X11 Tooltip exception investigation

[erri120]

On some Linux systems you get a DBus exception The name is not activatable when hovering over an item that will open a tooltip.

Here are my findings:

Using dbus-monitor we can see the messages being send over DBus. When a tooltip opens, this happens:

method call time=1741258811.468008 sender=:1.142 -> destination=com.canonical.AppMenu.Registrar serial=144 path=/com/canonical/AppMenu/Registrar; interface=com.canonical.AppMenu.Registrar; member=RegisterWindow
   uint32 27263131
   object path "/net/avaloniaui/dbusmenu/db202851e5414c6989c5773735428af5"
error time=1741258811.468016 sender=org.freedesktop.DBus -> destination=:1.142 error_name=org.freedesktop.DBus.Error.ServiceUnknown reply_serial=144
   string "The name is not activatable"

The interface that causes the issue is com.canonical.AppMenu.Registrar. The method on that interface RegisterWindow is called by Avalonia X11 for every new window:

https://github.com/AvaloniaUI/Avalonia/blob/603a2bdb43b7e8b2d1c8919f9d0669af7b33f117/src/Avalonia.FreeDesktop/DBusMenuExporter.cs#L110-L122

https://github.com/AvaloniaUI/Avalonia/blob/603a2bdb43b7e8b2d1c8919f9d0669af7b33f117/src/Avalonia.X11/X11Window.cs#L239-L240

The reason we get this for tooltips is because tooltips are implemented as popups, which are implemented as new X11 windows:

https://github.com/AvaloniaUI/Avalonia/blob/603a2bdb43b7e8b2d1c8919f9d0669af7b33f117/src/Avalonia.X11/X11Window.cs#L1221-L1222

As such, when a tooltip opens up, we create a new X11 Window, which tries to register the window on the DBus.

We can either disable DBus native menus or simply don't have tooltips as new X11 windows.