ERROR: cursor variable must be a simple variable (LINE XX: OPEN vQuery.cursorReturn FOR )

[Burke, William J Collins]

Hello,

I encountered the following error when compiling a pgsql function after an 
upgrade from PostgresSQL 9.3 on RHEL7 to PostgreSQL 12.9 on RHEL8, and could 
use some help from the community to figure out why.

ERROR: cursor variable must be a simple variable
LINE XX: OPEN vQuery.cursorReturn FOR
              ^
SQL state: 42804

After looking through the CURSOR documentation for PG9.3 and PG12, I noticed 
that the following statement is identical for both versions of PostgreSQL:

The cursor variable is opened and given the specified query to execute. The 
cursor cannot be open already, and it must have been declared as an unbound 
cursor variable (that is, as a simple refcursor variable). The query must be a 
SELECT, or something else that returns rows (such as EXPLAIN). The query is 
treated in the same way as other SQL commands in PL/pgSQL: PL/pgSQL variable 
names are substituted, and the query plan is cached for possible reuse. When a 
PL/pgSQL variable is substituted into the cursor query, the value that is 
substituted is the one it has at the time of the OPEN; subsequent changes to 
the variable will not affect the cursor's behavior. The SCROLL and NO SCROLL 
options have the same meanings as for a bound cursor.

Based on the statement highlighted above, I understand the error message. 
However, what I cannot figure out is why we did not get this error during 
compilation on PostgreSQL 9.3 with RHEL. Why does it work on PG9.3, but not on 
PG12? I feel like I am missing something.

Below is a sample pgsql function and composite type that are causing the error.

Custom composite type:

CREATE TYPE customCompositeType AS
(
       cursorReturn refcursor,
       code integer,
       message text
);

Function:

CREATE OR REPLACE FUNCTION getData()
  RETURNS record AS
$BODY$
DECLARE
   vQuery  customCompositeType;

BEGIN
   vQuery.cursorReturn := 'cursorName';
   vQuery.code         := 0;
   vQuery.message      := 'TEST;

   -- Open Cursor
   OPEN vQuery.cursorReturn FOR
     SELECT column1,
            column2,
            column3
     FROM sampleTable
     ORDER BY column3 ASC;

   RETURN(vQuery);

END;
$BODY$
  LANGUAGE plpgsql
  COST 100;


I would appreciate any advice or feedback that the community has on this issue.

Thanks,
William