feat(code_pipeline_actions): variables for source action

Adds `variables` method that allows to retrieve action's
[variables](https://docs.aws.amazon.com/codepipeline/latest/userguide/reference-variables.html)
using type safe approach.
With that we can rely on compiler to pick up incorrect access instead
of hacking it with plain strings.

fixes: #17807

packages/@aws-cdk/aws-codepipeline-actions/lib/codestar-connections/source-action.ts

@@ -8,6 +8,24 @@ import { sourceArtifactBounds } from '../common';
 // eslint-disable-next-line no-duplicate-imports, import/order
 import { Construct } from '@aws-cdk/core';
 
+/**
+ * The CodePipeline variables emitted by CodeStar source Action.
+ */
+export interface CodeStarSourceVariables {
+  /** The name of the repository this action points to. */
+  readonly fullRepositoryName: string;
+  /** The name of the branch this action tracks. */
+  readonly branchName: string;
+  /** The date the currently last commit on the tracked branch was authored, in ISO-8601 format. */
+  readonly authorDate: string;
+  /** The SHA1 hash of the currently last commit on the tracked branch. */
+  readonly commitId: string;
+  /** The message of the currently last commit on the tracked branch. */
+  readonly commitMessage: string;
+  /** The connection ARN this source uses. */
+  readonly connectionArn: string;
+}
+
 /**
  * Construction properties for {@link CodeStarConnectionsSourceAction}.
  */
@@ -101,6 +119,18 @@ export class CodeStarConnectionsSourceAction extends Action {
     this.props = props;
   }
 
+  /** The variables emitted by this action. */
+  public get variables(): CodeStarSourceVariables {
+    return {
+      fullRepositoryName: this.variableExpression('FullRepositoryName'),
+      branchName: this.variableExpression('BranchName'),
+      authorDate: this.variableExpression('AuthorDate'),
+      commitId: this.variableExpression('CommitId'),
+      commitMessage: this.variableExpression('CommitMessage'),
+      connectionArn: this.variableExpression('ConnectionArn'),
+    };
+  }
+
   protected bound(_scope: Construct, _stage: codepipeline.IStage, options: codepipeline.ActionBindOptions): codepipeline.ActionConfig {
     // https://docs.aws.amazon.com/codepipeline/latest/userguide/security-iam.html#how-to-update-role-new-services
     options.role.addToPolicy(new iam.PolicyStatement({

packages/@aws-cdk/aws-codepipeline-actions/test/codestar-connections/codestar-connections-source-action.test.ts

@@ -1,5 +1,5 @@
 import '@aws-cdk/assert-internal/jest';
-import { arrayWith, objectLike } from '@aws-cdk/assert-internal';
+import { arrayWith, objectLike, SynthUtils } from '@aws-cdk/assert-internal';
 import * as codebuild from '@aws-cdk/aws-codebuild';
 import * as codepipeline from '@aws-cdk/aws-codepipeline';
 import { Stack } from '@aws-cdk/core';
@@ -148,27 +148,155 @@ describe('CodeStar Connections source Action', () => {
       ],
     });
 
+  });
+
+  test('exposes variables', () => {
+    const stack = new Stack();
+
+    createBitBucketAndCodeBuildPipeline(stack, {
+      triggerOnPush: false,
+    });
+
+    expect(stack).toHaveResourceLike('AWS::CodePipeline::Pipeline', {
+      'Stages': [
+        {
+          'Name': 'Source',
+        },
+        {
+          'Name': 'Build',
+          'Actions': [
+            {
+              'Name': 'CodeBuild',
+              'Configuration': {
+                'EnvironmentVariables': '[{"name":"CommitId","type":"PLAINTEXT","value":"#{Source_BitBucket_NS.CommitId}"}]',
+              },
+            },
+          ],
+        },
+      ],
+    });
 
