fn trait_predicates_eq<'tcx>(
predicate1: Predicate<'tcx>,
predicate2: Predicate<'tcx>,
) -> bool
Expand description
Checks if some predicate on the specializing impl (predicate1
) is the same
as some predicate on the base impl (predicate2
).
This basically just checks syntactic equivalence, but is a little more
forgiving since we want to equate T: Tr
with T: ~const Tr
so this can work:
ⓘ
#[rustc_specialization_trait]
trait Specialize { }
impl<T: Bound> Tr for T { }
impl<T: ~const Bound + Specialize> const Tr for T { }
However, we don’t want to allow the reverse, i.e., when the bound on the specializing impl is not as const as the bound on the base impl:
ⓘ
impl<T: ~const Bound> const Tr for T { }
impl<T: Bound + Specialize> const Tr for T { } // should be T: ~const Bound
So we make that check in this function and try to raise a helpful error message.