Add explicit validation error for tool calls. (#34438)

Signed-off-by: juliendenize <julien.denize@mistral.ai>

vllm/tokenizers/mistral.py

@@ -17,6 +17,7 @@ from mistral_common.tokens.tokenizers.sentencepiece import (
     SentencePieceTokenizer,
 )
 from mistral_common.tokens.tokenizers.tekken import Tekkenizer
+from pydantic import ValidationError
 
 from vllm.entrypoints.chat_utils import ChatCompletionMessageParam
 from vllm.entrypoints.openai.chat_completion.protocol import ChatCompletionRequest
@@ -64,14 +65,16 @@ def maybe_serialize_tool_calls(request: "MistralChatCompletionRequest"):
     # TODO: remove when pydantic v2.11 is released
     for i, message in enumerate(request.messages):
         if message.get("role") == "assistant":
-            tool_calls_validator = message.get("tool_calls", ().__iter__())
-            validated_tool_calls = []
-            while True:
+            if (tool_calls_validator := message.get("tool_calls", None)) is not None:
                 try:
-                    tool_call = next(tool_calls_validator)  # type: ignore
-                    validated_tool_calls.append(tool_call)
-                except StopIteration:
-                    break
+                    validated_tool_calls = list(tool_calls_validator)
+                except ValidationError as e:
+                    raise ValueError(
+                        "Validating messages' `tool_calls` raised an error. "
+                        "Please ensure `tool_calls` are iterable of tool calls."
+                    ) from e
+            else:
+                validated_tool_calls = []
 
             request.messages[i]["tool_calls"] = validated_tool_calls