Function lower_fn_sig_recovering_infer_ret_ty

fn lower_fn_sig_recovering_infer_ret_ty<'tcx>(
    icx: &ItemCtxt<'tcx>,
    sig: &'tcx FnSig<'tcx>,
    generics: &'tcx Generics<'tcx>,
    def_id: LocalDefId,
) -> PolyFnSig<'tcx>