feat: Add a new input flag to avoid commenting on stacks that have not changed.

README.md

@@ -135,3 +135,20 @@ jobs:
           failOnDestructiveChanges: false
           githubToken: ${{ secrets.GITHUB_TOKEN }}
 ```
+
+### Hide comments for unchanged stages
+
+If you want to prevent unnecessary comments by hiding comments for stacks that
+have not changed, you can enable this feature.  This defaults to off, showing
+comments for all stacks.
+
+```yml
+jobs:
+  Synth:
+    steps:
+      - name: Diff
+        uses: corymhall/cdk-diff-action@v1
+        with:
+          ignoreUnchangedStacks: true
+          githubToken: ${{ secrets.GITHUB_TOKEN }}
+```

src/action.ts

@@ -13,6 +13,7 @@ export async function run() {
     noDiffForStages: getInput('noDiffForStages').split(','),
     noFailOnDestructiveChanges: getInput('noFailOnDestructiveChanges').split(','),
     cdkOutDir: getInput('cdkOutDir') ?? 'cdk.out',
+    ignoreUnchangedStacks: getBooleanInput('ignoreUnchangedStacks')
   };
   const octokit = github.getOctokit(inputs.githubToken);
   const context = github.context;
@@ -26,7 +27,7 @@ export async function run() {
       });
     }
     const comments = new Comments(octokit, context);
-    const processor = new StageProcessor(stages, inputs.allowedDestroyTypes);
+    const processor = new StageProcessor(stages, inputs.allowedDestroyTypes, inputs.ignoreUnchangedStacks);
     try {
       await processor.processStages(inputs.noFailOnDestructiveChanges);
     } catch (e: any) {

src/inputs.ts

@@ -43,4 +43,11 @@ export interface Inputs {
    * @default cdk.out
    */
   cdkOutDir: string;
+
+  /**
+   * Whether the workflow will comment for unchanged stacks
+   *
+   * @default - comment for unchanged stacks
+   */
+  ignoreUnchangedStacks: boolean;
 }

src/stage-processor.ts

@@ -40,6 +40,7 @@ export class StageProcessor {
   constructor(
     private readonly stages: StageInfo[],
     private readonly allowedDestroyTypes: string[],
+    private readonly ignoreUnchangedStacks: boolean,
   ) {
     this.stages.forEach(stage => {
       this.stageComments[stage.name] = {
@@ -72,10 +73,12 @@ export class StageProcessor {
     for (const stage of this.stages) {
       for (const stack of stage.stacks) {
         try {
-          const { comment, changes } = await this.diffStack(stack);
-          this.stageComments[stage.name].stackComments[stack.name].push(...comment);
+          const { comment, destructiveChanges, anyChanges } = await this.diffStack(stack);
+          if (anyChanges || !this.ignoreUnchangedStacks) {
+            this.stageComments[stage.name].stackComments[stack.name].push(...comment);
+          }
           if (!ignoreDestructiveChanges.includes(stage.name)) {
-            this.stageComments[stage.name].destructiveChanges += changes;
+            this.stageComments[stage.name].destructiveChanges += destructiveChanges;
           }
         } catch (e: any) {
           console.error('Error processing stages: ', e);
@@ -93,6 +96,9 @@ export class StageProcessor {
           stackName,
         }));
         const stackComment = this.getCommentForStack(stageName, stackName, comment);
+        if (stackComment.length == 0) {
+          continue;
+        }
         if (stackComment.join('\n').length > MAX_COMMENT_LENGTH) {
           throw new Error(`Comment for stack ${stackName} is too long, please report this as a bug https://github.com/corymhall/cdk-diff-action/issues/new`);
         }
@@ -145,13 +151,14 @@ export class StageProcessor {
     return false;
   }
 
-  private async diffStack(stack: StackInfo): Promise<{comment: string[]; changes: number}> {
+  private async diffStack(stack: StackInfo): Promise<{comment: string[]; destructiveChanges: number, anyChanges: boolean}> {
     try {
       const stackDiff = new StackDiff(stack, this.allowedDestroyTypes);
       const { diff, changes } = await stackDiff.diffStack();
       return {
         comment: this.formatStackComment(stack.name, diff, changes),
-        changes: changes.destructiveChanges.length,
+        destructiveChanges: changes.destructiveChanges.length,
+        anyChanges: changes.destructiveChanges.length > 0 || changes.removedResources > 0 || changes.updatedResources > 0 || changes.createdResources > 0,
       };
 
     } catch (e: any) {

test/stage-processor.test.ts

@@ -69,7 +69,7 @@ describe('StageProcessor', () => {
         name: 'Stage1',
         stacks: [stackInfo],
       },
-    ], []);
+    ], [], false);
     await processor.processStages();
     const p = (processor as any).stageComments;
     expect(p).toEqual({
@@ -78,6 +78,27 @@ describe('StageProcessor', () => {
     expect(p.Stage1.stackComments['my-stack']).toEqual(['No Changes for stack: my-stack :white_check_mark:']);
   });
 
+  test('stage with no diffs and ignored', async () => {
+    cfnMock.on(GetTemplateCommand)
+        .resolves({
+          TemplateBody: JSON.stringify(stackInfo.content),
+        });
+    const processor = new StageProcessor([
+      {
+        name: 'Stage1',
+        stacks: [stackInfo],
+      },
+    ], [], true);
+    await processor.processStages();
+    const p = (processor as any).stageComments;
+    expect(p).toEqual({
+      Stage1: expect.any(Object),
+    });
+    expect(p.Stage1.stackComments['my-stack']).toEqual([]);
+    expect(createCommentMock).toHaveBeenCalledTimes(0);
+    expect(updateCommentMock).toHaveBeenCalledTimes(0);
+  });
+
   test('stage with diff', async () => {
     cfnMock.on(GetTemplateCommand)
       .resolves({
@@ -101,7 +122,7 @@ describe('StageProcessor', () => {
           },
         }],
       },
-    ], []);
+    ], [], false);
     await processor.processStages();
     const p = (processor as any).stageComments;
     expect(p).toEqual({
@@ -134,7 +155,7 @@ describe('StageProcessor', () => {
           },
         }],
       },
-    ], []);
+    ], [], false);
     await processor.processStages(['Stage1']);
     const p = (processor as any).stageComments;
     expect(p).toEqual({
@@ -167,7 +188,7 @@ describe('StageProcessor', () => {
           },
         }],
       },
-    ], []);
+    ], [], false);
     await processor.processStages(['Stage1']);
     await processor.commentStages(new Comments({} as any, {} as any));
     expect(createCommentMock).toHaveBeenCalledTimes(1);
@@ -198,7 +219,7 @@ describe('StageProcessor', () => {
           },
         }],
       },
-    ], []);
+    ], [], false);
     findPreviousMock.mockResolvedValue(1);
     await processor.processStages(['Stage1']);
     await processor.commentStages(new Comments({} as any, {} as any));
@@ -231,7 +252,7 @@ describe('StageProcessor', () => {
         name: 'Stage1',
         stacks: createStacks(10),
       },
-    ], []);
+    ], [], false);
     findPreviousMock.mockResolvedValue(1);
     await processor.processStages(['Stage1']);
     await processor.commentStages(new Comments({} as any, {} as any));