[Perf] Validate @config in pre-commit instead of dynamically

.pre-commit-config.yaml

@@ -160,6 +160,13 @@ repos:
     types: [python]
     pass_filenames: false
     additional_dependencies: [pathspec, regex]
+  - id: validate-config
+    name: Validate configuration has default values and that each field has a docstring
+    entry: python tools/validate_config.py
+    language: python
+    types: [python]
+    pass_filenames: true
+    files: vllm/config.py|tests/test_config.py
   # Keep `suggestion` last
   - id: suggestion
     name: Suggestion

tests/test_config.py

@@ -2,49 +2,16 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
 from dataclasses import MISSING, Field, asdict, dataclass, field
-from typing import Literal, Union
 
 import pytest
 
 from vllm.compilation.backends import VllmBackend
 from vllm.config import (LoadConfig, ModelConfig, PoolerConfig, VllmConfig,
-                         config, get_field)
+                         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_compile_config_repr_succeeds():
     # setup: VllmBackend mutates the config object
     config = VllmConfig()

tests/tools/test_config_validator.py

@@ -0,0 +1,49 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import ast
+
+import pytest
+
+from tools.validate_config import validate_ast
+
+_TestConfig1 = '''
+@config
+class _TestConfig1:
+    pass
+'''
+
+_TestConfig2 = '''
+@config
+@dataclass
+class _TestConfig2:
+    a: int
+    """docstring"""
+'''
+
+_TestConfig3 = '''
+@config
+@dataclass
+class _TestConfig3:
+    a: int = 1
+'''
+
+_TestConfig4 = '''
+@config
+@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):
+    tree = ast.parse(test_config)
+    with pytest.raises(Exception, match=expected_error):
+        validate_ast(tree)

