fix: function.latestVersion points to wrong ARN

The `IFunctionRef` implementation of `LatestVersion` returns the
underlying function ARN, instead of the version's ARN.

This is a similar situation and fix to #35545.

Author: rix0rrr

packages/aws-cdk-lib/aws-lambda/lib/function-base.ts

@@ -866,12 +866,15 @@ class LatestVersion extends FunctionBase implements IVersion {
 
   public get versionRef(): VersionReference {
     return {
-      functionArn: this.functionRef.functionArn,
+      functionArn: this.functionArn,
     };
   }
 
-  public get functionRef() {
-    return this.lambda.functionRef;
+  public get functionRef(): FunctionReference {
+    return {
+      functionArn: this.functionArn,
+      functionName: this.functionName,
+    };
   }
 
   public get functionArn() {

packages/aws-cdk-lib/aws-lambda/test/alias.test.ts

@@ -657,4 +657,24 @@ describe('alias', () => {
       Qualifier: aliasName,
     });
   });
+
+  test('alias\' implementation of IFunctionRef should point to the alias', () => {
+    // GIVEN
+    const stack = new Stack();
+    const fn = new lambda.Function(stack, 'MyLambda', {
+      code: new lambda.InlineCode('hello()'),
+      handler: 'index.hello',
+      runtime: lambda.Runtime.NODEJS_LATEST,
+    });
+    const aliasName = 'prod';
+
+    // WHEN
+    const alias = new lambda.Alias(stack, 'Alias', {
+      aliasName,
+      version: fn.currentVersion,
+    });
+
+    // THEN
+    expect(alias.functionRef.functionArn).toEqual(alias.functionArn);
+  });
 });

packages/aws-cdk-lib/aws-lambda/test/function.test.ts

@@ -2764,6 +2764,21 @@ describe('function', () => {
     expect(stack.resolve(version2.functionArn)).toEqual(expectedArn);
   });
 
+  test('latestVersion functionRef ARN is the version ARN, not the plain ARN', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+
+    // WHEN
+    const fn = new lambda.Function(stack, 'MyLambda', {
+      code: new lambda.InlineCode('hello()'),
+      handler: 'index.hello',
+      runtime: lambda.Runtime.NODEJS_LATEST,
+    });
+
+    // THEN
+    expect(fn.latestVersion.functionRef.functionArn).toEqual(fn.latestVersion.functionArn);
+  });
+
   test('default function with kmsKeyArn, environmentEncryption passed as props', () => {
     // GIVEN
     const stack = new cdk.Stack();

packages/aws-cdk-lib/aws-lambda/test/lambda-version.test.ts

@@ -229,4 +229,22 @@ describe('lambda version', () => {
       version.addFunctionUrl();
     }).toThrow(/FunctionUrl cannot be used with a Version/);
   });
+
+  test('version\'s implementation of IFunctionRef should point to the version', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const fn = new lambda.Function(stack, 'MyLambda', {
+      code: new lambda.InlineCode('hello()'),
+      handler: 'index.hello',
+      runtime: lambda.Runtime.NODEJS_LATEST,
+    });
+
+    // WHEN
+    const ver = new lambda.Version(stack, 'Version', {
+      lambda: fn,
+    });
+
+    // THEN
+    expect(ver.functionRef.functionArn).toEqual(ver.functionArn);
+  });
 });