Experimental backfill for ios-experimental branch.

app_dart/lib/src/request_handlers/scheduler/backfill_grid.dart

@@ -200,6 +200,17 @@ final class BackfillTask {
   /// The LUCI scheduling priority of backfilling this task.
   final int priority;
 
+  /// Creates a copy of `this` with the provided properties replaced.
+  @useResult
+  BackfillTask copyWith({int? priority}) {
+    return BackfillTask._from(
+      task,
+      target: target,
+      commit: commit,
+      priority: priority ?? this.priority,
+    );
+  }
+
   @override
   String toString() {
     return 'BackfillTask ${const JsonEncoder.withIndent('  ').convert({

app_dart/lib/src/request_handlers/scheduler/batch_backfiller.dart

@@ -51,9 +51,26 @@ final class BatchBackfiller extends RequestHandler {
   Future<Response> get(Request request) async {
     await _backfillReleaseBranch(Config.flutterSlug);
     await Future.forEach(config.supportedRepos, _backfillDefaultBranch);
+    await _backfillExperimentalBranch(Config.flutterSlug);
     return Response.emptyOk;
   }
 
+  // TODO(matanlurey): Remove or make a formal supported feature.
+  //
+  // Hardcodes running a branch named `ios-experimental`, which is being tried
+  // by the iOS team to do MacOS 15.5 validation. It will appear similar to
+  // any other branch, but use lower-priority scheduling.
+  //
+  // See https://github.com/flutter/flutter/issues/168738.
+  Future<void> _backfillExperimentalBranch(RepositorySlug slug) async {
+    final fsGrid = await _firestore.queryRecentCommitsAndTasks(
+      slug,
+      commitLimit: config.backfillerCommitLimit,
+      branch: 'ios-experimental',
+    );
+    await _doBackfillFrom(slug, fsGrid, forceLowPriority: true);
+  }
+
   Future<void> _backfillReleaseBranch(RepositorySlug slug) async {
     log.debug('Running release branch backfiller for "$slug"');
     final branches = await _branchService.getReleaseBranches(slug: slug);
@@ -82,8 +99,9 @@ final class BatchBackfiller extends RequestHandler {
 
   Future<void> _doBackfillFrom(
     RepositorySlug slug,
-    List<CommitAndTasks> fsGrid,
-  ) async {
+    List<CommitAndTasks> fsGrid, {
+    bool forceLowPriority = false,
+  }) async {
     if (fsGrid.isEmpty) {
       log.warn('No commits to backfill');
       return;
@@ -141,6 +159,15 @@ final class BatchBackfiller extends RequestHandler {
       'Backfilling ${toBackfillTasks.length} tasks (pruned from $beforePruning)',
     );
 
+    if (forceLowPriority) {
+      log.debug('Overriding ${toBackfillTasks.length} tasks to low priority');
+      for (var i = 0; i < toBackfillTasks.length; i++) {
+        toBackfillTasks[i] = toBackfillTasks[i].copyWith(
+          priority: LuciBuildService.kBackfillPriority,
+        );
+      }
+    }
+
     // Update the database first before we schedule builds.
     await _updateFirestore(toBackfillTasks, grid.skippableTasks);
     log.info('Wrote updates to ${toBackfillTasks.length} tasks for backfill');

app_dart/test/request_handlers/scheduler/backfill_grid_test.dart

@@ -162,4 +162,26 @@ void main() {
       ]),
     );
   });
+
+  test('can override BackfillTask priority after creation', () {
+    final commit = generateFirestoreCommit(1).toRef();
+    final task = generateFirestoreTask(2, commitSha: commit.sha).toRef();
+    final target = generateTarget(1, name: task.name);
+
+    final grid = BackfillGrid.from(
+      [
+        (commit, [task]),
+      ],
+      tipOfTreeTargets: [target],
+    );
+
+    expect(
+      grid.createBackfillTask(task, priority: 1001).copyWith(priority: 1002),
+      isBackfillTask
+          .hasTask(task)
+          .hasTarget(target)
+          .hasCommit(commit)
+          .hasPriority(1002),
+    );
+  });
 }

app_dart/test/request_handlers/scheduler/batch_backfiller_test.dart

@@ -5,22 +5,22 @@
 import 'package:cocoon_common/rpc_model.dart' as rpc;
 import 'package:cocoon_common/task_status.dart';
 import 'package:cocoon_server_test/test_logging.dart';
+import 'package:cocoon_service/src/model/commit_ref.dart';
 import 'package:cocoon_service/src/request_handlers/scheduler/backfill_grid.dart';
 import 'package:cocoon_service/src/request_handlers/scheduler/backfill_strategy.dart';
 import 'package:cocoon_service/src/request_handlers/scheduler/batch_backfiller.dart';
 import 'package:cocoon_service/src/service/config.dart';
 import 'package:cocoon_service/src/service/luci_build_service.dart';
+import 'package:cocoon_service/src/service/luci_build_service/pending_task.dart';
 import 'package:collection/collection.dart';
 import 'package:github/github.dart';
 import 'package:mockito/mockito.dart';
 import 'package:test/test.dart';
 
