Improve ruff config

[AlexWaygood]

• Add fix = true to pyproject.toml. This means ruff will apply autofixes when possible if ruff . is run (and will apply autofixes to PRs).
• Remove isort as a test dependency; just use ruff instead. It has the same import-sorting style, is faster, and requires less configuration.
• Remove an outdated paragraph in CONTRIBUTING.md about how you'll get a CI failure if you don't run black and isort before filing a PR. This is no longer true since we switched to using pre-commit.ci.

[hauntsaninja]

If we're going to have fix on by default, can we mark the following as unfixable:

unfixable = [
    "F841",  # unused variable. ruff keeps the call, but mostly we want to get rid of it all
    "F601",  # automatic fix might obscure issue
    "F602",  # automatic fix might obscure issue
    "B018",  # automatic fix might obscure issue
]

[ikonst]

So I gather they "autofix" B018 ("Found useless expression. Either assign it to a variable or remove it.") by ... removing the expression rather than assigning it?

Update: https://beta.ruff.rs/docs/rules/#flake8-bugbear-b doesn't suggest B018 has a fixer currently. Are you adding it just as a precaution?

[AlexWaygood]

Update: https://beta.ruff.rs/docs/rules/#flake8-bugbear-b doesn't suggest B018 has a fixer currently. Are you adding it just as a precaution?

I just went with Shantanu's suggestions here, but I definitely agree that it's good in general to be cautious with autofixes, and I agree that if they were to add an autofix for B018, we probably wouldn't want it

[hauntsaninja]

Oh hmmm I don't remember why I marked B018 unfixable, possibly just defensive, possibly I just looked at some undesirable change and got confused about what "fixed" it. I added ruff to my work codebase a couple weeks ago and my suggestion^ is just whatever I'd decided was good at that time.

In case you're curious, this is what I have currently at work:

select = [
    "E", "F", "W", "B", "C4", "ASYNC", "PIE",
    # grab bag of random things
    "DTZ003", "DTZ004",
    "PLE1310", "PLW0120",
    "SIM101", "SIM110", "SIM201", "SIM202", "SIM222", "SIM223",
    "S506",
    "RET501", "RET502",  # RET503 is also nice, but there's currently some noise
    "RUF006", "RUF200",
    "COM819",
]
ignore = [
    "E402",   # people usually know what they're doing
    "E501",   # line too long. black does a good enough job
    "E731",   # lambda expression assignments. these are nice sometimes
    "E741",   # variable names like "l"
    "B011",   # assert false. we don't use python -O
    "C408",   # we often use dict with keyword args
]
unfixable = [
    "F841",  # unused variable. ruff keeps the call, but mostly we want to get rid of it all
    "F601",  # automatic fix might obscure issue
    "F602",  # automatic fix might obscure issue
    "B018",  # automatic fix might obscure issue
    "SIM222",  # automatic fix might obscure issue
    "SIM223",  # automatic fix might obscure issue
]

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