BUG #8153: check constraint results in a lot of casts

The following bug has been logged on the website:

Bug reference: 8153
Logged by: Marc Mamin
Email address: marc(at)intershop(dot)de
PostgreSQL version: 9.2.4
Operating system: Linux & windows
Description:

hello,

This is not a functional bugs, but it appers (at least for me...) that
following constraint gets defined with some unecessary overweight:

create table test (a varchar);

(1) alter table test add constraint test_ck check ( a in ('a','b'));

I'd expect this to be resolved in CHECK (a = ANY (ARRAY['a'::character
varying, 'b'::character varying]) ).
I've tried further variantes. (3) looks better but there is always a cast on
the table side.

(2) alter table test add constraint test_ck_2 check ( a = ANY
(ARRAY['a'::character varying, 'b'::character varying] ));
(3) alter table test add constraint test_ck_3 check ( a = ANY
(ARRAY['a'::text, 'b'] ));

\d+ test
Table "public.test"
Column | Type | Modifiers | Storage | Stats target |
Description
--------+-------------------+-----------+----------+--------------+-------------
a | character varying | | extended | |
Check constraints:
"test_ck" CHECK (a::text = ANY (ARRAY['a'::character varying,
'b'::character varying]::text[]))
"test_ck_2" CHECK (a::text = ANY (ARRAY['a'::character varying,
'b'::character varying]::text[]))
"test_ck_3" CHECK (a::text = ANY (ARRAY['a'::text, 'b'::text]))

best regards,

Marc Mamin