Re: BUG #18953: Planner fails to build plan for complex query with LATERAL references

... BTW, looking at these two patches again, I wonder if it'd be
better to put the hackery for SubLink conversion into
identify_current_nestloop_params?  That'd remove the need to argue
that we don't have to fix both copies of a nestloop-parameter PHV.
The responsibility doesn't clearly belong to
identify_current_nestloop_params, but it doesn't clearly belong
to create_nestloop_plan either, so neither choice seems superior
from a modularity standpoint.

I've discovered a query which fails with an error after a16ef313f with
both v2 patches applied:
create temp table t(i int primary key);
select * from
    (select k from
        (select i, coalesce(i, j) as k from
            (select i from t union all select 1)
            join (select 1 as j limit 1) on i = j)
        right join (select 1) on true
        join (select 1) on i is not null
    ),
    lateral (select k offset 1);
ERROR:  XX000: variable not found in subplan target list
LOCATION:  fix_upper_expr_mutator, setrefs.c:3310

Thank you for working on this!

Best regards,
Alexander