[Bugfix] Avoid leaking Pydantic repr in tool_choice error message (#47028)

Signed-off-by: muhammadfawaz1 <[email protected]>
Co-authored-by: Mahad Durrani <[email protected]>

tests/entrypoints/openai/chat_completion/test_serving_chat.py

@@ -2124,6 +2124,13 @@ async def test_tool_choice_validation_without_parser():
     assert isinstance(response_named, ErrorResponse)
     assert "tool_choice" in response_named.error.message
     assert "--tool-call-parser" in response_named.error.message
+    # The function name should appear in a clean, readable form -
+    # guards against leaking Pydantic's internal repr of the
+    # ChatCompletionNamedToolChoiceParam/ChatCompletionNamedFunction
+    # objects directly into the client-facing error message.
+    assert "get_weather" in response_named.error.message
+    assert "ChatCompletionNamedFunction" not in response_named.error.message
+    assert "ChatCompletionNamedToolChoiceParam" not in response_named.error.message
 
 
 @pytest.mark.asyncio

vllm/renderers/online_renderer.py

@@ -12,6 +12,7 @@ from vllm.entrypoints.chat_utils import (
     ConversationMessage,
 )
 from vllm.entrypoints.openai.chat_completion.protocol import (
+    ChatCompletionNamedToolChoiceParam,
     ChatCompletionRequest,
 )
 from vllm.entrypoints.openai.completion.protocol import (
@@ -134,8 +135,12 @@ class OnlineRenderer:
                 )
             elif request.tool_choice != "auto":
                 # "required" or named tool requires tool parser
+                if isinstance(request.tool_choice, ChatCompletionNamedToolChoiceParam):
+                    tool_choice_desc = f'function "{request.tool_choice.function.name}"'
+                else:
+                    tool_choice_desc = f'"{request.tool_choice}"'
                 return self.create_error_response(
-                    f'tool_choice="{request.tool_choice}" requires '
+                    f"tool_choice={tool_choice_desc} requires "
                     "--tool-call-parser to be set"
                 )