bug#47498: 28.0.50; follow-mode misses a line with tiling window manager

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Tue, 30 Mar 2021 12:30:42 +0000
> 
> I see one hidden line when using follow-mode.
> 
> Steps to reproduce:
> 
> 0. emacs -Q
> 1. C-h i
> 2. C-x 2
> 3. M-x follow-mode RET
> 
> There is now one line missing from the display.  When using
> `display-line-numbers-mode', this effect is more obvious.

>From my POV, follow-mode's design is fundamentally flawed, when
variable-size fonts and fractional line display are considered.  It
attempts to solve several problems that cannot be solved in principle,
unless the only font on display is the default face's font, and the
windows display an integral number of text lines.  It's a small wonder
in my eyes that display problems caused by follow-mode are so minor,
even subtle.  My advice is to stay away of it, if you want perfect
display.