inputs().get(*i) {
387 diag.span_suggestion(
389 "change the parameter type to match the trait",
391 Applicability::MachineApplicable,
401 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
402 Some(infer::ValuePairs::Terms(ExpectedFound {
403 expected: trait_fty.into(),
404 found: impl_fty.into(),
411 return Err(diag.emit());
414 // Check that all obligations are satisfied by the implementation's
416 let errors = ocx.select_all_or_error();
417 if !errors.is_empty() {
418 let reported = infcx.report_fulfillment_errors(&errors, None, false);
419 return Err(reported);
422 // Finally, resolve all regions. This catches wily misuses of
423 // lifetime parameters.
424 let outlives_environment = OutlivesEnvironment::with_bounds(
427 infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys),
429 infcx.check_region_obligations_and_report_errors(
430 impl_m.def_id.expect_local(),
431 &outlives_environment,
438 pub fn collect_trait_impl_trait_tys<'tcx>(
441 ) -> Result<&'tcx FxHashMap<DefId, Ty<'tcx>>, ErrorGuaranteed> {
442 let impl_m = tcx.opt_associated_item(def_id).unwrap();
443 let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap();
444 let impl_trait_ref = tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap();
445 let param_env = tcx.param_env(def_id);
447 let trait_to_impl_substs = impl_trait_ref.substs;
449 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
450 let return_span = tcx.hir().fn_decl_by_hir_id(impl_m_hir_id).unwrap().output.span();
451 let cause = ObligationCause::new(
454 ObligationCauseCode::CompareImplItemObligation {
455 impl_item_def_id: impl_m.def_id.expect_local(),
456 trait_item_def_id: trait_m.def_id,
461 // Create mapping from impl to placeholder.
462 let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
464 // Create mapping from trait to placeholder.
465 let trait_to_placeholder_substs =
466 impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs);
468 tcx.infer_ctxt().enter(|ref infcx| {
469 let ocx = ObligationCtxt::new(infcx);
471 let norm_cause = ObligationCause::misc(return_span, impl_m_hir_id);
472 let impl_return_ty = ocx.normalize(
476 .replace_bound_vars_with_fresh_vars(
478 infer::HigherRankedType,
479 tcx.fn_sig(impl_m.def_id),
485 ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_hir_id);
486 let unnormalized_trait_return_ty = tcx
487 .liberate_late_bound_regions(
489 tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs),
492 .fold_with(&mut collector);
493 let trait_return_ty =
494 ocx.normalize(norm_cause.clone(), param_env, unnormalized_trait_return_ty);
496 let wf_tys = FxHashSet::from_iter([unnormalized_trait_return_ty, trait_return_ty]);
498 match infcx.at(&cause, param_env).eq(trait_return_ty, impl_return_ty) {
499 Ok(infer::InferOk { value: (), obligations }) => {
500 ocx.register_obligations(obligations);
503 let mut diag = struct_span_err!(
507 "method `{}` has an incompatible return type for trait",
514 hir.get_if_local(impl_m.def_id)
515 .and_then(|node| node.fn_decl())
516 .map(|decl| (decl.output.span(), "return type in trait".to_owned())),
517 Some(infer::ValuePairs::Terms(ExpectedFound {
518 expected: trait_return_ty.into(),
519 found: impl_return_ty.into(),
525 return Err(diag.emit());
529 // Check that all obligations are satisfied by the implementation's
531 let errors = ocx.select_all_or_error();
532 if !errors.is_empty() {
533 let reported = infcx.report_fulfillment_errors(&errors, None, false);
534 return Err(reported);
537 // Finally, resolve all regions. This catches wily misuses of
538 // lifetime parameters.
539 let outlives_environment = OutlivesEnvironment::with_bounds(
542 infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys),
544 infcx.check_region_obligations_and_report_errors(
545 impl_m.def_id.expect_local(),
546 &outlives_environment,
549 let mut collected_tys = FxHashMap::default();
550 for (def_id, (ty, substs)) in collector.types {
551 match infcx.fully_resolve(ty) {
553 // `ty` contains free regions that we created earlier while liberating the
554 // trait fn signature. However, projection normalization expects `ty` to
555 // contains `def_id`'s early-bound regions.
