Re: Common function for percent placeholder replacement

From: Nathan Bossart <nathandbossart(at)gmail(dot)com>
To: Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>
Cc: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Common function for percent placeholder replacement
Date: 2023-01-04 00:37:00
Message-ID: 20230104003700.GB289060@nathanxps13
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In general, +1.

On Tue, Dec 20, 2022 at 06:30:40AM +0100, Peter Eisentraut wrote:
> (Still need to think about Robert's comment about lack of error context.)

Would adding the name of the GUC be sufficient?

(errmsg("could not build %s", guc_name),
errdetail("string ends unexpectedly after escape character \"%%\"")));

> + * A value may be NULL. If the corresponding placeholder is found in the
> + * input string, the whole function returns NULL.

This appears to be carried over from BuildRestoreCommand(), and AFAICT it
is only necessary because pg_rewind doesn't support %r in restore_command.
IMHO this behavior is counterintuitive and possibly error-prone and should
result in an ERROR instead. Since pg_rewind is the only special case, it
could independently check for %r before building the command.

Nathan Bossart
Amazon Web Services:

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