$ git clone -n https://src.fedoraproject.org/rpms/rust-cxx /var/lib/mock/f42-build-3451963-45484/root/chroot_tmpdir/scmroot/rust-cxx
Cloning into '/var/lib/mock/f42-build-3451963-45484/root/chroot_tmpdir/scmroot/rust-cxx'...
$ git fetch origin f9fc959c98789575266a7df07b273a5c7a04e477:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-cxx
 * [new ref]         f9fc959c98789575266a7df07b273a5c7a04e477 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f9fc959 Update to version 1.0.150 (rhbz#2346636)