diff --git a/lib/date_symbol_data_custom.dart b/lib/date_symbol_data_custom.dart
index 40a9afc..45f91db 100644
--- a/lib/date_symbol_data_custom.dart
+++ b/lib/date_symbol_data_custom.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2017, 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
 
 /// API to allow setting Date/Time formatting in a custom way.
 ///
diff --git a/lib/date_symbol_data_file.dart b/lib/date_symbol_data_file.dart
index 6a4f33d..620b987 100644
--- a/lib/date_symbol_data_file.dart
+++ b/lib/date_symbol_data_file.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// This file should be imported, along with date_format.dart in order to read
 /// locale data from files in the file system.
diff --git a/lib/date_symbol_data_http_request.dart b/lib/date_symbol_data_http_request.dart
index 0950856..2c767db 100644
--- a/lib/date_symbol_data_http_request.dart
+++ b/lib/date_symbol_data_http_request.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// This file should be imported, along with date_format.dart in order to read
 /// locale data via http requests to a web server..
diff --git a/lib/date_symbol_data_local.dart b/lib/date_symbol_data_local.dart
index 1d95aa3..4e7e7b6 100644
--- a/lib/date_symbol_data_local.dart
+++ b/lib/date_symbol_data_local.dart
@@ -3,6 +3,7 @@
 // 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.
+// @dart=2.9
 
 /// Date/time formatting symbols for all locales.
 ///
diff --git a/lib/date_symbols.dart b/lib/date_symbols.dart
index da43178..86322fd 100644
--- a/lib/date_symbols.dart
+++ b/lib/date_symbols.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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 date_symbols;
 
 // Suppress naming lints, as changes would be breaking.
diff --git a/lib/date_time_patterns.dart b/lib/date_time_patterns.dart
index dfce6cf..ec18613 100644
--- a/lib/date_time_patterns.dart
+++ b/lib/date_time_patterns.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2014, 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
 
 /// Date/time formatting symbols for a large subset of locales.
 ///
diff --git a/lib/intl.dart b/lib/intl.dart
index cf22be2..5bd873c 100644
--- a/lib/intl.dart
+++ b/lib/intl.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// This library provides internationalization and localization. This includes
 /// message formatting and replacement, date and number formatting and parsing,
diff --git a/lib/intl_browser.dart b/lib/intl_browser.dart
index 28d45ed..3a9db49 100644
--- a/lib/intl_browser.dart
+++ b/lib/intl_browser.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// This provides facilities for Internationalization that are only available
 /// when running in the web browser. You should import only one of this or
diff --git a/lib/intl_standalone.dart b/lib/intl_standalone.dart
index 90563fc..626ac22 100644
--- a/lib/intl_standalone.dart
+++ b/lib/intl_standalone.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// This provides facilities for Internationalization that are only available
 /// when running standalone. You should import only one of this or
diff --git a/lib/locale.dart b/lib/locale.dart
index 14b65d0..ea24a87 100644
--- a/lib/locale.dart
+++ b/lib/locale.dart
@@ -1,2 +1,3 @@
 /// This library provides access to the [Locale] class.
+// @dart=2.9
 export 'src/locale.dart';
diff --git a/lib/message_format.dart b/lib/message_format.dart
index 44b68e9..be010fa 100644
--- a/lib/message_format.dart
+++ b/lib/message_format.dart
@@ -1,6 +1,7 @@
 // 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
 
 /// `MessageFormat` is a "locale aware printf", with plural / gender support.
 ///
diff --git a/lib/message_lookup_by_library.dart b/lib/message_lookup_by_library.dart
index 1e41981..a8d83be 100644
--- a/lib/message_lookup_by_library.dart
+++ b/lib/message_lookup_by_library.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Message/plural format library with locale support. This can have different
 /// implementations based on the mechanism for finding the localized versions of
diff --git a/lib/number_symbols.dart b/lib/number_symbols.dart
index 9dd6c9f..8441bd0 100644
--- a/lib/number_symbols.dart
+++ b/lib/number_symbols.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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 number_symbols;
 
