Run pre-commit-hooks on CI

[chshersh]

To enforce that they're actually used.

[marcellourbani]

I'll have a go at this

[marcellourbani]

I see 3 possible ways to do this:

• [pre-commit ci] (https://pre-commit.ci/) - recommended by pre-commit and free for open source, but will require to add it to this repo
• pre-commit action in github - deprecated, maintenance mode only
• just install and run the CLI in the current CI workflow

Any preference?

[chshersh]

That's a difficult question to answer 😅

Now I'm not even sure how to do this properly 🤔 In the future, pre-commit hooks will run tools like hlint and fourmolu. This means, the environment needs to install them somehow and this might be a bit involved.

We also have a job for running HLint on CI so we don't need duplication. Not sure if it makes sense to combine them under the single pre-commit umbrella or keep them separate 🤔 I'd love to avoid job duplication.

[marcellourbani]

my understanding is that pre-commit installs the required tools automatically, so that wouldn't be a problem . We might have to create our own plugins if they don't exist already

[marcellourbani]

I did consider adding this to say the cabal workflow but would run once per architecture, which seems overkill. As of pre-commit, my understanding is that to add hlint and formolou in pre-commit is only a matter of setting it in .pre-commit-config.yaml If you mean running it in regular pre-commit but not in CI, I think it's possible setting separate sections in the same file.

Not too sure, never heard about pre-commit until doing this

[chshersh]

I think I'm closing this issue without adding pre-commit hooks to CI with the following reasoning:

• We already have an HLint job on CI. I'd like to avoid job duplication. This means a more complicated pre-commit setup.
• I'm not sure pre-commit will install the same HLint version as on CI. And this will become worse for multiple tools. We'll need something like nix-shell and use it consistently on both CI and locally to avoid version mismatches. This is going to be a lot of work.
• I see pre-commit mostly as a local dev requirement, not a CI config.
• I mostly want pre-commit for the whitespace check. But it should be resolved after adding fourmolu anyway so pre-commit won't bring much to the table.

@marcellourbani Thanks for providing all the options and participating in the discussion! It really helped me to understand the desired workflow 🙂

I've also created a separate issue to add HLint as a pre-commit hook:

• https://github.com/chshersh/iris/issues/86

Even if we can't guarantee the same version as on CI, I believe it's still useful. HLint doesn't break behaviour too often.