code: # coding=utf-8
  # Copyright 2020 The Facebook AI Research Team Authors and The HuggingFace Inc. team.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  """TF BART model, ported from the fairseq repo."""
  
  import math
  import random
  import warnings
  from typing import Dict, Optional, Tuple, Union
  
  import numpy as np
  import tensorflow as tf
  
  from ...activations_tf import ACT2FN
  from ...file_utils import (
      add_code_sample_docstrings,
      add_start_docstrings,
      add_start_docstrings_to_model_forward,
      replace_return_docstrings,
  )
  from ...modeling_tf_outputs import (
      TFBaseModelOutput,
      TFBaseModelOutputWithPast,
      TFSeq2SeqLMOutput,
      TFSeq2SeqModelOutput,
  )
  
  # Public API
  from ...modeling_tf_utils import (
      DUMMY_INPUTS,
      TFPreTrainedModel,
      TFSharedEmbeddings,
      TFWrappedEmbeddings,
      input_processing,
      keras_serializable,
      shape_list,
  )
  from ...utils import logging
  from .configuration_bart import BartConfig
  
  
  logger = logging.get_logger(__name__)
  
  _CONFIG_FOR_DOC = "BartConfig"
  _TOKENIZER_FOR_DOC = "BartTokenizer"
  
  LARGE_NEGATIVE = -1e8
  
  
  def shift_tokens_right(input_ids: tf.Tensor, pad_token_id: int, eos_token_id: int):
      shifted_input_ids = tf.cast(input_ids, tf.int32)
      shifted_input_ids = tf.roll(shifted_input_ids, 1, axis=-1)
      start_tokens = tf.fill((shape_list(shifted_input_ids)[0], 1), eos_token_id)
      shifted_input_ids = tf.concat([start_tokens, shifted_input_ids[:, 1:]], -1)
      # replace possible -100 values in labels by `pad_token_id`
      shifted_input_ids = tf.where(
          shifted_input_ids == -100, tf.fill(shape_list(shifted_input_ids), pad_token_id), shifted_input_ids
      )
  
      # "Verify that `labels` has only positive values and -100"
      assert_gte0 = tf.debugging.assert_greater_equal(shifted_input_ids, tf.cast(0, tf.int32))
  
      # Make sure the assertion op is called by wrapping the result in an identity no-op
      with tf.control_dependencies([assert_gte0]):
          shifted_input_ids = tf.identity(shifted_input_ids)
  
      return shifted_input_ids
  
  
  def _make_causal_mask(input_ids_shape: tf.TensorShape, past_key_values_length: int = 0):
      """
      Make causal mask used for bi-directional self-attention.
      """
      bsz, tgt_len = input_ids_shape
      mask = tf.ones((tgt_len, tgt_len), dtype=tf.float32) * LARGE_NEGATIVE
      mask_cond = tf.range(shape_list(mask)[-1])
  
      mask = tf.where(mask_cond < tf.reshape(mask_cond + 1, (shape_list(mask)[-1], 1)), 0.0, mask)
      mask = tf.cast(mask, tf.float32)
  
      if past_key_values_length > 0:
          mask = tf.concat([tf.zeros((tgt_len, past_key_values_length), dtype=tf.float32), mask], axis=-1)
      return tf.broadcast_to(mask[None, None, :, :], (bsz, 1, tgt_len, tgt_len + past_key_values_length))
  
  
  def _expand_mask(mask: tf.Tensor, tgt_len: Optional[int] = None):
      """
      Expands attention_mask from `[bsz, seq_len]` to `[bsz, 1, tgt_seq_len, src_seq_len]`.
      """
      bsz, src_len = shape_list(mask)
      tgt_len = tgt_len if tgt_len is not None else src_len
  
      expanded_mask = tf.cast(tf.broadcast_to(mask[:, None, None, :], (bsz, 1, tgt_len, src_len)), tf.float32)
  
      return (1.0 - expanded_mask) * LARGE_NEGATIVE
  
  
  class TFBartLearnedPositionalEmbedding(TFSharedEmbeddings):
      """
      This module learns positional embeddings up to a fixed maximum size. Padding ids are ignored by either offsetting
      based on padding_idx or by setting padding_idx to None and ensuring that the appropriate position ids are passed to
      the forward function.
      """
  
      def __init__(self, num_embeddings: int, embedding_dim: int, padding_idx: int, offset, **kwargs):
          # Bart is set up so that if padding_idx is specified then offset the embedding ids by 2
          # and adjust num_embeddings appropriately. Other models dont have this hack
          self.offset = offset
          assert padding_idx is not None, "padding_idx cannot be None"
          num_embeddings += offset
          super().__init__(num_embeddings, embedding_dim, **kwargs)
  
      def call(self, input_shape: tf.TensorShape, past_key_values_length: int = 0):
          """Input is expected to be of size [bsz x seqlen]."""
          bsz, seq_len = input_shape[:2]
  
          positions = tf.range(
              past_key_values_length, seq_len + past_key_values_length, delta=1, dtype=tf.int32, name="range"
          )
          return super().call(positions + self.offset)  # super object is not callable for some reason
  
  
  class TFBartSinusoidalPositionalEmbedding(tf.keras.layers.Embedding):
      """This module produces sinusoidal positional embeddings of any length."""
  
      def __init__(self, num_positions: int, embedding_dim: int, **kwargs):
  
          if embedding_dim % 2 != 0:
              raise NotImplementedError(f"odd embedding_dim {embedding_dim} not supported")
          super().__init__(
              num_positions,
              embedding_dim,
              **kwargs,
          )
  
      def build(self, input_shape: tf.TensorShape):
          """
          Build shared token embedding layer Shared weights logic adapted from
          https://github.com/tensorflow/models/blob/a009f4fb9d2fc4949e32192a944688925ef78659/official/transformer/v2/embedding_layer.py#L24
          """
          super().build(input_shape)  # Instantiates self.weight so it can be loaded
          weight: np.ndarray = self._init_weight(self.input_dim, self.output_dim)
          self.set_weights([weight])  # overwrite self.weight to correct value
  
      @staticmethod
      def _init_weight(n_pos: int, dim: int):
          """
          Identical to the XLM create_sinusoidal_embeddings except features are not interleaved. The cos features are in
          the 2nd half of the vector. [dim // 2:]
          """
          position_enc = np.array(
              [[pos / np.power(10000, 2 * (j // 2) / dim) for j in range(dim)] for pos in range(n_pos)]
          )
          # index 0 is all zero
          position_enc[:, 0 : dim // 2] = np.sin(position_enc[:, 0::2])
          position_enc[:, dim // 2 :] = np.cos(position_enc[:, 1::2])
          # convert to tensor
          table = tf.convert_to_tensor(position_enc, dtype=tf.float32)
          tf.stop_gradient(table)
          return table
  
      def call(self, input_shape: tf.TensorShape, past_key_values_length: int = 0):
          """Input is expected to be of size [bsz x seqlen]."""
          bsz, seq_len = input_shape[:2]
  
          positions = tf.range(
              past_key_values_length, seq_len + past_key_values_length, delta=1, dtype=tf.int32, name="range"
          )
          return super().call(positions)
  
  
  class TFBartAttention(tf.keras.layers.Layer):
      """Multi-headed attention from "Attention Is All You Need"""
  
