fix(cx-api): cannot detect CloudAssembly across different library versions

Author: mrgrain

packages/@aws-cdk/toolkit/lib/api/cloud-assembly/private/source-builder.ts

@@ -1,3 +1,4 @@
+import * as cxapi from '@aws-cdk/cx-api';
 import * as fs from 'fs-extra';
 import type { ICloudAssemblySource } from '../';
 import { ContextAwareCloudAssembly, ContextAwareCloudAssemblyProps } from './context-aware-source';
@@ -9,6 +10,12 @@ import { ToolkitError } from '../../errors';
 import { debug } from '../../io/private';
 import { AssemblyBuilder, CdkAppSourceProps } from '../source-builder';
 
+// bypass loading from disk if we already have a supported object
+const CLOUD_ASSEMBLY_SYMBOL = Symbol.for('@aws-cdk/cx-api.CloudAssembly');
+function isCloudAssembly(x: any): x is cxapi.CloudAssembly {
+  return x !== null && typeof(x) === 'object' && CLOUD_ASSEMBLY_SYMBOL in x;
+}
+
 export abstract class CloudAssemblySourceBuilder {
 
   /**
@@ -40,13 +47,19 @@ export abstract class CloudAssemblySourceBuilder {
         produce: async () => {
           const outdir = determineOutputDirectory(props.outdir);
           const env = await prepareDefaultEnvironment(services, { outdir });
-          return changeDir(async () =>
+          const assembly = await changeDir(async () =>
             withContext(context.all, env, props.synthOptions ?? {}, async (envWithContext, ctx) =>
               withEnv(envWithContext, () => builder({
                 outdir,
                 context: ctx,
               })),
             ), props.workingDirectory);
+
+          if (isCloudAssembly(assembly)) {
+            return assembly;
+          }
+
+          return new cxapi.CloudAssembly(assembly.directory);
         },
       },
       contextAssemblyProps,

packages/@aws-cdk/toolkit/lib/api/cloud-assembly/source-builder.ts

@@ -1,5 +1,3 @@
-import type * as cxapi from '@aws-cdk/cx-api';
-
 export interface AppProps {
   /**
    * The output directory into which to the builder app will emit synthesized artifacts.
@@ -12,7 +10,14 @@ export interface AppProps {
   readonly context?: { [key: string]: any };
 }
 
-export type AssemblyBuilder = (props: AppProps) => Promise<cxapi.CloudAssembly>;
+export type AssemblyBuilder = (props: AppProps) => Promise<ICloudAssembly>;
+
+export interface ICloudAssembly {
+  /**
+   * The root directory of the cloud assembly.
+   */
+  readonly directory: string;
+}
 
 /**
  * Configuration for creating a CLI from an AWS CDK App directory

packages/@aws-cdk/toolkit/test/_fixtures/external-context/index.ts

@@ -7,5 +7,5 @@ export default async () => {
   new s3.Bucket(stack, 'MyBucket', {
     bucketName: app.node.tryGetContext('externally-provided-bucket-name'),
   });
-  return app.synth() as any;
+  return app.synth();
 };

packages/@aws-cdk/toolkit/test/_fixtures/stack-with-bucket/index.js

@@ -5,5 +5,5 @@ export default async () => {
   const app = new core.App();
   const stack = new core.Stack(app, 'Stack1');
   new s3.Bucket(stack, 'MyBucket');
-  return app.synth() as any;
+  return app.synth();
 };

packages/@aws-cdk/toolkit/test/_fixtures/stack-with-bucket/index.ts

@@ -5,6 +5,5 @@ export default async () => {
   new core.Stack(app, 'Stack1');
   new core.Stack(app, 'Stack2');
 
-  // @todo fix api
-  return app.synth() as any;
+  return app.synth();
 };

packages/@aws-cdk/toolkit/test/_fixtures/two-empty-stacks/index.js

@@ -8,6 +8,8 @@ import { CloudArtifact } from './cloud-artifact';
 import { topologicalSort } from './toposort';
 import * as cxschema from '../../cloud-assembly-schema';
 
+const CLOUD_ASSEMBLY_SYMBOL = Symbol.for('@aws-cdk/cx-api.CloudAssembly');
+
 /**
  * The name of the root manifest file of the assembly.
  */
@@ -17,6 +19,15 @@ const MANIFEST_FILE = 'manifest.json';
  * Represents a deployable cloud application.
  */
 export class CloudAssembly {
+  /**
+   * Return whether the given object is a Stack.
+   *
+   * We do attribute detection since we can't reliably use 'instanceof'.
+   */
+  public static isCloudAssembly(x: any): x is CloudAssembly {
+    return x !== null && typeof(x) === 'object' && CLOUD_ASSEMBLY_SYMBOL in x;
+  }
+
   /**
    * The root directory of the cloud assembly.
    */