From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Thomas Munro <thomas.munro@enterprisedb.com>,
 Jeff Janes <jeff.janes@gmail.com>,
 Alvaro Herrera <alvherre@2ndquadrant.com>,
 Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Making tab-complete.c easier to maintain
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
 message dated "Thu, 22 Oct 2015 17:29:51 -0400"
Date: Thu, 22 Oct 2015 14:36:53 -0700
Message-ID: <51382.1445549813@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Oct 21, 2015 at 8:54 PM, Thomas Munro
> <thomas.munro@enterprisedb.com> wrote:
>> (Apologies for sending so many versions.  tab-complete.c keeps moving
>> and I want to keep a version that applies on top of master out there,
>> for anyone interested in looking at this.  As long as no one objects
>> and there is interest in the patch, I'll keep doing that.)

> I don't want to rain on the parade since other people seem to like
> this, but I'm sort of unimpressed by this.  Yes, it removes >1000
> lines of code, and that's not nothing.  But it's all mechanical code,
> so, not to be dismissive, but who really cares?  Is it really worth
> replacing the existing notation that we all know with a new one that
> we have to learn?  I'm not violently opposed if someone else wants to
> commit this, but I'm unexcited about it.

What I would like is to find a way to auto-generate basically this entire
file from gram.y.  That would imply going over to something at least
somewhat parser-based, instead of the current way that is more or less
totally ad-hoc.  That would be a very good thing though, because the
current way gives wrong answers not-infrequently, even discounting cases
that it's simply not been taught about.

I have no very good idea how to do that, though.  Bison does have a
notion of which symbols are possible as the next symbol at any given
parse point, but it doesn't really make that accessible.  There's a lack
of cooperation on the readline side too: we'd need to be able to see the
whole query buffer not just the current line.

			regards, tom lane


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