Cocoa: parent windows shows on screen when they should be hidden

The reason is the cocoa method that adds a window as a child of another,
it ends up showing both the parent and the child window regardless.
And this could in some cases also cause a crash.
So we therefore need to be careful when calling that function, and be
sure that the parent is actually visible. In addition, addChildWindow
reset the stacking level of the child window, and made e.g. normal
child windows pop in front of tool child windows. This could easily
be seen in e.g. Designer.

Task-number: QTBUG-12866
Reviewed-by: prasanth
(cherry picked from commit cc6dc0aeefde881a95f5fea2b26f2f3d7bdc6e15)

1 files changed, 16 insertions, 6 deletions

diff --git a/src/gui/kernel/qwidget_mac.mm b/src/gui/kernel/qwidget_mac.mm
index c2af6af..65128ec 100644
--- a/src/gui/kernel/qwidget_mac.mm
+++ b/src/gui/kernel/qwidget_mac.mm
@@ -2796,10 +2796,16 @@ void QWidgetPrivate::setSubWindowStacking(bool set)
 
     if (QWidget *parent = q->parentWidget()) {
         if (parent->testAttribute(Qt::WA_WState_Created)) {
-            if (set)
-                [qt_mac_window_for(parent) addChildWindow:qt_mac_window_for(q) ordered:NSWindowAbove];
-            else
+            if (set) {
+                if (parent->isVisible()) {
+                    NSWindow *childwin = qt_mac_window_for(q);
+                    int childLevel = [childwin level];
+                    [qt_mac_window_for(parent) addChildWindow:childwin ordered:NSWindowAbove];
+                    [childwin setLevel:childLevel];
+                }
+            } else {
                 [qt_mac_window_for(parent) removeChildWindow:qt_mac_window_for(q)];
+            }
         }
     }
 
@@ -2807,10 +2813,14 @@ void QWidgetPrivate::setSubWindowStacking(bool set)
     for (int i=0; i<widgets.size(); ++i) {
         QWidget *child = widgets.at(i);
         if (child->isWindow() && child->testAttribute(Qt::WA_WState_Created) && child->isVisibleTo(q)) {
-            if (set)
-                [qt_mac_window_for(q) addChildWindow:qt_mac_window_for(child) ordered:NSWindowAbove];
-            else
+            if (set) {
+                NSWindow *childwin = qt_mac_window_for(child);
+                int childLevel = [childwin level];
+                [qt_mac_window_for(q) addChildWindow:childwin ordered:NSWindowAbove];
+                [childwin setLevel:childLevel];
+            } else {
                 [qt_mac_window_for(q) removeChildWindow:qt_mac_window_for(child)];
+            }
         }
     }
 }