[Feature][V1] Support `tool_choice: required` when using Xgrammar as the...

[Feature][V1]  Support `tool_choice: required` when using Xgrammar as the `StructuredOutputBackend`. (#17845)
Signed-off-by: chaunceyjiang <chaunceyjiang@gmail.com>

requirements/common.txt

@@ -22,7 +22,7 @@ lm-format-enforcer >= 0.10.11, < 0.11
 llguidance >= 0.7.11, < 0.8.0; platform_machine == "x86_64" or platform_machine == "arm64" or platform_machine == "aarch64"
 outlines == 0.1.11
 lark == 1.2.2
-xgrammar == 0.1.18; platform_machine == "x86_64" or platform_machine == "aarch64"
+xgrammar == 0.1.19; platform_machine == "x86_64" or platform_machine == "aarch64"
 typing_extensions >= 4.10
 filelock >= 3.16.1 # need to contain https://github.com/tox-dev/filelock/pull/317
 partial-json-parser # used for parsing partial JSON outputs

tests/entrypoints/openai/test_completion_with_function_calling.py

+# SPDX-License-Identifier: Apache-2.0
+
+import openai  # use the official client for correctness check
+import pytest
+import pytest_asyncio
+
+# downloading lora to test lora requests
+from ...utils import RemoteOpenAIServer
+
+# any model with a chat template should work here
+MODEL_NAME = "Qwen/Qwen2.5-1.5B-Instruct"
+
+
+@pytest.fixture(scope="module")
+def server():  # noqa: F811
+    args = [
+        # use half precision for speed and memory savings in CI environment
+        "--dtype",
+        "half",
+        "--enable-auto-tool-choice",
+        "--guided-decoding-backend",
+        "xgrammar",
+        "--tool-call-parser",
+        "hermes"
+    ]
+
+    with RemoteOpenAIServer(MODEL_NAME, args) as remote_server:
+        yield remote_server
+
+
+@pytest_asyncio.fixture
+async def client(server):
+    async with server.get_async_client() as async_client:
+        yield async_client
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("model_name", [MODEL_NAME])
+async def test_required_tool_use(client: openai.AsyncOpenAI, model_name: str):
+    tools = [
+        {
+            "type": "function",
+            "function": {
+                "name": "get_current_weather",
+                "description": "Get the current weather in a given location",
+                "parameters": {
+                    "type": "object",
+                    "properties": {
+                        "city": {
+                            "type": "string",
+                            "description":
+                            "The city to find the weather for, e.g. 'Vienna'",
+                            "default": "Vienna",
+                        },
+                        "country": {
+                            "type":
+                            "string",
+                            "description":
+                            "The country that the city is in, e.g. 'Austria'",
+                        },
+                        "unit": {
+                            "type": "string",
+                            "description":
+                            "The unit to fetch the temperature in",
+                            "enum": ["celsius", "fahrenheit"],
+                        },
+                    },
+                    "required": ["country", "unit"],
+                },
+            },
+        },
+        {
+            "type": "function",
+            "function": {
+                "name": "get_forecast",
+                "description": "Get the weather forecast for a given location",
+                "parameters": {
+                    "type": "object",
+                    "properties": {
+                        "city": {
+                            "type": "string",
+                            "description":
+                            "The city to get the forecast for, e.g. 'Vienna'",
+                            "default": "Vienna",
+                        },
+                        "country": {
+                            "type":
+                            "string",
+                            "description":
+                            "The country that the city is in, e.g. 'Austria'",
+                        },
+                        "days": {
+                            "type":
+                            "integer",
+                            "description":
+                            "Number of days to get the forecast for (1-7)",
+                        },
+                        "unit": {
+                            "type": "string",
+                            "description":
+                            "The unit to fetch the temperature in",
+                            "enum": ["celsius", "fahrenheit"],
+                        },
+                    },
+                    "required": ["country", "days", "unit"],
+                },
+            },
+        },
+    ]
+
+    messages = [
+        {
+            "role": "user",
+            "content": "Hi! How are you doing today?"
+        },
+        {
+            "role": "assistant",
+            "content": "I'm doing well! How can I help you?"
+        },
+        {
+            "role":
+            "user",
+            "content":
+            "Can you tell me what the current weather is in Berlin and the "\
+            "forecast for the next 5 days, in fahrenheit?",
+        },
+    ]
+
+    # Non-streaming test
+    chat_completion = await client.chat.completions.create(
+        messages=messages,
+        model=model_name,
+        tools=tools,
+        tool_choice="required",
+    )
+
+    assert chat_completion.choices[0].message.tool_calls is not None
+    assert len(chat_completion.choices[0].message.tool_calls) > 0
+
+    # Streaming test
+    stream = await client.chat.completions.create(
+        messages=messages,
+        model=model_name,
+        tools=tools,
+        tool_choice="required",
+        stream=True,
+    )
+
+    output = []
+    async for chunk in stream:
+        if chunk.choices and chunk.choices[0].delta.tool_calls:
+            output.extend(chunk.choices[0].delta.tool_calls)
+
+    assert len(output) > 0

tests/v1/entrypoints/conftest.py

@@ -74,7 +74,9 @@ def sample_json_schema():
                     },
                     "required": ["company", "duration", "position"],
                     "additionalProperties": False
-                }
+                },
+                "minItems": 0,
+                "maxItems": 3
             }
         },
         "required":

tests/v1/structured_output/test_utils.py

@@ -57,14 +57,6 @@ def unsupported_array_schemas():
             "type": "array",
             "maxContains": 5
         },
-        {
-            "type": "array",
-            "minItems": 1
-        },
-        {
-            "type": "array",
-            "maxItems": 10
-        },
     ]
 
 

vllm/v1/structured_output/backend_xgrammar.py

@@ -215,9 +215,8 @@ def has_xgrammar_unsupported_json_features(schema: dict[str, Any]) -> bool:
 
         # Check for array unsupported keywords
         if obj.get("type") == "array" and any(
-                key in obj
-                for key in ("uniqueItems", "contains", "minContains",
-                            "maxContains", "minItems", "maxItems")):
+                key in obj for key in ("uniqueItems", "contains",
+                                       "minContains", "maxContains")):
             return True
 
         # Unsupported keywords for strings