$ git clone -n https://src.fedoraproject.org/rpms/rust-proc-macro2-0.4.git /var/lib/mock/f41-build-side-1-3134892-39763/root/chroot_tmpdir/scmroot/rust-proc-macro2-0.4
Cloning into '/var/lib/mock/f41-build-side-1-3134892-39763/root/chroot_tmpdir/scmroot/rust-proc-macro2-0.4'...
$ git fetch origin 18884398aa7f28b43d8e659cecd6d77994f646d7:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rust-proc-macro2-0.4
 * [new ref]         18884398aa7f28b43d8e659cecd6d77994f646d7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 1888439 compat package no longer needed