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Only check outlives goals on impl compared to trait

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This commit is contained in:
Jack Huey 2023-03-19 14:35:38 -04:00
parent a6f8aa5a09
commit 3028dc4ef7
3 changed files with 77 additions and 12 deletions
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51
compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
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@ -1,7 +1,7 @@
use super::potentially_plural_count;
use crate::errors::LifetimesOrBoundsMismatchOnTrait;
use hir::def_id::{DefId, LocalDefId};
use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
use rustc_errors::{
pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed, MultiSpan,
};
@ -265,7 +265,6 @@ fn compare_method_predicate_entailment<'tcx>(
infer::HigherRankedType,
tcx.fn_sig(impl_m.def_id).instantiate_identity(),
);
let unnormalized_impl_fty = Ty::new_fn_ptr(tcx, ty::Binder::dummy(unnormalized_impl_sig));
let norm_cause = ObligationCause::misc(impl_m_span, impl_m_def_id);
let impl_sig = ocx.normalize(&norm_cause, param_env, unnormalized_impl_sig);
@ -309,16 +308,44 @@ fn compare_method_predicate_entailment<'tcx>(
}
if check_implied_wf == CheckImpliedWfMode::Check && !(impl_sig, trait_sig).references_error() {
// 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::Clause(ty::ClauseKind::WellFormed(
unnormalized_impl_fty.into(),
))),
));
// See #108544. Annoying, we can end up in cases where, because of winnowing,
// we pick param env candidates over a more general impl, leading to more
// stricter lifetime requirements than we would otherwise need. This can
// trigger the lint. Instead, let's only consider type outlives and
// region outlives obligations.
//
// FIXME(-Ztrait-solver=next): Try removing this hack again once
// the new solver is stable.
let mut wf_args: smallvec::SmallVec<[_; 4]> =
unnormalized_impl_sig.inputs_and_output.iter().map(|ty| ty.into()).collect();
// Annoyingly, asking for the WF predicates of an array (with an unevaluated const (only?))
// will give back the well-formed predicate of the same array.
let mut wf_args_seen: FxHashSet<_> = wf_args.iter().copied().collect();
while let Some(arg) = wf_args.pop() {
let Some(obligations) = rustc_trait_selection::traits::wf::obligations(
infcx,
param_env,
impl_m_def_id,
0,
arg,
impl_m_span,
) else {
continue;
};
for obligation in obligations {
match obligation.predicate.kind().skip_binder() {
ty::PredicateKind::Clause(
ty::ClauseKind::RegionOutlives(..) | ty::ClauseKind::TypeOutlives(..),
) => ocx.register_obligation(obligation),
ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
if wf_args_seen.insert(arg) {
wf_args.push(arg)
}
}
_ => {}
}
}
}
}
// Check that all obligations are satisfied by the implementation's