fix(cli): hotswap cannot evaluate nested stacks within nested stacks (#28080)

This line 


https://github.com/aws/aws-cdk/blob/25ee8ef61d6b33628923a0fee4c042a0f0f2441e/packages/aws-cdk/lib/api/evaluate-cloudformation-template.ts#L390

doesn't actually finds the nested stack in the tree but only at the top
level which causes references made to second (or more) level nested
stacks return undefined. This causes hotswap to fail
Closes #<issue number here>. #28077

----

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

Author: udaypant

packages/aws-cdk/lib/api/evaluate-cloudformation-template.ts

@@ -387,7 +387,7 @@ export class EvaluateCloudFormationTemplate {
 
     if (foundResource.ResourceType == 'AWS::CloudFormation::Stack' && attribute?.startsWith('Outputs.')) {
       // need to resolve attributes from another stack's Output section
-      const dependantStackName = this.nestedStackNames[logicalId]?.nestedStackPhysicalName;
+      const dependantStackName = this.findNestedStack(logicalId, this.nestedStackNames);
       if (!dependantStackName) {
         //this is a newly created nested stack and cannot be hotswapped
         return undefined;
@@ -406,6 +406,19 @@ export class EvaluateCloudFormationTemplate {
     return this.formatResourceAttribute(foundResource, attribute);
   }
 
+  private findNestedStack(logicalId: string, nestedStackNames: {
+    [nestedStackLogicalId: string]: NestedStackNames;
+  }): string | undefined {
+    for (const [nestedStackLogicalId, { nestedChildStackNames, nestedStackPhysicalName }] of Object.entries(nestedStackNames)) {
+      if (nestedStackLogicalId === logicalId) {
+        return nestedStackPhysicalName;
+      }
+      const checkInNestedChildStacks = this.findNestedStack(logicalId, nestedChildStackNames);
+      if (checkInNestedChildStacks) return checkInNestedChildStacks;
+    }
+    return undefined;
+  }
+
   private formatResourceAttribute(resource: AWS.CloudFormation.StackResourceSummary, attribute: string | undefined): string | undefined {
     const physicalId = resource.PhysicalResourceId;
 

packages/aws-cdk/test/api/hotswap/nested-stacks-hotswap.test.ts

@@ -826,10 +826,12 @@ describe.each([HotswapMode.FALL_BACK, HotswapMode.HOTSWAP_ONLY])('%p mode', (hot
     });
   });
 
-  test('can hotswap a lambda function in a 1-level nested stack with dependency on a output of sibling stack', async () => {
-    // GIVEN: RootStack has two child stacks `NestedLambdaStack` and `NestedSiblingStack`. `NestedLambdaStack`
-    // takes two parameters s3Key and s3Bucket and use them for a Lambda function.
-    // RootStack resolves s3Bucket from a root template parameter and s3Key through output of `NestedSiblingStack`
+  test('can hotswap a lambda function in a 2-level nested stack with dependency on a output of 2nd level sibling stack', async () => {
+    // GIVEN: RootStack has one child stack `FirstLevelRootStack` which further has two child stacks
+    // `NestedLambdaStack` and `NestedSiblingStack`. `NestedLambdaStack` takes two parameters s3Key
+    // and s3Bucket and use them for a Lambda function.
+    // RootStack resolves s3Bucket from a root template parameter and passed to FirstLevelRootStack which
+    // resolves s3Key through output of `NestedSiblingStack`
     hotswapMockSdkProvider = setup.setupHotswapNestedStackTests('RootStack');
     mockUpdateLambdaCode = jest.fn().mockReturnValue({});
     hotswapMockSdkProvider.stubLambda({
@@ -838,6 +840,34 @@ describe.each([HotswapMode.FALL_BACK, HotswapMode.HOTSWAP_ONLY])('%p mode', (hot
 
     const rootStack = testStack({
       stackName: 'RootStack',
+      template: {
+        Resources: {
+          FirstLevelRootStack: {
+            Type: 'AWS::CloudFormation::Stack',
+            Properties: {
+              TemplateURL: 'https://www.magic-url.com',
+              Parameters: {
+                S3BucketParam: {
+                  Ref: 'S3BucketParam',
+                },
+              },
+            },
+            Metadata: {
+              'aws:asset:path': 'one-stack-with-two-nested-stacks-stack.template.json',
+            },
+          },
+        },
+        Parameters: {
+          S3BucketParam: {
+            Type: 'String',
+            Description: 'S3 bucket for asset',
+          },
+        },
+      },
+    });
+
+    const firstLevelRootStack = testStack({
+      stackName: 'FirstLevelRootStack',
       template: {
         Resources: {
           NestedLambdaStack: {
@@ -869,11 +899,11 @@ describe.each([HotswapMode.FALL_BACK, HotswapMode.HOTSWAP_ONLY])('%p mode', (hot
               'aws:asset:path': 'one-output-stack.nested.template.json',
             },
           },
-          Parameters: {
-            S3BucketParam: {
-              Type: 'String',
-              Description: 'S3 bucket for asset',
-            },
+        },
+        Parameters: {
+          S3BucketParam: {
+            Type: 'String',
+            Description: 'S3 bucket for asset',
           },
         },
       },
@@ -913,10 +943,17 @@ describe.each([HotswapMode.FALL_BACK, HotswapMode.HOTSWAP_ONLY])('%p mode', (hot
     });
 
     setup.addTemplateToCloudFormationLookupMock(rootStack);
+    setup.addTemplateToCloudFormationLookupMock(firstLevelRootStack);
     setup.addTemplateToCloudFormationLookupMock(nestedLambdaStack);
     setup.addTemplateToCloudFormationLookupMock(nestedSiblingStack);
 
     setup.pushNestedStackResourceSummaries('RootStack',
+      setup.stackSummaryOf('FirstLevelRootStack', 'AWS::CloudFormation::Stack',
+        'arn:aws:cloudformation:bermuda-triangle-1337:123456789012:stack/FirstLevelRootStack/abcd',
+      ),
+    );
+
+    setup.pushNestedStackResourceSummaries('FirstLevelRootStack',
       setup.stackSummaryOf('NestedLambdaStack', 'AWS::CloudFormation::Stack',
         'arn:aws:cloudformation:bermuda-triangle-1337:123456789012:stack/NestedLambdaStack/abcd',
       ),

packages/aws-cdk/test/nested-stack-templates/one-stack-with-two-nested-stacks-stack.template.json

@@ -0,0 +1,38 @@
+{
+  "Resources": {
+    "NestedLambdaStack": {
+      "Type": "AWS::CloudFormation::Stack",
+      "Properties": {
+        "TemplateURL": "https://www.magic-url.com",
+        "Parameters": {
+          "referenceToS3BucketParam": {
+            "Ref": "S3BucketParam"
+          },
+          "referenceToS3StackKeyOutput": {
+            "Fn::GetAtt": [
+              "NestedSiblingStack",
+              "Outputs.NestedOutput"
+            ]
+          }
+        }
+      },
+      "Metadata": {
+        "aws:asset:path": "one-lambda-stack-with-dependency-on-sibling-stack-output.nested.template.json"
+      }
+    },
+    "NestedSiblingStack": {
+      "Type": "AWS::CloudFormation::Stack",
+      "Properties": {
+        "TemplateURL": "https://www.magic-url.com"
+      },
+      "Metadata": {
+        "aws:asset:path": "one-output-stack.nested.template.json"
+      }
+    }
+  },
+  "Parameters": {
+    "S3BucketParam": {
+      "Type": "String"
+    }
+  }
+}