Adding upstream version 1.68.2+dfsg1.upstream/1.68.2+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 0 insertions, 1943 deletions

diff --git a/compiler/rustc_hir_analysis/src/check/compare_method.rs b/compiler/rustc_hir_analysis/src/check/compare_method.rs
deleted file mode 100644
index db150ebf0..000000000
--- a/compiler/rustc_hir_analysis/src/check/compare_method.rs
+++ /dev/null
@@ -1,1943 +0,0 @@
-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};
-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(crate) 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);
-
-    if let Err(_) = compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref) {
-        return;
-    }
-
-    if let Err(_) = compare_number_of_generics(tcx, impl_m, trait_m, trait_item_span, false) {
-        return;
-    }
-
-    if let Err(_) = compare_generic_param_kinds(tcx, impl_m, trait_m, false) {
-        return;
-    }
-
-    if let Err(_) =
-        compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
-    {
-        return;
-    }
-
-    if let Err(_) = compare_synthetic_generics(tcx, impl_m, trait_m) {
-        return;
-    }
-
-    if let Err(_) = compare_predicate_entailment(
-        tcx,
-        impl_m,
-        impl_m_span,
-        trait_m,
-        impl_trait_ref,
-        CheckImpliedWfMode::Check,
-    ) {
-        return;
-    }
-}
-
-/// 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_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).predicates);
-
-    // 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 iter::zip(impl_m_own_bounds.predicates, impl_m_own_bounds.spans) {
-        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_fty = ocx.normalize(&norm_cause, param_env, unnormalized_impl_fty);
-    debug!("compare_impl_method: impl_fty={:?}", impl_fty);
-
-    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_fty, impl_fty);
-
-    if let Err(terr) = result {
-        debug!(?terr, "sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
-
-        let emitted = report_trait_method_mismatch(
-            &infcx,
-            cause,
-            terr,
-            (trait_m, trait_fty),
-            (impl_m, impl_fty),
-            trait_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())),
-        ));
-    }
-    let emit_implied_wf_lint = || {
-        infcx.tcx.struct_span_lint_hir(
-            rustc_session::lint::builtin::IMPLIED_BOUNDS_ENTAILMENT,
-            impl_m_hir_id,
-            infcx.tcx.def_span(impl_m.def_id),
-            "impl method assumes more implied bounds than the corresponding trait method",
-            |lint| lint,
-        );
-    };
-
-    // 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_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();
-                });
-            }
-            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_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();
-                });
-            }
-            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(())
-}
-
-#[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_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,
-}
-
-#[instrument(skip(tcx), level = "debug", ret)]
-pub fn collect_trait_impl_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();
-    let param_env = tcx.param_env(def_id);
-
-    // First, check a few of the same thing as `compare_impl_method`, just so we don't ICE during substitutions 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),
-        ),
-    );
-    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);
-    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");
-
-    let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig));
-    let impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(impl_sig));
-
-    // 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_predicate_entailment`.
-    match ocx.eq(&cause, param_env, trait_fty, impl_fty) {
-        Ok(()) => {}
-        Err(terr) => {
-            // This function gets called during `compare_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_predicate_entailment` will not report the error
-            // when normalization fails.
-            let emitted = report_trait_method_mismatch(
-                infcx,
-                cause,
-                terr,
-                (trait_m, trait_fty),
-                (impl_m, impl_fty),
-                trait_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.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(&region.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::Projection(proj) = ty.kind()
-            && self.tcx().def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
-        {
-            if let Some((ty, _)) = self.types.get(&proj.item_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.item_def_id, (infer_ty, proj.substs));
-            // Recurse into bounds
-            for (pred, pred_span) in self.tcx().bound_explicit_item_bounds(proj.item_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.item_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_fty): (&ty::AssocItem, Ty<'tcx>),
-    (impl_m, impl_fty): (&ty::AssocItem, Ty<'tcx>),
-    trait_sig: 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 span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
-                ImplItemKind::Fn(ref sig, body) => 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),
-                _ => bug!("{:?} is not a method", impl_m),
-            };
-
-            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.
