$ git clone -n https://src.fedoraproject.org/rpms/rust-git2_0.13.git /var/lib/mock/f40-build-2657647-66916/root/chroot_tmpdir/scmroot/rust-git2_0.13
Cloning into '/var/lib/mock/f40-build-2657647-66916/root/chroot_tmpdir/scmroot/rust-git2_0.13'...
$ git fetch origin a5bff689a6ab8e95d9cd2e0146da5ec185c3d480:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-git2_0.13
 * [new ref]         a5bff689a6ab8e95d9cd2e0146da5ec185c3d480 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a5bff68 Regenerate with rust2rpm v24