Restore applications contents at login under Wayland

[Stefano Crocco]

Hello to everyone,
after the release of Plasma 6.8 which removed X11 support, I started 
investigating whether it was possible for applications to support session 
restoring under Wayland, so that I could add that functionality to Konqueror.

>From what I gathered searching on-line, Wayland and KWin automatically restore 
windows (including their position and size) but restoring window contents is 
up to the applications. However, none of the pages containing that 
statement gave hints about how the applications should do so.

Since Konqueror already saves its state at regular intervals to be able to 
restore it in case of crashes, I hoped to be able to reuse that functionality. 
As far as I can tell, however, there's no way to do so: when Konqueror is 
closed correctly, it removes the saved state because in that case it shouldn't 
be restored. However, looking at the Qt and Frameworks documentation, I 
couldn't find a way to distinguish between the user closing the application and 
the Wayland session closing. I thought that 
QGuiApplication::commitDataRequest() would be emitted, since (according to 
https://doc.qt.io/qt-6/session.html) it is also supported on Windows and 
macOS, but my tests show this is not the case.

My question is: is there a way for application to restore contents on Wayland 
or does this require support from Qt or Frameworks which isn't yet there? If 
it can be done now, where can I find information on how to do so?

Thanks in advance

Stefano