feat(cli): support Fn::ImportValue intrinsic function for hotswap d…

…eployments (#27292)

## Purpose 🎯 

Extend the `EvaluateCloudFormationTemplate` class to support the `Fn::ImportValue` intrinsic function. This allows for more diverse templates to be evaluated for the purposes of determining eligibility for `--hotswap` deployments

Closes aws/aws-cdk#21320

## Approach 🧠 

Implement `LazyLookupExport` in similar fashion to `LazyListStackResources` to cache required CloudFormation API calls _(preference was to implement using a generator function instead so style is not entirely consistent, is this an issue?)_

Add some basic unit tests for `EvaluateCloudFormationTemplate.evaluateCfnExpression()` is they were absent, then add some tests for `Fn::ImportValue`

## Todo 📝 

- [x] Update doco where appropriate
- [x] Add to hotswap deployment tests
- [x] Look for appropriate integration tests to update

----

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

packages/@aws-cdk-testing/cli-integ/resources/cdk-apps/app/app.js

@@ -252,8 +252,12 @@ class LambdaHotswapStack extends cdk.Stack {
       handler: 'index.handler',
       description: process.env.DYNAMIC_LAMBDA_PROPERTY_VALUE ?? "description",
       environment: {
-        SomeVariable: process.env.DYNAMIC_LAMBDA_PROPERTY_VALUE ?? "environment",
-      }
+        SomeVariable:
+          process.env.DYNAMIC_LAMBDA_PROPERTY_VALUE ?? "environment",
+        ImportValueVariable: process.env.USE_IMPORT_VALUE_LAMBDA_PROPERTY
+          ? cdk.Fn.importValue(TEST_EXPORT_OUTPUT_NAME)
+          : "no-import",
+      },
     });
 
     new cdk.CfnOutput(this, 'FunctionName', { value: fn.functionName });
@@ -343,6 +347,22 @@ class ConditionalResourceStack extends cdk.Stack {
   }
 }
 
+const TEST_EXPORT_OUTPUT_NAME = 'test-export-output';
+
+class ExportValueStack extends cdk.Stack {
+  constructor(parent, id, props) {
+    super(parent, id, props);
+
+    // just need any resource to exist within the stack
+    const topic = new sns.Topic(this, 'Topic');
+
+    new cdk.CfnOutput(this, 'ExportValueOutput', {
+      exportName: TEST_EXPORT_OUTPUT_NAME,
+      value: topic.topicArn,
+    });
+  }
+}
+
 class BundlingStage extends cdk.Stage {
   constructor(parent, id, props) {
     super(parent, id, props);
@@ -450,6 +470,8 @@ switch (stackSet) {
 
     new ImportableStack(app, `${stackPrefix}-importable-stack`);
 
+    new ExportValueStack(app, `${stackPrefix}-export-value-stack`);
+
     new BundlingStage(app, `${stackPrefix}-bundling-stage`);
     break;
 

packages/@aws-cdk-testing/cli-integ/tests/cli-integ-tests/cli.integtest.ts

@@ -1226,6 +1226,48 @@ integTest('hotswap deployment supports Lambda function\'s description and enviro
   expect(deployOutput).toContain(`Lambda Function '${functionName}' hotswapped!`);
 }));
 
+integTest('hotswap deployment supports Fn::ImportValue intrinsic', withDefaultFixture(async (fixture) => {
+  // GIVEN
+  try {
+    await fixture.cdkDeploy('export-value-stack');
+    const stackArn = await fixture.cdkDeploy('lambda-hotswap', {
+      captureStderr: false,
+      modEnv: {
+        DYNAMIC_LAMBDA_PROPERTY_VALUE: 'original value',
+        USE_IMPORT_VALUE_LAMBDA_PROPERTY: 'true',
+      },
+    });
+
+    // WHEN
+    const deployOutput = await fixture.cdkDeploy('lambda-hotswap', {
+      options: ['--hotswap'],
+      captureStderr: true,
+      onlyStderr: true,
+      modEnv: {
+        DYNAMIC_LAMBDA_PROPERTY_VALUE: 'new value',
+        USE_IMPORT_VALUE_LAMBDA_PROPERTY: 'true',
+      },
+    });
+
+    const response = await fixture.aws.cloudFormation('describeStacks', {
+      StackName: stackArn,
+    });
+    const functionName = response.Stacks?.[0].Outputs?.[0].OutputValue;
+
+    // THEN
+
+    // The deployment should not trigger a full deployment, thus the stack's status must remains
+    // "CREATE_COMPLETE"
+    expect(response.Stacks?.[0].StackStatus).toEqual('CREATE_COMPLETE');
+    expect(deployOutput).toContain(`Lambda Function '${functionName}' hotswapped!`);
+
+  } finally {
+    // Ensure cleanup in reverse order due to use of import/export
+    await fixture.cdkDestroy('lambda-hotswap');
+    await fixture.cdkDestroy('export-value-stack');
+  }
+}));
+
 async function listChildren(parent: string, pred: (x: string) => Promise<boolean>) {
   const ret = new Array<string>();
   for (const child of await fs.readdir(parent, { encoding: 'utf-8' })) {