diff --git a/pkg/dev_compiler/bin/dartdevc.dart b/pkg/dev_compiler/bin/dartdevc.dart
index baf9c9a3659..87da5bb8690 100755
--- a/pkg/dev_compiler/bin/dartdevc.dart
+++ b/pkg/dev_compiler/bin/dartdevc.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
+
 /// Command line entry point for Dart Development Compiler (dartdevc), used to
 /// compile a collection of dart libraries into a single JS module
 
diff --git a/pkg/dev_compiler/lib/dev_compiler.dart b/pkg/dev_compiler/lib/dev_compiler.dart
index ca0a8bdbf27..899fd4fd3b9 100644
--- a/pkg/dev_compiler/lib/dev_compiler.dart
+++ b/pkg/dev_compiler/lib/dev_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
+
 // The dev_compiler does not have a publishable public API, instead this is
 // intended for other consumers within the Dart SDK.
 export 'src/compiler/module_builder.dart' show ModuleFormat, parseModuleFormat;
diff --git a/pkg/dev_compiler/lib/src/compiler/js_metalet.dart b/pkg/dev_compiler/lib/src/compiler/js_metalet.dart
index 8941bb0286e..d9ff9c17052 100644
--- a/pkg/dev_compiler/lib/src/compiler/js_metalet.dart
+++ b/pkg/dev_compiler/lib/src/compiler/js_metalet.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // TODO(jmesserly): import from its own package
 import '../js_ast/js_ast.dart';
 import 'js_names.dart' show TemporaryId;
diff --git a/pkg/dev_compiler/lib/src/compiler/js_names.dart b/pkg/dev_compiler/lib/src/compiler/js_names.dart
index 647f6fb8069..7d3ff1e8df4 100644
--- a/pkg/dev_compiler/lib/src/compiler/js_names.dart
+++ b/pkg/dev_compiler/lib/src/compiler/js_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
+
 import 'dart:collection';
 
 import '../js_ast/js_ast.dart';
diff --git a/pkg/dev_compiler/lib/src/compiler/js_typerep.dart b/pkg/dev_compiler/lib/src/compiler/js_typerep.dart
index f5e355b3c1a..c1291a3c369 100644
--- a/pkg/dev_compiler/lib/src/compiler/js_typerep.dart
+++ b/pkg/dev_compiler/lib/src/compiler/js_typerep.dart
@@ -1,4 +1,7 @@
 /// An abstraction of the JS types
+
+// @dart = 2.9
+
 abstract class JSType {
   const JSType();
 
diff --git a/pkg/dev_compiler/lib/src/compiler/js_utils.dart b/pkg/dev_compiler/lib/src/compiler/js_utils.dart
index 8b936e742c5..f6feb7d243b 100644
--- a/pkg/dev_compiler/lib/src/compiler/js_utils.dart
+++ b/pkg/dev_compiler/lib/src/compiler/js_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 '../js_ast/js_ast.dart';
 
 /// Simplify `(args) => (() => { ... })()` to `(args) => { ... }`.
diff --git a/pkg/dev_compiler/lib/src/compiler/module_builder.dart b/pkg/dev_compiler/lib/src/compiler/module_builder.dart
index dd1cc909589..847185dc6cd 100644
--- a/pkg/dev_compiler/lib/src/compiler/module_builder.dart
+++ b/pkg/dev_compiler/lib/src/compiler/module_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:args/args.dart' show ArgParser, ArgResults;
 import 'package:dev_compiler/src/compiler/shared_compiler.dart';
 import 'package:path/path.dart' as p;
diff --git a/pkg/dev_compiler/lib/src/compiler/shared_command.dart b/pkg/dev_compiler/lib/src/compiler/shared_command.dart
index 358f238caad..cf67f914449 100644
--- a/pkg/dev_compiler/lib/src/compiler/shared_command.dart
+++ b/pkg/dev_compiler/lib/src/compiler/shared_command.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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/dev_compiler/lib/src/compiler/shared_compiler.dart b/pkg/dev_compiler/lib/src/compiler/shared_compiler.dart
index 542552a8af8..0269dd306de 100644
--- a/pkg/dev_compiler/lib/src/compiler/shared_compiler.dart
+++ b/pkg/dev_compiler/lib/src/compiler/shared_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
+
 import 'dart:collection';
 import 'package:meta/meta.dart';
 
