Fix #8316: run fix-whitespace --check as CI workflow

[andreasabel]

Fix #8316: run fix-whitespace --check as CI workflow.

Also: fix existing whitespace violations (separate commit).

The whitespace checker can be configured in fix-whitespace.yaml.

[Mikolaj]

Would it make sense to add a line to CONTRIBUTING explaining how to run the check locally?

[ulysses4ever]

Lgtm modulo minor comments. Thank you!

[andreasabel]

Weird, how come my latest push of workflow whitespace.yml checked out latest master and thus found a whitespace violation that wasn't on the branch of this PR??
https://github.com/haskell/cabal/runs/7515526901?check_suite_focus=true#step:7:7

Run $HOME/.local/bin/fix-whitespace --check
[ Violation detected ] release-notes/Cabal-3.8.1.0.md
Error: Process completed with exit code 1.

The violation is a "No newline at end of file" at

cabal/release-notes/Cabal-3.8.1.0.md

Line 169 in 0ac0feb

- Previously, for unknown new versions of GHC, it was not filtering GHC arguments at all, while now it filters them in the same way as for the last known GHC version. This seems a better default and it's one less place to update at release time. Perhaps erroring out or emitting a warning would be safer, but we already emit a general warning elsewhere.

I am using the vanilla actions/checkout: https://github.com/haskell/cabal/pull/8320/files#diff-0ea7b088f801fe875e2de46ed9180c6e04bb6f0bd9e7311428786195831e6b90R19

[andreasabel]

Would it make sense to add a line to CONTRIBUTING explaining how to run the check locally?

Just pushed a commit to that extend.

[Mikolaj]

Would it make sense to add a line to CONTRIBUTING explaining how to run the check locally?

Just pushed a commit to that extend.

Looks fine, thank you.

[chshersh]

The fix-whitespace tool is cool, I might want to use it in my own projects as well 🙂

[andreasabel]

I reorganized the 6 commits into 3, but these 3 are independent and should be kept separate.

Why didn't label "merge me" do anything in 4 hours?

[ulysses4ever]

Because of #8285.

[andreasabel]

Sorry, I skipped the 2-day waiting period because this PR would rot too fast: it would get broken every time someone introduces a whitespace violation into the code base.

[ulysses4ever]

tldr; We need to backport this to 3.8 if we want a working CI on 3.8

Reasoning: see #8503 and #8505. They are required for working CI since ghcup updated the recommended GHC -- no matter the branch. And #8505 mentions the whitespace job, so it couldn't be (easily) backported without this one being backported first.

[ulysses4ever]

@mergify backport 3.8

[mergify]

backport 3.8

✅ Backports have been created

• #8518 Fix #8316: run fix-whitespace --check as CI workflow (backport #8320) has been created for branch 3.8