use super::potentially_plural_count; use crate::errors::LifetimesOrBoundsMismatchOnTrait; use hir::def_id::{DefId, LocalDefId}; use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet}; use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed}; use rustc_hir as hir; use rustc_hir::def::{DefKind, Res}; use rustc_hir::intravisit; use rustc_hir::{GenericParamKind, ImplItemKind}; 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::fold::BottomUpFolder; use rustc_middle::ty::util::ExplicitSelf; use rustc_middle::ty::ToPredicate; use rustc_middle::ty::{ self, GenericArgs, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt, }; use rustc_middle::ty::{GenericParamDefKind, TyCtxt}; use rustc_span::{Span, DUMMY_SP}; 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::borrow::Cow; use std::iter; mod refine; /// 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 /// - `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>, ) { debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref); let _: Result<_, ErrorGuaranteed> = try { check_method_is_structurally_compatible(tcx, impl_m, trait_m, impl_trait_ref, false)?; compare_method_predicate_entailment(tcx, impl_m, trait_m, impl_trait_ref)?; refine::check_refining_return_position_impl_trait_in_trait( tcx, impl_m, trait_m, impl_trait_ref, ); }; } /// Checks a bunch of different properties of the impl/trait methods for /// compatibility, such as asyncness, number of argument, self receiver kind, /// and number of early- and late-bound generics. fn check_method_is_structurally_compatible<'tcx>( tcx: TyCtxt<'tcx>, impl_m: ty::AssocItem, trait_m: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, delay: bool, ) -> Result<(), ErrorGuaranteed> { compare_self_type(tcx, impl_m, trait_m, impl_trait_ref, delay)?; compare_number_of_generics(tcx, impl_m, trait_m, delay)?; compare_generic_param_kinds(tcx, impl_m, trait_m, delay)?; compare_number_of_method_arguments(tcx, impl_m, trait_m, delay)?; compare_synthetic_generics(tcx, impl_m, trait_m, delay)?; compare_asyncness(tcx, impl_m, trait_m, delay)?; check_region_bounds_on_impl_item(tcx, impl_m, trait_m, delay)?; Ok(()) } /// This function is best explained by example. Consider a trait with its implementation: /// /// ```rust /// trait Trait<'t, T> { /// // `trait_m` /// fn method<'a, M>(t: &'t T, m: &'a M) -> Self; /// } /// /// struct Foo; /// /// impl<'i, 'j, U> Trait<'j, &'i U> for Foo { /// // `impl_m` /// fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo { 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_args`, that maps the trait /// type parameters to impl type parameters. This is taken from the /// impl trait reference: /// /// ```rust,ignore (pseudo-Rust) /// trait_to_impl_args = {'t => 'j, T => &'i U, Self => Foo} /// ``` /// /// We create a mapping `dummy_args` 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). /// /// ```rust,ignore (pseudo-Rust) /// impl_to_placeholder_args = {'i => 'i0, U => U0, N => N0 } /// ``` /// /// Now we can apply `placeholder_args` to the type of the impl method /// to yield a new function type in terms of our fresh, placeholder /// types: /// /// ```rust,ignore (pseudo-Rust) /// <'b> fn(t: &'i0 U0, m: &'b N0) -> 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_args` and /// `impl_to_placeholder_args`, and also adding a mapping for the method /// type parameters. We extend the mapping to also include /// the method parameters. /// /// ```rust,ignore (pseudo-Rust) /// trait_to_placeholder_args = { T => &'i0 U0, Self => Foo, M => N0 } /// ``` /// /// Applying this to the trait method type yields: /// /// ```rust,ignore (pseudo-Rust) /// <'a> fn(t: &'i0 U0, m: &'a N0) -> 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_args`. We then build /// `trait_to_placeholder_args` 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_trait_ref))] fn compare_method_predicate_entailment<'tcx>( tcx: TyCtxt<'tcx>, impl_m: ty::AssocItem, trait_m: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { let trait_to_impl_args = impl_trait_ref.args; // 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_def_id = impl_m.def_id.expect_local(); let impl_m_span = tcx.def_span(impl_m_def_id); let cause = ObligationCause::new( impl_m_span, impl_m_def_id, ObligationCauseCode::CompareImplItemObligation { impl_item_def_id: impl_m_def_id, trait_item_def_id: trait_m.def_id, kind: impl_m.kind, }, ); // Create mapping from impl to placeholder. let impl_to_placeholder_args = GenericArgs::identity_for_item(tcx, impl_m.def_id); // Create mapping from trait to placeholder. let trait_to_placeholder_args = impl_to_placeholder_args.