      def __init__(
          self,
          embed_dim: int,
          num_heads: int,
          dropout: float = 0.0,
          is_decoder: bool = False,
          bias: bool = True,
          **kwargs,
      ):
          super().__init__(**kwargs)
          self.embed_dim = embed_dim
  
          self.num_heads = num_heads
          self.dropout = tf.keras.layers.Dropout(dropout)
          self.head_dim = embed_dim // num_heads
          assert self.head_dim * num_heads == self.embed_dim, "embed_dim must be divisible by num_heads"
          self.scaling = self.head_dim ** -0.5
          self.is_decoder = is_decoder
  
          self.k_proj = tf.keras.layers.Dense(embed_dim, use_bias=bias, name="k_proj")
          self.q_proj = tf.keras.layers.Dense(embed_dim, use_bias=bias, name="q_proj")
          self.v_proj = tf.keras.layers.Dense(embed_dim, use_bias=bias, name="v_proj")
          self.out_proj = tf.keras.layers.Dense(embed_dim, use_bias=bias, name="out_proj")
  
      def _shape(self, tensor: tf.Tensor, seq_len: int, bsz: int):
          return tf.transpose(tf.reshape(tensor, (bsz, seq_len, self.num_heads, self.head_dim)), (0, 2, 1, 3))
  
      def call(
          self,
          hidden_states: tf.Tensor,
          key_value_states: Optional[tf.Tensor] = None,
          past_key_value: Optional[Tuple[Tuple[tf.Tensor]]] = None,
          attention_mask: Optional[tf.Tensor] = None,
          training=False,
      ) -> Tuple[tf.Tensor, Optional[tf.Tensor]]:
          """Input shape: Batch x Time x Channel"""
  
          # if key_value_states are provided this layer is used as a cross-attention layer
          # for the decoder
          is_cross_attention = key_value_states is not None
          bsz, tgt_len, embed_dim = shape_list(hidden_states)
  
          # get query proj
          query_states = self.q_proj(hidden_states) * self.scaling
          # get key, value proj
          if is_cross_attention and past_key_value is not None:
              # reuse k,v, cross_attentions
              key_states = past_key_value[0]
              value_states = past_key_value[1]
          elif is_cross_attention:
              # cross_attentions
              key_states = self._shape(self.k_proj(key_value_states), -1, bsz)
              value_states = self._shape(self.v_proj(key_value_states), -1, bsz)
          elif past_key_value is not None:
              # reuse k, v, self_attention
              key_states = self._shape(self.k_proj(hidden_states), -1, bsz)
              value_states = self._shape(self.v_proj(hidden_states), -1, bsz)
              key_states = tf.concat([past_key_value[0], key_states], axis=2)
              value_states = tf.concat([past_key_value[1], value_states], axis=2)
          else:
              # self_attention
              key_states = self._shape(self.k_proj(hidden_states), -1, bsz)
              value_states = self._shape(self.v_proj(hidden_states), -1, bsz)
  
          if self.is_decoder:
              # if cross_attention save Tuple(tf.Tensor, tf.Tensor) of all cross attention key/value_states.
              # Further calls to cross_attention layer can then reuse all cross-attention
              # key/value_states (first "if" case)
              # if uni-directional self-attention (decoder) save Tuple(tf.Tensor, tf.Tensor) of
              # all previous decoder key/value_states. Further calls to uni-directional self-attention
              # can concat previous decoder key/value_states to current projected key/value_states (third "elif" case)
              # if encoder bi-directional self-attention `past_key_value` is always `None`
              past_key_value = (key_states, value_states)
  
          proj_shape = (bsz * self.num_heads, -1, self.head_dim)
          query_states = tf.reshape(self._shape(query_states, tgt_len, bsz), proj_shape)
          key_states = tf.reshape(key_states, proj_shape)
          value_states = tf.reshape(value_states, proj_shape)
  
          src_len = shape_list(key_states)[1]
          attn_weights = tf.matmul(query_states, key_states, transpose_b=True)
  
          tf.debugging.assert_equal(
              shape_list(attn_weights),
              [bsz * self.num_heads, tgt_len, src_len],
              message=f"Attention weights should be of size {(bsz * self.num_heads, tgt_len, src_len)}, but is {shape_list(attn_weights)}",
          )
  
          if attention_mask is not None:
              tf.debugging.assert_equal(
                  shape_list(attention_mask),
                  [bsz, 1, tgt_len, src_len],
                  message=f"Attention mask should be of size {(bsz, 1, tgt_len, src_len)}, but is {shape_list(attention_mask)}",
              )
              attn_weights = tf.reshape(attn_weights, (bsz, self.num_heads, tgt_len, src_len)) + attention_mask
              attn_weights = tf.reshape(attn_weights, (bsz * self.num_heads, tgt_len, src_len))
  
          attn_weights = tf.nn.softmax(attn_weights, axis=-1)
  
          attn_probs = self.dropout(attn_weights, training=training)
  
          attn_output = tf.matmul(attn_probs, value_states)
  
          tf.debugging.assert_equal(
              shape_list(attn_output),
              [bsz * self.num_heads, tgt_len, self.head_dim],
              message=f"`attn_output` should be of size {(bsz, self.num_heads, tgt_len, self.head_dim)}, but is {shape_list(attn_output)}",
          )
  
          attn_output = tf.transpose(
              tf.reshape(attn_output, (bsz, self.num_heads, tgt_len, self.head_dim)), (0, 2, 1, 3)
          )
          attn_output = tf.reshape(attn_output, (bsz, tgt_len, embed_dim))
  
          attn_output = self.out_proj(attn_output)
          attn_weights: tf.Tensor = tf.reshape(attn_weights, (bsz, self.num_heads, tgt_len, src_len))
  
          return attn_output, attn_weights, past_key_value
  
  
  class TFBartEncoderLayer(tf.keras.layers.Layer):
      def __init__(self, config: BartConfig, **kwargs):
          super().__init__(**kwargs)
          self.embed_dim = config.d_model
          self.self_attn = TFBartAttention(
              self.embed_dim, config.encoder_attention_heads, dropout=config.attention_dropout, name="self_attn"
          )
          self.normalize_before = config.normalize_before
          self.self_attn_layer_norm = tf.keras.layers.LayerNormalization(epsilon=1e-5, name="self_attn_layer_norm")
          self.dropout = tf.keras.layers.Dropout(config.dropout)
          self.activation_fn = ACT2FN[config.activation_function]
          self.activation_dropout = tf.keras.layers.Dropout(config.activation_dropout)
          self.fc1 = tf.keras.layers.Dense(config.encoder_ffn_dim, name="fc1")
          self.fc2 = tf.keras.layers.Dense(self.embed_dim, name="fc2")
          self.final_layer_norm = tf.keras.layers.LayerNormalization(epsilon=1e-5, name="final_layer_norm")
  
      def call(self, hidden_states: tf.Tensor, attention_mask: tf.Tensor, training=False):
          """
          Args:
              hidden_states (:obj:`tf.Tensor`): input to the layer of shape `(seq_len, batch, embed_dim)`
              attention_mask (:obj:`tf.Tensor`): attention mask of size
                  `(batch, 1, tgt_len, src_len)` where padding elements are indicated by very large negative values.
          """
          residual = hidden_states
          if self.normalize_before:
              hidden_states = self.self_attn_layer_norm(hidden_states)
          hidden_states, self_attn_weights, _ = self.self_attn(
              hidden_states=hidden_states, attention_mask=attention_mask
          )
          tf.debugging.assert_equal(
              shape_list(hidden_states),
              shape_list(residual),
              message=f"Self attn modified the shape of query {shape_list(residual)} to {shape_list(hidden_states)}",
          )
          hidden_states = self.dropout(hidden_states, training=training)
          hidden_states = residual + hidden_states
          if not self.normalize_before:
              hidden_states = self.self_attn_layer_norm(hidden_states)
  
