bug#17823: 24.3.91; end-of-visual-line: incorrect behaviour with truncate-lines and a line-prefix

[Eli Zaretskii]

> From: Nicolas Richard <theonewiththeevillook@yahoo.fr>
> Date: Fri, 20 Jun 2014 19:40:24 +0200
> 
> (progn
>   (insert (make-string 500 ?x))
>   (column-number-mode) ;; just to see it. plays no role.
>   (beginning-of-line)
>   (setq line-prefix (make-string 10 ? ))
>   (visual-line-mode)
>   (toggle-truncate-lines 1))
> 
> then hit C-e (end-of-visual-line) a few times. After some hits, the
> cursor doesn't move anymore, although it's not at the end of the line.
> On my machine, it goes to column 70, then 100, then stops there even
> when hitting C-e again.
> 
> I expect emacs to scroll horizontally instead

Why do you expect that?  "Visual line" means the line that is on
display.  What isn't on display does not exist for this purpose.

Is there some real-life use case behind this?  If so, please show it.