Re: BUG #17767: psql: tab-completion causes warnings when standard_conforming_strings = off

At Thu, 02 Feb 2023 00:51:07 -0500, Tom Lane <tgl@sss.pgh.pa.us> wrote in 
> Kyotaro Horiguchi <horikyota.ntt@gmail.com> writes:
> > I personally fine with the current behavior for the same reason as you
> > raised. We could enclose completion queries by "BEGIN; SET LOCAL
> > standard_... = on;" and "COMMIT;" in exec_query but I think you don't
> > like that (and me neither).
> 
> Yeah ... also that's problematic if we're in a transaction, especially
> an already-failed one.
(Oops!)

> Eventually I would like to remove the standard_conforming_strings GUC
> altogether, primarily for the reason given at the top of gram.y:
> 
>  *      In general, nothing in this file should initiate database accesses
>  *      nor depend on changeable state (such as SET variables).  If you do
>  *      database accesses, your code will fail when we have aborted the
>  *      current transaction and are just parsing commands to find the next
>  *      ROLLBACK or COMMIT.  If you make use of SET variables, then you
>  *      will do the wrong thing in multi-query strings like this:
>  *            SET constraint_exclusion TO off; SELECT * FROM foo;
>  *      because the entire string is parsed by gram.y before the SET gets
>  *      executed.  Anything that depends on the database or changeable state
>  *      should be handled during parse analysis so that it happens at the
>  *      right time not the wrong time.
> 
> Now, I don't foresee that actually happening any time soon (and every
> report of somebody still using standard_conforming_strings = off
> pushes out my idea of when it could happen).  But perhaps allowing
> minor annoyances like this to go unfixed would start to light a
> fire under people to get off of that setting.

That seems like the right decision for to-be-obsolete features.  Or,
we can explicitly mar that variables as OBSOLETE then rip off it a few
years later.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center