From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] user-defined numeric data types triggering ERROR:
 unsupported type
In-reply-to: <07b0dcd6-45f7-a2d3-99c6-115490b2cc98@2ndquadrant.com>
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Comments: In-reply-to Tomas Vondra <tomas.vondra@2ndquadrant.com>
	message dated "Sun, 04 Mar 2018 19:49:53 +0100"
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Date: Sun, 04 Mar 2018 14:37:15 -0500
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Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> FWIW I originally constructed the tests merely to verify that the fix
> actually fixes the issue, but I think we should add some tests to make
> sure it does not get broken in the future. It took quite a bit of time
> until someone even hit the issue, so a breakage may easily get unnoticed
> for a long time.

Oh, well, that was another problem I had with it: those tests do basically
nothing to ensure that we won't add another such problem in the future.
If somebody added support for a new type FOO, and forgot to ensure that
FOO-vs-not-FOO cases behaved sanely, these tests wouldn't catch it.
(At least, not unless the somebody added a FOO-vs-not-FOO case to these
tests, but it's hardly likely they'd do that if they hadn't considered
the possibility.)

I think actually having put in the coding patterns for what to do with
unsupported cases is our best defense against similar oversights in
future: probably people will copy those coding patterns.  Maybe the bytea
precedent proves that some people will fail to think about it no matter
what, but I don't know what more we can do.

			regards, tom lane