556 let id_substs = InternalSubsts::identity_for_item(tcx, def_id);
557 debug!(?id_substs, ?substs);
558 let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> = substs
561 .map(|(index, arg)| (arg, id_substs[index]))
565 let ty = tcx.fold_regions(ty, |region, _| {
566 if let ty::ReFree(_) = region.kind() {
567 map[®ion.into()].expect_region()
573 collected_tys.insert(def_id, ty);
576 tcx.sess.delay_span_bug(
578 format!("could not fully resolve: {ty} => {err:?}"),
580 collected_tys.insert(def_id, tcx.ty_error());
585 Ok(&*tcx.arena.alloc(collected_tys))
589 struct ImplTraitInTraitCollector<'a, 'tcx> {
590 ocx: &'a ObligationCtxt<'a, 'tcx>,
591 types: FxHashMap<DefId, (Ty<'tcx>, ty::SubstsRef<'tcx>)>,
593 param_env: ty::ParamEnv<'tcx>,
597 impl<'a, 'tcx> ImplTraitInTraitCollector<'a, 'tcx> {
599 ocx: &'a ObligationCtxt<'a, 'tcx>,
601 param_env: ty::ParamEnv<'tcx>,
604 ImplTraitInTraitCollector { ocx, types: FxHashMap::default(), span, param_env, body_id }
608 impl<'tcx> TypeFolder<'tcx> for ImplTraitInTraitCollector<'_, 'tcx> {
609 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
613 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
614 if let ty::Projection(proj) = ty.kind()
615 && self.tcx().def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
617 if let Some((ty, _)) = self.types.get(&proj.item_def_id) {
620 //FIXME(RPITIT): Deny nested RPITIT in substs too
621 if proj.substs.has_escaping_bound_vars() {
622 bug!("FIXME(RPITIT): error here");
624 // Replace with infer var
625 let infer_ty = self.ocx.infcx.next_ty_var(TypeVariableOrigin {
627 kind: TypeVariableOriginKind::MiscVariable,
629 self.types.insert(proj.item_def_id, (infer_ty, proj.substs));
630 // Recurse into bounds
631 for pred in self.tcx().bound_explicit_item_bounds(proj.item_def_id).transpose_iter() {
632 let pred_span = pred.0.1;
634 let pred = pred.map_bound(|(pred, _)| *pred).subst(self.tcx(), proj.substs);
635 let pred = pred.fold_with(self);
636 let pred = self.ocx.normalize(
637 ObligationCause::misc(self.span, self.body_id),
642 self.ocx.register_obligation(traits::Obligation::new(
643 ObligationCause::new(
646 ObligationCauseCode::BindingObligation(proj.item_def_id, pred_span),
654 ty.super_fold_with(self)
659 fn check_region_bounds_on_impl_item<'tcx>(
661 impl_m: &ty::AssocItem,
662 trait_m: &ty::AssocItem,
663 trait_generics: &ty::Generics,
664 impl_generics: &ty::Generics,
665 ) -> Result<(), ErrorGuaranteed> {
666 let trait_params = trait_generics.own_counts().lifetimes;
667 let impl_params = impl_generics.own_counts().lifetimes;
670 "check_region_bounds_on_impl_item: \
671 trait_generics={:?} \
673 trait_generics, impl_generics
676 // Must have same number of early-bound lifetime parameters.
677 // Unfortunately, if the user screws up the bounds, then this
678 // will change classification between early and late. E.g.,
679 // if in trait we have `<'a,'b:'a>`, and in impl we just have
680 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
681 // in trait but 0 in the impl. But if we report "expected 2
682 // but found 0" it's confusing, because it looks like there
683 // are zero. Since I don't quite know how to phrase things at
684 // the moment, give a kind of vague error message.
685 if trait_params != impl_params {
688 .get_generics(impl_m.def_id.expect_local())
689 .expect("expected impl item to have generics or else we can't compare them")
691 let generics_span = if let Some(local_def_id) = trait_m.def_id.as_local() {
694 .get_generics(local_def_id)
695 .expect("expected trait item to have generics or else we can't compare them")
702 let reported = tcx.sess.emit_err(LifetimesOrBoundsMismatchOnTrait {
704 item_kind: assoc_item_kind_str(impl_m),
705 ident: impl_m.ident(tcx),
708 return Err(reported);
714 #[instrument(level = "debug", skip(infcx))]
715 fn extract_spans_for_error_reporting<'a, 'tcx>(
716 infcx: &infer::InferCtxt<'a, 'tcx>,
718 cause: &ObligationCause<'tcx>,
719 impl_m: &ty::AssocItem,
720 trait_m: &ty::AssocItem,
721 ) -> (Span, Option<Span>) {
723 let mut impl_args = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
724 ImplItemKind::Fn(ref sig, _) => {
725 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
727 _ => bug!("{:?} is not a method", impl_m),
730 trait_m.def_id.as_local().map(|def_id| match tcx.hir().expect_trait_item(def_id).kind {
731 TraitItemKind::Fn(ref sig, _) => {
732 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
734 _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
738 TypeError::ArgumentMutability(i) => {
739 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
741 TypeError::ArgumentSorts(ExpectedFound { .. }, i) => {
742 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
744 _ => (cause.span(), tcx.hir().span_if_local(trait_m.def_id)),
748 fn compare_self_type<'tcx>(
750 impl_m: &ty::AssocItem,
752 trait_m: &ty::AssocItem,
753 impl_trait_ref: ty::TraitRef<'tcx>,
754 ) -> Result<(), ErrorGuaranteed> {
755 // Try to give more informative error messages about self typing
756 // mismatches. Note that any mismatch will also be detected
757 // below, where we construct a canonical function type that
