$ git clone -n https://src.fedoraproject.org/rpms/R-cpp11.git /var/lib/mock/f42-build-side-110318-58924630-6569303/root/chroot_tmpdir/scmroot/R-cpp11
Cloning into '/var/lib/mock/f42-build-side-110318-58924630-6569303/root/chroot_tmpdir/scmroot/R-cpp11'...
$ git fetch origin 3c93495ee0591614d431e88ccc90928c9a3b3784:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-cpp11
 * [new ref]         3c93495ee0591614d431e88ccc90928c9a3b3784 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3c93495 R-maint-sig mass rebuild