[QTBUG-27420] Make Q{Box,Grid,Form}Layout::takeAt() unparent a nested layout

QStackedLayout doesn't have support for QLayout, only QWidget, so
the issue doesn't arise there.

(cherry-picked from qtbase/716d33d2a73ade42eb31be3e8ecbaeecdd5ddd21)
(only change: s/reset()/clear()/ in the tests)

Reported-by: Johannes Schaub
Task-number: QTBUG-27420

Change-Id: I7f3c4b1996e954428c00d4dda1095712efa91367
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/src/gui/kernel/qgridlayout.cpp b/src/gui/kernel/qgridlayout.cpp
index cb0dc90..3f11faa 100644
--- a/src/gui/kernel/qgridlayout.cpp
+++ b/src/gui/kernel/qgridlayout.cpp
@@ -156,15 +156,20 @@ public:
             return 0;
     }
     inline QLayoutItem *takeAt(int index) {
-        QLayoutItem *item = 0;
+        Q_Q(QGridLayout);
         if (index < things.count()) {
-            QGridBox *b = things.takeAt(index);
-            if (b) {
-                item = b->takeItem();
+            if (QGridBox *b = things.takeAt(index)) {
+                QLayoutItem *item = b->takeItem();
+                if (QLayout *l = item->layout()) {
+                    // sanity check in case the user passed something weird to QObject::setParent()
+                    if (l->parent() == q)
+                        l->setParent(0);
+                }
                 delete b;
+                return item;
             }
         }
-        return item;
+        return 0;
     }
 
     void getItemPosition(int index, int *row, int *column, int *rowSpan, int *columnSpan) {