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Bring back ParamEnv deduplication

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This commit is contained in:
Tatsuyuki Ishi 2018-02-27 17:30:20 +09:00
parent 29f5c699b1
commit f297f56e76
1 changed files with 5 additions and 2 deletions
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7
src/librustc/traits/project.rs
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@ -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