diff --git a/pkg/dev_compiler/lib/src/js_ast/builder.dart b/pkg/dev_compiler/lib/src/js_ast/builder.dart
index cf9c5c245f3..ed3c8e396a2 100644
--- a/pkg/dev_compiler/lib/src/js_ast/builder.dart
+++ b/pkg/dev_compiler/lib/src/js_ast/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
+
 // ignore_for_file: slash_for_doc_comments, unnecessary_new
 // ignore_for_file: always_declare_return_types, prefer_single_quotes
 // ignore_for_file: prefer_collection_literals, omit_local_variable_types
diff --git a/pkg/dev_compiler/lib/src/js_ast/characters.dart b/pkg/dev_compiler/lib/src/js_ast/characters.dart
index e3382c3d3bf..1ce0d4824e2 100644
--- a/pkg/dev_compiler/lib/src/js_ast/characters.dart
+++ b/pkg/dev_compiler/lib/src/js_ast/characters.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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 int $EOF = 0;
 const int $STX = 2;
 const int $BS = 8;
diff --git a/pkg/dev_compiler/lib/src/js_ast/js_ast.dart b/pkg/dev_compiler/lib/src/js_ast/js_ast.dart
index 61402257084..373547e22fd 100644
--- a/pkg/dev_compiler/lib/src/js_ast/js_ast.dart
+++ b/pkg/dev_compiler/lib/src/js_ast/js_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
+
 // ignore_for_file: directives_ordering
 
 library js_ast;
diff --git a/pkg/dev_compiler/lib/src/js_ast/nodes.dart b/pkg/dev_compiler/lib/src/js_ast/nodes.dart
index 14db1729d51..137bfd46e14 100644
--- a/pkg/dev_compiler/lib/src/js_ast/nodes.dart
+++ b/pkg/dev_compiler/lib/src/js_ast/nodes.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // ignore_for_file: slash_for_doc_comments, prefer_single_quotes
 // ignore_for_file: always_declare_return_types, prefer_final_fields
 // ignore_for_file: always_require_non_null_named_parameters
diff --git a/pkg/dev_compiler/lib/src/js_ast/precedence.dart b/pkg/dev_compiler/lib/src/js_ast/precedence.dart
index f149dc29c35..50f69edc216 100644
--- a/pkg/dev_compiler/lib/src/js_ast/precedence.dart
+++ b/pkg/dev_compiler/lib/src/js_ast/precedence.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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 EXPRESSION = 0;
 // TODO(nshahan) No longer used for the spread operator.
 // All precedence levels need to be updated to be more accurate.
diff --git a/pkg/dev_compiler/lib/src/js_ast/printer.dart b/pkg/dev_compiler/lib/src/js_ast/printer.dart
index ccf327513f4..d62126b8b48 100644
--- a/pkg/dev_compiler/lib/src/js_ast/printer.dart
+++ b/pkg/dev_compiler/lib/src/js_ast/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
+
 // ignore_for_file: slash_for_doc_comments, unnecessary_const
 // ignore_for_file: always_declare_return_types, prefer_single_quotes
 // ignore_for_file: prefer_collection_literals, omit_local_variable_types
diff --git a/pkg/dev_compiler/lib/src/js_ast/source_map_printer.dart b/pkg/dev_compiler/lib/src/js_ast/source_map_printer.dart
index 6acee34a017..e770e99e0bb 100644
--- a/pkg/dev_compiler/lib/src/js_ast/source_map_printer.dart
+++ b/pkg/dev_compiler/lib/src/js_ast/source_map_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
+
 // ignore_for_file: always_declare_return_types, omit_local_variable_types
 
 import 'package:source_maps/source_maps.dart' hide Printer;
diff --git a/pkg/dev_compiler/lib/src/js_ast/template.dart b/pkg/dev_compiler/lib/src/js_ast/template.dart
index 73d840b766f..4cdad6d838a 100644
--- a/pkg/dev_compiler/lib/src/js_ast/template.dart
+++ b/pkg/dev_compiler/lib/src/js_ast/template.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 // ignore_for_file: slash_for_doc_comments, omit_local_variable_types
 // ignore_for_file: always_declare_return_types, prefer_collection_literals
 // ignore_for_file: prefer_single_quotes, prefer_generic_function_type_aliases
diff --git a/pkg/dev_compiler/lib/src/kernel/command.dart b/pkg/dev_compiler/lib/src/kernel/command.dart
index 6598642fa37..65404979c9d 100644
--- a/pkg/dev_compiler/lib/src/kernel/command.dart
+++ b/pkg/dev_compiler/lib/src/kernel/command.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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' show json;
 import 'dart:io';
diff --git a/pkg/dev_compiler/lib/src/kernel/compiler.dart b/pkg/dev_compiler/lib/src/kernel/compiler.dart
index 153240b1864..d54ecef6368 100644
--- a/pkg/dev_compiler/lib/src/kernel/compiler.dart
+++ b/pkg/dev_compiler/lib/src/kernel/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
+
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:math' show max, min;
diff --git a/pkg/dev_compiler/lib/src/kernel/constants.dart b/pkg/dev_compiler/lib/src/kernel/constants.dart
index 54005776377..d5b538f4844 100644
--- a/pkg/dev_compiler/lib/src/kernel/constants.dart
+++ b/pkg/dev_compiler/lib/src/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
+
 import 'package:kernel/kernel.dart';
 import 'package:kernel/target/targets.dart';
 