tools/validate_config.py

@@ -0,0 +1,158 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Ensures all fields in a config dataclass have default values
+and that each field has a docstring.
+"""
+
+import ast
+import inspect
+import sys
+
+
+def get_attr_docs(cls_node: ast.ClassDef) -> dict[str, str]:
+    """
+    Get any docstrings placed after attribute assignments in a class body.
+
+    Adapted from https://davidism.com/attribute-docstrings/
+    https://davidism.com/mit-license/
+    """
+
+    def pairwise(iterable):
+        """
+        Manually implement https://docs.python.org/3/library/itertools.html#itertools.pairwise
+
+        Can be removed when Python 3.9 support is dropped.
+        """
+        iterator = iter(iterable)
+        a = next(iterator, None)
+
+        for b in iterator:
+            yield a, b
+            a = b
+
+    out = {}
+
+    # Consider each pair of nodes.
+    for a, b in pairwise(cls_node.body):
+        # Must be an assignment then a constant string.
+        if (not isinstance(a, (ast.Assign, ast.AnnAssign))
+                or not isinstance(b, ast.Expr)
+                or not isinstance(b.value, ast.Constant)
+                or not isinstance(b.value.value, str)):
+            continue
+
+        doc = inspect.cleandoc(b.value.value)
+
+        # An assignment can have multiple targets (a = b = v), but an
+        # annotated assignment only has one target.
+        targets = a.targets if isinstance(a, ast.Assign) else [a.target]
+
+        for target in targets:
+            # Must be assigning to a plain name.
+            if not isinstance(target, ast.Name):
+                continue
+
+            out[target.id] = doc
+
+    return out
+
+
+class ConfigValidator(ast.NodeVisitor):
+
+    def __init__(self):
+        ...
+
+    def visit_ClassDef(self, node):
+        # Validate class with both @config and @dataclass decorators
+        decorators = [
+            id for d in node.decorator_list if (isinstance(d, ast.Name) and (
+                (id := d.id) == 'config' or id == 'dataclass')) or
+            (isinstance(d, ast.Call) and (isinstance(d.func, ast.Name) and
+                                          (id := d.func.id) == 'dataclass'))
+        ]
+
+        if set(decorators) == {'config', 'dataclass'}:
+            validate_class(node)
+        elif set(decorators) == {'config'}:
+            fail(
+                f"Class {node.name} with config decorator must be a dataclass.",
+                node)
+
+        self.generic_visit(node)
+
+
+def validate_class(class_node: ast.ClassDef):
+    attr_docs = get_attr_docs(class_node)
+
+    for stmt in class_node.body:
+        # A field is defined as a class variable that has a type annotation.
+        if isinstance(stmt, ast.AnnAssign):
+            # Skip ClassVar
+            # see https://docs.python.org/3/library/dataclasses.html#class-variables
+            if isinstance(stmt.annotation, ast.Subscript) and isinstance(
+                    stmt.annotation.value,
+                    ast.Name) and stmt.annotation.value.id == "ClassVar":
+                continue
+
+            if isinstance(stmt.target, ast.Name):
+                field_name = stmt.target.id
+                if stmt.value is None:
+                    fail(
+                        f"Field '{field_name}' in {class_node.name} must have "
+                        "a default value.", stmt)
+
+                if field_name not in attr_docs:
+                    fail(
+                        f"Field '{field_name}' in {class_node.name} must have "
+                        "a docstring.", stmt)
+
+                if isinstance(stmt.annotation, ast.Subscript) and \
+                   isinstance(stmt.annotation.value, ast.Name) \
+                    and stmt.annotation.value.id == "Union" and \
+                        isinstance(stmt.annotation.slice, ast.Tuple):
+                    args = stmt.annotation.slice.elts
+                    literal_args = [
+                        arg for arg in args
+                        if isinstance(arg, ast.Subscript) and isinstance(
+                            arg.value, ast.Name) and arg.value.id == "Literal"
+                    ]
+                    if len(literal_args) > 1:
+                        fail(
+                            f"Field '{field_name}' in {class_node.name} must "
+                            "use a single "
+                            "Literal type. Please use 'Literal[Literal1, "
+                            "Literal2]' instead of 'Union[Literal1, Literal2]'"
+                            ".", stmt)
+
+
+def validate_ast(tree: ast.stmt):
+    ConfigValidator().visit(tree)
+
+
+def validate_file(file_path: str):
+    try:
+        print(f"validating {file_path} config dataclasses ", end="")
+        with open(file_path, encoding="utf-8") as f:
+            source = f.read()
+
+        tree = ast.parse(source, filename=file_path)
+        validate_ast(tree)
+    except ValueError as e:
+        print(e)
+        SystemExit(2)
+    else:
+        print("✅")
+
+
+def fail(message: str, node: ast.stmt):
+    raise ValueError(f"❌ line({node.lineno}): {message}")
+
+
+def main():
+    for filename in sys.argv[1:]:
+        validate_file(filename)
+
+
+if __name__ == "__main__":
+    main()

vllm/config.py

@@ -18,7 +18,7 @@
 from importlib.util import find_spec
 from pathlib import Path
 from typing import (TYPE_CHECKING, Any, Callable, ClassVar, Literal, Optional,
-                    Protocol, TypeVar, Union, cast, get_args, get_origin)
+                    Protocol, TypeVar, Union, cast, get_args)
 
 import regex as re
 import torch
@@ -193,28 +193,10 @@ def config(cls: ConfigT) -> ConfigT:
     (i.e. `ConfigT(**json.loads(cli_arg))`). However, if a particular `ConfigT`
     requires custom construction from CLI (i.e. `CompilationConfig`), it can
     have a `from_cli` method, which will be called instead.
-    """
-    if not is_dataclass(cls):
-        raise TypeError("The decorated class must be a dataclass.")
-    attr_docs = get_attr_docs(cls)
-    for f in fields(cls):
-        if f.init and f.default is MISSING and f.default_factory is MISSING:
-            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]'.")
+    Config validation is performed by the tools/validate_config.py
+    script, which is invoked during the pre-commit checks.
+    """
     return cls
 
 
@@ -1798,7 +1780,7 @@ class ParallelConfig:
     eplb_step_interval: int = 3000
     """
     Interval for rearranging experts in expert parallelism.
-    
+
     Note that if this is greater than the EPLB window size, only the metrics
     of the last `eplb_window_size` steps will be used for rearranging experts.
     """