1 use super::potentially_plural_count;
2 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
3 use hir::def_id::{DefId, LocalDefId};
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::TypeErrCtxtExt;
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 let infcx = &tcx.infer_ctxt().build();
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()) {
333 ExplicitSelf::ByValue => "self".to_owned(),
334 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
335 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
336 _ => format!("self: {ty}"),
339 // When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
340 // span points only at the type `Box<Self`>, but we want to cover the whole
341 // argument pattern and type.
342 let span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
343 ImplItemKind::Fn(ref sig, body) => tcx
345 .body_param_names(body)
346 .zip(sig.decl.inputs.iter())
347 .map(|(param, ty)| param.span.to(ty.span))
349 .unwrap_or(impl_err_span),
350 _ => bug!("{:?} is not a method", impl_m),
353 diag.span_suggestion(
355 "change the self-receiver type to match the trait",
357 Applicability::MachineApplicable,
360 TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => {
361 if trait_sig.inputs().len() == *i {
362 // Suggestion to change output type. We do not suggest in `async` functions
363 // to avoid complex logic or incorrect output.
364 match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
365 ImplItemKind::Fn(ref sig, _)
366 if sig.header.asyncness == hir::IsAsync::NotAsync =>
368 let msg = "change the output type to match the trait";
369 let ap = Applicability::MachineApplicable;
370 match sig.decl.output {
371 hir::FnRetTy::DefaultReturn(sp) => {
372 let sugg = format!("-> {} ", trait_sig.output());
373 diag.span_suggestion_verbose(sp, msg, sugg, ap);
375 hir::FnRetTy::Return(hir_ty) => {
376 let sugg = trait_sig.output();
377 diag.span_suggestion(hir_ty.span, msg, sugg, ap);
383 } else if let Some(trait_ty) = trait_sig.inputs().get(*i) {
384 diag.span_suggestion(
386 "change the parameter type to match the trait",
388 Applicability::MachineApplicable,
395 infcx.err_ctxt().note_type_err(
398 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
399 Some(infer::ValuePairs::Terms(ExpectedFound {
400 expected: trait_fty.into(),
401 found: impl_fty.into(),
408 return Err(diag.emit());
411 // Check that all obligations are satisfied by the implementation's
413 let errors = ocx.select_all_or_error();
414 if !errors.is_empty() {
415 let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
416 return Err(reported);
419 // Finally, resolve all regions. This catches wily misuses of
420 // lifetime parameters.
421 let outlives_environment = OutlivesEnvironment::with_bounds(
424 infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys),
426 infcx.check_region_obligations_and_report_errors(
427 impl_m.def_id.expect_local(),
428 &outlives_environment,
434 pub fn collect_trait_impl_trait_tys<'tcx>(
437 ) -> Result<&'tcx FxHashMap<DefId, Ty<'tcx>>, ErrorGuaranteed> {
438 let impl_m = tcx.opt_associated_item(def_id).unwrap();
439 let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap();
440 let impl_trait_ref = tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap();
441 let param_env = tcx.param_env(def_id);
443 let trait_to_impl_substs = impl_trait_ref.substs;
445 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
446 let return_span = tcx.hir().fn_decl_by_hir_id(impl_m_hir_id).unwrap().output.span();
447 let cause = ObligationCause::new(
450 ObligationCauseCode::CompareImplItemObligation {
451 impl_item_def_id: impl_m.def_id.expect_local(),
452 trait_item_def_id: trait_m.def_id,
457 // Create mapping from impl to placeholder.
458 let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
460 // Create mapping from trait to placeholder.
461 let trait_to_placeholder_substs =
462 impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs);
464 let infcx = &tcx.infer_ctxt().build();
465 let ocx = ObligationCtxt::new(infcx);
467 let norm_cause = ObligationCause::misc(return_span, impl_m_hir_id);
468 let impl_return_ty = ocx.normalize(
472 .replace_bound_vars_with_fresh_vars(
474 infer::HigherRankedType,
475 tcx.fn_sig(impl_m.def_id),
480 let mut collector = ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_hir_id);
481 let unnormalized_trait_return_ty = tcx
482 .liberate_late_bound_regions(
484 tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs),
487 .fold_with(&mut collector);
488 let trait_return_ty =
489 ocx.normalize(norm_cause.clone(), param_env, unnormalized_trait_return_ty);
491 let wf_tys = FxHashSet::from_iter([unnormalized_trait_return_ty, trait_return_ty]);
493 match infcx.at(&cause, param_env).eq(trait_return_ty, impl_return_ty) {
494 Ok(infer::InferOk { value: (), obligations }) => {
495 ocx.register_obligations(obligations);
498 let mut diag = struct_span_err!(
502 "method `{}` has an incompatible return type for trait",
506 infcx.err_ctxt().note_type_err(
509 hir.get_if_local(impl_m.def_id)
510 .and_then(|node| node.fn_decl())
511 .map(|decl| (decl.output.span(), "return type in trait".to_owned())),
512 Some(infer::ValuePairs::Terms(ExpectedFound {
513 expected: trait_return_ty.into(),
514 found: impl_return_ty.into(),
520 return Err(diag.emit());
524 // Check that all obligations are satisfied by the implementation's
526 let errors = ocx.select_all_or_error();
527 if !errors.is_empty() {
528 let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
529 return Err(reported);
532 // Finally, resolve all regions. This catches wily misuses of
533 // lifetime parameters.
