SUMMARY When Breeze GTK is preloaded along with the rest of Plasma, the Plasma desktop doesn't automatically configure Breeze GTK as the default. I would expect that when Breeze GTK is installed, it should be automatically used. OBSERVED RESULT The KCM shows a blank entry, and GTK falls back to Adwaita. EXPECTED RESULT The KCM shows Breeze selected, and GTK uses Breeze. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Fedora Linux 35 (KDE Plasma) (available in About System) KDE Plasma Version: 5.23.3 KDE Frameworks Version: 5.88.0 Qt Version: 5.15.2 ADDITIONAL INFORMATION Downstream KDE SIG issue: https://pagure.io/fedora-kde/SIG/issue/141
It looks like this KCM's Defaults button isn't active on the GTK page. Perhaps the problem is that we have no default value...?
Yep, that seems to be it. The combobox gets its default value from GtkPage::gtkThemeFromConfig() ...Which returns m_gtkConfigInterface.gtkTheme().value(); ...And m_gtkConfigInterface is a DBus interface that queries org.kde.GtkConfig /GtkConfig So we are not going through the kconfigxt mechanism here and are implicitly relying on the setting to have a default value from GTK-land. But it may very well not. And it certainly won't be set to Breeze by default. I wonder how we should fix this, though. We can't just unconditionally set Breeze to be the default since it might not be installed. Maybe we can do that if it uses a fallback mechanism when Breeze isn't installed? There is also the following code: void GtkPage::defaults() { Q_EMIT selectGtkThemeInCombobox(QStringLiteral("Breeze")); } Clicking the "Defaults" button works and resets the combobox to show Breeze. However the button is disabled on the GTK page and does not become enabled when you change anything on the GTK page; it only becomes enabled when something on the other page is changed.
FYI KConfigXT allows to "compute" a default value using C++ code, so we could probably check whether breeze is installed from there? Maybe that helps