$ git clone -n https://src.fedoraproject.org/rpms/R-rprojroot.git /var/lib/mock/f42-build-side-1-3501336-45974/root/chroot_tmpdir/scmroot/R-rprojroot
Cloning into '/var/lib/mock/f42-build-side-1-3501336-45974/root/chroot_tmpdir/scmroot/R-rprojroot'...
$ git fetch origin cca60d884ff135645c52030878320e34802a7ab2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-rprojroot
 * [new ref]         cca60d884ff135645c52030878320e34802a7ab2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cca60d8 R-maint-sig mass rebuild