[flutter_tools] separate concept of null safe language version from current...

[flutter_tools] separate concept of null safe language version from current language version (#79052)

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -14,6 +14,7 @@ import '../../artifacts.dart';
 import '../../base/file_system.dart';
 import '../../base/io.dart';
 import '../../build_info.dart';
+import '../../cache.dart';
 import '../../dart/language_version.dart';
 import '../../dart/package_map.dart';
 import '../../globals.dart' as globals;
@@ -103,6 +104,7 @@ class WebEntrypointTarget extends Target {
     final LanguageVersion languageVersion = determineLanguageVersion(
       environment.fileSystem.file(targetFile),
       packageConfig[flutterProject.manifest.appName],
+      Cache.flutterRoot,
     );
 
     // Use the PackageConfig to find the correct package-scheme import path

packages/flutter_tools/lib/src/dart/language_version.dart

@@ -2,9 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:file/file.dart';
 import 'package:package_config/package_config.dart';
 
+import '../base/version.dart';
+
 final RegExp _languageVersion = RegExp(r'\/\/\s*@dart\s*=\s*([0-9])\.([0-9]+)');
 final RegExp _declarationEnd = RegExp('(import)|(library)|(part)');
 const String _blockCommentStart = '/*';
@@ -13,6 +17,28 @@ const String _blockCommentEnd = '*/';
 /// The first language version where null safety was available by default.
 final LanguageVersion nullSafeVersion = LanguageVersion(2, 12);
 
+LanguageVersion? _currentLanguageVersion;
+
+/// Lookup the current Dart language version.
+LanguageVersion currentLanguageVersion(FileSystem fileSystem, String flutterRoot) {
+  if (_currentLanguageVersion != null) {
+    return _currentLanguageVersion!;
+  }
+  // Either reading the file or parsing the version could fail on a corrupt Dart SDK.
+  // let it crash so it shows up in crash logging.
+  final File versionFile = fileSystem.file(fileSystem.path.join(flutterRoot, 'bin', 'cache', 'dart-sdk', 'version'));
+  if (!versionFile.existsSync() && _inUnitTest()) {
+    return LanguageVersion(2, 12);
+  }
+  final Version version = Version.parse(versionFile.readAsStringSync())!;
+  return _currentLanguageVersion = LanguageVersion(version.major, version.minor);
+}
+
+// Whether the tool is executing in a unit test.
+bool _inUnitTest() {
+  return Zone.current[#test.declarer] != null;
+}
+
 /// Attempts to read the language version of a dart [file].
 ///
 /// If this is not present, falls back to the language version defined in
@@ -22,7 +48,7 @@ final LanguageVersion nullSafeVersion = LanguageVersion(2, 12);
 ///
 /// The specification for the language version tag is defined at:
 /// https://github.com/dart-lang/language/blob/master/accepted/future-releases/language-versioning/feature-specification.md#individual-library-language-version-override
-LanguageVersion determineLanguageVersion(File file, Package package) {
+LanguageVersion determineLanguageVersion(File file, Package package, String flutterRoot) {
   int blockCommentDepth = 0;
   // If reading the file fails, default to a null-safe version. The
   // command will likely fail later in the process with a better error
@@ -31,7 +57,7 @@ LanguageVersion determineLanguageVersion(File file, Package package) {
   try {
     lines = file.readAsLinesSync();
   } on FileSystemException {
-    return nullSafeVersion;
+    return currentLanguageVersion(file.fileSystem, flutterRoot);
   }
 
   for (final String line in lines) {
@@ -84,8 +110,8 @@ LanguageVersion determineLanguageVersion(File file, Package package) {
 
   // If the language version cannot be found, use the package version.
   if (package != null) {
-    return package.languageVersion ?? nullSafeVersion;
+    return package.languageVersion ?? currentLanguageVersion(file.fileSystem, flutterRoot);
   }
-  // Default to 2.12
-  return nullSafeVersion;
+  // Default to current version.
+  return currentLanguageVersion(file.fileSystem, flutterRoot);
 }

packages/flutter_tools/lib/src/isolated/resident_web_runner.dart

@@ -25,6 +25,7 @@ import '../base/time.dart';
 import '../base/utils.dart';
 import '../build_info.dart';
 import '../build_system/targets/web.dart';
+import '../cache.dart';
 import '../dart/language_version.dart';
 import '../devfs.dart';
 import '../device.dart';
@@ -678,6 +679,7 @@ class ResidentWebRunner extends ResidentRunner {
       final LanguageVersion languageVersion =  determineLanguageVersion(
         _fileSystem.file(mainUri),
         packageConfig[flutterProject.manifest.appName],
+        Cache.flutterRoot,
       );
 
       final String entrypoint = <String>[

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -892,6 +892,7 @@ abstract class FlutterCommand extends Command<void> {
         final LanguageVersion languageVersion = determineLanguageVersion(
           entrypointFile,
           packageConfig.packageOf(entrypointFile.absolute.uri),
+          Cache.flutterRoot,
         );
         // Extra frontend options are only provided if explicitly
         // requested.

packages/flutter_tools/lib/src/test/flutter_platform.dart

@@ -14,6 +14,7 @@ import 'package:test_core/src/platform.dart'; // ignore: implementation_imports
 import '../base/common.dart';
 import '../base/file_system.dart';
 import '../base/io.dart';
+import '../cache.dart';
 import '../compile.dart';
 import '../convert.dart';
 import '../dart/language_version.dart';
@@ -512,6 +513,7 @@ class FlutterPlatform extends PlatformPlugin {
     final LanguageVersion languageVersion = determineLanguageVersion(
       file,
       packageConfig[flutterProject?.manifest?.appName],
+      Cache.flutterRoot,
     );
     return generateTestBootstrap(
       testUrl: testUrl,

packages/flutter_tools/lib/src/test/web_test_compiler.dart

@@ -16,6 +16,7 @@ import '../base/logger.dart';
 import '../base/platform.dart';
 import '../build_info.dart';
 import '../bundle.dart';
+import '../cache.dart';
 import '../compile.dart';
 import '../dart/language_version.dart';
 import '../web/bootstrap.dart';
@@ -63,7 +64,7 @@ class WebTestCompiler {
       }
     } else if (buildInfo.nullSafetyMode == NullSafetyMode.sound) {
       platformDillArtifact = Artifact.webPlatformSoundKernelDill;
-      languageVersion = nullSafeVersion;
+      languageVersion = currentLanguageVersion(_fileSystem, Cache.flutterRoot);
       if (!extraFrontEndOptions.contains('--sound-null-safety')) {
         extraFrontEndOptions.add('--sound-null-safety');
       }