use core::ops::ControlFlow; use std::borrow::Cow; use std::iter; use hir::def_id::{DefId, DefIdMap, LocalDefId}; use rustc_data_structures::fx::{FxIndexMap, FxIndexSet}; use rustc_errors::codes::*; use rustc_errors::{Applicability, ErrorGuaranteed, MultiSpan, pluralize, struct_span_code_err}; use rustc_hir::def::{DefKind, Res}; use rustc_hir::intravisit::VisitorExt; use rustc_hir::{self as hir, AmbigArg, GenericParamKind, ImplItemKind, intravisit}; use rustc_infer::infer::{self, BoundRegionConversionTime, InferCtxt, TyCtxtInferExt}; use rustc_infer::traits::util; use rustc_middle::ty::error::{ExpectedFound, TypeError}; use rustc_middle::ty::{ self, BottomUpFolder, GenericArgs, GenericParamDefKind, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable, TypeVisitableExt, TypeVisitor, TypingMode, Upcast, }; use rustc_middle::{bug, span_bug}; use rustc_span::{DUMMY_SP, Span}; use rustc_trait_selection::error_reporting::InferCtxtErrorExt; use rustc_trait_selection::infer::InferCtxtExt; use rustc_trait_selection::regions::InferCtxtRegionExt; use rustc_trait_selection::traits::{ self, FulfillmentError, ObligationCause, ObligationCauseCode, ObligationCtxt, }; use tracing::{debug, instrument}; use super::potentially_plural_count; use crate::errors::{LifetimesOrBoundsMismatchOnTrait, MethodShouldReturnFuture}; pub(super) mod refine; /// Call the query `tcx.compare_impl_item()` directly instead. pub(super) fn compare_impl_item( tcx: TyCtxt<'_>, impl_item_def_id: LocalDefId, ) -> Result<(), ErrorGuaranteed> { let impl_item = tcx.associated_item(impl_item_def_id); let trait_item = tcx.associated_item(impl_item.expect_trait_impl()?); let impl_trait_ref = tcx.impl_trait_ref(impl_item.container_id(tcx)).unwrap().instantiate_identity(); debug!(?impl_trait_ref); match impl_item.kind { ty::AssocKind::Fn { .. } => compare_impl_method(tcx, impl_item, trait_item, impl_trait_ref), ty::AssocKind::Type { .. } => compare_impl_ty(tcx, impl_item, trait_item, impl_trait_ref), ty::AssocKind::Const { .. } => { compare_impl_const(tcx, impl_item, trait_item, impl_trait_ref) } } } /// 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 #[instrument(level = "debug", skip(tcx))] fn compare_impl_method<'tcx>( tcx: TyCtxt<'tcx>, impl_m: ty::AssocItem, trait_m: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { 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)?; Ok(()) } /// 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)?; 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 instantiate the type of the *trait* /// method and compare it. To do so, we must create a compound /// instantiation 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 generic parameters to ensure that all declared bounds /// are satisfied by the implementation's method. /// /// We do this by creating a parameter environment which contains a /// generic parameter 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> { // 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::CompareImplItem { impl_item_def_id: impl_m_def_id, trait_item_def_id: trait_m.def_id, kind: impl_m.kind, }, ); // Create mapping from trait method to impl method. let impl_def_id = impl_m.container_id(tcx); let trait_to_impl_args = GenericArgs::identity_for_item(tcx, impl_m.def_id).rebase_onto( tcx, impl_m.container_id(tcx), impl_trait_ref.args, ); debug!(?trait_to_impl_args); let impl_m_predicates = tcx.predicates_of(impl_m.def_id); let trait_m_predicates = tcx.predicates_of(trait_m.def_id); // 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. let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap()); let mut hybrid_preds = impl_predicates.instantiate_identity(tcx).predicates; hybrid_preds.extend( trait_m_predicates.instantiate_own(tcx, trait_to_impl_args).map(|(predicate, _)| predicate), ); let is_conditionally_const = tcx.is_conditionally_const(impl_def_id); if is_conditionally_const { // Augment the hybrid param-env with the const conditions // of the impl header and the trait method. hybrid_preds.extend( tcx.const_conditions(impl_def_id) .instantiate_identity(tcx) .into_iter() .chain( tcx.const_conditions(trait_m.def_id).instantiate_own(tcx, trait_to_impl_args), ) .map(|(trait_ref, _)| { trait_ref.to_host_effect_clause(tcx, ty::BoundConstness::Maybe) }), ); } let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_def_id); let param_env = ty::ParamEnv::new(tcx.mk_clauses(&hybrid_preds)); let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause); debug!