[Frontend] Add Early Validation For Chat Template / Tool Call Parser (#9151)

Signed-off-by: Alex-Brooks <Alex.Brooks@ibm.com>

tests/entrypoints/openai/test_cli_args.py

 import json
-import unittest
 
-from vllm.entrypoints.openai.cli_args import make_arg_parser
+import pytest
+
+from vllm.entrypoints.openai.cli_args import (make_arg_parser,
+                                              validate_parsed_serve_args)
 from vllm.entrypoints.openai.serving_engine import LoRAModulePath
 from vllm.utils import FlexibleArgumentParser
 
+from ...utils import VLLM_PATH
+
 LORA_MODULE = {
     "name": "module2",
     "path": "/path/to/module2",
     "base_model_name": "llama"
 }
+CHATML_JINJA_PATH = VLLM_PATH / "examples/template_chatml.jinja"
+assert CHATML_JINJA_PATH.exists()
 
 
-class TestLoraParserAction(unittest.TestCase):
+@pytest.fixture
+def serve_parser():
+    parser = FlexibleArgumentParser(description="vLLM's remote OpenAI server.")
+    return make_arg_parser(parser)
 
-    def setUp(self):
-        # Setting up argparse parser for tests
-        parser = FlexibleArgumentParser(
-            description="vLLM's remote OpenAI server.")
-        self.parser = make_arg_parser(parser)
 
-    def test_valid_key_value_format(self):
-        # Test old format: name=path
-        args = self.parser.parse_args([
-            '--lora-modules',
-            'module1=/path/to/module1',
+### Tests for Lora module parsing
+def test_valid_key_value_format(serve_parser):
+    # Test old format: name=path
+    args = serve_parser.parse_args([
+        '--lora-modules',
+        'module1=/path/to/module1',
+    ])
+    expected = [LoRAModulePath(name='module1', path='/path/to/module1')]
+    assert args.lora_modules == expected
+
+
+def test_valid_json_format(serve_parser):
+    # Test valid JSON format input
+    args = serve_parser.parse_args([
+        '--lora-modules',
+        json.dumps(LORA_MODULE),
+    ])
+    expected = [
+        LoRAModulePath(name='module2',
+                       path='/path/to/module2',
+                       base_model_name='llama')
+    ]
+    assert args.lora_modules == expected
+
+
+def test_invalid_json_format(serve_parser):
+    # Test invalid JSON format input, missing closing brace
+    with pytest.raises(SystemExit):
+        serve_parser.parse_args([
+            '--lora-modules', '{"name": "module3", "path": "/path/to/module3"'
         ])
-        expected = [LoRAModulePath(name='module1', path='/path/to/module1')]
-        self.assertEqual(args.lora_modules, expected)
 
-    def test_valid_json_format(self):
-        # Test valid JSON format input
-        args = self.parser.parse_args([
+
+def test_invalid_type_error(serve_parser):
+    # Test type error when values are not JSON or key=value
+    with pytest.raises(SystemExit):
+        serve_parser.parse_args([
             '--lora-modules',
-            json.dumps(LORA_MODULE),
+            'invalid_format'  # This is not JSON or key=value format
         ])
-        expected = [
-            LoRAModulePath(name='module2',
-                           path='/path/to/module2',
-                           base_model_name='llama')
-        ]
-        self.assertEqual(args.lora_modules, expected)
-
-    def test_invalid_json_format(self):
-        # Test invalid JSON format input, missing closing brace
-        with self.assertRaises(SystemExit):
-            self.parser.parse_args([
-                '--lora-modules',
-                '{"name": "module3", "path": "/path/to/module3"'
-            ])
-
-    def test_invalid_type_error(self):
-        # Test type error when values are not JSON or key=value
-        with self.assertRaises(SystemExit):
-            self.parser.parse_args([
-                '--lora-modules',
-                'invalid_format'  # This is not JSON or key=value format
-            ])
-
-    def test_invalid_json_field(self):
-        # Test valid JSON format but missing required fields
-        with self.assertRaises(SystemExit):
-            self.parser.parse_args([
-                '--lora-modules',
-                '{"name": "module4"}'  # Missing required 'path' field
-            ])
-
-    def test_empty_values(self):
-        # Test when no LoRA modules are provided
-        args = self.parser.parse_args(['--lora-modules', ''])
-        self.assertEqual(args.lora_modules, [])
-
-    def test_multiple_valid_inputs(self):
-        # Test multiple valid inputs (both old and JSON format)
-        args = self.parser.parse_args([
+
+
+def test_invalid_json_field(serve_parser):
+    # Test valid JSON format but missing required fields
+    with pytest.raises(SystemExit):
+        serve_parser.parse_args([
             '--lora-modules',
-            'module1=/path/to/module1',
-            json.dumps(LORA_MODULE),
+            '{"name": "module4"}'  # Missing required 'path' field
         ])
-        expected = [
-            LoRAModulePath(name='module1', path='/path/to/module1'),
-            LoRAModulePath(name='module2',
-                           path='/path/to/module2',
-                           base_model_name='llama')
-        ]
-        self.assertEqual(args.lora_modules, expected)
 
