[BUG FIX] upgrade fschat version to 0.2.23 (#650)

Co-authored-by: hao.yu <hao.yu@cn-c017.server.mila.quebec>

vllm/entrypoints/openai/api_server.py

@@ -7,6 +7,7 @@ from http import HTTPStatus
 import json
 import time
 from typing import AsyncGenerator, Dict, List, Optional
+from packaging import version
 
 import fastapi
 from fastapi import BackgroundTasks, Request
@@ -31,6 +32,7 @@ from vllm.transformers_utils.tokenizer import get_tokenizer
 from vllm.utils import random_uuid
 
 try:
+    import fastchat
     from fastchat.conversation import Conversation, SeparatorStyle
     from fastchat.model.model_adapter import get_conversation_template
     _fastchat_available = True
@@ -72,10 +74,16 @@ async def get_gen_prompt(request) -> str:
             "fastchat is not installed. Please install fastchat to use "
             "the chat completion and conversation APIs: `$ pip install fschat`"
         )
+    if version.parse(fastchat.__version__) < version.parse("0.2.23"):
+        raise ImportError(
+            f"fastchat version is low. Current version: {fastchat.__version__} "
+            "Please upgrade fastchat to use: `$ pip install -U fschat`")
+
     conv = get_conversation_template(request.model)
     conv = Conversation(
         name=conv.name,
-        system=conv.system,
+        system_template=conv.system_template,
+        system_message=conv.system_message,
         roles=conv.roles,
         messages=list(conv.messages),  # prevent in-place modification
         offset=conv.offset,
@@ -92,7 +100,7 @@ async def get_gen_prompt(request) -> str:
         for message in request.messages:
             msg_role = message["role"]
             if msg_role == "system":
-                conv.system = message["content"]
+                conv.system_message = message["content"]
             elif msg_role == "user":
                 conv.append_message(conv.roles[0], message["content"])
             elif msg_role == "assistant":