BUG #18187: Unexpected error: "variable not found in subplan target lists" triggered by JOIN

The following bug has been logged on the website:

Bug reference: 18187
Logged by: Zuming Jiang
Email address: zuming(dot)jiang(at)inf(dot)ethz(dot)ch
PostgreSQL version: 16.0
Operating system: Ubuntu 20.04
Description:

My fuzzer finds a bug in Postgres 17devel, which triggers an unexpected
error.

--- Set up database ---
create table t2 (vkey int4, c9 text, primary key(vkey));
create view t4 as select 1 as c_2, 1 as c_3;
create view t5 as
select
1 as c_0,
case when '1' ~<=~ ref_0.c9 then 1 else 1 end as c_3
from
((t2 as ref_0
inner join t2 as ref_1
on (ref_0.vkey = ref_1.vkey))
right outer join t2 as ref_2
on (ref_1.vkey = ref_2.vkey ));
------------------------

The fuzzer generates a test case:

--- Test case ---
select
ref_5.c_3
from
(((select ref_1.c_3 as c_0 from t4 as ref_1) as subq_0
right outer join t5 as ref_5
on (subq_0.c_0 = ref_5.c_0))
right outer join t4 as ref_6
on (subq_0.c_0 = ref_6.c_2));
------------------------

--- Expected behavior ---
The test case should not trigger any error.

--- Actual behavior ---
The test case trigger an error:

ERROR: variable not found in subplan target lists

--- Postgres version ---
Github commit: 3c551ebede46194237f82062b54b92e474b5c743
Version: PostgreSQL 17devel on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu
9.4.0-1ubuntu1~20.04.1) 9.4.0, 64-bit

--- Platform information ---
Platform: Ubuntu 20.04
Kernel: Linux 5.4.0-147-generic