(caller_bounds=?param_env.caller_bounds()); let infcx = &tcx.infer_ctxt().build(TypingMode::non_body_analysis()); let ocx = ObligationCtxt::new_with_diagnostics(infcx); // Create obligations for each predicate declared by the impl // definition in the context of the hybrid param-env. This makes // sure that the impl's method's where clauses are not more // restrictive than the trait's method (and the impl itself). let impl_m_own_bounds = impl_m_predicates.instantiate_own_identity(); 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::CompareImplItem { 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)); } // If we're within a const implementation, we need to make sure that the method // does not assume stronger `[const]` bounds than the trait definition. // // This registers the `[const]` bounds of the impl method, which we will prove // using the hybrid param-env that we earlier augmented with the const conditions // from the impl header and trait method declaration. if is_conditionally_const { for (const_condition, span) in tcx.const_conditions(impl_m.def_id).instantiate_own_identity() { let normalize_cause = traits::ObligationCause::misc(span, impl_m_def_id); let const_condition = ocx.normalize(&normalize_cause, param_env, const_condition); let cause = ObligationCause::new( span, impl_m_def_id, ObligationCauseCode::CompareImplItem { 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, const_condition.to_host_effect_clause(tcx, ty::BoundConstness::Maybe), )); } } // 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: We manually instantiate the trait method here as we need // to manually compute its implied bounds. Otherwise this could just // be `ocx.sub(impl_sig, trait_sig)`. let mut wf_tys = FxIndexSet::default(); let unnormalized_impl_sig = infcx.instantiate_binder_with_fresh_vars( impl_m_span, BoundRegionConversionTime::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!(?impl_sig); let trait_sig = tcx.fn_sig(trait_m.def_id).instantiate(tcx, trait_to_impl_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()); debug!(?trait_sig); // 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, param_env, terr, (trait_m, trait_sig), (impl_m, impl_sig), impl_trait_ref, ); return Err(emitted); } if !(impl_sig, trait_sig).references_error() { for ty in unnormalized_impl_sig.inputs_and_output { ocx.register_obligation(traits::Obligation::new( infcx.tcx, cause.clone(), param_env, ty::ClauseKind::WellFormed(ty.into()), )); } } // 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 errors = infcx.resolve_regions(impl_m_def_id, param_env, wf_tys); 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 RemapLateParam<'tcx> { tcx: TyCtxt<'tcx>, mapping: FxIndexMap, } impl<'tcx> TypeFolder> for RemapLateParam<'tcx> { fn cx(&self) -> TyCtxt<'tcx> { self.tcx } fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { if let ty::ReLateParam(fr) = r.kind() { ty::Region::new_late_param( self.tcx, fr.scope, self.mapping.get(&fr.kind).copied().unwrap_or(fr.kind), ) } else { r } } } /// 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 DefIdMap>>, ErrorGuaranteed> { let impl_m = tcx.associated_item(impl_m_def_id.to_def_id()); let trait_m = tcx.associated_item(impl_m.expect_trait_impl()?); let impl_trait_ref = tcx.impl_trait_ref(tcx.parent(impl_m_def_id.to_def_id())).unwrap().instantiate_identity(); // First, check a few of the same things as `compare_impl_method`, // just so we don't ICE during instantiation later. check_method_is_structurally_compatible(tcx, impl_m, trait_m, impl_trait_ref, true)?; 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::CompareImplItem { impl_item_def_id: impl_m_def_id, trait_item_def_id: trait_m.def_id, kind: impl_m.kind, }, ); // Create mapping from trait to impl (i.e. impl trait header + impl method identity args). let trait_to_impl_args = GenericArgs::identity_for_item(tcx, impl_m.def_id).rebase_onto( tcx, impl_m.container_id(tcx), impl_trait_ref.