$ git clone -n https://src.fedoraproject.org/rpms/ghc.git /var/lib/mock/f40-build-2164917-50972/root/chroot_tmpdir/scmroot/ghc
Cloning into '/var/lib/mock/f40-build-2164917-50972/root/chroot_tmpdir/scmroot/ghc'...
$ git fetch origin f3741279b306a52c893e92474c7d605c1451eee5:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ghc
 * [new ref]         f3741279b306a52c893e92474c7d605c1451eee5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f374127 BR ghc-*-devel instead of ghc-*-static