qDebug not displaying anything

The solution is simple: add CONFIG += console to your .pro file and rebuild the whole project.

Solution for me, As stated in https://bugzilla.redhat.com/show_bug.cgi?id=1227295#c10 was :

1. look for qtlogging.ini in /etc/xdg/QtProject/ .
2. edit the current (or create the file qtlogging.ini if missing)

[Rules]
*.debug=false

to

[Rules]
*.debug=true
qt.*.debug=false

3. recompile and check!