Fix QListView assert when the last row is moved in IconMode

After the last row is moved, 0 will be returned when obtaining
row and column data. At this time, QListView::doitemslayout will
not call d->doitemslayout, so the QBspTree data structure will
not be cleaned up, leaving a stale tree structure behind. This
will trigger an assert during paintEvent handling if QListView is
set to IconMode

In QListView::ListMode the test for a valid model index doesn't
use an assert.

Call QListViewPrivate::clear explicitly if the column count is 0
so that the QBspTree and other data structures are cleared.

Add a test case that simulates this scenario by implementing a
model that returns a 0 column count for an index after the model
structure was changed through a move of rows.

Done-with: Volker Hilsheimer
Fixes: QTBUG-95463
Pick-to: 5.15 6.1 6.2
Change-Id: I36419be5459b8ced930c619f538482ea1db4ad03
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/widgets/itemviews/qlistview.cpp b/src/widgets/itemviews/qlistview.cpp
index 68d5d7612f..f9e3082962 100644
--- a/src/widgets/itemviews/qlistview.cpp
+++ b/src/widgets/itemviews/qlistview.cpp
@@ -1575,12 +1575,14 @@ void QListView::doItemsLayout()
     setState(ExpandingState);
     if (d->model->columnCount(d->root) > 0) { // no columns means no contents
         d->resetBatchStartRow();
-        if (layoutMode() == SinglePass)
+        if (layoutMode() == SinglePass) {
             d->doItemsLayout(d->model->rowCount(d->root)); // layout everything
-        else if (!d->batchLayoutTimer.isActive()) {
+        } else if (!d->batchLayoutTimer.isActive()) {
             if (!d->doItemsLayout(d->batchSize)) // layout is done
                 d->batchLayoutTimer.start(0, this); // do a new batch as fast as possible
         }
+    } else { // clear the QBspTree generated by the last layout
+        d->clear();
     }
     QAbstractItemView::doItemsLayout();
     setState(oldState);        // restoring the oldState