Migrate protocol_discovery to null safety (#91267)

packages/flutter_tools/lib/src/custom_devices/custom_device.dart

@@ -385,7 +385,6 @@ class CustomDeviceAppSession {
     final ProtocolDiscovery discovery = ProtocolDiscovery.observatory(
       logReader,
       portForwarder: _device._config.usesPortForwarding ? _device.portForwarder : null,
-      hostPort: null, devicePort: null,
       logger: _logger,
       ipv6: ipv6,
     );

packages/flutter_tools/lib/src/device.dart

@@ -214,7 +214,7 @@ abstract class DeviceManager {
   ///
   /// * If [flutterProject] is null, then assume the project supports all
   /// device types.
-  Future<List<Device>> findTargetDevices(FlutterProject flutterProject, { Duration? timeout }) async {
+  Future<List<Device>> findTargetDevices(FlutterProject? flutterProject, { Duration? timeout }) async {
     if (timeout != null) {
       // Reset the cache with the specified timeout.
       await refreshAllConnectedDevices(timeout: timeout);
@@ -317,7 +317,7 @@ abstract class DeviceManager {
   ///
   /// This exists to allow the check to be overridden for google3 clients. If
   /// [flutterProject] is null then return true.
-  bool isDeviceSupportedForProject(Device device, FlutterProject flutterProject) {
+  bool isDeviceSupportedForProject(Device device, FlutterProject? flutterProject) {
     if (flutterProject == null) {
       return true;
     }

packages/flutter_tools/lib/src/protocol_discovery.dart

@@ -2,12 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
-import 'package:meta/meta.dart';
-
 import 'base/io.dart';
 import 'base/logger.dart';
 import 'device.dart';
@@ -20,28 +16,27 @@ class ProtocolDiscovery {
     this.logReader,
     this.serviceName, {
     this.portForwarder,
-    this.throttleDuration,
+    required this.throttleDuration,
     this.hostPort,
     this.devicePort,
-    this.ipv6,
+    required this.ipv6,
-    Logger logger,
+    required Logger logger,
   }) : _logger = logger,
        assert(logReader != null) {
     _deviceLogSubscription = logReader.logLines.listen(
       _handleLine,
       onDone: _stopScrapingLogs,
     );
-    _uriStreamController = _BufferedStreamController<Uri>();
   }
 
   factory ProtocolDiscovery.observatory(
     DeviceLogReader logReader, {
-    DevicePortForwarder portForwarder,
+    DevicePortForwarder? portForwarder,
-    Duration throttleDuration,
+    Duration? throttleDuration,
-    @required int hostPort,
+    int? hostPort,
-    @required int devicePort,
+    int? devicePort,
-    @required bool ipv6,
+    required bool ipv6,
-    @required Logger logger,
+    required Logger logger,
   }) {
     const String kObservatoryService = 'Observatory';
     return ProtocolDiscovery._(
@@ -58,17 +53,17 @@ class ProtocolDiscovery {
 
   final DeviceLogReader logReader;
   final String serviceName;
-  final DevicePortForwarder portForwarder;
+  final DevicePortForwarder? portForwarder;
-  final int hostPort;
+  final int? hostPort;
-  final int devicePort;
+  final int? devicePort;
   final bool ipv6;
   final Logger _logger;
 
   /// The time to wait before forwarding a new observatory URIs from [logReader].
   final Duration throttleDuration;
 
-  StreamSubscription<String> _deviceLogSubscription;
+  StreamSubscription<String>? _deviceLogSubscription;
-  _BufferedStreamController<Uri> _uriStreamController;
+  final _BufferedStreamController<Uri> _uriStreamController = _BufferedStreamController<Uri>();
 
   /// The discovered service URL.
   ///
@@ -76,7 +71,7 @@ class ProtocolDiscovery {
   ///
   /// Use [uris] instead.
   // TODO(egarciad): replace `uri` for `uris`.
-  Future<Uri> get uri async {
+  Future<Uri?> get uri async {
     try {
       return await uris.first;
     } on StateError {
@@ -103,26 +98,26 @@ class ProtocolDiscovery {
   Future<void> cancel() => _stopScrapingLogs();
 
