IBus ForwardKeyEvent() signal cannot be received

Original bug report is https://bugzilla.redhat.com/show_bug.cgi?id=1368757

I try to implement "ForwardKeyEvent" signal in QT5 IBus module and I investigated libibusplatforminputcontextplugin.so but it cannot receive ForwardKeyEvent dbus signal.

When "CommitText" signal is received, QIBusInputContextProxy::qt_static_metacall() receives the signal correctly in the trace stack:

#0 0x00007f0730053ff9 in QIBusPlatformInputContext::commitText(QDBusVariant const&) (this=0x2417930, text=...) at qibusplatforminputcontext.cpp:257
#1 0x00007f0730061b3b in QIBusPlatformInputContext::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) (_o=0x2417930, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x7ffeffa60440)
at .moc/moc_qibusplatforminputcontext.cpp:117
#2 0x00007f074d2367b1 in QMetaObject::activate(QObject*, int, int, void**) () at /lib64/libQt5Core.so.5
#3 0x00007f07300644e0 in QIBusInputContextProxy::CommitText(QDBusVariant const&) (this=0x2411a50, _t1=...) at .moc/moc_qibusinputcontextproxy.cpp:515
#4 0x00007f073006317b in QIBusInputContextProxy::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) (_o=0x2411a50, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x7ffeffa60880) at .moc/moc_qibusinputcontextproxy.cpp:218
#5 0x00007f0730064458 in QIBusInputContextProxy::qt_metacall(QMetaObject::Call, int, void**) (this=0x2411a50, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x7ffeffa60880) at .moc/moc_qibusinputcontextproxy.cpp:501
#6 0x00007f073aeb6640 in QDBusConnectionPrivate::deliverCall(QObject*, int, QDBusMessage const&, QVector<int> const&, int) () at /lib64/libQt5DBus.so.5
#7 0x00007f074d237879 in QObject::event(QEvent*) ()
at /lib64/libQt5Core.so.5
#8 0x00007f074cabdecc in QApplicationPrivate::notify_helper(QObject*, QEvent*
) () at /lib64/libQt5Widgets.so.5
#9 0x00007f074cac5671 in QApplication::notify(QObject*, QEvent*) ()
at /lib64/libQt5Widgets.so.5
#10 0x00007f074d20f7aa in QCoreApplication::notifyInternal2(QObject*, QEvent*) () at /lib64/libQt5Core.so.5
#11 0x00007f074d211e90 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () at /lib64/libQt5Core.so.5
#12 0x00007f074d25d6a3 in postEventSourceDispatch(_GSource*, int (void*), void*) () at /lib64/libQt5Core.so.5
#13 0x00007f07485e3e42 in g_main_context_dispatch ()
at /lib64/libglib-2.0.so.0
#14 0x00007f07485e41c0 in g_main_context_iterate.isra ()
at /lib64/libglib-2.0.so.0
#15 0x00007f07485e426c in g_main_context_iteration ()
at /lib64/libglib-2.0.so.0
#16 0x00007f074d25d71f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /lib64/libQt5Core.so.5
#17 0x00007f074d20e73a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /lib64/libQt5Core.so.5
#18 0x00007f074d21623c in QCoreApplication::exec() ()
at /lib64/libQt5Core.so.5
#19 0x000000000040225d in main(int, char**) (argc=1, argv=0x7ffeffa611c8)
at qt_entry.c:102

But QIBusInputContextProxy::qt_static_metacall() cannot receive "ForwardKeyEvent" signal.

Do you have any ideas about which part blocks the signal?

You can test "ForwardKeyEvent" signal in any IBus engines.
E.g. ibus-tmpl's python engine can have the following test:
https://github.com/ibus/ibus-tmpl

— /usr/share/ibus-tmpl/engine.py.orig
+++ /usr/share/ibus-tmpl/engine.py
@@ -49,6 +49,10 @@ class EngineEnchant(IBus.Engine):
if not is_press:
return False

+ if keyval == IBus.KEY_j:
+ print('test forward_key_event', keyval, keycode, state)
+ self.forward_key_event(keyval, keycode, state)
+ return True
if self.__preedit_string:
if keyval == keysyms.Return:
self._commit_string(self._preedit_string)