diff --git a/.dart_tool/package_config.json b/.dart_tool/package_config.json
index 9257edd2ff6..dfab19ef8bb 100644
--- a/.dart_tool/package_config.json
+++ b/.dart_tool/package_config.json
@@ -1,6 +1,6 @@
 {
   "copyright": [
-    "Copyright (c) 2020, the Dart project authors. Please see the AUTHORS ",
+    "Copyright (c) 2021, the Dart project authors. Please see the AUTHORS ",
     "file for details. All rights reserved. Use of this source code is ",
     "governed by a BSD-style license that can be found in the LICENSE file."
   ],
@@ -11,7 +11,7 @@
     "constraint, update this by running tools/generate_package_config.dart."
   ],
   "configVersion": 2,
-  "generated": "2020-12-16T11:30:30.799202",
+  "generated": "2021-01-16T20:34:15.774260",
   "generator": "tools/generate_package_config.dart",
   "packages": [
     {
@@ -273,7 +273,7 @@
       "name": "front_end",
       "rootUri": "../pkg/front_end",
       "packageUri": "lib/",
-      "languageVersion": "2.6"
+      "languageVersion": "2.12"
     },
     {
       "name": "front_end_testcases",
@@ -367,7 +367,7 @@
       "name": "kernel",
       "rootUri": "../pkg/kernel",
       "packageUri": "lib/",
-      "languageVersion": "2.6"
+      "languageVersion": "2.12"
     },
     {
       "name": "language_versioning_2.7_test",
diff --git a/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart b/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart
index f5498a2265f..612de52e496 100644
--- a/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart
@@ -1,4 +1,4 @@
-// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
diff --git a/pkg/front_end/benchmarks/ikg/dart2js.dart b/pkg/front_end/benchmarks/ikg/dart2js.dart
index ebc4b217cdf..3877ff268bd 100644
--- a/pkg/front_end/benchmarks/ikg/dart2js.dart
+++ b/pkg/front_end/benchmarks/ikg/dart2js.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'package:compiler/src/dart2js.dart' as dart2js;
 
 main(args) => dart2js.main(args);
diff --git a/pkg/front_end/lib/src/api_prototype/compiler_options.dart b/pkg/front_end/lib/src/api_prototype/compiler_options.dart
index 7639c95e30b..5e0b86bc3b7 100644
--- a/pkg/front_end/lib/src/api_prototype/compiler_options.dart
+++ b/pkg/front_end/lib/src/api_prototype/compiler_options.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library front_end.compiler_options;
 
 import 'package:_fe_analyzer_shared/src/messages/diagnostic_message.dart'
diff --git a/pkg/front_end/lib/src/api_prototype/constant_evaluator.dart b/pkg/front_end/lib/src/api_prototype/constant_evaluator.dart
index 98dd0ab5a63..5427e63b55e 100644
--- a/pkg/front_end/lib/src/api_prototype/constant_evaluator.dart
+++ b/pkg/front_end/lib/src/api_prototype/constant_evaluator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library front_end.constant_evaluator;
 
 export '../fasta/kernel/constant_evaluator.dart'
diff --git a/pkg/front_end/lib/src/api_prototype/experimental_flags.dart b/pkg/front_end/lib/src/api_prototype/experimental_flags.dart
index d0057f71872..088b5171937 100644
--- a/pkg/front_end/lib/src/api_prototype/experimental_flags.dart
+++ b/pkg/front_end/lib/src/api_prototype/experimental_flags.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart' show Version;
 
 part 'experimental_flags_generated.dart';
diff --git a/pkg/front_end/lib/src/api_prototype/experimental_flags_generated.dart b/pkg/front_end/lib/src/api_prototype/experimental_flags_generated.dart
index 9be22afc71f..dfdef386cf6 100644
--- a/pkg/front_end/lib/src/api_prototype/experimental_flags_generated.dart
+++ b/pkg/front_end/lib/src/api_prototype/experimental_flags_generated.dart
@@ -1,7 +1,9 @@
-// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // NOTE: THIS FILE IS GENERATED. DO NOT EDIT.
 //
 // Instead modify 'tools/experimental_features.yaml' and run
diff --git a/pkg/front_end/lib/src/api_prototype/front_end.dart b/pkg/front_end/lib/src/api_prototype/front_end.dart
index 3830dbe1512..1ef9263431b 100644
--- a/pkg/front_end/lib/src/api_prototype/front_end.dart
+++ b/pkg/front_end/lib/src/api_prototype/front_end.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// The Dart Front End contains logic to build summaries and kernel programs
 /// from Dart sources. The APIs exposed here are designed for tools in the Dart
 /// ecosystem that need to load sources and convert them to these formats.
diff --git a/pkg/front_end/lib/src/api_prototype/incremental_kernel_generator.dart b/pkg/front_end/lib/src/api_prototype/incremental_kernel_generator.dart
index e5b1bc233d8..1e2a4463ee2 100644
--- a/pkg/front_end/lib/src/api_prototype/incremental_kernel_generator.dart
+++ b/pkg/front_end/lib/src/api_prototype/incremental_kernel_generator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/scanner/string_scanner.dart'
     show StringScanner;
 
diff --git a/pkg/front_end/lib/src/api_prototype/kernel_generator.dart b/pkg/front_end/lib/src/api_prototype/kernel_generator.dart
index 27857a9e427..6e80dc540fd 100644
--- a/pkg/front_end/lib/src/api_prototype/kernel_generator.dart
+++ b/pkg/front_end/lib/src/api_prototype/kernel_generator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Defines the front-end API for converting source code to Dart Kernel objects.
 library front_end.kernel_generator;
 
diff --git a/pkg/front_end/lib/src/api_prototype/language_version.dart b/pkg/front_end/lib/src/api_prototype/language_version.dart
index 02db78fe949..84b27fdd4b1 100644
--- a/pkg/front_end/lib/src/api_prototype/language_version.dart
+++ b/pkg/front_end/lib/src/api_prototype/language_version.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:typed_data' show Uint8List;
 
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart'
diff --git a/pkg/front_end/lib/src/api_prototype/lowering_predicates.dart b/pkg/front_end/lib/src/api_prototype/lowering_predicates.dart
index 391be7ed0c1..50da5f6ed3e 100644
--- a/pkg/front_end/lib/src/api_prototype/lowering_predicates.dart
+++ b/pkg/front_end/lib/src/api_prototype/lowering_predicates.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart';
 import '../fasta/kernel/late_lowering.dart';
 import '../fasta/source/source_extension_builder.dart' show extensionThisName;
diff --git a/pkg/front_end/lib/src/api_prototype/memory_file_system.dart b/pkg/front_end/lib/src/api_prototype/memory_file_system.dart
index e077d8d4d63..194393b6276 100644
--- a/pkg/front_end/lib/src/api_prototype/memory_file_system.dart
+++ b/pkg/front_end/lib/src/api_prototype/memory_file_system.dart
@@ -87,7 +87,7 @@ class MemoryFileSystemEntity implements FileSystemEntity {
 
   @override
   Future<List<int>> readAsBytes() async {
-    Uint8List contents = _fileSystem._files[uri];
+    Uint8List? contents = _fileSystem._files[uri];
     if (contents == null) {
       throw new FileSystemException(uri, 'File $uri does not exist.');
     }
diff --git a/pkg/front_end/lib/src/api_prototype/standard_file_system.dart b/pkg/front_end/lib/src/api_prototype/standard_file_system.dart
index a8bbc0b59f8..bc1a4bc07e9 100644
--- a/pkg/front_end/lib/src/api_prototype/standard_file_system.dart
+++ b/pkg/front_end/lib/src/api_prototype/standard_file_system.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library front_end.standard_file_system;
 
 import 'dart:io' as io;
diff --git a/pkg/front_end/lib/src/api_prototype/summary_generator.dart b/pkg/front_end/lib/src/api_prototype/summary_generator.dart
index d5795363189..04922893686 100644
--- a/pkg/front_end/lib/src/api_prototype/summary_generator.dart
+++ b/pkg/front_end/lib/src/api_prototype/summary_generator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Defines the front-end API for converting source code to summaries.
 library front_end.summary_generator;
 
diff --git a/pkg/front_end/lib/src/api_unstable/bazel_worker.dart b/pkg/front_end/lib/src/api_unstable/bazel_worker.dart
index 48df5c91a2d..9cfd890e549 100644
--- a/pkg/front_end/lib/src/api_unstable/bazel_worker.dart
+++ b/pkg/front_end/lib/src/api_unstable/bazel_worker.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// API needed by `utils/front_end/summary_worker.dart`, a tool used to compute
 /// summaries in build systems like bazel, pub-build, and package-build.
 
diff --git a/pkg/front_end/lib/src/api_unstable/compiler_state.dart b/pkg/front_end/lib/src/api_unstable/compiler_state.dart
index 9baa0b7a01d..97779f8bae0 100644
--- a/pkg/front_end/lib/src/api_unstable/compiler_state.dart
+++ b/pkg/front_end/lib/src/api_unstable/compiler_state.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import '../api_prototype/compiler_options.dart' show CompilerOptions;
 
 import '../base/processed_options.dart' show ProcessedOptions;
diff --git a/pkg/front_end/lib/src/api_unstable/dart2js.dart b/pkg/front_end/lib/src/api_unstable/dart2js.dart
index 9a102ac234c..358c006de1c 100644
--- a/pkg/front_end/lib/src/api_unstable/dart2js.dart
+++ b/pkg/front_end/lib/src/api_unstable/dart2js.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/messages/codes.dart'
     show messageMissingMain;
 
diff --git a/pkg/front_end/lib/src/api_unstable/ddc.dart b/pkg/front_end/lib/src/api_unstable/ddc.dart
index b28384f9d1c..c3de1465ef8 100644
--- a/pkg/front_end/lib/src/api_unstable/ddc.dart
+++ b/pkg/front_end/lib/src/api_unstable/ddc.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/messages/diagnostic_message.dart'
     show DiagnosticMessageHandler;
 
diff --git a/pkg/front_end/lib/src/api_unstable/modular_incremental_compilation.dart b/pkg/front_end/lib/src/api_unstable/modular_incremental_compilation.dart
index eb80f977b15..7086aad1583 100644
--- a/pkg/front_end/lib/src/api_unstable/modular_incremental_compilation.dart
+++ b/pkg/front_end/lib/src/api_unstable/modular_incremental_compilation.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart' show Component, CanonicalName, Library;
 
 import 'package:kernel/target/targets.dart' show Target;
diff --git a/pkg/front_end/lib/src/api_unstable/util.dart b/pkg/front_end/lib/src/api_unstable/util.dart
index cc5f7fcdfa0..2200effb583 100644
--- a/pkg/front_end/lib/src/api_unstable/util.dart
+++ b/pkg/front_end/lib/src/api_unstable/util.dart
@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-bool equalLists<T>(List<T> a, List<T> b) {
+bool equalLists<T>(List<T>? a, List<T>? b) {
   if (identical(a, b)) return true;
   if (a == null || b == null) return false;
   if (a.length != b.length) return false;
@@ -12,7 +12,7 @@ bool equalLists<T>(List<T> a, List<T> b) {
   return true;
 }
 
-bool equalSets<K>(Set<K> a, Set<K> b) {
+bool equalSets<K>(Set<K>? a, Set<K>? b) {
   if (identical(a, b)) return true;
   if (a == null || b == null) return false;
   if (a.length != b.length) return false;
@@ -22,7 +22,7 @@ bool equalSets<K>(Set<K> a, Set<K> b) {
   return true;
 }
 
-bool equalMaps<K, V>(Map<K, V> a, Map<K, V> b) {
+bool equalMaps<K, V>(Map<K, V>? a, Map<K, V>? b) {
   if (identical(a, b)) return true;
   if (a == null || b == null) return false;
   if (a.length != b.length) return false;
diff --git a/pkg/front_end/lib/src/api_unstable/vm.dart b/pkg/front_end/lib/src/api_unstable/vm.dart
index 65963f9551d..c816637bed3 100644
--- a/pkg/front_end/lib/src/api_unstable/vm.dart
+++ b/pkg/front_end/lib/src/api_unstable/vm.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 export 'package:_fe_analyzer_shared/src/messages/diagnostic_message.dart'
     show DiagnosticMessage, DiagnosticMessageHandler, getMessageUri;
 
diff --git a/pkg/front_end/lib/src/base/instrumentation.dart b/pkg/front_end/lib/src/base/instrumentation.dart
index 8cf71703fa4..24876a6bf13 100644
--- a/pkg/front_end/lib/src/base/instrumentation.dart
+++ b/pkg/front_end/lib/src/base/instrumentation.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' show DartType, Member;
 import 'package:kernel/src/text_util.dart';
 
diff --git a/pkg/front_end/lib/src/base/libraries_specification.dart b/pkg/front_end/lib/src/base/libraries_specification.dart
index 52a18dc13a9..61f002886d9 100644
--- a/pkg/front_end/lib/src/base/libraries_specification.dart
+++ b/pkg/front_end/lib/src/base/libraries_specification.dart
@@ -106,7 +106,7 @@ class LibrariesSpecification {
   /// The library specification for a given [target], or throws if none is
   /// available.
   TargetLibrariesSpecification specificationFor(String target) {
-    TargetLibrariesSpecification targetSpec = _targets[target];
+    TargetLibrariesSpecification? targetSpec = _targets[target];
     if (targetSpec == null) {
       throw new LibrariesSpecificationException(
           'No library specification for target "$target"');
@@ -119,15 +119,15 @@ class LibrariesSpecification {
   ///
   /// May throw an exception if [json] is not properly formatted or contains
   /// invalid values.
-  static LibrariesSpecification parse(Uri baseUri, String json) {
+  static LibrariesSpecification parse(Uri baseUri, String? json) {
     if (json == null) return const LibrariesSpecification();
     Map<String, dynamic> jsonData;
     try {
       dynamic data = jsonDecode(json);
-      if (data is! Map) {
+      if (data is! Map<String, dynamic>) {
         return _reportError('top-level specification is not a map');
       }
-      jsonData = data as Map;
+      jsonData = data;
     } on FormatException catch (e) {
       throw new LibrariesSpecificationException(e);
     }
@@ -145,11 +145,11 @@ class LibrariesSpecification {
             "for '$targetName' doesn't have a libraries entry");
       }
       dynamic librariesData = targetData["libraries"];
-      if (librariesData is! Map) {
+      if (librariesData is! Map<String, dynamic>) {
         return _reportError("libraries entry for '$targetName' is not a map");
       }
       librariesData.forEach((String name, data) {
-        if (data is! Map) {
+        if (data is! Map<String, dynamic>) {
           return _reportError(
               "library data for '$name' in target '$targetName' is not a map");
         }
@@ -233,7 +233,7 @@ class TargetLibrariesSpecification {
       [this._libraries = const <String, LibraryInfo>{}]);
 
   /// Details about a library whose import is `dart:$name`.
-  LibraryInfo libraryInfoFor(String name) => _libraries[name];
+  LibraryInfo? libraryInfoFor(String name) => _libraries[name];
 
   Iterable<LibraryInfo> get allLibraries => _libraries.values;
 }
diff --git a/pkg/front_end/lib/src/base/library_info.dart b/pkg/front_end/lib/src/base/library_info.dart
index f7541dac26b..a8186f3cafb 100644
--- a/pkg/front_end/lib/src/base/library_info.dart
+++ b/pkg/front_end/lib/src/base/library_info.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// A bit flag used by [LibraryInfo] indicating that a library is used by
 /// dart2js.
 ///
diff --git a/pkg/front_end/lib/src/base/processed_options.dart b/pkg/front_end/lib/src/base/processed_options.dart
index ec366d016b8..84f9e63466f 100644
--- a/pkg/front_end/lib/src/base/processed_options.dart
+++ b/pkg/front_end/lib/src/base/processed_options.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show exitCode;
 
 import 'dart:typed_data' show Uint8List;
diff --git a/pkg/front_end/lib/src/compute_platform_binaries_location.dart b/pkg/front_end/lib/src/compute_platform_binaries_location.dart
index 2c36d10ff9e..3060afb34de 100644
--- a/pkg/front_end/lib/src/compute_platform_binaries_location.dart
+++ b/pkg/front_end/lib/src/compute_platform_binaries_location.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:io" show File, Platform;
 
 import 'package:kernel/ast.dart' show Source;
diff --git a/pkg/front_end/lib/src/fasta/builder/builder.dart b/pkg/front_end/lib/src/fasta/builder/builder.dart
index 709c4cfcc17..4f2897d2962 100644
--- a/pkg/front_end/lib/src/fasta/builder/builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.declaration;
 
 import '../problems.dart' show unsupported;
diff --git a/pkg/front_end/lib/src/fasta/builder/builtin_type_declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/builtin_type_declaration_builder.dart
index 24d258e835a..7f39862221a 100644
--- a/pkg/front_end/lib/src/fasta/builder/builtin_type_declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/builtin_type_declaration_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.builtin_type_builder;
 
 import 'package:kernel/ast.dart' show DartType, Nullability;
diff --git a/pkg/front_end/lib/src/fasta/builder/class_builder.dart b/pkg/front_end/lib/src/fasta/builder/class_builder.dart
index 6b97dd97fd1..d7784469c6b 100644
--- a/pkg/front_end/lib/src/fasta/builder/class_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/class_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.class_builder;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/builder/constructor_builder.dart b/pkg/front_end/lib/src/fasta/builder/constructor_builder.dart
index 03f46c73312..e9628800f7e 100644
--- a/pkg/front_end/lib/src/fasta/builder/constructor_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/constructor_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:_fe_analyzer_shared/src/scanner/token.dart' show Token;
diff --git a/pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart b/pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart
index eb66bc860c1..824d08f9481 100644
--- a/pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/constructor_reference_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.constructor_reference_builder;
 
 import '../messages.dart' show noLength, templateConstructorNotFound;
diff --git a/pkg/front_end/lib/src/fasta/builder/declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/declaration_builder.dart
index 01d9fb000ef..0ba64f4d3aa 100644
--- a/pkg/front_end/lib/src/fasta/builder/declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/declaration_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/lib/src/fasta/builder/dynamic_type_declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/dynamic_type_declaration_builder.dart
index b5e9b807bbe..cdc6f30129a 100644
--- a/pkg/front_end/lib/src/fasta/builder/dynamic_type_declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/dynamic_type_declaration_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.dynamic_type_builder;
 
 import 'package:kernel/ast.dart' show DartType;
diff --git a/pkg/front_end/lib/src/fasta/builder/enum_builder.dart b/pkg/front_end/lib/src/fasta/builder/enum_builder.dart
index 6920c7be090..7101cf229d6 100644
--- a/pkg/front_end/lib/src/fasta/builder/enum_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/enum_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.enum_builder;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/builder/extension_builder.dart b/pkg/front_end/lib/src/fasta/builder/extension_builder.dart
index b3618114dc5..b0bc5db28fb 100644
--- a/pkg/front_end/lib/src/fasta/builder/extension_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/extension_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/lib/src/fasta/builder/field_builder.dart b/pkg/front_end/lib/src/fasta/builder/field_builder.dart
index 2d5ad31fdb7..1e3fce0e7b4 100644
--- a/pkg/front_end/lib/src/fasta/builder/field_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/field_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.field_builder;
 
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart' show Token;
diff --git a/pkg/front_end/lib/src/fasta/builder/fixed_type_builder.dart b/pkg/front_end/lib/src/fasta/builder/fixed_type_builder.dart
index d6eb9549014..3f9109860ee 100644
--- a/pkg/front_end/lib/src/fasta/builder/fixed_type_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/fixed_type_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' hide MapEntry;
 
 import '../problems.dart';
diff --git a/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart b/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
index 626190e4806..8a9751d3492 100644
--- a/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.formal_parameter_builder;
 
 import 'package:_fe_analyzer_shared/src/parser/formal_parameter_kind.dart'
diff --git a/pkg/front_end/lib/src/fasta/builder/function_builder.dart b/pkg/front_end/lib/src/fasta/builder/function_builder.dart
index 129c01a61e9..4bdfca5ac0f 100644
--- a/pkg/front_end/lib/src/fasta/builder/function_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/function_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.procedure_builder;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/builder/function_type_builder.dart b/pkg/front_end/lib/src/fasta/builder/function_type_builder.dart
index 3143c2d8643..1f5bbe7e797 100644
--- a/pkg/front_end/lib/src/fasta/builder/function_type_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/function_type_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.function_type_builder;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/builder/future_or_type_declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/future_or_type_declaration_builder.dart
index bc3c29690e5..3e3e05094b8 100644
--- a/pkg/front_end/lib/src/fasta/builder/future_or_type_declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/future_or_type_declaration_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.future_or_type_builder;
 
 import 'package:kernel/ast.dart' show DartType, FutureOrType, Nullability;
diff --git a/pkg/front_end/lib/src/fasta/builder/invalid_type_declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/invalid_type_declaration_builder.dart
index d101dfa078c..bce176c57ed 100644
--- a/pkg/front_end/lib/src/fasta/builder/invalid_type_declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/invalid_type_declaration_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.invalid_type_builder;
 
 import 'package:kernel/ast.dart' show DartType, InvalidType, Nullability;
diff --git a/pkg/front_end/lib/src/fasta/builder/library_builder.dart b/pkg/front_end/lib/src/fasta/builder/library_builder.dart
index 7f80ef3eb82..f318572dd3c 100644
--- a/pkg/front_end/lib/src/fasta/builder/library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/library_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.library_builder;
 
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
diff --git a/pkg/front_end/lib/src/fasta/builder/member_builder.dart b/pkg/front_end/lib/src/fasta/builder/member_builder.dart
index 2d3168dd92b..d28c5acb120 100644
--- a/pkg/front_end/lib/src/fasta/builder/member_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/member_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.member_builder;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/builder/metadata_builder.dart b/pkg/front_end/lib/src/fasta/builder/metadata_builder.dart
index 80978bb43c6..910119c02b9 100644
--- a/pkg/front_end/lib/src/fasta/builder/metadata_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/metadata_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.metadata_builder;
 
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart' show Token;
diff --git a/pkg/front_end/lib/src/fasta/builder/mixin_application_builder.dart b/pkg/front_end/lib/src/fasta/builder/mixin_application_builder.dart
index e78679d9d51..e1439c52d7b 100644
--- a/pkg/front_end/lib/src/fasta/builder/mixin_application_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/mixin_application_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.mixin_application_builder;
 
 import 'package:kernel/ast.dart' show InterfaceType, Supertype, TypedefType;
diff --git a/pkg/front_end/lib/src/fasta/builder/modifier_builder.dart b/pkg/front_end/lib/src/fasta/builder/modifier_builder.dart
index 7820923f21f..8836414db75 100644
--- a/pkg/front_end/lib/src/fasta/builder/modifier_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/modifier_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.modifier_builder;
 
 import '../modifier.dart';
diff --git a/pkg/front_end/lib/src/fasta/builder/name_iterator.dart b/pkg/front_end/lib/src/fasta/builder/name_iterator.dart
index 165dfb30b57..653a49b636b 100644
--- a/pkg/front_end/lib/src/fasta/builder/name_iterator.dart
+++ b/pkg/front_end/lib/src/fasta/builder/name_iterator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.name_iterator;
 
 import 'builder.dart';
diff --git a/pkg/front_end/lib/src/fasta/builder/named_type_builder.dart b/pkg/front_end/lib/src/fasta/builder/named_type_builder.dart
index 54cd164b132..1618af130d7 100644
--- a/pkg/front_end/lib/src/fasta/builder/named_type_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/named_type_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.named_type_builder;
 