 import '../../src/fake_config.dart';
-import '../../src/request_handling/fake_pubsub.dart';
 import '../../src/request_handling/request_handler_tester.dart';
 import '../../src/service/fake_ci_yaml_fetcher.dart';
 import '../../src/service/fake_firestore_service.dart';
-import '../../src/service/fake_luci_build_service.dart';
 import '../../src/utilities/entity_generators.dart';
 import '../../src/utilities/mocks.mocks.dart';
 
@@ -31,11 +31,10 @@ void main() {
   late BatchBackfiller handler;
 
   // Dependencies.
-  late FakePubSub pubSub;
-  late MockGithubChecksUtil mockGithubChecksUtil;
   late FakeConfig config;
   late FakeFirestoreService firestore;
   late FakeCiYamlFetcher ciYamlFetcher;
+  late _FakeLuciBuildService fakeLuciBuildService;
 
   // Used to implement BranchService.getBranches.
   late List<rpc.Branch>? branchesForRepository;
@@ -44,22 +43,14 @@ void main() {
   late RequestHandlerTester tester;
 
   setUp(() {
-    pubSub = FakePubSub();
-    mockGithubChecksUtil = MockGithubChecksUtil();
     firestore = FakeFirestoreService();
     config = FakeConfig(
       backfillerCommitLimitValue: 10,
       backfillerTargetLimitValue: 100,
       supportedReposValue: {Config.flutterSlug},
     );
     ciYamlFetcher = FakeCiYamlFetcher();
-
-    final luciBuildService = FakeLuciBuildService(
-      config: config,
-      pubsub: pubSub,
-      githubChecksUtil: mockGithubChecksUtil,
-      firestore: firestore,
-    );
+    fakeLuciBuildService = _FakeLuciBuildService();
 
     final branchService = MockBranchService();
     branchesForRepository = [];
@@ -79,7 +70,7 @@ void main() {
     handler = BatchBackfiller(
       config: config,
       ciYamlFetcher: ciYamlFetcher,
-      luciBuildService: luciBuildService,
+      luciBuildService: fakeLuciBuildService,
       backfillerStrategy: const _NaiveBackfillStrategy(),
       firestore: firestore,
       branchService: branchService,
@@ -362,6 +353,59 @@ void main() {
     ]);
     // dart format on
   });
+
+  // https://github.com/flutter/flutter/issues/168738
+  test('schedules low-priority targets for "ios-experimental"', () async {
+    branchesForRepository = [
+      // Intentionally left blank.
+    ];
+
+    // dart format off
+    await fillStorageAndSetCiYaml([
+      [$N, $I, $F, $S],
+      [$N, $N, $N, $N],
+    ], branch: 'ios-experimental');
+    // dart format on
+
+    // BEFORE:
+    expect(
+      await visualizeFirestoreGrid(commits: 2, branch: 'ios-experimental'),
+      // dart format off
+      [
+      '🧑‍💼 ⬜ 🟨 🟥 🟩',
+      '🧑‍💼 ⬜ ⬜ ⬜ ⬜',
+      ],
+      // dart format on
+    );
+
+    await tester.get(handler);
+
+    // AFTER:
+    expect(
+      await visualizeFirestoreGrid(commits: 2, branch: 'ios-experimental'),
+      // dart format off
+      [
+      '🧑‍💼 🟨 🟨 🟥 🟩',
+      '🧑‍💼 ⬜ 🟨 🟨 🟨',
+      ],
+      // dart format on
+    );
+
+    expect(
+      fakeLuciBuildService.scheduledPostsubmitBuilds,
+      allOf(
+        hasLength(4),
+        everyElement(
+          isA<PendingTask>().having(
+            (t) => t.priority,
+            'priority',
+            LuciBuildService.kBackfillPriority,
+          ),
+        ),
+      ),
+      reason: 'Should use a low priority for all executions',
+    );
+  });
 }
 
 /// A very hermetic but dumb backfilling algorithm.
@@ -385,3 +429,16 @@ final class _NaiveBackfillStrategy extends BackfillStrategy {
     ];
   }
 }
+
+final class _FakeLuciBuildService extends Fake implements LuciBuildService {
+  final scheduledPostsubmitBuilds = <PendingTask>[];
+
+  @override
+  Future<List<PendingTask>> schedulePostsubmitBuilds({
+    required CommitRef commit,
+    required List<PendingTask> toBeScheduled,
+  }) async {
+    scheduledPostsubmitBuilds.addAll(toBeScheduled);
+    return [];
+  }
+}