Improve literal dataclass field conversion to argparse argument (#17391)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

tests/engine/test_arg_utils.py

@@ -11,7 +11,8 @@ import pytest
 from vllm.config import PoolerConfig, config
 from vllm.engine.arg_utils import (EngineArgs, contains_type, get_kwargs,
                                    get_type, is_not_builtin, is_type,
-                                   nullable_kvs, optional_type)
+                                   literal_to_kwargs, nullable_kvs,
+                                   optional_type)
 from vllm.utils import FlexibleArgumentParser
 
 
@@ -71,6 +72,21 @@ def test_get_type(type_hints, type, expected):
     assert get_type(type_hints, type) == expected
 
 
+@pytest.mark.parametrize(("type_hints", "expected"), [
+    ({Literal[1, 2]}, {
+        "type": int,
+        "choices": [1, 2]
+    }),
+    ({Literal[1, "a"]}, Exception),
+])
+def test_literal_to_kwargs(type_hints, expected):
+    context = nullcontext()
+    if expected is Exception:
+        context = pytest.raises(expected)
+    with context:
+        assert literal_to_kwargs(type_hints) == expected
+
+
 @config
 @dataclass
 class DummyConfigClass:
@@ -81,11 +97,15 @@ class DummyConfigClass:
     optional_literal: Optional[Literal["x", "y"]] = None
     """Optional literal with default None"""
     tuple_n: tuple[int, ...] = field(default_factory=lambda: (1, 2, 3))
-    """Tuple with default (1, 2, 3)"""
+    """Tuple with variable length"""
     tuple_2: tuple[int, int] = field(default_factory=lambda: (1, 2))
-    """Tuple with default (1, 2)"""
+    """Tuple with fixed length"""
     list_n: list[int] = field(default_factory=lambda: [1, 2, 3])
-    """List with default [1, 2, 3]"""
+    """List with variable length"""
+    list_literal: list[Literal[1, 2]] = field(default_factory=list)
+    """List with literal choices"""
+    literal_literal: Literal[Literal[1], Literal[2]] = 1
+    """Literal of literals with default 1"""
 
 
 @pytest.mark.parametrize(("type_hint", "expected"), [
@@ -111,6 +131,12 @@ def test_get_kwargs():
     # lists should work
     assert kwargs["list_n"]["type"] is int
     assert kwargs["list_n"]["nargs"] == "+"
+    # lists with literals should have the correct choices
+    assert kwargs["list_literal"]["type"] is int
+    assert kwargs["list_literal"]["nargs"] == "+"
+    assert kwargs["list_literal"]["choices"] == [1, 2]
+    # literals of literals should have merged choices
+    assert kwargs["literal_literal"]["choices"] == [1, 2]
 
 
 @pytest.mark.parametrize(("arg", "expected"), [

tests/test_config.py

@@ -1,14 +1,47 @@
 # SPDX-License-Identifier: Apache-2.0
 
 from dataclasses import MISSING, Field, asdict, dataclass, field
+from typing import Literal, Union
 
 import pytest
 
-from vllm.config import ModelConfig, PoolerConfig, get_field
+from vllm.config import ModelConfig, PoolerConfig, config, get_field
 from vllm.model_executor.layers.pooler import PoolingType
 from vllm.platforms import current_platform
 
 
+class TestConfig1:
+    pass
+
+
+@dataclass
+class TestConfig2:
+    a: int
+    """docstring"""
+
+
+@dataclass
+class TestConfig3:
+    a: int = 1
+
+
+@dataclass
+class TestConfig4:
+    a: Union[Literal[1], Literal[2]] = 1
+    """docstring"""
+
+
+@pytest.mark.parametrize(("test_config", "expected_error"), [
+    (TestConfig1, "must be a dataclass"),
+    (TestConfig2, "must have a default"),
+    (TestConfig3, "must have a docstring"),
+    (TestConfig4, "must use a single Literal"),
+])
+def test_config(test_config, expected_error):
+    with pytest.raises(Exception, match=expected_error):
+        config(test_config)
+
+
 def test_get_field():
 
