BUG #18710: "pg_get_viewdef" triggers assertions in special scenarios

The following bug has been logged on the website:

Bug reference: 18710
Logged by: Man Zeng
Email address: zengman(at)halodbtech(dot)com
PostgreSQL version: 14.14
Operating system: centos-8
Description:

A prototype of the problem from
https://github.com/duckdb/pg_duckdb/issues/435
This exception can be reliably triggered by calling "pg_get_viewdef"

Step 1 ：
CREATE VIEW view_a AS
WITH RECURSIVE outermost(x) AS (
SELECT 1
UNION (WITH innermost1 AS (
SELECT 2)
SELECT * FROM outermost
UNION SELECT * FROM innermost1)
)
SELECT * FROM outermost ORDER BY 1;

Step 2 ：
SELECT oid FROM pg_class where relname = 'view_a';

Step 3：
SELECT pg_get_viewdef( this oid ); -- error

The abnormalities appear as follows
[postgres(at)iZuf6hwo0wgeev4dvua4csZ postgres]$ psql
psql (14.14)
Type "help" for help.

postgres=# CREATE VIEW view_a AS
postgres-# WITH RECURSIVE outermost(x) AS (
postgres(# SELECT 1
postgres(# UNION (WITH innermost1 AS (
postgres(# SELECT 2)
postgres(# SELECT * FROM outermost
postgres(# UNION SELECT * FROM innermost1)
postgres(# )
postgres-# SELECT * FROM outermost ORDER BY 1;
CREATE VIEW
postgres=# SELECT * FROM pg_class where relname = 'view_a';
oid | relname | relnamespace | reltype | reloftype | relowner | relam |
relfilenode | reltablespace | relpages | reltuples | relallvisible |
reltoastrelid | relhasindex | relisshared | relpersistence | relkind |
relnatt
s | relchecks | relhasrules | relhastriggers | relhassubclass |
relrowsecurity | relforcerowsecurity | relispopulated | relreplident |
relispartition | relrewrite | relfrozenxid | relminmxid | relacl |
reloptions | relpart
bound
-------+---------+--------------+---------+-----------+----------+-------+-------------+---------------+----------+-----------+---------------+---------------+-------------+-------------+----------------+---------+--------
--+-----------+-------------+----------------+----------------+----------------+---------------------+----------------+--------------+----------------+------------+--------------+------------+--------+------------+--------
------
32768 | view_a | 2200 | 32770 | 0 | 10 | 0 |
0 | 0 | 0 | -1 | 0 |
0 | f | f | p | v |
1 | 0 | t | f | f | f
| f | t | n | f |
0 | 0 | 0 | | |
(1 row)

postgres=# select pg_get_viewdef(32768);
TRAP: FailedAssertion("subquery->setOperations == NULL", File:
"ruleutils.c", Line: 6094, PID: 325948)
postgres: postgres postgres [local]
SELECT(ExceptionalCondition+0xb9)[0xb1a6c1]
postgres: postgres postgres [local] SELECT[0xa95d6b]
postgres: postgres postgres [local] SELECT[0xa960b5]
......

Maybe we can comment out the assertion that raises the exception, because I
looked up the code and found that the assertion doesn't seem to make a lot
of sense here.
I look forward to your discussion.