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
diff --git a/pkg/front_end/lib/src/fasta/builder/never_type_declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/never_type_declaration_builder.dart
index 509dd32139b..c4d2e42ba7c 100644
--- a/pkg/front_end/lib/src/fasta/builder/never_type_declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/never_type_declaration_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.never_type_builder;
 
 import 'package:kernel/ast.dart' show DartType, NullType, Nullability;
diff --git a/pkg/front_end/lib/src/fasta/builder/null_type_declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/null_type_declaration_builder.dart
index cbfd853354b..4e81719f886 100644
--- a/pkg/front_end/lib/src/fasta/builder/null_type_declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/null_type_declaration_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.null_type_declaration_builder;
 
 import 'package:kernel/ast.dart' show DartType, Nullability;
diff --git a/pkg/front_end/lib/src/fasta/builder/nullability_builder.dart b/pkg/front_end/lib/src/fasta/builder/nullability_builder.dart
index 4d7b983d819..d14f2dcad64 100644
--- a/pkg/front_end/lib/src/fasta/builder/nullability_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/nullability_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/lib/src/fasta/builder/prefix_builder.dart b/pkg/front_end/lib/src/fasta/builder/prefix_builder.dart
index 4fe2571f8f8..0635ea959d2 100644
--- a/pkg/front_end/lib/src/fasta/builder/prefix_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/prefix_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.prefix_builder;
 
 import 'package:kernel/ast.dart' show LibraryDependency;
diff --git a/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart b/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
index 20ed8f77b37..a56d97498ab 100644
--- a/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:front_end/src/fasta/dill/dill_member_builder.dart';
diff --git a/pkg/front_end/lib/src/fasta/builder/type_alias_builder.dart b/pkg/front_end/lib/src/fasta/builder/type_alias_builder.dart
index 9de74f1c56c..c4c5502d115 100644
--- a/pkg/front_end/lib/src/fasta/builder/type_alias_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/type_alias_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.function_type_alias_builder;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/builder/type_builder.dart b/pkg/front_end/lib/src/fasta/builder/type_builder.dart
index d1ff518978c..2aed2136f87 100644
--- a/pkg/front_end/lib/src/fasta/builder/type_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/type_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.type_builder;
 
 import 'package:kernel/ast.dart' show DartType, Supertype, TypedefType;
diff --git a/pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart
index a8c16a1c48c..cdfac5c6a96 100644
--- a/pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/type_declaration_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.type_declaration_builder;
 
 import 'package:kernel/ast.dart' show DartType, Nullability;
diff --git a/pkg/front_end/lib/src/fasta/builder/type_variable_builder.dart b/pkg/front_end/lib/src/fasta/builder/type_variable_builder.dart
index b73ea200f26..d8d4a271de7 100644
--- a/pkg/front_end/lib/src/fasta/builder/type_variable_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/type_variable_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.type_variable_builder;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/builder/unresolved_type.dart b/pkg/front_end/lib/src/fasta/builder/unresolved_type.dart
index f90ac591fbc..8925e6bda5a 100644
--- a/pkg/front_end/lib/src/fasta/builder/unresolved_type.dart
+++ b/pkg/front_end/lib/src/fasta/builder/unresolved_type.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.unresolved_type;
 
 import '../scope.dart';
diff --git a/pkg/front_end/lib/src/fasta/builder/variable_builder.dart b/pkg/front_end/lib/src/fasta/builder/variable_builder.dart
index cc006cb6849..17eb7f26b5a 100644
--- a/pkg/front_end/lib/src/fasta/builder/variable_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/variable_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.kernel_variable_builder;
 
 import 'package:kernel/ast.dart' show VariableDeclaration;
diff --git a/pkg/front_end/lib/src/fasta/builder/void_type_declaration_builder.dart b/pkg/front_end/lib/src/fasta/builder/void_type_declaration_builder.dart
index 25c676071a8..b50507a8712 100644
--- a/pkg/front_end/lib/src/fasta/builder/void_type_declaration_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/void_type_declaration_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.void_type_builder;
 
 import 'package:kernel/ast.dart' show DartType;
diff --git a/pkg/front_end/lib/src/fasta/builder_graph.dart b/pkg/front_end/lib/src/fasta/builder_graph.dart
index 79539fd3dc0..f6f447aa4d0 100644
--- a/pkg/front_end/lib/src/fasta/builder_graph.dart
+++ b/pkg/front_end/lib/src/fasta/builder_graph.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.builder_graph;
 
 import 'package:kernel/kernel.dart' show LibraryDependency, LibraryPart;
diff --git a/pkg/front_end/lib/src/fasta/command_line_reporting.dart b/pkg/front_end/lib/src/fasta/command_line_reporting.dart
index d8f6c95cd3c..2b05cc699a5 100644
--- a/pkg/front_end/lib/src/fasta/command_line_reporting.dart
+++ b/pkg/front_end/lib/src/fasta/command_line_reporting.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Provides a default implementation of the report and format methods of
 /// [CompilerContext] that are suitable for command-line tools. The methods in
 /// this library aren't intended to be called directly, instead, one should use
diff --git a/pkg/front_end/lib/src/fasta/compiler_context.dart b/pkg/front_end/lib/src/fasta/compiler_context.dart
index e64cd29900e..a1d200574fe 100644
--- a/pkg/front_end/lib/src/fasta/compiler_context.dart
+++ b/pkg/front_end/lib/src/fasta/compiler_context.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.compiler_context;
 
 import 'dart:async' show Zone, runZoned;
diff --git a/pkg/front_end/lib/src/fasta/configuration.dart b/pkg/front_end/lib/src/fasta/configuration.dart
index d12a43ab6d0..f24e5bf699e 100644
--- a/pkg/front_end/lib/src/fasta/configuration.dart
+++ b/pkg/front_end/lib/src/fasta/configuration.dart
@@ -9,6 +9,7 @@ class Configuration {
   final String dottedName;
   final String condition;
   final String importUri;
+
   Configuration(
       this.charOffset, this.dottedName, this.condition, this.importUri);
 }
diff --git a/pkg/front_end/lib/src/fasta/crash.dart b/pkg/front_end/lib/src/fasta/crash.dart
index 1ad20fcf33d..82e44be86ae 100644
--- a/pkg/front_end/lib/src/fasta/crash.dart
+++ b/pkg/front_end/lib/src/fasta/crash.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.crash;
 
 import 'dart:convert' show jsonEncode;
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart b/pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart
index a548f80c5f2..93ee9390026 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_class_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.dill_class_builder;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_extension_builder.dart b/pkg/front_end/lib/src/fasta/dill/dill_extension_builder.dart
index a114dc6c56a..b460387e1ed 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_extension_builder.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_extension_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_extension_member_builder.dart b/pkg/front_end/lib/src/fasta/dill/dill_extension_member_builder.dart
index 02aa0556acd..d946f726480 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_extension_member_builder.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_extension_member_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart b/pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart
index 08d16559d72..f4ddeff7de0 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.dill_library_builder;
 
 import 'dart:convert' show jsonDecode;
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_loader.dart b/pkg/front_end/lib/src/fasta/dill/dill_loader.dart
index 2ce2498f961..8cbf07719d2 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_loader.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_loader.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.dill_loader;
 
 import 'package:kernel/ast.dart' show Class, Component, DartType, Library;
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_member_builder.dart b/pkg/front_end/lib/src/fasta/dill/dill_member_builder.dart
index 272a08b81a2..861e245dadd 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_member_builder.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_member_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.dill_member_builder;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_target.dart b/pkg/front_end/lib/src/fasta/dill/dill_target.dart
index 52fa5155a6c..9901f81bfeb 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_target.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_target.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.dill_target;
 
 import 'package:front_end/src/fasta/builder/library_builder.dart'
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_type_alias_builder.dart b/pkg/front_end/lib/src/fasta/dill/dill_type_alias_builder.dart
index 9cf8bad25ca..9020e688e3c 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_type_alias_builder.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_type_alias_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.dill_typedef_builder;
 
 import 'package:kernel/ast.dart' show DartType, InvalidType, NullType, Typedef;
diff --git a/pkg/front_end/lib/src/fasta/export.dart b/pkg/front_end/lib/src/fasta/export.dart
index e57cf8dce14..8ed7105711b 100644
--- a/pkg/front_end/lib/src/fasta/export.dart
+++ b/pkg/front_end/lib/src/fasta/export.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.export;
 
 import 'builder/builder.dart';
diff --git a/pkg/front_end/lib/src/fasta/fasta_codes.dart b/pkg/front_end/lib/src/fasta/fasta_codes.dart
index 50f79c1c76e..446cd7268d8 100644
--- a/pkg/front_end/lib/src/fasta/fasta_codes.dart
+++ b/pkg/front_end/lib/src/fasta/fasta_codes.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.codes;
 
 import 'package:_fe_analyzer_shared/src/messages/codes.dart'
diff --git a/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart b/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart
index 40b62281197..a145ee79b43 100644
--- a/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart
+++ b/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart
@@ -1,7 +1,9 @@
-// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // NOTE: THIS FILE IS GENERATED. DO NOT EDIT.
 //
 // Instead modify 'pkg/front_end/messages.yaml' and run
diff --git a/pkg/front_end/lib/src/fasta/get_dependencies.dart b/pkg/front_end/lib/src/fasta/get_dependencies.dart
index 3a237780315..903c1b0c003 100644
--- a/pkg/front_end/lib/src/fasta/get_dependencies.dart
+++ b/pkg/front_end/lib/src/fasta/get_dependencies.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.get_dependencies;
 
 import 'package:kernel/kernel.dart' show Component, loadComponentFromBytes;
diff --git a/pkg/front_end/lib/src/fasta/hybrid_file_system.dart b/pkg/front_end/lib/src/fasta/hybrid_file_system.dart
index 3a78a1c33d3..9f1a08b2021 100644
--- a/pkg/front_end/lib/src/fasta/hybrid_file_system.dart
+++ b/pkg/front_end/lib/src/fasta/hybrid_file_system.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// A memory + physical file system used to mock input for tests but provide
 /// sdk sources from disk.
 library front_end.src.hybrid_file_system;
diff --git a/pkg/front_end/lib/src/fasta/identifiers.dart b/pkg/front_end/lib/src/fasta/identifiers.dart
index 64d6f9232a4..f7dcd4f1fd9 100644
--- a/pkg/front_end/lib/src/fasta/identifiers.dart
+++ b/pkg/front_end/lib/src/fasta/identifiers.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.qualified_name;
 
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart' show Token;
diff --git a/pkg/front_end/lib/src/fasta/ignored_parser_errors.dart b/pkg/front_end/lib/src/fasta/ignored_parser_errors.dart
index fbd01f977f1..04b0e4ac16a 100644
--- a/pkg/front_end/lib/src/fasta/ignored_parser_errors.dart
+++ b/pkg/front_end/lib/src/fasta/ignored_parser_errors.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.ignored_parser_errors;
 
 import 'package:_fe_analyzer_shared/src/parser/parser.dart' show optional;
diff --git a/pkg/front_end/lib/src/fasta/import.dart b/pkg/front_end/lib/src/fasta/import.dart
index fe41e88a70e..6a510332be7 100644
--- a/pkg/front_end/lib/src/fasta/import.dart
+++ b/pkg/front_end/lib/src/fasta/import.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.import;
 
 import 'package:kernel/ast.dart' show LibraryDependency;
diff --git a/pkg/front_end/lib/src/fasta/incremental_compiler.dart b/pkg/front_end/lib/src/fasta/incremental_compiler.dart
index e629ce0c3f6..22a3f8ba340 100644
--- a/pkg/front_end/lib/src/fasta/incremental_compiler.dart
+++ b/pkg/front_end/lib/src/fasta/incremental_compiler.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.incremental_compiler;
 
 import 'package:front_end/src/api_prototype/experimental_flags.dart';
diff --git a/pkg/front_end/lib/src/fasta/incremental_serializer.dart b/pkg/front_end/lib/src/fasta/incremental_serializer.dart
index 4581f1645bf..208022ea92a 100644
--- a/pkg/front_end/lib/src/fasta/incremental_serializer.dart
+++ b/pkg/front_end/lib/src/fasta/incremental_serializer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.incremental_serializer;
 
 import 'dart:typed_data' show Uint8List;
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index a4789387bdd..7cd5823dc82 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.body_builder;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/kernel/class_hierarchy_builder.dart b/pkg/front_end/lib/src/fasta/kernel/class_hierarchy_builder.dart
index 9bd74a8218d..a0fc2ac6e3f 100644
--- a/pkg/front_end/lib/src/fasta/kernel/class_hierarchy_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/class_hierarchy_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.class_hierarchy_builder;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/kernel/collections.dart b/pkg/front_end/lib/src/fasta/kernel/collections.dart
index 79b99c0e72e..1e2f994ec3c 100644
--- a/pkg/front_end/lib/src/fasta/kernel/collections.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/collections.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library fasta.collections;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/kernel/combined_member_signature.dart b/pkg/front_end/lib/src/fasta/kernel/combined_member_signature.dart
index 6dfd603d1b5..00467edd8a4 100644
--- a/pkg/front_end/lib/src/fasta/kernel/combined_member_signature.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/combined_member_signature.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' hide MapEntry;
 
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchyBase;
diff --git a/pkg/front_end/lib/src/fasta/kernel/constant_collection_builders.dart b/pkg/front_end/lib/src/fasta/kernel/constant_collection_builders.dart
index f10419df809..6d95ecf7a0a 100644
--- a/pkg/front_end/lib/src/fasta/kernel/constant_collection_builders.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/constant_collection_builders.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 part of 'constant_evaluator.dart';
 
 abstract class _ListOrSetConstantBuilder<L extends Expression> {
diff --git a/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart b/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart
index 9ca957266fb..e332dbdac7f 100644
--- a/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// This library implements a kernel2kernel constant evaluation transformation.
 ///
 /// Even though it is expected that the frontend does not emit kernel AST which
diff --git a/pkg/front_end/lib/src/fasta/kernel/constant_int_folder.dart b/pkg/front_end/lib/src/fasta/kernel/constant_int_folder.dart
index 84dfd1365ed..8d0c5b0f4bf 100644
--- a/pkg/front_end/lib/src/fasta/kernel/constant_int_folder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/constant_int_folder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/lib/src/fasta/kernel/expression_generator.dart b/pkg/front_end/lib/src/fasta/kernel/expression_generator.dart
index d42d1d5492e..24a39093549 100644
--- a/pkg/front_end/lib/src/fasta/kernel/expression_generator.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/expression_generator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// A library to help generate expression.
 library fasta.expression_generator;
 
diff --git a/pkg/front_end/lib/src/fasta/kernel/expression_generator_helper.dart b/pkg/front_end/lib/src/fasta/kernel/expression_generator_helper.dart
index 1666a650ac6..eaa24687bcb 100644
--- a/pkg/front_end/lib/src/fasta/kernel/expression_generator_helper.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/expression_generator_helper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.expression_generator_helper;
 
 import 'package:_fe_analyzer_shared/src/scanner/token.dart' show Token;
diff --git a/pkg/front_end/lib/src/fasta/kernel/forest.dart b/pkg/front_end/lib/src/fasta/kernel/forest.dart
index 75946bbcf56..4c6d8d92978 100644
--- a/pkg/front_end/lib/src/fasta/kernel/forest.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/forest.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.fangorn;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/kernel/forwarding_node.dart b/pkg/front_end/lib/src/fasta/kernel/forwarding_node.dart
index 3bb758d1bfd..a647cbf1289 100644
--- a/pkg/front_end/lib/src/fasta/kernel/forwarding_node.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/forwarding_node.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:kernel/ast.dart"
     show
         Arguments,
diff --git a/pkg/front_end/lib/src/fasta/kernel/implicit_field_type.dart b/pkg/front_end/lib/src/fasta/kernel/implicit_field_type.dart
index ba124c98c25..f37b35c3eea 100644
--- a/pkg/front_end/lib/src/fasta/kernel/implicit_field_type.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/implicit_field_type.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.implicit_type;
 
 import 'package:_fe_analyzer_shared/src/scanner/token.dart' show Token;
diff --git a/pkg/front_end/lib/src/fasta/kernel/implicit_type_argument.dart b/pkg/front_end/lib/src/fasta/kernel/implicit_type_argument.dart
index 2ab9dfbe29b..c6daddfe021 100644
--- a/pkg/front_end/lib/src/fasta/kernel/implicit_type_argument.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/implicit_type_argument.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.implicit_type_argument;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart b/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart
index 7762bfb52b4..e7f9b2a7d8f 100644
--- a/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:_fe_analyzer_shared/src/util/link.dart';
diff --git a/pkg/front_end/lib/src/fasta/kernel/internal_ast.dart b/pkg/front_end/lib/src/fasta/kernel/internal_ast.dart
index 1f6acdd88e5..b5160f0feec 100644
--- a/pkg/front_end/lib/src/fasta/kernel/internal_ast.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/internal_ast.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
diff --git a/pkg/front_end/lib/src/fasta/kernel/invalid_type.dart b/pkg/front_end/lib/src/fasta/kernel/invalid_type.dart
index fd05fdb34be..c361101d5e8 100644
--- a/pkg/front_end/lib/src/fasta/kernel/invalid_type.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/invalid_type.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' hide MapEntry;
 import 'package:kernel/visitor.dart';
 
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_api.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_api.dart
index c8165a2778c..8724cfa0cd0 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_api.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_api.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// This library exports all API from Kernel that can be used throughout fasta.
 library fasta.kernel_api;
 
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_ast_api.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_ast_api.dart
index 19f4d2eaf87..4733e7b88ac 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_ast_api.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_ast_api.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// This library exports all API from Kernel's ast.dart that can be used
 /// throughout fasta.
 library fasta.kernel_ast_api;
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_builder.dart
index c0b145931b7..93eed480396 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.kernel_builder;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_constants.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_constants.dart
index cf9d6cbde34..55c93c57cef 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_constants.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_constants.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.kernel_constants;
 
 import 'package:front_end/src/fasta/builder/library_builder.dart';
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
index 6ca84c63b7b..8e75d57badc 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.kernel_target;
 
 import 'package:front_end/src/api_prototype/experimental_flags.dart';
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_variable_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_variable_builder.dart
index c3400b11bdc..31afc3900f6 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_variable_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_variable_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.kernel_variable_builder;
 
 import 'package:kernel/ast.dart' show VariableDeclaration;
diff --git a/pkg/front_end/lib/src/fasta/kernel/late_lowering.dart b/pkg/front_end/lib/src/fasta/kernel/late_lowering.dart
index 93eea7f9c45..577359b1152 100644
--- a/pkg/front_end/lib/src/fasta/kernel/late_lowering.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/late_lowering.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' hide MapEntry;
 import 'package:kernel/core_types.dart';
 
diff --git a/pkg/front_end/lib/src/fasta/kernel/load_library_builder.dart b/pkg/front_end/lib/src/fasta/kernel/load_library_builder.dart
index 81ea7a7e5e7..3639f4a19e7 100644
--- a/pkg/front_end/lib/src/fasta/kernel/load_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/load_library_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart'
     show
         Arguments,
diff --git a/pkg/front_end/lib/src/fasta/kernel/member_covariance.dart b/pkg/front_end/lib/src/fasta/kernel/member_covariance.dart
index 6a5eaaf4797..6d4a9f19436 100644
--- a/pkg/front_end/lib/src/fasta/kernel/member_covariance.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/member_covariance.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:math';
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/kernel/metadata_collector.dart b/pkg/front_end/lib/src/fasta/kernel/metadata_collector.dart
index 82f84f50677..f77e230b1c4 100644
--- a/pkg/front_end/lib/src/fasta/kernel/metadata_collector.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/metadata_collector.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart' show Member, MetadataRepository, NamedNode;
 
 /// The collector to add target specific metadata to.
diff --git a/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart b/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
index 3a12ab45e33..0d82df2eb1c 100644
--- a/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.redirecting_factory_body;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/kernel/transform_collections.dart b/pkg/front_end/lib/src/fasta/kernel/transform_collections.dart
index 6d2a8e6b8f0..b90df057f70 100644
--- a/pkg/front_end/lib/src/fasta/kernel/transform_collections.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/transform_collections.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.transform_collections;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/kernel/transform_set_literals.dart b/pkg/front_end/lib/src/fasta/kernel/transform_set_literals.dart
index e9d59693c24..250493fd2ec 100644
--- a/pkg/front_end/lib/src/fasta/kernel/transform_set_literals.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/transform_set_literals.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.transform_set_literals;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/kernel/type_algorithms.dart b/pkg/front_end/lib/src/fasta/kernel/type_algorithms.dart
index 48a5c3fcc9d..8b6464ebc0b 100644
--- a/pkg/front_end/lib/src/fasta/kernel/type_algorithms.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/type_algorithms.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart'
     show
         BottomType,
diff --git a/pkg/front_end/lib/src/fasta/kernel/type_builder_computer.dart b/pkg/front_end/lib/src/fasta/kernel/type_builder_computer.dart
index ee11a134757..82a9dc9b74e 100644
--- a/pkg/front_end/lib/src/fasta/kernel/type_builder_computer.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/type_builder_computer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.type_builder_computer;
 
 import 'package:_fe_analyzer_shared/src/parser/parser.dart'
diff --git a/pkg/front_end/lib/src/fasta/kernel/type_labeler.dart b/pkg/front_end/lib/src/fasta/kernel/type_labeler.dart
index aca88106889..4784bf255fa 100644
--- a/pkg/front_end/lib/src/fasta/kernel/type_labeler.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/type_labeler.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:convert' show json;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/kernel/utils.dart b/pkg/front_end/lib/src/fasta/kernel/utils.dart
index 1eaf2b367f5..e55e3257a70 100644
--- a/pkg/front_end/lib/src/fasta/kernel/utils.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/utils.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show BytesBuilder, File, IOSink;
 
 import 'dart:typed_data' show Uint8List;
diff --git a/pkg/front_end/lib/src/fasta/kernel/verifier.dart b/pkg/front_end/lib/src/fasta/kernel/verifier.dart
index a15a5c977d4..a5b190ff7d3 100644
--- a/pkg/front_end/lib/src/fasta/kernel/verifier.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/verifier.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.verifier;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/library_graph.dart b/pkg/front_end/lib/src/fasta/library_graph.dart
index 5a75f859378..5b93e51b414 100644
--- a/pkg/front_end/lib/src/fasta/library_graph.dart
+++ b/pkg/front_end/lib/src/fasta/library_graph.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.library_graph;
 
 import 'package:kernel/kernel.dart'
diff --git a/pkg/front_end/lib/src/fasta/loader.dart b/pkg/front_end/lib/src/fasta/loader.dart
index 0c917db3f4d..41da0094c6b 100644
--- a/pkg/front_end/lib/src/fasta/loader.dart
+++ b/pkg/front_end/lib/src/fasta/loader.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.loader;
 
 import 'dart:collection' show Queue;
diff --git a/pkg/front_end/lib/src/fasta/messages.dart b/pkg/front_end/lib/src/fasta/messages.dart
index 396f054fcc6..3f1330a235a 100644
--- a/pkg/front_end/lib/src/fasta/messages.dart
+++ b/pkg/front_end/lib/src/fasta/messages.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.messages;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/modifier.dart b/pkg/front_end/lib/src/fasta/modifier.dart
index c93ef12b861..32a6aa21280 100644
--- a/pkg/front_end/lib/src/fasta/modifier.dart
+++ b/pkg/front_end/lib/src/fasta/modifier.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.modifier;
 
 import 'problems.dart' show unhandled;
diff --git a/pkg/front_end/lib/src/fasta/names.dart b/pkg/front_end/lib/src/fasta/names.dart
index 229b64b1057..ba20ec84a96 100644
--- a/pkg/front_end/lib/src/fasta/names.dart
+++ b/pkg/front_end/lib/src/fasta/names.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library front_end.src.fasta.names;
 
 import 'package:kernel/ast.dart' show Name;
diff --git a/pkg/front_end/lib/src/fasta/operator.dart b/pkg/front_end/lib/src/fasta/operator.dart
index 1617a5a804f..917c3855a50 100644
--- a/pkg/front_end/lib/src/fasta/operator.dart
+++ b/pkg/front_end/lib/src/fasta/operator.dart
@@ -31,7 +31,7 @@ enum Operator {
   unaryMinus,
 }
 
