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 fn compare_predicate_entailment<'tcx>(
148 impl_trait_ref: ty::TraitRef<'tcx>,
149 ) -> Result<(), ErrorGuaranteed> {
150 let trait_to_impl_substs = impl_trait_ref.substs;
152 // This node-id should be used for the `body_id` field on each
153 // `ObligationCause` (and the `FnCtxt`).
155 // FIXME(@lcnr): remove that after removing `cause.body_id` from
157 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
158 // We sometimes modify the span further down.
159 let mut cause = ObligationCause::new(
162 ObligationCauseCode::CompareImplItemObligation {
163 impl_item_def_id: impl_m.def_id.expect_local(),
164 trait_item_def_id: trait_m.def_id,
169 // Create mapping from impl to placeholder.
170 let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
172 // Create mapping from trait to placeholder.
173 let trait_to_placeholder_substs =
174 impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs);
175 debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs);
177 let impl_m_generics = tcx.generics_of(impl_m.def_id);
178 let trait_m_generics = tcx.generics_of(trait_m.def_id);
179 let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
180 let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
182 // Check region bounds.
183 check_region_bounds_on_impl_item(tcx, impl_m, trait_m, &trait_m_generics, &impl_m_generics)?;
185 // Create obligations for each predicate declared by the impl
186 // definition in the context of the trait's parameter
187 // environment. We can't just use `impl_env.caller_bounds`,
188 // however, because we want to replace all late-bound regions with
190 let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
191 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
193 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
195 // This is the only tricky bit of the new way we check implementation methods
196 // We need to build a set of predicates where only the method-level bounds
197 // are from the trait and we assume all other bounds from the implementation
198 // to be previously satisfied.
200 // We then register the obligations from the impl_m and check to see
201 // if all constraints hold.
204 .extend(trait_m_predicates.instantiate_own(tcx, trait_to_placeholder_substs).predicates);
206 // Construct trait parameter environment and then shift it into the placeholder viewpoint.
207 // The key step here is to update the caller_bounds's predicates to be
208 // the new hybrid bounds we computed.
209 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
210 let param_env = ty::ParamEnv::new(
211 tcx.intern_predicates(&hybrid_preds.predicates),
213 hir::Constness::NotConst,
215 let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
217 tcx.infer_ctxt().enter(|ref infcx| {
218 let ocx = ObligationCtxt::new(infcx);
220 debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds());
222 let mut selcx = traits::SelectionContext::new(&infcx);
223 let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs);
224 for (predicate, span) in iter::zip(impl_m_own_bounds.predicates, impl_m_own_bounds.spans) {
225 let normalize_cause = traits::ObligationCause::misc(span, impl_m_hir_id);
226 let traits::Normalized { value: predicate, obligations } =
227 traits::normalize(&mut selcx, param_env, normalize_cause, predicate);
229 ocx.register_obligations(obligations);
230 let cause = ObligationCause::new(
233 ObligationCauseCode::CompareImplItemObligation {
234 impl_item_def_id: impl_m.def_id.expect_local(),
235 trait_item_def_id: trait_m.def_id,
239 ocx.register_obligation(traits::Obligation::new(cause, param_env, predicate));
242 // We now need to check that the signature of the impl method is
243 // compatible with that of the trait method. We do this by
244 // checking that `impl_fty <: trait_fty`.
246 // FIXME. Unfortunately, this doesn't quite work right now because
247 // associated type normalization is not integrated into subtype
248 // checks. For the comparison to be valid, we need to
249 // normalize the associated types in the impl/trait methods
250 // first. However, because function types bind regions, just
251 // calling `normalize_associated_types_in` would have no effect on
252 // any associated types appearing in the fn arguments or return
255 // Compute placeholder form of impl and trait method tys.
258 let mut wf_tys = FxHashSet::default();
260 let impl_sig = infcx.replace_bound_vars_with_fresh_vars(
262 infer::HigherRankedType,
263 tcx.fn_sig(impl_m.def_id),
266 let norm_cause = ObligationCause::misc(impl_m_span, impl_m_hir_id);
267 let impl_sig = ocx.normalize(norm_cause.clone(), param_env, impl_sig);
268 let impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(impl_sig));
269 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
271 let trait_sig = tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs);
272 let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_sig);
274 // Next, add all inputs and output as well-formed tys. Importantly,
275 // we have to do this before normalization, since the normalized ty may
276 // not contain the input parameters. See issue #87748.
277 wf_tys.extend(trait_sig.inputs_and_output.iter());
278 let trait_sig = ocx.normalize(norm_cause, param_env, trait_sig);
279 // We also have to add the normalized trait signature
280 // as we don't normalize during implied bounds computation.
281 wf_tys.extend(trait_sig.inputs_and_output.iter());
282 let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig));
284 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
286 // FIXME: We'd want to keep more accurate spans than "the method signature" when
287 // processing the comparison between the trait and impl fn, but we sadly lose them
288 // and point at the whole signature when a trait bound or specific input or output
289 // type would be more appropriate. In other places we have a `Vec<Span>`
290 // corresponding to their `Vec<Predicate>`, but we don't have that here.
291 // Fixing this would improve the output of test `issue-83765.rs`.
292 let mut result = infcx
293 .at(&cause, param_env)
294 .sup(trait_fty, impl_fty)
295 .map(|infer_ok| ocx.register_infer_ok_obligations(infer_ok));
297 // HACK(RPITIT): #101614. When we are trying to infer the hidden types for
298 // RPITITs, we need to equate the output tys instead of just subtyping. If
299 // we just use `sup` above, we'll end up `&'static str <: _#1t`, which causes
300 // us to infer `_#1t = #'_#2r str`, where `'_#2r` is unconstrained, which gets
301 // fixed up to `ReEmpty`, and which is certainly not what we want.
