    def init_constraints(self, batch_constraints: Optional[Tensor], beam_size: int):
        """Initialize constraint states for constrained decoding (if supported).

        Args:
            batch_constraints: (torch.Tensor, optional)
                the list of constraints, in packed form
            beam_size: (int)
                the beam size
        Returns:
            *encoder_out* rearranged according to *new_order*
        """
        pass
Initialize constraint states for constrained decoding (if supported).

Args:
batch_constraints: (torch.Tensor, optional)
the list of constraints, in packed form
beam_size: (int)
the beam size
Returns:
*encoder_out* rearranged according to *new_order*
fairseq/search.py