QDockAreaLayout: implement widget based add() and remove()

The item_list of a QDockAreaLayoutInfo has abstraction methods for
reading the item list. Adding to and removing from the item list is
done directly, by using the QList api.

Implement an abstraction, that takes a QWidget *.
The argument may either be a QDockWidgetGroupWindow or a QDockWidget.

Task-number: QTBUG-118578
Task-number: QTBUG-118579
Pick-to: 6.5
Change-Id: Ib2ccd7557a21a43b68f184fe4575018f2a97004b
Reviewed-by: David Faure <david.faure@kdab.com>
(cherry picked from commit 2c96f517714eb67a9af821141a90eed68b8714ed)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/widgets/qdockarealayout.cpp

@@ -1018,6 +1018,14 @@ void QDockAreaLayoutInfo::remove(const QList<int> &path)
     }
 }
 
+void QDockAreaLayoutInfo::remove(QWidget *widget)
+{
+    const QList<int> path = indexOf(widget);
+    if (path.isEmpty())
+        return;
+    remove(path);
+}
+
 QLayoutItem *QDockAreaLayoutInfo::plug(const QList<int> &path)
 {
     Q_ASSERT(!path.isEmpty());
@@ -1148,8 +1156,6 @@ bool QDockAreaLayoutInfo::insertGap(const QList<int> &path, QLayoutItem *dockWid
         index = -index - 1;
     }
 
-//    dump(qDebug() << "insertGap() before:" << index << tabIndex, *this, QString());
-
     if (path.size() > 1) {
         QDockAreaLayoutItem &item = item_list[index];
 
@@ -1778,6 +1784,26 @@ QLayoutItem *QDockAreaLayoutInfo::takeAt(int *x, int index)
     return nullptr;
 }
 
+// Add a dock widget or dock widget group window to the item list
+void QDockAreaLayoutInfo::add(QWidget *widget)
+{
+    // Do not add twice
+    if (!indexOf(widget).isEmpty())
+        return;
+
+    if (auto *dockWidget = qobject_cast<QDockWidget *>(widget)) {
+        item_list.append(QDockAreaLayoutItem(new QDockWidgetItem(dockWidget)));
+        return;
+    }
+
+    if (auto *groupWindow = qobject_cast<QDockWidgetGroupWindow *>(widget)) {
+        item_list.append(QDockAreaLayoutItem(new QDockWidgetGroupWindowItem(groupWindow)));
+        return;
+    }
+
+    qFatal("Coding error. Add supports only QDockWidget and QDockWidgetGroupWindow");
+}
+
 void QDockAreaLayoutInfo::deleteAllLayoutItems()
 {
     for (int i = 0; i < item_list.size(); ++i) {
@@ -1971,6 +1997,7 @@ bool QDockAreaLayoutInfo::restoreState(QDataStream &stream, QList<QDockWidget*>
                 if (testing) {
                     //was it is not really added to the layout, we need to delete the object here
                     delete item.widgetItem;
+                    item.widgetItem = nullptr;
                 }
             }
         } else if (nextMarker == SequenceMarker) {

src/widgets/widgets/qdockarealayout_p.h

@@ -109,6 +109,7 @@ public:
     QList<int> gapIndex(const QPoint &pos, bool nestingEnabled,
                             TabMode tabMode) const;
     void remove(const QList<int> &path);
+    void remove(QWidget *widget);
     void unnest(int index);
     void split(int index, Qt::Orientation orientation, QLayoutItem *dockWidgetItem);
 #if QT_CONFIG(tabbar)
@@ -156,6 +157,7 @@ public:
 
     QLayoutItem *itemAt(int *x, int index) const;
     QLayoutItem *takeAt(int *x, int index);
+    void add(QWidget *widget);
     void deleteAllLayoutItems();
 
     QMainWindowLayout *mainWindowLayout() const;

src/widgets/widgets/qmainwindowlayout.cpp

@@ -1224,7 +1224,7 @@ bool QMainWindowLayoutState::restoreState(QDataStream &_stream,
                             if (info == nullptr) {
                                 continue;
                             }
-                            info->item_list.append(QDockAreaLayoutItem(new QDockWidgetItem(w)));
+                            info->add(w);
                         }
                     }
                 }