bug#32002: 24.4; Scroll bar start, end not correct

[Eli Zaretskii]

> From: Mike Kupfer <mkupfer@alum.berkeley.edu>
> cc: kurn@sfu.ca, 32002@debbugs.gnu.org
> Date: Sun, 15 Jul 2018 18:47:56 -0700
> 
> What I see is that in scroll-bar-drag-1, portion-whole is (1 . 1), both
> when I drag the mouse down and when I drag it up.  So scroll-bar-drag-1
> always does (goto-char (point-max)).
> 
> Should scroll-bar-drag-1 be doing the correction to account for
> scroll-bar-adjust-thumb-portion, or should that be done higher up the
> stack?  (If scroll-bar-drag-1 needs to apply a correction, then I
> suspect there are other functions that also need to apply a correction.
> Perhaps it would be cleaner to make the correction early on, so that it
> only needs to be done once.  But I'm not familiar with the code, so
> there may well be aspects to this that I'm missing.)

The question is what kind of correction can be applied here?  I
understand that when scroll-bar-adjust-thumb-portion is nil, the thumb
doesn't move, and so we don't even know that the thumb was dragged
upwards, is that true?  If so, how can we know that the user meant
scrolling up?