GNU bug report logs - #17284
24.3.90; Host name completion in shell mode take 45 seconds

Previous Next

Full log

View this message in rfc822 format

From: martin rudalics <rudalics <at> gmx.at>
To: Drew Adams <drew.adams <at> oracle.com>, Svend Sorensen <svend <at> ciffer.net>,  Nicolas Richard <theonewiththeevillook <at> yahoo.fr>
Cc: 17284 <at> debbugs.gnu.org
Subject: bug#17284: Host name completion in shell mode take 45 seconds
Date: Sat, 04 Apr 2015 10:29:52 +0200

> 1. Is it really about LIMIT?  Or is it instead about looking back
>     at a literal string of chars?  And typically a short string.
>     I'm guessing that that is the use case to pursue here.

Right.

> 2. Instead of (or in addition to) a byte-compiler warning for
>     `looking-back', how about adding a function `chars-before'?

This would be useful.

> Since I use multiple Emacs versions, some quite old, I use this.
> But I'm sure that a much better (including prettier) definition
> can be had for recent Emacs.  Or (better) define it in C.

I guess something like

(defun string-before-p (string)
  "Return t if string before `point' equals STRING."
  (let ((start (- (point) (length string))))
    (and (>= start (point-min))
	 (string-equal
	  (buffer-substring-no-properties start (point))
	  string))))

would do.  And for simpler cases giving `char-before' a second argument
to specify the position of the character before `point' might help too.

But many occurrences of `looking-back' in the code base are inherently
tied to regexps specified via defcustoms or passed as arguments and it
doesn't seem easy to get rid of them.  Hence we should probably add a
TODO item to fix all occurrences of `looking-back' either via the LIMIT
argument, by string or character comparison.  An appetizing formulation
of such an item would be very welcome.

martin

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.