{"ast_node_type":"function","tokens":[{"end":60,"kind":"keyword","start":0,"text":"fn"}]}
    fn new(node_flow_data: &'a NodeFlowData<Node>) -> Self {
impl<'a, Node: Idx> SpantreeBuilder<'a, Node> {
        let NodeFlowData { supernodes, succ_supernodes } = node_flow_data;