[cfe] Add symbolic language versions for testing

Change-Id: I0f8bb91d30fac442d781710b24908cd933d86388
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/365142
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

pkg/_fe_analyzer_shared/lib/src/testing/id_generation.dart

@@ -6,6 +6,8 @@ import 'package:_fe_analyzer_shared/src/testing/annotated_code_helper.dart';
 import 'package:_fe_analyzer_shared/src/testing/id.dart';
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart';
 
+String _noProcessing(String text) => text;
+
 Map<Uri, List<Annotation>> computeAnnotationsPerUri<T>(
     Map<Uri, AnnotatedCode> annotatedCode,
     Map<String, MemberAnnotations<IdValue>> expectedMaps,
@@ -13,7 +15,8 @@ Map<Uri, List<Annotation>> computeAnnotationsPerUri<T>(
     Map<String, Map<Uri, Map<Id, ActualData<T>>>> actualData,
     DataInterpreter<T> dataInterpreter,
     {Annotation? Function(Annotation? expected, Annotation? actual)? createDiff,
-    bool forceUpdate = false}) {
+    bool forceUpdate = false,
+    String Function(String) postProcessData = _noProcessing}) {
   Set<Uri> uriSet = {};
   Set<String> actualMarkers = actualData.keys.toSet();
   Map<Uri, Map<Id, Map<String, IdValue>>> idValuePerUri = {};
@@ -64,7 +67,10 @@ Map<Uri, List<Annotation>> computeAnnotationsPerUri<T>(
       // Annotations are not computed from synthesized code.
       result[uri] = _computeAnnotations(code, expectedMaps.keys, actualMarkers,
           idValuePerId, actualDataPerId, dataInterpreter,
-          sortMarkers: false, createDiff: createDiff, forceUpdate: forceUpdate);
+          sortMarkers: false,
+          createDiff: createDiff,
+          forceUpdate: forceUpdate,
+          postProcessData: postProcessData);
     }
   }
   return result;
@@ -81,7 +87,8 @@ List<Annotation> _computeAnnotations<T>(
     String defaultSuffix = '*/',
     bool sortMarkers = true,
     Annotation? Function(Annotation? expected, Annotation? actual)? createDiff,
-    bool forceUpdate = false}) {
+    bool forceUpdate = false,
+    required String Function(String) postProcessData}) {
   Annotation createAnnotationFromData(
       ActualData<T> actualData, Annotation? annotation) {
     String getIndentationFromOffset(int offset) {
@@ -142,8 +149,10 @@ List<Annotation> _computeAnnotations<T>(
         annotation?.columnNo ?? -1,
         offset,
         prefix,
-        IdValue.idToString(actualData.id,
+        IdValue.idToString(
-            dataInterpreter.getText(actualData.value, indentation)),
+            actualData.id,
+            postProcessData(
+                dataInterpreter.getText(actualData.value, indentation))),
         suffix);
   }
 

pkg/_fe_analyzer_shared/lib/src/testing/id_testing.dart

@@ -263,6 +263,7 @@ TestData computeTestData(FileSystemEntity testFile,
     {required Iterable<String> supportedMarkers,
     required Uri createTestUri(Uri uri, String fileName),
     required void onFailure(String message),
+    String Function(String) preprocessFile = _noProcessing,
     bool preserveWhitespaceInAnnotations = false,
     bool preserveInfixWhitespaceInAnnotations = false}) {
   Uri? entryPoint;
@@ -296,7 +297,8 @@ TestData computeTestData(FileSystemEntity testFile,
     throw new UnimplementedError();
   }
 
-  String annotatedCode = new File.fromUri(mainTestFile!.uri).readAsStringSync();
+  String annotatedCode =
+      preprocessFile(new File.fromUri(mainTestFile!.uri).readAsStringSync());
   Map<Uri, AnnotatedCode> code = {
     entryPoint!:
         new AnnotatedCode.fromText(annotatedCode, commentStart, commentEnd)
@@ -320,7 +322,7 @@ TestData computeTestData(FileSystemEntity testFile,
       String libFileName = additionalFileData.key;
       File libEntity = additionalFileData.value;
       Uri libFileUri = createTestUri(libEntity.uri, libFileName);
-      String libCode = libEntity.readAsStringSync();
+      String libCode = preprocessFile(libEntity.readAsStringSync());
       AnnotatedCode annotatedLibCode =
           new AnnotatedCode.fromText(libCode, commentStart, commentEnd);
       memorySourceFiles[libFileUri.path] = annotatedLibCode.sourceCode;
@@ -820,6 +822,8 @@ const List<Option> idTestOptions = [
   Options.forceUpdate,
 ];
 
