$ git clone -n https://src.fedoraproject.org/rpms/R-purrr.git /var/lib/mock/f42-build-side-110318-58925984-6569303/root/chroot_tmpdir/scmroot/R-purrr
Cloning into '/var/lib/mock/f42-build-side-110318-58925984-6569303/root/chroot_tmpdir/scmroot/R-purrr'...
$ git fetch origin 3511a4d261c082600429f51693c32aae1676f522:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-purrr
 * [new ref]         3511a4d261c082600429f51693c32aae1676f522 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3511a4d R-maint-sig mass rebuild