Cocoa integration - inconsistent window types/styles

NSWindow does not support 'utility window' style, but NSPanel - does.
If we first create a normal widget, then later make it a Qt::Tool,
we still have NSWindow with (now) invalid 'floating panel' window level
(but no 'utility window' style) - it's a window that stays on top even
when we switch to a different application.

Change-Id: I691bc6f681cdf8bc2a9637444da33e7e6200ee2f
Task-number: QTBUG-45938
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/plugins/platforms/cocoa/qcocoawindow.h

@@ -275,6 +275,7 @@ protected:
     void syncWindowState(Qt::WindowState newState);
     void reinsertChildWindow(QCocoaWindow *child);
     void removeChildWindow(QCocoaWindow *child);
+    bool isNativeWindowTypeInconsistent();
 
 // private:
 public: // for QNSView

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -652,7 +652,7 @@ void QCocoaWindow::setVisible(bool visible)
 
     if (visible) {
         // We need to recreate if the modality has changed as the style mask will need updating
-        if (m_windowModality != window()->modality())
+        if (m_windowModality != window()->modality() || isNativeWindowTypeInconsistent())
             recreateWindow(parent());
 
         // Register popup windows. The Cocoa platform plugin will forward mouse events
@@ -1531,6 +1531,17 @@ void QCocoaWindow::removeChildWindow(QCocoaWindow *child)
     [m_nsWindow removeChildWindow:child->m_nsWindow];
 }
 
+bool QCocoaWindow::isNativeWindowTypeInconsistent()
+{
+    if (!m_nsWindow)
+        return false;
+
+    const bool isPanel = [m_nsWindow isKindOfClass:[QNSPanel class]];
+    const bool usePanel = shouldUseNSPanel();
+
+    return isPanel != usePanel;
+}
+
 void QCocoaWindow::removeMonitor()
 {
     if (!monitor)