diff --git a/pkg/dev_compiler/lib/src/kernel/expression_compiler.dart b/pkg/dev_compiler/lib/src/kernel/expression_compiler.dart
index e57a2fb97e3..3af0ea9b3e4 100644
--- a/pkg/dev_compiler/lib/src/kernel/expression_compiler.dart
+++ b/pkg/dev_compiler/lib/src/kernel/expression_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
+
 import 'dart:async';
 
 import 'package:_fe_analyzer_shared/src/messages/diagnostic_message.dart'
diff --git a/pkg/dev_compiler/lib/src/kernel/expression_compiler_worker.dart b/pkg/dev_compiler/lib/src/kernel/expression_compiler_worker.dart
index a1b995c3c67..ec08c67fcfd 100644
--- a/pkg/dev_compiler/lib/src/kernel/expression_compiler_worker.dart
+++ b/pkg/dev_compiler/lib/src/kernel/expression_compiler_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
+
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
diff --git a/pkg/dev_compiler/lib/src/kernel/js_interop.dart b/pkg/dev_compiler/lib/src/kernel/js_interop.dart
index 9c01d89498c..ae20b094b82 100644
--- a/pkg/dev_compiler/lib/src/kernel/js_interop.dart
+++ b/pkg/dev_compiler/lib/src/kernel/js_interop.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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 'kernel_helpers.dart';
 
diff --git a/pkg/dev_compiler/lib/src/kernel/js_typerep.dart b/pkg/dev_compiler/lib/src/kernel/js_typerep.dart
index 4c4dd952f22..6206452d62e 100644
--- a/pkg/dev_compiler/lib/src/kernel/js_typerep.dart
+++ b/pkg/dev_compiler/lib/src/kernel/js_typerep.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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/core_types.dart';
 import 'package:kernel/kernel.dart';
diff --git a/pkg/dev_compiler/lib/src/kernel/kernel_helpers.dart b/pkg/dev_compiler/lib/src/kernel/kernel_helpers.dart
index a2c50dd9c29..eb1c8b11ca6 100644
--- a/pkg/dev_compiler/lib/src/kernel/kernel_helpers.dart
+++ b/pkg/dev_compiler/lib/src/kernel/kernel_helpers.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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';
 import 'package:front_end/src/api_unstable/ddc.dart';
 import 'package:kernel/core_types.dart';
diff --git a/pkg/dev_compiler/lib/src/kernel/module_metadata.dart b/pkg/dev_compiler/lib/src/kernel/module_metadata.dart
index 72868432862..29496ff40ba 100644
--- a/pkg/dev_compiler/lib/src/kernel/module_metadata.dart
+++ b/pkg/dev_compiler/lib/src/kernel/module_metadata.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Module metadata format version
 ///
 /// Module reader always creates the current version but is able to read
diff --git a/pkg/dev_compiler/lib/src/kernel/native_types.dart b/pkg/dev_compiler/lib/src/kernel/native_types.dart
index bf340b1703a..2aa3164330a 100644
--- a/pkg/dev_compiler/lib/src/kernel/native_types.dart
+++ b/pkg/dev_compiler/lib/src/kernel/native_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 'dart:collection';
 import 'package:kernel/core_types.dart';
 import 'package:kernel/kernel.dart';
diff --git a/pkg/dev_compiler/lib/src/kernel/nullable_inference.dart b/pkg/dev_compiler/lib/src/kernel/nullable_inference.dart
index 32c687fe6b6..5269391ea7a 100644
--- a/pkg/dev_compiler/lib/src/kernel/nullable_inference.dart
+++ b/pkg/dev_compiler/lib/src/kernel/nullable_inference.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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';
 import 'package:kernel/core_types.dart';
 import 'package:kernel/kernel.dart';
diff --git a/pkg/dev_compiler/lib/src/kernel/property_model.dart b/pkg/dev_compiler/lib/src/kernel/property_model.dart
index cee7fb98c0a..ea0eade596d 100644
--- a/pkg/dev_compiler/lib/src/kernel/property_model.dart
+++ b/pkg/dev_compiler/lib/src/kernel/property_model.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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' show HashMap, HashSet, Queue;
 
