Merge pull request #359 from akaihola/config-option-for-darker-config

Author: akaihola

CHANGES.rst

@@ -24,6 +24,9 @@ Fixed
 - Update ``cachix/install-nix-action`` to ``v17`` to fix macOS build error.
 - Downgrade Python from 3.10 to 3.9 in the macOS NixOS build on GitHub due to a build
   error with Python 3.10.
+- Darker now reads its own configuration from the file specified using
+  ``-c``/``--config``, or in case a directory is specified, from ``pyproject.toml``
+  inside that directory.
 
 
 1.4.2_ - 2022-03-12

src/darker/command_line.py

@@ -106,9 +106,10 @@ def parse_command_line(argv: List[str]) -> Tuple[Namespace, DarkerConfig, Darker
     parser_for_srcs = make_argument_parser(require_src=False)
     args = parser_for_srcs.parse_args(argv)
 
-    # 2. Locate `pyproject.toml` based on those paths, or in the current directory if no
-    #    paths were given. Load Darker configuration from it.
-    pyproject_config = load_config(args.src)
+    # 2. Locate `pyproject.toml` based on the `-c`/`--config` command line option, or
+    #    if it's not provided, based on the paths to process, or in the current
+    #    directory if no paths were given. Load Darker configuration from it.
+    pyproject_config = load_config(args.config, args.src)
     config = override_color_with_environment(pyproject_config)
 
     # 3. Use configuration as defaults for re-parsing command line arguments, and don't

src/darker/config.py

@@ -5,7 +5,7 @@
 import sys
 from argparse import ArgumentParser, Namespace
 from pathlib import Path
-from typing import Iterable, List, cast
+from typing import Iterable, List, Optional, cast
 
 import toml
 
@@ -117,23 +117,41 @@ def override_color_with_environment(pyproject_config: DarkerConfig) -> DarkerCon
     return config
 
 
-def load_config(srcs: Iterable[str]) -> DarkerConfig:
-    """Find and load Darker configuration from given path or pyproject.toml
+def load_config(path: Optional[str], srcs: Iterable[str]) -> DarkerConfig:
+    """Find and load Darker configuration from a TOML configuration file
 
-    :param srcs: File(s) and directory/directories which will be processed. Their paths
-                 are used to look for the ``pyproject.toml`` configuration file.
+    Darker determines the location for the configuration file by trying the following:
+    - the file path in the `path` argument, given using the ``-c``/``--config`` command
+      line option
+    - ``pyproject.toml`` inside the directory specified by the `path` argument
+    - ``pyproject.toml`` from a common parent directory to all items in `srcs`
+    - ``pyproject.toml`` in the current working directory if `srcs` is empty
+
+    :param path: The file or directory specified using the ``-c``/``--config`` command
+                 line option, or `None` if the option was omitted.
+    :param srcs: File(s) and directory/directories to be processed by Darker.
 
     """
-    path = find_project_root(tuple(srcs or ["."])) / "pyproject.toml"
-    if path.is_file():
-        pyproject_toml = toml.load(path)
-        config = cast(
-            DarkerConfig, pyproject_toml.get("tool", {}).get("darker", {}) or {}
-        )
-        replace_log_level_name(config)
-        validate_config_output_mode(config)
-        return config
-    return {}
+    if path:
+        for candidate_path in [Path(path), Path(path, "pyproject.toml")]:
+            if candidate_path.is_file():
+                config_path = candidate_path
+                break
+        else:
+            if Path(path).is_dir() or path.endswith(os.sep):
+                raise ConfigurationError(
+                    f"Configuration file {Path(path, 'pyproject.toml')} not found"
+                )
+            raise ConfigurationError(f"Configuration file {path} not found")
+    else:
+        config_path = find_project_root(tuple(srcs or ["."])) / "pyproject.toml"
+        if not config_path.is_file():
+            return {}
+    pyproject_toml = toml.load(config_path)
+    config = cast(DarkerConfig, pyproject_toml.get("tool", {}).get("darker", {}) or {})
+    replace_log_level_name(config)
+    validate_config_output_mode(config)
+    return config
 
 
 def get_effective_config(args: Namespace) -> DarkerConfig:

src/darker/tests/test_command_line.py

@@ -91,6 +91,36 @@ def test_parse_command_line_config_src(
         assert filter_dict(dict(modified_cfg), "src") == expect
 
 
+@pytest.mark.kwparametrize(
+    dict(argv=["."], expect="pylint"),
+    dict(argv=["./subdir/"], expect="flake8"),
+    dict(argv=["--config", "./pyproject.toml", "."], expect="pylint"),
+    dict(argv=["--config", "./subdir/pyproject.toml", "."], expect="flake8"),
+    dict(argv=["--config", "./pyproject.toml", "subdir/"], expect="pylint"),
+    dict(argv=["--config", "./subdir/pyproject.toml", "subdir/"], expect="flake8"),
+)
+def test_parse_command_line_config_location_specified(
+    tmp_path,
+    monkeypatch,
+    argv,
+    expect,
+):
+    """Darker configuration is read from file pointed to using ``-c``/``--config``"""
+    monkeypatch.chdir(tmp_path)
+    subdir = tmp_path / "subdir"
+    subdir.mkdir()
+    root_config = tmp_path / "pyproject.toml"
+    subdir_config = subdir / "pyproject.toml"
+    root_config.write_text(toml.dumps({"tool": {"darker": {"lint": "pylint"}}}))
+    subdir_config.write_text(toml.dumps({"tool": {"darker": {"lint": "flake8"}}}))
+
+    args, effective_cfg, modified_cfg = parse_command_line(argv)
+
+    assert args.lint == expect
+    assert effective_cfg["lint"] == expect
+    assert modified_cfg["lint"] == expect
+
+
 @pytest.mark.kwparametrize(
     dict(
         argv=["."],
@@ -212,6 +242,18 @@ def test_parse_command_line_config_src(
         expect_config=("config", "my.cfg"),
         expect_modified=("config", "my.cfg"),
     ),
+    dict(
+        argv=["-c", "subdir_with_config", "."],
+        expect_value=("config", "subdir_with_config"),
+        expect_config=("config", "subdir_with_config"),
+        expect_modified=("config", "subdir_with_config"),
+    ),
+    dict(
+        argv=["--config=subdir_with_config", "."],
+        expect_value=("config", "subdir_with_config"),
+        expect_config=("config", "subdir_with_config"),
+        expect_modified=("config", "subdir_with_config"),
+    ),
     dict(
         argv=["."],
         expect_value=("log_level", 30),
@@ -375,6 +417,9 @@ def test_parse_command_line(
     """``parse_command_line()`` parses options correctly"""
     monkeypatch.chdir(tmp_path)
     (tmp_path / "dummy.py").touch()
+    (tmp_path / "my.cfg").touch()
+    (tmp_path / "subdir_with_config").mkdir()
+    (tmp_path / "subdir_with_config" / "pyproject.toml").touch()
     with patch.dict(os.environ, environ, clear=True), raises_if_exception(
         expect_value
     ) as expect_exception: