diff --git a/packages/flutter_tools/bin/flutter_tools.dart b/packages/flutter_tools/bin/flutter_tools.dart
index 2caa134a35..1cad0ded07 100644
--- a/packages/flutter_tools/bin/flutter_tools.dart
+++ b/packages/flutter_tools/bin/flutter_tools.dart
@@ -2,6 +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 'package:flutter_tools/executable.dart' as executable;
 
 void main(List<String> args) {
diff --git a/packages/flutter_tools/bin/fuchsia_asset_builder.dart b/packages/flutter_tools/bin/fuchsia_asset_builder.dart
index 033df4df0d..4debac7ef7 100644
--- a/packages/flutter_tools/bin/fuchsia_asset_builder.dart
+++ b/packages/flutter_tools/bin/fuchsia_asset_builder.dart
@@ -2,6 +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 'package:args/args.dart';
 import 'package:flutter_tools/src/asset.dart' hide defaultManifestPath;
 import 'package:flutter_tools/src/base/context.dart';
diff --git a/packages/flutter_tools/bin/fuchsia_attach.dart b/packages/flutter_tools/bin/fuchsia_attach.dart
index 677ff379bd..6ee4340b19 100644
--- a/packages/flutter_tools/bin/fuchsia_attach.dart
+++ b/packages/flutter_tools/bin/fuchsia_attach.dart
@@ -2,6 +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 'package:args/args.dart';
 
 import 'package:flutter_tools/runner.dart' as runner;
diff --git a/packages/flutter_tools/bin/fuchsia_tester.dart b/packages/flutter_tools/bin/fuchsia_tester.dart
index e6ee664d60..d5d5d88fe5 100644
--- a/packages/flutter_tools/bin/fuchsia_tester.dart
+++ b/packages/flutter_tools/bin/fuchsia_tester.dart
@@ -2,6 +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:convert' show json;
 import 'dart:math' as math;
 
diff --git a/packages/flutter_tools/bin/tool_backend.dart b/packages/flutter_tools/bin/tool_backend.dart
index b4b67681bf..813a3e8ff5 100644
--- a/packages/flutter_tools/bin/tool_backend.dart
+++ b/packages/flutter_tools/bin/tool_backend.dart
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.9
+// @dart = 2.8
 
 // Do not add package imports to this file.
 import 'dart:convert'; // ignore: dart_convert_import.
diff --git a/packages/flutter_tools/lib/executable.dart b/packages/flutter_tools/lib/executable.dart
index 626f6def99..70499824e6 100644
--- a/packages/flutter_tools/lib/executable.dart
+++ b/packages/flutter_tools/lib/executable.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import 'runner.dart' as runner;
diff --git a/packages/flutter_tools/lib/runner.dart b/packages/flutter_tools/lib/runner.dart
index ee73598c88..152e94006b 100644
--- a/packages/flutter_tools/lib/runner.dart
+++ b/packages/flutter_tools/lib/runner.dart
@@ -2,6 +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:args/command_runner.dart';
diff --git a/packages/flutter_tools/lib/src/android/adb.dart b/packages/flutter_tools/lib/src/android/adb.dart
index a500a1b3ee..c74838f747 100644
--- a/packages/flutter_tools/lib/src/android/adb.dart
+++ b/packages/flutter_tools/lib/src/android/adb.dart
@@ -2,6 +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
+
 final RegExp _whitespace = RegExp(r'\s+');
 
 /// Convert adb device names into more human readable descriptions.
diff --git a/packages/flutter_tools/lib/src/android/android.dart b/packages/flutter_tools/lib/src/android/android.dart
index 6ecd6b6938..26a35b7ac3 100644
--- a/packages/flutter_tools/lib/src/android/android.dart
+++ b/packages/flutter_tools/lib/src/android/android.dart
@@ -2,6 +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
+
 const int minApiLevel = 16;
 const String minVersionName = 'Jelly Bean';
 const String minVersionText = '4.1.x';
diff --git a/packages/flutter_tools/lib/src/android/android_builder.dart b/packages/flutter_tools/lib/src/android/android_builder.dart
index 9f9107c607..c35ad1b225 100644
--- a/packages/flutter_tools/lib/src/android/android_builder.dart
+++ b/packages/flutter_tools/lib/src/android/android_builder.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../android/gradle_errors.dart';
diff --git a/packages/flutter_tools/lib/src/android/android_console.dart b/packages/flutter_tools/lib/src/android/android_console.dart
index b20639f96e..69d5e7cfea 100644
--- a/packages/flutter_tools/lib/src/android/android_console.dart
+++ b/packages/flutter_tools/lib/src/android/android_console.dart
@@ -2,6 +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 'package:async/async.dart';
 import '../base/io.dart';
 import '../convert.dart';
diff --git a/packages/flutter_tools/lib/src/android/android_device.dart b/packages/flutter_tools/lib/src/android/android_device.dart
index f1dcfffa47..e5af683cf6 100644
--- a/packages/flutter_tools/lib/src/android/android_device.dart
+++ b/packages/flutter_tools/lib/src/android/android_device.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/android/android_device_discovery.dart b/packages/flutter_tools/lib/src/android/android_device_discovery.dart
index ad08368684..b712fbdeb3 100644
--- a/packages/flutter_tools/lib/src/android/android_device_discovery.dart
+++ b/packages/flutter_tools/lib/src/android/android_device_discovery.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/android/android_emulator.dart b/packages/flutter_tools/lib/src/android/android_emulator.dart
index aee624a55c..4378d26341 100644
--- a/packages/flutter_tools/lib/src/android/android_emulator.dart
+++ b/packages/flutter_tools/lib/src/android/android_emulator.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/android/android_sdk.dart b/packages/flutter_tools/lib/src/android/android_sdk.dart
index 674227a57a..2a6b45ccce 100644
--- a/packages/flutter_tools/lib/src/android/android_sdk.dart
+++ b/packages/flutter_tools/lib/src/android/android_sdk.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/android/android_studio.dart b/packages/flutter_tools/lib/src/android/android_studio.dart
index c0e5e83f04..e9f71df7a2 100644
--- a/packages/flutter_tools/lib/src/android/android_studio.dart
+++ b/packages/flutter_tools/lib/src/android/android_studio.dart
@@ -2,6 +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 '../base/context.dart';
 import '../base/file_system.dart';
 import '../base/io.dart';
diff --git a/packages/flutter_tools/lib/src/android/android_studio_validator.dart b/packages/flutter_tools/lib/src/android/android_studio_validator.dart
index d76170c436..85c8254706 100644
--- a/packages/flutter_tools/lib/src/android/android_studio_validator.dart
+++ b/packages/flutter_tools/lib/src/android/android_studio_validator.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/config.dart';
diff --git a/packages/flutter_tools/lib/src/android/android_workflow.dart b/packages/flutter_tools/lib/src/android/android_workflow.dart
index db2426e50c..cc3a55630a 100644
--- a/packages/flutter_tools/lib/src/android/android_workflow.dart
+++ b/packages/flutter_tools/lib/src/android/android_workflow.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/android/build_validation.dart b/packages/flutter_tools/lib/src/android/build_validation.dart
index 15ce8261d0..850b81d307 100644
--- a/packages/flutter_tools/lib/src/android/build_validation.dart
+++ b/packages/flutter_tools/lib/src/android/build_validation.dart
@@ -2,6 +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 '../base/common.dart';
 import '../build_info.dart';
 
diff --git a/packages/flutter_tools/lib/src/android/gradle.dart b/packages/flutter_tools/lib/src/android/gradle.dart
index a9074b1fce..026061cc0e 100644
--- a/packages/flutter_tools/lib/src/android/gradle.dart
+++ b/packages/flutter_tools/lib/src/android/gradle.dart
@@ -2,6 +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 'package:crypto/crypto.dart';
 import 'package:meta/meta.dart';
 import 'package:xml/xml.dart';
diff --git a/packages/flutter_tools/lib/src/android/gradle_errors.dart b/packages/flutter_tools/lib/src/android/gradle_errors.dart
index 4f0e0e7f15..febda4d901 100644
--- a/packages/flutter_tools/lib/src/android/gradle_errors.dart
+++ b/packages/flutter_tools/lib/src/android/gradle_errors.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/error_handling_io.dart';
diff --git a/packages/flutter_tools/lib/src/android/gradle_utils.dart b/packages/flutter_tools/lib/src/android/gradle_utils.dart
index 6ea8890448..b13f878fa0 100644
--- a/packages/flutter_tools/lib/src/android/gradle_utils.dart
+++ b/packages/flutter_tools/lib/src/android/gradle_utils.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/application_package.dart b/packages/flutter_tools/lib/src/application_package.dart
index 724a635bfd..740674ab2b 100644
--- a/packages/flutter_tools/lib/src/application_package.dart
+++ b/packages/flutter_tools/lib/src/application_package.dart
@@ -2,6 +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:collection';
 
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/artifacts.dart b/packages/flutter_tools/lib/src/artifacts.dart
index fce6e3b1c1..a43d6eb71d 100644
--- a/packages/flutter_tools/lib/src/artifacts.dart
+++ b/packages/flutter_tools/lib/src/artifacts.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/asset.dart b/packages/flutter_tools/lib/src/asset.dart
index a6c59bae07..2dd08fda97 100644
--- a/packages/flutter_tools/lib/src/asset.dart
+++ b/packages/flutter_tools/lib/src/asset.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 
diff --git a/packages/flutter_tools/lib/src/base/analyze_size.dart b/packages/flutter_tools/lib/src/base/analyze_size.dart
index 21f84b03a9..0fb9608a99 100644
--- a/packages/flutter_tools/lib/src/base/analyze_size.dart
+++ b/packages/flutter_tools/lib/src/base/analyze_size.dart
@@ -2,6 +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 'package:archive/archive.dart';
 import 'package:archive/archive_io.dart';
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/base/async_guard.dart b/packages/flutter_tools/lib/src/base/async_guard.dart
index 237964a43c..19e9f66c6f 100644
--- a/packages/flutter_tools/lib/src/base/async_guard.dart
+++ b/packages/flutter_tools/lib/src/base/async_guard.dart
@@ -2,6 +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';
 
 /// Runs [fn] with special handling of asynchronous errors.
diff --git a/packages/flutter_tools/lib/src/base/bot_detector.dart b/packages/flutter_tools/lib/src/base/bot_detector.dart
index 2049f0d1d3..94d39c04d0 100644
--- a/packages/flutter_tools/lib/src/base/bot_detector.dart
+++ b/packages/flutter_tools/lib/src/base/bot_detector.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/base/build.dart b/packages/flutter_tools/lib/src/base/build.dart
index 1a5c615754..f8213eaedc 100644
--- a/packages/flutter_tools/lib/src/base/build.dart
+++ b/packages/flutter_tools/lib/src/base/build.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/base/command_help.dart b/packages/flutter_tools/lib/src/base/command_help.dart
index d1d5fc3df1..6e9df74cef 100644
--- a/packages/flutter_tools/lib/src/base/command_help.dart
+++ b/packages/flutter_tools/lib/src/base/command_help.dart
@@ -2,6 +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:math' as math;
 
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/base/common.dart b/packages/flutter_tools/lib/src/base/common.dart
index 6a6a62bc66..1c2e105163 100644
--- a/packages/flutter_tools/lib/src/base/common.dart
+++ b/packages/flutter_tools/lib/src/base/common.dart
@@ -2,6 +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
+
 /// Throw a specialized exception for expected situations
 /// where the tool should exit with a clear message to the user
 /// and no stack trace unless the --verbose option is specified.
diff --git a/packages/flutter_tools/lib/src/base/config.dart b/packages/flutter_tools/lib/src/base/config.dart
index 5841fd38fd..3161e611e0 100644
--- a/packages/flutter_tools/lib/src/base/config.dart
+++ b/packages/flutter_tools/lib/src/base/config.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../convert.dart';
diff --git a/packages/flutter_tools/lib/src/base/context.dart b/packages/flutter_tools/lib/src/base/context.dart
index 362532ef95..d76cb04755 100644
--- a/packages/flutter_tools/lib/src/base/context.dart
+++ b/packages/flutter_tools/lib/src/base/context.dart
@@ -2,6 +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 'dart:collection';
 
diff --git a/packages/flutter_tools/lib/src/base/dds.dart b/packages/flutter_tools/lib/src/base/dds.dart
index d0ce5a8392..3b6cccdb5f 100644
--- a/packages/flutter_tools/lib/src/base/dds.dart
+++ b/packages/flutter_tools/lib/src/base/dds.dart
@@ -2,6 +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:dds/dds.dart' as dds;
diff --git a/packages/flutter_tools/lib/src/base/error_handling_io.dart b/packages/flutter_tools/lib/src/base/error_handling_io.dart
index 337e652696..ced497c0be 100644
--- a/packages/flutter_tools/lib/src/base/error_handling_io.dart
+++ b/packages/flutter_tools/lib/src/base/error_handling_io.dart
@@ -2,6 +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:convert';
 import 'dart:io' as io show Directory, File, Link, ProcessException, ProcessResult, ProcessSignal, systemEncoding, Process, ProcessStartMode;
 import 'dart:typed_data';
diff --git a/packages/flutter_tools/lib/src/base/file_system.dart b/packages/flutter_tools/lib/src/base/file_system.dart
index 4752748337..eedda2c2f6 100644
--- a/packages/flutter_tools/lib/src/base/file_system.dart
+++ b/packages/flutter_tools/lib/src/base/file_system.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/local.dart' as local_fs;
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/base/fingerprint.dart b/packages/flutter_tools/lib/src/base/fingerprint.dart
index 301ebb5146..61fa64ccc6 100644
--- a/packages/flutter_tools/lib/src/base/fingerprint.dart
+++ b/packages/flutter_tools/lib/src/base/fingerprint.dart
@@ -2,6 +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 'package:crypto/crypto.dart' show md5;
 import 'package:meta/meta.dart';
 
diff --git a/packages/flutter_tools/lib/src/base/io.dart b/packages/flutter_tools/lib/src/base/io.dart
index cd60b5c7ce..9693bd7d4a 100644
--- a/packages/flutter_tools/lib/src/base/io.dart
+++ b/packages/flutter_tools/lib/src/base/io.dart
@@ -2,6 +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
+
 /// This file serves as the single point of entry into the `dart:io` APIs
 /// within Flutter tools.
 ///
diff --git a/packages/flutter_tools/lib/src/base/logger.dart b/packages/flutter_tools/lib/src/base/logger.dart
index 038ec4cdcc..4ab30fac29 100644
--- a/packages/flutter_tools/lib/src/base/logger.dart
+++ b/packages/flutter_tools/lib/src/base/logger.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/base/net.dart b/packages/flutter_tools/lib/src/base/net.dart
index 7bff3c4aae..45c1074c4d 100644
--- a/packages/flutter_tools/lib/src/base/net.dart
+++ b/packages/flutter_tools/lib/src/base/net.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/base/os.dart b/packages/flutter_tools/lib/src/base/os.dart
index d5210d9411..6dd472973c 100644
--- a/packages/flutter_tools/lib/src/base/os.dart
+++ b/packages/flutter_tools/lib/src/base/os.dart
@@ -2,6 +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 'package:archive/archive.dart';
 import 'package:file/file.dart';
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/base/platform.dart b/packages/flutter_tools/lib/src/base/platform.dart
index 0af28eb7fd..1420b110ba 100644
--- a/packages/flutter_tools/lib/src/base/platform.dart
+++ b/packages/flutter_tools/lib/src/base/platform.dart
@@ -2,6 +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:io' as io show Platform, stdin, stdout;
 
 /// Provides API parity with the `Platform` class in `dart:io`, but using
diff --git a/packages/flutter_tools/lib/src/base/process.dart b/packages/flutter_tools/lib/src/base/process.dart
index a910795da9..e4b8e052c9 100644
--- a/packages/flutter_tools/lib/src/base/process.dart
+++ b/packages/flutter_tools/lib/src/base/process.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/base/project_migrator.dart b/packages/flutter_tools/lib/src/base/project_migrator.dart
index 1ba453f44e..e81e3508db 100644
--- a/packages/flutter_tools/lib/src/base/project_migrator.dart
+++ b/packages/flutter_tools/lib/src/base/project_migrator.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import 'file_system.dart';
diff --git a/packages/flutter_tools/lib/src/base/signals.dart b/packages/flutter_tools/lib/src/base/signals.dart
index fe156f8b69..1496930af8 100644
--- a/packages/flutter_tools/lib/src/base/signals.dart
+++ b/packages/flutter_tools/lib/src/base/signals.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/base/template.dart b/packages/flutter_tools/lib/src/base/template.dart
index 5072e6de5f..44462693b9 100644
--- a/packages/flutter_tools/lib/src/base/template.dart
+++ b/packages/flutter_tools/lib/src/base/template.dart
@@ -2,6 +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
+
 /// An indirection around our mustache templating system to avoid a
 /// dependency on mustache..
 abstract class TemplateRenderer {
diff --git a/packages/flutter_tools/lib/src/base/terminal.dart b/packages/flutter_tools/lib/src/base/terminal.dart
index 969bca752e..d2820b8241 100644
--- a/packages/flutter_tools/lib/src/base/terminal.dart
+++ b/packages/flutter_tools/lib/src/base/terminal.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../convert.dart';
diff --git a/packages/flutter_tools/lib/src/base/time.dart b/packages/flutter_tools/lib/src/base/time.dart
index dc989df383..baf0bde4c1 100644
--- a/packages/flutter_tools/lib/src/base/time.dart
+++ b/packages/flutter_tools/lib/src/base/time.dart
@@ -2,6 +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
+
 /// A class for making time based operations testable.
 class SystemClock {
   /// A const constructor to allow subclasses to be const.
diff --git a/packages/flutter_tools/lib/src/base/user_messages.dart b/packages/flutter_tools/lib/src/base/user_messages.dart
index 0b53f73e88..90009be34d 100644
--- a/packages/flutter_tools/lib/src/base/user_messages.dart
+++ b/packages/flutter_tools/lib/src/base/user_messages.dart
@@ -2,6 +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 'context.dart';
 import 'platform.dart';
 
diff --git a/packages/flutter_tools/lib/src/base/utils.dart b/packages/flutter_tools/lib/src/base/utils.dart
index 4bf9f64513..5e6e85a9be 100644
--- a/packages/flutter_tools/lib/src/base/utils.dart
+++ b/packages/flutter_tools/lib/src/base/utils.dart
@@ -2,6 +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 'dart:math' as math;
 
diff --git a/packages/flutter_tools/lib/src/base/version.dart b/packages/flutter_tools/lib/src/base/version.dart
index edaf12a7b2..76a064ba9e 100644
--- a/packages/flutter_tools/lib/src/base/version.dart
+++ b/packages/flutter_tools/lib/src/base/version.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 @immutable
diff --git a/packages/flutter_tools/lib/src/build_info.dart b/packages/flutter_tools/lib/src/build_info.dart
index ac41b1c713..b24033a603 100644
--- a/packages/flutter_tools/lib/src/build_info.dart
+++ b/packages/flutter_tools/lib/src/build_info.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config_types.dart';
 
diff --git a/packages/flutter_tools/lib/src/build_system/build_system.dart b/packages/flutter_tools/lib/src/build_system/build_system.dart
index 0ba1185ee4..48013e80e0 100644
--- a/packages/flutter_tools/lib/src/build_system/build_system.dart
+++ b/packages/flutter_tools/lib/src/build_system/build_system.dart
@@ -2,6 +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 'package:async/async.dart';
 import 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/depfile.dart b/packages/flutter_tools/lib/src/build_system/depfile.dart
index 975a8c5916..2ac1be952c 100644
--- a/packages/flutter_tools/lib/src/build_system/depfile.dart
+++ b/packages/flutter_tools/lib/src/build_system/depfile.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/error_handling_io.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/exceptions.dart b/packages/flutter_tools/lib/src/build_system/exceptions.dart
index b7ae0ef9f6..55a2a01dad 100644
--- a/packages/flutter_tools/lib/src/build_system/exceptions.dart
+++ b/packages/flutter_tools/lib/src/build_system/exceptions.dart
@@ -2,6 +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 '../base/file_system.dart';
 
 import 'build_system.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/file_store.dart b/packages/flutter_tools/lib/src/build_system/file_store.dart
index cdb0bdb560..dab105497f 100644
--- a/packages/flutter_tools/lib/src/build_system/file_store.dart
+++ b/packages/flutter_tools/lib/src/build_system/file_store.dart
@@ -2,6 +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:collection';
 import 'dart:typed_data';
 
diff --git a/packages/flutter_tools/lib/src/build_system/hash.dart b/packages/flutter_tools/lib/src/build_system/hash.dart
index bd3b3760d2..3e5ac4011d 100644
--- a/packages/flutter_tools/lib/src/build_system/hash.dart
+++ b/packages/flutter_tools/lib/src/build_system/hash.dart
@@ -2,6 +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:typed_data';
 
