Fix `xxx_length` behavior when using XLNet in pipeline (#5319)

src/transformers/pipelines.py

@@ -586,7 +586,7 @@ class TextGenerationPipeline(Pipeline):
     father initially slaps him for making such an accusation, Rasputin watches as the
     man is chased outside and beaten. Twenty years later, Rasputin sees a vision of
     the Virgin Mary, prompting him to become a priest. Rasputin quickly becomes famous,
-    with people, even a bishop, begging for his blessing. <eod> </s> <eos>"""
+    with people, even a bishop, begging for his blessing. """
 
     ALLOWED_MODELS = [
         "XLNetLMHeadModel",
@@ -619,8 +619,18 @@ class TextGenerationPipeline(Pipeline):
             # Manage correct placement of the tensors
             with self.device_placement():
                 if self.model.__class__.__name__ in ["XLNetLMHeadModel", "TransfoXLLMHeadModel"]:
+                    # For XLNet and TransformerXL we had an article to the prompt to give more state to the model.
+                    padding_text = self.PADDING_TEXT + self.tokenizer.eos_token
+                    padding = self._parse_and_tokenize(padding_text, padding=False, add_special_tokens=False)
+                    # This impacts max_length and min_length argument that need adjusting.
+                    padding_length = padding["input_ids"].shape[-1]
+                    if "max_length" in generate_kwargs and generate_kwargs["max_length"] is not None:
+                        generate_kwargs["max_length"] += padding_length
+                    if "min_length" in generate_kwargs and generate_kwargs["min_length"] is not None:
+                        generate_kwargs["min_length"] += padding_length
+
                     inputs = self._parse_and_tokenize(
-                        self.PADDING_TEXT + prompt_text, padding=False, add_special_tokens=False
+                        padding_text + prompt_text, padding=False, add_special_tokens=False
                     )
                 else:
                     inputs = self._parse_and_tokenize(prompt_text, padding=False, add_special_tokens=False)