fix(lambda-nodejs): cannot bundle when entry file is named index.ts (#9724)

Do not rename the dist file if it's already named `index.js`.

Fixes #9709


----

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

Author: jogold

packages/@aws-cdk/aws-lambda-nodejs/lib/bundling.ts

@@ -168,7 +168,7 @@ export class Bundling {
       // Always rename dist file to index.js because Lambda doesn't support filenames
       // with multiple dots and we can end up with multiple dots when using automatic
       // entry lookup
-      `mv ${cdk.AssetStaging.BUNDLING_OUTPUT_DIR}/${distFile} ${cdk.AssetStaging.BUNDLING_OUTPUT_DIR}/index.js`,
+      distFile !== 'index.js' ? `mv ${cdk.AssetStaging.BUNDLING_OUTPUT_DIR}/${distFile} ${cdk.AssetStaging.BUNDLING_OUTPUT_DIR}/index.js` : '',
     ]);
 
     let installer = Installer.NPM;

packages/@aws-cdk/aws-lambda-nodejs/test/bundling.test.ts

@@ -74,6 +74,25 @@ test('Parcel bundling', () => {
   expect(findUpMock).toHaveBeenCalledWith('package.json', '/project/folder');
 });
 
+test('Parcel bundling with handler named index.ts', () => {
+  Bundling.parcel({
+    entry: '/project/folder/index.ts',
+    runtime: Runtime.NODEJS_12_X,
+    projectRoot: '/project',
+  });
+
+  // Correctly bundles with parcel
+  expect(Code.fromAsset).toHaveBeenCalledWith('/project', {
+    assetHashType: AssetHashType.BUNDLE,
+    bundling: expect.objectContaining({
+      command: [
+        'bash', '-c',
+        '$(node -p "require.resolve(\'parcel\')") build /asset-input/folder/index.ts --target cdk-lambda --dist-dir /asset-output --no-autoinstall --no-scope-hoist',
+      ],
+    }),
+  });
+});
+
 test('Parcel with Windows paths', () => {
   Bundling.parcel({
     entry: 'C:\\my-project\\lib\\entry.ts',