302 if trait_fty.has_infer_types() {
303 result = result.and_then(|()| {
305 .at(&cause, param_env)
306 .eq(trait_sig.output(), impl_sig.output())
307 .map(|infer_ok| ocx.register_infer_ok_obligations(infer_ok))
311 if let Err(terr) = result {
312 debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
314 let (impl_err_span, trait_err_span) =
315 extract_spans_for_error_reporting(&infcx, terr, &cause, impl_m, trait_m);
317 cause.span = impl_err_span;
319 let mut diag = struct_span_err!(
323 "method `{}` has an incompatible type for trait",
327 TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0)
328 if trait_m.fn_has_self_parameter =>
330 let ty = trait_sig.inputs()[0];
331 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) => {
336 "&mut self".to_owned()
338 _ => format!("self: {ty}"),
341 // When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
342 // span points only at the type `Box<Self`>, but we want to cover the whole
343 // argument pattern and type.
344 let span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
345 ImplItemKind::Fn(ref sig, body) => tcx
347 .body_param_names(body)
348 .zip(sig.decl.inputs.iter())
349 .map(|(param, ty)| param.span.to(ty.span))
351 .unwrap_or(impl_err_span),
352 _ => bug!("{:?} is not a method", impl_m),
355 diag.span_suggestion(
357 "change the self-receiver type to match the trait",
359 Applicability::MachineApplicable,
362 TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => {
363 if trait_sig.inputs().len() == *i {
364 // Suggestion to change output type. We do not suggest in `async` functions
365 // to avoid complex logic or incorrect output.
366 match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
367 ImplItemKind::Fn(ref sig, _)
368 if sig.header.asyncness == hir::IsAsync::NotAsync =>
370 let msg = "change the output type to match the trait";
371 let ap = Applicability::MachineApplicable;
372 match sig.decl.output {
373 hir::FnRetTy::DefaultReturn(sp) => {
374 let sugg = format!("-> {} ", trait_sig.output());
375 diag.span_suggestion_verbose(sp, msg, sugg, ap);
377 hir::FnRetTy::Return(hir_ty) => {
378 let sugg = trait_sig.output();
379 diag.span_suggestion(hir_ty.span, msg, sugg, ap);
385 } else if let Some(trait_ty) = trait_sig.inputs().get(*i) {
386 diag.span_suggestion(
388 "change the parameter type to match the trait",
390 Applicability::MachineApplicable,
400 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
401 Some(infer::ValuePairs::Terms(ExpectedFound {
402 expected: trait_fty.into(),
403 found: impl_fty.into(),
410 return Err(diag.emit());
413 // Check that all obligations are satisfied by the implementation's
415 let errors = ocx.select_all_or_error();
416 if !errors.is_empty() {
417 let reported = infcx.report_fulfillment_errors(&errors, None, false);
418 return Err(reported);
421 // Finally, resolve all regions. This catches wily misuses of
422 // lifetime parameters.
423 let outlives_environment = OutlivesEnvironment::with_bounds(
426 infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys),
428 infcx.check_region_obligations_and_report_errors(
429 impl_m.def_id.expect_local(),
430 &outlives_environment,
437 pub fn collect_trait_impl_trait_tys<'tcx>(
440 ) -> Result<&'tcx FxHashMap<DefId, Ty<'tcx>>, ErrorGuaranteed> {
441 let impl_m = tcx.opt_associated_item(def_id).unwrap();
442 let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap();
443 let impl_trait_ref = tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap();
444 let param_env = tcx.param_env(def_id);
446 let trait_to_impl_substs = impl_trait_ref.substs;
448 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
449 let return_span = tcx.hir().fn_decl_by_hir_id(impl_m_hir_id).unwrap().output.span();
450 let cause = ObligationCause::new(
453 ObligationCauseCode::CompareImplItemObligation {
454 impl_item_def_id: impl_m.def_id.expect_local(),
455 trait_item_def_id: trait_m.def_id,
460 // Create mapping from impl to placeholder.
461 let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
463 // Create mapping from trait to placeholder.
464 let trait_to_placeholder_substs =
465 impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs);
467 tcx.infer_ctxt().enter(|ref infcx| {
468 let ocx = ObligationCtxt::new(infcx);
470 let norm_cause = ObligationCause::misc(return_span, impl_m_hir_id);
471 let impl_return_ty = ocx.normalize(
475 .replace_bound_vars_with_fresh_vars(
477 infer::HigherRankedType,
478 tcx.fn_sig(impl_m.def_id),
484 ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_hir_id);
485 let unnormalized_trait_return_ty = tcx
486 .liberate_late_bound_regions(
488 tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs),
491 .fold_with(&mut collector);
492 let trait_return_ty =
493 ocx.normalize(norm_cause.clone(), param_env, unnormalized_trait_return_ty);
495 let wf_tys = FxHashSet::from_iter([unnormalized_trait_return_ty, trait_return_ty]);
497 match infcx.at(&cause, param_env).eq(trait_return_ty, impl_return_ty) {
498 Ok(infer::InferOk { value: (), obligations }) => {
499 ocx.register_obligations(obligations);
502 let mut diag = struct_span_err!(
506 "method `{}` has an incompatible return type for trait",
513 hir.get_if_local(impl_m.def_id)
514 .and_then(|node| node.fn_decl())
515 .map(|decl| (decl.output.span(), "return type in trait".to_owned())),
516 Some(infer::ValuePairs::Terms(ExpectedFound {
517 expected: trait_return_ty.into(),
518 found: impl_return_ty.into(),
524 return Err(diag.emit());
528 // Check that all obligations are satisfied by the implementation's
530 let errors = ocx.select_all_or_error();
531 if !errors.is_empty() {
532 let reported = infcx.report_fulfillment_errors(&errors, None, false);
533 return Err(reported);
536 // Finally, resolve all regions. This catches wily misuses of
537 // lifetime parameters.