          residual = hidden_states
          if self.normalize_before:
              hidden_states = self.final_layer_norm(hidden_states)
          hidden_states = self.activation_fn(self.fc1(hidden_states))
          hidden_states = self.activation_dropout(hidden_states, training=training)
          hidden_states = self.fc2(hidden_states)
          hidden_states = self.dropout(hidden_states, training=training)
          hidden_states = residual + hidden_states
          if not self.normalize_before:
              hidden_states = self.final_layer_norm(hidden_states)
  
          return hidden_states, self_attn_weights
  
  
  class TFBartDecoderLayer(tf.keras.layers.Layer):
      def __init__(self, config: BartConfig, **kwargs):
          super().__init__(**kwargs)
          self.embed_dim = config.d_model
          self.self_attn = TFBartAttention(
              embed_dim=self.embed_dim,
              num_heads=config.decoder_attention_heads,
              dropout=config.attention_dropout,
              name="self_attn",
              is_decoder=True,
          )
          self.dropout = tf.keras.layers.Dropout(config.dropout)
          self.activation_fn = ACT2FN[config.activation_function]
          self.activation_dropout = tf.keras.layers.Dropout(config.activation_dropout)
          self.normalize_before = config.normalize_before
  
          self.self_attn_layer_norm = tf.keras.layers.LayerNormalization(epsilon=1e-5, name="self_attn_layer_norm")
          self.encoder_attn = TFBartAttention(
              self.embed_dim,
              config.decoder_attention_heads,
              dropout=config.attention_dropout,
              name="encoder_attn",
              is_decoder=True,
          )
          self.encoder_attn_layer_norm = tf.keras.layers.LayerNormalization(epsilon=1e-5, name="encoder_attn_layer_norm")
          self.fc1 = tf.keras.layers.Dense(config.decoder_ffn_dim, name="fc1")
          self.fc2 = tf.keras.layers.Dense(self.embed_dim, name="fc2")
          self.final_layer_norm = tf.keras.layers.LayerNormalization(epsilon=1e-5, name="final_layer_norm")
  
      def call(
          self,
          hidden_states,
          attention_mask: Optional[tf.Tensor] = None,
          encoder_hidden_states: Optional[tf.Tensor] = None,
          encoder_attention_mask: Optional[tf.Tensor] = None,
          past_key_value: Optional[Tuple[tf.Tensor]] = None,
          training=False,
      ) -> Tuple[tf.Tensor, tf.Tensor, Tuple[Tuple[tf.Tensor]]]:
          """
          Args:
              hidden_states (:obj:`tf.Tensor`): input to the layer of shape `(seq_len, batch, embed_dim)`
              attention_mask (:obj:`tf.Tensor`): attention mask of size
                  `(batch, 1, tgt_len, src_len)` where padding elements are indicated by very large negative values.
              encoder_hidden_states (:obj:`tf.Tensor`): cross attention input to the layer of shape `(seq_len, batch, embed_dim)`
              encoder_attention_mask (:obj:`tf.Tensor`): encoder attention mask of size
                  `(batch, 1, tgt_len, src_len)` where padding elements are indicated by very large negative values.
              past_key_value (:obj:`Tuple(tf.Tensor)`): cached past key and value projection states
          """
          residual = hidden_states
          if self.normalize_before:
              hidden_states = self.self_attn_layer_norm(hidden_states)
  
          # Self Attention
          # decoder uni-directional self-attention cached key/values tuple is at positions 1,2
          self_attn_past_key_value = past_key_value[:2] if past_key_value is not None else None
          # add present self-attn cache to positions 1,2 of present_key_value tuple
          hidden_states, self_attn_weights, present_key_value = self.self_attn(
              hidden_states=hidden_states,
              past_key_value=self_attn_past_key_value,
              attention_mask=attention_mask,
          )
          hidden_states = self.dropout(hidden_states, training=training)
          hidden_states = residual + hidden_states
          if not self.normalize_before:
              hidden_states = self.self_attn_layer_norm(hidden_states)
  
          # Cross-Attention Block
          cross_attn_present_key_value = None
          if encoder_hidden_states is not None:
              residual = hidden_states
              if self.normalize_before:
                  hidden_states = self.encoder_attn_layer_norm(hidden_states)
  
              # cross_attn cached key/values tuple is at positions 3,4 of present_key_value tuple
              cross_attn_past_key_value = past_key_value[-2:] if past_key_value is not None else None
              hidden_states, _, cross_attn_present_key_value = self.encoder_attn(
                  hidden_states=hidden_states,
                  key_value_states=encoder_hidden_states,
                  attention_mask=encoder_attention_mask,
                  past_key_value=cross_attn_past_key_value,
              )
              hidden_states = self.dropout(hidden_states, training=training)
              hidden_states = residual + hidden_states
              if not self.normalize_before:
                  hidden_states = self.encoder_attn_layer_norm(hidden_states)
  
              # add cross-attn to positions 3,4 of present_key_value tuple
              present_key_value = present_key_value + cross_attn_present_key_value
  
          # Fully Connected
          residual = hidden_states
          if self.normalize_before:
              hidden_states = self.final_layer_norm(hidden_states)
          hidden_states = self.activation_fn(self.fc1(hidden_states))
          hidden_states = self.activation_dropout(hidden_states, training=training)
          hidden_states = self.fc2(hidden_states)
          hidden_states = self.dropout(hidden_states, training=training)
          hidden_states = residual + hidden_states
  
          if not self.normalize_before:
              hidden_states = self.final_layer_norm(hidden_states)
  
          return (
              hidden_states,
              self_attn_weights,
              present_key_value,
          )
  
  
  class TFBartPretrainedModel(TFPreTrainedModel):
      config_class = BartConfig
      base_model_prefix = "model"
  
      @property
      def dummy_inputs(self):
          pad_token = 1
          input_ids = tf.cast(tf.constant(DUMMY_INPUTS), tf.int32)
          decoder_input_ids = tf.cast(tf.constant(DUMMY_INPUTS), tf.int32)
          dummy_inputs = {
              "decoder_input_ids": decoder_input_ids,
              "attention_mask": tf.math.not_equal(input_ids, pad_token),
              "input_ids": input_ids,
          }
          return dummy_inputs
  
  
  class TFPretrainedBartModel(TFBartPretrainedModel):
      def __init_subclass__(self):
          warnings.warn(
              "The class `TFPretrainedBartModel` has been deprecated, please use `TFBartPretrainedModel` instead.",
              FutureWarning,
          )
  
  
  BART_START_DOCSTRING = r"""
      This model inherits from :class:`~transformers.TFPreTrainedModel`. Check the superclass documentation for the
      generic methods the library implements for all its model (such as downloading or saving, resizing the input
      embeddings, pruning heads etc.)
  
      This model is also a `tf.keras.Model <https://www.tensorflow.org/api_docs/python/tf/keras/Model>`__ subclass. Use
      it as a regular TF 2.0 Keras Model and refer to the TF 2.0 documentation for all matter related to general usage
      and behavior.
  
