qquickdeliveryagent: Fix drag events being sent in the wrong order

When a former drag event target is on a higher or the same z-level as the new target, send the QDragLeaveEvent before the QDragEnterEvent.

[ChangeLog][Quick][Fix] Now sends DragArea leave events before enter events when appropriate (QTBUG-82263)

Fixes: QTBUG-82263
Change-Id: Ibe76000cbe76748ee8928e4b98a92c38eff5b59c
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
(cherry picked from commit 4a5b0ad84fbc0f814c38b0abcccb7b5421f41a19)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 76 insertions, 20 deletions

diff --git a/src/quick/util/qquickdeliveryagent.cpp b/src/quick/util/qquickdeliveryagent.cpp
index 0cea513b78..f613e74d53 100644
--- a/src/quick/util/qquickdeliveryagent.cpp
+++ b/src/quick/util/qquickdeliveryagent.cpp
@@ -2052,6 +2052,7 @@ void QQuickDeliveryAgentPrivate::deliverMatchingPointsToItem(QQuickItem *item, b
 #if QT_CONFIG(quick_draganddrop)
 void QQuickDeliveryAgentPrivate::deliverDragEvent(QQuickDragGrabber *grabber, QEvent *event)
 {
+    QObject *formerTarget = grabber->target();
     grabber->resetTarget();
     QQuickDragGrabber::iterator grabItem = grabber->begin();
     if (grabItem != grabber->end()) {
@@ -2095,7 +2096,8 @@ void QQuickDeliveryAgentPrivate::deliverDragEvent(QQuickDragGrabber *grabber, QE
                     moveEvent->buttons(),
                     moveEvent->modifiers());
             QQuickDropEventEx::copyActions(&enterEvent, *moveEvent);
-            event->setAccepted(deliverDragEvent(grabber, rootItem, &enterEvent, &currentGrabItems));
+            event->setAccepted(deliverDragEvent(grabber, rootItem, &enterEvent, &currentGrabItems,
+                                                formerTarget));
 
             for (grabItem = grabber->begin(); grabItem != grabber->end(); ++grabItem) {
                 int i = currentGrabItems.indexOf(**grabItem);
@@ -2136,7 +2138,9 @@ void QQuickDeliveryAgentPrivate::deliverDragEvent(QQuickDragGrabber *grabber, QE
     }
 }
 
-bool QQuickDeliveryAgentPrivate::deliverDragEvent(QQuickDragGrabber *grabber, QQuickItem *item, QDragMoveEvent *event, QVarLengthArray<QQuickItem*, 64> *currentGrabItems)
+bool QQuickDeliveryAgentPrivate::deliverDragEvent(
+        QQuickDragGrabber *grabber, QQuickItem *item, QDragMoveEvent *event,
+        QVarLengthArray<QQuickItem *, 64> *currentGrabItems, QObject *formerTarget)
 {
     QQuickItemPrivate *itemPrivate = QQuickItemPrivate::get(item);
     if (!item->isVisible() || !item->isEnabled() || QQuickItemPrivate::get(item)->culled)
@@ -2161,7 +2165,7 @@ bool QQuickDeliveryAgentPrivate::deliverDragEvent(QQuickDragGrabber *grabber, QQ
     for (int ii = children.count() - 1; ii >= 0; --ii) {
         if (children.at(ii)->z() < 0)
             continue;
-        if (deliverDragEvent(grabber, children.at(ii), &enterEvent, currentGrabItems))
+        if (deliverDragEvent(grabber, children.at(ii), &enterEvent, currentGrabItems, formerTarget))
             return true;
     }
 
