Thread: 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@halodbtech.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@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.