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MudChart: Fix Sankey hang on circular edge definitions - #13322
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danielchalmers merged 1 commit intoJun 19, 2026
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Sankey's CalculateNodeColumns ran a BFS that always re-enqueued every target to find the longest path. With circular edges (e.g. A->B, B->A) no node is a root, so the source-node fallback treats every node as a source and the column keeps increasing on each pass around the cycle. The queue never drains and the render hangs. Only enqueue a target when the edge pushes it into a deeper column, and cap the column at the node count (the longest path in a graph of N nodes spans at most N-1 edges). This terminates on cyclic input while producing identical columns for valid acyclic graphs. Adds a regression test rendering a two-node cycle.
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A Sankey chart whose edges form a cycle (e.g.
A -> B,B -> A) hangs the render.Sankey.CalculateNodeColumnsruns a BFS that always re-enqueues every target to find the longest path. With a cycle there is no root node, so the source-node fallback treats every node as a source and each pass around the cycle increases the column — the queue never drains and rendering loops forever.The fix is to only enqueue a target when the edge actually pushes it into a deeper column and cap the column at the node count (the longest path in a graph of
Nnodes spans at mostN-1edges). This terminates on cyclic input while producing identical columns for valid acyclic graphs, so existing layout behaviour is unchanged.Checklist: