$ git clone -n https://src.fedoraproject.org/rpms/R-XVector.git /var/lib/mock/f42-build-side-1-3500313-45970/root/chroot_tmpdir/scmroot/R-XVector
Cloning into '/var/lib/mock/f42-build-side-1-3500313-45970/root/chroot_tmpdir/scmroot/R-XVector'...
$ git fetch origin 0e2d1596a5968bbdd071de5f2f84594b0cef1608:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-XVector
 * [new ref]         0e2d1596a5968bbdd071de5f2f84594b0cef1608 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0e2d159 R-maint-sig mass rebuild