Schedule Merge Queue builds

app_dart/.gitignore

@@ -4,3 +4,5 @@
 
 # Conventional directory for build output.
 build/
+
+coverage/

app_dart/lib/src/request_handlers/github/webhook_subscription.dart

@@ -224,6 +224,7 @@ class GithubWebhookSubscription extends SubscriptionHandler {
     final mergeGroupEvent = MergeGroupEvent.fromJson(request);
     final MergeGroupEvent(:mergeGroup, :action) = mergeGroupEvent;
     final headSha = mergeGroup.headSha;
+    final slug = mergeGroupEvent.repository!.slug();
 
     // See the API reference:
     // https://docs.github.com/en/webhooks/webhook-events-and-payloads#merge_group
@@ -234,24 +235,33 @@ class GithubWebhookSubscription extends SubscriptionHandler {
       // into the main branch. Cocoon should kick off CI jobs needed to verify
       // the PR group.
       case 'checks_requested':
-        log.fine('Simulating checks requests for merge queue @ $headSha');
+        log.fine('Checks requests for merge queue @ $headSha');
+
+        if (!await _shaExistsInGob(slug, headSha)) {
+          throw InternalServerError(
+            '$slug/$headSha was not found on GoB. Failing so this event can be retried',
+          );
+        }
+        log.fine('$slug/$headSha was found on GoB mirror. Scheduling merge group tasks');
         await scheduler.triggerMergeGroupTargets(mergeGroupEvent: mergeGroupEvent);
-        break;
 
       // A merge group was deleted. This can happen when a PR is pulled from the
       // merge queue. All CI jobs pertaining to this merge group should be
       // stopped to save CI resources, as Github will no longer merge this group
       // into the main branch.
       case 'destroyed':
-        log.fine('Simulating destruction of a merge group @ $headSha');
+        log.fine('Merge group destroyed for $slug/$headSha');
         await scheduler.cancelMergeGroupTargets(headSha: headSha);
-        break;
     }
   }
 
   Future<bool> _commitExistsInGob(PullRequest pr) async {
     final RepositorySlug slug = pr.base!.repo!.slug();
     final String sha = pr.mergeCommitSha!;
+    return _shaExistsInGob(slug, sha);
+  }
+
+  Future<bool> _shaExistsInGob(RepositorySlug slug, String sha) async {
     final GerritCommit? gobCommit = await gerritService.findMirroredCommit(slug, sha);
     return gobCommit != null;
   }

app_dart/lib/src/service/luci_build_service.dart

@@ -774,6 +774,63 @@ class LuciBuildService {
     return <Tuple<Target, Task, int>>[];
   }
 
+  /// Schedules [targets] for building of prod artifacts while in a merge queue.
+  Future<void> scheduleMergeGroupBuilds({
+    required Commit commit,
+    required List<Target> targets,
+  }) async {
+    final buildRequests = <bbv2.BatchRequest_Request>[];
+
+    final Set<String> availableBuilderSet;
+    try {
+      availableBuilderSet = await getAvailableBuilderSet(
+        project: 'flutter',
+        bucket: 'prod',
+      );
+    } catch (error) {
+      log.warning('Failed to get buildbucket builder list', error);
+      throw 'Failed to get buildbucket builder list due to $error';
+    }
+    log.info('Available builder list: $availableBuilderSet');
+    for (var target in targets) {
+      // Non-existing builder target will be skipped from scheduling.
+      if (!availableBuilderSet.contains(target.value.name)) {
+        log.warning(
+          'Found no available builder for ${target.value.name}, commit ${commit.sha}',
+        );
+        continue;
+      }
+      log.info(
+        'create postsubmit schedule request for target: ${target.value} in commit ${commit.sha}',
+      );
+
+      final scheduleBuildRequest = await _createMergeGroupScheduleBuild(
+        commit: commit,
+        target: target,
+      );
+      buildRequests.add(bbv2.BatchRequest_Request(scheduleBuild: scheduleBuildRequest));
+      log.info(
+        'created postsubmit schedule request for target: ${target.value} in commit ${commit.sha}',
+      );
+    }
+
+    final batchRequest = bbv2.BatchRequest(requests: buildRequests);
+    log.fine(batchRequest);
+    final List<String> messageIds;
+
+    try {
+      messageIds = await pubsub.publish(
+        'cocoon-scheduler-requests',
+        batchRequest.toProto3Json(),
+      );
+      log.info('Published $messageIds for commit ${commit.sha}');
+    } catch (error) {
+      log.severe('Failed to publish message to pub/sub due to $error');
+      rethrow;
+    }
+    log.info('Published a request with ${buildRequests.length} builds');
+  }
+
   /// Create a Presubmit ScheduleBuildRequest using the [slug], [sha], and
   /// [checkName] for the provided [build] with the provided [checkRunId].
   bbv2.ScheduleBuildRequest _createPresubmitScheduleBuild({
@@ -991,15 +1048,102 @@ class LuciBuildService {
     );
   }
 