534 let outlives_environment = OutlivesEnvironment::with_bounds(
537 infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys),
539 infcx.check_region_obligations_and_report_errors(
540 impl_m.def_id.expect_local(),
541 &outlives_environment,
544 let mut collected_tys = FxHashMap::default();
545 for (def_id, (ty, substs)) in collector.types {
546 match infcx.fully_resolve(ty) {
548 // `ty` contains free regions that we created earlier while liberating the
549 // trait fn signature. However, projection normalization expects `ty` to
550 // contains `def_id`'s early-bound regions.
551 let id_substs = InternalSubsts::identity_for_item(tcx, def_id);
552 debug!(?id_substs, ?substs);
553 let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> =
554 substs.iter().enumerate().map(|(index, arg)| (arg, id_substs[index])).collect();
557 let ty = tcx.fold_regions(ty, |region, _| {
558 if let ty::ReFree(_) = region.kind() {
559 map[®ion.into()].expect_region()
565 collected_tys.insert(def_id, ty);
568 tcx.sess.delay_span_bug(
570 format!("could not fully resolve: {ty} => {err:?}"),
572 collected_tys.insert(def_id, tcx.ty_error());
577 Ok(&*tcx.arena.alloc(collected_tys))
580 struct ImplTraitInTraitCollector<'a, 'tcx> {
581 ocx: &'a ObligationCtxt<'a, 'tcx>,
582 types: FxHashMap<DefId, (Ty<'tcx>, ty::SubstsRef<'tcx>)>,
584 param_env: ty::ParamEnv<'tcx>,
588 impl<'a, 'tcx> ImplTraitInTraitCollector<'a, 'tcx> {
590 ocx: &'a ObligationCtxt<'a, 'tcx>,
592 param_env: ty::ParamEnv<'tcx>,
595 ImplTraitInTraitCollector { ocx, types: FxHashMap::default(), span, param_env, body_id }
599 impl<'tcx> TypeFolder<'tcx> for ImplTraitInTraitCollector<'_, 'tcx> {
600 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
604 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
605 if let ty::Projection(proj) = ty.kind()
606 && self.tcx().def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
608 if let Some((ty, _)) = self.types.get(&proj.item_def_id) {
611 //FIXME(RPITIT): Deny nested RPITIT in substs too
612 if proj.substs.has_escaping_bound_vars() {
613 bug!("FIXME(RPITIT): error here");
615 // Replace with infer var
616 let infer_ty = self.ocx.infcx.next_ty_var(TypeVariableOrigin {
618 kind: TypeVariableOriginKind::MiscVariable,
620 self.types.insert(proj.item_def_id, (infer_ty, proj.substs));
621 // Recurse into bounds
622 for pred in self.tcx().bound_explicit_item_bounds(proj.item_def_id).transpose_iter() {
623 let pred_span = pred.0.1;
625 let pred = pred.map_bound(|(pred, _)| *pred).subst(self.tcx(), proj.substs);
626 let pred = pred.fold_with(self);
627 let pred = self.ocx.normalize(
628 ObligationCause::misc(self.span, self.body_id),
633 self.ocx.register_obligation(traits::Obligation::new(
634 ObligationCause::new(
637 ObligationCauseCode::BindingObligation(proj.item_def_id, pred_span),
645 ty.super_fold_with(self)
650 fn check_region_bounds_on_impl_item<'tcx>(
652 impl_m: &ty::AssocItem,
653 trait_m: &ty::AssocItem,
654 trait_generics: &ty::Generics,
655 impl_generics: &ty::Generics,
656 ) -> Result<(), ErrorGuaranteed> {
657 let trait_params = trait_generics.own_counts().lifetimes;
658 let impl_params = impl_generics.own_counts().lifetimes;
661 "check_region_bounds_on_impl_item: \
662 trait_generics={:?} \
664 trait_generics, impl_generics
667 // Must have same number of early-bound lifetime parameters.
668 // Unfortunately, if the user screws up the bounds, then this
669 // will change classification between early and late. E.g.,
670 // if in trait we have `<'a,'b:'a>`, and in impl we just have
671 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
672 // in trait but 0 in the impl. But if we report "expected 2
673 // but found 0" it's confusing, because it looks like there
674 // are zero. Since I don't quite know how to phrase things at
675 // the moment, give a kind of vague error message.
