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Diffstat (limited to 'compiler/rustc_hir_analysis/src/check/compare_impl_item.rs')
| -rw-r--r-- | compiler/rustc_hir_analysis/src/check/compare_impl_item.rs | 2084 |
1 files changed, 2084 insertions, 0 deletions
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs new file mode 100644 index 000000000..cfebcceef --- /dev/null +++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs @@ -0,0 +1,2084 @@ +use super::potentially_plural_count; +use crate::errors::LifetimesOrBoundsMismatchOnTrait; +use hir::def_id::{DefId, LocalDefId}; +use rustc_data_structures::fx::{FxHashMap, FxIndexSet}; +use rustc_errors::{ + pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed, MultiSpan, +}; +use rustc_hir as hir; +use rustc_hir::def::{DefKind, Res}; +use rustc_hir::intravisit; +use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind}; +use rustc_infer::infer::outlives::env::OutlivesEnvironment; +use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; +use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt}; +use rustc_infer::traits::util; +use rustc_middle::ty::error::{ExpectedFound, TypeError}; +use rustc_middle::ty::util::ExplicitSelf; +use rustc_middle::ty::{ + self, DefIdTree, InternalSubsts, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable, +}; +use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt}; +use rustc_span::Span; +use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt; +use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _; +use rustc_trait_selection::traits::{ + self, ObligationCause, ObligationCauseCode, ObligationCtxt, Reveal, +}; +use std::iter; + +/// Checks that a method from an impl conforms to the signature of +/// the same method as declared in the trait. +/// +/// # Parameters +/// +/// - `impl_m`: type of the method we are checking +/// - `impl_m_span`: span to use for reporting errors +/// - `trait_m`: the method in the trait +/// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation +pub(super) fn compare_impl_method<'tcx>( + tcx: TyCtxt<'tcx>, + impl_m: &ty::AssocItem, + trait_m: &ty::AssocItem, + impl_trait_ref: ty::TraitRef<'tcx>, + trait_item_span: Option<Span>, +) { + debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref); + + let impl_m_span = tcx.def_span(impl_m.def_id); + + let _: Result<_, ErrorGuaranteed> = try { + compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)?; + compare_number_of_generics(tcx, impl_m, trait_m, trait_item_span, false)?; + compare_generic_param_kinds(tcx, impl_m, trait_m, false)?; + compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)?; + compare_synthetic_generics(tcx, impl_m, trait_m)?; + compare_asyncness(tcx, impl_m, impl_m_span, trait_m, trait_item_span)?; + compare_method_predicate_entailment( + tcx, + impl_m, + impl_m_span, + trait_m, + impl_trait_ref, + CheckImpliedWfMode::Check, + )?; + }; +} + +/// This function is best explained by example. Consider a trait: +/// +/// trait Trait<'t, T> { +/// // `trait_m` +/// fn method<'a, M>(t: &'t T, m: &'a M) -> Self; +/// } +/// +/// And an impl: +/// +/// impl<'i, 'j, U> Trait<'j, &'i U> for Foo { +/// // `impl_m` +/// fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo; +/// } +/// +/// We wish to decide if those two method types are compatible. +/// For this we have to show that, assuming the bounds of the impl hold, the +/// bounds of `trait_m` imply the bounds of `impl_m`. +/// +/// We start out with `trait_to_impl_substs`, that maps the trait +/// type parameters to impl type parameters. This is taken from the +/// impl trait reference: +/// +/// trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo} +/// +/// We create a mapping `dummy_substs` that maps from the impl type +/// parameters to fresh types and regions. For type parameters, +/// this is the identity transform, but we could as well use any +/// placeholder types. For regions, we convert from bound to free +/// regions (Note: but only early-bound regions, i.e., those +/// declared on the impl or used in type parameter bounds). +/// +/// impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 } +/// +/// Now we can apply `placeholder_substs` to the type of the impl method +/// to yield a new function type in terms of our fresh, placeholder +/// types: +/// +/// <'b> fn(t: &'i0 U0, m: &'b) -> Foo +/// +/// We now want to extract and substitute the type of the *trait* +/// method and compare it. To do so, we must create a compound +/// substitution by combining `trait_to_impl_substs` and +/// `impl_to_placeholder_substs`, and also adding a mapping for the method +/// type parameters. We extend the mapping to also include +/// the method parameters. +/// +/// trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 } +/// +/// Applying this to the trait method type yields: +/// +/// <'a> fn(t: &'i0 U0, m: &'a) -> Foo +/// +/// This type is also the same but the name of the bound region (`'a` +/// vs `'b`). However, the normal subtyping rules on fn types handle +/// this kind of equivalency just fine. +/// +/// We now use these substitutions to ensure that all declared bounds are +/// satisfied by the implementation's method. +/// +/// We do this by creating a parameter environment which contains a +/// substitution corresponding to `impl_to_placeholder_substs`. We then build +/// `trait_to_placeholder_substs` and use it to convert the predicates contained +/// in the `trait_m` generics to the placeholder form. +/// +/// Finally we register each of these predicates as an obligation and check that +/// they hold. +#[instrument(level = "debug", skip(tcx, impl_m_span, impl_trait_ref))] +fn compare_method_predicate_entailment<'tcx>( + tcx: TyCtxt<'tcx>, + impl_m: &ty::AssocItem, + impl_m_span: Span, + trait_m: &ty::AssocItem, + impl_trait_ref: ty::TraitRef<'tcx>, + check_implied_wf: CheckImpliedWfMode, +) -> Result<(), ErrorGuaranteed> { + let trait_to_impl_substs = impl_trait_ref.substs; + + // This node-id should be used for the `body_id` field on each + // `ObligationCause` (and the `FnCtxt`). + // + // FIXME(@lcnr): remove that after removing `cause.body_id` from + // obligations. + let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local()); + let cause = ObligationCause::new( + impl_m_span, + impl_m_hir_id, + ObligationCauseCode::CompareImplItemObligation { + impl_item_def_id: impl_m.def_id.expect_local(), + trait_item_def_id: trait_m.def_id, + kind: impl_m.kind, + }, + ); + + // Create mapping from impl to placeholder. + let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id); + + // Create mapping from trait to placeholder. + let trait_to_placeholder_substs = + impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs); + debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs); + + let impl_m_predicates = tcx.predicates_of(impl_m.def_id); + let trait_m_predicates = tcx.predicates_of(trait_m.def_id); + + // Check region bounds. + check_region_bounds_on_impl_item(tcx, impl_m, trait_m, false)?; + + // Create obligations for each predicate declared by the impl + // definition in the context of the trait's parameter + // environment. We can't just use `impl_env.caller_bounds`, + // however, because we want to replace all late-bound regions with + // region variables. + let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap()); + let mut hybrid_preds = impl_predicates.instantiate_identity(tcx); + + debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds); + + // This is the only tricky bit of the new way we check implementation methods + // We need to build a set of predicates where only the method-level bounds + // are from the trait and we assume all other bounds from the implementation + // to be previously satisfied. + // + // We then register the obligations from the impl_m and check to see + // if all constraints hold. + hybrid_preds.predicates.extend( + trait_m_predicates + .instantiate_own(tcx, trait_to_placeholder_substs) + .map(|(predicate, _)| predicate), + ); + + // Construct trait parameter environment and then shift it into the placeholder viewpoint. + // The key step here is to update the caller_bounds's predicates to be + // the new hybrid bounds we computed. + let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id); + let param_env = ty::ParamEnv::new( + tcx.intern_predicates(&hybrid_preds.predicates), + Reveal::UserFacing, + hir::Constness::NotConst, + ); + let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause); + + let infcx = &tcx.infer_ctxt().build(); + let ocx = ObligationCtxt::new(infcx); + + debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds()); + + let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs); + for (predicate, span) in impl_m_own_bounds { + let normalize_cause = traits::ObligationCause::misc(span, impl_m_hir_id); + let predicate = ocx.normalize(&normalize_cause, param_env, predicate); + + let cause = ObligationCause::new( + span, + impl_m_hir_id, + ObligationCauseCode::CompareImplItemObligation { + impl_item_def_id: impl_m.def_id.expect_local(), + trait_item_def_id: trait_m.def_id, + kind: impl_m.kind, + }, + ); + ocx.register_obligation(traits::Obligation::new(tcx, cause, param_env, predicate)); + } + + // We now need to check that the signature of the impl method is + // compatible with that of the trait method. We do this by + // checking that `impl_fty <: trait_fty`. + // + // FIXME. Unfortunately, this doesn't quite work right now because + // associated type normalization is not integrated into subtype + // checks. For the comparison to be valid, we need to + // normalize the associated types in the impl/trait methods + // first. However, because function types bind regions, just + // calling `normalize_associated_types_in` would have no effect on + // any associated types appearing in the fn arguments or return + // type. + + // Compute placeholder form of impl and trait method tys. + let tcx = infcx.tcx; + + let mut wf_tys = FxIndexSet::default(); + + let unnormalized_impl_sig = infcx.replace_bound_vars_with_fresh_vars( + impl_m_span, + infer::HigherRankedType, + tcx.fn_sig(impl_m.def_id), + ); + let unnormalized_impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(unnormalized_impl_sig)); + + let norm_cause = ObligationCause::misc(impl_m_span, impl_m_hir_id); + let impl_sig = ocx.normalize(&norm_cause, param_env, unnormalized_impl_sig); + debug!("compare_impl_method: impl_fty={:?}", impl_sig); + + let trait_sig = tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs); + let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_sig); + + // Next, add all inputs and output as well-formed tys. Importantly, + // we have to do this before normalization, since the normalized ty may + // not contain the input parameters. See issue #87748. + wf_tys.extend(trait_sig.inputs_and_output.iter()); + let trait_sig = ocx.normalize(&norm_cause, param_env, trait_sig); + // We also have to add the normalized trait signature + // as we don't normalize during implied bounds computation. + wf_tys.extend(trait_sig.inputs_and_output.iter()); + let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig)); + + debug!("compare_impl_method: trait_fty={:?}", trait_fty); + + // FIXME: We'd want to keep more accurate spans than "the method signature" when + // processing the comparison between the trait and impl fn, but we sadly lose them + // and point at the whole signature when a trait bound or specific input or output + // type would be more appropriate. In other places we have a `Vec<Span>` + // corresponding to their `Vec<Predicate>`, but we don't have that here. + // Fixing this would improve the output of test `issue-83765.rs`. + let result = ocx.sup(&cause, param_env, trait_sig, impl_sig); + + if let Err(terr) = result { + debug!(?impl_sig, ?trait_sig, ?terr, "sub_types failed"); + + let emitted = report_trait_method_mismatch( + &infcx, + cause, + terr, + (trait_m, trait_sig), + (impl_m, impl_sig), + impl_trait_ref, + ); + return Err(emitted); + } + + if check_implied_wf == CheckImpliedWfMode::Check { + // We need to check that the impl's args are well-formed given + // the hybrid param-env (impl + trait method where-clauses). + ocx.register_obligation(traits::Obligation::new( + infcx.tcx, + ObligationCause::dummy(), + param_env, + ty::Binder::dummy(ty::PredicateKind::WellFormed(unnormalized_impl_fty.into())), + )); + } + + // Check that all obligations are satisfied by the implementation's + // version. + let errors = ocx.select_all_or_error(); + if !errors.is_empty() { + match check_implied_wf { + CheckImpliedWfMode::Check => { + return compare_method_predicate_entailment( + tcx, + impl_m, + impl_m_span, + trait_m, + impl_trait_ref, + CheckImpliedWfMode::Skip, + ) + .map(|()| { + // If the skip-mode was successful, emit a lint. + emit_implied_wf_lint(infcx.tcx, impl_m, impl_m_hir_id, vec![]); + }); + } + CheckImpliedWfMode::Skip => { + let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None); + return Err(reported); + } + } + } + + // Finally, resolve all regions. This catches wily misuses of + // lifetime parameters. + let outlives_env = OutlivesEnvironment::with_bounds( + param_env, + Some(infcx), + infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys.clone()), + ); + infcx.process_registered_region_obligations( + outlives_env.region_bound_pairs(), + outlives_env.param_env, + ); + let errors = infcx.resolve_regions(&outlives_env); + if !errors.is_empty() { + // FIXME(compiler-errors): This can be simplified when IMPLIED_BOUNDS_ENTAILMENT + // becomes a hard error (i.e. ideally we'd just call `resolve_regions_and_report_errors` + match check_implied_wf { + CheckImpliedWfMode::Check => { + return compare_method_predicate_entailment( + tcx, + impl_m, + impl_m_span, + trait_m, + impl_trait_ref, + CheckImpliedWfMode::Skip, + ) + .map(|()| { + let bad_args = extract_bad_args_for_implies_lint( + tcx, + &errors, + (trait_m, trait_sig), + // Unnormalized impl sig corresponds to the HIR types written + (impl_m, unnormalized_impl_sig), + impl_m_hir_id, + ); + // If the skip-mode was successful, emit a lint. + emit_implied_wf_lint(tcx, impl_m, impl_m_hir_id, bad_args); + }); + } + CheckImpliedWfMode::Skip => { + if infcx.tainted_by_errors().is_none() { + infcx.err_ctxt().report_region_errors(impl_m.def_id.expect_local(), &errors); + } + return Err(tcx + .sess + .delay_span_bug(rustc_span::DUMMY_SP, "error should have been emitted")); + } + } + } + + Ok(()) +} + +fn extract_bad_args_for_implies_lint<'tcx>( + tcx: TyCtxt<'tcx>, + errors: &[infer::RegionResolutionError<'tcx>], + (trait_m, trait_sig): (&ty::AssocItem, ty::FnSig<'tcx>), + (impl_m, impl_sig): (&ty::AssocItem, ty::FnSig<'tcx>), + hir_id: hir::HirId, +) -> Vec<(Span, Option<String>)> { + let mut blame_generics = vec![]; + for error in errors { + // Look for the subregion origin that contains an input/output type + let origin = match error { + infer::RegionResolutionError::ConcreteFailure(o, ..) => o, + infer::RegionResolutionError::GenericBoundFailure(o, ..) => o, + infer::RegionResolutionError::SubSupConflict(_, _, o, ..) => o, + infer::RegionResolutionError::UpperBoundUniverseConflict(.., o, _) => o, + }; + // Extract (possible) input/output types from origin + match origin { + infer::SubregionOrigin::Subtype(trace) => { + if let Some((a, b)) = trace.values.ty() { + blame_generics.extend([a, b]); + } + } + infer::SubregionOrigin::RelateParamBound(_, ty, _) => blame_generics.push(*ty), + infer::SubregionOrigin::ReferenceOutlivesReferent(ty, _) => blame_generics.push(*ty), + _ => {} + } + } + + let fn_decl = tcx.hir().fn_decl_by_hir_id(hir_id).unwrap(); + let opt_ret_ty = match fn_decl.output { + hir::FnRetTy::DefaultReturn(_) => None, + hir::FnRetTy::Return(ty) => Some(ty), + }; + + // Map late-bound regions from trait to impl, so the names are right. + let mapping = std::iter::zip( + tcx.fn_sig(trait_m.def_id).bound_vars(), + tcx.fn_sig(impl_m.def_id).bound_vars(), + ) + .filter_map(|(impl_bv, trait_bv)| { + if let ty::BoundVariableKind::Region(impl_bv) = impl_bv + && let ty::BoundVariableKind::Region(trait_bv) = trait_bv + { + Some((impl_bv, trait_bv)) + } else { + None + } + }) + .collect(); + + // For each arg, see if it was in the "blame" of any of the region errors. + // If so, then try to produce a suggestion to replace the argument type with + // one from the trait. + let mut bad_args = vec![]; + for (idx, (ty, hir_ty)) in + std::iter::zip(impl_sig.inputs_and_output, fn_decl.inputs.iter().chain(opt_ret_ty)) + .enumerate() + { + let expected_ty = trait_sig.inputs_and_output[idx] + .fold_with(&mut RemapLateBound { tcx, mapping: &mapping }); + if blame_generics.iter().any(|blame| ty.contains(*blame)) { + let expected_ty_sugg = expected_ty.to_string(); + bad_args.push(( + hir_ty.span, + // Only suggest something if it actually changed. + (expected_ty_sugg != ty.to_string()).then_some(expected_ty_sugg), + )); + } + } + + bad_args +} + +struct RemapLateBound<'a, 'tcx> { + tcx: TyCtxt<'tcx>, + mapping: &'a FxHashMap<ty::BoundRegionKind, ty::BoundRegionKind>, +} + +impl<'tcx> TypeFolder<'tcx> for RemapLateBound<'_, 'tcx> { + fn tcx(&self) -> TyCtxt<'tcx> { + self.tcx + } + + fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { + if let ty::ReFree(fr) = *r { + self.tcx.mk_region(ty::ReFree(ty::FreeRegion { + bound_region: self + .mapping + .get(&fr.bound_region) + .copied() + .unwrap_or(fr.bound_region), + ..fr + })) + } else { + r + } + } +} + +fn emit_implied_wf_lint<'tcx>( + tcx: TyCtxt<'tcx>, + impl_m: &ty::AssocItem, + hir_id: hir::HirId, + bad_args: Vec<(Span, Option<String>)>, +) { + let span: MultiSpan = if bad_args.is_empty() { + tcx.def_span(impl_m.def_id).into() + } else { + bad_args.iter().map(|(span, _)| *span).collect::<Vec<_>>().into() + }; + tcx.struct_span_lint_hir( + rustc_session::lint::builtin::IMPLIED_BOUNDS_ENTAILMENT, + hir_id, + span, + "impl method assumes more implied bounds than the corresponding trait method", + |lint| { + let bad_args: Vec<_> = + bad_args.into_iter().filter_map(|(span, sugg)| Some((span, sugg?))).collect(); + if !bad_args.is_empty() { + lint.multipart_suggestion( + format!