+String _noProcessing(String s) => s;
+
 /// Check code for all tests in [dataDir] using [runTest].
 Future<void> runTests<T>(Directory dataDir,
     {List<String> args = const <String>[],
@@ -832,7 +836,9 @@ Future<void> runTests<T>(Directory dataDir,
     List<String>? skipList,
     Map<String, List<String>>? skipMap,
     bool preserveWhitespaceInAnnotations = false,
-    bool preserveInfixWhitespaceInAnnotations = false}) async {
+    bool preserveInfixWhitespaceInAnnotations = false,
+    String Function(String) preprocessFile = _noProcessing,
+    String Function(String) postProcessData = _noProcessing}) async {
   ParsedOptions parsedOptions = ParsedOptions.parse(args, idTestOptions);
   MarkerOptions markerOptions =
       new MarkerOptions.fromDataDir(dataDir, shouldFindScript: shards == 1);
@@ -903,7 +909,8 @@ Future<void> runTests<T>(Directory dataDir,
         onFailure: onFailure,
         preserveWhitespaceInAnnotations: preserveWhitespaceInAnnotations,
         preserveInfixWhitespaceInAnnotations:
-            preserveInfixWhitespaceInAnnotations);
+            preserveInfixWhitespaceInAnnotations,
+        preprocessFile: preprocessFile);
     print('Test: ${testData.testFileUri}');
 
     Map<String, TestResult<T>> results = await runTest(markerOptions, testData,
@@ -966,7 +973,8 @@ Future<void> runTests<T>(Directory dataDir,
             testData.entryPoint,
             actualData,
             dataInterpreter!,
-            forceUpdate: forceUpdate);
+            forceUpdate: forceUpdate,
+            postProcessData: postProcessData);
         annotations.forEach((Uri uri, List<Annotation> annotations) {
           AnnotatedCode? code = testData.code[uri];
           assert(code != null,

pkg/front_end/test/incremental_suite.dart

@@ -74,6 +74,7 @@ import "incremental_utils.dart" as util;
 import 'test_utils.dart';
 import 'testing_utils.dart' show checkEnvironment;
 import 'utils/io_utils.dart' show computeRepoDir;
+import 'utils/symbolic_language_versions.dart';
 import 'utils/values.dart';
 
 void main([List<String> arguments = const []]) => internalMain(createContext,
@@ -772,14 +773,6 @@ Future<Map<String, List<int>>> createModules(
   return moduleResult;
 }
 
-String doStringReplacements(String input) {
-  Version enableNonNullableVersion =
-      ExperimentalFlag.nonNullable.experimentEnabledVersion;
-  String output = input.replaceAll("%NNBD_VERSION_MARKER%",
-      "${enableNonNullableVersion.major}.${enableNonNullableVersion.minor}");
-  return output;
-}
-
 class ExpressionCompilation {
   final bool errors;
   final bool warnings;
@@ -1250,7 +1243,7 @@ class NewWorldTest {
           packagesUri = uri;
         }
         if (world.enableStringReplacement) {
-          data = doStringReplacements(data);
+          data = replaceMarkersWithVersions(data);
         }
         fs.entityForUri(uri).writeAsStringSync(data);
       }

pkg/front_end/test/language_versioning/data/allowed_experiments_with_json/foo/bin/bin_file.dart

@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /*library: 
- languageVersion=2.8,
+ languageVersion=%CURRENT_VERSION_MARKER%,
  packageUri=package:collection
 */
 

pkg/front_end/test/language_versioning/data/allowed_experiments_with_json/foo/lib/foo.dart

@@ -2,6 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 method2() {}

pkg/front_end/test/language_versioning/data/allowed_experiments_with_json/foo/test/test_file.dart

