feat(pipelines): temporarily disable self-mutation (aws#10466)

The self-mutation feature of the `CdkPipeline` might at times get in the way of the pipeline development workflow. Each change to the pipeline must be pushed to git, otherwise, after the pipeline was updated using `cdk deploy`, it will automatically revert to the state found in git.

To make the development more convenient, the self-mutation feature can be turned off temporarily, by passing `selfMutating: false` property, example:

```ts
const pipeline = new CdkPipeline(this, 'Pipeline', {
  selfMutating: false,
  ...
});
```

----

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

packages/@aws-cdk/pipelines/README.md

@@ -544,6 +544,24 @@ class MyPipelineStack extends Stack {
 }
 ```
 
+### Developing the pipeline
+
+The self-mutation feature of the `CdkPipeline` might at times get in the way
+of the pipeline development workflow. Each change to the pipeline must be pushed
+to git, otherwise, after the pipeline was updated using `cdk deploy`, it will
+automatically revert to the state found in git.
+
+To make the development more convenient, the self-mutation feature can be turned
+off temporarily, by passing `selfMutating: false` property, example:
+
+```ts
+const pipeline = new CdkPipeline(this, 'Pipeline', {
+  selfMutating: false,
+  ...  
+});
+```
+
+
 ## CDK Environment Bootstrapping
 
 An *environment* is an *(account, region)* pair where you want to deploy a

packages/@aws-cdk/pipelines/lib/pipeline.ts

@@ -105,6 +105,20 @@ export interface CdkPipelineProps {
    * @default - All private subnets.
    */
   readonly subnetSelection?: ec2.SubnetSelection;
+
+  /**
+   * Whether the pipeline will update itself
+   *
+   * This needs to be set to `true` to allow the pipeline to reconfigure
+   * itself when assets or stages are being added to it, and `true` is the
+   * recommended setting.
+   *
+   * You can temporarily set this to `false` while you are iterating
+   * on the pipeline itself and prefer to deploy changes using `cdk deploy`.
+   *
+   * @default true
+   */
+  readonly selfMutating?: boolean;
 }
 
 /**
@@ -178,15 +192,17 @@ export class CdkPipeline extends CoreConstruct {
       });
     }
 
-    this._pipeline.addStage({
-      stageName: 'UpdatePipeline',
-      actions: [new UpdatePipelineAction(this, 'UpdatePipeline', {
-        cloudAssemblyInput: this._cloudAssemblyArtifact,
-        pipelineStackName: pipelineStack.stackName,
-        cdkCliVersion: props.cdkCliVersion,
-        projectName: maybeSuffix(props.pipelineName, '-selfupdate'),
-      })],
-    });
+    if (props.selfMutating ?? true) {
+      this._pipeline.addStage({
+        stageName: 'UpdatePipeline',
+        actions: [new UpdatePipelineAction(this, 'UpdatePipeline', {
+          cloudAssemblyInput: this._cloudAssemblyArtifact,
+          pipelineStackName: pipelineStack.stackName,
+          cdkCliVersion: props.cdkCliVersion,
+          projectName: maybeSuffix(props.pipelineName, '-selfupdate'),
+        })],
+      });
+    }
 
     this._assets = new AssetPublishing(this, 'Assets', {
       cloudAssemblyInput: this._cloudAssemblyArtifact,

packages/@aws-cdk/pipelines/test/pipeline.test.ts

@@ -1,6 +1,15 @@
 import * as fs from 'fs';
 import * as path from 'path';
-import { anything, arrayWith, Capture, deepObjectLike, encodedJson, objectLike, stringLike } from '@aws-cdk/assert';
+import {
+  anything,
+  arrayWith,
+  Capture,
+  deepObjectLike,
+  encodedJson,
+  notMatching,
+  objectLike,
+  stringLike,
+} from '@aws-cdk/assert';
 import '@aws-cdk/assert/jest';
 import * as cp from '@aws-cdk/aws-codepipeline';
 import * as cpa from '@aws-cdk/aws-codepipeline-actions';
@@ -332,6 +341,23 @@ test('selfmutation stage correctly identifies nested assembly of pipeline stack'
   });
 });
 
+test('selfmutation feature can be turned off', () => {
+  const stack = new Stack();
+  const cloudAssemblyArtifact = new cp.Artifact();
+  // WHEN
+  new TestGitHubNpmPipeline(stack, 'Cdk', {
+    cloudAssemblyArtifact,
+    selfMutating: false,
+  });
+  // THEN
+  expect(stack).toHaveResourceLike('AWS::CodePipeline::Pipeline', {
+    Stages: notMatching(arrayWith({
+      Name: 'UpdatePipeline',
+      Actions: anything(),
+    })),
+  });
+});
+
 test('overridden stack names are respected', () => {
   // WHEN
   pipeline.addApplicationStage(new OneStackAppWithCustomName(app, 'App1'));