fn structurally_same_type_impl<'tcx>( seen_types: &mut UnordSet<(Ty<'tcx>, Ty<'tcx>)>, tcx: TyCtxt<'tcx>, typing_env: TypingEnv<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>, ckind: CItemKind, ) -> bool