@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /*library: 
- languageVersion=2.8,
+ languageVersion=%CURRENT_VERSION_MARKER%,
  packageUri=package:collection
 */
 

pkg/front_end/test/language_versioning/data/allowed_experiments_with_json/main.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 import 'foo/bin/bin_file.dart';
 import 'foo/test/test_file.dart';

pkg/front_end/test/language_versioning/data/both_packages_and_json/foo2/foo.dart

@@ -1,4 +1,4 @@
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 String foo() {
   return "42";

pkg/front_end/test/language_versioning/data/both_packages_and_json/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   var result = foo();

pkg/front_end/test/language_versioning/data/issue42661a/.dart_tool/package_config.json

@@ -4,7 +4,7 @@
     {
       "name": "pack",
       "rootUri": "../pack/lib/",
-      "languageVersion": "2.7"
+      "languageVersion": "%VERSION_MARKER2%"
     }
   ]
 }

pkg/front_end/test/language_versioning/data/issue42661a/main.dart

@@ -1,3 +1,3 @@
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 import 'pack/web/pack.dart';

pkg/front_end/test/language_versioning/data/issue42661a/pack/web/pack.dart

@@ -1,4 +1,4 @@
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 library pack;
 
 part /*error: errors=LanguageVersionMismatchInPart*/ 'package:pack/src/part.dart';

pkg/front_end/test/language_versioning/data/issue42661b/.dart_tool/package_config.json

@@ -5,7 +5,7 @@
       "name": "pack",
       "rootUri": "../",
       "packageUri": "lib/",
-      "languageVersion": "2.7"
+      "languageVersion": "%VERSION_MARKER2%"
     }
   ]
 }

pkg/front_end/test/language_versioning/data/issue42661b/main.dart

@@ -1,5 +1,5 @@
 /*library: 
- languageVersion=2.7,
+ languageVersion=%VERSION_MARKER2%,
  packageUri=package:pack
 */
 

pkg/front_end/test/language_versioning/data/issue42661b/web/pack.dart

@@ -1,5 +1,5 @@
 /*library: 
- languageVersion=2.7,
+ languageVersion=%VERSION_MARKER2%,
  packageUri=package:pack
 */
 library pack;

pkg/front_end/test/language_versioning/data/library_with_bad_version.dart

@@ -3,11 +3,10 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /*error: errors=LanguageVersionTooHigh*/
-// @dart = 3.5
+// @dart = %TOO_HIGH_VERSION_MARKER%
 
-// If no valid language version is specified, we default to the most reason one.
+// If no valid language version is specified, we default to the most recent one.
-// In the tests this is hard-coded to 2.8.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 main() {}

pkg/front_end/test/language_versioning/data/library_with_bad_version_before_good_version.dart

@@ -3,13 +3,13 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /*error: errors=LanguageVersionTooHigh*/
-// @dart = 3.5
+// @dart = %TOO_HIGH_VERSION_MARKER%
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
 
 // If the first language version specified is not a valid language version,
-// we default to the most reason one.  In the tests this is hard-coded to 2.8.
+// we default to the most recent one.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 main() {}

pkg/front_end/test/language_versioning/data/library_with_no_version.dart

@@ -3,9 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 
 // If no language version is specified, and none if given in a
-// .dart_tool/package_config.json file,
+// .dart_tool/package_config.json file, we default to the most recent one.
-// we default to the most reason one. In the tests this is hard-coded to 2.8.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 main() {}

pkg/front_end/test/language_versioning/data/library_with_two_versions.dart

@@ -4,9 +4,9 @@
 
 // With several valid versions the first one wins.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 main() {}

pkg/front_end/test/language_versioning/data/library_with_two_versions_2.dart

@@ -4,9 +4,9 @@
 
 // With several versions where the first one is valid, the first one wins.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
-// @dart = 42.5
+// @dart = %TOO_HIGH_VERSION_MARKER%
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 main() {}

pkg/front_end/test/language_versioning/data/library_with_version.dart

@@ -2,8 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {}

pkg/front_end/test/language_versioning/data/package_default_version/.dart_tool/package_config.json