      .. note::
  
          TF 2.0 models accepts two formats as inputs:
  
          - having all inputs as keyword arguments (like PyTorch models), or
          - having all inputs as a list, tuple or dict in the first positional arguments.
  
          This second option is useful when using :meth:`tf.keras.Model.fit` method which currently requires having all
          the tensors in the first argument of the model call function: :obj:`model(inputs)`.
  
          If you choose this second option, there are three possibilities you can use to gather all the input Tensors in
          the first positional argument :
  
          - a single Tensor with :obj:`input_ids` only and nothing else: :obj:`model(input_ids)`
          - a list of varying length with one or several input Tensors IN THE ORDER given in the docstring:
            :obj:`model([input_ids, attention_mask])` or :obj:`model([input_ids, attention_mask, token_type_ids])`
          - a dictionary with one or several input Tensors associated to the input names given in the docstring:
            :obj:`model({"input_ids": input_ids, "token_type_ids": token_type_ids})`
  
      Args:
          config (:class:`~transformers.BartConfig`): Model configuration class with all the parameters of the model.
              Initializing with a config file does not load the weights associated with the model, only the
              configuration. Check out the :meth:`~transformers.TFPreTrainedModel.from_pretrained` method to load the
              model weights.
  """
  
  BART_INPUTS_DOCSTRING = r"""
      Args:
          input_ids (:obj:`tf.Tensor` of shape :obj:`({0})`):
              Indices of input sequence tokens in the vocabulary.
  
              Indices can be obtained using :class:`~transformers.BertTokenizer`. See
              :meth:`transformers.PreTrainedTokenizer.encode` and :meth:`transformers.PreTrainedTokenizer.__call__` for
              details.
  
              `What are input IDs? <../glossary.html#input-ids>`__
          attention_mask (:obj:`tf.Tensor` of shape :obj:`({0})`, `optional`):
              Mask to avoid performing attention on padding token indices. Mask values selected in ``[0, 1]``:
  
              - 1 for tokens that are **not masked**,
              - 0 for tokens that are **masked**.
  
              `What are attention masks? <../glossary.html#attention-mask>`__
          decoder_input_ids (:obj:`tf.Tensor` of shape :obj:`(batch_size, target_sequence_length)`, `optional`):
              Provide for translation and summarization training. By default, the model will create this tensor by
              shifting the input_ids right, following the paper.
          decoder_attention_mask (:obj:`tf.Tensor` of shape :obj:`(batch_size, tgt_seq_len)`, `optional`):
              will be made by default and ignore pad tokens. It is not recommended to set this for most use cases.
          encoder_outputs (:obj:`tf.FloatTensor`, `optional`):
              hidden states at the output of the last layer of the encoder. Used in the cross-attention of the decoder.
              of shape :obj:`(batch_size, sequence_length, hidden_size)` is a sequence of
          past_key_values (:obj:`Tuple[Tuple[tf.Tensor]]` of length :obj:`config.n_layers`)
              contains precomputed key and value hidden states of the attention blocks. Can be used to speed up decoding.
              If :obj:`past_key_values` are used, the user can optionally input only the last :obj:`decoder_input_ids`
              (those that don't have their past key value states given to this model) of shape :obj:`(batch_size, 1)`
              instead of all :obj:`decoder_input_ids` of shape :obj:`(batch_size, sequence_length)`.
          use_cache (:obj:`bool`, `optional`, defaults to :obj:`True`):
              If set to :obj:`True`, :obj:`past_key_values` key value states are returned and can be used to speed up
              decoding (see :obj:`past_key_values`). Set to :obj:`False` during training, :obj:`True` during generation
          output_attentions (:obj:`bool`, `optional`):
              Whether or not to return the attentions tensors of all attention layers. See ``attentions`` under returned
              tensors for more detail.
          output_hidden_states (:obj:`bool`, `optional`):
              Whether or not to return the hidden states of all layers. See ``hidden_states`` under returned tensors for
              more detail.
          return_dict (:obj:`bool`, `optional`):
              Whether or not to return a :class:`~transformers.file_utils.TFModelOutput` instead of a plain tuple.
          training (:obj:`bool`, `optional`, defaults to :obj:`False`):
              Whether or not to use the model in training mode (some modules like dropout modules have different
              behaviors between training and evaluation).
  """
  
  
  @keras_serializable
  class TFBartEncoder(tf.keras.layers.Layer):
      config_class = BartConfig
      """
      Transformer encoder consisting of *config.encoder_layers* self attention layers. Each layer is a
      :class:`TFBartEncoderLayer`.
  
      Args:
          config: BartConfig
      """
  
      def __init__(self, config: BartConfig, embed_tokens: Optional[TFSharedEmbeddings] = None, **kwargs):
          super().__init__(**kwargs)
          self.config = config
          self.dropout = tf.keras.layers.Dropout(config.dropout)
          self.layerdrop = config.encoder_layerdrop
          self.embed_scale = math.sqrt(config.d_model) if config.scale_embedding else 1.0
          self.padding_idx = config.pad_token_id
          self.max_source_positions = config.max_position_embeddings
  
          self.embed_tokens = embed_tokens
          if config.static_position_embeddings:
              self.embed_positions = TFBartSinusoidalPositionalEmbedding(
                  config.max_position_embeddings,
                  config.d_model,
                  name="embed_positions",
              )
          else:
              self.embed_positions = TFBartLearnedPositionalEmbedding(
                  config.max_position_embeddings,
                  config.d_model,
                  self.padding_idx,
                  config.extra_pos_embeddings,
                  name="embed_positions",
              )
          self.layers = [TFBartEncoderLayer(config, name=f"layers.{i}") for i in range(config.encoder_layers)]
          self.layernorm_embedding = (
              tf.keras.layers.LayerNormalization(epsilon=1e-5, name="layernorm_embedding")
              if config.normalize_embedding
              else tf.keras.layers.Layer()
          )
          self.layer_norm = (
              tf.keras.layers.LayerNormalization(epsilon=1e-5, name="layer_norm")
              if config.add_final_layer_norm
              else None
          )
  
      def call(
          self,
          input_ids=None,
          inputs_embeds=None,
          attention_mask=None,
          output_attentions=None,
          output_hidden_states=None,
          return_dict=None,
          training=False,
          **kwargs,
      ):
          """
          Args:
              input_ids (:obj:`tf.Tensor` of shape :obj:`(batch_size, sequence_length)`):
                  Indices of input sequence tokens in the vocabulary. Padding will be ignored by default should you
                  provide it.
  
                  Indices can be obtained using :class:`~transformers.BartTokenizer`. See
                  :meth:`transformers.PreTrainedTokenizer.encode` and :meth:`transformers.PreTrainedTokenizer.__call__`
                  for details.
  
                  `What are input IDs? <../glossary.html#input-ids>`__
              attention_mask (:obj:`tf.Tensor` of shape :obj:`(batch_size, sequence_length)`, `optional`):
                  Mask to avoid performing attention on padding token indices. Mask values selected in ``[0, 1]``:
  
                  - 1 for tokens that are **not masked**,
                  - 0 for tokens that are **masked**.
  
