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Prefer lower TraitUpcasting candidates

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This commit is contained in:
Michael Goulet 2025-01-14 17:54:53 +00:00
parent 2ae9916816
commit bf545ce2fe
6 changed files with 54 additions and 6 deletions
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12
compiler/rustc_trait_selection/src/traits/select/mod.rs
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@ -1895,6 +1895,18 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
Some(None) => {}
None => return None,
}
// Same for upcasting.
let upcast_bound = candidates
.iter()
.filter_map(|c| {
if let TraitUpcastingUnsizeCandidate(i) = c.candidate { Some(i) } else { None }
})
.try_reduce(|c1, c2| if has_non_region_infer { None } else { Some(c1.min(c2)) });
match upcast_bound {
Some(Some(index)) => return Some(TraitUpcastingUnsizeCandidate(index)),
Some(None) => {}
None => return None,
}
// Finally, handle overlapping user-written impls.
let impls = candidates.iter().filter_map(|c| {