QAbstractItemModel: fix persistent index corruption when moving columns

QHeaderView creates persistent indexes in
_q_sectionsAboutToBeChanged(), called by the slot connected to
rowsAboutToBeMoved/columnsAboutToBeMoved.

In the case of rows, QAbstractItemModel emits the signal *before*
preparing to update persistent indexes in itemsAboutToBeMoved(),
so it can see the ones newly created by QHeaderView, all is well.

In the case of columns, the emit was done *after* calling
itemsAboutToBeMoved(), so the additional persistent indexes created by
QHeaderView were ignored, and in endMoveRows() we could end up with:
ASSERT failure in QPersistentModelIndex::~QPersistentModelIndex: "persistent model indexes corrupted"

This bug has been there since the very beginning of beginMoveColumns(),
but was undetected because moving columns in a model is pretty rare
(in my case there's a QTransposeProxyModel that turns columns into
rows in the underlying model, and a proxy that handles dropMimeData...)

Pick-to: 6.3 6.2 5.15
Change-Id: I74bad137594019a04c2a19c2abb351ff3065c25a
Reviewed-by: Andreas Buhr <andreas.buhr@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/src/corelib/itemmodels/qabstractitemmodel.cpp b/src/corelib/itemmodels/qabstractitemmodel.cpp
index 8c34734408..5181d81140 100644
--- a/src/corelib/itemmodels/qabstractitemmodel.cpp
+++ b/src/corelib/itemmodels/qabstractitemmodel.cpp
@@ -3354,9 +3354,8 @@ bool QAbstractItemModel::beginMoveColumns(const QModelIndex &sourceParent, int s
     destinationChange.needsAdjust = destinationParent.isValid() && destinationParent.row() >= sourceLast && destinationParent.parent() == sourceParent;
     d->changes.push(destinationChange);
 
-    d->itemsAboutToBeMoved(sourceParent, sourceFirst, sourceLast, destinationParent, destinationChild, Qt::Horizontal);
-
     emit columnsAboutToBeMoved(sourceParent, sourceFirst, sourceLast, destinationParent, destinationChild, QPrivateSignal());
+    d->itemsAboutToBeMoved(sourceParent, sourceFirst, sourceLast, destinationParent, destinationChild, Qt::Horizontal);
     return true;
 }
 
@@ -3389,7 +3388,6 @@ void QAbstractItemModel::endMoveColumns()
       adjustedSource = createIndex(adjustedSource.row(), adjustedSource.column() + numMoved, adjustedSource.internalPointer());
 
     d->itemsMoved(adjustedSource, removeChange.first, removeChange.last, adjustedDestination, insertChange.first, Qt::Horizontal);
-
     emit columnsMoved(adjustedSource, removeChange.first, removeChange.last, adjustedDestination, insertChange.first, QPrivateSignal());
 }