Function supertrait_vtable_slot

pub(crate) fn supertrait_vtable_slot<'tcx>(
    tcx: TyCtxt<'tcx>,
    key: (Ty<'tcx>, Ty<'tcx>),
) -> Option<usize>

Given a dyn Subtrait and dyn Supertrait trait object, find the slot of the trait vptr in the subtrait’s vtable.

A return value of None means that the original vtable can be reused.