Fixing support batch_size and num_return_Sequences in text-generation pipeline (#15318)

* Fixing support `batch_size` and `num_return_Sequences` in
`text-generation` pipeline

And `text2text-generation` too.

The bug was caused by the batch_size containing both the incoming batch
**and** the generated `num_sequences`.

The fix simply consists into splitting both of these again into
different dimensions.

* TF support.

* Odd backward compatibility script in the way.

tests/test_pipelines_text2text_generation.py

@@ -40,6 +40,26 @@ class Text2TextGenerationPipelineTests(unittest.TestCase, metaclass=PipelineTest
         # These are encoder decoder, they don't just append to incoming string
         self.assertFalse(outputs[0]["generated_text"].startswith("Something there"))
 
+        outputs = generator(["This is great !", "Something else"], num_return_sequences=2, do_sample=True)
+        self.assertEqual(
+            outputs,
+            [
+                [{"generated_text": ANY(str)}, {"generated_text": ANY(str)}],
+                [{"generated_text": ANY(str)}, {"generated_text": ANY(str)}],
+            ],
+        )
+
+        outputs = generator(
+            ["This is great !", "Something else"], num_return_sequences=2, batch_size=2, do_sample=True
+        )
+        self.assertEqual(
+            outputs,
+            [
+                [{"generated_text": ANY(str)}, {"generated_text": ANY(str)}],
+                [{"generated_text": ANY(str)}, {"generated_text": ANY(str)}],
+            ],
+        )
+
         with self.assertRaises(ValueError):
             generator(4)
 

tests/test_pipelines_text_generation.py

@@ -113,6 +113,27 @@ class TextGenerationPipelineTests(unittest.TestCase, metaclass=PipelineTestCaseM
         self.assertEqual(outputs, [{"generated_text": ANY(str)}])
         self.assertTrue(outputs[0]["generated_text"].startswith("This is a test"))
 
+        outputs = text_generator(["This is great !", "Something else"], num_return_sequences=2, do_sample=True)
+        self.assertEqual(
+            outputs,
+            [
+                [{"generated_text": ANY(str)}, {"generated_text": ANY(str)}],
+                [{"generated_text": ANY(str)}, {"generated_text": ANY(str)}],
+            ],
+        )
+
+        if text_generator.tokenizer.pad_token is not None:
+            outputs = text_generator(
+                ["This is great !", "Something else"], num_return_sequences=2, batch_size=2, do_sample=True
+            )
+            self.assertEqual(
+                outputs,
+                [
+                    [{"generated_text": ANY(str)}, {"generated_text": ANY(str)}],
+                    [{"generated_text": ANY(str)}, {"generated_text": ANY(str)}],
+                ],
+            )
+
         # Empty prompt is slighly special
         # it requires BOS token to exist.
         # Special case for Pegasus which will always append EOS so will