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Auto merge of #102334 - compiler-errors:rpitit-substs-issue, r=cjgillot

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Fix subst issues with return-position `impl Trait` in trait

1. Fix an issue where we were rebase impl substs onto trait method substs, instead of trait substs
2. Fix an issue where early-bound regions aren't being mapped correctly for RPITIT hidden types

Fixes #102301
Fixes #102310
Fixes #102334
Fixes #102918
This commit is contained in:
bors 2022-10-16 10:10:44 +00:00
commit 8be3ce9056
5 changed files with 117 additions and 23 deletions
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83
compiler/rustc_hir_analysis/src/check/compare_method.rs
View file

@ -465,30 +465,30 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
let ocx = ObligationCtxt::new(infcx);
let norm_cause = ObligationCause::misc(return_span, impl_m_hir_id);
let impl_return_ty = ocx.normalize(
let impl_sig = ocx.normalize(
norm_cause.clone(),
param_env,
infcx
.replace_bound_vars_with_fresh_vars(
return_span,
infer::HigherRankedType,
tcx.fn_sig(impl_m.def_id),
)
.output(),
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();
let mut collector = ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_hir_id);
let unnormalized_trait_return_ty = tcx
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),
)
.output()
.fold_with(&mut collector);
let trait_return_ty =
ocx.normalize(norm_cause.clone(), param_env, unnormalized_trait_return_ty);
let trait_sig = ocx.normalize(norm_cause.clone(), param_env, unnormalized_trait_sig);
let trait_return_ty = trait_sig.output();
let wf_tys = FxHashSet::from_iter([unnormalized_trait_return_ty, trait_return_ty]);
let wf_tys = FxHashSet::from_iter(
unnormalized_trait_sig.inputs_and_output.iter().chain(trait_sig.inputs_and_output.iter()),
);
match infcx.at(&cause, param_env).eq(trait_return_ty, impl_return_ty) {
Ok(infer::InferOk { value: (), obligations }) => {
@ -521,6 +521,26 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
}
}
// 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 infcx
.at(&cause, param_env)
.eq(tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig)), tcx.mk_fn_ptr(ty::Binder::dummy(impl_sig)))
{
Ok(infer::InferOk { value: (), obligations }) => {
ocx.register_obligations(obligations);
}
Err(terr) => {
let guar = tcx.sess.delay_span_bug(
return_span,
format!("could not unify `{trait_sig}` and `{impl_sig}`: {terr:?}"),
);
return Err(guar);
}
}
// Check that all obligations are satisfied by the implementation's
// RPITs.
let errors = ocx.select_all_or_error();
@ -551,15 +571,40 @@ pub fn collect_trait_impl_trait_tys<'tcx>(
let id_substs = InternalSubsts::identity_for_item(tcx, def_id);
debug!(?id_substs, ?substs);
let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> =
substs.iter().enumerate().map(|(index, arg)| (arg, id_substs[index])).collect();
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, _| {
if let ty::ReFree(_) = region.kind() {
map[&region.into()].expect_region()
} else {
region
}
let ty::ReFree(_) = region.kind() else { return region; };
let ty::ReEarlyBound(e) = map[&region.into()].expect_region().kind()
else { bug!("expected ReFree to map to ReEarlyBound"); };
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);