TransactionToken* token) override;
  Status CreateDir(const std::string& dirname,
                   TransactionToken* token) override;
  Status Stat(const std::string& fname, TransactionToken* token,
              FileStatistics* stat) override;
  Status IsDirectory(const std::string& fname,
                     TransactionToken* token) override;
  Status GetFileSize(const std::string& fname, TransactionToken* token,

  bool (*is_directory)(const TF_Filesystem* filesystem, const char* path,
                       TF_Status* status);

  /// Returns the size of the file given by `path`.
  ///
  /// If `status` is not `TF_OK`, return value is undefined. Otherwise, returns
  /// the same as `length` member of a `TF_FileStatistics` that would be used on
  /// the equivalent call of `stat`.
  ///
  /// Plugins:

      new GradientTape<Gradient, BackwardFunction, TapeTensor>(false));
  AccumulatorCallState& call_state = call_state_.top();
  call_state.backward_tape = tape.get();
  auto pop_backward_tape =
      gtl::MakeCleanup([&call_state] { call_state.backward_tape = nullptr; });
  std::vector<Gradient*> forwardprop_aids;
  std::vector<int64_t> sources;
  std::unordered_set<int64_t> sources_set;