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_impl_args)) .map(|(clause, _)| clause); let param_env = ty::ParamEnv::new(tcx.mk_clauses_from_iter(hybrid_preds)); 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(TypingMode::non_body_analysis()); let ocx = ObligationCtxt::new_with_diagnostics(infcx); // Check that the where clauses of the impl are satisfied by the hybrid param env. // You might ask -- what does this have to do with RPITIT inference? Nothing. // We check these because if the where clauses of the signatures do not match // up, then we don't want to give spurious other errors that point at the RPITITs. // They're not necessary to check, though, because we already check them in // `compare_method_predicate_entailment`. let impl_m_own_bounds = tcx.predicates_of(impl_m_def_id).instantiate_own_identity(); 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::CompareImplItem { 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)); } // 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, infcx.instantiate_binder_with_fresh_vars( return_span, BoundRegionConversionTime::HigherRankedType, 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 = tcx .liberate_late_bound_regions( impl_m.def_id, tcx.fn_sig(trait_m.def_id).instantiate(tcx, trait_to_impl_args), ) .fold_with(&mut collector); 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 instantiated 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 = ty::BoundVar::ZERO; let mapping: FxIndexMap<_, _> = 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: 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_code_err!( tcx.dcx(), cause.span, E0053, "method `{}` has an incompatible return type for trait", trait_m.name() ); infcx.err_ctxt().note_type_err( &mut diag, &cause, tcx.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"), false)), Some(param_env.and(infer::ValuePairs::Terms(ExpectedFound { expected: trait_return_ty.into(), found: impl_return_ty.into(), }))), terr, false, None, ); 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, param_env, terr, (trait_m, trait_sig), (impl_m, impl_sig), impl_trait_ref, ); return Err(emitted); } } if !unnormalized_trait_sig.output().references_error() && collector.types.is_empty() { tcx.dcx().delayed_bug( "expect >0 RPITITs in call to `collect_return_position_impl_trait_in_trait_tys`", ); } // 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() { if let Err(guar) = try_report_async_mismatch(tcx, infcx, &errors, trait_m, impl_m, impl_sig) { return Err(guar); } let guar = infcx.err_ctxt().report_fulfillment_errors(errors); return Err(guar); } // Finally, resolve all regions. This catches wily misuses of // lifetime parameters. ocx.resolve_regions_and_report_errors(impl_m_def_id, param_env, wf_tys)?; let mut remapped_types = DefIdMap::default(); for (def_id, (ty, args)) in collected_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_args = GenericArgs::identity_for_item(tcx, def_id); debug!(?id_args, ?args); let map: FxIndexMap<_, _> = 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 uninstantiated 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 generic parameters 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 = impl_trait_ref.args.len(); let num_impl_args = tcx.generics_of(impl_m.container_id(tcx)).own_params.len(); let ty = match ty.try_fold_with(&mut RemapHiddenTyRegions { tcx, map, num_trait_args, num_impl_args, def_id, impl_m_def_id: impl_m.def_id, ty, return_span, }) { Ok(ty) => ty, Err(guar) => Ty::new_error(tcx, guar), }; remapped_types.insert(def_id, ty::EarlyBinder::bind(ty)); } Err(err) => { // This code path is not reached in any tests, but may be // reachable. If this is triggered, it should be converted to // `span_delayed_bug` and the triggering case turned into a // test. tcx.dcx() .span_bug(return_span, format!("could not fully resolve: {ty} => {err:?}")); } } } // 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, E> { ocx: &'a ObligationCtxt<'a, 'tcx, E>, types: FxIndexMap, ty::GenericArgsRef<'tcx>)>, span: Span, param_env: ty::ParamEnv<'tcx>, body_id: LocalDefId, } impl<'a, 'tcx, E> ImplTraitInTraitCollector<'a, 'tcx, E> where E: 'tcx, { fn new( ocx: &'a ObligationCtxt<'a, 'tcx, E>, span: Span, param_env: ty::ParamEnv<'tcx>, body_id: LocalDefId, ) -> Self { ImplTraitInTraitCollector { ocx, types: FxIndexMap::default(), span, param_env, body_id } } } impl<'tcx, E> TypeFolder> for ImplTraitInTraitCollector<'_, 'tcx, E> where E: 'tcx, { fn cx(&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.cx().