Re: A solution to display completion candidates after point in a minibuffer

[Gregory Heytings via "Emacs development discussions." <emacs-devel@gnu.org>]

>>>> I don't know, but I'm not sure about that.  If you (set-window-start 
>>>> nil 1) unconditionally in window-scroll-functions, this setting will 
>>>> be obeyed by redisplay, even if point is not visible anymore.
>>>
>>> Oh, indeed, in that case it would move point instead.
>>
>> No, that's not what I meant.  In that case redisplay does not scroll 
>> and does not move point.  Point simply becomes invisible.
>
> No, redisplay will never accept a result that point is invisible.  If it 
> ever does display such situations, it's a bug that needs to be fixed.
>

Never say never...

>> It becomes visible again after the next redisplay, a second or two 
>> later.
>
> If such a situation exists, please describe how to reproduce it, because 
> it's a bug we need to fix.  Emacs should never display a window where 
> point is not fully visible.
>

Here's a recipe:

emacs -Q
(defun recipe ()
   (interactive)
   (set-frame-width nil 80)
   (set-frame-height nil 30)
   (switch-to-buffer (get-buffer-create "*Recipe*"))
   (goto-char 1)
   (let ((i 0)) (while (< i 60) (setq i (1+ i)) (insert (format "L%d\n" i))))
   (goto-char 148)
   (sit-for 0.25)
   (add-hook 'window-scroll-functions (lambda (&rest args) (set-window-start nil 1)))
   (forward-line 13))
M-x recipe
press C-n

You will see the cursor on the first line, after "L1", but in fact point 
is at that moment not visible anymore, it is still on "L54".  A second or 
two later, point has actually moved, and you will see the cursor blinking 
on "L14".  This works at least with Emacs 23, 24, 25, 26, 27 and 28.

The bug is more visible with Emacs 23 and 24, because you don't see the 
cursor on the first line after pressing C-n, you see a window without any 
cursor during a second or two.  With Emacs 25, 26, 27 and 28 the cursor 
after "L1" does not correspond to point (and as far as I understand does 
not correspond to anything).