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_args); debug!("compare_impl_method: trait_to_placeholder_args={:?}", trait_to_placeholder_args); let impl_m_predicates = tcx.predicates_of(impl_m.def_id); let trait_m_predicates = tcx.predicates_of(trait_m.def_id); // 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_args) .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_def_id); let param_env = ty::ParamEnv::new(tcx.mk_clauses(&hybrid_preds.predicates), Reveal::UserFacing); 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_args); for (predicate, span) in impl_m_own_bounds { let normalize_cause = traits::ObligationCause::misc(span, impl_m_def_id); let predicate = ocx.normalize(&normalize_cause, param_env, predicate); let cause = ObligationCause::new( span, impl_m_def_id, ObligationCauseCode::CompareImplItemObligation { impl_item_def_id: impl_m_def_id, 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 mut wf_tys = FxIndexSet::default(); let unnormalized_impl_sig = infcx.instantiate_binder_with_fresh_vars( impl_m_span, infer::HigherRankedType, tcx.fn_sig(impl_m.def_id).instantiate_identity(), ); let norm_cause = ObligationCause::misc(impl_m_span, impl_m_def_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.fn_sig(trait_m.def_id).instantiate(tcx, trait_to_placeholder_args); 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 = Ty::new_fn_ptr(tcx, 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 !(impl_sig, trait_sig).references_error() { // Select obligations to make progress on inference before processing // the wf obligation below. // FIXME(-Znext-solver): Not needed when the hack below is removed. let errors = ocx.select_where_possible(); if !errors.is_empty() { let reported = infcx.err_ctxt().report_fulfillment_errors(errors); return Err(reported); } // See #108544. Annoying, we can end up in cases where, because of winnowing, // we pick param env candidates over a more general impl, leading to more // stricter lifetime requirements than we would otherwise need. This can // trigger the lint. Instead, let's only consider type outlives and // region outlives obligations. // // FIXME(-Znext-solver): Try removing this hack again once the new // solver is stable. We should just be able to register a WF pred for // the fn sig. let mut wf_args: smallvec::SmallVec<[_; 4]> = unnormalized_impl_sig.inputs_and_output.iter().map(|ty| ty.into()).collect(); // Annoyingly, asking for the WF predicates of an array (with an unevaluated const (only?)) // will give back the well-formed predicate of the same array. let mut wf_args_seen: FxHashSet<_> = wf_args.iter().copied().collect(); while let Some(arg) = wf_args.pop() { let Some(obligations) = rustc_trait_selection::traits::wf::obligations( infcx, param_env, impl_m_def_id, 0, arg, impl_m_span, ) else { continue; }; for obligation in obligations { debug!(?obligation); match obligation.predicate.kind().skip_binder() { // We need to register Projection oblgiations too, because we may end up with // an implied `X::Item: 'a`, which gets desugared into `X::Item = ?0`, `?0: 'a`. // If we only register the region outlives obligation, this leads to an unconstrained var. // See `implied_bounds_entailment_alias_var.rs` test. ty::PredicateKind::Clause( ty::ClauseKind::RegionOutlives(..) | ty::ClauseKind::TypeOutlives(..) | ty::ClauseKind::Projection(..), ) => ocx.register_obligation(obligation), ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => { if wf_args_seen.insert(arg) { wf_args.push(arg) } } _ => {} } } } } // 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); return Err(reported); } // Finally, resolve all regions. This catches wily misuses of // lifetime parameters. let outlives_env = OutlivesEnvironment::with_bounds( param_env, infcx.implied_bounds_tys(param_env, impl_m_def_id, wf_tys), ); let errors = infcx.resolve_regions(&outlives_env); if !errors.is_empty() { return Err(infcx .tainted_by_errors() .unwrap_or_else(|| infcx.err_ctxt().report_region_errors(impl_m_def_id, &errors))); } Ok(()) } struct RemapLateBound<'a, 'tcx> { tcx: TyCtxt<'tcx>, mapping: &'a FxHashMap, } impl<'tcx> TypeFolder> for RemapLateBound<'_, 'tcx> { fn interner(&self) -> TyCtxt<'tcx> { self.tcx } fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { if let ty::ReLateParam(fr) = *r { ty::Region::new_late_param( self.tcx, fr.scope, self.mapping.get(&fr.bound_region).copied().unwrap_or(fr.bound_region), ) } else { r } } } fn compare_asyncness<'tcx>( tcx: TyCtxt<'tcx>, impl_m: ty::AssocItem, trait_m: ty::AssocItem, delay: bool, ) -> Result<(), ErrorGuaranteed> { if tcx.asyncness(trait_m.def_id).is_async() { match tcx.fn_sig(impl_m.def_id).skip_binder().