 /// Data from a non-linear mathematical function that functions as
diff --git a/packages/flutter_tools/lib/src/build_system/source.dart b/packages/flutter_tools/lib/src/build_system/source.dart
index 15aa58bd5c..7a173d781f 100644
--- a/packages/flutter_tools/lib/src/build_system/source.dart
+++ b/packages/flutter_tools/lib/src/build_system/source.dart
@@ -2,6 +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 '../artifacts.dart';
 import '../base/file_system.dart';
 import '../build_info.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/targets/android.dart b/packages/flutter_tools/lib/src/build_system/targets/android.dart
index 8d9d0c84b8..6b03abf9bb 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/android.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/android.dart
@@ -2,6 +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 '../../artifacts.dart';
 import '../../base/build.dart';
 import '../../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/targets/assets.dart b/packages/flutter_tools/lib/src/build_system/targets/assets.dart
index 5eb1790412..a5a9a419ab 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/assets.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/assets.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:pool/pool.dart';
 
diff --git a/packages/flutter_tools/lib/src/build_system/targets/common.dart b/packages/flutter_tools/lib/src/build_system/targets/common.dart
index 3105ae0684..a9803a87b3 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/common.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/common.dart
@@ -2,6 +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 'package:package_config/package_config.dart';
 
 import '../../artifacts.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/targets/desktop.dart b/packages/flutter_tools/lib/src/build_system/targets/desktop.dart
index 20c1bf46f2..0b883b3407 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/desktop.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/desktop.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/targets/icon_tree_shaker.dart b/packages/flutter_tools/lib/src/build_system/targets/icon_tree_shaker.dart
index 8becc63dd7..4eb4dc5ca8 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/icon_tree_shaker.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/icon_tree_shaker.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 import 'package:mime/mime.dart' as mime;
diff --git a/packages/flutter_tools/lib/src/build_system/targets/ios.dart b/packages/flutter_tools/lib/src/build_system/targets/ios.dart
index 166ab2e54d..24f0dd16ac 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/ios.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/ios.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../../artifacts.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/targets/linux.dart b/packages/flutter_tools/lib/src/build_system/targets/linux.dart
index 8e3d284369..f28fe24aba 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/linux.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/linux.dart
@@ -2,6 +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 '../../artifacts.dart';
 import '../../base/file_system.dart';
 import '../../build_info.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/targets/localizations.dart b/packages/flutter_tools/lib/src/build_system/targets/localizations.dart
index d2b22049ef..f5a995fc7a 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/localizations.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/localizations.dart
@@ -2,6 +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 '../../base/file_system.dart';
 import '../../convert.dart';
 import '../../globals.dart' as globals;
diff --git a/packages/flutter_tools/lib/src/build_system/targets/macos.dart b/packages/flutter_tools/lib/src/build_system/targets/macos.dart
index 8e8bd3181c..7621d1e72e 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/macos.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/macos.dart
@@ -2,6 +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 '../../artifacts.dart';
 import '../../base/build.dart';
 import '../../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/targets/web.dart b/packages/flutter_tools/lib/src/build_system/targets/web.dart
index 98387ca739..2fe6288a0d 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/web.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/web.dart
@@ -2,6 +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:math';
 
 import 'package:crypto/crypto.dart';
diff --git a/packages/flutter_tools/lib/src/build_system/targets/windows.dart b/packages/flutter_tools/lib/src/build_system/targets/windows.dart
index 3ee2157193..0ebc85efe2 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/windows.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/windows.dart
@@ -2,6 +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 '../../artifacts.dart';
 import '../../base/file_system.dart';
 import '../../build_info.dart';
diff --git a/packages/flutter_tools/lib/src/bundle.dart b/packages/flutter_tools/lib/src/bundle.dart
index 1eb23f2333..8263c32a51 100644
--- a/packages/flutter_tools/lib/src/bundle.dart
+++ b/packages/flutter_tools/lib/src/bundle.dart
@@ -2,6 +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 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/cache.dart b/packages/flutter_tools/lib/src/cache.dart
index 177ab4564c..2eef212dca 100644
--- a/packages/flutter_tools/lib/src/cache.dart
+++ b/packages/flutter_tools/lib/src/cache.dart
@@ -2,6 +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:crypto/crypto.dart';
diff --git a/packages/flutter_tools/lib/src/cmake.dart b/packages/flutter_tools/lib/src/cmake.dart
index c611e98a26..7dd735d9c0 100644
--- a/packages/flutter_tools/lib/src/cmake.dart
+++ b/packages/flutter_tools/lib/src/cmake.dart
@@ -2,6 +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 'project.dart';
 
 /// Extracts the `BINARY_NAME` from a project's CMake file.
diff --git a/packages/flutter_tools/lib/src/commands/analyze.dart b/packages/flutter_tools/lib/src/commands/analyze.dart
index eada25bff7..8b014f5e65 100644
--- a/packages/flutter_tools/lib/src/commands/analyze.dart
+++ b/packages/flutter_tools/lib/src/commands/analyze.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/commands/analyze_base.dart b/packages/flutter_tools/lib/src/commands/analyze_base.dart
index ca5eb827e4..b9ee1081e9 100644
--- a/packages/flutter_tools/lib/src/commands/analyze_base.dart
+++ b/packages/flutter_tools/lib/src/commands/analyze_base.dart
@@ -2,6 +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 'package:args/args.dart';
 import 'package:meta/meta.dart';
 import 'package:process/process.dart';
diff --git a/packages/flutter_tools/lib/src/commands/analyze_continuously.dart b/packages/flutter_tools/lib/src/commands/analyze_continuously.dart
index dd118df46e..84aa07e175 100644
--- a/packages/flutter_tools/lib/src/commands/analyze_continuously.dart
+++ b/packages/flutter_tools/lib/src/commands/analyze_continuously.dart
@@ -2,6 +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 'package:args/args.dart';
 import 'package:meta/meta.dart';
 import 'package:process/process.dart';
diff --git a/packages/flutter_tools/lib/src/commands/analyze_once.dart b/packages/flutter_tools/lib/src/commands/analyze_once.dart
index d4e9bd03ec..6a559092c2 100644
--- a/packages/flutter_tools/lib/src/commands/analyze_once.dart
+++ b/packages/flutter_tools/lib/src/commands/analyze_once.dart
@@ -2,6 +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:args/args.dart';
diff --git a/packages/flutter_tools/lib/src/commands/assemble.dart b/packages/flutter_tools/lib/src/commands/assemble.dart
index 535be1b330..bd4e24f72a 100644
--- a/packages/flutter_tools/lib/src/commands/assemble.dart
+++ b/packages/flutter_tools/lib/src/commands/assemble.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/attach.dart b/packages/flutter_tools/lib/src/commands/attach.dart
index ddc877b4a8..0a80363a44 100644
--- a/packages/flutter_tools/lib/src/commands/attach.dart
+++ b/packages/flutter_tools/lib/src/commands/attach.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/commands/build.dart b/packages/flutter_tools/lib/src/commands/build.dart
index 23472a66b3..faa1da9917 100644
--- a/packages/flutter_tools/lib/src/commands/build.dart
+++ b/packages/flutter_tools/lib/src/commands/build.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../build_info.dart';
diff --git a/packages/flutter_tools/lib/src/commands/build_aar.dart b/packages/flutter_tools/lib/src/commands/build_aar.dart
index 1836c42938..8f7d125d47 100644
--- a/packages/flutter_tools/lib/src/commands/build_aar.dart
+++ b/packages/flutter_tools/lib/src/commands/build_aar.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../android/android_builder.dart';
diff --git a/packages/flutter_tools/lib/src/commands/build_apk.dart b/packages/flutter_tools/lib/src/commands/build_apk.dart
index 0ff87c1690..ef2c22b208 100644
--- a/packages/flutter_tools/lib/src/commands/build_apk.dart
+++ b/packages/flutter_tools/lib/src/commands/build_apk.dart
@@ -2,6 +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 '../android/android_builder.dart';
 import '../android/build_validation.dart';
 import '../android/gradle_utils.dart';
diff --git a/packages/flutter_tools/lib/src/commands/build_appbundle.dart b/packages/flutter_tools/lib/src/commands/build_appbundle.dart
index 5a9499a34a..157a9f665c 100644
--- a/packages/flutter_tools/lib/src/commands/build_appbundle.dart
+++ b/packages/flutter_tools/lib/src/commands/build_appbundle.dart
@@ -2,6 +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 '../android/android_builder.dart';
 import '../android/build_validation.dart';
 import '../android/gradle_utils.dart';
diff --git a/packages/flutter_tools/lib/src/commands/build_bundle.dart b/packages/flutter_tools/lib/src/commands/build_bundle.dart
index d3adce062b..86e51c63a1 100644
--- a/packages/flutter_tools/lib/src/commands/build_bundle.dart
+++ b/packages/flutter_tools/lib/src/commands/build_bundle.dart
@@ -2,6 +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 '../base/common.dart';
 import '../build_info.dart';
 import '../bundle.dart';
diff --git a/packages/flutter_tools/lib/src/commands/build_fuchsia.dart b/packages/flutter_tools/lib/src/commands/build_fuchsia.dart
index bea8733edc..3fd1cd9880 100644
--- a/packages/flutter_tools/lib/src/commands/build_fuchsia.dart
+++ b/packages/flutter_tools/lib/src/commands/build_fuchsia.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/build_ios.dart b/packages/flutter_tools/lib/src/commands/build_ios.dart
index 1afc7c2a3c..ec03765e7c 100644
--- a/packages/flutter_tools/lib/src/commands/build_ios.dart
+++ b/packages/flutter_tools/lib/src/commands/build_ios.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:meta/meta.dart';
 
diff --git a/packages/flutter_tools/lib/src/commands/build_ios_framework.dart b/packages/flutter_tools/lib/src/commands/build_ios_framework.dart
index 55cf7c5cef..561dcc7c40 100644
--- a/packages/flutter_tools/lib/src/commands/build_ios_framework.dart
+++ b/packages/flutter_tools/lib/src/commands/build_ios_framework.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:meta/meta.dart';
 
diff --git a/packages/flutter_tools/lib/src/commands/build_linux.dart b/packages/flutter_tools/lib/src/commands/build_linux.dart
index a83027aaca..693e7988f1 100644
--- a/packages/flutter_tools/lib/src/commands/build_linux.dart
+++ b/packages/flutter_tools/lib/src/commands/build_linux.dart
@@ -2,6 +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 '../base/analyze_size.dart';
 import '../base/common.dart';
 import '../build_info.dart';
diff --git a/packages/flutter_tools/lib/src/commands/build_macos.dart b/packages/flutter_tools/lib/src/commands/build_macos.dart
index d14d9e6c5c..5bfec4570d 100644
--- a/packages/flutter_tools/lib/src/commands/build_macos.dart
+++ b/packages/flutter_tools/lib/src/commands/build_macos.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/analyze_size.dart';
diff --git a/packages/flutter_tools/lib/src/commands/build_web.dart b/packages/flutter_tools/lib/src/commands/build_web.dart
index 20d99ba5ae..5756232961 100644
--- a/packages/flutter_tools/lib/src/commands/build_web.dart
+++ b/packages/flutter_tools/lib/src/commands/build_web.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/build_windows.dart b/packages/flutter_tools/lib/src/commands/build_windows.dart
index 17f648ca79..dfa46cae84 100644
--- a/packages/flutter_tools/lib/src/commands/build_windows.dart
+++ b/packages/flutter_tools/lib/src/commands/build_windows.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/analyze_size.dart';
diff --git a/packages/flutter_tools/lib/src/commands/channel.dart b/packages/flutter_tools/lib/src/commands/channel.dart
index 02b1487cbb..8f2d030f19 100644
--- a/packages/flutter_tools/lib/src/commands/channel.dart
+++ b/packages/flutter_tools/lib/src/commands/channel.dart
@@ -2,6 +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 '../base/common.dart';
 import '../cache.dart';
 import '../globals.dart' as globals;
diff --git a/packages/flutter_tools/lib/src/commands/clean.dart b/packages/flutter_tools/lib/src/commands/clean.dart
index 5c3b64f5e6..a2b2d14105 100644
--- a/packages/flutter_tools/lib/src/commands/clean.dart
+++ b/packages/flutter_tools/lib/src/commands/clean.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/commands/config.dart b/packages/flutter_tools/lib/src/commands/config.dart
index c726602da4..d9f44b9355 100644
--- a/packages/flutter_tools/lib/src/commands/config.dart
+++ b/packages/flutter_tools/lib/src/commands/config.dart
@@ -2,6 +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 '../android/android_studio.dart';
 import '../base/common.dart';
 import '../convert.dart';
diff --git a/packages/flutter_tools/lib/src/commands/create.dart b/packages/flutter_tools/lib/src/commands/create.dart
index 4147bd85d1..99b3044614 100644
--- a/packages/flutter_tools/lib/src/commands/create.dart
+++ b/packages/flutter_tools/lib/src/commands/create.dart
@@ -2,6 +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 '../android/gradle_utils.dart' as gradle;
 import '../base/common.dart';
 import '../base/context.dart';
diff --git a/packages/flutter_tools/lib/src/commands/create_base.dart b/packages/flutter_tools/lib/src/commands/create_base.dart
index 5b5729f630..dcb7db856a 100644
--- a/packages/flutter_tools/lib/src/commands/create_base.dart
+++ b/packages/flutter_tools/lib/src/commands/create_base.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:uuid/uuid.dart';
 
diff --git a/packages/flutter_tools/lib/src/commands/daemon.dart b/packages/flutter_tools/lib/src/commands/daemon.dart
index 16c457b2ae..640098662d 100644
--- a/packages/flutter_tools/lib/src/commands/daemon.dart
+++ b/packages/flutter_tools/lib/src/commands/daemon.dart
@@ -2,6 +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:async/async.dart';
diff --git a/packages/flutter_tools/lib/src/commands/devices.dart b/packages/flutter_tools/lib/src/commands/devices.dart
index 59829b3d38..73d4267daa 100644
--- a/packages/flutter_tools/lib/src/commands/devices.dart
+++ b/packages/flutter_tools/lib/src/commands/devices.dart
@@ -2,6 +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 '../base/common.dart';
 import '../base/utils.dart';
 import '../convert.dart';
diff --git a/packages/flutter_tools/lib/src/commands/doctor.dart b/packages/flutter_tools/lib/src/commands/doctor.dart
index 32e045e0e3..6f3d2f560f 100644
--- a/packages/flutter_tools/lib/src/commands/doctor.dart
+++ b/packages/flutter_tools/lib/src/commands/doctor.dart
@@ -2,6 +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 '../android/android_workflow.dart';
 import '../base/common.dart';
 import '../globals.dart' as globals;
diff --git a/packages/flutter_tools/lib/src/commands/downgrade.dart b/packages/flutter_tools/lib/src/commands/downgrade.dart
index ddf98c2597..71dfec2bd0 100644
--- a/packages/flutter_tools/lib/src/commands/downgrade.dart
+++ b/packages/flutter_tools/lib/src/commands/downgrade.dart
@@ -2,6 +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 'package:process/process.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/drive.dart b/packages/flutter_tools/lib/src/commands/drive.dart
index 8b8b343c98..b7b3f079f9 100644
--- a/packages/flutter_tools/lib/src/commands/drive.dart
+++ b/packages/flutter_tools/lib/src/commands/drive.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/commands/emulators.dart b/packages/flutter_tools/lib/src/commands/emulators.dart
index 580e3223b0..44827210f1 100644
--- a/packages/flutter_tools/lib/src/commands/emulators.dart
+++ b/packages/flutter_tools/lib/src/commands/emulators.dart
@@ -2,6 +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 '../base/common.dart';
 import '../base/utils.dart';
 import '../doctor.dart';
diff --git a/packages/flutter_tools/lib/src/commands/format.dart b/packages/flutter_tools/lib/src/commands/format.dart
index 4ec89311ce..cd2f32ebb7 100644
--- a/packages/flutter_tools/lib/src/commands/format.dart
+++ b/packages/flutter_tools/lib/src/commands/format.dart
@@ -2,6 +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 '../artifacts.dart';
 import '../base/common.dart';
 import '../globals.dart' as globals;
diff --git a/packages/flutter_tools/lib/src/commands/generate.dart b/packages/flutter_tools/lib/src/commands/generate.dart
index d815d05d0e..a79aeef104 100644
--- a/packages/flutter_tools/lib/src/commands/generate.dart
+++ b/packages/flutter_tools/lib/src/commands/generate.dart
@@ -2,6 +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 '../globals.dart' as globals;
 import '../runner/flutter_command.dart';
 
diff --git a/packages/flutter_tools/lib/src/commands/generate_localizations.dart b/packages/flutter_tools/lib/src/commands/generate_localizations.dart
index 0076ade80a..9a9c23d922 100644
--- a/packages/flutter_tools/lib/src/commands/generate_localizations.dart
+++ b/packages/flutter_tools/lib/src/commands/generate_localizations.dart
@@ -2,6 +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 '../base/common.dart';
 import '../base/file_system.dart';
 import '../base/logger.dart';
diff --git a/packages/flutter_tools/lib/src/commands/ide_config.dart b/packages/flutter_tools/lib/src/commands/ide_config.dart
index 4f229454ff..723bac0b8e 100644
--- a/packages/flutter_tools/lib/src/commands/ide_config.dart
+++ b/packages/flutter_tools/lib/src/commands/ide_config.dart
@@ -2,6 +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 '../base/common.dart';
 import '../base/file_system.dart';
 import '../cache.dart';
diff --git a/packages/flutter_tools/lib/src/commands/install.dart b/packages/flutter_tools/lib/src/commands/install.dart
index 6485a9e6f0..e61218e82e 100644
--- a/packages/flutter_tools/lib/src/commands/install.dart
+++ b/packages/flutter_tools/lib/src/commands/install.dart
@@ -2,6 +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 '../android/android_device.dart';
 import '../application_package.dart';
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/logs.dart b/packages/flutter_tools/lib/src/commands/logs.dart
index 058779ff3c..731eb30974 100644
--- a/packages/flutter_tools/lib/src/commands/logs.dart
+++ b/packages/flutter_tools/lib/src/commands/logs.dart
@@ -2,6 +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 '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/make_host_app_editable.dart b/packages/flutter_tools/lib/src/commands/make_host_app_editable.dart
index 907ce6090b..3fcb8669f1 100644
--- a/packages/flutter_tools/lib/src/commands/make_host_app_editable.dart
+++ b/packages/flutter_tools/lib/src/commands/make_host_app_editable.dart
@@ -2,6 +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 '../runner/flutter_command.dart';
 
 class MakeHostAppEditableCommand extends FlutterCommand {
diff --git a/packages/flutter_tools/lib/src/commands/packages.dart b/packages/flutter_tools/lib/src/commands/packages.dart
index badca15a40..40357c1faa 100644
--- a/packages/flutter_tools/lib/src/commands/packages.dart
+++ b/packages/flutter_tools/lib/src/commands/packages.dart
@@ -2,6 +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 'package:args/args.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/precache.dart b/packages/flutter_tools/lib/src/commands/precache.dart
index 58b151b8ad..d631ade1b4 100644
--- a/packages/flutter_tools/lib/src/commands/precache.dart
+++ b/packages/flutter_tools/lib/src/commands/precache.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/run.dart b/packages/flutter_tools/lib/src/commands/run.dart
index e9cf68b40e..00a6099a22 100644
--- a/packages/flutter_tools/lib/src/commands/run.dart
+++ b/packages/flutter_tools/lib/src/commands/run.dart
@@ -2,6 +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 '../android/android_device.dart';
diff --git a/packages/flutter_tools/lib/src/commands/screenshot.dart b/packages/flutter_tools/lib/src/commands/screenshot.dart
index 937dfe25a6..d9aaeb37ab 100644
--- a/packages/flutter_tools/lib/src/commands/screenshot.dart
+++ b/packages/flutter_tools/lib/src/commands/screenshot.dart
@@ -2,6 +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 'package:vm_service/vm_service.dart' as vm_service;
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/shell_completion.dart b/packages/flutter_tools/lib/src/commands/shell_completion.dart
index b5f7eaee7c..2732b673f6 100644
--- a/packages/flutter_tools/lib/src/commands/shell_completion.dart
+++ b/packages/flutter_tools/lib/src/commands/shell_completion.dart
@@ -2,6 +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 'package:completion/completion.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/commands/symbolize.dart b/packages/flutter_tools/lib/src/commands/symbolize.dart
index 014083db98..49982a9320 100644
--- a/packages/flutter_tools/lib/src/commands/symbolize.dart
+++ b/packages/flutter_tools/lib/src/commands/symbolize.dart
@@ -2,6 +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 'dart:typed_data';
 
diff --git a/packages/flutter_tools/lib/src/commands/test.dart b/packages/flutter_tools/lib/src/commands/test.dart
index a2760aea44..ce2e184b6f 100644
--- a/packages/flutter_tools/lib/src/commands/test.dart
+++ b/packages/flutter_tools/lib/src/commands/test.dart
@@ -2,6 +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:math' as math;
 
 import '../asset.dart';
diff --git a/packages/flutter_tools/lib/src/commands/update_packages.dart b/packages/flutter_tools/lib/src/commands/update_packages.dart
index 027c102850..5cbe425a8b 100644
--- a/packages/flutter_tools/lib/src/commands/update_packages.dart
+++ b/packages/flutter_tools/lib/src/commands/update_packages.dart
@@ -2,6 +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:collection';
 
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/commands/upgrade.dart b/packages/flutter_tools/lib/src/commands/upgrade.dart
index 62077310f3..957568dff5 100644
--- a/packages/flutter_tools/lib/src/commands/upgrade.dart
+++ b/packages/flutter_tools/lib/src/commands/upgrade.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/compile.dart b/packages/flutter_tools/lib/src/compile.dart
index 49e224c802..76923c2746 100644
--- a/packages/flutter_tools/lib/src/compile.dart
+++ b/packages/flutter_tools/lib/src/compile.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/context_runner.dart b/packages/flutter_tools/lib/src/context_runner.dart
index baad4222df..ae436f5611 100644
--- a/packages/flutter_tools/lib/src/context_runner.dart
+++ b/packages/flutter_tools/lib/src/context_runner.dart
@@ -2,6 +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:process/process.dart';
diff --git a/packages/flutter_tools/lib/src/convert.dart b/packages/flutter_tools/lib/src/convert.dart
index 88de8fcb75..8e2af7005e 100644
--- a/packages/flutter_tools/lib/src/convert.dart
+++ b/packages/flutter_tools/lib/src/convert.dart
@@ -2,6 +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
+
 // Hide the original utf8 [Codec] so that we can export our own implementation
 // which adds additional error handling.
 import 'dart:convert' hide utf8;
diff --git a/packages/flutter_tools/lib/src/dart/analysis.dart b/packages/flutter_tools/lib/src/dart/analysis.dart
index 8ccb376133..ef873b2b37 100644
--- a/packages/flutter_tools/lib/src/dart/analysis.dart
+++ b/packages/flutter_tools/lib/src/dart/analysis.dart
@@ -2,6 +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 'dart:math' as math;
 
diff --git a/packages/flutter_tools/lib/src/dart/generate_synthetic_packages.dart b/packages/flutter_tools/lib/src/dart/generate_synthetic_packages.dart
index 2803eead07..815691f185 100644
--- a/packages/flutter_tools/lib/src/dart/generate_synthetic_packages.dart
+++ b/packages/flutter_tools/lib/src/dart/generate_synthetic_packages.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:yaml/yaml.dart';
 
diff --git a/packages/flutter_tools/lib/src/dart/language_version.dart b/packages/flutter_tools/lib/src/dart/language_version.dart
index b36faebff6..08fae2d46d 100644
--- a/packages/flutter_tools/lib/src/dart/language_version.dart
+++ b/packages/flutter_tools/lib/src/dart/language_version.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:package_config/package_config.dart';
 
diff --git a/packages/flutter_tools/lib/src/dart/package_map.dart b/packages/flutter_tools/lib/src/dart/package_map.dart
index 981369a7b1..68735fa40d 100644
--- a/packages/flutter_tools/lib/src/dart/package_map.dart
+++ b/packages/flutter_tools/lib/src/dart/package_map.dart
@@ -2,6 +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:typed_data';
 
