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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
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