qt5 applications crash when opening file chooser in gtk desktops

[djcj]

Issue is apparently related to qt5-gtk-platformtheme. When you're in a non-Qt desktop environment and you open a file selection dialog from a Qt app it crashes.

See also:
https://bugzilla.redhat.com/show_bug.cgi?id=1392605
https://bugs.archlinux.org/task/57984
https://github.com/TheAssassin/AppImageLauncher/issues/218

In my opinion this is a very serious issue and if newer Qt releases have fixed this it should be backported.

[Dmitry Shachnev (mitya57)]

Can you please specify some more details about this issue:

1) Which Ubuntu release are you using? 18.04 (Bionic), 19.04 (Disco), 19.10 (Eoan) or some other?
2) What is the version of Qt package? I.e. the output of “apt policy qt5-gtk-platformtheme”.
3) What desktop environment does this happen on? Is this X11 or Wayland? If Wayland, is Qt using XWayland or running natively (does this happen when you run app with “-platform wayland”)?
4) What applications does this happen with? If this happens with many applications please name a few, so that I can look for crash logs in our error tracker.

[djcj (djcj)]

Ubuntu 18.04
qt5-gtk-platformtheme 5.9.5+dfsg-0ubuntu2.1
DE is Mate 1.20.0
It's X11, running with “-platform wayland” doesn't work: This application failed to start because it could not find or load the Qt platform plugin "wayland"
in "".

It happens with the thridparty app AppImageLauncher when I run "AppImageLauncher Settings": https://github.com/TheAssassin/AppImageLauncher
The devs of AppImageLauncher said it's a Qt related issue and not an issue with their program.

[Dmitry Shachnev (mitya57)]

I just managed to reproduce the crash locally. Just before the crash, the following lines are printed to stderr:

(AppImageLauncherSettings:27871): Gtk-WARNING **: 21:45:01.935: Could not load a pixbuf from icon theme.
This may indicate that pixbuf loaders or the mime database could not be found.
**
Gtk:ERROR:../../../../gtk/gtkiconhelper.c:494:ensure_surface_for_gicon: assertion failed (error == NULL): Failed to load /usr/share/icons/Adwaita/16x16/status/image-missing.png: Fatal error reading PNG image file: bad parameters to zlib (gdk-pixbuf-error-quark, 0)

I think most important part here is “bad parameters to zlib”. AppImageLauncher uses its own static zlib (lib/AppImageUpdate/lib/zsync2/lib/zlib/libzsync2_libz.a) which is incompatible with public zlib (/lib/x86_64-linux-gnu/libz.so.1) that GTK was compiled against.

Recompiling AppImageLauncher with system zlib should help, but I haven’t found a way to do that. I suggest you to ask AppImageLauncher developer about that.

Attaching a stacktrace for future reference.