 // Suppress naming issues as changes would be breaking.
diff --git a/lib/number_symbols_data.dart b/lib/number_symbols_data.dart
index 8536d1c..11d60eb 100644
--- a/lib/number_symbols_data.dart
+++ b/lib/number_symbols_data.dart
@@ -3,6 +3,7 @@
 // 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.
+// @dart=2.9
 
 /// Date/time formatting symbols for all locales.
 ///
diff --git a/lib/src/data/dates/locale_list.dart b/lib/src/data/dates/locale_list.dart
index 1581cca..40bdc31 100644
--- a/lib/src/data/dates/locale_list.dart
+++ b/lib/src/data/dates/locale_list.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this sourcecode is governed by a
 // BSD-style license that can be found in the LICENSE file.
+// @dart=2.9
 
 /// Hard-coded list of all available locales for dates.
 final availableLocalesForDateFormatting = const [
diff --git a/lib/src/date_format_internal.dart b/lib/src/date_format_internal.dart
index f0ac494..08c9129 100644
--- a/lib/src/date_format_internal.dart
+++ b/lib/src/date_format_internal.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// This contains internal implementation details of the date formatting code
 /// which are exposed as public functions because they must be called by other
diff --git a/lib/src/file_data_reader.dart b/lib/src/file_data_reader.dart
index 10b6edc..d64e0f0 100644
--- a/lib/src/file_data_reader.dart
+++ b/lib/src/file_data_reader.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// This contains a reader that accesses data from local files, so it can't
 /// be run in the browser.
diff --git a/lib/src/http_request_data_reader.dart b/lib/src/http_request_data_reader.dart
index da11908..2155f43 100644
--- a/lib/src/http_request_data_reader.dart
+++ b/lib/src/http_request_data_reader.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// This contains a reader that accesses data using the HttpRequest
 /// facility, and thus works only in the web browser.
diff --git a/lib/src/intl/bidi_formatter.dart b/lib/src/intl/bidi_formatter.dart
index f275d23..7cccfdd 100644
--- a/lib/src/intl/bidi_formatter.dart
+++ b/lib/src/intl/bidi_formatter.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 part of intl;
 
diff --git a/lib/src/intl/bidi_utils.dart b/lib/src/intl/bidi_utils.dart
index 7e8be01..60a268b 100644
--- a/lib/src/intl/bidi_utils.dart
+++ b/lib/src/intl/bidi_utils.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 part of intl;
 
diff --git a/lib/src/intl/compact_number_format.dart b/lib/src/intl/compact_number_format.dart
index 162d739..5ac6442 100644
--- a/lib/src/intl/compact_number_format.dart
+++ b/lib/src/intl/compact_number_format.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.
+// @dart=2.9
 
 part of intl;
 
diff --git a/lib/src/intl/date_format.dart b/lib/src/intl/date_format.dart
index 282d3ef..70e23a0 100644
--- a/lib/src/intl/date_format.dart
+++ b/lib/src/intl/date_format.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 part of intl;
 