 
-if __name__ == '__main__':
-    unittest.main()
+def test_empty_values(serve_parser):
+    # Test when no LoRA modules are provided
+    args = serve_parser.parse_args(['--lora-modules', ''])
+    assert args.lora_modules == []
+
+
+def test_multiple_valid_inputs(serve_parser):
+    # Test multiple valid inputs (both old and JSON format)
+    args = serve_parser.parse_args([
+        '--lora-modules',
+        'module1=/path/to/module1',
+        json.dumps(LORA_MODULE),
+    ])
+    expected = [
+        LoRAModulePath(name='module1', path='/path/to/module1'),
+        LoRAModulePath(name='module2',
+                       path='/path/to/module2',
+                       base_model_name='llama')
+    ]
+    assert args.lora_modules == expected
+
+
+### Tests for serve argument validation that run prior to loading
+def test_enable_auto_choice_passes_without_tool_call_parser(serve_parser):
+    """Ensure validation fails if tool choice is enabled with no call parser"""
+    # If we enable-auto-tool-choice, explode with no tool-call-parser
+    args = serve_parser.parse_args(args=["--enable-auto-tool-choice"])
+    with pytest.raises(TypeError):
+        validate_parsed_serve_args(args)
+
+
+def test_enable_auto_choice_passes_with_tool_call_parser(serve_parser):
+    """Ensure validation passes with tool choice enabled with a call parser"""
+    args = serve_parser.parse_args(args=[
+        "--enable-auto-tool-choice",
+        "--tool-call-parser",
+        "mistral",
+    ])
+    validate_parsed_serve_args(args)
+
+
+def test_chat_template_validation_for_happy_paths(serve_parser):
+    """Ensure validation passes if the chat template exists"""
+    args = serve_parser.parse_args(
+        args=["--chat-template",
+              CHATML_JINJA_PATH.absolute().as_posix()])
+    validate_parsed_serve_args(args)
+
+
+def test_chat_template_validation_for_sad_paths(serve_parser):
+    """Ensure validation fails if the chat template doesn't exist"""
+    args = serve_parser.parse_args(args=["--chat-template", "does/not/exist"])
+    with pytest.raises(ValueError):
+        validate_parsed_serve_args(args)

vllm/entrypoints/chat_utils.py

@@ -303,6 +303,28 @@ class AsyncMultiModalContentParser(BaseMultiModalContentParser):
         self._add_placeholder(placeholder)
 