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 .create_err(crate::errors::AsyncTraitImplShouldBeAsync { span: tcx.def_span(impl_m.def_id), method_name: trait_m.name, trait_item_span: tcx.hir().span_if_local(trait_m.def_id), }) .emit_unless(delay)); } }; } 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: /// /// ``` /// 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>, impl_m_def_id: LocalDefId, ) -> Result<&'tcx FxHashMap>>, ErrorGuaranteed> { let impl_m = tcx.opt_associated_item(impl_m_def_id.to_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().instantiate_identity(); // First, check a few of the same things as `compare_impl_method`, // just so we don't ICE during substitution later. check_method_is_structurally_compatible(tcx, impl_m, trait_m, impl_trait_ref, true)?; let trait_to_impl_args = impl_trait_ref.args; let impl_m_hir_id = tcx.local_def_id_to_hir_id(impl_m_def_id); 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_def_id, ObligationCauseCode::CompareImplItemObligation { impl_item_def_id: impl_m_def_id, trait_item_def_id: trait_m.def_id, kind: impl_m.kind, }, ); // Create mapping from impl to placeholder. let impl_to_placeholder_args = GenericArgs::identity_for_item(tcx, impl_m.def_id); // Create mapping from trait to placeholder. let trait_to_placeholder_args = impl_to_placeholder_args.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_args); let hybrid_preds = tcx .predicates_of(impl_m.container_id(tcx)) .instantiate_identity(tcx) .into_iter() .chain(tcx.predicates_of(trait_m.def_id).instantiate_own(tcx, trait_to_placeholder_args)) .map(|(clause, _)| clause); let param_env = ty::ParamEnv::new(tcx.mk_clauses_from_iter(hybrid_preds), Reveal::UserFacing); let param_env = traits::normalize_param_env_or_error( tcx, param_env, ObligationCause::misc(tcx.def_span(impl_m_def_id), impl_m_def_id), ); let infcx = &tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(infcx); // Normalize the impl signature with fresh variables for lifetime inference. let misc_cause = ObligationCause::misc(return_span, impl_m_def_id); let impl_sig = ocx.normalize( &misc_cause, param_env, tcx.liberate_late_bound_regions( impl_m.def_id, tcx.fn_sig(impl_m.def_id).instantiate_identity(), ), ); 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_def_id); let unnormalized_trait_sig = infcx .instantiate_binder_with_fresh_vars( return_span, infer::HigherRankedType, tcx.fn_sig(trait_m.def_id).instantiate(tcx, trait_to_placeholder_args), ) .fold_with(&mut collector); if !unnormalized_trait_sig.output().references_error() { debug_assert_ne!( collector.types.len(), 0, "expect >1 RPITITs in call to `collect_return_position_impl_trait_in_trait_tys`" ); } let trait_sig = ocx.normalize(&misc_cause, param_env, unnormalized_trait_sig); trait_sig.error_reported()?; let trait_return_ty = trait_sig.output(); // RPITITs are allowed to use the implied predicates of the method that // defines them. This is because we want code like: // ``` // trait Foo { // fn test<'a, T>(_: &'a T) -> impl Sized; // } // impl Foo for () { // fn test<'a, T>(x: &'a T) -> &'a T { x } // } // ``` // .. to compile. However, since we use both the normalized and unnormalized // inputs and outputs from the substituted trait signature, we will end up // seeing the hidden type of an RPIT in the signature itself. Naively, this // means that we will use the hidden type to imply the hidden type's own // well-formedness. // // To avoid this, we replace the infer vars used for hidden type inference // with placeholders, which imply nothing about outlives bounds, and then // prove below that the hidden types are well formed. let universe = infcx.create_next_universe(); let mut idx = 0; let mapping: FxHashMap<_, _> = collector .types .iter() .map(|(_, &(ty, _))| { assert!( infcx.resolve_vars_if_possible(ty) == ty && ty.is_ty_var(), "{ty:?} should not have been constrained via normalization", ty = infcx.resolve_vars_if_possible(ty) ); idx += 1; ( ty, Ty::new_placeholder( tcx, ty::Placeholder { universe, bound: ty::BoundTy { var: ty::BoundVar::from_usize(idx), kind: ty::BoundTyKind::Anon, }, }, ), ) }) .collect(); let mut type_mapper = BottomUpFolder { tcx, ty_op: |ty| *mapping.get(&ty).unwrap_or(&ty), lt_op: |lt| lt, ct_op: |ct| ct, }; let wf_tys = FxIndexSet::from_iter( unnormalized_trait_sig .inputs_and_output .iter() .chain(trait_sig.inputs_and_output.iter()) .map(|ty| ty.fold_with(&mut type_mapper)), ); 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(), Cow::from("return type in trait"))), 