[Bugfix] Mistral tool calling when content is list (#18729)

Signed-off-by: mgoin <mgoin64@gmail.com>

tests/tokenization/test_mistral_tokenizer.py

 # SPDX-License-Identifier: Apache-2.0
 
 import pytest
-from mistral_common.protocol.instruct.messages import UserMessage
+from mistral_common.protocol.instruct.messages import (AssistantMessage,
+                                                       ToolMessage,
+                                                       UserMessage)
 from mistral_common.protocol.instruct.request import ChatCompletionRequest
-from mistral_common.protocol.instruct.tool_calls import Function, Tool
+from mistral_common.protocol.instruct.tool_calls import (Function,
+                                                         FunctionCall, Tool,
+                                                         ToolCall)
 
 from vllm.transformers_utils.tokenizers.mistral import (
     make_mistral_chat_completion_request)
 
 
-# yapf: enable
 @pytest.mark.parametrize(
     "openai_request,expected_mistral_request",
     [(
@@ -78,6 +81,107 @@ from vllm.transformers_utils.tokenizers.mistral import (
 )
 def test_make_mistral_chat_completion_request(openai_request,
                                               expected_mistral_request):
-    assert (make_mistral_chat_completion_request(
-        openai_request["messages"],
-        openai_request["tools"]) == expected_mistral_request)
+    actual_request = make_mistral_chat_completion_request(
+        openai_request["messages"], openai_request["tools"])
+    assert actual_request == expected_mistral_request
+
+
+# Tool use with list content and reasoning_content
+@pytest.mark.parametrize("openai_request,expected_mistral_request", [(
+    {
+        "messages": [
+            {
+                "role": "user",
+                "content": "What's the weather in Paris?",
+            },
+            {
+                "role":
+                "assistant",
+                "reasoning_content":
+                None,
+                "content":
+                None,
+                "tool_calls": [{
+                    "id": "call123",
+                    "type": "function",
+                    "function": {
+                        "name": "get_weather",
+                        "arguments": '{"city": "Paris"}',
+                    },
+                }],
+            },
+            {
+                "role": "tool",
+                "content": [{
+                    "type": "text",
+                    "text": "Rainy"
+                }],
+                "name": "get_weather",
+                "tool_call_id": "call123",
+            },
+        ],
+        "tools": [{
+            "type": "function",
+            "function": {
+                "name": "get_weather",
+                "description": "Gets the current weather in a city.",
+                "parameters": {
+                    "type": "object",
+                    "properties": {
+                        "city": {
+                            "type": "string",
+                            "description": "The city name"
+                        }
+                    },
+                    "required": ["city"],
+                },
+            },
+        }],
+    },
+    ChatCompletionRequest(
+        messages=[
+            UserMessage(content="What's the weather in Paris?"),
+            AssistantMessage(
+                content=None,
+                tool_calls=[
+                    ToolCall(
+                        id="call123",
+                        function=FunctionCall(
+                            name="get_weather",
+                            arguments='{"city": "Paris"}',
+                        ),
+                    )
+                ],
+            ),
+            ToolMessage(
+                content="Rainy",
+                tool_call_id="call123",
+                name="get_weather",
+            ),
+        ],
+        tools=[
+            Tool(
+                type="function",
+                function=Function(
+                    name="get_weather",
+                    description="Gets the current weather in a city.",
+                    parameters={
+                        "type": "object",
+                        "properties": {
+                            "city": {
+                                "type": "string",
+                                "description": "The city name"
+                            }
+                        },
+                        "required": ["city"],
+                    },
+                ),
+            )
+        ],
+    ),
+)])
+def test_make_mistral_chat_completion_request_list_content(
+        openai_request, expected_mistral_request):
+    actual_request = make_mistral_chat_completion_request(
+        openai_request["messages"], openai_request["tools"])
+    assert actual_request == expected_mistral_request

vllm/transformers_utils/tokenizers/mistral.py

@@ -156,7 +156,11 @@ def make_mistral_chat_completion_request(
     #
     # [1]: https://github.com/mistralai/mistral-common/blob/f4a06998b75ed78bbf5aaf569590b772ea26c9f6/src/mistral_common/protocol/instruct/messages.py#L80
     for message in messages:
-        if message.get("role") == "assistant":
+        # Remove reasoning_content as unsupported by Mistral
+        _ = message.pop("reasoning_content", None)  # type: ignore
+
+        # Convert list text content to string
+        if message.get("role") in ("assistant", "tool"):
             content = message.get("content")
             if isinstance(content, list):
                 content = "\n".join(chunk.get("text") for chunk in content)