Eli Zaretskii <eliz@gnu.org> writes:

>> From: Jonas Bernoulli <jonas@bernoul.li>
>> Date: Sat, 31 Dec 2016 14:26:06 +0100
>> 
>> Custom buffers contain two long lines, the first separating the initial
>> buttons from the options shown below, and the second is for symmetry, I
>> suppose.  This is implemented in `custom-group-value-create'.
>> 
>> These lines are 999 characters long.  When point ends up on the "line
>> line", then it ends up at the *end* of that line, scrolling all content
>> except for the line itself off-window.  This happens both with C-n/C-p,
>> as well as when using the mouse scroll wheel.
>
> The scrolling only happens for me if I set truncate-lines to a non-nil
> value.  Is that what you see?  Or perhaps you invoke Customize in a
> partial-width window, in which case truncate-partial-width-windows is
> non-nil by default?
>
> If lines are not truncated, there's no horizontal scrolling.

I see the same thing here.

>> If that is considered to be too ugly, then I would suggest setting the
>> `:align-to' to be just long enough to reach the edge of the window (but
>> never longer) at the time `custom-group-value-create' is called, using
>> something like:
>> 
>> (list 'space :align-to
>>       `(+ (0 . right)
>>           ,(min (window-hscroll)
>>                 (- (line-end-position)
>>                    (line-beginning-position)))))
>
> Does this really work when a window has its lines truncated?

Yes, it works on both text based and graphical displays.  Please see
the attached patch.

Lars suggested to remove the lines entirely, but I think I prefer to
not change that for now.  Perhaps it would make more sense as part of
a bigger overhaul of the look and feel of customize.

Any comments?

Best regards,
Stefan Kangas