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>

vllm/engine/arg_utils.py

@@ -15,7 +15,7 @@ from typing import (Annotated, Any, Callable, Dict, List, Literal, Optional,
 
 import regex as re
 import torch
-from pydantic import SkipValidation, TypeAdapter, ValidationError
+from pydantic import TypeAdapter, ValidationError
 from typing_extensions import TypeIs, deprecated
 
 import vllm.envs as envs
@@ -151,17 +151,29 @@ def is_not_builtin(type_hint: TypeHint) -> bool:
     return type_hint.__module__ != "builtins"
 
 
+def get_type_hints(type_hint: TypeHint) -> set[TypeHint]:
+    """Extract type hints from Annotated or Union type hints."""
+    type_hints: set[TypeHint] = set()
+    origin = get_origin(type_hint)
+    args = get_args(type_hint)
+
+    if origin is Annotated:
+        type_hints.update(get_type_hints(args[0]))
+    elif origin is Union:
+        for arg in args:
+            type_hints.update(get_type_hints(arg))
+    else:
+        type_hints.add(type_hint)
+
+    return type_hints
+
+
 def get_kwargs(cls: ConfigType) -> dict[str, Any]:
     cls_docs = get_attr_docs(cls)
     kwargs = {}
     for field in fields(cls):
         # Get the set of possible types for the field
-        type_hints: set[TypeHint] = set()
-        if get_origin(field.type) in {Union, Annotated}:
-            predicate = lambda arg: not isinstance(arg, SkipValidation)
-            type_hints.update(filter(predicate, get_args(field.type)))
-        else:
-            type_hints.add(field.type)
+        type_hints: set[TypeHint] = get_type_hints(field.type)
 
         # If the field is a dataclass, we can use the model_validate_json
         generator = (th for th in type_hints if is_dataclass(th))