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); } } // FIXME: This has the same issue as #108544, but since this isn't breaking // existing code, I'm not particularly inclined to do the same hack as above // where we process wf obligations manually. This can be fixed in a forward- // compatible way later. let collected_types = collector.types; for (_, &(ty, _)) in &collected_types { ocx.register_obligation(traits::Obligation::new( tcx, misc_cause.clone(), param_env, ty::ClauseKind::WellFormed(ty.into()), )); } // 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); return Err(reported); } // Finally, resolve all regions. This catches wily misuses of // lifetime parameters. let outlives_env = OutlivesEnvironment::with_bounds( param_env, infcx.implied_bounds_tys(param_env, impl_m_def_id, wf_tys), ); ocx.resolve_regions_and_report_errors(impl_m_def_id, &outlives_env)?; let mut remapped_types = FxHashMap::default(); for (def_id, (ty, args)) in collected_types { match infcx.fully_resolve((ty, args)) { Ok((ty, args)) => { // `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_args = GenericArgs::identity_for_item(tcx, def_id); debug!(?id_args, ?args); let map: FxHashMap<_, _> = std::iter::zip(args, id_args) .skip(tcx.generics_of(trait_m.def_id).count()) .filter_map(|(a, b)| Some((a.as_region()?, b.as_region()?))) .collect(); debug!(?map); // NOTE(compiler-errors): RPITITs, like all other RPITs, have early-bound // region args that are synthesized during AST lowering. These are args // that are appended to the parent args (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 args 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 args for the RPITIT in the impl. // Since early region parameters are index-based, we can't just rebase these // (trait method) early-bound region args onto the impl, and there's no // guarantee that the indices from the trait args and impl args line up. // So to fix this, we subtract the number of trait args and add the number of // impl args 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 args, // since we previously enforce that the trait method and impl method have the // same generics. let num_trait_args = trait_to_impl_args.len(); let num_impl_args = tcx.generics_of(impl_m.container_id(tcx)).params.len(); let ty = match ty.try_fold_with(&mut RemapHiddenTyRegions { tcx, map, num_trait_args, num_impl_args, def_id, impl_def_id: impl_m.container_id(tcx), ty, return_span, }) { Ok(ty) => ty, Err(guar) => Ty::new_error(tcx, guar), }; remapped_types.insert(def_id, ty::EarlyBinder::bind(ty)); } Err(err) => { let reported = tcx.sess.span_delayed_bug( return_span, format!("could not fully resolve: {ty} => {err:?}"), ); remapped_types.insert(def_id, ty::EarlyBinder::bind(Ty::new_error(tcx, reported))); } } } // We may not collect all RPITITs that we see in the HIR for a trait signature // because an RPITIT was located within a missing item. Like if we have a sig // returning `-> Missing`, that gets converted to `-> [type error]`, // and when walking through the signature we end up never collecting the def id // of the `impl Sized`. Insert that here, so we don't ICE later. for assoc_item in tcx.associated_types_for_impl_traits_in_associated_fn(trait_m.def_id) { if !remapped_types.contains_key(assoc_item) { remapped_types.insert( *assoc_item, ty::EarlyBinder::bind(Ty::new_error_with_message( tcx, return_span, "missing synthetic item for RPITIT", )), ); } } Ok(&*tcx.arena.alloc(remapped_types)) } struct ImplTraitInTraitCollector<'a, 'tcx> { ocx: &'a ObligationCtxt<'a, 'tcx>, types: FxHashMap, ty::GenericArgsRef<'tcx>)>, span: Span, param_env: ty::ParamEnv<'tcx>, body_id: LocalDefId, } impl<'a, 'tcx> ImplTraitInTraitCollector<'a, 'tcx> { fn new( ocx: &'a ObligationCtxt<'a, 'tcx>, span: Span, param_env: ty::ParamEnv<'tcx>, body_id: LocalDefId, ) -> Self { ImplTraitInTraitCollector { ocx, types: FxHashMap::default(), span, param_env, body_id } } } impl<'tcx> TypeFolder> for ImplTraitInTraitCollector<'_, 'tcx> { fn interner(&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.interner().is_impl_trait_in_trait(proj.def_id) { if let Some((ty, _)) = self.types.get(&proj.def_id) { return *ty; } //FIXME(RPITIT): Deny nested RPITIT in args too if proj.args.