676 if trait_params != impl_params {
679 .get_generics(impl_m.def_id.expect_local())
680 .expect("expected impl item to have generics or else we can't compare them")
682 let generics_span = if let Some(local_def_id) = trait_m.def_id.as_local() {
685 .get_generics(local_def_id)
686 .expect("expected trait item to have generics or else we can't compare them")
693 let reported = tcx.sess.emit_err(LifetimesOrBoundsMismatchOnTrait {
695 item_kind: assoc_item_kind_str(impl_m),
696 ident: impl_m.ident(tcx),
699 return Err(reported);
705 #[instrument(level = "debug", skip(infcx))]
706 fn extract_spans_for_error_reporting<'tcx>(
707 infcx: &infer::InferCtxt<'tcx>,
709 cause: &ObligationCause<'tcx>,
710 impl_m: &ty::AssocItem,
711 trait_m: &ty::AssocItem,
712 ) -> (Span, Option<Span>) {
714 let mut impl_args = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
715 ImplItemKind::Fn(ref sig, _) => {
716 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
718 _ => bug!("{:?} is not a method", impl_m),
721 trait_m.def_id.as_local().map(|def_id| match tcx.hir().expect_trait_item(def_id).kind {
722 TraitItemKind::Fn(ref sig, _) => {
723 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
725 _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
729 TypeError::ArgumentMutability(i) => {
730 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
732 TypeError::ArgumentSorts(ExpectedFound { .. }, i) => {
733 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
735 _ => (cause.span(), tcx.hir().span_if_local(trait_m.def_id)),
739 fn compare_self_type<'tcx>(
741 impl_m: &ty::AssocItem,
743 trait_m: &ty::AssocItem,
744 impl_trait_ref: ty::TraitRef<'tcx>,
745 ) -> Result<(), ErrorGuaranteed> {
746 // Try to give more informative error messages about self typing
747 // mismatches. Note that any mismatch will also be detected
748 // below, where we construct a canonical function type that
749 // includes the self parameter as a normal parameter. It's just
750 // that the error messages you get out of this code are a bit more
751 // inscrutable, particularly for cases where one method has no
754 let self_string = |method: &ty::AssocItem| {
755 let untransformed_self_ty = match method.container {
756 ty::ImplContainer => impl_trait_ref.self_ty(),
757 ty::TraitContainer => tcx.types.self_param,
759 let self_arg_ty = tcx.fn_sig(method.def_id).input(0);
760 let param_env = ty::ParamEnv::reveal_all();
762 let infcx = tcx.infer_ctxt().build();
763 let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty);
764 let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
765 match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
766 ExplicitSelf::ByValue => "self".to_owned(),
767 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
768 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
769 _ => format!("self: {self_arg_ty}"),
773 match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
774 (false, false) | (true, true) => {}
777 let self_descr = self_string(impl_m);
778 let mut err = struct_span_err!(
782 "method `{}` has a `{}` declaration in the impl, but not in the trait",
786 err.span_label(impl_m_span, format!("`{self_descr}` used in impl"));
787 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
788 err.span_label(span, format!("trait method declared without `{self_descr}`"));
790 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
792 let reported = err.emit();
793 return Err(reported);
797 let self_descr = self_string(trait_m);
798 let mut err = struct_span_err!(
802 "method `{}` has a `{}` declaration in the trait, but not in the impl",
806 err.span_label(impl_m_span, format!("expected `{self_descr}` in impl"));
807 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
808 err.span_label(span, format!("`{self_descr}` used in trait"));
810 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
812 let reported = err.emit();
813 return Err(reported);
820 /// Checks that the number of generics on a given assoc item in a trait impl is the same
821 /// as the number of generics on the respective assoc item in the trait definition.
823 /// For example this code emits the errors in the following code:
830 /// impl Trait for () {
833 /// type Assoc = u32;
838 /// Notably this does not error on `foo<T>` implemented as `foo<const N: u8>` or
839 /// `foo<const N: u8>` implemented as `foo<const N: u32>`. This is handled in
840 /// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters
841 fn compare_number_of_generics<'tcx>(
843 impl_: &ty::AssocItem,
845 trait_: &ty::AssocItem,
846 trait_span: Option<Span>,
847 ) -> Result<(), ErrorGuaranteed> {
848 let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
849 let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
851 // This avoids us erroring on `foo<T>` implemented as `foo<const N: u8>` as this is implemented
852 // in `compare_generic_param_kinds` which will give a nicer error message than something like:
853 // "expected 1 type parameter, found 0 type parameters"
854 if (trait_own_counts.types + trait_own_counts.consts)
855 == (impl_own_counts.types + impl_own_counts.consts)
861 ("type", trait_own_counts.types, impl_own_counts.types),
862 ("const", trait_own_counts.consts, impl_own_counts.consts),
865 let item_kind = assoc_item_kind_str(impl_);
867 let mut err_occurred = None;
868 for (kind, trait_count, impl_count) in matchings {
869 if impl_count != trait_count {
870 let arg_spans = |kind: ty::AssocKind, generics: &hir::Generics<'_>| {
871 let mut spans = generics
874 .filter(|p| match p.kind {
875 hir::GenericParamKind::Lifetime {
876 kind: hir::LifetimeParamKind::Elided,
878 // A fn can have an arbitrary number of extra elided lifetimes for the
880 !matches!(kind, ty::AssocKind::Fn)
885 .collect::<Vec<Span>>();
886 if spans.is_empty() {
887 spans = vec![generics.span]
891 let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
892 let trait_item = tcx.hir().expect_trait_item(def_id);
893 let arg_spans: Vec<Span> = arg_spans(trait_.kind, trait_item.generics);
894 let impl_trait_spans: Vec<Span> = trait_item
898 .filter_map(|p| match p.kind {
