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Subtype predicates only exist on inference types, so we can allow them to register opaque types within them. #123979

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Merged
merged 1 commit into from
Apr 16, 2024
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Subtype predicates only exist on inference types, so we can allow them to register opaque types within them. #123979

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17 changes: 15 additions & 2 deletions compiler/rustc_infer/src/infer/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -945,14 +945,27 @@ impl<'tcx> InferCtxt<'tcx> {
(&ty::Infer(ty::TyVar(a_vid)), &ty::Infer(ty::TyVar(b_vid))) => {
return Err((a_vid, b_vid));
}
// We don't silently want to constrain hidden types here, so we assert that either one side is
// an infer var, so it'll get constrained to whatever the other side is, or there are no opaque
// types involved.
// We don't expect this to actually get hit, but if it does, we now at least know how to write
// a test for it.
(_, ty::Infer(ty::TyVar(_))) => {}
(ty::Infer(ty::TyVar(_)), _) => {}
_ if (r_a, r_b).has_opaque_types() => {
span_bug!(
cause.span(),
"opaque types got hidden types registered from within subtype predicate: {r_a:?} vs {r_b:?}"
)
}
_ => {}
}

self.enter_forall(predicate, |ty::SubtypePredicate { a_is_expected, a, b }| {
if a_is_expected {
Ok(self.at(cause, param_env).sub(DefineOpaqueTypes::No, a, b))
Ok(self.at(cause, param_env).sub(DefineOpaqueTypes::Yes, a, b))
} else {
Ok(self.at(cause, param_env).sup(DefineOpaqueTypes::No, b, a))
Ok(self.at(cause, param_env).sup(DefineOpaqueTypes::Yes, b, a))
}
})
}
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