 import 'package:kernel/core_types.dart';
diff --git a/pkg/dev_compiler/lib/src/kernel/target.dart b/pkg/dev_compiler/lib/src/kernel/target.dart
index 2982b8de22e..3e6eea6c611 100644
--- a/pkg/dev_compiler/lib/src/kernel/target.dart
+++ b/pkg/dev_compiler/lib/src/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
+
 import 'dart:collection';
 import 'dart:core' hide MapEntry;
 
diff --git a/pkg/dev_compiler/lib/src/kernel/type_table.dart b/pkg/dev_compiler/lib/src/kernel/type_table.dart
index 8f8a002b395..179a59be352 100644
--- a/pkg/dev_compiler/lib/src/kernel/type_table.dart
+++ b/pkg/dev_compiler/lib/src/kernel/type_table.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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 '../compiler/js_names.dart' as js_ast;
diff --git a/pkg/dev_compiler/test/expression_compiler/expression_compiler_test.dart b/pkg/dev_compiler/test/expression_compiler/expression_compiler_test.dart
index 4e4068e6ba6..fb971e78ac7 100644
--- a/pkg/dev_compiler/test/expression_compiler/expression_compiler_test.dart
+++ b/pkg/dev_compiler/test/expression_compiler/expression_compiler_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:cli_util/cli_util.dart';
diff --git a/pkg/dev_compiler/test/expression_compiler/expression_compiler_worker_test.dart b/pkg/dev_compiler/test/expression_compiler/expression_compiler_worker_test.dart
index 25474d0ee67..1e649aa9afb 100644
--- a/pkg/dev_compiler/test/expression_compiler/expression_compiler_worker_test.dart
+++ b/pkg/dev_compiler/test/expression_compiler/expression_compiler_worker_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:async';
 import 'dart:convert';
 import 'dart:io' show Directory, File, Platform, Process, stderr, stdout;
diff --git a/pkg/dev_compiler/test/js/builder_test.dart b/pkg/dev_compiler/test/js/builder_test.dart
index 9a1ac180226..acfb55c6f41 100644
--- a/pkg/dev_compiler/test/js/builder_test.dart
+++ b/pkg/dev_compiler/test/js/builder_test.dart
@@ -1,3 +1,5 @@
+// @dart = 2.9
+
 import 'package:dev_compiler/src/js_ast/js_ast.dart';
 import 'package:test/test.dart';
 
diff --git a/pkg/dev_compiler/test/modular_suite.dart b/pkg/dev_compiler/test/modular_suite.dart
index 3d47edc45b5..79181e5274c 100644
--- a/pkg/dev_compiler/test/modular_suite.dart
+++ b/pkg/dev_compiler/test/modular_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
+
 /// Test the modular compilation pipeline of ddc.
 ///
 /// This is a shell that runs multiple tests, one per folder under `data/`.
diff --git a/pkg/dev_compiler/test/modular_suite_nnbd.dart b/pkg/dev_compiler/test/modular_suite_nnbd.dart
index 66774655e90..aaf92a3968c 100644
--- a/pkg/dev_compiler/test/modular_suite_nnbd.dart
+++ b/pkg/dev_compiler/test/modular_suite_nnbd.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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 the modular compilation pipeline of ddc.
 ///
 /// This is a shell that runs multiple tests, one per folder under `data/`.
diff --git a/pkg/dev_compiler/test/module_metadata_test.dart b/pkg/dev_compiler/test/module_metadata_test.dart
index 93f9d7ba147..2751e944e27 100644
--- a/pkg/dev_compiler/test/module_metadata_test.dart
+++ b/pkg/dev_compiler/test/module_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/dev_compiler/test/nullable_inference_test.dart b/pkg/dev_compiler/test/nullable_inference_test.dart
index bbaefa10881..4c9d9a2a5a1 100644
--- a/pkg/dev_compiler/test/nullable_inference_test.dart
+++ b/pkg/dev_compiler/test/nullable_inference_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:async';
 import 'dart:io';
 import 'package:front_end/src/api_unstable/ddc.dart' as fe;
diff --git a/pkg/dev_compiler/test/sdk_source_map_test.dart b/pkg/dev_compiler/test/sdk_source_map_test.dart
index 799c1b152c3..84e603846bb 100644
--- a/pkg/dev_compiler/test/sdk_source_map_test.dart
+++ b/pkg/dev_compiler/test/sdk_source_map_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:expect/expect.dart';
diff --git a/pkg/dev_compiler/test/sourcemap/common.dart b/pkg/dev_compiler/test/sourcemap/common.dart
index d28dc9e8a92..3e9564d59c3 100644
--- a/pkg/dev_compiler/test/sourcemap/common.dart
+++ b/pkg/dev_compiler/test/sourcemap/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
+
 import 'dart:async' show Future;
 
