bug#65720: Digression about Git implementations (was Re: bug#65720: Guile-Git-managed checkouts grow way too much)

[Simon Tournier <zimon.toutoune@gmail.com>]

Hi Ludo,

On Fri, 08 Sep 2023 at 19:08, Ludovic Courtès <ludo@gnu.org> wrote:

> Years ago, Andy Wingo sketched a plan for GNU hackers to implement Git
> in pure Scheme.  That was on April 1st though, so people mistakenly
> assumed it was a joke and the project was never carried out.

Well, that is a piece of work. :-)

Maybe there is an hope with: git-std-lib.

    Subject: Proposal/Discussion: Turning parts of Git into libraries
    From: Emily Shaffer <nasamuffin@google.com>
    To: Git List <git@vger.kernel.org>
    Date: Fri, 17 Feb 2023 13:12:23 -0800	    
    https://lore.kernel.org/git/CAJoAoZ=Cig_kLocxKGax31sU7Xe4==BGzC__Bg2_pr7krNq6MA@mail.gmail.com/

And some patches are starting to float around.
https://public-inbox.org/git/20230810163346.274132-1-calvinwan@google.com/


> I digress, but I wonder: is there not even a viable Haskell or OCaml
> implementation of Git?

It depends on what means “viable”. :-)

https://github.com/mirage/ocaml-git
https://hackage.haskell.org/package/git

Irmin [1] is an OCaml library for building mergeable, branchable
distributed data stores – A Distributed Database Built on the Same
Principles as Git.  And irmin relies on ocaml-git.

1: https://github.com/mirage/irmin

Then there is a pure Go implementation and another using Java.

https://git-scm.com/book/en/v2/Appendix-B%3A-Embedding-Git-in-your-Applications-go-git
https://git-scm.com/book/en/v2/Appendix-B%3A-Embedding-Git-in-your-Applications-JGit

I do not know all that are “viable”.  Well, I do not know if ’git gc’ is
implemented.  And I do not know which plumbing is implemented and which
porcelain is available.

Last, SWH uses dulwich [2] which is a pure Python implementation of Git.

2: https://www.dulwich.io/

To my knowledge, there is no “dulwich gc” but they implement “dulwich
fsck” and “dulwich repack”.

Back on 10 Years of Guix or at UNESCO on February – I do not remember
exactly when – we were discussing about implementation of Git.  And we
mentioned an implementation in Rust.  Maybe this one:

https://github.com/Byron/gitoxide

Cheers,
simon