( + "replace {} type{} to make the impl signature compatible", + pluralize!("this", bad_args.len()), + pluralize!(bad_args.len()) + ), + bad_args, + Applicability::MaybeIncorrect, + ); + } + lint + }, + ); +} + +#[derive(Debug, PartialEq, Eq)] +enum CheckImpliedWfMode { + /// Checks implied well-formedness of the impl method. If it fails, we will + /// re-check with `Skip`, and emit a lint if it succeeds. + Check, + /// Skips checking implied well-formedness of the impl method, but will emit + /// a lint if the `compare_method_predicate_entailment` succeeded. This means that + /// the reason that we had failed earlier during `Check` was due to the impl + /// having stronger requirements than the trait. + Skip, +} + +fn compare_asyncness<'tcx>( + tcx: TyCtxt<'tcx>, + impl_m: &ty::AssocItem, + impl_m_span: Span, + trait_m: &ty::AssocItem, + trait_item_span: Option<Span>, +) -> Result<(), ErrorGuaranteed> { + if tcx.asyncness(trait_m.def_id) == hir::IsAsync::Async { + match tcx.fn_sig(impl_m.def_id).skip_binder().output().kind() { + ty::Alias(ty::Opaque, ..) => { + // allow both `async fn foo()` and `fn foo() -> impl Future` + } + ty::Error(_) => { + // We don't know if it's ok, but at least it's already an error. + } + _ => { + return Err(tcx.sess.emit_err(crate::errors::AsyncTraitImplShouldBeAsync { + span: impl_m_span, + method_name: trait_m.name, + trait_item_span, + })); + } + }; + } + + Ok(()) +} + +/// Given a method def-id in an impl, compare the method signature of the impl +/// against the trait that it's implementing. In doing so, infer the hidden types +/// that this method's signature provides to satisfy each return-position `impl Trait` +/// in the trait signature. +/// +/// The method is also responsible for making sure that the hidden types for each +/// RPITIT actually satisfy the bounds of the `impl Trait`, i.e. that if we infer +/// `impl Trait = Foo`, that `Foo: Trait` holds. +/// +/// For example, given the sample code: +/// +/// ``` +/// #![feature(return_position_impl_trait_in_trait)] +/// +/// use std::ops::Deref; +/// +/// trait Foo { +/// fn bar() -> impl Deref<Target = impl Sized>; +/// // ^- RPITIT #1 ^- RPITIT #2 +/// } +/// +/// impl Foo for () { +/// fn bar() -> Box<String> { Box::new(String::new()) } +/// } +/// ``` +/// +/// The hidden types for the RPITITs in `bar` would be inferred to: +/// * `impl Deref` (RPITIT #1) = `Box<String>` +/// * `impl Sized` (RPITIT #2) = `String` +/// +/// The relationship between these two types is straightforward in this case, but +/// may be more tenuously connected via other `impl`s and normalization rules for +/// cases of more complicated nested RPITITs. +#[instrument(skip(tcx), level = "debug", ret)] +pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>( + tcx: TyCtxt<'tcx>, + def_id: DefId, +) -> Result<&'tcx FxHashMap<DefId, Ty<'tcx>>, ErrorGuaranteed> { + let impl_m = tcx.opt_associated_item(def_id).unwrap(); + let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap(); + let impl_trait_ref = + tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap().subst_identity(); + let param_env = tcx.param_env(def_id); + + // First, check a few of the same things as `compare_impl_method`, + // just so we don't ICE during substitution later. + compare_number_of_generics(tcx, impl_m, trait_m, tcx.hir().span_if_local(impl_m.def_id), true)?; + compare_generic_param_kinds(tcx, impl_m, trait_m, true)?; + check_region_bounds_on_impl_item(tcx, impl_m, trait_m, true)?; + + let trait_to_impl_substs = impl_trait_ref.substs; + + let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local()); + let return_span = tcx.hir().fn_decl_by_hir_id(impl_m_hir_id).unwrap().output.span(); + let cause = ObligationCause::new( + return_span, + impl_m_hir_id, + ObligationCauseCode::CompareImplItemObligation { + impl_item_def_id: impl_m.def_id.expect_local(), + trait_item_def_id: trait_m.def_id, + kind: impl_m.kind, + }, + ); + + // Create mapping from impl to placeholder. + let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id); + + // Create mapping from trait to placeholder. + let trait_to_placeholder_substs = + impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs); + + let infcx = &tcx.infer_ctxt().build(); + let ocx = ObligationCtxt::new(infcx); + + // Normalize the impl signature with fresh variables for lifetime inference. + let norm_cause = ObligationCause::misc(return_span, impl_m_hir_id); + let impl_sig = ocx.normalize( + &norm_cause, + param_env, + infcx.replace_bound_vars_with_fresh_vars( + return_span, + infer::HigherRankedType, + tcx.fn_sig(impl_m.def_id), + ), + ); + impl_sig.error_reported()?; + let impl_return_ty = impl_sig.output(); + + // Normalize the trait signature with liberated bound vars, passing it through + // the ImplTraitInTraitCollector, which gathers all of the RPITITs and replaces + // them with inference variables. + // We will use these inference variables to collect the hidden types of RPITITs. + let mut collector = ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_hir_id); + let unnormalized_trait_sig = tcx + .liberate_late_bound_regions( + impl_m.def_id, + tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs), + ) + .fold_with(&mut collector); + let trait_sig = ocx.normalize(&norm_cause, param_env, unnormalized_trait_sig); + trait_sig.error_reported()?; + let trait_return_ty = trait_sig.output(); + + let wf_tys = FxIndexSet::from_iter( + unnormalized_trait_sig.inputs_and_output.iter().chain(trait_sig.inputs_and_output.iter()), + ); + + match ocx.eq(&cause, param_env, trait_return_ty, impl_return_ty) { + Ok(()) => {} + Err(terr) => { + let mut diag = struct_span_err!( + tcx.sess, + cause.span(), + E0053, + "method `{}` has an incompatible return type for trait", + trait_m.name + ); + let hir = tcx.hir(); + infcx.err_ctxt().note_type_err( + &mut diag, + &cause, + hir.get_if_local(impl_m.def_id) + .and_then(|node| node.fn_decl()) + .map(|decl| (decl.output.span(), "return type in trait".to_owned())), + Some(infer::ValuePairs::Terms(ExpectedFound { + expected: trait_return_ty.into(), + found: impl_return_ty.into(), + })), + terr, + false, + false, + ); + return Err(diag.emit()); + } + } + + debug!(?trait_sig, ?impl_sig, "equating function signatures"); + + // Unify the whole function signature. We need to do this to fully infer + // the lifetimes of the return type, but do this after unifying just the + // return types, since we want to avoid duplicating errors from + // `compare_method_predicate_entailment`. + match ocx.eq(&cause, param_env, trait_sig, impl_sig) { + Ok(()) => {} + Err(terr) => { + // This function gets called during `compare_method_predicate_entailment` when normalizing a + // signature that contains RPITIT. When the method signatures don't match, we have to + // emit an error now because `compare_method_predicate_entailment` will not report the error + // when normalization fails. + let emitted = report_trait_method_mismatch( + infcx, + cause, + terr, + (trait_m, trait_sig), + (impl_m, impl_sig), + impl_trait_ref, + ); + return Err(emitted); + } + } + + // Check that all obligations are satisfied by the implementation's + // RPITs. + let errors = ocx.select_all_or_error(); + if !errors.is_empty() { + let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None); + return Err(reported); + } + + // Finally, resolve all regions. This catches wily misuses of + // lifetime parameters. + let outlives_environment = OutlivesEnvironment::with_bounds( + param_env, + Some(infcx), + infcx.implied_bounds_tys(param_env, impl_m_hir_id, wf_tys), + ); + infcx.err_ctxt().check_region_obligations_and_report_errors( + impl_m.def_id.expect_local(), + &outlives_environment, + )?; + + let mut collected_tys = FxHashMap::default(); + for (def_id, (ty, substs)) in collector.types { + match infcx.fully_resolve(ty) { + Ok(ty) => { + // `ty` contains free regions that we created earlier while liberating the + // trait fn signature. However, projection normalization expects `ty` to + // contains `def_id`'s early-bound regions. + let id_substs = InternalSubsts::identity_for_item(tcx, def_id); + debug!