 import 'dart:io';
diff --git a/pkg/dev_compiler/test/sourcemap/ddc_common.dart b/pkg/dev_compiler/test/sourcemap/ddc_common.dart
index 37b78f752c5..b090d7674bc 100644
--- a/pkg/dev_compiler/test/sourcemap/ddc_common.dart
+++ b/pkg/dev_compiler/test/sourcemap/ddc_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
+
 library dev_compiler.test.sourcemap.ddc_common;
 
 import 'dart:io';
diff --git a/pkg/dev_compiler/test/sourcemap/sourcemaps_ddk_suite.dart b/pkg/dev_compiler/test/sourcemap/sourcemaps_ddk_suite.dart
index 9a07e3221ed..0a88bc09cfd 100644
--- a/pkg/dev_compiler/test/sourcemap/sourcemaps_ddk_suite.dart
+++ b/pkg/dev_compiler/test/sourcemap/sourcemaps_ddk_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:async';
 import 'dart:io';
 
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_ddk_suite.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_ddk_suite.dart
index d7cb5710a75..e93433a7e3e 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_ddk_suite.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_ddk_suite.dart
@@ -1,3 +1,5 @@
+// @dart = 2.9
+
 import 'package:front_end/src/api_unstable/ddc.dart' as fe;
 import 'package:testing/testing.dart';
 
