JsonOutputFunctionParser: Fix mutation in place bug (#8758)

Fixes mutation in place in the JsonOutputFunctionParser. This causes
issues when trying to re-use the original AI message.

libs/langchain/langchain/output_parsers/openai_functions.py

@@ -1,3 +1,4 @@
+import copy
 import json
 from typing import Any, Dict, List, Type, Union
 
@@ -25,8 +26,8 @@ class OutputFunctionsParser(BaseGenerationOutputParser[Any]):
             )
         message = generation.message
         try:
-            func_call = message.additional_kwargs["function_call"]
-        except ValueError as exc:
+            func_call = copy.deepcopy(message.additional_kwargs["function_call"])
+        except KeyError as exc:
             raise OutputParserException(f"Could not parse function call: {exc}")
 
         if self.args_only:
@@ -38,11 +39,16 @@ class JsonOutputFunctionsParser(OutputFunctionsParser):
     """Parse an output as the Json object."""
 
     def parse_result(self, result: List[Generation]) -> Any:
-        func = super().parse_result(result)
+        function_call_info = super().parse_result(result)
         if self.args_only:
-            return json.loads(func)
-        func["arguments"] = json.loads(func["arguments"])
-        return func
+            try:
+                return json.loads(function_call_info)
+            except (json.JSONDecodeError, TypeError) as exc:
+                raise OutputParserException(
+                    f"Could not parse function call data: {exc}"
+                )
+        function_call_info["arguments"] = json.loads(function_call_info["arguments"])
+        return function_call_info
 
 
 class JsonKeyOutputFunctionsParser(JsonOutputFunctionsParser):

libs/langchain/tests/unit_tests/output_parsers/test_openai_functions.py

@@ -0,0 +1,76 @@
+import json
+
+import pytest
+
+from langchain.output_parsers.openai_functions import (
+    JsonOutputFunctionsParser,
+)
+from langchain.schema import BaseMessage, ChatGeneration, OutputParserException
+from langchain.schema.messages import AIMessage, HumanMessage
+
+
+@pytest.fixture
+def ai_message() -> AIMessage:
+    """Return a simple AIMessage."""
+    content = "This is a test message"
+
+    args = json.dumps(
+        {
+            "arg1": "value1",
+        }
+    )
+
+    function_call = {"name": "function_name", "arguments": args}
+    additional_kwargs = {"function_call": function_call}
+    return AIMessage(content=content, additional_kwargs=additional_kwargs)
+
+
+def test_json_output_function_parser(ai_message: AIMessage) -> None:
+    """Test that the JsonOutputFunctionsParser with full output."""
+    chat_generation = ChatGeneration(message=ai_message)
+
+    # Full output
+    parser = JsonOutputFunctionsParser(args_only=False)
+    result = parser.parse_result([chat_generation])
+    assert result == {"arguments": {"arg1": "value1"}, "name": "function_name"}
+
+    # Args only
+    parser = JsonOutputFunctionsParser(args_only=True)
+    result = parser.parse_result([chat_generation])
+    assert result == {"arg1": "value1"}
+
+    # Verify that the original message is not modified
+    assert ai_message.additional_kwargs == {
+        "function_call": {"name": "function_name", "arguments": '{"arg1": "value1"}'}
+    }
+
+
+@pytest.mark.parametrize(
+    "bad_message",
+    [
+        # Human message has no function call
+        HumanMessage(content="This is a test message"),
+        # AIMessage has no function call information.
+        AIMessage(content="This is a test message", additional_kwargs={}),
+        # Bad function call information (arguments should be a string)
+        AIMessage(
+            content="This is a test message",
+            additional_kwargs={
+                "function_call": {"name": "function_name", "arguments": {}}
+            },
+        ),
+        # Bad function call information (arguments should be proper json)
+        AIMessage(
+            content="This is a test message",
+            additional_kwargs={
+                "function_call": {"name": "function_name", "arguments": "noqweqwe"}
+            },
+        ),
+    ],
+)
+def test_exceptions_raised_while_parsing(bad_message: BaseMessage) -> None:
+    """Test exceptions raised correctly while using JSON parser."""
+    chat_generation = ChatGeneration(message=bad_message)
+
+    with pytest.raises(OutputParserException):
+        JsonOutputFunctionsParser().parse_result([chat_generation])