Running newer versions of Gnome (on Wayland), you can't restart the shell with Alt+F2, entering r & then Enter – which used to restart the shell without logging the user out of the session.
More recently, on Fedora systems you used to be able to restart by sending SIGHUP to the gnome-shell process – using top or whatever. However now on Fedora 28 atleast this kills the session and sends the user back to the login screen.
Restarting the shell leaving the session intact is very useful in the event of installing/modifying an extension, or (hopefully not anymore!) having to restart gnome due to it bugging out and using 100% CPU. Is there a current alternative please?
EDIT: I have also tried SIGQUIT, and gnome-shell --replace (with export DISPLAY=:0 if on a TTY), and the result is to still be kicked back to the login screen
Best Answer
In an Xorg session one can restart GNOME shell without losing application state as applications are running against a separate server (X). But unlike Xorg in case of a Wayland session GNOME shell is not separate from the Wayland protocol, GNOME itself acts as the display server.
So there isn't any way to restart GNOME shell in Wayland without losing application state as the display server also goes down. It's similar to restarting X server in an Xorg session.
That is the reason why this shell restart option is disabled in Wayland (recall that usually the key sequence to kill the X server is also disabled by default in the Xorg session) and there will probably never be any non-destructive way to restart GNOME shell in Wayland.