bug#57962: 29.0.50; Odd font choices

[Lars Ingebrigtsen]

I'm not sure when this started happening, but probably not more than a
month ago.

An image to illustrate the problem:

>From "emacs -Q" (but not with my normal font choices), the font used for
the help-key-binding face is larger than the rest of the text, making
various things kinda ugly.

The normal text uses:

    ftcrhb:-DAMA-Ubuntu Mono-regular-normal-normal-*-45-*-*-*-m-0-iso10646-1 
(#x55)

The keyboard text is:

    ftcrhb:-PfEd-DejaVu Sans 
Mono-regular-normal-normal-*-45-*-*-*-m-0-iso10646-1 (#x52)

And the help-key-binding face is:

(defface help-key-binding
  '((((class color) (min-colors 88) (background light))
[...]
     :inherit fixed-pitch)

and

(defface fixed-pitch
  '((t :family "Monospace"))
  "The basic fixed-pitch face."
  :group 'basic-faces)

So this chooses a different font than

(defface default
  '((t nil)) ; If this were nil, face-defface-spec would not be set.
  "Basic default face."
  :group 'basic-faces)

?

Hm...  but on the other hand, perhaps I started seeing this because I
switched from Debian to Ubuntu?  I'm seeing the same in Emacs 28 if I
use the fixed-pitch face there (but in Emacs 28, help-key-binding
doesn't inherit from fixed-pitch).

So it's possibly that we've just never noticed before, because we
haven't used `fixed-pitch' in these contexts before.

In any case, it's unfortunate that it doesn't look very pleasant with
"emacs -Q" in a major distribution like Ubuntu, so I think we should do
something, but I'm not sure what.



In GNU Emacs 29.0.50 (build 61, x86_64-pc-linux-gnu, GTK+ Version
 3.24.33, cairo version 1.16.0) of 2022-09-16 built on joga
Repository revision: 7d39453fd64e355526291b0ca5672e838de5fb58
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101003
System Description: Ubuntu 22.04.1 LTS

Configured using:
 'configure -C'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB