$ git clone -n https://src.fedoraproject.org/rpms/rust-clang-ast.git /var/lib/mock/f39-build-1455211-32913/root/chroot_tmpdir/scmroot/rust-clang-ast
Cloning into '/var/lib/mock/f39-build-1455211-32913/root/chroot_tmpdir/scmroot/rust-clang-ast'...
$ git fetch origin cabf0ded8c1251888a8a87f95da2441a59bd0e41:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-clang-ast
 * [new ref]         cabf0ded8c1251888a8a87f95da2441a59bd0e41 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cabf0de Update to version 0.1.21 (rhbz#2246461)