feat(codepipeline): Pipeline Variables (#5604)

* feat(codepipeline): CodePipeline Variables

Added support for the CodePipeline Variables feature,
by adding action class-specific interfaces that represent the
collection of variables they emit,
and a readonly property of the action instance that returns that interface.
Plus a class representing the global pipeline variables
with static properties.

Fixes #5219

* Change the tokens to force a lazy variableExpression().

* Rename the variables interfaces to remove the `I` prefix.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

packages/@aws-cdk/aws-codepipeline-actions/README.md

@@ -44,6 +44,26 @@ pipeline.addStage({
 });
 ```
 
+The CodeCommit source action emits variables:
+
+```typescript
+const sourceAction = new codepipeline_actions.CodeCommitSourceAction({
+  // ...
+  variablesNamespace: 'MyNamespace', // optional - by default, a name will be generated for you
+});
+
+// later:
+
+new codepipeline_actions.CodeBuildAction({
+  // ...
+  environmentVariables: {
+    COMMIT_ID: {
+      value: sourceAction.variables.commitId,
+    },
+  },
+});
+```
+
 #### GitHub
 
 To use GitHub as the source of a CodePipeline:
@@ -66,6 +86,26 @@ pipeline.addStage({
 });
 ```
 
+The GitHub source action emits variables:
+
+```typescript
+const sourceAction = new codepipeline_actions.GitHubSourceAction({
+  // ...
+  variablesNamespace: 'MyNamespace', // optional - by default, a name will be generated for you
+});
+
+// later:
+
+new codepipeline_actions.CodeBuildAction({
+  // ...
+  environmentVariables: {
+    COMMIT_URL: {
+      value: sourceAction.variables.commitUrl,
+    },
+  },
+});
+```
+
 #### AWS S3
 
 To use an S3 Bucket as a source in CodePipeline:
@@ -116,6 +156,26 @@ const sourceAction = new codepipeline_actions.S3SourceAction({
 });
 ```
 
+The S3 source action emits variables:
+
+```typescript
+const sourceAction = new codepipeline_actions.S3SourceAction({
+  // ...
+  variablesNamespace: 'MyNamespace', // optional - by default, a name will be generated for you
+});
+
+// later:
+
+new codepipeline_actions.CodeBuildAction({
+  // ...
+  environmentVariables: {
+    VERSION_ID: {
+      value: sourceAction.variables.versionId,
+    },
+  },
+});
+```
+
 #### AWS ECR
 
 To use an ECR Repository as a source in a Pipeline:
@@ -137,6 +197,26 @@ pipeline.addStage({
 });
 ```
 
+The ECR source action emits variables:
+
+```typescript
+const sourceAction = new codepipeline_actions.EcrSourceAction({
+  // ...
+  variablesNamespace: 'MyNamespace', // optional - by default, a name will be generated for you
+});
+
+// later:
+
+new codepipeline_actions.CodeBuildAction({
+  // ...
+  environmentVariables: {
+    IMAGE_URI: {
+      value: sourceAction.variables.imageUri,
+    },
+  },
+});
+```
+
 ### Build & test
 
 #### AWS CodeBuild
@@ -266,6 +346,48 @@ const project = new codebuild.PipelineProject(this, 'MyProject', {
 });
 ```
 
+##### Variables
+
+The CodeBuild action emits variables.
+Unlike many other actions, the variables are not static,
+but dynamic, defined in the buildspec,
+in the 'exported-variables' subsection of the 'env' section.
+Example:
+
+```typescript
+const buildAction = new codepipeline_actions.CodeBuildAction({
+  actionName: 'Build1',
+  input: sourceOutput,
+  project: new codebuild.PipelineProject(this, 'Project', {
+    buildSpec: codebuild.BuildSpec.fromObject({
+      version: '0.2',
+      env: {
+        'exported-variables': [
+          'MY_VAR',
+        ],
+      },
+      phases: {
+        build: {
+          commands: 'export MY_VAR="some value"',
+        },
+      }, 
+    }),
+  }),
+  variablesNamespace: 'MyNamespace', // optional - by default, a name will be generated for you
+});
+
+// later:
+
+new codepipeline_actions.CodeBuildAction({
+  // ...
+  environmentVariables: {
+    MyVar: {
+      value: buildAction.variable('MY_VAR'),
+    },
+  },
+});
+```
+
 #### Jenkins
 
 In order to use Jenkins Actions in the Pipeline,
@@ -304,7 +426,7 @@ const buildAction = new codepipeline_actions.JenkinsAction({
   actionName: 'JenkinsBuild',
   jenkinsProvider: jenkinsProvider,
   projectName: 'MyProject',
-  type: ccodepipeline_actions.JenkinsActionType.BUILD,
+  type: codepipeline_actions.JenkinsActionType.BUILD,
 });
 ```
 