899 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
903 (Some(arg_spans), impl_trait_spans)
905 (trait_span.map(|s| vec![s]), vec![])
908 let impl_item = tcx.hir().expect_impl_item(impl_.def_id.expect_local());
909 let impl_item_impl_trait_spans: Vec<Span> = impl_item
913 .filter_map(|p| match p.kind {
914 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
918 let spans = arg_spans(impl_.kind, impl_item.generics);
919 let span = spans.first().copied();
921 let mut err = tcx.sess.struct_span_err_with_code(
924 "{} `{}` has {} {kind} parameter{} but its trait \
925 declaration has {} {kind} parameter{}",
929 pluralize!(impl_count),
931 pluralize!(trait_count),
934 DiagnosticId::Error("E0049".into()),
937 let mut suffix = None;
939 if let Some(spans) = trait_spans {
940 let mut spans = spans.iter();
941 if let Some(span) = spans.next() {
945 "expected {} {} parameter{}",
948 pluralize!(trait_count),
953 err.span_label(*span, "");
956 suffix = Some(format!(", expected {trait_count}"));
959 if let Some(span) = span {
963 "found {} {} parameter{}{}",
966 pluralize!(impl_count),
967 suffix.unwrap_or_else(String::new),
972 for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
973 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
976 let reported = err.emit();
977 err_occurred = Some(reported);
981 if let Some(reported) = err_occurred { Err(reported) } else { Ok(()) }
984 fn compare_number_of_method_arguments<'tcx>(
986 impl_m: &ty::AssocItem,
988 trait_m: &ty::AssocItem,
989 trait_item_span: Option<Span>,
990 ) -> Result<(), ErrorGuaranteed> {
991 let impl_m_fty = tcx.fn_sig(impl_m.def_id);
992 let trait_m_fty = tcx.fn_sig(trait_m.def_id);
993 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
994 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
995 if trait_number_args != impl_number_args {
996 let trait_span = if let Some(def_id) = trait_m.def_id.as_local() {
997 match tcx.hir().expect_trait_item(def_id).kind {
998 TraitItemKind::Fn(ref trait_m_sig, _) => {
999 let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
1000 if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
1004 arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo())
1010 _ => bug!("{:?} is not a method", impl_m),
1015 let impl_span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
1016 ImplItemKind::Fn(ref impl_m_sig, _) => {
1017 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
1018 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
1022 arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo())
1028 _ => bug!("{:?} is not a method", impl_m),
1030 let mut err = struct_span_err!(
1034 "method `{}` has {} but the declaration in trait `{}` has {}",
1036 potentially_plural_count(impl_number_args, "parameter"),
1037 tcx.def_path_str(trait_m.def_id),
1040 if let Some(trait_span) = trait_span {
1044 "trait requires {}",
1045 potentially_plural_count(trait_number_args, "parameter")
1049 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
1054 "expected {}, found {}",
1055 potentially_plural_count(trait_number_args, "parameter"),
1059 let reported = err.emit();
1060 return Err(reported);
1066 fn compare_synthetic_generics<'tcx>(
1068 impl_m: &ty::AssocItem,
1069 trait_m: &ty::AssocItem,
1070 ) -> Result<(), ErrorGuaranteed> {
1071 // FIXME(chrisvittal) Clean up this function, list of FIXME items:
1072 // 1. Better messages for the span labels
1073 // 2. Explanation as to what is going on
1074 // If we get here, we already have the same number of generics, so the zip will
1076 let mut error_found = None;
1077 let impl_m_generics = tcx.generics_of(impl_m.def_id);
1078 let trait_m_generics = tcx.generics_of(trait_m.def_id);
1079 let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
1080 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
1081 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
1083 let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
1084 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
1085 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
1087 for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
1088 iter::zip(impl_m_type_params, trait_m_type_params)
1090 if impl_synthetic != trait_synthetic {
1091 let impl_def_id = impl_def_id.expect_local();
1092 let impl_span = tcx.def_span(impl_def_id);
1093 let trait_span = tcx.def_span(trait_def_id);
1094 let mut err = struct_span_err!(
1098 "method `{}` has incompatible signature for trait",
1101 err.span_label(trait_span, "declaration in trait here");
1102 match (impl_synthetic, trait_synthetic) {
1103 // The case where the impl method uses `impl Trait` but the trait method uses
1104 // explicit generics
1106 err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
1108 // try taking the name from the trait impl
1109 // FIXME: this is obviously suboptimal since the name can already be used
1110 // as another generic argument
1111 let new_name = tcx.opt_item_name(trait_def_id)?;
1112 let trait_m = trait_m.def_id.as_local()?;
1113 let trait_m = tcx.hir().expect_trait_item(trait_m);
1115 let impl_m = impl_m.def_id.as_local()?;
1116 let impl_m = tcx.hir().expect_impl_item(impl_m);
1118 // in case there are no generics, take the spot between the function name
1119 // and the opening paren of the argument list
1120 let new_generics_span = tcx.def_ident_span(impl_def_id)?.shrink_to_hi();
1121 // in case there are generics, just replace them
1123 impl_m.generics.span.substitute_dummy(new_generics_span);
1124 // replace with the generics from the trait
1126 tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
1128 err.multipart_suggestion(
1129 "try changing the `impl Trait` argument to a generic parameter",
1131 // replace `impl Trait` with `T`
1132 (impl_span, new_name.to_string()),
1133 // replace impl method generics with trait method generics
1134 // This isn't quite right, as users might have changed the names
1135 // of the generics, but it works for the common case
1136 (generics_span, new_generics),
1138 Applicability::MaybeIncorrect,
1143 // The case where the trait method uses `impl Trait`, but the impl method uses
1144 // explicit generics.
