From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael Paquier <michael@paquier.xyz>
cc: Merlin Moncure <mmoncure@gmail.com>,
 Dmitry Dolgov <9erthalion6@gmail.com>,
        yarexeray@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #15940: json_populate_recordset fails with ERROR: record type
 has not been registered
In-reply-to: <20190809023505.GE3194@paquier.xyz>
References: <15940-2ab76dc58ffb85b6@postgresql.org>
 <20190806073209.GI32256@paquier.xyz>
 <CA+q6zcVYyjDEh9hkKi3eG81TBghMRjVySNA4gAsQU0q4gJPbFQ@mail.gmail.com>
 <5154.1565120306@sss.pgh.pa.us>
 <CAHyXU0yu3otAqneN=B+6oRXgDqEAqJt5EtYBn55vGX_PzBpj=w@mail.gmail.com>
 <20190809023505.GE3194@paquier.xyz>
Comments: In-reply-to Michael Paquier <michael@paquier.xyz>
	message dated "Fri, 09 Aug 2019 11:35:05 +0900"
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Date: Mon, 19 Aug 2019 18:04:25 -0400
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Michael Paquier <michael@paquier.xyz> writes:
> On Tue, Aug 06, 2019 at 02:53:45PM -0500, Merlin Moncure wrote:
>> For posterity I agree that OP was essentially exploiting undefined, or
>> at least poorly defined, behavior.  For my money, I'd advise using
>> this function for cases where you don't want to use an in place type,
>> just a column list:

> If I were to change something here, that would be this error string
> exposed to the user.  With the current error, there is no real way
> that the user knows what is wrong and why he/she should not do that.
> Could it be possible to add some recommendation for example on top of
> an error "cannot do that because blah"?

I concluded that we'd better restore the former behavior, or people
will complain that this is a regression.  We can however do better
than the "record type has not been registered" error, at least for
the case where the error is being thrown at runtime.  I went with

ERROR:  could not determine row type for result of json_populate_record
HINT:  Provide a non-null record argument, or call the function in the FRO=
M clause using a column definition list.

			regards, tom lane