Fix the chat template for QWen (#83)

python/sglang/lang/chat_template.py

-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from enum import Enum, auto
-from typing import Callable, Dict, List, Tuple
+from typing import Callable, Dict, List, Tuple, Optional
 
 
 class ChatTemplateStyle(Enum):
@@ -13,6 +13,7 @@ class ChatTemplate:
     name: str
     default_system_prompt: str
     role_prefix_and_suffix: Dict[str, Tuple[str]]
+    stop_str: List[str] = ()
     image_token: str = "<image>"
     style: ChatTemplateStyle = ChatTemplateStyle.PLAIN
 
@@ -110,6 +111,7 @@ register_chat_template(
             "assistant": ("<|im_start|>assistant\n", "\n<|im_end|>\n"),
         },
         style=ChatTemplateStyle.PLAIN,
+        stop_str=('<|im_end|>',)
     )
 )
 

python/sglang/lang/interpreter.py

@@ -486,6 +486,12 @@ class StreamExecutor:
                 if clone is None:
                     clone = self.default_sampling_para.clone()
                 setattr(clone, item, value)
+
+        if self.chat_template.stop_str:
+            if not clone:
+                clone = self.default_sampling_para.clone()
+            clone.stop += self.chat_template.stop_str
+
         return clone or self.default_sampling_para
 
     def __del__(self):