$ git clone -n https://src.fedoraproject.org/rpms/rubygem-rake-compiler.git /var/lib/mock/f42-build-side-1-3500257-45970/root/chroot_tmpdir/scmroot/rubygem-rake-compiler
Cloning into '/var/lib/mock/f42-build-side-1-3500257-45970/root/chroot_tmpdir/scmroot/rubygem-rake-compiler'...
$ git fetch origin 4cfb8d66c8193ef38c5718012fbcf3629b04ca40:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-rake-compiler
 * [new ref]         4cfb8d66c8193ef38c5718012fbcf3629b04ca40 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4cfb8d6 1.3.0