fix(cli): diff always prints stack name (#304)

Fixes #302 

In #264, we capture the output of
the Formatter into a stream, and that is then converted to a string.
This diff only gets printed if the diff isn't empty, but by some quirk
`formatStackDiff` used to print the stack name _outside_ of the stream,
thus creating the (correct) behavior. #264 made sure that `format`
doesn't print, so we need to make sure that the consumer of
`formatStackDiff` prints the relevant info.

This PR makes sure that the stack name is returned as the formatted diff
even if the actual diff is empty. We will print the right information
when we print the formatted diff now.

I also made similar modifications to `formatSecurityDiff`, as we should
move away from `format` methods printing anything at all.

BEFORE (cdk 2.1006.0):

<img width="326" alt="Screenshot 2025-04-02 at 9 04 04 AM"
src="https://github.com/user-attachments/assets/03b92517-e475-4c27-a4c1-52217be824c8"
/>


AFTER (my local cdk):

<img width="322" alt="Screenshot 2025-04-02 at 9 03 11 AM"
src="https://github.com/user-attachments/assets/53a7d3e0-2e62-45ca-898b-93c923028346"
/>


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

---------

Signed-off-by: github-actions <[email protected]>
Co-authored-by: github-actions <[email protected]>

Author: kaizencc

packages/@aws-cdk/tmp-toolkit-helpers/src/api/diff/diff-formatter.ts

@@ -208,7 +208,7 @@ export class DiffFormatter {
     try {
       // must output the stack name if there are differences, even if quiet
       if (stackName && (!options.quiet || !diff.isEmpty)) {
-        stream.write(format('Stack %s\n', chalk.bold(stackName)));
+        stream.write(format(`Stack ${chalk.bold(stackName)}\n`));
       }
 
       if (!options.quiet && options.isImport) {
@@ -239,20 +239,19 @@ export class DiffFormatter {
           ...logicalIdMapFromTemplate(this.oldTemplate),
           ...buildLogicalToPathMap(this.newTemplate),
         }, options.context);
-
-        // store the stream containing a formatted stack diff
-        formattedDiff = stream.toString();
       } else if (!options.quiet) {
-        options.ioDefaultHelper.info(chalk.green('There were no differences'));
+        stream.write(chalk.green('There were no differences\n'));
+      }
+
+      if (filteredChangesCount > 0) {
+        stream.write(chalk.yellow(`Omitted ${filteredChangesCount} changes because they are likely mangled non-ASCII characters. Use --strict to print them.\n`));
       }
     } finally {
+      // store the stream containing a formatted stack diff
+      formattedDiff = stream.toString();
       stream.end();
     }
 
-    if (filteredChangesCount > 0) {
-      options.ioDefaultHelper.info(chalk.yellow(`Omitted ${filteredChangesCount} changes because they are likely mangled non-ASCII characters. Use --strict to print them.`));
-    }
-
     for (const nestedStackLogicalId of Object.keys(nestedStackTemplates ?? {})) {
       if (!nestedStackTemplates) {
         break;
@@ -285,18 +284,18 @@ export class DiffFormatter {
     const diff = fullDiff(this.oldTemplate, this.newTemplate.template, options.changeSet);
 
     if (diffRequiresApproval(diff, options.requireApproval)) {
-      ioDefaultHelper.info(format('Stack %s\n', chalk.bold(options.stackName)));
-
-      // eslint-disable-next-line max-len
-      ioDefaultHelper.warning(`This deployment will make potentially sensitive changes according to your current security approval level (--require-approval ${options.requireApproval}).`);
-      ioDefaultHelper.warning('Please confirm you intend to make the following modifications:\n');
-
       // The security diff is formatted via `Formatter`, which takes in a stream
       // and sends its output directly to that stream. To faciliate use of the
       // global CliIoHost, we create our own stream to capture the output of
       // `Formatter` and return the output as a string for the consumer of
       // `formatSecurityDiff` to decide what to do with it.
       const stream = new StringWriteStream();
+
+      stream.write(format(`Stack ${chalk.bold(options.stackName)}\n`));
+
+      // eslint-disable-next-line max-len
+      ioDefaultHelper.warning(`This deployment will make potentially sensitive changes according to your current security approval level (--require-approval ${options.requireApproval}).`);
+      ioDefaultHelper.warning('Please confirm you intend to make the following modifications:\n');
       try {
         // formatSecurityChanges updates the stream with the formatted security diff
         formatSecurityChanges(stream, diff, buildLogicalToPathMap(this.newTemplate));

packages/@aws-cdk/tmp-toolkit-helpers/test/api/diff/diff.test.ts

@@ -55,7 +55,7 @@ describe('formatStackDiff', () => {
     } as any;
   });
 