@@ -485,15 +486,19 @@
   DateFormat.j([locale]) : this('j', locale);
   DateFormat.jm([locale]) : this('jm', locale);
   DateFormat.jms([locale]) : this('jms', locale);
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   DateFormat.jmv([locale]) : this('jmv', locale);
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   DateFormat.jmz([locale]) : this('jmz', locale);
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   DateFormat.jv([locale]) : this('jv', locale);
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   DateFormat.jz([locale]) : this('jz', locale);
@@ -544,15 +549,19 @@
   DateFormat add_j() => addPattern('j');
   DateFormat add_jm() => addPattern('jm');
   DateFormat add_jms() => addPattern('jms');
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   DateFormat add_jmv() => addPattern('jmv');
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   DateFormat add_jmz() => addPattern('jmz');
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   DateFormat add_jv() => addPattern('jv');
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   DateFormat add_jz() => addPattern('jz');
@@ -596,15 +605,19 @@
   static const String HOUR = 'j';
   static const String HOUR_MINUTE = 'jm';
   static const String HOUR_MINUTE_SECOND = 'jms';
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   static const String HOUR_MINUTE_GENERIC_TZ = 'jmv';
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   static const String HOUR_MINUTE_TZ = 'jmz';
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   static const String HOUR_GENERIC_TZ = 'jv';
+
   /// NOT YET IMPLEMENTED.
   // TODO(https://github.com/dart-lang/intl/issues/74)
   static const String HOUR_TZ = 'jz';
diff --git a/lib/src/intl/date_format_field.dart b/lib/src/intl/date_format_field.dart
index 360998c..ad7f087 100644
--- a/lib/src/intl/date_format_field.dart
+++ b/lib/src/intl/date_format_field.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 part of intl;
 
diff --git a/lib/src/intl/date_format_helpers.dart b/lib/src/intl/date_format_helpers.dart
index be42b84..3097dc2 100644
--- a/lib/src/intl/date_format_helpers.dart
+++ b/lib/src/intl/date_format_helpers.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 part of intl;
 
diff --git a/lib/src/intl/number_format.dart b/lib/src/intl/number_format.dart
index 000da63..61b4ce5 100644
--- a/lib/src/intl/number_format.dart
+++ b/lib/src/intl/number_format.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 part of intl;
 
diff --git a/lib/src/intl_helpers.dart b/lib/src/intl_helpers.dart
index 356d00c..3f5d9e2 100644
--- a/lib/src/intl_helpers.dart
+++ b/lib/src/intl_helpers.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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 library for general helper code associated with the intl library
 /// rather than confined to specific parts of it.
diff --git a/lib/src/lazy_locale_data.dart b/lib/src/lazy_locale_data.dart
index 0620033..caddc95 100644
--- a/lib/src/lazy_locale_data.dart
+++ b/lib/src/lazy_locale_data.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// This defines a class for loading locale data incrementally from
 /// an external source as JSON. The external sources expected are either
diff --git a/lib/src/locale.dart b/lib/src/locale.dart
index d2c53c9..d3d1d3b 100644
--- a/lib/src/locale.dart
+++ b/lib/src/locale.dart
@@ -1,6 +1,7 @@
 // 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 'locale/locale_implementation.dart';
 import 'locale/locale_parser.dart' show LocaleParser;
diff --git a/lib/src/locale/locale_deprecations.dart b/lib/src/locale/locale_deprecations.dart
index 5dd0922..31adf3b 100644
--- a/lib/src/locale/locale_deprecations.dart
+++ b/lib/src/locale/locale_deprecations.dart
@@ -1,6 +1,7 @@
 // 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
 
 /// Replaces deprecated language subtags.
 ///
diff --git a/lib/src/locale/locale_extensions.dart b/lib/src/locale/locale_extensions.dart
index 245ecbf..e7ff25a 100644
--- a/lib/src/locale/locale_extensions.dart
+++ b/lib/src/locale/locale_extensions.dart
@@ -1,6 +1,7 @@
 // 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
 
 /// Locale extensions as defined for [Unicode Locale
 /// Identifiers](http://www.unicode.org/reports/tr35/#Unicode_locale_identifier).
diff --git a/lib/src/locale/locale_implementation.dart b/lib/src/locale/locale_implementation.dart
index ed3dea3..bd397be 100644
--- a/lib/src/locale/locale_implementation.dart
+++ b/lib/src/locale/locale_implementation.dart
@@ -1,6 +1,7 @@
 // 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 'package:intl/src/locale.dart' show Locale;
 
diff --git a/lib/src/locale/locale_parser.dart b/lib/src/locale/locale_parser.dart
index 8c151b0..1390d16 100644
--- a/lib/src/locale/locale_parser.dart
+++ b/lib/src/locale/locale_parser.dart
@@ -1,6 +1,7 @@
 // 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 'locale_deprecations.dart';
 import 'locale_extensions.dart';
diff --git a/lib/src/plural_rules.dart b/lib/src/plural_rules.dart
index 656bf62..0ad0493 100644
--- a/lib/src/plural_rules.dart
+++ b/lib/src/plural_rules.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.
+// @dart=2.9
 