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/null_instance_field.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/null_instance_field.dart
index 2a36f88ca3c..d0ec2378f98 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/null_instance_field.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/null_instance_field.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*1:main*/ test(Class());
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/null_interceptor_field.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/null_interceptor_field.dart
index d43b10b0207..a7bace6207f 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/null_interceptor_field.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/null_interceptor_field.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 class MyType {
   int get length => 3; // ensures we build an interceptor for `.length`
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/rethrow.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/rethrow.dart
index 908eb8f90bc..3bff9923235 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/rethrow.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/rethrow.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*1:main*/ test();
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_async.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_async.dart
index e1e10f8f9c5..c2357bd8154 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_async.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_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
+
 void main() {
   /*1:main*/ test();
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_awaited_async.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_awaited_async.dart
index 0458fc941db..740a9e4b865 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_awaited_async.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_awaited_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
+
 void main() {
   /*1:main*/ test1();
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_constructor.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_constructor.dart
index f57db8f1ff3..b610f05dac1 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_constructor.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_constructor.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   // ignore: UNUSED_LOCAL_VARIABLE
   var /*ddc.1:main*/ c = /*ddk.1:main*/ Class();
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_constructor_from_async.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_constructor_from_async.dart
index 37467ae3102..62f002db849 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_constructor_from_async.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_constructor_from_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
+
 void main() {
   // This call is no longer on the stack when the error is thrown.
   /*1:main*/ test();
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_instance_method.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_instance_method.dart
index 84dac4e3619..ecdfe70dd68 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_instance_method.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_instance_method.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   var c = Class();
   c. /*1:main*/ test();
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_main.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_main.dart
index c7043fea3dd..854840383fd 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_main.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_main.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*1:main*/ throw '>ExceptionMarker<';
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_static_method.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_static_method.dart
index e0b974ce2e3..cdd06f460f4 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_static_method.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_static_method.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*ddc.1:main*/ Class. /*ddk.1:main*/ test();
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_top_level_method.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_top_level_method.dart
index 799c9c04cc1..125bc2d063c 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_top_level_method.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_top_level_method.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*1:main*/ test();
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_top_level_method_from_async.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_top_level_method_from_async.dart
index 06ec99f54ac..5dd30d161ac 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_top_level_method_from_async.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_top_level_method_from_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
+
 void main() {
   /*1:main*/ test1();
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_try_catch.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_try_catch.dart
index d02b31bda10..3c2bd99258f 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_try_catch.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_try_catch.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*1:main*/ test();
 }
diff --git a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_try_finally.dart b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_try_finally.dart
index 211f9ed175d..b92875b3d74 100644
--- a/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_try_finally.dart
+++ b/pkg/dev_compiler/test/sourcemap/stacktrace_testfiles/throw_in_try_finally.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*1:main*/ test();
 }
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/breakpoint_on_function_line_breaks_in_body.dart b/pkg/dev_compiler/test/sourcemap/testfiles/breakpoint_on_function_line_breaks_in_body.dart
index b38f08212d5..0748c25af56 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/breakpoint_on_function_line_breaks_in_body.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/breakpoint_on_function_line_breaks_in_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
+
 void main() {
   foo();
 }
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/call_on_field_in_class.dart b/pkg/dev_compiler/test/sourcemap/testfiles/call_on_field_in_class.dart
index 86d5250d368..51c0dcc6765 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/call_on_field_in_class.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/call_on_field_in_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
+
 void main() {
   /* bl */ var foo = /*sl:1*/ Foo();
   foo.foo = foo. /*sl:2*/ fooMethod;
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/hello_async.dart b/pkg/dev_compiler/test/sourcemap/testfiles/hello_async.dart
index 62fba8c4834..11023f474be 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/hello_async.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/hello_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
+
 void main() {
   /*bl*/
   /*s:1*/ foo();
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/hello_call.dart b/pkg/dev_compiler/test/sourcemap/testfiles/hello_call.dart
index 1f28925cbbb..6f9398189af 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/hello_call.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/hello_call.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*bl*/
   /*s:1*/ foo();
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/hello_class_call.dart b/pkg/dev_compiler/test/sourcemap/testfiles/hello_class_call.dart
index 05bdd910fbf..a1cc9fd24cf 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/hello_class_call.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/hello_class_call.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*bl*/
   var foo = Foo();
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/hello_sane_column_on_print_return_value.dart b/pkg/dev_compiler/test/sourcemap/testfiles/hello_sane_column_on_print_return_value.dart
index 2f1663c97f5..54b020d0526 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/hello_sane_column_on_print_return_value.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/hello_sane_column_on_print_return_value.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*bc:3*/ print(/*bc:1*/ foo());
 }
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/hello_world.dart b/pkg/dev_compiler/test/sourcemap/testfiles/hello_world.dart
index e8181f7bf65..a034e08408f 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/hello_world.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/hello_world.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /*nb*/ // no break on empty line
   /*bl*/ print('Hello, World!');
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/method_call_with_named_parameters.dart b/pkg/dev_compiler/test/sourcemap/testfiles/method_call_with_named_parameters.dart
index 2ea7844b08f..cbf1689b0b3 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/method_call_with_named_parameters.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/method_call_with_named_parameters.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   foo(/*bc:1*/ bar(), baz: /*bc:2*/ baz());
   /*nbb:0:4*/
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/method_call_with_named_parameters_no_given.dart b/pkg/dev_compiler/test/sourcemap/testfiles/method_call_with_named_parameters_no_given.dart
index 4f5ee7d06d5..a47263dabc8 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/method_call_with_named_parameters_no_given.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/method_call_with_named_parameters_no_given.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   foo(/*bc:1*/ bar());
   /*nbb:0:3*/
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assert.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assert.dart
index eab2e718dce..478deefa969 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assert.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assert.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 void main() {
   assert(/*bc:1*/ foo());
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assign_call_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assign_call_test.dart
index b46fd9a1cc4..5da999c0665 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assign_call_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assign_call_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
+
 /*Debugger:stepOver*/
 void main() {
   /*nb*/ int a;
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assign_int_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assign_int_test.dart
index 7a80ef38895..d73151f8537 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assign_int_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_assign_int_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
+
 /*Debugger:stepOver*/
 void main() {
   /*nb*/ int a;
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_catch_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_catch_test.dart
index 705a73f4ba4..93b9271f61a 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_catch_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_catch_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
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_for_each_loop_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_for_each_loop_test.dart
index 20c74c10e84..d9a8a770497 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_for_each_loop_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_for_each_loop_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
+
 /*Debugger:stepOver*/
 void main() {
   /*bl*/ /*sl:1*/ var data = [1, 2, 3];
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_for_loop_with_break_and_continue_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_for_loop_with_break_and_continue_test.dart
index a3e61485fba..962f8fc6246 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_for_loop_with_break_and_continue_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_for_loop_with_break_and_continue_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
+
 /*Debugger:stepOver*/
 void main() {
   /*bl*/ /*sl:1*/ var count = 0;
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_is_and_as_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_is_and_as_test.dart
index 93c9cde3df7..d984c0d968f 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_is_and_as_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_is_and_as_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
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_map_creation.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_map_creation.dart
index 8d38e837453..53eb14d04d9 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_map_creation.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_map_creation.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_multi_catch_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_multi_catch_test.dart
index e2990e96666..57e1ce9aa7f 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_multi_catch_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_multi_catch_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
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_on_super_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_on_super_test.dart
index 4bdda3d59b1..bfd9266ceb8 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_on_super_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_on_super_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
+
 /*Debugger:stepOver*/
 
