Appears there is a problem finding the opclass when indexing a domain.
CREATE DOMAIN newint as int4;
CREATE TABLE tab (col newint unique);
ERROR: data type newint has no default operator class for access method
"btree"
You must specify an operator class for the index or define a
default operator class for the data type
Specifically, GetDefaultOpClass() finds 0 exact matches and 3 binary
compatible matches. Fetching getBaseType() of the attribute fixes the
problem for domains (see attachment).
However, I have to wonder why GetDefaultOpClass doesn't simply use the
first Binary Compatible opclass. When there is more than one usable it
doesn't do anything useful.