                  `What are attention masks? <../glossary.html#attention-mask>`__
              inputs_embeds (:obj:`tf.Tensor` of shape :obj:`(batch_size, sequence_length, hidden_size)`, `optional`):
                  Optionally, instead of passing :obj:`input_ids` you can choose to directly pass an embedded
                  representation. This is useful if you want more control over how to convert :obj:`input_ids` indices
                  into associated vectors than the model's internal embedding lookup matrix.
              output_attentions (:obj:`bool`, `optional`):
                  Whether or not to return the attentions tensors of all attention layers. See ``attentions`` under
                  returned tensors for more detail.
              output_hidden_states (:obj:`bool`, `optional`):
                  Whether or not to return the hidden states of all layers. See ``hidden_states`` under returned tensors
                  for more detail.
              return_dict (:obj:`bool`, `optional`):
                  Whether or not to return a :class:`~transformers.file_utils.ModelOutput` instead of a plain tuple.
          """
          inputs = input_processing(
              func=self.call,
              config=self.config,
              input_ids=input_ids,
              attention_mask=attention_mask,
              inputs_embeds=inputs_embeds,
              output_attentions=output_attentions,
              output_hidden_states=output_hidden_states,
              return_dict=return_dict,
              training=training,
              kwargs_call=kwargs,
          )
  
          if inputs["input_ids"] is not None and inputs["inputs_embeds"] is not None:
              raise ValueError("You cannot specify both input_ids and inputs_embeds at the same time")
          elif inputs["input_ids"] is not None:
              input_shape = shape_list(inputs["input_ids"])
          elif inputs["inputs_embeds"] is not None:
              input_shape = shape_list(inputs["inputs_embeds"])[:-1]
          else:
              raise ValueError("You have to specify either input_ids or inputs_embeds")
  
          if inputs["inputs_embeds"] is None:
              inputs["inputs_embeds"] = self.embed_tokens(inputs["input_ids"])
          else:
              inputs["inputs_embeds"] = inputs["inputs_embeds"]
  
          inputs["inputs_embeds"] = inputs["inputs_embeds"] * self.embed_scale
  
          embed_pos = self.embed_positions(input_shape)
          hidden_states = inputs["inputs_embeds"] + embed_pos
          hidden_states = self.layernorm_embedding(hidden_states)
          hidden_states = self.dropout(hidden_states, training=inputs["training"])
  
          # check attention mask and invert
          if inputs["attention_mask"] is not None:
              # [bsz, seq_len] -> [bsz, 1, tgt_seq_len, src_seq_len]
              inputs["attention_mask"] = _expand_mask(inputs["attention_mask"])
  
          encoder_states = () if inputs["output_hidden_states"] else None
          all_attentions = () if inputs["output_attentions"] else None
  
          # encoder layers
          for encoder_layer in self.layers:
  
              if inputs["output_hidden_states"]:
                  encoder_states = encoder_states + (hidden_states,)
              # add LayerDrop (see https://arxiv.org/abs/1909.11556 for description)
              dropout_probability = random.uniform(0, 1)
              if inputs["training"] and (dropout_probability < self.layerdrop):  # skip the layer
                  continue
  
              hidden_states, attn = encoder_layer(hidden_states, inputs["attention_mask"])
  
              if inputs["output_attentions"]:
                  all_attentions += (attn,)
          if self.layer_norm:
              hidden_states = self.layer_norm(hidden_states)
          if inputs["output_hidden_states"]:
              encoder_states = encoder_states + (hidden_states,)
  
          if not inputs["return_dict"]:
              return tuple(v for v in [hidden_states, encoder_states, all_attentions] if v is not None)
          return TFBaseModelOutput(
              last_hidden_state=hidden_states, hidden_states=encoder_states, attentions=all_attentions
          )
  
  
  @keras_serializable
  class TFBartDecoder(tf.keras.layers.Layer):
      config_class = BartConfig
      """
      Transformer decoder consisting of *config.decoder_layers* layers. Each layer is a :class:`TFBartDecoderLayer`
  
      Args:
          config: BartConfig
          embed_tokens: output embedding
      """
  
      def __init__(self, config: BartConfig, embed_tokens: Optional[TFSharedEmbeddings] = None, **kwargs):
          super().__init__(**kwargs)
          self.config = config
          self.padding_idx = config.pad_token_id
          self.embed_tokens = embed_tokens
          self.embed_scale = math.sqrt(config.d_model) if config.scale_embedding else 1.0
          self.layerdrop = config.decoder_layerdrop
          if config.static_position_embeddings:
              self.embed_positions = TFBartSinusoidalPositionalEmbedding(
                  config.max_position_embeddings,
                  config.d_model,
                  name="embed_positions",
              )
          else:
              self.embed_positions = TFBartLearnedPositionalEmbedding(
                  config.max_position_embeddings,
                  config.d_model,
                  self.padding_idx,
                  config.extra_pos_embeddings,
                  name="embed_positions",
              )
          self.layers = [TFBartDecoderLayer(config, name=f"layers.{i}") for i in range(config.decoder_layers)]
          self.layernorm_embedding = (
              tf.keras.layers.LayerNormalization(epsilon=1e-5, name="layernorm_embedding")
              if config.normalize_embedding
              else tf.keras.layers.Layer()
          )
          self.layer_norm = (
              tf.keras.layers.LayerNormalization(epsilon=1e-5, name="layer_norm")
              if config.add_final_layer_norm
              else None
          )
  
          self.dropout = tf.keras.layers.Dropout(config.dropout)
          self.do_blenderbot_90_layernorm = config.do_blenderbot_90_layernorm
  
      def call(
          self,
          input_ids=None,
          inputs_embeds=None,
          attention_mask=None,
          encoder_hidden_states=None,
          encoder_attention_mask=None,
          past_key_values=None,
          use_cache=None,
          output_attentions=None,
          output_hidden_states=None,
          return_dict=None,
          training=False,
          **kwargs,
      ):
          r"""
          Args:
              input_ids (:obj:`tf.Tensor` of shape :obj:`(batch_size, sequence_length)`):
                  Indices of input sequence tokens in the vocabulary. Padding will be ignored by default should you
                  provide it.
  
                  Indices can be obtained using :class:`~transformers.BartTokenizer`. See
                  :meth:`transformers.PreTrainedTokenizer.encode` and :meth:`transformers.PreTrainedTokenizer.__call__`
                  for details.
  
                  `What are input IDs? <../glossary.html#input-ids>`__
              attention_mask (:obj:`tf.Tensor` of shape :obj:`(batch_size, sequence_length)`, `optional`):
                  Mask to avoid performing attention on padding token indices. Mask values selected in ``[0, 1]``:
  
                  - 1 for tokens that are **not masked**,
                  - 0 for tokens that are **masked**.
  
                  `What are attention masks? <../glossary.html#attention-mask>`__
              encoder_hidden_states (:obj:`tf.Tensor` of shape :obj:`(batch_size, encoder_sequence_length, hidden_size)`, `optional`):
                  Sequence of hidden-states at the output of the last layer of the encoder. Used in the cross-attention
                  of the decoder.
              encoder_attention_mask (:obj:`tf.Tensor` of shape :obj:`(batch_size, encoder_sequence_length)`, `optional`):
                  Mask to avoid performing cross-attention on padding tokens indices of encoder input_ids. Mask values
                  selected in ``[0, 1]``:
  
                  - 1 for tokens that are **not masked**,
                  - 0 for tokens that are **masked**.
  
