Porting themes to Plasma 6

SonicDE's desktop is based on Plasma 6, so global themes written for Plasma 5 need several changes to work on it.

#Strict theme packaging

All themes are now handled as a kpackage, which means a metadata.json file is required. The metadata.json file of a global theme needs the JSON key "KPackageStructure": "Plasma/LookAndFeel", otherwise it isn't shown in the "Global Theme" settings.

#No symlinks allowed

Because of the kpackage format, symlinks can no longer be used to load a global theme. Global themes must be in one of the two main folders, /usr/share/plasma/look-and-feel and ~/.local/share/plasma/look-and-feel.

#Renamed QML imports

Various QML imports have been renamed, so existing Plasma 5 theme QML files need to be edited accordingly. The sonic-workspace and sonic-silver repositories have current examples.

Notable changes are QtGraphicalEffects becoming Qt5Compat.GraphicalEffects, and PlasmaCore.DataSource becoming org.kde.plasma.plasma5support.DataSource, but there are many others.

#Changes for desktop layout scripts

Layout scripts such as contents/layouts/org.kde.plasma.desktop-layout.js have not changed very much, and the API mostly stays the same. The version of the desktop scripting API, frequently used in boilerplate such as var plasma = getApiVersion(1);, has not changed. The configuration options for panels and widgets have been adapted for new features, though, such as floating panels. See sonic-silver's layout templates for examples.

#Changes for custom lock screens

Custom lock screens are normally in contents/lockscreen/LockScreen.qml. The authenticator object provided by the screen locker has changed, to support passwordless authentication. If your theme uses a Connections { target: authenticator }, its handlers need adapting: onPrompt became onPromptChanged, and onInfoMessage and onErrorMessage became onInfoMessageChanged and onErrorMessageChanged.

Authentication is now started with authenticator.startAuthenticating() instead of authenticator.tryUnlock(). The onPromptForSecret handler became onPromptForSecretChanged. The password is still sent with authenticator.respond(myPasswordInput.text).

#Changes for custom window switchers

If your theme has a window switcher (called a TabBox in SonicWin), it is affected by the renamed QML imports too. There are also specific SonicWin renames, such as KWin.WindowThumbnailItem becoming KWin.WindowThumbnail; see the sonic-win source repository.