538 let outlives_environment = OutlivesEnvironment::with_bounds(
541 infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys),
543 infcx.check_region_obligations_and_report_errors(
544 impl_m.def_id.expect_local(),
545 &outlives_environment,
548 let mut collected_tys = FxHashMap::default();
549 for (def_id, (ty, substs)) in collector.types {
550 match infcx.fully_resolve(ty) {
552 // `ty` contains free regions that we created earlier while liberating the
553 // trait fn signature. However, projection normalization expects `ty` to
554 // contains `def_id`'s early-bound regions.
555 let id_substs = InternalSubsts::identity_for_item(tcx, def_id);
556 debug!(?id_substs, ?substs);
557 let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> = substs
560 .map(|(index, arg)| (arg, id_substs[index]))
564 let ty = tcx.fold_regions(ty, |region, _| {
565 if let ty::ReFree(_) = region.kind() {
566 map[®ion.into()].expect_region()
572 collected_tys.insert(def_id, ty);
575 tcx.sess.delay_span_bug(
577 format!("could not fully resolve: {ty} => {err:?}"),
579 collected_tys.insert(def_id, tcx.ty_error());
584 Ok(&*tcx.arena.alloc(collected_tys))
588 struct ImplTraitInTraitCollector<'a, 'tcx> {
589 ocx: &'a ObligationCtxt<'a, 'tcx>,
590 types: FxHashMap<DefId, (Ty<'tcx>, ty::SubstsRef<'tcx>)>,
592 param_env: ty::ParamEnv<'tcx>,
596 impl<'a, 'tcx> ImplTraitInTraitCollector<'a, 'tcx> {
598 ocx: &'a ObligationCtxt<'a, 'tcx>,
600 param_env: ty::ParamEnv<'tcx>,
603 ImplTraitInTraitCollector { ocx, types: FxHashMap::default(), span, param_env, body_id }
607 impl<'tcx> TypeFolder<'tcx> for ImplTraitInTraitCollector<'_, 'tcx> {
608 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
612 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
613 if let ty::Projection(proj) = ty.kind()
614 && self.tcx().def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
616 if let Some((ty, _)) = self.types.get(&proj.item_def_id) {
619 //FIXME(RPITIT): Deny nested RPITIT in substs too
620 if proj.substs.has_escaping_bound_vars() {
621 bug!("FIXME(RPITIT): error here");
623 // Replace with infer var
624 let infer_ty = self.ocx.infcx.next_ty_var(TypeVariableOrigin {
626 kind: TypeVariableOriginKind::MiscVariable,
628 self.types.insert(proj.item_def_id, (infer_ty, proj.substs));
629 // Recurse into bounds
630 for pred in self.tcx().bound_explicit_item_bounds(proj.item_def_id).transpose_iter() {
631 let pred_span = pred.0.1;
633 let pred = pred.map_bound(|(pred, _)| *pred).subst(self.tcx(), proj.substs);
634 let pred = pred.fold_with(self);
635 let pred = self.ocx.normalize(
636 ObligationCause::misc(self.span, self.body_id),
641 self.ocx.register_obligation(traits::Obligation::new(
642 ObligationCause::new(
645 ObligationCauseCode::BindingObligation(proj.item_def_id, pred_span),
653 ty.super_fold_with(self)
658 fn check_region_bounds_on_impl_item<'tcx>(
660 impl_m: &ty::AssocItem,
661 trait_m: &ty::AssocItem,
662 trait_generics: &ty::Generics,
663 impl_generics: &ty::Generics,
664 ) -> Result<(), ErrorGuaranteed> {
665 let trait_params = trait_generics.own_counts().lifetimes;
666 let impl_params = impl_generics.own_counts().lifetimes;
669 "check_region_bounds_on_impl_item: \
670 trait_generics={:?} \
672 trait_generics, impl_generics
675 // Must have same number of early-bound lifetime parameters.
676 // Unfortunately, if the user screws up the bounds, then this
677 // will change classification between early and late. E.g.,
678 // if in trait we have `<'a,'b:'a>`, and in impl we just have
679 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
680 // in trait but 0 in the impl. But if we report "expected 2
681 // but found 0" it's confusing, because it looks like there
682 // are zero. Since I don't quite know how to phrase things at
683 // the moment, give a kind of vague error message.