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.args)); // Recurse into bounds for (pred, pred_span) in self .interner() .explicit_item_bounds(proj.def_id) .iter_instantiated_copied(self.interner(), proj.args) { 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.interner(), 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) } } } struct RemapHiddenTyRegions<'tcx> { tcx: TyCtxt<'tcx>, map: FxHashMap, ty::Region<'tcx>>, num_trait_args: usize, num_impl_args: usize, def_id: DefId, impl_def_id: DefId, ty: Ty<'tcx>, return_span: Span, } impl<'tcx> ty::FallibleTypeFolder> for RemapHiddenTyRegions<'tcx> { type Error = ErrorGuaranteed; fn interner(&self) -> TyCtxt<'tcx> { self.tcx } fn try_fold_ty(&mut self, t: Ty<'tcx>) -> Result, Self::Error> { if let ty::Alias(ty::Opaque, ty::AliasTy { args, def_id, .. }) = *t.kind() { let mut mapped_args = Vec::with_capacity(args.len()); for (arg, v) in std::iter::zip(args, self.tcx.variances_of(def_id)) { mapped_args.push(match (arg.unpack(), v) { // Skip uncaptured opaque args (ty::GenericArgKind::Lifetime(_), ty::Bivariant) => arg, _ => arg.try_fold_with(self)?, }); } Ok(Ty::new_opaque(self.tcx, def_id, self.tcx.mk_args(&mapped_args))) } else { t.try_super_fold_with(self) } } fn try_fold_region( &mut self, region: ty::Region<'tcx>, ) -> Result, Self::Error> { match region.kind() { // Remap late-bound regions from the function. ty::ReLateParam(_) => {} // Remap early-bound regions as long as they don't come from the `impl` itself, // in which case we don't really need to renumber them. ty::ReEarlyParam(ebr) if self.tcx.parent(ebr.def_id) != self.impl_def_id => {} _ => return Ok(region), } let e = if let Some(id_region) = self.map.get(®ion) { if let ty::ReEarlyParam(e) = id_region.kind() { e } else { bug!( "expected to map region {region} to early-bound identity region, but got {id_region}" ); } } else { let guar = match region.kind() { ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. }) | ty::ReLateParam(ty::LateParamRegion { bound_region: ty::BoundRegionKind::BrNamed(def_id, _), .. }) => { let return_span = if let ty::Alias(ty::Opaque, opaque_ty) = self.ty.kind() { self.tcx.def_span(opaque_ty.def_id) } else { self.return_span }; self.tcx .sess .struct_span_err( return_span, "return type captures more lifetimes than trait definition", ) .span_label(self.tcx.def_span(def_id), "this lifetime was captured") .span_note( self.tcx.def_span(self.def_id), "hidden type must only reference lifetimes captured by this impl trait", ) .note(format!("hidden type inferred to be `{}`", self.ty)) .emit() } _ => { self.tcx.sess.span_delayed_bug(DUMMY_SP, "should've been able to remap region") } }; return Err(guar); }; Ok(ty::Region::new_early_param( self.tcx, ty::EarlyParamRegion { def_id: e.def_id, name: e.name, index: (e.index as usize - self.num_trait_args + self.num_impl_args) as u32, }, )) } } 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| 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 (sig, body) = tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).expect_fn(); 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, Cow::from("type in trait"))), Some(infer::ValuePairs::PolySigs(ExpectedFound { expected: ty::Binder::dummy(trait_sig), found: ty::Binder::dummy(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 (sig, _) = tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).expect_fn(); 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 (sig, _) = tcx.hir().expect_trait_item(def_id).expect_fn(); 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, trait_m: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, delay: bool, ) -> 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).instantiate_identity().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); 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 impl_m_span = tcx.def_span(impl_m.def_id); 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_unless(delay)); } (true, false) => { let self_descr = self_string(trait_m); let impl_m_span = tcx.def_span(impl_m.def_id); 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_unless(delay)); } } 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: /// ```rust,compile_fail /// 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, 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(()); } // We never need to emit a separate error for RPITITs, since if an RPITIT // has mismatched type or const generic arguments, then the method that it's // inheriting the generics from will also have mismatched arguments, and // we'll report an error for that instead. Delay a bug for safety, though. if trait_.is_impl_trait_in_trait() { return Err(tcx.sess.span_delayed_bug( rustc_span::DUMMY_SP, "errors comparing numbers of generics of trait/impl functions were not emitted", )); } 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 { let trait_span = tcx.hir().span_if_local(trait_.def_id); (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 msg = format!("expected {trait_count} {kind} parameter{}", pluralize!