(?id_substs, ?substs); + let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> = + std::iter::zip(substs, id_substs).collect(); + debug!(?map); + + // NOTE(compiler-errors): RPITITs, like all other RPITs, have early-bound + // region substs that are synthesized during AST lowering. These are substs + // that are appended to the parent substs (trait and trait method). However, + // we're trying to infer the unsubstituted type value of the RPITIT inside + // the *impl*, so we can later use the impl's method substs to normalize + // an RPITIT to a concrete type (`confirm_impl_trait_in_trait_candidate`). + // + // Due to the design of RPITITs, during AST lowering, we have no idea that + // an impl method corresponds to a trait method with RPITITs in it. Therefore, + // we don't have a list of early-bound region substs for the RPITIT in the impl. + // Since early region parameters are index-based, we can't just rebase these + // (trait method) early-bound region substs onto the impl, and there's no + // guarantee that the indices from the trait substs and impl substs line up. + // So to fix this, we subtract the number of trait substs and add the number of + // impl substs to *renumber* these early-bound regions to their corresponding + // indices in the impl's substitutions list. + // + // Also, we only need to account for a difference in trait and impl substs, + // since we previously enforce that the trait method and impl method have the + // same generics. + let num_trait_substs = trait_to_impl_substs.len(); + let num_impl_substs = tcx.generics_of(impl_m.container_id(tcx)).params.len(); + let ty = tcx.fold_regions(ty, |region, _| { + match region.kind() { + // Remap all free regions, which correspond to late-bound regions in the function. + ty::ReFree(_) => {} + // Remap early-bound regions as long as they don't come from the `impl` itself. + ty::ReEarlyBound(ebr) if tcx.parent(ebr.def_id) != impl_m.container_id(tcx) => {} + _ => return region, + } + let Some(ty::ReEarlyBound(e)) = map.get(®ion.into()).map(|r| r.expect_region().kind()) + else { + tcx + .sess + .delay_span_bug( + return_span, + "expected ReFree to map to ReEarlyBound" + ); + return tcx.lifetimes.re_static; + }; + tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { + def_id: e.def_id, + name: e.name, + index: (e.index as usize - num_trait_substs + num_impl_substs) as u32, + })) + }); + debug!(%ty); + collected_tys.insert(def_id, ty); + } + Err(err) => { + let reported = tcx.sess.delay_span_bug( + return_span, + format!("could not fully resolve: {ty} => {err:?}"), + ); + collected_tys.insert(def_id, tcx.ty_error_with_guaranteed(reported)); + } + } + } + + Ok(&*tcx.arena.alloc(collected_tys)) +} + +struct ImplTraitInTraitCollector<'a, 'tcx> { + ocx: &'a ObligationCtxt<'a, 'tcx>, + types: FxHashMap<DefId, (Ty<'tcx>, ty::SubstsRef<'tcx>)>, + span: Span, + param_env: ty::ParamEnv<'tcx>, + body_id: hir::HirId, +} + +impl<'a, 'tcx> ImplTraitInTraitCollector<'a, 'tcx> { + fn new( + ocx: &'a ObligationCtxt<'a, 'tcx>, + span: Span, + param_env: ty::ParamEnv<'tcx>, + body_id: hir::HirId, + ) -> Self { + ImplTraitInTraitCollector { ocx, types: FxHashMap::default(), span, param_env, body_id } + } +} + +impl<'tcx> TypeFolder<'tcx> for ImplTraitInTraitCollector<'_, 'tcx> { + fn tcx<'a>(&'a self) -> TyCtxt<'tcx> { + self.ocx.infcx.tcx + } + + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + if let ty::Alias(ty::Projection, proj) = ty.kind() + && self.tcx().def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder + { + if let Some((ty, _)) = self.types.get(&proj.def_id) { + return *ty; + } + //FIXME(RPITIT): Deny nested RPITIT in substs too + if proj.substs.has_escaping_bound_vars() { + bug!("FIXME(RPITIT): error here"); + } + // Replace with infer var + let infer_ty = self.ocx.infcx.next_ty_var(TypeVariableOrigin { + span: self.span, + kind: TypeVariableOriginKind::MiscVariable, + }); + self.types.insert(proj.def_id, (infer_ty, proj.substs)); + // Recurse into bounds + for (pred, pred_span) in self.tcx().bound_explicit_item_bounds(proj.def_id).subst_iter_copied(self.tcx(), proj.substs) { + let pred = pred.fold_with(self); + let pred = self.ocx.normalize( + &ObligationCause::misc(self.span, self.body_id), + self.param_env, + pred, + ); + + self.ocx.register_obligation(traits::Obligation::new( + self.tcx(), + ObligationCause::new( + self.span, + self.body_id, + ObligationCauseCode::BindingObligation(proj.def_id, pred_span), + ), + self.param_env, + pred, + )); + } + infer_ty + } else { + ty.super_fold_with(self) + } + } +} + +fn report_trait_method_mismatch<'tcx>( + infcx: &InferCtxt<'tcx>, + mut cause: ObligationCause<'tcx>, + terr: TypeError<'tcx>, + (trait_m, trait_sig): (&ty::AssocItem, ty::FnSig<'tcx>), + (impl_m, impl_sig): (&ty::AssocItem, ty::FnSig<'tcx>), + impl_trait_ref: ty::TraitRef<'tcx>, +) -> ErrorGuaranteed { + let tcx = infcx.tcx; + let (impl_err_span, trait_err_span) = + extract_spans_for_error_reporting(&infcx, terr, &cause, impl_m, trait_m); + + let mut diag = struct_span_err!( + tcx.sess, + impl_err_span, + E0053, + "method `{}` has an incompatible type for trait", + trait_m.name + ); + match &terr { + TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0) + if trait_m.fn_has_self_parameter => + { + let ty = trait_sig.inputs()[0]; + let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty()) { + ExplicitSelf::ByValue => "self".to_owned(), + ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(), + ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(), + _ => format!("self: {ty}"), + }; + + // When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the + // span points only at the type `Box<Self`>, but we want to cover the whole + // argument pattern and type. + let ImplItemKind::Fn(ref sig, body) = tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind else { bug!("{impl_m:?} is not a method") }; + let span = tcx + .hir() + .body_param_names(body) + .zip(sig.decl.inputs.iter()) + .map(|(param, ty)| param.span.to(ty.span)) + .next() + .unwrap_or(impl_err_span); + + diag.span_suggestion( + span, + "change the self-receiver type to match the trait", + sugg, + Applicability::MachineApplicable, + ); + } + TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => { + if trait_sig.inputs().len() == *i { + // Suggestion to change output type. We do not suggest in `async` functions + // to avoid complex logic or incorrect output. + if let ImplItemKind::Fn(sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind + && !sig.header.asyncness.is_async() + { + let msg = "change the output type to match the trait"; + let ap = Applicability::MachineApplicable; + match sig.decl.output { + hir::FnRetTy::DefaultReturn(sp) => { + let sugg = format!("-> {} ", trait_sig.output()); + diag.span_suggestion_verbose(sp, msg, sugg, ap); + } + hir::FnRetTy::Return(hir_ty) => { + let sugg = trait_sig.output(); + diag.span_suggestion(hir_ty.span, msg, sugg, ap); + } + }; + }; + } else if let Some(trait_ty) = trait_sig.inputs().get(*i) { + diag.span_suggestion( + impl_err_span, + "change the parameter type to match the trait", + trait_ty, + Applicability::MachineApplicable, + ); + } + } + _ => {} + } + + cause.span = impl_err_span; + infcx.err_ctxt().note_type_err( + &mut diag, + &cause, + trait_err_span.map(|sp| (sp, "type in trait".to_owned())), + Some(infer::ValuePairs::Sigs(ExpectedFound { expected: trait_sig, found: impl_sig })), + terr, + false, + false, + ); + + return diag.emit(); +} + +fn check_region_bounds_on_impl_item<'tcx>( + tcx: TyCtxt<'tcx>, + impl_m: &ty::AssocItem, + trait_m: &ty::AssocItem, + delay: bool, +) -> Result<(), ErrorGuaranteed> { + let impl_generics = tcx.generics_of(impl_m.def_id); + let impl_params = impl_generics.own_counts().lifetimes; + + let trait_generics = tcx.generics_of(trait_m.def_id); + let trait_params = trait_generics.own_counts().lifetimes; + + debug!( + "check_region_bounds_on_impl_item: \ + trait_generics={:?