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Deduplicate ParamCandidates with the same value except for bound vars

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This commit is contained in:
Jack Huey 2021-04-25 15:11:49 -04:00
parent 58bdb08947
commit 9f0693969a
2 changed files with 31 additions and 1 deletions
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12
compiler/rustc_trait_selection/src/traits/select/mod.rs
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@ -1361,7 +1361,17 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
) => false,
(ParamCandidate(other), ParamCandidate(victim)) => {
if other.value == victim.value && victim.constness == Constness::NotConst {
let value_same_except_bound_vars = other.value.skip_binder()
== victim.value.skip_binder()
&& !other.value.skip_binder().has_escaping_bound_vars();
if value_same_except_bound_vars {
// See issue #84398. In short, we can generate multiple ParamCandidates which are
// the same except for unused bound vars. Just pick the current one (the should
// both evaluate to the same answer). This is probably best characterized as a
// "hack", since we might prefer to just do our best to *not* create essentially
// duplicate candidates in the first place.
true
} else if other.value == victim.value && victim.constness == Constness::NotConst {
// Drop otherwise equivalent non-const candidates in favor of const candidates.
true
} else {