[flutter_conductor] ensure release branch point is always tagged (#93082)

dev/conductor/core/lib/src/globals.dart

@@ -8,6 +8,8 @@ import 'proto/conductor_state.pb.dart' as pb;
 
 const String gsutilBinary = 'gsutil.py';
 
+const String kFrameworkDefaultBranch = 'master';
+
 const List<String> kReleaseChannels = <String>[
   'stable',
   'beta',

dev/conductor/core/lib/src/start.dart

@@ -362,26 +362,9 @@ class StartContext {
         framework.upstreamRemote.name, candidateBranch,
         exact: false,
     ))..ensureValid(candidateBranch, incrementLetter);
-    Version nextVersion;
-    if (incrementLetter == 'm') {
-      nextVersion = Version.fromCandidateBranch(candidateBranch);
-    } else {
-      if (incrementLetter == 'z') {
-        if (lastVersion.type == VersionType.stable) {
-          nextVersion = Version.increment(lastVersion, incrementLetter);
-        } else {
-          // This is the first stable release, so hardcode the z as 0
-          nextVersion = Version(
-            x: lastVersion.x,
-            y: lastVersion.y,
-            z: 0,
-            type: VersionType.stable,
-          );
-        }
-      } else {
-        nextVersion = Version.increment(lastVersion, incrementLetter);
-      }
-    }
+    Version nextVersion = calculateNextVersion(lastVersion);
+    nextVersion = await ensureBranchPointTagged(nextVersion, framework);
+
     state.releaseVersion = nextVersion.toString();
 
     final String frameworkHead = await framework.reverseParse('HEAD');
@@ -417,6 +400,54 @@ class StartContext {
     state_import.writeStateToFile(stateFile, state, logs);
   }
 
+  /// Determine this release's version number from the [lastVersion] and the [incrementLetter].
+  Version calculateNextVersion(Version lastVersion) {
+    if (incrementLetter == 'm') {
+      return Version.fromCandidateBranch(candidateBranch);
+    }
+    if (incrementLetter == 'z') {
+      if (lastVersion.type == VersionType.stable) {
+        return Version.increment(lastVersion, incrementLetter);
+      }
+      // This is the first stable release, so hardcode the z as 0
+      return Version(
+          x: lastVersion.x,
+          y: lastVersion.y,
+          z: 0,
+          type: VersionType.stable,
+      );
+    }
+    return Version.increment(lastVersion, incrementLetter);
+  }
+
+  /// Ensures the branch point [candidateBranch] and `master` has a version tag.
+  ///
+  /// This is necessary for version reporting for users on the `master` channel
+  /// to be correct.
+  Future<Version> ensureBranchPointTagged(
+    Version requestedVersion,
+    FrameworkRepository framework,
+  ) async {
+    if (incrementLetter != 'm') {
+      // in this case, there must have been a previous tagged release, so skip
+      // tagging the branch point
+      return requestedVersion;
+    }
+    final String branchPoint = await framework.branchPoint(
+      candidateBranch,
+      kFrameworkDefaultBranch,
+    );
+    stdio.printStatus('Applying the tag $requestedVersion at the branch point $branchPoint');
+    await framework.tag(
+      branchPoint,
+      requestedVersion.toString(),
+      frameworkUpstream,
+    );
+    final Version nextVersion = Version.increment(requestedVersion, 'n');
+    stdio.printStatus('The actual release will be version $nextVersion.');
+    return nextVersion;
+  }
+
   // To minimize merge conflicts, sort the commits by rev-list order.
   Future<List<String>> _sortCherrypicks({
     required Repository repository,

dev/conductor/core/test/start_test.dart

@@ -125,10 +125,14 @@ void main() {
     test('creates state file if provided correct inputs', () async {
       const String revision2 = 'def789';
       const String revision3 = '123abc';
+      const String branchPointRevision='deadbeef';
       const String previousDartRevision = '171876a4e6cf56ee6da1f97d203926bd7afda7ef';
       const String nextDartRevision = 'f6c91128be6b77aef8351e1e3a9d07c85bc2e46e';
       const String previousVersion = '1.2.0-1.0.pre';
-      const String nextVersion = '1.2.0-3.0.pre';
+      // This is a git tag applied to the branch point, not an actual release
+      const String branchPointTag = '1.2.0-3.0.pre';
+      // This is what this release will be
+      const String nextVersion = '1.2.0-3.1.pre';
       const String incrementLevel = 'm';
 
       final Directory engine = fileSystem.directory(checkoutsParentDirectory)
@@ -243,6 +247,16 @@ void main() {
           ],
           stdout: '$previousVersion-42-gabc123',
         ),
+        const FakeCommand(
+          command: <String>['git', 'merge-base', candidateBranch, 'master'],
+          stdout: branchPointRevision,
+        ),
+        const FakeCommand(
+          command: <String>['git', 'tag', branchPointTag, branchPointRevision],
+        ),
+        const FakeCommand(
+          command: <String>['git', 'push', FrameworkRepository.defaultUpstream, branchPointTag],
+        ),
         const FakeCommand(
           command: <String>['git', 'rev-parse', 'HEAD'],
           stdout: revision3,
@@ -300,6 +314,9 @@ void main() {
       expect(state.currentPhase, ReleasePhase.APPLY_ENGINE_CHERRYPICKS);
       expect(state.conductorVersion, conductorVersion);
       expect(state.incrementLevel, incrementLevel);
+      expect(stdio.stdout, contains('Applying the tag $branchPointTag at the branch point $branchPointRevision'));
+      expect(stdio.stdout, contains('The actual release will be version $nextVersion'));
+      expect(branchPointTag != nextVersion, true);
     });
 
     test('can convert from dev style version to stable version', () async {