$ git clone -n https://src.fedoraproject.org/rpms/rust.git /var/lib/mock/f42-build-3222382-41049/root/chroot_tmpdir/scmroot/rust
Cloning into '/var/lib/mock/f42-build-3222382-41049/root/chroot_tmpdir/scmroot/rust'...
$ git fetch origin 0f308eb7723e0f2b87103b9aee3842ce7e46143c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust
 * [new ref]         0f308eb7723e0f2b87103b9aee3842ce7e46143c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0f308eb Exclude target shared libraries