From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter@eisentraut.org>
cc: pgsql-bugs <pgsql-bugs@postgresql.org>
Subject: Re: CREATE CAST allows creation of binary-coercible cast to range
 over domain
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References: <076968e1-0852-40a9-bc0b-117cd3f0e43c@eisentraut.org>
Comments: In-reply-to Peter Eisentraut <peter@eisentraut.org>
	message dated "Tue, 20 Aug 2024 11:00:21 +0200"
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Date: Tue, 20 Aug 2024 10:46:15 -0400
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Peter Eisentraut <peter@eisentraut.org> writes:
> CREATE CAST disallows creating a binary-coercible cast to a domain 
> (because that would bypass checking the domain constraints).  But it 
> allows it if the domain is wrapped inside a range type:
> ...
> This particular case seems straightforward to fix, but maybe there are 
> also cases with more nesting to consider.

I think it's an oversight that we allow binary-coercible casts
involving range types at all.  There are no other nesting cases to
worry about, because CreateCast already rejects binary-coercible casts
applied to composites and arrays, explaining

         * We know that composite, enum and array types are never binary-
         * compatible with each other.  They all have OIDs embedded in them.

But range types also embed their own OID, so I don't see why that
concern doesn't apply to them.

			regards, tom lane