TableView: start a new selection when using Qt::ShiftModifier

If no selection exists in TableView from before, and the
user shift-clicks on a cell, then start a new selection
from the current cell towards the clicked cell. This
is already how it works if a selection is started using
the keyboard, and also standard selection behavior for
other item view implementations outside of Qt (e.g Finder
on macOS).

Fixes: QTBUG-120628
Pick-to: 6.6 6.5
Change-Id: I2fd34e680eed9992dd7c405fbd58ae4f5b0834ec
Reviewed-by: Santhosh Kumar <santhosh.kumar.selvaraj@qt.io>
(cherry picked from commit aecb62403e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/quick/items/qquicktableview.cpp

@@ -1645,6 +1645,7 @@ bool QQuickTableViewPrivate::startSelection(const QPointF &pos)
 
 void QQuickTableViewPrivate::setSelectionStartPos(const QPointF &pos)
 {
+    Q_Q(QQuickTableView);
     if (loadedItems.isEmpty())
         return;
     if (!selectionModel) {
@@ -1663,12 +1664,20 @@ void QQuickTableViewPrivate::setSelectionStartPos(const QPointF &pos)
     }
 
     const QRect prevSelection = selection();
-    const QPoint clampedCell = clampedCellAtPos(pos);
+
+    QPoint clampedCell;
+    if (pos.x() == -1) {
+        // Special case: use current cell as start cell
+        clampedCell = q->cellAtIndex(selectionModel->currentIndex());
+    } else {
+        clampedCell = clampedCellAtPos(pos);
+        if (cellIsValid(clampedCell))
+            setCurrentIndex(clampedCell);
+    }
+
     if (!cellIsValid(clampedCell))
         return;
 
-    setCurrentIndex(clampedCell);
-
     switch (selectionBehavior) {
     case QQuickTableView::SelectCells:
         selectionStartCell = clampedCell;

src/quicktemplates/qquickselectionrectangle.cpp

@@ -196,9 +196,14 @@ QQuickSelectionRectanglePrivate::QQuickSelectionRectanglePrivate()
             return;
 
         if (modifiers & Qt::ShiftModifier) {
-            // Extend the existing selection towards the pressed cell
-            if (!m_active)
-                return;
+            // Extend the selection towards the pressed cell. If there is no
+            // existing selection, start a new selection from the current item
+            // to the pressed item.
+            if (!m_active) {
+                if (!m_selectable->startSelection(pos))
+                    return;
+                m_selectable->setSelectionStartPos(QPoint{-1, -1});
+            }
             m_selectable->setSelectionEndPos(pos);
             updateHandles();
             updateActiveState(true);

tests/auto/quickcontrols/controls/data/tst_selectionrectangle.qml

@@ -318,7 +318,14 @@ TestCase {
         verify(tableView.selectionModel.isSelected(tableView.selectionModel.model.index(0, 1)))
     }
 
-    function test_tableView_contiguousSelection() {
+    function test_tableView_contiguousSelection_data() {
+        return [
+            { startFromCurrentIndex: false },
+            { startFromCurrentIndex: true },
+        ]
+    }
+
+    function test_tableView_contiguousSelection(data) {
         let tableView = createTemporaryObject(tableviewComp, testCase)
         verify(tableView)
         let selectionRectangle = tableView.selectionRectangle
@@ -327,13 +334,21 @@ TestCase {
         selectionRectangle.selectionMode = SelectionRectangle.Drag
         tableView.selectionMode = TableView.ContiguousSelection
 
-        // Select two cells by dragging
-        verify(!tableView.selectionModel.hasSelection)
-        mouseDrag(tableView, 1, 1, (cellWidth * 2) - 2, 1, Qt.LeftButton)
-        verify(tableView.selectionModel.hasSelection)
-        compare(tableView.selectionModel.selectedIndexes.length, 2)
-        verify(tableView.selectionModel.isSelected(tableView.model.index(0, 0)))
-        verify(tableView.selectionModel.isSelected(tableView.model.index(0, 1)))
+        if (data.startFromCurrentIndex) {
+            // Click on a cell to set current index, but set no selection.
+            // A later shift-click should then start a new selection from the
+            // current cell.
+            mouseClick(tableView, 1, 1, Qt.LeftButton, Qt.NoModifier)
+            verify(!tableView.selectionModel.hasSelection)
+            compare(tableView.selectionModel.currentIndex, tableView.index(0, 0))
+        } else {
+            // Start a new selection by dragging on two cells
+            mouseDrag(tableView, 1, 1, (cellWidth * 2) - 2, 1, Qt.LeftButton)
+            verify(tableView.selectionModel.hasSelection)
+            compare(tableView.selectionModel.selectedIndexes.length, 2)
+            verify(tableView.selectionModel.isSelected(tableView.model.index(0, 0)))
+            verify(tableView.selectionModel.isSelected(tableView.model.index(0, 1)))
+        }
 
         // A shift click should extend the selection
         mouseClick(tableView, (cellWidth * 4) - 3, 1, Qt.LeftButton, Qt.ShiftModifier)