a11y: add more nullptr checks for the view

Interface implementations related to child navigation might be
called while the object is getting destroyed, in which case the view
might already be degenerated to a widget. In that case, qobject_cast
will fail and we would dereference a nullptr later.

Prevent that by adding more nullptr checks. As a drive-by, reuse the
down-cast pointer in more of the implementation.

Pick-to: 6.5
Fixes: QTBUG-129582
Change-Id: I06a80576a5d71150787f493e2b6c9a58696eac99
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
Reviewed-by: Dheerendra Purohit <dheerendra@pthinks.com>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 9965f9a191a426e65e32b3f833f2aedcc19ef405)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/accessible/itemviews.cpp

@@ -545,6 +545,8 @@ QAccessibleInterface *QAccessibleTable::focusChild() const
 int QAccessibleTable::childCount() const
 {
     const QAbstractItemView *theView = view();
+    if (!theView)
+        return 0;
     const QAbstractItemModel *theModel = theView->model();
     if (!theModel)
         return 0;
@@ -557,6 +559,8 @@ int QAccessibleTable::childCount() const
 int QAccessibleTable::indexOfChild(const QAccessibleInterface *iface) const
 {
     const QAbstractItemView *theView = view();
+    if (!theView)
+        return -1;
     const QAbstractItemModel *theModel = theView->model();
     if (!theModel)
         return -1;
@@ -614,6 +618,9 @@ QAccessibleInterface *QAccessibleTable::parent() const
 QAccessibleInterface *QAccessibleTable::child(int logicalIndex) const
 {
     QAbstractItemView *theView = view();
+    if (!theView)
+        return nullptr;
+
     const QAbstractItemModel *theModel = theView->model();
     if (!theModel)
         return nullptr;
@@ -804,11 +811,13 @@ QModelIndex QAccessibleTree::indexFromLogical(int row, int column) const
 QAccessibleInterface *QAccessibleTree::childAt(int x, int y) const
 {
     const QAbstractItemView *theView = view();
+    if (!theView)
+        return nullptr;
     const QAbstractItemModel *theModel = theView->model();
     if (!theModel)
         return nullptr;
 
-    const QPoint viewportOffset = theView->viewport()->mapTo(view(), QPoint(0, 0));
+    const QPoint viewportOffset = theView->viewport()->mapTo(theView, QPoint(0, 0));
     const QPoint indexPosition = theView->mapFromGlobal(QPoint(x, y) - viewportOffset);
 
     const QModelIndex index = theView->indexAt(indexPosition);
@@ -826,6 +835,8 @@ QAccessibleInterface *QAccessibleTree::childAt(int x, int y) const
 QAccessibleInterface *QAccessibleTree::focusChild() const
 {
     const QAbstractItemView *theView = view();
+    if (!theView)
+        return nullptr;
     const QAbstractItemModel *theModel = theView->model();
     const QModelIndex index = theView->currentIndex();
     if (!index.isValid())
@@ -842,7 +853,8 @@ QAccessibleInterface *QAccessibleTree::focusChild() const
 int QAccessibleTree::childCount() const
 {
     const QTreeView *treeView = qobject_cast<const QTreeView*>(view());
-    Q_ASSERT(treeView);
+    if (!treeView)
+        return 0;
     const QAbstractItemModel *theModel = treeView->model();
     if (!theModel)
         return 0;
@@ -854,7 +866,9 @@ int QAccessibleTree::childCount() const
 
 QAccessibleInterface *QAccessibleTree::child(int logicalIndex) const
 {
-    const QAbstractItemView *theView = view();
+    QAbstractItemView *theView = view();
+    if (!theView)
+        return nullptr;
     const QAbstractItemModel *theModel = theView->model();
     const QModelIndex rootIndex = theView->rootIndex();
     if (logicalIndex < 0 || !theModel || !theModel->columnCount(rootIndex))
@@ -869,7 +883,7 @@ QAccessibleInterface *QAccessibleTree::child(int logicalIndex) const
 
     if (horizontalHeader()) {
         if (index < theModel->columnCount(rootIndex))
-            iface = new QAccessibleTableHeaderCell(view(), index, Qt::Horizontal);
+            iface = new QAccessibleTableHeaderCell(theView, index, Qt::Horizontal);
         else
             index -= theModel->columnCount(rootIndex);
     }
@@ -880,7 +894,7 @@ QAccessibleInterface *QAccessibleTree::child(int logicalIndex) const
         const QModelIndex modelIndex = indexFromLogical(row, column);
         if (!modelIndex.isValid())
             return nullptr;
-        iface = new QAccessibleTableCell(view(), modelIndex, cellRole());
+        iface = new QAccessibleTableCell(theView, modelIndex, cellRole());
     }
     QAccessible::registerAccessibleInterface(iface);
     childToId.insert(logicalIndex, QAccessible::uniqueId(iface));
@@ -890,18 +904,21 @@ QAccessibleInterface *QAccessibleTree::child(int logicalIndex) const
 int QAccessibleTree::rowCount() const
 {
     const QTreeView *treeView = qobject_cast<const QTreeView*>(view());
-    Q_ASSERT(treeView);
+    if (!treeView)
+        return 0;
     return treeView->d_func()->viewItems.size();
 }
 
 int QAccessibleTree::indexOfChild(const QAccessibleInterface *iface) const
 {
     const QAbstractItemView *theView = view();
+    if (!theView)
+        return -1;
     const QAbstractItemModel *theModel = theView->model();
     if (!theModel)
         return -1;
     QAccessibleInterface *parent = iface->parent();
-    if (parent->object() != view())
+    if (parent->object() != theView)
         return -1;
 
     if (iface->role() == QAccessible::TreeItem) {
@@ -990,6 +1007,8 @@ bool QAccessibleTree::selectRow(int row)
 QAccessibleInterface *QAccessibleList::child(int logicalIndex) const
 {
     QAbstractItemView *theView = view();
+    if (!theView)
+        return nullptr;
     const QAbstractItemModel *theModel = theView->model();
     if (!theModel)
         return nullptr;