} \ + impl_generics={:?}", + trait_generics, impl_generics + ); + + // Must have same number of early-bound lifetime parameters. + // Unfortunately, if the user screws up the bounds, then this + // will change classification between early and late. E.g., + // if in trait we have `<'a,'b:'a>`, and in impl we just have + // `<'a,'b>`, then we have 2 early-bound lifetime parameters + // in trait but 0 in the impl. But if we report "expected 2 + // but found 0" it's confusing, because it looks like there + // are zero. Since I don't quite know how to phrase things at + // the moment, give a kind of vague error message. + if trait_params != impl_params { + let span = tcx + .hir() + .get_generics(impl_m.def_id.expect_local()) + .expect("expected impl item to have generics or else we can't compare them") + .span; + + let mut generics_span = None; + let mut bounds_span = vec![]; + let mut where_span = None; + if let Some(trait_node) = tcx.hir().get_if_local(trait_m.def_id) + && let Some(trait_generics) = trait_node.generics() + { + generics_span = Some(trait_generics.span); + // FIXME: we could potentially look at the impl's bounds to not point at bounds that + // *are* present in the impl. + for p in trait_generics.predicates { + if let hir::WherePredicate::BoundPredicate(pred) = p { + for b in pred.bounds { + if let hir::GenericBound::Outlives(lt) = b { + bounds_span.push(lt.ident.span); + } + } + } + } + if let Some(impl_node) = tcx.hir().get_if_local(impl_m.def_id) + && let Some(impl_generics) = impl_node.generics() + { + let mut impl_bounds = 0; + for p in impl_generics.predicates { + if let hir::WherePredicate::BoundPredicate(pred) = p { + for b in pred.bounds { + if let hir::GenericBound::Outlives(_) = b { + impl_bounds += 1; + } + } + } + } + if impl_bounds == bounds_span.len() { + bounds_span = vec![]; + } else if impl_generics.has_where_clause_predicates { + where_span = Some(impl_generics.where_clause_span); + } + } + } + let reported = tcx + .sess + .create_err(LifetimesOrBoundsMismatchOnTrait { + span, + item_kind: assoc_item_kind_str(impl_m), + ident: impl_m.ident(tcx), + generics_span, + bounds_span, + where_span, + }) + .emit_unless(delay); + return Err(reported); + } + + Ok(()) +} + +#[instrument(level = "debug", skip(infcx))] +fn extract_spans_for_error_reporting<'tcx>( + infcx: &infer::InferCtxt<'tcx>, + terr: TypeError<'_>, + cause: &ObligationCause<'tcx>, + impl_m: &ty::AssocItem, + trait_m: &ty::AssocItem, +) -> (Span, Option<Span>) { + let tcx = infcx.tcx; + let mut impl_args = { + let ImplItemKind::Fn(sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind else { bug!("{:?} is not a method", impl_m) }; + sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span())) + }; + + let trait_args = trait_m.def_id.as_local().map(|def_id| { + let TraitItemKind::Fn(sig, _) = &tcx.hir().expect_trait_item(def_id).kind else { bug!("{:?} is not a TraitItemKind::Fn", trait_m) }; + sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span())) + }); + + match terr { + TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(ExpectedFound { .. }, i) => { + (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i))) + } + _ => (cause.span(), tcx.hir().span_if_local(trait_m.def_id)), + } +} + +fn compare_self_type<'tcx>( + tcx: TyCtxt<'tcx>, + impl_m: &ty::AssocItem, + impl_m_span: Span, + trait_m: &ty::AssocItem, + impl_trait_ref: ty::TraitRef<'tcx>, +) -> Result<(), ErrorGuaranteed> { + // Try to give more informative error messages about self typing + // mismatches. Note that any mismatch will also be detected + // below, where we construct a canonical function type that + // includes the self parameter as a normal parameter. It's just + // that the error messages you get out of this code are a bit more + // inscrutable, particularly for cases where one method has no + // self. + + let self_string = |method: &ty::AssocItem| { + let untransformed_self_ty = match method.container { + ty::ImplContainer => impl_trait_ref.self_ty(), + ty::TraitContainer => tcx.types.self_param, + }; + let self_arg_ty = tcx.fn_sig(method.def_id).input(0); + let param_env = ty::ParamEnv::reveal_all(); + + let infcx = tcx.infer_ctxt().build(); + let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty); + let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok(); + match ExplicitSelf::determine(self_arg_ty, can_eq_self) { + ExplicitSelf::ByValue => "self".to_owned(), + ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(), + ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(), + _ => format!("self: {self_arg_ty}"), + } + }; + + match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) { + (false, false) | (true, true) => {} + + (false, true) => { + let self_descr = self_string(impl_m); + let mut err = struct_span_err!( + tcx.sess, + impl_m_span, + E0185, + "method `{}` has a `{}` declaration in the impl, but not in the trait", + trait_m.name, + self_descr + ); + err.span_label(impl_m_span, format!("`{self_descr}` used in impl")); + if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) { + err.span_label(span, format!("trait method declared without `{self_descr}`")); + } else { + err.note_trait_signature(trait_m.name, trait_m.signature(tcx)); + } + return Err(err.emit()); + } + + (true, false) => { + let self_descr = self_string(trait_m); + let mut err = struct_span_err!( + tcx.sess, + impl_m_span, + E0186, + "method `{}` has a `{}` declaration in the trait, but not in the impl", + trait_m.name, + self_descr + ); + err.span_label(impl_m_span, format!("expected `{self_descr}` in impl")); + if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) { + err.span_label(span, format!("`{self_descr}` used in trait")); + } else { + err.note_trait_signature(trait_m.name, trait_m.signature(tcx)); + } + + return Err(err.emit()); + } + } + + Ok(()) +} + +/// Checks that the number of generics on a given assoc item in a trait impl is the same +/// as the number of generics on the respective assoc item in the trait definition. +/// +/// For example this code emits the errors in the following code: +/// ``` +/// trait Trait { +/// fn foo(); +/// type Assoc<T>; +/// } +/// +/// impl Trait for () { +/// fn foo<T>() {} +/// //~^ error +/// type Assoc = u32; +/// //~^ error +/// } +/// ``` +/// +/// Notably this does not error on `foo<T>` implemented as `foo<const N: u8>` or +/// `foo<const N: u8>` implemented as `foo<const N: u32>`. This is handled in +/// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters +fn compare_number_of_generics<'tcx>( + tcx: TyCtxt<'tcx>, + impl_: &ty::AssocItem, + trait_: &ty::AssocItem, + trait_span: Option<Span>, + 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<T>` implemented as `foo<const N: u8>` as this is implemented + // in `compare_generic_param_kinds` which will give a nicer error message than something like: + // "expected 1 type parameter, found 0 type parameters" + if (trait_own_counts.types + trait_own_counts.consts) + == (impl_own_counts.types + impl_own_counts.consts) + { + return Ok(()); + } + + let matchings = [ + ("type", trait_own_counts.types, impl_own_counts.types), + ("const", trait_own_counts.consts, impl_own_counts.consts), + ]; + + let item_kind = assoc_item_kind_str(impl_); + + let mut err_occurred = None; + for (kind, trait_count, impl_count) in matchings { + if impl_count != trait_count { + let arg_spans = |kind: ty::AssocKind, generics: &hir::Generics<'_>| { + let mut spans = generics + .params + .iter() + .filter(|p| match p.kind { + hir::GenericParamKind::Lifetime { + kind: hir::LifetimeParamKind::Elided, + } => { + // A fn can have an arbitrary number of extra elided lifetimes for the + // same signature. + !matches!(kind, ty::AssocKind::Fn) + } + _ => true, + }) + .map(|p| p.span) + .collect::<Vec<Span>>(); + 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<Span> = arg_spans(trait_.kind, trait_item.generics); + let impl_trait_spans: Vec<Span> = trait_item + .generics + .params + .iter() + .filter_map(|p| match p.kind { + GenericParamKind::Type { synthetic: true, .. } => Some(p.span), + _ => None, + }) + .collect(); + (Some(arg_spans), impl_trait_spans) + } else { + (trait_span.map(|s| vec![s]), vec![]) + }; + + let impl_item = tcx.hir().expect_impl_item(impl_.def_id.expect_local()); + let impl_item_impl_trait_spans: Vec<Span> = impl_item + .generics + .params + .iter() + .filter_map(|p| match p.kind { + GenericParamKind::Type { synthetic: true, .. } => Some(p.span), + _ => None, + }) + .collect(); + let spans = arg_spans(impl_.kind, impl_item.generics); + let span = spans.first().copied(); + + let mut err = tcx.sess.struct_span_err_with_code( + spans, + &format!