QDBus: Document that calls to local objects are never asynchronous

This is a limitation of current implementation.

Task-number: QTBUG-92107
Change-Id: Idb1543f432348e66ca20aa67a2498034c2f05fa6
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/dbus/qdbusabstractinterface.cpp

@@ -500,6 +500,9 @@ QDBusMessage QDBusAbstractInterface::callWithArgumentList(QDBus::CallMode mode,
 
     Normally, you should place calls using asyncCall().
 
+    \note Method calls to objects registered by the application itself are never
+    asynchronous due to implementation limitations.
+
     \threadsafe
 */
 QDBusPendingCall QDBusAbstractInterface::asyncCallWithArgumentList(const QString& method,
@@ -536,6 +539,9 @@ QDBusPendingCall QDBusAbstractInterface::asyncCallWithArgumentList(const QString
     parameter as its last or only parameter.  The \a errorMethod must
     have a QDBusError as its only parameter.
 
+    \note Method calls to objects registered by the application itself are never
+    asynchronous due to implementation limitations.
+
     \since 4.3
     \sa QDBusError, QDBusMessage
  */
@@ -763,6 +769,9 @@ void QDBusAbstractInterface::internalPropSet(const char *propname, const QVarian
 
     \note Before Qt 5.14, this function accepted a maximum of just eight (8) arguments.
 
+    \note Method calls to local \c{QDBusServer}'s are never asynchronous
+    due to implementation limitations.
+
     \sa asyncCallWithArgumentList()
 */
 

src/dbus/qdbusconnection.cpp

@@ -431,6 +431,9 @@ QDBusMessage QDBusConnection::call(const QDBusMessage &message, QDBus::CallMode
 
     See the QDBusInterface::asyncCall() function for a more friendly way
     of placing calls.
+
+    \note Method calls to objects registered by the application itself are never
+    asynchronous due to implementation limitations.
 */
 QDBusPendingCall QDBusConnection::asyncCall(const QDBusMessage &message, int timeout) const
 {