   Future<void> _stopScrapingLogs() async {
-    await _uriStreamController?.close();
+    await _uriStreamController.close();
     await _deviceLogSubscription?.cancel();
     _deviceLogSubscription = null;
   }
 
-  Match _getPatternMatch(String line) {
+  Match? _getPatternMatch(String line) {
     final RegExp r = RegExp(RegExp.escape(serviceName) + r' listening on ((http|//)[a-zA-Z0-9:/=_\-\.\[\]]+)');
     return r.firstMatch(line);
   }
 
-  Uri _getObservatoryUri(String line) {
+  Uri? _getObservatoryUri(String line) {
-    final Match match = _getPatternMatch(line);
+    final Match? match = _getPatternMatch(line);
     if (match != null) {
-      return Uri.parse(match[1]);
+      return Uri.parse(match[1]!);
     }
     return null;
   }
 
   void _handleLine(String line) {
-    Uri uri;
+    Uri? uri;
     try {
       uri = _getObservatoryUri(line);
     } on FormatException catch (error, stackTrace) {
@@ -142,9 +137,10 @@ class ProtocolDiscovery {
     _logger.printTrace('$serviceName URL on device: $deviceUri');
     Uri hostUri = deviceUri;
 
-    if (portForwarder != null) {
+    final DevicePortForwarder? forwarder = portForwarder;
+    if (forwarder != null) {
       final int actualDevicePort = deviceUri.port;
-      final int actualHostPort = await portForwarder.forward(actualDevicePort, hostPort: hostPort);
+      final int actualHostPort = await forwarder.forward(actualDevicePort, hostPort: hostPort);
       _logger.printTrace('Forwarded host port $actualHostPort to device port $actualDevicePort for $serviceName');
       hostUri = deviceUri.replace(port: actualHostPort);
     }
@@ -167,25 +163,24 @@ class _BufferedStreamController<T> {
     return _streamController.stream;
   }
 
-  StreamController<T> _streamControllerInstance;
+  late final StreamController<T> _streamController = () {
-
+    final StreamController<T> streamControllerInstance = StreamController<T>.broadcast();
-  StreamController<T> get _streamController {
+      streamControllerInstance.onListen = () {
-    _streamControllerInstance ??= StreamController<T>.broadcast(onListen: () {
       for (final dynamic event in _events) {
         assert(T is! List);
         if (event is T) {
-          _streamControllerInstance.add(event);
+          streamControllerInstance.add(event);
         } else {
-          _streamControllerInstance.addError(
+          streamControllerInstance.addError(
             (event as Iterable<dynamic>).first as Object,
-            (event as Iterable<dynamic>).last as StackTrace,
+            event.last as StackTrace,
           );
         }
       }
       _events.clear();
-    });
+    };
-    return _streamControllerInstance;
+    return streamControllerInstance;
-  }
+  }();
 
   final List<dynamic> _events;
 
@@ -200,7 +195,7 @@ class _BufferedStreamController<T> {
   }
 
   /// Sends or enqueues an error event.
-  void addError(Object error, [StackTrace stackTrace]) {
+  void addError(Object error, [StackTrace? stackTrace]) {
     if (_streamController.hasListener) {
       _streamController.addError(error, stackTrace);
     } else {
@@ -220,13 +215,13 @@ class _BufferedStreamController<T> {
 /// and arrival times: `a (0ms), b (5ms), c (11ms), d (21ms)`.
 /// The events `a`, `c`, and `d` will be produced as a result.
 StreamTransformer<S, S> _throttle<S>({
-  @required Duration waitDuration,
+  required Duration waitDuration,
 }) {
   assert(waitDuration != null);
 