( + "{} `{}` has {} {kind} parameter{} but its trait \ + declaration has {} {kind} parameter{}", + item_kind, + trait_.name, + impl_count, + pluralize!(impl_count), + trait_count, + pluralize!(trait_count), + kind = kind, + ), + DiagnosticId::Error("E0049".into()), + ); + + let mut suffix = None; + + if let Some(spans) = trait_spans { + let mut spans = spans.iter(); + if let Some(span) = spans.next() { + err.span_label( + *span, + format!( + "expected {} {} parameter{}", + trait_count, + kind, + pluralize!(trait_count), + ), + ); + } + for span in spans { + err.span_label(*span, ""); + } + } else { + suffix = Some(format!(", expected {trait_count}")); + } + + if let Some(span) = span { + err.span_label( + span, + format!( + "found {} {} parameter{}{}", + impl_count, + kind, + pluralize!(impl_count), + suffix.unwrap_or_else(String::new), + ), + ); + } + + for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) { + err.span_label(*span, "`impl Trait` introduces an implicit type parameter"); + } + + let reported = err.emit_unless(delay); + err_occurred = Some(reported); + } + } + + if let Some(reported) = err_occurred { Err(reported) } else { Ok(()) } +} + +fn compare_number_of_method_arguments<'tcx>( + tcx: TyCtxt<'tcx>, + impl_m: &ty::AssocItem, + impl_m_span: Span, + trait_m: &ty::AssocItem, + trait_item_span: Option<Span>, +) -> Result<(), ErrorGuaranteed> { + let impl_m_fty = tcx.fn_sig(impl_m.def_id); + let trait_m_fty = tcx.fn_sig(trait_m.def_id); + let trait_number_args = trait_m_fty.inputs().skip_binder().len(); + let impl_number_args = impl_m_fty.inputs().skip_binder().len(); + + if trait_number_args != impl_number_args { + let trait_span = trait_m + .def_id + .as_local() + .and_then(|def_id| { + let TraitItemKind::Fn(trait_m_sig, _) = &tcx.hir().expect_trait_item(def_id).kind else { bug!("{:?} is not a method", impl_m) }; + let pos = trait_number_args.saturating_sub(1); + trait_m_sig.decl.inputs.get(pos).map(|arg| { + if pos == 0 { + arg.span + } else { + arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo()) + } + }) + }) + .or(trait_item_span); + + let ImplItemKind::Fn(impl_m_sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind else { bug!("{:?} is not a method", impl_m) }; + let pos = impl_number_args.saturating_sub(1); + let impl_span = impl_m_sig + .decl + .inputs + .get(pos) + .map(|arg| { + if pos == 0 { + arg.span + } else { + arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo()) + } + }) + .unwrap_or(impl_m_span); + + let mut err = struct_span_err!( + tcx.sess, + impl_span, + E0050, + "method `{}` has {} but the declaration in trait `{}` has {}", + trait_m.name, + potentially_plural_count(impl_number_args, "parameter"), + tcx.def_path_str(trait_m.def_id), + trait_number_args + ); + + if let Some(trait_span) = trait_span { + err.span_label( + trait_span, + format!( + "trait requires {}", + potentially_plural_count(trait_number_args, "parameter") + ), + ); + } else { + err.note_trait_signature(trait_m.name, trait_m.signature(tcx)); + } + + err.span_label( + impl_span, + format!( + "expected {}, found {}", + potentially_plural_count(trait_number_args, "parameter"), + impl_number_args + ), + ); + + return Err(err.emit()); + } + + Ok(()) +} + +fn compare_synthetic_generics<'tcx>( + tcx: TyCtxt<'tcx>, + impl_m: &ty::AssocItem, + trait_m: &ty::AssocItem, +) -> Result<(), ErrorGuaranteed> { + // FIXME(chrisvittal) Clean up this function, list of FIXME items: + // 1. Better messages for the span labels + // 2. Explanation as to what is going on + // If we get here, we already have the same number of generics, so the zip will + // be okay. + let mut error_found = None; + let impl_m_generics = tcx.generics_of(impl_m.def_id); + let trait_m_generics = tcx.generics_of(trait_m.def_id); + let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind { + GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)), + GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None, + }); + let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind { + GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)), + GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None, + }); + for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in + iter::zip(impl_m_type_params, trait_m_type_params) + { + if impl_synthetic != trait_synthetic { + let impl_def_id = impl_def_id.expect_local(); + let impl_span = tcx.def_span(impl_def_id); + let trait_span = tcx.def_span(trait_def_id); + let mut err = struct_span_err!( + tcx.sess, + impl_span, + E0643, + "method `{}` has incompatible signature for trait", + trait_m.name + ); + err.span_label(trait_span, "declaration in trait here"); + match (impl_synthetic, trait_synthetic) { + // The case where the impl method uses `impl Trait` but the trait method uses + // explicit generics + (true, false) => { + err.span_label(impl_span, "expected generic parameter, found `impl Trait`"); + let _: Option<_> = try { + // try taking the name from the trait impl + // FIXME: this is obviously suboptimal since the name can already be used + // as another generic argument + let new_name = tcx.opt_item_name(trait_def_id)?; + let trait_m = trait_m.def_id.as_local()?; + let trait_m = tcx.hir().expect_trait_item(trait_m); + + let impl_m = impl_m.def_id.as_local()?; + let impl_m = tcx.hir().expect_impl_item(impl_m); + + // in case there are no generics, take the spot between the function name + // and the opening paren of the argument list + let new_generics_span = tcx.def_ident_span(impl_def_id)?.shrink_to_hi(); + // in case there are generics, just replace them + let generics_span = + impl_m.generics.span.substitute_dummy(new_generics_span); + // replace with the generics from the trait + let new_generics = + tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?; + + err.multipart_suggestion( + "try changing the `impl Trait` argument to a generic parameter", + vec![ + // replace `impl Trait` with `T` + (impl_span, new_name.to_string()), + // replace impl method generics with trait method generics + // This isn't quite right, as users might have changed the names + // of the generics, but it works for the common case + (generics_span, new_generics), + ], + Applicability::MaybeIncorrect, + ); + }; + } + // The case where the trait method uses `impl Trait`, but the impl method uses + // explicit generics. + (false, true) => { + err.span_label(impl_span, "expected `impl Trait`, found generic parameter"); + let _: Option<_> = try { + let impl_m = impl_m.def_id.as_local()?; + let impl_m = tcx.hir().expect_impl_item(impl_m); + let hir::ImplItemKind::Fn(sig, _) = &impl_m.kind else { unreachable!() }; + let input_tys = sig.decl.inputs; + + struct Visitor(Option<Span>, hir::def_id::LocalDefId); + impl<'v> intravisit::Visitor<'v> for Visitor { + fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) { + intravisit::walk_ty(self, ty); + if let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = ty.kind + && let Res::Def(DefKind::TyParam, def_id) = path.res + && def_id == self.1.to_def_id() + { + self.0 = Some(ty.span); + } + } + } + + let mut visitor = Visitor(None, impl_def_id); + for ty in input_tys { + intravisit::Visitor::visit_ty(&mut visitor, ty); + } + let span = visitor.0?; + + let bounds = impl_m.generics.bounds_for_param(impl_def_id).next()?.bounds; + let bounds = bounds.first()?.span().to(bounds.last()?.span()); + let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?; + + err.multipart_suggestion( + "try removing the generic parameter and using `impl Trait` instead", + vec![ + // delete generic parameters + (impl_m.generics.span, String::new()), + // replace param usage with `impl Trait` + (span, format!("impl {bounds}")), + ], + Applicability::MaybeIncorrect, + ); + }; + } + _ => unreachable!(), + } + error_found = Some(err.emit()); + } + } + if let Some(reported) = error_found { Err(reported) } else { Ok(()) } +} + +/// Checks that all parameters in the generics of a given assoc item in a trait impl have +/// the same kind as the respective generic parameter in the trait def. +/// +/// For example all 4 errors in the following code are emitted here: +/// ``` +/// trait Foo { +/// fn foo<const N: u8>(); +/// type bar<const N: u8>; +/// fn baz<const N: u32>(); +/// type blah<T>; +/// } +/// +/// impl Foo for () { +/// fn foo<const N: u64>() {} +/// //~^ error +/// type bar<const N: u64> {} +/// //~^ error +/// fn baz<T>() {} +/// //~^ error +/// type blah<const N: i64> = u32; +/// //~^ error +/// } +/// ``` +/// +/// This function does not handle lifetime parameters +fn compare_generic_param_kinds<'tcx>( + tcx: TyCtxt<'tcx>, + impl_item: &ty::AssocItem, + trait_item: &ty::AssocItem, + delay: bool, +) -> Result<(), ErrorGuaranteed> { + assert_eq!