684 if trait_params != impl_params {
687 .get_generics(impl_m.def_id.expect_local())
688 .expect("expected impl item to have generics or else we can't compare them")
690 let generics_span = if let Some(local_def_id) = trait_m.def_id.as_local() {
693 .get_generics(local_def_id)
694 .expect("expected trait item to have generics or else we can't compare them")
701 let reported = tcx.sess.emit_err(LifetimesOrBoundsMismatchOnTrait {
703 item_kind: assoc_item_kind_str(impl_m),
704 ident: impl_m.ident(tcx),
707 return Err(reported);
713 #[instrument(level = "debug", skip(infcx))]
714 fn extract_spans_for_error_reporting<'a, 'tcx>(
715 infcx: &infer::InferCtxt<'a, 'tcx>,
717 cause: &ObligationCause<'tcx>,
718 impl_m: &ty::AssocItem,
719 trait_m: &ty::AssocItem,
720 ) -> (Span, Option<Span>) {
722 let mut impl_args = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
723 ImplItemKind::Fn(ref sig, _) => {
724 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
726 _ => bug!("{:?} is not a method", impl_m),
729 trait_m.def_id.as_local().map(|def_id| match tcx.hir().expect_trait_item(def_id).kind {
730 TraitItemKind::Fn(ref sig, _) => {
731 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
733 _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
737 TypeError::ArgumentMutability(i) => {
738 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
740 TypeError::ArgumentSorts(ExpectedFound { .. }, i) => {
741 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
743 _ => (cause.span(), tcx.hir().span_if_local(trait_m.def_id)),
747 fn compare_self_type<'tcx>(
749 impl_m: &ty::AssocItem,
751 trait_m: &ty::AssocItem,
752 impl_trait_ref: ty::TraitRef<'tcx>,
753 ) -> Result<(), ErrorGuaranteed> {
754 // Try to give more informative error messages about self typing
755 // mismatches. Note that any mismatch will also be detected
756 // below, where we construct a canonical function type that
757 // includes the self parameter as a normal parameter. It's just
758 // that the error messages you get out of this code are a bit more
759 // inscrutable, particularly for cases where one method has no
762 let self_string = |method: &ty::AssocItem| {
763 let untransformed_self_ty = match method.container {
764 ty::ImplContainer => impl_trait_ref.self_ty(),
765 ty::TraitContainer => tcx.types.self_param,
767 let self_arg_ty = tcx.fn_sig(method.def_id).input(0);
768 let param_env = ty::ParamEnv::reveal_all();
770 tcx.infer_ctxt().enter(|infcx| {
771 let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty);
772 let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
773 match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
774 ExplicitSelf::ByValue => "self".to_owned(),
775 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
776 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
777 _ => format!("self: {self_arg_ty}"),
782 match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
783 (false, false) | (true, true) => {}
786 let self_descr = self_string(impl_m);
787 let mut err = struct_span_err!(
791 "method `{}` has a `{}` declaration in the impl, but not in the trait",
795 err.span_label(impl_m_span, format!("`{self_descr}` used in impl"));
796 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
797 err.span_label(span, format!("trait method declared without `{self_descr}`"));
799 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
801 let reported = err.emit();
802 return Err(reported);
806 let self_descr = self_string(trait_m);
807 let mut err = struct_span_err!(
811 "method `{}` has a `{}` declaration in the trait, but not in the impl",
815 err.span_label(impl_m_span, format!("expected `{self_descr}` in impl"));
816 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
817 err.span_label(span, format!("`{self_descr}` used in trait"));
819 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
821 let reported = err.emit();
822 return Err(reported);
829 /// Checks that the number of generics on a given assoc item in a trait impl is the same
830 /// as the number of generics on the respective assoc item in the trait definition.
832 /// For example this code emits the errors in the following code:
839 /// impl Trait for () {
842 /// type Assoc = u32;
847 /// Notably this does not error on `foo<T>` implemented as `foo<const N: u8>` or
848 /// `foo<const N: u8>` implemented as `foo<const N: u32>`. This is handled in
849 /// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters
850 fn compare_number_of_generics<'tcx>(
852 impl_: &ty::AssocItem,
854 trait_: &ty::AssocItem,
855 trait_span: Option<Span>,
856 ) -> Result<(), ErrorGuaranteed> {
857 let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
858 let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
860 // This avoids us erroring on `foo<T>` implemented as `foo<const N: u8>` as this is implemented
861 // in `compare_generic_param_kinds` which will give a nicer error message than something like:
862 // "expected 1 type parameter, found 0 type parameters"
863 if (trait_own_counts.types + trait_own_counts.consts)
864 == (impl_own_counts.types + impl_own_counts.consts)
870 ("type", trait_own_counts.types, impl_own_counts.types),
871 ("const", trait_own_counts.consts, impl_own_counts.consts),
874 let item_kind = assoc_item_kind_str(impl_);
876 let mut err_occurred = None;
877 for (kind, trait_count, impl_count) in matchings {
878 if impl_count != trait_count {
879 let arg_spans = |kind: ty::AssocKind, generics: &hir::Generics<'_>| {
880 let mut spans = generics
883 .filter(|p| match p.kind {
884 hir::GenericParamKind::Lifetime {
885 kind: hir::LifetimeParamKind::Elided,
887 // A fn can have an arbitrary number of extra elided lifetimes for the
889 !matches!(kind, ty::AssocKind::Fn)
894 .collect::<Vec<Span>>();
895 if spans.is_empty() {
896 spans = vec![generics.span]
900 let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
901 let trait_item = tcx.hir().expect_trait_item(def_id);
902 let arg_spans: Vec<Span> = arg_spans(trait_.kind, trait_item.generics);
903 let impl_trait_spans: Vec<Span> = trait_item
907 .filter_map(|p| match p.kind {
908 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
912 (Some(arg_spans), impl_trait_spans)
914 (trait_span.map(|s| vec![s]), vec![])
917 let impl_item = tcx.hir().expect_impl_item(impl_.def_id.expect_local());
918 let impl_item_impl_trait_spans: Vec<Span> = impl_item
922 .filter_map(|p| match p.kind {
923 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
927 let spans = arg_spans(impl_.kind, impl_item.generics);
928 let span = spans.first().copied();
930 let mut err = tcx.sess.struct_span_err_with_code(
933 "{} `{}` has {} {kind} parameter{} but its trait \
934 declaration has {} {kind} parameter{}",
938 pluralize!(impl_count),
940 pluralize!(trait_count),
943 DiagnosticId::Error("E0049".into()),
946 let mut suffix = None;
948 if let Some(spans) = trait_spans {
949 let mut spans = spans.iter();
950 if let Some(span) = spans.next() {
