The update didn’t fix the issue, but I noticed I did the workaround wrong.
The correct workaround is:
rm -r ~/snap/snapname/common/.cache/fontconfig
touch ~/snap/snapname/common/.cache/fontconfig
instead of the ~/snapname/current/.config/fontconfig which I did by accident. That works atleast for now.
However, that workaround is not ideal as it causes the dialog boxes to take a long time to open up every time you launch the program.
I have a similar issue on Ubuntu Core 18 with squares instead of fonts and not working icons in my gtkmm application using gnome-3-28. My application is built with the core 18 image. Snap works fine on Ubuntu16.04 and ubuntu18.04 but it fails on Ubuntu core 18 with mir-kiosk and wayland. Non of the workarounds above works for me in this case. Also when I run application I got warnings:
gtk-update-icon-cache: The generated cache was invalid.
WARNING: icon cache generation failed for /root/snap/gsapples/x1/.local/share/icons/Humanity-Dark
gtk-update-icon-cache: Could not rename /root/snap/gsapples/x1/.local/share/icons/Humanity/.icon-theme.cache to /root/snap/gsapples/x1/.local/share/icons/Humanity/icon-theme.cache: No such file or directory
WARNING: icon cache generation failed for /root/snap/gsapples/x1/.local/share/icons/Humanity
note that the gnome extension only ships the dejavu font, if your kiosk app uses or expects anything else you should ship the expected fonts in your app snap … (and make sure the fonts can be found in the font path).
also recent snapcraft generates a configure hook for you that calls fc-cache i think, not sure how that works in case of kiosk snaps … (the only one i have that is using the gnome extension atm doesnt need any fonts (https://github.com/ogra1/picviewer-kiosk))
Right now I’m using sans font, which counts as dejavu I think - so it is not non default font problem.
For the similar test to the one that was done earlier in this thread I installed Inkscape in ubuntu core 18 and effect is simillar - no fonts. No one really needs Inkscape in Ubuntu Core so it is not a problem in itself - but it shows that “build once and install anywhere” does not work in Ubuntu Core for Gtk applications.
I use snapcraft 4.4.2, so I think that this is up to date version. This configure hook, is it something that I have to specify in my snapcraft.yaml file explicitly or is it something that suppose to just work in newer snapcraft version?
as i understood it should just work (though my own desktop related snaps simply already use that config hook and their own font cache (i.e. see the zoom-snap) similar to what inkscape does) … if inkscape does not work this indicates that the fix wont work on core either …
OTOH i dont think anyone ever stated anything about “build once and install everywhere” in regards to Ubuntu Core which is completely focused on embedded, IoT and industrial currently. Graphical apps o Core are expected to be standalone, separately packaged kiosk apps that ship everything necessary along in their package.
Ubuntu Core does not even have a user concept ATM and is lacking any pieces to spawn a user session beyond providing an ssh login for developers (the typical use-case is completely user-less, managed through an agent snap that is hooked up to a central fleet management service or as an appliance with a minimal initial configuration tool)
Ok, I understand. I just wanted to show to you my error because I thought it is simillar to the error from this thread. I don’t think that every desktop app should work out of the box on Ubuntu Core system - I understand the system purpouse and its limitations. In earlier post though you stated that gnome extensions package dejavu fonts inside. The fact that these fonts are not displayed in installed app looks like the error worth to be mention here, especially that official documentation and tutorials claim to support gtk on Ubuntu Core systems.
well, i actually think they should 
(to have a kiosk picviwewer, why not be able to install the eog snap and be able to call "snap set eog kiosk=true) but today it isnt like that and you need to snap the whole set of supporting bits inside your package …
gtk apps work fine on Ubuntu Core on top of mir-kiosk as do electron, java, Qt or nodejs apps but the packaging has rather different requirements and you need to explicitly include all bits and pieces inside your kiosk snap to make it work, it isnt just a seamless “install this desktop app” but rather a “create a kiosk snap from scratch including all desktop pieces the app requires”
note that the gnome extensions are not being tested (or designed) in this context currently, so yes, for a future where we can simply use the extensions on core this is definitely worthy to be mentioned but will not help the issue with desktop systems (where the reason likely is a version discrepancy between the fontconfig running on the desktop environment vs the version running inside the snap package)
VSCodium still not fixed.
https://github.com/VSCodium/vscodium/issues/426#issuecomment-734314190
Hi, I think my snap packaging of Folding at Home has some users hitting the same problem -> Missing fonts issue
Same issue in openSUSE Tumbleweed (KDE desktop). Fonts appear as squares in dialog boxes, within the following snaps:
hey-mail, teams, telegram-desktop, standard-notes
I’ve had a user who experienced this issue even after upgrading to use Gnome extensions built with 4.4+; the old fix of regenerating font config caches didn’t work, instead, but this seemed to have some effect.
sed -i '/cachedir prefix="xdg"/ d' ~/snap/example-snap/current/.config/fontconfig/fonts.conf
(Change the snap name as relevant)
It’ll reset everytime the snap upgrades to a new revision and need to be run again. A substantial amount of font caches will still exist in $SNAP_COMMON, mitigating any delay this would probably cause.
Probably the same as what starfox saw, but on arch rather than openSUSE. Dialog boxes that show up when clicking the teams tray have all text replaced with squares, while general text within the app itself works fine.
Switching to teams from AUR fixed it.
This worked for me as well, for Signal, on Fedora 33.
I confirm that this works for Signal, on Fedora 33.
@ijohnson can you expand what you mean by gnome-extensions? Do you mean upgrading to using snapcraft 4.4 and using this extension? https://snapcraft.io/docs/gnome-3-28-extension
Or do you mean something different?
Yes that’s exactly what I meant
Any recommendation for those using the GTK2 desktop part?
My snap of Folding at Home has the same issue: https://github.com/fcole90/fah-snap/issues/12
Upgrading to core20 seems to alleviate this issue in a lot of cases so might be worth trying even in the case of GTK2.
It could potentially come back in the future though, my knowledge of Linux fonts isn’t amazing, but I think the tl;dr is core18 fontconfig libraries are incompatible with some newer fontconfig caches, core20 has newer fontconfig, hence compatible with newer caches; in the future core20 fontconfig might be obsoleted by something newer and the problem may come back but for the time being it’s worth trying.