anchor.diff:  import 'package:_fe_analyzer_shared/src/scanner/scanner.dart'
       show LanguageVersionToken, Scanner, ScannerConfiguration, scan;
   
  -import 'package:kernel/ast.dart' show Version, defaultLanguageVersion;
  +import 'package:kernel/ast.dart' show Version;
   export 'package:kernel/ast.dart' show Version;
   
   import 'package:package_config/package_config.dart'
  
positive.code: 
  import 'compiler_options.dart' show CompilerOptions;
  
  import 'file_system.dart' show FileSystem, FileSystemException;
  
  /// Gets the language version for a specific URI.
  
negative.code:   });
  }
  
  /// Returns `true` if the language version of [uri] does not support null
  /// safety.
  Future<bool> uriUsesLegacyLanguageVersion(
      Uri uri, CompilerOptions options) async {
    // This method is here in order to use the opt out hack here for test
    // sources.
    if (SourceLibraryBuilder.isOptOutTest(uri)) return true;
    Version uriVersion = await languageVersionForUri(uri, options);
    return (uriVersion < experimentReleasedVersion[ExperimentalFlag.nonNullable]);
  }
  