954 "expected {} {} parameter{}",
957 pluralize!(trait_count),
962 err.span_label(*span, "");
965 suffix = Some(format!(", expected {trait_count}"));
968 if let Some(span) = span {
972 "found {} {} parameter{}{}",
975 pluralize!(impl_count),
976 suffix.unwrap_or_else(String::new),
981 for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
982 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
985 let reported = err.emit();
986 err_occurred = Some(reported);
990 if let Some(reported) = err_occurred { Err(reported) } else { Ok(()) }
993 fn compare_number_of_method_arguments<'tcx>(
995 impl_m: &ty::AssocItem,
997 trait_m: &ty::AssocItem,
998 trait_item_span: Option<Span>,
999 ) -> Result<(), ErrorGuaranteed> {
1000 let impl_m_fty = tcx.fn_sig(impl_m.def_id);
1001 let trait_m_fty = tcx.fn_sig(trait_m.def_id);
1002 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
1003 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
1004 if trait_number_args != impl_number_args {
1005 let trait_span = if let Some(def_id) = trait_m.def_id.as_local() {
1006 match tcx.hir().expect_trait_item(def_id).kind {
1007 TraitItemKind::Fn(ref trait_m_sig, _) => {
1008 let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
1009 if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
1013 arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo())
1019 _ => bug!("{:?} is not a method", impl_m),
1024 let impl_span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
1025 ImplItemKind::Fn(ref impl_m_sig, _) => {
1026 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
1027 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
1031 arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo())
1037 _ => bug!("{:?} is not a method", impl_m),
1039 let mut err = struct_span_err!(
1043 "method `{}` has {} but the declaration in trait `{}` has {}",
1045 potentially_plural_count(impl_number_args, "parameter"),
1046 tcx.def_path_str(trait_m.def_id),
1049 if let Some(trait_span) = trait_span {
1053 "trait requires {}",
1054 potentially_plural_count(trait_number_args, "parameter")
1058 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
1063 "expected {}, found {}",
1064 potentially_plural_count(trait_number_args, "parameter"),
1068 let reported = err.emit();
1069 return Err(reported);
1075 fn compare_synthetic_generics<'tcx>(
1077 impl_m: &ty::AssocItem,
1078 trait_m: &ty::AssocItem,
1079 ) -> Result<(), ErrorGuaranteed> {
1080 // FIXME(chrisvittal) Clean up this function, list of FIXME items:
1081 // 1. Better messages for the span labels
1082 // 2. Explanation as to what is going on
1083 // If we get here, we already have the same number of generics, so the zip will
1085 let mut error_found = None;
1086 let impl_m_generics = tcx.generics_of(impl_m.def_id);
1087 let trait_m_generics = tcx.generics_of(trait_m.def_id);
1088 let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
1089 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
1090 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
1092 let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
1093 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
1094 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
1096 for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
1097 iter::zip(impl_m_type_params, trait_m_type_params)
1099 if impl_synthetic != trait_synthetic {
1100 let impl_def_id = impl_def_id.expect_local();
1101 let impl_span = tcx.def_span(impl_def_id);
1102 let trait_span = tcx.def_span(trait_def_id);
1103 let mut err = struct_span_err!(
1107 "method `{}` has incompatible signature for trait",
1110 err.span_label(trait_span, "declaration in trait here");
1111 match (impl_synthetic, trait_synthetic) {
1112 // The case where the impl method uses `impl Trait` but the trait method uses
1113 // explicit generics
1115 err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
1117 // try taking the name from the trait impl
1118 // FIXME: this is obviously suboptimal since the name can already be used
1119 // as another generic argument
1120 let new_name = tcx.opt_item_name(trait_def_id)?;
1121 let trait_m = trait_m.def_id.as_local()?;
1122 let trait_m = tcx.hir().expect_trait_item(trait_m);
1124 let impl_m = impl_m.def_id.as_local()?;
1125 let impl_m = tcx.hir().expect_impl_item(impl_m);
1127 // in case there are no generics, take the spot between the function name
1128 // and the opening paren of the argument list
1129 let new_generics_span = tcx.def_ident_span(impl_def_id)?.shrink_to_hi();
1130 // in case there are generics, just replace them
1132 impl_m.generics.span.substitute_dummy(new_generics_span);
1133 // replace with the generics from the trait
1135 tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
1137 err.multipart_suggestion(
1138 "try changing the `impl Trait` argument to a generic parameter",
1140 // replace `impl Trait` with `T`
1141 (impl_span, new_name.to_string()),
1142 // replace impl method generics with trait method generics
1143 // This isn't quite right, as users might have changed the names
1144 // of the generics, but it works for the common case
1145 (generics_span, new_generics),
1147 Applicability::MaybeIncorrect,
1152 // The case where the trait method uses `impl Trait`, but the impl method uses
1153 // explicit generics.
1155 err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
1157 let impl_m = impl_m.def_id.as_local()?;
1158 let impl_m = tcx.hir().expect_impl_item(impl_m);
1159 let input_tys = match impl_m.kind {
1160 hir::ImplItemKind::Fn(ref sig, _) => sig.decl.inputs,
1161 _ => unreachable!(),
1163 struct Visitor(Option<Span>, hir::def_id::LocalDefId);
1164 impl<'v> intravisit::Visitor<'v> for Visitor {
1165 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
1166 intravisit::walk_ty(self, ty);
1167 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
1169 && let Res::Def(DefKind::TyParam, def_id) = path.res
1170 && def_id == self.1.to_def_id()
1172 self.0 = Some(ty.span);
1176 let mut visitor = Visitor(None, impl_def_id);
1177 for ty in input_tys {
1178 intravisit::Visitor::visit_ty(&mut visitor, ty);
1180 let span = visitor.0?;
1182 let bounds = impl_m.generics.bounds_for_param(impl_def_id).next()?.bounds;
1183 let bounds = bounds.first()?.span().to(bounds.last()?.span());
1184 let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
1186 err.multipart_suggestion(
1187 "try removing the generic parameter and using `impl Trait` instead",
1189 // delete generic parameters
1190 (impl_m.generics.span, String::new()),
1191 // replace param usage with `impl Trait`
1192 (span, format!("impl {bounds}")),
1194 Applicability::MaybeIncorrect,
1199 _ => unreachable!(),
1201 let reported = err.emit();
1202 error_found = Some(reported);
1205 if let Some(reported) = error_found { Err(reported) } else { Ok(()) }
1208 /// Checks that all parameters in the generics of a given assoc item in a trait impl have
1209 /// the same kind as the respective generic parameter in the trait def.