   S latestLine;
-  int lastExecution;
+  int? lastExecution;
-  Future<void> throttleFuture;
+  Future<void>? throttleFuture;
   bool done = false;
 
   return StreamTransformer<S, S>
@@ -237,7 +232,7 @@ StreamTransformer<S, S> _throttle<S>({
         final bool isFirstMessage = lastExecution == null;
         final int currentTime = DateTime.now().millisecondsSinceEpoch;
         lastExecution ??= currentTime;
-        final int remainingTime = currentTime - lastExecution;
+        final int remainingTime = currentTime - lastExecution!;
 
         // Always send the first event immediately.
         final int nextExecutionTime = isFirstMessage || remainingTime > waitDuration.inMilliseconds

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:fake_async/fake_async.dart';
@@ -14,7 +12,6 @@ import 'package:flutter_tools/src/base/user_messages.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/device.dart';
 import 'package:flutter_tools/src/project.dart';
-import 'package:meta/meta.dart';
 import 'package:test/fake.dart';
 
 import '../src/common.dart';
@@ -491,37 +488,37 @@ void main() {
 class TestDeviceManager extends DeviceManager {
   TestDeviceManager(
     List<Device> allDevices, {
-    List<DeviceDiscovery> deviceDiscoveryOverrides,
+    List<DeviceDiscovery>? deviceDiscoveryOverrides,
-    @required Logger logger,
+    required Logger logger,
-    @required Terminal terminal,
+    required Terminal terminal,
-    String wellKnownId,
+    String? wellKnownId,
-  }) : super(logger: logger, terminal: terminal, userMessages: UserMessages()) {
+  }) : _fakeDeviceDiscoverer = FakePollingDeviceDiscovery(),
-    _fakeDeviceDiscoverer = FakePollingDeviceDiscovery();
+       _deviceDiscoverers = <DeviceDiscovery>[],
+       super(logger: logger, terminal: terminal, userMessages: UserMessages()) {
     if (wellKnownId != null) {
       _fakeDeviceDiscoverer.wellKnownIds.add(wellKnownId);
     }
-    _deviceDiscoverers = <DeviceDiscovery>[
+    _deviceDiscoverers.add(_fakeDeviceDiscoverer);
-      _fakeDeviceDiscoverer,
+    if (deviceDiscoveryOverrides != null) {
-      if (deviceDiscoveryOverrides != null)
+      _deviceDiscoverers.addAll(deviceDiscoveryOverrides);
-        ...deviceDiscoveryOverrides
+    }
-    ];
     resetDevices(allDevices);
   }
   @override
   List<DeviceDiscovery> get deviceDiscoverers => _deviceDiscoverers;
-  List<DeviceDiscovery> _deviceDiscoverers;
+  final List<DeviceDiscovery> _deviceDiscoverers;
-  FakePollingDeviceDiscovery _fakeDeviceDiscoverer;
+  final FakePollingDeviceDiscovery _fakeDeviceDiscoverer;
 
   void resetDevices(List<Device> allDevices) {
     _fakeDeviceDiscoverer.setDevices(allDevices);
   }
 
-  bool isAlwaysSupportedOverride;
+  bool? isAlwaysSupportedOverride;
 
   @override
-  bool isDeviceSupportedForProject(Device device, FlutterProject flutterProject) {
+  bool isDeviceSupportedForProject(Device device, FlutterProject? flutterProject) {
     if (isAlwaysSupportedOverride != null) {
-      return isAlwaysSupportedOverride;
+      return isAlwaysSupportedOverride!;
     }
     return super.isDeviceSupportedForProject(device, flutterProject);
   }
@@ -543,7 +540,7 @@ class MockDeviceDiscovery extends Fake implements DeviceDiscovery {
   }
 
   @override
-  Future<List<Device>> discoverDevices({Duration timeout}) async {
+  Future<List<Device>> discoverDevices({Duration? timeout}) async {
     discoverDevicesCalled += 1;
     return deviceValues;
   }
@@ -560,18 +557,18 @@ class LongPollingDeviceDiscovery extends PollingDeviceDiscovery {
   final Completer<List<Device>> _completer = Completer<List<Device>>();
 
