QTableView: fix infinite loop when resizing rows/columns on model reset

When a slot is connected to the modelReset signal before the model is
set on the view, then such a slot might try to resize the columns or
rows to fit the contents before the view had a chance to perform layout
work.

In that case, the while-loop that calculated the size hint of a rows
(or column) by checking the size hint of each cell might not exit, as
cached information about visual indexes would be invalid.

To prevent this, don't loop over the cells if the actual last row/column
of the model (after the reset) is less than the first (cached) visible
row/column. Also, make sure we increase the counter for number of
rows/columns processed with each iteration.

Add a test (that loops infinitely without the fix, resulting in the
test being killed by the framework), and make the 'actual' variables
constant for clarity.

Fixes: QTBUG-124301
Change-Id: I0adb2f1e8a1e78760ef7c19e9686c9572eca8be6
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit 960867566a75931c338f67cfe429c0756f41ad89)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/itemviews/qtableview.cpp

@@ -2432,12 +2432,12 @@ int QTableView::sizeHintForRow(int row) const
             break;
     }
 
-    int actualRight = d->model->columnCount(d->root) - 1;
+    const int actualRight = d->model->columnCount(d->root) - 1;
     int idxLeft = left;
     int idxRight = column - 1;
 
-    if (maximumProcessCols == 0)
-        columnsProcessed = 0; // skip the while loop
+    if (maximumProcessCols == 0 || actualRight < idxLeft)
+        columnsProcessed = maximumProcessCols; // skip the while loop
 
     while (columnsProcessed != maximumProcessCols && (idxLeft > 0 || idxRight < actualRight)) {
         int logicalIdx  = -1;
@@ -2461,11 +2461,10 @@ int QTableView::sizeHintForRow(int row) const
                 break;
             }
         }
-        if (logicalIdx < 0)
-            continue;
-
-        index = d->model->index(row, logicalIdx, d->root);
-        hint = d->heightHintForIndex(index, hint, option);
+        if (logicalIdx >= 0) {
+            index = d->model->index(row, logicalIdx, d->root);
+            hint = d->heightHintForIndex(index, hint, option);
+        }
         ++columnsProcessed;
     }
 
@@ -2521,12 +2520,12 @@ int QTableView::sizeHintForColumn(int column) const
             break;
     }
 
-    int actualBottom = d->model->rowCount(d->root) - 1;
+    const int actualBottom = d->model->rowCount(d->root) - 1;
     int idxTop = top;
     int idxBottom = row - 1;
 
-    if (maximumProcessRows == 0)
-        rowsProcessed = 0;  // skip the while loop
+    if (maximumProcessRows == 0 || actualBottom < idxTop)
+        rowsProcessed = maximumProcessRows;  // skip the while loop
 
     while (rowsProcessed != maximumProcessRows && (idxTop > 0 || idxBottom < actualBottom)) {
         int logicalIdx  = -1;
@@ -2550,11 +2549,10 @@ int QTableView::sizeHintForColumn(int column) const
                 break;
             }
         }
-        if (logicalIdx < 0)
-            continue;
-
-        index = d->model->index(logicalIdx, column, d->root);
-        hint = d->widthHintForIndex(index, hint, option);
+        if (logicalIdx >= 0) {
+            index = d->model->index(logicalIdx, column, d->root);
+            hint = d->widthHintForIndex(index, hint, option);
+        }
         ++rowsProcessed;
     }
 

tests/auto/widgets/itemviews/qtableview/tst_qtableview.cpp

@@ -391,6 +391,7 @@ private slots:
 
     void resizeToContents();
     void resizeToContentsSpans();
+    void resizeToContentsEarly();
 
     void tabFocus();
     void bigModel();
@@ -3777,6 +3778,35 @@ void tst_QTableView::resizeToContentsSpans()
     QCOMPARE(view2.columnWidth(0), view3.columnWidth(0) - view2.columnWidth(1));
 }
 
+void tst_QTableView::resizeToContentsEarly()
+{
+    QStringListModel model;
+    QTableView view;
+
+    // connect to the model before setting it on the view
+    connect(&model, &QStringListModel::modelReset, &model, [&view]{
+        view.resizeColumnsToContents();
+    });
+    connect(&model, &QStringListModel::modelReset, &model, [&view]{
+        view.resizeRowsToContents();
+    });
+
+    // the view only connects now to the model's signals, so responds to the
+    // reset signal *after* the lambdas above
+    view.setModel(&model);
+
+    QStringList data(200, QString("Hello World"));
+    model.setStringList(data);
+
+    view.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&view));
+
+    view.verticalScrollBar()->setValue(view.verticalScrollBar()->maximum());
+
+    data = data.sliced(data.size() / 2);
+    model.setStringList(data);
+}
+
 QT_BEGIN_NAMESPACE
 extern bool Q_WIDGETS_EXPORT qt_tab_all_widgets(); // qapplication.cpp
 QT_END_NAMESPACE