[Misc] Enhance warning information to user-defined chat template (#15408)

Signed-off-by: wwl2755 <wangwenlong2755@gmail.com>

vllm/entrypoints/openai/api_server.py

@@ -35,7 +35,9 @@ from vllm.engine.async_llm_engine import AsyncLLMEngine  # type: ignore
 from vllm.engine.multiprocessing.client import MQLLMEngineClient
 from vllm.engine.multiprocessing.engine import run_mp_engine
 from vllm.engine.protocol import EngineClient
-from vllm.entrypoints.chat_utils import load_chat_template
+from vllm.entrypoints.chat_utils import (load_chat_template,
+                                         resolve_hf_chat_template,
+                                         resolve_mistral_chat_template)
 from vllm.entrypoints.launcher import serve_http
 from vllm.entrypoints.logger import RequestLogger
 from vllm.entrypoints.openai.cli_args import (make_arg_parser,
@@ -84,6 +86,7 @@ from vllm.entrypoints.utils import load_aware_call, with_cancellation
 from vllm.logger import init_logger
 from vllm.transformers_utils.config import (
     maybe_register_config_serialize_by_value)
+from vllm.transformers_utils.tokenizer import MistralTokenizer
 from vllm.usage.usage_lib import UsageContext
 from vllm.utils import (Device, FlexibleArgumentParser, get_open_zmq_ipc_path,
                         is_valid_ipv6_address, set_ulimit)
@@ -883,8 +886,26 @@ async def init_app_state(
 
     resolved_chat_template = load_chat_template(args.chat_template)
     if resolved_chat_template is not None:
-        logger.info("Using supplied chat template:\n%s",
-                    resolved_chat_template)
+        # Get the tokenizer to check official template
+        tokenizer = await engine_client.get_tokenizer()
+
+        if isinstance(tokenizer, MistralTokenizer):
+            # The warning is logged in resolve_mistral_chat_template.
+            resolved_chat_template = resolve_mistral_chat_template(
+                chat_template=resolved_chat_template)
+        else:
+            hf_chat_template = resolve_hf_chat_template(
+                tokenizer,
+                chat_template=None,
+                tools=None,
+                trust_remote_code=model_config.trust_remote_code)
+
+            if hf_chat_template != resolved_chat_template:
+                logger.warning(
+                    "Using supplied chat template: %s\n"
+                    "It is different from official chat template '%s'. "
+                    "This discrepancy may lead to performance degradation.",
+                    resolved_chat_template, args.model)
 
     state.openai_serving_models = OpenAIServingModels(
         engine_client=engine_client,