$ git clone -n https://src.fedoraproject.org/rpms/rust-rand /var/lib/mock/f42-build-3453401-45488/root/chroot_tmpdir/scmroot/rust-rand
Cloning into '/var/lib/mock/f42-build-3453401-45488/root/chroot_tmpdir/scmroot/rust-rand'...
$ git fetch origin ab41faa30321f7755e3459e0b71f02e6d54486a6:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-rand
 * [new ref]         ab41faa30321f7755e3459e0b71f02e6d54486a6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ab41faa Update to version 0.9.0; Fixes RHBZ#2342267