style: modernize config.py and satisfy linters

src/darker/__main__.py

@@ -490,7 +490,7 @@ def main(  # noqa: C901,PLR0912,PLR0915
     # Make sure there aren't invalid option combinations after merging configuration and
     # command line options.
     OutputMode.validate_diff_stdout(args.diff, args.stdout)
-    OutputMode.validate_stdout_src(args.stdout, args.src, args.stdin_filename)
+    OutputMode.validate_stdout_src(args.src, args.stdin_filename, stdout=args.stdout)
     validate_config_output_mode(config)
 
     setup_logging(args.log_level)

src/darker/command_line.py

@@ -136,5 +136,5 @@ def parse_command_line(
         show_config_deprecations,
     )
     OutputMode.validate_diff_stdout(args.diff, args.stdout)
-    OutputMode.validate_stdout_src(args.stdout, args.src, args.stdin_filename)
+    OutputMode.validate_stdout_src(args.src, args.stdin_filename, stdout=args.stdout)
     return args, effective_cfg, modified_cfg

src/darker/config.py

@@ -2,14 +2,16 @@
 
 from __future__ import annotations
 
-from argparse import Namespace
 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Dict, List, Optional, Set, Union
+from typing import TYPE_CHECKING
 
 from darkgraylib.config import BaseConfig, ConfigurationError
 
-UnvalidatedConfig = Dict[str, Union[List[str], str, bool, int]]
+if TYPE_CHECKING:
+    from argparse import Namespace
+
+UnvalidatedConfig = dict[str, list[str] | str | bool | int]
 
 
 REMOVED_CONFIG_OPTIONS = {
@@ -31,7 +33,7 @@ class DarkerConfig(BaseConfig, total=False):
     diff: bool
     check: bool
     isort: bool
-    lint: List[str]
+    lint: list[str]
     skip_string_normalization: bool
     skip_magic_trailing_comma: bool
     line_length: int
@@ -65,7 +67,7 @@ def validate_diff_stdout(diff: bool, stdout: bool) -> None:
 
     @staticmethod
     def validate_stdout_src(
-        stdout: bool, src: List[str], stdin_filename: Optional[str]
+        src: list[str], stdin_filename: str | None, *, stdout: bool,
     ) -> None:
         """Raise an exception in ``stdout`` mode if not exactly one input is provided"""
         if not stdout:
@@ -104,6 +106,6 @@ class Exclusions:
 
     """
 
-    black: Set[str] = field(default_factory=set)
-    isort: Set[str] = field(default_factory=set)
-    flynt: Set[str] = field(default_factory=set)
+    black: set[str] = field(default_factory=set)
+    isort: set[str] = field(default_factory=set)
+    flynt: set[str] = field(default_factory=set)

src/darker/tests/test_config.py

@@ -107,8 +107,7 @@ def test_output_mode_validate_stdout_src(
     Path("first.py").touch()
     Path("second.py").touch()
     with raises_if_exception(expect):
-
-        OutputMode.validate_stdout_src(stdout, src, stdin_filename)
+        OutputMode.validate_stdout_src(src, stdin_filename, stdout=stdout)
 
 
 @pytest.mark.kwparametrize(