1146 err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
1148 let impl_m = impl_m.def_id.as_local()?;
1149 let impl_m = tcx.hir().expect_impl_item(impl_m);
1150 let input_tys = match impl_m.kind {
1151 hir::ImplItemKind::Fn(ref sig, _) => sig.decl.inputs,
1152 _ => unreachable!(),
1154 struct Visitor(Option<Span>, hir::def_id::LocalDefId);
1155 impl<'v> intravisit::Visitor<'v> for Visitor {
1156 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
1157 intravisit::walk_ty(self, ty);
1158 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
1160 && let Res::Def(DefKind::TyParam, def_id) = path.res
1161 && def_id == self.1.to_def_id()
1163 self.0 = Some(ty.span);
1167 let mut visitor = Visitor(None, impl_def_id);
1168 for ty in input_tys {
1169 intravisit::Visitor::visit_ty(&mut visitor, ty);
1171 let span = visitor.0?;
1173 let bounds = impl_m.generics.bounds_for_param(impl_def_id).next()?.bounds;
1174 let bounds = bounds.first()?.span().to(bounds.last()?.span());
1175 let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
1177 err.multipart_suggestion(
1178 "try removing the generic parameter and using `impl Trait` instead",
1180 // delete generic parameters
1181 (impl_m.generics.span, String::new()),
1182 // replace param usage with `impl Trait`
1183 (span, format!("impl {bounds}")),
1185 Applicability::MaybeIncorrect,
1190 _ => unreachable!(),
1192 let reported = err.emit();
1193 error_found = Some(reported);
1196 if let Some(reported) = error_found { Err(reported) } else { Ok(()) }
1199 /// Checks that all parameters in the generics of a given assoc item in a trait impl have
1200 /// the same kind as the respective generic parameter in the trait def.
1202 /// For example all 4 errors in the following code are emitted here:
1205 /// fn foo<const N: u8>();
1206 /// type bar<const N: u8>;
1207 /// fn baz<const N: u32>();
1211 /// impl Foo for () {
1212 /// fn foo<const N: u64>() {}
1214 /// type bar<const N: u64> {}
1218 /// type blah<const N: i64> = u32;
1223 /// This function does not handle lifetime parameters
1224 fn compare_generic_param_kinds<'tcx>(
1226 impl_item: &ty::AssocItem,
1227 trait_item: &ty::AssocItem,
1228 ) -> Result<(), ErrorGuaranteed> {
1229 assert_eq!(impl_item.kind, trait_item.kind);
1231 let ty_const_params_of = |def_id| {
1232 tcx.generics_of(def_id).params.iter().filter(|param| {
1235 GenericParamDefKind::Const { .. } | GenericParamDefKind::Type { .. }
1240 for (param_impl, param_trait) in
1241 iter::zip(ty_const_params_of(impl_item.def_id), ty_const_params_of(trait_item.def_id))
1243 use GenericParamDefKind::*;
1244 if match (¶m_impl.kind, ¶m_trait.kind) {
1245 (Const { .. }, Const { .. })
1246 if tcx.type_of(param_impl.def_id) != tcx.type_of(param_trait.def_id) =>
1250 (Const { .. }, Type { .. }) | (Type { .. }, Const { .. }) => true,
1251 // this is exhaustive so that anyone adding new generic param kinds knows
1252 // to make sure this error is reported for them.
1253 (Const { .. }, Const { .. }) | (Type { .. }, Type { .. }) => false,
1254 (Lifetime { .. }, _) | (_, Lifetime { .. }) => unreachable!(),
1256 let param_impl_span = tcx.def_span(param_impl.def_id);
1257 let param_trait_span = tcx.def_span(param_trait.def_id);
1259 let mut err = struct_span_err!(
1263 "{} `{}` has an incompatible generic parameter for trait `{}`",
1264 assoc_item_kind_str(&impl_item),
1266 &tcx.def_path_str(tcx.parent(trait_item.def_id))
1269 let make_param_message = |prefix: &str, param: &ty::GenericParamDef| match param.kind {
1271 format!("{} const parameter of type `{}`", prefix, tcx.type_of(param.def_id))
1273 Type { .. } => format!("{} type parameter", prefix),
1274 Lifetime { .. } => unreachable!(),
1277 let trait_header_span = tcx.def_ident_span(tcx.parent(trait_item.def_id)).unwrap();
1278 err.span_label(trait_header_span, "");
1279 err.span_label(param_trait_span, make_param_message("expected", param_trait));
1281 let impl_header_span = tcx.def_span(tcx.parent(impl_item.def_id));
1282 err.span_label(impl_header_span, "");
1283 err.span_label(param_impl_span, make_param_message("found", param_impl));
1285 let reported = err.emit();
1286 return Err(reported);
1293 /// Use `tcx.compare_assoc_const_impl_item_with_trait_item` instead
1294 pub(crate) fn raw_compare_const_impl<'tcx>(
1296 (impl_const_item_def, trait_const_item_def): (LocalDefId, DefId),
1297 ) -> Result<(), ErrorGuaranteed> {
1298 let impl_const_item = tcx.associated_item(impl_const_item_def);
1299 let trait_const_item = tcx.associated_item(trait_const_item_def);
1300 let impl_trait_ref = tcx.impl_trait_ref(impl_const_item.container_id(tcx)).unwrap();
1301 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
1303 let impl_c_span = tcx.def_span(impl_const_item_def.to_def_id());
1305 let infcx = tcx.infer_ctxt().build();
1306 let param_env = tcx.param_env(impl_const_item_def.to_def_id());
1307 let ocx = ObligationCtxt::new(&infcx);
1309 // The below is for the most part highly similar to the procedure
1310 // for methods above. It is simpler in many respects, especially
1311 // because we shouldn't really have to deal with lifetimes or
1312 // predicates. In fact some of this should probably be put into
1313 // shared functions because of DRY violations...