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(self.span); self.types.insert(proj.def_id, (infer_ty, proj.args)); // Recurse into bounds for (pred, pred_span) in self .cx() .explicit_item_bounds(proj.def_id) .iter_instantiated_copied(self.cx(), 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.cx(), ObligationCause::new( self.span, self.body_id, ObligationCauseCode::WhereClause(proj.def_id, pred_span), ), self.param_env, pred, )); } infer_ty } else { ty.super_fold_with(self) } } } struct RemapHiddenTyRegions<'tcx> { tcx: TyCtxt<'tcx>, /// Map from early/late params of the impl to identity regions of the RPITIT (GAT) /// in the trait. map: FxIndexMap, ty::Region<'tcx>>, num_trait_args: usize, num_impl_args: usize, /// Def id of the RPITIT (GAT) in the *trait*. def_id: DefId, /// Def id of the impl method which owns the opaque hidden type we're remapping. impl_m_def_id: DefId, /// The hidden type we're remapping. Useful for diagnostics. ty: Ty<'tcx>, /// Span of the return type. Useful for diagnostics. return_span: Span, } impl<'tcx> ty::FallibleTypeFolder> for RemapHiddenTyRegions<'tcx> { type Error = ErrorGuaranteed; fn cx(&self) -> TyCtxt<'tcx> { self.tcx } fn try_fold_region( &mut self, region: ty::Region<'tcx>, ) -> Result, Self::Error> { match region.kind() { // Never remap bound regions or `'static` ty::ReBound(..) | ty::ReStatic | ty::ReError(_) => return Ok(region), // We always remap liberated 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 ebr.index as usize >= self.num_impl_args { // Remap } else { return Ok(region); } } ty::ReVar(_) | ty::RePlaceholder(_) | ty::ReErased => unreachable!( "should not have leaked vars or placeholders into hidden type of RPITIT" ), } 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.opt_param_def_id(self.tcx, self.impl_m_def_id) { Some(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 .dcx() .struct_span_err( return_span, "return type captures more lifetimes than trait definition", ) .with_span_label(self.tcx.def_span(def_id), "this lifetime was captured") .with_span_note( self.tcx.def_span(self.def_id), "hidden type must only reference lifetimes captured by this impl trait", ) .with_note(format!("hidden type inferred to be `{}`", self.ty)) .emit() } None => { // This code path is not reached in any tests, but may be // reachable. If this is triggered, it should be converted // to `delayed_bug` and the triggering case turned into a // test. self.tcx.dcx().bug("should've been able to remap region"); } }; return Err(guar); }; Ok(ty::Region::new_early_param( self.tcx, ty::EarlyParamRegion { name: e.name, index: (e.index as usize - self.num_trait_args + self.num_impl_args) as u32, }, )) } } /// Gets the string for an explicit self declaration, e.g. "self", "&self", /// etc. fn get_self_string<'tcx, P>(self_arg_ty: Ty<'tcx>, is_self_ty: P) -> String where P: Fn(Ty<'tcx>) -> bool, { if is_self_ty(self_arg_ty) { "self".to_owned() } else if let ty::Ref(_, ty, mutbl) = self_arg_ty.kind() && is_self_ty(*ty) { match mutbl { hir::Mutability::Not => "&self".to_owned(), hir::Mutability::Mut => "&mut self".to_owned(), } } else { format!("self: {self_arg_ty}") } } fn report_trait_method_mismatch<'tcx>( infcx: &InferCtxt<'tcx>, mut cause: ObligationCause<'tcx>, param_env: ty::ParamEnv<'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_code_err!( tcx.dcx(), 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.is_method() => { let ty = trait_sig.inputs()[0]; let sugg = get_self_string(ty, |ty| ty == impl_trait_ref.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_idents(body) .zip(sig.decl.inputs.iter()) .map(|(param_ident, ty)| { if let Some(param_ident) = param_ident { param_ident.span.to(ty.span) } else { ty.span } }) .next() .unwrap_or(impl_err_span); diag.span_suggestion_verbose( 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_verbose(hir_ty.span, msg, sugg, ap); } }; }; } else if let Some(trait_ty) = trait_sig.inputs().get(*i) { diag.span_suggestion_verbose( 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"), false)), Some(param_env.and(infer::ValuePairs::PolySigs(ExpectedFound { expected: ty::Binder::dummy(trait_sig), found: ty::Binder::dummy(impl_sig), }))), terr, false, None, ); 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!(?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 { return Ok(()); } if !delay && let Some(guar) = check_region_late_boundedness(tcx, impl_m, trait_m) { return Err(guar); } 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 { match p.kind { hir::WherePredicateKind::BoundPredicate(hir::WhereBoundPredicate { bounds, .. }) | hir::WherePredicateKind::RegionPredicate(hir::WhereRegionPredicate { bounds, .. }) => { for b in *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 { match p.kind { hir::WherePredicateKind::BoundPredicate(hir::WhereBoundPredicate { bounds, .. }) | hir::WherePredicateKind::RegionPredicate(hir::WhereRegionPredicate { bounds, .. }) => { for b in *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 .dcx() .create_err(LifetimesOrBoundsMismatchOnTrait { span, item_kind: impl_m.descr(), ident: