fix(aws-cdk): cdk bootstrap print JSON template when using --json option (#21852)

Fix for the issue #21456.

Added support of `--json` option for `cdk bootstrap --show-template` command.

`cdk bootstrap --show-template` - will print YAML template
`cdk bootstrap --show-template --json` - will print JSON template

**How I tested it locally?**

- Prepared a package with fix with `yarn package` and installed with `npm install -g dist/js/aws-cdk-0.0.0.tgz`

- Reproduced steps from the bug #21456

- Ensured that the issue is fixed

### All Submissions:

* [x] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md)

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

Author: arewa

packages/aws-cdk/lib/api/bootstrap/bootstrap-environment.ts

@@ -2,7 +2,7 @@ import { info } from 'console';
 import * as path from 'path';
 import * as cxapi from '@aws-cdk/cx-api';
 import { warning } from '../../logging';
-import { loadStructuredFile, toYAML } from '../../serialize';
+import { loadStructuredFile, serializeStructure } from '../../serialize';
 import { rootDir } from '../../util/directories';
 import { SdkProvider } from '../aws-auth';
 import { DeployStackResult } from '../deploy-stack';
@@ -33,9 +33,9 @@ export class Bootstrapper {
     }
   }
 
-  public async showTemplate() {
+  public async showTemplate(json: boolean) {
     const template = await this.loadTemplate();
-    process.stdout.write(`${toYAML(template)}\n`);
+    process.stdout.write(`${serializeStructure(template, json)}\n`);
   }
 
   /**

packages/aws-cdk/lib/cli.ts

@@ -431,7 +431,7 @@ async function initCommandLine() {
         const bootstrapper = new Bootstrapper(source);
 
         if (args.showTemplate) {
-          return bootstrapper.showTemplate();
+          return bootstrapper.showTemplate(args.json);
         }
 
         return cli.bootstrap(args.ENVIRONMENTS, bootstrapper, {

packages/aws-cdk/test/api/bootstrap.test.ts

@@ -1,4 +1,5 @@
 import { CreateChangeSetInput } from 'aws-sdk/clients/cloudformation';
+import { parse } from 'yaml';
 import { Bootstrapper } from '../../lib/api/bootstrap';
 import { deserializeStructure } from '../../lib/serialize';
 import { MockSdkProvider, SyncHandlerSubsetOf } from '../util/mock-sdk';
@@ -297,3 +298,23 @@ test('stack is termination protected when set', async () => {
   expect(executed).toBeTruthy();
   expect(protectedTermination).toBeTruthy();
 });
+
+test('do showTemplate YAML', async () => {
+  process.stdout.write = jest.fn().mockImplementationOnce((template) => {
+    // THEN
+    expect(parse(template)).toHaveProperty('Description', 'The CDK Toolkit Stack. It was created by `cdk bootstrap` and manages resources necessary for managing your Cloud Applications with AWS CDK.');
+  });
+
+  // WHEN
+  await bootstrapper.showTemplate(false);
+});
+
+test('do showTemplate JSON', async () => {
+  process.stdout.write = jest.fn().mockImplementationOnce((template) => {
+    // THEN
+    expect(JSON.parse(template)).toHaveProperty('Description', 'The CDK Toolkit Stack. It was created by `cdk bootstrap` and manages resources necessary for managing your Cloud Applications with AWS CDK.');
+  });
+
+  // WHEN
+  await bootstrapper.showTemplate(true);
+});