{"ast_node_type":"variable","tokens":[{"end":71,"kind":"keyword","start":0,"text":"let"}]}
    let ty::FnDef(def_id, args) = *func_ty.kind() else { return None };
) -> Option<(Symbol, GenericArgsRef<'tcx>)> {
    let intrinsic = tcx.intrinsic(def_id)?;