$ git clone -n https://src.fedoraproject.org/rpms/rust-rand_chacha /var/lib/mock/f42-build-3453392-45488/root/chroot_tmpdir/scmroot/rust-rand_chacha
Cloning into '/var/lib/mock/f42-build-3453392-45488/root/chroot_tmpdir/scmroot/rust-rand_chacha'...
$ git fetch origin dee69297459b7cc80d0d9ce66c86c7ffb6a4618e:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-rand_chacha
 * [new ref]         dee69297459b7cc80d0d9ce66c86c7ffb6a4618e -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at dee6929 Update to version 0.9.0; Fixes RHBZ#2342268