Assertion failure with assignment to array elem

postgres=# CREATE OR REPLACE FUNCTION f_test() RETURNS VOID AS $$
DECLARE
     arr text[];
     lr text;
     i integer;
   BEGIN
     i := 1;
     SELECT 'foo' INTO lr;
     arr[COALESCE(i, (SELECT NULL::integer))] := COALESCE(lr, (SELECT
NULL::text));
   END;
$$ LANGUAGE PLPGSQL;
CREATE FUNCTION
postgres=# SELECT f_test();
server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.

TRAP: FailedAssertion("!(estate->eval_tuptable == ((void *)0))", File:
"pl_exec.c", Line: 4264)

This happens when both the array subscript and the expression been
assigned are "non-simple". The purpose of the funny-looking COALESCE
expressions in the above example is to force them to be non-simple.

This bug applies to all supported versions.

The problem is that exec_assign_value() is passed a value that came from
the current 'estate', but when exec_assign_value() evaluates the array
subscript, we don't expect there to already be an open result set in
'estate'.

A simple fix would be to make a copy of the value being assigned in
exec_assign_expr and calling exec_eval_cleanup() before the call to
exec_assign_value(). But I wonder if the performance impact would be too
high - one extra copy isn't that expensive, but it would affect every
single assignment of pass-by-reference variables.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com