chore: import upstream snapshot with attribution

decoding/GAD/fairseq/models/fairseq_decoder.py

@@ -0,0 +1,105 @@
+# 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 typing import Dict, List, Optional, Tuple
+
+import torch.nn as nn
+from fairseq import utils
+from torch import Tensor
+
+
+class FairseqDecoder(nn.Module):
+    """Base class for decoders."""
+
+    def __init__(self, dictionary):
+        super().__init__()
+        self.dictionary = dictionary
+        self.onnx_trace = False
+        self.adaptive_softmax = None
+
+
+    def forward(self, prev_output_tokens, encoder_out=None, **kwargs):
+        """
+        Args:
+            prev_output_tokens (LongTensor): shifted output tokens of shape
+                `(batch, tgt_len)`, for teacher forcing
+            encoder_out (dict, optional): output from the encoder, used for
+                encoder-side attention
+
+        Returns:
+            tuple:
+                - the decoder's output of shape `(batch, tgt_len, vocab)`
+                - a dictionary with any model-specific outputs
+        """
+        x, extra = self.extract_features(
+            prev_output_tokens, encoder_out=encoder_out, **kwargs
+        )
+        x = self.output_layer(x)
+        return x, extra
+
+    def extract_features(self, prev_output_tokens, encoder_out=None, **kwargs):
+        """
+        Returns:
+            tuple:
+                - the decoder's features of shape `(batch, tgt_len, embed_dim)`
+                - a dictionary with any model-specific outputs
+        """
+        raise NotImplementedError
+
+    def output_layer(self, features, **kwargs):
+        """
+        Project features to the default output size, e.g., vocabulary size.
+
+        Args:
+            features (Tensor): features returned by *extract_features*.
+        """
+        raise NotImplementedError
+
+    def get_normalized_probs(
+        self,
+        net_output: Tuple[Tensor, Optional[Dict[str, List[Optional[Tensor]]]]],
+        log_probs: bool,
+        sample: Optional[Dict[str, Tensor]] = None,
+    ):
+        """Get normalized probabilities (or log probs) from a net's output."""
+        return self.get_normalized_probs_scriptable(net_output, log_probs, sample)
+
+    # TorchScript doesn't support super() method so that the scriptable Subclass
+    # can't access the base class model in Torchscript.
+    # Current workaround is to add a helper function with different name and
+    # call the helper function from scriptable Subclass.
+    def get_normalized_probs_scriptable(
+        self,
+        net_output: Tuple[Tensor, Optional[Dict[str, List[Optional[Tensor]]]]],
+        log_probs: bool,
+        sample: Optional[Dict[str, Tensor]] = None,
+    ):
+        """Get normalized probabilities (or log probs) from a net's output."""
+
+        if hasattr(self, "adaptive_softmax") and self.adaptive_softmax is not None:
+            if sample is not None:
+                assert "target" in sample
+                target = sample["target"]
+            else:
+                target = None
+            out = self.adaptive_softmax.get_log_prob(net_output[0], target=target)
+            return out.exp_() if not log_probs else out
+
+        logits = net_output[0]
+        if log_probs:
+            return utils.log_softmax(logits, dim=-1, onnx_trace=self.onnx_trace)
+        else:
+            return utils.softmax(logits, dim=-1, onnx_trace=self.onnx_trace)
+
+    def max_positions(self):
+        """Maximum input length supported by the decoder."""
+        return 1e6  # an arbitrary large number
+
+    def upgrade_state_dict_named(self, state_dict, name):
+        """Upgrade old state dicts to work with newer code."""
+        return state_dict
+
+    def prepare_for_onnx_export_(self):
+        self.onnx_trace = True