 class Class2 {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_on_this_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_on_this_test.dart
index 30d90f519a6..7fc64b2ba82 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_on_this_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_on_this_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
+
 /*Debugger:stepOver*/
 
 class Class2 {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_test.dart
index 3171aba5511..9351447bea0 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_operator_bracket_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
+
 /*Debugger:stepOver*/
 
 class Class2 {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_static_set.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_static_set.dart
index 7bdd6e40439..e63b7fff38f 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_static_set.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_static_set.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 
 var bar = 0;
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_string_concatenation.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_string_concatenation.dart
index a27ac2f55a4..02d4137c4f0 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_string_concatenation.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_string_concatenation.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_string_plus.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_string_plus.dart
index 3025bf2e6a5..f395f55f840 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_string_plus.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_string_plus.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_throw.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_throw.dart
index d62bd947206..bc00462c6e4 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_throw.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_throw.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_variable_set.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_variable_set.dart
index 54e362bfd7a..cce899b81bb 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_variable_set.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_variable_set.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_yield.dart b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_yield.dart
index c141ab51f38..62694a2c774 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/next_through_yield.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/next_through_yield.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_constructor_line.dart b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_constructor_line.dart
index b5d935b55c3..8a143f88b53 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_constructor_line.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_constructor_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
+
 void main() {
   // ignore: unused_local_variable
   var foo = Foo();
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_function_line.dart b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_function_line.dart
index 8b3b281c108..5c2966bec3b 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_function_line.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_function_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
+
 void main() {
   var foo = Foo();
   foo.foo();
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_line.dart b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_line.dart
index f7943d63320..92781ce9953 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_line.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_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
+
 void main() {
   var foo = Foo();
   foo.foo();
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_named_constructor_line.dart b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_named_constructor_line.dart
index 9c7130285fb..75e9030b2ae 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_named_constructor_line.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_class_named_constructor_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
+
 void main() {
   // ignore: unused_local_variable
   var foo = Foo.named();
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_function_line.dart b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_function_line.dart
index 4683e61dcfa..eedeb22e49e 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_function_line.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/no_mapping_on_function_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
+
 /*nm*/
 void main() {
   foo();
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/printing_class_fields.dart b/pkg/dev_compiler/test/sourcemap/testfiles/printing_class_fields.dart
index 58fe7efb9d0..cf2726353ce 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/printing_class_fields.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/printing_class_fields.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 void main() {
   /*bl*/
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/printing_class_fields_step_into.dart b/pkg/dev_compiler/test/sourcemap/testfiles/printing_class_fields_step_into.dart
index 2b7406d1c83..1508da94b39 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/printing_class_fields_step_into.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/printing_class_fields_step_into.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*nb*/
 void main() {
   /*bl*/
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_async_star_yield.dart b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_async_star_yield.dart
index cef8d5ae40f..82e0be2c90c 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_async_star_yield.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_async_star_yield.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() async {
   await for (var i in foobar()) {
     print(i);
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_await_for.dart b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_await_for.dart
index 20fc828710b..1dd65481f19 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_await_for.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_await_for.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() async {
   /* bl */
   /*sl:1 */ print('About to loop!');
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_conditional_expression.dart b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_conditional_expression.dart
index 519529cd798..fc19ec0b70d 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_conditional_expression.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_conditional_expression.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_if_and_identical.dart b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_if_and_identical.dart
index 33e727377cd..0e57fdaa73c 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_if_and_identical.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_if_and_identical.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /*Debugger:stepOver*/
 
 void main() {
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_property_get_test.dart b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_property_get_test.dart
index 4bec5db7761..2e5bcad1c10 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_property_get_test.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_property_get_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
+
 void main() {
   var bar = Bar();
   bar.doStuff();
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_sync_star.dart b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_sync_star.dart
index 4ce057b93eb..2aaec1547e5 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/step_through_sync_star.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/step_through_sync_star.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   /* bl */
   /*sl:1*/ var iterator = naturalsTo(2);
diff --git a/pkg/dev_compiler/test/sourcemap/testfiles/stops_at_ending_brace.dart b/pkg/dev_compiler/test/sourcemap/testfiles/stops_at_ending_brace.dart
index d322e4c5316..0e1347df120 100644
--- a/pkg/dev_compiler/test/sourcemap/testfiles/stops_at_ending_brace.dart
+++ b/pkg/dev_compiler/test/sourcemap/testfiles/stops_at_ending_brace.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 void main() {
   Foo();
   // Comment to push the ending brace back a bit.
diff --git a/pkg/dev_compiler/test/string_to_uri_test.dart b/pkg/dev_compiler/test/string_to_uri_test.dart
index bac36378f64..bfd74be57c7 100755
--- a/pkg/dev_compiler/test/string_to_uri_test.dart
+++ b/pkg/dev_compiler/test/string_to_uri_test.dart
@@ -1,3 +1,5 @@
+// @dart = 2.9
+
 import 'dart:io';
 import 'package:dev_compiler/src/compiler/shared_command.dart';
 import 'package:test/test.dart';
diff --git a/pkg/dev_compiler/test/testing.dart b/pkg/dev_compiler/test/testing.dart
index 2f178d195b6..136b9936b8a 100644
--- a/pkg/dev_compiler/test/testing.dart
+++ b/pkg/dev_compiler/test/testing.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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 dev_compiler.src.testing;
 
