feat(codepipeline): make Pipeline importable by ARN (#3469)

Add the capability to import an externally-defined CodePipeline using Pipeline.fromPipelineArn().

Fixes #3467

Author: skinny85

Diff for: packages/@aws-cdk/aws-codepipeline/lib/pipeline.ts

@@ -103,8 +103,8 @@ export interface PipelineProps {
 }
 
 abstract class PipelineBase extends Resource implements IPipeline {
-  public abstract pipelineName: string;
-  public abstract pipelineArn: string;
+  public abstract readonly pipelineName: string;
+  public abstract readonly pipelineArn: string;
 
   /**
    * Defines an event rule triggered by this CodePipeline.
@@ -159,6 +159,22 @@ abstract class PipelineBase extends Resource implements IPipeline {
  * // ... add more stages
  */
 export class Pipeline extends PipelineBase {
+  /**
+   * Import a pipeline into this app.
+   *
+   * @param scope the scope into which to import this pipeline
+   * @param id the logical ID of the returned pipeline construct
+   * @param pipelineArn The ARN of the pipeline (e.g. `arn:aws:codepipeline:us-east-1:123456789012:MyDemoPipeline`)
+   */
+  public static fromPipelineArn(scope: Construct, id: string, pipelineArn: string): IPipeline {
+    class Import extends PipelineBase {
+      public readonly pipelineName = Stack.of(scope).parseArn(pipelineArn).resource;
+      public readonly pipelineArn = pipelineArn;
+    }
+
+    return new Import(scope, id);
+  }
+
   /**
    * The IAM role AWS CodePipeline will use to perform actions or assume roles for actions with
    * a more specific IAM role.

Diff for: packages/@aws-cdk/aws-codepipeline/test/test.pipeline.ts

@@ -28,5 +28,17 @@ export = {
 
       test.done();
     },
+
+    'can be imported by ARN'(test: Test) {
+      const stack = new cdk.Stack();
+
+      const pipeline = codepipeline.Pipeline.fromPipelineArn(stack, 'Pipeline',
+        'arn:aws:codepipeline:us-east-1:123456789012:MyPipeline');
+
+      test.equal(pipeline.pipelineArn, 'arn:aws:codepipeline:us-east-1:123456789012:MyPipeline');
+      test.equal(pipeline.pipelineName, 'MyPipeline');
+
+      test.done();
+    },
   },
 };