@@ -421,7 +543,7 @@ const func = new lambda.Function(lambdaStack, 'Lambda', {
   runtime: lambda.Runtime.NODEJS_10_X,
 });
 // used to make sure each CDK synthesis produces a different Version
-const version = func.addVersion('NewVersion')
+const version = func.addVersion('NewVersion');
 const alias = new lambda.Alias(lambdaStack, 'LambdaAlias', {
   aliasName: 'Prod',
   version,
@@ -598,5 +720,48 @@ const lambdaAction = new codepipeline_actions.LambdaInvokeAction({
 });
 ```
 
+The Lambda invoke action emits variables.
+Unlike many other actions, the variables are not static,
+but dynamic, defined by the function calling the `PutJobSuccessResult`
+API with the `outputVariables` property filled with the map of variables
+Example:
+
+```typescript
+import lambda = require('@aws-cdk/aws-lambda');
+
+const lambdaInvokeAction = new codepipeline_actions.LambdaInvokeAction({
+  actionName: 'Lambda',
+  lambda: new lambda.Function(this, 'Func', {
+    runtime: lambda.Runtime.NODEJS_10_X,
+    handler: 'index.handler',
+    code: lambda.Code.fromInline(`
+        var AWS = require('aws-sdk');
+
+        exports.handler = async function(event, context) {
+            var codepipeline = new AWS.CodePipeline();
+            await codepipeline.putJobSuccessResult({
+                jobId: event['CodePipeline.job'].id,
+                outputVariables: {
+                    MY_VAR: "some value",
+                },
+            }).promise();
+        }
+    `),
+  }),
+  variablesNamespace: 'MyNamespace', // optional - by default, a name will be generated for you
+});
+
+// later:
+
+new codepipeline_actions.CodeBuildAction({
+  // ...
+  environmentVariables: {
+    MyVar: {
+      value: lambdaInvokeAction.variable('MY_VAR'),
+    },
+  },
+});
+```
+
 See [the AWS documentation](https://docs.aws.amazon.com/codepipeline/latest/userguide/actions-invoke-lambda-function.html)
 on how to write a Lambda function invoked from CodePipeline.

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

@@ -1,6 +1,6 @@
 import * as codepipeline from '@aws-cdk/aws-codepipeline';
 import * as events from '@aws-cdk/aws-events';
-import { Construct } from '@aws-cdk/core';
+import { Construct, Lazy } from '@aws-cdk/core';
 
 /**
  * Low-level class for generic CodePipeline Actions.
@@ -13,12 +13,34 @@ import { Construct } from '@aws-cdk/core';
  * @experimental
  */
 export abstract class Action implements codepipeline.IAction {
+  public readonly actionProperties: codepipeline.ActionProperties;
   private _pipeline?: codepipeline.IPipeline;
   private _stage?: codepipeline.IStage;
   private _scope?: Construct;
+  private readonly customerProvidedNamespace?: string;
+  private readonly namespaceOrToken: string;
+  private actualNamespace?: string;
+  private variableReferenced = false;
 
-  constructor(public readonly actionProperties: codepipeline.ActionProperties) {
-    // nothing to do
+  protected constructor(actionProperties: codepipeline.ActionProperties) {
+    this.customerProvidedNamespace = actionProperties.variablesNamespace;
+    this.namespaceOrToken = Lazy.stringValue({ produce: () => {
+      // make sure the action was bound (= added to a pipeline)
+      if (this.actualNamespace !== undefined) {
+        return this.customerProvidedNamespace !== undefined
+          // if a customer passed a namespace explicitly, always use that
+          ? this.customerProvidedNamespace
+          // otherwise, only return a namespace if any variable was referenced
+          : (this.variableReferenced ? this.actualNamespace : undefined);
+      } else {
+        throw new Error(`Cannot reference variables of action '${this.actionProperties.actionName}', ` +
