Add GitLfs post-checkout, post-commit and post-merge hooks

[proinsias]

#479 added the pre-push hook for git-lfs.

This PR adds the additional hooks that are now available with git-lfs.

[proinsias]

Not sure how to fix the following type of error:

Overcommit::Hook::PostCheckout::GitLfs when git lfs hook exits successfully should pass the check
     Failure/Error: result = execute(['git', 'lfs', 'post-checkout', previous_head, new_head, branch_checkout?])
       #<Double "context"> received unexpected message :branch_checkout? with (no args)

[sds]

Thanks for the pull request, @proinsias. I think you've done more work than what's necessary, and can simplify substantially.

[sds]

You shouldn't need to perform this check explicitly. Simply specify the required_executable option in the hook configuration.

I can see that you're trying to provide a bit extra information, but my hope is that the existing error message is pretty straightforward, and that anyone working with a repo using LFS knows what Git LFS is.

[sds]

Have you read the documentation for adding existing Git hooks? If you are just executing a ready-made hook, you don't need to write any Ruby code.

[proinsias]

Yes. I've had the following two issues with this approach before, and so thought it would be helpful to have specific hooks (a la the git-lfs pre-push ones) in overcommit:

I believe the required_executable has to checked into git, and so:

1. I have to put the hook manually in every repo.
2. I can't use this approach for shared repos at work, where I'm the only one using overcommit.

[sds]

Thanks for clarifying, @proinsias. I think when we added that restriction many years ago we were being overly cautious. Thinking on this, seems reasonable to allow ad hoc hooks to reference executables that are in your PATH.

The danger comes from someone creating/modifying a hook that changes the command to rm -rf / or similar, but this should be caught by the hook signing logic for the hook's configuration itself.

I'm open to a PR that modifies the HookSigner to support this. Otherwise I'll get to it when I can. Thanks!

[sds]

Hey @proinsias, I took a stab at adding support for arbitrary commands as ad hoc hooks hooks in 5a0a4ec.

Could you try rebasing and rebuilding these hooks using that? Would love to get your feedback. Thanks!

[proinsias]

Looking into this now!

[proinsias]

@sds – looks good to me!