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/dart/pub.dart b/packages/flutter_tools/lib/src/dart/pub.dart
index 8ce4834466..8828c278ac 100644
--- a/packages/flutter_tools/lib/src/dart/pub.dart
+++ b/packages/flutter_tools/lib/src/dart/pub.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
diff --git a/packages/flutter_tools/lib/src/desktop_device.dart b/packages/flutter_tools/lib/src/desktop_device.dart
index 6b4d9322f7..0a8d1b9c3e 100644
--- a/packages/flutter_tools/lib/src/desktop_device.dart
+++ b/packages/flutter_tools/lib/src/desktop_device.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/devfs.dart b/packages/flutter_tools/lib/src/devfs.dart
index 5c6f98ea5a..6efb7dea2a 100644
--- a/packages/flutter_tools/lib/src/devfs.dart
+++ b/packages/flutter_tools/lib/src/devfs.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/device.dart b/packages/flutter_tools/lib/src/device.dart
index cbbf9e5fee..d6bbc427c9 100644
--- a/packages/flutter_tools/lib/src/device.dart
+++ b/packages/flutter_tools/lib/src/device.dart
@@ -2,6 +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 'dart:math' as math;
 
diff --git a/packages/flutter_tools/lib/src/devtools_launcher.dart b/packages/flutter_tools/lib/src/devtools_launcher.dart
index 7592a5c075..8cc1e53f85 100644
--- a/packages/flutter_tools/lib/src/devtools_launcher.dart
+++ b/packages/flutter_tools/lib/src/devtools_launcher.dart
@@ -2,6 +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:http/http.dart' as http;
diff --git a/packages/flutter_tools/lib/src/doctor.dart b/packages/flutter_tools/lib/src/doctor.dart
index 0f1f9fedca..badb2943d5 100644
--- a/packages/flutter_tools/lib/src/doctor.dart
+++ b/packages/flutter_tools/lib/src/doctor.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/drive/drive_service.dart b/packages/flutter_tools/lib/src/drive/drive_service.dart
index b9f7bff39b..fc2e2c8f1c 100644
--- a/packages/flutter_tools/lib/src/drive/drive_service.dart
+++ b/packages/flutter_tools/lib/src/drive/drive_service.dart
@@ -2,6 +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 'package:dds/dds.dart' as dds;
 import 'package:file/file.dart';
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/drive/web_driver_service.dart b/packages/flutter_tools/lib/src/drive/web_driver_service.dart
index 481d071554..c571ae0d73 100644
--- a/packages/flutter_tools/lib/src/drive/web_driver_service.dart
+++ b/packages/flutter_tools/lib/src/drive/web_driver_service.dart
@@ -2,6 +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 'dart:math' as math;
 
diff --git a/packages/flutter_tools/lib/src/emulator.dart b/packages/flutter_tools/lib/src/emulator.dart
index f8600eb1d5..e825ea2bbd 100644
--- a/packages/flutter_tools/lib/src/emulator.dart
+++ b/packages/flutter_tools/lib/src/emulator.dart
@@ -2,6 +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:math' as math;
 
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/features.dart b/packages/flutter_tools/lib/src/features.dart
index f168f680b0..f4535eb7a4 100644
--- a/packages/flutter_tools/lib/src/features.dart
+++ b/packages/flutter_tools/lib/src/features.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import 'base/config.dart';
diff --git a/packages/flutter_tools/lib/src/flutter_manifest.dart b/packages/flutter_tools/lib/src/flutter_manifest.dart
index d3f303a6de..797cf230e6 100644
--- a/packages/flutter_tools/lib/src/flutter_manifest.dart
+++ b/packages/flutter_tools/lib/src/flutter_manifest.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:pub_semver/pub_semver.dart';
 import 'package:yaml/yaml.dart';
diff --git a/packages/flutter_tools/lib/src/flutter_project_metadata.dart b/packages/flutter_tools/lib/src/flutter_project_metadata.dart
index 3ae7c62038..b41b5458d8 100644
--- a/packages/flutter_tools/lib/src/flutter_project_metadata.dart
+++ b/packages/flutter_tools/lib/src/flutter_project_metadata.dart
@@ -2,6 +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 'package:yaml/yaml.dart';
 
 import 'base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/fuchsia/amber_ctl.dart b/packages/flutter_tools/lib/src/fuchsia/amber_ctl.dart
index 1c27476dd3..89db609ffb 100644
--- a/packages/flutter_tools/lib/src/fuchsia/amber_ctl.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/amber_ctl.dart
@@ -2,6 +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 '../base/process.dart';
 
 import 'fuchsia_device.dart';
diff --git a/packages/flutter_tools/lib/src/fuchsia/application_package.dart b/packages/flutter_tools/lib/src/fuchsia/application_package.dart
index 4626cc04af..29c7d04682 100644
--- a/packages/flutter_tools/lib/src/fuchsia/application_package.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/application_package.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../application_package.dart';
diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_build.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_build.dart
index d297c63522..fcb5a7efb8 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_build.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_build.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../artifacts.dart';
diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_dev_finder.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_dev_finder.dart
index 687238776d..4086dfcbb3 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_dev_finder.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_dev_finder.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart
index 7824ebb98d..984f089f30 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_kernel_compiler.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_kernel_compiler.dart
index 5facd74a6d..3aab6d842d 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_kernel_compiler.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_kernel_compiler.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../artifacts.dart';
diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_pm.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_pm.dart
index 65fd72f7d6..c2f8e40580 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_pm.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_pm.dart
@@ -2,6 +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 '../base/common.dart';
 import '../base/file_system.dart';
 import '../base/io.dart';
diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart
index f4bfd22f44..80e3c45d34 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart
@@ -2,6 +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 '../base/context.dart';
diff --git a/packages/flutter_tools/lib/src/fuchsia/fuchsia_workflow.dart b/packages/flutter_tools/lib/src/fuchsia/fuchsia_workflow.dart
index d3e1dfc604..23ab33dfe6 100644
--- a/packages/flutter_tools/lib/src/fuchsia/fuchsia_workflow.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/fuchsia_workflow.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/context.dart';
diff --git a/packages/flutter_tools/lib/src/fuchsia/tiles_ctl.dart b/packages/flutter_tools/lib/src/fuchsia/tiles_ctl.dart
index 21ab56f3b4..190df58770 100644
--- a/packages/flutter_tools/lib/src/fuchsia/tiles_ctl.dart
+++ b/packages/flutter_tools/lib/src/fuchsia/tiles_ctl.dart
@@ -2,6 +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 '../base/process.dart';
 import '../globals.dart' as globals;
 
diff --git a/packages/flutter_tools/lib/src/globals.dart b/packages/flutter_tools/lib/src/globals.dart
index 755f23d67e..9288e75a0b 100644
--- a/packages/flutter_tools/lib/src/globals.dart
+++ b/packages/flutter_tools/lib/src/globals.dart
@@ -2,6 +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 'package:process/process.dart';
 
 import 'android/android_sdk.dart';
diff --git a/packages/flutter_tools/lib/src/intellij/intellij.dart b/packages/flutter_tools/lib/src/intellij/intellij.dart
index f63b132c48..541c69d381 100644
--- a/packages/flutter_tools/lib/src/intellij/intellij.dart
+++ b/packages/flutter_tools/lib/src/intellij/intellij.dart
@@ -2,6 +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 'package:archive/archive.dart';
 import 'package:meta/meta.dart';
 
diff --git a/packages/flutter_tools/lib/src/intellij/intellij_validator.dart b/packages/flutter_tools/lib/src/intellij/intellij_validator.dart
index 7845c82706..fa23965177 100644
--- a/packages/flutter_tools/lib/src/intellij/intellij_validator.dart
+++ b/packages/flutter_tools/lib/src/intellij/intellij_validator.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/ios/bitcode.dart b/packages/flutter_tools/lib/src/ios/bitcode.dart
index fec5a376b7..ecc703652a 100644
--- a/packages/flutter_tools/lib/src/ios/bitcode.dart
+++ b/packages/flutter_tools/lib/src/ios/bitcode.dart
@@ -2,6 +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 '../artifacts.dart';
 import '../base/common.dart';
 import '../base/context.dart';
diff --git a/packages/flutter_tools/lib/src/ios/code_signing.dart b/packages/flutter_tools/lib/src/ios/code_signing.dart
index bb6c9145e2..20708d1d2e 100644
--- a/packages/flutter_tools/lib/src/ios/code_signing.dart
+++ b/packages/flutter_tools/lib/src/ios/code_signing.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/ios/devices.dart b/packages/flutter_tools/lib/src/ios/devices.dart
index 720e61b508..868de33364 100644
--- a/packages/flutter_tools/lib/src/ios/devices.dart
+++ b/packages/flutter_tools/lib/src/ios/devices.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/ios/ios_deploy.dart b/packages/flutter_tools/lib/src/ios/ios_deploy.dart
index 5e492eaf88..9980d77741 100644
--- a/packages/flutter_tools/lib/src/ios/ios_deploy.dart
+++ b/packages/flutter_tools/lib/src/ios/ios_deploy.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/ios/ios_emulators.dart b/packages/flutter_tools/lib/src/ios/ios_emulators.dart
index f54748b1b6..7678edd941 100644
--- a/packages/flutter_tools/lib/src/ios/ios_emulators.dart
+++ b/packages/flutter_tools/lib/src/ios/ios_emulators.dart
@@ -2,6 +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 '../base/process.dart';
 import '../device.dart';
 import '../emulator.dart';
diff --git a/packages/flutter_tools/lib/src/ios/ios_workflow.dart b/packages/flutter_tools/lib/src/ios/ios_workflow.dart
index 9b26832d1b..a5e2d99b45 100644
--- a/packages/flutter_tools/lib/src/ios/ios_workflow.dart
+++ b/packages/flutter_tools/lib/src/ios/ios_workflow.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/platform.dart';
diff --git a/packages/flutter_tools/lib/src/ios/iproxy.dart b/packages/flutter_tools/lib/src/ios/iproxy.dart
index 852bf02a6c..6ce94554ee 100644
--- a/packages/flutter_tools/lib/src/ios/iproxy.dart
+++ b/packages/flutter_tools/lib/src/ios/iproxy.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/ios/mac.dart b/packages/flutter_tools/lib/src/ios/mac.dart
index 3473b715cf..9aeaf00802 100644
--- a/packages/flutter_tools/lib/src/ios/mac.dart
+++ b/packages/flutter_tools/lib/src/ios/mac.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/ios/migrations/project_base_configuration_migration.dart b/packages/flutter_tools/lib/src/ios/migrations/project_base_configuration_migration.dart
index 27cbbe857b..0457db5493 100644
--- a/packages/flutter_tools/lib/src/ios/migrations/project_base_configuration_migration.dart
+++ b/packages/flutter_tools/lib/src/ios/migrations/project_base_configuration_migration.dart
@@ -2,6 +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 '../../base/file_system.dart';
 import '../../base/logger.dart';
 import '../../base/project_migrator.dart';
diff --git a/packages/flutter_tools/lib/src/ios/migrations/project_build_location_migration.dart b/packages/flutter_tools/lib/src/ios/migrations/project_build_location_migration.dart
index e0bed32027..a4266aa722 100644
--- a/packages/flutter_tools/lib/src/ios/migrations/project_build_location_migration.dart
+++ b/packages/flutter_tools/lib/src/ios/migrations/project_build_location_migration.dart
@@ -2,6 +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 '../../base/file_system.dart';
 import '../../base/logger.dart';
 import '../../base/project_migrator.dart';
diff --git a/packages/flutter_tools/lib/src/ios/migrations/remove_framework_link_and_embedding_migration.dart b/packages/flutter_tools/lib/src/ios/migrations/remove_framework_link_and_embedding_migration.dart
index 222d117004..ddc2f3ef44 100644
--- a/packages/flutter_tools/lib/src/ios/migrations/remove_framework_link_and_embedding_migration.dart
+++ b/packages/flutter_tools/lib/src/ios/migrations/remove_framework_link_and_embedding_migration.dart
@@ -2,6 +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 '../../base/common.dart';
 import '../../base/file_system.dart';
 import '../../base/logger.dart';
diff --git a/packages/flutter_tools/lib/src/ios/migrations/xcode_build_system_migration.dart b/packages/flutter_tools/lib/src/ios/migrations/xcode_build_system_migration.dart
index 4472e2acf2..9675ee3bd8 100644
--- a/packages/flutter_tools/lib/src/ios/migrations/xcode_build_system_migration.dart
+++ b/packages/flutter_tools/lib/src/ios/migrations/xcode_build_system_migration.dart
@@ -2,6 +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 '../../base/file_system.dart';
 import '../../base/logger.dart';
 import '../../base/project_migrator.dart';
diff --git a/packages/flutter_tools/lib/src/ios/plist_parser.dart b/packages/flutter_tools/lib/src/ios/plist_parser.dart
index 183637d446..46efe26132 100644
--- a/packages/flutter_tools/lib/src/ios/plist_parser.dart
+++ b/packages/flutter_tools/lib/src/ios/plist_parser.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/ios/simulators.dart b/packages/flutter_tools/lib/src/ios/simulators.dart
index 98b729412e..05d4a1df62 100644
--- a/packages/flutter_tools/lib/src/ios/simulators.dart
+++ b/packages/flutter_tools/lib/src/ios/simulators.dart
@@ -2,6 +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 'dart:math' as math;
 
diff --git a/packages/flutter_tools/lib/src/ios/xcodeproj.dart b/packages/flutter_tools/lib/src/ios/xcodeproj.dart
index 9ea4427402..0391511e71 100644
--- a/packages/flutter_tools/lib/src/ios/xcodeproj.dart
+++ b/packages/flutter_tools/lib/src/ios/xcodeproj.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:meta/meta.dart';
 import 'package:process/process.dart';
diff --git a/packages/flutter_tools/lib/src/isolated/devfs_web.dart b/packages/flutter_tools/lib/src/isolated/devfs_web.dart
index a50670a0e5..317c7d6ac1 100644
--- a/packages/flutter_tools/lib/src/isolated/devfs_web.dart
+++ b/packages/flutter_tools/lib/src/isolated/devfs_web.dart
@@ -2,6 +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 'dart:typed_data';
 
diff --git a/packages/flutter_tools/lib/src/isolated/mustache_template.dart b/packages/flutter_tools/lib/src/isolated/mustache_template.dart
index 8e21ec7efd..be02adfe71 100644
--- a/packages/flutter_tools/lib/src/isolated/mustache_template.dart
+++ b/packages/flutter_tools/lib/src/isolated/mustache_template.dart
@@ -2,6 +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 'package:mustache_template/mustache_template.dart';
 
 import '../base/template.dart';
diff --git a/packages/flutter_tools/lib/src/isolated/resident_web_runner.dart b/packages/flutter_tools/lib/src/isolated/resident_web_runner.dart
index 2e1d911c3d..0461727d73 100644
--- a/packages/flutter_tools/lib/src/isolated/resident_web_runner.dart
+++ b/packages/flutter_tools/lib/src/isolated/resident_web_runner.dart
@@ -2,6 +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:dwds/dwds.dart';
diff --git a/packages/flutter_tools/lib/src/license_collector.dart b/packages/flutter_tools/lib/src/license_collector.dart
index 36de22ed25..1a595237d6 100644
--- a/packages/flutter_tools/lib/src/license_collector.dart
+++ b/packages/flutter_tools/lib/src/license_collector.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 
diff --git a/packages/flutter_tools/lib/src/linux/application_package.dart b/packages/flutter_tools/lib/src/linux/application_package.dart
index acc80f2a83..26b6d93661 100644
--- a/packages/flutter_tools/lib/src/linux/application_package.dart
+++ b/packages/flutter_tools/lib/src/linux/application_package.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../application_package.dart';
diff --git a/packages/flutter_tools/lib/src/linux/build_linux.dart b/packages/flutter_tools/lib/src/linux/build_linux.dart
index daf4756ee2..ca6518cd69 100644
--- a/packages/flutter_tools/lib/src/linux/build_linux.dart
+++ b/packages/flutter_tools/lib/src/linux/build_linux.dart
@@ -2,6 +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 '../artifacts.dart';
 import '../base/analyze_size.dart';
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/linux/linux_device.dart b/packages/flutter_tools/lib/src/linux/linux_device.dart
index a860d164ec..e122cea9a8 100644
--- a/packages/flutter_tools/lib/src/linux/linux_device.dart
+++ b/packages/flutter_tools/lib/src/linux/linux_device.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/linux/linux_doctor.dart b/packages/flutter_tools/lib/src/linux/linux_doctor.dart
index 2ff3adff4f..73fa32fcb9 100644
--- a/packages/flutter_tools/lib/src/linux/linux_doctor.dart
+++ b/packages/flutter_tools/lib/src/linux/linux_doctor.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/linux/linux_workflow.dart b/packages/flutter_tools/lib/src/linux/linux_workflow.dart
index e1bcfb3bd1..e13e2f65d8 100644
--- a/packages/flutter_tools/lib/src/linux/linux_workflow.dart
+++ b/packages/flutter_tools/lib/src/linux/linux_workflow.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/platform.dart';
diff --git a/packages/flutter_tools/lib/src/localizations/gen_l10n.dart b/packages/flutter_tools/lib/src/localizations/gen_l10n.dart
index faf53b8c37..45663543ee 100644
--- a/packages/flutter_tools/lib/src/localizations/gen_l10n.dart
+++ b/packages/flutter_tools/lib/src/localizations/gen_l10n.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/localizations/gen_l10n_templates.dart b/packages/flutter_tools/lib/src/localizations/gen_l10n_templates.dart
index b8487fbe54..4bd85cd0a8 100644
--- a/packages/flutter_tools/lib/src/localizations/gen_l10n_templates.dart
+++ b/packages/flutter_tools/lib/src/localizations/gen_l10n_templates.dart
@@ -2,6 +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
+
 const String emptyPubspecTemplate = '''
 # Generated by the flutter tool
 name: synthetic_package
diff --git a/packages/flutter_tools/lib/src/localizations/gen_l10n_types.dart b/packages/flutter_tools/lib/src/localizations/gen_l10n_types.dart
index 2329f06f10..1d289f25b9 100644
--- a/packages/flutter_tools/lib/src/localizations/gen_l10n_types.dart
+++ b/packages/flutter_tools/lib/src/localizations/gen_l10n_types.dart
@@ -2,6 +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 'package:intl/locale.dart';
 
 import '../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/localizations/language_subtag_registry.dart b/packages/flutter_tools/lib/src/localizations/language_subtag_registry.dart
index 6372d6dfca..b7bc68fa95 100644
--- a/packages/flutter_tools/lib/src/localizations/language_subtag_registry.dart
+++ b/packages/flutter_tools/lib/src/localizations/language_subtag_registry.dart
@@ -2,6 +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
+
 /// Cache of https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry.
 const String languageSubtagRegistry = '''
 File-Date: 2020-03-16
diff --git a/packages/flutter_tools/lib/src/localizations/localizations_utils.dart b/packages/flutter_tools/lib/src/localizations/localizations_utils.dart
index 7eb0ab9619..267adf6c49 100644
--- a/packages/flutter_tools/lib/src/localizations/localizations_utils.dart
+++ b/packages/flutter_tools/lib/src/localizations/localizations_utils.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:yaml/yaml.dart';
 
diff --git a/packages/flutter_tools/lib/src/macos/application_package.dart b/packages/flutter_tools/lib/src/macos/application_package.dart
index 27e93f8fc1..02b6354519 100644
--- a/packages/flutter_tools/lib/src/macos/application_package.dart
+++ b/packages/flutter_tools/lib/src/macos/application_package.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../application_package.dart';
diff --git a/packages/flutter_tools/lib/src/macos/build_macos.dart b/packages/flutter_tools/lib/src/macos/build_macos.dart
index 3f08c6aafc..8b1778dce2 100644
--- a/packages/flutter_tools/lib/src/macos/build_macos.dart
+++ b/packages/flutter_tools/lib/src/macos/build_macos.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/analyze_size.dart';
diff --git a/packages/flutter_tools/lib/src/macos/cocoapod_utils.dart b/packages/flutter_tools/lib/src/macos/cocoapod_utils.dart
index bfa7c1d167..771e9136c1 100644
--- a/packages/flutter_tools/lib/src/macos/cocoapod_utils.dart
+++ b/packages/flutter_tools/lib/src/macos/cocoapod_utils.dart
@@ -2,6 +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 '../base/fingerprint.dart';
 import '../build_info.dart';
 import '../cache.dart';
diff --git a/packages/flutter_tools/lib/src/macos/cocoapods.dart b/packages/flutter_tools/lib/src/macos/cocoapods.dart
index 226de788ed..de0106401a 100644
--- a/packages/flutter_tools/lib/src/macos/cocoapods.dart
+++ b/packages/flutter_tools/lib/src/macos/cocoapods.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:meta/meta.dart';
 import 'package:process/process.dart';
diff --git a/packages/flutter_tools/lib/src/macos/cocoapods_validator.dart b/packages/flutter_tools/lib/src/macos/cocoapods_validator.dart
index 0fb55bc67d..539938d6f0 100644
--- a/packages/flutter_tools/lib/src/macos/cocoapods_validator.dart
+++ b/packages/flutter_tools/lib/src/macos/cocoapods_validator.dart
@@ -2,6 +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 '../base/user_messages.dart';
 import '../doctor.dart';
 import 'cocoapods.dart';
diff --git a/packages/flutter_tools/lib/src/macos/macos_device.dart b/packages/flutter_tools/lib/src/macos/macos_device.dart
index b3b68bed12..175255fc50 100644
--- a/packages/flutter_tools/lib/src/macos/macos_device.dart
+++ b/packages/flutter_tools/lib/src/macos/macos_device.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/macos/macos_workflow.dart b/packages/flutter_tools/lib/src/macos/macos_workflow.dart
index 5360ca7757..6ff0392609 100644
--- a/packages/flutter_tools/lib/src/macos/macos_workflow.dart
+++ b/packages/flutter_tools/lib/src/macos/macos_workflow.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/platform.dart';
diff --git a/packages/flutter_tools/lib/src/macos/migrations/remove_macos_framework_link_and_embedding_migration.dart b/packages/flutter_tools/lib/src/macos/migrations/remove_macos_framework_link_and_embedding_migration.dart
index c1f6fcf353..dc40299458 100644
--- a/packages/flutter_tools/lib/src/macos/migrations/remove_macos_framework_link_and_embedding_migration.dart
+++ b/packages/flutter_tools/lib/src/macos/migrations/remove_macos_framework_link_and_embedding_migration.dart
@@ -2,6 +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 '../../base/common.dart';
 import '../../base/file_system.dart';
 import '../../base/logger.dart';
diff --git a/packages/flutter_tools/lib/src/macos/xcode.dart b/packages/flutter_tools/lib/src/macos/xcode.dart
index 99a4008864..034b0d9e9b 100644
--- a/packages/flutter_tools/lib/src/macos/xcode.dart
+++ b/packages/flutter_tools/lib/src/macos/xcode.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/lib/src/macos/xcode_validator.dart b/packages/flutter_tools/lib/src/macos/xcode_validator.dart
index 500004117f..33da8b0d58 100644
--- a/packages/flutter_tools/lib/src/macos/xcode_validator.dart
+++ b/packages/flutter_tools/lib/src/macos/xcode_validator.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/user_messages.dart';
diff --git a/packages/flutter_tools/lib/src/mdns_discovery.dart b/packages/flutter_tools/lib/src/mdns_discovery.dart
index 695ccb8a1f..edd2d0996f 100644
--- a/packages/flutter_tools/lib/src/mdns_discovery.dart
+++ b/packages/flutter_tools/lib/src/mdns_discovery.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:multicast_dns/multicast_dns.dart';
 
diff --git a/packages/flutter_tools/lib/src/migrations/cmake_custom_command_migration.dart b/packages/flutter_tools/lib/src/migrations/cmake_custom_command_migration.dart
index 1721e53f71..1162051197 100644
--- a/packages/flutter_tools/lib/src/migrations/cmake_custom_command_migration.dart
+++ b/packages/flutter_tools/lib/src/migrations/cmake_custom_command_migration.dart
@@ -2,6 +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 '../base/file_system.dart';
 import '../base/logger.dart';
 import '../base/project_migrator.dart';
diff --git a/packages/flutter_tools/lib/src/persistent_tool_state.dart b/packages/flutter_tools/lib/src/persistent_tool_state.dart
index f0bfbf3948..921d0d45ca 100644
--- a/packages/flutter_tools/lib/src/persistent_tool_state.dart
+++ b/packages/flutter_tools/lib/src/persistent_tool_state.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import 'base/config.dart';
diff --git a/packages/flutter_tools/lib/src/platform_plugins.dart b/packages/flutter_tools/lib/src/platform_plugins.dart
index d451636391..d41fa7426e 100644
--- a/packages/flutter_tools/lib/src/platform_plugins.dart
+++ b/packages/flutter_tools/lib/src/platform_plugins.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:yaml/yaml.dart';
 
diff --git a/packages/flutter_tools/lib/src/plugins.dart b/packages/flutter_tools/lib/src/plugins.dart
index 759f7c6f46..42c31fcdfd 100644
--- a/packages/flutter_tools/lib/src/plugins.dart
+++ b/packages/flutter_tools/lib/src/plugins.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 import 'package:path/path.dart' as path; // ignore: package_path_import
diff --git a/packages/flutter_tools/lib/src/project.dart b/packages/flutter_tools/lib/src/project.dart
index d617a222d4..f8dd7aff7c 100644
--- a/packages/flutter_tools/lib/src/project.dart
+++ b/packages/flutter_tools/lib/src/project.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:xml/xml.dart';
 import 'package:yaml/yaml.dart';
diff --git a/packages/flutter_tools/lib/src/protocol_discovery.dart b/packages/flutter_tools/lib/src/protocol_discovery.dart
index c47b9bb4ce..bfcc5a26a5 100644
--- a/packages/flutter_tools/lib/src/protocol_discovery.dart
+++ b/packages/flutter_tools/lib/src/protocol_discovery.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/proxy_validator.dart b/packages/flutter_tools/lib/src/proxy_validator.dart
index 7359875d36..d917b587c0 100644
--- a/packages/flutter_tools/lib/src/proxy_validator.dart
+++ b/packages/flutter_tools/lib/src/proxy_validator.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import 'base/platform.dart';
diff --git a/packages/flutter_tools/lib/src/reporting/crash_reporting.dart b/packages/flutter_tools/lib/src/reporting/crash_reporting.dart
index 1e021c59c1..1f59b36f26 100644
--- a/packages/flutter_tools/lib/src/reporting/crash_reporting.dart
+++ b/packages/flutter_tools/lib/src/reporting/crash_reporting.dart
@@ -2,6 +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
+
 part of reporting;
 
