cocoa: don't override NSApplication-sendEvent if configured as AA_MacPluginApplication

Change-Id: I48cebbcb814ee8e97583c3165e7cb668077cfbad
Task-number: QTBUG-40409
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

src/corelib/global/qnamespace.qdoc

@@ -125,7 +125,7 @@
            to author a plugin. This includes avoiding loading our nib for the main
            menu and not taking possession of the native menu bar. When setting this
            attribute to true will also set the AA_DontUseNativeMenuBar attribute
-           to true.
+           to true. It also disables native event filters.
 
     \value AA_DontUseNativeMenuBar All menubars created while this attribute is
            set to true won't be used as a native menubar (e.g, the menubar at

src/corelib/kernel/qcoreapplication.cpp

@@ -2528,6 +2528,9 @@ void QCoreApplication::removeLibraryPath(const QString &path)
     \note The filter function set here receives native messages,
     i.e. MSG or XCB event structs.
 
+    \note Native event filters will be disabled when the application the
+    Qt::AA_MacPluginApplication attribute is set.
+
     For maximum portability, you should always try to use QEvents
     and QObject::installEventFilter() whenever possible.
 
@@ -2537,6 +2540,11 @@ void QCoreApplication::removeLibraryPath(const QString &path)
 */
 void QCoreApplication::installNativeEventFilter(QAbstractNativeEventFilter *filterObj)
 {
+    if (QCoreApplication::testAttribute(Qt::AA_MacPluginApplication)) {
+        qWarning("Native event filters are not applied when the Qt::AA_MacPluginApplication attribute is set");
+        return;
+    }
+
     QAbstractEventDispatcher *eventDispatcher = QAbstractEventDispatcher::instance(QCoreApplicationPrivate::theMainThread);
     if (!filterObj || !eventDispatcher)
         return;

src/plugins/platforms/cocoa/qcocoaapplication.mm

@@ -189,6 +189,12 @@ QT_BEGIN_NAMESPACE
 
 void qt_redirectNSApplicationSendEvent()
 {
+    if (QCoreApplication::testAttribute(Qt::AA_MacPluginApplication))
+        // In a plugin we cannot chain sendEvent hooks: a second plugin could
+        // store the implementation of the first, which during the program flow
+        // can be unloaded.
+        return;
+
     if ([NSApp isMemberOfClass:[QNSApplication class]]) {
         // No need to change implementation since Qt
         // already controls a subclass of NSApplication
@@ -209,6 +215,10 @@ void qt_redirectNSApplicationSendEvent()
 
 void qt_resetNSApplicationSendEvent()
 {
+    if (QCoreApplication::testAttribute(Qt::AA_MacPluginApplication))
+        return;
+
+
     qt_cocoa_change_back_implementation([NSApplication class],
                                          @selector(sendEvent:),
                                          @selector(QT_MANGLE_NAMESPACE(qt_sendEvent_original):));