@@ -4,7 +4,7 @@
         {
             "name": "foo",
             "rootUri": "../lib/",
-            "languageVersion": "2.5"
+            "languageVersion": "%VERSION_MARKER1%"
         }
     ]
 }

pkg/front_end/test/language_versioning/data/package_default_version/lib/foo.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 import 'foo2.dart';
 import 'foo3.dart';

pkg/front_end/test/language_versioning/data/package_default_version/lib/foo2.dart

@@ -2,9 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 foo2() {
   print("Hello from foo2!");

pkg/front_end/test/language_versioning/data/package_default_version/lib/foo3.dart

@@ -2,12 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// .dart_tool/package_config.json specifies 2.5, this library tries to go above
+// .dart_tool/package_config.json specifies %VERSION_MARKER1%, this library
-// that, which is fine.
+// tries to go above that, which is fine.
 
-// @dart = 2.6
+// @dart = %VERSION_MARKER2%
 
-/*library: languageVersion=2.6*/
+/*library: languageVersion=%VERSION_MARKER2%*/
 
 foo3() {
   print("Hello from foo3!");

pkg/front_end/test/language_versioning/data/package_default_version/lib/foo4.dart

@@ -2,15 +2,15 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// .dart_tool/package_config.json specifies 2.5, this library tries to go above
+// .dart_tool/package_config.json specifies %VERSION_MARKER1%, this library
-// that, which is fine, except it still has to be within the range of the sdk.
+// tries to go above that, which is fine, except it still has to be within the
-// The library stays on the .dart_tool/package_config.json specified one (2.5)
+// range of the sdk. The library stays on the .dart_tool/package_config.json
-// and an error is issued.
+// specified one (%VERSION_MARKER1%) and an error is issued.
 
 /*error: errors=LanguageVersionTooHigh*/
-// @dart = 2.9
+// @dart = %TOO_HIGH_VERSION_MARKER%
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 foo4() {
   print("Hello from foo4!");

pkg/front_end/test/language_versioning/data/package_default_version/lib/foo_with_part.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 part 'foos_part.dart';
 

pkg/front_end/test/language_versioning/data/package_default_version/main.dart

@@ -5,12 +5,12 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 import 'package:foo/foo_with_part.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/package_default_version_is_empty/lib/foo.dart

@@ -3,7 +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.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 import 'foo2.dart';
 

pkg/front_end/test/language_versioning/data/package_default_version_is_empty/lib/foo2.dart

@@ -3,9 +3,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 foo2() {
   print("Hello from foo2!");

pkg/front_end/test/language_versioning/data/package_default_version_is_empty/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong/lib/foo.dart

@@ -3,7 +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.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 import 'foo2.dart';
 

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong/lib/foo2.dart

@@ -3,9 +3,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 foo2() {
   print("Hello from foo2!");

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_2/.dart_tool/package_config.json

@@ -5,7 +5,7 @@
             "name": "foo",
             "rootUri": "../lib/",
             "languageVersion": "arglebargle",
-            "languageVersion": "2.5"
+            "languageVersion": "%VERSION_MARKER1%"
         }
     ]
 }

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_2/lib/foo.dart

@@ -3,7 +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.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 import 'foo2.dart';
 

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_2/lib/foo2.dart

@@ -3,9 +3,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 foo2() {
   print("Hello from foo2!");

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_2/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_3/.dart_tool/package_config.json

@@ -5,7 +5,7 @@
         {
             "name": "foo",
             "rootUri": "../lib/",
-            "languageVersion": "2.5",
+            "languageVersion": "%VERSION_MARKER1%",
             "languageVersion": "arglebargle"
         }
     ]

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_3/lib/foo.dart

@@ -3,7 +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.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 import 'foo2.dart';
 

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_3/lib/foo2.dart

@@ -3,9 +3,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 foo2() {
   print("Hello from foo2!");

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_3/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_4/lib/foo.dart

@@ -3,7 +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.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 import 'foo2.dart';
 

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_4/lib/foo2.dart

@@ -3,9 +3,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 foo2() {
   print("Hello from foo2!");

pkg/front_end/test/language_versioning/data/package_default_version_is_wrong_4/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/package_no_default_version/lib/foo.dart

@@ -3,10 +3,9 @@
 // BSD-style license that can be found in the LICENSE file.
 
