def lm_token_preprocessing(dataset, training):
  """Concatenates inputs, 0, targets, with masking only for targets."""
  del training

  def concat_and_add_mask(x):
    inp = x['inputs']
    targets = x['targets']
    pad = tf.expand_dims(tf.zeros_like(inp[0]), axis=0)
    concat = tf.concat([inp, pad, targets], axis=0)
    mask = tf.concat([tf.zeros_like(inp), pad, tf.ones_like(targets)], axis=0)
    x['inputs'] = concat
    x['targets'] = concat
    x['mask'] = mask
    return x

  dataset = dataset.map(concat_and_add_mask)
  return dataset
Concatenates inputs, 0, targets, with masking only for targets.
trax/data/tf_inputs.py