 import 'dart:mirrors';
diff --git a/pkg/dev_compiler/test/worker/worker_test.dart b/pkg/dev_compiler/test/worker/worker_test.dart
index 4a650da4d54..916f797f92a 100644
--- a/pkg/dev_compiler/test/worker/worker_test.dart
+++ b/pkg/dev_compiler/test/worker/worker_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:async';
 import 'dart:convert';
 import 'dart:io';
diff --git a/pkg/dev_compiler/tool/check_nnbd_sdk.dart b/pkg/dev_compiler/tool/check_nnbd_sdk.dart
index 01eddae6533..80ba657f207 100644
--- a/pkg/dev_compiler/tool/check_nnbd_sdk.dart
+++ b/pkg/dev_compiler/tool/check_nnbd_sdk.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
+
 /// Command-line tool that runs dartanalyzer on a sdk under the perspective of
 /// one tool.
 // TODO(sigmund): generalize this to support other tools, not just ddc.
diff --git a/pkg/dev_compiler/tool/compile_dartdevc_sdk.dart b/pkg/dev_compiler/tool/compile_dartdevc_sdk.dart
index f24c12e39c6..2fcc44e95e6 100644
--- a/pkg/dev_compiler/tool/compile_dartdevc_sdk.dart
+++ b/pkg/dev_compiler/tool/compile_dartdevc_sdk.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
+
 /// Tool that consumes the .dill file of an entire dart-sdk and produces the
 /// corresponding Javascript module.
 
diff --git a/pkg/dev_compiler/tool/ddb b/pkg/dev_compiler/tool/ddb
index 302aa18f9e8..915c1fe4e8a 100755
--- a/pkg/dev_compiler/tool/ddb
+++ b/pkg/dev_compiler/tool/ddb
@@ -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
+
 //
 // Compiles code with DDC and runs the resulting code with either node or
 // chrome.
diff --git a/pkg/dev_compiler/tool/kernel_sdk.dart b/pkg/dev_compiler/tool/kernel_sdk.dart
index dda7022924c..64ace35afa5 100755
--- a/pkg/dev_compiler/tool/kernel_sdk.dart
+++ b/pkg/dev_compiler/tool/kernel_sdk.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:convert' show json;
 import 'dart:io';
diff --git a/pkg/dev_compiler/tool/patch_sdk.dart b/pkg/dev_compiler/tool/patch_sdk.dart
index 143935f3a25..dd83595e557 100755
--- a/pkg/dev_compiler/tool/patch_sdk.dart
+++ b/pkg/dev_compiler/tool/patch_sdk.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
+
 /// Command line tool to merge the SDK libraries and our patch files.
 /// This is currently designed as an offline tool, but we could automate it.
 
diff --git a/pkg/dev_compiler/web/source_map_stack_trace.dart b/pkg/dev_compiler/web/source_map_stack_trace.dart
index 4617b805b3b..aa9eaa665d3 100644
--- a/pkg/dev_compiler/web/source_map_stack_trace.dart
+++ b/pkg/dev_compiler/web/source_map_stack_trace.dart
@@ -2,6 +2,8 @@
 // for details. All rights 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:path/path.dart' as p;
 import 'package:source_maps/source_maps.dart';
 import 'package:stack_trace/stack_trace.dart';
diff --git a/pkg/dev_compiler/web/stack_trace_mapper.dart b/pkg/dev_compiler/web/stack_trace_mapper.dart
index a4daaa9513c..51df77d95d5 100644
--- a/pkg/dev_compiler/web/stack_trace_mapper.dart
+++ b/pkg/dev_compiler/web/stack_trace_mapper.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+// @dart = 2.9
+
 /// Standalone utility that manages loading source maps for all Dart scripts
 /// on the page compiled with DDC.
 ///