 // If no language version is specified, and none if given in a
-// .dart_tool/package_config.json file,
+// .dart_tool/package_config.json file, we default to the most recent one.
-// we default to the most reason one. In the tests this is hard-coded to 2.8.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 foo() {
   print("Hello from foo!");

pkg/front_end/test/language_versioning/data/package_no_default_version/main.dart

@@ -2,11 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/package_non_package_default_version/.dart_tool/package_config.json

@@ -5,7 +5,7 @@
             "name": "foo",
             "rootUri": "../",
             "packageUri": "lib/",
-            "languageVersion": "2.5"
+            "languageVersion": "%VERSION_MARKER1%"
         }
     ]
 }

pkg/front_end/test/language_versioning/data/package_non_package_default_version/lib/foo.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 foo() {
   print("Hello from foo!");

pkg/front_end/test/language_versioning/data/package_non_package_default_version/main.dart

@@ -7,7 +7,7 @@ import 'package:foo/foo.dart';
 // Version comes from the package foo having this file in it's root uri.
 
 /*library: 
- languageVersion=2.5,
+ languageVersion=%VERSION_MARKER1%,
  packageUri=package:foo
 */
 

pkg/front_end/test/language_versioning/data/package_non_package_no_default_version/.dart_tool/package_config.json

@@ -4,7 +4,7 @@
         {
             "name": "foo",
             "rootUri": "../lib/",
-            "languageVersion": "2.5"
+            "languageVersion": "%VERSION_MARKER1%"
         }
     ]
 }

pkg/front_end/test/language_versioning/data/package_non_package_no_default_version/lib/foo.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 foo() {
   print("Hello from foo!");

pkg/front_end/test/language_versioning/data/package_non_package_no_default_version/main.dart

@@ -4,7 +4,7 @@
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/package_to_high_default_version/.dart_tool/package_config.json

@@ -4,7 +4,7 @@
         {
             "name": "foo",
             "rootUri": "../lib/",
-            "languageVersion": "2.9"
+            "languageVersion": "%TOO_HIGH_VERSION_MARKER%"
         }
     ]
 }

pkg/front_end/test/language_versioning/data/package_to_high_default_version/lib/foo.dart

@@ -3,7 +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.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 import 'foo2.dart';
 import 'foo3.dart';

pkg/front_end/test/language_versioning/data/package_to_high_default_version/lib/foo2.dart

@@ -4,9 +4,9 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /*error: errors=LanguageVersionTooHigh*/
-// @dart = 2.9
+// @dart = %TOO_HIGH_VERSION_MARKER%
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 foo2() {
   print("Hello from foo2!");

pkg/front_end/test/language_versioning/data/package_to_high_default_version/lib/foo3.dart

@@ -3,9 +3,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.7
+// @dart = %VERSION_MARKER2%
 
-/*library: languageVersion=2.7*/
+/*library: languageVersion=%VERSION_MARKER2%*/
 
 foo3() {
   print("Hello from foo3!");

pkg/front_end/test/language_versioning/data/package_to_high_default_version/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/package_with_test_json/foo/bin/bin_file.dart

@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /*library: 
- languageVersion=2.8,
+ languageVersion=%CURRENT_VERSION_MARKER%,
  packageUri=package:foo
 */
 

pkg/front_end/test/language_versioning/data/package_with_test_json/foo/lib/foo.dart

@@ -2,6 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 method2() {}

pkg/front_end/test/language_versioning/data/package_with_test_json/foo/test/test_file.dart

@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /*library: 
- languageVersion=2.8,
+ languageVersion=%CURRENT_VERSION_MARKER%,
  packageUri=package:foo
 */
 

pkg/front_end/test/language_versioning/data/package_with_test_json/main.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 // Test that bin and test files within the root folder of a package are
 // associated with the package.

pkg/front_end/test/language_versioning/data/package_without_test_json/foo/bin/bin_file.dart

@@ -2,6 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 method1() {}

pkg/front_end/test/language_versioning/data/package_without_test_json/foo/lib/foo.dart