758 // includes the self parameter as a normal parameter. It's just
759 // that the error messages you get out of this code are a bit more
760 // inscrutable, particularly for cases where one method has no
763 let self_string = |method: &ty::AssocItem| {
764 let untransformed_self_ty = match method.container {
765 ty::ImplContainer => impl_trait_ref.self_ty(),
766 ty::TraitContainer => tcx.types.self_param,
768 let self_arg_ty = tcx.fn_sig(method.def_id).input(0);
769 let param_env = ty::ParamEnv::reveal_all();
771 tcx.infer_ctxt().enter(|infcx| {
772 let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty);
773 let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
774 match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
775 ExplicitSelf::ByValue => "self".to_owned(),
776 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
777 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
778 _ => format!("self: {self_arg_ty}"),
783 match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
784 (false, false) | (true, true) => {}
787 let self_descr = self_string(impl_m);
788 let mut err = struct_span_err!(
792 "method `{}` has a `{}` declaration in the impl, but not in the trait",
796 err.span_label(impl_m_span, format!("`{self_descr}` used in impl"));
797 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
798 err.span_label(span, format!("trait method declared without `{self_descr}`"));
800 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
802 let reported = err.emit();
803 return Err(reported);
807 let self_descr = self_string(trait_m);
808 let mut err = struct_span_err!(
812 "method `{}` has a `{}` declaration in the trait, but not in the impl",
816 err.span_label(impl_m_span, format!("expected `{self_descr}` in impl"));
817 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
818 err.span_label(span, format!("`{self_descr}` used in trait"));
820 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
822 let reported = err.emit();
823 return Err(reported);
830 /// Checks that the number of generics on a given assoc item in a trait impl is the same
831 /// as the number of generics on the respective assoc item in the trait definition.
833 /// For example this code emits the errors in the following code:
840 /// impl Trait for () {
843 /// type Assoc = u32;
848 /// Notably this does not error on `foo<T>` implemented as `foo<const N: u8>` or
849 /// `foo<const N: u8>` implemented as `foo<const N: u32>`. This is handled in
850 /// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters
851 fn compare_number_of_generics<'tcx>(
853 impl_: &ty::AssocItem,
855 trait_: &ty::AssocItem,
856 trait_span: Option<Span>,
857 ) -> Result<(), ErrorGuaranteed> {
858 let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
859 let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
861 // This avoids us erroring on `foo<T>` implemented as `foo<const N: u8>` as this is implemented
862 // in `compare_generic_param_kinds` which will give a nicer error message than something like:
863 // "expected 1 type parameter, found 0 type parameters"
864 if (trait_own_counts.types + trait_own_counts.consts)
865 == (impl_own_counts.types + impl_own_counts.consts)
871 ("type", trait_own_counts.types, impl_own_counts.types),
872 ("const", trait_own_counts.consts, impl_own_counts.consts),
875 let item_kind = assoc_item_kind_str(impl_);
877 let mut err_occurred = None;
878 for (kind, trait_count, impl_count) in matchings {
879 if impl_count != trait_count {
880 let arg_spans = |kind: ty::AssocKind, generics: &hir::Generics<'_>| {
881 let mut spans = generics
884 .filter(|p| match p.kind {
885 hir::GenericParamKind::Lifetime {
886 kind: hir::LifetimeParamKind::Elided,
888 // A fn can have an arbitrary number of extra elided lifetimes for the
890 !matches!(kind, ty::AssocKind::Fn)
895 .collect::<Vec<Span>>();
896 if spans.is_empty() {
897 spans = vec![generics.span]
901 let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
902 let trait_item = tcx.hir().expect_trait_item(def_id);
903 let arg_spans: Vec<Span> = arg_spans(trait_.kind, trait_item.generics);
904 let impl_trait_spans: Vec<Span> = trait_item
908 .filter_map(|p| match p.kind {
909 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
913 (Some(arg_spans), impl_trait_spans)
915 (trait_span.map(|s| vec![s]), vec![])
918 let impl_item = tcx.hir().expect_impl_item(impl_.def_id.expect_local());
919 let impl_item_impl_trait_spans: Vec<Span> = impl_item
923 .filter_map(|p| match p.kind {
924 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
928 let spans = arg_spans(impl_.kind, impl_item.generics);
929 let span = spans.first().copied();
931 let mut err = tcx.sess.struct_span_err_with_code(
934 "{} `{}` has {} {kind} parameter{} but its trait \
935 declaration has {} {kind} parameter{}",
939 pluralize!(impl_count),
941 pluralize!(trait_count),
944 DiagnosticId::Error("E0049".into()),
947 let mut suffix = None;
949 if let Some(spans) = trait_spans {
950 let mut spans = spans.iter();
951 if let Some(span) = spans.next() {
955 "expected {} {} parameter{}",
958 pluralize!(trait_count),
963 err.span_label(*span, "");
966 suffix = Some(format!(", expected {trait_count}"));
