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

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From: Mark Lillibridge <mark.lillibridge <at> hp.com>
To: bug-gnu-emacs <at> gnu.org
Subject: bug#4996: 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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