use super::potentially_plural_count; use crate::errors::LifetimesOrBoundsMismatchOnTrait; use hir::def_id::{DefId, LocalDefId}; use rustc_data_structures::fx::{FxHashMap, FxIndexSet}; use rustc_errors::{ pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed, MultiSpan, }; use rustc_hir as hir; use rustc_hir::def::{DefKind, Res}; use rustc_hir::intravisit; use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind}; use rustc_infer::infer::outlives::env::OutlivesEnvironment; use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt}; use rustc_infer::traits::util; use rustc_middle::ty::error::{ExpectedFound, TypeError}; use rustc_middle::ty::util::ExplicitSelf; use rustc_middle::ty::{ self, DefIdTree, InternalSubsts, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable, }; use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt}; use rustc_span::Span; use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt; use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _; use rustc_trait_selection::traits::{ self, ObligationCause, ObligationCauseCode, ObligationCtxt, Reveal, }; use std::iter; /// Checks that a method from an impl conforms to the signature of /// the same method as declared in the trait. /// /// # Parameters /// /// - `impl_m`: type of the method we are checking /// - `impl_m_span`: span to use for reporting errors /// - `trait_m`: the method in the trait /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation pub(super) fn compare_impl_method<'tcx>( tcx: TyCtxt<'tcx>, impl_m: &ty::AssocItem, trait_m: &ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, trait_item_span: Option, ) { debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref); let impl_m_span = tcx.def_span(impl_m.def_id); let _: Result<_, ErrorGuaranteed> = try { compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)?; compare_number_of_generics(tcx, impl_m, trait_m, trait_item_span, false)?; compare_generic_param_kinds(tcx, impl_m, trait_m, false)?; compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)?; compare_synthetic_generics(tcx, impl_m, trait_m)?; compare_asyncness(tcx, impl_m, impl_m_span, trait_m, trait_item_span)?; compare_method_predicate_entailment( tcx, impl_m, impl_m_span, trait_m, impl_trait_ref, CheckImpliedWfMode::Check, )?; }; } /// This function is best explained by example. Consider a trait: /// /// trait Trait<'t, T> { /// // `trait_m` /// fn method<'a, M>(t: &'t T, m: &'a M) -> Self; /// } /// /// And an impl: /// /// impl<'i, 'j, U> Trait<'j, &'i U> for Foo { /// // `impl_m` /// fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo; /// } /// /// We wish to decide if those two method types are compatible. /// For this we have to show that, assuming the bounds of the impl hold, the /// bounds of `trait_m` imply the bounds of `impl_m`. /// /// We start out with `trait_to_impl_substs`, that maps the trait /// type parameters to impl type parameters. This is taken from the /// impl trait reference: /// /// trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo} /// /// We create a mapping `dummy_substs` that maps from the impl type /// parameters to fresh types and regions. For type parameters, /// this is the identity transform, but we could as well use any /// placeholder types. For regions, we convert from bound to free /// regions (Note: but only early-bound regions, i.e., those /// declared on the impl or used in type parameter bounds). /// /// impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 } /// /// Now we can apply `placeholder_substs` to the type of the impl method /// to yield a new function type in terms of our fresh, placeholder /// types: /// /// <'b> fn(t: &'i0 U0, m: &'b) -> Foo /// /// We now want to extract and substitute the type of the *trait* /// method and compare it. To do so, we must create a compound /// substitution by combining `trait_to_impl_substs` and /// `impl_to_placeholder_substs`, and also adding a mapping for the method /// type parameters. We extend the mapping to also include /// the method parameters. /// /// trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 } /// /// Applying this to the trait method type yields: /// /// <'a> fn(t: &'i0 U0, m: &'a) -> Foo /// /// This type is also the same but the name of the bound region (`'a` /// vs `'b`). However, the normal subtyping rules on fn types handle /// this kind of equivalency just fine. /// /// We now use these substitutions to ensure that all declared bounds are /// satisfied by the implementation's method. /// /// We do this by creating a parameter environment which contains a /// substitution corresponding to `impl_to_placeholder_substs`. We then build /// `trait_to_placeholder_substs` and use it to convert the predicates contained /// in the `trait_m` generics to the placeholder form. /// /// Finally we register each of these predicates as an obligation and check that /// they hold. #[instrument(level = "debug", skip(tcx, impl_m_span, impl_trait_ref))] fn compare_method_predicate_entailment<'tcx>( tcx: TyCtxt<'tcx>, impl_m: &ty::AssocItem, impl_m_span: Span, trait_m: &ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, check_implied_wf: CheckImpliedWfMode, ) -> Result<(), ErrorGuaranteed> { let trait_to_impl_substs = impl_trait_ref.substs; // This node-id should be used for the `body_id` field on each // `ObligationCause` (and the `FnCtxt`). // // FIXME(@lcnr): remove that after removing `cause.body_id` from // obligations. let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local()); let cause = ObligationCause::new( impl_m_span, impl_m_hir_id, ObligationCauseCode::CompareImplItemObligation { impl_item_def_id: impl_m.def_id.expect_local(), trait_item_def_id: trait_m.def_id, kind: impl_m.kind, }, ); // Create mapping from impl to placeholder. let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id); // Create mapping from trait to placeholder. let trait_to_placeholder_substs = impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs); debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs); let impl_m_predicates = tcx.predicates_of(impl_m.def_id); let trait_m_predicates = tcx.predicates_of(trait_m.def_id); // Check region bounds. check_region_bounds_on_impl_item(tcx, impl_m, trait_m, false)?; // Create obligations for each predicate declared by the impl // definition in the context of the trait's parameter // environment. We can't just use `impl_env.caller_bounds`, // however, because we want to replace all late-bound regions with // region variables. let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap()); let mut hybrid_preds = impl_predicates.instantiate_identity(tcx); debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds); // This is the only tricky bit of the new way we check implementation methods // We need to build a set of predicates where only the method-level bounds // are from the trait and we assume all other bounds from the implementation // to be previously satisfied. // // We then register the obligations from the impl_m and check to see // if all constraints hold. hybrid_preds.predicates.extend( trait_m_predicates .instantiate_own(tcx, trait_to_placeholder_substs) .map(|(predicate, _)| predicate), ); // Construct trait parameter environment and then shift it into the placeholder viewpoint. // The key step here is to update the caller_bounds's predicates to be // the new hybrid bounds we computed. let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id); let param_env = ty::ParamEnv::new( tcx.intern_predicates(&hybrid_preds.predicates), Reveal::UserFacing, hir::Constness::NotConst, ); let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause); let infcx = &tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(infcx); debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds()); let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs); for (predicate, span) in impl_m_own_bounds { let normalize_cause = traits::ObligationCause::misc(span, impl_m_hir_id); let predicate = ocx.normalize(&normalize_cause, param_env, predicate); let cause = ObligationCause::new( span, impl_m_hir_id, ObligationCauseCode::CompareImplItemObligation { impl_item_def_id: impl_m.def_id.expect_local(), trait_item_def_id: trait_m.def_id, kind: impl_m.kind, }, ); ocx.register_obligation(traits::Obligation::new(tcx, cause, param_env, predicate)); } // We now need to check that the signature of the impl method is // compatible with that of the trait method. We do this by // checking that `impl_fty <: trait_fty`. // // FIXME. Unfortunately, this doesn't quite work right now because // associated type normalization is not integrated into subtype // checks. For the comparison to be valid, we need to // normalize the associated types in the impl/trait methods // first. However, because function types bind regions, just // calling `normalize_associated_types_in` would have no effect on // any associated types appearing in the fn arguments or return // type. // Compute placeholder form of impl and trait method tys. let tcx = infcx.tcx; let mut wf_tys = FxIndexSet::default(); let unnormalized_impl_sig = infcx.replace_bound_vars_with_fresh_vars( impl_m_span, infer::HigherRankedType, tcx.fn_sig(impl_m.def_id), ); let unnormalized_impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(unnormalized_impl_sig)); let norm_cause = ObligationCause::misc(impl_m_span, impl_m_hir_id); let impl_sig = ocx.normalize(&norm_cause, param_env, unnormalized_impl_sig); debug!("compare_impl_method: impl_fty={:?}", impl_sig); let trait_sig = tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs); let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_sig); // Next, add all inputs and output as well-formed tys. Importantly, // we have to do this before normalization, since the normalized ty may // not contain the input parameters. See issue #87748. wf_tys.extend(trait_sig.inputs_and_output.iter()); let trait_sig = ocx.normalize(&norm_cause, param_env, trait_sig); // We also have to add the normalized trait signature // as we don't normalize during implied bounds computation. wf_tys.extend(trait_sig.inputs_and_output.iter()); let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig)); debug!("compare_impl_method: trait_fty={:?}", trait_fty); // FIXME: We'd want to keep more accurate spans than "the method signature" when // processing the comparison between the trait and impl fn, but we sadly lose them // and point at the whole signature when a trait bound or specific input or output // type would be more appropriate. In other places we have a `Vec` // corresponding to their `Vec`, but we don't have that here. // Fixing this would improve the output of test `issue-83765.rs`. let result = ocx.sup(&cause, param_env, trait_sig, impl_sig); if let Err(terr) = result { debug!(?impl_sig, ?trait_sig, ?terr, "sub_types failed"); let emitted = report_trait_method_mismatch( &infcx, cause, terr, (trait_m, trait_sig), (impl_m, impl_sig), impl_trait_ref, ); return Err(emitted); } if check_implied_wf == CheckImpliedWfMode::Check { // We need to check that the impl's args are well-formed given // the hybrid param-env (impl + trait method where-clauses). ocx.register_obligation(traits::Obligation::new( infcx.tcx, ObligationCause::dummy(), param_env, ty::Binder::dummy(ty::PredicateKind::WellFormed(unnormalized_impl_fty.into())), )); } // Check that all obligations are satisfied by the implementation's // version. let errors = ocx.select_all_or_error(); if !errors.is_empty() { match check_implied_wf { CheckImpliedWfMode::Check => { return compare_method_predicate_entailment( tcx, impl_m, impl_m_span, trait_m, impl_trait_ref, CheckImpliedWfMode::Skip, ) .map(|()| { // If the skip-mode was successful, emit a lint. emit_implied_wf_lint(infcx.tcx, impl_m, impl_m_hir_id, vec![]); }); } CheckImpliedWfMode::Skip => { let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None); return Err(reported); } } } // Finally, resolve all regions. This catches wily misuses of // lifetime parameters. let outlives_env = OutlivesEnvironment::with_bounds( param_env, Some(infcx), infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys.clone()), ); infcx.process_registered_region_obligations( outlives_env.region_bound_pairs(), outlives_env.param_env, ); let errors = infcx.resolve_regions(&outlives_env); if !errors.is_empty() { // FIXME(compiler-errors): This can be simplified when IMPLIED_BOUNDS_ENTAILMENT // becomes a hard error (i.e. ideally we'd just call `resolve_regions_and_report_errors` match check_implied_wf { CheckImpliedWfMode::Check => { return compare_method_predicate_entailment( tcx, impl_m, impl_m_span, trait_m, impl_trait_ref, CheckImpliedWfMode::Skip, ) .map(|()| { let bad_args = extract_bad_args_for_implies_lint( tcx, &errors, (trait_m, trait_sig), // Unnormalized impl sig corresponds to the HIR types written (impl_m, unnormalized_impl_sig), impl_m_hir_id, ); // If the skip-mode was successful, emit a lint. emit_implied_wf_lint(tcx, impl_m, impl_m_hir_id, bad_args); }); } CheckImpliedWfMode::Skip => { if infcx.tainted_by_errors().is_none() { infcx.err_ctxt().report_region_errors(impl_m.def_id.expect_local(), &errors); } return Err(tcx .sess .delay_span_bug(rustc_span::DUMMY_SP, "error should have been emitted")); } } } Ok(()) } fn extract_bad_args_for_implies_lint<'tcx>( tcx: TyCtxt<'tcx>, errors: &[infer::RegionResolutionError<'tcx>], (trait_m, trait_sig): (&ty::AssocItem, ty::FnSig<'tcx>), (impl_m, impl_sig): (&ty::AssocItem, ty::FnSig<'tcx>), hir_id: hir::HirId, ) -> Vec<(Span, Option)> { let mut blame_generics = vec![]; for error in errors { // Look for the subregion origin that contains an input/output type let origin = match error { infer::RegionResolutionError::ConcreteFailure(o, ..) => o, infer::RegionResolutionError::GenericBoundFailure(o, ..) => o, infer::RegionResolutionError::SubSupConflict(_, _, o, ..) => o, infer::RegionResolutionError::UpperBoundUniverseConflict(.., o, _) => o, }; // Extract (possible) input/output types from origin match origin { infer::SubregionOrigin::Subtype(trace) => { if let Some((a, b)) = trace.values.ty() { blame_generics.extend([a, b]); } } infer::SubregionOrigin::RelateParamBound(_, ty, _) => blame_generics.push(*ty), infer::SubregionOrigin::ReferenceOutlivesReferent(ty, _) => blame_generics.push(*ty), _ => {} } } let fn_decl = tcx.hir().fn_decl_by_hir_id(hir_id).unwrap(); let opt_ret_ty = match fn_decl.output { hir::FnRetTy::DefaultReturn(_) => None, hir::FnRetTy::Return(ty) => Some(ty), }; // Map late-bound regions from trait to impl, so the names are right. let mapping = std::iter::zip( tcx.fn_sig(trait_m.def_id).bound_vars(), tcx.fn_sig(impl_m.def_id).bound_vars(), ) .filter_map(|(impl_bv, trait_bv)| { if let ty::BoundVariableKind::Region(impl_bv) = impl_bv && let ty::BoundVariableKind::Region(trait_bv) = trait_bv { Some((impl_bv, trait_bv)) } else { None } }) .collect(); // For each arg, see if it was in the "blame" of any of the region errors. // If so, then try to produce a suggestion to replace the argument type with // one from the trait. let mut bad_args = vec![]; for (idx, (ty, hir_ty)) in std::iter::zip(impl_sig.inputs_and_output, fn_decl.inputs.iter().chain(opt_ret_ty)) .enumerate() { let expected_ty = trait_sig.inputs_and_output[idx] .fold_with(&mut RemapLateBound { tcx, mapping: &mapping }); if blame_generics.iter().any(|blame| ty.contains(*blame)) { let expected_ty_sugg = expected_ty.to_string(); bad_args.push(( hir_ty.span, // Only suggest something if it actually changed. (expected_ty_sugg != ty.to_string()).then_some(expected_ty_sugg), )); } } bad_args } struct RemapLateBound<'a, 'tcx> { tcx: TyCtxt<'tcx>, mapping: &'a FxHashMap, } impl<'tcx> TypeFolder<'tcx> for RemapLateBound<'_, 'tcx> { fn tcx(&self) -> TyCtxt<'tcx> { self.tcx } fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { if let ty::ReFree(fr) = *r { self.tcx.mk_region(ty::ReFree(ty::FreeRegion { bound_region: self .mapping .get(&fr.bound_region) .copied() .unwrap_or(fr.bound_region), ..fr })) } else { r } } } fn emit_implied_wf_lint<'tcx>( tcx: TyCtxt<'tcx>, impl_m: &ty::AssocItem, hir_id: hir::HirId, bad_args: Vec<(Span, Option)>, ) { let span: MultiSpan = if bad_args.is_empty() { tcx.def_span(impl_m.def_id).into() } else { bad_args.iter().map(|(span, _)| *span).collect::>().into() }; tcx.struct_span_lint_hir( rustc_session::lint::builtin::IMPLIED_BOUNDS_ENTAILMENT, hir_id, span, "impl method assumes more implied bounds than the corresponding trait method", |lint| { let bad_args: Vec<_> = bad_args.into_iter().filter_map(|(span, sugg)| Some((span, sugg?))).collect(); if !bad_args.is_empty() { lint.multipart_suggestion( format!