@@ -2175,13 +2179,20 @@ bool QQuickDeliveryAgentPrivate::deliverDragEvent(QQuickDragGrabber *grabber, QQ
         }
 
         if (event->type() == QEvent::DragMove || itemPrivate->flags & QQuickItem::ItemAcceptsDrops) {
-            QDragMoveEvent translatedEvent(
-                    p.toPoint(),
-                    event->possibleActions(),
-                    event->mimeData(),
-                    event->buttons(),
-                    event->modifiers(),
-                    event->type());
+            if (event->type() == QEvent::DragEnter && formerTarget) {
+                QQuickItem *formerTargetItem = qobject_cast<QQuickItem *>(formerTarget);
+                if (formerTargetItem && currentGrabItems) {
+                    QDragLeaveEvent leaveEvent;
+                    QCoreApplication::sendEvent(formerTarget, &leaveEvent);
+
+                    // Remove the item from the currentGrabItems so a leave event won't be generated
+                    // later on
+                    currentGrabItems->removeAll(formerTarget);
+                }
+            }
+
+            QDragMoveEvent translatedEvent(p.toPoint(), event->possibleActions(), event->mimeData(),
+                                           event->buttons(), event->modifiers(), event->type());
             QQuickDropEventEx::copyActions(&translatedEvent, *event);
             translatedEvent.setAccepted(event->isAccepted());
             QCoreApplication::sendEvent(item, &translatedEvent);
@@ -2203,7 +2214,7 @@ bool QQuickDeliveryAgentPrivate::deliverDragEvent(QQuickDragGrabber *grabber, QQ
     for (int ii = children.count() - 1; ii >= 0; --ii) {
         if (children.at(ii)->z() >= 0)
             continue;
-        if (deliverDragEvent(grabber, children.at(ii), &enterEvent, currentGrabItems))
+        if (deliverDragEvent(grabber, children.at(ii), &enterEvent, currentGrabItems, formerTarget))
             return true;
     }
 
diff --git a/src/quick/util/qquickdeliveryagent_p_p.h b/src/quick/util/qquickdeliveryagent_p_p.h
index f9095158e8..4ea1ef0d36 100644
--- a/src/quick/util/qquickdeliveryagent_p_p.h
+++ b/src/quick/util/qquickdeliveryagent_p_p.h
@@ -199,7 +199,9 @@ public:
 
 #if QT_CONFIG(quick_draganddrop)
     void deliverDragEvent(QQuickDragGrabber *, QEvent *);
-    bool deliverDragEvent(QQuickDragGrabber *, QQuickItem *, QDragMoveEvent *, QVarLengthArray<QQuickItem*, 64> *currentGrabItems = nullptr);
+    bool deliverDragEvent(QQuickDragGrabber *, QQuickItem *, QDragMoveEvent *,
+                          QVarLengthArray<QQuickItem *, 64> *currentGrabItems = nullptr,
+                          QObject *formerTarget = nullptr);
 #endif
 
     static bool dragOverThreshold(qreal d, Qt::Axis axis, QMouseEvent *event, int startDragThreshold = -1);
diff --git a/tests/auto/quick/qquickdroparea/tst_qquickdroparea.cpp b/tests/auto/quick/qquickdroparea/tst_qquickdroparea.cpp
index dbf090bfed..6bbe0d522b 100644
--- a/tests/auto/quick/qquickdroparea/tst_qquickdroparea.cpp
+++ b/tests/auto/quick/qquickdroparea/tst_qquickdroparea.cpp
@@ -80,6 +80,7 @@ private slots:
     void dropStuff();
     void nestedDropAreas_data();
     void nestedDropAreas();
+    void signalOrder();
 
