fix(cx-api): bootstrap stack is validated even if the custom synthesi…

…zer does not require it (aws#21518)

This fixes aws#21324

The property `requiresBootstrapStackVersion` of the class `AssetManifestArtifact` is a [required property of type number](https://github.com/aws/aws-cdk/blob/34e31b90c8cdd51b8af61f352aa0ab7a0332ed4c/packages/%40aws-cdk/cx-api/lib/artifacts/asset-manifest-artifact.ts#L38-L41) that is [defaulted to `1`]((https://github.com/aws/aws-cdk/blob/34e31b90c8cdd51b8af61f352aa0ab7a0332ed4c/packages/%40aws-cdk/cx-api/lib/artifacts/asset-manifest-artifact.ts#L58)). This behavior prevents the custom synthesizers from disabling the validation of the bootstrap stack when it knows that it does not need this stack. 

This change allows the property to be `undefined`, removes the behaviour of defaulting it to `1`, and adds a breaking unit test. 

----

### All Submissions:

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### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

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

allowed-breaking-changes.txt

@@ -139,3 +139,8 @@ removed:@aws-cdk/aws-lambda-event-sources.SelfManagedKafkaEventSourceProps.onFai
 
 # removed kubernetes version from EKS
 removed:@aws-cdk/aws-eks.KubernetesVersion.V1_22
+
+# changed the type of requiresBootstrapStackVersion to Optional<number> (formerly number)
+# to allow the CLI to skip validating the bootstrap stack when the stack is not needed
+changed-type:@aws-cdk/cx-api.AssetManifestArtifact.requiresBootstrapStackVersion
+

packages/@aws-cdk/core/test/stack-synthesis/new-style-synthesis.test.ts

@@ -1,7 +1,9 @@
 import * as fs from 'fs';
 import * as cxschema from '@aws-cdk/cloud-assembly-schema';
+import { ArtifactType } from '@aws-cdk/cloud-assembly-schema';
 import * as cxapi from '@aws-cdk/cx-api';
 import { App, Aws, CfnResource, ContextProvider, DefaultStackSynthesizer, FileAssetPackaging, Stack } from '../../lib';
+import { ISynthesisSession } from '../../lib/stack-synthesizers/types';
 import { evaluateCFN } from '../evaluate-cfn';
 
 const CFN_CONTEXT = {
@@ -60,14 +62,18 @@ describe('new style synthesis', () => {
 
   });
 
-  test('version check is added to template', () => {
+  test('version check is added to both template and manifest artifact', () => {
     // GIVEN
     new CfnResource(stack, 'Resource', {
       type: 'Some::Resource',
     });
 
     // THEN
-    const template = app.synth().getStackByName('Stack').template;
+    const asm = app.synth();
+    const manifestArtifact = getAssetManifest(asm);
+    expect(manifestArtifact.requiresBootstrapStackVersion).toEqual(6);
+
+    const template = asm.getStackByName('Stack').template;
     expect(template?.Parameters?.BootstrapVersion?.Type).toEqual('AWS::SSM::Parameter::Value<String>');
     expect(template?.Parameters?.BootstrapVersion?.Default).toEqual('/cdk-bootstrap/hnb659fds/version');
     expect(template?.Parameters?.BootstrapVersion?.Description).toContain(cxapi.SSMPARAM_NO_INVALIDATE);
@@ -79,8 +85,6 @@ describe('new style synthesis', () => {
         { 'Fn::Contains': [['1', '2', '3', '4', '5'], { Ref: 'BootstrapVersion' }] },
       ],
     });
-
-
   });
 
   test('version check is not added to template if disabled', () => {
@@ -124,8 +128,46 @@ describe('new style synthesis', () => {
 
     // THEN - the asset manifest has an SSM parameter entry
     expect(manifestArtifact.bootstrapStackVersionSsmParameter).toEqual('stack-version-parameter');
+  });
+
+  test('contains asset but not requiring a specific version parameter', () => {
+    // GIVEN
+    class BootstraplessStackSynthesizer extends DefaultStackSynthesizer {
+
+
+      /**
+       * Synthesize the associated bootstrap stack to the session.
+       */
+      public synthesize(session: ISynthesisSession): void {
+        if (!this.stack) {
+          throw new Error('You must call bind() with a stack instance first');
+        }
+        this.synthesizeStackTemplate(this.stack, session);
+        session.assembly.addArtifact('FAKE_ARTIFACT_ID', {
+          type: ArtifactType.ASSET_MANIFEST,
+          properties: {
+            file: 'FAKE_ARTIFACT_ID.json',
+          },
+        });
+        this.emitStackArtifact(this.stack, session, {
+          additionalDependencies: ['FAKE_ARTIFACT_ID'],
+        });
+      }
+    }
+
+    const myapp = new App();
 
+    // WHEN
+    new Stack(myapp, 'mystack', {
+      synthesizer: new BootstraplessStackSynthesizer(),
+    });
+
+    // THEN
+    const asm = myapp.synth();
+    const manifestArtifact = getAssetManifest(asm);
 
+    // THEN - the asset manifest should not define a required bootstrap stack version
+    expect(manifestArtifact.requiresBootstrapStackVersion).toEqual(undefined);
   });
 
   test('generates missing context with the lookup role ARN as one of the missing context properties', () => {

packages/@aws-cdk/cx-api/lib/artifacts/asset-manifest-artifact.ts

@@ -38,7 +38,7 @@ export class AssetManifestArtifact extends CloudArtifact {
   /**
    * Version of bootstrap stack required to deploy this stack
    */
-  public readonly requiresBootstrapStackVersion: number;
+  public readonly requiresBootstrapStackVersion: number | undefined;
 
   /**
    * Name of SSM parameter with bootstrap stack version
@@ -55,7 +55,7 @@ export class AssetManifestArtifact extends CloudArtifact {
       throw new Error('Invalid AssetManifestArtifact. Missing "file" property');
     }
     this.file = path.resolve(this.assembly.directory, properties.file);
-    this.requiresBootstrapStackVersion = properties.requiresBootstrapStackVersion ?? 1;
+    this.requiresBootstrapStackVersion = properties.requiresBootstrapStackVersion;
     this.bootstrapStackVersionSsmParameter = properties.bootstrapStackVersionSsmParameter;
   }
 }