GNU bug report logs - #11025
23.1; re-search-backward does not find the right beginning of the regexp

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Jack Duthen <duthen.mac.01 <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 23.1;
	re-search-backward does not find the right beginning of the regexp
Date: Fri, 16 Mar 2012 12:40:22 +0100

--text follows this line--

Hello,

I'm editing a ".el" file, in emacs-lisp-mode,
and I use the standard value of `comment-start-skip':
;;; (insert comment-start-skip)
"\(\(^\|[^\\
]\)\(\\\\\)*\);+ *"  <-- I added the quotes here

;;; Test #1

;;; (progn (beginning-of-line) (looking-at comment-start-skip))
;;; Move the point at the end of the previous line and type C-x C-e
;;; It moves the point at the beginning of the line and returns T. Ok.

;;; (progn (previous-line) (re-search-forward comment-start-skip))
;;; Move the point at the end of the previous line and type C-x C-e
;;; It moves the point on the first "(". Ok.

;;; Thus the string "^;;; " matches the regexp `comment-start-skip'.

;;; (re-search-backward comment-start-skip)
;;; Move the point at the end of the previous line and type C-x C-e
;;; It moves the point just one character AFTER the first semicolon.
;;; I would expect it to move the point at the beginning of the line
;;; since, as shown previously, it matches the regexp and this match
;;; includes the match actually found.

;;; Test #2

; (setq re1 (concat comment-start-skip "--+\n" comment-start-skip " [^ ].*\n"))
; (setq re (concat "\\(" re1 "\\)+"))
; Move the point at the end of the next line and type C-x C-e to see the match
; (progn (forward-char) (and (looking-at re) (re-search-forward re)))
; ----------
; this yes
; ----------
; this no
; ----------
;
; (re-search-backward re)
; Move the point at the end of the previous line and type C-x C-e
; The point moves to the beginning of the line before "this no".
; => Bug



In GNU Emacs 23.1.1 (i686-pc-linux-gnu, GTK+ Version 2.22.0)
 of 2011-03-04 on roseapple, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.10900000
configured using `configure  '--build=i686-linux-gnu'
'--host=i686-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib'
'--libexecdir=/usr/lib' '--localstatedir=/var/lib'
'--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes'
'--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.1/leim'
'--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars'
'build_alias=i686-linux-gnu' 'host_alias=i686-linux-gnu'
'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: fr_FR.utf8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Emacs-Lisp

Minor modes in effect:
  which-function-mode: t
  diff-auto-refine-mode: t
  eldoc-mode: t
  show-paren-mode: t
  recentf-mode: t
  desktop-save-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<menu-bar> <help-menu> <send-emacs-bug-report>

Recent messages:
/usr/bin/mail is not an executable.  Setting mail-interactive to t.

)jack(

Message #8 received at 11025 <at> debbugs.gnu.org (full text, mbox):

From: Jack Duthen <duthen.mac.01 <at> gmail.com>
To: 11025 <at> debbugs.gnu.org
Subject: Fwd: bug#9681: Broken behaviour of re-search-backward (.+ matching
	only a single character)
Date: Fri, 16 Mar 2012 17:29:20 +0100

Oops!  It's a feature, not a bug...
Sorry for the noise.

I just found the same problem addressed in bug#9681.
I understood the current behavior of re-search-backward.
see my reply.
sincerely
)jack(

---------- Forwarded message ----------
From: Jack Duthen <duthen.mac.01 <at> gmail.com>
Date: 2012/3/16
Subject: Re: bug#9681: Broken behaviour of re-search-backward (.+
matching only a single character)
To: bug-gnu-emacs <at> gnu.org

On Thu, Oct 06, 2011 at 08:57:09AM -0400, Stefan Monnier wrote:
> re-search-* stops at the first character position that has a match.
> And then it chooses the longest match at that position.

Stepan wrote:
> So, again: it definitely needs better documentation,
> and IMO it also needs fixing.

Hi!

For my own imenu-prev-index-position-function, I needed
a backward regexp search which would match something like ".+"
the way one (like Stepan) can expect rather than the way it actually
does (as described by Stefan).

So, I just wrote a function to do that.

The way it handles the COUNT variable is not as good as one could want
but, as I almost never use it, I don't care.
It's not very efficient but, since I can't notice the time it takes
when used in the "*rescan" menu and since I can't imagine a better algorithm,
it's ok for me.

(defun jd-re-search-backward (regexp &optional bound noerror count)
 (let ((orig-point (point)) bom)
   (when (re-search-backward regexp bound noerror count)
     (setq bom (point)) ; should not be useful
     (goto-char (point-min))
     (while (re-search-forward regexp orig-point 'noerror)
       ;; remember the last beginning of match
       (setq bom (match-beginning 0)))
     (goto-char bom)
     ;; set match data (erased by the last failing search) and return T
     (looking-at regexp))))

HTH
)jack(

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