 /// Tells crash backend that the error is from the Flutter CLI.
diff --git a/packages/flutter_tools/lib/src/reporting/disabled_usage.dart b/packages/flutter_tools/lib/src/reporting/disabled_usage.dart
index b77303b8a9..858ae7175a 100644
--- a/packages/flutter_tools/lib/src/reporting/disabled_usage.dart
+++ b/packages/flutter_tools/lib/src/reporting/disabled_usage.dart
@@ -2,6 +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
+
 part of reporting;
 
 class DisabledUsage implements Usage {
diff --git a/packages/flutter_tools/lib/src/reporting/events.dart b/packages/flutter_tools/lib/src/reporting/events.dart
index a57a889277..a668511d66 100644
--- a/packages/flutter_tools/lib/src/reporting/events.dart
+++ b/packages/flutter_tools/lib/src/reporting/events.dart
@@ -2,6 +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
+
 part of reporting;
 
 /// A generic usage even that does not involve custom dimensions.
diff --git a/packages/flutter_tools/lib/src/reporting/first_run.dart b/packages/flutter_tools/lib/src/reporting/first_run.dart
index 49acb1e24b..d5fa8497a3 100644
--- a/packages/flutter_tools/lib/src/reporting/first_run.dart
+++ b/packages/flutter_tools/lib/src/reporting/first_run.dart
@@ -2,6 +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 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/lib/src/reporting/github_template.dart b/packages/flutter_tools/lib/src/reporting/github_template.dart
index 376a4d272e..cae85aa6c0 100644
--- a/packages/flutter_tools/lib/src/reporting/github_template.dart
+++ b/packages/flutter_tools/lib/src/reporting/github_template.dart
@@ -2,6 +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
+
 part of reporting;
 
 /// Provide suggested GitHub issue templates to user when Flutter encounters an error.
diff --git a/packages/flutter_tools/lib/src/reporting/reporting.dart b/packages/flutter_tools/lib/src/reporting/reporting.dart
index 6ef1a663f4..d9a2ea3410 100644
--- a/packages/flutter_tools/lib/src/reporting/reporting.dart
+++ b/packages/flutter_tools/lib/src/reporting/reporting.dart
@@ -2,6 +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
+
 library reporting;
 
 import 'dart:async';
diff --git a/packages/flutter_tools/lib/src/reporting/usage.dart b/packages/flutter_tools/lib/src/reporting/usage.dart
index 972f0387c8..7dfbd7e91e 100644
--- a/packages/flutter_tools/lib/src/reporting/usage.dart
+++ b/packages/flutter_tools/lib/src/reporting/usage.dart
@@ -2,6 +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
+
 part of reporting;
 
 const String _kFlutterUA = 'UA-67589403-6';
diff --git a/packages/flutter_tools/lib/src/resident_runner.dart b/packages/flutter_tools/lib/src/resident_runner.dart
index a10cf15be2..14b94402aa 100644
--- a/packages/flutter_tools/lib/src/resident_runner.dart
+++ b/packages/flutter_tools/lib/src/resident_runner.dart
@@ -2,6 +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:dds/dds.dart' as dds;
diff --git a/packages/flutter_tools/lib/src/run_cold.dart b/packages/flutter_tools/lib/src/run_cold.dart
index 7b825e1849..8064e0b85e 100644
--- a/packages/flutter_tools/lib/src/run_cold.dart
+++ b/packages/flutter_tools/lib/src/run_cold.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/run_hot.dart b/packages/flutter_tools/lib/src/run_hot.dart
index 5bc1af09b6..46f29354f0 100644
--- a/packages/flutter_tools/lib/src/run_hot.dart
+++ b/packages/flutter_tools/lib/src/run_hot.dart
@@ -2,6 +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:package_config/package_config.dart';
 import 'package:vm_service/vm_service.dart' as vm_service;
diff --git a/packages/flutter_tools/lib/src/runner/flutter_command.dart b/packages/flutter_tools/lib/src/runner/flutter_command.dart
index 1d926b3512..54afac9758 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command.dart
@@ -2,6 +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 'package:args/args.dart';
 import 'package:args/command_runner.dart';
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart b/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart
index 3dc7929dd1..2ec90fedc1 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart
@@ -2,6 +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 'package:args/args.dart';
 import 'package:args/command_runner.dart';
 import 'package:completion/completion.dart';
diff --git a/packages/flutter_tools/lib/src/runner/local_engine.dart b/packages/flutter_tools/lib/src/runner/local_engine.dart
index 82a9a5178f..3c0b899c4a 100644
--- a/packages/flutter_tools/lib/src/runner/local_engine.dart
+++ b/packages/flutter_tools/lib/src/runner/local_engine.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 
diff --git a/packages/flutter_tools/lib/src/template.dart b/packages/flutter_tools/lib/src/template.dart
index f6dc6c2475..8fdbef89d0 100644
--- a/packages/flutter_tools/lib/src/template.dart
+++ b/packages/flutter_tools/lib/src/template.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 import 'package:package_config/package_config_types.dart';
diff --git a/packages/flutter_tools/lib/src/test/coverage_collector.dart b/packages/flutter_tools/lib/src/test/coverage_collector.dart
index 207690d906..73d18c5c27 100644
--- a/packages/flutter_tools/lib/src/test/coverage_collector.dart
+++ b/packages/flutter_tools/lib/src/test/coverage_collector.dart
@@ -2,6 +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 'package:coverage/coverage.dart' as coverage;
 import 'package:meta/meta.dart';
 import 'package:vm_service/vm_service.dart' as vm_service;
diff --git a/packages/flutter_tools/lib/src/test/event_printer.dart b/packages/flutter_tools/lib/src/test/event_printer.dart
index 7bbf071c1e..7fec4dd35f 100644
--- a/packages/flutter_tools/lib/src/test/event_printer.dart
+++ b/packages/flutter_tools/lib/src/test/event_printer.dart
@@ -2,6 +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 '../convert.dart';
 import '../globals.dart' as globals;
 import 'watcher.dart';
diff --git a/packages/flutter_tools/lib/src/test/flutter_platform.dart b/packages/flutter_tools/lib/src/test/flutter_platform.dart
index be3b216543..46c8344a70 100644
--- a/packages/flutter_tools/lib/src/test/flutter_platform.dart
+++ b/packages/flutter_tools/lib/src/test/flutter_platform.dart
@@ -2,6 +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 'dart:io' as io; // ignore: dart_io_import;
 
diff --git a/packages/flutter_tools/lib/src/test/flutter_web_goldens.dart b/packages/flutter_tools/lib/src/test/flutter_web_goldens.dart
index cbc54565cb..b0fc70682b 100644
--- a/packages/flutter_tools/lib/src/test/flutter_web_goldens.dart
+++ b/packages/flutter_tools/lib/src/test/flutter_web_goldens.dart
@@ -2,6 +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
+
 // ignore_for_file: implementation_imports
 
 import 'dart:async';
diff --git a/packages/flutter_tools/lib/src/test/flutter_web_platform.dart b/packages/flutter_tools/lib/src/test/flutter_web_platform.dart
index 3f337d4b41..1f53a642a6 100644
--- a/packages/flutter_tools/lib/src/test/flutter_web_platform.dart
+++ b/packages/flutter_tools/lib/src/test/flutter_web_platform.dart
@@ -2,6 +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
+
 // ignore_for_file: implementation_imports
 
 import 'dart:async';
diff --git a/packages/flutter_tools/lib/src/test/runner.dart b/packages/flutter_tools/lib/src/test/runner.dart
index 469451fe0d..9c58e0d184 100644
--- a/packages/flutter_tools/lib/src/test/runner.dart
+++ b/packages/flutter_tools/lib/src/test/runner.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../artifacts.dart';
diff --git a/packages/flutter_tools/lib/src/test/test_compiler.dart b/packages/flutter_tools/lib/src/test/test_compiler.dart
index e3dce77f5d..1d9fd413ae 100644
--- a/packages/flutter_tools/lib/src/test/test_compiler.dart
+++ b/packages/flutter_tools/lib/src/test/test_compiler.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/test/test_config.dart b/packages/flutter_tools/lib/src/test/test_config.dart
index ded1010ee8..c2ead26d9f 100644
--- a/packages/flutter_tools/lib/src/test/test_config.dart
+++ b/packages/flutter_tools/lib/src/test/test_config.dart
@@ -2,6 +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 '../base/file_system.dart';
 import '../globals.dart' as globals;
 
diff --git a/packages/flutter_tools/lib/src/test/test_wrapper.dart b/packages/flutter_tools/lib/src/test/test_wrapper.dart
index 2fa918f4e2..5dcf9a485c 100644
--- a/packages/flutter_tools/lib/src/test/test_wrapper.dart
+++ b/packages/flutter_tools/lib/src/test/test_wrapper.dart
@@ -2,6 +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:test_core/src/executable.dart' as test; // ignore: implementation_imports
diff --git a/packages/flutter_tools/lib/src/test/watcher.dart b/packages/flutter_tools/lib/src/test/watcher.dart
index a8a4fa0f94..b68d36f827 100644
--- a/packages/flutter_tools/lib/src/test/watcher.dart
+++ b/packages/flutter_tools/lib/src/test/watcher.dart
@@ -2,6 +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 '../base/io.dart' show Process;
 
 /// Callbacks for reporting progress while running tests.
diff --git a/packages/flutter_tools/lib/src/test/web_test_compiler.dart b/packages/flutter_tools/lib/src/test/web_test_compiler.dart
index c86feea697..5ee47bf225 100644
--- a/packages/flutter_tools/lib/src/test/web_test_compiler.dart
+++ b/packages/flutter_tools/lib/src/test/web_test_compiler.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 import 'package:process/process.dart';
diff --git a/packages/flutter_tools/lib/src/tester/flutter_tester.dart b/packages/flutter_tools/lib/src/tester/flutter_tester.dart
index 6f138bfb31..d99e7efd1c 100644
--- a/packages/flutter_tools/lib/src/tester/flutter_tester.dart
+++ b/packages/flutter_tools/lib/src/tester/flutter_tester.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/tracing.dart b/packages/flutter_tools/lib/src/tracing.dart
index 9c6a64ae1a..d3ffb21d13 100644
--- a/packages/flutter_tools/lib/src/tracing.dart
+++ b/packages/flutter_tools/lib/src/tracing.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/version.dart b/packages/flutter_tools/lib/src/version.dart
index 39e0fb59f7..8def800c0b 100644
--- a/packages/flutter_tools/lib/src/version.dart
+++ b/packages/flutter_tools/lib/src/version.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import 'base/common.dart';
diff --git a/packages/flutter_tools/lib/src/vmservice.dart b/packages/flutter_tools/lib/src/vmservice.dart
index 9e45e553d2..a0760316fb 100644
--- a/packages/flutter_tools/lib/src/vmservice.dart
+++ b/packages/flutter_tools/lib/src/vmservice.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:meta/meta.dart' show required;
 import 'package:vm_service/vm_service.dart' as vm_service;
diff --git a/packages/flutter_tools/lib/src/vscode/vscode.dart b/packages/flutter_tools/lib/src/vscode/vscode.dart
index 1282a7d49f..3eb345fd4d 100644
--- a/packages/flutter_tools/lib/src/vscode/vscode.dart
+++ b/packages/flutter_tools/lib/src/vscode/vscode.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/vscode/vscode_validator.dart b/packages/flutter_tools/lib/src/vscode/vscode_validator.dart
index 3d9a3f68b7..fa7c11e905 100644
--- a/packages/flutter_tools/lib/src/vscode/vscode_validator.dart
+++ b/packages/flutter_tools/lib/src/vscode/vscode_validator.dart
@@ -2,6 +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 '../base/file_system.dart';
 import '../base/platform.dart';
 import '../base/user_messages.dart';
diff --git a/packages/flutter_tools/lib/src/web/bootstrap.dart b/packages/flutter_tools/lib/src/web/bootstrap.dart
index 76a0d040d7..8909f2cc46 100644
--- a/packages/flutter_tools/lib/src/web/bootstrap.dart
+++ b/packages/flutter_tools/lib/src/web/bootstrap.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 
diff --git a/packages/flutter_tools/lib/src/web/chrome.dart b/packages/flutter_tools/lib/src/web/chrome.dart
index b0e75ecb6b..427f1d85da 100644
--- a/packages/flutter_tools/lib/src/web/chrome.dart
+++ b/packages/flutter_tools/lib/src/web/chrome.dart
@@ -2,6 +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';
diff --git a/packages/flutter_tools/lib/src/web/compile.dart b/packages/flutter_tools/lib/src/web/compile.dart
index 160f41de47..6038971d34 100644
--- a/packages/flutter_tools/lib/src/web/compile.dart
+++ b/packages/flutter_tools/lib/src/web/compile.dart
@@ -2,6 +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 '../artifacts.dart';
 import '../base/common.dart';
 import '../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/web/memory_fs.dart b/packages/flutter_tools/lib/src/web/memory_fs.dart
index 85e3f6f381..6b9ea60cab 100644
--- a/packages/flutter_tools/lib/src/web/memory_fs.dart
+++ b/packages/flutter_tools/lib/src/web/memory_fs.dart
@@ -2,6 +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:typed_data';
 
 import '../base/file_system.dart';
diff --git a/packages/flutter_tools/lib/src/web/web_device.dart b/packages/flutter_tools/lib/src/web/web_device.dart
index cfa5a25e58..df30ecec26 100644
--- a/packages/flutter_tools/lib/src/web/web_device.dart
+++ b/packages/flutter_tools/lib/src/web/web_device.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/web/web_runner.dart b/packages/flutter_tools/lib/src/web/web_runner.dart
index ba3862d60b..a98512d80a 100644
--- a/packages/flutter_tools/lib/src/web/web_runner.dart
+++ b/packages/flutter_tools/lib/src/web/web_runner.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/context.dart';
diff --git a/packages/flutter_tools/lib/src/web/web_validator.dart b/packages/flutter_tools/lib/src/web/web_validator.dart
index 9940437827..1d5f18c5ce 100644
--- a/packages/flutter_tools/lib/src/web/web_validator.dart
+++ b/packages/flutter_tools/lib/src/web/web_validator.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/platform.dart';
diff --git a/packages/flutter_tools/lib/src/web/workflow.dart b/packages/flutter_tools/lib/src/web/workflow.dart
index 0f7839cb24..6e86bdeb7a 100644
--- a/packages/flutter_tools/lib/src/web/workflow.dart
+++ b/packages/flutter_tools/lib/src/web/workflow.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/platform.dart';
diff --git a/packages/flutter_tools/lib/src/windows/application_package.dart b/packages/flutter_tools/lib/src/windows/application_package.dart
index 8051b06d6c..94623bc617 100644
--- a/packages/flutter_tools/lib/src/windows/application_package.dart
+++ b/packages/flutter_tools/lib/src/windows/application_package.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../application_package.dart';
diff --git a/packages/flutter_tools/lib/src/windows/build_windows.dart b/packages/flutter_tools/lib/src/windows/build_windows.dart
index 1c0639038d..8ca132b1cd 100644
--- a/packages/flutter_tools/lib/src/windows/build_windows.dart
+++ b/packages/flutter_tools/lib/src/windows/build_windows.dart
@@ -2,6 +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 '../artifacts.dart';
 import '../base/analyze_size.dart';
 import '../base/common.dart';
diff --git a/packages/flutter_tools/lib/src/windows/visual_studio.dart b/packages/flutter_tools/lib/src/windows/visual_studio.dart
index 31e99e4150..0aedcbb1a6 100644
--- a/packages/flutter_tools/lib/src/windows/visual_studio.dart
+++ b/packages/flutter_tools/lib/src/windows/visual_studio.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/windows/visual_studio_validator.dart b/packages/flutter_tools/lib/src/windows/visual_studio_validator.dart
index a1426608a6..a739ba613a 100644
--- a/packages/flutter_tools/lib/src/windows/visual_studio_validator.dart
+++ b/packages/flutter_tools/lib/src/windows/visual_studio_validator.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/context.dart';
diff --git a/packages/flutter_tools/lib/src/windows/windows_device.dart b/packages/flutter_tools/lib/src/windows/windows_device.dart
index 3b41a4e2e9..479802938d 100644
--- a/packages/flutter_tools/lib/src/windows/windows_device.dart
+++ b/packages/flutter_tools/lib/src/windows/windows_device.dart
@@ -2,6 +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 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
diff --git a/packages/flutter_tools/lib/src/windows/windows_workflow.dart b/packages/flutter_tools/lib/src/windows/windows_workflow.dart
index 2144f62f7e..5661af76c8 100644
--- a/packages/flutter_tools/lib/src/windows/windows_workflow.dart
+++ b/packages/flutter_tools/lib/src/windows/windows_workflow.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import '../base/context.dart';
diff --git a/packages/flutter_tools/pubspec.yaml b/packages/flutter_tools/pubspec.yaml
index 3c17cf3e5e..a7cc745839 100644
--- a/packages/flutter_tools/pubspec.yaml
+++ b/packages/flutter_tools/pubspec.yaml
@@ -4,7 +4,7 @@ homepage: https://flutter.dev
 author: Flutter Authors <flutter-dev@googlegroups.com>
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   # To update these, use "flutter update-packages --force-upgrade".
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/analyze_continuously_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/analyze_continuously_test.dart
index 2b9f93b9c3..38d8086595 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/analyze_continuously_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/analyze_continuously_test.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/analyze_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/analyze_test.dart
index 9537fddcb0..520b9fd524 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/analyze_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/analyze_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/cache.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/assemble_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/assemble_test.dart
index baca0ba31d..7e05ed45b9 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/assemble_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/assemble_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/attach_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/attach_test.dart
index 1b69f13964..5609b5284d 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/attach_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/attach_test.dart
@@ -2,6 +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 'dart:io';
 
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/build_fuchsia_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/build_fuchsia_test.dart
index ae52726778..0ec608b113 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/build_fuchsia_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/build_fuchsia_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/build_ios_framework_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/build_ios_framework_test.dart
index 26e1071606..91d0f633f5 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/build_ios_framework_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/build_ios_framework_test.dart
@@ -2,6 +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:io';
 
 import 'package:file/memory.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/build_ipa_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/build_ipa_test.dart
index 484e7ed337..abe3452c39 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/build_ipa_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/build_ipa_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/build_linux_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/build_linux_test.dart
index cf22b60d10..a38c01ccd4 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/build_linux_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/build_linux_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/build_macos_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/build_macos_test.dart
index 17266b7b57..52f1ad5826 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/build_macos_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/build_macos_test.dart
@@ -2,6 +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:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/build_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/build_test.dart
index d96e3e2f6f..92168505a3 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/build_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/build_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/runner/flutter_command.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart
index 7f2178feeb..d5ac8d647f 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/build_windows_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/build_windows_test.dart
index 6be30f511c..64da20c407 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/build_windows_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/build_windows_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/clean_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/clean_test.dart
index 9f341f1c5a..fbdbffeb15 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/clean_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/clean_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/config_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/config_test.dart
index 248c63b209..b5b52cf455 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/config_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/config_test.dart
@@ -2,6 +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:convert';
 
 import 'package:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/create_usage_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/create_usage_test.dart
index 676a7595bf..4641985d52 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/create_usage_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/create_usage_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/cache.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/daemon_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/daemon_test.dart
index ad6f727eed..cf248731e8 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/daemon_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/daemon_test.dart
@@ -2,6 +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:flutter_tools/src/android/android_workflow.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/devices_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/devices_test.dart
index 0fe5362c3c..42b89425ab 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/devices_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/devices_test.dart
@@ -2,6 +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:convert';
 
 import 'package:flutter_tools/src/android/android_sdk.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/doctor_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/doctor_test.dart
index e9f41640c5..0c15e0cf6a 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/doctor_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/doctor_test.dart
@@ -2,6 +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:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/downgrade_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/downgrade_test.dart
index 8a5e2dfba1..7193904f30 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/downgrade_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/downgrade_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/generate_localizations_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/generate_localizations_test.dart
index 5c6dca665c..2a250328e5 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/generate_localizations_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/generate_localizations_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/ide_config_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/ide_config_test.dart
index 9f0dcd95ff..1714ec3864 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/ide_config_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/ide_config_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/cache.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/install_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/install_test.dart
index 25cea448cc..9aea64ba9c 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/install_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/install_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:flutter_tools/src/application_package.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/precache_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/precache_test.dart
index c5396e7ff3..25a9c68c0f 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/precache_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/precache_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/cache.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/proxy_validator_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/proxy_validator_test.dart
index 4f667e9c1d..bab856c42d 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/proxy_validator_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/proxy_validator_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/doctor.dart';
 import 'package:flutter_tools/src/proxy_validator.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/pub_get_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/pub_get_test.dart
index 55dabbbca5..b73360ed49 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/pub_get_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/pub_get_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/run_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/run_test.dart
index 8506b839dc..9a597bc91e 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/run_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/run_test.dart
@@ -2,6 +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:file/file.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/shell_completion_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/shell_completion_test.dart
index 8a4dc012e4..4b06cda96f 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/shell_completion_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/shell_completion_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/context.dart';
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/symbolize_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/symbolize_test.dart
index 6069d7301a..f656c58292 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/symbolize_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/symbolize_test.dart
@@ -2,6 +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 'dart:typed_data';
 
