src/transformers/models/rag/retrieval_rag.py/LegacyIndex/__init__
class LegacyIndex:    def __init__(self, vector_size, index_path):
        self.index_id_to_db_id = []
        self.index_path = index_path
        self.passages = self._load_passages()
        self.vector_size = vector_size
        self.index = None
        self._index_initialized = False