Revert "Fix case where only system messages are passed to Gemini (#9992)" (#10027)

This reverts commit 2afd922f8c.

litellm/llms/vertex_ai/gemini/transformation.py

@@ -331,7 +331,7 @@ def _gemini_convert_messages_with_history(  # noqa: PLR0915
         raise e
 
 
-def _transform_request_body( # noqa: PLR0915
+def _transform_request_body(
     messages: List[AllMessageValues],
     model: str,
     optional_params: dict,
@@ -342,35 +342,13 @@ def _transform_request_body( # noqa: PLR0915
     """
     Common transformation logic across sync + async Gemini /generateContent calls.
     """
-    # Duplicate system message as user message for Gemini 
-    duplicate_system_as_user = optional_params.pop("duplicate_system_as_user_for_gemini", True)
-
-    # Check if all messages are system messages
-    all_system_messages = all(message["role"] == "system" for message in messages)
-
     # Separate system prompt from rest of message
     supports_system_message = get_supports_system_message(
         model=model, custom_llm_provider=custom_llm_provider
     )
-
+    system_instructions, messages = _transform_system_message(
-    system_instructions = None
+        supports_system_message=supports_system_message, messages=messages
-    # If all messages are system messages, add a user message to the end
+    )
-    if (all_system_messages and supports_system_message and messages):
-        # Always create system instruction
-        system_content = messages[0].get("content", "")
-        system_part = PartType(text=system_content) # type: ignore
-        system_instructions = SystemInstructions(parts=[system_part])
-        
-        # Only duplicate as user message if flag is set
-        if duplicate_system_as_user or litellm.modify_params:
-            user_message = cast(AllMessageValues, {
-                "role": "user",
-                "content": system_content
-            })
-            messages = [user_message]
-        else:
-            messages = []
-
     # Checks for 'response_schema' support - if passed in
     if "response_schema" in optional_params:
         supports_response_schema = get_supports_response_schema(

tests/litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py

@@ -8,7 +8,6 @@ from litellm import ModelResponse
 from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import (
     VertexGeminiConfig,
 )
-from litellm.llms.vertex_ai.gemini.transformation import _transform_request_body
 from litellm.types.utils import ChoiceLogprobs
 
 
@@ -63,71 +62,3 @@ def test_get_model_name_from_gemini_spec_model():
     model = "gemini/ft-uuid-123"
     result = VertexGeminiConfig._get_model_name_from_gemini_spec_model(model)
     assert result == "ft-uuid-123"
-
-def test_system_message_conversion_gemini():
-    """Test that system-only messages are properly handled for Gemini"""
-    # Case 1: Default behavior - duplicate system as user
-    messages = [{"role": "system", "content": "You are a helpful assistant"}]
-    
-    # Create mock objects for the test
-    model = "gemini-2.0-flash"
-    custom_llm_provider = "gemini"
-    optional_params = {}
-    litellm_params = {}
-    
-    result = _transform_request_body(
-        messages=messages, # type: ignore
-        model=model,
-        optional_params=optional_params,
-        custom_llm_provider=custom_llm_provider,
-        litellm_params=litellm_params,
-        cached_content=None
-    )
-    
-    # Verify that contents has user message
-    assert len(result["contents"]) > 0
-    assert result["contents"][0]["role"] == "user" # type: ignore
-    assert "system_instruction" in result
-    
-    # Case 2: Disable duplication
-    optional_params = {"duplicate_system_as_user_for_gemini": False}
-    
-    # Save original modify_params value
-    original_modify_params = litellm.modify_params
-    litellm.modify_params = False
-    
-    result_no_duplicate = _transform_request_body(
-        messages=messages.copy(), # type: ignore
-        model=model,
-        optional_params=optional_params,
-        custom_llm_provider=custom_llm_provider,
-        litellm_params={},
-        cached_content=None
-    )
-    
-    # Restore original modify_params value
-    litellm.modify_params = original_modify_params
-    
-    # With duplication disabled and modify_params False,
-    # we'd expect an empty contents field
-    # This might actually raise an exception in practice
-    assert "system_instruction" in result_no_duplicate
-    
-    # Case 3: With litellm.modify_params=True it should duplicate even with parameter set to False
-    litellm.modify_params = True
-    
-    result_with_modify_params = _transform_request_body(
-        messages=messages.copy(), # type: ignore
-        model=model,
-        optional_params={"duplicate_system_as_user_for_gemini": False},
-        custom_llm_provider=custom_llm_provider,
-        litellm_params={},
-        cached_content=None
-    )
-    
-    # Restore original modify_params value
-    litellm.modify_params = original_modify_params
-    
-    # Verify that contents has user message due to modify_params=True
-    assert len(result_with_modify_params["contents"]) > 0
-    assert result_with_modify_params["contents"][0]["role"] == "user" # type: ignore