anchor.diff:  import 'package:analyzer/file_system/physical_file_system.dart';
   import 'package:analyzer/src/dart/analysis/analysis_context_collection.dart';
   import 'package:analyzer/src/dart/analysis/driver_based_analysis_context.dart';
  +import 'package:analyzer/src/dart/analysis/experiments.dart';
   import 'package:analyzer/src/error/codes.dart';
   import 'package:analyzer/src/generated/source.dart';
   import 'package:analyzer/src/util/sdk.dart';
  
positive.code:     logger.stdout('Migrating ${options.directory}');
      logger.stdout('');
  
      if (hasMultipleAnalysisContext) {
        logger
            .stdout('Note: more than one project found; migrating the top-level '
                'project.');
        logger.stdout('');
      }
  
  
negative.code:   static const String cmdName = 'migrate';
  
    static const String cmdDescription =
        'Perform a null safety migration on a project or package.';
  
    static const String migrationGuideLink =
        'See https://dart.dev/go/null-safety-migration for a migration guide.';
  
    static const String preFlagFlipCaveat =
        'Note: this tool is currently running on an SDK version where null '
        'safety is not yet enabled by default. You may encounter issues in the '
        'migration process - some aspects of the toolchain assume that they are '
        'running on an SDK where null safety has been enabled by default.';
  
    /// Return whether the SDK has null safety on by default.
    static bool get nullSafetyOnByDefault => IsEnabledByDefault.non_nullable;
  
    final bool verbose;
  
  