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/test_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/test_test.dart
index d17b034431..e6c36f5e2f 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/test_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/test_test.dart
@@ -2,6 +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:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/commands.shard/permeable/analyze_once_test.dart b/packages/flutter_tools/test/commands.shard/permeable/analyze_once_test.dart
index 1ed1c988f1..b2857bb50c 100644
--- a/packages/flutter_tools/test/commands.shard/permeable/analyze_once_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/analyze_once_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/error_handling_io.dart';
 import 'package:flutter_tools/src/base/user_messages.dart';
 import 'package:flutter_tools/src/globals.dart' as globals;
diff --git a/packages/flutter_tools/test/commands.shard/permeable/build_aar_test.dart b/packages/flutter_tools/test/commands.shard/permeable/build_aar_test.dart
index eb78656b5f..730c04af41 100644
--- a/packages/flutter_tools/test/commands.shard/permeable/build_aar_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/build_aar_test.dart
@@ -2,6 +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:io' show Process, ProcessResult;
 
 import 'package:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/commands.shard/permeable/build_apk_test.dart b/packages/flutter_tools/test/commands.shard/permeable/build_apk_test.dart
index 421e1db71c..9455c4ed3b 100644
--- a/packages/flutter_tools/test/commands.shard/permeable/build_apk_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/build_apk_test.dart
@@ -2,6 +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:io';
 
 import 'package:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/commands.shard/permeable/build_appbundle_test.dart b/packages/flutter_tools/test/commands.shard/permeable/build_appbundle_test.dart
index decfc46310..ba800a5627 100644
--- a/packages/flutter_tools/test/commands.shard/permeable/build_appbundle_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/build_appbundle_test.dart
@@ -2,6 +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:io';
 
 import 'package:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/commands.shard/permeable/build_bundle_test.dart b/packages/flutter_tools/test/commands.shard/permeable/build_bundle_test.dart
index ca0cc305ac..d0452f0521 100644
--- a/packages/flutter_tools/test/commands.shard/permeable/build_bundle_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/build_bundle_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/commands.shard/permeable/create_test.dart b/packages/flutter_tools/test/commands.shard/permeable/create_test.dart
index 696fc2dda8..c3f882a698 100755
--- a/packages/flutter_tools/test/commands.shard/permeable/create_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/create_test.dart
@@ -2,6 +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 'dart:convert';
 import 'dart:typed_data';
diff --git a/packages/flutter_tools/test/commands.shard/permeable/devices_test.dart b/packages/flutter_tools/test/commands.shard/permeable/devices_test.dart
index a7c902a3a3..e62d85886c 100644
--- a/packages/flutter_tools/test/commands.shard/permeable/devices_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/devices_test.dart
@@ -2,6 +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:convert';
 
 import 'package:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/commands.shard/permeable/format_test.dart b/packages/flutter_tools/test/commands.shard/permeable/format_test.dart
index b5912750d1..3512f066d8 100644
--- a/packages/flutter_tools/test/commands.shard/permeable/format_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/format_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/cache.dart';
diff --git a/packages/flutter_tools/test/commands.shard/permeable/packages_test.dart b/packages/flutter_tools/test/commands.shard/permeable/packages_test.dart
index 57624fc1c4..40b756b9a7 100644
--- a/packages/flutter_tools/test/commands.shard/permeable/packages_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/packages_test.dart
@@ -2,6 +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:convert';
 
 import 'package:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/commands.shard/permeable/upgrade_test.dart b/packages/flutter_tools/test/commands.shard/permeable/upgrade_test.dart
index ed40a4e6fa..c394676d10 100644
--- a/packages/flutter_tools/test/commands.shard/permeable/upgrade_test.dart
+++ b/packages/flutter_tools/test/commands.shard/permeable/upgrade_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/platform.dart';
diff --git a/packages/flutter_tools/test/general.shard/analytics_test.dart b/packages/flutter_tools/test/general.shard/analytics_test.dart
index 82cdbd0eeb..fea1b517f8 100644
--- a/packages/flutter_tools/test/general.shard/analytics_test.dart
+++ b/packages/flutter_tools/test/general.shard/analytics_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/config.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/adb_log_reader_test.dart b/packages/flutter_tools/test/general.shard/android/adb_log_reader_test.dart
index e9dadfacfd..39fb1bd789 100644
--- a/packages/flutter_tools/test/general.shard/android/adb_log_reader_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/adb_log_reader_test.dart
@@ -2,6 +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:flutter_tools/src/android/android_device.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_device_discovery_test.dart b/packages/flutter_tools/test/general.shard/android/android_device_discovery_test.dart
index f1a8001ba4..d0f0324e40 100644
--- a/packages/flutter_tools/test/general.shard/android/android_device_discovery_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_device_discovery_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_device_discovery.dart';
 import 'package:flutter_tools/src/android/android_sdk.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_device_port_forwarder_test.dart b/packages/flutter_tools/test/general.shard/android/android_device_port_forwarder_test.dart
index aa7f6c6740..75d6b23191 100644
--- a/packages/flutter_tools/test/general.shard/android/android_device_port_forwarder_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_device_port_forwarder_test.dart
@@ -2,6 +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 'package:flutter_tools/src/android/android_device.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_device_start_test.dart b/packages/flutter_tools/test/general.shard/android/android_device_start_test.dart
index c26f4e1890..b4c9a7cb56 100644
--- a/packages/flutter_tools/test/general.shard/android/android_device_start_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_device_start_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_device.dart';
 import 'package:flutter_tools/src/android/android_sdk.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_device_stop_test.dart b/packages/flutter_tools/test/general.shard/android/android_device_stop_test.dart
index b25a2cf47b..1c1c27d390 100644
--- a/packages/flutter_tools/test/general.shard/android/android_device_stop_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_device_stop_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_device.dart';
 import 'package:flutter_tools/src/android/android_sdk.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_device_test.dart b/packages/flutter_tools/test/general.shard/android/android_device_test.dart
index d1ae8cdbca..bd057fa210 100644
--- a/packages/flutter_tools/test/general.shard/android/android_device_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_device_test.dart
@@ -2,6 +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 'dart:convert';
 import 'dart:typed_data';
diff --git a/packages/flutter_tools/test/general.shard/android/android_emulator_test.dart b/packages/flutter_tools/test/general.shard/android/android_emulator_test.dart
index 82a1b108c4..a3cdf7ace7 100644
--- a/packages/flutter_tools/test/general.shard/android/android_emulator_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_emulator_test.dart
@@ -2,6 +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:flutter_tools/src/android/android_emulator.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_install_test.dart b/packages/flutter_tools/test/general.shard/android/android_install_test.dart
index 1d088d26aa..2c454b87ad 100644
--- a/packages/flutter_tools/test/general.shard/android/android_install_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_install_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_device.dart';
 import 'package:flutter_tools/src/android/android_sdk.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_sdk_test.dart b/packages/flutter_tools/test/general.shard/android/android_sdk_test.dart
index f6ceb5f9e6..b64575cd9a 100644
--- a/packages/flutter_tools/test/general.shard/android/android_sdk_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_sdk_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_sdk.dart';
 import 'package:flutter_tools/src/base/config.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_studio_test.dart b/packages/flutter_tools/test/general.shard/android/android_studio_test.dart
index 0b25590006..bd3812920e 100644
--- a/packages/flutter_tools/test/general.shard/android/android_studio_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_studio_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_studio.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_studio_validator_test.dart b/packages/flutter_tools/test/general.shard/android/android_studio_validator_test.dart
index b1aa51fc15..325ce70806 100644
--- a/packages/flutter_tools/test/general.shard/android/android_studio_validator_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_studio_validator_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_studio_validator.dart';
 import 'package:flutter_tools/src/base/config.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/android_workflow_test.dart b/packages/flutter_tools/test/general.shard/android/android_workflow_test.dart
index 3a377ff9f1..a964622c75 100644
--- a/packages/flutter_tools/test/general.shard/android/android_workflow_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/android_workflow_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_sdk.dart';
 import 'package:flutter_tools/src/android/android_workflow.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/build_validation_test.dart b/packages/flutter_tools/test/general.shard/android/build_validation_test.dart
index 886662379f..6f90ce091d 100644
--- a/packages/flutter_tools/test/general.shard/android/build_validation_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/build_validation_test.dart
@@ -2,6 +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 'package:flutter_tools/src/android/build_validation.dart';
 import 'package:flutter_tools/src/build_info.dart';
 
diff --git a/packages/flutter_tools/test/general.shard/android/gradle_errors_test.dart b/packages/flutter_tools/test/general.shard/android/gradle_errors_test.dart
index c2c549a6b4..1594f18420 100644
--- a/packages/flutter_tools/test/general.shard/android/gradle_errors_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/gradle_errors_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/android/gradle_errors.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/gradle_test.dart b/packages/flutter_tools/test/general.shard/android/gradle_test.dart
index 0183d9ae98..db91c1e764 100644
--- a/packages/flutter_tools/test/general.shard/android/gradle_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/gradle_test.dart
@@ -2,6 +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 'package:archive/archive.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_sdk.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/gradle_utils_test.dart b/packages/flutter_tools/test/general.shard/android/gradle_utils_test.dart
index 34c05b2dc2..e1dfccb02b 100644
--- a/packages/flutter_tools/test/general.shard/android/gradle_utils_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/gradle_utils_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/gradle_utils.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/android_plugin_test.dart b/packages/flutter_tools/test/general.shard/android_plugin_test.dart
index e411cac5c4..b3855fb4d1 100644
--- a/packages/flutter_tools/test/general.shard/android_plugin_test.dart
+++ b/packages/flutter_tools/test/general.shard/android_plugin_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/platform_plugins.dart';
diff --git a/packages/flutter_tools/test/general.shard/application_package_test.dart b/packages/flutter_tools/test/general.shard/application_package_test.dart
index b99339c992..583403fbbb 100644
--- a/packages/flutter_tools/test/general.shard/application_package_test.dart
+++ b/packages/flutter_tools/test/general.shard/application_package_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/general.shard/artifact_updater_test.dart b/packages/flutter_tools/test/general.shard/artifact_updater_test.dart
index 6ecb664841..ef9db567de 100644
--- a/packages/flutter_tools/test/general.shard/artifact_updater_test.dart
+++ b/packages/flutter_tools/test/general.shard/artifact_updater_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file/src/interface/file.dart';
 import 'package:file_testing/file_testing.dart';
diff --git a/packages/flutter_tools/test/general.shard/artifacts_test.dart b/packages/flutter_tools/test/general.shard/artifacts_test.dart
index 2ca82bcb9a..6a2f6cf14a 100644
--- a/packages/flutter_tools/test/general.shard/artifacts_test.dart
+++ b/packages/flutter_tools/test/general.shard/artifacts_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/asset_bundle_package_fonts_test.dart b/packages/flutter_tools/test/general.shard/asset_bundle_package_fonts_test.dart
index adcc1241d5..a312ea9197 100644
--- a/packages/flutter_tools/test/general.shard/asset_bundle_package_fonts_test.dart
+++ b/packages/flutter_tools/test/general.shard/asset_bundle_package_fonts_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/general.shard/asset_bundle_package_test.dart b/packages/flutter_tools/test/general.shard/asset_bundle_package_test.dart
index a141058544..a733bd2f51 100644
--- a/packages/flutter_tools/test/general.shard/asset_bundle_package_test.dart
+++ b/packages/flutter_tools/test/general.shard/asset_bundle_package_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/general.shard/asset_bundle_test.dart b/packages/flutter_tools/test/general.shard/asset_bundle_test.dart
index e544b23494..2d4546b55a 100644
--- a/packages/flutter_tools/test/general.shard/asset_bundle_test.dart
+++ b/packages/flutter_tools/test/general.shard/asset_bundle_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/general.shard/asset_bundle_variant_test.dart b/packages/flutter_tools/test/general.shard/asset_bundle_variant_test.dart
index f1ae756d02..7ae9dd1f42 100644
--- a/packages/flutter_tools/test/general.shard/asset_bundle_variant_test.dart
+++ b/packages/flutter_tools/test/general.shard/asset_bundle_variant_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/general.shard/asset_test.dart b/packages/flutter_tools/test/general.shard/asset_test.dart
index 89e4d392c6..55b7f507bb 100644
--- a/packages/flutter_tools/test/general.shard/asset_test.dart
+++ b/packages/flutter_tools/test/general.shard/asset_test.dart
@@ -2,6 +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 'package:flutter_tools/src/asset.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/globals.dart' as globals;
diff --git a/packages/flutter_tools/test/general.shard/base/analyze_size_test.dart b/packages/flutter_tools/test/general.shard/base/analyze_size_test.dart
index e09dfb7194..2c60d375c1 100644
--- a/packages/flutter_tools/test/general.shard/base/analyze_size_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/analyze_size_test.dart
@@ -2,6 +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 'package:archive/archive.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/analyze_size.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/async_guard_test.dart b/packages/flutter_tools/test/general.shard/base/async_guard_test.dart
index f85080d0c7..e5caf00e7f 100644
--- a/packages/flutter_tools/test/general.shard/base/async_guard_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/async_guard_test.dart
@@ -2,6 +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:flutter_tools/src/base/async_guard.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/bot_detector_test.dart b/packages/flutter_tools/test/general.shard/base/bot_detector_test.dart
index b2eedc56d6..ff0122f582 100644
--- a/packages/flutter_tools/test/general.shard/base/bot_detector_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/bot_detector_test.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/build_test.dart b/packages/flutter_tools/test/general.shard/base/build_test.dart
index d82f916eb7..10f2a91367 100644
--- a/packages/flutter_tools/test/general.shard/base/build_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/build_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/build.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/command_help_test.dart b/packages/flutter_tools/test/general.shard/base/command_help_test.dart
index 5c67519f96..4ad556baeb 100644
--- a/packages/flutter_tools/test/general.shard/base/command_help_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/command_help_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/command_help.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/platform.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/common_test.dart b/packages/flutter_tools/test/general.shard/base/common_test.dart
index 0ffb6c2899..365bf499f2 100644
--- a/packages/flutter_tools/test/general.shard/base/common_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/common_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/context.dart';
 
diff --git a/packages/flutter_tools/test/general.shard/base/context_test.dart b/packages/flutter_tools/test/general.shard/base/context_test.dart
index 23bd25ba00..2534e8f7e6 100644
--- a/packages/flutter_tools/test/general.shard/base/context_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/context_test.dart
@@ -2,6 +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:flutter_tools/src/base/context.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/error_handling_io_test.dart b/packages/flutter_tools/test/general.shard/base/error_handling_io_test.dart
index cf14d98a78..eb8971787d 100644
--- a/packages/flutter_tools/test/general.shard/base/error_handling_io_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/error_handling_io_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/file_system_test.dart b/packages/flutter_tools/test/general.shard/base/file_system_test.dart
index 2c9161cbf0..b16451b882 100644
--- a/packages/flutter_tools/test/general.shard/base/file_system_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/file_system_test.dart
@@ -2,6 +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 'dart:io' as io;
 
diff --git a/packages/flutter_tools/test/general.shard/base/fingerprint_test.dart b/packages/flutter_tools/test/general.shard/base/fingerprint_test.dart
index 1a1d03418e..388348fa1c 100644
--- a/packages/flutter_tools/test/general.shard/base/fingerprint_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/fingerprint_test.dart
@@ -2,6 +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:convert' show json;
 
 import 'package:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/io_test.dart b/packages/flutter_tools/test/general.shard/base/io_test.dart
index 105599f518..375a8cfd17 100644
--- a/packages/flutter_tools/test/general.shard/base/io_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/io_test.dart
@@ -2,6 +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 'dart:io' as io;
 
diff --git a/packages/flutter_tools/test/general.shard/base/logger_test.dart b/packages/flutter_tools/test/general.shard/base/logger_test.dart
index 752361d637..abdabfc620 100644
--- a/packages/flutter_tools/test/general.shard/base/logger_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/logger_test.dart
@@ -2,6 +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:flutter_tools/executable.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/logs_test.dart b/packages/flutter_tools/test/general.shard/base/logs_test.dart
index 3b2286504b..21426b37ed 100644
--- a/packages/flutter_tools/test/general.shard/base/logs_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/logs_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/commands/logs.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/net_test.dart b/packages/flutter_tools/test/general.shard/base/net_test.dart
index 1517e9987a..c25915e65a 100644
--- a/packages/flutter_tools/test/general.shard/base/net_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/net_test.dart
@@ -2,6 +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 'dart:convert';
 
diff --git a/packages/flutter_tools/test/general.shard/base/os_test.dart b/packages/flutter_tools/test/general.shard/base/os_test.dart
index db72bc269c..0178dbe9ee 100644
--- a/packages/flutter_tools/test/general.shard/base/os_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/os_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/os_utils_test.dart b/packages/flutter_tools/test/general.shard/base/os_utils_test.dart
index 098262f218..5a21ab7ff7 100644
--- a/packages/flutter_tools/test/general.shard/base/os_utils_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/os_utils_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/os.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/platform_test.dart b/packages/flutter_tools/test/general.shard/base/platform_test.dart
index bdfb05279a..d60928e5f0 100644
--- a/packages/flutter_tools/test/general.shard/base/platform_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/platform_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/platform.dart';
 
 import '../../src/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/process_test.dart b/packages/flutter_tools/test/general.shard/base/process_test.dart
index 8367ee5abc..e9a924a1ed 100644
--- a/packages/flutter_tools/test/general.shard/base/process_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/process_test.dart
@@ -2,6 +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:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/signals_test.dart b/packages/flutter_tools/test/general.shard/base/signals_test.dart
index 5333fb9df8..11d5653d3d 100644
--- a/packages/flutter_tools/test/general.shard/base/signals_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/signals_test.dart
@@ -2,6 +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 'dart:io' as io;
 
diff --git a/packages/flutter_tools/test/general.shard/base/terminal_test.dart b/packages/flutter_tools/test/general.shard/base/terminal_test.dart
index 865980e64d..3fb9c0c710 100644
--- a/packages/flutter_tools/test/general.shard/base/terminal_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/terminal_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/platform.dart';
diff --git a/packages/flutter_tools/test/general.shard/base/user_messages_test.dart b/packages/flutter_tools/test/general.shard/base/user_messages_test.dart
index ec51fada9a..cdd9c8be00 100644
--- a/packages/flutter_tools/test/general.shard/base/user_messages_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/user_messages_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/base/user_messages.dart';
 
diff --git a/packages/flutter_tools/test/general.shard/base_utils_test.dart b/packages/flutter_tools/test/general.shard/base_utils_test.dart
index 42f8f6cb56..be46386507 100644
--- a/packages/flutter_tools/test/general.shard/base_utils_test.dart
+++ b/packages/flutter_tools/test/general.shard/base_utils_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/utils.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_info_test.dart b/packages/flutter_tools/test/general.shard/build_info_test.dart
index 596d1f8887..c4c116c176 100644
--- a/packages/flutter_tools/test/general.shard/build_info_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_info_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/build_info.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/build_system_test.dart b/packages/flutter_tools/test/general.shard/build_system/build_system_test.dart
index 50569133a0..def49d672e 100644
--- a/packages/flutter_tools/test/general.shard/build_system/build_system_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/build_system_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/depfile_test.dart b/packages/flutter_tools/test/general.shard/build_system/depfile_test.dart
index 086fcad989..e4ea27535e 100644
--- a/packages/flutter_tools/test/general.shard/build_system/depfile_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/depfile_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/exceptions_test.dart b/packages/flutter_tools/test/general.shard/build_system/exceptions_test.dart
index 66e040540e..ed493e7658 100644
--- a/packages/flutter_tools/test/general.shard/build_system/exceptions_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/exceptions_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/build_system/build_system.dart';
 import 'package:flutter_tools/src/build_system/exceptions.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/file_store_test.dart b/packages/flutter_tools/test/general.shard/build_system/file_store_test.dart
index 26a4c1db84..7a7d4dd866 100644
--- a/packages/flutter_tools/test/general.shard/build_system/file_store_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/file_store_test.dart
@@ -2,6 +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:typed_data';
 
 import 'package:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/hash_test.dart b/packages/flutter_tools/test/general.shard/build_system/hash_test.dart
index 69dab5afb9..7b0cca9781 100644
--- a/packages/flutter_tools/test/general.shard/build_system/hash_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/hash_test.dart
@@ -2,6 +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:convert';
 import 'dart:typed_data';
 
diff --git a/packages/flutter_tools/test/general.shard/build_system/source_test.dart b/packages/flutter_tools/test/general.shard/build_system/source_test.dart
index 0c69bb5869..47a8120e30 100644
--- a/packages/flutter_tools/test/general.shard/build_system/source_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/source_test.dart
@@ -2,6 +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 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/platform.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/android_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/android_test.dart
index 462b03dbf0..cff11c47e6 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/android_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/android_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/assets_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/assets_test.dart
index ae7cd2d4e9..bc48963f74 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/assets_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/assets_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/common_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/common_test.dart
index 647e9935dd..8ba91bcea8 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/common_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/common_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/desktop_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/desktop_test.dart
index 65baadfd63..221644c669 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/desktop_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/desktop_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/icon_tree_shaker_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/icon_tree_shaker_test.dart
index f7b91d7a5c..75c070cb8f 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/icon_tree_shaker_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/icon_tree_shaker_test.dart
@@ -2,6 +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:convert';
 import 'dart:io';
 
