Allow hyphens for option keys in pyproject.toml

CHANGES.rst

@@ -52,6 +52,10 @@ Fixed
 - Linting fixes: Use ``stacklevel=2`` in ``warnings.warn()`` calls as suggested by
   Flake8; skip Bandit check for virtualenv creation in the GitHub Action;
   use ``ignore[method-assign]`` as suggested by Mypy.
+- Configuration options spelled with hyphens in ``pyproject.toml``
+  (e.g. ``line-length = 88``) are now supported.
+- In debug log output mode, configuration options are now always spelled with hyphens
+  instead of underscores.
 
 
 1.7.0_ - 2023-02-11

src/darker/config.py

@@ -6,7 +6,7 @@
 from argparse import ArgumentParser, Namespace
 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Iterable, List, Optional, Set, cast
+from typing import Dict, Iterable, List, Optional, Set, Union, cast
 
 import toml
 
@@ -26,6 +26,9 @@ def dump_list(self, v: Iterable[object]) -> str:
         return "[{}\n]".format("".join(f"\n    {self.dump_value(item)}," for item in v))
 
 
+UnvalidatedConfig = Dict[str, Union[List[str], str, bool, int]]
+
+
 class DarkerConfig(TypedDict, total=False):
     """Dictionary representing ``[tool.darker]`` from ``pyproject.toml``"""
 
@@ -92,6 +95,40 @@ class ConfigurationError(Exception):
     """Exception class for invalid configuration values"""
 
 
+def convert_config_characters(
+    config: UnvalidatedConfig, pattern: str, replacement: str
+) -> UnvalidatedConfig:
+    """Convert a character in config keys to a different character"""
+    return {key.replace(pattern, replacement): value for key, value in config.items()}
+
+
+def convert_hyphens_to_underscores(config: UnvalidatedConfig) -> UnvalidatedConfig:
+    """Convert hyphenated config keys to underscored keys"""
+    return convert_config_characters(config, "-", "_")
+
+
+def convert_underscores_to_hyphens(config: DarkerConfig) -> UnvalidatedConfig:
+    """Convert underscores in config keys to hyphens"""
+    return convert_config_characters(cast(UnvalidatedConfig, config), "_", "-")
+
+
+def validate_config_keys(config: UnvalidatedConfig) -> None:
+    """Raise an exception if any keys in the configuration are invalid.
+
+    :param config: The configuration read from ``pyproject.toml``
+    :raises ConfigurationError: Raised if unknown options are present
+
+    """
+    if set(config).issubset(DarkerConfig.__annotations__):
+        return
+    unknown_keys = ", ".join(
+        sorted(set(config).difference(DarkerConfig.__annotations__))
+    )
+    raise ConfigurationError(
+        f"Invalid [tool.darker] keys in pyproject.toml: {unknown_keys}"
+    )
+
+
 def replace_log_level_name(config: DarkerConfig) -> None:
     """Replace numeric log level in configuration with the name of the log level"""
     if "log_level" in config:
@@ -165,7 +202,11 @@ def load_config(path: Optional[str], srcs: Iterable[str]) -> DarkerConfig:
         if not config_path.is_file():
             return {}
     pyproject_toml = toml.load(config_path)
-    config = cast(DarkerConfig, pyproject_toml.get("tool", {}).get("darker", {}) or {})
+    tool_darker_config = convert_hyphens_to_underscores(
+        pyproject_toml.get("tool", {}).get("darker", {}) or {}
+    )
+    validate_config_keys(tool_darker_config)
+    config = cast(DarkerConfig, tool_darker_config)
     replace_log_level_name(config)
     validate_config_output_mode(config)
     return config
@@ -195,7 +236,9 @@ def get_modified_config(parser: ArgumentParser, args: Namespace) -> DarkerConfig
 
 def dump_config(config: DarkerConfig) -> str:
     """Return the configuration in TOML format"""
-    dump = toml.dumps(config, encoder=TomlArrayLinesEncoder())
+    dump = toml.dumps(
+        convert_underscores_to_hyphens(config), encoder=TomlArrayLinesEncoder()
+    )
     return f"[tool.darker]\n{dump}"