(impl_item.kind, trait_item.kind); + + let ty_const_params_of = |def_id| { + tcx.generics_of(def_id).params.iter().filter(|param| { + matches!( + param.kind, + GenericParamDefKind::Const { .. } | GenericParamDefKind::Type { .. } + ) + }) + }; + + for (param_impl, param_trait) in + iter::zip(ty_const_params_of(impl_item.def_id), ty_const_params_of(trait_item.def_id)) + { + use GenericParamDefKind::*; + if match (¶m_impl.kind, ¶m_trait.kind) { + (Const { .. }, Const { .. }) + if tcx.type_of(param_impl.def_id) != tcx.type_of(param_trait.def_id) => + { + true + } + (Const { .. }, Type { .. }) | (Type { .. }, Const { .. }) => true, + // this is exhaustive so that anyone adding new generic param kinds knows + // to make sure this error is reported for them. + (Const { .. }, Const { .. }) | (Type { .. }, Type { .. }) => false, + (Lifetime { .. }, _) | (_, Lifetime { .. }) => unreachable!(), + } { + let param_impl_span = tcx.def_span(param_impl.def_id); + let param_trait_span = tcx.def_span(param_trait.def_id); + + let mut err = struct_span_err!( + tcx.sess, + param_impl_span, + E0053, + "{} `{}` has an incompatible generic parameter for trait `{}`", + assoc_item_kind_str(&impl_item), + trait_item.name, + &tcx.def_path_str(tcx.parent(trait_item.def_id)) + ); + + let make_param_message = |prefix: &str, param: &ty::GenericParamDef| match param.kind { + Const { .. } => { + format!("{} const parameter of type `{}`", prefix, tcx.type_of(param.def_id)) + } + Type { .. } => format!("{} type parameter", prefix), + Lifetime { .. } => unreachable!(), + }; + + let trait_header_span = tcx.def_ident_span(tcx.parent(trait_item.def_id)).unwrap(); + err.span_label(trait_header_span, ""); + err.span_label(param_trait_span, make_param_message("expected", param_trait)); + + let impl_header_span = tcx.def_span(tcx.parent(impl_item.def_id)); + err.span_label(impl_header_span, ""); + err.span_label(param_impl_span, make_param_message("found", param_impl)); + + let reported = err.emit_unless(delay); + return Err(reported); + } + } + + Ok(()) +} + +/// Use `tcx.compare_impl_const` instead +pub(super) fn compare_impl_const_raw( + tcx: TyCtxt<'_>, + (impl_const_item_def, trait_const_item_def): (LocalDefId, DefId), +) -> Result<(), ErrorGuaranteed> { + let impl_const_item = tcx.associated_item(impl_const_item_def); + let trait_const_item = tcx.associated_item(trait_const_item_def); + let impl_trait_ref = + tcx.impl_trait_ref(impl_const_item.container_id(tcx)).unwrap().subst_identity(); + debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref); + + let impl_c_span = tcx.def_span(impl_const_item_def.to_def_id()); + + let infcx = tcx.infer_ctxt().build(); + let param_env = tcx.param_env(impl_const_item_def.to_def_id()); + let ocx = ObligationCtxt::new(&infcx); + + // The below is for the most part highly similar to the procedure + // for methods above. It is simpler in many respects, especially + // because we shouldn't really have to deal with lifetimes or + // predicates. In fact some of this should probably be put into + // shared functions because of DRY violations... + let trait_to_impl_substs = impl_trait_ref.substs; + + // Create a parameter environment that represents the implementation's + // method. + let impl_c_hir_id = tcx.hir().local_def_id_to_hir_id(impl_const_item_def); + + // Compute placeholder form of impl and trait const tys. + let impl_ty = tcx.type_of(impl_const_item_def.to_def_id()); + let trait_ty = tcx.bound_type_of(trait_const_item_def).subst(tcx, trait_to_impl_substs); + let mut cause = ObligationCause::new( + impl_c_span, + impl_c_hir_id, + ObligationCauseCode::CompareImplItemObligation { + impl_item_def_id: impl_const_item_def, + trait_item_def_id: trait_const_item_def, + kind: impl_const_item.kind, + }, + ); + + // There is no "body" here, so just pass dummy id. + let impl_ty = ocx.normalize(&cause, param_env, impl_ty); + + debug!("compare_const_impl: impl_ty={:?}", impl_ty); + + let trait_ty = ocx.normalize(&cause, param_env, trait_ty); + + debug!("compare_const_impl: trait_ty={:?}", trait_ty); + + let err = ocx.sup(&cause, param_env, trait_ty, impl_ty); + + if let Err(terr) = err { + debug!( + "checking associated const for compatibility: impl ty {:?}, trait ty {:?}", + impl_ty, trait_ty + ); + + // Locate the Span containing just the type of the offending impl + let ImplItemKind::Const(ty, _) = tcx.hir().expect_impl_item(impl_const_item_def).kind else { bug!("{impl_const_item:?} is not a impl const") }; + cause.span = ty.span; + + let mut diag = struct_span_err!( + tcx.sess, + cause.span, + E0326, + "implemented const `{}` has an incompatible type for trait", + trait_const_item.name + ); + + let trait_c_span = trait_const_item_def.as_local().map(|trait_c_def_id| { + // Add a label to the Span containing just the type of the const + let TraitItemKind::Const(ty, _) = tcx.hir().expect_trait_item(trait_c_def_id).kind else { bug!("{trait_const_item:?} is not a trait const") }; + ty.span + }); + + infcx.err_ctxt().note_type_err( + &mut diag, + &cause, + trait_c_span.map(|span| (span, "type in trait".to_owned())), + Some(infer::ValuePairs::Terms(ExpectedFound { + expected: trait_ty.into(), + found: impl_ty.into(), + })), + terr, + false, + false, + ); + return Err(diag.emit()); + }; + + // Check that all obligations are satisfied by the implementation's + // version. + let errors = ocx.select_all_or_error(); + if !errors.is_empty() { + return Err(infcx.err_ctxt().report_fulfillment_errors(&errors, None)); + } + + let outlives_environment = OutlivesEnvironment::new(param_env); + infcx + .err_ctxt() + .check_region_obligations_and_report_errors(impl_const_item_def, &outlives_environment)?; + Ok(()) +} + +pub(super) fn compare_impl_ty<'tcx>( + tcx: TyCtxt<'tcx>, + impl_ty: &ty::AssocItem, + impl_ty_span: Span, + trait_ty: &ty::AssocItem, + impl_trait_ref: ty::TraitRef<'tcx>, + trait_item_span: Option<Span>, +) { + debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref); + + let _: Result<(), ErrorGuaranteed> = try { + compare_number_of_generics(tcx, impl_ty, trait_ty, trait_item_span, false)?; + + compare_generic_param_kinds(tcx, impl_ty, trait_ty, false)?; + + let sp = tcx.def_span(impl_ty.def_id); + compare_type_predicate_entailment(tcx, impl_ty, sp, trait_ty, impl_trait_ref)?; + + check_type_bounds(tcx, trait_ty, impl_ty, impl_ty_span, impl_trait_ref)?; + }; +} + +/// The equivalent of [compare_method_predicate_entailment], but for associated types +/// instead of associated functions. +fn compare_type_predicate_entailment<'tcx>( + tcx: TyCtxt<'tcx>, + impl_ty: &ty::AssocItem, + impl_ty_span: Span, + trait_ty: &ty::AssocItem, + impl_trait_ref: ty::TraitRef<'tcx>, +) -> Result<(), ErrorGuaranteed> { + let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id); + let trait_to_impl_substs = + impl_substs.rebase_onto(tcx, impl_ty.container_id(tcx), impl_trait_ref.substs); + + let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id); + let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id); + + check_region_bounds_on_impl_item(tcx, impl_ty, trait_ty, false)?; + + let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs); + if impl_ty_own_bounds.len() == 0 { + // Nothing to check. + return Ok(()); + } + + // This `HirId` should be used for the `body_id` field on each + // `ObligationCause` (and the `FnCtxt`). This is what + // `regionck_item` expects. + let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local()); + debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs); + + // The predicates declared by the impl definition, the trait and the + // associated type in the trait are assumed. + let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap()); + let mut hybrid_preds = impl_predicates.instantiate_identity(tcx); + hybrid_preds.predicates.extend( + trait_ty_predicates + .instantiate_own(tcx, trait_to_impl_substs) + .map(|(predicate, _)| predicate), + ); + + debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds); + + let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id); + let param_env = ty::ParamEnv::new( + tcx.intern_predicates(&hybrid_preds.predicates), + Reveal::UserFacing, + hir::Constness::NotConst, + ); + let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause); + let infcx = tcx.infer_ctxt().build(); + let