$ git clone -n https://src.fedoraproject.org/rpms/rust-gengo.git /var/lib/mock/f42-build-side-1-3580016-46816/root/chroot_tmpdir/scmroot/rust-gengo
Cloning into '/var/lib/mock/f42-build-side-1-3580016-46816/root/chroot_tmpdir/scmroot/rust-gengo'...
$ git fetch origin ffdae02bb20206cf45da52a5d4306edc8b9ca0b4:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-gengo
 * [new ref]         ffdae02bb20206cf45da52a5d4306edc8b9ca0b4 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ffdae02 Update to version 0.13.0 (rhbz#2361954)