This PR aims to implement basic sparse checkout functionality into LibGit2 building on @jochenhz's original PR.

What does it do?

• Status / Diff takes GIT_INDEX_ENTRY_SKIP_WORKTREE into account
• sparse-checkout file is treated as an attr_file, hence following gitignore rules
• Skips sparse files on checkout
• Sparse checkout can be enabled with core.sparseCheckout
• support init, set, add, reapply and disable commands all supported
• Expose an interface function git_sparse_check_path to query whether or not a file is excluded from checkout
• Set GIT_INDEX_ENTRY_SKIP_WORKTREE flag on git_index_read_tree based on the sparse checkout ruleset.

What does it not do?

• Smart trickery to determine whether or not a full tree is sparse (would be a very welcome optimization)
• Support core.sparseCheckoutCone
• No sparse checkout option on clone (but this can be achieved with GIT_CHECKOUT_NONE and git_index_read_tree)

Note

• I've got some tests around worktrees, they seem to work
• Given how complex sparse checkout can be, I'm almost certain I haven't gotten this implementation 100% correct, though feel free to prove me wrong 👍

Bump. Is there anything I can do to help progress this further?

@YuKitsune Is this PR in a state that it's working for you? I would like to patch it into a project that I'm working on and wondering if there are any rough edges I should know about.

Thanks for your work in continuing on this!

@VinnyOG We haven't gotten around to making use of this. Our use-case requires a new build of LibGit2Sharp, which proved to be too much of a pain.

I wish this would be getting attention

I've mucked up the rebase and the PR auto-closed... 🤦 Doesn't seem to let me re-open it, so I've created a new one over here https://github.com/libgit2/libgit2/pull/6394 Sorry for the mess 😅