Only run the pre-commit hook on changed files

[drsooch]

Using an external action to grab all changed files, and pass that to the pre-commit check to reduce false-negatives.

NOTES:

Alternatively, could pass the arguments: pre-commit ... --from-ref HEAD^ --to-ref HEAD to run the action on the last commit. However, will only capture a single commit, even if the branch received multiple commits on a push.

I'm not even sure this get-diff-action will even do what I expect.

TESTING NOTES:

1. first commit with no haskell source changes, worked as expected. Skipped all the steps when there were no diffs.
2. Committing a single haskell source change is matched.
3. Diffs across multiple commits are captured (looks like the get-diff action compares the PR to main branch so this will always be the case)
4. probably need to split the GIT_DIFF variable to pass files appropriately to pre-commit - done

This seems to work as expected I refactored a bit to skip the pre-commit hook if there are no hs files in the changelog. (not that it saves any time).

This should enable us to be green for pre-commit check

[kokobd]

Nice! Thank you!

[Ailrun]

Does --from-ref origin/master (or similar using github.base_ref) work? If so, I think it might be better to use that for pr, and for merged commit, we can use HEAD^.

[drsooch]

Does --from-ref origin/master (or similar using github.base_ref) work? If so, I think it might be better to use that for pr, and for merged commit, we can use HEAD^.

I believe the current 3rd party GitHub action does a simple compare to the branch we are merging to.

I guess it could just get tricky with all possible enumerations of which commit to count towards the change list. Pre-commit itself even suggested the following: --from-ref HEAD^^^ --to-ref HEAD.

Really what I was going for is anything new, we want to make sure we try to keep formatted. And didn't want to try to cover everything.

[Ailrun]

I guess it could just get tricky with all possible enumerations of which commit to count towards the change list.

I mean, if pre-commit supports target branch names like origin/master for --from-ref, it's not really hard, is it? Or you mean that pre-commit doesn't support that?

I believe the current 3rd party GitHub action does a simple compare to the branch we are merging to.

IMO, if pre-commit already supports the feature, it'd be better not to introduce more dependency (which will be maintenance burden).

[drsooch]

I guess it could just get tricky with all possible enumerations of which commit to count towards the change list.

I mean, if pre-commit supports target branch names like origin/master for --from-ref, it's not really hard, is it? Or you mean that pre-commit doesn't support that?

The docs I was reading, didn't use a specific ref like origin/master it used --from-ref HEAD^^^ --to-ref HEAD. I can experiment with using a specific ref like master. I started reading up on trying to figure out which HEAD^^^ or HEAD^ to use and there were so many edge cases I didn't even bother trying something simple like origin/master

I believe the current 3rd party GitHub action does a simple compare to the branch we are merging to.

IMO, if pre-commit already supports the feature, it'd be better not to introduce more dependency (which will be maintenance burden).

Definitely agree, I will try some other experiments when I can