969 if let Some(span) = span {
973 "found {} {} parameter{}{}",
976 pluralize!(impl_count),
977 suffix.unwrap_or_else(String::new),
982 for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
983 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
986 let reported = err.emit();
987 err_occurred = Some(reported);
991 if let Some(reported) = err_occurred { Err(reported) } else { Ok(()) }
994 fn compare_number_of_method_arguments<'tcx>(
996 impl_m: &ty::AssocItem,
998 trait_m: &ty::AssocItem,
999 trait_item_span: Option<Span>,
1000 ) -> Result<(), ErrorGuaranteed> {
1001 let impl_m_fty = tcx.fn_sig(impl_m.def_id);
1002 let trait_m_fty = tcx.fn_sig(trait_m.def_id);
1003 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
1004 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
1005 if trait_number_args != impl_number_args {
1006 let trait_span = if let Some(def_id) = trait_m.def_id.as_local() {
1007 match tcx.hir().expect_trait_item(def_id).kind {
1008 TraitItemKind::Fn(ref trait_m_sig, _) => {
1009 let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
1010 if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
1014 arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo())
1020 _ => bug!("{:?} is not a method", impl_m),
1025 let impl_span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
1026 ImplItemKind::Fn(ref impl_m_sig, _) => {
1027 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
1028 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
1032 arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo())
1038 _ => bug!("{:?} is not a method", impl_m),
1040 let mut err = struct_span_err!(
1044 "method `{}` has {} but the declaration in trait `{}` has {}",
1046 potentially_plural_count(impl_number_args, "parameter"),
1047 tcx.def_path_str(trait_m.def_id),
1050 if let Some(trait_span) = trait_span {
1054 "trait requires {}",
1055 potentially_plural_count(trait_number_args, "parameter")
1059 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
1064 "expected {}, found {}",
1065 potentially_plural_count(trait_number_args, "parameter"),
1069 let reported = err.emit();
1070 return Err(reported);
1076 fn compare_synthetic_generics<'tcx>(
1078 impl_m: &ty::AssocItem,
1079 trait_m: &ty::AssocItem,
1080 ) -> Result<(), ErrorGuaranteed> {
1081 // FIXME(chrisvittal) Clean up this function, list of FIXME items:
1082 // 1. Better messages for the span labels
1083 // 2. Explanation as to what is going on
1084 // If we get here, we already have the same number of generics, so the zip will
1086 let mut error_found = None;
1087 let impl_m_generics = tcx.generics_of(impl_m.def_id);
1088 let trait_m_generics = tcx.generics_of(trait_m.def_id);
1089 let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
1090 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
1091 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
1093 let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
1094 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
1095 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
1097 for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
1098 iter::zip(impl_m_type_params, trait_m_type_params)
1100 if impl_synthetic != trait_synthetic {
1101 let impl_def_id = impl_def_id.expect_local();
1102 let impl_span = tcx.def_span(impl_def_id);
1103 let trait_span = tcx.def_span(trait_def_id);
1104 let mut err = struct_span_err!(
1108 "method `{}` has incompatible signature for trait",
1111 err.span_label(trait_span, "declaration in trait here");
1112 match (impl_synthetic, trait_synthetic) {
1113 // The case where the impl method uses `impl Trait` but the trait method uses
1114 // explicit generics
1116 err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
1118 // try taking the name from the trait impl
1119 // FIXME: this is obviously suboptimal since the name can already be used
1120 // as another generic argument
1121 let new_name = tcx.opt_item_name(trait_def_id)?;
1122 let trait_m = trait_m.def_id.as_local()?;
1123 let trait_m = tcx.hir().expect_trait_item(trait_m);
1125 let impl_m = impl_m.def_id.as_local()?;
1126 let impl_m = tcx.hir().expect_impl_item(impl_m);
1128 // in case there are no generics, take the spot between the function name
1129 // and the opening paren of the argument list
1130 let new_generics_span = tcx.def_ident_span(impl_def_id)?.shrink_to_hi();
1131 // in case there are generics, just replace them
1133 impl_m.generics.span.substitute_dummy(new_generics_span);
1134 // replace with the generics from the trait
1136 tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
1138 err.multipart_suggestion(
1139 "try changing the `impl Trait` argument to a generic parameter",
1141 // replace `impl Trait` with `T`
1142 (impl_span, new_name.to_string()),
1143 // replace impl method generics with trait method generics
1144 // This isn't quite right, as users might have changed the names
1145 // of the generics, but it works for the common case
1146 (generics_span, new_generics),
1148 Applicability::MaybeIncorrect,
1153 // The case where the trait method uses `impl Trait`, but the impl method uses
1154 // explicit generics.
