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Date: Wed, 21 Aug 2024 08:14:23 +0200
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Subject: Re: CREATE CAST allows creation of binary-coercible cast to range
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-bugs <pgsql-bugs@postgresql.org>
References: <076968e1-0852-40a9-bc0b-117cd3f0e43c@eisentraut.org>
 <1537781.1724165175@sss.pgh.pa.us> <1611527.1724175039@sss.pgh.pa.us>
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From: Peter Eisentraut <peter@eisentraut.org>
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On 20.08.24 19:30, Tom Lane wrote:
> I wrote:
>> 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.
> 
> In short, more or less as attached.  (I didn't bother with a
> regression test, since none of the adjacent error checks are
> covered either.)

This patch looks right.

> I'm unsure whether to back-patch this.  If somebody were using
> such a cast today, it might seem to mostly work, as long as the
> two kinds of ranges had the same behavior.  So they might not
> appreciate us breaking it in a minor release.  Maybe we should
> put this into 17 but not further back.

Yeah, 17 and up seems ok to me.