GNU bug report logs - #4996
23.1; linum mode fails to number lines properly when just scrolling buffer

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From: help-debbugs <at> gnu.org (Emacs bug Tracking System)
To: mark.lillibridge <at> hp.com
Subject: bug#4996 closed by Stefan Monnier <monnier <at> IRO.UMontreal.CA> (Re:
 bug#4996: problem found)
Date: Tue, 24 Nov 2009 22:35:09 +0000

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This is an automatic notification regarding your bug report
which was filed against the emacs package:

#4996: 23.1; linum mode fails to number lines properly when just   scrolling buffer

It has been closed by Stefan Monnier <monnier <at> IRO.UMontreal.CA>.

Their explanation is attached below along with your original report.
If this explanation is unsatisfactory and you have not received a
better one in a separate message then please contact Stefan Monnier <monnier <at> IRO.UMontreal.CA> by
replying to this email.


-- 
4996: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=4996
Emacs Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
To: Markus Triska <markus.triska <at> gmx.at>
Subject: Re: bug#4996: problem found
Date: Tue, 24 Nov 2009 17:28:27 -0500

>> I propose changing that line to:
>> 
>> (let ((old-inhibit inhibit-point-motion-hooks))
>> (setq inhibit-point-motion-hooks t)
>> (forward-line)
>> (setq inhibit-point-motion-hooks old-inhibit))

> I suggest:

>       (let ((inhibit-point-motion-hooks t))
>         (forward-line))

Thanks, installed,


        Stefan

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From: Mark Lillibridge <mark.lillibridge <at> hp.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 23.1; linum mode fails to number lines properly when just
   scrolling buffer
Date: Fri, 20 Nov 2009 21:30:46 -0800

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the bug-gnu-emacs <at> gnu.org mailing list,
and to the gnu.emacs.bug news group.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:


    In emacs, invoke report-emacs-bug :-) while global-linum-mode is on.
Observe that there is some kind of overlay that occupies 9 lines before
this point.  That is, the spot where this paragraph starts is labeled
line 7.  Now page down (^v) and back (esc v).  Observe that now every
display line, including inside the overlay, has a line number.  *BUG*
What was line 7 is now shown as line 17.

    As soon as you do another command like a right arrow, the line
numbers revert to the original correct line numbering.


Linum has a hook for window-scroll-functions:

linum.el:74:
(define-minor-mode linum-mode
  "Toggle display of line numbers in the left margin."
  :lighter ""                           ; for desktop.el
  (if linum-mode
      (progn
        (if linum-eager
            (add-hook 'post-command-hook (if linum-delay
                                             'linum-schedule
                                           'linum-update-current) nil t)
          (add-hook 'after-change-functions 'linum-after-change nil t))
        (add-hook 'window-scroll-functions 'linum-after-scroll nil t)
        (add-hook 'window-size-change-functions 'linum-after-size nil t)
        (add-hook 'change-major-mode-hook 'linum-delete-overlays nil t)
        (add-hook 'window-configuration-change-hook
                  'linum-after-config nil t)
        (linum-update-current))


linum.el:175:
(defun linum-after-scroll (win start)
  (linum-update (window-buffer win)))


If I disable this function by doing (via {esc}:):

(defun linum-after-scroll (win start)
  t)

the bug goes away.  


    I am investigating further, but the problem appears to be that
forward-line acts differently during window-scroll-functions hook then
normally.  Some sort of dynamic variable binding, perhaps?

- Mark

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