anchor.diff:      int hostPort,
       bool ipv6,
       bool disableServiceAuthCodes, {
  -    @required Logger logger,
  +    required Logger logger,
     }) async {
       final Uri ddsUri = Uri(
         scheme: 'http',
  
positive.code:         io.InternetAddress.loopbackIPv6 :
          io.InternetAddress.loopbackIPv4
        ).host,
        port: hostPort ?? 0,
      );
      logger.printTrace(
        'Launching a Dart Developer Service (DDS) instance at $ddsUri, '
  
negative.code: /// Helper class to launch a [dds.DartDevelopmentService]. Allows for us to
  /// mock out this functionality for testing purposes.
  class DartDevelopmentService {
    dds.DartDevelopmentService? _ddsInstance;
  
    Uri? get uri => _ddsInstance?.uri ?? _existingDdsUri;
    Uri? _existingDdsUri;
  
    Future<void> get done => _completer.future;
    final Completer<void> _completer = Completer<void>();
  