From: Tom Lane <tgl@sss.pgh.pa.us>
To: Fabien COELHO <coelho@cri.ensmp.fr>
Cc: Corey Huinker <corey.huinker@gmail.com>
Cc: Daniel Verite <daniel@manitou-mail.org>
Cc: David G. Johnston <david.g.johnston@gmail.com>
Cc: Greg Stark <stark@mit.edu>
Cc: Erik Rijkers <er@xs4all.nl>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Jim Nasby <Jim.Nasby@bluetreble.com>
Cc: PostgreSQL <pgsql-hackers@postgresql.org>
Cc: pgsql-hackers-owner@postgresql.org
Subject: Re: \if, \elseif, \else, \endif (was Re: PSQL commands: \quit_if, \quit_unless)
Date: Fri, 17 Mar 2017 10:37:13 -0400
Message-ID: <30537.1489761433@sss.pgh.pa.us> (raw)
In-Reply-To: <alpine.DEB.2.20.1703170710320.4278@lancre>
References: <df2c433c-b9ff-4d41-ad08-b0d420b403b8@manitou-mail.org>
<15875.1489440118@sss.pgh.pa.us>
<CADkLM=fzjNr2it+a75CJgs7nPPSb-S=q=taa7=7mtxa5pKJSbQ@mail.gmail.com>
<24741.1489698878@sss.pgh.pa.us>
<CADkLM=fHrBW4Z+ixPD35Ad+4oKG1KX0UK7xDY+0G9gdNnDQS8A@mail.gmail.com>
<alpine.DEB.2.20.1703170710320.4278@lancre>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-hackers>
Fabien COELHO <coelho@cri.ensmp.fr> writes:
> ISTM that I've tried to suggest to work around that complexity by:
> - document that \if-related commands should only occur at line start
> (and extend to eol).
> - detect and complain when this is not the case.
I think this is a lousy definition, and would never be considered if we
were working in a green field. Moreover, preventing such cases would be
pretty darn ugly/messy as well.
I also fear that there are corner cases where the behavior would still
be inconsistent. Consider
\if ...
\set foo `echo \endif should not appear here`
If the \if succeeds, the result of the second line would be to set foo
to "endif should not appear here" (and we'd remain in the \if block).
But if the \if fails and we need to skip the \set command, any approach
that involves changing the argument parsing rules will fail to recognize
the backtick construct, and then will see the \endif as a command.
Similar examples can be constructed using \copy.
It's possible that we could keep the implementation that uses an early exit
from exec_command() if we were to move argument collection for all
backslash commands up to the start of the function. It would still be
a bit invasive, but perhaps not too awful: I'm imagining that instead of
else if (strcmp(cmd, "setenv") == 0)
{
char *envvar = psql_scan_slash_option(scan_state,
OT_NORMAL, NULL, false);
char *envval = psql_scan_slash_option(scan_state,
OT_NORMAL, NULL, false);
we'd write
else if (strcmp(cmd, "setenv") == 0)
{
char *envvar = args[0];
char *envval = args[1];
where the args array had been filled at the top of the function.
The top-of-function code would have to know all the cases where
commands didn't use basic OT_NORMAL processing, but there aren't
that many of those, I think.
regards, tom lane
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, coelho@cri.ensmp.fr, corey.huinker@gmail.com, daniel@manitou-mail.org, david.g.johnston@gmail.com, stark@mit.edu, er@xs4all.nl, robertmhaas@gmail.com, Jim.Nasby@bluetreble.com, pgsql-hackers-owner@postgresql.org
Subject: Re: \if, \elseif, \else, \endif (was Re: PSQL commands: \quit_if, \quit_unless)
In-Reply-To: <30537.1489761433@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox