Matching domains-over-enums to anyenum types

Hello,

A colleague of mine was surprised to discover the following statements raised
an error:

postgres=# CREATE TYPE abc_enum AS ENUM ('a', 'b', 'c');
CREATE TYPE
postgres=# CREATE DOMAIN abc_domain AS abc_enum;
CREATE DOMAIN
postgres=# SELECT 'a'::abc_domain = 'a'::abc_domain;
ERROR: operator does not exist: abc_domain = abc_domain
LINE 1: SELECT 'a'::abc_domain = 'a'::abc_domain;
^
HINT: No operator matches the given name and argument types. You might need
to add explicit type casts.

This has been already discussed a long time ago, and the idea was rejected at
the time since there was no demand for it:

https://www.postgresql.org/message-id/flat/BANLkTi%3DaGxDbGPSF043V2K-C2vF2YzGz9w%40mail.gmail.com#da4826d2cbbaca20e3440aadb3093158

Given that we implemented that behaviour for domains over ranges and
multiranges, I don't see the harm in doing the same for domains over enums.

What do you think ?

--
Ronan Dunklau