chore(cli): print detected cycle if work graph stalls (#25830)

To help with diagnosing #25806, if the work graph can't make any progress anymore because of a dependency cycle, print the cycle that was found instead of all the remaining nodes.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk/lib/util/work-graph.ts

@@ -272,7 +272,7 @@ export class WorkGraph {
  this.readyPool.sort((a, b) => (b.priority ?? 0) - (a.priority ?? 0));
 
  if (this.readyPool.length === 0 && activeCount === 0 && pendingCount > 0) {
- throw new Error(`Unable to make progress anymore among: ${this}`);
+ throw new Error(`Unable to make progress anymore, dependency cycle between remaining artifacts: ${this.findCycle().join(' -> ')}`);
  }
  }
 
@@ -283,6 +283,42 @@ export class WorkGraph {
  }
  }
  }
+
+ /**
+ * Find cycles in a graph
+ *
+ * Not the fastest, but effective and should be rare
+ */
+ private findCycle(): string[] {
+ const seen = new Set<string>();
+ const self = this;
+ for (const nodeId of Object.keys(this.nodes)) {
+ const cycle = recurse(nodeId, [nodeId]);
+ if (cycle) { return cycle; }
+ }
+ return ['No cycle found!'];
+
+ function recurse(nodeId: string, path: string[]): string[] | undefined {
+ if (seen.has(nodeId)) {
+ return undefined;
+ }
+ try {
+ for (const dep of self.nodes[nodeId].dependencies ?? []) {
+ const index = path.indexOf(dep);
+ if (index > -1) {
+ return [...path.slice(index), dep];
+ }
+
+ const cycle = recurse(dep, [...path, dep]);
+ if (cycle) { return cycle; }
+ }
+
+ return undefined;
+ } finally {
+ seen.add(nodeId);
+ }
+ }
+ }
 }
 
 export interface WorkGraphActions {
@@ -297,4 +333,4 @@ function sum(xs: number[]) {
  ret += x;
  }
  return ret;
-}
+}

packages/aws-cdk/test/work-graph.test.ts

@@ -328,13 +328,15 @@ describe('WorkGraph', () => {
  toDeploy: createArtifacts([
  { id: 'A', type: 'stack', stackDependencies: ['A'] },
  ]),
+ expectedError: 'A -> A',
  },
  {
  scenario: 'A -> B, B -> A',
  toDeploy: createArtifacts([
  { id: 'A', type: 'stack', stackDependencies: ['B'] },
  { id: 'B', type: 'stack', stackDependencies: ['A'] },
  ]),
+ expectedError: 'A -> B -> A',
  },
  {
  scenario: 'A, B -> C, C -> D, D -> B',
@@ -344,12 +346,13 @@ describe('WorkGraph', () => {
  { id: 'C', type: 'stack', stackDependencies: ['D'] },
  { id: 'D', type: 'stack', stackDependencies: ['B'] },
  ]),
+ expectedError: 'B -> C -> D -> B',
  },
- ])('Failure - Graph Circular Dependencies - $scenario', async ({ toDeploy }) => {
+ ])('Failure - Graph Circular Dependencies - $scenario', async ({ toDeploy, expectedError }) => {
  const graph = new WorkGraph();
  addTestArtifactsToGraph(toDeploy, graph);
 
- await expect(graph.doParallel(1, callbacks)).rejects.toThrowError(/Unable to make progress anymore/);
+ await expect(graph.doParallel(1, callbacks)).rejects.toThrowError(new RegExp(`Unable to make progress.*${expectedError}`));
  });
 });