bug#70386: 30.0.50; (recenter 0 t) does not put point on top of the window

[Ihor Radchenko <yantar92@posteo.net>]

Eli Zaretskii <eliz@gnu.org> writes:

>> 1. emacs -Q
>> 2. Insert the following into scratch buffer and put point at "recenter"
>
> Which "recenter": the one in the comment or the one in (recenter 0 t) ?

The "(recenter 0 t))" line.

>> (progn
>>   (require 'pixel-scroll)
>>   (pixel-scroll-precision-interpolate
>>    (* -1 (line-pixel-height)
>>       (max 0 (- (count-screen-lines (window-start) (point)) 2)))
>>    nil 1)
>>   ;; Call original recenter for final adjustment.
>>   (recenter 0 t))
>> 
>> 3. M-x eval-buffer
>> 4. Observe that scroll is not set to line 0, despite calling `recenter'
>
> I don't think I understand what you mean by "scroll is not set to line
> 0".  Please explain in more detail what you expected to happen (and
> why), and what did happen.

Expected is as per docstring:

    With a numeric prefix argument ARG, recenter putting point on screen line ARG
    relative to the selected window.

So, I expect that (recenter 0 t) will put the line at point on top of
the window and that (recenter 1 t) will put the line at point at the
second top line.

My expectation is met when I simply do emacs -Q M-: (recenter 0 t) or
emacs -Q M-: (recenter 1 t) on master.

Observed:

1. Line at point slowly scrolls up until it reaches top of the window
(`pixel-scroll-precision-interpolate' call)

2. Line at point is reset back to its initial scroll position
   (`recenter' call)

Sometimes, I also observe line at point moving beyond the screen.

-- 
Ihor Radchenko // yantar92,
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