Re: Making tab-complete.c easier to maintain

From: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
To: alvherre(at)2ndquadrant(dot)com, michael(dot)paquier(at)gmail(dot)com, thomas(dot)munro(at)enterprisedb(dot)com
Cc: jeff(dot)janes(at)gmail(dot)com, tgl(at)sss(dot)pgh(dot)pa(dot)us, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Making tab-complete.c easier to maintain
Date: 2015-11-17 10:25:24
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Hello, I tried to implement the mini-language, which is a
simplified reglar expression for this specific use.

As a ultra-POC, the attached patch has very ad-hoc preprocess
function and does on-the-fly preprocessing, compilation then
execution of regular expression. And it is applied to only the
first ten or so matchings in psql_completion().

The first attachment is the same with that of previous patchset.

Every matching line looks like the following,

> else if (RM("ALTER {AGGREGATE|FUNCTION} [#id](.."))

As a temporary desin, "{}" means grouping, "|" means alternatives,
"[]" means capture and '#id' means any identifier.

The largest problem of this would be its computation cost:( This
in turn might be too slow if about three hundred matches run...

I see no straight-forward way to preprocess these strings.. A
possible solution would be extracting these strings then
auto-generate a c-srouce to preprocess them. And when running,
RM() retrieves the compiled regular expression using the string
as the key.

At Tue, 17 Nov 2015 15:35:43 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote in <20151117(dot)153543(dot)183036803(dot)horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
> At Mon, 16 Nov 2015 12:16:07 -0300, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote in <20151116151606(dot)GW614468(at)alvherre(dot)pgsql>
> > I don't think this is an improvement. It seems to me that a lot more
> > work is required to maintain these regular expressions, which while
> > straightforward are not entirely trivial (harder to read).
> >
> > If we could come up with a reasonable format that is pre-processed to a
> > regexp, that might be better. I think Thomas' proposed patch is closer
> > to that than Horiguchi-san's.
> I aimed that matching mechanism can handle optional elements in
> syntexes more robustly. But as all you are saying, bare regular
> expression is too complex here.

At Tue, 17 Nov 2015 16:09:25 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote in <20151117(dot)160925(dot)45883793(dot)horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
> if (Match("^,ALTER,TABLE,\id,$") ||
> Match("^,ALTER,TABLE,IF,EXISTS,\id,$"))...
> Interpreting this kind of mini-language into regular expressions
> could be doable..


Kyotaro Horiguchi
NTT Open Source Software Center

Attachment Content-Type Size
0001-Allow-regex-module-to-be-used-outside-server.patch text/x-patch 4.3 KB
0002-Replace-previous-matching-rule-with-regexps-take-2.patch text/x-patch 15.1 KB

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