1211 /// For example all 4 errors in the following code are emitted here:
1214 /// fn foo<const N: u8>();
1215 /// type bar<const N: u8>;
1216 /// fn baz<const N: u32>();
1220 /// impl Foo for () {
1221 /// fn foo<const N: u64>() {}
1223 /// type bar<const N: u64> {}
1227 /// type blah<const N: i64> = u32;
1232 /// This function does not handle lifetime parameters
1233 fn compare_generic_param_kinds<'tcx>(
1235 impl_item: &ty::AssocItem,
1236 trait_item: &ty::AssocItem,
1237 ) -> Result<(), ErrorGuaranteed> {
1238 assert_eq!(impl_item.kind, trait_item.kind);
1240 let ty_const_params_of = |def_id| {
1241 tcx.generics_of(def_id).params.iter().filter(|param| {
1244 GenericParamDefKind::Const { .. } | GenericParamDefKind::Type { .. }
1249 for (param_impl, param_trait) in
1250 iter::zip(ty_const_params_of(impl_item.def_id), ty_const_params_of(trait_item.def_id))
1252 use GenericParamDefKind::*;
1253 if match (¶m_impl.kind, ¶m_trait.kind) {
1254 (Const { .. }, Const { .. })
1255 if tcx.type_of(param_impl.def_id) != tcx.type_of(param_trait.def_id) =>
1259 (Const { .. }, Type { .. }) | (Type { .. }, Const { .. }) => true,
1260 // this is exhaustive so that anyone adding new generic param kinds knows
1261 // to make sure this error is reported for them.
1262 (Const { .. }, Const { .. }) | (Type { .. }, Type { .. }) => false,
1263 (Lifetime { .. }, _) | (_, Lifetime { .. }) => unreachable!(),
1265 let param_impl_span = tcx.def_span(param_impl.def_id);
1266 let param_trait_span = tcx.def_span(param_trait.def_id);
1268 let mut err = struct_span_err!(
1272 "{} `{}` has an incompatible generic parameter for trait `{}`",
1273 assoc_item_kind_str(&impl_item),
1275 &tcx.def_path_str(tcx.parent(trait_item.def_id))
1278 let make_param_message = |prefix: &str, param: &ty::GenericParamDef| match param.kind {
1280 format!("{} const parameter of type `{}`", prefix, tcx.type_of(param.def_id))
1282 Type { .. } => format!("{} type parameter", prefix),
1283 Lifetime { .. } => unreachable!(),
1286 let trait_header_span = tcx.def_ident_span(tcx.parent(trait_item.def_id)).unwrap();
1287 err.span_label(trait_header_span, "");
1288 err.span_label(param_trait_span, make_param_message("expected", param_trait));
1290 let impl_header_span = tcx.def_span(tcx.parent(impl_item.def_id));
1291 err.span_label(impl_header_span, "");
1292 err.span_label(param_impl_span, make_param_message("found", param_impl));
1294 let reported = err.emit();
1295 return Err(reported);
1302 pub(crate) fn compare_const_impl<'tcx>(
1304 impl_c: &ty::AssocItem,
1306 trait_c: &ty::AssocItem,
1307 impl_trait_ref: ty::TraitRef<'tcx>,
1309 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
1311 tcx.infer_ctxt().enter(|infcx| {
1312 let param_env = tcx.param_env(impl_c.def_id);
1313 let ocx = ObligationCtxt::new(&infcx);
1315 // The below is for the most part highly similar to the procedure
1316 // for methods above. It is simpler in many respects, especially
1317 // because we shouldn't really have to deal with lifetimes or
1318 // predicates. In fact some of this should probably be put into
1319 // shared functions because of DRY violations...
1320 let trait_to_impl_substs = impl_trait_ref.substs;
1322 // Create a parameter environment that represents the implementation's
1324 let impl_c_hir_id = tcx.hir().local_def_id_to_hir_id(impl_c.def_id.expect_local());
1326 // Compute placeholder form of impl and trait const tys.
1327 let impl_ty = tcx.type_of(impl_c.def_id);
1328 let trait_ty = tcx.bound_type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
1329 let mut cause = ObligationCause::new(
1332 ObligationCauseCode::CompareImplItemObligation {
1333 impl_item_def_id: impl_c.def_id.expect_local(),
1334 trait_item_def_id: trait_c.def_id,
1339 // There is no "body" here, so just pass dummy id.
1340 let impl_ty = ocx.normalize(cause.clone(), param_env, impl_ty);
1342 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
1344 let trait_ty = ocx.normalize(cause.clone(), param_env, trait_ty);
1346 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
1349 .at(&cause, param_env)
1350 .sup(trait_ty, impl_ty)
1351 .map(|ok| ocx.register_infer_ok_obligations(ok));
1353 if let Err(terr) = err {
1355 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
1359 // Locate the Span containing just the type of the offending impl
1360 match tcx.hir().expect_impl_item(impl_c.def_id.expect_local()).kind {
1361 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
1362 _ => bug!("{:?} is not a impl const", impl_c),
1365 let mut diag = struct_span_err!(
1369 "implemented const `{}` has an incompatible type for trait",
1373 let trait_c_span = trait_c.def_id.as_local().map(|trait_c_def_id| {
1374 // Add a label to the Span containing just the type of the const
1375 match tcx.hir().expect_trait_item(trait_c_def_id).kind {
1376 TraitItemKind::Const(ref ty, _) => ty.span,
1377 _ => bug!("{:?} is not a trait const", trait_c),
1381 infcx.note_type_err(
1384 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1385 Some(infer::ValuePairs::Terms(ExpectedFound {
1386 expected: trait_ty.into(),
1387 found: impl_ty.into(),
1396 // Check that all obligations are satisfied by the implementation's
1398 let errors = ocx.select_all_or_error();
1399 if !errors.is_empty() {
1400 infcx.report_fulfillment_errors(&errors, None, false);
1404 let outlives_environment = OutlivesEnvironment::new(param_env);
1405 infcx.check_region_obligations_and_report_errors(
1406 impl_c.def_id.expect_local(),
1407 &outlives_environment,
1412 pub(crate) fn compare_ty_impl<'tcx>(
1414 impl_ty: &ty::AssocItem,
1416 trait_ty: &ty::AssocItem,
1417 impl_trait_ref: ty::TraitRef<'tcx>,
1418 trait_item_span: Option<Span>,
1420 debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1422 let _: Result<(), ErrorGuaranteed> = (|| {
1423 compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1425 compare_generic_param_kinds(tcx, impl_ty, trait_ty)?;
1427 let sp = tcx.def_span(impl_ty.def_id);
1428 compare_type_predicate_entailment(tcx, impl_ty, sp, trait_ty, impl_trait_ref)?;
1430 check_type_bounds(tcx, trait_ty, impl_ty, impl_ty_span, impl_trait_ref)
1434 /// The equivalent of [compare_predicate_entailment], but for associated types
1435 /// instead of associated functions.