( "replace {} type{} to make the impl signature compatible", pluralize!("this", bad_args.len()), pluralize!(bad_args.len()) ), bad_args, Applicability::MaybeIncorrect, ); } lint }, ); } #[derive(Debug, PartialEq, Eq)] enum CheckImpliedWfMode { /// Checks implied well-formedness of the impl method. If it fails, we will /// re-check with `Skip`, and emit a lint if it succeeds. Check, /// Skips checking implied well-formedness of the impl method, but will emit /// a lint if the `compare_method_predicate_entailment` succeeded. This means that /// the reason that we had failed earlier during `Check` was due to the impl /// having stronger requirements than the trait. Skip, } fn compare_asyncness<'tcx>( tcx: TyCtxt<'tcx>, impl_m: &ty::AssocItem, impl_m_span: Span, trait_m: &ty::AssocItem, trait_item_span: Option, ) -> Result<(), ErrorGuaranteed> { if tcx.asyncness(trait_m.def_id) == hir::IsAsync::Async { match tcx.fn_sig(impl_m.def_id).skip_binder().output().kind() { ty::Alias(ty::Opaque, ..) => { // allow both `async fn foo()` and `fn foo() -> impl Future` } ty::Error(_) => { // We don't know if it's ok, but at least it's already an error. } _ => { return Err(tcx.sess.emit_err(crate::errors::AsyncTraitImplShouldBeAsync { span: impl_m_span, method_name: trait_m.name, trait_item_span, })); } }; } Ok(()) } /// Given a method def-id in an impl, compare the method signature of the impl /// against the trait that it's implementing. In doing so, infer the hidden types /// that this method's signature provides to satisfy each return-position `impl Trait` /// in the trait signature. /// /// The method is also responsible for making sure that the hidden types for each /// RPITIT actually satisfy the bounds of the `impl Trait`, i.e. that if we infer /// `impl Trait = Foo`, that `Foo: Trait` holds. /// /// For example, given the sample code: /// /// ``` /// #![feature(return_position_impl_trait_in_trait)] /// /// use std::ops::Deref; /// /// trait Foo { /// fn bar() -> impl Deref; /// // ^- RPITIT #1 ^- RPITIT #2 /// } /// /// impl Foo for () { /// fn bar() -> Box { Box::new(String::new()) } /// } /// ``` /// /// The hidden types for the RPITITs in `bar` would be inferred to: /// * `impl Deref` (RPITIT #1) = `Box` /// * `impl Sized` (RPITIT #2) = `String` /// /// The relationship between these two types is straightforward in this case, but /// may be more tenuously connected via other `impl`s and normalization rules for /// cases of more complicated nested RPITITs. #[instrument(skip(tcx), level = "debug", ret)] pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>( tcx: TyCtxt<'tcx>, def_id: DefId, ) -> Result<&'tcx FxHashMap>, ErrorGuaranteed> { let impl_m = tcx.opt_associated_item(def_id).unwrap(); let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap(); let impl_trait_ref = tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap().subst_identity(); let param_env = tcx.param_env(def_id); // First, check a few of the same things as `compare_impl_method`, // just so we don't ICE during substitution later. compare_number_of_generics(tcx, impl_m, trait_m, tcx.hir().span_if_local(impl_m.def_id), true)?; compare_generic_param_kinds(tcx, impl_m, trait_m, true)?; check_region_bounds_on_impl_item(tcx, impl_m, trait_m, true)?; let trait_to_impl_substs = impl_trait_ref.substs; let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local()); let return_span = tcx.hir().fn_decl_by_hir_id(impl_m_hir_id).unwrap().output.span(); let cause = ObligationCause::new( return_span, impl_m_hir_id, ObligationCauseCode::CompareImplItemObligation { impl_item_def_id: impl_m.def_id.expect_local(), trait_item_def_id: trait_m.def_id, kind: impl_m.kind, }, ); // Create mapping from impl to placeholder. let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id); // Create mapping from trait to placeholder. let trait_to_placeholder_substs = impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs); let infcx = &tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(infcx); // Normalize the impl signature with fresh variables for lifetime inference. let norm_cause = ObligationCause::misc(return_span, impl_m_hir_id); let impl_sig = ocx.normalize( &norm_cause, param_env, infcx.replace_bound_vars_with_fresh_vars( return_span, infer::HigherRankedType, tcx.fn_sig(impl_m.def_id), ), ); impl_sig.error_reported()?; let impl_return_ty = impl_sig.output(); // Normalize the trait signature with liberated bound vars, passing it through // the ImplTraitInTraitCollector, which gathers all of the RPITITs and replaces // them with inference variables. // We will use these inference variables to collect the hidden types of RPITITs. let mut collector = ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_hir_id); let unnormalized_trait_sig = tcx .liberate_late_bound_regions( impl_m.def_id, tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs), ) .fold_with(&mut collector); let trait_sig = ocx.normalize(&norm_cause, param_env, unnormalized_trait_sig); trait_sig.error_reported()?; let trait_return_ty = trait_sig.output(); let wf_tys = FxIndexSet::from_iter( unnormalized_trait_sig.inputs_and_output.iter().chain(trait_sig.inputs_and_output.iter()), ); match ocx.eq(&cause, param_env, trait_return_ty, impl_return_ty) { Ok(()) => {} Err(terr) => { let mut diag = struct_span_err!( tcx.sess, cause.span(), E0053, "method `{}` has an incompatible return type for trait", trait_m.name ); let hir = tcx.hir(); infcx.err_ctxt().note_type_err( &mut diag, &cause, hir.get_if_local(impl_m.def_id) .and_then(|node| node.fn_decl()) .map(|decl| (decl.output.span(), "return type in trait".to_owned())), Some(infer::ValuePairs::Terms(ExpectedFound { expected: trait_return_ty.into(), found: impl_return_ty.into(), })), terr, false, false, ); return Err(diag.emit()); } } debug!(?trait_sig, ?impl_sig, "equating function signatures"); // Unify the whole function signature. We need to do this to fully infer // the lifetimes of the return type, but do this after unifying just the // return types, since we want to avoid duplicating errors from // `compare_method_predicate_entailment`. match ocx.eq(&cause, param_env, trait_sig, impl_sig) { Ok(()) => {} Err(terr) => { // This function gets called during `compare_method_predicate_entailment` when normalizing a // signature that contains RPITIT. When the method signatures don't match, we have to // emit an error now because `compare_method_predicate_entailment` will not report the error // when normalization fails. let emitted = report_trait_method_mismatch( infcx, cause, terr, (trait_m, trait_sig), (impl_m, impl_sig), impl_trait_ref, ); return Err(emitted); } } // Check that all obligations are satisfied by the implementation's // RPITs. let errors = ocx.select_all_or_error(); if !errors.is_empty() { let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None); return Err(reported); } // Finally, resolve all regions. This catches wily misuses of // lifetime parameters. let outlives_environment = OutlivesEnvironment::with_bounds( param_env, Some(infcx), infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys), ); infcx.err_ctxt().check_region_obligations_and_report_errors( impl_m.def_id.expect_local(), &outlives_environment, )?; let mut collected_tys = FxHashMap::default(); for (def_id, (ty, substs)) in collector.types { match infcx.fully_resolve(ty) { Ok(ty) => { // `ty` contains free regions that we created earlier while liberating the // trait fn signature. However, projection normalization expects `ty` to // contains `def_id`'s early-bound regions. let id_substs = InternalSubsts::identity_for_item(tcx, def_id); debug!