$ git clone -n https://src.fedoraproject.org/rpms/R-cliapp.git /var/lib/mock/f42-build-3530684-46321/root/chroot_tmpdir/scmroot/R-cliapp
Cloning into '/var/lib/mock/f42-build-3530684-46321/root/chroot_tmpdir/scmroot/R-cliapp'...
$ git fetch origin eec2a0f359500187b7706abd19bffe89589fed77:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-cliapp
 * [new ref]         eec2a0f359500187b7706abd19bffe89589fed77 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at eec2a0f R-maint-sig mass rebuild