1314 let trait_to_impl_substs = impl_trait_ref.substs;
1316 // Create a parameter environment that represents the implementation's
1318 let impl_c_hir_id = tcx.hir().local_def_id_to_hir_id(impl_const_item_def);
1320 // Compute placeholder form of impl and trait const tys.
1321 let impl_ty = tcx.type_of(impl_const_item_def.to_def_id());
1322 let trait_ty = tcx.bound_type_of(trait_const_item_def).subst(tcx, trait_to_impl_substs);
1323 let mut cause = ObligationCause::new(
1326 ObligationCauseCode::CompareImplItemObligation {
1327 impl_item_def_id: impl_const_item_def,
1328 trait_item_def_id: trait_const_item_def,
1329 kind: impl_const_item.kind,
1333 // There is no "body" here, so just pass dummy id.
1334 let impl_ty = ocx.normalize(cause.clone(), param_env, impl_ty);
1336 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
1338 let trait_ty = ocx.normalize(cause.clone(), param_env, trait_ty);
1340 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
1343 .at(&cause, param_env)
1344 .sup(trait_ty, impl_ty)
1345 .map(|ok| ocx.register_infer_ok_obligations(ok));
1347 if let Err(terr) = err {
1349 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
1353 // Locate the Span containing just the type of the offending impl
1354 match tcx.hir().expect_impl_item(impl_const_item_def).kind {
1355 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
1356 _ => bug!("{:?} is not a impl const", impl_const_item),
1359 let mut diag = struct_span_err!(
1363 "implemented const `{}` has an incompatible type for trait",
1364 trait_const_item.name
1367 let trait_c_span = trait_const_item_def.as_local().map(|trait_c_def_id| {
1368 // Add a label to the Span containing just the type of the const
1369 match tcx.hir().expect_trait_item(trait_c_def_id).kind {
1370 TraitItemKind::Const(ref ty, _) => ty.span,
1371 _ => bug!("{:?} is not a trait const", trait_const_item),
1375 infcx.err_ctxt().note_type_err(
1378 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1379 Some(infer::ValuePairs::Terms(ExpectedFound {
1380 expected: trait_ty.into(),
1381 found: impl_ty.into(),
1387 return Err(diag.emit());
1390 // Check that all obligations are satisfied by the implementation's
1392 let errors = ocx.select_all_or_error();
1393 if !errors.is_empty() {
1394 return Err(infcx.err_ctxt().report_fulfillment_errors(&errors, None, false));
1397 // FIXME return `ErrorReported` if region obligations error?
1398 let outlives_environment = OutlivesEnvironment::new(param_env);
1399 infcx.check_region_obligations_and_report_errors(impl_const_item_def, &outlives_environment);
1403 pub(crate) fn compare_ty_impl<'tcx>(
1405 impl_ty: &ty::AssocItem,
1407 trait_ty: &ty::AssocItem,
1408 impl_trait_ref: ty::TraitRef<'tcx>,
1409 trait_item_span: Option<Span>,
1411 debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1413 let _: Result<(), ErrorGuaranteed> = (|| {
1414 compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1416 compare_generic_param_kinds(tcx, impl_ty, trait_ty)?;
1418 let sp = tcx.def_span(impl_ty.def_id);
1419 compare_type_predicate_entailment(tcx, impl_ty, sp, trait_ty, impl_trait_ref)?;
1421 check_type_bounds(tcx, trait_ty, impl_ty, impl_ty_span, impl_trait_ref)
1425 /// The equivalent of [compare_predicate_entailment], but for associated types
1426 /// instead of associated functions.
1427 fn compare_type_predicate_entailment<'tcx>(
1429 impl_ty: &ty::AssocItem,
1431 trait_ty: &ty::AssocItem,
1432 impl_trait_ref: ty::TraitRef<'tcx>,
1433 ) -> Result<(), ErrorGuaranteed> {
1434 let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1435 let trait_to_impl_substs =
1436 impl_substs.rebase_onto(tcx, impl_ty.container_id(tcx), impl_trait_ref.substs);
1438 let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1439 let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1440 let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1441 let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1443 check_region_bounds_on_impl_item(
1451 let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1453 if impl_ty_own_bounds.is_empty() {
1454 // Nothing to check.