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/ios_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/ios_test.dart
index ac04ec0c6a..575d09a8ac 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/ios_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/ios_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/linux_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/linux_test.dart
index bf3519920c..bbfaae4ca0 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/linux_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/linux_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/localizations_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/localizations_test.dart
index 0015cf8b57..4b951e1701 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/localizations_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/localizations_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/macos_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/macos_test.dart
index 0c850a9fc0..10a7779e1d 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/macos_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/macos_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart
index 3547d2d2b7..188d501f4b 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart
@@ -2,6 +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 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/build_system/targets/windows_test.dart b/packages/flutter_tools/test/general.shard/build_system/targets/windows_test.dart
index f5455bab98..fc2e0e9f8b 100644
--- a/packages/flutter_tools/test/general.shard/build_system/targets/windows_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/targets/windows_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/bundle_shim_test.dart b/packages/flutter_tools/test/general.shard/bundle_shim_test.dart
index e8634c92a3..189f791be8 100644
--- a/packages/flutter_tools/test/general.shard/bundle_shim_test.dart
+++ b/packages/flutter_tools/test/general.shard/bundle_shim_test.dart
@@ -2,6 +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 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/build_system/build_system.dart';
 import 'package:flutter_tools/src/bundle.dart';
diff --git a/packages/flutter_tools/test/general.shard/cache_test.dart b/packages/flutter_tools/test/general.shard/cache_test.dart
index d61cf94b0d..a59fdd535c 100644
--- a/packages/flutter_tools/test/general.shard/cache_test.dart
+++ b/packages/flutter_tools/test/general.shard/cache_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
diff --git a/packages/flutter_tools/test/general.shard/channel_test.dart b/packages/flutter_tools/test/general.shard/channel_test.dart
index ff323ef3e3..2156143c48 100644
--- a/packages/flutter_tools/test/general.shard/channel_test.dart
+++ b/packages/flutter_tools/test/general.shard/channel_test.dart
@@ -2,6 +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 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/cold_test.dart b/packages/flutter_tools/test/general.shard/cold_test.dart
index 81a24948b9..c3b209bf12 100644
--- a/packages/flutter_tools/test/general.shard/cold_test.dart
+++ b/packages/flutter_tools/test/general.shard/cold_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/general.shard/commands/analyze_base_test.dart b/packages/flutter_tools/test/general.shard/commands/analyze_base_test.dart
index 5033aeb8db..2c56d2bea1 100644
--- a/packages/flutter_tools/test/general.shard/commands/analyze_base_test.dart
+++ b/packages/flutter_tools/test/general.shard/commands/analyze_base_test.dart
@@ -2,6 +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 'package:flutter_tools/src/commands/analyze_base.dart';
 
 import '../../src/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/commands/build_test.dart b/packages/flutter_tools/test/general.shard/commands/build_test.dart
index a3fad1c23b..80cde3758a 100644
--- a/packages/flutter_tools/test/general.shard/commands/build_test.dart
+++ b/packages/flutter_tools/test/general.shard/commands/build_test.dart
@@ -2,6 +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 'package:args/args.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/commands/attach.dart';
diff --git a/packages/flutter_tools/test/general.shard/commands/flutter_root_test.dart b/packages/flutter_tools/test/general.shard/commands/flutter_root_test.dart
index 5a44537f3e..203377a89f 100644
--- a/packages/flutter_tools/test/general.shard/commands/flutter_root_test.dart
+++ b/packages/flutter_tools/test/general.shard/commands/flutter_root_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/platform.dart';
diff --git a/packages/flutter_tools/test/general.shard/common_test.dart b/packages/flutter_tools/test/general.shard/common_test.dart
index 0507aecd86..bfe7e4785f 100644
--- a/packages/flutter_tools/test/general.shard/common_test.dart
+++ b/packages/flutter_tools/test/general.shard/common_test.dart
@@ -2,6 +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 '../src/common.dart';
 
 void main() {
diff --git a/packages/flutter_tools/test/general.shard/compile_batch_test.dart b/packages/flutter_tools/test/general.shard/compile_batch_test.dart
index e35a9a4fe3..0805f51d3c 100644
--- a/packages/flutter_tools/test/general.shard/compile_batch_test.dart
+++ b/packages/flutter_tools/test/general.shard/compile_batch_test.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/compile_expression_test.dart b/packages/flutter_tools/test/general.shard/compile_expression_test.dart
index 41a34a2b9f..c2cf844dcd 100644
--- a/packages/flutter_tools/test/general.shard/compile_expression_test.dart
+++ b/packages/flutter_tools/test/general.shard/compile_expression_test.dart
@@ -2,6 +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:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/compile_incremental_test.dart b/packages/flutter_tools/test/general.shard/compile_incremental_test.dart
index 48f12eb9cc..7e2747a843 100644
--- a/packages/flutter_tools/test/general.shard/compile_incremental_test.dart
+++ b/packages/flutter_tools/test/general.shard/compile_incremental_test.dart
@@ -2,6 +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:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/compile_test.dart b/packages/flutter_tools/test/general.shard/compile_test.dart
index 4540f0ca38..fe71034261 100644
--- a/packages/flutter_tools/test/general.shard/compile_test.dart
+++ b/packages/flutter_tools/test/general.shard/compile_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/compile.dart';
diff --git a/packages/flutter_tools/test/general.shard/config_test.dart b/packages/flutter_tools/test/general.shard/config_test.dart
index 425c19f5e9..38d8764ac3 100644
--- a/packages/flutter_tools/test/general.shard/config_test.dart
+++ b/packages/flutter_tools/test/general.shard/config_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/config.dart';
 import 'package:flutter_tools/src/base/error_handling_io.dart';
diff --git a/packages/flutter_tools/test/general.shard/coverage_collector_test.dart b/packages/flutter_tools/test/general.shard/coverage_collector_test.dart
index 5648feb299..6ae6a71513 100644
--- a/packages/flutter_tools/test/general.shard/coverage_collector_test.dart
+++ b/packages/flutter_tools/test/general.shard/coverage_collector_test.dart
@@ -2,6 +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 'package:flutter_tools/src/test/coverage_collector.dart';
 import 'package:vm_service/vm_service.dart' as vm_service;
 
diff --git a/packages/flutter_tools/test/general.shard/crash_reporting_test.dart b/packages/flutter_tools/test/general.shard/crash_reporting_test.dart
index b0dad606fa..d83e7f03ef 100644
--- a/packages/flutter_tools/test/general.shard/crash_reporting_test.dart
+++ b/packages/flutter_tools/test/general.shard/crash_reporting_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/general.shard/create_config_test.dart b/packages/flutter_tools/test/general.shard/create_config_test.dart
index 1699de1528..bb60690392 100644
--- a/packages/flutter_tools/test/general.shard/create_config_test.dart
+++ b/packages/flutter_tools/test/general.shard/create_config_test.dart
@@ -2,6 +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 'package:flutter_tools/src/commands/create_base.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/dart/generate_synthetic_packages_test.dart b/packages/flutter_tools/test/general.shard/dart/generate_synthetic_packages_test.dart
index 0a418f1580..1b203713eb 100644
--- a/packages/flutter_tools/test/general.shard/dart/generate_synthetic_packages_test.dart
+++ b/packages/flutter_tools/test/general.shard/dart/generate_synthetic_packages_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/dart/language_version_test.dart b/packages/flutter_tools/test/general.shard/dart/language_version_test.dart
index 1abebfca01..abb07efc56 100644
--- a/packages/flutter_tools/test/general.shard/dart/language_version_test.dart
+++ b/packages/flutter_tools/test/general.shard/dart/language_version_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/convert.dart';
diff --git a/packages/flutter_tools/test/general.shard/dart/pub_get_test.dart b/packages/flutter_tools/test/general.shard/dart/pub_get_test.dart
index 948a3e590c..d37b76565d 100644
--- a/packages/flutter_tools/test/general.shard/dart/pub_get_test.dart
+++ b/packages/flutter_tools/test/general.shard/dart/pub_get_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/bot_detector.dart';
diff --git a/packages/flutter_tools/test/general.shard/desktop_device_test.dart b/packages/flutter_tools/test/general.shard/desktop_device_test.dart
index 8b87d39f1f..af307da882 100644
--- a/packages/flutter_tools/test/general.shard/desktop_device_test.dart
+++ b/packages/flutter_tools/test/general.shard/desktop_device_test.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/devfs_test.dart b/packages/flutter_tools/test/general.shard/devfs_test.dart
index e9268bac31..f8a8b8d8a3 100644
--- a/packages/flutter_tools/test/general.shard/devfs_test.dart
+++ b/packages/flutter_tools/test/general.shard/devfs_test.dart
@@ -2,6 +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 'dart:convert';
 
diff --git a/packages/flutter_tools/test/general.shard/device_test.dart b/packages/flutter_tools/test/general.shard/device_test.dart
index ebd812669b..c4bfe1b00c 100644
--- a/packages/flutter_tools/test/general.shard/device_test.dart
+++ b/packages/flutter_tools/test/general.shard/device_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/terminal.dart';
diff --git a/packages/flutter_tools/test/general.shard/devtools_launcher_test.dart b/packages/flutter_tools/test/general.shard/devtools_launcher_test.dart
index 8086e7f740..fc24ad0d8d 100644
--- a/packages/flutter_tools/test/general.shard/devtools_launcher_test.dart
+++ b/packages/flutter_tools/test/general.shard/devtools_launcher_test.dart
@@ -2,6 +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:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/doctor.dart b/packages/flutter_tools/test/general.shard/doctor.dart
index cc2ae8c75b..43940d5e9c 100644
--- a/packages/flutter_tools/test/general.shard/doctor.dart
+++ b/packages/flutter_tools/test/general.shard/doctor.dart
@@ -2,6 +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 'package:flutter_tools/src/doctor.dart';
 import 'package:flutter_tools/src/features.dart';
 import 'package:flutter_tools/src/linux/linux_doctor.dart';
diff --git a/packages/flutter_tools/test/general.shard/drive/drive_service_test.dart b/packages/flutter_tools/test/general.shard/drive/drive_service_test.dart
index 24265fb7a1..bf3a6b4bc5 100644
--- a/packages/flutter_tools/test/general.shard/drive/drive_service_test.dart
+++ b/packages/flutter_tools/test/general.shard/drive/drive_service_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/application_package.dart';
diff --git a/packages/flutter_tools/test/general.shard/drive/web_driver_service_test.dart b/packages/flutter_tools/test/general.shard/drive/web_driver_service_test.dart
index 91f2c776fb..35fbe6f81f 100644
--- a/packages/flutter_tools/test/general.shard/drive/web_driver_service_test.dart
+++ b/packages/flutter_tools/test/general.shard/drive/web_driver_service_test.dart
@@ -2,6 +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 'package:flutter_tools/src/drive/web_driver_service.dart';
 import 'package:webdriver/sync_io.dart' as sync_io;
 
diff --git a/packages/flutter_tools/test/general.shard/emulator_test.dart b/packages/flutter_tools/test/general.shard/emulator_test.dart
index 04097b47aa..77aa8c1ee2 100644
--- a/packages/flutter_tools/test/general.shard/emulator_test.dart
+++ b/packages/flutter_tools/test/general.shard/emulator_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/android/android_workflow.dart';
diff --git a/packages/flutter_tools/test/general.shard/features_test.dart b/packages/flutter_tools/test/general.shard/features_test.dart
index d3c76653de..f7c82e1ac1 100644
--- a/packages/flutter_tools/test/general.shard/features_test.dart
+++ b/packages/flutter_tools/test/general.shard/features_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/config.dart';
 import 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/features.dart';
diff --git a/packages/flutter_tools/test/general.shard/flutter_manifest_test.dart b/packages/flutter_tools/test/general.shard/flutter_manifest_test.dart
index e23c93dd51..3afb3936e1 100644
--- a/packages/flutter_tools/test/general.shard/flutter_manifest_test.dart
+++ b/packages/flutter_tools/test/general.shard/flutter_manifest_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/flutter_platform_test.dart b/packages/flutter_tools/test/general.shard/flutter_platform_test.dart
index de1d50d9ba..cf12f3304f 100644
--- a/packages/flutter_tools/test/general.shard/flutter_platform_test.dart
+++ b/packages/flutter_tools/test/general.shard/flutter_platform_test.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/flutter_project_metadata_test.dart b/packages/flutter_tools/test/general.shard/flutter_project_metadata_test.dart
index d9e2ba6bbf..24981dd9a1 100644
--- a/packages/flutter_tools/test/general.shard/flutter_project_metadata_test.dart
+++ b/packages/flutter_tools/test/general.shard/flutter_project_metadata_test.dart
@@ -2,6 +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 'package:flutter_tools/src/flutter_project_metadata.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
@@ -83,4 +85,4 @@ project_type: {}
 
     expect(logger.traceText, contains('.metadata project_type version is malformed.'));
   });
-}
\ No newline at end of file
+}
diff --git a/packages/flutter_tools/test/general.shard/flutter_validator_test.dart b/packages/flutter_tools/test/general.shard/flutter_validator_test.dart
index 5ade6cb9ae..12079a488d 100644
--- a/packages/flutter_tools/test/general.shard/flutter_validator_test.dart
+++ b/packages/flutter_tools/test/general.shard/flutter_validator_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/os.dart';
diff --git a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_dev_finder_test.dart b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_dev_finder_test.dart
index 9ee52a7aa9..f70b019b2c 100644
--- a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_dev_finder_test.dart
+++ b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_dev_finder_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_device_test.dart b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_device_test.dart
index 7141439be0..dff03316da 100644
--- a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_device_test.dart
+++ b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_device_test.dart
@@ -2,6 +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 'dart:convert';
 
diff --git a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_kernel_compiler_test.dart b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_kernel_compiler_test.dart
index b9f3ea2ea1..623ab4212e 100644
--- a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_kernel_compiler_test.dart
+++ b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_kernel_compiler_test.dart
@@ -2,6 +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 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/fuchsia/fuchsia_kernel_compiler.dart';
 
diff --git a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_pm_test.dart b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_pm_test.dart
index 60c5e60407..066c0abf16 100644
--- a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_pm_test.dart
+++ b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_pm_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_workflow_test.dart b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_workflow_test.dart
index c50b8c2920..067f092f0d 100644
--- a/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_workflow_test.dart
+++ b/packages/flutter_tools/test/general.shard/fuchsia/fuchsia_workflow_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/platform.dart';
diff --git a/packages/flutter_tools/test/general.shard/generate_localizations_test.dart b/packages/flutter_tools/test/general.shard/generate_localizations_test.dart
index bd8b011e95..8bc30b8e48 100644
--- a/packages/flutter_tools/test/general.shard/generate_localizations_test.dart
+++ b/packages/flutter_tools/test/general.shard/generate_localizations_test.dart
@@ -2,6 +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:io';
 
 import 'package:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/github_template_test.dart b/packages/flutter_tools/test/general.shard/github_template_test.dart
index 81d6124cd4..ae66086e4c 100644
--- a/packages/flutter_tools/test/general.shard/github_template_test.dart
+++ b/packages/flutter_tools/test/general.shard/github_template_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/general.shard/hot_test.dart b/packages/flutter_tools/test/general.shard/hot_test.dart
index 080e9f2d43..05592a336f 100644
--- a/packages/flutter_tools/test/general.shard/hot_test.dart
+++ b/packages/flutter_tools/test/general.shard/hot_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/platform.dart';
diff --git a/packages/flutter_tools/test/general.shard/intellij/intellij_test.dart b/packages/flutter_tools/test/general.shard/intellij/intellij_test.dart
index d50ee4184a..fcb74a9c4f 100644
--- a/packages/flutter_tools/test/general.shard/intellij/intellij_test.dart
+++ b/packages/flutter_tools/test/general.shard/intellij/intellij_test.dart
@@ -2,6 +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:convert';
 
 import 'package:archive/archive.dart';
diff --git a/packages/flutter_tools/test/general.shard/intellij/intellij_validator_test.dart b/packages/flutter_tools/test/general.shard/intellij/intellij_validator_test.dart
index 6aab33f8a6..3081bb537a 100644
--- a/packages/flutter_tools/test/general.shard/intellij/intellij_validator_test.dart
+++ b/packages/flutter_tools/test/general.shard/intellij/intellij_validator_test.dart
@@ -2,6 +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 'package:archive/archive.dart';
 import 'package:file/file.dart';
 import 'package:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/code_signing_test.dart b/packages/flutter_tools/test/general.shard/ios/code_signing_test.dart
index 5391df4730..46e5ac43ec 100644
--- a/packages/flutter_tools/test/general.shard/ios/code_signing_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/code_signing_test.dart
@@ -2,6 +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:convert';
 
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/devices_test.dart b/packages/flutter_tools/test/general.shard/ios/devices_test.dart
index d26a01ac38..16acd10379 100644
--- a/packages/flutter_tools/test/general.shard/ios/devices_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/devices_test.dart
@@ -2,6 +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:file/file.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/ios_deploy_test.dart b/packages/flutter_tools/test/general.shard/ios/ios_deploy_test.dart
index 38db1f055e..37ad924148 100644
--- a/packages/flutter_tools/test/general.shard/ios/ios_deploy_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/ios_deploy_test.dart
@@ -2,6 +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 'dart:convert';
 
diff --git a/packages/flutter_tools/test/general.shard/ios/ios_device_install_test.dart b/packages/flutter_tools/test/general.shard/ios/ios_device_install_test.dart
index cd87eab33f..260b399d80 100644
--- a/packages/flutter_tools/test/general.shard/ios/ios_device_install_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/ios_device_install_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/application_package.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/ios_device_logger_test.dart b/packages/flutter_tools/test/general.shard/ios/ios_device_logger_test.dart
index f866c8561c..38aa90bdb9 100644
--- a/packages/flutter_tools/test/general.shard/ios/ios_device_logger_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/ios_device_logger_test.dart
@@ -2,6 +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:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/ios_device_port_forwarder_test.dart b/packages/flutter_tools/test/general.shard/ios/ios_device_port_forwarder_test.dart
index 28ebc35a96..a0771222ce 100644
--- a/packages/flutter_tools/test/general.shard/ios/ios_device_port_forwarder_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/ios_device_port_forwarder_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/os.dart';
 import 'package:flutter_tools/src/ios/devices.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/ios_device_project_test.dart b/packages/flutter_tools/test/general.shard/ios/ios_device_project_test.dart
index d59ff0a32c..5c24219dcc 100644
--- a/packages/flutter_tools/test/general.shard/ios/ios_device_project_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/ios_device_project_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/ios_device_start_nonprebuilt_test.dart b/packages/flutter_tools/test/general.shard/ios/ios_device_start_nonprebuilt_test.dart
index 41d707b8f7..fa9658d91d 100644
--- a/packages/flutter_tools/test/general.shard/ios/ios_device_start_nonprebuilt_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/ios_device_start_nonprebuilt_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/application_package.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/ios_device_start_prebuilt_test.dart b/packages/flutter_tools/test/general.shard/ios/ios_device_start_prebuilt_test.dart
index 55bd131352..311a97d651 100644
--- a/packages/flutter_tools/test/general.shard/ios/ios_device_start_prebuilt_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/ios_device_start_prebuilt_test.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/ios_project_migration_test.dart b/packages/flutter_tools/test/general.shard/ios/ios_project_migration_test.dart
index c0c591b7e1..e0ba783740 100644
--- a/packages/flutter_tools/test/general.shard/ios/ios_project_migration_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/ios_project_migration_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/ios_workflow_test.dart b/packages/flutter_tools/test/general.shard/ios/ios_workflow_test.dart
index 47f9cbce3e..fb7e9dbda9 100644
--- a/packages/flutter_tools/test/general.shard/ios/ios_workflow_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/ios_workflow_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/ios/ios_workflow.dart';
 import 'package:flutter_tools/src/ios/xcodeproj.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/mac_test.dart b/packages/flutter_tools/test/general.shard/ios/mac_test.dart
index eda3faa915..95d51076d9 100644
--- a/packages/flutter_tools/test/general.shard/ios/mac_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/mac_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/simulators_test.dart b/packages/flutter_tools/test/general.shard/ios/simulators_test.dart
index d4d1807044..9942e9b0be 100644
--- a/packages/flutter_tools/test/general.shard/ios/simulators_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/simulators_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/application_package.dart';
diff --git a/packages/flutter_tools/test/general.shard/ios/xcodeproj_test.dart b/packages/flutter_tools/test/general.shard/ios/xcodeproj_test.dart
index c7ff0104bb..72a4245b8e 100644
--- a/packages/flutter_tools/test/general.shard/ios/xcodeproj_test.dart
+++ b/packages/flutter_tools/test/general.shard/ios/xcodeproj_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/license_collector_test.dart b/packages/flutter_tools/test/general.shard/license_collector_test.dart
index 94a45679b6..f45b2516c4 100644
--- a/packages/flutter_tools/test/general.shard/license_collector_test.dart
+++ b/packages/flutter_tools/test/general.shard/license_collector_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/convert.dart';
diff --git a/packages/flutter_tools/test/general.shard/linux/linux_device_test.dart b/packages/flutter_tools/test/general.shard/linux/linux_device_test.dart
index 2767cd9e4a..07efaec735 100644
--- a/packages/flutter_tools/test/general.shard/linux/linux_device_test.dart
+++ b/packages/flutter_tools/test/general.shard/linux/linux_device_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/linux/linux_doctor_test.dart b/packages/flutter_tools/test/general.shard/linux/linux_doctor_test.dart
index 14a455c3d7..cd99342c75 100644
--- a/packages/flutter_tools/test/general.shard/linux/linux_doctor_test.dart
+++ b/packages/flutter_tools/test/general.shard/linux/linux_doctor_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/user_messages.dart';
 import 'package:flutter_tools/src/doctor.dart';
 import 'package:flutter_tools/src/linux/linux_doctor.dart';
diff --git a/packages/flutter_tools/test/general.shard/linux/linux_workflow_test.dart b/packages/flutter_tools/test/general.shard/linux/linux_workflow_test.dart
index ff3510ad64..6124862a6d 100644
--- a/packages/flutter_tools/test/general.shard/linux/linux_workflow_test.dart
+++ b/packages/flutter_tools/test/general.shard/linux/linux_workflow_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/features.dart';
 import 'package:flutter_tools/src/linux/linux_workflow.dart';
diff --git a/packages/flutter_tools/test/general.shard/macos/application_package_test.dart b/packages/flutter_tools/test/general.shard/macos/application_package_test.dart
index 36848b5ad9..ff69b1def0 100644
--- a/packages/flutter_tools/test/general.shard/macos/application_package_test.dart
+++ b/packages/flutter_tools/test/general.shard/macos/application_package_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/general.shard/macos/cocoapods_test.dart b/packages/flutter_tools/test/general.shard/macos/cocoapods_test.dart
index 79226490ee..c2ab75b4a5 100644
--- a/packages/flutter_tools/test/general.shard/macos/cocoapods_test.dart
+++ b/packages/flutter_tools/test/general.shard/macos/cocoapods_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/macos/cocoapods_validator_test.dart b/packages/flutter_tools/test/general.shard/macos/cocoapods_validator_test.dart
index 23c83c4797..c540e63688 100644
--- a/packages/flutter_tools/test/general.shard/macos/cocoapods_validator_test.dart
+++ b/packages/flutter_tools/test/general.shard/macos/cocoapods_validator_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/user_messages.dart';
 import 'package:flutter_tools/src/doctor.dart';
 import 'package:flutter_tools/src/macos/cocoapods.dart';
diff --git a/packages/flutter_tools/test/general.shard/macos/macos_device_test.dart b/packages/flutter_tools/test/general.shard/macos/macos_device_test.dart
index 9ed7e2b555..201bb6966d 100644
--- a/packages/flutter_tools/test/general.shard/macos/macos_device_test.dart
+++ b/packages/flutter_tools/test/general.shard/macos/macos_device_test.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/macos/macos_project_migration_test.dart b/packages/flutter_tools/test/general.shard/macos/macos_project_migration_test.dart
index 16914273a4..92c2bd9334 100644
--- a/packages/flutter_tools/test/general.shard/macos/macos_project_migration_test.dart
+++ b/packages/flutter_tools/test/general.shard/macos/macos_project_migration_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/macos/macos_workflow_test.dart b/packages/flutter_tools/test/general.shard/macos/macos_workflow_test.dart
index 37e4d3080b..465d664ea7 100644
--- a/packages/flutter_tools/test/general.shard/macos/macos_workflow_test.dart
+++ b/packages/flutter_tools/test/general.shard/macos/macos_workflow_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/macos/macos_workflow.dart';
 