   });
+
+  test('exposes variables with custom namespace', () => {
+    const stack = new Stack();
+
+    createBitBucketAndCodeBuildPipeline(stack, {
+      triggerOnPush: false,
+      variablesNamespace: 'kornicameister',
+    });
+
+    expect(stack).toHaveResourceLike('AWS::CodePipeline::Pipeline', {
+      'Stages': [
+        {
+          'Name': 'Source',
+          'Actions': [
+            {
+              'Name': 'BitBucket',
+              'Namespace': 'kornicameister',
+            },
+          ],
+        },
+        {
+          'Name': 'Build',
+          'Actions': [
+            {
+              'Name': 'CodeBuild',
+              'Configuration': {
+                'EnvironmentVariables': '[{"name":"CommitId","type":"PLAINTEXT","value":"#{kornicameister.CommitId}"}]',
+              },
+            },
+          ],
+        },
+      ],
+    });
+
+
+  });
+
+  test('fail if variable from unused action is referenced', () => {
+    const stack = new Stack();
+
+    createUnreferencedVariablePipeline(stack);
+
+    expect(() => {
+      SynthUtils.synthesize(stack);
+    }).toThrow(/Cannot reference variables of action 'BitBucketUnused', as that action was never added to a pipeline/);
+
+  });
+
+  test('fail if variable from unused action with custom namespace is referenced', () => {
+    const stack = new Stack();
+
+    createUnreferencedVariablePipeline(stack, 'kornicameister');
+
+    expect(() => {
+      SynthUtils.synthesize(stack);
+    }).toThrow(/Cannot reference variables of action 'BitBucketUnused', as that action was never added to a pipeline/);
+
+  });
+
 });
 
-function createBitBucketAndCodeBuildPipeline(stack: Stack, props: Partial<cpactions.BitBucketSourceActionProps>): void {
+function createUnreferencedVariablePipeline(stack: Stack, variablesNamespace?: string) {
   const sourceOutput = new codepipeline.Artifact();
+  const sourceAction = new cpactions.CodeStarConnectionsSourceAction({
+    actionName: 'BitBucketUsed',
+    owner: 'aws',
+    repo: 'aws-cdk',
+    output: sourceOutput,
+    connectionArn: 'arn:aws:codestar-connections:us-east-1:123456789012:connection/12345678-abcd-12ab-34cdef5678gh',
+  });
+  const unusedSourceAction = new cpactions.CodeStarConnectionsSourceAction({
+    actionName: 'BitBucketUnused',
+    owner: 'aws',
+    repo: 'aws-cdk',
+    output: sourceOutput,
+    connectionArn: 'arn:aws:codestar-connections:us-east-1:123456789012:connection/12345678-abcd-12ab-34cdef5678gh',
+    variablesNamespace: variablesNamespace,
+  });
+
   new codepipeline.Pipeline(stack, 'Pipeline', {
     stages: [
       {
         stageName: 'Source',
+        actions: [sourceAction],
+      },
+      {
+        stageName: 'Build',
         actions: [
-          new cpactions.CodeStarConnectionsSourceAction({
-            actionName: 'BitBucket',
-            owner: 'aws',
-            repo: 'aws-cdk',
-            output: sourceOutput,
-            connectionArn: 'arn:aws:codestar-connections:us-east-1:123456789012:connection/12345678-abcd-12ab-34cdef5678gh',
-            ...props,
+          new cpactions.CodeBuildAction({
+            actionName: 'CodeBuild',
+            project: new codebuild.PipelineProject(stack, 'MyProject'),
+            input: sourceOutput,
+            outputs: [new codepipeline.Artifact()],
+            environmentVariables: {
+              CommitId: { value: unusedSourceAction.variables.commitId },
+            },
           }),
         ],
       },
+    ],
+  });
+}
+
+function createBitBucketAndCodeBuildPipeline(stack: Stack, props: Partial<cpactions.BitBucketSourceActionProps>): void {
+  const sourceOutput = new codepipeline.Artifact();
+  const sourceAction = new cpactions.CodeStarConnectionsSourceAction({
+    actionName: 'BitBucket',
+    owner: 'aws',
+    repo: 'aws-cdk',
+    output: sourceOutput,
+    connectionArn: 'arn:aws:codestar-connections:us-east-1:123456789012:connection/12345678-abcd-12ab-34cdef5678gh',
+    ...props,
+  });
+
+  new codepipeline.Pipeline(stack, 'Pipeline', {
+    stages: [
+      {
+        stageName: 'Source',
+        actions: [sourceAction],
+      },
       {
         stageName: 'Build',
         actions: [
@@ -177,6 +305,9 @@ function createBitBucketAndCodeBuildPipeline(stack: Stack, props: Partial<cpacti
             project: new codebuild.PipelineProject(stack, 'MyProject'),
             input: sourceOutput,
             outputs: [new codepipeline.Artifact()],
+            environmentVariables: {
+              CommitId: { value: sourceAction.variables.commitId },
+            },
           }),
         ],
       },