1458 // This `HirId` should be used for the `body_id` field on each
1459 // `ObligationCause` (and the `FnCtxt`). This is what
1460 // `regionck_item` expects.
1461 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1462 debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1464 // The predicates declared by the impl definition, the trait and the
1465 // associated type in the trait are assumed.
1466 let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1467 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1470 .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1472 debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1474 let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1475 let param_env = ty::ParamEnv::new(
1476 tcx.intern_predicates(&hybrid_preds.predicates),
1478 hir::Constness::NotConst,
1480 let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
1481 let infcx = tcx.infer_ctxt().build();
1482 let ocx = ObligationCtxt::new(&infcx);
1484 debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
1486 let mut selcx = traits::SelectionContext::new(&infcx);
1488 assert_eq!(impl_ty_own_bounds.predicates.len(), impl_ty_own_bounds.spans.len());
1489 for (span, predicate) in std::iter::zip(impl_ty_own_bounds.spans, impl_ty_own_bounds.predicates)
1491 let cause = ObligationCause::misc(span, impl_ty_hir_id);
1492 let traits::Normalized { value: predicate, obligations } =
1493 traits::normalize(&mut selcx, param_env, cause, predicate);
1495 let cause = ObligationCause::new(
1498 ObligationCauseCode::CompareImplItemObligation {
1499 impl_item_def_id: impl_ty.def_id.expect_local(),
1500 trait_item_def_id: trait_ty.def_id,
1504 ocx.register_obligations(obligations);
1505 ocx.register_obligation(traits::Obligation::new(cause, param_env, predicate));
1508 // Check that all obligations are satisfied by the implementation's
1510 let errors = ocx.select_all_or_error();
1511 if !errors.is_empty() {
1512 let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
1513 return Err(reported);
1516 // Finally, resolve all regions. This catches wily misuses of
1517 // lifetime parameters.
1518 let outlives_environment = OutlivesEnvironment::new(param_env);
1519 infcx.check_region_obligations_and_report_errors(
1520 impl_ty.def_id.expect_local(),
1521 &outlives_environment,
1527 /// Validate that `ProjectionCandidate`s created for this associated type will
1532 /// trait X { type Y: Copy } impl X for T { type Y = S; }
1534 /// We are able to normalize `<T as X>::U` to `S`, and so when we check the
1535 /// impl is well-formed we have to prove `S: Copy`.
1537 /// For default associated types the normalization is not possible (the value
1538 /// from the impl could be overridden). We also can't normalize generic
1539 /// associated types (yet) because they contain bound parameters.
1540 #[instrument(level = "debug", skip(tcx))]
1541 pub fn check_type_bounds<'tcx>(
1543 trait_ty: &ty::AssocItem,
1544 impl_ty: &ty::AssocItem,
1546 impl_trait_ref: ty::TraitRef<'tcx>,
1547 ) -> Result<(), ErrorGuaranteed> {
1550 // impl<A, B> Foo<u32> for (A, B) {
1554 // - `impl_trait_ref` would be `<(A, B) as Foo<u32>>
1555 // - `impl_ty_substs` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0)
1556 // - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from
1557 // the *trait* with the generic associated type parameters (as bound vars).
1559 // A note regarding the use of bound vars here:
1560 // Imagine as an example
1563 // type Member<C: Eq>;
1566 // impl Family for VecFamily {
1567 // type Member<C: Eq> = i32;
1570 // Here, we would generate
1572 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
1574 // when we really would like to generate
1576 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) :- Implemented(C: Eq) }
1578 // But, this is probably fine, because although the first clause can be used with types C that
1579 // do not implement Eq, for it to cause some kind of problem, there would have to be a
1580 // VecFamily::Member<X> for some type X where !(X: Eq), that appears in the value of type
1581 // Member<C: Eq> = .... That type would fail a well-formedness check that we ought to be doing
1582 // elsewhere, which would check that any <T as Family>::Member<X> meets the bounds declared in
1583 // the trait (notably, that X: Eq and T: Family).