@@ -2,6 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 method2() {}

pkg/front_end/test/language_versioning/data/package_without_test_json/foo/test/test_file.dart

@@ -2,6 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 method3() {}

pkg/front_end/test/language_versioning/data/package_without_test_json/main.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 // Test that bin and test files within the root folder of a package are
 // associated with the package.

pkg/front_end/test/language_versioning/data/parts_agreeing/main.dart

@@ -2,11 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
 
 part 'part.dart';
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 main() {
   // foo();

pkg/front_end/test/language_versioning/data/parts_agreeing/part.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
 
 part of 'main.dart';
 

pkg/front_end/test/language_versioning/data/parts_agreeing_two_versions/main.dart

@@ -2,12 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 part 'part.dart';
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 main() {
   // foo();

pkg/front_end/test/language_versioning/data/parts_agreeing_two_versions/part.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
 
 part of 'main.dart';
 

pkg/front_end/test/language_versioning/data/parts_disagreeing/main.dart

@@ -2,11 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
 
 part /*error: errors=LanguageVersionMismatchInPart*/ 'part.dart';
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 main() {
   foo();

pkg/front_end/test/language_versioning/data/parts_disagreeing/part.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 part of 'main.dart';
 

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package/.dart_tool/package_config.json

@@ -4,7 +4,7 @@
         {
             "name": "foo",
             "rootUri": "../lib/",
-            "languageVersion": "2.5"
+            "languageVersion": "%VERSION_MARKER1%"
         }
     ]
 }

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package/lib/foo.dart

@@ -2,14 +2,15 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// The library and its part is both technically at language version 2.5,
+// The library and its part is both technically at language version
-// but one is explicitly set, the other is not. That's an error.
+// %VERSION_MARKER1%, but one is explicitly set, the other is not. That's an
+// error.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
 
 part /*error: errors=LanguageVersionMismatchInPart*/ 'part.dart';
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 foo() {
   bar();

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   main();

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package_2/.dart_tool/package_config.json

@@ -4,7 +4,7 @@
         {
             "name": "foo",
             "rootUri": "../lib/",
-            "languageVersion": "2.5"
+            "languageVersion": "%VERSION_MARKER1%"
         }
     ]
 }

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package_2/lib/foo.dart

@@ -2,12 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// The library and its part is both technically at language version 2.5,
+// The library and its part is both technically at language version
-// but one is explicitly set, the other is not. That's an error.
+// %VERSION_MARKER1%, but one is explicitly set, the other is not. That's an
+// error.
 
 part /*error: errors=LanguageVersionMismatchInPart*/ 'part.dart';
 
-/*library: languageVersion=2.5*/
+/*library: languageVersion=%VERSION_MARKER1%*/
 
 foo() {
   bar();

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package_2/lib/part.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.5
+// @dart = %VERSION_MARKER1%
 
 part of 'foo.dart';
 

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package_2/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   main();

pkg/front_end/test/language_versioning/data/specified_packages_01/foo2/foo.dart

@@ -1,4 +1,4 @@
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 String foo() {
   return "42";

pkg/front_end/test/language_versioning/data/specified_packages_01/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   var result = foo();

pkg/front_end/test/language_versioning/data/specified_packages_02/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import /*error: errors=UntranslatableUri*/ 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   var result = /*error: errors=MethodNotFound*/ notNamedFoo();

pkg/front_end/test/language_versioning/data/specified_packages_03/foo2/foo.dart

@@ -1,4 +1,4 @@
-/*library: languageVersion=2.8*/
+/*library: languageVersion=%CURRENT_VERSION_MARKER%*/
 
 String foo() {
   return "42";

pkg/front_end/test/language_versioning/data/specified_packages_03/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   var result = foo();

pkg/front_end/test/language_versioning/data/specified_packages_04/main.dart

@@ -5,11 +5,11 @@
 // Set version of this file (not technically in package) explicitly to test as
 // much as possibly separately.
 
