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| # Copyright (c) Facebook, Inc. and its affiliates. | |
| # All rights reserved. | |
| # | |
| # This source code is licensed under the license found in the | |
| # LICENSE file in the root directory of this source tree. | |
| from argparse import Namespace | |
| import contextlib | |
| import copy | |
| import math | |
| import numpy as np | |
| import torch | |
| import torch.nn as nn | |
| import torch.nn.functional as F | |
| from dataclasses import dataclass, field | |
| from omegaconf import MISSING, II, open_dict | |
| from typing import Any, Optional | |
| from fairseq import checkpoint_utils, tasks, utils | |
| from fairseq.dataclass import FairseqDataclass | |
| from fairseq.dataclass.utils import convert_namespace_to_omegaconf | |
| from fairseq.tasks import FairseqTask | |
| from fairseq.models import ( | |
| BaseFairseqModel, | |
| FairseqEncoder, | |
| FairseqEncoderDecoderModel, | |
| FairseqIncrementalDecoder, | |
| register_model, | |
| ) | |
| # from fairseq.models.wav2vec.wav2vec2 import MASKING_DISTRIBUTION_CHOICES | |
| from fairseq.modules import ( | |
| LayerNorm, | |
| PositionalEmbedding, | |
| TransformerDecoderLayer, | |
| ) | |
| class TransformerDecoder(FairseqIncrementalDecoder): | |
| """ | |
| Transformer decoder consisting of *args.decoder_layers* layers. Each layer | |
| is a :class:`TransformerDecoderLayer`. | |
| Args: | |
| args (argparse.Namespace): parsed command-line arguments | |
| dictionary (~fairseq.data.Dictionary): decoding dictionary | |
| embed_tokens (torch.nn.Embedding): output embedding | |
| no_encoder_attn (bool, optional): whether to attend to encoder outputs | |
| (default: False). | |
| """ | |
| def __init__( | |
| self, | |
| cfg, | |
| dictionary, | |
| embed_tokens, | |
| no_encoder_attn=False, | |
| ): | |
| super().__init__(dictionary) | |
| self.dropout = cfg.decoder_dropout | |
| self.share_input_output_embed = cfg.share_decoder_input_output_embed | |
| input_embed_dim = embed_tokens.embedding_dim | |
| embed_dim = cfg.decoder_embed_dim | |
| self.output_embed_dim = cfg.decoder_embed_dim | |
| self.layerdrop = cfg.decoder_layerdrop | |
| padding_idx = embed_tokens.padding_idx | |
| self.max_target_positions = cfg.max_target_positions | |
| self.embed_tokens = embed_tokens | |
| # self.embed_scale = math.sqrt(embed_dim) # todo: try with input_embed_dim | |
| self.embed_scale = 1.0 if cfg.no_scale_embedding else math.sqrt(embed_dim) | |
| self.project_in_dim = ( | |
| Linear(input_embed_dim, embed_dim, bias=False) | |
| if embed_dim != input_embed_dim | |
| else None | |
| ) | |
| self.embed_positions = ( | |
| PositionalEmbedding( | |
| cfg.max_target_positions, | |
| embed_dim, | |
| padding_idx, | |
| learned=cfg.decoder_learned_pos, | |
| ) | |
| if not cfg.no_token_positional_embeddings | |
| else None | |
| ) | |
| # TODO: update this when transformer gets converted to dataclass configs | |
| transformer_cfg = copy.deepcopy(cfg) | |
| # with open_dict(transformer_cfg): | |
| transformer_cfg.dropout = transformer_cfg.decoder_dropout | |
| transformer_cfg.attention_dropout = ( | |
| transformer_cfg.decoder_attention_dropout | |
| ) | |
| transformer_cfg.activation_dropout = ( | |
| transformer_cfg.decoder_activation_dropout | |
| ) | |
| self.layers = nn.ModuleList([]) | |
| self.layers.extend( | |
| [ | |
| TransformerDecoderLayer(transformer_cfg, no_encoder_attn) | |
| for _ in range(transformer_cfg.decoder_layers) | |
| ] | |
| ) | |
| if not self.share_input_output_embed: | |
| self.embed_out = nn.Parameter( | |
| torch.Tensor(len(dictionary), self.output_embed_dim) | |
| ) | |
| nn.init.normal_(self.embed_out, mean=0, std=self.output_embed_dim ** -0.5) | |
| if transformer_cfg.decoder_normalize_before: | |
| self.layer_norm = LayerNorm(embed_dim) | |
| else: | |
