Add a feature that allows treating presubmit: false as true, conditionally. (#3256)

Closes flutter/flutter#138430 and I believe flutter/flutter#111418.

As @CaseyHillers mentions in flutter/flutter#138430, this would _not_ be sufficient to understand the addition of a label (only if the PR is _first created_ with a label, or a commit is pushed after the label is added), but it might be worth merging as-is (assuming I got all of the assumptions correct).

Author: matanlurey

app_dart/lib/src/service/scheduler.dart

@@ -436,10 +436,25 @@ class Scheduler {
     log.info('Collecting presubmit targets for ${pullRequest.number}');
 
     // Filter out schedulers targets with schedulers different than luci or cocoon.
-    final Iterable<Target> presubmitTargets = ciYaml.presubmitTargets.where(
-      (Target target) =>
-          target.value.scheduler == pb.SchedulerSystem.luci || target.value.scheduler == pb.SchedulerSystem.cocoon,
-    );
+    final List<Target> presubmitTargets = ciYaml.presubmitTargets
+        .where(
+          (Target target) =>
+              target.value.scheduler == pb.SchedulerSystem.luci || target.value.scheduler == pb.SchedulerSystem.cocoon,
+        )
+        .toList();
+
+    // See https://github.com/flutter/flutter/issues/138430.
+    if (_includePostsubmitAsPresubmit(ciYaml, pullRequest)) {
+      log.info('Including postsubmit targets as presubmit for ${pullRequest.number}');
+
+      for (Target target in ciYaml.postsubmitTargets) {
+        // We don't want to include a presubmit twice
+        // We don't want to run the builder_cache target as a presubmit
+        if (!target.value.presubmit && !target.value.properties.containsKey('cache_name')) {
+          presubmitTargets.add(target);
+        }
+      }
+    }
 
     log.info('Collected ${presubmitTargets.length} presubmit targets.');
     // Release branches should run every test.
@@ -462,6 +477,19 @@ class Scheduler {
     return getTargetsToRun(presubmitTargets, files);
   }
 
+  /// Returns `true` if [ciYaml.postsubmitTargets] should be ran during presubmit.
+  static bool _includePostsubmitAsPresubmit(CiYaml ciYaml, PullRequest pullRequest) {
+    // Only allow this for flutter/engine.
+    // See https://github.com/flutter/cocoon/pull/3256#issuecomment-1811624351.
+    if (ciYaml.slug != Config.engineSlug) {
+      return false;
+    }
+    if (pullRequest.labels?.any((label) => label.name.contains('test: all')) ?? false) {
+      return true;
+    }
+    return false;
+  }
+
   /// Reschedules a failed build using a [CheckRunEvent]. The CheckRunEvent is
   /// generated when someone clicks the re-run button from a failed build from
   /// the Github UI.

app_dart/test/service/scheduler_test.dart

@@ -690,6 +690,72 @@ targets:
         );
       });
 
+      group('treats postsubmit as presubmit if a label is present', () {
+        final IssueLabel runAllTests = IssueLabel(name: 'test: all');
+        setUp(() async {
+          httpClient = MockClient((http.Request request) async {
+            if (request.url.path.contains('.ci.yaml')) {
+              return http.Response(
+                '''
+  enabled_branches:
+    - master
+  targets:
+    - name: Linux Presubmit
+      presubmit: true
+      scheduler: luci
+    - name: Linux Postsubmit
+      presubmit: false
+      scheduler: luci
+    - name: Linux Cache
+      presubmit: false
+      scheduler: luci
+      properties:
+        cache_name: "builder"
+  ''',
+                200,
+              );
+            }
+            throw Exception('Failed to find ${request.url.path}');
+          });
+        });
+
+        test('with a specific label in the flutter/engine repo', () async {
+          final enginePr = generatePullRequest(
+            labels: <IssueLabel>[runAllTests],
+            repo: Config.engineSlug.name,
+          );
+          final List<Target> presubmitTargets = await scheduler.getPresubmitTargets(enginePr);
+          expect(
+            presubmitTargets.map((Target target) => target.value.name).toList(),
+            <String>['Linux Presubmit', 'Linux Postsubmit'],
+          );
+        });
+
+        test('with a specific label in the flutter/flutter repo', () async {
+          final enginePr = generatePullRequest(
+            labels: <IssueLabel>[runAllTests],
+            repo: Config.flutterSlug.name,
+          );
+          final List<Target> presubmitTargets = await scheduler.getPresubmitTargets(enginePr);
+          expect(
+            presubmitTargets.map((Target target) => target.value.name).toList(),
+            <String>['Linux Presubmit'],
+          );
+        });
+
+        test('without a specific label', () async {
+          final enginePr = generatePullRequest(
+            labels: <IssueLabel>[],
+            repo: Config.engineSlug.name,
+          );
+          final List<Target> presubmitTargets = await scheduler.getPresubmitTargets(enginePr);
+          expect(
+            presubmitTargets.map((Target target) => target.value.name).toList(),
+            (<String>['Linux Presubmit']),
+          );
+        });
+      });
+
       test('checks for release branches', () async {
         const String branch = 'flutter-1.24-candidate.1';
         httpClient = MockClient((http.Request request) async {