(?id_substs, ?substs); let map: FxHashMap, ty::GenericArg<'tcx>> = std::iter::zip(substs, id_substs).collect(); debug!(?map); // NOTE(compiler-errors): RPITITs, like all other RPITs, have early-bound // region substs that are synthesized during AST lowering. These are substs // that are appended to the parent substs (trait and trait method). However, // we're trying to infer the unsubstituted type value of the RPITIT inside // the *impl*, so we can later use the impl's method substs to normalize // an RPITIT to a concrete type (`confirm_impl_trait_in_trait_candidate`). // // Due to the design of RPITITs, during AST lowering, we have no idea that // an impl method corresponds to a trait method with RPITITs in it. Therefore, // we don't have a list of early-bound region substs for the RPITIT in the impl. // Since early region parameters are index-based, we can't just rebase these // (trait method) early-bound region substs onto the impl, and there's no // guarantee that the indices from the trait substs and impl substs line up. // So to fix this, we subtract the number of trait substs and add the number of // impl substs to *renumber* these early-bound regions to their corresponding // indices in the impl's substitutions list. // // Also, we only need to account for a difference in trait and impl substs, // since we previously enforce that the trait method and impl method have the // same generics. let num_trait_substs = trait_to_impl_substs.len(); let num_impl_substs = tcx.generics_of(impl_m.container_id(tcx)).params.len(); let ty = tcx.fold_regions(ty, |region, _| { match region.kind() { // Remap all free regions, which correspond to late-bound regions in the function. ty::ReFree(_) => {} // Remap early-bound regions as long as they don't come from the `impl` itself. ty::ReEarlyBound(ebr) if tcx.parent(ebr.def_id) != impl_m.container_id(tcx) => {} _ => return region, } let Some(ty::ReEarlyBound(e)) = map.get(®ion.into()).map(|r| r.expect_region().kind()) else { tcx .sess .delay_span_bug( return_span, "expected ReFree to map to ReEarlyBound" ); return tcx.lifetimes.re_static; }; tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: e.def_id, name: e.name, index: (e.index as usize - num_trait_substs + num_impl_substs) as u32, })) }); debug!(%ty); collected_tys.insert(def_id, ty); } Err(err) => { let reported = tcx.sess.delay_span_bug( return_span, format!("could not fully resolve: {ty} => {err:?}"), ); collected_tys.insert(def_id, tcx.ty_error_with_guaranteed(reported)); } } } Ok(&*tcx.arena.alloc(collected_tys)) } struct ImplTraitInTraitCollector<'a, 'tcx> { ocx: &'a ObligationCtxt<'a, 'tcx>, types: FxHashMap, ty::SubstsRef<'tcx>)>, span: Span, param_env: ty::ParamEnv<'tcx>, body_id: hir::HirId, } impl<'a, 'tcx> ImplTraitInTraitCollector<'a, 'tcx> { fn new( ocx: &'a ObligationCtxt<'a, 'tcx>, span: Span, param_env: ty::ParamEnv<'tcx>, body_id: hir::HirId, ) -> Self { ImplTraitInTraitCollector { ocx, types: FxHashMap::default(), span, param_env, body_id } } } impl<'tcx> TypeFolder<'tcx> for ImplTraitInTraitCollector<'_, 'tcx> { fn tcx<'a>(&'a self) -> TyCtxt<'tcx> { self.ocx.infcx.tcx } fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { if let ty::Alias(ty::Projection, proj) = ty.kind() && self.tcx().def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder { if let Some((ty, _)) = self.types.get(&proj.def_id) { return *ty; } //FIXME(RPITIT): Deny nested RPITIT in substs too if proj.substs.has_escaping_bound_vars() { bug!("FIXME(RPITIT): error here"); } // Replace with infer var let infer_ty = self.ocx.infcx.next_ty_var(TypeVariableOrigin { span: self.span, kind: TypeVariableOriginKind::MiscVariable, }); self.types.insert(proj.def_id, (infer_ty, proj.substs)); // Recurse into bounds for (pred, pred_span) in self.tcx().bound_explicit_item_bounds(proj.def_id).subst_iter_copied(self.tcx(), proj.substs) { let pred = pred.fold_with(self); let pred = self.ocx.normalize( &ObligationCause::misc(self.span, self.body_id), self.param_env, pred, ); self.ocx.register_obligation(traits::Obligation::new( self.tcx(), ObligationCause::new( self.span, self.body_id, ObligationCauseCode::BindingObligation(proj.def_id, pred_span), ), self.param_env, pred, )); } infer_ty } else { ty.super_fold_with(self) } } } fn report_trait_method_mismatch<'tcx>( infcx: &InferCtxt<'tcx>, mut cause: ObligationCause<'tcx>, terr: TypeError<'tcx>, (trait_m, trait_sig): (&ty::AssocItem, ty::FnSig<'tcx>), (impl_m, impl_sig): (&ty::AssocItem, ty::FnSig<'tcx>), impl_trait_ref: ty::TraitRef<'tcx>, ) -> ErrorGuaranteed { let tcx = infcx.tcx; let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(&infcx, terr, &cause, impl_m, trait_m); let mut diag = struct_span_err!( tcx.sess, impl_err_span, E0053, "method `{}` has an incompatible type for trait", trait_m.name ); match &terr { TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0) if trait_m.fn_has_self_parameter => { let ty = trait_sig.inputs()[0]; let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty()) { ExplicitSelf::ByValue => "self".to_owned(), ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(), ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(), _ => format!("self: {ty}"), }; // When the `impl` receiver is an arbitrary self type, like `self: Box`, the // span points only at the type `Box, but we want to cover the whole // argument pattern and type. let ImplItemKind::Fn(ref sig, body) = tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind else { bug!("{impl_m:?} is not a method") }; let span = tcx .hir() .body_param_names(body) .zip(sig.decl.inputs.iter()) .map(|(param, ty)| param.span.to(ty.span)) .next() .unwrap_or(impl_err_span); diag.span_suggestion( span, "change the self-receiver type to match the trait", sugg, Applicability::MachineApplicable, ); } TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => { if trait_sig.inputs().len() == *i { // Suggestion to change output type. We do not suggest in `async` functions // to avoid complex logic or incorrect output. if let ImplItemKind::Fn(sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind && !sig.header.asyncness.is_async() { let msg = "change the output type to match the trait"; let ap = Applicability::MachineApplicable; match sig.decl.output { hir::FnRetTy::DefaultReturn(sp) => { let sugg = format!("-> {} ", trait_sig.output()); diag.span_suggestion_verbose(sp, msg, sugg, ap); } hir::FnRetTy::Return(hir_ty) => { let sugg = trait_sig.output(); diag.span_suggestion(hir_ty.span, msg, sugg, ap); } }; }; } else if let Some(trait_ty) = trait_sig.inputs().get(*i) { diag.span_suggestion( impl_err_span, "change the parameter type to match the trait", trait_ty, Applicability::MachineApplicable, ); } } _ => {} } cause.span = impl_err_span; infcx.err_ctxt().note_type_err( &mut diag, &cause, trait_err_span.map(|sp| (sp, "type in trait".to_owned())), Some(infer::ValuePairs::Sigs(ExpectedFound { expected: trait_sig, found: impl_sig })), terr, false, false, ); return diag.emit(); } fn check_region_bounds_on_impl_item<'tcx>( tcx: TyCtxt<'tcx>, impl_m: &ty::AssocItem, trait_m: &ty::AssocItem, delay: bool, ) -> Result<(), ErrorGuaranteed> { let impl_generics = tcx.generics_of(impl_m.def_id); let impl_params = impl_generics.own_counts().lifetimes; let trait_generics = tcx.generics_of(trait_m.def_id); let trait_params = trait_generics.own_counts().lifetimes; debug!( "check_region_bounds_on_impl_item: \ trait_generics={:?} \ impl_generics={:?