RFC: libgit2 is slow/inefficient; switch to git command?

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi,

While attempting to bisect against the Linux kernel tree, the
performance of libgit2 quickly became problematic, to the point where
simply cloning the repo became a multiple hours affair, using upward to
3 GiB of RAM for the clone and indexing of the objects (!)

Given that:

* the git CLI doesn't suffer from such poor performance;
* This kind of performance problem has been known for years in libgit2
  [0] with no fix in sight;
* other projects such as Cargo support using the git CLI and that
  projects are using it for that reason [1];

Would it make sense to switch to use the git command directly instead of
calling into this libgit2 C library that ends up being slower?  It would
provide a hefty speed-up when using 'guix refresh' or building new
packages fetched from git without substitutes, or using 'git-checkout',
etc.

What do you think?

[0] https://github.com/libgit2/libgit2/issues/4674
[1] https://github.com/artichoke/playground/pull/700

-- 
Thanks,
Maxim