1156 err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
1158 let impl_m = impl_m.def_id.as_local()?;
1159 let impl_m = tcx.hir().expect_impl_item(impl_m);
1160 let input_tys = match impl_m.kind {
1161 hir::ImplItemKind::Fn(ref sig, _) => sig.decl.inputs,
1162 _ => unreachable!(),
1164 struct Visitor(Option<Span>, hir::def_id::LocalDefId);
1165 impl<'v> intravisit::Visitor<'v> for Visitor {
1166 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
1167 intravisit::walk_ty(self, ty);
1168 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
1170 && let Res::Def(DefKind::TyParam, def_id) = path.res
1171 && def_id == self.1.to_def_id()
1173 self.0 = Some(ty.span);
1177 let mut visitor = Visitor(None, impl_def_id);
1178 for ty in input_tys {
1179 intravisit::Visitor::visit_ty(&mut visitor, ty);
1181 let span = visitor.0?;
1183 let bounds = impl_m.generics.bounds_for_param(impl_def_id).next()?.bounds;
1184 let bounds = bounds.first()?.span().to(bounds.last()?.span());
1185 let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
1187 err.multipart_suggestion(
1188 "try removing the generic parameter and using `impl Trait` instead",
1190 // delete generic parameters
1191 (impl_m.generics.span, String::new()),
1192 // replace param usage with `impl Trait`
1193 (span, format!("impl {bounds}")),
1195 Applicability::MaybeIncorrect,
1200 _ => unreachable!(),
1202 let reported = err.emit();
1203 error_found = Some(reported);
1206 if let Some(reported) = error_found { Err(reported) } else { Ok(()) }
1209 /// Checks that all parameters in the generics of a given assoc item in a trait impl have
1210 /// the same kind as the respective generic parameter in the trait def.
1212 /// For example all 4 errors in the following code are emitted here:
1215 /// fn foo<const N: u8>();
1216 /// type bar<const N: u8>;
1217 /// fn baz<const N: u32>();
1221 /// impl Foo for () {
1222 /// fn foo<const N: u64>() {}
1224 /// type bar<const N: u64> {}
1228 /// type blah<const N: i64> = u32;
1233 /// This function does not handle lifetime parameters
1234 fn compare_generic_param_kinds<'tcx>(
1236 impl_item: &ty::AssocItem,
1237 trait_item: &ty::AssocItem,
1238 ) -> Result<(), ErrorGuaranteed> {
1239 assert_eq!(impl_item.kind, trait_item.kind);
1241 let ty_const_params_of = |def_id| {
1242 tcx.generics_of(def_id).params.iter().filter(|param| {
1245 GenericParamDefKind::Const { .. } | GenericParamDefKind::Type { .. }
1250 for (param_impl, param_trait) in
1251 iter::zip(ty_const_params_of(impl_item.def_id), ty_const_params_of(trait_item.def_id))
1253 use GenericParamDefKind::*;
1254 if match (¶m_impl.kind, ¶m_trait.kind) {
1255 (Const { .. }, Const { .. })
1256 if tcx.type_of(param_impl.def_id) != tcx.type_of(param_trait.def_id) =>
1260 (Const { .. }, Type { .. }) | (Type { .. }, Const { .. }) => true,
1261 // this is exhaustive so that anyone adding new generic param kinds knows
1262 // to make sure this error is reported for them.
1263 (Const { .. }, Const { .. }) | (Type { .. }, Type { .. }) => false,
1264 (Lifetime { .. }, _) | (_, Lifetime { .. }) => unreachable!(),
1266 let param_impl_span = tcx.def_span(param_impl.def_id);
1267 let param_trait_span = tcx.def_span(param_trait.def_id);
1269 let mut err = struct_span_err!(
1273 "{} `{}` has an incompatible generic parameter for trait `{}`",
1274 assoc_item_kind_str(&impl_item),
1276 &tcx.def_path_str(tcx.parent(trait_item.def_id))
1279 let make_param_message = |prefix: &str, param: &ty::GenericParamDef| match param.kind {
1281 format!("{} const parameter of type `{}`", prefix, tcx.type_of(param.def_id))
1283 Type { .. } => format!("{} type parameter", prefix),
1284 Lifetime { .. } => unreachable!(),
1287 let trait_header_span = tcx.def_ident_span(tcx.parent(trait_item.def_id)).unwrap();
1288 err.span_label(trait_header_span, "");
1289 err.span_label(param_trait_span, make_param_message("expected", param_trait));
1291 let impl_header_span = tcx.def_span(tcx.parent(impl_item.def_id));
1292 err.span_label(impl_header_span, "");
1293 err.span_label(param_impl_span, make_param_message("found", param_impl));
1295 let reported = err.emit();
1296 return Err(reported);
1303 pub(crate) fn compare_const_impl<'tcx>(
1305 impl_c: &ty::AssocItem,
1307 trait_c: &ty::AssocItem,
1308 impl_trait_ref: ty::TraitRef<'tcx>,
1310 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
1312 tcx.infer_ctxt().enter(|infcx| {
1313 let param_env = tcx.param_env(impl_c.def_id);
1314 let ocx = ObligationCtxt::new(&infcx);
1316 // The below is for the most part highly similar to the procedure
1317 // for methods above. It is simpler in many respects, especially
1318 // because we shouldn't really have to deal with lifetimes or
1319 // predicates. In fact some of this should probably be put into
1320 // shared functions because of DRY violations...