}", trait_generics, impl_generics ); // Must have same number of early-bound lifetime parameters. // Unfortunately, if the user screws up the bounds, then this // will change classification between early and late. E.g., // if in trait we have `<'a,'b:'a>`, and in impl we just have // `<'a,'b>`, then we have 2 early-bound lifetime parameters // in trait but 0 in the impl. But if we report "expected 2 // but found 0" it's confusing, because it looks like there // are zero. Since I don't quite know how to phrase things at // the moment, give a kind of vague error message. if trait_params != impl_params { let span = tcx .hir() .get_generics(impl_m.def_id.expect_local()) .expect("expected impl item to have generics or else we can't compare them") .span; let mut generics_span = None; let mut bounds_span = vec![]; let mut where_span = None; if let Some(trait_node) = tcx.hir().get_if_local(trait_m.def_id) && let Some(trait_generics) = trait_node.generics() { generics_span = Some(trait_generics.span); // FIXME: we could potentially look at the impl's bounds to not point at bounds that // *are* present in the impl. for p in trait_generics.predicates { if let hir::WherePredicate::BoundPredicate(pred) = p { for b in pred.bounds { if let hir::GenericBound::Outlives(lt) = b { bounds_span.push(lt.ident.span); } } } } if let Some(impl_node) = tcx.hir().get_if_local(impl_m.def_id) && let Some(impl_generics) = impl_node.generics() { let mut impl_bounds = 0; for p in impl_generics.predicates { if let hir::WherePredicate::BoundPredicate(pred) = p { for b in pred.bounds { if let hir::GenericBound::Outlives(_) = b { impl_bounds += 1; } } } } if impl_bounds == bounds_span.len() { bounds_span = vec![]; } else if impl_generics.has_where_clause_predicates { where_span = Some(impl_generics.where_clause_span); } } } let reported = tcx .sess .create_err(LifetimesOrBoundsMismatchOnTrait { span, item_kind: assoc_item_kind_str(impl_m), ident: impl_m.ident(tcx), generics_span, bounds_span, where_span, }) .emit_unless(delay); return Err(reported); } Ok(()) } #[instrument(level = "debug", skip(infcx))] fn extract_spans_for_error_reporting<'tcx>( infcx: &infer::InferCtxt<'tcx>, terr: TypeError<'_>, cause: &ObligationCause<'tcx>, impl_m: &ty::AssocItem, trait_m: &ty::AssocItem, ) -> (Span, Option) { let tcx = infcx.tcx; let mut impl_args = { let ImplItemKind::Fn(sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind else { bug!("{:?} is not a method", impl_m) }; sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span())) }; let trait_args = trait_m.def_id.as_local().map(|def_id| { let TraitItemKind::Fn(sig, _) = &tcx.hir().expect_trait_item(def_id).kind else { bug!("{:?} is not a TraitItemKind::Fn", trait_m) }; sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span())) }); match terr { TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(ExpectedFound { .. }, i) => { (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i))) } _ => (cause.span(), tcx.hir().span_if_local(trait_m.def_id)), } } fn compare_self_type<'tcx>( tcx: TyCtxt<'tcx>, impl_m: &ty::AssocItem, impl_m_span: Span, trait_m: &ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { // Try to give more informative error messages about self typing // mismatches. Note that any mismatch will also be detected // below, where we construct a canonical function type that // includes the self parameter as a normal parameter. It's just // that the error messages you get out of this code are a bit more // inscrutable, particularly for cases where one method has no // self. let self_string = |method: &ty::AssocItem| { let untransformed_self_ty = match method.container { ty::ImplContainer => impl_trait_ref.self_ty(), ty::TraitContainer => tcx.types.self_param, }; let self_arg_ty = tcx.fn_sig(method.def_id).input(0); let param_env = ty::ParamEnv::reveal_all(); let infcx = tcx.infer_ctxt().build(); let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty); let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok(); match ExplicitSelf::determine(self_arg_ty, can_eq_self) { ExplicitSelf::ByValue => "self".to_owned(), ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(), ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(), _ => format!("self: {self_arg_ty}"), } }; match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) { (false, false) | (true, true) => {} (false, true) => { let self_descr = self_string(impl_m); let mut err = struct_span_err!( tcx.sess, impl_m_span, E0185, "method `{}` has a `{}` declaration in the impl, but not in the trait", trait_m.name, self_descr ); err.span_label(impl_m_span, format!("`{self_descr}` used in impl")); if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) { err.span_label(span, format!("trait method declared without `{self_descr}`")); } else { err.note_trait_signature(trait_m.name, trait_m.signature(tcx)); } return Err(err.emit()); } (true, false) => { let self_descr = self_string(trait_m); let mut err = struct_span_err!( tcx.sess, impl_m_span, E0186, "method `{}` has a `{}` declaration in the trait, but not in the impl", trait_m.name, self_descr ); err.span_label(impl_m_span, format!("expected `{self_descr}` in impl")); if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) { err.span_label(span, format!("`{self_descr}` used in trait")); } else { err.note_trait_signature(trait_m.name, trait_m.signature(tcx)); } return Err(err.emit()); } } Ok(()) } /// Checks that the number of generics on a given assoc item in a trait impl is the same /// as the number of generics on the respective assoc item in the trait definition. /// /// For example this code emits the errors in the following code: /// ``` /// trait Trait { /// fn foo(); /// type Assoc; /// } /// /// impl Trait for () { /// fn foo() {} /// //~^ error /// type Assoc = u32; /// //~^ error /// } /// ``` /// /// Notably this does not error on `foo` implemented as `foo` or /// `foo` implemented as `foo`. This is handled in /// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters fn compare_number_of_generics<'tcx>( tcx: TyCtxt<'tcx>, impl_: &ty::AssocItem, trait_: &ty::AssocItem, trait_span: Option, delay: bool, ) -> Result<(), ErrorGuaranteed> { let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts(); let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts(); // This avoids us erroring on `foo` implemented as `foo` as this is implemented // in `compare_generic_param_kinds` which will give a nicer error message than something like: // "expected 1 type parameter, found 0 type parameters" if (trait_own_counts.types + trait_own_counts.consts) == (impl_own_counts.types + impl_own_counts.consts) { return Ok(()); } let matchings = [ ("type", trait_own_counts.types, impl_own_counts.types), ("const", trait_own_counts.consts, impl_own_counts.consts), ]; let item_kind = assoc_item_kind_str(impl_); let mut err_occurred = None; for (kind, trait_count, impl_count) in matchings { if impl_count != trait_count { let arg_spans = |kind: ty::AssocKind, generics: &hir::Generics<'_>| { let mut spans = generics .params .iter() .filter(|p| match p.kind { hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Elided, } => { // A fn can have an arbitrary number of extra elided lifetimes for the // same signature. !matches!(kind, ty::AssocKind::Fn) } _ => true, }) .map(|p| p.span) .collect::>(); if spans.is_empty() { spans = vec![generics.span] } spans }; let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() { let trait_item = tcx.hir().expect_trait_item(def_id); let arg_spans: Vec = arg_spans(trait_.kind, trait_item.generics); let impl_trait_spans: Vec = trait_item .generics .params .iter() .filter_map(|p| match p.kind { GenericParamKind::Type { synthetic: true, .. } => Some(p.span), _ => None, }) .collect(); (Some(arg_spans), impl_trait_spans) } else { (trait_span.map(|s| vec![s]), vec![]) }; let impl_item = tcx.hir().expect_impl_item(impl_.def_id.expect_local()); let impl_item_impl_trait_spans: Vec = impl_item .generics .params .iter() .filter_map(|p| match p.kind { GenericParamKind::Type { synthetic: true, .. } => Some(p.span), _ => None, }) .collect(); let spans = arg_spans(impl_.kind, impl_item.generics); let span = spans.first().copied(); let mut err = tcx.sess.struct_span_err_with_code( spans, &format!