(trait_count),); if let Some(spans) = trait_spans { let mut spans = spans.iter(); if let Some(span) = spans.next() { err.span_label(*span, msg); } for span in spans { err.span_label(*span, ""); } } else { err.span_label(tcx.def_span(trait_.def_id), msg); } if let Some(span) = span { err.span_label( span, format!("found {} {} parameter{}", impl_count, kind, pluralize!(impl_count),), ); } 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, trait_m: ty::AssocItem, delay: bool, ) -> 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.skip_binder().inputs().skip_binder().len(); let impl_number_args = impl_m_fty.skip_binder().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 (trait_m_sig, _) = &tcx.hir().expect_trait_item(def_id).expect_fn(); 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_else(|| tcx.hir().span_if_local(trait_m.def_id)); let (impl_m_sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).expect_fn(); 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_else(|| tcx.def_span(impl_m.def_id)); 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_unless(delay)); } Ok(()) } fn compare_synthetic_generics<'tcx>( tcx: TyCtxt<'tcx>, impl_m: ty::AssocItem, trait_m: ty::AssocItem, delay: bool, ) -> 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"); if impl_synthetic { // The case where the impl method uses `impl Trait` but the trait method uses // explicit generics 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, ); }; } else { // The case where the trait method uses `impl Trait`, but the impl method uses // explicit generics. 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 (sig, _) = impl_m.expect_fn(); 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, ); }; } error_found = Some(err.emit_unless(delay)); } } 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: /// ```rust,ignore (pseudo-Rust) /// 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 { .. }) => { bug!("lifetime params are expected to be filtered by `ty_const_params_of`") } } { 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).instantiate_identity() ) } Type { .. } => format!("{prefix} type parameter"), Lifetime { .. } => span_bug!( tcx.def_span(param.def_id), "lifetime params are expected to be filtered by `ty_const_params_of`" ), }; 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().instantiate_identity(); debug!("compare_impl_const(impl_trait_ref={:?})", impl_trait_ref); compare_number_of_generics(tcx, impl_const_item, trait_const_item, false)?; compare_generic_param_kinds(tcx, impl_const_item, trait_const_item, false)?; compare_const_predicate_entailment(tcx, impl_const_item, trait_const_item, impl_trait_ref) } /// The equivalent of [compare_method_predicate_entailment], but for associated constants /// instead of associated functions. // FIXME(generic_const_items): If possible extract the common parts of `compare_{type,const}_predicate_entailment`. fn compare_const_predicate_entailment<'tcx>( tcx: TyCtxt<'tcx>, impl_ct: ty::AssocItem, trait_ct: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { let impl_ct_def_id = impl_ct.def_id.expect_local(); let impl_ct_span = tcx.def_span(impl_ct_def_id); // 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 impl_args = GenericArgs::identity_for_item(tcx, impl_ct.def_id); let trait_to_impl_args = impl_args.rebase_onto(tcx, impl_ct.container_id(tcx), impl_trait_ref.args); // Create a parameter environment that represents the implementation's // method. // Compute placeholder form of impl and trait const tys. let impl_ty = tcx.type_of(impl_ct_def_id).instantiate_identity(); let trait_ty = tcx.type_of(trait_ct.def_id).instantiate(tcx, trait_to_impl_args); let code = ObligationCauseCode::CompareImplItemObligation { impl_item_def_id: impl_ct_def_id, trait_item_def_id: trait_ct.def_id, kind: impl_ct.kind, }; let mut cause = ObligationCause::new(impl_ct_span, impl_ct_def_id, code.clone()); let impl_ct_predicates = tcx.predicates_of(impl_ct.def_id); let trait_ct_predicates = tcx.predicates_of(trait_ct.def_id); check_region_bounds_on_impl_item(tcx, impl_ct, trait_ct, false)?; // The predicates declared by the impl definition, the trait and the // associated const in the trait are assumed. let impl_predicates = tcx.predicates_of(impl_ct_predicates.parent.unwrap()); let mut hybrid_preds = impl_predicates.instantiate_identity(tcx); hybrid_preds.predicates.extend( trait_ct_predicates .instantiate_own(tcx, trait_to_impl_args) .map(|(predicate, _)| predicate), ); let param_env = ty::ParamEnv::new(tcx.mk_clauses(&hybrid_preds.predicates), Reveal::UserFacing); let param_env = traits::normalize_param_env_or_error( tcx, param_env, ObligationCause::misc(impl_ct_span, impl_ct_def_id), ); let infcx = tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(&infcx); let impl_ct_own_bounds = impl_ct_predicates.instantiate_own(tcx, impl_args); for (predicate, span) in impl_ct_own_bounds { let cause = ObligationCause::misc(span, impl_ct_def_id); let predicate = ocx.normalize(&cause, param_env, predicate); let cause = ObligationCause::new(span, impl_ct_def_id, code.clone()); ocx.register_obligation(traits::Obligation::new(tcx, cause, param_env, predicate)); } // 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 (ty, _) = tcx.hir().expect_impl_item(impl_ct_def_id).expect_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_ct.name ); let trait_c_span = trait_ct.def_id.as_local().map(|trait_ct_def_id| { // Add a label to the Span containing just the type of the const let (ty, _) = tcx.hir().expect_trait_item(trait_ct_def_id).expect_const(); ty.span }); infcx.err_ctxt().note_type_err( &mut diag, &cause, trait_c_span.map(|span| (span, Cow::from("type in trait"))), 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)); } let outlives_env = OutlivesEnvironment::new(param_env); ocx.resolve_regions_and_report_errors(impl_ct_def_id, &outlives_env) } pub(super) fn compare_impl_ty<'tcx>( tcx: TyCtxt<'tcx>, impl_ty: ty::AssocItem, trait_ty: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) { debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref); let _: Result<(), ErrorGuaranteed> = try { compare_number_of_generics(tcx, impl_ty, trait_ty, false)?; compare_generic_param_kinds(tcx, impl_ty, trait_ty, false)?; compare_type_predicate_entailment(tcx, impl_ty, trait_ty, impl_trait_ref)?; check_type_bounds(tcx, trait_ty, impl_ty, 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, trait_ty: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { let impl_args = GenericArgs::identity_for_item(tcx, impl_ty.def_id); let trait_to_impl_args = impl_args.rebase_onto(tcx, impl_ty.container_id(tcx), impl_trait_ref.args); 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_args); if impl_ty_own_bounds.len() == 0 { // Nothing to check. return Ok(()); } // This `DefId` should be used for the `body_id` field on each // `ObligationCause` (and the `FnCtxt`). This is what // `regionck_item` expects. let impl_ty_def_id = impl_ty.def_id.expect_local(); debug!("compare_type_predicate_entailment: trait_to_impl_args={:?}", trait_to_impl_args); // 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_args) .map(|(predicate, _)| predicate), ); debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds); let impl_ty_span = tcx.def_span(impl_ty_def_id); let normalize_cause = ObligationCause::misc(impl_ty_span, impl_ty_def_id); let param_env = ty::ParamEnv::new(tcx.mk_clauses(&hybrid_preds.predicates), Reveal::UserFacing); 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_def_id); let predicate = ocx.normalize(&cause, param_env, predicate); let cause = ObligationCause::new( span, impl_ty_def_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); return Err(reported); } // Finally, resolve all regions. This catches wily misuses of // lifetime parameters. let outlives_env = OutlivesEnvironment::new(param_env); ocx.resolve_regions_and_report_errors(impl_ty_def_id, &outlives_env) } /// 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 `::Y` 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_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { let param_env = tcx.param_env(impl_ty.def_id); debug!(?param_env); let container_id = impl_ty.container_id(tcx); let impl_ty_def_id = impl_ty.def_id.expect_local(); let impl_ty_args = GenericArgs::identity_for_item(tcx, impl_ty.def_id); let rebased_args = impl_ty_args.rebase_onto(tcx, container_id, impl_trait_ref.args); let infcx = tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(&infcx); // A synthetic impl Trait for RPITIT desugaring has no HIR, which we currently use to get the // span for an impl's associated type. Instead, for these, use the def_span for the synthesized // associated type. let impl_ty_span = if impl_ty.is_impl_trait_in_trait() { tcx.def_span(impl_ty_def_id) } else { match tcx.hir_node_by_def_id(impl_ty_def_id) { hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Type(_, Some(ty)), .. }) => ty.span, hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Type(ty), .. }) => ty.span, item => span_bug!( tcx.def_span(impl_ty_def_id), "cannot call `check_type_bounds` on item: {item:?