QMainWindow: fix restoreState() for toolbars

Restoring the toolbar state of a QMainWindow could not update
QWidgetPrivate::widgetItem for the QToolBar, because at that point it
was still holding the pointer to the widgetItem of the previous state.
Later on, when the new state was successfully applied, the previous
state was deleted, and the corresponding widgetItem was reset to
nullptr.

This patch explicitly resets the QToolBar's widgetItem while updating
the state, so that it is later correctly updated while creating a
new QWidgetItemV2.

Fixes: QTBUG-102395
Pick-to: 6.4 6.3 6.2 5.15
Change-Id: I17613d62423edcc0faf85ecb0a714865a50d87e8
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/widgets/widgets/qtoolbararealayout.cpp b/src/widgets/widgets/qtoolbararealayout.cpp
index 09929e7234..adddfbc529 100644
--- a/src/widgets/widgets/qtoolbararealayout.cpp
+++ b/src/widgets/widgets/qtoolbararealayout.cpp
@@ -1328,6 +1328,10 @@ bool QToolBarAreaLayout::restoreState(QDataStream &stream, const QList<QToolBar*
             }
 
             if (applyingLayout) {
+                // Clear the previous widgetItem for the toolBar, so that it's
+                // assigned correctly in QWidgetItemV2 constructor.
+                auto *toolBarPrivate = QWidgetPrivate::get(toolBar);
+                toolBarPrivate->widgetItem = nullptr;
                 item.widgetItem = new QWidgetItemV2(toolBar);
                 toolBar->setOrientation(floating ? ((shown & 2) ? Qt::Vertical : Qt::Horizontal) : dock.o);
                 toolBar->setVisible(shown & 1);