Adding a new return_full_text parameter to TextGenerationPipeline. (#9852)

* Adding a new `return_full_text` parameter to TextGenerationPipeline.

For text-generation, it's sometimes used as prompting text.
In that context, prefixing `generated_text` with the actual input
forces the caller to take an extra step to remove it.

The proposed change adds a new parameter (for backward compatibility).
`return_full_text` that enables the caller to prevent adding the prefix.

* Doc quality.

tests/test_pipelines_text_generation.py

@@ -15,6 +15,7 @@
 import unittest
 
 from transformers import pipeline
+from transformers.testing_utils import require_torch
 
 from .test_pipelines_common import MonoInputPipelineCommonMixin
 
@@ -41,3 +42,21 @@ class TextGenerationPipelineTests(MonoInputPipelineCommonMixin, unittest.TestCas
         self.assertEqual(type(outputs[0][0]["generated_text"]), str)
         self.assertEqual(list(outputs[1][0].keys()), ["generated_text"])
         self.assertEqual(type(outputs[1][0]["generated_text"]), str)
+
+    @require_torch
+    def test_generation_output_style(self):
+        text_generator = pipeline(task="text-generation", model=self.small_models[0])
+        # text-generation is non-deterministic by nature, we can't fully test the output
+
+        outputs = text_generator("This is a test")
+        self.assertIn("This is a test", outputs[0]["generated_text"])
+
+        outputs = text_generator("This is a test", return_full_text=False)
+        self.assertNotIn("This is a test", outputs[0]["generated_text"])
+
+        text_generator = pipeline(task="text-generation", model=self.small_models[0], return_full_text=False)
+        outputs = text_generator("This is a test")
+        self.assertNotIn("This is a test", outputs[0]["generated_text"])
+
+        outputs = text_generator("This is a test", return_full_text=True)
+        self.assertIn("This is a test", outputs[0]["generated_text"])