 
+def validate_chat_template(chat_template: Optional[Union[Path, str]]):
+    """Raises if the provided chat template appears invalid."""
+    if chat_template is None:
+        return
+
+    elif isinstance(chat_template, Path) and not chat_template.exists():
+        raise FileNotFoundError(
+            "the supplied chat template path doesn't exist")
+
+    elif isinstance(chat_template, str):
+        JINJA_CHARS = "{}\n"
+        if not any(c in chat_template
+                   for c in JINJA_CHARS) and not Path(chat_template).exists():
+            raise ValueError(
+                f"The supplied chat template string ({chat_template}) "
+                f"appears path-like, but doesn't exist!")
+
+    else:
+        raise TypeError(
+            f"{type(chat_template)} is not a valid chat template type")
+
+
 def load_chat_template(
         chat_template: Optional[Union[Path, str]]) -> Optional[str]:
     if chat_template is None:

vllm/entrypoints/openai/api_server.py

@@ -31,7 +31,8 @@ from vllm.engine.multiprocessing.engine import run_mp_engine
 from vllm.engine.protocol import EngineClient
 from vllm.entrypoints.launcher import serve_http
 from vllm.entrypoints.logger import RequestLogger
-from vllm.entrypoints.openai.cli_args import make_arg_parser
+from vllm.entrypoints.openai.cli_args import (make_arg_parser,
+                                              validate_parsed_serve_args)
 # yapf conflicts with isort for this block
 # yapf: disable
 from vllm.entrypoints.openai.protocol import (ChatCompletionRequest,
@@ -577,5 +578,6 @@ if __name__ == "__main__":
         description="vLLM OpenAI-Compatible RESTful API server.")
     parser = make_arg_parser(parser)
     args = parser.parse_args()
+    validate_parsed_serve_args(args)
 
     uvloop.run(run_server(args))

vllm/entrypoints/openai/cli_args.py

@@ -10,6 +10,7 @@ import ssl
 from typing import List, Optional, Sequence, Union
 
 from vllm.engine.arg_utils import AsyncEngineArgs, nullable_str
+from vllm.entrypoints.chat_utils import validate_chat_template
 from vllm.entrypoints.openai.serving_engine import (LoRAModulePath,
                                                     PromptAdapterPath)
 from vllm.entrypoints.openai.tool_parsers import ToolParserManager
@@ -231,6 +232,20 @@ def make_arg_parser(parser: FlexibleArgumentParser) -> FlexibleArgumentParser:
     return parser
 
 
+def validate_parsed_serve_args(args: argparse.Namespace):
+    """Quick checks for model serve args that raise prior to loading."""
+    if hasattr(args, "subparser") and args.subparser != "serve":
+        return
+
+    # Ensure that the chat template is valid; raises if it likely isn't
+    validate_chat_template(args.chat_template)
+
+    # Enable auto tool needs a tool call parser to be valid
+    if args.enable_auto_tool_choice and not args.tool_call_parser:
+        raise TypeError("Error: --enable-auto-tool-choice requires "
+                        "--tool-call-parser")
+
+
 def create_parser_for_docs() -> FlexibleArgumentParser:
     parser_for_docs = FlexibleArgumentParser(
         prog="-m vllm.entrypoints.openai.api_server")

vllm/scripts.py

@@ -11,7 +11,8 @@ from openai.types.chat import ChatCompletionMessageParam
 
 from vllm.engine.arg_utils import EngineArgs
 from vllm.entrypoints.openai.api_server import run_server
-from vllm.entrypoints.openai.cli_args import make_arg_parser
+from vllm.entrypoints.openai.cli_args import (make_arg_parser,
+                                              validate_parsed_serve_args)
 from vllm.logger import init_logger
 from vllm.utils import FlexibleArgumentParser
 
@@ -142,7 +143,7 @@ def main():
     env_setup()
 
     parser = FlexibleArgumentParser(description="vLLM CLI")
-    subparsers = parser.add_subparsers(required=True)
+    subparsers = parser.add_subparsers(required=True, dest="subparser")
 
     serve_parser = subparsers.add_parser(
         "serve",
@@ -186,6 +187,9 @@ def main():
     chat_parser.set_defaults(dispatch_function=interactive_cli, command="chat")
 
     args = parser.parse_args()
+    if args.subparser == "serve":
+        validate_parsed_serve_args(args)
+
     # One of the sub commands should be executed.
     if hasattr(args, "dispatch_function"):
         args.dispatch_function(args)