I believe we set dirstate parents to nullid before widening pull because in
ellipses cases, the parent might be stripped off with a new changeset. However
the second ds.setparents() call invalidate my assumption. I am not sure why we
do this. So here is a patch.
This patch also adds tests showing we break nothing in non-ellipses cases.
You have add the requirement earlier in the series, so you can just use that here? (I suspect this is a leftover from an earlier version of this patch.)