1584 let defs: &ty::Generics = tcx.generics_of(impl_ty.def_id);
1585 let mut substs = smallvec::SmallVec::with_capacity(defs.count());
1586 if let Some(def_id) = defs.parent {
1587 let parent_defs = tcx.generics_of(def_id);
1588 InternalSubsts::fill_item(&mut substs, tcx, parent_defs, &mut |param, _| {
1589 tcx.mk_param_from_def(param)
1592 let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> =
1593 smallvec::SmallVec::with_capacity(defs.count());
1594 InternalSubsts::fill_single(&mut substs, defs, &mut |param, _| match param.kind {
1595 GenericParamDefKind::Type { .. } => {
1596 let kind = ty::BoundTyKind::Param(param.name);
1597 let bound_var = ty::BoundVariableKind::Ty(kind);
1598 bound_vars.push(bound_var);
1599 tcx.mk_ty(ty::Bound(
1601 ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1605 GenericParamDefKind::Lifetime => {
1606 let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
1607 let bound_var = ty::BoundVariableKind::Region(kind);
1608 bound_vars.push(bound_var);
1609 tcx.mk_region(ty::ReLateBound(
1611 ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1615 GenericParamDefKind::Const { .. } => {
1616 let bound_var = ty::BoundVariableKind::Const;
1617 bound_vars.push(bound_var);
1618 tcx.mk_const(ty::ConstS {
1619 ty: tcx.type_of(param.def_id),
1620 kind: ty::ConstKind::Bound(
1622 ty::BoundVar::from_usize(bound_vars.len() - 1),
1628 let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter());
1629 let impl_ty_substs = tcx.intern_substs(&substs);
1630 let container_id = impl_ty.container_id(tcx);
1632 let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs);
1633 let impl_ty_value = tcx.type_of(impl_ty.def_id);
1635 let param_env = tcx.param_env(impl_ty.def_id);
1637 // When checking something like
1639 // trait X { type Y: PartialEq<<Self as X>::Y> }
1640 // impl X for T { default type Y = S; }
1642 // We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
1643 // we want <T as X>::Y to normalize to S. This is valid because we are
1644 // checking the default value specifically here. Add this equality to the
1645 // ParamEnv for normalization specifically.
1646 let normalize_param_env = {
1647 let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
1648 match impl_ty_value.kind() {
1649 ty::Projection(proj)
1650 if proj.item_def_id == trait_ty.def_id && proj.substs == rebased_substs =>
1652 // Don't include this predicate if the projected type is
1653 // exactly the same as the projection. This can occur in
1654 // (somewhat dubious) code like this:
1656 // impl<T> X for T where T: X { type Y = <T as X>::Y; }
1658 _ => predicates.push(
1659 ty::Binder::bind_with_vars(
1660 ty::ProjectionPredicate {
1661 projection_ty: ty::ProjectionTy {
1662 item_def_id: trait_ty.def_id,
1663 substs: rebased_substs,
1665 term: impl_ty_value.into(),
1673 tcx.intern_predicates(&predicates),
1675 param_env.constness(),
1678 debug!(?normalize_param_env);
1680 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1681 let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1682 let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs);
1684 let infcx = tcx.infer_ctxt().build();
1685 let ocx = ObligationCtxt::new(&infcx);
1687 let assumed_wf_types =
1688 ocx.assumed_wf_types(param_env, impl_ty_span, impl_ty.def_id.expect_local());
1690 let mut selcx = traits::SelectionContext::new(&infcx);
1691 let normalize_cause = ObligationCause::new(
1694 ObligationCauseCode::CheckAssociatedTypeBounds {
1695 impl_item_def_id: impl_ty.def_id.expect_local(),
1696 trait_item_def_id: trait_ty.def_id,
1699 let mk_cause = |span: Span| {
1700 let code = if span.is_dummy() {
1701 traits::ItemObligation(trait_ty.def_id)
1703 traits::BindingObligation(trait_ty.def_id, span)
1705 ObligationCause::new(impl_ty_span, impl_ty_hir_id, code)
1708 let obligations = tcx
1709 .bound_explicit_item_bounds(trait_ty.def_id)
1711 .map(|e| e.map_bound(|e| *e).transpose_tuple2())
1712 .map(|(bound, span)| {
1714 // this is where opaque type is found
1715 let concrete_ty_bound = bound.subst(tcx, rebased_substs);
1716 debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
1718 traits::Obligation::new(mk_cause(span.0), param_env, concrete_ty_bound)
1721 debug!("check_type_bounds: item_bounds={:?}", obligations);
1723 for mut obligation in util::elaborate_obligations(tcx, obligations) {
1724 let traits::Normalized { value: normalized_predicate, obligations } = traits::normalize(
1726 normalize_param_env,
1727 normalize_cause.clone(),
1728 obligation.predicate,
1730 debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
1731 obligation.predicate = normalized_predicate;
1733 ocx.register_obligations(obligations);
1734 ocx.register_obligation(obligation);
1736 // Check that all obligations are satisfied by the implementation's
1738 let errors = ocx.select_all_or_error();
1739 if !errors.is_empty() {
1740 let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
1741 return Err(reported);
1744 // Finally, resolve all regions. This catches wily misuses of
1745 // lifetime parameters.
1746 let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_hir_id, assumed_wf_types);
1747 let outlives_environment =
1748 OutlivesEnvironment::with_bounds(param_env, Some(&infcx), implied_bounds);
1750 infcx.check_region_obligations_and_report_errors(
1751 impl_ty.def_id.expect_local(),
1752 &outlives_environment,
1755 let constraints = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
1756 for (key, value) in constraints {
1759 .report_mismatched_types(
1760 &ObligationCause::misc(
1761 value.hidden_type.span,
1762 tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local()),
1764 tcx.mk_opaque(key.def_id.to_def_id(), key.substs),
1765 value.hidden_type.ty,
1766 TypeError::Mismatch,
1774 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1775 match impl_item.kind {
1776 ty::AssocKind::Const => "const",
1777 ty::AssocKind::Fn => "method",
1778 ty::AssocKind::Type => "type",