     @dataclass

vllm/config.py

@@ -17,7 +17,7 @@ from dataclasses import (MISSING, dataclass, field, fields, is_dataclass,
 from importlib.util import find_spec
 from pathlib import Path
 from typing import (TYPE_CHECKING, Any, Callable, ClassVar, Final, Literal,
-                    Optional, Protocol, TypeVar, Union, get_args)
+                    Optional, Protocol, TypeVar, Union, get_args, get_origin)
 
 import torch
 from pydantic import BaseModel, Field, PrivateAttr
@@ -177,9 +177,19 @@ def config(cls: ConfigT) -> ConfigT:
             raise ValueError(
                 f"Field '{f.name}' in {cls.__name__} must have a default value."
             )
+
         if f.name not in attr_docs:
             raise ValueError(
                 f"Field '{f.name}' in {cls.__name__} must have a docstring.")
+
+        if get_origin(f.type) is Union:
+            args = get_args(f.type)
+            literal_args = [arg for arg in args if get_origin(arg) is Literal]
+            if len(literal_args) > 1:
+                raise ValueError(
+                    f"Field '{f.name}' in {cls.__name__} must use a single "
+                    "Literal type. Please use 'Literal[Literal1, Literal2]' "
+                    "instead of 'Union[Literal1, Literal2]'.")
     return cls
 
 
@@ -3166,6 +3176,8 @@ def get_served_model_name(model: str,
 GuidedDecodingBackendV0 = Literal["auto", "outlines", "lm-format-enforcer",
                                   "xgrammar", "guidance"]
 GuidedDecodingBackendV1 = Literal["auto", "xgrammar", "guidance"]
+GuidedDecodingBackend = Literal[GuidedDecodingBackendV0,
+                                GuidedDecodingBackendV1]
 
 
 @config
@@ -3173,9 +3185,8 @@ GuidedDecodingBackendV1 = Literal["auto", "xgrammar", "guidance"]
 class DecodingConfig:
     """Dataclass which contains the decoding strategy of the engine."""
 
-    guided_decoding_backend: Union[
-        GuidedDecodingBackendV0,
-        GuidedDecodingBackendV1] = "auto" if envs.VLLM_USE_V1 else "xgrammar"
+    guided_decoding_backend: GuidedDecodingBackend = \
+        "auto" if envs.VLLM_USE_V1 else "xgrammar"
     """Which engine will be used for guided decoding (JSON schema / regex etc)
     by default. With "auto", we will make opinionated choices based on request
     contents and what the backend libraries currently support, so the behavior

vllm/engine/arg_utils.py

@@ -116,6 +116,18 @@ def get_type(type_hints: set[TypeHint], type: TypeHintT) -> TypeHintT:
     return next((th for th in type_hints if is_type(th, type)), None)
 
 
+def literal_to_kwargs(type_hints: set[TypeHint]) -> dict[str, Any]:
+    """Convert Literal type hints to argparse kwargs."""
+    type_hint = get_type(type_hints, Literal)
+    choices = get_args(type_hint)
+    choice_type = type(choices[0])
+    if not all(isinstance(choice, choice_type) for choice in choices):
+        raise ValueError(
+            "All choices must be of the same type. "
+            f"Got {choices} with types {[type(c) for c in choices]}")
+    return {"type": choice_type, "choices": sorted(choices)}
+
+
 def is_not_builtin(type_hint: TypeHint) -> bool:
     """Check if the class is not a built-in type."""
     return type_hint.__module__ != "builtins"
@@ -151,15 +163,7 @@ def get_kwargs(cls: ConfigType) -> dict[str, Any]:
             # Creates --no-<name> and --<name> flags
             kwargs[name]["action"] = argparse.BooleanOptionalAction
         elif contains_type(type_hints, Literal):
-            # Creates choices from Literal arguments
-            type_hint = get_type(type_hints, Literal)
-            choices = sorted(get_args(type_hint))
-            kwargs[name]["choices"] = choices
-            choice_type = type(choices[0])
-            assert all(type(c) is choice_type for c in choices), (
-                "All choices must be of the same type. "
-                f"Got {choices} with types {[type(c) for c in choices]}")
-            kwargs[name]["type"] = choice_type
+            kwargs[name].update(literal_to_kwargs(type_hints))
         elif contains_type(type_hints, tuple):
             type_hint = get_type(type_hints, tuple)
             types = get_args(type_hint)
@@ -191,6 +195,11 @@ def get_kwargs(cls: ConfigType) -> dict[str, Any]:
             raise ValueError(
                 f"Unsupported type {type_hints} for argument {name}.")
 
+        # If the type hint was a sequence of literals, use the helper function
+        # to update the type and choices
+        if get_origin(kwargs[name].get("type")) is Literal:
+            kwargs[name].update(literal_to_kwargs({kwargs[name]["type"]}))
+
         # If None is in type_hints, make the argument optional.
         # But not if it's a bool, argparse will handle this better.
         if type(None) in type_hints and not contains_type(type_hints, bool):