1436 fn compare_type_predicate_entailment<'tcx>(
1438 impl_ty: &ty::AssocItem,
1440 trait_ty: &ty::AssocItem,
1441 impl_trait_ref: ty::TraitRef<'tcx>,
1442 ) -> Result<(), ErrorGuaranteed> {
1443 let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1444 let trait_to_impl_substs =
1445 impl_substs.rebase_onto(tcx, impl_ty.container_id(tcx), impl_trait_ref.substs);
1447 let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1448 let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1449 let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1450 let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1452 check_region_bounds_on_impl_item(
1460 let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1462 if impl_ty_own_bounds.is_empty() {
1463 // Nothing to check.
1467 // This `HirId` should be used for the `body_id` field on each
1468 // `ObligationCause` (and the `FnCtxt`). This is what
1469 // `regionck_item` expects.
1470 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1471 debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1473 // The predicates declared by the impl definition, the trait and the
1474 // associated type in the trait are assumed.
1475 let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1476 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1479 .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1481 debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1483 let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1484 let param_env = ty::ParamEnv::new(
1485 tcx.intern_predicates(&hybrid_preds.predicates),
1487 hir::Constness::NotConst,
1489 let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
1490 tcx.infer_ctxt().enter(|infcx| {
1491 let ocx = ObligationCtxt::new(&infcx);
1493 debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
1495 let mut selcx = traits::SelectionContext::new(&infcx);
1497 assert_eq!(impl_ty_own_bounds.predicates.len(), impl_ty_own_bounds.spans.len());
1498 for (span, predicate) in
1499 std::iter::zip(impl_ty_own_bounds.spans, impl_ty_own_bounds.predicates)
1501 let cause = ObligationCause::misc(span, impl_ty_hir_id);
1502 let traits::Normalized { value: predicate, obligations } =
1503 traits::normalize(&mut selcx, param_env, cause, predicate);
1505 let cause = ObligationCause::new(
1508 ObligationCauseCode::CompareImplItemObligation {
1509 impl_item_def_id: impl_ty.def_id.expect_local(),
1510 trait_item_def_id: trait_ty.def_id,
1514 ocx.register_obligations(obligations);
1515 ocx.register_obligation(traits::Obligation::new(cause, param_env, predicate));
1518 // Check that all obligations are satisfied by the implementation's
1520 let errors = ocx.select_all_or_error();
1521 if !errors.is_empty() {
1522 let reported = infcx.report_fulfillment_errors(&errors, None, false);
1523 return Err(reported);
1526 // Finally, resolve all regions. This catches wily misuses of
1527 // lifetime parameters.
1528 let outlives_environment = OutlivesEnvironment::new(param_env);
1529 infcx.check_region_obligations_and_report_errors(
1530 impl_ty.def_id.expect_local(),
1531 &outlives_environment,
1538 /// Validate that `ProjectionCandidate`s created for this associated type will
1543 /// trait X { type Y: Copy } impl X for T { type Y = S; }
1545 /// We are able to normalize `<T as X>::U` to `S`, and so when we check the
1546 /// impl is well-formed we have to prove `S: Copy`.
1548 /// For default associated types the normalization is not possible (the value
1549 /// from the impl could be overridden). We also can't normalize generic
1550 /// associated types (yet) because they contain bound parameters.
1551 #[instrument(level = "debug", skip(tcx))]
1552 pub fn check_type_bounds<'tcx>(
1554 trait_ty: &ty::AssocItem,
1555 impl_ty: &ty::AssocItem,
1557 impl_trait_ref: ty::TraitRef<'tcx>,
1558 ) -> Result<(), ErrorGuaranteed> {
1561 // impl<A, B> Foo<u32> for (A, B) {
1565 // - `impl_trait_ref` would be `<(A, B) as Foo<u32>>
1566 // - `impl_ty_substs` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0)
1567 // - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from
1568 // the *trait* with the generic associated type parameters (as bound vars).
1570 // A note regarding the use of bound vars here:
1571 // Imagine as an example
1574 // type Member<C: Eq>;
1577 // impl Family for VecFamily {
1578 // type Member<C: Eq> = i32;
1581 // Here, we would generate
1583 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
1585 // when we really would like to generate
1587 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) :- Implemented(C: Eq) }
1589 // But, this is probably fine, because although the first clause can be used with types C that
1590 // do not implement Eq, for it to cause some kind of problem, there would have to be a
1591 // VecFamily::Member<X> for some type X where !(X: Eq), that appears in the value of type
1592 // Member<C: Eq> = .... That type would fail a well-formedness check that we ought to be doing
1593 // elsewhere, which would check that any <T as Family>::Member<X> meets the bounds declared in
1594 // the trait (notably, that X: Eq and T: Family).
