$ git clone -n https://src.fedoraproject.org/rpms/rust-cxx.git /var/lib/mock/f38-build-side-43-rust-devel-1397669-31053/root/chroot_tmpdir/scmroot/rust-cxx
Cloning into '/var/lib/mock/f38-build-side-43-rust-devel-1397669-31053/root/chroot_tmpdir/scmroot/rust-cxx'...
$ git fetch origin 6421b388d279a893a62c2c3ff8a11cccccb8e1aa:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-cxx
 * [new ref]         6421b388d279a893a62c2c3ff8a11cccccb8e1aa -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 6421b38 Update to version 1.0.107; Fixes RHBZ#2235878