-Operator operatorFromString(String string) {
+Operator? operatorFromString(String string) {
   if (identical("+", string)) return Operator.add;
   if (identical("&", string)) return Operator.bitwiseAnd;
   if (identical("~", string)) return Operator.bitwiseNot;
@@ -101,7 +101,6 @@ String operatorToString(Operator operator) {
     case Operator.unaryMinus:
       return "unary-";
   }
-  return null;
 }
 
 int operatorRequiredArgumentCount(Operator operator) {
@@ -133,5 +132,4 @@ int operatorRequiredArgumentCount(Operator operator) {
     case Operator.indexSet:
       return 2;
   }
-  return -1;
 }
diff --git a/pkg/front_end/lib/src/fasta/problems.dart b/pkg/front_end/lib/src/fasta/problems.dart
index f1d61a2fcdc..db9552fef96 100644
--- a/pkg/front_end/lib/src/fasta/problems.dart
+++ b/pkg/front_end/lib/src/fasta/problems.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.problems;
 
 import 'package:_fe_analyzer_shared/src/messages/severity.dart'
diff --git a/pkg/front_end/lib/src/fasta/scope.dart b/pkg/front_end/lib/src/fasta/scope.dart
index 709e438b795..5fa0edfcf06 100644
--- a/pkg/front_end/lib/src/fasta/scope.dart
+++ b/pkg/front_end/lib/src/fasta/scope.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.scope;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/front_end/lib/src/fasta/source/diet_listener.dart b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
index bc81fc64a2c..27875146460 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.diet_listener;
 
 import 'package:_fe_analyzer_shared/src/parser/parser.dart'
diff --git a/pkg/front_end/lib/src/fasta/source/directive_listener.dart b/pkg/front_end/lib/src/fasta/source/directive_listener.dart
index f912c9e7897..3c29fe13a4b 100644
--- a/pkg/front_end/lib/src/fasta/source/directive_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/directive_listener.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Listener used in combination with `TopLevelParser` to extract the URIs of
 /// import, part, and export directives.
 library front_end.src.fasta.source.directive_listener;
diff --git a/pkg/front_end/lib/src/fasta/source/outline_builder.dart b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
index 98a5907ed42..c8aa4b51b1b 100644
--- a/pkg/front_end/lib/src/fasta/source/outline_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.outline_builder;
 
 import 'package:_fe_analyzer_shared/src/parser/parser.dart'
diff --git a/pkg/front_end/lib/src/fasta/source/scope_listener.dart b/pkg/front_end/lib/src/fasta/source/scope_listener.dart
index 29bbad1ad8c..c4454036b9e 100644
--- a/pkg/front_end/lib/src/fasta/source/scope_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/scope_listener.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.scope_listener;
 
 import 'package:_fe_analyzer_shared/src/parser/block_kind.dart' show BlockKind;
diff --git a/pkg/front_end/lib/src/fasta/source/source_class_builder.dart b/pkg/front_end/lib/src/fasta/source/source_class_builder.dart
index 7debb1ae41f..5d920b5c56c 100644
--- a/pkg/front_end/lib/src/fasta/source/source_class_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_class_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.source_class_builder;
 
 import 'package:front_end/src/fasta/kernel/combined_member_signature.dart';
diff --git a/pkg/front_end/lib/src/fasta/source/source_extension_builder.dart b/pkg/front_end/lib/src/fasta/source/source_extension_builder.dart
index 28b3fb8d336..744ce0751fc 100644
--- a/pkg/front_end/lib/src/fasta/source/source_extension_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_extension_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
index 945cd989b1b..7a2103d1703 100644
--- a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.source_library_builder;
 
 import 'dart:convert' show jsonEncode;
diff --git a/pkg/front_end/lib/src/fasta/source/source_loader.dart b/pkg/front_end/lib/src/fasta/source/source_loader.dart
index 1dbe91f6e99..bfcc018cbc2 100644
--- a/pkg/front_end/lib/src/fasta/source/source_loader.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_loader.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.source_loader;
 
 import 'dart:convert' show utf8;
diff --git a/pkg/front_end/lib/src/fasta/source/source_type_alias_builder.dart b/pkg/front_end/lib/src/fasta/source/source_type_alias_builder.dart
index 4061bcec098..dc61bf96515 100644
--- a/pkg/front_end/lib/src/fasta/source/source_type_alias_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_type_alias_builder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.source_type_alias_builder;
 
 import 'package:kernel/ast.dart'
diff --git a/pkg/front_end/lib/src/fasta/source/stack_listener_impl.dart b/pkg/front_end/lib/src/fasta/source/stack_listener_impl.dart
index 543eaa45c9f..83721d7270f 100644
--- a/pkg/front_end/lib/src/fasta/source/stack_listener_impl.dart
+++ b/pkg/front_end/lib/src/fasta/source/stack_listener_impl.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.stack_listener_impl;
 
 import 'package:_fe_analyzer_shared/src/messages/codes.dart' show Message;
diff --git a/pkg/front_end/lib/src/fasta/source/value_kinds.dart b/pkg/front_end/lib/src/fasta/source/value_kinds.dart
index e533e56b309..3fc36ccda8b 100644
--- a/pkg/front_end/lib/src/fasta/source/value_kinds.dart
+++ b/pkg/front_end/lib/src/fasta/source/value_kinds.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/parser/stack_listener.dart'
     show NullValue;
 
diff --git a/pkg/front_end/lib/src/fasta/target.dart b/pkg/front_end/lib/src/fasta/target.dart
index 8d2efd92511..82ecb310bd2 100644
--- a/pkg/front_end/lib/src/fasta/target.dart
+++ b/pkg/front_end/lib/src/fasta/target.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.target;
 
 import 'package:kernel/ast.dart' show Component;
diff --git a/pkg/front_end/lib/src/fasta/target_implementation.dart b/pkg/front_end/lib/src/fasta/target_implementation.dart
index 2b8a091619e..8acd6b83492 100644
--- a/pkg/front_end/lib/src/fasta/target_implementation.dart
+++ b/pkg/front_end/lib/src/fasta/target_implementation.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.target_implementation;
 
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
diff --git a/pkg/front_end/lib/src/fasta/ticker.dart b/pkg/front_end/lib/src/fasta/ticker.dart
index b785cbafb23..3c9d9c58a26 100644
--- a/pkg/front_end/lib/src/fasta/ticker.dart
+++ b/pkg/front_end/lib/src/fasta/ticker.dart
@@ -9,7 +9,7 @@ class Ticker {
 
   bool isVerbose;
 
-  Duration previousTick;
+  late Duration previousTick;
 
   Ticker({this.isVerbose: true}) {
     previousTick = sw.elapsed;
diff --git a/pkg/front_end/lib/src/fasta/type_inference/closure_context.dart b/pkg/front_end/lib/src/fasta/type_inference/closure_context.dart
index 4de83154901..78dc0c59306 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/closure_context.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/closure_context.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 part of 'type_inferrer.dart';
 
 /// Keeps track of information about the innermost function or closure being
diff --git a/pkg/front_end/lib/src/fasta/type_inference/factor_type.dart b/pkg/front_end/lib/src/fasta/type_inference/factor_type.dart
index 871022268d8..1083882b7d6 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/factor_type.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/factor_type.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' hide MapEntry;
 import 'package:kernel/type_environment.dart';
 
diff --git a/pkg/front_end/lib/src/fasta/type_inference/inference_helper.dart b/pkg/front_end/lib/src/fasta/type_inference/inference_helper.dart
index 92193132fe4..40395197e49 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/inference_helper.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/inference_helper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/lib/src/fasta/type_inference/standard_bounds.dart b/pkg/front_end/lib/src/fasta/type_inference/standard_bounds.dart
index 4d04ad4561b..43b4e0e728a 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/standard_bounds.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/standard_bounds.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' show DartType, Library, NeverType, Nullability;
 
 import 'package:kernel/src/standard_bounds.dart';
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_constraint_gatherer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_constraint_gatherer.dart
index 4b5d0f8303d..5e3122c63fe 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_constraint_gatherer.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_constraint_gatherer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' hide MapEntry;
 
 import 'package:kernel/core_types.dart';
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_demotion.dart b/pkg/front_end/lib/src/fasta/type_inference/type_demotion.dart
index 85bbacdbd61..25d68b19d3e 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_demotion.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_demotion.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' hide MapEntry;
 import 'package:kernel/src/replacement_visitor.dart';
 
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inference_engine.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inference_engine.dart
index 1a58eb6751a..9d674c08fa3 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inference_engine.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inference_engine.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/flow_analysis/flow_analysis.dart';
 import 'package:front_end/src/fasta/kernel/internal_ast.dart';
 
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
index 37f51ab6f6a..b183c322a6c 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'dart:core' hide MapEntry;
 
 import 'package:_fe_analyzer_shared/src/flow_analysis/flow_analysis.dart'
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart b/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
index 2ae32bf031f..f94934e98a8 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_promotion.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart'
     show DartType, Expression, TypeParameterType, VariableDeclaration;
 
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_schema.dart b/pkg/front_end/lib/src/fasta/type_inference/type_schema.dart
index 0e935263787..883df406b0f 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_schema.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_schema.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart'
     show
         DartType,
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_schema_elimination.dart b/pkg/front_end/lib/src/fasta/type_inference/type_schema_elimination.dart
index e6338be5bff..f07e42ab1b5 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_schema_elimination.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_schema_elimination.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' hide MapEntry;
 import 'package:kernel/src/replacement_visitor.dart';
 
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart b/pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart
index 3d12c45fc35..0e12020aded 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' hide MapEntry;
 
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
diff --git a/pkg/front_end/lib/src/fasta/uri_translator.dart b/pkg/front_end/lib/src/fasta/uri_translator.dart
index be2af3c7432..55222b2747f 100644
--- a/pkg/front_end/lib/src/fasta/uri_translator.dart
+++ b/pkg/front_end/lib/src/fasta/uri_translator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.uri_translator;
 
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
diff --git a/pkg/front_end/lib/src/fasta/util/bytes_sink.dart b/pkg/front_end/lib/src/fasta/util/bytes_sink.dart
index d945e924672..4e3b61fef4f 100644
--- a/pkg/front_end/lib/src/fasta/util/bytes_sink.dart
+++ b/pkg/front_end/lib/src/fasta/util/bytes_sink.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show BytesBuilder;
 
 // TODO(ahe): https://github.com/dart-lang/sdk/issues/28316
diff --git a/pkg/front_end/lib/src/fasta/util/direct_parser_ast.dart b/pkg/front_end/lib/src/fasta/util/direct_parser_ast.dart
index 3331e017152..9a2fcea4793 100644
--- a/pkg/front_end/lib/src/fasta/util/direct_parser_ast.dart
+++ b/pkg/front_end/lib/src/fasta/util/direct_parser_ast.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:typed_data' show Uint8List;
 
 import 'dart:io' show File;
diff --git a/pkg/front_end/lib/src/fasta/util/direct_parser_ast_helper.dart b/pkg/front_end/lib/src/fasta/util/direct_parser_ast_helper.dart
index 70be18169b4..cc765768401 100644
--- a/pkg/front_end/lib/src/fasta/util/direct_parser_ast_helper.dart
+++ b/pkg/front_end/lib/src/fasta/util/direct_parser_ast_helper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/parser/assert.dart';
 import 'package:_fe_analyzer_shared/src/parser/block_kind.dart';
 import 'package:_fe_analyzer_shared/src/parser/declaration_kind.dart';
diff --git a/pkg/front_end/lib/src/fasta/util/textual_outline.dart b/pkg/front_end/lib/src/fasta/util/textual_outline.dart
index 6b5d823be68..3f1cb922b3e 100644
--- a/pkg/front_end/lib/src/fasta/util/textual_outline.dart
+++ b/pkg/front_end/lib/src/fasta/util/textual_outline.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:typed_data' show Uint8List;
 
 import 'dart:io' show File;
diff --git a/pkg/front_end/lib/src/kernel_generator_impl.dart b/pkg/front_end/lib/src/kernel_generator_impl.dart
index d4ec55d96cc..ac5247491d2 100644
--- a/pkg/front_end/lib/src/kernel_generator_impl.dart
+++ b/pkg/front_end/lib/src/kernel_generator_impl.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Defines the front-end API for converting source code to Dart Kernel objects.
 library front_end.kernel_generator_impl;
 
diff --git a/pkg/front_end/lib/src/scheme_based_file_system.dart b/pkg/front_end/lib/src/scheme_based_file_system.dart
index c2b3981c21b..f52f2140637 100644
--- a/pkg/front_end/lib/src/scheme_based_file_system.dart
+++ b/pkg/front_end/lib/src/scheme_based_file_system.dart
@@ -12,7 +12,7 @@ class SchemeBasedFileSystem implements FileSystem {
 
   @override
   FileSystemEntity entityForUri(Uri uri) {
-    FileSystem delegate = fileSystemByScheme[uri.scheme];
+    FileSystem? delegate = fileSystemByScheme[uri.scheme];
     if (delegate == null) {
       throw new FileSystemException(
           uri,
diff --git a/pkg/front_end/lib/src/testing/compiler_common.dart b/pkg/front_end/lib/src/testing/compiler_common.dart
index 3164c83a50e..5f0e775e093 100644
--- a/pkg/front_end/lib/src/testing/compiler_common.dart
+++ b/pkg/front_end/lib/src/testing/compiler_common.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Common compiler options and helper functions used for testing.
 library front_end.testing.compiler_options_common;
 
diff --git a/pkg/front_end/lib/src/testing/id_extractor.dart b/pkg/front_end/lib/src/testing/id_extractor.dart
index 5216459ba45..11247a0d471 100644
--- a/pkg/front_end/lib/src/testing/id_extractor.dart
+++ b/pkg/front_end/lib/src/testing/id_extractor.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/testing/id.dart';
 import 'package:kernel/ast.dart';
 import '../api_prototype/lowering_predicates.dart';
diff --git a/pkg/front_end/lib/src/testing/id_testing_helper.dart b/pkg/front_end/lib/src/testing/id_testing_helper.dart
index 8d98cff5a84..82e3414d865 100644
--- a/pkg/front_end/lib/src/testing/id_testing_helper.dart
+++ b/pkg/front_end/lib/src/testing/id_testing_helper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
 import 'package:_fe_analyzer_shared/src/testing/id.dart'
     show ActualData, ClassId, Id, IdKind, IdValue, MemberId, NodeId;
diff --git a/pkg/front_end/lib/src/testing/id_testing_utils.dart b/pkg/front_end/lib/src/testing/id_testing_utils.dart
index 74b47409de7..a277ce282b6 100644
--- a/pkg/front_end/lib/src/testing/id_testing_utils.dart
+++ b/pkg/front_end/lib/src/testing/id_testing_utils.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart';
 
 import '../fasta/builder/class_builder.dart';
diff --git a/pkg/front_end/lib/widget_cache.dart b/pkg/front_end/lib/widget_cache.dart
index 5c9f6d3c7f7..695ed832ddf 100644
--- a/pkg/front_end/lib/widget_cache.dart
+++ b/pkg/front_end/lib/widget_cache.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/kernel.dart';
 
diff --git a/pkg/front_end/pubspec.yaml b/pkg/front_end/pubspec.yaml
index 20a36d80d37..6893010e096 100644
--- a/pkg/front_end/pubspec.yaml
+++ b/pkg/front_end/pubspec.yaml
@@ -6,7 +6,7 @@ name: front_end
 publish_to: none
 
 environment:
-  sdk: '>=2.6.0 <3.0.0'
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   _fe_analyzer_shared:
diff --git a/pkg/front_end/test/analyser_ignored/load_dill_twice_lib_1.dart b/pkg/front_end/test/analyser_ignored/load_dill_twice_lib_1.dart
index ca76918fbbb..443c3b51955 100644
--- a/pkg/front_end/test/analyser_ignored/load_dill_twice_lib_1.dart
+++ b/pkg/front_end/test/analyser_ignored/load_dill_twice_lib_1.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 export 'load_dill_twice_lib_2.dart';
 
 // Use annotation to force proper printing.
diff --git a/pkg/front_end/test/analyser_ignored/load_dill_twice_lib_2.dart b/pkg/front_end/test/analyser_ignored/load_dill_twice_lib_2.dart
index 5e9d38adb8a..0ba97dde22c 100644
--- a/pkg/front_end/test/analyser_ignored/load_dill_twice_lib_2.dart
+++ b/pkg/front_end/test/analyser_ignored/load_dill_twice_lib_2.dart
@@ -2,4 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 int foo() => 42;
diff --git a/pkg/front_end/test/analyser_ignored/load_dill_twice_test.dart b/pkg/front_end/test/analyser_ignored/load_dill_twice_test.dart
index ba07019c73a..922ff5d715f 100644
--- a/pkg/front_end/test/analyser_ignored/load_dill_twice_test.dart
+++ b/pkg/front_end/test/analyser_ignored/load_dill_twice_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Platform, exit;
 
 import 'package:kernel/binary/ast_from_binary.dart' show BinaryBuilder;
diff --git a/pkg/front_end/test/ast_nodes_has_to_string_test.dart b/pkg/front_end/test/ast_nodes_has_to_string_test.dart
index 9b0dc9f78cf..028bedfbc00 100644
--- a/pkg/front_end/test/ast_nodes_has_to_string_test.dart
+++ b/pkg/front_end/test/ast_nodes_has_to_string_test.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+// @dart = 2.9
+
 import 'dart:io' show File, Platform, stdin, exitCode;
 
 import 'package:front_end/src/api_prototype/compiler_options.dart';
diff --git a/pkg/front_end/test/binary_md_dill_reader.dart b/pkg/front_end/test/binary_md_dill_reader.dart
index 271ffd8fb22..d25607ec5bf 100644
--- a/pkg/front_end/test/binary_md_dill_reader.dart
+++ b/pkg/front_end/test/binary_md_dill_reader.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:math" as math;
 
 class BinaryMdDillReader {
diff --git a/pkg/front_end/test/binary_md_vm_tags_and_version_test.dart b/pkg/front_end/test/binary_md_vm_tags_and_version_test.dart
index d9f412e0960..fdf53304b0b 100644
--- a/pkg/front_end/test/binary_md_vm_tags_and_version_test.dart
+++ b/pkg/front_end/test/binary_md_vm_tags_and_version_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show File, Platform;
 
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
diff --git a/pkg/front_end/test/comments_on_certain_arguments_tool.dart b/pkg/front_end/test/comments_on_certain_arguments_tool.dart
index 41045b527c7..d83bf847e8d 100644
--- a/pkg/front_end/test/comments_on_certain_arguments_tool.dart
+++ b/pkg/front_end/test/comments_on_certain_arguments_tool.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:convert' show utf8;
 import 'dart:io'
     show Directory, File, FileSystemEntity, exitCode, stdin, stdout;
diff --git a/pkg/front_end/test/compile_dart2js_with_no_sdk_test.dart b/pkg/front_end/test/compile_dart2js_with_no_sdk_test.dart
index 4939c1163b6..513b868fb9a 100644
--- a/pkg/front_end/test/compile_dart2js_with_no_sdk_test.dart
+++ b/pkg/front_end/test/compile_dart2js_with_no_sdk_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/api_prototype/compiler_options.dart';
 
 import 'incremental_load_from_dill_suite.dart'
diff --git a/pkg/front_end/test/compile_with_no_sdk_test.dart b/pkg/front_end/test/compile_with_no_sdk_test.dart
index b096688da59..5c7f5ca87de 100644
--- a/pkg/front_end/test/compile_with_no_sdk_test.dart
+++ b/pkg/front_end/test/compile_with_no_sdk_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/api_prototype/compiler_options.dart';
 import 'package:front_end/src/api_prototype/memory_file_system.dart';
 
diff --git a/pkg/front_end/test/constant_evaluator_benchmark.dart b/pkg/front_end/test/constant_evaluator_benchmark.dart
index f0e722c526d..5de0a0aedc4 100644
--- a/pkg/front_end/test/constant_evaluator_benchmark.dart
+++ b/pkg/front_end/test/constant_evaluator_benchmark.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show File;
 import 'dart:typed_data' show Uint8List;
 
diff --git a/pkg/front_end/test/covariance_check/covariance_check_test.dart b/pkg/front_end/test/covariance_check/covariance_check_test.dart
index 99dcbbca703..ed0e2237daf 100644
--- a/pkg/front_end/test/covariance_check/covariance_check_test.dart
+++ b/pkg/front_end/test/covariance_check/covariance_check_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart';
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/crashing_test_case_minimizer.dart b/pkg/front_end/test/crashing_test_case_minimizer.dart
index ea8ac645383..46ce8f78ceb 100644
--- a/pkg/front_end/test/crashing_test_case_minimizer.dart
+++ b/pkg/front_end/test/crashing_test_case_minimizer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:convert' show jsonDecode;
 
 import 'dart:io' show File;
diff --git a/pkg/front_end/test/crashing_test_case_minimizer_impl.dart b/pkg/front_end/test/crashing_test_case_minimizer_impl.dart
index 22ffcf87117..6e8344cc47a 100644
--- a/pkg/front_end/test/crashing_test_case_minimizer_impl.dart
+++ b/pkg/front_end/test/crashing_test_case_minimizer_impl.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:async' show Future, StreamSubscription;
 
 import 'dart:convert' show JsonEncoder, jsonDecode, utf8;
diff --git a/pkg/front_end/test/deps_test.dart b/pkg/front_end/test/deps_test.dart
index 3bb12a7e69a..c542bc5dad7 100644
--- a/pkg/front_end/test/deps_test.dart
+++ b/pkg/front_end/test/deps_test.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'package:_fe_analyzer_shared/src/messages/severity.dart';
diff --git a/pkg/front_end/test/desugar_test.dart b/pkg/front_end/test/desugar_test.dart
index b61a6a73a09..3ebad1ed6cc 100644
--- a/pkg/front_end/test/desugar_test.dart
+++ b/pkg/front_end/test/desugar_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Test to ensure that desugaring APIs used by clients like dart2js are
 /// always up to date.
 ///
diff --git a/pkg/front_end/test/dijkstras_sssp_algorithm.dart b/pkg/front_end/test/dijkstras_sssp_algorithm.dart
index b8f9789b6ce..0c93386fb8d 100644
--- a/pkg/front_end/test/dijkstras_sssp_algorithm.dart
+++ b/pkg/front_end/test/dijkstras_sssp_algorithm.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:collection';
 
 /// Dijkstra's algorithm for single source shortest path.
diff --git a/pkg/front_end/test/dill_round_trip_test.dart b/pkg/front_end/test/dill_round_trip_test.dart
index a04c5e1570d..2842c9eeb98 100644
--- a/pkg/front_end/test/dill_round_trip_test.dart
+++ b/pkg/front_end/test/dill_round_trip_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/fasta/kernel/utils.dart' show serializeComponent;
 
 import 'package:kernel/ast.dart' show Component;
diff --git a/pkg/front_end/test/enable_non_nullable/enable_non_nullable_test.dart b/pkg/front_end/test/enable_non_nullable/enable_non_nullable_test.dart
index 88873060eb7..85cce5b85d6 100644
--- a/pkg/front_end/test/enable_non_nullable/enable_non_nullable_test.dart
+++ b/pkg/front_end/test/enable_non_nullable/enable_non_nullable_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'package:expect/expect.dart';
diff --git a/pkg/front_end/test/explicit_creation_test.dart b/pkg/front_end/test/explicit_creation_test.dart
index 7e8246aca34..a0378d2210c 100644
--- a/pkg/front_end/test/explicit_creation_test.dart
+++ b/pkg/front_end/test/explicit_creation_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'package:_fe_analyzer_shared/src/messages/severity.dart';
diff --git a/pkg/front_end/test/extensions/extensions_test.dart b/pkg/front_end/test/extensions/extensions_test.dart
index 9cf6d7e2e61..5ccb1e853b9 100644
--- a/pkg/front_end/test/extensions/extensions_test.dart
+++ b/pkg/front_end/test/extensions/extensions_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart';
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart';
diff --git a/pkg/front_end/test/fasta/ambiguous_export_test.dart b/pkg/front_end/test/fasta/ambiguous_export_test.dart
index 1bb1c23e8a3..b1e492b43ae 100644
--- a/pkg/front_end/test/fasta/ambiguous_export_test.dart
+++ b/pkg/front_end/test/fasta/ambiguous_export_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:async_helper/async_helper.dart' show asyncTest;
 
 import 'package:expect/expect.dart' show Expect;
diff --git a/pkg/front_end/test/fasta/analyze_src_with_lints_test.dart b/pkg/front_end/test/fasta/analyze_src_with_lints_test.dart
index 8ede953bbf2..652d6b7902a 100644
--- a/pkg/front_end/test/fasta/analyze_src_with_lints_test.dart
+++ b/pkg/front_end/test/fasta/analyze_src_with_lints_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:testing/src/run_tests.dart" as testing show main;
 
 main() async {
diff --git a/pkg/front_end/test/fasta/analyze_test.dart b/pkg/front_end/test/fasta/analyze_test.dart
index cf52a507534..044385e8945 100644
--- a/pkg/front_end/test/fasta/analyze_test.dart
+++ b/pkg/front_end/test/fasta/analyze_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:testing/src/run_tests.dart" as testing show main;
 
 main() {
diff --git a/pkg/front_end/test/fasta/assert_locations_test.dart b/pkg/front_end/test/fasta/assert_locations_test.dart
index 532b311f390..c94a1e46a5c 100644
--- a/pkg/front_end/test/fasta/assert_locations_test.dart
+++ b/pkg/front_end/test/fasta/assert_locations_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.assert_locations_test;
 
 import 'package:async_helper/async_helper.dart' show asyncTest;
diff --git a/pkg/front_end/test/fasta/bootstrap_test.dart b/pkg/front_end/test/fasta/bootstrap_test.dart
index f48318ac169..bc7578749ab 100644
--- a/pkg/front_end/test/fasta/bootstrap_test.dart
+++ b/pkg/front_end/test/fasta/bootstrap_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, File, Platform;
 
 import 'package:async_helper/async_helper.dart' show asyncEnd, asyncStart;
diff --git a/pkg/front_end/test/fasta/expression_suite.dart b/pkg/front_end/test/fasta/expression_suite.dart
index 2b29aa0a410..ddf7d4806a4 100644
--- a/pkg/front_end/test/fasta/expression_suite.dart
+++ b/pkg/front_end/test/fasta/expression_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.expression_test;
 
 import "dart:convert" show JsonEncoder;
diff --git a/pkg/front_end/test/fasta/fast_strong_suite.dart b/pkg/front_end/test/fasta/fast_strong_suite.dart
index 8a0d844d88a..e4395cb05ce 100644
--- a/pkg/front_end/test/fasta/fast_strong_suite.dart
+++ b/pkg/front_end/test/fasta/fast_strong_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.fast_strong_test;
 
 import 'dart:io' show Platform;
diff --git a/pkg/front_end/test/fasta/generator_to_string_test.dart b/pkg/front_end/test/fasta/generator_to_string_test.dart
index 3ebb5117af6..6adfa4caafe 100644
--- a/pkg/front_end/test/fasta/generator_to_string_test.dart
+++ b/pkg/front_end/test/fasta/generator_to_string_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Test of toString on generators.
 
