fix(pipelines): "Node with duplicate id" on duplicate stack names (#31328)

When having 2 stacks with the same name in the same stage (which makes sense when deploying them to different environments), the CodePipeline Action name is derived from the stack name, and will be duplicated.

Detect if an graph node name is already being used and if so, use environment information to try and make the name unique.

Closes #30960.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

Author: rix0rrr

Diff for: packages/aws-cdk-lib/pipelines/lib/helpers-internal/graph.ts

@@ -230,6 +230,10 @@ export class Graph<A> extends GraphNode<A> {
     return this.children.get(name);
   }
 
+  public containsId(id: string) {
+    return this.tryGetChild(id) !== undefined;
+  }
+
   public contains(node: GraphNode<A>) {
     return this.nodes.has(node);
   }

Diff for: packages/aws-cdk-lib/pipelines/lib/helpers-internal/pipeline-graph.ts

@@ -134,7 +134,12 @@ export class PipelineGraph {
     const stackGraphs = new Map<StackDeployment, AGraph>();
 
     for (const stack of stage.stacks) {
-      const stackGraph: AGraph = Graph.of(this.simpleStackName(stack.stackName, stage.stageName), { type: 'stack-group', stack });
+      const stackGraphName = findUniqueName(retGraph, [
+        this.simpleStackName(stack.stackName, stage.stageName),
+        ...stack.account ? [stack.account] : [],
+        ...stack.region ? [stack.region] : [],
+      ]);
+      const stackGraph: AGraph = Graph.of(stackGraphName, { type: 'stack-group', stack });
       const prepareNode: AGraphNode | undefined = this.prepareStep ? aGraphNode('Prepare', { type: 'prepare', stack }) : undefined;
       const deployNode: AGraphNode = aGraphNode('Deploy', {
         type: 'execute',
@@ -412,4 +417,14 @@ function aGraphNode(id: string, x: GraphAnnotation): AGraphNode {
 
 function stripPrefix(s: string, prefix: string) {
   return s.startsWith(prefix) ? s.slice(prefix.length) : s;
+}
+
+function findUniqueName(parent: Graph<any>, parts: string[]): string {
+  for (let i = 1; i <= parts.length; i++) {
+    const candidate = parts.slice(0, i).join('.');
+    if (!parent.containsId(candidate)) {
+      return candidate;
+    }
+  }
+  return parts.join('.');
 }

Diff for: packages/aws-cdk-lib/pipelines/test/compliance/basic-behavior.test.ts

@@ -81,6 +81,33 @@ test('overridden stack names are respected', () => {
   });
 });
 
+test('two stacks can have the same name', () => {
+  const pipeline = new ModernTestGitHubNpmPipeline(pipelineStack, 'Cdk', { useChangeSets: false });
+  pipeline.addStage(new TwoStacksApp(app, 'App'));
+
+  Template.fromStack(pipelineStack).hasResourceProperties('AWS::CodePipeline::Pipeline', {
+    Stages: Match.arrayWith([
+      {
+        Name: 'App',
+        Actions: Match.arrayWith([
+          Match.objectLike({
+            Name: stringLike('MyFancyStack.Deploy'),
+            Configuration: Match.objectLike({
+              StackName: 'MyFancyStack',
+            }),
+          }),
+          Match.objectLike({
+            Name: stringLike('MyFancyStack.eu-west-2.Deploy'),
+            Configuration: Match.objectLike({
+              StackName: 'MyFancyStack',
+            }),
+          }),
+        ]),
+      },
+    ]),
+  });
+});
+
 test('changing CLI version leads to a different pipeline structure (restarting it)', () => {
 
   // GIVEN
@@ -154,3 +181,17 @@ class OneStackAppWithCustomName extends Stage {
     });
   }
 }
+
+class TwoStacksApp extends Stage {
+  constructor(scope: Construct, id: string, props?: StageProps) {
+    super(scope, id, props);
+    new BucketStack(this, 'Stack1', {
+      env: { region: 'eu-west-1' },
+      stackName: 'MyFancyStack',
+    });
+    new BucketStack(this, 'Stack2', {
+      env: { region: 'eu-west-2' },
+      stackName: 'MyFancyStack',
+    });
+  }
+}