$ git clone -n https://src.fedoraproject.org/rpms/swift-lang.git /var/lib/mock/f42-bootstrap-3462952-45593/root/chroot_tmpdir/scmroot/swift-lang
Cloning into '/var/lib/mock/f42-bootstrap-3462952-45593/root/chroot_tmpdir/scmroot/swift-lang'...
$ git fetch origin 4b5590325b48c34e8f18a269b474ce5d2aaededa:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/swift-lang
 * [new ref]         4b5590325b48c34e8f18a269b474ce5d2aaededa -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4b55903 Added bugzilla number