{"ast_node_type":"variable","tokens":[{"end":84,"kind":"keyword","start":0,"text":"let"}]}
        let Self { ref span_edges, ref is_unvisited, ref counter_terms, .. } = self;
    fn finish(self) -> IndexVec<Node, Vec<CounterTerm<Node>>> {
        assert!(is_unvisited.is_empty(), "some nodes were never visited: {is_unvisited:?}");