1321 let trait_to_impl_substs = impl_trait_ref.substs;
1323 // Create a parameter environment that represents the implementation's
1325 let impl_c_hir_id = tcx.hir().local_def_id_to_hir_id(impl_c.def_id.expect_local());
1327 // Compute placeholder form of impl and trait const tys.
1328 let impl_ty = tcx.type_of(impl_c.def_id);
1329 let trait_ty = tcx.bound_type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
1330 let mut cause = ObligationCause::new(
1333 ObligationCauseCode::CompareImplItemObligation {
1334 impl_item_def_id: impl_c.def_id.expect_local(),
1335 trait_item_def_id: trait_c.def_id,
1340 // There is no "body" here, so just pass dummy id.
1341 let impl_ty = ocx.normalize(cause.clone(), param_env, impl_ty);
1343 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
1345 let trait_ty = ocx.normalize(cause.clone(), param_env, trait_ty);
1347 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
1350 .at(&cause, param_env)
1351 .sup(trait_ty, impl_ty)
1352 .map(|ok| ocx.register_infer_ok_obligations(ok));
1354 if let Err(terr) = err {
1356 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
1360 // Locate the Span containing just the type of the offending impl
1361 match tcx.hir().expect_impl_item(impl_c.def_id.expect_local()).kind {
1362 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
1363 _ => bug!("{:?} is not a impl const", impl_c),
1366 let mut diag = struct_span_err!(
1370 "implemented const `{}` has an incompatible type for trait",
1374 let trait_c_span = trait_c.def_id.as_local().map(|trait_c_def_id| {
1375 // Add a label to the Span containing just the type of the const
1376 match tcx.hir().expect_trait_item(trait_c_def_id).kind {
1377 TraitItemKind::Const(ref ty, _) => ty.span,
1378 _ => bug!("{:?} is not a trait const", trait_c),
1382 infcx.note_type_err(
1385 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1386 Some(infer::ValuePairs::Terms(ExpectedFound {
1387 expected: trait_ty.into(),
1388 found: impl_ty.into(),
1397 // Check that all obligations are satisfied by the implementation's
1399 let errors = ocx.select_all_or_error();
1400 if !errors.is_empty() {
1401 infcx.report_fulfillment_errors(&errors, None, false);
1405 let outlives_environment = OutlivesEnvironment::new(param_env);
1406 infcx.check_region_obligations_and_report_errors(
1407 impl_c.def_id.expect_local(),
1408 &outlives_environment,
1413 pub(crate) fn compare_ty_impl<'tcx>(
1415 impl_ty: &ty::AssocItem,
1417 trait_ty: &ty::AssocItem,
1418 impl_trait_ref: ty::TraitRef<'tcx>,
1419 trait_item_span: Option<Span>,
1421 debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1423 let _: Result<(), ErrorGuaranteed> = (|| {
1424 compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1426 compare_generic_param_kinds(tcx, impl_ty, trait_ty)?;
1428 let sp = tcx.def_span(impl_ty.def_id);
1429 compare_type_predicate_entailment(tcx, impl_ty, sp, trait_ty, impl_trait_ref)?;
1431 check_type_bounds(tcx, trait_ty, impl_ty, impl_ty_span, impl_trait_ref)
1435 /// The equivalent of [compare_predicate_entailment], but for associated types
1436 /// instead of associated functions.
1437 fn compare_type_predicate_entailment<'tcx>(
1439 impl_ty: &ty::AssocItem,
1441 trait_ty: &ty::AssocItem,
1442 impl_trait_ref: ty::TraitRef<'tcx>,
1443 ) -> Result<(), ErrorGuaranteed> {
1444 let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1445 let trait_to_impl_substs =
1446 impl_substs.rebase_onto(tcx, impl_ty.container_id(tcx), impl_trait_ref.substs);
1448 let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1449 let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1450 let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1451 let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1453 check_region_bounds_on_impl_item(
1461 let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1463 if impl_ty_own_bounds.is_empty() {
1464 // Nothing to check.
1468 // This `HirId` should be used for the `body_id` field on each
1469 // `ObligationCause` (and the `FnCtxt`). This is what
1470 // `regionck_item` expects.
1471 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1472 debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1474 // The predicates declared by the impl definition, the trait and the
1475 // associated type in the trait are assumed.
