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Rollup merge of #136554 - compiler-errors:opt-alias-variances, r=lcnr

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Add `opt_alias_variances` and use it in outlives code

...so to fix some subtle outlives bugs with precise capturing in traits, and eventually make it easier to compute variances for "forced unconstrained" trait lifetimes.

r? lcnr
This commit is contained in:
Matthias Krüger 2025-02-07 21:31:00 +01:00 • committed by GitHub
commit 7ca0fd18f6
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12 changed files with 117 additions and 50 deletions
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8
compiler/rustc_middle/src/ty/context.rs
View file

@ -194,6 +194,14 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
self.variances_of(def_id)
}
fn opt_alias_variances(
self,
kind: impl Into<ty::AliasTermKind>,
def_id: DefId,
) -> Option<&'tcx [ty::Variance]> {
self.opt_alias_variances(kind, def_id)
}
fn type_of(self, def_id: DefId) -> ty::EarlyBinder<'tcx, Ty<'tcx>> {
self.type_of(def_id)
}

23
compiler/rustc_middle/src/ty/util.rs
View file

@ -948,6 +948,29 @@ impl<'tcx> TyCtxt<'tcx> {
ty
}
// Computes the variances for an alias (opaque or RPITIT) that represent
// its (un)captured regions.
pub fn opt_alias_variances(
self,
kind: impl Into<ty::AliasTermKind>,
def_id: DefId,
) -> Option<&'tcx [ty::Variance]> {
match kind.into() {
ty::AliasTermKind::ProjectionTy => {
if self.is_impl_trait_in_trait(def_id) {
Some(self.variances_of(def_id))
} else {
None
}
}
ty::AliasTermKind::OpaqueTy => Some(self.variances_of(def_id)),
ty::AliasTermKind::InherentTy
| ty::AliasTermKind::WeakTy
| ty::AliasTermKind::UnevaluatedConst
| ty::AliasTermKind::ProjectionConst => None,
}
}
}
struct OpaqueTypeExpander<'tcx> {