-// @dart = 2.4
+// @dart = %VERSION_MARKER0%
 
 import /*error: errors=UntranslatableUri*/ 'package:foo/foo.dart';
 
-/*library: languageVersion=2.4*/
+/*library: languageVersion=%VERSION_MARKER0%*/
 
 main() {
   var result = /*error: errors=MethodNotFound*/ notNamedFoo();

pkg/front_end/test/language_versioning/language_versioning_test.dart

@@ -25,6 +25,8 @@ import 'package:front_end/src/testing/id_testing_helper.dart'
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' show Component, Library, Version;
 
+import '../utils/symbolic_language_versions.dart';
+
 Future<void> main(List<String> args) async {
   // Fix default/max major and minor version so we can test it.
   // This config sets it to 2.8.
@@ -40,7 +42,9 @@ Future<void> main(List<String> args) async {
       skipList: [
         // Two language versions specified, the last one is ok and is used here.
         "package_default_version_is_wrong_2",
-      ]);
+      ],
+      preprocessFile: replaceMarkersWithVersions,
+      postProcessData: replaceVersionsWithMarkers);
 }
 
 class TestConfigWithLanguageVersion extends CfeTestConfig {
@@ -50,7 +54,8 @@ class TestConfigWithLanguageVersion extends CfeTestConfig {
   @override
   CompilerOptions customizeCompilerOptions(
       CompilerOptions options, TestData testData) {
-    options.currentSdkVersion = "2.8";
+    options.currentSdkVersion =
+        SymbolicLanguageVersion.currentVersion.version.toText();
 
     File f = new File.fromUri(testData.testFileUri.resolve("test.options"));
     if (f.existsSync()) {

pkg/front_end/test/patching/data/opt_in/origin.dart

@@ -4,6 +4,6 @@
 
 /*cfe:nnbd.library: nnbd=true*/
 
-// @dart=2.9999
+// @dart=%NNBD_VERSION_MARKER%
 
 external int method(int? i);

pkg/front_end/test/patching/data/opt_in/patch.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.9999
+// @dart=%NNBD_VERSION_MARKER%
 
 // ignore: import_internal_library
 import 'dart:_internal';

pkg/front_end/test/patching/data/opt_in_patch/origin.dart

@@ -4,6 +4,6 @@
 
 /*cfe:nnbd.library: nnbd=false*/
 
-// @dart=2.6
+// @dart=%LEGACY_VERSION_MARKER%
 
 external int method(int i);

pkg/front_end/test/patching/data/opt_in_patch/patch.dart

@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /*cfe:nnbd.error: message=The language version override has to be the same in the library and its patch(es).*/
-// @dart=2.9999
+// @dart=%NNBD_VERSION_MARKER%
 
 // ignore: import_internal_library
 import 'dart:_internal';

pkg/front_end/test/patching/data/opt_out/origin.dart

@@ -4,6 +4,6 @@
 
 /*cfe:nnbd.library: nnbd=false*/
 
-// @dart=2.6
+// @dart=%LEGACY_VERSION_MARKER%
 
 external int method();

pkg/front_end/test/patching/data/opt_out/patch.dart

@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.6
+// @dart=%LEGACY_VERSION_MARKER%
 
 // ignore: import_internal_library
 import 'dart:_internal';

pkg/front_end/test/patching/data/opt_out_patch/origin.dart

@@ -4,6 +4,6 @@
 
 /*cfe:nnbd.library: nnbd=true*/
 
-// @dart=2.9999
+// @dart=%NNBD_VERSION_MARKER%
 
 external int method();

pkg/front_end/test/patching/data/opt_out_patch/patch.dart

@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /*cfe:nnbd.error: message=The language version override has to be the same in the library and its patch(es).*/
-// @dart=2.6
+// @dart=%LEGACY_VERSION_MARKER%
 
 // ignore: import_internal_library
 import 'dart:_internal';

pkg/front_end/test/patching/patching_test.dart

@@ -20,6 +20,7 @@ import 'package:front_end/src/fasta/scope.dart';
 import 'package:front_end/src/testing/id_testing_helper.dart';
 import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart';
+import '../utils/symbolic_language_versions.dart';
 
