BUG #1705: nextval being evaluated more than once

The following bug has been logged online:

Bug reference: 1705
Logged by: Nick Farrell
Email address: nick(at)farrell(dot)name
PostgreSQL version: 8.0.3
Operating system: ubuntu linux (warty warthog)
Description: nextval being evaluated more than once
Details:

If I use embed nextval in a string which is EVALUATEd, the insert rule below
does not get the correct primary key value, but the next one! ie: NEW.p1 is
not the actual value of p1, but is the result of re-executing nextval().

Workaround is to evaluate nextval in the function, and EVALUATE with a
literal key value. This is shown in the good_fn below.

Apologies in advance if you already know about this one, or this is someone
intended behaviour.

Nick.

--------------- snip ---------------------
create table a (
p1 integer primary key,
v1 integer
);
create sequence s;

create table b (
p2 serial,
fk integer not null references a
);

create rule a_ins AS ON INSERT TO a DO INSERT INTO b (fk) values (NEW.p1);

create or replace function bad_fn() returns integer AS '
DECLARE
result INTEGER;
BEGIN
EXECUTE '' insert into a values (nextval(''''s''''), 2); '';
result := 0;
return result;
END;
' language plpgsql;

create or replace function good_fn() returns integer AS '
DECLARE
result INTEGER;
BEGIN
result := 0;
EXECUTE '' insert into a values ('' || nextval(''s'') || '', 2); '';
return result;
END;
' language plpgsql;

select good_fn();
select good_fn();
select bad_fn();