impl_m.ident(tcx), generics_span, bounds_span, where_span, }) .emit_unless_delay(delay); Err(reported) } #[allow(unused)] enum LateEarlyMismatch<'tcx> { EarlyInImpl(DefId, DefId, ty::Region<'tcx>), LateInImpl(DefId, DefId, ty::Region<'tcx>), } fn check_region_late_boundedness<'tcx>( tcx: TyCtxt<'tcx>, impl_m: ty::AssocItem, trait_m: ty::AssocItem, ) -> Option { if !impl_m.is_fn() { return None; } let (infcx, param_env) = tcx .infer_ctxt() .build_with_typing_env(ty::TypingEnv::non_body_analysis(tcx, impl_m.def_id)); let impl_m_args = infcx.fresh_args_for_item(DUMMY_SP, impl_m.def_id); let impl_m_sig = tcx.fn_sig(impl_m.def_id).instantiate(tcx, impl_m_args); let impl_m_sig = tcx.liberate_late_bound_regions(impl_m.def_id, impl_m_sig); let trait_m_args = infcx.fresh_args_for_item(DUMMY_SP, trait_m.def_id); let trait_m_sig = tcx.fn_sig(trait_m.def_id).instantiate(tcx, trait_m_args); let trait_m_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_m_sig); let ocx = ObligationCtxt::new(&infcx); // Equate the signatures so that we can infer whether a late-bound param was present where // an early-bound param was expected, since we replace the late-bound lifetimes with // `ReLateParam`, and early-bound lifetimes with infer vars, so the early-bound args will // resolve to `ReLateParam` if there is a mismatch. let Ok(()) = ocx.eq( &ObligationCause::dummy(), param_env, ty::Binder::dummy(trait_m_sig), ty::Binder::dummy(impl_m_sig), ) else { return None; }; let errors = ocx.select_where_possible(); if !errors.is_empty() { return None; } let mut mismatched = vec![]; let impl_generics = tcx.generics_of(impl_m.def_id); for (id_arg, arg) in std::iter::zip(ty::GenericArgs::identity_for_item(tcx, impl_m.def_id), impl_m_args) { if let ty::GenericArgKind::Lifetime(r) = arg.kind() && let ty::ReVar(vid) = r.kind() && let r = infcx .inner .borrow_mut() .unwrap_region_constraints() .opportunistic_resolve_var(tcx, vid) && let ty::ReLateParam(ty::LateParamRegion { kind: ty::LateParamRegionKind::Named(trait_param_def_id), .. }) = r.kind() && let ty::ReEarlyParam(ebr) = id_arg.expect_region().kind() { mismatched.push(LateEarlyMismatch::EarlyInImpl( impl_generics.region_param(ebr, tcx).def_id, trait_param_def_id, id_arg.expect_region(), )); } } let trait_generics = tcx.generics_of(trait_m.def_id); for (id_arg, arg) in std::iter::zip(ty::GenericArgs::identity_for_item(tcx, trait_m.def_id), trait_m_args) { if let ty::GenericArgKind::Lifetime(r) = arg.kind() && let ty::ReVar(vid) = r.kind() && let r = infcx .inner .borrow_mut() .unwrap_region_constraints() .opportunistic_resolve_var(tcx, vid) && let ty::ReLateParam(ty::LateParamRegion { kind: ty::LateParamRegionKind::Named(impl_param_def_id), .. }) = r.kind() && let ty::ReEarlyParam(ebr) = id_arg.expect_region().kind() { mismatched.push(LateEarlyMismatch::LateInImpl( impl_param_def_id, trait_generics.region_param(ebr, tcx).def_id, id_arg.expect_region(), )); } } if mismatched.is_empty() { return None; } let spans: Vec<_> = mismatched .iter() .map(|param| { let (LateEarlyMismatch::EarlyInImpl(impl_param_def_id, ..) | LateEarlyMismatch::LateInImpl(impl_param_def_id, ..)) = param; tcx.def_span(impl_param_def_id) }) .collect(); let mut diag = tcx .dcx() .struct_span_err(spans, "lifetime parameters do not match the trait definition") .with_note("lifetime parameters differ in whether they are early- or late-bound") .with_code(E0195); for mismatch in mismatched { match mismatch { LateEarlyMismatch::EarlyInImpl( impl_param_def_id, trait_param_def_id, early_bound_region, ) => { let mut multispan = MultiSpan::from_spans(vec![ tcx.def_span(impl_param_def_id), tcx.def_span(trait_param_def_id), ]); multispan .push_span_label(tcx.def_span(tcx.parent(impl_m.def_id)), "in this impl..."); multispan .push_span_label(tcx.def_span(tcx.parent(trait_m.def_id)), "in this trait..."); multispan.push_span_label( tcx.def_span(impl_param_def_id), format!("`{}` is early-bound", tcx.item_name(impl_param_def_id)), ); multispan.push_span_label( tcx.def_span(trait_param_def_id), format!("`{}` is late-bound", tcx.item_name(trait_param_def_id)), ); if let Some(span) = find_region_in_predicates(tcx, impl_m.def_id, early_bound_region) { multispan.push_span_label( span, format!( "this lifetime bound makes `{}` early-bound", tcx.item_name(impl_param_def_id) ), ); } diag.span_note( multispan, format!( "`{}` differs between the trait and impl", tcx.item_name(impl_param_def_id) ), ); } LateEarlyMismatch::LateInImpl( impl_param_def_id, trait_param_def_id, early_bound_region, ) => { let mut multispan = MultiSpan::from_spans(vec![ tcx.def_span(impl_param_def_id), tcx.def_span(trait_param_def_id), ]); multispan .push_span_label(tcx.def_span(tcx.parent(impl_m.def_id)), "in this impl..."); multispan .push_span_label(tcx.def_span(tcx.parent(trait_m.def_id)), "in this trait..."); multispan.push_span_label( tcx.def_span(impl_param_def_id), format!("`{}` is late-bound", tcx.item_name(impl_param_def_id)), ); multispan.push_span_label( tcx.def_span(trait_param_def_id), format!("`{}` is early-bound", tcx.item_name(trait_param_def_id)), ); if let Some(span) = find_region_in_predicates(tcx, trait_m.def_id, early_bound_region) { multispan.push_span_label( span, format!( "this lifetime bound makes `{}` early-bound", tcx.item_name(trait_param_def_id) ), ); } diag.span_note( multispan, format!( "`{}` differs between the trait and impl", tcx.item_name(impl_param_def_id) ), ); } } } Some(diag.emit()) } fn find_region_in_predicates<'tcx>( tcx: TyCtxt<'tcx>, def_id: DefId, early_bound_region: ty::Region<'tcx>, ) -> Option { for (pred, span) in tcx.explicit_predicates_of(def_id).instantiate_identity(tcx) { if pred.visit_with(&mut FindRegion(early_bound_region)).is_break() { return Some(span); } } struct FindRegion<'tcx>(ty::Region<'tcx>); impl<'tcx> TypeVisitor> for FindRegion<'tcx> { type Result = ControlFlow<()>; fn visit_region(&mut self, r: ty::Region<'tcx>) -> Self::Result { if r == self.0 { ControlFlow::Break(()) } else { ControlFlow::Continue(()) } } } None } #[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::AssocContainer::InherentImpl | ty::AssocContainer::TraitImpl(_) => { impl_trait_ref.self_ty() } ty::AssocContainer::Trait => tcx.types.self_param, }; let self_arg_ty = tcx.fn_sig(method.def_id).instantiate_identity().input(0); let (infcx, param_env) = tcx .infer_ctxt() .build_with_typing_env(ty::TypingEnv::non_body_analysis(tcx, method.def_id)); 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); get_self_string(self_arg_ty, can_eq_self) }; match (trait_m.is_method(), impl_m.is_method()) { (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_code_err!( tcx.dcx(), 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(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_code_err!( tcx.dcx(), 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(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() { // FIXME: no tests trigger this. If you find example code that does // trigger this, please add it to the test suite. tcx.dcx() .bug("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 = impl_.descr(); let mut err_occurred = None; for (kind, trait_count, impl_count) in matchings { if impl_count != trait_count { let arg_spans = |item: &ty::AssocItem, 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. !item.is_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_, 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_, impl_item.generics); let span = spans.first().copied(); let mut err = tcx.dcx().struct_span_err( 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, ), ); err.code(E0049); 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(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_code_err!( tcx.dcx(), 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(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.own_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.own_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_code_err!( tcx.dcx(), 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(hir::def_id::LocalDefId); impl<'v> intravisit::Visitor<'v> for Visitor { type Result = ControlFlow; fn visit_ty(&mut self, ty: &'v hir::Ty<'v, AmbigArg>) -> Self::Result { if let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = ty.kind && let Res::Def(DefKind::TyParam, def_id) = path.res && def_id == self.0.to_def_id() { ControlFlow::Break(ty.span) } else { intravisit::walk_ty(self, ty) } } } let span = input_tys .iter() .find_map(|ty| Visitor(impl_def_id).visit_ty_unambig(ty).break_value())?; 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(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.as_tag(), trait_item.as_tag()); let ty_const_params_of = |def_id| { tcx.generics_of(def_id).own_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_code_err!