$ git clone -n https://src.fedoraproject.org/rpms/rust-git2_0.14.git /var/lib/mock/f40-build-2590495-62623/root/chroot_tmpdir/scmroot/rust-git2_0.14
Cloning into '/var/lib/mock/f40-build-2590495-62623/root/chroot_tmpdir/scmroot/rust-git2_0.14'...
$ git fetch origin c9c6606bb00b3a4ac297a5fb437d291b0214ebe3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-git2_0.14
 * [new ref]         c9c6606bb00b3a4ac297a5fb437d291b0214ebe3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c9c6606 compat package no longer needed