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart'
diff --git a/pkg/front_end/test/fasta/incremental_expectations.dart b/pkg/front_end/test/fasta/incremental_expectations.dart
index 6ac7b34e303..9839f4d6f00 100644
--- a/pkg/front_end/test/fasta/incremental_expectations.dart
+++ b/pkg/front_end/test/fasta/incremental_expectations.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library fasta.test.incremental_expectations;
 
 import "dart:convert" show JsonDecoder, JsonEncoder;
diff --git a/pkg/front_end/test/fasta/incremental_hello_test.dart b/pkg/front_end/test/fasta/incremental_hello_test.dart
index f7435f645f6..4e10f32b6bd 100644
--- a/pkg/front_end/test/fasta/incremental_hello_test.dart
+++ b/pkg/front_end/test/fasta/incremental_hello_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.incremental_dynamic_test;
 
 import 'package:async_helper/async_helper.dart' show asyncTest;
diff --git a/pkg/front_end/test/fasta/incremental_source_files.dart b/pkg/front_end/test/fasta/incremental_source_files.dart
index c6d6931072c..4108b62555f 100644
--- a/pkg/front_end/test/fasta/incremental_source_files.dart
+++ b/pkg/front_end/test/fasta/incremental_source_files.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.incremental_source_files;
 
 /// Expand a file with diffs in common merge conflict format into a [List] that
diff --git a/pkg/front_end/test/fasta/incremental_suite.dart b/pkg/front_end/test/fasta/incremental_suite.dart
index 46c13e97bd1..0fc43309d5e 100644
--- a/pkg/front_end/test/fasta/incremental_suite.dart
+++ b/pkg/front_end/test/fasta/incremental_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.incremental_test;
 
 import "dart:convert" show JsonEncoder;
diff --git a/pkg/front_end/test/fasta/link_test.dart b/pkg/front_end/test/fasta/link_test.dart
index 1eec73e21b1..a0b7b06a7e1 100644
--- a/pkg/front_end/test/fasta/link_test.dart
+++ b/pkg/front_end/test/fasta/link_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/util/link.dart' show Link, LinkBuilder;
 
 import 'package:expect/expect.dart' show Expect;
diff --git a/pkg/front_end/test/fasta/messages_suite.dart b/pkg/front_end/test/fasta/messages_suite.dart
index 8e04b8103ae..9795ed40d5d 100644
--- a/pkg/front_end/test/fasta/messages_suite.dart
+++ b/pkg/front_end/test/fasta/messages_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:convert" show utf8;
 
 import 'dart:io' show File, Platform;
diff --git a/pkg/front_end/test/fasta/object_supertype_test.dart b/pkg/front_end/test/fasta/object_supertype_test.dart
index 1f37142b62d..d6e0ae67fa0 100644
--- a/pkg/front_end/test/fasta/object_supertype_test.dart
+++ b/pkg/front_end/test/fasta/object_supertype_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:convert" show json;
 
 import "package:_fe_analyzer_shared/src/messages/diagnostic_message.dart"
diff --git a/pkg/front_end/test/fasta/outline_suite.dart b/pkg/front_end/test/fasta/outline_suite.dart
index 4bb4b5863c4..0c9fbfdf769 100644
--- a/pkg/front_end/test/fasta/outline_suite.dart
+++ b/pkg/front_end/test/fasta/outline_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.outline_test;
 
 import 'testing/suite.dart';
diff --git a/pkg/front_end/test/fasta/parser/literal_entry_info_test.dart b/pkg/front_end/test/fasta/parser/literal_entry_info_test.dart
index 8e0033fd589..791ecbe1e43 100644
--- a/pkg/front_end/test/fasta/parser/literal_entry_info_test.dart
+++ b/pkg/front_end/test/fasta/parser/literal_entry_info_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/parser/parser.dart';
 import 'package:_fe_analyzer_shared/src/parser/async_modifier.dart';
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart';
diff --git a/pkg/front_end/test/fasta/parser/parser_suite.dart b/pkg/front_end/test/fasta/parser/parser_suite.dart
index 8ea1adaf4e1..9c9f13ac724 100644
--- a/pkg/front_end/test/fasta/parser/parser_suite.dart
+++ b/pkg/front_end/test/fasta/parser/parser_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/parser/parser.dart'
     show ParserError, parse;
 
diff --git a/pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart b/pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart
index 5445a78629e..3d2633923bb 100644
--- a/pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart
+++ b/pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/parser/token_stream_rewriter.dart';
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart'
     show ScannerResult, scanString;
diff --git a/pkg/front_end/test/fasta/parser/type_info_test.dart b/pkg/front_end/test/fasta/parser/type_info_test.dart
index 3536cb41587..a14f5e0ac30 100644
--- a/pkg/front_end/test/fasta/parser/type_info_test.dart
+++ b/pkg/front_end/test/fasta/parser/type_info_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/parser/parser.dart';
 import 'package:_fe_analyzer_shared/src/parser/type_info.dart';
 import 'package:_fe_analyzer_shared/src/parser/type_info_impl.dart';
diff --git a/pkg/front_end/test/fasta/reexport_test.dart b/pkg/front_end/test/fasta/reexport_test.dart
index 62112e058cd..c754291e240 100644
--- a/pkg/front_end/test/fasta/reexport_test.dart
+++ b/pkg/front_end/test/fasta/reexport_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:async_helper/async_helper.dart" show asyncTest;
 
 import "package:front_end/src/testing/compiler_common.dart" show compileUnit;
diff --git a/pkg/front_end/test/fasta/scanner/scanner_suite.dart b/pkg/front_end/test/fasta/scanner/scanner_suite.dart
index e71149ee05f..7039a407834 100644
--- a/pkg/front_end/test/fasta/scanner/scanner_suite.dart
+++ b/pkg/front_end/test/fasta/scanner/scanner_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'package:testing/testing.dart' show Chain, ChainContext, Step, runMe;
 
 import '../../utils/scanner_chain.dart' show Read, Scan;
diff --git a/pkg/front_end/test/fasta/sdk_test.dart b/pkg/front_end/test/fasta/sdk_test.dart
index 27073c48f79..00d03a61089 100644
--- a/pkg/front_end/test/fasta/sdk_test.dart
+++ b/pkg/front_end/test/fasta/sdk_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.sdk_test;
 
 import 'testing/suite.dart';
diff --git a/pkg/front_end/test/fasta/strong1_suite.dart b/pkg/front_end/test/fasta/strong1_suite.dart
index cb30b7e5f63..7fbcb8dcf11 100644
--- a/pkg/front_end/test/fasta/strong1_suite.dart
+++ b/pkg/front_end/test/fasta/strong1_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'strong_tester.dart';
 
 main(List<String> arguments) {
diff --git a/pkg/front_end/test/fasta/strong2_suite.dart b/pkg/front_end/test/fasta/strong2_suite.dart
index 10fafaf03e7..311509bb13b 100644
--- a/pkg/front_end/test/fasta/strong2_suite.dart
+++ b/pkg/front_end/test/fasta/strong2_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'strong_tester.dart';
 
 main(List<String> arguments) {
diff --git a/pkg/front_end/test/fasta/strong3_suite.dart b/pkg/front_end/test/fasta/strong3_suite.dart
index 044c7e8a0ef..5bb59134e63 100644
--- a/pkg/front_end/test/fasta/strong3_suite.dart
+++ b/pkg/front_end/test/fasta/strong3_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'strong_tester.dart';
 
 main(List<String> arguments) {
diff --git a/pkg/front_end/test/fasta/strong4_suite.dart b/pkg/front_end/test/fasta/strong4_suite.dart
index 9e459e32de8..9db43678aaa 100644
--- a/pkg/front_end/test/fasta/strong4_suite.dart
+++ b/pkg/front_end/test/fasta/strong4_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'strong_tester.dart';
 
 main(List<String> arguments) {
diff --git a/pkg/front_end/test/fasta/strong_tester.dart b/pkg/front_end/test/fasta/strong_tester.dart
index 83d9ab3fd4e..c514438186f 100644
--- a/pkg/front_end/test/fasta/strong_tester.dart
+++ b/pkg/front_end/test/fasta/strong_tester.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.strong_test;
 
 import 'dart:io' show Platform;
diff --git a/pkg/front_end/test/fasta/super_mixins_test.dart b/pkg/front_end/test/fasta/super_mixins_test.dart
index c776f0acb3f..ecfe1c90265 100644
--- a/pkg/front_end/test/fasta/super_mixins_test.dart
+++ b/pkg/front_end/test/fasta/super_mixins_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.incremental_dynamic_test;
 
 import "package:_fe_analyzer_shared/src/messages/diagnostic_message.dart"
diff --git a/pkg/front_end/test/fasta/testing/suite.dart b/pkg/front_end/test/fasta/testing/suite.dart
index 0dd5247c22d..e52916f2f05 100644
--- a/pkg/front_end/test/fasta/testing/suite.dart
+++ b/pkg/front_end/test/fasta/testing/suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.testing.suite;
 
 import 'dart:convert' show jsonDecode;
diff --git a/pkg/front_end/test/fasta/text_serialization1_suite.dart b/pkg/front_end/test/fasta/text_serialization1_suite.dart
index 1a9ba5eec8f..bccfbcd70f8 100644
--- a/pkg/front_end/test/fasta/text_serialization1_suite.dart
+++ b/pkg/front_end/test/fasta/text_serialization1_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'text_serialization_tester.dart';
 
 main(List<String> arguments) {
diff --git a/pkg/front_end/test/fasta/text_serialization2_suite.dart b/pkg/front_end/test/fasta/text_serialization2_suite.dart
index b922a214e86..8b5b2ca8ba3 100644
--- a/pkg/front_end/test/fasta/text_serialization2_suite.dart
+++ b/pkg/front_end/test/fasta/text_serialization2_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'text_serialization_tester.dart';
 
 main(List<String> arguments) {
diff --git a/pkg/front_end/test/fasta/text_serialization3_suite.dart b/pkg/front_end/test/fasta/text_serialization3_suite.dart
index f14949c5cba..682d4860d3e 100644
--- a/pkg/front_end/test/fasta/text_serialization3_suite.dart
+++ b/pkg/front_end/test/fasta/text_serialization3_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'text_serialization_tester.dart';
 
 main(List<String> arguments) {
diff --git a/pkg/front_end/test/fasta/text_serialization4_suite.dart b/pkg/front_end/test/fasta/text_serialization4_suite.dart
index 98072927d0b..c6043fcf7b2 100644
--- a/pkg/front_end/test/fasta/text_serialization4_suite.dart
+++ b/pkg/front_end/test/fasta/text_serialization4_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'text_serialization_tester.dart';
 
 main(List<String> arguments) {
diff --git a/pkg/front_end/test/fasta/text_serialization_tester.dart b/pkg/front_end/test/fasta/text_serialization_tester.dart
index 13ee1814705..25c40819e7d 100644
--- a/pkg/front_end/test/fasta/text_serialization_tester.dart
+++ b/pkg/front_end/test/fasta/text_serialization_tester.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.text_serialization_test;
 
 import 'dart:io' show Platform;
diff --git a/pkg/front_end/test/fasta/textual_outline_suite.dart b/pkg/front_end/test/fasta/textual_outline_suite.dart
index 8e3827762e5..7688f80ee59 100644
--- a/pkg/front_end/test/fasta/textual_outline_suite.dart
+++ b/pkg/front_end/test/fasta/textual_outline_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.textual_outline_test;
 
 import 'dart:io';
diff --git a/pkg/front_end/test/fasta/tool_test.dart b/pkg/front_end/test/fasta/tool_test.dart
index fe44a8ba50b..6f77ade9810 100644
--- a/pkg/front_end/test/fasta/tool_test.dart
+++ b/pkg/front_end/test/fasta/tool_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Tests the tool `pkg/front_end/tool/fasta`.
 
 import "dart:io";
diff --git a/pkg/front_end/test/fasta/type_inference/factor_type_test.dart b/pkg/front_end/test/fasta/type_inference/factor_type_test.dart
index f68d6d50cb4..aec0ef13ea6 100644
--- a/pkg/front_end/test/fasta/type_inference/factor_type_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/factor_type_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/flow_analysis/factory_type_test_helper.dart';
 import 'package:expect/expect.dart';
 import 'package:front_end/src/api_prototype/compiler_options.dart';
diff --git a/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_nnbd_test.dart b/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_nnbd_test.dart
index 9bc5b5d1053..889f6c60d1a 100644
--- a/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_nnbd_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_nnbd_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/fasta/type_inference/type_constraint_gatherer.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema_environment.dart';
diff --git a/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart b/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart
index d690cbaf91e..ec32ecfc805 100644
--- a/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/fasta/type_inference/type_constraint_gatherer.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema_environment.dart';
diff --git a/pkg/front_end/test/fasta/type_inference/type_inference_engine_test.dart b/pkg/front_end/test/fasta/type_inference/type_inference_engine_test.dart
index a804319e2a3..1f063e3f7b2 100644
--- a/pkg/front_end/test/fasta/type_inference/type_inference_engine_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/type_inference_engine_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/fasta/type_inference/type_inference_engine.dart';
 import 'package:kernel/ast.dart';
 import 'package:test/test.dart';
diff --git a/pkg/front_end/test/fasta/type_inference/type_schema_elimination_nnbd_test.dart b/pkg/front_end/test/fasta/type_inference/type_schema_elimination_nnbd_test.dart
index aa491ccd2eb..1643d2f8c9b 100644
--- a/pkg/front_end/test/fasta/type_inference/type_schema_elimination_nnbd_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/type_schema_elimination_nnbd_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/fasta/type_inference/type_schema.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema_elimination.dart'
     as typeSchemaElimination;
diff --git a/pkg/front_end/test/fasta/type_inference/type_schema_elimination_test.dart b/pkg/front_end/test/fasta/type_inference/type_schema_elimination_test.dart
index 3d30f92623d..55e7235ed78 100644
--- a/pkg/front_end/test/fasta/type_inference/type_schema_elimination_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/type_schema_elimination_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/fasta/type_inference/type_schema.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema_elimination.dart'
     as typeSchemaElimination;
diff --git a/pkg/front_end/test/fasta/type_inference/type_schema_environment_nnbd_test.dart b/pkg/front_end/test/fasta/type_inference/type_schema_environment_nnbd_test.dart
index 5818a50d73b..68f81d6fccd 100644
--- a/pkg/front_end/test/fasta/type_inference/type_schema_environment_nnbd_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/type_schema_environment_nnbd_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/fasta/type_inference/type_schema.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema_environment.dart';
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/test/fasta/type_inference/type_schema_environment_test.dart b/pkg/front_end/test/fasta/type_inference/type_schema_environment_test.dart
index e57d799d7b7..7f6b961ca5e 100644
--- a/pkg/front_end/test/fasta/type_inference/type_schema_environment_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/type_schema_environment_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/fasta/type_inference/type_schema.dart';
 import 'package:front_end/src/fasta/type_inference/type_schema_environment.dart';
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/test/fasta/type_inference/type_schema_test.dart b/pkg/front_end/test/fasta/type_inference/type_schema_test.dart
index 8c6f5a2a8c6..28919155225 100644
--- a/pkg/front_end/test/fasta/type_inference/type_schema_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/type_schema_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/fasta/type_inference/type_schema.dart';
 import 'package:kernel/ast.dart';
 import 'package:kernel/visitor.dart';
diff --git a/pkg/front_end/test/fasta/types/dart2js_benchmark.dart b/pkg/front_end/test/fasta/types/dart2js_benchmark.dart
index 414a69ad438..7ef67e3ea6d 100644
--- a/pkg/front_end/test/fasta/types/dart2js_benchmark.dart
+++ b/pkg/front_end/test/fasta/types/dart2js_benchmark.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:io" show Platform;
 
 import "subtypes_benchmark.dart" show run;
diff --git a/pkg/front_end/test/fasta/types/dart2js_benchmark_test.dart b/pkg/front_end/test/fasta/types/dart2js_benchmark_test.dart
index 551647dd30f..b3084eae129 100644
--- a/pkg/front_end/test/fasta/types/dart2js_benchmark_test.dart
+++ b/pkg/front_end/test/fasta/types/dart2js_benchmark_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart2js_benchmark.dart" as bench show main;
 
 main() => bench.main();
diff --git a/pkg/front_end/test/fasta/types/dill_hierachy_test.dart b/pkg/front_end/test/fasta/types/dill_hierachy_test.dart
index 3250327b35e..a5bd0e47272 100644
--- a/pkg/front_end/test/fasta/types/dill_hierachy_test.dart
+++ b/pkg/front_end/test/fasta/types/dill_hierachy_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:async_helper/async_helper.dart" show asyncTest;
 
 import "package:expect/expect.dart" show Expect;
diff --git a/pkg/front_end/test/fasta/types/fasta_legacy_upper_bound_test.dart b/pkg/front_end/test/fasta/types/fasta_legacy_upper_bound_test.dart
index b1ac139fc23..653a912cf99 100644
--- a/pkg/front_end/test/fasta/types/fasta_legacy_upper_bound_test.dart
+++ b/pkg/front_end/test/fasta/types/fasta_legacy_upper_bound_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:kernel/ast.dart" show DartType, Library;
 
 import "package:kernel/target/targets.dart" show NoneTarget, TargetFlags;
diff --git a/pkg/front_end/test/fasta/types/fasta_types_test.dart b/pkg/front_end/test/fasta/types/fasta_types_test.dart
index bfbde701352..25778ab6176 100644
--- a/pkg/front_end/test/fasta/types/fasta_types_test.dart
+++ b/pkg/front_end/test/fasta/types/fasta_types_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:async_helper/async_helper.dart" show asyncTest;
 
 import "package:kernel/ast.dart" show Component, DartType;
diff --git a/pkg/front_end/test/fasta/types/hashcode_test.dart b/pkg/front_end/test/fasta/types/hashcode_test.dart
index 404d4464a47..e27c2fea52d 100644
--- a/pkg/front_end/test/fasta/types/hashcode_test.dart
+++ b/pkg/front_end/test/fasta/types/hashcode_test.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+// @dart = 2.9
+
 import 'package:expect/expect.dart';
 import 'package:kernel/kernel.dart';
 
diff --git a/pkg/front_end/test/fasta/types/kernel_legacy_upper_bound_test.dart b/pkg/front_end/test/fasta/types/kernel_legacy_upper_bound_test.dart
index e353327a250..cddafb7445e 100644
--- a/pkg/front_end/test/fasta/types/kernel_legacy_upper_bound_test.dart
+++ b/pkg/front_end/test/fasta/types/kernel_legacy_upper_bound_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "legacy_upper_bound_helper.dart" show LegacyUpperBoundTest;
 
 import "package:kernel/ast.dart" show DartType, Library;
diff --git a/pkg/front_end/test/fasta/types/kernel_type_parser_test.dart b/pkg/front_end/test/fasta/types/kernel_type_parser_test.dart
index fef974ee27f..8d54c8a5b8f 100644
--- a/pkg/front_end/test/fasta/types/kernel_type_parser_test.dart
+++ b/pkg/front_end/test/fasta/types/kernel_type_parser_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/expect.dart" show Expect;
 
 import "package:kernel/ast.dart" show Component, DartType, Library;
diff --git a/pkg/front_end/test/fasta/types/large_app_benchmark.dart b/pkg/front_end/test/fasta/types/large_app_benchmark.dart
index 94a5601fd8f..45e9417b61f 100644
--- a/pkg/front_end/test/fasta/types/large_app_benchmark.dart
+++ b/pkg/front_end/test/fasta/types/large_app_benchmark.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:io" show Platform;
 
 import "subtypes_benchmark.dart" show run;
diff --git a/pkg/front_end/test/fasta/types/large_app_benchmark_test.dart b/pkg/front_end/test/fasta/types/large_app_benchmark_test.dart
index 4dca6c81527..4dc83bef7ca 100644
--- a/pkg/front_end/test/fasta/types/large_app_benchmark_test.dart
+++ b/pkg/front_end/test/fasta/types/large_app_benchmark_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "large_app_benchmark.dart" as bench show main;
 
 main() => bench.main();
diff --git a/pkg/front_end/test/fasta/types/legacy_upper_bound_helper.dart b/pkg/front_end/test/fasta/types/legacy_upper_bound_helper.dart
index 5a50c9ed41c..3d4c7d6f7e0 100644
--- a/pkg/front_end/test/fasta/types/legacy_upper_bound_helper.dart
+++ b/pkg/front_end/test/fasta/types/legacy_upper_bound_helper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:async_helper/async_helper.dart" show asyncTest;
 
 import "package:expect/expect.dart" show Expect;
diff --git a/pkg/front_end/test/fasta/types/shared_type_tests.dart b/pkg/front_end/test/fasta/types/shared_type_tests.dart
index fa1d750da6e..fc8f7e39f43 100644
--- a/pkg/front_end/test/fasta/types/shared_type_tests.dart
+++ b/pkg/front_end/test/fasta/types/shared_type_tests.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/expect.dart" show Expect;
 
 import "package:kernel/type_environment.dart";
diff --git a/pkg/front_end/test/fasta/types/subtypes_benchmark.dart b/pkg/front_end/test/fasta/types/subtypes_benchmark.dart
index 8a81b6153bd..ef6dfb04d58 100644
--- a/pkg/front_end/test/fasta/types/subtypes_benchmark.dart
+++ b/pkg/front_end/test/fasta/types/subtypes_benchmark.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:convert" show json, utf8;
 