}", ), } }; let assumed_wf_types = ocx.assumed_wf_types_and_report_errors(param_env, impl_ty_def_id)?; let normalize_cause = ObligationCause::new( impl_ty_span, impl_ty_def_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_def_id, code) }; let obligations: Vec<_> = tcx .explicit_item_bounds(trait_ty.def_id) .iter_instantiated_copied(tcx, rebased_args) .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); // Normalize predicates with the assumption that the GAT may always normalize // to its definition type. This should be the param-env we use to *prove* the // predicate too, but we don't do that because of performance issues. // See . let normalize_param_env = param_env_with_gat_bounds(tcx, impl_ty, impl_trait_ref); for mut obligation in util::elaborate(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); 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_def_id, assumed_wf_types); let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds); ocx.resolve_regions_and_report_errors(impl_ty_def_id, &outlives_env) } /// Install projection predicates that allow GATs to project to their own /// definition types. This is not allowed in general in cases of default /// associated types in trait definitions, or when specialization is involved, /// but is needed when checking these definition types actually satisfy the /// trait bounds of the GAT. /// /// # How it works /// /// ```ignore (example) /// impl Foo for (A, B) { /// type Bar = Wrapper /// } /// ``` /// /// - `impl_trait_ref` would be `<(A, B) as Foo>` /// - `normalize_impl_ty_args` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0) /// - `normalize_impl_ty` would be `Wrapper` /// - `rebased_args` would be `[(A, B), u32, ^0.0]`, combining the args 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 /// ```ignore (pseudo-rust) /// forall { Normalize(::Member => i32) } /// ``` /// /// when we really would like to generate /// ```ignore (pseudo-rust) /// 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`). fn param_env_with_gat_bounds<'tcx>( tcx: TyCtxt<'tcx>, impl_ty: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) -> ty::ParamEnv<'tcx> { let param_env = tcx.param_env(impl_ty.def_id); let container_id = impl_ty.container_id(tcx); let mut predicates = param_env.caller_bounds().to_vec(); // for RPITITs, we should install predicates that allow us to project all // of the RPITITs associated with the same body. This is because checking // the item bounds of RPITITs often involves nested RPITITs having to prove // bounds about themselves. let impl_tys_to_install = match impl_ty.opt_rpitit_info { None => vec![impl_ty], Some( ty::ImplTraitInTraitData::Impl { fn_def_id } | ty::ImplTraitInTraitData::Trait { fn_def_id, .. }, ) => tcx .associated_types_for_impl_traits_in_associated_fn(fn_def_id) .iter() .map(|def_id| tcx.associated_item(*def_id)) .collect(), }; for impl_ty in impl_tys_to_install { let trait_ty = match impl_ty.container { ty::AssocItemContainer::TraitContainer => impl_ty, ty::AssocItemContainer::ImplContainer => { tcx.associated_item(impl_ty.trait_item_def_id.unwrap()) } }; let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> = smallvec::SmallVec::with_capacity(tcx.generics_of(impl_ty.def_id).params.len()); // Extend the impl's identity args with late-bound GAT vars let normalize_impl_ty_args = ty::GenericArgs::identity_for_item(tcx, container_id) .extend_to(tcx, impl_ty.def_id, |param, _| match param.kind { GenericParamDefKind::Type { .. } => { let kind = ty::BoundTyKind::Param(param.def_id, param.name); let bound_var = ty::BoundVariableKind::Ty(kind); bound_vars.push(bound_var); Ty::new_bound( tcx, 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); ty::Region::new_bound( tcx, 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); ty::Const::new_bound( tcx, ty::INNERMOST, ty::BoundVar::from_usize(bound_vars.len() - 1), tcx.type_of(param.def_id) .no_bound_vars() .expect("const parameter types cannot be generic"), ) .into() } }); // 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_impl_ty = tcx.type_of(impl_ty.def_id).instantiate(tcx, normalize_impl_ty_args); let rebased_args = normalize_impl_ty_args.rebase_onto(tcx, container_id, impl_trait_ref.args); let bound_vars = tcx.mk_bound_variable_kinds(&bound_vars); match normalize_impl_ty.kind() { ty::Alias(ty::Projection, proj) if proj.def_id == trait_ty.def_id && proj.args == rebased_args => { // 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: ty::AliasTy::new(tcx, trait_ty.def_id, rebased_args), term: normalize_impl_ty.into(), }, bound_vars, ) .to_predicate(tcx), ), }; } ty::ParamEnv::new(tcx.mk_clauses(&predicates), Reveal::UserFacing) } 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", } }