Add huggingface submodule and GPT2 model (#1019)

Summary: Pull Request resolved: fairinternal/fairseq-py#1019

Differential Revision: D20044785

Pulled By: myleott

fbshipit-source-id: 022a49f696c0093d577422af5598f6f326022569

.gitmodules

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+[submodule "fairseq/models/huggingface/transformers"]
+    path = fairseq/models/huggingface/transformers
+    url = https://github.com/huggingface/transformers.git

fairseq/models/huggingface/__init__.py

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+# Copyright (c) Facebook, Inc. and its affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from .hf_gpt2 import *  # noqa

fairseq/models/huggingface/hf_gpt2.py

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+# Copyright (c) Facebook, Inc. and its affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+import logging
+import os
+import sys
+from typing import Dict, List, Optional
+
+import torch
+from fairseq.models import (
+    FairseqIncrementalDecoder,
+    FairseqLanguageModel,
+    register_model,
+    register_model_architecture,
+)
+
+
+logger = logging.getLogger(__name__)
+
+
+DEFAULT_MAX_TARGET_POSITIONS = 1024
+
+
+@register_model('hf_gpt2')
+class HuggingFaceGPT2LanguageModel(FairseqLanguageModel):
+
+    def __init__(self, decoder):
+        super().__init__(decoder)
+
+    @staticmethod
+    def add_args(parser):
+        """Add model-specific arguments to the parser."""
+        # fmt: off
+        parser.add_argument('--embed-dim', type=int, metavar='N',
+                            help='embedding dimension')
+        parser.add_argument('--num-attention-heads', type=int, metavar='N',
+                            help='num attention heads')
+        parser.add_argument('--num-layers', type=int, metavar='N',
+                            help='num layers')
+        parser.add_argument('--dropout', type=float, metavar='D',
+                            help='dropout probability for all fully connected layers '
+                                 'in the embeddings, encoder, and pooler')
+        parser.add_argument('--attention-dropout', type=float, metavar='D',
+                            help='dropout probability for attention weights')
+        # fmt: on
+
+    @classmethod
+    def build_model(cls, args, task):
+        """Build a new model instance."""
+        default_architecture(args)
+        return cls(HuggingFaceGPT2Decoder(args, task))
+
+
+class HuggingFaceGPT2Decoder(FairseqIncrementalDecoder):
+
+    def __init__(self, args, task):
+        super().__init__(task.target_dictionary)
+
+        try:
+            # Prepend the transformers submodule to the path, so that
+            # it's prioritized over other installations. This allows
+            # making local changes in the submodule.
+            sys.path.insert(
+                0, os.path.join(os.path.dirname(__file__), 'transformers', 'src')
+            )
+            from transformers import GPT2Config, GPT2LMHeadModel
+        except ImportError:
+            raise ImportError(
+                '\n\nPlease install huggingface/transformers with:'
+                '\n\n  pip install transformers'
+                '\n\nOr to make local edits, install the submodule:'
+                '\n\n  git submodule update --init '
+                'fairseq/models/huggingface/transformers'
+            )
+
+        config = GPT2Config(
+            vocab_size=len(task.target_dictionary),
+            n_positions=args.max_target_positions,
+            n_ctx=args.max_target_positions,
+            n_embd=args.embed_dim,
+            n_layer=args.num_layers,
+            n_head=args.num_attention_heads,
+            resid_pdrop=args.dropout,
+            embd_pdrop=args.dropout,
+            attn_pdrop=args.attention_dropout,
+            layer_norm_epsilon=1e-6,
+        )
+        self.model = GPT2LMHeadModel(config)
+
+        # set zero embedding for padding symbol
+        self.pad_idx = task.target_dictionary.pad()
+        self.model.transformer.wte.weight.data[self.pad_idx].zero_()
+        self.model.transformer.wpe.weight.data[0].zero_()
+
+    def forward(
+        self,
+        prev_output_tokens,
+        src_lengths=None,
+        incremental_state: Optional[Dict[str, List[torch.Tensor]]] = None,
+    ):
+        features = self.extract_features(prev_output_tokens, incremental_state)
+        lm_logits = self.model.lm_head(features)
+        return (lm_logits, )
+
+    def extract_features(
+        self,
+        prev_output_tokens,
+        incremental_state: Optional[Dict[str, List[torch.Tensor]]] = None,
+    ):
+        if incremental_state is not None:
+            past = self.get_incremental_state("past")
+        else:
+            past = None
+
+        # don't attend to padding symbols
+        attention_mask = prev_output_tokens.ne(self.pad_idx).int()
+
+        # set position ids to exclude padding symbols
+        position_ids = attention_mask * (
+            torch.arange(1, 1 + prev_output_tokens.size(1))
+            .to(prev_output_tokens)
+            .repeat(prev_output_tokens.size(0), 1)
+        )
+
+        outputs = self.model.transformer(
+            input_ids=prev_output_tokens,
+            past=past,
+            attention_mask=attention_mask,
+            position_ids=position_ids,
+        )
+        last_hidden_states = outputs[0]
+
+        if incremental_state is not None:
+            self.set_incremental_state(incremental_state, "past", outputs[1])
+
+        return last_hidden_states
+
+    def max_positions(self):
+        return self.model.config.n_positions
+
+
+@register_model_architecture('hf_gpt2', 'hf_gpt2')
+def default_architecture(args):
+    if getattr(args, 'max_target_positions', None) is None:
+        args.max_target_positions = getattr(
+            args, 'tokens_per_sample', DEFAULT_MAX_TARGET_POSITIONS
+        )
+    args.embed_dim = getattr(args, 'embed_dim', 768)
+    args.num_attention_heads = getattr(args, 'num_attention_heads', 12)
+    args.num_layers = getattr(args, 'num_layers', 12)
+    args.dropout = getattr(args, 'dropout', 0.1)
+    args.attention_dropout = getattr(args, 'attention_dropout', 0.1)
+
+
+@register_model_architecture('hf_gpt2', 'hf_gpt2_medium')
+def hf_gpt2_medium(args):
+    args.embed_dim = getattr(args, 'embed_dim', 1024)
+    args.num_attention_heads = getattr(args, 'num_attention_heads', 16)
+    args.num_layers = getattr(args, 'num_layers', 24)
+    default_architecture(args)
+
+
+@register_model_architecture('hf_gpt2', 'hf_gpt2_large')
+def hf_gpt2_large(args):
+    args.embed_dim = getattr(args, 'embed_dim', 1280)
+    args.num_attention_heads = getattr(args, 'num_attention_heads', 20)
+    args.num_layers = getattr(args, 'num_layers', 36)
+    default_architecture(args)
+
+
+@register_model_architecture('hf_gpt2', 'hf_gpt2_xl')
+def hf_gpt2_xl(args):
+    args.embed_dim = getattr(args, 'embed_dim', 1600)
+    args.num_attention_heads = getattr(args, 'num_attention_heads', 25)
+    args.num_layers = getattr(args, 'num_layers', 48)
+    default_architecture(args)