 /// Provides locale-specific plural rules. Based on pluralrules.js from Closure.
 ///
diff --git a/test/bidi_format_test.dart b/test/bidi_format_test.dart
index ca69e85..0846907 100644
--- a/test/bidi_format_test.dart
+++ b/test/bidi_format_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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 bidi_format_test;
 
diff --git a/test/bidi_utils_test.dart b/test/bidi_utils_test.dart
index a0a2e95..1001817 100644
--- a/test/bidi_utils_test.dart
+++ b/test/bidi_utils_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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 bidi_utils_test;
 
diff --git a/test/brazil_timezone_test.dart b/test/brazil_timezone_test.dart
index 6fb5bd4..78edb79 100644
--- a/test/brazil_timezone_test.dart
+++ b/test/brazil_timezone_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2017, 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
 
 /// Test date formatting and parsing while the system time zone is set to
 /// America/Sao Paulo.
diff --git a/test/compact_number_test_data.dart b/test/compact_number_test_data.dart
index b862ef3..946938d 100644
--- a/test/compact_number_test_data.dart
+++ b/test/compact_number_test_data.dart
@@ -3,6 +3,7 @@
 // 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.
+// @dart=2.9
 
 /// Test data for compact number formatting.
 ///
diff --git a/test/compact_number_test_data_33.dart b/test/compact_number_test_data_33.dart
index 0951c15..9ceaf61 100644
--- a/test/compact_number_test_data_33.dart
+++ b/test/compact_number_test_data_33.dart
@@ -3,6 +3,7 @@
 // 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.
+// @dart=2.9
 
 /// Test data for compact number formatting.
 ///
diff --git a/test/data_directory.dart b/test/data_directory.dart
index e43a8ad..15c7705 100644
--- a/test/data_directory.dart
+++ b/test/data_directory.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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 utility function for test and tools that compensates (at least for very
 /// simple cases) for file-dependent programs being run from different
diff --git a/test/data_directory_opensource.dart b/test/data_directory_opensource.dart
index 2bb9fa3..a8d3d4f 100644
--- a/test/data_directory_opensource.dart
+++ b/test/data_directory_opensource.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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 utility function for test and tools that compensates (at least for very
 /// simple cases) for file-dependent programs being run from different
diff --git a/test/date_format_flake_test.dart b/test/date_format_flake_test.dart
index c71158f..9be5168 100644
--- a/test/date_format_flake_test.dart
+++ b/test/date_format_flake_test.dart
@@ -1,6 +1,7 @@
 // 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
 
 // Tests for what happens when DateTime instance creation does flaky things.
 
diff --git a/test/date_time_format_custom_test.dart b/test/date_time_format_custom_test.dart
index 6a1e64d..5341f52 100644
--- a/test/date_time_format_custom_test.dart
+++ b/test/date_time_format_custom_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2017, 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
 
 /// Test date formatting and parsing using custom locale data, which we get
 /// from the local copy.
diff --git a/test/date_time_format_file_even_test.dart b/test/date_time_format_file_even_test.dart
index 2e55022..b0be291 100644
--- a/test/date_time_format_file_even_test.dart
+++ b/test/date_time_format_file_even_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Tests date formatting and parsing using locale data read from the
 /// local file system. This tests one half the locales, since testing all
diff --git a/test/date_time_format_file_odd_test.dart b/test/date_time_format_file_odd_test.dart
index 687b392..527caff 100644
--- a/test/date_time_format_file_odd_test.dart
+++ b/test/date_time_format_file_odd_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Tests date formatting and parsing using locale data read from the
 /// local file system. This tests one half the locales, since testing all
diff --git a/test/date_time_format_local_even_test.dart b/test/date_time_format_local_even_test.dart
index e52cb31..86582e5 100644
--- a/test/date_time_format_local_even_test.dart
+++ b/test/date_time_format_local_even_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Test date formatting and parsing using locale data which is available
 /// directly in the program as a constant. This tests one half the locales,
diff --git a/test/date_time_format_local_odd_test.dart b/test/date_time_format_local_odd_test.dart
index ecede2d..7ec22f7 100644
--- a/test/date_time_format_local_odd_test.dart
+++ b/test/date_time_format_local_odd_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Test date formatting and parsing using locale data which is available
 /// directly in the program as a constant. This tests one half the locales,
diff --git a/test/date_time_format_test_core.dart b/test/date_time_format_test_core.dart
index 3c7a539..9a699d2 100644
--- a/test/date_time_format_test_core.dart
+++ b/test/date_time_format_test_core.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Tests the DateFormat library in dart. This file contains core tests that are
 /// run regardless of where the locale data is found, so it doesn't expect to be
diff --git a/test/date_time_format_test_data.dart b/test/date_time_format_test_data.dart
index a0a57f7..9109c65 100644
--- a/test/date_time_format_test_data.dart
+++ b/test/date_time_format_test_data.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Test data for one particular date formatted for a small number of locales.
 /// Provides at least a basic check on formatting, including formatting with
diff --git a/test/date_time_format_test_stub.dart b/test/date_time_format_test_stub.dart
index c8344ac..17980ae 100644
--- a/test/date_time_format_test_stub.dart
+++ b/test/date_time_format_test_stub.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Test date formatting and parsing using locale data which is available
 /// directly in the program as a constant.
diff --git a/test/date_time_format_uninitialized_test.dart b/test/date_time_format_uninitialized_test.dart
index 79b09f9..7374cc1 100644
--- a/test/date_time_format_uninitialized_test.dart
+++ b/test/date_time_format_uninitialized_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Tests date formatting and parsing using locale data read from the
 /// local file system.
diff --git a/test/date_time_loose_parsing_test.dart b/test/date_time_loose_parsing_test.dart
index b0e000a..c28f124 100644
--- a/test/date_time_loose_parsing_test.dart
+++ b/test/date_time_loose_parsing_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2014, 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
 
 /// Tests for the loose option when parsing dates and times, which accept
 /// mixed-case input and are able to skip missing delimiters. Such valid input
diff --git a/test/date_time_strict_test.dart b/test/date_time_strict_test.dart
index 730ceeb..04f9f75 100644
--- a/test/date_time_strict_test.dart
+++ b/test/date_time_strict_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2014, 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
 
 /// Tests for the strict option when parsing dates and times, which are
 /// relatively locale-independent, depending only on the being a valid date
diff --git a/test/england_timezone_test.dart b/test/england_timezone_test.dart
index 33e8901..a2479c0 100644
--- a/test/england_timezone_test.dart
+++ b/test/england_timezone_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2017, 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
 
