Assert failure in CTE inlining with view and correlated subquery

Hi,

it seems there's something wrong with CTE inlining when there's a view
containing a correlated subquery referencing the CTE. Consider a simple
example like this:

create table results (
id serial primary key,
run text,
tps float4
);

create view results_agg as
with base_tps as (
select run, tps from results
)
select
run,
count(*) as runs,

(select tps from base_tps b where b.run = r.run) AS base_tps

from results r
group by
run
order by
run;

explain SELECT run FROM results_agg ORDER BY 1;

This crashes on this assert in inline_cte():

Assert(context.refcount == 0);

because the refcount value remains 1. There's a backtrace attached.

I don't know why exactly this happens, my knowledge of CTE inlining is
somewhat limited. The counter is clearly out of sync

but a couple more observations:

1) it fails all the way back to PG12, where CTE inlining was added

2) it does not happen if the CTE is defined as MATERIALIZED

QUERY PLAN
-----------------------------------------
Subquery Scan on results_agg
-> Sort
Sort Key: r.run
CTE base_tps
-> Seq Scan on results
-> HashAggregate
Group Key: r.run
-> Seq Scan on results r
(8 rows)

3) without asserts, it seems to work and the query generates this plan

QUERY PLAN
-----------------------------------------
Subquery Scan on results_agg
-> Sort
Sort Key: r.run
-> HashAggregate
Group Key: r.run
-> Seq Scan on results r
(6 rows)

4) it does not seem to happen without the view, i.e. this works

explain
with base_tps as (
select run, tps from results
)
select run from (
select
run,
count(*) as runs,

(select tps from base_tps b where b.run = r.run) AS base_tps

from results r
group by
run
order by
run
) results_agg order by 1;

The difference between plans in (2) and (3) is interesting, because it
seems the CTE got inlined, so why was the refcount not decremented?

regards

--
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company