( "{} `{}` has {} {kind} parameter{} but its trait \ declaration has {} {kind} parameter{}", item_kind, trait_.name, impl_count, pluralize!(impl_count), trait_count, pluralize!(trait_count), kind = kind, ), DiagnosticId::Error("E0049".into()), ); let mut suffix = None; if let Some(spans) = trait_spans { let mut spans = spans.iter(); if let Some(span) = spans.next() { err.span_label( *span, format!( "expected {} {} parameter{}", trait_count, kind, pluralize!(trait_count), ), ); } for span in spans { err.span_label(*span, ""); } } else { suffix = Some(format!(", expected {trait_count}")); } if let Some(span) = span { err.span_label( span, format!( "found {} {} parameter{}{}", impl_count, kind, pluralize!(impl_count), suffix.unwrap_or_else(String::new), ), ); } for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) { err.span_label(*span, "`impl Trait` introduces an implicit type parameter"); } let reported = err.emit_unless(delay); err_occurred = Some(reported); } } if let Some(reported) = err_occurred { Err(reported) } else { Ok(()) } } fn compare_number_of_method_arguments<'tcx>( tcx: TyCtxt<'tcx>, impl_m: &ty::AssocItem, impl_m_span: Span, trait_m: &ty::AssocItem, trait_item_span: Option, ) -> Result<(), ErrorGuaranteed> { let impl_m_fty = tcx.fn_sig(impl_m.def_id); let trait_m_fty = tcx.fn_sig(trait_m.def_id); let trait_number_args = trait_m_fty.inputs().skip_binder().len(); let impl_number_args = impl_m_fty.inputs().skip_binder().len(); if trait_number_args != impl_number_args { let trait_span = trait_m .def_id .as_local() .and_then(|def_id| { let TraitItemKind::Fn(trait_m_sig, _) = &tcx.hir().expect_trait_item(def_id).kind else { bug!("{:?} is not a method", impl_m) }; let pos = trait_number_args.saturating_sub(1); trait_m_sig.decl.inputs.get(pos).map(|arg| { if pos == 0 { arg.span } else { arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo()) } }) }) .or(trait_item_span); let ImplItemKind::Fn(impl_m_sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind else { bug!("{:?} is not a method", impl_m) }; let pos = impl_number_args.saturating_sub(1); let impl_span = impl_m_sig .decl .inputs .get(pos) .map(|arg| { if pos == 0 { arg.span } else { arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo()) } }) .unwrap_or(impl_m_span); let mut err = struct_span_err!( tcx.sess, impl_span, E0050, "method `{}` has {} but the declaration in trait `{}` has {}", trait_m.name, potentially_plural_count(impl_number_args, "parameter"), tcx.def_path_str(trait_m.def_id), trait_number_args ); if let Some(trait_span) = trait_span { err.span_label( trait_span, format!( "trait requires {}", potentially_plural_count(trait_number_args, "parameter") ), ); } else { err.note_trait_signature(trait_m.name, trait_m.signature(tcx)); } err.span_label( impl_span, format!( "expected {}, found {}", potentially_plural_count(trait_number_args, "parameter"), impl_number_args ), ); return Err(err.emit()); } Ok(()) } fn compare_synthetic_generics<'tcx>( tcx: TyCtxt<'tcx>, impl_m: &ty::AssocItem, trait_m: &ty::AssocItem, ) -> Result<(), ErrorGuaranteed> { // FIXME(chrisvittal) Clean up this function, list of FIXME items: // 1. Better messages for the span labels // 2. Explanation as to what is going on // If we get here, we already have the same number of generics, so the zip will // be okay. let mut error_found = None; let impl_m_generics = tcx.generics_of(impl_m.def_id); let trait_m_generics = tcx.generics_of(trait_m.def_id); let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind { GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)), GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None, }); let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind { GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)), GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None, }); for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in iter::zip(impl_m_type_params, trait_m_type_params) { if impl_synthetic != trait_synthetic { let impl_def_id = impl_def_id.expect_local(); let impl_span = tcx.def_span(impl_def_id); let trait_span = tcx.def_span(trait_def_id); let mut err = struct_span_err!( tcx.sess, impl_span, E0643, "method `{}` has incompatible signature for trait", trait_m.name ); err.span_label(trait_span, "declaration in trait here"); match (impl_synthetic, trait_synthetic) { // The case where the impl method uses `impl Trait` but the trait method uses // explicit generics (true, false) => { err.span_label(impl_span, "expected generic parameter, found `impl Trait`"); let _: Option<_> = try { // try taking the name from the trait impl // FIXME: this is obviously suboptimal since the name can already be used // as another generic argument let new_name = tcx.opt_item_name(trait_def_id)?; let trait_m = trait_m.def_id.as_local()?; let trait_m = tcx.hir().expect_trait_item(trait_m); let impl_m = impl_m.def_id.as_local()?; let impl_m = tcx.hir().expect_impl_item(impl_m); // in case there are no generics, take the spot between the function name // and the opening paren of the argument list let new_generics_span = tcx.def_ident_span(impl_def_id)?.shrink_to_hi(); // in case there are generics, just replace them let generics_span = impl_m.generics.span.substitute_dummy(new_generics_span); // replace with the generics from the trait let new_generics = tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?; err.multipart_suggestion( "try changing the `impl Trait` argument to a generic parameter", vec![ // replace `impl Trait` with `T` (impl_span, new_name.to_string()), // replace impl method generics with trait method generics // This isn't quite right, as users might have changed the names // of the generics, but it works for the common case (generics_span, new_generics), ], Applicability::MaybeIncorrect, ); }; } // The case where the trait method uses `impl Trait`, but the impl method uses // explicit generics. (false, true) => { err.span_label(impl_span, "expected `impl Trait`, found generic parameter"); let _: Option<_> = try { let impl_m = impl_m.def_id.as_local()?; let impl_m = tcx.hir().expect_impl_item(impl_m); let hir::ImplItemKind::Fn(sig, _) = &impl_m.kind else { unreachable!() }; let input_tys = sig.decl.inputs; struct Visitor(Option, hir::def_id::LocalDefId); impl<'v> intravisit::Visitor<'v> for Visitor { fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) { intravisit::walk_ty(self, ty); if let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = ty.kind && let Res::Def(DefKind::TyParam, def_id) = path.res && def_id == self.1.to_def_id() { self.0 = Some(ty.span); } } } let mut visitor = Visitor(None, impl_def_id); for ty in input_tys { intravisit::Visitor::visit_ty(&mut visitor, ty); } let span = visitor.0?; let bounds = impl_m.generics.bounds_for_param(impl_def_id).next()?.bounds; let bounds = bounds.first()?.span().to(bounds.last()?.span()); let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?; err.multipart_suggestion( "try removing the generic parameter and using `impl Trait` instead", vec![ // delete generic parameters (impl_m.generics.span, String::new()), // replace param usage with `impl Trait` (span, format!("impl {bounds}")), ], Applicability::MaybeIncorrect, ); }; } _ => unreachable!(), } error_found = Some(err.emit()); } } if let Some(reported) = error_found { Err(reported) } else { Ok(()) } } /// Checks that all parameters in the generics of a given assoc item in a trait impl have /// the same kind as the respective generic parameter in the trait def. /// /// For example all 4 errors in the following code are emitted here: /// ``` /// trait Foo { /// fn foo(); /// type bar; /// fn baz(); /// type blah; /// } /// /// impl Foo for () { /// fn foo() {} /// //~^ error /// type bar {} /// //~^ error /// fn baz() {} /// //~^ error /// type blah = u32; /// //~^ error /// } /// ``` /// /// This function does not handle lifetime parameters fn compare_generic_param_kinds<'tcx>( tcx: TyCtxt<'tcx>, impl_item: &ty::AssocItem, trait_item: &ty::AssocItem, delay: bool, ) -> Result<(), ErrorGuaranteed> { assert_eq!