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Bring back ParamEnv deduplication #48576

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Merged
bors merged 1 commit into from
Feb 28, 2018
Merged

Bring back ParamEnv deduplication #48576

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7 changes: 5 additions & 2 deletions src/librustc/traits/project.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -142,8 +142,11 @@ impl<'tcx> ProjectionTyCandidateSet<'tcx> {
true
}
Single(current) => {
// No duplicates are expected.
assert_ne!(current, &candidate);
// Duplicates can happen inside ParamEnv. In the case, we
// perform a lazy deduplication.
if current == &candidate {
return false;
}
// Prefer where-clauses. As in select, if there are multiple
// candidates, we prefer where-clause candidates over impls. This
// may seem a bit surprising, since impls are the source of
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