chore(core): inject TreeMetadata resource at the end (during synthe…

…sis) (#22780)

The `TreeMetadata` resource was being created as part of the `App` constructor, which meant that you could not add any context to the App node (you must add context _before_ any constructs are added). This moves the creation of `TreeMetadata` to be injected during `synthesis` similar to how we currently inject the metadata resource.

A side effect of this change is that we will now include tree metadata for resources that are added in `Stack.synthesize()` methods. The [synthesizeTree](https://github.com/aws/aws-cdk/blob/95e9e0f54a1dfb628d5146bd9b69c292547cf090/packages/@aws-cdk/core/lib/private/synthesis.ts#L193-L210) function visits nodes in the order that they were added to the tree. Previously the `TreeMetadata` was the first node so the TreeMetadata was generated first. Then if any Stacks would call `Stack.synthesize()` and add additional constructs (e.g. `BootstrapVersion`) these would not be added to the tree.

re #22749

----

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

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

@@ -2,7 +2,6 @@ import * as cxapi from '@aws-cdk/cx-api';
 import { Construct } from 'constructs';
 import * as fs from 'fs-extra';
 import { addCustomSynthesis, ICustomSynthesis } from './private/synthesis';
-import { TreeMetadata } from './private/tree-metadata';
 import { Stage } from './stage';
 
 const APP_SYMBOL = Symbol.for('@aws-cdk/core.App');
@@ -133,6 +132,13 @@ export class App extends Stage {
     return APP_SYMBOL in obj;
   }
 
+  /**
+   * Include construct tree metadata as part of the Cloud Assembly.
+   *
+   * @internal
+   */
+  public readonly _treeMetadata: boolean;
+
   /**
    * Initializes a CDK application.
    * @param props initialization properties
@@ -163,9 +169,7 @@ export class App extends Stage {
       process.once('beforeExit', () => this.synth());
     }
 
-    if (props.treeMetadata === undefined || props.treeMetadata) {
-      new TreeMetadata(this);
-    }
+    this._treeMetadata = props.treeMetadata ?? true;
   }
 
   private loadContext(defaults: { [key: string]: string } = { }, final: { [key: string]: string } = {}) {

packages/@aws-cdk/core/lib/private/synthesis.ts

@@ -1,6 +1,7 @@
 import * as cxapi from '@aws-cdk/cx-api';
 import { IConstruct } from 'constructs';
 import { Annotations } from '../annotations';
+import { App } from '../app';
 import { Aspects, IAspect } from '../aspect';
 import { Stack } from '../stack';
 import { ISynthesisSession } from '../stack-synthesizers/types';
@@ -21,6 +22,8 @@ export interface SynthesisOptions extends StageSynthesisOptions {
 }
 
 export function synthesize(root: IConstruct, options: SynthesisOptions = { }): cxapi.CloudAssembly {
+  // add the TreeMetadata resource to the App first
+  injectTreeMetadata(root);
   // we start by calling "synth" on all nested assemblies (which will take care of all their children)
   synthNestedAssemblies(root, options);
 
@@ -166,6 +169,22 @@ function injectMetadataResources(root: IConstruct) {
   });
 }
 
+/**
+ * Find the root App and add the TreeMetadata resource (if enabled).
+ *
+ * There is no good generic place to do this. Can't do it in the constructor
+ * (because adding a child construct makes it impossible to set context on the
+ * node), and the generic prepare phase is deprecated.
+ */
+function injectTreeMetadata(root: IConstruct) {
+  visit(root, 'post', construct => {
+    if (!App.isApp(construct) || !construct._treeMetadata) return;
+    const CDKTreeMetadata = 'Tree';
+    if (construct.node.tryFindChild(CDKTreeMetadata)) return;
+    new TreeMetadata(construct);
+  });
+}
+
 /**
  * Synthesize children in post-order into the given builder
  *

