core[patch], openai[patch]: Handle OpenAI developer msg (#28794)

- Convert developer openai messages to SystemMessage
- store additional_kwargs={"__openai_role__": "developer"} so that the
correct role can be reconstructed if needed
- update ChatOpenAI to read in openai_role

---------

Co-authored-by: Erick Friis <erick@langchain.dev>

libs/core/langchain_core/messages/utils.py

@@ -221,14 +221,14 @@ def _create_message_from_message_type(
         tool_call_id: (str) the tool call id. Default is None.
         tool_calls: (list[dict[str, Any]]) the tool calls. Default is None.
         id: (str) the id of the message. Default is None.
-        **additional_kwargs: (dict[str, Any]) additional keyword arguments.
+        additional_kwargs: (dict[str, Any]) additional keyword arguments.
 
     Returns:
         a message of the appropriate type.
 
     Raises:
         ValueError: if the message type is not one of "human", "user", "ai",
-            "assistant", "system", "function", or "tool".
+            "assistant", "function", "tool", "system", or "developer".
     """
     kwargs: dict[str, Any] = {}
     if name is not None:
@@ -261,7 +261,10 @@ def _create_message_from_message_type(
         message: BaseMessage = HumanMessage(content=content, **kwargs)
     elif message_type in ("ai", "assistant"):
         message = AIMessage(content=content, **kwargs)
-    elif message_type == "system":
+    elif message_type in ("system", "developer"):
+        if message_type == "developer":
+            kwargs["additional_kwargs"] = kwargs.get("additional_kwargs") or {}
+            kwargs["additional_kwargs"]["__openai_role__"] = "developer"
         message = SystemMessage(content=content, **kwargs)
     elif message_type == "function":
         message = FunctionMessage(content=content, **kwargs)
@@ -273,7 +276,7 @@ def _create_message_from_message_type(
     else:
         msg = (
             f"Unexpected message type: '{message_type}'. Use one of 'human',"
-            f" 'user', 'ai', 'assistant', 'function', 'tool', or 'system'."
+            f" 'user', 'ai', 'assistant', 'function', 'tool', 'system', or 'developer'."
         )
         msg = create_message(message=msg, error_code=ErrorCode.MESSAGE_COERCION_FAILURE)
         raise ValueError(msg)
@@ -1385,7 +1388,7 @@ def _get_message_openai_role(message: BaseMessage) -> str:
     elif isinstance(message, ToolMessage):
         return "tool"
     elif isinstance(message, SystemMessage):
-        return "system"
+        return message.additional_kwargs.get("__openai_role__", "system")
     elif isinstance(message, FunctionMessage):
         return "function"
     elif isinstance(message, ChatMessage):

libs/core/tests/unit_tests/messages/test_utils.py

@@ -469,6 +469,7 @@ def test_convert_to_messages() -> None:
     message_like: list = [
         # BaseMessage
         SystemMessage("1"),
+        SystemMessage("1.1", additional_kwargs={"__openai_role__": "developer"}),
         HumanMessage([{"type": "image_url", "image_url": {"url": "2.1"}}], name="2.2"),
         AIMessage(
             [
@@ -503,6 +504,7 @@ def test_convert_to_messages() -> None:
         ToolMessage("5.1", tool_call_id="5.2", name="5.3"),
         # OpenAI dict
         {"role": "system", "content": "6"},
+        {"role": "developer", "content": "6.1"},
         {
             "role": "user",
             "content": [{"type": "image_url", "image_url": {"url": "7.1"}}],
@@ -526,6 +528,7 @@ def test_convert_to_messages() -> None:
         {"role": "tool", "content": "10.1", "tool_call_id": "10.2"},
         # Tuple/List
         ("system", "11.1"),
+        ("developer", "11.2"),
         ("human", [{"type": "image_url", "image_url": {"url": "12.1"}}]),
         (
             "ai",
@@ -551,6 +554,9 @@ def test_convert_to_messages() -> None:
     ]
     expected = [
         SystemMessage(content="1"),
+        SystemMessage(
+            content="1.1", additional_kwargs={"__openai_role__": "developer"}
+        ),
         HumanMessage(
             content=[{"type": "image_url", "image_url": {"url": "2.1"}}], name="2.2"
         ),
@@ -586,6 +592,9 @@ def test_convert_to_messages() -> None:
         ),
         ToolMessage(content="5.1", name="5.3", tool_call_id="5.2"),
         SystemMessage(content="6"),
+        SystemMessage(
+            content="6.1", additional_kwargs={"__openai_role__": "developer"}
+        ),
         HumanMessage(
             content=[{"type": "image_url", "image_url": {"url": "7.1"}}], name="7.2"
         ),
@@ -603,6 +612,9 @@ def test_convert_to_messages() -> None:
         ),
         ToolMessage(content="10.1", tool_call_id="10.2"),
         SystemMessage(content="11.1"),
+        SystemMessage(
+            content="11.2", additional_kwargs={"__openai_role__": "developer"}
+        ),
         HumanMessage(content=[{"type": "image_url", "image_url": {"url": "12.1"}}]),
         AIMessage(
             content=[
@@ -937,3 +949,12 @@ def test_convert_to_openai_messages_mixed_content_types() -> None:
     assert isinstance(result[0]["content"][0], dict)
     assert isinstance(result[0]["content"][1], dict)
     assert isinstance(result[0]["content"][2], dict)
+
+
+def test_convert_to_openai_messages_developer() -> None:
+    messages: list = [
+        SystemMessage("a", additional_kwargs={"__openai_role__": "developer"}),
+        {"role": "developer", "content": "a"},
+    ]
+    result = convert_to_openai_messages(messages)
+    assert result == [{"role": "developer", "content": "a"}] * 2