bug#52542: 29.0.50; Emoji makes lines taller

[Eli Zaretskii]

> Date: Thu, 16 Dec 2021 09:28:14 +0100
> From:  Rudolf Adamkovič via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> On macOS 11/12, in Emacs 28/29, any emoji (e.g. alien) makes the line with it 
> taller than the lines with no emojis, which breaks various things across 
> Emacs, such as avatars in telega.el (see the attachment).
> 
> To reproduce:
> 
> 1. start 'emacs -Q'
> 
> 2. type
> 
> > foo
> > 👽 bar
> > baz

Emacs displays the line as tall as needed for the tallest character
shown on that line.  This is normal, and not a bug.

> 3. delete the alien
> 
> Actual: the line with "bar" becomes less tall
> 
> Expected: all lines always have constant height

Your expectations are unfounded, IMO.  Emacs cannot possibly change
the fonts you have on your system, and cannot truncate glyphs of the
Emoji characters if they are taller than the font used for the default
face.  So it has no alternative but to make the line's height larger.

The only solution to that could be if you configure the fonts
installed on your system to have a font which supports Emoji and whose
height is not larger than that of the font used for the default face.

Bottom line is: I don't see how this is an Emacs bug nor how to solve
this in Emacs.

Thanks.