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best_blame_constraint: add a special case to recover object lifetime default notes

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dianne 2024-12-12 08:45:32 -08:00
parent ac922245f0
commit 2864906fce
6 changed files with 51 additions and 38 deletions
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22
compiler/rustc_borrowck/src/region_infer/mod.rs
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@ -1945,7 +1945,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
target_test: impl Fn(RegionVid) -> bool,
) -> (BlameConstraint<'tcx>, Vec<OutlivesConstraint<'tcx>>) {
// Find all paths
let (path, _) = self
let (path, target_region) = self
.find_constraint_paths_between_regions(from_region, target_test)
.or_else(|| {
self.find_constraint_paths_between_regions(from_region, |r| {
@ -2071,6 +2071,26 @@ impl<'tcx> RegionInferenceContext<'tcx> {
}
}
Some(_)
if target_region == self.universal_regions().fr_static
&& let Some(old_best) = path.iter().min_by_key(|p| p.category)
&& matches!(old_best.category, ConstraintCategory::Cast {
is_implicit_coercion: true,
unsize_to: Some(_)
}) =>
{
// FIXME(dianne): This is a hack in order to emit the subdiagnostic
// `BorrowExplanation::add_object_lifetime_default_note` more often, e.g. on
// `tests/ui/traits/trait-object-lifetime-default-note.rs`. The subdiagnostic
// depends on a coercion being blamed, so we fall back to an earlier version of this
// function's blaming logic to keep the test result the same. A proper fix will
// require rewriting the subdiagnostic not to rely on a coercion being blamed.
// For examples of where notes are missing, see #131008 and
// `tests/ui/suggestions/impl-on-dyn-trait-with-implicit-static-bound-needing-more-suggestions.rs`.
// As part of fixing those, this case should be removed.
*old_best
}
Some(i) => path[i],
None => {