Re: Embedded modifiers in the regex engine

[Eli Zaretskii <eliz@gnu.org>]

> From: Dima Kogan <dima@secretsauce.net>
> Date: Wed, 24 Feb 2016 17:32:01 -0800
> 
> I've been thinking of ways to make some fancier aspects of isearch and
> hi-lock work better, specifically, the way we handle the different
> modes: case-fold, char-fold, lax-whitespace, etc.
> 
> The relevant bugs I filed recently:
> 
>   http://debbugs.gnu.org/22541
>   http://debbugs.gnu.org/22520
>   http://debbugs.gnu.org/22479
> 
> In short, different parts of emacs (isearch, isearch history, hi-lock,
> etc) treat these modes inconsistently, which results in unexpected
> behavior.
> 
> The best solution I can think of to clean this up is also the most
> intrusive: adding support for pcre-style embedded modifiers to
> activate/deactivate the modes.
> 
> So for instance "\\(?i\\)asdf" would be interpreted as a case-folding
> regex regardless of the value of case-fold-search. I think this would be
> a great thing to have in general, but for the specific issues in the
> bugs above, it'd make things simpler and more correct.

I hope you are not proposing this as a replacement for the M-s
toggles, because if so, I'm very much opposed.

> As an example, currently hi-lock generates a complicated-looking regex
> to emulate char-folding and case-folding. If we supported the modifiers,
> this change would simply be a prepend of "\\(?i\\)" or whatever other
> modes we want. This is simple and expected to be bug-free on the hi-lock
> level. Bugs such as hi-lock not supporting char-fold and case-fold at
> the same time would not happen.

They will also not happen once character-folding is implemented via
translation tables, instead of regular expressions.  The current
implementation will go away at some point (one hopes).