fn visit_for_cycles(
index: usize,
plan: &Plan,
colors: &mut [VisitColor],
) -> Result<(), String>Expand description
DFS cycle check on the plan arena following only sequence/parallel child edges.
Uses White/Gray/Black marks: entering a Gray node means a back-edge to an ancestor.
RTDL_DO nodes have no children in this graph. Returns Ok when the subgraph from
index is acyclic; otherwise an error naming the node where the cycle was found.