 import "dart:io" show File, gzip;
diff --git a/pkg/front_end/test/fasta/uri_translator_test.dart b/pkg/front_end/test/fasta/uri_translator_test.dart
index 9d2935200ca..15733f8c6e4 100644
--- a/pkg/front_end/test/fasta/uri_translator_test.dart
+++ b/pkg/front_end/test/fasta/uri_translator_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/base/libraries_specification.dart';
 import 'package:front_end/src/fasta/uri_translator.dart';
 import 'package:package_config/package_config.dart';
diff --git a/pkg/front_end/test/fasta/util/direct_parser_ast_test.dart b/pkg/front_end/test/fasta/util/direct_parser_ast_test.dart
index 4f2c82ffafe..aab38dd3d75 100644
--- a/pkg/front_end/test/fasta/util/direct_parser_ast_test.dart
+++ b/pkg/front_end/test/fasta/util/direct_parser_ast_test.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+// @dart = 2.9
+
 import 'dart:convert';
 import 'dart:io';
 
diff --git a/pkg/front_end/test/fasta/weak_suite.dart b/pkg/front_end/test/fasta/weak_suite.dart
index 604a4801bb4..ec9df5ed0ca 100644
--- a/pkg/front_end/test/fasta/weak_suite.dart
+++ b/pkg/front_end/test/fasta/weak_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.test.weak_test;
 
 import 'testing/suite.dart';
diff --git a/pkg/front_end/test/ffi_test.dart b/pkg/front_end/test/ffi_test.dart
index f032f752d92..b617fa0a738 100644
--- a/pkg/front_end/test/ffi_test.dart
+++ b/pkg/front_end/test/ffi_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:expect/expect.dart';
 
 main() {
diff --git a/pkg/front_end/test/flutter_gallery_leak_tester.dart b/pkg/front_end/test/flutter_gallery_leak_tester.dart
index fa3a9496a5f..37b66be3438 100644
--- a/pkg/front_end/test/flutter_gallery_leak_tester.dart
+++ b/pkg/front_end/test/flutter_gallery_leak_tester.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
diff --git a/pkg/front_end/test/hot_reload_e2e_test.dart b/pkg/front_end/test/hot_reload_e2e_test.dart
index eb41174af8f..419354b1b02 100644
--- a/pkg/front_end/test/hot_reload_e2e_test.dart
+++ b/pkg/front_end/test/hot_reload_e2e_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Integration test that runs the incremental compiler, runs the compiled
 /// program, incrementally rebuild portions of the app, and triggers a hot
 /// reload on the running program.
diff --git a/pkg/front_end/test/id_testing/data/library_with_name.dart b/pkg/front_end/test/id_testing/data/library_with_name.dart
index cd9b07e69f3..fabca663b3e 100644
--- a/pkg/front_end/test/id_testing/data/library_with_name.dart
+++ b/pkg/front_end/test/id_testing/data/library_with_name.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*library: file=main.dart,name=lib*/
 library lib;
 
diff --git a/pkg/front_end/test/id_testing/id_testing_test.dart b/pkg/front_end/test/id_testing/id_testing_test.dart
index 6de53f551ff..590515a60f7 100644
--- a/pkg/front_end/test/id_testing/id_testing_test.dart
+++ b/pkg/front_end/test/id_testing/id_testing_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/testing/id.dart' show ActualData, Id;
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
     show DataInterpreter, StringDataInterpreter, runTests;
diff --git a/pkg/front_end/test/id_tests/assigned_variables_test.dart b/pkg/front_end/test/id_tests/assigned_variables_test.dart
index 51832e2ebf3..b0a7d7a14e3 100644
--- a/pkg/front_end/test/id_tests/assigned_variables_test.dart
+++ b/pkg/front_end/test/id_tests/assigned_variables_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 
 import 'package:_fe_analyzer_shared/src/flow_analysis/flow_analysis.dart';
diff --git a/pkg/front_end/test/id_tests/constant_test.dart b/pkg/front_end/test/id_tests/constant_test.dart
index 8de3c2e4855..3091acfd234 100644
--- a/pkg/front_end/test/id_tests/constant_test.dart
+++ b/pkg/front_end/test/id_tests/constant_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart' show ActualData, Id;
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/id_tests/definite_assignment_test.dart b/pkg/front_end/test/id_tests/definite_assignment_test.dart
index 68b66ed6add..5dd584d8b0b 100644
--- a/pkg/front_end/test/id_tests/definite_assignment_test.dart
+++ b/pkg/front_end/test/id_tests/definite_assignment_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart' show ActualData, Id;
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/id_tests/definite_unassignment_test.dart b/pkg/front_end/test/id_tests/definite_unassignment_test.dart
index b22affba4af..fdc8ce2ab61 100644
--- a/pkg/front_end/test/id_tests/definite_unassignment_test.dart
+++ b/pkg/front_end/test/id_tests/definite_unassignment_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart' show ActualData, Id;
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/id_tests/inheritance_test.dart b/pkg/front_end/test/id_tests/inheritance_test.dart
index f39b8d21a84..261efa65bed 100644
--- a/pkg/front_end/test/id_tests/inheritance_test.dart
+++ b/pkg/front_end/test/id_tests/inheritance_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 
 import 'package:_fe_analyzer_shared/src/testing/id.dart';
diff --git a/pkg/front_end/test/id_tests/nullability_test.dart b/pkg/front_end/test/id_tests/nullability_test.dart
index 7b1e6039866..4980ffb06e8 100644
--- a/pkg/front_end/test/id_tests/nullability_test.dart
+++ b/pkg/front_end/test/id_tests/nullability_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart' show ActualData, Id;
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/id_tests/reachability_test.dart b/pkg/front_end/test/id_tests/reachability_test.dart
index 1cdf867f9c8..cf37a574102 100644
--- a/pkg/front_end/test/id_tests/reachability_test.dart
+++ b/pkg/front_end/test/id_tests/reachability_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart' show ActualData, Id;
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/id_tests/type_promotion_test.dart b/pkg/front_end/test/id_tests/type_promotion_test.dart
index 5e963c7559a..1ac5fb3ad3c 100644
--- a/pkg/front_end/test/id_tests/type_promotion_test.dart
+++ b/pkg/front_end/test/id_tests/type_promotion_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart' show ActualData, Id;
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/incremental_bulk_compiler_full.dart b/pkg/front_end/test/incremental_bulk_compiler_full.dart
index 03ac98029fb..ac018cb44f6 100644
--- a/pkg/front_end/test/incremental_bulk_compiler_full.dart
+++ b/pkg/front_end/test/incremental_bulk_compiler_full.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:expect/expect.dart' show Expect;
 
 import 'package:front_end/src/api_prototype/compiler_options.dart'
diff --git a/pkg/front_end/test/incremental_bulk_compiler_smoke_suite.dart b/pkg/front_end/test/incremental_bulk_compiler_smoke_suite.dart
index 28f3352a2d1..98f1f3bf4dc 100644
--- a/pkg/front_end/test/incremental_bulk_compiler_smoke_suite.dart
+++ b/pkg/front_end/test/incremental_bulk_compiler_smoke_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:testing/testing.dart' show Chain, runMe;
 
 import 'incremental_bulk_compiler_full.dart' show Context;
diff --git a/pkg/front_end/test/incremental_compiler_leak_test.dart b/pkg/front_end/test/incremental_compiler_leak_test.dart
index 9cefae530af..d304ccb2b2b 100644
--- a/pkg/front_end/test/incremental_compiler_leak_test.dart
+++ b/pkg/front_end/test/incremental_compiler_leak_test.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+// @dart = 2.9
+
 import 'dart:async';
 import 'dart:io';
 
diff --git a/pkg/front_end/test/incremental_dart2js_load_from_dill_test.dart b/pkg/front_end/test/incremental_dart2js_load_from_dill_test.dart
index 844ecd52eb7..13eaccb7380 100644
--- a/pkg/front_end/test/incremental_dart2js_load_from_dill_test.dart
+++ b/pkg/front_end/test/incremental_dart2js_load_from_dill_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, File;
 
 import 'package:expect/expect.dart' show Expect;
diff --git a/pkg/front_end/test/incremental_dart2js_test.dart b/pkg/front_end/test/incremental_dart2js_test.dart
index 1ea9b17e07e..5fef9dca780 100644
--- a/pkg/front_end/test/incremental_dart2js_test.dart
+++ b/pkg/front_end/test/incremental_dart2js_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "incremental_dart2js_tester.dart";
 
 main(List<String> args) async {
diff --git a/pkg/front_end/test/incremental_dart2js_tester.dart b/pkg/front_end/test/incremental_dart2js_tester.dart
index 05b55381722..8cadcc19b85 100644
--- a/pkg/front_end/test/incremental_dart2js_tester.dart
+++ b/pkg/front_end/test/incremental_dart2js_tester.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:developer";
 import 'dart:io' show Platform;
 
diff --git a/pkg/front_end/test/incremental_flutter_tester.dart b/pkg/front_end/test/incremental_flutter_tester.dart
index 4d2aa120a8d..10bb00ed8ba 100644
--- a/pkg/front_end/test/incremental_flutter_tester.dart
+++ b/pkg/front_end/test/incremental_flutter_tester.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, File, exit;
 
 import 'package:front_end/src/api_prototype/compiler_options.dart'
diff --git a/pkg/front_end/test/incremental_load_from_dill_suite.dart b/pkg/front_end/test/incremental_load_from_dill_suite.dart
index 84c74bc18a4..371df2957a8 100644
--- a/pkg/front_end/test/incremental_load_from_dill_suite.dart
+++ b/pkg/front_end/test/incremental_load_from_dill_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:developer' show debugger;
 
 import 'dart:io' show Directory, File;
diff --git a/pkg/front_end/test/incremental_load_from_invalid_dill_test.dart b/pkg/front_end/test/incremental_load_from_invalid_dill_test.dart
index 1f8b19aed36..6f1bc12d771 100644
--- a/pkg/front_end/test/incremental_load_from_invalid_dill_test.dart
+++ b/pkg/front_end/test/incremental_load_from_invalid_dill_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show File;
 
 import 'package:_fe_analyzer_shared/src/messages/diagnostic_message.dart'
diff --git a/pkg/front_end/test/incremental_utils.dart b/pkg/front_end/test/incremental_utils.dart
index f91e82342e2..0d7251b5432 100644
--- a/pkg/front_end/test/incremental_utils.dart
+++ b/pkg/front_end/test/incremental_utils.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:convert' show utf8;
 
 import "package:front_end/src/api_prototype/file_system.dart" show FileSystem;
diff --git a/pkg/front_end/test/issue_34856_test.dart b/pkg/front_end/test/issue_34856_test.dart
index 7e78eb1fb2d..8d41b6f481c 100644
--- a/pkg/front_end/test/issue_34856_test.dart
+++ b/pkg/front_end/test/issue_34856_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show File;
 
 import 'package:async_helper/async_helper.dart' show asyncTest;
diff --git a/pkg/front_end/test/kernel_generator_test.dart b/pkg/front_end/test/kernel_generator_test.dart
index 20e3b57d897..209e8533541 100644
--- a/pkg/front_end/test/kernel_generator_test.dart
+++ b/pkg/front_end/test/kernel_generator_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart'
     show EmptyStatement, Component, ReturnStatement, StaticInvocation;
 
diff --git a/pkg/front_end/test/language_versioning/language_versioning_test.dart b/pkg/front_end/test/language_versioning/language_versioning_test.dart
index b44c90d2bf4..912905ce0cc 100644
--- a/pkg/front_end/test/language_versioning/language_versioning_test.dart
+++ b/pkg/front_end/test/language_versioning/language_versioning_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, File, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart' show ActualData, Id;
 import 'package:_fe_analyzer_shared/src/testing/features.dart';
diff --git a/pkg/front_end/test/language_versioning/language_versioning_up_to_date_test.dart b/pkg/front_end/test/language_versioning/language_versioning_up_to_date_test.dart
index 3e20772c6b6..16a442b502e 100644
--- a/pkg/front_end/test/language_versioning/language_versioning_up_to_date_test.dart
+++ b/pkg/front_end/test/language_versioning/language_versioning_up_to_date_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Platform, Process, ProcessResult;
 
 import 'package:front_end/src/api_prototype/compiler_options.dart';
diff --git a/pkg/front_end/test/lint_suite.dart b/pkg/front_end/test/lint_suite.dart
index 85471967ee7..d5b0da7f081 100644
--- a/pkg/front_end/test/lint_suite.dart
+++ b/pkg/front_end/test/lint_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, File, FileSystemEntity;
 
 import 'dart:typed_data' show Uint8List;
diff --git a/pkg/front_end/test/member_covariance_test.dart b/pkg/front_end/test/member_covariance_test.dart
index 6f541df4906..62d44a3a039 100644
--- a/pkg/front_end/test/member_covariance_test.dart
+++ b/pkg/front_end/test/member_covariance_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:expect/expect.dart';
 import 'package:front_end/src/fasta/kernel/kernel_ast_api.dart';
 import 'package:front_end/src/fasta/kernel/member_covariance.dart';
diff --git a/pkg/front_end/test/memory_file_system_test.dart b/pkg/front_end/test/memory_file_system_test.dart
index 4364582c360..802eace7581 100644
--- a/pkg/front_end/test/memory_file_system_test.dart
+++ b/pkg/front_end/test/memory_file_system_test.dart
@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 // SharedOptions=--supermixin
 
+// @dart = 2.9
+
 library front_end.test.memory_file_system_test;
 
 import 'dart:convert';
diff --git a/pkg/front_end/test/messages_json_test.dart b/pkg/front_end/test/messages_json_test.dart
index 55c6e768fd8..e8fe28a0b7d 100644
--- a/pkg/front_end/test/messages_json_test.dart
+++ b/pkg/front_end/test/messages_json_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/messages/diagnostic_message.dart'
     show DiagnosticMessage, getMessageUri;
 
diff --git a/pkg/front_end/test/mixin_export_test.dart b/pkg/front_end/test/mixin_export_test.dart
index bf97cc22cf2..6b75f194f67 100644
--- a/pkg/front_end/test/mixin_export_test.dart
+++ b/pkg/front_end/test/mixin_export_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:async_helper/async_helper.dart' show asyncTest;
 
 import 'package:front_end/src/testing/compiler_common.dart';
diff --git a/pkg/front_end/test/packages_format_error_test.dart b/pkg/front_end/test/packages_format_error_test.dart
index 14f97c8adc6..7514228b824 100644
--- a/pkg/front_end/test/packages_format_error_test.dart
+++ b/pkg/front_end/test/packages_format_error_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/messages/diagnostic_message.dart'
     show DiagnosticMessage, getMessageCodeObject;
 
diff --git a/pkg/front_end/test/parser_all_suite.dart b/pkg/front_end/test/parser_all_suite.dart
index 9b60aae131e..837567f8762 100644
--- a/pkg/front_end/test/parser_all_suite.dart
+++ b/pkg/front_end/test/parser_all_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:testing/testing.dart' show Chain, ChainContext, runMe;
 
 import 'parser_suite.dart';
diff --git a/pkg/front_end/test/parser_suite.dart b/pkg/front_end/test/parser_suite.dart
index 3bc79a2fd38..6221db75fb1 100644
--- a/pkg/front_end/test/parser_suite.dart
+++ b/pkg/front_end/test/parser_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:convert' show jsonDecode;
 
 import 'dart:io' show File;
diff --git a/pkg/front_end/test/parser_test_listener_creator.dart b/pkg/front_end/test/parser_test_listener_creator.dart
index 18c215209d1..787e7f62ec2 100644
--- a/pkg/front_end/test/parser_test_listener_creator.dart
+++ b/pkg/front_end/test/parser_test_listener_creator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:io';
 import 'dart:typed_data';
 
diff --git a/pkg/front_end/test/parser_test_parser.dart b/pkg/front_end/test/parser_test_parser.dart
index 8033a377661..fd3ed9b60b0 100644
--- a/pkg/front_end/test/parser_test_parser.dart
+++ b/pkg/front_end/test/parser_test_parser.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/parser/assert.dart';
 import 'package:_fe_analyzer_shared/src/parser/block_kind.dart';
 import 'package:_fe_analyzer_shared/src/parser/declaration_kind.dart';
diff --git a/pkg/front_end/test/parser_test_parser_creator.dart b/pkg/front_end/test/parser_test_parser_creator.dart
index aa1e5735c8d..d1ab0c59ace 100644
--- a/pkg/front_end/test/parser_test_parser_creator.dart
+++ b/pkg/front_end/test/parser_test_parser_creator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 import 'dart:typed_data';
 
diff --git a/pkg/front_end/test/patching/patching_test.dart b/pkg/front_end/test/patching/patching_test.dart
index 9e5e116257a..e22e19f127a 100644
--- a/pkg/front_end/test/patching/patching_test.dart
+++ b/pkg/front_end/test/patching/patching_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 
 import 'package:_fe_analyzer_shared/src/testing/id.dart' show ActualData, Id;
diff --git a/pkg/front_end/test/precedence_info_test.dart b/pkg/front_end/test/precedence_info_test.dart
index 61244aa94f4..fd88c3e13ef 100644
--- a/pkg/front_end/test/precedence_info_test.dart
+++ b/pkg/front_end/test/precedence_info_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart';
 import 'package:_fe_analyzer_shared/src/scanner/abstract_scanner.dart'
     show AbstractScanner;
diff --git a/pkg/front_end/test/predicates/predicate_test.dart b/pkg/front_end/test/predicates/predicate_test.dart
index ffe5ec2ebe9..5d98cffa618 100644
--- a/pkg/front_end/test/predicates/predicate_test.dart
+++ b/pkg/front_end/test/predicates/predicate_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart';
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/read_dill_from_binary_md_test.dart b/pkg/front_end/test/read_dill_from_binary_md_test.dart
index 2331db59554..fc735458bd7 100644
--- a/pkg/front_end/test/read_dill_from_binary_md_test.dart
+++ b/pkg/front_end/test/read_dill_from_binary_md_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show File, Platform;
 
 import 'package:kernel/target/targets.dart' show NoneTarget, TargetFlags;
diff --git a/pkg/front_end/test/relativize_test.dart b/pkg/front_end/test/relativize_test.dart
index bc8a1321d9d..28c4acce2c3 100644
--- a/pkg/front_end/test/relativize_test.dart
+++ b/pkg/front_end/test/relativize_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/util/relativize.dart';
 import 'package:test/test.dart';
 
diff --git a/pkg/front_end/test/resolve_input_uri_test.dart b/pkg/front_end/test/resolve_input_uri_test.dart
index f8eda338804..37054409f80 100644
--- a/pkg/front_end/test/resolve_input_uri_test.dart
+++ b/pkg/front_end/test/resolve_input_uri_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/util/relativize.dart';
 import 'package:expect/expect.dart' show Expect;
 import 'package:front_end/src/fasta/resolve_input_uri.dart';
diff --git a/pkg/front_end/test/scanner_fasta_test.dart b/pkg/front_end/test/scanner_fasta_test.dart
index 08f0bc6f26c..7b595234533 100644
--- a/pkg/front_end/test/scanner_fasta_test.dart
+++ b/pkg/front_end/test/scanner_fasta_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:convert';
 
 import 'package:_fe_analyzer_shared/src/scanner/error_token.dart' as fasta;
diff --git a/pkg/front_end/test/scanner_replacement_test.dart b/pkg/front_end/test/scanner_replacement_test.dart
index a5237936cfa..867e68e24e5 100644
--- a/pkg/front_end/test/scanner_replacement_test.dart
+++ b/pkg/front_end/test/scanner_replacement_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart' as fasta;
 import 'package:_fe_analyzer_shared/src/scanner/token.dart' as fasta;
 import 'package:_fe_analyzer_shared/src/scanner/error_token.dart' as fasta;
diff --git a/pkg/front_end/test/scanner_test.dart b/pkg/front_end/test/scanner_test.dart
index d6cdad2871d..4a62db47d67 100644
--- a/pkg/front_end/test/scanner_test.dart
+++ b/pkg/front_end/test/scanner_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/base/errors.dart';
 import 'package:_fe_analyzer_shared/src/scanner/abstract_scanner.dart'
     show AbstractScanner, ScannerConfiguration;
diff --git a/pkg/front_end/test/scheme_based_file_system_test.dart b/pkg/front_end/test/scheme_based_file_system_test.dart
index e6b374b8c73..f5c018e6994 100644
--- a/pkg/front_end/test/scheme_based_file_system_test.dart
+++ b/pkg/front_end/test/scheme_based_file_system_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/api_prototype/file_system.dart';
 import 'package:front_end/src/scheme_based_file_system.dart';
 
diff --git a/pkg/front_end/test/severity_index_test.dart b/pkg/front_end/test/severity_index_test.dart
index 2077e6d0f35..8dc6f148535 100644
--- a/pkg/front_end/test/severity_index_test.dart
+++ b/pkg/front_end/test/severity_index_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
 
 /// Test that Severity has the expected indexes. Note that this is important
diff --git a/pkg/front_end/test/simple_stats.dart b/pkg/front_end/test/simple_stats.dart
index 062d59d1dfd..b163e673af8 100644
--- a/pkg/front_end/test/simple_stats.dart
+++ b/pkg/front_end/test/simple_stats.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+// @dart = 2.9
+
 import 'dart:math' as math;
 
 class SimpleTTestStat {
diff --git a/pkg/front_end/test/spell_checking_cleanup_lists.dart b/pkg/front_end/test/spell_checking_cleanup_lists.dart
index af7d5bd6286..6f389912272 100644
--- a/pkg/front_end/test/spell_checking_cleanup_lists.dart
+++ b/pkg/front_end/test/spell_checking_cleanup_lists.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'spell_checking_utils.dart' as spell;
diff --git a/pkg/front_end/test/spell_checking_utils.dart b/pkg/front_end/test/spell_checking_utils.dart
index b0f33a38a38..c08fb4c0f24 100644
--- a/pkg/front_end/test/spell_checking_utils.dart
+++ b/pkg/front_end/test/spell_checking_utils.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show File, stdin, stdout;
 
 import "utils/io_utils.dart";
diff --git a/pkg/front_end/test/spell_checking_utils_test.dart b/pkg/front_end/test/spell_checking_utils_test.dart
index 658c88e7c53..07c8904c15c 100644
--- a/pkg/front_end/test/spell_checking_utils_test.dart
+++ b/pkg/front_end/test/spell_checking_utils_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'spell_checking_utils.dart';
 
 void main() {
diff --git a/pkg/front_end/test/spelling_test_base.dart b/pkg/front_end/test/spelling_test_base.dart
index bd0ea9f2f37..f63a61c7a45 100644
--- a/pkg/front_end/test/spelling_test_base.dart
+++ b/pkg/front_end/test/spelling_test_base.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show File, Platform;
 
 import 'dart:typed_data' show Uint8List;
diff --git a/pkg/front_end/test/spelling_test_external_targets.dart b/pkg/front_end/test/spelling_test_external_targets.dart
index 79ff96c0017..9bae907bcd5 100644
--- a/pkg/front_end/test/spelling_test_external_targets.dart
+++ b/pkg/front_end/test/spelling_test_external_targets.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, File, FileSystemEntity;
 
 import 'package:testing/testing.dart'
diff --git a/pkg/front_end/test/spelling_test_not_src_suite.dart b/pkg/front_end/test/spelling_test_not_src_suite.dart
index a6205de9a67..6504052af4c 100644
--- a/pkg/front_end/test/spelling_test_not_src_suite.dart
+++ b/pkg/front_end/test/spelling_test_not_src_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:testing/testing.dart' show Chain, runMe;
 
 import 'spelling_test_base.dart';
diff --git a/pkg/front_end/test/spelling_test_src_suite.dart b/pkg/front_end/test/spelling_test_src_suite.dart
index dfd1117fce2..4ea5bb09144 100644
--- a/pkg/front_end/test/spelling_test_src_suite.dart
+++ b/pkg/front_end/test/spelling_test_src_suite.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:testing/testing.dart' show Chain, runMe;
 
 import 'spelling_test_base.dart';
diff --git a/pkg/front_end/test/split_dill_test.dart b/pkg/front_end/test/split_dill_test.dart
index 0ed6a0fa54c..24e47822564 100644
--- a/pkg/front_end/test/split_dill_test.dart
+++ b/pkg/front_end/test/split_dill_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, File, Platform, Process, ProcessResult;
 
 import 'dart:typed_data' show Uint8List;
diff --git a/pkg/front_end/test/src/base/libraries_specification_test.dart b/pkg/front_end/test/src/base/libraries_specification_test.dart
index 9d488aa9c9b..14cbae13aee 100644
--- a/pkg/front_end/test/src/base/libraries_specification_test.dart
+++ b/pkg/front_end/test/src/base/libraries_specification_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/base/libraries_specification.dart';
 import 'package:test/test.dart';
 
diff --git a/pkg/front_end/test/src/base/processed_options_test.dart b/pkg/front_end/test/src/base/processed_options_test.dart
index b004fb1386c..f8a87cbb7fe 100644
--- a/pkg/front_end/test/src/base/processed_options_test.dart
+++ b/pkg/front_end/test/src/base/processed_options_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/api_prototype/compiler_options.dart';
 import 'package:front_end/src/api_prototype/memory_file_system.dart';
 import 'package:front_end/src/base/processed_options.dart';
diff --git a/pkg/front_end/test/standard_file_system_test.dart b/pkg/front_end/test/standard_file_system_test.dart
index 5f5fd02f77b..a7becd79725 100644
--- a/pkg/front_end/test/standard_file_system_test.dart
+++ b/pkg/front_end/test/standard_file_system_test.dart
@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 // SharedOptions=--supermixin
 
