GNU bug report logs - #19873
Ill-formed regular expression is constructed in forward-paragraph.

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From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Alan Mackenzie <acm <at> muc.de>
Cc: Marcin Borkowski <mbork <at> amu.edu.pl>, 19873 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>
Subject: bug#19873: Ill-formed regular expression is constructed in forward-paragraph.
Date: Fri, 03 Dec 2021 17:15:18 +0100

Alan Mackenzie <acm <at> muc.de> writes:

> Back when the bug was new, I started writing a library to analyse a
> regular expression and convert it into an equivalent well formed regular
> expression.  It's actually working, but is incomplete.  It's currently
> 2757 lines long, including pretty complete unit testing.  I actually
> looked at it again at the start of November.

Interesting.

> It strikes me as one of these things which needs to be done
> systematically, which, as I said, I've already tried (and not yet given
> up).  The question presents itself, would the effort be better spent
> improving Emacs's regexp engine?

Indeed -- making the Emacs regexp engine transform these complex regexps
into simpler, equivalent forms would be great.  We wouldn't have to use
it on all regexps -- the problem usually rears its head when we're
combining several user-defined regexps into a large one, so if we had a
`simplify-regexp' function that we could stick in here, that'd solve the
issue here (and in similar circumstances elsewhere).

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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