anchor.diff:        results["update-cfe"] as bool ||
         results["update"] as bool;
   
  +  var nnbd = results["nnbd"] as bool;
  +
     if (!removeAnalyzer && !removeCfe && !insertAnalyzer && !insertCfe) {
       _usageError(
           parser, "Must provide at least one flag for an operation to perform.");
  
positive.code:           removeAnalyzer: removeAnalyzer,
            removeCfe: removeCfe,
            insertAnalyzer: insertAnalyzer,
            insertCfe: insertCfe);
      }
    }
  }
  
negative.code:     bool removeAnalyzer,
      bool removeCfe,
      bool insertAnalyzer,
      bool insertCfe,
      bool nnbd}) async {
    stdout.write("${file.path}...");
    var source = file.readAsStringSync();
    var testFile = TestFile.parse(Path("."), file.absolute.path, source);
  
    var experiments = [
      if (nnbd) "non-nullable",
      if (testFile.experiments.isNotEmpty) ...testFile.experiments
    ];
  
    var options = [
      ...testFile.sharedOptions,
      if (experiments.isNotEmpty) "--enable-experiment=${experiments.join(',')}"
    ];
  
    var errors = <StaticError>[];
    if (insertAnalyzer) {
  