Without supporting sha256, nixos-rebuild complains that sha256 isn't a supported object format on my system configuration flake utilizing sha256 via git init --object-format sha256.

This seems to involve adding -DEXPERIMENTAL_SHA256=ON when building libgit2 at the moment. See https://github.com/libgit2/libgit2/releases/tag/v1.6.1 for more information.

Git >=2.42 supports this. Not sure if github supports it but gitlab and gitea do.

Patches

See https://github.com/theoparis/nix

The libgit2 library pkgconf file is renamed to libgit2-experimental.pc. This requires a change to configure.ac and rerunning autoreconf -fi. It also requires symlinking the git2 include path from git2-experimental to git2. The libgit2 tests also seem to fail 😕
A better solution here might be to patch libgit2's cmake files to remove the -experimental suffix.

The other issue is that I don't know when libgit2 will remove the experimental flag requirement. There doesn't seem to be anything about it other than the notes in that specific release.