   @override
-  Future<List<Device>> pollingGetDevices({ Duration timeout }) async {
+  Future<List<Device>> pollingGetDevices({ Duration? timeout }) async {
     return _completer.future;
   }
 
   @override
   Future<void> stopPolling() async {
-    _completer.complete();
+    _completer.complete(<Device>[]);
   }
 
   @override
   Future<void> dispose() async {
-    _completer.complete();
+    _completer.complete(<Device>[]);
   }
 
   @override
@@ -588,7 +585,7 @@ class ThrowingPollingDeviceDiscovery extends PollingDeviceDiscovery {
   ThrowingPollingDeviceDiscovery() : super('throw');
 
   @override
-  Future<List<Device>> pollingGetDevices({ Duration timeout }) async {
+  Future<List<Device>> pollingGetDevices({ Duration? timeout }) async {
     throw const ProcessException('fake-discovery', <String>[]);
   }
 
@@ -614,15 +611,15 @@ class FakeTerminal extends Fake implements Terminal {
     _nextResult = result;
   }
 
-  List<String> _nextPrompt;
+  List<String>? _nextPrompt;
-  String _nextResult;
+  late String _nextResult;
 
   @override
   Future<String> promptForCharInput(
     List<String> acceptedCharacters, {
-    Logger logger,
+    Logger? logger,
-    String prompt,
+    String? prompt,
-    int defaultChoiceIndex,
+    int? defaultChoiceIndex,
     bool displayAcceptedCharacters = true,
   }) async {
     expect(acceptedCharacters, _nextPrompt);

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:fake_async/fake_async.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/device_port_forwarder.dart';
@@ -14,16 +12,14 @@ import '../src/fake_devices.dart';
 
 void main() {
   group('service_protocol discovery', () {
-    FakeDeviceLogReader logReader;
+    late FakeDeviceLogReader logReader;
-    ProtocolDiscovery discoverer;
+    late ProtocolDiscovery discoverer;
 
     setUp(() {
       logReader = FakeDeviceLogReader();
       discoverer = ProtocolDiscovery.observatory(
         logReader,
         ipv6: false,
-        hostPort: null,
-        devicePort: null,
         throttleDuration: const Duration(milliseconds: 5),
         logger: BufferLogger.test(),
       );
@@ -42,20 +38,20 @@ void main() {
       testWithoutContext('discovers uri if logs already produced output', () async {
         logReader.addLine('HELLO WORLD');
         logReader.addLine('Observatory listening on http://127.0.0.1:9999');
-        final Uri uri = await discoverer.uri;
+        final Uri uri = (await discoverer.uri)!;
         expect(uri.port, 9999);
         expect('$uri', 'http://127.0.0.1:9999');
       });
 
       testWithoutContext('does not discover uri with no host', () async {
-        final Future<Uri> pendingUri = discoverer.uri;
+        final Future<Uri?> pendingUri = discoverer.uri;
         logReader.addLine('Observatory listening on http12asdasdsd9999');
         await Future<void>.delayed(const Duration(milliseconds: 10));
         logReader.addLine('Observatory listening on http://127.0.0.1:9999');
 
         await Future<void>.delayed(Duration.zero);
 
-        final Uri uri = await pendingUri;
+        final Uri uri = (await pendingUri)!;
         expect(uri, isNotNull);
         expect(uri.port, 9999);
         expect('$uri', 'http://127.0.0.1:9999');
@@ -67,7 +63,7 @@ void main() {
 
         await Future<void>.delayed(Duration.zero);
 
