Partial indexes on VARCHAR get double converted from text

create table stately ( id int, filename varchar(255), state varchar(255) );

create index on stately(state) where state in ( 'pending', 'waiting',
'done' );

\d stately
Table "public.stately"
Column | Type | Modifiers
----------+------------------------+-----------
id | integer |
filename | character varying(255) |
state | character varying(255) |
Indexes:
"stately_state_idx" btree (state) WHERE state::text = ANY
(ARRAY['pending'::character varying, 'waiting'::character varying,
'done'::character varying]::text[])

There is no combination of typecasting which will prevent this outcome.
I've tried.

Further, it seems to me from testing that this double type conversion
affects the planner's costing of the index, causing it to not want to
use the index.

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com