feat(cdk): treat the "fake" CFN intrinsics (Fn::GetArtifactAtt, Fn::GetParam) specially when stringifying JSON. (#1605)

Fn::GetArtifactAtt and Fn::GetParam are not really intrinsics,
they're functions that can be used only in CodePipeline CFN Actions,
in the `parameterOverride` property.

More information: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/continuous-delivery-codepipeline-parameter-override-functions.html

Fixes #1588

Author: skinny85

packages/@aws-cdk/aws-codepipeline/test/integ.pipeline-cfn.expected.json

@@ -207,7 +207,8 @@
                       "CfnChangeSetRole6F05F6FC",
                       "Arn"
                     ]
-                  }
+                  },
+                  "ParameterOverrides": "{\"BucketName\":{\"Fn::GetArtifactAtt\":[\"SourceArtifact\",\"BucketName\"]},\"ObjectKey\":{\"Fn::GetArtifactAtt\":[\"SourceArtifact\",\"ObjectKey\"]},\"Url\":{\"Fn::GetArtifactAtt\":[\"SourceArtifact\",\"URL\"]},\"OtherParam\":{\"Fn::GetParam\":[\"SourceArtifact\",\"params.json\",\"OtherParam\"]}}"
                 },
                 "InputArtifacts": [
                   {

packages/@aws-cdk/aws-codepipeline/test/integ.pipeline-cfn.ts

@@ -39,6 +39,12 @@ new cfn.PipelineCreateReplaceChangeSetAction(stack, 'DeployCFN', {
   role,
   templatePath: source.outputArtifact.atPath('test.yaml'),
   adminPermissions: false,
+  parameterOverrides: {
+    BucketName: source.outputArtifact.bucketName,
+    ObjectKey: source.outputArtifact.objectKey,
+    Url: source.outputArtifact.url,
+    OtherParam: source.outputArtifact.getParam('params.json', 'OtherParam'),
+  },
 });
 
 app.run();

packages/@aws-cdk/cdk/lib/cloudformation/instrinsics.ts

@@ -37,7 +37,15 @@ export function isIntrinsic(x: any) {
   const keys = Object.keys(x);
   if (keys.length !== 1) { return false; }
 
-  return keys[0] === 'Ref' || keys[0].startsWith('Fn::');
+  return keys[0] === 'Ref' || isNameOfCloudFormationIntrinsic(keys[0]);
+}
+
+export function isNameOfCloudFormationIntrinsic(name: string): boolean {
+  if (!name.startsWith('Fn::')) {
+    return false;
+  }
+  // these are 'fake' intrinsics, only usable inside the parameter overrides of a CFN CodePipeline Action
+  return name !== 'Fn::GetArtifactAtt' && name !== 'Fn::GetParam';
 }
 
 /**

packages/@aws-cdk/cdk/test/cloudformation/evaluate-cfn.ts

@@ -3,6 +3,8 @@
  *
  * Note that this function is not production quality, it exists to support tests.
  */
+import { isNameOfCloudFormationIntrinsic } from '../../lib/cloudformation/instrinsics';
+
 export function evaluateCFN(object: any, context: {[key: string]: string} = {}): any {
   const intrinsics: any = {
     'Fn::Join'(separator: string, args: string[]) {
@@ -34,7 +36,7 @@ export function evaluateCFN(object: any, context: {[key: string]: string} = {}):
 
     if (typeof obj === 'object') {
       const keys = Object.keys(obj);
-      if (keys.length === 1 && (keys[0].startsWith('Fn::') || keys[0] === 'Ref')) {
+      if (keys.length === 1 && (isNameOfCloudFormationIntrinsic(keys[0]) || keys[0] === 'Ref')) {
         return evaluateIntrinsic(keys[0], obj[keys[0]]);
       }
 

packages/@aws-cdk/cdk/test/cloudformation/test.cloudformation-json.ts

@@ -92,6 +92,29 @@ export = {
     test.done();
   },
 
+  'fake intrinsics are serialized to objects'(test: Test) {
+    const stack = new Stack();
+    const fakeIntrinsics = new Token(() => ({
+      a: {
+        'Fn::GetArtifactAtt': {
+          key: 'val',
+        },
+      },
+      b: {
+        'Fn::GetParam': [
+          'val1',
+          'val2',
+        ],
+      },
+    }));
+
+    const stringified = CloudFormationJSON.stringify(fakeIntrinsics, stack);
+    test.equal(evaluateCFN(stack.node.resolve(stringified)),
+        '{"a":{"Fn::GetArtifactAtt":{"key":"val"}},"b":{"Fn::GetParam":["val1","val2"]}}');
+
+    test.done();
+  },
+
   'embedded string literals in intrinsics are escaped when calling TokenJSON.stringify()'(test: Test) {
     // GIVEN
     const stack = new Stack();