KWin's TabBox (Alt+Tab) implementation uses a QAbstractItemModel which is exposed to QML. The implementation provides a Q_INVOKABLE longestCaption() method (can be found in kde-workspace/kwin/tabbox/clientmodel.(h|cpp)).

For virtual desktops there is another QAbstractItemModel which is found in desktopmodel.(h|cpp). This model does not provide the longestCaption() method, but it is used from some QML switchers.

This task is to implement this method with a similar semantic in the DesktopModel.

For this task a build-environment of kde-workspace on top of Qt5 and KF5 is required. If you don't have such a setup follow the steps of https://community.kde.org/Frameworks/Building - be aware that this is time consuming. Please only claim the task if you have this setup.