 /// Test date formatting and parsing while the system time zone is set to
 /// Europe/London.
diff --git a/test/find_default_locale_browser_test.dart b/test/find_default_locale_browser_test.dart
index cfc19f5..a93dda9 100644
--- a/test/find_default_locale_browser_test.dart
+++ b/test/find_default_locale_browser_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 @TestOn('browser')
 library find_default_locale_browser_test;
diff --git a/test/find_default_locale_standalone_test.dart b/test/find_default_locale_standalone_test.dart
index e212848..217c281 100644
--- a/test/find_default_locale_standalone_test.dart
+++ b/test/find_default_locale_standalone_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 @TestOn('vm')
 import 'package:intl/intl.dart';
diff --git a/test/fixnum_test.dart b/test/fixnum_test.dart
index 8f9f874..3c7b6bc 100644
--- a/test/fixnum_test.dart
+++ b/test/fixnum_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2014, 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 fixnum_test;
 
diff --git a/test/gmt_timezone_test.dart b/test/gmt_timezone_test.dart
index f8374ce..1f61575 100644
--- a/test/gmt_timezone_test.dart
+++ b/test/gmt_timezone_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2017, 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
 
 /// Test date formatting and parsing while the system time zone is set to
 /// GMT.
diff --git a/test/intl_test.dart b/test/intl_test.dart
index 77f10c5..0ba2f8e 100644
--- a/test/intl_test.dart
+++ b/test/intl_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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 intl_test;
 
diff --git a/test/locale_test.dart b/test/locale_test.dart
index 6698e4d..69d0cf4 100644
--- a/test/locale_test.dart
+++ b/test/locale_test.dart
@@ -1,6 +1,7 @@
 // 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
 
 /// Tests for the Locale class.
 ///
diff --git a/test/locale_test_data.dart b/test/locale_test_data.dart
index 9cd6f70..40b7a10 100644
--- a/test/locale_test_data.dart
+++ b/test/locale_test_data.dart
@@ -1,6 +1,7 @@
 // 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
 
 /// Test data for Locale handling.
 ///
diff --git a/test/message_format_test.dart b/test/message_format_test.dart
index 03a2b47..f61abee 100644
--- a/test/message_format_test.dart
+++ b/test/message_format_test.dart
@@ -1,6 +1,7 @@
 // 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
 
 /// Tests for the MessageFormat class.
 ///
diff --git a/test/more_compact_number_test_data.dart b/test/more_compact_number_test_data.dart
index b443c0d..cef3f3a 100644
--- a/test/more_compact_number_test_data.dart
+++ b/test/more_compact_number_test_data.dart
@@ -1,6 +1,7 @@
 // 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
 
 class CompactRoundingTestCase {
   CompactRoundingTestCase(this.number, this.expected,
diff --git a/test/number_closure_test.dart b/test/number_closure_test.dart
index 558b2dc..3e25e60 100644
--- a/test/number_closure_test.dart
+++ b/test/number_closure_test.dart
@@ -1,6 +1,7 @@
 /// Copyright (c) 2012, 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
 
 /// Tests based on the closure number formatting tests.
 library number_closure_test;
diff --git a/test/number_format_compact_icu_test.dart b/test/number_format_compact_icu_test.dart
index da7b2e1..51ee653 100644
--- a/test/number_format_compact_icu_test.dart
+++ b/test/number_format_compact_icu_test.dart
@@ -3,9 +3,11 @@
 /// These tests check that the test cases match what ICU produces. They are not
 /// testing the package:intl implementation, they only help verify consistent
 /// behaviour across platforms.
+// @dart=2.9
 @TestOn("!browser")
 @Tags(['ffi'])
-@Skip("currently failing (see issue https://github.com/dart-lang/intl/issues/240)")
+@Skip(
+    "currently failing (see issue https://github.com/dart-lang/intl/issues/240)")
 import 'dart:ffi';
 import 'package:ffi/ffi.dart';
 import 'package:test/test.dart';
diff --git a/test/number_format_compact_test.dart b/test/number_format_compact_test.dart
index a1e44bb..1fe900e 100644
--- a/test/number_format_compact_test.dart
+++ b/test/number_format_compact_test.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.
+// @dart=2.9
 
