chore(core): use key instead of logicalId for key when provided (#28075)

In CDK Migrate, when a user has a construct with the same name as their CfnOutput key, it creates a naming collision.

This change enables us to name the construct something else and still use the correct key in creating the output. Note that the logicalId only makes it into the synthesized template as the output key so this change won't impact existing apps using the CfnOutput construct.

Closes #<issue number here>.

----

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

packages/aws-cdk-lib/core/lib/cfn-output.ts

@@ -10,6 +10,11 @@ export interface CfnOutputProps {
    */
   readonly description?: string;
 
+  /**
+   * The key of the property returned by aws cloudformation describe-stacks command.
+   */
+  readonly key?: string;
+
   /**
    * The value of the property returned by the aws cloudformation describe-stacks command.
    * The value of an output can include literals, parameter references, pseudo-parameters,
@@ -38,6 +43,7 @@ export interface CfnOutputProps {
 export class CfnOutput extends CfnElement {
   private _description?: string;
   private _condition?: CfnCondition;
+  private _key?: string;
   private _value?: any;
   private _exportName?: string;
 
@@ -58,6 +64,7 @@ export class CfnOutput extends CfnElement {
     }
 
     this._description = props.description;
+    this._key = props.key;
     this._value = props.value;
     this._condition = props.condition;
     this._exportName = props.exportName;
@@ -160,7 +167,7 @@ export class CfnOutput extends CfnElement {
   public _toCloudFormation(): object {
     return {
       Outputs: {
-        [this.logicalId]: {
+        [this._key ?? this.logicalId]: {
           Description: this._description,
           Value: this._value,
           Export: this._exportName != null ? { Name: this._exportName } : undefined,

packages/aws-cdk-lib/core/test/output.test.ts

@@ -9,7 +9,7 @@ beforeEach(() => {
 });
 
 describe('output', () => {
-  test('outputs can be added to the stack', () => {
+  test('outputs can be added to the stack with no key provided', () => {
     const res = new CfnResource(stack, 'MyResource', { type: 'R' });
     const ref = res.ref;
 
@@ -32,6 +32,30 @@ describe('output', () => {
     });
   });
 
+  test('outputs can be added to the stack with a key provided', () => {
+    const res = new CfnResource(stack, 'MyResource', { type: 'R' });
+    const ref = res.ref;
+
+    new CfnOutput(stack, 'MyOutput', {
+      exportName: 'ExportName',
+      key: 'MyOutputWithKey',
+      value: ref,
+      description: 'CfnOutput properties',
+    });
+    expect(toCloudFormation(stack)).toEqual({
+      Resources: { MyResource: { Type: 'R' } },
+      Outputs:
+      {
+        MyOutputWithKey:
+        {
+          Description: 'CfnOutput properties',
+          Export: { Name: 'ExportName' },
+          Value: { Ref: 'MyResource' },
+        },
+      },
+    });
+  });
+
   test('No export is created by default', () => {
     // WHEN
     new CfnOutput(stack, 'SomeOutput', { value: 'x' });