anchor.diff:  /// used to obtain resolved ASTs, and these are fed into kernel code generation
   /// logic.
   class IncrementalKernelGeneratorImpl implements IncrementalKernelGenerator {
  +  /// The version of data format, should be incremented on every format change.
  +  static const int DATA_VERSION = 1;
  +
     /// The compiler options, such as the [FileSystem], the SDK dill location,
     /// etc.
     final ProcessedOptions _options;
  
positive.code:       for (_LibraryCycleResult result in results) {
          for (Library library in result.kernelLibraries) {
            Uri uri = library.importUri;
            if (_uriToLatestSignature[uri] != result.signature) {
              _uriToLatestSignature[uri] = result.signature;
              program.libraries.add(library);
            }
          }
  
negative.code:       String signature;
        {
          var signatureBuilder = new ApiSignature();
          signatureBuilder.addBytes(_salt);
          Set<FileState> transitiveFiles = cycle.libraries
              .map((library) => library.transitiveFiles)
              .expand((files) => files)
  