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*

Author: rix0rrr

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}`));
   });
 });