ocx = ObligationCtxt::new(&infcx); + + debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds()); + + for (predicate, span) in impl_ty_own_bounds { + let cause = ObligationCause::misc(span, impl_ty_hir_id); + let predicate = ocx.normalize(&cause, param_env, predicate); + + let cause = ObligationCause::new( + span, + impl_ty_hir_id, + ObligationCauseCode::CompareImplItemObligation { + impl_item_def_id: impl_ty.def_id.expect_local(), + trait_item_def_id: trait_ty.def_id, + kind: impl_ty.kind, + }, + ); + ocx.register_obligation(traits::Obligation::new(tcx, cause, param_env, predicate)); + } + + // Check that all obligations are satisfied by the implementation's + // version. + let errors = ocx.select_all_or_error(); + if !errors.is_empty() { + let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None); + return Err(reported); + } + + // Finally, resolve all regions. This catches wily misuses of + // lifetime parameters. + let outlives_environment = OutlivesEnvironment::new(param_env); + infcx.err_ctxt().check_region_obligations_and_report_errors( + impl_ty.def_id.expect_local(), + &outlives_environment, + )?; + + Ok(()) +} + +/// Validate that `ProjectionCandidate`s created for this associated type will +/// be valid. +/// +/// Usually given +/// +/// trait X { type Y: Copy } impl X for T { type Y = S; } +/// +/// We are able to normalize `<T as X>::U` to `S`, and so when we check the +/// impl is well-formed we have to prove `S: Copy`. +/// +/// For default associated types the normalization is not possible (the value +/// from the impl could be overridden). We also can't normalize generic +/// associated types (yet) because they contain bound parameters. +#[instrument(level = "debug", skip(tcx))] +pub(super) fn check_type_bounds<'tcx>( + tcx: TyCtxt<'tcx>, + trait_ty: &ty::AssocItem, + impl_ty: &ty::AssocItem, + impl_ty_span: Span, + impl_trait_ref: ty::TraitRef<'tcx>, +) -> Result<(), ErrorGuaranteed> { + // Given + // + // impl<A, B> Foo<u32> for (A, B) { + // type Bar<C> =... + // } + // + // - `impl_trait_ref` would be `<(A, B) as Foo<u32>> + // - `impl_ty_substs` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0) + // - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from + // the *trait* with the generic associated type parameters (as bound vars). + // + // A note regarding the use of bound vars here: + // Imagine as an example + // ``` + // trait Family { + // type Member<C: Eq>; + // } + // + // impl Family for VecFamily { + // type Member<C: Eq> = i32; + // } + // ``` + // Here, we would generate + // ```notrust + // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) } + // ``` + // when we really would like to generate + // ```notrust + // forall<C> { Normalize(<VecFamily as Family>::Member<C> => 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<X> for some type X where !(X: Eq), that appears in the value of type + // Member<C: Eq> = .... That type would fail a well-formedness check that we ought to be doing + // elsewhere, which would check that any <T as Family>::Member<X> meets the bounds declared in + // the trait (notably, that X: Eq and T: Family). + let defs: &ty::Generics = tcx.generics_of(impl_ty.def_id); + let mut substs = smallvec::SmallVec::with_capacity(defs.count()); + if let Some(def_id) = defs.parent { + let parent_defs = tcx.generics_of(def_id); + InternalSubsts::fill_item(&mut substs, tcx, parent_defs, &mut |param, _| { + tcx.mk_param_from_def(param) + }); + } + let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> = + smallvec::SmallVec::with_capacity(defs.count()); + InternalSubsts::fill_single(&mut substs, defs, &mut |param, _| match param.kind { + GenericParamDefKind::Type { .. } => { + let kind = ty::BoundTyKind::Param(param.name); + let bound_var = ty::BoundVariableKind::Ty(kind); + bound_vars.push(bound_var); + tcx.mk_ty(ty::Bound( + ty::INNERMOST, + ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind }, + )) + .into() + } + GenericParamDefKind::Lifetime => { + let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name); + let bound_var = ty::BoundVariableKind::Region(kind); + bound_vars.push(bound_var); + tcx.mk_region(ty::ReLateBound( + ty::INNERMOST, + ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind }, + )) + .into() + } + GenericParamDefKind::Const { .. } => { + let bound_var = ty::BoundVariableKind::Const; + bound_vars.push(bound_var); + tcx.mk_const( + ty::ConstKind::Bound(ty::INNERMOST, ty::BoundVar::from_usize(bound_vars.len() - 1)), + tcx.type_of(param.def_id), + ) + .into() + } + }); + let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter()); + let impl_ty_substs = tcx.intern_substs(&substs); + let container_id = impl_ty.container_id(tcx); + + let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs); + let impl_ty_value = tcx.type_of(impl_ty.def_id); + + let param_env = tcx.param_env(impl_ty.def_id); + + // When checking something like + // + // trait X { type Y: PartialEq<<Self as X>::Y> } + // impl X for T { default type Y = S; } + // + // We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case + // we want <T as X>::Y to normalize to S. This is valid because we are + // checking the default value specifically here. Add this equality to the + // ParamEnv for normalization specifically. + let normalize_param_env = { + let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>(); + match impl_ty_value.kind() { + ty::Alias(ty::Projection, proj) + if proj.def_id == trait_ty.def_id && proj.substs == rebased_substs => + { + // Don't include this predicate if the projected type is + // exactly the same as the projection. This can occur in + // (somewhat dubious) code like this: + // + // impl<T> X for T where T: X { type Y = <T as X>::Y; } + } + _ => predicates.push( + ty::Binder::bind_with_vars( + ty::ProjectionPredicate { + projection_ty: tcx.mk_alias_ty(trait_ty.def_id, rebased_substs), + term: impl_ty_value.into(), + }, + bound_vars, + ) + .to_predicate(tcx), + ), + }; + ty::ParamEnv::new( + tcx.intern_predicates(&predicates), + Reveal::UserFacing, + param_env.constness(), + ) + }; + debug!(?normalize_param_env); + + let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local()); + let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id); + let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs); + + let infcx = tcx.infer_ctxt().build(); + let ocx = ObligationCtxt::new(&infcx); + + let assumed_wf_types = + ocx.assumed_wf_types(param_env, impl_ty_span, impl_ty.def_id.expect_local()); + + let normalize_cause = ObligationCause::new( + impl_ty_span, + impl_ty_hir_id, + ObligationCauseCode::CheckAssociatedTypeBounds { + impl_item_def_id: impl_ty.def_id.expect_local(), + trait_item_def_id: trait_ty.def_id, + }, + ); + let mk_cause = |span: Span| { + let code = if span.is_dummy() { + traits::ItemObligation(trait_ty.def_id) + } else { + traits::BindingObligation(trait_ty.def_id, span) + }; + ObligationCause::new(impl_ty_span, impl_ty_hir_id, code) + }; + + let obligations = tcx + .bound_explicit_item_bounds(trait_ty.def_id) + .subst_iter_copied(tcx, rebased_substs) + .map(|(concrete_ty_bound, span)| { + debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound); + traits::Obligation::new(tcx, mk_cause(span), param_env, concrete_ty_bound) + }) + .collect(); + debug!("check_type_bounds: item_bounds={:?}", obligations); + + for mut obligation in util::elaborate_obligations(tcx, obligations) { + let normalized_predicate = + ocx.normalize(&normalize_cause, normalize_param_env, obligation.predicate); + debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate); + obligation.predicate = normalized_predicate; + + ocx.register_obligation(obligation); + } + // Check that all obligations are satisfied by the implementation's + // version. + let errors = ocx.select_all_or_error(); + if !errors.is_empty() { + let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None); + return Err(reported); + } + + // Finally, resolve all regions. This catches wily misuses of + // lifetime parameters. + let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_hir_id, assumed_wf_types); + let outlives_environment = + OutlivesEnvironment::with_bounds(param_env, Some(&infcx), implied_bounds); + + infcx.err_ctxt().check_region_obligations_and_report_errors( + impl_ty.def_id.expect_local(), + &outlives_environment, + )?; + + Ok(()) +} + +fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str { + match impl_item.kind { + ty::AssocKind::Const => "const", + ty::AssocKind::Fn => "method", + ty::AssocKind::Type => "type", + } +} |