( tcx.dcx(), param_impl_span, E0053, "{} `{}` has an incompatible generic parameter for trait `{}`", impl_item.descr(), 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(delay); return Err(reported); } } Ok(()) } fn compare_impl_const<'tcx>( tcx: TyCtxt<'tcx>, impl_const_item: ty::AssocItem, trait_const_item: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { compare_number_of_generics(tcx, impl_const_item, trait_const_item, false)?; compare_generic_param_kinds(tcx, impl_const_item, trait_const_item, false)?; check_region_bounds_on_impl_item(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`. #[instrument(level = "debug", skip(tcx))] 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 trait_to_impl_args = GenericArgs::identity_for_item(tcx, impl_ct.def_id).rebase_onto( tcx, impl_ct.container_id(tcx), impl_trait_ref.args, ); // Create a parameter environment that represents the implementation's // associated const. 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::CompareImplItem { 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); // 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).predicates; hybrid_preds.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)); 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(TypingMode::non_body_analysis()); let ocx = ObligationCtxt::new_with_diagnostics(&infcx); let impl_ct_own_bounds = impl_ct_predicates.instantiate_own_identity(); 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!(?impl_ty); let trait_ty = ocx.normalize(&cause, param_env, trait_ty); debug!(?trait_ty); let err = ocx.sup(&cause, param_env, trait_ty, impl_ty); if let Err(terr) = err { debug!(?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_code_err!( tcx.dcx(), 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"), false)), Some(param_env.and(infer::ValuePairs::Terms(ExpectedFound { expected: trait_ty.into(), found: impl_ty.into(), }))), terr, false, None, ); 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)); } ocx.resolve_regions_and_report_errors(impl_ct_def_id, param_env, []) } #[instrument(level = "debug", skip(tcx))] fn compare_impl_ty<'tcx>( tcx: TyCtxt<'tcx>, impl_ty: ty::AssocItem, trait_ty: ty::AssocItem, impl_trait_ref: ty::TraitRef<'tcx>, ) -> Result<(), ErrorGuaranteed> { compare_number_of_generics(tcx, impl_ty, trait_ty, false)?; compare_generic_param_kinds(tcx, impl_ty, trait_ty, false)?; check_region_bounds_on_impl_item(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. #[instrument(level = "debug", skip(tcx))] 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_def_id = impl_ty.container_id(tcx); let trait_to_impl_args = GenericArgs::identity_for_item(tcx, impl_ty.def_id).rebase_onto( tcx, impl_def_id, 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); let impl_ty_own_bounds = impl_ty_predicates.instantiate_own_identity(); // If there are no bounds, then there are no const conditions, so no need to check that here. 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!(?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).predicates; hybrid_preds.extend( trait_ty_predicates .instantiate_own(tcx, trait_to_impl_args) .map(|(predicate, _)| predicate), ); debug!(?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 is_conditionally_const = tcx.is_conditionally_const(impl_ty.def_id); if is_conditionally_const { // Augment the hybrid param-env with the const conditions // of the impl header and the trait assoc type. hybrid_preds.extend( tcx.const_conditions(impl_ty_predicates.parent.unwrap()) .instantiate_identity(tcx) .into_iter() .chain( tcx.const_conditions(trait_ty.def_id).instantiate_own(tcx, trait_to_impl_args), ) .map(|(trait_ref, _)| { trait_ref.to_host_effect_clause(tcx, ty::BoundConstness::Maybe) }), ); } let param_env = ty::ParamEnv::new(tcx.mk_clauses(&hybrid_preds)); let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause); debug!(caller_bounds=?param_env.caller_bounds()); let infcx = tcx.infer_ctxt().build(TypingMode::non_body_analysis()); let ocx = ObligationCtxt::new_with_diagnostics(&infcx); 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::CompareImplItem { 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)); } if is_conditionally_const { // Validate the const conditions of the impl associated type. let impl_ty_own_const_conditions = tcx.const_conditions(impl_ty.def_id).instantiate_own_identity(); for (const_condition, span) in impl_ty_own_const_conditions { let normalize_cause = traits::ObligationCause::misc(span, impl_ty_def_id); let const_condition = ocx.normalize(&normalize_cause, param_env, const_condition); let cause = ObligationCause::new( span, impl_ty_def_id, ObligationCauseCode::CompareImplItem { impl_item_def_id: impl_ty_def_id, trait_item_def_id: trait_ty.def_id, kind: