bug#57962: 29.0.50; Odd font choices

[Lars Ingebrigtsen]

I've poked around some more here, experimenting with different fonts
with -fn, and the thing is that everything works as expected with most
fonts (i.e., the height of `fixed-pitch' and `default' fonts are the
same, which is the problem, really) -- but with the default font in
Ubuntu, "Ubuntu Mono", that's not the case.

So Emacs has chosen these two fonts for `default' and `fixed-pitch',
respectively:

    ftcrhb:-DAMA-Ubuntu Mono-regular-normal-normal-*-48-*-*-*-m-0-iso10646-1 
(#x2C)
    ftcrhb:-PfEd-DejaVu Sans 
Mono-regular-normal-normal-*-48-*-*-*-m-0-iso10646-1 (#x26)

Is there something more Emacs could be doing to try to ensure that it
picks equal-sized fonts?  By somehow looking at actual font metrics?  (I
guess we're currently just saying "give me this font in size 48"?  And
that the actual size of the glyphs may vary between fonts?)