1476 let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1477 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1480 .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1482 debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1484 let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1485 let param_env = ty::ParamEnv::new(
1486 tcx.intern_predicates(&hybrid_preds.predicates),
1488 hir::Constness::NotConst,
1490 let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
1491 tcx.infer_ctxt().enter(|infcx| {
1492 let ocx = ObligationCtxt::new(&infcx);
1494 debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
1496 let mut selcx = traits::SelectionContext::new(&infcx);
1498 assert_eq!(impl_ty_own_bounds.predicates.len(), impl_ty_own_bounds.spans.len());
1499 for (span, predicate) in
1500 std::iter::zip(impl_ty_own_bounds.spans, impl_ty_own_bounds.predicates)
1502 let cause = ObligationCause::misc(span, impl_ty_hir_id);
1503 let traits::Normalized { value: predicate, obligations } =
1504 traits::normalize(&mut selcx, param_env, cause, predicate);
1506 let cause = ObligationCause::new(
1509 ObligationCauseCode::CompareImplItemObligation {
1510 impl_item_def_id: impl_ty.def_id.expect_local(),
1511 trait_item_def_id: trait_ty.def_id,
1515 ocx.register_obligations(obligations);
1516 ocx.register_obligation(traits::Obligation::new(cause, param_env, predicate));
1519 // Check that all obligations are satisfied by the implementation's
1521 let errors = ocx.select_all_or_error();
1522 if !errors.is_empty() {
1523 let reported = infcx.report_fulfillment_errors(&errors, None, false);
1524 return Err(reported);
1527 // Finally, resolve all regions. This catches wily misuses of
1528 // lifetime parameters.
1529 let outlives_environment = OutlivesEnvironment::new(param_env);
1530 infcx.check_region_obligations_and_report_errors(
1531 impl_ty.def_id.expect_local(),
1532 &outlives_environment,
1539 /// Validate that `ProjectionCandidate`s created for this associated type will
1544 /// trait X { type Y: Copy } impl X for T { type Y = S; }
1546 /// We are able to normalize `<T as X>::U` to `S`, and so when we check the
1547 /// impl is well-formed we have to prove `S: Copy`.
1549 /// For default associated types the normalization is not possible (the value
1550 /// from the impl could be overridden). We also can't normalize generic
1551 /// associated types (yet) because they contain bound parameters.
1552 #[instrument(level = "debug", skip(tcx))]
1553 pub fn check_type_bounds<'tcx>(
1555 trait_ty: &ty::AssocItem,
1556 impl_ty: &ty::AssocItem,
1558 impl_trait_ref: ty::TraitRef<'tcx>,
1559 ) -> Result<(), ErrorGuaranteed> {
1562 // impl<A, B> Foo<u32> for (A, B) {
1566 // - `impl_trait_ref` would be `<(A, B) as Foo<u32>>
1567 // - `impl_ty_substs` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0)
1568 // - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from
1569 // the *trait* with the generic associated type parameters (as bound vars).
1571 // A note regarding the use of bound vars here:
1572 // Imagine as an example
1575 // type Member<C: Eq>;
1578 // impl Family for VecFamily {
1579 // type Member<C: Eq> = i32;
1582 // Here, we would generate
1584 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
1586 // when we really would like to generate
1588 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) :- Implemented(C: Eq) }
1590 // But, this is probably fine, because although the first clause can be used with types C that
1591 // do not implement Eq, for it to cause some kind of problem, there would have to be a
1592 // VecFamily::Member<X> for some type X where !(X: Eq), that appears in the value of type
1593 // Member<C: Eq> = .... That type would fail a well-formedness check that we ought to be doing
1594 // elsewhere, which would check that any <T as Family>::Member<X> meets the bounds declared in
1595 // the trait (notably, that X: Eq and T: Family).
1596 let defs: &ty::Generics = tcx.generics_of(impl_ty.def_id);
1597 let mut substs = smallvec::SmallVec::with_capacity(defs.count());
1598 if let Some(def_id) = defs.parent {
1599 let parent_defs = tcx.generics_of(def_id);
1600 InternalSubsts::fill_item(&mut substs, tcx, parent_defs, &mut |param, _| {
1601 tcx.mk_param_from_def(param)
1604 let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> =
1605 smallvec::SmallVec::with_capacity(defs.count());
1606 InternalSubsts::fill_single(&mut substs, defs, &mut |param, _| match param.kind {
1607 GenericParamDefKind::Type { .. } => {
1608 let kind = ty::BoundTyKind::Param(param.name);
1609 let bound_var = ty::BoundVariableKind::Ty(kind);
1610 bound_vars.push(bound_var);
1611 tcx.mk_ty(ty::Bound(
1613 ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1617 GenericParamDefKind::Lifetime => {
1618 let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
1619 let bound_var = ty::BoundVariableKind::Region(kind);
1620 bound_vars.push(bound_var);
1621 tcx.mk_region(ty::ReLateBound(
1623 ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1627 GenericParamDefKind::Const { .. } => {
1628 let bound_var = ty::BoundVariableKind::Const;
1629 bound_vars.push(bound_var);
1630 tcx.mk_const(ty::ConstS {
1631 ty: tcx.type_of(param.def_id),
1632 kind: ty::ConstKind::Bound(
1634 ty::BoundVar::from_usize(bound_vars.len() - 1),
1640 let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter());
1641 let impl_ty_substs = tcx.intern_substs(&substs);
1642 let container_id = impl_ty.container_id(tcx);
1644 let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs);
1645 let impl_ty_value = tcx.type_of(impl_ty.def_id);
1647 let param_env = tcx.param_env(impl_ty.def_id);
1649 // When checking something like
1651 // trait X { type Y: PartialEq<<Self as X>::Y> }
1652 // impl X for T { default type Y = S; }
1654 // We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
1655 // we want <T as X>::Y to normalize to S. This is valid because we are
1656 // checking the default value specifically here. Add this equality to the
1657 // ParamEnv for normalization specifically.
