[flutter_tools] fix RangeError in flutter channel command (#103766)

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

@@ -79,6 +79,10 @@ class ChannelCommand extends FlutterCommand {
 
     for (final String line in rawOutput) {
       final List<String> split = line.split('/');
+      if (split.length != 2) {
+        // We don't know how to parse this line, skip it.
+        continue;
+      }
       final String branch = split[1];
       if (split.length > 1) {
         final int index = officialChannels.indexOf(branch);

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

@@ -136,6 +136,38 @@ void main() {
       FileSystem: () => MemoryFileSystem.test(),
     });
 
+    testUsingContext('ignores lines with unexpected output', () async {
+      fakeProcessManager.addCommand(
+        const FakeCommand(
+          command: <String>['git', 'branch', '-r'],
+          stdout: 'origin/beta\n'
+              'origin/stable\n'
+              'upstream/beta\n'
+              'upstream/stable\n'
+              'foo',
+        ),
+      );
+
+      final ChannelCommand command = ChannelCommand();
+      final CommandRunner<void> runner = createTestCommandRunner(command);
+      await runner.run(<String>['channel']);
+
+      expect(fakeProcessManager.hasRemainingExpectations, isFalse);
+      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.trim())
+        .where((String line) => line?.isNotEmpty == true)
+        .skip(1); // remove `Flutter channels:` line
+
+      expect(rows, <String>['beta', 'stable', 'Currently not on an official channel.']);
+    }, overrides: <Type, Generator>{
+      ProcessManager: () => fakeProcessManager,
+      FileSystem: () => MemoryFileSystem.test(),
+    });
+
     testUsingContext('removes duplicates', () async {
       fakeProcessManager.addCommand(
         const FakeCommand(