anchor.diff:      var outputPath = path.url.join(path.url.dirname(id.path), mappingsFileName);
       var generatedAssetId = new AssetId(id.package, outputPath);
   
  -    _transformEntryFile(
  -        transform, resolver, mappingsFileName, mappingsClassName);
  +    if (!_transformEntryFile(
  +        transform, resolver, mappingsFileName, mappingsClassName)) return;
   
       var mappingsFile = new MappingsGenerator(resolver, id, _options.formatCode)
           .generate(mappingsClassName, _options.libraryNames);
  
positive.code:     transform.addOutput(new Asset.fromString(generatedAssetId, mappingsFile));
    }
  
    void _transformEntryFile(Transform transform, Resolver resolver,
        String mappingsFileName, String mappingsClassName) {
      AssetId id = transform.primaryInput.id;
      var lib = resolver.getLibrary(id);
      var unit = lib.definingCompilationUnit.computeNode();
      var transaction = resolver.createTextEditTransaction(lib);
  
      var importParameters = _getImportParameters(unit);
  
negative.code:     var printer = transaction.commit();
      printer.build(id.path);
      transform.addOutput(new Asset.fromString(id, printer.text));
  
      return true;
    }
  
    _EntryPointImportParameters _getImportParameters(dynamic unit) {
  