fix(cli): displays a nag message for flags that don't need configuring

packages/@aws-cdk/toolkit-lib/lib/toolkit/types.ts

@@ -123,5 +123,5 @@ export interface FeatureFlag {
   readonly recommendedValue: unknown;
   readonly userValue?: unknown;
   readonly explanation?: string;
-  readonly unconfiguredBehavesLike?: { [key: string]: any };
+  readonly unconfiguredBehavesLike?: { v2?: any };
 }

packages/aws-cdk/lib/cli/cdk-toolkit.ts

@@ -2113,11 +2113,29 @@ async function askUserConfirmation(
   });
 }
 
+/**
+ * Display a warning if there are flags that are different from the recommended value
+ *
+ * This happens if both of the following are true:
+ *
+ * - The user didn't configure the value
+ * - The default value for the flag (unconfiguredBehavesLike) is different from the recommended value
+ */
 export async function displayFlagsMessage(ioHost: IoHelper, toolkit: InternalToolkit, cloudExecutable: CloudExecutable): Promise<void> {
-  let numUnconfigured = (await toolkit.flags(cloudExecutable))
+  const flags = await toolkit.flags(cloudExecutable);
+
+  // The "unconfiguredBehavesLike" information got added later. If none of the flags have this information,
+  // we don't have enough information to reliably display this information without scaring users, so don't do anything.
+  if (flags.every(flag => flag.unconfiguredBehavesLike === undefined)) {
+    return;
+  }
+
+  const unconfiguredFlags = flags
     .filter(flag => !OBSOLETE_FLAGS.includes(flag.name))
-    .filter(flag => flag.userValue === undefined).length;
+    .filter(flag => (flag.unconfiguredBehavesLike?.v2 ?? false) !== flag.recommendedValue)
+    .filter(flag => flag.userValue === undefined);
 
+  const numUnconfigured = unconfiguredFlags.length;
   if (numUnconfigured > 0) {
     await ioHost.defaults.warn(`${numUnconfigured} feature flags are not configured. Run 'cdk --unstable=flags flags' to learn more.`);
   }

packages/aws-cdk/test/cli/display-flags-message.test.ts

@@ -30,20 +30,23 @@ describe('displayFlagsMessage', () => {
         recommendedValue: 'true',
         explanation: 'Test flag',
         module: 'aws-cdk-lib',
+        unconfiguredBehavesLike: { v2: true },
       },
       {
         name: '@aws-cdk/s3:anotherFlag',
         userValue: 'false',
         recommendedValue: 'false',
         explanation: 'Another test flag',
         module: 'aws-cdk-lib',
+        unconfiguredBehavesLike: { v2: true },
       },
       {
         name: '@aws-cdk/core:enableStackNameDuplicates',
         userValue: undefined,
         recommendedValue: 'true',
         explanation: 'Obsolete flag',
         module: 'aws-cdk-lib',
+        unconfiguredBehavesLike: { v2: true },
       },
     ];
 
@@ -56,14 +59,16 @@ describe('displayFlagsMessage', () => {
       message: expect.stringContaining('1 feature flags are not configured'),
     }));
   });
+
   test('does not display a message when user has no unconfigured flags', async () => {
     const mockFlagsData = [
       {
         name: '@aws-cdk/s3:anotherFlag',
-        userValue: 'false',
-        recommendedValue: 'false',
+        userValue: false,
+        recommendedValue: false,
         explanation: 'Another test flag',
         module: 'aws-cdk-lib',
+        unconfiguredBehavesLike: { v2: true },
       },
     ];
     mockToolkit.flags.mockResolvedValue(mockFlagsData);
@@ -73,5 +78,23 @@ describe('displayFlagsMessage', () => {
     expect(mockToolkit.flags).toHaveBeenCalledWith(mockCloudExecutable);
     expect(ioHost.notifySpy).not.toHaveBeenCalled();
   });
+
+  test('does not display a message when unconfigured behaviors is the same as recommended behavior', async () => {
+    const mockFlagsData = [
+      {
+        name: '@aws-cdk/s3:anotherFlag',
+        // userValue is undefined, meaning it is unconfigured
+        recommendedValue: false,
+        explanation: 'Another test flag',
+        module: 'aws-cdk-lib',
+        unconfiguredBehavesLike: { v2: false },
+      },
+    ];
+    mockToolkit.flags.mockResolvedValue(mockFlagsData);
+
+    await displayFlagsMessage(ioHost.asHelper(), mockToolkit as any, mockCloudExecutable);
+
+    expect(ioHost.notifySpy).not.toHaveBeenCalled();
+  });
 });