[flutter_tools] Do not use the logcat -T flag on Android versions before Lollipop (#49327)

packages/flutter_tools/lib/src/android/android_device.dart

@@ -10,7 +10,7 @@ import '../android/android_builder.dart';
 import '../android/android_sdk.dart';
 import '../android/android_workflow.dart';
 import '../application_package.dart';
-import '../base/common.dart' show throwToolExit;
+import '../base/common.dart' show throwToolExit, unawaited;
 import '../base/file_system.dart';
 import '../base/io.dart';
 import '../base/logger.dart';
@@ -1014,29 +1014,36 @@ class _AdbLogReader extends DeviceLogReader {
   @override
   String get name => device.name;
 
-  void _start() {
+  Future<void> _start() async {
     final String lastTimestamp = device.lastLogcatTimestamp;
     // Start the adb logcat process and filter the most recent logs since `lastTimestamp`.
     final List<String> args = <String>[
       'logcat',
       '-v',
       'time',
+    ];
+    // logcat -T is not supported on Android releases before Lollipop.
+    const int kLollipopVersionCode = 21;
+    final int apiVersion = int.tryParse(await device._apiVersion);
+    if (apiVersion != null && apiVersion >= kLollipopVersionCode) {
+      args.addAll(<String>[
         '-T',
         lastTimestamp ?? '', // Empty `-T` means the timestamp of the logcat command invocation.
-    ];
+      ]);
-    processUtils.start(device.adbCommandForDevice(args)).then<void>((Process process) {
+    }
-      _process = process;
+
+    _process = await processUtils.start(device.adbCommandForDevice(args));
+
     // We expect logcat streams to occasionally contain invalid utf-8,
     // see: https://github.com/flutter/flutter/pull/8864.
     const Utf8Decoder decoder = Utf8Decoder(reportErrors: false);
     _process.stdout.transform<String>(decoder).transform<String>(const LineSplitter()).listen(_onLine);
     _process.stderr.transform<String>(decoder).transform<String>(const LineSplitter()).listen(_onLine);
-      _process.exitCode.whenComplete(() {
+    unawaited(_process.exitCode.whenComplete(() {
       if (_linesController.hasListener) {
         _linesController.close();
       }
-      });
+    }));
-    });
   }
 
   // 'W/ActivityManager(pid): '

packages/flutter_tools/test/general.shard/android/android_device_test.dart

@@ -717,21 +717,38 @@ flutter:
     setUp(() {
       mockAndroidSdk = MockAndroidSdk();
       mockProcessManager = MockProcessManager();
+
+      when(mockProcessManager.run(
+        argThat(contains('getprop')),
+        stderrEncoding: anyNamed('stderrEncoding'),
+        stdoutEncoding: anyNamed('stdoutEncoding'),
+      )).thenAnswer((_) {
+        final StringBuffer buf = StringBuffer()
+          ..writeln('[ro.build.version.sdk]: [28]');
+        final ProcessResult result = ProcessResult(1, 0, buf.toString(), '');
+        return Future<ProcessResult>.value(result);
+      });
     });
 
     testUsingContext('calls adb logcat with expected flags', () async {
-      const String klastLocatcatTimestamp = '11-27 15:39:04.506';
+      const String kLastLogcatTimestamp = '11-27 15:39:04.506';
       when(mockAndroidSdk.adbPath).thenReturn('adb');
       when(mockProcessManager.runSync(<String>['adb', '-s', '1234', 'shell', '-x', 'logcat', '-v', 'time', '-t', '1']))
-        .thenReturn(ProcessResult(0, 0, '$klastLocatcatTimestamp I/flutter: irrelevant', ''));
+        .thenReturn(ProcessResult(0, 0, '$kLastLogcatTimestamp I/flutter: irrelevant', ''));
+
+      final Completer<void> logcatCompleter = Completer<void>();
       when(mockProcessManager.start(argThat(contains('logcat'))))
-        .thenAnswer((_) => Future<Process>.value(createMockProcess()));
+        .thenAnswer((_) {
+          logcatCompleter.complete();
+          return Future<Process>.value(createMockProcess());
+        });
 
       final AndroidDevice device = AndroidDevice('1234');
       final DeviceLogReader logReader = device.getLogReader();
       logReader.logLines.listen((_) {});
+      await logcatCompleter.future;
 
-      verify(mockProcessManager.start(const <String>['adb', '-s', '1234', 'logcat', '-v', 'time', '-T', klastLocatcatTimestamp]))
+      verify(mockProcessManager.start(const <String>['adb', '-s', '1234', 'logcat', '-v', 'time', '-T', kLastLogcatTimestamp]))
         .called(1);
     }, overrides: <Type, Generator>{
       AndroidSdk: () => mockAndroidSdk,
@@ -742,12 +759,18 @@ flutter:
       when(mockAndroidSdk.adbPath).thenReturn('adb');
       when(mockProcessManager.runSync(<String>['adb', '-s', '1234', 'shell', '-x', 'logcat', '-v', 'time', '-t', '1']))
         .thenReturn(ProcessResult(0, 0, '', ''));
+
+      final Completer<void> logcatCompleter = Completer<void>();
       when(mockProcessManager.start(argThat(contains('logcat'))))
-        .thenAnswer((_) => Future<Process>.value(createMockProcess()));
+        .thenAnswer((_) {
+          logcatCompleter.complete();
+          return Future<Process>.value(createMockProcess());
+        });
 
       final AndroidDevice device = AndroidDevice('1234');
       final DeviceLogReader logReader = device.getLogReader();
       logReader.logLines.listen((_) {});
+      await logcatCompleter.future;
 
       verify(mockProcessManager.start(const <String>['adb', '-s', '1234', 'logcat', '-v', 'time', '-T', '']))
         .called(1);