+// @dart = 2.9
+
 library front_end.test.standard_file_system_test;
 
 import 'dart:convert';
diff --git a/pkg/front_end/test/static_types/analysis_helper.dart b/pkg/front_end/test/static_types/analysis_helper.dart
index 805194f894a..539d58e5e1b 100644
--- a/pkg/front_end/test/static_types/analysis_helper.dart
+++ b/pkg/front_end/test/static_types/analysis_helper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:convert' as json;
 import 'dart:io';
 
diff --git a/pkg/front_end/test/static_types/cfe_allowed.json b/pkg/front_end/test/static_types/cfe_allowed.json
index 20c1a54befb..63088f01b96 100644
--- a/pkg/front_end/test/static_types/cfe_allowed.json
+++ b/pkg/front_end/test/static_types/cfe_allowed.json
@@ -3,9 +3,6 @@
     "Dynamic invocation of 'split'.": 1
   },
   "pkg/front_end/lib/src/base/libraries_specification.dart": {
-    "Dynamic invocation of 'containsKey'.": 1,
-    "Dynamic invocation of '[]'.": 8,
-    "Dynamic invocation of 'forEach'.": 1,
     "Dynamic invocation of 'toList'.": 1,
     "Dynamic invocation of 'map'.": 1,
     "Dynamic invocation of '[]='.": 1
diff --git a/pkg/front_end/test/static_types/cfe_dynamic_test.dart b/pkg/front_end/test/static_types/cfe_dynamic_test.dart
index 306dc85e509..672ff9d7d98 100644
--- a/pkg/front_end/test/static_types/cfe_dynamic_test.dart
+++ b/pkg/front_end/test/static_types/cfe_dynamic_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'analysis_helper.dart';
 
 /// Filter function used to only analysis cfe source code.
diff --git a/pkg/front_end/test/static_types/static_type_test.dart b/pkg/front_end/test/static_types/static_type_test.dart
index cad8d52d84a..c90118c55bf 100644
--- a/pkg/front_end/test/static_types/static_type_test.dart
+++ b/pkg/front_end/test/static_types/static_type_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart';
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/summary_generator_test.dart b/pkg/front_end/test/summary_generator_test.dart
index d64123478b9..04deb3b7219 100644
--- a/pkg/front_end/test/summary_generator_test.dart
+++ b/pkg/front_end/test/summary_generator_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:front_end/src/api_prototype/front_end.dart';
 import 'package:front_end/src/testing/compiler_common.dart';
 import 'package:kernel/ast.dart';
diff --git a/pkg/front_end/test/test_generator_test.dart b/pkg/front_end/test/test_generator_test.dart
index 2ad6f365a2a..8e35ddce4cd 100644
--- a/pkg/front_end/test/test_generator_test.dart
+++ b/pkg/front_end/test/test_generator_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show exitCode, File, stdout;
 
 import 'package:front_end/src/api_prototype/compiler_options.dart';
diff --git a/pkg/front_end/test/testing_utils.dart b/pkg/front_end/test/testing_utils.dart
index b966e7477e8..ba228a052db 100644
--- a/pkg/front_end/test/testing_utils.dart
+++ b/pkg/front_end/test/testing_utils.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Process, ProcessResult;
 
 import 'package:testing/testing.dart' show Chain, TestDescription;
diff --git a/pkg/front_end/test/text_representation/empty_reference_test.dart b/pkg/front_end/test/text_representation/empty_reference_test.dart
index 362672b709e..22643b39211 100644
--- a/pkg/front_end/test/text_representation/empty_reference_test.dart
+++ b/pkg/front_end/test/text_representation/empty_reference_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:expect/expect.dart';
 import 'package:kernel/ast.dart';
 import 'text_representation_test.dart';
diff --git a/pkg/front_end/test/text_representation/internal_ast_text_representation_test.dart b/pkg/front_end/test/text_representation/internal_ast_text_representation_test.dart
index c0fd0e7af8a..a71ada8a2a8 100644
--- a/pkg/front_end/test/text_representation/internal_ast_text_representation_test.dart
+++ b/pkg/front_end/test/text_representation/internal_ast_text_representation_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:expect/expect.dart';
 import 'package:front_end/src/fasta/kernel/collections.dart';
 import 'package:front_end/src/fasta/kernel/forest.dart';
diff --git a/pkg/front_end/test/text_representation/text_representation_test.dart b/pkg/front_end/test/text_representation/text_representation_test.dart
index 8d572608c48..f8043857f23 100644
--- a/pkg/front_end/test/text_representation/text_representation_test.dart
+++ b/pkg/front_end/test/text_representation/text_representation_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart';
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart'
diff --git a/pkg/front_end/test/textual_outline_test.dart b/pkg/front_end/test/textual_outline_test.dart
index 4a059e8771f..b6ea904bbef 100644
--- a/pkg/front_end/test/textual_outline_test.dart
+++ b/pkg/front_end/test/textual_outline_test.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+// @dart = 2.9
+
 import "dart:convert";
 import "package:front_end/src/fasta/util/textual_outline.dart";
 
diff --git a/pkg/front_end/test/token_test.dart b/pkg/front_end/test/token_test.dart
index d1d2a03f395..4a1249c3ea3 100644
--- a/pkg/front_end/test/token_test.dart
+++ b/pkg/front_end/test/token_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart'
     show ScannerConfiguration, scanString;
 import 'package:_fe_analyzer_shared/src/scanner/token.dart';
diff --git a/pkg/front_end/test/tool/reload.dart b/pkg/front_end/test/tool/reload.dart
index 78d669e5137..6d86a82db6f 100644
--- a/pkg/front_end/test/tool/reload.dart
+++ b/pkg/front_end/test/tool/reload.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// A helper library to connect to an existing VM and trigger a hot-reload via
 /// its service protocol.
 ///
diff --git a/pkg/front_end/test/type_labeler_test.dart b/pkg/front_end/test/type_labeler_test.dart
index aea5433fa73..8814e5eaa7c 100644
--- a/pkg/front_end/test/type_labeler_test.dart
+++ b/pkg/front_end/test/type_labeler_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart';
 
 import 'package:front_end/src/fasta/kernel/type_labeler.dart';
diff --git a/pkg/front_end/test/unit_test_suites.dart b/pkg/front_end/test/unit_test_suites.dart
index 8e256f67eaf..fde99ac07c2 100644
--- a/pkg/front_end/test/unit_test_suites.dart
+++ b/pkg/front_end/test/unit_test_suites.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'dart:async' show Timer;
 import 'dart:convert' show jsonEncode;
 import 'dart:io' show File, Platform, exitCode;
diff --git a/pkg/front_end/test/utils/io_utils.dart b/pkg/front_end/test/utils/io_utils.dart
index 7fdd197df71..6cd9daaaca6 100644
--- a/pkg/front_end/test/utils/io_utils.dart
+++ b/pkg/front_end/test/utils/io_utils.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'dart:io' show Directory, File, Platform, Process, ProcessResult;
 
 String computeRepoDir() {
diff --git a/pkg/front_end/test/utils/kernel_chain.dart b/pkg/front_end/test/utils/kernel_chain.dart
index b76a823faa9..5afe9416346 100644
--- a/pkg/front_end/test/utils/kernel_chain.dart
+++ b/pkg/front_end/test/utils/kernel_chain.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.testing.kernel_chain;
 
 import 'dart:io' show Directory, File, IOSink, Platform;
diff --git a/pkg/front_end/test/utils/scanner_chain.dart b/pkg/front_end/test/utils/scanner_chain.dart
index 1bf5b4502eb..635ef6d5690 100644
--- a/pkg/front_end/test/utils/scanner_chain.dart
+++ b/pkg/front_end/test/utils/scanner_chain.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library fasta.testing.scanner_chain;
 
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart'
diff --git a/pkg/front_end/test/utils/validating_instrumentation.dart b/pkg/front_end/test/utils/validating_instrumentation.dart
index 9680b32f0d0..184e7cb5a2e 100644
--- a/pkg/front_end/test/utils/validating_instrumentation.dart
+++ b/pkg/front_end/test/utils/validating_instrumentation.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'dart:convert' show utf8;
 
 import 'dart:io' show File;
diff --git a/pkg/front_end/test/vm_service_coverage.dart b/pkg/front_end/test/vm_service_coverage.dart
index 7c69754e3c7..f5fd80513c7 100644
--- a/pkg/front_end/test/vm_service_coverage.dart
+++ b/pkg/front_end/test/vm_service_coverage.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+// @dart = 2.9
+
 import 'dart:async';
 
 import 'vm_service_helper.dart' as vmService;
diff --git a/pkg/front_end/test/vm_service_coverage_constant_evaluator.dart b/pkg/front_end/test/vm_service_coverage_constant_evaluator.dart
index d0420775793..5ea2bd06b31 100644
--- a/pkg/front_end/test/vm_service_coverage_constant_evaluator.dart
+++ b/pkg/front_end/test/vm_service_coverage_constant_evaluator.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE.md file.
+
+// @dart = 2.9
+
 import 'vm_service_coverage.dart' as helper;
 
 main(List<String> args) async {
diff --git a/pkg/front_end/test/vm_service_for_leak_detection.dart b/pkg/front_end/test/vm_service_for_leak_detection.dart
index 748756ebbcc..6df63cc1e65 100644
--- a/pkg/front_end/test/vm_service_for_leak_detection.dart
+++ b/pkg/front_end/test/vm_service_for_leak_detection.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 import 'dart:io';
 
 import "vm_service_heap_helper.dart" as helper;
diff --git a/pkg/front_end/test/vm_service_heap_finder.dart b/pkg/front_end/test/vm_service_heap_finder.dart
index 2e851845002..6fb49d91cbb 100644
--- a/pkg/front_end/test/vm_service_heap_finder.dart
+++ b/pkg/front_end/test/vm_service_heap_finder.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:io";
 
 import "vm_service_helper.dart" as vmService;
diff --git a/pkg/front_end/test/vm_service_heap_helper.dart b/pkg/front_end/test/vm_service_heap_helper.dart
index f4841d0455f..c011aea2e3c 100644
--- a/pkg/front_end/test/vm_service_heap_helper.dart
+++ b/pkg/front_end/test/vm_service_heap_helper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dijkstras_sssp_algorithm.dart";
 import "vm_service_helper.dart" as vmService;
 
diff --git a/pkg/front_end/test/vm_service_helper.dart b/pkg/front_end/test/vm_service_helper.dart
index a80eb5afd0a..8906a438107 100644
--- a/pkg/front_end/test/vm_service_helper.dart
+++ b/pkg/front_end/test/vm_service_helper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "dart:convert";
 import "dart:io";
 
diff --git a/pkg/front_end/tool/_fasta/abcompile.dart b/pkg/front_end/tool/_fasta/abcompile.dart
index 63ea80b6dec..26f815a90ba 100644
--- a/pkg/front_end/tool/_fasta/abcompile.dart
+++ b/pkg/front_end/tool/_fasta/abcompile.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:async';
 import 'dart:convert';
 import 'dart:math';
diff --git a/pkg/front_end/tool/_fasta/additional_targets.dart b/pkg/front_end/tool/_fasta/additional_targets.dart
index 6e9399a2123..098cd0dfdd9 100644
--- a/pkg/front_end/tool/_fasta/additional_targets.dart
+++ b/pkg/front_end/tool/_fasta/additional_targets.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 library fasta.tool.additional_targets;
 
 import 'package:kernel/target/targets.dart' show TargetFlags, targets;
diff --git a/pkg/front_end/tool/_fasta/additional_targets_test.dart b/pkg/front_end/tool/_fasta/additional_targets_test.dart
index daffd49b43d..d9fea70a8ac 100644
--- a/pkg/front_end/tool/_fasta/additional_targets_test.dart
+++ b/pkg/front_end/tool/_fasta/additional_targets_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 library fasta.tool.additional_targets_test;
 
 import 'package:kernel/target/targets.dart' show targets;
diff --git a/pkg/front_end/tool/_fasta/batch.dart b/pkg/front_end/tool/_fasta/batch.dart
index 968014e8597..ac34ce62c27 100644
--- a/pkg/front_end/tool/_fasta/batch.dart
+++ b/pkg/front_end/tool/_fasta/batch.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'entry_points.dart' show batchEntryPoint;
 
 main(List<String> arguments) => batchEntryPoint(arguments);
diff --git a/pkg/front_end/tool/_fasta/bench_maker.dart b/pkg/front_end/tool/_fasta/bench_maker.dart
index 6623d7a0882..dbfbb79de0a 100644
--- a/pkg/front_end/tool/_fasta/bench_maker.dart
+++ b/pkg/front_end/tool/_fasta/bench_maker.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 library fasta.tool.entry_points;
 
 import "dart:convert" show JsonEncoder;
diff --git a/pkg/front_end/tool/_fasta/command_line.dart b/pkg/front_end/tool/_fasta/command_line.dart
index 9c275d4729e..4eb70836754 100644
--- a/pkg/front_end/tool/_fasta/command_line.dart
+++ b/pkg/front_end/tool/_fasta/command_line.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 library fasta.tool.command_line;
 
 import 'dart:io' show exit;
diff --git a/pkg/front_end/tool/_fasta/compile.dart b/pkg/front_end/tool/_fasta/compile.dart
index 2165cf1b066..0fa58c95054 100644
--- a/pkg/front_end/tool/_fasta/compile.dart
+++ b/pkg/front_end/tool/_fasta/compile.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'entry_points.dart' show compileEntryPoint;
 
 main(List<String> arguments) => compileEntryPoint(arguments);
diff --git a/pkg/front_end/tool/_fasta/compile_platform.dart b/pkg/front_end/tool/_fasta/compile_platform.dart
index c9791fb291e..352e1f04d8f 100644
--- a/pkg/front_end/tool/_fasta/compile_platform.dart
+++ b/pkg/front_end/tool/_fasta/compile_platform.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'entry_points.dart' show compilePlatformEntryPoint;
 
 main(List<String> arguments) => compilePlatformEntryPoint(arguments);
diff --git a/pkg/front_end/tool/_fasta/compile_platform_legacy_test.dart b/pkg/front_end/tool/_fasta/compile_platform_legacy_test.dart
index 985026c2bbd..1f624d384db 100644
--- a/pkg/front_end/tool/_fasta/compile_platform_legacy_test.dart
+++ b/pkg/front_end/tool/_fasta/compile_platform_legacy_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart=2.9
+
 library fasta.test.compile_platform_test;
 
 import 'dart:io';
diff --git a/pkg/front_end/tool/_fasta/compile_platform_test.dart b/pkg/front_end/tool/_fasta/compile_platform_test.dart
index 985026c2bbd..1f624d384db 100644
--- a/pkg/front_end/tool/_fasta/compile_platform_test.dart
+++ b/pkg/front_end/tool/_fasta/compile_platform_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart=2.9
+
 library fasta.test.compile_platform_test;
 
 import 'dart:io';
diff --git a/pkg/front_end/tool/_fasta/deps.dart b/pkg/front_end/tool/_fasta/deps.dart
index 3b83d0f06c0..3e8c7bef53f 100644
--- a/pkg/front_end/tool/_fasta/deps.dart
+++ b/pkg/front_end/tool/_fasta/deps.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'entry_points.dart' show depsEntryPoint;
 
 main(List<String> arguments) => depsEntryPoint(arguments);
diff --git a/pkg/front_end/tool/_fasta/direct_parser_ast_helper_creator.dart b/pkg/front_end/tool/_fasta/direct_parser_ast_helper_creator.dart
index 8b7cf187748..3fde7d03f74 100644
--- a/pkg/front_end/tool/_fasta/direct_parser_ast_helper_creator.dart
+++ b/pkg/front_end/tool/_fasta/direct_parser_ast_helper_creator.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:io';
 import 'dart:typed_data';
 
diff --git a/pkg/front_end/tool/_fasta/entry_points.dart b/pkg/front_end/tool/_fasta/entry_points.dart
index b05374d5f4a..9733184bde6 100644
--- a/pkg/front_end/tool/_fasta/entry_points.dart
+++ b/pkg/front_end/tool/_fasta/entry_points.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 library fasta.tool.entry_points;
 
 import 'dart:convert' show LineSplitter, jsonDecode, jsonEncode, utf8;
diff --git a/pkg/front_end/tool/_fasta/generate_experimental_flags.dart b/pkg/front_end/tool/_fasta/generate_experimental_flags.dart
index 8f16842f6b1..5911b3a9c98 100644
--- a/pkg/front_end/tool/_fasta/generate_experimental_flags.dart
+++ b/pkg/front_end/tool/_fasta/generate_experimental_flags.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:io' show File, Platform;
 
 import 'package:_fe_analyzer_shared/src/scanner/characters.dart'
@@ -57,10 +59,12 @@ String generateKernelFile() {
   StringBuffer sb = new StringBuffer();
 
   sb.write('''
-// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // NOTE: THIS FILE IS GENERATED. DO NOT EDIT.
 //
 // Instead modify 'tools/experimental_features.yaml' and run
@@ -91,10 +95,12 @@ String generateCfeFile() {
   StringBuffer sb = new StringBuffer();
 
   sb.write('''
-// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // NOTE: THIS FILE IS GENERATED. DO NOT EDIT.
 //
 // Instead modify 'tools/experimental_features.yaml' and run
diff --git a/pkg/front_end/tool/_fasta/generate_experimental_flags_test.dart b/pkg/front_end/tool/_fasta/generate_experimental_flags_test.dart
index d826ea5bdaf..8320f374e0e 100644
--- a/pkg/front_end/tool/_fasta/generate_experimental_flags_test.dart
+++ b/pkg/front_end/tool/_fasta/generate_experimental_flags_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import "dart:io" show File, exitCode;
 
 import "generate_experimental_flags.dart"
diff --git a/pkg/front_end/tool/_fasta/generate_messages.dart b/pkg/front_end/tool/_fasta/generate_messages.dart
index 4cde3ecedd6..23a348748b8 100644
--- a/pkg/front_end/tool/_fasta/generate_messages.dart
+++ b/pkg/front_end/tool/_fasta/generate_messages.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:io';
 
 import 'dart:isolate';
@@ -53,11 +55,15 @@ Future<Messages> generateMessagesFiles() async {
   StringBuffer sharedMessages = new StringBuffer();
   StringBuffer cfeMessages = new StringBuffer();
 
-  const String preamble = """
-// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+  const String preamble1 = """
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+""";
+
+  const String preamble2 = """
+
 // NOTE: THIS FILE IS GENERATED. DO NOT EDIT.
 //
 // Instead modify 'pkg/front_end/messages.yaml' and run
@@ -66,12 +72,19 @@ Future<Messages> generateMessagesFiles() async {
 // ignore_for_file: lines_longer_than_80_chars
 """;
 
-  sharedMessages.writeln(preamble);
+  sharedMessages.writeln(preamble1);
+  sharedMessages.writeln(preamble2);
   sharedMessages.writeln("""
 part of _fe_analyzer_shared.messages.codes;
 """);
 
-  cfeMessages.writeln(preamble);
+  cfeMessages.writeln(preamble1);
+  cfeMessages.writeln("""
+
+// @dart = 2.9
+
+""");
+  cfeMessages.writeln(preamble2);
   cfeMessages.writeln("""
 part of fasta.codes;
 """);
diff --git a/pkg/front_end/tool/_fasta/generate_messages_test.dart b/pkg/front_end/tool/_fasta/generate_messages_test.dart
index 303be618aa6..ccbff6af56e 100644
--- a/pkg/front_end/tool/_fasta/generate_messages_test.dart
+++ b/pkg/front_end/tool/_fasta/generate_messages_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import "dart:io" show File;
 
 import "package:async_helper/async_helper.dart" show asyncTest;
diff --git a/pkg/front_end/tool/_fasta/log_analyzer.dart b/pkg/front_end/tool/_fasta/log_analyzer.dart
index c93e916c0b7..1a794a0fe38 100644
--- a/pkg/front_end/tool/_fasta/log_analyzer.dart
+++ b/pkg/front_end/tool/_fasta/log_analyzer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:convert' show jsonDecode, jsonEncode;
 
 import 'dart:io';
diff --git a/pkg/front_end/tool/_fasta/log_collector.dart b/pkg/front_end/tool/_fasta/log_collector.dart
index b35250d6c63..95dc56f7b31 100644
--- a/pkg/front_end/tool/_fasta/log_collector.dart
+++ b/pkg/front_end/tool/_fasta/log_collector.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:convert' show jsonDecode, utf8;
 
 import 'dart:isolate' show RawReceivePort;
diff --git a/pkg/front_end/tool/_fasta/outline.dart b/pkg/front_end/tool/_fasta/outline.dart
index dfba5cbbaff..2a4d7f907e4 100644
--- a/pkg/front_end/tool/_fasta/outline.dart
+++ b/pkg/front_end/tool/_fasta/outline.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'entry_points.dart' show outlineEntryPoint;
 
 main(List<String> arguments) => outlineEntryPoint(arguments);
diff --git a/pkg/front_end/tool/compare_dill.dart b/pkg/front_end/tool/compare_dill.dart
index f537a0f111f..f7e24b33ec6 100644
--- a/pkg/front_end/tool/compare_dill.dart
+++ b/pkg/front_end/tool/compare_dill.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// @dart=2.9
+
 import 'dart:io' show File;
 
 import '../test/binary_md_dill_reader.dart' show DillComparer;
diff --git a/pkg/front_end/tool/fasta.dart b/pkg/front_end/tool/fasta.dart
index f2ecaaf5bac..b2b8d26aaa6 100644
--- a/pkg/front_end/tool/fasta.dart
+++ b/pkg/front_end/tool/fasta.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:io';
 
 import '../test/utils/io_utils.dart' show computeRepoDir;
diff --git a/pkg/front_end/tool/fasta_perf.dart b/pkg/front_end/tool/fasta_perf.dart
index 385ec39b8f1..cd920617ac1 100644
--- a/pkg/front_end/tool/fasta_perf.dart
+++ b/pkg/front_end/tool/fasta_perf.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 /// An entrypoint used to run portions of fasta and measure its performance.
 library front_end.tool.fasta_perf;
 
diff --git a/pkg/front_end/tool/fasta_perf_test.dart b/pkg/front_end/tool/fasta_perf_test.dart
index f366e734343..fb850f04fc8 100644
--- a/pkg/front_end/tool/fasta_perf_test.dart
+++ b/pkg/front_end/tool/fasta_perf_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 /// The only purpose of this file is to enable analyzer tests on `perf.dart`,
 /// the code here just has a dummy import to the rest of the code.
 library front_end.tool.perf_test;
diff --git a/pkg/front_end/tool/incremental_perf.dart b/pkg/front_end/tool/incremental_perf.dart
index 617e448410a..50c922c7e38 100644
--- a/pkg/front_end/tool/incremental_perf.dart
+++ b/pkg/front_end/tool/incremental_perf.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 /// An entrypoint used to measure performance of the incremental compiler.
 ///
 /// Given an input a program and a .json file describing edits, this script will
diff --git a/pkg/front_end/tool/incremental_perf_test.dart b/pkg/front_end/tool/incremental_perf_test.dart
index 73e08939eac..72deb007b2d 100644
--- a/pkg/front_end/tool/incremental_perf_test.dart
+++ b/pkg/front_end/tool/incremental_perf_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 /// Test to ensure that incremental_perf.dart is running without errors.
 
