Add function to safely access the shared application on Apple platforms

Change-Id: I52910309ba94d84d69f049b5c1990f1f866e1698
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/corelib/kernel/qcore_mac_objc.mm

@@ -167,6 +167,28 @@ bool qt_apple_isApplicationExtension()
     return isExtension;
 }
 
+#if !defined(QT_BOOTSTRAPPED) && !defined(Q_OS_WATCHOS)
+AppleApplication *qt_apple_sharedApplication()
+{
+    // Application extensions are not allowed to access the shared application
+    if (qt_apple_isApplicationExtension()) {
+        qWarning() << "accessing the shared" << [AppleApplication class]
+            << "is not allowed in application extensions";
+
+        // In practice the application is actually available, but the the App
+        // review process will likely catch uses of it, so we return nil just
+        // in case, unless we don't care about being App Store compliant.
+#if QT_CONFIG(appstore_compliant)
+        return nil;
+#endif
+    }
+
+    // We use performSelector so that building with -fapplication-extension will
+    // not mistakenly think we're using the shared application in extensions.
+    return [[AppleApplication class] performSelector:@selector(sharedApplication)];
+}
+#endif
+
 #ifdef Q_OS_MACOS
 /*
     Ensure that Objective-C objects auto-released in main(), directly or indirectly,

src/corelib/kernel/qcore_mac_p.h

@@ -160,6 +160,19 @@ QDebug operator<<(QDebug debug, const QMacAutoReleasePool *pool);
 Q_CORE_EXPORT void qt_apple_check_os_version();
 Q_CORE_EXPORT bool qt_apple_isApplicationExtension();
 
+#if !defined(QT_BOOTSTRAPPED) && !defined(Q_OS_WATCHOS)
+QT_END_NAMESPACE
+# if defined(Q_OS_MACOS)
+Q_FORWARD_DECLARE_OBJC_CLASS(NSApplication);
+using AppleApplication = NSApplication;
+# else
+Q_FORWARD_DECLARE_OBJC_CLASS(UIApplication);
+using AppleApplication = UIApplication;
+# endif
+QT_BEGIN_NAMESPACE
+Q_CORE_EXPORT AppleApplication *qt_apple_sharedApplication();
+#endif
+
 // --------------------------------------------------------------------------
 
 #if !defined(QT_BOOTSTRAPPED) && (QT_MACOS_PLATFORM_SDK_EQUAL_OR_ABOVE(__MAC_10_12) || !defined(Q_OS_MACOS))

src/corelib/kernel/qeventdispatcher_cf.mm

@@ -72,17 +72,12 @@ QT_NAMESPACE_ALIAS_OBJC_CLASS(RunLoopModeTracker);
     if (self = [super init]) {
         m_runLoopModes.push(kCFRunLoopDefaultMode);
 
-        [[NSNotificationCenter defaultCenter]
-            addObserver:self
-            selector:@selector(receivedNotification:)
-            name:nil
-#ifdef Q_OS_OSX
-            object:[NSApplication sharedApplication]];
-#elif defined(Q_OS_WATCHOS)
-            object:[WKExtension sharedExtension]];
-#else
-            // Use performSelector so this can work in an App Extension
-            object:[[UIApplication class] performSelector:@selector(sharedApplication)]];
+#if !defined(Q_OS_WATCHOS)
+        if (!qt_apple_isApplicationExtension()) {
+            [[NSNotificationCenter defaultCenter]
+                addObserver:self selector:@selector(receivedNotification:)
+                name:nil object:qt_apple_sharedApplication()];
+        }
 #endif
     }