feat: allow previously merged PRs, but block automerge

lib/workers/repository/update/branch/index.spec.ts

@@ -289,6 +289,21 @@ describe('workers/repository/update/branch/index', () => {
       expect(scm.deleteBranch).toHaveBeenCalledTimes(1);
     });
 
+    it('allows branch but disables automerge if merged PR found', async () => {
+      schedule.isScheduledNow.mockReturnValueOnce(false);
+      scm.branchExists.mockResolvedValue(true);
+      config.automerge = true;
+      config.updateType = 'digest';
+      checkExisting.prAlreadyExisted.mockResolvedValueOnce(
+        partial<Pr>({
+          number: 13,
+          state: 'merged',
+        })
+      );
+      await branchWorker.processBranch(config);
+      expect(reuse.shouldReuseExistingBranch).toHaveBeenCalledTimes(0);
+    });
+
     it('skips branch if closed minor PR found', async () => {
       schedule.isScheduledNow.mockReturnValueOnce(false);
       scm.branchExists.mockResolvedValue(true);

lib/workers/repository/update/branch/index.ts

@@ -113,8 +113,19 @@ export async function processBranch(
   const artifactErrorTopic = emojify(':warning: Artifact update problem');
   try {
     // Check if branch already existed
-    const existingPr = branchPr ? undefined : await prAlreadyExisted(config);
-    if (existingPr && !dependencyDashboardCheck) {
+    const existingPr =
+      !branchPr || config.automerge
+        ? await prAlreadyExisted(config)
+        : undefined;
+    if (existingPr?.state === 'merged') {
+      logger.debug(`Matching PR #${existingPr.number} was merged previously`);
+      if (config.automerge) {
+        logger.debug('Disabling automerge because PR was merged previously');
+        config.automerge = false;
+        config.automergedPreviously = true;
+      }
+    }
+    if (!branchPr && existingPr && !dependencyDashboardCheck) {
       logger.debug(
         { prTitle: config.prTitle },
         'Closed PR already exists. Skipping branch.'

lib/workers/repository/update/pr/body/config-description.spec.ts

@@ -87,5 +87,15 @@ describe('workers/repository/update/pr/body/config-description', () => {
       const res = getPrConfigDescription({ ...config, automerge: true });
       expect(res).toContain(`**Automerge**: Enabled.`);
     });
+
+    it('renders blocked automerge', () => {
+      const res = getPrConfigDescription({
+        ...config,
+        automergedPreviously: true,
+      });
+      expect(res).toContain(
+        `**Automerge**: Disabled because a matching PR was automerged previously.`
+      );
+    });
   });
 });

lib/workers/repository/update/pr/body/config-description.ts

@@ -15,6 +15,8 @@ export function getPrConfigDescription(config: BranchConfig): string {
   prBody += emojify(':vertical_traffic_light: **Automerge**: ');
   if (config.automerge) {
     prBody += 'Enabled.';
+  } else if (config.automergedPreviously) {
+    prBody += 'Disabled because a matching PR was automerged previously.';
   } else {
     prBody +=
       'Disabled by config. Please merge this manually once you are satisfied.';

lib/workers/types.ts

@@ -111,6 +111,7 @@ export interface BranchConfig
     PlatformPrOptions {
   automergeComment?: string;
   automergeType?: string;
+  automergedPreviously?: boolean;
   baseBranch: string;
   errors?: ValidationMessage[];
   hasTypes?: boolean;