git-lfs support

[extrawurst]

Our current bug #2809 (our broken pre-push hook support) led me down the rabbit hole of "what else is required to properly support git-lfs in gitui.

We are looking at basically three things:

1. properly run pre-push hook (thats Pushing throws pre-push hook error on repository with LFS. #2809)
2. hook into filter logic and run them on all checkout-like operations (smudge)
3. hook into filter logic and run them on all worktree->index operations (clean)

Now libgit2 exposes an API to hook into filters but git2-rs does not expose this right now (open issue).

Since our end goal is to be libgit2 independent I call out whats needed to do this all using gitoxide:

1. we need to migrate all our git-checkout locations to gitoxide
2. migrate all worktree->index operations to gitoxide
3. use gitoxide machinery to hook into filters
4. forward filter logic via shellout (git-lfs clean, git-lfs smudge or git-lfs filter-process)
5. finally we support git-lfs

This issue is more of an epic, I would love to see contributions to take on individual steps here. especially 1 and 2 can be parallelized.

cc @Byron @cruessler correct me if I am wrong but from the gitoxide side all this is ready to be used or am I wrong?

Further reading: #1089

[Byron]

Thanks for the summary! Here are my notes:

we need to migrate all our git-checkout locations to gitoxide

This will already work as long as you only checkout individual files, see filter_pipeline.

migrate all worktree->index operations to gitoxide

This will also work as long as checkins are per-file, see filter_pipeline.

use gitoxide machinery to hook into filters

I don't understand where this requirement is coming from, I am just missing a hint on the feature that this supports.
My potshot here is that in theory, as filters are invoked by gitui on a per-file basis, pre- and post- filter hooks are naturally present.

forward filter logic via shellout (git-lfs clean, git-lfs smudge or git-lfs filter-process)

Standard Git filters are naturally supported and invoked, there is no extra action needed unless gitui wants to support git-lfs specifics that aren't covered by standard Git filters.

finally we support git-lfs

I think the crux here would be that gitoxide has no mechanism of doing a worktree checkout yet, and the one that's planned will be a brute force "apply the changes that are needed to turn tree A into tree B", overwriting anything in its path. It will be very much on the plumbing side of things. GitButler needs such a primitive as it does the analysis on what to do with changed or untracked files that would be in the way. Something like it would have to be ported to over then, while just adhering to the 'Git-style' of doing this (i.e. force, non-force, for starters).

cc @Byron @cruessler correct me if I am wrong but from the gitoxide side all this is ready to be used or am I wrong?

Besides the checkout, there are weaknesses when interacting with the .git/index - it's very much expert mode and plumbing level. But GitButler uses that to get what it needs, so it can be done.