I wrote:
> Andres Freund <andres@anarazel.de> writes:
>> Is there a guarantee that input functions are stable or immutable?
> There's a project policy that that should be true. That justifies
> marking things like record_in as stable --- if the per-column input
> functions could be volatile, record_in would need to be as well.
> There are other dependencies on it; see e.g. aab353a60, 3db6524fe.
I dug in the archives and found the thread leading up to aab353a60:
https://www.postgresql.org/message-id/flat/AANLkTik8v7O9QR9jjHNVh62h-COC1B0FDUNmEYMdtKjR%40mail.gmail.com
regards, tom lane