 /// Tests for compact format numbers, e.g. 1.2M rather than 1,200,000
 import 'dart:math';
diff --git a/test/number_format_compact_web_test.dart b/test/number_format_compact_web_test.dart
index a6c60e1..950775b 100644
--- a/test/number_format_compact_web_test.dart
+++ b/test/number_format_compact_web_test.dart
@@ -4,6 +4,7 @@
 /// consistency when the bug is fixed. Also fix documentation and perhaps
 /// merge tests: these tests currently also touch non-compact currency
 /// formatting.
+// @dart=2.9
 
 /// We use @Tags rather than @TestOn to be able to specify something that can be
 /// ignored when using a build system that can't read dart_test.yaml. This
diff --git a/test/number_format_test_core.dart b/test/number_format_test_core.dart
index 372b555..7f30a76 100644
--- a/test/number_format_test_core.dart
+++ b/test/number_format_test_core.dart
@@ -1,6 +1,7 @@
 /// Copyright (c) 2012, 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 number_format_test;
 
diff --git a/test/number_format_vm_test.dart b/test/number_format_vm_test.dart
index 8c04b58..6bc8e39 100644
--- a/test/number_format_vm_test.dart
+++ b/test/number_format_vm_test.dart
@@ -1,6 +1,7 @@
 /// Copyright (c) 2012, 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
 
 /// Number tests for the VM - includes numbers that can only be compiled for the
 /// VM.
diff --git a/test/number_format_web_test.dart b/test/number_format_web_test.dart
index 86db381..293e9f7 100644
--- a/test/number_format_web_test.dart
+++ b/test/number_format_web_test.dart
@@ -1,6 +1,7 @@
 /// Copyright (c) 2012, 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
 
 /// Number format tests for the web - excludes numbers too big to compile for
 /// the web.
diff --git a/test/number_test_data.dart b/test/number_test_data.dart
index 10ed7ad..c3549d4 100644
--- a/test/number_test_data.dart
+++ b/test/number_test_data.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2014, 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
 
 /// Test data for numeric formatting from a large set of locales.
 ///
diff --git a/test/plural_test.dart b/test/plural_test.dart
index f3da8ba..045455d 100644
--- a/test/plural_test.dart
+++ b/test/plural_test.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.
+// @dart=2.9
 
 /// Test plurals without translation.
 ///
diff --git a/test/scorbeysund_timezone_test.dart b/test/scorbeysund_timezone_test.dart
index 873b75d..1463f08 100644
--- a/test/scorbeysund_timezone_test.dart
+++ b/test/scorbeysund_timezone_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2017, 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
 
 /// Test date formatting and parsing while the system time zone is set to
 /// America/Scoresbysund.
diff --git a/test/timezone_local_even_test_helper.dart b/test/timezone_local_even_test_helper.dart
index 7df4ea6..46d6c81 100644
--- a/test/timezone_local_even_test_helper.dart
+++ b/test/timezone_local_even_test_helper.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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
 
 /// Test date formatting and parsing using locale data directly imported.
 ///
diff --git a/test/timezone_test_core.dart b/test/timezone_test_core.dart
index 14f3188..d6e9285 100644
--- a/test/timezone_test_core.dart
+++ b/test/timezone_test_core.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2017, 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
 
 /// Test date formatting and parsing while the system time zone is set.
 import 'dart:convert';
diff --git a/test/utc_timezone_test.dart b/test/utc_timezone_test.dart
index 7c7d494..d085e7b 100644
--- a/test/utc_timezone_test.dart
+++ b/test/utc_timezone_test.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2017, 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
 
 /// Test date formatting and parsing while the system time zone is set to
 /// UTC.
diff --git a/tool/generate_locale_data_files.dart b/tool/generate_locale_data_files.dart
index 2f6a575..9a398c6 100644
--- a/tool/generate_locale_data_files.dart
+++ b/tool/generate_locale_data_files.dart
@@ -1,6 +1,7 @@
 // Copyright (c) 2012, 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 utility program to take locale data represented as a Dart map whose keys
 /// are locale names and write it into individual JSON files named by locale.