-        final Uri uri = await discoverer.uri;
+        final Uri uri = (await discoverer.uri)!;
         expect(uri, isNotNull);
         expect(uri.port, 9999);
         expect('$uri', 'http://127.0.0.1:9999');
@@ -82,16 +78,16 @@ void main() {
       });
 
       testWithoutContext('discovers uri if logs not yet produced output', () async {
-        final Future<Uri> uriFuture = discoverer.uri;
+        final Future<Uri?> uriFuture = discoverer.uri;
         logReader.addLine('Observatory listening on http://127.0.0.1:3333');
-        final Uri uri = await uriFuture;
+        final Uri uri = (await uriFuture)!;
         expect(uri.port, 3333);
         expect('$uri', 'http://127.0.0.1:3333');
       });
 
       testWithoutContext('discovers uri with Ascii Esc code', () async {
         logReader.addLine('Observatory listening on http://127.0.0.1:3333\x1b[');
-        final Uri uri = await discoverer.uri;
+        final Uri uri = (await discoverer.uri)!;
         expect(uri.port, 3333);
         expect('$uri', 'http://127.0.0.1:3333');
       });
@@ -102,17 +98,17 @@ void main() {
       });
 
       testWithoutContext('uri is null when the log reader closes early', () async {
-        final Future<Uri> uriFuture = discoverer.uri;
+        final Future<Uri?> uriFuture = discoverer.uri;
         await logReader.dispose();
 
         expect(await uriFuture, isNull);
       });
 
       testWithoutContext('uri waits for correct log line', () async {
-        final Future<Uri> uriFuture = discoverer.uri;
+        final Future<Uri?> uriFuture = discoverer.uri;
         logReader.addLine('Observatory not listening...');
         final Uri timeoutUri = Uri.parse('http://timeout');
-        final Uri actualUri = await uriFuture.timeout(
+        final Uri? actualUri = await uriFuture.timeout(
           const Duration(milliseconds: 100),
           onTimeout: () => timeoutUri,
         );
@@ -121,23 +117,23 @@ void main() {
 
       testWithoutContext('discovers uri if log line contains Android prefix', () async {
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:52584');
-        final Uri uri = await discoverer.uri;
+        final Uri uri = (await discoverer.uri)!;
         expect(uri.port, 52584);
         expect('$uri', 'http://127.0.0.1:52584');
       });
 
       testWithoutContext('discovers uri if log line contains auth key', () async {
-        final Future<Uri> uriFuture = discoverer.uri;
+        final Future<Uri?> uriFuture = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:54804/PTwjm8Ii8qg=/');
-        final Uri uri = await uriFuture;
+        final Uri uri = (await uriFuture)!;
         expect(uri.port, 54804);
         expect('$uri', 'http://127.0.0.1:54804/PTwjm8Ii8qg=/');
       });
 
