Adding LM Head to Transfo-XL and first step to fixing problem with Adaptive Embeddings in TransfoXL (#3286)

* first commit

* work in progress

* make language generation task pass

* update to working version for LM

* delete print

* remove dead code

* make style

tests/test_modeling_tf_transfo_xl.py

@@ -26,7 +26,7 @@ from .utils import CACHE_DIR, require_tf, slow
 
 if is_tf_available():
     import tensorflow as tf
-    from transformers.modeling_tf_transfo_xl import (
+    from transformers import (
         TFTransfoXLModel,
         TFTransfoXLLMHeadModel,
         TF_TRANSFO_XL_PRETRAINED_MODEL_ARCHIVE_MAP,
@@ -364,7 +364,7 @@ class TFTransfoXLModelLanguageGenerationTest(unittest.TestCase):
                     0,
                 ]
             ],
-            dtype=tf.int31,
+            dtype=tf.int32,
         )
         #  In 1991 , the remains of Russian Tsar Nicholas II and his family
         #  ( except for Alexei and Maria ) are discovered .
@@ -570,8 +570,5 @@ class TFTransfoXLModelLanguageGenerationTest(unittest.TestCase):
         # Nicholas II and his family were discovered. The voice of <unk> young son,
         # Tsarevich Alexei Nikolaevich, narrates the remainder of the story.<eos>
 
-        # TODO: add this test when trasnfo-xl-lmhead is implemented
-        with self.assertRaises(NotImplementedError):
-            model.generate(input_ids, max_length=200, do_sample=False)
-            print(expected_output_ids)
-        # self.assertListEqual(output_ids[0].numpy().tolist(), expected_output_ids) TODO: (PVP) to add when transfo-xl is implemented
+        output_ids = model.generate(input_ids, max_length=200, do_sample=False)
+        self.assertListEqual(output_ids[0].numpy().tolist(), expected_output_ids)