Fix interaction between Optional and Annotated in CLI typing (#19093)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Co-authored-by: Yikun Jiang <yikun@apache.org>

tests/engine/test_arg_utils.py

@@ -5,14 +5,14 @@ import json
 from argparse import ArgumentError, ArgumentTypeError
 from contextlib import nullcontext
 from dataclasses import dataclass, field
-from typing import Literal, Optional
+from typing import Annotated, Literal, Optional
 
 import pytest
 
 from vllm.config import CompilationConfig, config
 from vllm.engine.arg_utils import (EngineArgs, contains_type, get_kwargs,
-                                   get_type, is_not_builtin, is_type,
-                                   literal_to_kwargs, nullable_kvs,
+                                   get_type, get_type_hints, is_not_builtin,
+                                   is_type, literal_to_kwargs, nullable_kvs,
                                    optional_type, parse_type)
 from vllm.utils import FlexibleArgumentParser
 
@@ -160,6 +160,18 @@ def test_is_not_builtin(type_hint, expected):
     assert is_not_builtin(type_hint) == expected
 
 
+@pytest.mark.parametrize(
+    ("type_hint", "expected"), [
+        (Annotated[int, "annotation"], {int}),
+        (Optional[int], {int, type(None)}),
+        (Annotated[Optional[int], "annotation"], {int, type(None)}),
+        (Optional[Annotated[int, "annotation"]], {int, type(None)}),
+    ],
+    ids=["Annotated", "Optional", "Annotated_Optional", "Optional_Annotated"])
+def test_get_type_hints(type_hint, expected):
+    assert get_type_hints(type_hint) == expected
+
+
 def test_get_kwargs():
     kwargs = get_kwargs(DummyConfig)
     print(kwargs)