QAbstractItemView: Fix shift-select after changing index through model

When setting the current index through the related model's
QItemSelectionModel::setCurrentIndex(), the selection can also change.
However, attempting to shift-select after doing so would produce
an unexpected selection, because the internal variable that keeps
track of the start index of the current selection would still have
its old value.

This change moves where said variable is set: instead of doing that
in QAbstractItemView::setCurrentIndex(), it is now done inside the
currentChanged() slot instead. This slot will get called both when
the selection is modified through the QAbstractItemView class itself,
as well as when it's modified from the outside (e.g. from the model).

Pick-to: 6.7 6.5 6.2
Fixes: QTBUG-127381
Change-Id: I6d38320e656aa5a102ce079604590672c88ecad1
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit fb2d64bc57aadf5bf140c72cf7eb2a5f391b7d55)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/itemviews/qabstractitemview.cpp

@@ -1102,8 +1102,6 @@ void QAbstractItemView::setCurrentIndex(const QModelIndex &index)
         QItemSelectionModel::SelectionFlags command = selectionCommand(index, nullptr);
         d->selectionModel->setCurrentIndex(index, command);
         d->currentIndexSet = true;
-        if ((command & QItemSelectionModel::Current) == 0)
-            d->currentSelectionStartIndex = index;
     }
 }
 
@@ -3819,6 +3817,10 @@ void QAbstractItemView::currentChanged(const QModelIndex &current, const QModelI
         }
     }
 
+    QItemSelectionModel::SelectionFlags command = selectionCommand(current, nullptr);
+    if ((command & QItemSelectionModel::Current) == 0)
+        d->currentSelectionStartIndex = current;
+
     if (current.isValid() && !d->autoScrollTimer.isActive()) {
         if (isVisible()) {
             if (d->autoScroll)

src/widgets/itemviews/qtableview.cpp

@@ -3426,7 +3426,14 @@ void QTableViewPrivate::selectRow(int row, bool anchor)
         int column = horizontalHeader->logicalIndexAt(q->isRightToLeft() ? viewport->width() : 0);
         QModelIndex index = model->index(row, column, root);
         QItemSelectionModel::SelectionFlags command = q->selectionCommand(index);
-        selectionModel->setCurrentIndex(index, QItemSelectionModel::NoUpdate);
+
+        {
+            // currentSelectionStartIndex gets modified inside QAbstractItemView::currentChanged()
+            const auto startIndex = currentSelectionStartIndex;
+            selectionModel->setCurrentIndex(index, QItemSelectionModel::NoUpdate);
+            currentSelectionStartIndex = startIndex;
+        }
+
         if ((anchor && !(command & QItemSelectionModel::Current))
             || (q->selectionMode() == QTableView::SingleSelection))
             currentSelectionStartIndex = model->index(row, column, root);
@@ -3466,7 +3473,14 @@ void QTableViewPrivate::selectColumn(int column, bool anchor)
         int row = verticalHeader->logicalIndexAt(0);
         QModelIndex index = model->index(row, column, root);
         QItemSelectionModel::SelectionFlags command = q->selectionCommand(index);
-        selectionModel->setCurrentIndex(index, QItemSelectionModel::NoUpdate);
+
+        {
+            // currentSelectionStartIndex gets modified inside QAbstractItemView::currentChanged()
+            const auto startIndex = currentSelectionStartIndex;
+            selectionModel->setCurrentIndex(index, QItemSelectionModel::NoUpdate);
+            currentSelectionStartIndex = startIndex;
+        }
+
         if ((anchor && !(command & QItemSelectionModel::Current))
             || (q->selectionMode() == QTableView::SingleSelection))
             currentSelectionStartIndex = model->index(row, column, root);

tests/auto/widgets/itemviews/qabstractitemview/tst_qabstractitemview.cpp

@@ -152,6 +152,7 @@ private slots:
     void testSpinBoxAsEditor();
     void removeIndexWhileEditing();
     void focusNextOnHide();
+    void shiftSelectionAfterModelSetCurrentIndex();
 
 private:
     static QAbstractItemView *viewFromString(const QByteArray &viewType, QWidget *parent = nullptr)
@@ -3561,5 +3562,37 @@ void tst_QAbstractItemView::focusNextOnHide()
     QVERIFY(lineEdit.hasFocus());
 }
 
+// Tests for QTBUG-127381, where shift-selecting after calling
+// QItemSelectionModel::setCurrentIndex() would produce unexpected results.
+void tst_QAbstractItemView::shiftSelectionAfterModelSetCurrentIndex()
+{
+    QStandardItemModel model(5, 1);
+    QTreeView view;
+    view.setSelectionBehavior(QAbstractItemView::SelectRows);
+    view.setSelectionMode(QAbstractItemView::ExtendedSelection);
+    view.setModel(&model);
+
+    view.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&view));
+
+    QModelIndex index = model.index(0, 0);
+    view.setCurrentIndex(index);
+    index = model.index(2, 0);
+    view.selectionModel()->setCurrentIndex(index, QItemSelectionModel::ClearAndSelect | QItemSelectionModel::Rows);
+
+    QTest::keyPress(&view, Qt::Key_Down, Qt::ShiftModifier);
+
+    QItemSelection selection = view.selectionModel()->selection();
+    QCOMPARE(selection.size(), 1);
+    QCOMPARE(selection.first().top(), 2);
+    QCOMPARE(selection.first().bottom(), 3);
+
+    QTest::keyPress(&view, Qt::Key_Up, Qt::ShiftModifier);
+
+    selection = view.selectionModel()->selection();
+    QCOMPARE(selection.first().top(), 2);
+    QCOMPARE(selection.first().bottom(), 2);
+}
+
 QTEST_MAIN(tst_QAbstractItemView)
 #include "tst_qabstractitemview.moc"