                  `What are attention masks? <../glossary.html#attention-mask>`__
              past_key_values (:obj:`Tuple[Tuple[tf.Tensor]]` of length :obj:`config.n_layers` with each tuple having 2 tuples each of which has 2 tensors of shape :obj:`(batch_size, num_heads, sequence_length - 1, embed_size_per_head)`):
                  Contains precomputed key and value hidden-states of the attention blocks. Can be used to speed up
                  decoding.
  
                  If :obj:`past_key_values` are used, the user can optionally input only the last
                  :obj:`decoder_input_ids` (those that don't have their past key value states given to this model) of
                  shape :obj:`(batch_size, 1)` instead of all :obj:`decoder_input_ids`` of shape :obj:`(batch_size,
                  sequence_length)`.
              inputs_embeds (:obj:`tf.Tensor` of shape :obj:`(batch_size, sequence_length, hidden_size)`, `optional`):
                  Optionally, instead of passing :obj:`input_ids` you can choose to directly pass an embedded
                  representation. This is useful if you want more control over how to convert :obj:`input_ids` indices
                  into associated vectors than the model's internal embedding lookup matrix.
              output_attentions (:obj:`bool`, `optional`):
                  Whether or not to return the attentions tensors of all attention layers. See ``attentions`` under
                  returned tensors for more detail.
              output_hidden_states (:obj:`bool`, `optional`):
                  Whether or not to return the hidden states of all layers. See ``hidden_states`` under returned tensors
                  for more detail.
              return_dict (:obj:`bool`, `optional`):
                  Whether or not to return a :class:`~transformers.file_utils.ModelOutput` instead of a plain tuple.
          """
          inputs = input_processing(
              func=self.call,
              config=self.config,
              input_ids=input_ids,
              attention_mask=attention_mask,
              encoder_hidden_states=encoder_hidden_states,
              encoder_attention_mask=encoder_attention_mask,
              inputs_embeds=inputs_embeds,
              past_key_values=past_key_values,
              use_cache=use_cache,
              output_attentions=output_attentions,
              output_hidden_states=output_hidden_states,
              return_dict=return_dict,
              training=training,
              kwargs_call=kwargs,
          )
  
          if inputs["input_ids"] is not None and inputs["inputs_embeds"] is not None:
              raise ValueError("You cannot specify both decoder_input_ids and decoder_inputs_embeds at the same time")
          elif inputs["input_ids"] is not None:
              input_shape = shape_list(inputs["input_ids"])
          elif inputs["inputs_embeds"] is not None:
              input_shape = shape_list(inputs["inputs_embeds"])[:-1]
          else:
              raise ValueError("You have to specify either decoder_input_ids or decoder_inputs_embeds")
  
          past_key_values_length = (
              inputs["past_key_values"][0][0].shape[2] if inputs["past_key_values"] is not None else 0
          )
  
          # embed positions
          positions = self.embed_positions(input_shape, past_key_values_length)
  
          if inputs["inputs_embeds"] is None:
              inputs["inputs_embeds"] = self.embed_tokens(inputs["input_ids"])
  
          hidden_states = inputs["inputs_embeds"] * self.embed_scale
  
          # [bsz, seq_len] -> [bsz, 1, tgt_seq_len, src_seq_len]
          if input_shape[-1] > 1:
              combined_attention_mask = _make_causal_mask(input_shape, past_key_values_length=past_key_values_length)
          else:
              combined_attention_mask = _expand_mask(
                  tf.ones((input_shape[0], input_shape[1] + past_key_values_length)), tgt_len=input_shape[-1]
              )
  
          if inputs["attention_mask"] is None and inputs["input_ids"] is not None and input_shape[-1] > 1:
              inputs["attention_mask"] = tf.cast(
                  tf.math.not_equal(inputs["input_ids"], self.config.pad_token_id), inputs["input_ids"].dtype
              )
              inputs["attention_mask"] = tf.concat(
                  [
                      tf.ones((input_shape[0], past_key_values_length), dtype=inputs["attention_mask"].dtype),
                      inputs["attention_mask"],
                  ],
                  axis=-1,
              )
          else:
              inputs["attention_mask"] = tf.ones(
                  (input_shape[0], input_shape[1] + past_key_values_length), dtype=tf.int32
              )
  
          # [bsz, seq_len] -> [bsz, 1, tgt_seq_len, src_seq_len]
          combined_attention_mask = combined_attention_mask + _expand_mask(
              inputs["attention_mask"], tgt_len=input_shape[-1]
          )
  
          if inputs["encoder_hidden_states"] is not None and inputs["encoder_attention_mask"] is not None:
              # [bsz, seq_len] -> [bsz, 1, tgt_seq_len, src_seq_len]
              inputs["encoder_attention_mask"] = _expand_mask(inputs["encoder_attention_mask"], tgt_len=input_shape[-1])
  
          if self.do_blenderbot_90_layernorm:
              hidden_states = self.layernorm_embedding(hidden_states) + positions
          else:
              hidden_states = self.layernorm_embedding(hidden_states + positions)
          hidden_states = self.dropout(hidden_states, training=inputs["training"])
  
          # decoder layers
          all_hidden_states = ()
          all_self_attns = ()
          present_key_values = ()
          for idx, decoder_layer in enumerate(self.layers):
              # add LayerDrop (see https://arxiv.org/abs/1909.11556 for description)
              if inputs["output_hidden_states"]:
                  all_hidden_states += (hidden_states,)
              dropout_probability = random.uniform(0, 1)
  
              if inputs["training"] and (dropout_probability < self.layerdrop):
                  continue
  
              past_key_value = inputs["past_key_values"][idx] if inputs["past_key_values"] is not None else None
  
              hidden_states, layer_self_attn, present_key_value = decoder_layer(
                  hidden_states,
                  attention_mask=combined_attention_mask,
                  encoder_hidden_states=inputs["encoder_hidden_states"],
                  encoder_attention_mask=inputs["encoder_attention_mask"],
                  past_key_value=past_key_value,
              )
  
              if inputs["use_cache"]:
                  present_key_values += (present_key_value,)
  
              if inputs["output_attentions"]:
                  all_self_attns += (layer_self_attn,)
  
          if self.layer_norm is not None:  # same as if config.add_final_layer_norm
              hidden_states = self.layer_norm(hidden_states)
  
          # Convert to standard output format: (seq_len, BS, model_dim) -> (BS, seq_len, model_dim)
          if inputs["output_hidden_states"]:
              all_hidden_states += (hidden_states,)
          else:
              all_hidden_states = None
  
          all_self_attns = list(all_self_attns) if inputs["output_attentions"] else None
  
          present_key_values = (inputs["encoder_hidden_states"], present_key_values) if inputs["use_cache"] else None
  
          if not inputs["return_dict"]:
              return hidden_states, present_key_values, all_hidden_states, all_self_attns
          else:
              return TFBaseModelOutputWithPast(
                  last_hidden_state=hidden_states,
                  past_key_values=present_key_values,
                  hidden_states=all_hidden_states,
                  attentions=all_self_attns,
              )
  
  
  @add_start_docstrings(
      "The bare BART Model outputting raw hidden-states without any specific head on top.",
      BART_START_DOCSTRING,
  )
  @keras_serializable
  class TFBartModel(TFBartPretrainedModel):
      base_model_prefix = "model"
  
      def __init__(self, config: BartConfig, *inputs, **kwargs):
          super().__init__(config, *inputs, **kwargs)
          self.shared = TFSharedEmbeddings(config.vocab_size, config.d_model, config.pad_token_id, name="model.shared")
  
          with tf.compat.v1.variable_scope("model.shared") as shared_abs_scope_name:
              pass
  
