new_contents: # Copyright (c) Facebook, Inc. and its affiliates.
  #
  # This source code is licensed under the MIT license found in the
  # LICENSE file in the root directory of this source tree.
  
  from dataclasses import dataclass, field
  
  import numpy as np
  
  from fairseq.dataclass import FairseqDataclass
  from fairseq.scoring import BaseScorer, register_scorer
  
  
  @dataclass
  class BertScoreScorerConfig(FairseqDataclass):
      bert_score_lang: str = field(default="en", metadata={"help": "BERTScore language"})
  
  
  @register_scorer("bert_score", dataclass=BertScoreScorerConfig)
  class BertScoreScorer(BaseScorer):
      def __init__(self, cfg):
          super(BertScoreScorer, self).__init__(cfg)
          try:
              import bert_score as _bert_score
          except ImportError:
              raise ImportError("Please install BERTScore: pip install bert-score")
  
          self.cfg = cfg
          self._bert_score = _bert_score
          self.scores = None
  
      def add_string(self, ref, pred):
          self.ref.append(ref)
          self.pred.append(pred)
  
      def score(self, order=4):
          _, _, self.scores = self._bert_score.score(
              self.pred, self.ref, lang=self.cfg.bert_score_lang
          )
          self.scores = self.scores.numpy()
          return np.mean(self.scores)
  
      def result_string(self, order=4):
          return f"BERTScore: {self.score():.4f}"
  
subject: add BERTScore scorer