bjoernager/rust
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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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27
compiler/rustc_trait_selection/src/traits/select/mod.rs
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@ -1508,12 +1508,15 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
})
}
/// Return Some(true) if the obligation's predicate type applies to the env_predicate, and
/// Some(false) if it does not. Returns None in the case that the projection type is a GAT,
/// and applying this env_predicate constrains any of the obligation's GAT substitutions.
pub(super) fn match_projection_projections(
&mut self,
obligation: &ProjectionTyObligation<'tcx>,
env_predicate: PolyProjectionPredicate<'tcx>,
potentially_unnormalized_candidates: bool,
) -> bool {
) -> Option<bool> {
let mut nested_obligations = Vec::new();
let (infer_predicate, _) = self.infcx.replace_bound_vars_with_fresh_vars(
obligation.cause.span,
@ -1535,7 +1538,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
infer_predicate.projection_ty
};
self.infcx
let is_match = self
.infcx
.at(&obligation.cause, obligation.param_env)
.define_opaque_types(false)
.sup(obligation.predicate, infer_projection)
@ -1545,7 +1549,24 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
nested_obligations.into_iter().chain(obligations),
)
.map_or(false, |res| res.may_apply())
})
});
if is_match {
let generics = self.tcx().generics_of(obligation.predicate.item_def_id);
if !generics.params.is_empty() {
// If any of the obligation's predicate substs shallow-resolve to
// something new, that means that we must have newly inferred something
// about the GAT. We should give up with ambiguity in that case.
if obligation.predicate.substs[generics.parent_count..]
.iter()
.any(|&p| p.has_infer_types_or_consts() && self.infcx.shallow_resolve(p) != p)
{
return None;
}
}
}
Some(is_match)
}
///////////////////////////////////////////////////////////////////////////