refactor(core): move dependency logic to app and stack tags to synth

As a follow up to aws#7187, extract the rest of the code from `Stack.prepare`: the logic that converted construct-level dependencies to resource-level dependencies was moved to `App.prepare` and the logic that added top-level stack tags to the cloud assembly metadata was moved to `Stack.synthesize`.

packages/@aws-cdk/core/lib/private/prepare-app.ts

@@ -1,5 +1,6 @@
 import { ConstructOrder } from 'constructs';
-import { Construct } from '../construct-compat';
+import { CfnResource } from '../cfn-resource';
+import { Construct, IConstruct } from '../construct-compat';
 import { Stack } from '../stack';
 import { resolveReferences } from './refs';
 
@@ -18,6 +19,18 @@ export function prepareApp(root: Construct) {
     throw new Error('prepareApp must be called on the root node');
   }
 
+  // apply dependencies between resources in depending subtrees
+  for (const dependency of root.node.dependencies) {
+    const targetCfnResources = findCfnResources(dependency.target);
+    const sourceCfnResources = findCfnResources(dependency.source);
+
+    for (const target of targetCfnResources) {
+      for (const source of sourceCfnResources) {
+        source.addDependsOn(target);
+      }
+    }
+  }
+
   // depth-first (children first) queue of nested stacks. We will pop a stack
   // from the head of this queue to prepare it's template asset.
   const queue = findAllNestedStacks(root);
@@ -60,6 +73,13 @@ function findAllNestedStacks(root: Construct) {
   return result;
 }
 
+/**
+ * Find all resources in a set of constructs
+ */
+function findCfnResources(root: IConstruct): CfnResource[] {
+  return root.node.findAll().filter(CfnResource.isCfnResource);
+}
+
 interface INestedStackPrivateApi {
   _prepareTemplateAsset(): boolean;
 }

packages/@aws-cdk/core/lib/stack.ts

@@ -734,19 +734,6 @@ export class Stack extends Construct implements ITaggable {
    * Find all dependencies as well and add the appropriate DependsOn fields.
    */
   protected prepare() {
-    // Resource dependencies
-    for (const dependency of this.node.dependencies) {
-      for (const target of findCfnResources([ dependency.target ])) {
-        for (const source of findCfnResources([ dependency.source ])) {
-          source.addDependsOn(target);
-        }
-      }
-    }
-
-    if (this.tags.hasTags()) {
-      this.node.addMetadata(cxschema.ArtifactMetadataEntryType.STACK_TAGS, this.tags.renderTags());
-    }
-
     // if this stack is a roort (e.g. in unit tests), call `prepareApp` so that
     // we resolve cross-references and nested stack assets.
     if (!this.node.scope) {
@@ -771,9 +758,6 @@ export class Stack extends Construct implements ITaggable {
       return;
     }
 
-    const deps = this.dependencies.map(s => s.artifactId);
-    const meta = this.collectMetadata();
-
     // backwards compatibility since originally artifact ID was always equal to
     // stack name the stackName attribute is optional and if it is not specified
     // the CLI will use the artifact ID as the stack name. we *could have*
@@ -785,11 +769,21 @@ export class Stack extends Construct implements ITaggable {
       ? { }
       : { stackName: this.stackName };
 
+    // nested stack tags are applied at the AWS::CloudFormation::Stack resource
+    // level and are not needed in the cloud assembly.
+    // TODO: move these to the cloud assembly artifact properties instead of metadata
+    if (this.tags.hasTags()) {
+      this.node.addMetadata(cxschema.ArtifactMetadataEntryType.STACK_TAGS, this.tags.renderTags());
+    }
+
     const properties: cxapi.AwsCloudFormationStackProperties = {
       templateFile: this.templateFile,
       ...stackNameProperty,
     };
 
+    const deps = this.dependencies.map(s => s.artifactId);
+    const meta = this.collectMetadata();
+
     // add an artifact that represents this stack
     builder.addArtifact(this.artifactId, {
       type: cxschema.ArtifactType.AWS_CLOUDFORMATION_STACK,
@@ -1054,17 +1048,6 @@ import { IResolvable } from './resolvable';
 import { ITaggable, TagManager } from './tag-manager';
 import { Token } from './token';
 
-/**
- * Find all resources in a set of constructs
- */
-function findCfnResources(roots: Iterable<IConstruct>): CfnResource[] {
-  const ret = new Array<CfnResource>();
-  for (const root of roots) {
-    ret.push(...root.node.findAll().filter(CfnResource.isCfnResource));
-  }
-  return ret;
-}
-
 interface StackDependency {
   stack: Stack;
   reasons: string[];

packages/@aws-cdk/core/test/test.stack.ts

@@ -1,6 +1,8 @@
 import * as cxapi from '@aws-cdk/cx-api';
 import { Test } from 'nodeunit';
-import { App, CfnCondition, CfnInclude, CfnOutput, CfnParameter, CfnResource, Construct, ConstructNode, Lazy, ScopedAws, Stack, validateString } from '../lib';
+import {
+  App, CfnCondition, CfnInclude, CfnOutput, CfnParameter,
+  CfnResource, Construct, ConstructNode, Lazy, ScopedAws, Stack, Tag, validateString } from '../lib';
 import { Intrinsic } from '../lib/private/intrinsic';
 import { PostResolveToken } from '../lib/util';
 import { toCloudFormation } from './util';
@@ -828,6 +830,29 @@ export = {
     ]);
     test.done();
   },
+
+  'stack tags are reflected in the stack cloud assembly artifact'(test: Test) {
+    // GIVEN
+    const app = new App({ stackTraces: false });
+    const stack1 = new Stack(app, 'stack1');
+    const stack2 = new Stack(stack1, 'stack2');
+
+    // WHEN
+    Tag.add(app, 'foo', 'bar');
+
+    // THEN
+    const asm = app.synth();
+    const expected = [
+      {
+        type: 'aws:cdk:stack-tags',
+        data: [ { key: 'foo', value: 'bar' } ],
+      },
+    ];
+
+    test.deepEqual(asm.getStackArtifact(stack1.artifactId).manifest.metadata, { '/stack1': expected });
+    test.deepEqual(asm.getStackArtifact(stack2.artifactId).manifest.metadata, { '/stack1/stack2': expected });
+    test.done();
+  },
 };
 
 class StackWithPostProcessor extends Stack {