QMenuPrivate::init() calls QPlatformTheme::createPlatformMenu() to
create a platform menu, but on Linux, that returns null for now.
QSystemTrayIcon::setContextMenu() results in recursive calls to
QSystemTrayIconPrivate::addPlatformMenu() which then calls
QDBusTrayIcon::createMenu() for the context menu and each submenu.
However if a submenu is added afterwards, a corresponding platform
menu is not immediately created. Now copyActionToPlatformItem()
will detect and create the missing platform submenu, by calling
a new method: DBusPlatformMenu::createSubMenu(). This is because
there is no way of knowing that it's a tray-specific context menu
(which is so far the only case in which we use DBusPlatformMenu).
So, QPlatformMenu::createSubMenu() needs to exist as a new
QPA interface for this use case.
Task-number: QTBUG-45803
Change-Id: Ib319e873082196515ea0580d70d069099cf2c175
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>
d8bfd812c3