fn synthesize_auto_trait_impl<'tcx>(
cx: &mut DocContext<'tcx>,
ty: Ty<'tcx>,
trait_def_id: DefId,
param_env: ParamEnv<'tcx>,
item_def_id: DefId,
finder: &AutoTraitFinder<'tcx>,
discard_positive_impls: DiscardPositiveImpls,
) -> Option<Item>