diff --git a/packages/flutter_tools/test/general.shard/macos/xcode_test.dart b/packages/flutter_tools/test/general.shard/macos/xcode_test.dart
index 693ca624ef..a36155b9e8 100644
--- a/packages/flutter_tools/test/general.shard/macos/xcode_test.dart
+++ b/packages/flutter_tools/test/general.shard/macos/xcode_test.dart
@@ -2,6 +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:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/macos/xcode_validator_test.dart b/packages/flutter_tools/test/general.shard/macos/xcode_validator_test.dart
index d65c164c12..cf675ec882 100644
--- a/packages/flutter_tools/test/general.shard/macos/xcode_validator_test.dart
+++ b/packages/flutter_tools/test/general.shard/macos/xcode_validator_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/user_messages.dart';
 import 'package:flutter_tools/src/base/version.dart';
 import 'package:flutter_tools/src/doctor.dart';
diff --git a/packages/flutter_tools/test/general.shard/mdns_discovery_test.dart b/packages/flutter_tools/test/general.shard/mdns_discovery_test.dart
index 41c2c2b5c7..433a725e97 100644
--- a/packages/flutter_tools/test/general.shard/mdns_discovery_test.dart
+++ b/packages/flutter_tools/test/general.shard/mdns_discovery_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/device.dart';
diff --git a/packages/flutter_tools/test/general.shard/migrations/cmake_project_migration_test.dart b/packages/flutter_tools/test/general.shard/migrations/cmake_project_migration_test.dart
index 14f5b93425..c332f31b47 100644
--- a/packages/flutter_tools/test/general.shard/migrations/cmake_project_migration_test.dart
+++ b/packages/flutter_tools/test/general.shard/migrations/cmake_project_migration_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/persistent_tool_state_test.dart b/packages/flutter_tools/test/general.shard/persistent_tool_state_test.dart
index 94b32d36b0..fc199db87f 100644
--- a/packages/flutter_tools/test/general.shard/persistent_tool_state_test.dart
+++ b/packages/flutter_tools/test/general.shard/persistent_tool_state_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/plugin_parsing_test.dart b/packages/flutter_tools/test/general.shard/plugin_parsing_test.dart
index 96867c6fca..3158bc431f 100644
--- a/packages/flutter_tools/test/general.shard/plugin_parsing_test.dart
+++ b/packages/flutter_tools/test/general.shard/plugin_parsing_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/platform_plugins.dart';
diff --git a/packages/flutter_tools/test/general.shard/plugins_test.dart b/packages/flutter_tools/test/general.shard/plugins_test.dart
index 4e74f4a2cf..ce7fa22ff7 100644
--- a/packages/flutter_tools/test/general.shard/plugins_test.dart
+++ b/packages/flutter_tools/test/general.shard/plugins_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/general.shard/project_file_invalidator_test.dart b/packages/flutter_tools/test/general.shard/project_file_invalidator_test.dart
index cac35d40af..312fbb55c6 100644
--- a/packages/flutter_tools/test/general.shard/project_file_invalidator_test.dart
+++ b/packages/flutter_tools/test/general.shard/project_file_invalidator_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/project_test.dart b/packages/flutter_tools/test/general.shard/project_test.dart
index fc521f550a..2b7c86113e 100644
--- a/packages/flutter_tools/test/general.shard/project_test.dart
+++ b/packages/flutter_tools/test/general.shard/project_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/context.dart';
diff --git a/packages/flutter_tools/test/general.shard/protocol_discovery_test.dart b/packages/flutter_tools/test/general.shard/protocol_discovery_test.dart
index 0868df3049..929fb95970 100644
--- a/packages/flutter_tools/test/general.shard/protocol_discovery_test.dart
+++ b/packages/flutter_tools/test/general.shard/protocol_discovery_test.dart
@@ -2,6 +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 'package:flutter_tools/src/device.dart';
 import 'package:flutter_tools/src/protocol_discovery.dart';
 import 'package:fake_async/fake_async.dart';
diff --git a/packages/flutter_tools/test/general.shard/reporting/events_test.dart b/packages/flutter_tools/test/general.shard/reporting/events_test.dart
index 7140d672c7..f90b5cbc53 100644
--- a/packages/flutter_tools/test/general.shard/reporting/events_test.dart
+++ b/packages/flutter_tools/test/general.shard/reporting/events_test.dart
@@ -2,6 +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 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/doctor.dart';
 import 'package:flutter_tools/src/reporting/reporting.dart';
diff --git a/packages/flutter_tools/test/general.shard/reporting/first_run_test.dart b/packages/flutter_tools/test/general.shard/reporting/first_run_test.dart
index 4459410433..f61418252e 100644
--- a/packages/flutter_tools/test/general.shard/reporting/first_run_test.dart
+++ b/packages/flutter_tools/test/general.shard/reporting/first_run_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/persistent_tool_state.dart';
diff --git a/packages/flutter_tools/test/general.shard/resident_runner_test.dart b/packages/flutter_tools/test/general.shard/resident_runner_test.dart
index 85fb96ce2e..aad49a3740 100644
--- a/packages/flutter_tools/test/general.shard/resident_runner_test.dart
+++ b/packages/flutter_tools/test/general.shard/resident_runner_test.dart
@@ -2,6 +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:flutter_tools/src/base/dds.dart';
diff --git a/packages/flutter_tools/test/general.shard/resident_web_runner_cold_test.dart b/packages/flutter_tools/test/general.shard/resident_web_runner_cold_test.dart
index 0cd96a641d..f5141d04b4 100644
--- a/packages/flutter_tools/test/general.shard/resident_web_runner_cold_test.dart
+++ b/packages/flutter_tools/test/general.shard/resident_web_runner_cold_test.dart
@@ -2,6 +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:dwds/dwds.dart';
diff --git a/packages/flutter_tools/test/general.shard/resident_web_runner_test.dart b/packages/flutter_tools/test/general.shard/resident_web_runner_test.dart
index 3ef3137400..84332ac693 100644
--- a/packages/flutter_tools/test/general.shard/resident_web_runner_test.dart
+++ b/packages/flutter_tools/test/general.shard/resident_web_runner_test.dart
@@ -2,6 +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 'dart:convert';
 import 'dart:io';
diff --git a/packages/flutter_tools/test/general.shard/runner/flutter_command_runner_test.dart b/packages/flutter_tools/test/general.shard/runner/flutter_command_runner_test.dart
index 690f8a2a19..f6ea741e3f 100644
--- a/packages/flutter_tools/test/general.shard/runner/flutter_command_runner_test.dart
+++ b/packages/flutter_tools/test/general.shard/runner/flutter_command_runner_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/runner/flutter_command_test.dart b/packages/flutter_tools/test/general.shard/runner/flutter_command_test.dart
index 9033b580f6..d300632352 100644
--- a/packages/flutter_tools/test/general.shard/runner/flutter_command_test.dart
+++ b/packages/flutter_tools/test/general.shard/runner/flutter_command_test.dart
@@ -2,6 +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 'dart:io' as io;
 
diff --git a/packages/flutter_tools/test/general.shard/runner/local_engine_test.dart b/packages/flutter_tools/test/general.shard/runner/local_engine_test.dart
index ac2de2014f..43d2a0c2d8 100644
--- a/packages/flutter_tools/test/general.shard/runner/local_engine_test.dart
+++ b/packages/flutter_tools/test/general.shard/runner/local_engine_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/runner/runner_test.dart b/packages/flutter_tools/test/general.shard/runner/runner_test.dart
index cbb5328dbb..7d01e722c7 100644
--- a/packages/flutter_tools/test/general.shard/runner/runner_test.dart
+++ b/packages/flutter_tools/test/general.shard/runner/runner_test.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/runner/utils.dart b/packages/flutter_tools/test/general.shard/runner/utils.dart
index ee84de7cbd..e3a784e506 100644
--- a/packages/flutter_tools/test/general.shard/runner/utils.dart
+++ b/packages/flutter_tools/test/general.shard/runner/utils.dart
@@ -2,6 +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 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/reporting/reporting.dart';
 import 'package:flutter_tools/src/runner/flutter_command.dart';
diff --git a/packages/flutter_tools/test/general.shard/screenshot_command_test.dart b/packages/flutter_tools/test/general.shard/screenshot_command_test.dart
index 4891546593..cbd1edacc5 100644
--- a/packages/flutter_tools/test/general.shard/screenshot_command_test.dart
+++ b/packages/flutter_tools/test/general.shard/screenshot_command_test.dart
@@ -2,6 +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 'package:flutter_tools/src/commands/screenshot.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/terminal_handler_test.dart b/packages/flutter_tools/test/general.shard/terminal_handler_test.dart
index 5c0eea2ae9..de69d2f2cf 100644
--- a/packages/flutter_tools/test/general.shard/terminal_handler_test.dart
+++ b/packages/flutter_tools/test/general.shard/terminal_handler_test.dart
@@ -2,6 +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:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/test/event_printer_test.dart b/packages/flutter_tools/test/general.shard/test/event_printer_test.dart
index 558bb28c13..b113687008 100644
--- a/packages/flutter_tools/test/general.shard/test/event_printer_test.dart
+++ b/packages/flutter_tools/test/general.shard/test/event_printer_test.dart
@@ -2,6 +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 'package:flutter_tools/src/test/event_printer.dart';
 import 'package:flutter_tools/src/test/watcher.dart';
 
diff --git a/packages/flutter_tools/test/general.shard/test/test_compiler_test.dart b/packages/flutter_tools/test/general.shard/test/test_compiler_test.dart
index bdc763a74c..a18660f2e5 100644
--- a/packages/flutter_tools/test/general.shard/test/test_compiler_test.dart
+++ b/packages/flutter_tools/test/general.shard/test/test_compiler_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/testbed_test.dart b/packages/flutter_tools/test/general.shard/testbed_test.dart
index 5760817573..00103eaf24 100644
--- a/packages/flutter_tools/test/general.shard/testbed_test.dart
+++ b/packages/flutter_tools/test/general.shard/testbed_test.dart
@@ -2,6 +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 'dart:io';
 
diff --git a/packages/flutter_tools/test/general.shard/tester/flutter_tester_test.dart b/packages/flutter_tools/test/general.shard/tester/flutter_tester_test.dart
index 3ce21ab0d2..a4b9f349fe 100644
--- a/packages/flutter_tools/test/general.shard/tester/flutter_tester_test.dart
+++ b/packages/flutter_tools/test/general.shard/tester/flutter_tester_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
diff --git a/packages/flutter_tools/test/general.shard/time_test.dart b/packages/flutter_tools/test/general.shard/time_test.dart
index e0ebb98cdc..184b1ba094 100644
--- a/packages/flutter_tools/test/general.shard/time_test.dart
+++ b/packages/flutter_tools/test/general.shard/time_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/time.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/tracing_test.dart b/packages/flutter_tools/test/general.shard/tracing_test.dart
index d17cc85bf2..958eaf0ce4 100644
--- a/packages/flutter_tools/test/general.shard/tracing_test.dart
+++ b/packages/flutter_tools/test/general.shard/tracing_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/update_packages_test.dart b/packages/flutter_tools/test/general.shard/update_packages_test.dart
index 41d6190ac6..8fd327f32e 100644
--- a/packages/flutter_tools/test/general.shard/update_packages_test.dart
+++ b/packages/flutter_tools/test/general.shard/update_packages_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/utils_test.dart b/packages/flutter_tools/test/general.shard/utils_test.dart
index 6b61393d93..ae5ef7f822 100644
--- a/packages/flutter_tools/test/general.shard/utils_test.dart
+++ b/packages/flutter_tools/test/general.shard/utils_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/utils.dart';
 import 'package:flutter_tools/src/base/version.dart';
 import 'package:flutter_tools/src/base/terminal.dart';
diff --git a/packages/flutter_tools/test/general.shard/version_test.dart b/packages/flutter_tools/test/general.shard/version_test.dart
index bea187ca6f..615fb7f989 100644
--- a/packages/flutter_tools/test/general.shard/version_test.dart
+++ b/packages/flutter_tools/test/general.shard/version_test.dart
@@ -2,6 +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:convert';
 
 import 'package:collection/collection.dart' show ListEquality;
diff --git a/packages/flutter_tools/test/general.shard/vmservice_test.dart b/packages/flutter_tools/test/general.shard/vmservice_test.dart
index 2edce09740..4cf403c1a3 100644
--- a/packages/flutter_tools/test/general.shard/vmservice_test.dart
+++ b/packages/flutter_tools/test/general.shard/vmservice_test.dart
@@ -2,6 +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:flutter_tools/src/base/common.dart';
diff --git a/packages/flutter_tools/test/general.shard/vscode/vscode_test.dart b/packages/flutter_tools/test/general.shard/vscode/vscode_test.dart
index e43b72030c..f3c141f6b2 100644
--- a/packages/flutter_tools/test/general.shard/vscode/vscode_test.dart
+++ b/packages/flutter_tools/test/general.shard/vscode/vscode_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/version.dart';
 import 'package:flutter_tools/src/vscode/vscode.dart';
diff --git a/packages/flutter_tools/test/general.shard/vscode/vscode_validator_test.dart b/packages/flutter_tools/test/general.shard/vscode/vscode_validator_test.dart
index 78cdcb5fee..e60623840a 100644
--- a/packages/flutter_tools/test/general.shard/vscode/vscode_validator_test.dart
+++ b/packages/flutter_tools/test/general.shard/vscode/vscode_validator_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/platform.dart';
diff --git a/packages/flutter_tools/test/general.shard/web/bootstrap_test.dart b/packages/flutter_tools/test/general.shard/web/bootstrap_test.dart
index fba03e0412..04c21daf2a 100644
--- a/packages/flutter_tools/test/general.shard/web/bootstrap_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/bootstrap_test.dart
@@ -2,6 +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 'package:flutter_tools/src/web/bootstrap.dart';
 import 'package:package_config/package_config.dart';
 
diff --git a/packages/flutter_tools/test/general.shard/web/chrome_test.dart b/packages/flutter_tools/test/general.shard/web/chrome_test.dart
index 91a42c7cc8..14f474822f 100644
--- a/packages/flutter_tools/test/general.shard/web/chrome_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/chrome_test.dart
@@ -2,6 +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:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/web/devfs_web_test.dart b/packages/flutter_tools/test/general.shard/web/devfs_web_test.dart
index 325c832502..99f21cf3d4 100644
--- a/packages/flutter_tools/test/general.shard/web/devfs_web_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/devfs_web_test.dart
@@ -2,6 +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:io';
 
 import 'package:dwds/dwds.dart';
diff --git a/packages/flutter_tools/test/general.shard/web/devices_test.dart b/packages/flutter_tools/test/general.shard/web/devices_test.dart
index 14767c6c9a..be30916e17 100644
--- a/packages/flutter_tools/test/general.shard/web/devices_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/devices_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/platform.dart';
diff --git a/packages/flutter_tools/test/general.shard/web/golden_comparator_process_test.dart b/packages/flutter_tools/test/general.shard/web/golden_comparator_process_test.dart
index fe9a70426b..fc817d6f39 100644
--- a/packages/flutter_tools/test/general.shard/web/golden_comparator_process_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/golden_comparator_process_test.dart
@@ -2,6 +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:convert';
 
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/general.shard/web/golden_comparator_test.dart b/packages/flutter_tools/test/general.shard/web/golden_comparator_test.dart
index 76681f7de0..0f2b074c5c 100644
--- a/packages/flutter_tools/test/general.shard/web/golden_comparator_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/golden_comparator_test.dart
@@ -2,6 +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:convert';
 import 'dart:typed_data';
 
diff --git a/packages/flutter_tools/test/general.shard/web/memory_fs_test.dart b/packages/flutter_tools/test/general.shard/web/memory_fs_test.dart
index 26f95acb26..339599a8b1 100644
--- a/packages/flutter_tools/test/general.shard/web/memory_fs_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/memory_fs_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/memory.dart';
diff --git a/packages/flutter_tools/test/general.shard/web/web_asset_server_test.dart b/packages/flutter_tools/test/general.shard/web/web_asset_server_test.dart
index 7994c31154..c8c561fc49 100644
--- a/packages/flutter_tools/test/general.shard/web/web_asset_server_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/web_asset_server_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/general.shard/web/web_expression_compiler_test.dart b/packages/flutter_tools/test/general.shard/web/web_expression_compiler_test.dart
index cbb7295ea6..2b90afff47 100644
--- a/packages/flutter_tools/test/general.shard/web/web_expression_compiler_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/web_expression_compiler_test.dart
@@ -2,6 +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 'package:dwds/dwds.dart';
 import 'package:flutter_tools/src/compile.dart';
 import 'package:flutter_tools/src/isolated/devfs_web.dart';
diff --git a/packages/flutter_tools/test/general.shard/web/web_validator_test.dart b/packages/flutter_tools/test/general.shard/web/web_validator_test.dart
index 876906daec..1aeff82451 100644
--- a/packages/flutter_tools/test/general.shard/web/web_validator_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/web_validator_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/web/workflow_test.dart b/packages/flutter_tools/test/general.shard/web/workflow_test.dart
index ed36a0d16e..44dced99a0 100644
--- a/packages/flutter_tools/test/general.shard/web/workflow_test.dart
+++ b/packages/flutter_tools/test/general.shard/web/workflow_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/web/workflow.dart';
 
diff --git a/packages/flutter_tools/test/general.shard/windows/visual_studio_test.dart b/packages/flutter_tools/test/general.shard/windows/visual_studio_test.dart
index 77b67eb7e8..9e0e310903 100644
--- a/packages/flutter_tools/test/general.shard/windows/visual_studio_test.dart
+++ b/packages/flutter_tools/test/general.shard/windows/visual_studio_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart' show ProcessException;
diff --git a/packages/flutter_tools/test/general.shard/windows/visual_studio_validator_test.dart b/packages/flutter_tools/test/general.shard/windows/visual_studio_validator_test.dart
index 7b9461bbae..7f734ebb4b 100644
--- a/packages/flutter_tools/test/general.shard/windows/visual_studio_validator_test.dart
+++ b/packages/flutter_tools/test/general.shard/windows/visual_studio_validator_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/user_messages.dart' hide userMessages;
 import 'package:flutter_tools/src/doctor.dart';
 import 'package:flutter_tools/src/windows/visual_studio.dart';
diff --git a/packages/flutter_tools/test/general.shard/windows/windows_device_test.dart b/packages/flutter_tools/test/general.shard/windows/windows_device_test.dart
index c46e9a232c..6358d2f1e2 100644
--- a/packages/flutter_tools/test/general.shard/windows/windows_device_test.dart
+++ b/packages/flutter_tools/test/general.shard/windows/windows_device_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/general.shard/windows/windows_workflow_test.dart b/packages/flutter_tools/test/general.shard/windows/windows_workflow_test.dart
index 45f4bd2e4f..4efb34a715 100644
--- a/packages/flutter_tools/test/general.shard/windows/windows_workflow_test.dart
+++ b/packages/flutter_tools/test/general.shard/windows/windows_workflow_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/windows/windows_workflow.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/analyze_size_test.dart b/packages/flutter_tools/test/integration.shard/analyze_size_test.dart
index cb52599f72..5d59d7ab9a 100644
--- a/packages/flutter_tools/test/integration.shard/analyze_size_test.dart
+++ b/packages/flutter_tools/test/integration.shard/analyze_size_test.dart
@@ -2,6 +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 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/io.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/android_plugin_example_app_build_test.dart b/packages/flutter_tools/test/integration.shard/android_plugin_example_app_build_test.dart
index bc151a70c4..a39dc1e293 100644
--- a/packages/flutter_tools/test/integration.shard/android_plugin_example_app_build_test.dart
+++ b/packages/flutter_tools/test/integration.shard/android_plugin_example_app_build_test.dart
@@ -2,6 +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 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/background_isolate_test.dart b/packages/flutter_tools/test/integration.shard/background_isolate_test.dart
index 280daed6ea..7d22368ad8 100644
--- a/packages/flutter_tools/test/integration.shard/background_isolate_test.dart
+++ b/packages/flutter_tools/test/integration.shard/background_isolate_test.dart
@@ -2,6 +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:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/build_ios_config_only_test.dart b/packages/flutter_tools/test/integration.shard/build_ios_config_only_test.dart
index a2b86f5690..57402a436b 100644
--- a/packages/flutter_tools/test/integration.shard/build_ios_config_only_test.dart
+++ b/packages/flutter_tools/test/integration.shard/build_ios_config_only_test.dart
@@ -2,6 +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 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/integration.shard/command_output_test.dart b/packages/flutter_tools/test/integration.shard/command_output_test.dart
index af4c0f743d..4a890460a6 100644
--- a/packages/flutter_tools/test/integration.shard/command_output_test.dart
+++ b/packages/flutter_tools/test/integration.shard/command_output_test.dart
@@ -2,6 +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:convert';
 