          # Wraps layer to avoid problems with weight restoring and ensuring we're in the correct TF scope.
          embed_tokens = TFWrappedEmbeddings(self.shared, abs_scope_name=shared_abs_scope_name)
          embed_tokens.vocab_size = self.shared.vocab_size
          embed_tokens.hidden_size = self.shared.hidden_size
  
          self.encoder = TFBartEncoder(config, embed_tokens, name="encoder")
          self.decoder = TFBartDecoder(config, embed_tokens, name="decoder")
  
      def get_decoder(self):
          return self.decoder
  
      @add_start_docstrings_to_model_forward(BART_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
      @add_code_sample_docstrings(
          tokenizer_class=_TOKENIZER_FOR_DOC,
          checkpoint="facebook/bart-large",
          output_type=TFSeq2SeqModelOutput,
          config_class=_CONFIG_FOR_DOC,
      )
      def call(
          self,
          input_ids=None,
          attention_mask=None,
          decoder_input_ids=None,
          decoder_attention_mask=None,
          encoder_outputs: Optional[Union[Tuple, TFBaseModelOutput]] = None,
          past_key_values=None,
          inputs_embeds=None,
          decoder_inputs_embeds=None,
          use_cache=None,
          output_attentions=None,
          output_hidden_states=None,
          return_dict=None,
          training=False,
          **kwargs
      ):
          inputs = input_processing(
              func=self.call,
              config=self.config,
              input_ids=input_ids,
              attention_mask=attention_mask,
              decoder_input_ids=decoder_input_ids,
              decoder_attention_mask=decoder_attention_mask,
              encoder_outputs=encoder_outputs,
              past_key_values=past_key_values,
              inputs_embeds=inputs_embeds,
              decoder_inputs_embeds=decoder_inputs_embeds,
              use_cache=use_cache,
              output_attentions=output_attentions,
              output_hidden_states=output_hidden_states,
              return_dict=return_dict,
              training=training,
              kwargs_call=kwargs,
          )
  
          if inputs["decoder_input_ids"] is None and inputs["decoder_inputs_embeds"] is None:
              inputs["use_cache"] = False
  
          inputs["output_hidden_states"] = (
              inputs["output_hidden_states"]
              if inputs["output_hidden_states"] is not None
              else self.config.output_hidden_states
          )
  
          if inputs["decoder_input_ids"] is None and inputs["input_ids"] is not None:
              inputs["decoder_input_ids"] = shift_tokens_right(
                  inputs["input_ids"], self.config.pad_token_id, self.config.eos_token_id
              )
  
          if inputs["encoder_outputs"] is None:
              inputs["encoder_outputs"] = self.encoder(
                  input_ids=inputs["input_ids"],
                  attention_mask=inputs["attention_mask"],
                  inputs_embeds=inputs["inputs_embeds"],
                  output_attentions=inputs["output_attentions"],
                  output_hidden_states=inputs["output_hidden_states"],
                  return_dict=inputs["return_dict"],
                  training=inputs["training"],
              )
          # If the user passed a tuple for encoder_outputs, we wrap it in a TFBaseModelOutput when return_dict=True
          elif inputs["return_dict"] and not isinstance(inputs["encoder_outputs"], TFBaseModelOutput):
              inputs["encoder_outputs"] = TFBaseModelOutput(
                  last_hidden_state=inputs["encoder_outputs"][0],
                  hidden_states=inputs["encoder_outputs"][1] if len(inputs["encoder_outputs"]) > 1 else None,
                  attentions=inputs["encoder_outputs"][2] if len(inputs["encoder_outputs"]) > 2 else None,
              )
          # If the user passed a TFBaseModelOutput for encoder_outputs, we wrap it in a tuple when return_dict=False
          elif not inputs["return_dict"] and not isinstance(inputs["encoder_outputs"], tuple):
              inputs["encoder_outputs"] = inputs["encoder_outputs"].to_tuple()
  
          decoder_outputs = self.decoder(
              inputs["decoder_input_ids"],
              attention_mask=inputs["decoder_attention_mask"],
              encoder_hidden_states=inputs["encoder_outputs"][0],
              encoder_attention_mask=inputs["attention_mask"],
              past_key_values=inputs["past_key_values"],
              inputs_embeds=inputs["decoder_inputs_embeds"],
              use_cache=inputs["use_cache"],
              output_attentions=inputs["output_attentions"],
              output_hidden_states=inputs["output_hidden_states"],
              return_dict=inputs["return_dict"],
              training=inputs["training"],
          )
  
          if not inputs["return_dict"]:
              return decoder_outputs + inputs["encoder_outputs"]
  
          return TFSeq2SeqModelOutput(
              last_hidden_state=decoder_outputs.last_hidden_state,
              past_key_values=decoder_outputs.past_key_values,
              decoder_hidden_states=decoder_outputs.hidden_states,
              decoder_attentions=decoder_outputs.attentions,
              encoder_last_hidden_state=inputs["encoder_outputs"].last_hidden_state,
              encoder_hidden_states=inputs["encoder_outputs"].hidden_states,
              encoder_attentions=inputs["encoder_outputs"].attentions,
          )
  
      def get_input_embeddings(self):
          return self.shared
  
      def set_input_embeddings(self, value):
          self.shared = value
  
      def get_output_embeddings(self):
          return self.shared
  
  
  @add_start_docstrings(
      "The BART Model with a language modeling head. Can be used for summarization.",
      BART_START_DOCSTRING,
  )
  class TFBartForConditionalGeneration(TFBartPretrainedModel):
      _keys_to_ignore_on_load_unexpected = [
          r"model.encoder.embed_tokens.weight",
          r"model.decoder.embed_tokens.weight",
      ]
  
      def __init__(self, config, *inputs, **kwargs):
          super().__init__(config, *inputs, **kwargs)
          self.model = TFBartModel(config, name="model")
          self.use_cache = config.use_cache
          # final_bias_logits is registered as a buffer in pytorch, so not trainable for the the sake of consistency.
          self.final_logits_bias = self.add_weight(
              name="final_logits_bias", shape=[1, config.vocab_size], initializer="zeros", trainable=False
          )
  
      def get_decoder(self):
          return self.model.decoder
  
      def resize_token_embeddings(self, new_num_tokens):
          super().resize_token_embeddings(new_num_tokens=new_num_tokens)
  
          # BART is a special case where the bias has two dimensions
          # and not named just `bias`
          if new_num_tokens is not None:
              num_tokens_to_copy = min(self.final_logits_bias.shape[0], new_num_tokens)
              init_bias = tf.zeros((new_num_tokens,))
              init_bias[:num_tokens_to_copy] = self.final_logits_bias.value()[:num_tokens_to_copy]
              self.final_logits_bias = self.add_weight(
                  shape=(1, new_num_tokens),
                  initializer="zeros",
                  trainable=False,
                  name="final_logits_bias",
              )
              self.final_logits_bias.assign(init_bias)
  
