$ git clone -n https://src.fedoraproject.org/rpms/rust-git2_0.16.git /var/lib/mock/f40-build-2718139-72883/root/chroot_tmpdir/scmroot/rust-git2_0.16
Cloning into '/var/lib/mock/f40-build-2718139-72883/root/chroot_tmpdir/scmroot/rust-git2_0.16'...
$ git fetch origin 1cce2949181d0cb4005903bb43b7106d026bef8c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-git2_0.16
 * [new ref]         1cce2949181d0cb4005903bb43b7106d026bef8c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 1cce294 compat package no longer needed