packages/@aws-cdk/core/test/private/tree-metadata.test.ts

@@ -44,6 +44,22 @@ describe('tree metadata', () => {
             id: 'mystack',
             path: 'mystack',
             children: {
+              BootstrapVersion: {
+                constructInfo: {
+                  fqn: '@aws-cdk/core.CfnParameter',
+                  version: '0.0.0',
+                },
+                id: 'BootstrapVersion',
+                path: 'mystack/BootstrapVersion',
+              },
+              CheckBootstrapVersion: {
+                constructInfo: {
+                  fqn: '@aws-cdk/core.CfnRule',
+                  version: '0.0.0',
+                },
+                id: 'CheckBootstrapVersion',
+                path: 'mystack/CheckBootstrapVersion',
+              },
               myconstruct: expect.objectContaining({
                 id: 'myconstruct',
                 path: 'mystack/myconstruct',
@@ -53,7 +69,6 @@ describe('tree metadata', () => {
         },
       }),
     });
-
   });
 
   test('tree metadata for a Cfn resource', () => {
@@ -91,7 +106,7 @@ describe('tree metadata', () => {
           mystack: expect.objectContaining({
             id: 'mystack',
             path: 'mystack',
-            children: {
+            children: expect.objectContaining({
               mycfnresource: expect.objectContaining({
                 id: 'mycfnresource',
                 path: 'mystack/mycfnresource',
@@ -107,7 +122,7 @@ describe('tree metadata', () => {
                   },
                 },
               }),
-            },
+            }),
           }),
         },
       }),
@@ -156,14 +171,14 @@ describe('tree metadata', () => {
               fqn: expect.stringMatching(codeBuild ? /\bStack$/ : /\bStack$|^constructs.Construct$/),
               version: expect.any(String),
             },
-            children: {
+            children: expect.objectContaining({
               myconstruct: expect.objectContaining({
                 constructInfo: {
                   fqn: expect.stringMatching(codeBuild ? /\bCfnResource$/ : /\bCfnResource$|^constructs.Construct$/),
                   version: expect.any(String),
                 },
               }),
-            },
+            }),
           }),
         }),
       }),
@@ -205,7 +220,7 @@ describe('tree metadata', () => {
           mystack: expect.objectContaining({
             id: 'mystack',
             path: 'mystack',
-            children: {
+            children: expect.objectContaining({
               mycfnparam: expect.objectContaining({
                 id: 'mycfnparam',
                 path: 'mystack/mycfnparam',
@@ -221,7 +236,7 @@ describe('tree metadata', () => {
                   },
                 },
               }),
-            },
+            }),
           }),
         },
       }),
@@ -283,7 +298,7 @@ describe('tree metadata', () => {
           myfirststack: expect.objectContaining({
             id: 'myfirststack',
             path: 'myfirststack',
-            children: {
+            children: expect.objectContaining({
               myfirstresource: expect.objectContaining({
                 id: 'myfirstresource',
                 path: 'myfirststack/myfirstresource',
@@ -294,12 +309,12 @@ describe('tree metadata', () => {
                   },
                 },
               }),
-            },
+            }),
           }),
           mysecondstack: expect.objectContaining({
             id: 'mysecondstack',
             path: 'mysecondstack',
-            children: {
+            children: expect.objectContaining({
               mysecondresource: expect.objectContaining({
                 id: 'mysecondresource',
                 path: 'mysecondstack/mysecondresource',
@@ -310,13 +325,28 @@ describe('tree metadata', () => {
                   },
                 },
               }),
-            },
+            }),
           }),
         },
       }),
     });
+  });
+
+  test('tree metadata can be disabled', () => {
+    // GIVEN
+    const app = new App({
+      treeMetadata: false,
+    });
 
+    // WHEN
+    const stack = new Stack(app, 'mystack');
+    new Construct(stack, 'myconstruct');
+
+    const assembly = app.synth();
+    const treeArtifact = assembly.tree();
 
+    // THEN
+    expect(treeArtifact).not.toBeDefined();
   });
 
   test('failing nodes', () => {