(impl_item.kind, trait_item.kind); let ty_const_params_of = |def_id| { tcx.generics_of(def_id).params.iter().filter(|param| { matches!( param.kind, GenericParamDefKind::Const { .. } | GenericParamDefKind::Type { .. } ) }) }; for (param_impl, param_trait) in iter::zip(ty_const_params_of(impl_item.def_id), ty_const_params_of(trait_item.def_id)) { use GenericParamDefKind::*; if match (¶m_impl.kind, ¶m_trait.kind) { (Const { .. }, Const { .. }) if tcx.type_of(param_impl.def_id) != tcx.type_of(param_trait.def_id) => { true } (Const { .. }, Type { .. }) | (Type { .. }, Const { .. }) => true, // this is exhaustive so that anyone adding new generic param kinds knows // to make sure this error is reported for them. (Const { .. }, Const { .. }) | (Type { .. }, Type { .. }) => false, (Lifetime { .. }, _) | (_, Lifetime { .. }) => unreachable!(), } { let param_impl_span = tcx.def_span(param_impl.def_id); let param_trait_span = tcx.def_span(param_trait.def_id); let mut err = struct_span_err!( tcx.sess, param_impl_span, E0053, "{} `{}` has an incompatible generic parameter for trait `{}`", assoc_item_kind_str(&impl_item), trait_item.name, &tcx.def_path_str(tcx.parent(trait_item.def_id)) ); let make_param_message = |prefix: &str, param: &ty::GenericParamDef| match param.kind { Const { .. } => { format!("{} const parameter of type `{}`", prefix, tcx.type_of(param.def_id)) } Type { .. } => format!("{} type parameter", prefix), Lifetime { .. } => unreachable!(), }; let trait_header_span = tcx.def_ident_span(tcx.parent(trait_item.def_id)).unwrap(); err.span_label(trait_header_span, ""); err.span_label(param_trait_span, make_param_message("expected", param_trait)); let impl_header_span = tcx.def_span(tcx.parent(impl_item.def_id)); err.span_label(impl_header_span, ""); err.span_label(param_impl_span, make_param_message("found", param_impl)); let reported = err.emit_unless(delay); return Err(reported); } } Ok(()) } /// Use `tcx.compare_impl_const` instead pub(super) fn compare_impl_const_raw( tcx: TyCtxt<'_>, (impl_const_item_def, trait_const_item_def): (LocalDefId, DefId), ) -> Result<(), ErrorGuaranteed> { let impl_const_item = tcx.associated_item(impl_const_item_def); let trait_const_item = tcx.associated_item(trait_const_item_def); let impl_trait_ref = tcx.impl_trait_ref(impl_const_item.container_id(tcx)).unwrap().subst_identity(); debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref); let impl_c_span = tcx.def_span(impl_const_item_def.to_def_id()); let infcx = tcx.infer_ctxt().build(); let param_env = tcx.param_env(impl_const_item_def.to_def_id()); let ocx = ObligationCtxt::new(&infcx); // The below is for the most part highly similar to the procedure // for methods above. It is simpler in many respects, especially // because we shouldn't really have to deal with lifetimes or // predicates. In fact some of this should probably be put into // shared functions because of DRY violations... let trait_to_impl_substs = impl_trait_ref.substs; // Create a parameter environment that represents the implementation's // method. let impl_c_hir_id = tcx.hir().local_def_id_to_hir_id(impl_const_item_def); // Compute placeholder form of impl and trait const tys. let impl_ty = tcx.type_of(impl_const_item_def.to_def_id()); let trait_ty = tcx.bound_type_of(trait_const_item_def).subst(tcx, trait_to_impl_substs); let mut cause = ObligationCause::new( impl_c_span, impl_c_hir_id, ObligationCauseCode::CompareImplItemObligation { impl_item_def_id: impl_const_item_def, trait_item_def_id: trait_const_item_def, kind: impl_const_item.kind, }, ); // There is no "body" here, so just pass dummy id. let impl_ty = ocx.normalize(&cause, param_env, impl_ty); debug!("compare_const_impl: impl_ty={:?}", impl_ty); let trait_ty = ocx.normalize(&cause, param_env, trait_ty); debug!("compare_const_impl: trait_ty={:?}", trait_ty); let err = ocx.sup(&cause, param_env, trait_ty, impl_ty); if let Err(terr) = err { debug!( "checking associated const for compatibility: impl ty {:?}, trait ty {:?}", impl_ty, trait_ty ); // Locate the Span containing just the type of the offending impl let ImplItemKind::Const(ty, _) = tcx.hir().expect_impl_item(impl_const_item_def).kind else { bug!("{impl_const_item:?} is not a impl const") }; cause.span = ty.span; let mut diag = struct_span_err!( tcx.sess, cause.span, E0326, "implemented const `{}` has an incompatible type for trait", trait_const_item.name ); let trait_c_span = trait_const_item_def.as_local().map(|trait_c_def_id| { // Add a label to the Span containing just the type of the const let TraitItemKind::Const(ty, _) = tcx.hir().expect_trait_item(trait_c_def_id).kind else { bug!("{trait_const_item:?} is not a trait const") }; ty.span }); infcx.err_ctxt().note_type_err( &mut diag, &cause, trait_c_span.map(|span| (span, "type in trait".to_owned())), Some(infer::ValuePairs::Terms(ExpectedFound { expected: trait_ty.into(), found: impl_ty.into(), })), terr, false, false, ); return Err(diag.emit()); }; // Check that all obligations are satisfied by the implementation's // version. let errors = ocx.select_all_or_error(); if !errors.is_empty() { return Err(infcx.err_ctxt().report_fulfillment_errors(&errors, None)); } let outlives_environment = OutlivesEnvironment::new(param_env); infcx .err_ctxt() .check_region_obligations_and_report_errors(impl_const_item_def, &outlives_environment)?; Ok(()) } pub(super) fn compare_impl_ty<'tcx>( tcx: TyCtxt<'tcx>, impl_ty: &ty::AssocItem, impl_ty_span: Span, trait_ty: &ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, trait_item_span: Option, ) { debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref); let _: Result<(), ErrorGuaranteed> = try { compare_number_of_generics(tcx, impl_ty, trait_ty, trait_item_span, false)?; compare_generic_param_kinds(tcx, impl_ty, trait_ty, false)?; let sp = tcx.def_span(impl_ty.def_id); compare_type_predicate_entailment(tcx, impl_ty, sp, trait_ty, impl_trait_ref)?; check_type_bounds(tcx, trait_ty, impl_ty, impl_ty_span, impl_trait_ref)?; }; } /// The equivalent of [compare_method_predicate_entailment], but for associated types /// instead of associated functions. fn compare_type_predicate_entailment<'tcx>( tcx: TyCtxt<'tcx>, impl_ty: &ty::AssocItem, impl_ty_span: Span, trait_ty: &ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id); let trait_to_impl_substs = impl_substs.rebase_onto(tcx, impl_ty.container_id(tcx), impl_trait_ref.substs); let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id); let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id); check_region_bounds_on_impl_item(tcx, impl_ty, trait_ty, false)?; let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs); if impl_ty_own_bounds.len() == 0 { // Nothing to check. return Ok(()); } // This `HirId` should be used for the `body_id` field on each // `ObligationCause` (and the `FnCtxt`). This is what // `regionck_item` expects. let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local()); debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs); // The predicates declared by the impl definition, the trait and the // associated type in the trait are assumed. let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap()); let mut hybrid_preds = impl_predicates.instantiate_identity(tcx); hybrid_preds.predicates.extend( trait_ty_predicates .instantiate_own(tcx, trait_to_impl_substs) .map(|(predicate, _)| predicate), ); debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds); let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id); let param_env = ty::ParamEnv::new( tcx.intern_predicates(&hybrid_preds.predicates), Reveal::UserFacing, hir::Constness::NotConst, ); let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause); let infcx = tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(&infcx); debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds()); for (predicate, span) in