From: Tom Lane <tgl@sss.pgh.pa.us>
To: alias <postgres.rocks@gmail.com>
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: domain type with create cast not working on pg15,
 but work on pg14
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Comments: In-reply-to alias <postgres.rocks@gmail.com>
	message dated "Mon, 25 Apr 2022 11:37:49 +0530"
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Date: Mon, 25 Apr 2022 09:47:25 -0400
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alias <postgres.rocks@gmail.com> writes:
> create domain isodow as integer check(value between 1 and 7);
> create function testcast(in a timestamptz ,out isodow)
> as $$ select extract(dow from  a ) $$ language  sql;
> CREATE CAST (timestamptz AS isodow) WITH FUNCTION testcast(timestamptz) AS
> ASSIGNMENT;

For me, on either v14 or v15 that draws an informative warning:

WARNING:  cast will be ignored because the target data type is a domain

and that makes it unsurprising that this fails:

=# select '2022-04-23 19:00:01 +5:30'::timestamptz::isodow;
ERROR:  cannot cast type timestamp with time zone to isodow
LINE 1: select '2022-04-23 19:00:01 +5:30'::timestamptz::isodow;
                                                       ^

I don't see any difference in behavior between v13, v14, v15
on this.  The test case fails outright before v13, because
older versions wouldn't do the implied cast here:

=# create function testcast(in a timestamptz ,out isodow)
as $$ select extract(dow from  a ) $$ language  sql;
ERROR:  return type mismatch in function declared to return isodow
DETAIL:  Actual return type is double precision.
CONTEXT:  SQL function "testcast"

but with that corrected, the warning appears at least back to v10.

			regards, tom lane