$ git clone -n https://src.fedoraproject.org/rpms/swift-lang.git /var/lib/mock/f40-build-1897438-25065/root/chroot_tmpdir/scmroot/swift-lang
Cloning into '/var/lib/mock/f40-build-1897438-25065/root/chroot_tmpdir/scmroot/swift-lang'...
$ git fetch origin 4f6074a0c15ffff8c7a23994a99f4241e0a7cec5:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/swift-lang
 * [new ref]         4f6074a0c15ffff8c7a23994a99f4241e0a7cec5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4f6074a Minimize runtime/compile time dependencies