 Future<void> main(List<String> args) async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
@@ -46,7 +47,9 @@ Future<void> main(List<String> args) async {
           'opt_out',
           'opt_out_patch',
         ]
-      });
+      },
+      preprocessFile: replaceMarkersWithVersions,
+      postProcessData: replaceVersionsWithMarkers);
 }
 
 class TestConfigWithLanguageVersion extends CfeTestConfig {
@@ -61,7 +64,8 @@ class TestConfigWithLanguageVersion extends CfeTestConfig {
 
   @override
   void customizeCompilerOptions(CompilerOptions options, TestData testData) {
-    options.currentSdkVersion = "2.9999";
+    options.currentSdkVersion =
+        SymbolicLanguageVersion.nnbdVersion.version.toText();
   }
 }
 

pkg/front_end/test/utils/symbolic_language_versions.dart

@@ -0,0 +1,87 @@
+// Copyright (c) 2024, 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.
+
+import 'package:kernel/ast.dart';
+
+/// Symbolic language versions for use in testing.
+enum SymbolicLanguageVersion {
+  /// A valid language version the opts out of null safety.
+  legacyVersion("%LEGACY_VERSION_MARKER%", const Version(2, 6)),
+
+  /// A valid language version the opts in to null safety.
+  nnbdVersion("%NNBD_VERSION_MARKER%", const Version(2, 12)),
+
+  /// An invalid language version that is lower than [lowestVersion].
+  // TODO(johnniwinther): Report error on this.
+  tooLowVersion("%TOO_LOW_VERSION_MARKER%", const Version(1, 0)),
+
+  /// The lowest supported language version.
+  lowestVersion("%LOWEST_VERSION_MARKER%", const Version(2, 0)),
+
+  /// A valid language version larger than [lowestVersion] and lower than
+  /// [version1].
+  version0("%VERSION_MARKER0%", const Version(2, 4)),
+
+  /// A valid language version larger than [version0] and lower than
+  /// [version2].
+  version1("%VERSION_MARKER1%", const Version(2, 5)),
+
+  /// A valid language version larger than [version1] and lower than
+  /// [currentVersion].
+  version2("%VERSION_MARKER2%", const Version(2, 6)),
+
+  /// The current language version. This is also the highest supported version.
+  currentVersion("%CURRENT_VERSION_MARKER%", const Version(2, 8)),
+
+  /// An invalid language version that is higher than [currentVersion].
+  tooHighVersion("%TOO_HIGH_VERSION_MARKER%", const Version(2, 9999));
+
+  final String marker;
+  final Version version;
+
+  const SymbolicLanguageVersion(this.marker, this.version);
+}
+
+late final bool _validMarkers = _checkMarkers();
+
+bool _checkMarkers() {
+  return SymbolicLanguageVersion.tooLowVersion.version <
+          SymbolicLanguageVersion.lowestVersion.version &&
+      SymbolicLanguageVersion.lowestVersion.version <
+          SymbolicLanguageVersion.version0.version &&
+      SymbolicLanguageVersion.version0.version <
+          SymbolicLanguageVersion.version1.version &&
+      SymbolicLanguageVersion.version1.version <
+          SymbolicLanguageVersion.version2.version &&
+      SymbolicLanguageVersion.version2.version <
+          SymbolicLanguageVersion.currentVersion.version &&
+      SymbolicLanguageVersion.currentVersion.version <
+          SymbolicLanguageVersion.tooHighVersion.version;
+}
+
+/// Replaces all occurrences of symbolic language markers in [text] with their
+/// corresponding version as text.
+String replaceMarkersWithVersions(String text) {
+  assert(_validMarkers);
+  for (SymbolicLanguageVersion symbolicVersion
+      in SymbolicLanguageVersion.values) {
+    String marker = symbolicVersion.marker;
+    Version version = symbolicVersion.version;
+    text = text.replaceAll(marker, version.toText());
+  }
+  return text;
+}
+
+/// Replaces all occurrences language versions as text in [text] with the
+/// corresponding symbolic language markers.
+String replaceVersionsWithMarkers(String text) {
+  assert(_validMarkers);
+  for (SymbolicLanguageVersion symbolicVersion
+      in SymbolicLanguageVersion.values) {
+    String marker = symbolicVersion.marker;
+    Version version = symbolicVersion.version;
+    text = text.replaceAll(version.toText(), marker);
+  }
+  return text;
+}