Configuration file(s)

[akaihola]

Like with Black, it would be convenient to be able to set Darker's options not only on the command line but also in per-repository configuration files.

I was also thinking in a config file (pyproject.toml at the root of the repo?) having the ability to >give a revision to be used by default. But +1.
Originally posted by @Carreau in #43 (comment)

• highlighting for TOML configuration dump (using code in Linter highlighting #57, merge that first)

[akaihola]

We'll need to settle for (1) the location(s) of Darker configuration, and (2) the format of it.

My number one proposal would be pyproject.toml and a [tool.darker] section in it. This is what both Black and isort already support, and seems to be becoming the standard.

Mapping command line options to directly to pyproject.toml would suggest a format like this (with default values shown here):

[tool.darker]
src = []
revision = "HEAD"
diff = false
check = false
isort = false
lint = []
log_level = "WARNING"

So if I'd like to make these options default:

darker -vv -r master --check --diff --isort -L flake8 -L mypy -L pylint -L cov_to_lint.py src  

I would put this in pyproject.toml:

[tool.darker]
src = [
    "src",
]
revision = "master"
diff = true
check = true
isort = true
lint = [
    "flake8",
    "mypy",
    "pylint",
    "cov_to_lint.py",
]
log_level = "DEBUG"