 import 'dart:io';
diff --git a/pkg/front_end/tool/kernel_ast_file_rewriter.dart b/pkg/front_end/tool/kernel_ast_file_rewriter.dart
index bdefeaeb12d..64bd396fab5 100644
--- a/pkg/front_end/tool/kernel_ast_file_rewriter.dart
+++ b/pkg/front_end/tool/kernel_ast_file_rewriter.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import "dart:io" show File, Platform, stdout;
 import "dart:typed_data" show Uint8List;
 
diff --git a/pkg/front_end/tool/parser_direct_ast/console_helper.dart b/pkg/front_end/tool/parser_direct_ast/console_helper.dart
index d6a1d340974..d758c929ee6 100644
--- a/pkg/front_end/tool/parser_direct_ast/console_helper.dart
+++ b/pkg/front_end/tool/parser_direct_ast/console_helper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import "dart:async" show StreamSubscription, Timer;
 import "dart:io" show Platform, ProcessSignal, exit, stdin, stdout;
 import "dart:isolate" show RawReceivePort;
diff --git a/pkg/front_end/tool/parser_direct_ast/viewer.dart b/pkg/front_end/tool/parser_direct_ast/viewer.dart
index c516101d71a..276ea23c531 100644
--- a/pkg/front_end/tool/parser_direct_ast/viewer.dart
+++ b/pkg/front_end/tool/parser_direct_ast/viewer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import "dart:io" show File, Platform;
 import "dart:typed_data" show Uint8List;
 
diff --git a/pkg/front_end/tool/perf.dart b/pkg/front_end/tool/perf.dart
index 95b3ba5feb3..61ee9d34ae8 100644
--- a/pkg/front_end/tool/perf.dart
+++ b/pkg/front_end/tool/perf.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 /// An entrypoint used to run portions of analyzer and measure its performance.
 ///
 /// TODO(sigmund): rename to 'analyzer_perf.dart' in sync with changes to the
diff --git a/pkg/front_end/tool/perf_common.dart b/pkg/front_end/tool/perf_common.dart
index 7da7dcb1042..0ba1365aa25 100644
--- a/pkg/front_end/tool/perf_common.dart
+++ b/pkg/front_end/tool/perf_common.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 /// Shared code used by fasta_perf and incremental_perf.
 library front_end.tool.perf_common;
 
diff --git a/pkg/front_end/tool/perf_test.dart b/pkg/front_end/tool/perf_test.dart
index 7b54fb8a1f9..b246c05719c 100644
--- a/pkg/front_end/tool/perf_test.dart
+++ b/pkg/front_end/tool/perf_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 library front_end.tool.perf_test;
 
 import 'dart:io' show Platform;
diff --git a/pkg/front_end/tool/smoke_test_quick.dart b/pkg/front_end/tool/smoke_test_quick.dart
index 03d38401c9d..7427ee34e20 100644
--- a/pkg/front_end/tool/smoke_test_quick.dart
+++ b/pkg/front_end/tool/smoke_test_quick.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'dart:io' show Platform, Process, ProcessResult, exitCode;
 
 import '../test/utils/io_utils.dart' show computeRepoDir;
diff --git a/pkg/front_end/tool/stat_on_dash_v.dart b/pkg/front_end/tool/stat_on_dash_v.dart
index ead3e7b303c..c0ac7b40780 100644
--- a/pkg/front_end/tool/stat_on_dash_v.dart
+++ b/pkg/front_end/tool/stat_on_dash_v.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// @dart=2.9
+
 import "dart:io";
 
 import "../test/simple_stats.dart";
diff --git a/pkg/front_end/tool/update_all.dart b/pkg/front_end/tool/update_all.dart
index a4ff797775b..41ba6a1aea8 100644
--- a/pkg/front_end/tool/update_all.dart
+++ b/pkg/front_end/tool/update_all.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart' as id;
 import 'update_expectations.dart' as expectations;
 
diff --git a/pkg/front_end/tool/update_expectations.dart b/pkg/front_end/tool/update_expectations.dart
index 52bcd00ddf7..a1cc85cc878 100644
--- a/pkg/front_end/tool/update_expectations.dart
+++ b/pkg/front_end/tool/update_expectations.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart=2.9
+
 import 'fasta.dart' as fasta;
 
 const List<String> standardSuites = <String>[
diff --git a/pkg/kernel/bin/count_breakdown.dart b/pkg/kernel/bin/count_breakdown.dart
index 43450ffd5e2..13dd0737e23 100755
--- a/pkg/kernel/bin/count_breakdown.dart
+++ b/pkg/kernel/bin/count_breakdown.dart
@@ -3,6 +3,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 import 'package:kernel/kernel.dart';
 import 'package:kernel/src/tool/command_line_util.dart';
diff --git a/pkg/kernel/bin/dump.dart b/pkg/kernel/bin/dump.dart
index 0c3ab4795bc..c95a4e59716 100755
--- a/pkg/kernel/bin/dump.dart
+++ b/pkg/kernel/bin/dump.dart
@@ -3,6 +3,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'package:kernel/kernel.dart';
diff --git a/pkg/kernel/bin/size_breakdown.dart b/pkg/kernel/bin/size_breakdown.dart
index 298e1ec110d..979b8288543 100755
--- a/pkg/kernel/bin/size_breakdown.dart
+++ b/pkg/kernel/bin/size_breakdown.dart
@@ -3,6 +3,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'package:kernel/kernel.dart';
diff --git a/pkg/kernel/bin/split.dart b/pkg/kernel/bin/split.dart
index e3c99e8d8cc..61d5f0c6413 100755
--- a/pkg/kernel/bin/split.dart
+++ b/pkg/kernel/bin/split.dart
@@ -3,6 +3,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:async';
 import 'dart:io';
 
diff --git a/pkg/kernel/bin/type_check.dart b/pkg/kernel/bin/type_check.dart
index 5c3ef65802a..5c412443982 100755
--- a/pkg/kernel/bin/type_check.dart
+++ b/pkg/kernel/bin/type_check.dart
@@ -3,6 +3,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'package:kernel/error_formatter.dart';
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index 81fcfb64eee..4f81bdd0a05 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// -----------------------------------------------------------------------
 ///                          WHEN CHANGING THIS FILE:
 /// -----------------------------------------------------------------------
diff --git a/pkg/kernel/lib/binary/ast_from_binary.dart b/pkg/kernel/lib/binary/ast_from_binary.dart
index 0d81ce07c3d..e6a44562187 100644
--- a/pkg/kernel/lib/binary/ast_from_binary.dart
+++ b/pkg/kernel/lib/binary/ast_from_binary.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.ast_from_binary;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/kernel/lib/binary/ast_to_binary.dart b/pkg/kernel/lib/binary/ast_to_binary.dart
index 9a698fb3209..d706a362917 100644
--- a/pkg/kernel/lib/binary/ast_to_binary.dart
+++ b/pkg/kernel/lib/binary/ast_to_binary.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.ast_to_binary;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/kernel/lib/binary/tag.dart b/pkg/kernel/lib/binary/tag.dart
index 8e32adb1e87..410617c993f 100644
--- a/pkg/kernel/lib/binary/tag.dart
+++ b/pkg/kernel/lib/binary/tag.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
 library kernel.binary.tag;
 
 class Tag {
diff --git a/pkg/kernel/lib/canonical_name.dart b/pkg/kernel/lib/canonical_name.dart
index a5d6446ab3a..70f30045929 100644
--- a/pkg/kernel/lib/canonical_name.dart
+++ b/pkg/kernel/lib/canonical_name.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.canonical_name;
 
 import 'ast.dart';
diff --git a/pkg/kernel/lib/class_hierarchy.dart b/pkg/kernel/lib/class_hierarchy.dart
index 1a75d7ec34c..26ef3452255 100644
--- a/pkg/kernel/lib/class_hierarchy.dart
+++ b/pkg/kernel/lib/class_hierarchy.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.class_hierarchy;
 
 import 'dart:collection';
diff --git a/pkg/kernel/lib/clone.dart b/pkg/kernel/lib/clone.dart
index 4158c39e63e..83a94a1e0cf 100644
--- a/pkg/kernel/lib/clone.dart
+++ b/pkg/kernel/lib/clone.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.clone;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/kernel/lib/core_types.dart b/pkg/kernel/lib/core_types.dart
index e7c56468713..7c9a5663b70 100644
--- a/pkg/kernel/lib/core_types.dart
+++ b/pkg/kernel/lib/core_types.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.core_types;
 
 import 'package:kernel/type_algebra.dart';
diff --git a/pkg/kernel/lib/default_language_version.dart b/pkg/kernel/lib/default_language_version.dart
index 465988e46b2..8dbbe5b1522 100644
--- a/pkg/kernel/lib/default_language_version.dart
+++ b/pkg/kernel/lib/default_language_version.dart
@@ -1,7 +1,9 @@
-// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // NOTE: THIS FILE IS GENERATED. DO NOT EDIT.
 //
 // Instead modify 'tools/experimental_features.yaml' and run
diff --git a/pkg/kernel/lib/error_formatter.dart b/pkg/kernel/lib/error_formatter.dart
index 42265e71f06..aab719ed775 100644
--- a/pkg/kernel/lib/error_formatter.dart
+++ b/pkg/kernel/lib/error_formatter.dart
@@ -3,6 +3,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'package:kernel/naive_type_checker.dart';
 import 'package:kernel/text/ast_to_text.dart';
diff --git a/pkg/kernel/lib/external_name.dart b/pkg/kernel/lib/external_name.dart
index 157981d013a..253178065d5 100644
--- a/pkg/kernel/lib/external_name.dart
+++ b/pkg/kernel/lib/external_name.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.external_name;
 
 import 'ast.dart';
diff --git a/pkg/kernel/lib/import_table.dart b/pkg/kernel/lib/import_table.dart
index c85e9f35abc..c7662b4d894 100644
--- a/pkg/kernel/lib/import_table.dart
+++ b/pkg/kernel/lib/import_table.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.import_table;
 
 import 'ast.dart';
diff --git a/pkg/kernel/lib/kernel.dart b/pkg/kernel/lib/kernel.dart
index 45ccce9ac07..cae6df9f32e 100644
--- a/pkg/kernel/lib/kernel.dart
+++ b/pkg/kernel/lib/kernel.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Conventions for paths:
 ///
 /// - Use the [Uri] class for paths that may have the `file`, `dart` or
diff --git a/pkg/kernel/lib/library_index.dart b/pkg/kernel/lib/library_index.dart
index d8e36e7429d..f45aaa50081 100644
--- a/pkg/kernel/lib/library_index.dart
+++ b/pkg/kernel/lib/library_index.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.library_index;
 
 import 'ast.dart';
diff --git a/pkg/kernel/lib/naive_type_checker.dart b/pkg/kernel/lib/naive_type_checker.dart
index 76479c25942..250dde9d425 100644
--- a/pkg/kernel/lib/naive_type_checker.dart
+++ b/pkg/kernel/lib/naive_type_checker.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'class_hierarchy.dart';
 import 'core_types.dart';
 import 'kernel.dart';
diff --git a/pkg/kernel/lib/reference_from_index.dart b/pkg/kernel/lib/reference_from_index.dart
index fd999749292..0a2ca572dc2 100644
--- a/pkg/kernel/lib/reference_from_index.dart
+++ b/pkg/kernel/lib/reference_from_index.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "ast.dart"
     show
         Class,
diff --git a/pkg/kernel/lib/src/assumptions.dart b/pkg/kernel/lib/src/assumptions.dart
index 2e131a77eae..e8c759bf500 100644
--- a/pkg/kernel/lib/src/assumptions.dart
+++ b/pkg/kernel/lib/src/assumptions.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import '../ast.dart';
 
 /// Pairs of [TypeParameter]s that are currently assumed to be
diff --git a/pkg/kernel/lib/src/bounds_checks.dart b/pkg/kernel/lib/src/bounds_checks.dart
index a9c7859a2a6..d6e635b3ccc 100644
--- a/pkg/kernel/lib/src/bounds_checks.dart
+++ b/pkg/kernel/lib/src/bounds_checks.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import '../ast.dart'
     show
         BottomType,
diff --git a/pkg/kernel/lib/src/dart_type_equivalence.dart b/pkg/kernel/lib/src/dart_type_equivalence.dart
index 35eeff47ab9..ee4f758fffb 100644
--- a/pkg/kernel/lib/src/dart_type_equivalence.dart
+++ b/pkg/kernel/lib/src/dart_type_equivalence.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import '../ast.dart';
 import '../core_types.dart';
 import '../visitor.dart';
diff --git a/pkg/kernel/lib/src/future_value_type.dart b/pkg/kernel/lib/src/future_value_type.dart
index e3fd2702772..a77cef5f8d9 100644
--- a/pkg/kernel/lib/src/future_value_type.dart
+++ b/pkg/kernel/lib/src/future_value_type.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import '../ast.dart';
 import '../core_types.dart';
 
diff --git a/pkg/kernel/lib/src/hierarchy_based_type_environment.dart b/pkg/kernel/lib/src/hierarchy_based_type_environment.dart
index 947449692e8..e259b73c8f2 100644
--- a/pkg/kernel/lib/src/hierarchy_based_type_environment.dart
+++ b/pkg/kernel/lib/src/hierarchy_based_type_environment.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.hierarchy_based_type_environment;
 
 import '../ast.dart' show Class, DartType, InterfaceType, Library, Member, Name;
diff --git a/pkg/kernel/lib/src/legacy_erasure.dart b/pkg/kernel/lib/src/legacy_erasure.dart
index 362836890cd..c31e80bdc9a 100644
--- a/pkg/kernel/lib/src/legacy_erasure.dart
+++ b/pkg/kernel/lib/src/legacy_erasure.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import '../ast.dart' hide MapEntry;
 
 import 'replacement_visitor.dart';
diff --git a/pkg/kernel/lib/src/merge_visitor.dart b/pkg/kernel/lib/src/merge_visitor.dart
index 62eb99a7b23..dc1b77b6f3c 100644
--- a/pkg/kernel/lib/src/merge_visitor.dart
+++ b/pkg/kernel/lib/src/merge_visitor.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import '../ast.dart' hide MapEntry;
 import '../type_algebra.dart';
 
diff --git a/pkg/kernel/lib/src/nnbd_top_merge.dart b/pkg/kernel/lib/src/nnbd_top_merge.dart
index 9a56df4b0b2..fd5f9eb8ad0 100644
--- a/pkg/kernel/lib/src/nnbd_top_merge.dart
+++ b/pkg/kernel/lib/src/nnbd_top_merge.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import '../ast.dart' hide MapEntry;
 import '../core_types.dart';
 
diff --git a/pkg/kernel/lib/src/non_null.dart b/pkg/kernel/lib/src/non_null.dart
index 14e0c01a261..2a90dadb2e5 100644
--- a/pkg/kernel/lib/src/non_null.dart
+++ b/pkg/kernel/lib/src/non_null.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import '../ast.dart';
 
 /// Returns the type defines as `NonNull(type)` in the nnbd specification.
diff --git a/pkg/kernel/lib/src/norm.dart b/pkg/kernel/lib/src/norm.dart
index c8d0f71e48d..1b92f425a27 100644
--- a/pkg/kernel/lib/src/norm.dart
+++ b/pkg/kernel/lib/src/norm.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import '../ast.dart' hide MapEntry;
 import '../core_types.dart';
 import '../type_algebra.dart';
diff --git a/pkg/kernel/lib/src/printer.dart b/pkg/kernel/lib/src/printer.dart
index 0e9223d1404..c6a8f57a4d5 100644
--- a/pkg/kernel/lib/src/printer.dart
+++ b/pkg/kernel/lib/src/printer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import '../ast.dart';
 import 'text_util.dart';
 
diff --git a/pkg/kernel/lib/src/replacement_visitor.dart b/pkg/kernel/lib/src/replacement_visitor.dart
index ce7dbd1b4d4..e260919ccdc 100644
--- a/pkg/kernel/lib/src/replacement_visitor.dart
+++ b/pkg/kernel/lib/src/replacement_visitor.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import '../ast.dart' hide MapEntry;
 import '../type_algebra.dart';
 
diff --git a/pkg/kernel/lib/src/standard_bounds.dart b/pkg/kernel/lib/src/standard_bounds.dart
index d6224371fd0..de99a5e2a1b 100644
--- a/pkg/kernel/lib/src/standard_bounds.dart
+++ b/pkg/kernel/lib/src/standard_bounds.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 import 'dart:math' as math;
 
 import '../ast.dart'
diff --git a/pkg/kernel/lib/src/text_util.dart b/pkg/kernel/lib/src/text_util.dart
index 9fe573ff8b9..c7634ad3036 100644
--- a/pkg/kernel/lib/src/text_util.dart
+++ b/pkg/kernel/lib/src/text_util.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import '../ast.dart';
 
 String nullabilityToString(Nullability nullability) {
diff --git a/pkg/kernel/lib/src/tool/batch_util.dart b/pkg/kernel/lib/src/tool/batch_util.dart
index 9412c806491..69090878618 100644
--- a/pkg/kernel/lib/src/tool/batch_util.dart
+++ b/pkg/kernel/lib/src/tool/batch_util.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.batch_util;
 
 import 'dart:convert';
diff --git a/pkg/kernel/lib/src/tool/command_line_util.dart b/pkg/kernel/lib/src/tool/command_line_util.dart
index 1abadb2a92c..858e1b198b6 100644
--- a/pkg/kernel/lib/src/tool/command_line_util.dart
+++ b/pkg/kernel/lib/src/tool/command_line_util.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'package:kernel/kernel.dart';
diff --git a/pkg/kernel/lib/src/tool/find_referenced_libraries.dart b/pkg/kernel/lib/src/tool/find_referenced_libraries.dart
index e95c7df3a13..73733caef31 100644
--- a/pkg/kernel/lib/src/tool/find_referenced_libraries.dart
+++ b/pkg/kernel/lib/src/tool/find_referenced_libraries.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart';
 import 'package:kernel/visitor.dart';
 
diff --git a/pkg/kernel/lib/src/types.dart b/pkg/kernel/lib/src/types.dart
index 02a49338c42..4dcec694e41 100644
--- a/pkg/kernel/lib/src/types.dart
+++ b/pkg/kernel/lib/src/types.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import '../ast.dart'
     show
         BottomType,
diff --git a/pkg/kernel/lib/target/changed_structure_notifier.dart b/pkg/kernel/lib/target/changed_structure_notifier.dart
index e1b2c7f13b0..228a5d2eebe 100644
--- a/pkg/kernel/lib/target/changed_structure_notifier.dart
+++ b/pkg/kernel/lib/target/changed_structure_notifier.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' show Class;
 
 /// Meant for notifying the backend (the compiler) that the structure has
diff --git a/pkg/kernel/lib/target/targets.dart b/pkg/kernel/lib/target/targets.dart
index 8018658d35e..27f5ebace74 100644
--- a/pkg/kernel/lib/target/targets.dart
+++ b/pkg/kernel/lib/target/targets.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.target.targets;
 
 import '../ast.dart';
diff --git a/pkg/kernel/lib/testing/mock_sdk.dart b/pkg/kernel/lib/testing/mock_sdk.dart
index d4a937bd5e8..45a7d0cffb7 100644
--- a/pkg/kernel/lib/testing/mock_sdk.dart
+++ b/pkg/kernel/lib/testing/mock_sdk.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 const String mockSdk = """
 class Object;
 class Comparable<T>;
diff --git a/pkg/kernel/lib/testing/mock_sdk_component.dart b/pkg/kernel/lib/testing/mock_sdk_component.dart
index 180ad922d41..b317b60defa 100644
--- a/pkg/kernel/lib/testing/mock_sdk_component.dart
+++ b/pkg/kernel/lib/testing/mock_sdk_component.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart';
 
 /// Returns a [Component] object containing empty definitions of core SDK
diff --git a/pkg/kernel/lib/testing/type_parser.dart b/pkg/kernel/lib/testing/type_parser.dart
index ef288edde47..5842eeede7c 100644
--- a/pkg/kernel/lib/testing/type_parser.dart
+++ b/pkg/kernel/lib/testing/type_parser.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart' show Nullability;
 
 abstract class ParsedType {
diff --git a/pkg/kernel/lib/testing/type_parser_environment.dart b/pkg/kernel/lib/testing/type_parser_environment.dart
index 40484e63610..48a843a30fd 100644
--- a/pkg/kernel/lib/testing/type_parser_environment.dart
+++ b/pkg/kernel/lib/testing/type_parser_environment.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:kernel/ast.dart"
     show
         BottomType,
diff --git a/pkg/kernel/lib/text/ast_to_text.dart b/pkg/kernel/lib/text/ast_to_text.dart
index 2250af1e550..0ca1b4a6460 100644
--- a/pkg/kernel/lib/text/ast_to_text.dart
+++ b/pkg/kernel/lib/text/ast_to_text.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.ast_to_text;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/kernel/lib/text/serializer_combinators.dart b/pkg/kernel/lib/text/serializer_combinators.dart
index dc8fe50c7d1..3bd9e1d35d6 100644
--- a/pkg/kernel/lib/text/serializer_combinators.dart
+++ b/pkg/kernel/lib/text/serializer_combinators.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.serializer_combinators;
 
 import 'dart:convert' show json;
diff --git a/pkg/kernel/lib/text/text_reader.dart b/pkg/kernel/lib/text/text_reader.dart
index a6867e77aec..21fd49705ee 100644
--- a/pkg/kernel/lib/text/text_reader.dart
+++ b/pkg/kernel/lib/text/text_reader.dart
@@ -17,7 +17,7 @@ library kernel.text_reader;
 //
 // We use an iterator to read S-expressions.  The iterator produces a stream
 // of atoms (strings) and nested iterators (S-lists).
-class TextIterator implements Iterator<Object /* String | TextIterator */ > {
+class TextIterator implements Iterator<Object? /* String? | TextIterator? */ > {
   static int space = ' '.codeUnitAt(0);
   static int lparen = '('.codeUnitAt(0);
   static int rparen = ')'.codeUnitAt(0);
@@ -39,7 +39,7 @@ class TextIterator implements Iterator<Object /* String | TextIterator */ > {
   // Consume the rest of a nested S-expression and the closing delimiter.
   void skipToEndOfNested() {
     if (current is TextIterator) {
-      TextIterator it = current;
+      TextIterator it = current as TextIterator;
       while (it.moveNext()) {}
       index = it.index + 1;
     }
@@ -77,7 +77,7 @@ class TextIterator implements Iterator<Object /* String | TextIterator */ > {
   }
 
   @override
-  Object current = null;
+  Object? current = null;
 