impl_ty.kind, }, ); ocx.register_obligation(traits::Obligation::new( tcx, cause, param_env, const_condition.to_host_effect_clause(tcx, ty::BoundConstness::Maybe), )); } } // 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. ocx.resolve_regions_and_report_errors(impl_ty_def_id, param_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> { // Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in case // other `Foo` impls are incoherent. tcx.ensure_ok().coherent_trait(impl_trait_ref.def_id)?; 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(TypingMode::non_body_analysis()); let ocx = ObligationCtxt::new_with_diagnostics(&infcx); // A synthetic impl Trait for RPITIT desugaring or assoc type for effects 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 = ObligationCauseCode::WhereClause(trait_ty.def_id, span); ObligationCause::new(impl_ty_span, impl_ty_def_id, code) }; let mut obligations: Vec<_> = util::elaborate( tcx, tcx.explicit_item_bounds(trait_ty.def_id).iter_instantiated_copied(tcx, rebased_args).map( |(concrete_ty_bound, span)| { debug!(?concrete_ty_bound); traits::Obligation::new(tcx, mk_cause(span), param_env, concrete_ty_bound) }, ), ) .collect(); // Only in a const implementation do we need to check that the `[const]` item bounds hold. if tcx.is_conditionally_const(impl_ty_def_id) { obligations.extend(util::elaborate( tcx, tcx.explicit_implied_const_bounds(trait_ty.def_id) .iter_instantiated_copied(tcx, rebased_args) .map(|(c, span)| { traits::Obligation::new( tcx, mk_cause(span), param_env, c.to_host_effect_clause(tcx, ty::BoundConstness::Maybe), ) }), )); } debug!(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 obligation in &mut obligations { match ocx.deeply_normalize(&normalize_cause, normalize_param_env, obligation.predicate) { Ok(pred) => obligation.predicate = pred, Err(e) => { return Err(infcx.err_ctxt().report_fulfillment_errors(e)); } } } // Check that all obligations are satisfied by the implementation's // version. ocx.register_obligations(obligations); 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. ocx.resolve_regions_and_report_errors(impl_ty_def_id, param_env, assumed_wf_types) } /// 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.kind { ty::AssocKind::Type { data: ty::AssocTypeData::Rpitit( 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(), _ => vec![impl_ty], }; for impl_ty in impl_tys_to_install { let trait_ty = match impl_ty.container { ty::AssocContainer::InherentImpl => bug!(), ty::AssocContainer::Trait => impl_ty, ty::AssocContainer::TraitImpl(Err(_)) => continue, ty::AssocContainer::TraitImpl(Ok(trait_item_def_id)) => { tcx.associated_item(trait_item_def_id) } }; let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> = smallvec::SmallVec::with_capacity(tcx.generics_of(impl_ty.def_id).own_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); 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::Named(param.def_id); 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::BoundConst { var: ty::BoundVar::from_usize(bound_vars.len() - 1) }, ) .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_term: ty::AliasTerm::new_from_args( tcx, trait_ty.def_id, rebased_args, ), term: normalize_impl_ty.into(), }, bound_vars, ) .upcast(tcx), ), }; } ty::ParamEnv::new(tcx.mk_clauses(&predicates)) } /// Manually check here that `async fn foo()` wasn't matched against `fn foo()`, /// and extract a better error if so. fn try_report_async_mismatch<'tcx>( tcx: TyCtxt<'tcx>, infcx: &InferCtxt<'tcx>, errors: &[FulfillmentError<'tcx>], trait_m: ty::AssocItem, impl_m: ty::AssocItem, impl_sig: ty::FnSig<'tcx>, ) -> Result<(), ErrorGuaranteed> { if !tcx.asyncness(trait_m.def_id).is_async() { return Ok(()); } let ty::Alias(ty::Projection, ty::AliasTy { def_id: async_future_def_id, .. }) = *tcx.fn_sig(trait_m.def_id).skip_binder().skip_binder().output().kind() else { bug!("expected `async fn` to return an RPITIT"); }; for error in errors { if let ObligationCauseCode::WhereClause(def_id, _) = *error.root_obligation.cause.code() && def_id == async_future_def_id && let Some(proj) = error.root_obligation.predicate.as_projection_clause() && let Some(proj) = proj.no_bound_vars() && infcx.can_eq( error.root_obligation.param_env, proj.term.expect_type(), impl_sig.output(), ) { // FIXME: We should suggest making the fn `async`, but extracting // the right span is a bit difficult. return Err(tcx.sess.dcx().emit_err(MethodShouldReturnFuture { span: tcx.def_span(impl_m.def_id), method_name: tcx.item_ident(impl_m.def_id), trait_item_span: tcx.hir_span_if_local(trait_m.def_id), })); } } Ok(()) }