ERROR: cache lookup failed for function 0

[Re-sending to hackers, since the original message to pgsql-bugs has
not been approved for delivery in the last four days…apologies for any
duplicates.]

Howdy,

I ran into this error on 8.2 a while ago, and just figured out what
was causing it. Here's a quick example on 8.2:

BEGIN;

-- Compare name[]s more or less like 8.3 does.
CREATE OR REPLACE FUNCTION namearray_text(name[])
RETURNS TEXT AS 'SELECT textin(array_out($1));'
LANGUAGE sql IMMUTABLE STRICT;

CREATE CAST (name[] AS text) WITH FUNCTION namearray_text(name[]) AS
IMPLICIT;

CREATE OR REPLACE FUNCTION namearray_eq( name[], name[] )
RETURNS bool
AS 'SELECT $1::text = $2::text;'
LANGUAGE sql IMMUTABLE STRICT;

CREATE OPERATOR = (   LEFTARG    = name[],   RIGHTARG   = name[],   NEGATOR    = <>,   PROCEDURE  = namearray_eq
);

SELECT '{foo}'::name[] <> '{bar}'::name[];

ROLLBACK;

If you comment out the NEGATOR line, the error is changed to the more
useful
 ERROR:  operator is not unique: name[] <> name[]

I'm assuming that, if you did this for 8.3 (which has name[]
comparison operators in core, so it'd have to be an operator with some
other type), you'd get the same useless error.

Ideally, in the situation where a NEGATOR (or commutator, too?) is
specified but has not actually been defined, you'd get an error such as:
 ERROR:  operator not defined: name[] <> name[]

Thanks,

David