Function rustc_ty::ty::opaque_type_projection_predicates

fn opaque_type_projection_predicates(
    tcx: TyCtxt<'_>, 
    def_id: DefId
) -> &List<Predicate<'_>>

Opaque types don't have the same issues as associated types: the only predicates on an opaque type (excluding those it inherits from its parent item) should be of the form we're expecting.