-  test('returns no changes when templates are identical', () => {
+  test('returns no differences when templates are identical', () => {
     // WHEN
     const formatter = new DiffFormatter({
       ioHelper: mockIoHelper,
@@ -76,8 +76,12 @@ describe('formatStackDiff', () => {
 
     // THEN
     expect(result.numStacksWithChanges).toBe(0);
-    expect(result.formattedDiff).toBe('');
-    expect(mockIoDefaultMessages.info).toHaveBeenCalledWith(expect.stringContaining('no differences'));
+    expect(result.formattedDiff).toBeDefined();
+    const sanitizedDiff = result.formattedDiff!.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '').trim();
+    expect(sanitizedDiff).toBe(
+      'Stack test-stack\n' +
+      'There were no differences',
+    );
   });
 
   test('formats differences when changes exist', () => {
@@ -256,6 +260,7 @@ describe('formatSecurityDiff', () => {
     expect(result.formattedDiff).toBeDefined();
     const sanitizedDiff = result.formattedDiff!.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '').trim();
     expect(sanitizedDiff).toBe(
+      'Stack test-stack\n' +
       'IAM Statement Changes\n' +
       '┌───┬─────────────┬────────┬────────────────┬──────────────────────────────┬───────────┐\n' +
       '│   │ Resource    │ Effect │ Action         │ Principal                    │ Condition │\n' +
@@ -291,6 +296,7 @@ describe('formatSecurityDiff', () => {
     );
     const sanitizedDiff = result.formattedDiff!.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '').trim();
     expect(sanitizedDiff).toBe(
+      'Stack test-stack\n' +
       'IAM Statement Changes\n' +
       '┌───┬─────────────┬────────┬────────────────┬──────────────────────────────┬───────────┐\n' +
       '│   │ Resource    │ Effect │ Action         │ Principal                    │ Condition │\n' +

packages/aws-cdk/test/commands/diff.test.ts

@@ -865,7 +865,7 @@ describe('nested stacks', () => {
     });
 
     // THEN
-    const plainTextOutput = notifySpy.mock.calls[1][0].message.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '').replace(/[ \t]+$/gm, '');
+    const plainTextOutput = notifySpy.mock.calls[0][0].message.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '').replace(/[ \t]+$/gm, '');
     expect(plainTextOutput.trim()).toEqual(`Stack Parent
 Resources
 [~] AWS::CloudFormation::Stack AdditionChild
@@ -906,7 +906,10 @@ Resources
 
 Stack newGrandChild
 Resources
-[+] AWS::Something SomeResource`);
+[+] AWS::Something SomeResource
+
+Stack UnChangedChild
+There were no differences`);
 
     expect(notifySpy).toHaveBeenCalledWith(expect.objectContaining({
       message: expect.stringContaining('✨  Number of stacks with differences: 6'),
@@ -926,7 +929,7 @@ Resources
     });
 
     // THEN
-    const plainTextOutput = notifySpy.mock.calls[2][0].message.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '').replace(/[ \t]+$/gm, '');
+    const plainTextOutput = notifySpy.mock.calls[1][0].message.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '').replace(/[ \t]+$/gm, '');
     expect(plainTextOutput.trim()).toEqual(`Stack Parent
 Resources
 [~] AWS::CloudFormation::Stack AdditionChild
@@ -967,7 +970,10 @@ Resources
 
 Stack newGrandChild
 Resources
-[+] AWS::Something SomeResource`);
+[+] AWS::Something SomeResource
+
+Stack UnChangedChild
+There were no differences`);
 
     expect(notifySpy).toHaveBeenCalledWith(expect.objectContaining({
       message: expect.stringContaining('✨  Number of stacks with differences: 6'),