feat: only support preview = in [tool.black]

Avoids confusion about precendence.

README.rst

@@ -416,7 +416,6 @@ An example ``pyproject.toml`` configuration file:
  line-length = 80 # Passed to isort and Black, override their config
  target-version = ["py312"] # Passed to Black, overriding its config
  log_level = "INFO"
- preview = false # Passed to Black, overriding its config
 
  [tool.black]
  line-length = 88 # Overridden by [tool.darker] above
@@ -426,7 +425,7 @@ An example ``pyproject.toml`` configuration file:
  exclude = "test_*\.py"
  extend_exclude = "/generated/"
  force_exclude = ".*\.pyi"
- preview = true # Overridden above
+ preview = true # Only supported in [tool.black]
 
 
  [tool.isort]

src/darker/config.py

@@ -24,7 +24,6 @@ class DarkerConfig(BaseConfig, total=False):
  skip_magic_trailing_comma: bool
  line_length: int
  target_version: str
- preview: bool
 
 
 class OutputMode:

src/darker/tests/test_command_line.py

@@ -305,6 +305,19 @@ def test_parse_command_line_deprecated_option(
  assert {c.args[0] for c in warn.call_args_list} == expect_warn
 
 
+def test_parse_command_line_unknown_conffile_option(tmp_path, monkeypatch):
+ """`parse_command_line` warns about deprecated configuration options."""
+ monkeypatch.chdir(tmp_path)
+ config = {"unknown": "value", "preview": "true"}
+ (tmp_path / "pyproject.toml").write_text(toml.dumps({"tool": {"darker": config}}))
+ with pytest.raises(
+ ConfigurationError,
+ match=r"Invalid \[tool.darker\] keys in pyproject.toml: preview, unknown",
+ ):
+
+ parse_command_line(["-"])
+
+
 def test_help_description_without_isort_package(capsys):
  """``darker --help`` description shows how to add ``isort`` if it's not present"""
  with isort_present(False):
@@ -565,6 +578,16 @@ def test_black_options(monkeypatch, tmpdir, git_repo, options, expect):
  options=["-t", "py39"],
  expect=call(target_versions={TargetVersion.PY39}),
  ),
+ dict(
+ config=["preview = true"],
+ options=[],
+ expect=call(preview=True),
+ ),
+ dict(
+ config=["preview = false"],
+ options=["--preview"],
+ expect=call(preview=True),
+ ),
  dict(
  config=["preview = true"],
  options=["--preview"],