       testWithoutContext('discovers uri if log line contains non-localhost', () async {
-        final Future<Uri> uriFuture = discoverer.uri;
+        final Future<Uri?> uriFuture = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:54804/PTwjm8Ii8qg=/');
-        final Uri uri = await uriFuture;
+        final Uri uri = (await uriFuture)!;
         expect(uri.port, 54804);
         expect('$uri', 'http://127.0.0.1:54804/PTwjm8Ii8qg=/');
       });
@@ -146,15 +142,14 @@ void main() {
         discoverer = ProtocolDiscovery.observatory(
           logReader,
           ipv6: false,
-          hostPort: null,
           devicePort: 12346,
           throttleDuration: const Duration(milliseconds: 200),
           logger: BufferLogger.test(),
         );
-        final Future<Uri> uriFuture = discoverer.uri;
+        final Future<Uri?> uriFuture = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:12345/PTwjm8Ii8qg=/');
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:12346/PTwjm8Ii8qg=/');
-        final Uri uri = await uriFuture;
+        final Uri uri = (await uriFuture)!;
         expect(uri.port, 12346);
         expect('$uri', 'http://127.0.0.1:12346/PTwjm8Ii8qg=/');
       });
@@ -163,15 +158,14 @@ void main() {
         discoverer = ProtocolDiscovery.observatory(
           logReader,
           ipv6: false,
-          hostPort: null,
           devicePort: 12346,
           throttleDuration: const Duration(milliseconds: 200),
           logger: BufferLogger.test(),
         );
-        final Future<Uri> uriFuture = discoverer.uri;
+        final Future<Uri?> uriFuture = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:12346/PTwjm8Ii8qg=/');
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:12345/PTwjm8Ii8qg=/');
-        final Uri uri = await uriFuture;
+        final Uri uri = (await uriFuture)!;
         expect(uri.port, 12346);
         expect('$uri', 'http://127.0.0.1:12346/PTwjm8Ii8qg=/');
       });
@@ -188,7 +182,6 @@ void main() {
         discoverer = ProtocolDiscovery.observatory(
           logReader,
           ipv6: false,
-          hostPort: null,
           devicePort: 12345,
           throttleDuration: const Duration(milliseconds: 200),
           logger: BufferLogger.test(),
@@ -205,7 +198,6 @@ void main() {
         discoverer = ProtocolDiscovery.observatory(
           logReader,
           ipv6: false,
-          hostPort: null,
           devicePort: 12346,
           throttleDuration: const Duration(milliseconds: 10),
           logger: BufferLogger.test(),
@@ -227,8 +219,6 @@ void main() {
           discoverer = ProtocolDiscovery.observatory(
             logReader,
             ipv6: false,
-            hostPort: null,
-            devicePort: null,
             throttleDuration: kThrottleDuration,
             logger: BufferLogger.test(),
           );
@@ -263,7 +253,6 @@ void main() {
           discoverer = ProtocolDiscovery.observatory(
             logReader,
             ipv6: false,
-            hostPort: null,
             devicePort: 12345,
             throttleDuration: kThrottleTimeInMilliseconds,
             logger: BufferLogger.test(),
@@ -299,16 +288,14 @@ void main() {
         final ProtocolDiscovery discoverer = ProtocolDiscovery.observatory(
           logReader,
           portForwarder: MockPortForwarder(99),
-          hostPort: null,
-          devicePort: null,
           ipv6: false,
           logger: BufferLogger.test(),
         );
 
         // Get next port future.
-        final Future<Uri> nextUri = discoverer.uri;
+        final Future<Uri?> nextUri = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:54804/PTwjm8Ii8qg=/');
-        final Uri uri = await nextUri;
+        final Uri uri = (await nextUri)!;
         expect(uri.port, 99);
         expect('$uri', 'http://127.0.0.1:99/PTwjm8Ii8qg=/');
 
@@ -322,15 +309,14 @@ void main() {
           logReader,
           portForwarder: MockPortForwarder(99),
           hostPort: 1243,
-          devicePort: null,
           ipv6: false,
           logger: BufferLogger.test(),
         );
 
         // Get next port future.
-        final Future<Uri> nextUri = discoverer.uri;
+        final Future<Uri?> nextUri = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:54804/PTwjm8Ii8qg=/');
-        final Uri uri = await nextUri;
+        final Uri uri = (await nextUri)!;
         expect(uri.port, 1243);
         expect('$uri', 'http://127.0.0.1:1243/PTwjm8Ii8qg=/');
 
@@ -344,15 +330,14 @@ void main() {
           logReader,
           portForwarder: MockPortForwarder(99),
           hostPort: 0,
-          devicePort: null,
           ipv6: false,
           logger: BufferLogger.test(),
         );
 
         // Get next port future.
-        final Future<Uri> nextUri = discoverer.uri;
+        final Future<Uri?> nextUri = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:54804/PTwjm8Ii8qg=/');
-        final Uri uri = await nextUri;
+        final Uri uri = (await nextUri)!;
         expect(uri.port, 99);
         expect('$uri', 'http://127.0.0.1:99/PTwjm8Ii8qg=/');
 
@@ -367,14 +352,13 @@ void main() {
           portForwarder: MockPortForwarder(99),
           hostPort: 54777,
           ipv6: true,
-          devicePort: null,
           logger: BufferLogger.test(),
         );
 
         // Get next port future.
-        final Future<Uri> nextUri = discoverer.uri;
+        final Future<Uri?> nextUri = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://127.0.0.1:54804/PTwjm8Ii8qg=/');
-        final Uri uri = await nextUri;
+        final Uri uri = (await nextUri)!;
         expect(uri.port, 54777);
         expect('$uri', 'http://[::1]:54777/PTwjm8Ii8qg=/');
 
