TableView: start a new selection when using Qt::ShiftModifier (PressAndHold)

Follow up on previous patch to qquickselectionrectangle, and
implement starting a new selection when using Qt::ShiftModifier
also for PressAndHold. This configuration, PressAndHold + holding
Shift to start a selection, is normally not used in combination.
But at the same time, there seems to be no reason why it should't
work either, as using selections handles on desktop is allowed.

Task-number: QTBUG-120628
Pick-to: 6.5
Change-Id: I8a7589ffd4d16e339a5654605ee0916d96c8cbf0
Reviewed-by: Santhosh Kumar <santhosh.kumar.selvaraj@qt.io>
(cherry picked from commit 4335010)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 43ebd25)

Author: Richard Moe Gustavsen

src/quicktemplates/qquickselectionrectangle.cpp

@@ -242,9 +242,14 @@ QQuickSelectionRectanglePrivate::QQuickSelectionRectanglePrivate()
         }
 
         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

@@ -571,6 +571,31 @@ TestCase {
         verify(!tableView.selectionModel.hasSelection)
     }
 
+    function test_pressAndHoldPlussShift() {
+        let tableView = createTemporaryObject(tableviewComp, testCase)
+        verify(tableView)
+        let selectionRectangle = tableView.selectionRectangle
+        verify(selectionRectangle)
+
+        selectionRectangle.selectionMode = SelectionRectangle.Drag
+
+        verify(!tableView.selectionModel.hasSelection)
+        verify(!tableView.selectionModel.currentIndex.isValid)
+
+        // select cell 0,0
+        mouseClick(tableView, 1, 1, Qt.LeftButton)
+        compare(tableView.selectionModel.currentIndex, tableView.index(0, 0))
+
+        // do a long press on cell 1,0 while holding down Shift. This will
+        // select both cells.
+        mousePress(tableView, cellWidth + 1, 1, Qt.LeftButton, Qt.ShiftModifier)
+        mouseRelease(tableView, cellWidth + 1, 1, Qt.LeftButton, Qt.ShiftModifier, 2000)
+        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)))
+    }
+
     function test_pressAndHold_on_top_of_handle() {
         let tableView = createTemporaryObject(tableviewComp, testCase)
         verify(tableView)