+  /// Creates a build request for a commit in a merge queue which will notify
+  /// presubmit channels.
+  Future<bbv2.ScheduleBuildRequest> _createMergeGroupScheduleBuild({
+    required Commit commit,
+    required Target target,
+    int priority = kDefaultPriority,
+  }) async {
+    log.info(
+      'Creating merge group schedule builder for ${target.value.name} on commit ${commit.sha}',
+    );
+    final tags = <bbv2.StringPair>[];
+    tags.addAll([
+      bbv2.StringPair(
+        key: 'buildset',
+        value: 'commit/git/${commit.sha}',
+      ),
+      bbv2.StringPair(
+        key: 'buildset',
+        value: 'commit/gitiles/flutter.googlesource.com/mirrors/${commit.slug.name}/+/${commit.sha}',
+      ),
+      bbv2.StringPair(
+        key: 'user_agent',
+        value: 'flutter-cocoon',
+      ),
+      bbv2.StringPair(
+        key: 'scheduler_job_id',
+        value: 'flutter/${target.value.name}',
+      ),
+      bbv2.StringPair(
+        key: 'current_attempt',
+        value: '1',
+      ),
+    ]);
+
+    log.info(
+      'Scheduling builder: ${target.value.name} for commit ${commit.sha}',
+    );
+
+    final rawUserData = <String, dynamic>{};
+
+    await createPostsubmitCheckRun(
+      commit,
+      target,
+      rawUserData,
+    );
+
+    final processedProperties = target.getProperties().cast<String, Object?>();
+    processedProperties['git_branch'] = commit.branch!;
+    final cipdExe = 'refs/heads/${commit.branch}';
+    processedProperties['exe_cipd_version'] = cipdExe;
+    processedProperties['is_fusion'] = 'true';
+
+    final propertiesStruct = bbv2.Struct()..mergeFromProto3Json(processedProperties);
+    final requestedDimensions = target.getDimensions();
+    final executable = bbv2.Executable(cipdVersion: cipdExe);
+
+    log.info(
+      'Constructing the merge group schedule build request for ${target.value.name} on commit ${commit.sha}.',
+    );
+
+    return bbv2.ScheduleBuildRequest(
+      builder: bbv2.BuilderID(
+        project: 'flutter',
+        bucket: target.getBucket(),
+        builder: target.value.name,
+      ),
+      dimensions: requestedDimensions,
+      exe: executable,
+      gitilesCommit: bbv2.GitilesCommit(
+        project: 'mirrors/${commit.slug.name}',
+        host: 'flutter.googlesource.com',
+        ref: 'refs/heads/${commit.branch}',
+        id: commit.sha,
+      ),
+      notify: bbv2.NotificationConfig(
+        // IMPORTANT: We're not post-submit yet, so we want to handle updates to
+        // the MQ differently.
+        pubsubTopic: 'projects/flutter-dashboard/topics/build-bucket-presubmit',
+        userData: UserData.encodeUserDataToBytes(rawUserData),
+      ),
+      tags: tags,
+      properties: propertiesStruct,
+      priority: priority,
+    );
+  }
+
   /// Creates postsubmit check runs for prod targets in supported repositories.
   Future<void> createPostsubmitCheckRun(
     Commit commit,
     Target target,
     Map<String, dynamic> rawUserData,
   ) async {
     // We are not tracking this check run in the PrCheckRuns firestore doc because
-    // there is no PR to track here.
-    final github.CheckRun checkRun = await githubChecksUtil.createCheckRun(
+    // there is no PR to look up later. The check run is important because it
+    // informs the staging document setup for Merge Groups in triggerMergeGroupTargets.
+    final checkRun = await githubChecksUtil.createCheckRun(
       config,
       target.slug,
       commit.sha!,