fix: enable passing max_length for text2text-generation task (#5420)

* bug fix

* add unit test

* reformatting

* add release note

* add release note

* Update releasenotes/notes/enable-set-max-length-during-runtime-097d65e537bf800b.yaml

Co-authored-by: bogdankostic <bogdankostic@web.de>

* Update test/prompt/invocation_layer/test_hugging_face.py

Co-authored-by: bogdankostic <bogdankostic@web.de>

* Update test/prompt/invocation_layer/test_hugging_face.py

Co-authored-by: bogdankostic <bogdankostic@web.de>

* Update test/prompt/invocation_layer/test_hugging_face.py

Co-authored-by: bogdankostic <bogdankostic@web.de>

* Update test/prompt/invocation_layer/test_hugging_face.py

Co-authored-by: bogdankostic <bogdankostic@web.de>

* bug fix

---------

Co-authored-by: bogdankostic <bogdankostic@web.de>

haystack/nodes/prompt/invocation_layer/hugging_face.py

@@ -266,7 +266,7 @@ class HFLocalInvocationLayer(PromptModelInvocationLayer):
             if is_text_generation:
                 model_input_kwargs["max_new_tokens"] = model_input_kwargs.pop("max_length", self.max_length)
             else:
-                model_input_kwargs["max_length"] = self.max_length
+                model_input_kwargs["max_length"] = model_input_kwargs.pop("max_length", self.max_length)
 
             if stream:
                 stream_handler: TokenStreamingHandler = stream_handler or DefaultTokenStreamingHandler()

releasenotes/notes/enable-set-max-length-during-runtime-097d65e537bf800b.yaml

@@ -0,0 +1,4 @@
+---
+enhancements:
+  - |
+    Enable setting the `max_length` value when running PromptNodes using local HF text2text-generation models.

test/prompt/invocation_layer/test_hugging_face.py

@@ -523,6 +523,23 @@ def test_generation_kwargs_from_invoke():
     mock_call.assert_called_with(the_question, {}, {"do_sample": True, "top_p": 0.9, "max_length": 100}, {})
 
 
+@pytest.mark.unit
+def test_max_length_from_invoke(mock_auto_tokenizer, mock_pipeline, mock_get_task):
+    """
+    Test that max_length passed to invoke are passed to the underlying HF model
+    """
+    query = "What does 42 mean?"
+    # test that generation_kwargs are passed to the underlying HF model
+    layer = HFLocalInvocationLayer()
+    layer.invoke(prompt=query, generation_kwargs={"max_length": 200})
+    # find the call to pipeline invocation, and check that the kwargs are correct
+    assert any((call.kwargs == {"max_length": 200}) and (query in call.args) for call in mock_pipeline.mock_calls)
+
+    layer = HFLocalInvocationLayer()
+    layer.invoke(prompt=query, generation_kwargs=GenerationConfig(max_length=235))
+    assert any((call.kwargs == {"max_length": 235}) and (query in call.args) for call in mock_pipeline.mock_calls)
+
+
 @pytest.mark.unit
 def test_ensure_token_limit_positive_mock(mock_pipeline, mock_get_task, mock_auto_tokenizer):
     # prompt of length 5 + max_length of 3 = 8, which is less than model_max_length of 10, so no resize