      @add_start_docstrings_to_model_forward(BART_INPUTS_DOCSTRING)
      @replace_return_docstrings(output_type=TFSeq2SeqLMOutput, config_class=_CONFIG_FOR_DOC)
      def call(
          self,
          input_ids=None,
          attention_mask=None,
          decoder_input_ids=None,
          decoder_attention_mask=None,
          encoder_outputs: Optional[TFBaseModelOutput] = None,
          past_key_values=None,
          inputs_embeds=None,
          decoder_inputs_embeds=None,
          use_cache=None,
          output_attentions=None,
          output_hidden_states=None,
          return_dict=None,
          labels=None,
          training=False,
          **kwargs,
      ):
          """
          Returns:
  
          Examples::
  
              # Mask filling only works for bart-large
              from transformers import BartTokenizer, TFBartForConditionalGeneration
              import tensorflow as tf
              mname = 'facebook/bart-large'
              tokenizer = BartTokenizer.from_pretrained(mname)
              TXT = "My friends are <mask> but they eat too many carbs."
              model = TFBartForConditionalGeneration.from_pretrained(mname)
              batch = tokenizer([TXT], return_tensors='tf')
              logits = model(inputs=batch.input_ids).logits
              probs = tf.nn.softmax(logits[0])
              # probs[5] is associated with the mask token
          """
          inputs = input_processing(
              func=self.call,
              config=self.config,
              input_ids=input_ids,
              attention_mask=attention_mask,
              decoder_input_ids=decoder_input_ids,
              decoder_attention_mask=decoder_attention_mask,
              encoder_outputs=encoder_outputs,
              past_key_values=past_key_values,
              inputs_embeds=inputs_embeds,
              decoder_inputs_embeds=decoder_inputs_embeds,
              use_cache=use_cache,
              output_attentions=output_attentions,
              output_hidden_states=output_hidden_states,
              return_dict=return_dict,
              labels=labels,
              training=training,
              kwargs_call=kwargs,
          )
  
          if inputs["labels"] is not None:
              inputs["use_cache"] = False
              if inputs["decoder_input_ids"] is None:
                  inputs["decoder_input_ids"] = shift_tokens_right(
                      inputs["labels"], self.config.pad_token_id, self.config.eos_token_id
                  )
  
          outputs = self.model(
              inputs["input_ids"],
              attention_mask=inputs["attention_mask"],
              decoder_input_ids=inputs["decoder_input_ids"],
              encoder_outputs=inputs["encoder_outputs"],
              decoder_attention_mask=inputs["decoder_attention_mask"],
              past_key_values=inputs["past_key_values"],
              inputs_embeds=inputs["inputs_embeds"],
              decoder_inputs_embeds=inputs["decoder_inputs_embeds"],
              use_cache=inputs["use_cache"],
              output_attentions=inputs["output_attentions"],
              output_hidden_states=inputs["output_hidden_states"],
              return_dict=inputs["return_dict"],
              training=inputs["training"],
          )
          lm_logits = self.model.shared(outputs[0], mode="linear")
          lm_logits = lm_logits + self.final_logits_bias
          masked_lm_loss = None if inputs["labels"] is None else self.compute_loss(inputs["labels"], lm_logits)
  
          if not inputs["return_dict"]:
              output = (lm_logits,) + outputs[1:]
              return ((masked_lm_loss,) + output) if masked_lm_loss is not None else output
          return TFSeq2SeqLMOutput(
              loss=masked_lm_loss,
              logits=lm_logits,
              past_key_values=outputs.past_key_values,  # index 1 of d outputs
              decoder_hidden_states=outputs.decoder_hidden_states,  # index 2 of d outputs
              decoder_attentions=outputs.decoder_attentions,  # index 3 of d outputs
              encoder_last_hidden_state=outputs.last_hidden_state,  # index 0 of encoder outputs
              encoder_hidden_states=outputs.encoder_hidden_states,  # 1 of e out
              encoder_attentions=outputs.encoder_attentions,  # 2 of e out
          )
  
      def prepare_inputs_for_generation(self, decoder_input_ids, past, attention_mask, use_cache, **kwargs) -> Dict:
          assert past is not None and len(past) in {1, 2}, f"past has to be an iterable of length 1,2 got {past}"
          if len(past) == 1:
              assert isinstance(past[0], tf.Tensor), f"`past[0]` has to be of type `tf.Tensor`, but is {type(past[0])}"
              encoder_outputs = TFBaseModelOutput(last_hidden_state=past[0])
              past_key_values = None
          else:
              assert (
                  len(past) == 2
              ), "`past` has to be of length 2 with the encoder_outputs at the first position and past_key_values at the second position."
              encoder_outputs, past_key_values = past
              if isinstance(encoder_outputs, tuple):
                  assert isinstance(
                      encoder_outputs[0], tf.Tensor
                  ), f"`encoder_outputs[0]` has to be of type `tf.Tensor`, but is {type(encoder_outputs[0])}"
                  encoder_outputs = TFBaseModelOutput(last_hidden_state=encoder_outputs[0])
              elif isinstance(encoder_outputs, tf.Tensor):
                  encoder_outputs = TFBaseModelOutput(last_hidden_state=encoder_outputs)
              assert (
                  past_key_values
              ), f"decoder cached states must be truthy. got {past_key_values} from the 2nd element of past"
              decoder_input_ids = decoder_input_ids[:, -1:]
  
          assert isinstance(
              encoder_outputs, TFBaseModelOutput
          ), f"encoder_outputs should be a TFBaseModelOutput, Instead got {type(encoder_outputs)}."
          return {
              "input_ids": None,  # encoder_outputs is defined. input_ids not needed
              "encoder_outputs": encoder_outputs,
              "past_key_values": past_key_values,
              "decoder_input_ids": decoder_input_ids,
              "attention_mask": attention_mask,
              "use_cache": use_cache,  # change this to avoid caching (presumably for debugging)
          }
  
      @staticmethod
      def _reorder_cache(past, beam_idx):
          if len(past) == 1:
              return past
  
          past_key_values = past[1]
  
          reordered_past = ()
          for layer_past_key_values in past_key_values:
              reordered_past += (
                  tuple(tf.gather(layer_past_key_value, beam_idx) for layer_past_key_value in layer_past_key_values),
              )
          return (past[0], reordered_past)
  
      def adjust_logits_during_generation(self, logits, cur_len, max_length):
          if cur_len == 1 and self.config.force_bos_token_to_be_generated:
              vocab_range = tf.constant(range(self.config.vocab_size))
              return tf.where(vocab_range != self.config.bos_token_id, LARGE_NEGATIVE, logits)
          elif cur_len == max_length - 1:
              vocab_range = tf.constant(range(self.config.vocab_size))
              return tf.where(vocab_range != self.config.eos_token_id, LARGE_NEGATIVE, logits)
          else:
              return logits
  
      def get_output_embeddings(self):
          return self.model.shared
  
      def get_encoder(self):
          return self.model.encoder
  
      def compute_loss(self, labels, logits):
          """CrossEntropyLoss that ignores pad tokens"""
          loss_fn = tf.keras.losses.SparseCategoricalCrossentropy(
              from_logits=True,
              reduction=tf.keras.losses.Reduction.NONE,
          )
          melted_labels = tf.reshape(labels, (-1,))
          active_loss = tf.not_equal(melted_labels, self.config.pad_token_id)
          reduced_logits = tf.boolean_mask(tf.reshape(logits, (-1, shape_list(logits)[2])), active_loss)
          labels = tf.boolean_mask(melted_labels, active_loss)
          return loss_fn(labels, reduced_logits)
  