Re: PostgreSQL Bug with simple function unexpectedly treating varchar parameter as an array

Here's a reproducible test case that causes the problem in different
schemas. The issue appears to be related to creating a table and a
function that has the same name as the table with a prepended underscore.

rumpi_test -- table name
_rumpi_test -- function name

Here's the test case;

SELECT version();

drop table if exists rumpi_test;

create table rumpi_test( col1 varchar, col2 varchar);

drop function if exists rumpi_test;

CREATE OR REPLACE FUNCTION _rumpi_test( col1 varchar)

RETURNS varchar

LANGUAGE plpgsql

AS

$function$

declare

begin

raise info '%',_col1::varchar;

return('Done');

end;

$function$;

select _rumpi_test('hello');

Here what I get when I run this in psql:
xxx_pub_dev_2_db=> SELECT version();
version
---------------------------------------------------------------------------------------------------------
PostgreSQL 16.9 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0
20210514 (Red Hat 8.5.0-26), 64-bit
(1 row)

xxx_pub_dev_2_db=>
xxx_pub_dev_2_db=> drop table if exists rumpi_test;
DROP TABLE
xxx_pub_dev_2_db=>
xxx_pub_dev_2_db=> create table rumpi_test( col1 varchar, col2 varchar);
CREATE TABLE
xxx_pub_dev_2_db=>
xxx_pub_dev_2_db=>
xxx_pub_dev_2_db=>
xxx_pub_dev_2_db=> drop function if exists rumpi_test;
NOTICE: function rumpi_test() does not exist, skipping
DROP FUNCTION
xxx_pub_dev_2_db=>
xxx_pub_dev_2_db=> CREATE OR REPLACE FUNCTION _rumpi_test( col1 varchar)
xxx_pub_dev_2_db->
xxx_pub_dev_2_db-> RETURNS varchar
xxx_pub_dev_2_db->
xxx_pub_dev_2_db-> LANGUAGE plpgsql
xxx_pub_dev_2_db->
xxx_pub_dev_2_db-> AS
xxx_pub_dev_2_db->
xxx_pub_dev_2_db-> $function$
xxx_pub_dev_2_db$>
xxx_pub_dev_2_db$> declare
xxx_pub_dev_2_db$>
xxx_pub_dev_2_db$> begin
xxx_pub_dev_2_db$>
xxx_pub_dev_2_db$> raise info '%',_col1::varchar;
xxx_pub_dev_2_db$>
xxx_pub_dev_2_db$> return('Done');
xxx_pub_dev_2_db$>
xxx_pub_dev_2_db$> end;
xxx_pub_dev_2_db$>
xxx_pub_dev_2_db$> $function$;
CREATE FUNCTION
xxx_pub_dev_2_db=>
xxx_pub_dev_2_db=>
xxx_pub_dev_2_db=>
xxx_pub_dev_2_db=> select _rumpi_test('hello');
ERROR: malformed array literal: "hello"
LINE 1: select _rumpi_test('hello');
^
DETAIL: Array value must start with "{" or dimension information.
xxx_pub_dev_2_db=>

On Wed, Aug 6, 2025 at 4:43 PM David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
wrote:

> On Wednesday, August 6, 2025, Rumpi Gravenstein <rgravens(at)gmail(dot)com>
> wrote:
>
>>
>> xxx_pub_dev_2_db=# drop FUNCTION if exists _sa_setup_role;
>> DROP FUNCTION
>> xxx_pub_dev_2_db=# select proname, pronamespace, oid from pg_proc where
>> proname like '%sa_setup%';
>> proname | pronamespace | oid
>> ---------+--------------+-----
>> (0 rows)
>>
>> xxx_pub_dev_2_db=# select _sa_setup_role('af_repo_app');
>> ERROR: malformed array literal: "af_repo_app"
>> LINE 1: select _sa_setup_role('af_repo_app');
>> ^
>> DETAIL: Array value must start with "{" or dimension information.
>> xxx_pub_dev_2_db=#
>>
>
> Yeah, we’ve already pretty much decided this function has nothing to do
> with it. Go look at pg_type per the last example demonstrating the same
> error without the involvement of any user-defined function.
>
> David J.
>
>

--
Rumpi Gravenstein