| self.layer_norm = None | |
| def forward( | |
| self, prev_output_tokens, encoder_out=None, incremental_state=None, **unused | |
| ): | |
| """ | |
| Args: | |
| prev_output_tokens (LongTensor): previous decoder outputs of shape | |
| `(batch, tgt_len)`, for teacher forcing | |
| encoder_out (Tensor, optional): output from the encoder, used for | |
| encoder-side attention | |
| incremental_state (dict): dictionary used for storing state during | |
| :ref:`Incremental decoding` | |
| Returns: | |
| tuple: | |
| - the decoder's output of shape `(batch, tgt_len, vocab)` | |
| - a dictionary with any model-specific outputs | |
| """ | |
| prev_output_tokens = prev_output_tokens.long() | |
| x, extra = self.extract_features( | |
| prev_output_tokens, encoder_out, incremental_state | |
| ) | |
| x = self.output_layer(x) | |
| return x, extra | |
| def extract_features( | |
| self, prev_output_tokens, encoder_out=None, incremental_state=None, **unused | |
| ): | |
| """ | |
| Similar to *forward* but only return features. | |
| Returns: | |
| tuple: | |
| - the decoder's features of shape `(batch, tgt_len, embed_dim)` | |
| - a dictionary with any model-specific outputs | |
| """ | |
| # embed positions | |
| positions = ( | |
| self.embed_positions( | |
| prev_output_tokens, incremental_state=incremental_state | |
| ) | |
| if self.embed_positions is not None | |
| else None | |
| ) | |
| if incremental_state is not None: | |
| prev_output_tokens = prev_output_tokens[:, -1:] | |
| if positions is not None: | |
| positions = positions[:, -1:] | |
| # embed tokens and positions | |
| x = self.embed_scale * self.embed_tokens(prev_output_tokens) | |
| if self.project_in_dim is not None: | |
| x = self.project_in_dim(x) | |
| if positions is not None: | |
| x += positions | |
| x = F.dropout(x, p=self.dropout, training=self.training) | |
| # B x T x C -> T x B x C | |
| x = x.transpose(0, 1) | |
| attn = None | |
| inner_states = [x] | |
| # decoder layers | |
| for layer in self.layers: | |
| dropout_probability = np.random.random() | |
| if not self.training or (dropout_probability > self.layerdrop): | |
| x, attn, _ = layer( | |
| x, | |
| encoder_out["encoder_out"] if encoder_out is not None else None, | |
| encoder_out["padding_mask"] if encoder_out is not None else None, | |
| incremental_state, | |
| self_attn_mask=self.buffered_future_mask(x) | |
| if incremental_state is None | |
| else None, | |
| ) | |
| inner_states.append(x) | |
| if self.layer_norm: | |
| x = self.layer_norm(x) | |
| # T x B x C -> B x T x C | |
| x = x.transpose(0, 1) | |
| return x, {"attn": attn, "inner_states": inner_states} | |
| def output_layer(self, features, **kwargs): | |
| """Project features to the vocabulary size.""" | |
| # project back to size of vocabulary | |
| emb_mat = self.embed_tokens.weight if self.share_input_output_embed else self.embed_out | |
| return torch.matmul(features, emb_mat.transpose(0, 1)) | |
| # if self.share_input_output_embed: | |
| # return F.linear(features, self.embed_tokens.weight) | |
| # else: | |
| # return F.linear(features, self.embed_out) | |
| def max_positions(self): | |
| """Maximum output length supported by the decoder.""" | |
| if self.embed_positions is None: | |
| return self.max_target_positions | |
| return min(self.max_target_positions, self.embed_positions.max_positions) | |
| def buffered_future_mask(self, tensor): | |
| dim = tensor.size(0) | |
| if ( | |
| not hasattr(self, "_future_mask") | |
| or self._future_mask is None | |
| or self._future_mask.device != tensor.device | |
| or self._future_mask.size(0) < dim | |
| ): | |
| self._future_mask = torch.triu( | |
| utils.fill_with_neg_inf(tensor.new(dim, dim)), 1 | |
| ) | |
| return self._future_mask[:dim, :dim] | |
| def upgrade_state_dict_named(self, state_dict, name): | |
| return state_dict | |