bug#12277: 24.1.50; Graphical issues with linum-mode and fringe

[Robert Dallas Gray]

On 25 Aug 2012, at 20:01, Eli Zaretskii wrote:

>> From: Robert Dallas Gray <mail@robertdallasgray.com>
>> Date: Sat, 25 Aug 2012 15:43:05 +0100
>> 
>> On starting emacs and entering linum-mode, with a vertical split,
>> vertical border periodically disappears or becomes 'broken' while scrolling.
>> 
>> Changing fringe-mode to left-only fixes the problem, but only if it is
>> done in the minibuffer. Using fringe-mode, set-fringe-mode or
>> set-fringe-style from lisp code does not help.
> 
> Could you please provide a detailed recipe, starting with "emacs -Q",
> for reproducing the problem?  I cannot reproduce this on my system,
> but I'm not sure I understood the procedure (e.g., what are "vertical
> split" and "vertical border"?).
> 
> Also, you are using a very old snapshot of the development sources;
> could you update to the latest code and see if the problem is still
> there?
> 
> Thanks.

Bearing in mind this affects Cocoa Emacs on OS X, in windowed mode:

cd /Applications/Emacs.app/Contents/MacOS
./Emacs -Q
M-x scroll-bar-mode (to turn scroll bars off)
(now visit a file with contents large enough to require scrolling)
C-x 3 (to split the window vertically)
M-x linum-mode

Now scroll the right-hand window (using the mouse wheel seems to reproduce the 
glitch more often). The black vertical bar between the two windows 
intermittently disappears or becomes 'broken'.

Enlarging the window beyond the default startup size also seems to help 
reproduce the bug.

I have a screenshot of the bug occurring, but I'm not sure on the rules for 
posting images here.

I've just checked the default gtk+ version of Emacs in Ubuntu (which is v23) 
and am able to reproduce the bug there also).

Also confirmed the bug exists in Cocoa Emacs 24.1.50 HEAD.

I have found a workaround for this by doing:

(set-fringe-mode '(0 . 8))

in init.el (it seems the fringe-mode [mnemonic] command doesn't work properly 
when used from lisp code.