$ git clone -n https://src.fedoraproject.org/rpms/rust-slab.git /var/lib/mock/f42-build-side-1-3585847-46908/root/chroot_tmpdir/scmroot/rust-slab
Cloning into '/var/lib/mock/f42-build-side-1-3585847-46908/root/chroot_tmpdir/scmroot/rust-slab'...
$ git fetch origin 6c6f21ae902691b38198c86665eb30d92f7dc51d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-slab
 * [new ref]         6c6f21ae902691b38198c86665eb30d92f7dc51d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 6c6f21a Update to version 0.4.10; Fixes RHBZ#2372887