$ git clone -n https://src.fedoraproject.org/rpms/rust-instability.git /var/lib/mock/f42-build-3231274-41191/root/chroot_tmpdir/scmroot/rust-instability
Cloning into '/var/lib/mock/f42-build-3231274-41191/root/chroot_tmpdir/scmroot/rust-instability'...
$ git fetch origin ba9cb204eab0f7142f6ec89ee8351da2e222d0ad:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-instability
 * [new ref]         ba9cb204eab0f7142f6ec89ee8351da2e222d0ad -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ba9cb20 Update to version 0.3.7; Fixes RHBZ#2335544