fn execute_job_incr<Q, Qcx>(
    query: Q,
    qcx: Qcx,
    dep_graph_data: &DepGraphData<Qcx::Deps>,
    key: Q::Key,
    dep_node_opt: Option<DepNode>,
    job_id: QueryJobId
) -> (Q::Value, DepNodeIndex)where
    Q: QueryConfig<Qcx>,
    Qcx: QueryContext,