sort channels by stability upon running flutter channel (#48427)

packages/flutter_tools/lib/src/commands/channel.dart

@@ -55,7 +55,7 @@ class ChannelCommand extends FlutterCommand {
     // Beware: currentBranch could contain PII. See getBranchName().
     final String currentChannel = FlutterVersion.instance.channel;
     final String currentBranch = FlutterVersion.instance.getBranchName();
-    final Set<String> seenChannels = <String>{};
+    final Set<String> seenUnofficialChannels = <String>{};
     final List<String> rawOutput = <String>[];
 
     showAll = showAll || currentChannel != currentBranch;
@@ -65,25 +65,7 @@ class ChannelCommand extends FlutterCommand {
       <String>['git', 'branch', '-r'],
       workingDirectory: Cache.flutterRoot,
       mapFunction: (String line) {
-        if (verbose) {
-          rawOutput.add(line);
-        }
-        final List<String> split = line.split('/');
-        if (split.length < 2) {
-          return null;
-        }
-        final String branchName = split[1];
-        if (seenChannels.contains(branchName)) {
-          return null;
-        }
-        seenChannels.add(branchName);
-        if (branchName == currentBranch) {
-          return '* $branchName';
-        }
-        if (!branchName.startsWith('HEAD ') &&
-            (showAll || FlutterVersion.officialChannels.contains(branchName))) {
-          return '  $branchName';
-        }
+        rawOutput.add(line);
         return null;
       },
     );
@@ -91,6 +73,47 @@ class ChannelCommand extends FlutterCommand {
       final String details = verbose ? '\n${rawOutput.join('\n')}' : '';
       throwToolExit('List channels failed: $result$details', exitCode: result);
     }
+
+    final List<String> officialChannels = FlutterVersion.officialChannels.toList();
+    final List<bool> availableChannels = List<bool>.filled(officialChannels.length, false);
+
+    for (final String line in rawOutput) {
+      final List<String> split = line.split('/');
+      final String branch = split[1];
+      if (split.length > 1) {
+        final int index = officialChannels.indexOf(branch);
+
+        if (index != -1) { // Mark all available channels official channels from output
+          availableChannels[index] = true;
+        } else if (showAll && !seenUnofficialChannels.contains(branch)) {
+        // add other branches to seenUnofficialChannels if --all flag is given (to print later)
+          seenUnofficialChannels.add(branch);
+        }
+      }
+    }
+
+    // print all available official channels in sorted manner
+    for (int i = 0; i < officialChannels.length; i++) {
+      // only print non-missing channels
+      if (availableChannels[i]) {
+        String currentIndicator = ' ';
+        if (officialChannels[i] == currentChannel){
+          currentIndicator = '*';
+        }
+        globals.printStatus('$currentIndicator ${officialChannels[i]}');
+      }
+    }
+
+    // print all remaining channels if showAll is true
+    if (showAll) {
+      for (final String branch in seenUnofficialChannels) {
+        if (currentBranch == branch) {
+          globals.printStatus('* $branch');
+        } else if (!branch.startsWith('HEAD ')) {
+          globals.printStatus('  $branch');
+        }
+      }
+    }
   }
 
   Future<void> _switchChannel(String branchName) {

packages/flutter_tools/lib/src/version.dart

@@ -39,6 +39,7 @@ class FlutterVersion {
     return !<String>['dev', 'beta', 'stable'].contains(branchName);
   }
 
+  // Beware: Keep order in accordance with stability
   static const Set<String> officialChannels = <String>{
     'master',
     'dev',

packages/flutter_tools/test/general.shard/channel_test.dart

@@ -46,6 +46,97 @@ void main() {
       await simpleChannelTest(<String>['channel', '-v']);
     });
 
+    testUsingContext('sorted by stability', () async {
+      final Process processAll = createMockProcess(
+          stdout: 'origin/beta\n'
+                  'origin/master\n'
+                  'origin/dev\n'
+                  'origin/stable\n');
+      final Process processWithExtra = createMockProcess(
+          stdout: 'origin/beta\n'
+                  'origin/master\n'
+                  'origin/dependabot/bundler\n'
+                  'origin/dev\n'
+                  'origin/v1.4.5-hotfixes\n'
+                  'origin/stable\n');
+      final Process processWithMissing = createMockProcess(
+          stdout: 'origin/beta\n'
+                  'origin/dependabot/bundler\n'
+                  'origin/v1.4.5-hotfixes\n'
+                  'origin/stable\n');
+
+      final ChannelCommand command = ChannelCommand();
+      final CommandRunner<void> runner = createTestCommandRunner(command);
+
+      when(mockProcessManager.start(
+        <String>['git', 'branch', '-r'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).thenAnswer((_) => Future<Process>.value(processAll));
+      await runner.run(<String>['channel']);
+      verify(mockProcessManager.start(
+        <String>['git', 'branch', '-r'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).called(1);
+      expect(testLogger.errorText, hasLength(0));
+      // format the status text for a simpler assertion.
+      final Iterable<String> rows = testLogger.statusText
+        .split('\n')
+        .map((String line) => line.substring(2)); // remove '* ' or '  ' from output
+      expect(rows, containsAllInOrder(FlutterVersion.officialChannels));
+
+      // clear buffer for next process
+      testLogger.clear();
+
+      when(mockProcessManager.start(
+        <String>['git', 'branch', '-r'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).thenAnswer((_) => Future<Process>.value(processWithExtra));
+      await runner.run(<String>['channel']);
+      verify(mockProcessManager.start(
+        <String>['git', 'branch', '-r'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).called(1);
+      expect(testLogger.errorText, hasLength(0));
+      // format the status text for a simpler assertion.
+      final Iterable<String> rows2 = testLogger.statusText
+        .split('\n')
+        .map((String line) => line.substring(2)); // remove '* ' or '  ' from output
+      expect(rows2, containsAllInOrder(FlutterVersion.officialChannels));
+
+      // clear buffer for next process
+      testLogger.clear();
+
+      when(mockProcessManager.start(
+        <String>['git', 'branch', '-r'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).thenAnswer((_) => Future<Process>.value(processWithMissing));
+      await runner.run(<String>['channel']);
+      verify(mockProcessManager.start(
+        <String>['git', 'branch', '-r'],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).called(1);
+      expect(testLogger.errorText, hasLength(0));
+      // check if available official channels are in order of stability
+      int prev = -1;
+      int next = -1;
+      for (final String branch in FlutterVersion.officialChannels) {
+        next = testLogger.statusText.indexOf(branch);
+        if (next != -1) {
+          expect(prev < next, isTrue);
+          prev = next;
+        }
+      }
+
+    }, overrides: <Type, Generator>{
+      ProcessManager: () => mockProcessManager,
+    });
+
     testUsingContext('removes duplicates', () async {
       final Process process = createMockProcess(
           stdout: 'origin/dev\n'