Re: BUG #17575: row(NULL) IS NULL inconsistent with IS NOT DISTINCT FROM NULL

The following bug has been logged on the website:

Bug reference:      17575
Logged by:          Alexey Borschev
Email address:      aborschev@gmail.com
PostgreSQL version: 14.4
Operating system:   Ubuntu
Description:       

Hi, PG hackers!
I noticed strange behavior of ROW(NULL):
I expect, that  IS NULL  operator should give the same result as  IS NOT
DISTINCT FROM NULL
similarly, IS NOT NULL  operator should give the same result as  IS DISTINCT
FROM NULL:     

SELECT row(NULL::int) = row(NULL::int)              AS "test= "
      , row(NULL::int) IS NULL                      AS IS_NULL   
      , row(NULL::int) IS NOT NULL                  AS NOT_NULL 
      , row(NULL::int) IS DISTINCT FROM NULL        AS IS_DISTINCT_FROM_NULL

      , row(NULL::int) IS NOT DISTINCT FROM NULL    AS
NOT_DISTINCT_FROM_NULL   

 test=  | is_null | not_null | is_distinct_from_null |
not_distinct_from_null 
--------+---------+----------+-----------------------+------------------------
        | t       | f        | t                     | f                   


But here row(NULL::int) IS NULL -> true, and row(NULL::int) IS NOT DISTINCT
FROM NULL -> false !

 

Next point:
I expected that IS NULL and IS NOT NULL operators must always return
opposite results, but:

SELECT row(NULL::int, 'Bob'::TEXT) IS NULL                        AS
Row_IsNULL 
     , row(NULL::int, 'Bob'::TEXT) IS NOT NULL                    AS
Row_NotNULL ;

 row_isnull | row_notnull
------------+-------------
 f          | f
- They both return False on same input!

Can we fix or document this PG issue?