Compare variables of composite type with slightly different column types

Hi,
Researching on join selectivity improvement I stuck into the code in
rowtypes.c:

/*
* Have two matching columns, they must be same type
*/
if (att1->atttypid != att2->atttypid)
ereport(ERROR, ...

Why, for example, isn't allowed next trivial query:

SELECT *
FROM
(SELECT ROW(1::integer, 'robert'::text)) AS s1,
(SELECT ROW(1::bigint, 'robert'::name)) AS s2
WHERE s1 = s2;

I guess, here the compatible_oper() routine can be used to find a
appropriate operator, or something like that can be invented.
I looked into the 2cd7084 and a4424c5, but don't found any rationale.

--
Regards
Andrey Lepikhov
Postgres Professional