chore: import upstream snapshot with attribution

decoding/IAD/fairseq/docs/tasks.rst

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+.. role:: hidden
+    :class: hidden-section
+
+.. module:: fairseq.tasks
+
+.. _Tasks:
+
+Tasks
+=====
+
+Tasks store dictionaries and provide helpers for loading/iterating over
+Datasets, initializing the Model/Criterion and calculating the loss.
+
+Tasks can be selected via the ``--task`` command-line argument. Once selected, a
+task may expose additional command-line arguments for further configuration.
+
+Example usage::
+
+    # setup the task (e.g., load dictionaries)
+    task = fairseq.tasks.setup_task(args)
+
+    # build model and criterion
+    model = task.build_model(args)
+    criterion = task.build_criterion(args)
+
+    # load datasets
+    task.load_dataset('train')
+    task.load_dataset('valid')
+
+    # iterate over mini-batches of data
+    batch_itr = task.get_batch_iterator(
+        task.dataset('train'), max_tokens=4096,
+    )
+    for batch in batch_itr:
+        # compute the loss
+        loss, sample_size, logging_output = task.get_loss(
+            model, criterion, batch,
+        )
+        loss.backward()
+
+
+Translation
+-----------
+
+.. autoclass:: fairseq.tasks.translation.TranslationTask
+
+.. _language modeling:
+
+Language Modeling
+-----------------
+
+.. autoclass:: fairseq.tasks.language_modeling.LanguageModelingTask
+
+
+Adding new tasks
+----------------
+
+.. autofunction:: fairseq.tasks.register_task
+.. autoclass:: fairseq.tasks.FairseqTask
+    :members:
+    :undoc-members: