QFileSystemModel: don't emit invalid indexes

A subclass of QFileSystemModel might override columnCount to return a
value smalller than QFileSystemModelPrivate::NumColumns.

In that case, constructing the bottomRight index for the dataChange
signal would fail if we create it for column NumColumns - 1, and result
in undefined behavior where the topLeft and bottomRight indices do not
have the same parent.

So ask for the columnCount of the parent index explicitly to construct
the bottomRight index.

The assert can be triggered via the "filesystemexplorer" example in
qtdeclarative, which overrides columnCount to always return 1.

As a drive-by name the variables correctly, bottom and top where mixed
up.

Pick-to: 6.5
Fixes: QTBUG-110632
Change-Id: I8a635ec733348d1eda2037c156ac0f7b09a2183d
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 11 insertions, 4 deletions

diff --git a/src/gui/itemmodels/qfilesystemmodel.cpp b/src/gui/itemmodels/qfilesystemmodel.cpp
index 9944f095fa..9c5c21f303 100644
--- a/src/gui/itemmodels/qfilesystemmodel.cpp
+++ b/src/gui/itemmodels/qfilesystemmodel.cpp
@@ -240,7 +240,7 @@ QModelIndex QFileSystemModel::index(int row, int column, const QModelIndex &pare
 */
 QModelIndex QFileSystemModel::sibling(int row, int column, const QModelIndex &idx) const
 {
-    if (row == idx.row() && column < QFileSystemModelPrivate::NumColumns) {
+    if (row == idx.row() && column < columnCount(idx.parent())) {
         // cheap sibling operation: just adjust the column:
         return createIndex(row, column, idx.internalPointer());
     } else {
@@ -1995,9 +1995,16 @@ void QFileSystemModelPrivate::_q_fileSystemChanged(const QString &path,
             && visibleMin < parentNode->visibleChildren.size()
             && parentNode->visibleChildren.at(visibleMin) == min
             && visibleMax >= 0) {
-            QModelIndex bottom = q->index(translateVisibleLocation(parentNode, visibleMin), QFileSystemModelPrivate::NameColumn, parentIndex);
-            QModelIndex top = q->index(translateVisibleLocation(parentNode, visibleMax), QFileSystemModelPrivate::NumColumns - 1, parentIndex);
-            emit q->dataChanged(bottom, top);
+            // don't use NumColumns here, a subclass might override columnCount
+            const int lastColumn = q->columnCount(parentIndex) - 1;
+            const QModelIndex top = q->index(translateVisibleLocation(parentNode, visibleMin),
+                                             QFileSystemModelPrivate::NameColumn, parentIndex);
+            const QModelIndex bottom = q->index(translateVisibleLocation(parentNode, visibleMax),
+                                                lastColumn, parentIndex);
+            // We document that emitting dataChanged with indexes that don't have the
+            // same parent is undefined behavior.
+            Q_ASSERT(bottom.parent() == top.parent());
+            emit q->dataChanged(top, bottom);
         }
 
         /*min = QString();