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only mark projection as ambiguous if GAT substs are constrained

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This commit is contained in:
Michael Goulet 2022-02-10 22:45:58 -08:00
parent e646f3d2a9
commit 784c7a6cad
6 changed files with 88 additions and 43 deletions
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55
compiler/rustc_trait_selection/src/traits/project.rs
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@ -1073,16 +1073,6 @@ fn project<'cx, 'tcx>(
return Ok(Projected::Progress(Progress::error(selcx.tcx())));
}
// If the obligation contains any inference types or consts in associated
// type substs, then we don't assemble any candidates.
// This isn't really correct, but otherwise we can end up in a case where
// we constrain inference variables by selecting a single predicate, when
// we need to stay general. See issue #91762.
let (_, predicate_own_substs) = obligation.predicate.trait_ref_and_own_substs(selcx.tcx());
if predicate_own_substs.iter().any(|g| g.has_infer_types_or_consts()) {
return Err(ProjectionError::TooManyCandidates);
}
let mut candidates = ProjectionCandidateSet::None;
// Make sure that the following procedures are kept in order. ParamEnv
@ -1180,7 +1170,7 @@ fn assemble_candidates_from_trait_def<'cx, 'tcx>(
ProjectionCandidate::TraitDef,
bounds.iter(),
true,
)
);
}
/// In the case of a trait object like
@ -1245,27 +1235,34 @@ fn assemble_candidates_from_predicates<'cx, 'tcx>(
let bound_predicate = predicate.kind();
if let ty::PredicateKind::Projection(data) = predicate.kind().skip_binder() {
let data = bound_predicate.rebind(data);
let same_def_id = data.projection_def_id() == obligation.predicate.item_def_id;
if data.projection_def_id() != obligation.predicate.item_def_id {
continue;
}
let is_match = same_def_id
&& infcx.probe(|_| {
selcx.match_projection_projections(
obligation,
data,
potentially_unnormalized_candidates,
)
});
let is_match = infcx.probe(|_| {
selcx.match_projection_projections(
obligation,
data,
potentially_unnormalized_candidates,
)
});
if is_match {
candidate_set.push_candidate(ctor(data));
match is_match {
Some(true) => {
candidate_set.push_candidate(ctor(data));
if potentially_unnormalized_candidates
&& !obligation.predicate.has_infer_types_or_consts()
{
// HACK: Pick the first trait def candidate for a fully
// inferred predicate. This is to allow duplicates that
// differ only in normalization.
return;
if potentially_unnormalized_candidates
&& !obligation.predicate.has_infer_types_or_consts()
{
// HACK: Pick the first trait def candidate for a fully
// inferred predicate. This is to allow duplicates that
// differ only in normalization.
return;
}
}
Some(false) => {}
None => {
candidate_set.mark_ambiguous();
}
}
}