-                match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
-                    ImplItemKind::Fn(ref sig, _) if !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::Terms(ExpectedFound {
-            expected: trait_fty.into(),
-            found: impl_fty.into(),
-        })),
-        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 = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
-        ImplItemKind::Fn(ref sig, _) => {
-            sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
-        }
-        _ => bug!("{:?} is not a method", impl_m),
-    };
-    let trait_args =
-        trait_m.def_id.as_local().map(|def_id| match tcx.hir().expect_trait_item(def_id).kind {
-            TraitItemKind::Fn(ref sig, _) => {
-                sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
-            }
-            _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
-        });
-
-    match terr {
-        TypeError::ArgumentMutability(i) => {
-            (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(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));
-            }
-            let reported = err.emit();
-            return Err(reported);
-        }
-
-        (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));
-            }
-            let reported = err.emit();
-            return Err(reported);
-        }
-    }
-
-    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 = if let Some(def_id) = trait_m.def_id.as_local() {
-            match tcx.hir().expect_trait_item(def_id).kind {
-                TraitItemKind::Fn(ref trait_m_sig, _) => {
-                    let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
-                    if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
-                        Some(if pos == 0 {
-                            arg.span
-                        } else {
-                            arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo())
-                        })
-                    } else {
-                        trait_item_span
-                    }
-                }
-                _ => bug!("{:?} is not a method", impl_m),
-            }
-        } else {
-            trait_item_span
-        };
-        let impl_span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
-            ImplItemKind::Fn(ref impl_m_sig, _) => {
-                let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
-                if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
-                    if pos == 0 {
-                        arg.span
-                    } else {
-                        arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo())
-                    }
-                } else {
-                    impl_m_span
-                }
-            }
-            _ => bug!("{:?} is not a method", impl_m),
-        };
-        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
-            ),
-        );
-        let reported = err.emit();
-        return Err(reported);
-    }
-
-    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`");
-                    (|| {
-                        // 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,
-                        );
-                        Some(())
-                    })();
-                }
-                // 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 impl_m = impl_m.def_id.as_local()?;
-                        let impl_m = tcx.hir().expect_impl_item(impl_m);
-                        let input_tys = match impl_m.kind {
-                            hir::ImplItemKind::Fn(ref sig, _) => sig.decl.inputs,
-                            _ => unreachable!(),
-                        };
-                        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, ref 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,
-                        );
-                        Some(())
-                    })();
-                }
-                _ => unreachable!(),
-            }
-            let reported = err.emit();
-            error_found = Some(reported);
-        }
-    }
-    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 (&param_impl.kind, &param_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_assoc_const_impl_item_with_trait_item` instead
-pub(crate) fn raw_compare_const_impl<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    (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();
-    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
-        match tcx.hir().expect_impl_item(impl_const_item_def).kind {
-            ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
-            _ => bug!("{:?} is not a impl const", impl_const_item),
-        }
-
-        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
-            match tcx.hir().expect_trait_item(trait_c_def_id).kind {
-                TraitItemKind::Const(ref ty, _) => ty.span,
-                _ => bug!("{:?} is not a trait const", trait_const_item),
-            }
-        });
-
-        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));
-    }
-
-    // FIXME return `ErrorReported` if region obligations error?
-    let outlives_environment = OutlivesEnvironment::new(param_env);
-    infcx.check_region_obligations_and_report_errors(impl_const_item_def, &outlives_environment);
-    Ok(())
-}
-
-pub(crate) fn compare_ty_impl<'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> = (|| {
-        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_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.is_empty() {
-        // 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).predicates);
-
-    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());
-
-    assert_eq!(impl_ty_own_bounds.predicates.len(), impl_ty_own_bounds.spans.len());
-    for (span, predicate) in std::iter::zip(impl_ty_own_bounds.spans, impl_ty_own_bounds.predicates)
-    {
-        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.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 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::Projection(proj)
-                if proj.item_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: ty::ProjectionTy {
-                            item_def_id: trait_ty.def_id,
-                            substs: 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.check_region_obligations_and_report_errors(
-        impl_ty.def_id.expect_local(),
-        &outlives_environment,
-    );
-
-    let constraints = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
-    for (key, value) in constraints {
-        infcx
-            .err_ctxt()
-            .report_mismatched_types(
-                &ObligationCause::misc(
-                    value.hidden_type.span,
-                    tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local()),
-                ),
-                tcx.mk_opaque(key.def_id.to_def_id(), key.substs),
-                value.hidden_type.ty,
-                TypeError::Mismatch,
-            )
-            .emit();
-    }
-
-    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",
-    }
-}