impl_ty_own_bounds { let cause = ObligationCause::misc(span, impl_ty_hir_id); let predicate = ocx.normalize(&cause, param_env, predicate); let cause = ObligationCause::new( span, impl_ty_hir_id, ObligationCauseCode::CompareImplItemObligation { impl_item_def_id: impl_ty.def_id.expect_local(), trait_item_def_id: trait_ty.def_id, kind: impl_ty.kind, }, ); ocx.register_obligation(traits::Obligation::new(tcx, cause, param_env, predicate)); } // Check that all obligations are satisfied by the implementation's // version. let errors = ocx.select_all_or_error(); if !errors.is_empty() { let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None); return Err(reported); } // Finally, resolve all regions. This catches wily misuses of // lifetime parameters. let outlives_environment = OutlivesEnvironment::new(param_env); infcx.err_ctxt().check_region_obligations_and_report_errors( impl_ty.def_id.expect_local(), &outlives_environment, )?; Ok(()) } /// Validate that `ProjectionCandidate`s created for this associated type will /// be valid. /// /// Usually given /// /// trait X { type Y: Copy } impl X for T { type Y = S; } /// /// We are able to normalize `::U` to `S`, and so when we check the /// impl is well-formed we have to prove `S: Copy`. /// /// For default associated types the normalization is not possible (the value /// from the impl could be overridden). We also can't normalize generic /// associated types (yet) because they contain bound parameters. #[instrument(level = "debug", skip(tcx))] pub(super) fn check_type_bounds<'tcx>( tcx: TyCtxt<'tcx>, trait_ty: &ty::AssocItem, impl_ty: &ty::AssocItem, impl_ty_span: Span, impl_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { // Given // // impl Foo for (A, B) { // type Bar =... // } // // - `impl_trait_ref` would be `<(A, B) as Foo> // - `impl_ty_substs` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0) // - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from // the *trait* with the generic associated type parameters (as bound vars). // // A note regarding the use of bound vars here: // Imagine as an example // ``` // trait Family { // type Member; // } // // impl Family for VecFamily { // type Member = i32; // } // ``` // Here, we would generate // ```notrust // forall { Normalize(::Member => i32) } // ``` // when we really would like to generate // ```notrust // forall { Normalize(::Member => i32) :- Implemented(C: Eq) } // ``` // But, this is probably fine, because although the first clause can be used with types C that // do not implement Eq, for it to cause some kind of problem, there would have to be a // VecFamily::Member for some type X where !(X: Eq), that appears in the value of type // Member = .... That type would fail a well-formedness check that we ought to be doing // elsewhere, which would check that any ::Member meets the bounds declared in // the trait (notably, that X: Eq and T: Family). let defs: &ty::Generics = tcx.generics_of(impl_ty.def_id); let mut substs = smallvec::SmallVec::with_capacity(defs.count()); if let Some(def_id) = defs.parent { let parent_defs = tcx.generics_of(def_id); InternalSubsts::fill_item(&mut substs, tcx, parent_defs, &mut |param, _| { tcx.mk_param_from_def(param) }); } let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> = smallvec::SmallVec::with_capacity(defs.count()); InternalSubsts::fill_single(&mut substs, defs, &mut |param, _| match param.kind { GenericParamDefKind::Type { .. } => { let kind = ty::BoundTyKind::Param(param.name); let bound_var = ty::BoundVariableKind::Ty(kind); bound_vars.push(bound_var); tcx.mk_ty(ty::Bound( ty::INNERMOST, ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind }, )) .into() } GenericParamDefKind::Lifetime => { let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name); let bound_var = ty::BoundVariableKind::Region(kind); bound_vars.push(bound_var); tcx.mk_region(ty::ReLateBound( ty::INNERMOST, ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind }, )) .into() } GenericParamDefKind::Const { .. } => { let bound_var = ty::BoundVariableKind::Const; bound_vars.push(bound_var); tcx.mk_const( ty::ConstKind::Bound(ty::INNERMOST, ty::BoundVar::from_usize(bound_vars.len() - 1)), tcx.type_of(param.def_id), ) .into() } }); let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter()); let impl_ty_substs = tcx.intern_substs(&substs); let container_id = impl_ty.container_id(tcx); let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs); let impl_ty_value = tcx.type_of(impl_ty.def_id); let param_env = tcx.param_env(impl_ty.def_id); // When checking something like // // trait X { type Y: PartialEq<::Y> } // impl X for T { default type Y = S; } // // We will have to prove the bound S: PartialEq<::Y>. In this case // we want ::Y to normalize to S. This is valid because we are // checking the default value specifically here. Add this equality to the // ParamEnv for normalization specifically. let normalize_param_env = { let mut predicates = param_env.caller_bounds().iter().collect::>(); match impl_ty_value.kind() { ty::Alias(ty::Projection, proj) if proj.def_id == trait_ty.def_id && proj.substs == rebased_substs => { // Don't include this predicate if the projected type is // exactly the same as the projection. This can occur in // (somewhat dubious) code like this: // // impl X for T where T: X { type Y = ::Y; } } _ => predicates.push( ty::Binder::bind_with_vars( ty::ProjectionPredicate { projection_ty: tcx.mk_alias_ty(trait_ty.def_id, rebased_substs), term: impl_ty_value.into(), }, bound_vars, ) .to_predicate(tcx), ), }; ty::ParamEnv::new( tcx.intern_predicates(&predicates), Reveal::UserFacing, param_env.constness(), ) }; debug!(?normalize_param_env); let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local()); let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id); let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs); let infcx = tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(&infcx); let assumed_wf_types = ocx.assumed_wf_types(param_env, impl_ty_span, impl_ty.def_id.expect_local()); let normalize_cause = ObligationCause::new( impl_ty_span, impl_ty_hir_id, ObligationCauseCode::CheckAssociatedTypeBounds { impl_item_def_id: impl_ty.def_id.expect_local(), trait_item_def_id: trait_ty.def_id, }, ); let mk_cause = |span: Span| { let code = if span.is_dummy() { traits::ItemObligation(trait_ty.def_id) } else { traits::BindingObligation(trait_ty.def_id, span) }; ObligationCause::new(impl_ty_span, impl_ty_hir_id, code) }; let obligations = tcx .bound_explicit_item_bounds(trait_ty.def_id) .subst_iter_copied(tcx, rebased_substs) .map(|(concrete_ty_bound, span)| { debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound); traits::Obligation::new(tcx, mk_cause(span), param_env, concrete_ty_bound) }) .collect(); debug!("check_type_bounds: item_bounds={:?}", obligations); for mut obligation in util::elaborate_obligations(tcx, obligations) { let normalized_predicate = ocx.normalize(&normalize_cause, normalize_param_env, obligation.predicate); debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate); obligation.predicate = normalized_predicate; ocx.register_obligation(obligation); } // Check that all obligations are satisfied by the implementation's // version. let errors = ocx.select_all_or_error(); if !errors.is_empty() { let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None); return Err(reported); } // Finally, resolve all regions. This catches wily misuses of // lifetime parameters. let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_hir_id, assumed_wf_types); let outlives_environment = OutlivesEnvironment::with_bounds(param_env, Some(&infcx), implied_bounds); infcx.err_ctxt().check_region_obligations_and_report_errors( impl_ty.def_id.expect_local(), &outlives_environment, )?; Ok(()) } fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str { match impl_item.kind { ty::AssocKind::Const => "const", ty::AssocKind::Fn => "method", ty::AssocKind::Type => "type", } }