1595 let defs: &ty::Generics = tcx.generics_of(impl_ty.def_id);
1596 let mut substs = smallvec::SmallVec::with_capacity(defs.count());
1597 if let Some(def_id) = defs.parent {
1598 let parent_defs = tcx.generics_of(def_id);
1599 InternalSubsts::fill_item(&mut substs, tcx, parent_defs, &mut |param, _| {
1600 tcx.mk_param_from_def(param)
1603 let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> =
1604 smallvec::SmallVec::with_capacity(defs.count());
1605 InternalSubsts::fill_single(&mut substs, defs, &mut |param, _| match param.kind {
1606 GenericParamDefKind::Type { .. } => {
1607 let kind = ty::BoundTyKind::Param(param.name);
1608 let bound_var = ty::BoundVariableKind::Ty(kind);
1609 bound_vars.push(bound_var);
1610 tcx.mk_ty(ty::Bound(
1612 ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1616 GenericParamDefKind::Lifetime => {
1617 let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
1618 let bound_var = ty::BoundVariableKind::Region(kind);
1619 bound_vars.push(bound_var);
1620 tcx.mk_region(ty::ReLateBound(
1622 ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1626 GenericParamDefKind::Const { .. } => {
1627 let bound_var = ty::BoundVariableKind::Const;
1628 bound_vars.push(bound_var);
1629 tcx.mk_const(ty::ConstS {
1630 ty: tcx.type_of(param.def_id),
1631 kind: ty::ConstKind::Bound(
1633 ty::BoundVar::from_usize(bound_vars.len() - 1),
1639 let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter());
1640 let impl_ty_substs = tcx.intern_substs(&substs);
1641 let container_id = impl_ty.container_id(tcx);
1643 let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs);
1644 let impl_ty_value = tcx.type_of(impl_ty.def_id);
1646 let param_env = tcx.param_env(impl_ty.def_id);
1648 // When checking something like
1650 // trait X { type Y: PartialEq<<Self as X>::Y> }
1651 // impl X for T { default type Y = S; }
1653 // We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
1654 // we want <T as X>::Y to normalize to S. This is valid because we are
1655 // checking the default value specifically here. Add this equality to the
1656 // ParamEnv for normalization specifically.
1657 let normalize_param_env = {
1658 let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
1659 match impl_ty_value.kind() {
1660 ty::Projection(proj)
1661 if proj.item_def_id == trait_ty.def_id && proj.substs == rebased_substs =>
1663 // Don't include this predicate if the projected type is
1664 // exactly the same as the projection. This can occur in
1665 // (somewhat dubious) code like this:
1667 // impl<T> X for T where T: X { type Y = <T as X>::Y; }
1669 _ => predicates.push(
1670 ty::Binder::bind_with_vars(
1671 ty::ProjectionPredicate {
1672 projection_ty: ty::ProjectionTy {
1673 item_def_id: trait_ty.def_id,
1674 substs: rebased_substs,
1676 term: impl_ty_value.into(),
1684 tcx.intern_predicates(&predicates),
1686 param_env.constness(),
1689 debug!(?normalize_param_env);
1691 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1692 let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1693 let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs);
1695 tcx.infer_ctxt().enter(move |infcx| {
1696 let ocx = ObligationCtxt::new(&infcx);
1698 let assumed_wf_types =
1699 ocx.assumed_wf_types(param_env, impl_ty_span, impl_ty.def_id.expect_local());
1701 let mut selcx = traits::SelectionContext::new(&infcx);
1702 let normalize_cause = ObligationCause::new(
1705 ObligationCauseCode::CheckAssociatedTypeBounds {
1706 impl_item_def_id: impl_ty.def_id.expect_local(),
1707 trait_item_def_id: trait_ty.def_id,
1710 let mk_cause = |span: Span| {
1711 let code = if span.is_dummy() {
1712 traits::ItemObligation(trait_ty.def_id)
1714 traits::BindingObligation(trait_ty.def_id, span)
1716 ObligationCause::new(impl_ty_span, impl_ty_hir_id, code)
1719 let obligations = tcx
1720 .bound_explicit_item_bounds(trait_ty.def_id)
1722 .map(|e| e.map_bound(|e| *e).transpose_tuple2())
1723 .map(|(bound, span)| {
1725 // this is where opaque type is found
1726 let concrete_ty_bound = bound.subst(tcx, rebased_substs);
1727 debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
1729 traits::Obligation::new(mk_cause(span.0), param_env, concrete_ty_bound)
1732 debug!("check_type_bounds: item_bounds={:?}", obligations);
1734 for mut obligation in util::elaborate_obligations(tcx, obligations) {
1735 let traits::Normalized { value: normalized_predicate, obligations } = traits::normalize(
1737 normalize_param_env,
1738 normalize_cause.clone(),
1739 obligation.predicate,
1741 debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
1742 obligation.predicate = normalized_predicate;
1744 ocx.register_obligations(obligations);
1745 ocx.register_obligation(obligation);
1747 // Check that all obligations are satisfied by the implementation's
1749 let errors = ocx.select_all_or_error();
1750 if !errors.is_empty() {
1751 let reported = infcx.report_fulfillment_errors(&errors, None, false);
1752 return Err(reported);
1755 // Finally, resolve all regions. This catches wily misuses of
1756 // lifetime parameters.
1757 let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_hir_id, assumed_wf_types);
1758 let outlives_environment =
1759 OutlivesEnvironment::with_bounds(param_env, Some(&infcx), implied_bounds);
1761 infcx.check_region_obligations_and_report_errors(
1762 impl_ty.def_id.expect_local(),
1763 &outlives_environment,
1766 let constraints = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
1767 for (key, value) in constraints {
1769 .report_mismatched_types(
1770 &ObligationCause::misc(
1771 value.hidden_type.span,
1772 tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local()),
1774 tcx.mk_opaque(key.def_id.to_def_id(), key.substs),
1775 value.hidden_type.ty,
1776 TypeError::Mismatch,
1785 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1786 match impl_item.kind {
1787 ty::AssocKind::Const => "const",
1788 ty::AssocKind::Fn => "method",
1789 ty::AssocKind::Type => "type",