@@ -389,14 +373,13 @@ void main() {
           portForwarder: MockPortForwarder(99),
           hostPort: 54777,
           ipv6: true,
-          devicePort: null,
           logger: BufferLogger.test(),
         );
 
         // Get next port future.
-        final Future<Uri> nextUri = discoverer.uri;
+        final Future<Uri?> nextUri = discoverer.uri;
         logReader.addLine('I/flutter : Observatory listening on http://[::1]:54777/PTwjm8Ii8qg=/\x1b[');
-        final Uri uri = await nextUri;
+        final Uri uri = (await nextUri)!;
         expect(uri.port, 54777);
         expect('$uri', 'http://[::1]:54777/PTwjm8Ii8qg=/');
 
@@ -410,13 +393,13 @@ void main() {
 class MockPortForwarder extends DevicePortForwarder {
   MockPortForwarder([this.availablePort]);
 
-  final int availablePort;
+  final int? availablePort;
 
   @override
-  Future<int> forward(int devicePort, { int hostPort }) async {
+  Future<int> forward(int devicePort, { int? hostPort }) async {
     hostPort ??= 0;
     if (hostPort == 0) {
-      return availablePort;
+      return availablePort!;
     }
     return hostPort;
   }

packages/flutter_tools/test/src/fake_devices.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:flutter_tools/src/application_package.dart';
@@ -64,7 +62,7 @@ class FakeDevice extends Device {
     bool ephemeral = true,
     bool isSupported = true,
     PlatformType type = PlatformType.web,
-    LaunchResult launchResult,
+    LaunchResult? launchResult,
   }) : _isSupported = isSupported,
       _launchResult = launchResult ?? LaunchResult.succeeded(),
       super(
@@ -82,24 +80,24 @@ class FakeDevice extends Device {
 
   @override
   Future<LaunchResult> startApp(covariant ApplicationPackage package, {
-    String mainPath,
+    String? mainPath,
-    String route,
+    String? route,
-    DebuggingOptions debuggingOptions,
+    DebuggingOptions? debuggingOptions,
-    Map<String, dynamic> platformArgs,
+    Map<String, dynamic>? platformArgs,
     bool prebuiltApplication = false,
     bool ipv6 = false,
-    String userIdentifier,
+    String? userIdentifier,
   }) async => _launchResult;
 
   @override
   Future<bool> stopApp(covariant ApplicationPackage app, {
-    String userIdentifier,
+    String? userIdentifier,
   }) async => true;
 
   @override
   Future<bool> uninstallApp(
   covariant ApplicationPackage app, {
-    String userIdentifier,
+    String? userIdentifier,
   }) async => true;
 
   @override
@@ -140,12 +138,12 @@ class FakePollingDeviceDiscovery extends PollingDeviceDiscovery {
   final StreamController<Device> _onRemovedController = StreamController<Device>.broadcast();
 
   @override
-  Future<List<Device>> pollingGetDevices({ Duration timeout }) async {
+  Future<List<Device>> pollingGetDevices({ Duration? timeout }) async {
     lastPollingTimeout = timeout;
     return _devices;
   }
 
-  Duration lastPollingTimeout;
+  Duration? lastPollingTimeout;
 
   @override
   bool get supportsPlatform => true;
@@ -185,19 +183,15 @@ class FakeDeviceLogReader extends DeviceLogReader {
   @override
   String get name => 'FakeLogReader';
 
-  StreamController<String> _cachedLinesController;
-
   bool disposed = false;
 
   final List<String> _lineQueue = <String>[];
-  StreamController<String> get _linesController {
+  late final StreamController<String> _linesController =
-    _cachedLinesController ??= StreamController<String>
+    StreamController<String>
         .broadcast(onListen: () {
       _lineQueue.forEach(_linesController.add);
       _lineQueue.clear();
     });
-    return _cachedLinesController;
-  }
 
   @override
   Stream<String> get logLines => _linesController.stream;