+          'as that action was never added to a pipeline');
+      }
+    }});
+    this.actionProperties = {
+      ...actionProperties,
+      variablesNamespace: this.namespaceOrToken,
+    };
   }
 
   public bind(scope: Construct, stage: codepipeline.IStage, options: codepipeline.ActionBindOptions):
@@ -27,6 +49,11 @@ export abstract class Action implements codepipeline.IAction {
     this._stage = stage;
     this._scope = scope;
 
+    this.actualNamespace = this.customerProvidedNamespace === undefined
+      // default a namespace name, based on the stage and action names
+      ? `${stage.stageName}_${this.actionProperties.actionName}_NS`
+      : this.customerProvidedNamespace;
+
     return this.bound(scope, stage, options);
   }
 
@@ -45,6 +72,11 @@ export abstract class Action implements codepipeline.IAction {
     return rule;
   }
 
+  protected variableExpression(variableName: string): string {
+    this.variableReferenced = true;
+    return `#{${this.namespaceOrToken}.${variableName}}`;
+  }
+
   /**
    * The method called when an Action is attached to a Pipeline.
    * This method is guaranteed to be called only once for each Action instance.

packages/@aws-cdk/aws-codepipeline-actions/lib/codebuild/build-action.ts

@@ -92,6 +92,20 @@ export class CodeBuildAction extends Action {
     this.props = props;
   }
 
+  /**
+   * Reference a CodePipeline variable defined by the CodeBuild project this action points to.
+   * Variables in CodeBuild actions are defined using the 'exported-variables' subsection of the 'env'
+   * section of the buildspec.
+   *
+   * @param variableName the name of the variable to reference.
+   *   A variable by this name must be present in the 'exported-variables' section of the buildspec
+   *
+   * @see https://docs.aws.amazon.com/codebuild/latest/userguide/build-spec-ref.html#build-spec-ref-syntax
+   */
+  public variable(variableName: string): string {
+    return this.variableExpression(variableName);
+  }
+
   protected bound(scope: cdk.Construct, _stage: codepipeline.IStage, options: codepipeline.ActionBindOptions):
       codepipeline.ActionConfig {
     // check for a cross-account action if there are any outputs

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

@@ -29,6 +29,29 @@ export enum CodeCommitTrigger {
   EVENTS = 'Events',
 }
 
+/**
+ * The CodePipeline variables emitted by the CodeCommit source Action.
+ */
+export interface CodeCommitSourceVariables {
+  /** The name of the repository this action points to. */
+  readonly repositoryName: 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 date the currently last commit on the tracked branch was committed, in ISO-8601 format. */
+  readonly committerDate: 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;
+}
+
 /**
  * Construction properties of the {@link CodeCommitSourceAction CodeCommit source CodePipeline Action}.
  */
@@ -79,6 +102,18 @@ export class CodeCommitSourceAction extends Action {
     this.props = props;
   }
 
+  /** The variables emitted by this action. */
+  public get variables(): CodeCommitSourceVariables {
+    return {
+      repositoryName: this.variableExpression('RepositoryName'),
+      branchName: this.variableExpression('BranchName'),
+      authorDate: this.variableExpression('AuthorDate'),
+      committerDate: this.variableExpression('CommitterDate'),
+      commitId: this.variableExpression('CommitId'),
+      commitMessage: this.variableExpression('CommitMessage'),
+    };
+  }
+
   protected bound(_scope: Construct, stage: codepipeline.IStage, options: codepipeline.ActionBindOptions):
       codepipeline.ActionConfig {
     const createEvent = this.props.trigger === undefined ||