   @override
   bool moveNext() {
diff --git a/pkg/kernel/lib/text/text_serialization_verifier.dart b/pkg/kernel/lib/text/text_serialization_verifier.dart
index 0b983c2dbbd..0298ad7b7e1 100644
--- a/pkg/kernel/lib/text/text_serialization_verifier.dart
+++ b/pkg/kernel/lib/text/text_serialization_verifier.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:convert' show json;
 
 import '../ast.dart';
diff --git a/pkg/kernel/lib/text/text_serializer.dart b/pkg/kernel/lib/text/text_serializer.dart
index be1e4cf237b..f81886b53ae 100644
--- a/pkg/kernel/lib/text/text_serializer.dart
+++ b/pkg/kernel/lib/text/text_serializer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.text_serializer;
 
 import '../ast.dart';
diff --git a/pkg/kernel/lib/transformations/async.dart b/pkg/kernel/lib/transformations/async.dart
index 37c9ea9e6c7..e8ac7bac7d3 100644
--- a/pkg/kernel/lib/transformations/async.dart
+++ b/pkg/kernel/lib/transformations/async.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.transformations.async;
 
 import '../kernel.dart';
diff --git a/pkg/kernel/lib/transformations/continuation.dart b/pkg/kernel/lib/transformations/continuation.dart
index cf5e16ffe27..0df3e849bf2 100644
--- a/pkg/kernel/lib/transformations/continuation.dart
+++ b/pkg/kernel/lib/transformations/continuation.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.transformations.continuation;
 
 import 'dart:math' as math;
diff --git a/pkg/kernel/lib/transformations/empty.dart b/pkg/kernel/lib/transformations/empty.dart
index 5a264dd722f..c07883b6bdb 100644
--- a/pkg/kernel/lib/transformations/empty.dart
+++ b/pkg/kernel/lib/transformations/empty.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.transformations.empty;
 
 import '../ast.dart';
diff --git a/pkg/kernel/lib/transformations/flags.dart b/pkg/kernel/lib/transformations/flags.dart
index 32cd627f1f7..cb6bafd25cc 100644
--- a/pkg/kernel/lib/transformations/flags.dart
+++ b/pkg/kernel/lib/transformations/flags.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.transformations.flags;
 
 import '../ast.dart';
diff --git a/pkg/kernel/lib/transformations/mixin_full_resolution.dart b/pkg/kernel/lib/transformations/mixin_full_resolution.dart
index 6a9a8b8d8fd..8e17efa8c8f 100644
--- a/pkg/kernel/lib/transformations/mixin_full_resolution.dart
+++ b/pkg/kernel/lib/transformations/mixin_full_resolution.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.transformations.mixin_full_resolution;
 
 import '../ast.dart';
diff --git a/pkg/kernel/lib/transformations/scanner.dart b/pkg/kernel/lib/transformations/scanner.dart
index ce4b9fc0f81..5aac0a8a48f 100644
--- a/pkg/kernel/lib/transformations/scanner.dart
+++ b/pkg/kernel/lib/transformations/scanner.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.transformations.scanner;
 
 import '../ast.dart';
diff --git a/pkg/kernel/lib/transformations/track_widget_constructor_locations.dart b/pkg/kernel/lib/transformations/track_widget_constructor_locations.dart
index 0cdafba1fb0..2eeb952a1f3 100644
--- a/pkg/kernel/lib/transformations/track_widget_constructor_locations.dart
+++ b/pkg/kernel/lib/transformations/track_widget_constructor_locations.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.transformations.track_widget_constructor_locations;
 
 import 'package:meta/meta.dart';
diff --git a/pkg/kernel/lib/transformations/type_casts_optimizer.dart b/pkg/kernel/lib/transformations/type_casts_optimizer.dart
index 4df790fa5d0..5f901e6c372 100644
--- a/pkg/kernel/lib/transformations/type_casts_optimizer.dart
+++ b/pkg/kernel/lib/transformations/type_casts_optimizer.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart';
 import 'package:kernel/type_environment.dart'
     show StaticTypeContext, SubtypeCheckMode, TypeEnvironment;
diff --git a/pkg/kernel/lib/transformations/value_class.dart b/pkg/kernel/lib/transformations/value_class.dart
index 5e21e5c3ad8..0264e0a4fff 100644
--- a/pkg/kernel/lib/transformations/value_class.dart
+++ b/pkg/kernel/lib/transformations/value_class.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.transformations.value_class;
 
 import 'package:kernel/type_environment.dart';
diff --git a/pkg/kernel/lib/type_algebra.dart b/pkg/kernel/lib/type_algebra.dart
index e40c0fc989b..b8c60a0e775 100644
--- a/pkg/kernel/lib/type_algebra.dart
+++ b/pkg/kernel/lib/type_algebra.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.type_algebra;
 
 import 'ast.dart';
diff --git a/pkg/kernel/lib/type_checker.dart b/pkg/kernel/lib/type_checker.dart
index e68e34065de..4748f26708d 100644
--- a/pkg/kernel/lib/type_checker.dart
+++ b/pkg/kernel/lib/type_checker.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.type_checker;
 
 import 'ast.dart';
diff --git a/pkg/kernel/lib/type_environment.dart b/pkg/kernel/lib/type_environment.dart
index 7e0dedc9d99..4b993f500bc 100644
--- a/pkg/kernel/lib/type_environment.dart
+++ b/pkg/kernel/lib/type_environment.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.type_environment;
 
 import 'package:kernel/type_algebra.dart';
diff --git a/pkg/kernel/lib/util/graph.dart b/pkg/kernel/lib/util/graph.dart
index f54f8a4d334..4119f1b0284 100644
--- a/pkg/kernel/lib/util/graph.dart
+++ b/pkg/kernel/lib/util/graph.dart
@@ -34,7 +34,7 @@ List<List<T>> computeStrongComponents<T>(Graph<T> graph) {
 
     // Step 3: For each edge from [vertex] to a neighboring vertex [neighbor]:
     for (T neighbor in graph.neighborsOf(vertex)) {
-      int neighborPreorderNumber = preorderNumbers[neighbor];
+      int? neighborPreorderNumber = preorderNumbers[neighbor];
       if (neighborPreorderNumber == null) {
         // If the preorder number of [neighbor] has not yet been assigned,
         // recursively search [neighbor];
@@ -46,7 +46,7 @@ List<List<T>> computeStrongComponents<T>(Graph<T> graph) {
         // * Repeatedly pop vertices from [candidates] until the top element of
         //   [candidates] has a preorder number less than or equal to the
         //   preorder number of [neighbor].
-        while (preorderNumbers[candidates.last] > neighborPreorderNumber) {
+        while (preorderNumbers[candidates.last]! > neighborPreorderNumber) {
           candidates.removeLast();
         }
       }
diff --git a/pkg/kernel/lib/verifier.dart b/pkg/kernel/lib/verifier.dart
index ee38bc366f8..6bfbf066c7b 100644
--- a/pkg/kernel/lib/verifier.dart
+++ b/pkg/kernel/lib/verifier.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.checks;
 
 import 'ast.dart';
diff --git a/pkg/kernel/lib/visitor.dart b/pkg/kernel/lib/visitor.dart
index a8e984a73c5..fefa9708c21 100644
--- a/pkg/kernel/lib/visitor.dart
+++ b/pkg/kernel/lib/visitor.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.ast.visitor;
 
 import 'dart:core' hide MapEntry;
diff --git a/pkg/kernel/lib/vm/constants_native_effects.dart b/pkg/kernel/lib/vm/constants_native_effects.dart
index 8bb1bac1f23..401504a2d65 100644
--- a/pkg/kernel/lib/vm/constants_native_effects.dart
+++ b/pkg/kernel/lib/vm/constants_native_effects.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library vm.constants_native_effects;
 
 import '../ast.dart';
diff --git a/pkg/kernel/pubspec.yaml b/pkg/kernel/pubspec.yaml
index 36092330e6a..09b5348f6b2 100644
--- a/pkg/kernel/pubspec.yaml
+++ b/pkg/kernel/pubspec.yaml
@@ -6,7 +6,7 @@ name: kernel
 publish_to: none
 
 environment:
-  sdk: '>=2.6.0 <3.0.0'
+  sdk: '>=2.12.0 <3.0.0'
 dependencies:
   meta:
     path: ../meta
diff --git a/pkg/kernel/test/ast_membench.dart b/pkg/kernel/test/ast_membench.dart
index dc50ccc1b73..baf824508a1 100644
--- a/pkg/kernel/test/ast_membench.dart
+++ b/pkg/kernel/test/ast_membench.dart
@@ -2,6 +2,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'dart:io';
 
diff --git a/pkg/kernel/test/binary/can_read_platform_test.dart b/pkg/kernel/test/binary/can_read_platform_test.dart
index 2b447bc405d..2c8d8278835 100644
--- a/pkg/kernel/test/binary/can_read_platform_test.dart
+++ b/pkg/kernel/test/binary/can_read_platform_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'package:kernel/binary/ast_from_binary.dart';
diff --git a/pkg/kernel/test/binary/component_mode_test.dart b/pkg/kernel/test/binary/component_mode_test.dart
index 982270db6d7..b03ea0ac68b 100644
--- a/pkg/kernel/test/binary/component_mode_test.dart
+++ b/pkg/kernel/test/binary/component_mode_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/binary/ast_from_binary.dart';
 
 import 'utils.dart';
diff --git a/pkg/kernel/test/binary/invalid_index_size.dart b/pkg/kernel/test/binary/invalid_index_size.dart
index 46f9bc45616..454ede63371 100644
--- a/pkg/kernel/test/binary/invalid_index_size.dart
+++ b/pkg/kernel/test/binary/invalid_index_size.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/binary/ast_from_binary.dart' show ParseError;
 
 import 'utils.dart';
diff --git a/pkg/kernel/test/binary/lazy_reading_test.dart b/pkg/kernel/test/binary/lazy_reading_test.dart
index 601cb4eb818..7edfda98099 100644
--- a/pkg/kernel/test/binary/lazy_reading_test.dart
+++ b/pkg/kernel/test/binary/lazy_reading_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/binary/ast_from_binary.dart';
 import 'package:kernel/src/tool/find_referenced_libraries.dart';
 import 'utils.dart';
diff --git a/pkg/kernel/test/binary/library_flags_test.dart b/pkg/kernel/test/binary/library_flags_test.dart
index 04630d75431..0f80d249177 100644
--- a/pkg/kernel/test/binary/library_flags_test.dart
+++ b/pkg/kernel/test/binary/library_flags_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'utils.dart';
 
 /// Test that library flags are serialized and read correctly.
diff --git a/pkg/kernel/test/binary/utils.dart b/pkg/kernel/test/binary/utils.dart
index 10059091eb9..4253db8a05b 100644
--- a/pkg/kernel/test/binary/utils.dart
+++ b/pkg/kernel/test/binary/utils.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io' show BytesBuilder;
 
 import 'package:kernel/binary/ast_to_binary.dart' show BinaryPrinter;
diff --git a/pkg/kernel/test/binary_bench.dart b/pkg/kernel/test/binary_bench.dart
index a30296a91d5..be0a34136cd 100644
--- a/pkg/kernel/test/binary_bench.dart
+++ b/pkg/kernel/test/binary_bench.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // This files contains methods for benchmarking Kernel binary serialization
 // and deserialization routines.
 
diff --git a/pkg/kernel/test/class_hierarchy_basic.dart b/pkg/kernel/test/class_hierarchy_basic.dart
index b2b93227393..1a9b34e77bb 100644
--- a/pkg/kernel/test/class_hierarchy_basic.dart
+++ b/pkg/kernel/test/class_hierarchy_basic.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 library kernel.class_hierarchy_basic;
 
 import 'package:kernel/class_hierarchy.dart';
diff --git a/pkg/kernel/test/class_hierarchy_bench.dart b/pkg/kernel/test/class_hierarchy_bench.dart
index 0026781ecf6..97d3dcdd123 100644
--- a/pkg/kernel/test/class_hierarchy_bench.dart
+++ b/pkg/kernel/test/class_hierarchy_bench.dart
@@ -2,6 +2,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
diff --git a/pkg/kernel/test/class_hierarchy_membench.dart b/pkg/kernel/test/class_hierarchy_membench.dart
index a8763fbd301..2c650481a20 100644
--- a/pkg/kernel/test/class_hierarchy_membench.dart
+++ b/pkg/kernel/test/class_hierarchy_membench.dart
@@ -2,6 +2,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
diff --git a/pkg/kernel/test/class_hierarchy_self_check.dart b/pkg/kernel/test/class_hierarchy_self_check.dart
index 7bb0462c47a..182a2b76aa7 100644
--- a/pkg/kernel/test/class_hierarchy_self_check.dart
+++ b/pkg/kernel/test/class_hierarchy_self_check.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
diff --git a/pkg/kernel/test/class_hierarchy_test.dart b/pkg/kernel/test/class_hierarchy_test.dart
index 8cfe61d5a44..841f5b919da 100644
--- a/pkg/kernel/test/class_hierarchy_test.dart
+++ b/pkg/kernel/test/class_hierarchy_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/minitest.dart";
 
 import "package:kernel/ast.dart";
diff --git a/pkg/kernel/test/class_hierarchy_test_disabled.dart b/pkg/kernel/test/class_hierarchy_test_disabled.dart
index d1cd156b229..5cba5d7c125 100644
--- a/pkg/kernel/test/class_hierarchy_test_disabled.dart
+++ b/pkg/kernel/test/class_hierarchy_test_disabled.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'package:test/test.dart';
 import 'class_hierarchy_self_check.dart';
diff --git a/pkg/kernel/test/convert_field_to_setter_getter.dart b/pkg/kernel/test/convert_field_to_setter_getter.dart
index d4497350e70..8cc17a4e5e5 100644
--- a/pkg/kernel/test/convert_field_to_setter_getter.dart
+++ b/pkg/kernel/test/convert_field_to_setter_getter.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/binary/ast_from_binary.dart';
 import 'package:kernel/binary/ast_to_binary.dart';
 import 'binary/utils.dart';
diff --git a/pkg/kernel/test/dart_type_equivalence_test.dart b/pkg/kernel/test/dart_type_equivalence_test.dart
index 462c637d5f6..aeb980ef631 100644
--- a/pkg/kernel/test/dart_type_equivalence_test.dart
+++ b/pkg/kernel/test/dart_type_equivalence_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/kernel/test/flatten_test.dart b/pkg/kernel/test/flatten_test.dart
index 69834455e3f..00c707a78db 100644
--- a/pkg/kernel/test/flatten_test.dart
+++ b/pkg/kernel/test/flatten_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/kernel/test/future_value_type_test.dart b/pkg/kernel/test/future_value_type_test.dart
index 8a7bfacd6f7..5eed73f07d1 100644
--- a/pkg/kernel/test/future_value_type_test.dart
+++ b/pkg/kernel/test/future_value_type_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/kernel/test/graph_test.dart b/pkg/kernel/test/graph_test.dart
index 8a84aaf109e..28668f6c7fa 100644
--- a/pkg/kernel/test/graph_test.dart
+++ b/pkg/kernel/test/graph_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
+
 library kernel.test.graph_test;
 
 import 'package:expect/expect.dart' show Expect;
diff --git a/pkg/kernel/test/heap_test.dart b/pkg/kernel/test/heap_test.dart
index 32b294eb688..95071ef5e6f 100644
--- a/pkg/kernel/test/heap_test.dart
+++ b/pkg/kernel/test/heap_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/src/heap.dart';
 import 'package:test/test.dart';
 
diff --git a/pkg/kernel/test/import_table_test.dart b/pkg/kernel/test/import_table_test.dart
index daef20e7ec2..62c10f06c37 100644
--- a/pkg/kernel/test/import_table_test.dart
+++ b/pkg/kernel/test/import_table_test.dart
@@ -1,3 +1,9 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 import 'package:kernel/import_table.dart';
 
 main() {
diff --git a/pkg/kernel/test/legacy_erasure_test.dart b/pkg/kernel/test/legacy_erasure_test.dart
index 0a0902b9ffe..f62eba0012e 100644
--- a/pkg/kernel/test/legacy_erasure_test.dart
+++ b/pkg/kernel/test/legacy_erasure_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/kernel/test/load_concat_dill_keeps_source_test.dart b/pkg/kernel/test/load_concat_dill_keeps_source_test.dart
index a888455bb07..60af31f29cf 100644
--- a/pkg/kernel/test/load_concat_dill_keeps_source_test.dart
+++ b/pkg/kernel/test/load_concat_dill_keeps_source_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // Test that 79cc54e51924cd5a6bdc2bd1771f2d0ee7af8899 works as intended.
 
 import 'dart:convert';
diff --git a/pkg/kernel/test/metadata_test.dart b/pkg/kernel/test/metadata_test.dart
index 5b362f157c2..377ad22fe5c 100644
--- a/pkg/kernel/test/metadata_test.dart
+++ b/pkg/kernel/test/metadata_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:convert';
 import 'dart:io';
 
diff --git a/pkg/kernel/test/nnbd_top_merge_test.dart b/pkg/kernel/test/nnbd_top_merge_test.dart
index bd82a7ec8de..12968899bce 100644
--- a/pkg/kernel/test/nnbd_top_merge_test.dart
+++ b/pkg/kernel/test/nnbd_top_merge_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/kernel/test/non_null_test.dart b/pkg/kernel/test/non_null_test.dart
index d9a04aa4ffb..c4f257065e6 100644
--- a/pkg/kernel/test/non_null_test.dart
+++ b/pkg/kernel/test/non_null_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/kernel/test/norm_test.dart b/pkg/kernel/test/norm_test.dart
index c287025d9eb..5fe8429b33d 100644
--- a/pkg/kernel/test/norm_test.dart
+++ b/pkg/kernel/test/norm_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import "package:expect/expect.dart" show Expect;
 
 import 'package:kernel/ast.dart' hide MapEntry;
diff --git a/pkg/kernel/test/regression_37753_test.dart b/pkg/kernel/test/regression_37753_test.dart
index c5448acc201..f653337ac13 100644
--- a/pkg/kernel/test/regression_37753_test.dart
+++ b/pkg/kernel/test/regression_37753_test.dart
@@ -1,7 +1,9 @@
 // Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
-//
+
+// @dart = 2.9
+
 // Regression test for https://github.com/dart-lang/sdk/issues/37753.
 // A missing piece of transform logic caused nested sync* set to a variable
 // to not get transformed, which would either fail an assert or crash.
diff --git a/pkg/kernel/test/regression_40662_test.dart b/pkg/kernel/test/regression_40662_test.dart
index 140d34cb7c6..77eaf47bb60 100644
--- a/pkg/kernel/test/regression_40662_test.dart
+++ b/pkg/kernel/test/regression_40662_test.dart
@@ -1,7 +1,9 @@
 // Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
-//
+
+// @dart = 2.9
+
 // Regression test for https://github.com/dart-lang/sdk/issues/40662.
 
 import "package:expect/expect.dart" show Expect;
diff --git a/pkg/kernel/test/relink_test.dart b/pkg/kernel/test/relink_test.dart
index 37b0f7d8bbc..b50be8e15aa 100644
--- a/pkg/kernel/test/relink_test.dart
+++ b/pkg/kernel/test/relink_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/binary/ast_from_binary.dart';
 import 'package:kernel/binary/ast_to_binary.dart';
 import 'package:kernel/src/tool/find_referenced_libraries.dart';
diff --git a/pkg/kernel/test/round_trip.dart b/pkg/kernel/test/round_trip.dart
index 271293a7470..3766db04e9d 100644
--- a/pkg/kernel/test/round_trip.dart
+++ b/pkg/kernel/test/round_trip.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.round_trip;
 
 import 'dart:io';
diff --git a/pkg/kernel/test/round_trip_self_check.dart b/pkg/kernel/test/round_trip_self_check.dart
index a299f265860..da2e0e11085 100644
--- a/pkg/kernel/test/round_trip_self_check.dart
+++ b/pkg/kernel/test/round_trip_self_check.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.round_trip_test;
 
 import 'self_check_util.dart';
diff --git a/pkg/kernel/test/self_check_util.dart b/pkg/kernel/test/self_check_util.dart
index 1ebdd39c304..e742142ebe8 100644
--- a/pkg/kernel/test/self_check_util.dart
+++ b/pkg/kernel/test/self_check_util.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:async';
 
 import 'package:kernel/src/tool/batch_util.dart';
diff --git a/pkg/kernel/test/serialize_bench.dart b/pkg/kernel/test/serialize_bench.dart
index 3957ddb7072..0a413f963a5 100644
--- a/pkg/kernel/test/serialize_bench.dart
+++ b/pkg/kernel/test/serialize_bench.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'dart:io';
 
diff --git a/pkg/kernel/test/text_serializer_from_kernel_nodes_test.dart b/pkg/kernel/test/text_serializer_from_kernel_nodes_test.dart
index 00d19730e83..41daa5683b6 100644
--- a/pkg/kernel/test/text_serializer_from_kernel_nodes_test.dart
+++ b/pkg/kernel/test/text_serializer_from_kernel_nodes_test.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.text_serializer_from_kernel_nodes_test;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/kernel/test/text_serializer_test.dart b/pkg/kernel/test/text_serializer_test.dart
index 521aca4e532..e04d07ef9a0 100644
--- a/pkg/kernel/test/text_serializer_test.dart
+++ b/pkg/kernel/test/text_serializer_test.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.text_serializer_test;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/kernel/test/type_hashcode_quality.dart b/pkg/kernel/test/type_hashcode_quality.dart
index d90183a62b6..f33541e74f7 100644
--- a/pkg/kernel/test/type_hashcode_quality.dart
+++ b/pkg/kernel/test/type_hashcode_quality.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'dart:io';
 
diff --git a/pkg/kernel/test/type_hashcode_test.dart b/pkg/kernel/test/type_hashcode_test.dart
index b988507249b..9a16a72a5b7 100644
--- a/pkg/kernel/test/type_hashcode_test.dart
+++ b/pkg/kernel/test/type_hashcode_test.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'type_parser.dart';
 import 'package:test/test.dart';
diff --git a/pkg/kernel/test/type_parser.dart b/pkg/kernel/test/type_parser.dart
index 62b5a0fff17..f3928210ea4 100644
--- a/pkg/kernel/test/type_parser.dart
+++ b/pkg/kernel/test/type_parser.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 // A very simple parser for a subset of DartTypes for use in testing type
 // algebra.
 library kernel.test.type_parser;
diff --git a/pkg/kernel/test/type_parser_test.dart b/pkg/kernel/test/type_parser_test.dart
index 5a2e651be54..e015daa87f4 100644
--- a/pkg/kernel/test/type_parser_test.dart
+++ b/pkg/kernel/test/type_parser_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:expect/expect.dart' show Expect;
 
 import 'package:kernel/testing/type_parser.dart';
diff --git a/pkg/kernel/test/type_substitute_bounds_test.dart b/pkg/kernel/test/type_substitute_bounds_test.dart
index 7fb556ca880..c92d17a2a6d 100644
--- a/pkg/kernel/test/type_substitute_bounds_test.dart
+++ b/pkg/kernel/test/type_substitute_bounds_test.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.type_substitute_bounds_test;
 
 import 'package:kernel/kernel.dart';
diff --git a/pkg/kernel/test/type_substitution_identity_test.dart b/pkg/kernel/test/type_substitution_identity_test.dart
index d8fabbd1317..99d7fe7e425 100644
--- a/pkg/kernel/test/type_substitution_identity_test.dart
+++ b/pkg/kernel/test/type_substitution_identity_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'package:kernel/type_algebra.dart';
 import 'type_parser.dart';
diff --git a/pkg/kernel/test/typedef_unalias_test.dart b/pkg/kernel/test/typedef_unalias_test.dart
index 4f70f0463fb..18be6295bca 100644
--- a/pkg/kernel/test/typedef_unalias_test.dart
+++ b/pkg/kernel/test/typedef_unalias_test.dart
@@ -1,6 +1,9 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
+// @dart = 2.9
+
 library kernel.typedef_unalias_test;
 
 import 'package:kernel/ast.dart';
diff --git a/pkg/kernel/test/verify_bench.dart b/pkg/kernel/test/verify_bench.dart
index c5fc42e16f8..6326b894c84 100644
--- a/pkg/kernel/test/verify_bench.dart
+++ b/pkg/kernel/test/verify_bench.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 import 'package:kernel/kernel.dart';
diff --git a/pkg/kernel/test/verify_self_check.dart b/pkg/kernel/test/verify_self_check.dart
index bc9b184d5c1..bb2cd02c5a2 100644
--- a/pkg/kernel/test/verify_self_check.dart
+++ b/pkg/kernel/test/verify_self_check.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/kernel.dart';
 import 'package:kernel/verifier.dart';
 
diff --git a/pkg/kernel/test/verify_test.dart b/pkg/kernel/test/verify_test.dart
index 5d3f20d9b49..7b6a238d82c 100644
--- a/pkg/kernel/test/verify_test.dart
+++ b/pkg/kernel/test/verify_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'package:kernel/ast.dart';
 import 'package:kernel/text/ast_to_text.dart';
 import 'package:kernel/verifier.dart';
diff --git a/pkg/kernel/tool/smoke_test_quick.dart b/pkg/kernel/tool/smoke_test_quick.dart
index b5a0b9a3053..6ca6e19bf35 100644
--- a/pkg/kernel/tool/smoke_test_quick.dart
+++ b/pkg/kernel/tool/smoke_test_quick.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 import 'dart:io';
 
 final String repoDir = _computeRepoDir();