refactor(assets): remove content hash attribute (#4003)

as part of the ci/cd design, we wish to reduce the surface area
of cdk templates to a minimum. content hash can only be determined
after the asset has been "prepared" (docker build/zip directory).

if the need arises to reintroduce this, we can always query the
content hash through a custom resource.

asset content hash is currently not used anywhere in the framework
or the aws construct library and introduces unwanted coupling between
the toolchain and the framework/app.

this change initially just removes the API from IAsset (and S3/ECR Asset classes)
to ensure code does not take a dependency on it. in a subsequent change we will
also remove the content hash cloudformation parameter.

BREAKING CHANGE: assets no longer expose a property `contentHash`. Use `sourceHash`
as a good approximation. if you have a strong use case for content hashes, please
raise a github issue and we will figure out a solution.

packages/@aws-cdk/assets/lib/api.ts

@@ -8,13 +8,4 @@ export interface IAsset {
    * the content hash has changed.
    */
   readonly sourceHash: string;
-
-  /**
-   * A hash of the bundle for of this asset, which is only available at deployment time. As this is
-   * a late-bound token, it may not be used in construct IDs, but can be passed as a resource
-   * property in order to force a change on a resource when an asset is effectively updated. This is
-   * more reliable than `sourceHash` in particular for assets which bundling phase involve external
-   * resources that can change over time (such as Docker image builds).
-   */
-  readonly artifactHash: string;
 }

packages/@aws-cdk/aws-ecr-assets/lib/image-asset.ts

@@ -54,7 +54,6 @@ export class DockerImageAsset extends cdk.Construct implements assets.IAsset {
   public repository: ecr.IRepository;
 
   public readonly sourceHash: string;
-  public readonly artifactHash: string;
 
   /**
    * Directory where the source files are stored
@@ -115,7 +114,6 @@ export class DockerImageAsset extends cdk.Construct implements assets.IAsset {
     // haven't already started using the image.
     this.repository = new AdoptedRepository(this, 'AdoptRepository', { repositoryName });
     this.imageUri = `${this.repository.repositoryUri}@sha256:${imageSha}`;
-    this.artifactHash = imageSha;
   }
 }
 

packages/@aws-cdk/aws-ecr-assets/test/integ.assets-docker.expected.json

@@ -196,21 +196,6 @@
     }
   },
   "Outputs": {
-    "ArtifactHash": {
-      "Value": {
-        "Fn::Select": [
-          1,
-          {
-            "Fn::Split": [
-              "@sha256:",
-              {
-                "Ref": "DockerImageImageName266E5998"
-              }
-            ]
-          }
-        ]
-      }
-    },
     "ImageUri": {
       "Value": {
         "Fn::Join": [
@@ -319,4 +304,4 @@
       }
     }
   }
-}
+}

packages/@aws-cdk/aws-ecr-assets/test/integ.assets-docker.ts

@@ -9,7 +9,6 @@ const asset = new assets.DockerImageAsset(stack, 'DockerImage', {
   directory: path.join(__dirname, 'demo-image'),
 });
 
-new cdk.CfnOutput(stack, 'ArtifactHash', { value: asset.artifactHash });
 new cdk.CfnOutput(stack, 'ImageUri', { value: asset.imageUri });
 
 app.synth();

packages/@aws-cdk/aws-s3-assets/lib/asset.ts

@@ -68,7 +68,6 @@ export class Asset extends cdk.Construct implements assets.IAsset {
   public readonly isZipArchive: boolean;
 
   public readonly sourceHash: string;
-  public readonly artifactHash: string;
 
   /**
    * The S3 prefix where all different versions of this asset are stored
@@ -117,7 +116,6 @@ export class Asset extends cdk.Construct implements assets.IAsset {
     this.s3Prefix = cdk.Fn.select(0, cdk.Fn.split(cxapi.ASSET_PREFIX_SEPARATOR, keyParam.valueAsString)).toString();
     const s3Filename = cdk.Fn.select(1, cdk.Fn.split(cxapi.ASSET_PREFIX_SEPARATOR, keyParam.valueAsString)).toString();
     this.s3ObjectKey = `${this.s3Prefix}${s3Filename}`;
-    this.artifactHash = hashParam.valueAsString;
 
     this.bucket = s3.Bucket.fromBucketName(this, 'AssetBucket', this.s3BucketName);