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Fix trait upcasting to dyn type with no principal when there are projections

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This commit is contained in:
Michael Goulet 2025-04-05 19:33:47 +00:00
parent 0c478fdfe1
commit 45afefa7c0
2 changed files with 37 additions and 14 deletions
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24
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View file

@ -1090,12 +1090,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
{
// See `assemble_candidates_for_unsizing` for more info.
// We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`.
let iter = data_a
let existential_predicates = if data_b.principal().is_some() {
tcx.mk_poly_existential_predicates_from_iter(
data_a
.principal()
.filter(|_| {
// optionally drop the principal, if we're unsizing to no principal
data_b.principal().is_some()
})
.map(|b| b.map_bound(ty::ExistentialPredicate::Trait))
.into_iter()
.chain(
@ -1108,8 +1106,20 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
.auto_traits()
.map(ty::ExistentialPredicate::AutoTrait)
.map(ty::Binder::dummy),
);
let existential_predicates = tcx.mk_poly_existential_predicates_from_iter(iter);
),
)
} else {
// If we're unsizing to a dyn type that has no principal, then drop
// the principal and projections from the type. We use the auto traits
// from the RHS type since as we noted that we've checked for auto
// trait compatibility during unsizing.
tcx.mk_poly_existential_predicates_from_iter(
data_b
.auto_traits()
.map(ty::ExistentialPredicate::AutoTrait)
.map(ty::Binder::dummy),
)
};
let source_trait = Ty::new_dynamic(tcx, existential_predicates, r_b, dyn_a);
// Require that the traits involved in this upcast are **equal**;

13
tests/ui/traits/dyn-drop-principal-with-projections.rs Normal file
View file

@ -0,0 +1,13 @@
//@ check-pass
trait Tr {
type Assoc;
}
impl Tr for () {
type Assoc = ();
}
fn main() {
let x = &() as &(dyn Tr<Assoc = ()> + Send) as &dyn Send;
}