1658 let normalize_param_env = {
1659 let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
1660 match impl_ty_value.kind() {
1661 ty::Projection(proj)
1662 if proj.item_def_id == trait_ty.def_id && proj.substs == rebased_substs =>
1664 // Don't include this predicate if the projected type is
1665 // exactly the same as the projection. This can occur in
1666 // (somewhat dubious) code like this:
1668 // impl<T> X for T where T: X { type Y = <T as X>::Y; }
1670 _ => predicates.push(
1671 ty::Binder::bind_with_vars(
1672 ty::ProjectionPredicate {
1673 projection_ty: ty::ProjectionTy {
1674 item_def_id: trait_ty.def_id,
1675 substs: rebased_substs,
1677 term: impl_ty_value.into(),
1685 tcx.intern_predicates(&predicates),
1687 param_env.constness(),
1690 debug!(?normalize_param_env);
1692 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1693 let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1694 let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs);
1696 tcx.infer_ctxt().enter(move |infcx| {
1697 let ocx = ObligationCtxt::new(&infcx);
1699 let assumed_wf_types =
1700 ocx.assumed_wf_types(param_env, impl_ty_span, impl_ty.def_id.expect_local());
1702 let mut selcx = traits::SelectionContext::new(&infcx);
1703 let normalize_cause = ObligationCause::new(
1706 ObligationCauseCode::CheckAssociatedTypeBounds {
1707 impl_item_def_id: impl_ty.def_id.expect_local(),
1708 trait_item_def_id: trait_ty.def_id,
1711 let mk_cause = |span: Span| {
1712 let code = if span.is_dummy() {
1713 traits::ItemObligation(trait_ty.def_id)
1715 traits::BindingObligation(trait_ty.def_id, span)
1717 ObligationCause::new(impl_ty_span, impl_ty_hir_id, code)
1720 let obligations = tcx
1721 .bound_explicit_item_bounds(trait_ty.def_id)
1723 .map(|e| e.map_bound(|e| *e).transpose_tuple2())
1724 .map(|(bound, span)| {
1726 // this is where opaque type is found
1727 let concrete_ty_bound = bound.subst(tcx, rebased_substs);
1728 debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
1730 traits::Obligation::new(mk_cause(span.0), param_env, concrete_ty_bound)
1733 debug!("check_type_bounds: item_bounds={:?}", obligations);
1735 for mut obligation in util::elaborate_obligations(tcx, obligations) {
1736 let traits::Normalized { value: normalized_predicate, obligations } = traits::normalize(
1738 normalize_param_env,
1739 normalize_cause.clone(),
1740 obligation.predicate,
1742 debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
1743 obligation.predicate = normalized_predicate;
1745 ocx.register_obligations(obligations);
1746 ocx.register_obligation(obligation);
1748 // Check that all obligations are satisfied by the implementation's
1750 let errors = ocx.select_all_or_error();
1751 if !errors.is_empty() {
1752 let reported = infcx.report_fulfillment_errors(&errors, None, false);
1753 return Err(reported);
1756 // Finally, resolve all regions. This catches wily misuses of
1757 // lifetime parameters.
1758 let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_hir_id, assumed_wf_types);
1759 let outlives_environment =
1760 OutlivesEnvironment::with_bounds(param_env, Some(&infcx), implied_bounds);
1762 infcx.check_region_obligations_and_report_errors(
1763 impl_ty.def_id.expect_local(),
1764 &outlives_environment,
1767 let constraints = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
1768 for (key, value) in constraints {
1770 .report_mismatched_types(
1771 &ObligationCause::misc(
1772 value.hidden_type.span,
1773 tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local()),
1775 tcx.mk_opaque(key.def_id.to_def_id(), key.substs),
1776 value.hidden_type.ty,
1777 TypeError::Mismatch,
1786 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1787 match impl_item.kind {
1788 ty::AssocKind::Const => "const",
1789 ty::AssocKind::Fn => "method",
1790 ty::AssocKind::Type => "type",