$ git clone -n https://src.fedoraproject.org/rpms/rust-git2_0.13.git /var/lib/mock/f40-build-2571501-62241/root/chroot_tmpdir/scmroot/rust-git2_0.13
Cloning into '/var/lib/mock/f40-build-2571501-62241/root/chroot_tmpdir/scmroot/rust-git2_0.13'...
$ git fetch origin 64490e5beba8e09d97e014e073bed059f313a221:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-git2_0.13
 * [new ref]         64490e5beba8e09d97e014e073bed059f313a221 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 64490e5 compat package no longer needed