anchor.diff:    // tell which web errors are web-specific.
     List<StaticError> cfeErrors;
     if (insert.contains(ErrorSource.cfe) || insert.contains(ErrorSource.web)) {
  +    var cfeOptions = [
  +      if (testFile.requirements.contains(Feature.nnbdWeak)) "--nnbd-weak",
  +      if (testFile.requirements.contains(Feature.nnbdStrong)) "--nnbd-strong",
  +      ...options
  +    ];
       // Clear the previous line.
       stdout.write("\r${file.path}                      ");
       stdout.write("\r${file.path} (Running CFE...)");
  -    cfeErrors = await runCfe(file.absolute.path, options);
  +    cfeErrors = await runCfe(file.absolute.path, cfeOptions);
       if (cfeErrors == null) {
         print("Error: failed to update ${file.path}");
       } else if (insert.contains(ErrorSource.cfe)) {
  
positive.code:       allowed: sources);
  
    parser.addSeparator("Other flags:");
    parser.addFlag("null-safety",
        help: "Enable the 'non-nullable' experiment.", negatable: false);
  
    var results = parser.parse(args);
  
  
negative.code:   }
  
    var dryRun = results["dry-run"] as bool;
  
    var removeSources = <ErrorSource>{};
    var insertSources = <ErrorSource>{};
  