[Bug 1872800] [NEW] Problem with default monospace font

[Kenneth Hanson]

Public bug reported:

In Kubuntu 20.04, fontconfig refuses to prefer Noto Mono, Hack, and
other monospace fonts over Noto Sans Mono, Noto Sans Mono CJK, and other
non-latin fonts.

I discovered the problem after uninstalling all Noto fonts except for
Noto Sans CJK and Noto Serif CJK. I prefer to have only the Latin and
CJK fonts, as I don't need any other languages. Non-Latin fonts are
currently included in the same packages as the basic Latin fonts, so I
use manually installed Noto Sans/Serif/Mono fonts, which do not include
the non-Latin fonts. This worked fine in Kubuntu 19.10.

Now, fontconfig insists on using Noto Sans Mono CJK SC for the default
monospace font. This is true even though I have Noto Mono set as my
monospace font in the KDE font settings. It remains true even using the
default settings, which use Hack for the monospace font. Because of
this, applications like Firefox use an incorrect font.

If I install Noto Sans Mono, either manually or via the Ubuntu package,
fontspec insists on using that font instead.

I determined that at least part of the problem comes from a font configuration file:
  kubuntu-settings-desktop: /etc/fonts/conf.avail/56-kubuntu-noto.conf

This file specifies Noto Sans Mono, Noto Sans Mono CJK, and a host of
random non-Latin fonts, and even symbols and emoji, over normal fonts
like DejaVu Sans Mono. Noto Mono and Hack are absent entirely.

`dpkg -S` informs me that the package for this file is `kubuntu-
settings-desktop`, so I am reporting the bug here. My version is
20.04.9.

There seems to be an additional problem with KDE System Settings, since
I would expect the fonts I specify there to take precedence over system
defaults. But I don't understand fontconfig very well, so I will wait
for someone who knows better to confirm.

Additional info:

Noto Mono and Hack are recognized by fontconfig.

$ fc-match -a "monospace" | grep --line-number -e "Noto Mono"
128:NotoMono-Regular.ttf: "Noto Mono" "Regular"

$ fc-match -a "monospace" | grep --line-number -e "Hack"     
44:Hack-Regular.ttf: "Hack" "Regular"

I already purged my home directory of any `fonts.conf` files and
anything related to fontconfig except for my manually installed font
files.

** Affects: kubuntu-settings (Ubuntu)
     Importance: Undecided
         Status: New

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Title:
  Problem with default monospace font

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