fix(cdk): cdk diff --quiet to print stack name when there is diffs

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

@@ -1,5 +1,6 @@
 import * as path from 'path';
 import { format } from 'util';
+import * as cfnDiff from '@aws-cdk/cloudformation-diff';
 import * as cxapi from '@aws-cdk/cx-api';
 import * as chalk from 'chalk';
 import * as chokidar from 'chokidar';
@@ -153,10 +154,6 @@ export class CdkToolkit {
     } else {
       // Compare N stacks against deployed templates
       for (const stack of stacks.stackArtifacts) {
-        if (!quiet) {
-          stream.write(format('Stack %s\n', chalk.bold(stack.displayName)));
-        }
-
         const templateWithNames = await this.props.deployments.readCurrentTemplateWithNestedStacks(
           stack, options.compareAgainstProcessedTemplate,
         );
@@ -179,14 +176,19 @@ export class CdkToolkit {
           stream,
         }) : undefined;
 
+        const diff = cfnDiff.fullDiff(currentTemplate, stack.template, changeSet);
+        if (!quiet || !diff.isEmpty) {
+          stream.write(format('Stack %s\n', chalk.bold(stack.displayName)));
+        }
+
         if (resourcesToImport) {
           stream.write('Parameters and rules created during migration do not affect resource configuration.\n');
         }
 
         const stackCount =
         options.securityOnly
-          ? (numberFromBool(printSecurityDiff(currentTemplate, stack, RequireApproval.Broadening, changeSet)) > 0 ? 1 : 0)
-          : (printStackDiff(currentTemplate, stack, strict, contextLines, quiet, changeSet, stream) > 0 ? 1 : 0);
+          ? (numberFromBool(printSecurityDiff(currentTemplate, stack, RequireApproval.Broadening, changeSet, diff)) > 0 ? 1 : 0)
+          : (printStackDiff(currentTemplate, stack, strict, contextLines, quiet, changeSet, stream, diff) > 0 ? 1 : 0);
 
         diffs += stackCount + nestedStackCount;
       }

packages/aws-cdk/lib/diff.ts

@@ -23,9 +23,10 @@ export function printStackDiff(
   context: number,
   quiet: boolean,
   changeSet?: CloudFormation.DescribeChangeSetOutput,
-  stream?: cfnDiff.FormatStream): number {
+  stream?: cfnDiff.FormatStream,
+  stackDiff?: cfnDiff.TemplateDiff): number {
 
-  let diff = cfnDiff.fullDiff(oldTemplate, newTemplate.template, changeSet);
+  let diff = stackDiff ?? cfnDiff.fullDiff(oldTemplate, newTemplate.template, changeSet);
 
   // detect and filter out mangled characters from the diff
   let filteredChangesCount = 0;
@@ -81,8 +82,9 @@ export function printSecurityDiff(
   newTemplate: cxapi.CloudFormationStackArtifact,
   requireApproval: RequireApproval,
   changeSet?: CloudFormation.DescribeChangeSetOutput,
+  stackDiff?: cfnDiff.TemplateDiff,
 ): boolean {
-  const diff = cfnDiff.fullDiff(oldTemplate, newTemplate.template, changeSet);
+  const diff = stackDiff ?? cfnDiff.fullDiff(oldTemplate, newTemplate.template, changeSet);
 
   if (difRequiresApproval(diff, requireApproval)) {
     // eslint-disable-next-line max-len

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

@@ -281,15 +281,37 @@ describe('non-nested stacks', () => {
 
     // WHEN
     const exitCode = await toolkit.diff({
-      stackNames: ['A', 'A'],
+      stackNames: ['D'],
       stream: buffer,
       fail: false,
       quiet: true,
     });
 
     // THEN
-    expect(buffer.data.trim()).not.toContain('Stack A');
-    expect(buffer.data.trim()).not.toContain('There were no differences');
+    const plainTextOutput = buffer.data.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '');
+    expect(plainTextOutput).not.toContain('Stack D');
+    expect(plainTextOutput).not.toContain('There were no differences');
+    expect(buffer.data.trim()).toContain('✨  Number of stacks with differences: 0');
+    expect(exitCode).toBe(0);
+  });
+
+  test('when quiet mode is enabled, stacks with diffs should print stack name to stdout', async () => {
+    // GIVEN
+    const buffer = new StringWritable();
+
+    // WHEN
+    const exitCode = await toolkit.diff({
+      stackNames: ['A'],
+      stream: buffer,
+      fail: false,
+      quiet: true,
+    });
+
+    // THEN
+    const plainTextOutput = buffer.data.replace(/\x1B\[[0-?]*[ -/]*[@-~]/g, '');
+    expect(plainTextOutput).toContain('Stack A');
+    expect(plainTextOutput).not.toContain('There were no differences');
+    expect(buffer.data.trim()).toContain('✨  Number of stacks with differences: 1');
     expect(exitCode).toBe(0);
   });
 });