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/integration.shard/coverage_collection_test.dart b/packages/flutter_tools/test/integration.shard/coverage_collection_test.dart
index 3cf910a8d6..d6bbe45e68 100644
--- a/packages/flutter_tools/test/integration.shard/coverage_collection_test.dart
+++ b/packages/flutter_tools/test/integration.shard/coverage_collection_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file_testing/file_testing.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/daemon_mode_test.dart b/packages/flutter_tools/test/integration.shard/daemon_mode_test.dart
index f18735af57..f955624538 100644
--- a/packages/flutter_tools/test/integration.shard/daemon_mode_test.dart
+++ b/packages/flutter_tools/test/integration.shard/daemon_mode_test.dart
@@ -2,6 +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 'dart:convert';
 import 'dart:io';
diff --git a/packages/flutter_tools/test/integration.shard/debugger_stepping_test.dart b/packages/flutter_tools/test/integration.shard/debugger_stepping_test.dart
index 6564ec4860..36a604ef7d 100644
--- a/packages/flutter_tools/test/integration.shard/debugger_stepping_test.dart
+++ b/packages/flutter_tools/test/integration.shard/debugger_stepping_test.dart
@@ -2,6 +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:io';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/deprecated_gradle_settings_test.dart b/packages/flutter_tools/test/integration.shard/deprecated_gradle_settings_test.dart
index 24ed02bebc..c2c2ae4a68 100644
--- a/packages/flutter_tools/test/integration.shard/deprecated_gradle_settings_test.dart
+++ b/packages/flutter_tools/test/integration.shard/deprecated_gradle_settings_test.dart
@@ -2,6 +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 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/io.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/downgrade_upgrade_integration_test.dart b/packages/flutter_tools/test/integration.shard/downgrade_upgrade_integration_test.dart
index 53a3687e94..1ea1872135 100644
--- a/packages/flutter_tools/test/integration.shard/downgrade_upgrade_integration_test.dart
+++ b/packages/flutter_tools/test/integration.shard/downgrade_upgrade_integration_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
diff --git a/packages/flutter_tools/test/integration.shard/expression_evaluation_test.dart b/packages/flutter_tools/test/integration.shard/expression_evaluation_test.dart
index af962f0e5d..0b72890f28 100644
--- a/packages/flutter_tools/test/integration.shard/expression_evaluation_test.dart
+++ b/packages/flutter_tools/test/integration.shard/expression_evaluation_test.dart
@@ -2,6 +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:io';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/flutter_attach_test.dart b/packages/flutter_tools/test/integration.shard/flutter_attach_test.dart
index 31d849d6a7..f7cc4d1eba 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_attach_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_attach_test.dart
@@ -2,6 +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:io';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/flutter_gen_test.dart b/packages/flutter_tools/test/integration.shard/flutter_gen_test.dart
index f1b36a7c8a..53dfa92030 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_gen_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_gen_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/flutter_immediately_exit_test.dart b/packages/flutter_tools/test/integration.shard/flutter_immediately_exit_test.dart
index a55c05c928..f55ec37526 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_immediately_exit_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_immediately_exit_test.dart
@@ -2,6 +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 'package:file/file.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/integration.shard/flutter_run_test.dart b/packages/flutter_tools/test/integration.shard/flutter_run_test.dart
index 4baa3edb78..a6eb91cbbb 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_run_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_run_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:process/process.dart';
diff --git a/packages/flutter_tools/test/integration.shard/flutter_run_with_error_test.dart b/packages/flutter_tools/test/integration.shard/flutter_run_with_error_test.dart
index 15d548fc42..372ecb09c6 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_run_with_error_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_run_with_error_test.dart
@@ -2,6 +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:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/forbidden_imports_test.dart b/packages/flutter_tools/test/integration.shard/forbidden_imports_test.dart
index c43cd203e5..2c14356d86 100644
--- a/packages/flutter_tools/test/integration.shard/forbidden_imports_test.dart
+++ b/packages/flutter_tools/test/integration.shard/forbidden_imports_test.dart
@@ -2,6 +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 'package:file/file.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/integration.shard/gen_l10n_test.dart b/packages/flutter_tools/test/integration.shard/gen_l10n_test.dart
index 997d5a957b..a77341da0e 100644
--- a/packages/flutter_tools/test/integration.shard/gen_l10n_test.dart
+++ b/packages/flutter_tools/test/integration.shard/gen_l10n_test.dart
@@ -2,6 +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:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/generated_plugin_registrant_test.dart b/packages/flutter_tools/test/integration.shard/generated_plugin_registrant_test.dart
index 54b3307886..aa9be5c745 100644
--- a/packages/flutter_tools/test/integration.shard/generated_plugin_registrant_test.dart
+++ b/packages/flutter_tools/test/integration.shard/generated_plugin_registrant_test.dart
@@ -2,6 +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:args/command_runner.dart';
diff --git a/packages/flutter_tools/test/integration.shard/hot_reload_errors_test.dart b/packages/flutter_tools/test/integration.shard/hot_reload_errors_test.dart
index 7a08fcf19b..55b4625f2c 100644
--- a/packages/flutter_tools/test/integration.shard/hot_reload_errors_test.dart
+++ b/packages/flutter_tools/test/integration.shard/hot_reload_errors_test.dart
@@ -2,6 +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 'package:file/file.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/integration.shard/hot_reload_test.dart b/packages/flutter_tools/test/integration.shard/hot_reload_test.dart
index 4a852ed45f..62c5d76628 100644
--- a/packages/flutter_tools/test/integration.shard/hot_reload_test.dart
+++ b/packages/flutter_tools/test/integration.shard/hot_reload_test.dart
@@ -2,6 +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:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/hot_reload_with_asset_test.dart b/packages/flutter_tools/test/integration.shard/hot_reload_with_asset_test.dart
index eb4737036f..35308e8f68 100644
--- a/packages/flutter_tools/test/integration.shard/hot_reload_with_asset_test.dart
+++ b/packages/flutter_tools/test/integration.shard/hot_reload_with_asset_test.dart
@@ -2,6 +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:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/ios_content_validation_test.dart b/packages/flutter_tools/test/integration.shard/ios_content_validation_test.dart
index d769d20d5c..737add3172 100644
--- a/packages/flutter_tools/test/integration.shard/ios_content_validation_test.dart
+++ b/packages/flutter_tools/test/integration.shard/ios_content_validation_test.dart
@@ -2,6 +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 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/integration.shard/lifetime_test.dart b/packages/flutter_tools/test/integration.shard/lifetime_test.dart
index 395da59b44..7dde055937 100644
--- a/packages/flutter_tools/test/integration.shard/lifetime_test.dart
+++ b/packages/flutter_tools/test/integration.shard/lifetime_test.dart
@@ -2,6 +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 'package:file/file.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/integration.shard/macos_content_validation_test.dart b/packages/flutter_tools/test/integration.shard/macos_content_validation_test.dart
index 0e1dc6c2e5..f93bf8d3df 100644
--- a/packages/flutter_tools/test/integration.shard/macos_content_validation_test.dart
+++ b/packages/flutter_tools/test/integration.shard/macos_content_validation_test.dart
@@ -2,6 +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 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/integration.shard/migrate_test.dart b/packages/flutter_tools/test/integration.shard/migrate_test.dart
index 81d997e885..4faed35cc9 100644
--- a/packages/flutter_tools/test/integration.shard/migrate_test.dart
+++ b/packages/flutter_tools/test/integration.shard/migrate_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/observatory_port_test.dart b/packages/flutter_tools/test/integration.shard/observatory_port_test.dart
index 8128610e3a..bb3c44964c 100644
--- a/packages/flutter_tools/test/integration.shard/observatory_port_test.dart
+++ b/packages/flutter_tools/test/integration.shard/observatory_port_test.dart
@@ -2,6 +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:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/integration.shard/plist_parser_test.dart b/packages/flutter_tools/test/integration.shard/plist_parser_test.dart
index 0d5fd2d37c..17c6db6e6a 100644
--- a/packages/flutter_tools/test/integration.shard/plist_parser_test.dart
+++ b/packages/flutter_tools/test/integration.shard/plist_parser_test.dart
@@ -2,6 +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:convert';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/single_widget_reload_test.dart b/packages/flutter_tools/test/integration.shard/single_widget_reload_test.dart
index b01f43d316..6bd0b9f6ee 100644
--- a/packages/flutter_tools/test/integration.shard/single_widget_reload_test.dart
+++ b/packages/flutter_tools/test/integration.shard/single_widget_reload_test.dart
@@ -2,6 +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:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/integration.shard/stateless_stateful_hot_reload_test.dart b/packages/flutter_tools/test/integration.shard/stateless_stateful_hot_reload_test.dart
index bedc340d5c..2b21048c27 100644
--- a/packages/flutter_tools/test/integration.shard/stateless_stateful_hot_reload_test.dart
+++ b/packages/flutter_tools/test/integration.shard/stateless_stateful_hot_reload_test.dart
@@ -2,6 +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:file/file.dart';
diff --git a/packages/flutter_tools/test/integration.shard/template_manifest_test.dart b/packages/flutter_tools/test/integration.shard/template_manifest_test.dart
index b254833a28..b9dcb4a1ad 100644
--- a/packages/flutter_tools/test/integration.shard/template_manifest_test.dart
+++ b/packages/flutter_tools/test/integration.shard/template_manifest_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:flutter_tools/src/convert.dart';
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/integration.shard/test_data/background_project.dart b/packages/flutter_tools/test/integration.shard/test_data/background_project.dart
index a4664bebd0..b858b2a3cf 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/background_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/background_project.dart
@@ -2,6 +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 '../test_utils.dart';
 import 'project.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/basic_project.dart b/packages/flutter_tools/test/integration.shard/test_data/basic_project.dart
index 61e195e0fe..ea94b8d855 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/basic_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/basic_project.dart
@@ -2,6 +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 'project.dart';
 
 class BasicProject extends Project {
diff --git a/packages/flutter_tools/test/integration.shard/test_data/gen_l10n_project.dart b/packages/flutter_tools/test/integration.shard/test_data/gen_l10n_project.dart
index 278055a786..45265a043d 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/gen_l10n_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/gen_l10n_project.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:meta/meta.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_const_project.dart b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_const_project.dart
index fa870a91d3..a1d5637a70 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_const_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_const_project.dart
@@ -2,6 +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 '../test_utils.dart';
 import 'project.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_project.dart b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_project.dart
index 084b6bd565..406abfa5e5 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_project.dart
@@ -2,6 +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 '../test_utils.dart';
 import 'project.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_with_asset.dart b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_with_asset.dart
index 3b68c3f47f..3668b18f97 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_with_asset.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_with_asset.dart
@@ -2,6 +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 '../test_utils.dart';
 import 'project.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/project.dart b/packages/flutter_tools/test/integration.shard/test_data/project.dart
index 8942331e76..df281c0bf8 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/project.dart
@@ -2,6 +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 'package:file/file.dart';
 
 import '../test_utils.dart';
diff --git a/packages/flutter_tools/test/integration.shard/test_data/project_with_early_error.dart b/packages/flutter_tools/test/integration.shard/test_data/project_with_early_error.dart
index 10dc33e2bf..819d56cac6 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/project_with_early_error.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/project_with_early_error.dart
@@ -2,6 +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 'project.dart';
 
 class ProjectWithEarlyError extends Project {
diff --git a/packages/flutter_tools/test/integration.shard/test_data/project_with_immediate_exit.dart b/packages/flutter_tools/test/integration.shard/test_data/project_with_immediate_exit.dart
index 6273c9bd6d..61ec52d545 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/project_with_immediate_exit.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/project_with_immediate_exit.dart
@@ -2,6 +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 'project.dart';
 
 class ProjectWithImmediateExit extends Project {
diff --git a/packages/flutter_tools/test/integration.shard/test_data/single_widget_reload_project.dart b/packages/flutter_tools/test/integration.shard/test_data/single_widget_reload_project.dart
index 908376ab77..732fe50d57 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/single_widget_reload_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/single_widget_reload_project.dart
@@ -2,6 +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 '../test_utils.dart';
 import 'project.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/stateless_stateful_project.dart b/packages/flutter_tools/test/integration.shard/test_data/stateless_stateful_project.dart
index 587a8249e6..4ac309e035 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/stateless_stateful_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/stateless_stateful_project.dart
@@ -2,6 +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 '../test_utils.dart';
 import 'project.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/stepping_project.dart b/packages/flutter_tools/test/integration.shard/test_data/stepping_project.dart
index f9161dc5bd..5722a70c0a 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/stepping_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/stepping_project.dart
@@ -2,6 +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 'project.dart';
 
 class SteppingProject extends Project {
diff --git a/packages/flutter_tools/test/integration.shard/test_data/test_project.dart b/packages/flutter_tools/test/integration.shard/test_data/test_project.dart
index 279747afdc..6253e04617 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/test_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/test_project.dart
@@ -2,6 +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 'project.dart';
 
 class TestProject extends Project {
diff --git a/packages/flutter_tools/test/integration.shard/test_data/tests_project.dart b/packages/flutter_tools/test/integration.shard/test_data/tests_project.dart
index 2d526cfdaf..15b4c0c5a3 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/tests_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/tests_project.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/integration.shard/test_driver.dart b/packages/flutter_tools/test/integration.shard/test_driver.dart
index 408eb91f9c..1bab241ff9 100644
--- a/packages/flutter_tools/test/integration.shard/test_driver.dart
+++ b/packages/flutter_tools/test/integration.shard/test_driver.dart
@@ -2,6 +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 'dart:convert';
 import 'dart:io' as io; // ignore: dart_io_import
diff --git a/packages/flutter_tools/test/integration.shard/test_test.dart b/packages/flutter_tools/test/integration.shard/test_test.dart
index bda077ba44..71a84a11d4 100644
--- a/packages/flutter_tools/test/integration.shard/test_test.dart
+++ b/packages/flutter_tools/test/integration.shard/test_test.dart
@@ -2,6 +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 'dart:convert';
 
diff --git a/packages/flutter_tools/test/integration.shard/test_utils.dart b/packages/flutter_tools/test/integration.shard/test_utils.dart
index 3a3db0469e..45596f12cc 100644
--- a/packages/flutter_tools/test/integration.shard/test_utils.dart
+++ b/packages/flutter_tools/test/integration.shard/test_utils.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:file/local.dart';
 import 'package:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/integration.shard/unit_coverage_test.dart b/packages/flutter_tools/test/integration.shard/unit_coverage_test.dart
index 135d050b4b..56f0d2fab6 100644
--- a/packages/flutter_tools/test/integration.shard/unit_coverage_test.dart
+++ b/packages/flutter_tools/test/integration.shard/unit_coverage_test.dart
@@ -2,6 +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 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:process/process.dart';
diff --git a/packages/flutter_tools/test/integration.shard/vmservice_integration_test.dart b/packages/flutter_tools/test/integration.shard/vmservice_integration_test.dart
index e8c7c94844..7fccddfa66 100644
--- a/packages/flutter_tools/test/integration.shard/vmservice_integration_test.dart
+++ b/packages/flutter_tools/test/integration.shard/vmservice_integration_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:matcher/matcher.dart';
diff --git a/packages/flutter_tools/test/integration.shard/xcode_backend_test.dart b/packages/flutter_tools/test/integration.shard/xcode_backend_test.dart
index 11feaf6a5f..f2f94bcd21 100644
--- a/packages/flutter_tools/test/integration.shard/xcode_backend_test.dart
+++ b/packages/flutter_tools/test/integration.shard/xcode_backend_test.dart
@@ -2,6 +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:io' as io;
 
 import 'package:flutter_tools/src/base/io.dart';
diff --git a/packages/flutter_tools/test/src/android_common.dart b/packages/flutter_tools/test/src/android_common.dart
index cba857fc21..7fef28dad3 100644
--- a/packages/flutter_tools/test/src/android_common.dart
+++ b/packages/flutter_tools/test/src/android_common.dart
@@ -2,6 +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 'package:meta/meta.dart';
 
 import 'package:flutter_tools/src/globals.dart' as globals;
diff --git a/packages/flutter_tools/test/src/common.dart b/packages/flutter_tools/test/src/common.dart
index 9c52034df5..bc13fce248 100644
--- a/packages/flutter_tools/test/src/common.dart
+++ b/packages/flutter_tools/test/src/common.dart
@@ -2,6 +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:args/args.dart';
diff --git a/packages/flutter_tools/test/src/context.dart b/packages/flutter_tools/test/src/context.dart
index bca89a247c..cf3a1e6958 100644
--- a/packages/flutter_tools/test/src/context.dart
+++ b/packages/flutter_tools/test/src/context.dart
@@ -2,6 +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:flutter_tools/src/android/android_workflow.dart';
diff --git a/packages/flutter_tools/test/src/darwin_common.dart b/packages/flutter_tools/test/src/darwin_common.dart
index e3726ab1e6..b5bea318f3 100644
--- a/packages/flutter_tools/test/src/darwin_common.dart
+++ b/packages/flutter_tools/test/src/darwin_common.dart
@@ -2,6 +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:convert';
 
 import 'package:process/process.dart';
diff --git a/packages/flutter_tools/test/src/fake_devices.dart b/packages/flutter_tools/test/src/fake_devices.dart
index 36306204ed..504cafc41f 100644
--- a/packages/flutter_tools/test/src/fake_devices.dart
+++ b/packages/flutter_tools/test/src/fake_devices.dart
@@ -2,6 +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 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/device.dart';
 import 'package:flutter_tools/src/project.dart';
diff --git a/packages/flutter_tools/test/src/fake_process_manager.dart b/packages/flutter_tools/test/src/fake_process_manager.dart
index 203bac8150..5792ac4c8b 100644
--- a/packages/flutter_tools/test/src/fake_process_manager.dart
+++ b/packages/flutter_tools/test/src/fake_process_manager.dart
@@ -2,6 +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 'dart:convert';
 import 'dart:io' as io show ProcessSignal;
diff --git a/packages/flutter_tools/test/src/fakes.dart b/packages/flutter_tools/test/src/fakes.dart
index f6dcacacf6..af297e5ec3 100644
--- a/packages/flutter_tools/test/src/fakes.dart
+++ b/packages/flutter_tools/test/src/fakes.dart
@@ -2,6 +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:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/src/io.dart b/packages/flutter_tools/test/src/io.dart
index db4b5b8c9f..2bfbd40b52 100644
--- a/packages/flutter_tools/test/src/io.dart
+++ b/packages/flutter_tools/test/src/io.dart
@@ -2,6 +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:io' as io show IOOverrides, Directory, File, Link;
 
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/src/mocks.dart b/packages/flutter_tools/test/src/mocks.dart
index 1097386134..94cca225d6 100644
--- a/packages/flutter_tools/test/src/mocks.dart
+++ b/packages/flutter_tools/test/src/mocks.dart
@@ -2,6 +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 'dart:convert';
 import 'dart:io' as io show IOSink, ProcessSignal, Stdout, StdoutException;
diff --git a/packages/flutter_tools/test/src/pubspec_schema.dart b/packages/flutter_tools/test/src/pubspec_schema.dart
index 2da18a03ea..54b22dd396 100644
--- a/packages/flutter_tools/test/src/pubspec_schema.dart
+++ b/packages/flutter_tools/test/src/pubspec_schema.dart
@@ -2,6 +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 'package:flutter_tools/src/flutter_manifest.dart';
 import 'package:meta/meta.dart';
 import 'package:flutter_tools/src/globals.dart' as globals;
diff --git a/packages/flutter_tools/test/src/testbed.dart b/packages/flutter_tools/test/src/testbed.dart
index b43077765e..20abb1247e 100644
--- a/packages/flutter_tools/test/src/testbed.dart
+++ b/packages/flutter_tools/test/src/testbed.dart
@@ -2,6 +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 'dart:convert';
 import 'dart:io';
diff --git a/packages/flutter_tools/test/src/throwing_pub.dart b/packages/flutter_tools/test/src/throwing_pub.dart
index de4013684c..b5dfd85809 100644
--- a/packages/flutter_tools/test/src/throwing_pub.dart
+++ b/packages/flutter_tools/test/src/throwing_pub.dart
@@ -2,6 +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 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/dart/pub.dart';
 import 'package:meta/meta.dart';
diff --git a/packages/flutter_tools/test/template_test.dart b/packages/flutter_tools/test/template_test.dart
index fb7bde14c7..b704e85c5a 100644
--- a/packages/flutter_tools/test/template_test.dart
+++ b/packages/flutter_tools/test/template_test.dart
@@ -2,6 +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 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
diff --git a/packages/flutter_tools/test/web.shard/debugger_stepping_web_test.dart b/packages/flutter_tools/test/web.shard/debugger_stepping_web_test.dart
index d8d7ed57dc..9e22ea5066 100644
--- a/packages/flutter_tools/test/web.shard/debugger_stepping_web_test.dart
+++ b/packages/flutter_tools/test/web.shard/debugger_stepping_web_test.dart
@@ -2,6 +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:io';
 
 import 'package:file/file.dart';
diff --git a/packages/flutter_tools/test/web.shard/expression_evaluation_web_test.dart b/packages/flutter_tools/test/web.shard/expression_evaluation_web_test.dart
index df2d33ff34..4b0be2fbb4 100644
--- a/packages/flutter_tools/test/web.shard/expression_evaluation_web_test.dart
+++ b/packages/flutter_tools/test/web.shard/expression_evaluation_web_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:matcher/matcher.dart';
 import 'package:vm_service/vm_service.dart';
diff --git a/packages/flutter_tools/test/web.shard/hot_reload_web_test.dart b/packages/flutter_tools/test/web.shard/hot_reload_web_test.dart
index c319c7446b..eb4a47b26b 100644
--- a/packages/flutter_tools/test/web.shard/hot_reload_web_test.dart
+++ b/packages/flutter_tools/test/web.shard/hot_reload_web_test.dart
@@ -2,6 +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:file/file.dart';
diff --git a/packages/flutter_tools/test/web.shard/web_run_test.dart b/packages/flutter_tools/test/web.shard/web_run_test.dart
index b9f9d64df7..8c760cd12f 100644
--- a/packages/flutter_tools/test/web.shard/web_run_test.dart
+++ b/packages/flutter_tools/test/web.shard/web_run_test.dart
@@ -2,6 +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 'package:file/file.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 
diff --git a/packages/flutter_tools/tool/daemon_client.dart b/packages/flutter_tools/tool/daemon_client.dart
index abc9e58562..07f3fb0166 100644
--- a/packages/flutter_tools/tool/daemon_client.dart
+++ b/packages/flutter_tools/tool/daemon_client.dart
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.9
+// @dart = 2.8
 
 import 'dart:convert';
 import 'dart:io';
diff --git a/packages/flutter_tools/tool/global_count.dart b/packages/flutter_tools/tool/global_count.dart
index a1c269e3ce..cab9c59389 100644
--- a/packages/flutter_tools/tool/global_count.dart
+++ b/packages/flutter_tools/tool/global_count.dart
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.9
+// @dart = 2.8
 
 import 'dart:io';
 import 'package:path/path.dart' as path;
diff --git a/packages/flutter_tools/tool/unit_coverage.dart b/packages/flutter_tools/tool/unit_coverage.dart
index 1e7518c968..0b26d4a340 100644
--- a/packages/flutter_tools/tool/unit_coverage.dart
+++ b/packages/flutter_tools/tool/unit_coverage.dart
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.9
+// @dart = 2.8
 
 import 'dart:io';