Deduplicate ParamCandidates with the same value except for bound vars
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2 changed files with 31 additions and 1 deletions
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@ -1361,7 +1361,17 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
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) => false,
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) => false,
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(ParamCandidate(other), ParamCandidate(victim)) => {
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(ParamCandidate(other), ParamCandidate(victim)) => {
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if other.value == victim.value && victim.constness == Constness::NotConst {
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let value_same_except_bound_vars = other.value.skip_binder()
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== victim.value.skip_binder()
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&& !other.value.skip_binder().has_escaping_bound_vars();
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if value_same_except_bound_vars {
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// See issue #84398. In short, we can generate multiple ParamCandidates which are
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// the same except for unused bound vars. Just pick the current one (the should
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// both evaluate to the same answer). This is probably best characterized as a
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// "hack", since we might prefer to just do our best to *not* create essentially
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// duplicate candidates in the first place.
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true
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} else if other.value == victim.value && victim.constness == Constness::NotConst {
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// Drop otherwise equivalent non-const candidates in favor of const candidates.
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// Drop otherwise equivalent non-const candidates in favor of const candidates.
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true
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true
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} else {
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} else {
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20
src/test/ui/lifetimes/issue-84398.rs
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20
src/test/ui/lifetimes/issue-84398.rs
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@ -0,0 +1,20 @@
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// check-pass
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pub trait Deserialize<'de>: Sized {}
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pub trait DeserializeOwned: for<'de> Deserialize<'de> {}
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pub trait Extensible {
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type Config;
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}
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// The `C` here generates a `C: Sized` candidate
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pub trait Installer<C> {
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fn init<B: Extensible<Config = C>>(&mut self) -> ()
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where
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// This clause generates a `for<'de> C: Sized` candidate
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B::Config: DeserializeOwned,
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{
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}
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}
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fn main() {}
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