 private:
     QQmlEngine engine;
@@ -958,8 +959,8 @@ void tst_QQuickDropArea::simultaneousDrags()
                                        Qt::MouseButtons(), Qt::KeyboardModifiers());
     //Same as in the first case, dropArea2 already contains a drag, dropArea1 will get the event
     QCOMPARE(evaluate<bool>(dropArea1, "containsDrag"), true);
-    QCOMPARE(evaluate<int>(dropArea1, "enterEvents"), 1);
-    QCOMPARE(evaluate<int>(dropArea1, "exitEvents"), 0);
+    QCOMPARE(evaluate<int>(dropArea1, "enterEvents"), 2);
+    QCOMPARE(evaluate<int>(dropArea1, "exitEvents"), 1);
     QCOMPARE(evaluate<bool>(dropArea2, "containsDrag"), true);
     QCOMPARE(evaluate<int>(dropArea2, "enterEvents"), 0);
     QCOMPARE(evaluate<int>(dropArea2, "exitEvents"), 0);
@@ -967,8 +968,8 @@ void tst_QQuickDropArea::simultaneousDrags()
     QWindowSystemInterface::handleDrag(&alternateWindow, &data, QPoint(50, 50), Qt::CopyAction,
                                        Qt::MouseButtons(), Qt::KeyboardModifiers());
     QCOMPARE(evaluate<bool>(dropArea1, "containsDrag"), false);
-    QCOMPARE(evaluate<int>(dropArea1, "enterEvents"), 1);
-    QCOMPARE(evaluate<int>(dropArea1, "exitEvents"), 1);
+    QCOMPARE(evaluate<int>(dropArea1, "enterEvents"), 2);
+    QCOMPARE(evaluate<int>(dropArea1, "exitEvents"), 2);
     QCOMPARE(evaluate<bool>(dropArea2, "containsDrag"), true);
     QCOMPARE(evaluate<int>(dropArea2, "enterEvents"), 0);
     QCOMPARE(evaluate<int>(dropArea2, "exitEvents"), 0);
@@ -976,16 +977,16 @@ void tst_QQuickDropArea::simultaneousDrags()
     QWindowSystemInterface::handleDrag(&window, &data, QPoint(50, 50), Qt::CopyAction,
                                        Qt::MouseButtons(), Qt::KeyboardModifiers());
     QCOMPARE(evaluate<bool>(dropArea1, "containsDrag"), true);
-    QCOMPARE(evaluate<int>(dropArea1, "enterEvents"), 2);
-    QCOMPARE(evaluate<int>(dropArea1, "exitEvents"), 1);
+    QCOMPARE(evaluate<int>(dropArea1, "enterEvents"), 4);
+    QCOMPARE(evaluate<int>(dropArea1, "exitEvents"), 3);
     QCOMPARE(evaluate<bool>(dropArea2, "containsDrag"), true);
     QCOMPARE(evaluate<int>(dropArea2, "enterEvents"), 0);
     QCOMPARE(evaluate<int>(dropArea2, "exitEvents"), 0);
 
     evaluate<void>(dragItem1, "Drag.active = false");
     QCOMPARE(evaluate<bool>(dropArea1, "containsDrag"), true);
-    QCOMPARE(evaluate<int>(dropArea1, "enterEvents"), 2);
-    QCOMPARE(evaluate<int>(dropArea1, "exitEvents"), 1);
+    QCOMPARE(evaluate<int>(dropArea1, "enterEvents"), 4);
+    QCOMPARE(evaluate<int>(dropArea1, "exitEvents"), 3);
     QCOMPARE(evaluate<bool>(dropArea2, "containsDrag"), false);
     QCOMPARE(evaluate<int>(dropArea2, "enterEvents"), 0);
     QCOMPARE(evaluate<int>(dropArea2, "exitEvents"), 1);
@@ -1290,6 +1291,48 @@ void tst_QQuickDropArea::nestedDropAreas()
     QCOMPARE(window.rootObject()->property("innerExitEvents"), 2);
 }
 
+void tst_QQuickDropArea::signalOrder()
+{
+    QQuickWindow window;
+    QQmlComponent component(&engine);
+    component.setData("import QtQuick\n"
+                      "Item {\n"
+                      "    id: root\n"
+                      "    property var eventOrder: []\n"
+                      "    DropArea {\n"
+                      "    width: 100; height: 100\n"
+                      "    x: 0; y: 0\n"
+                      "    onEntered: eventOrder.push('entered1');\n"
+                      "    onExited: eventOrder.push('exited1');\n"
+                      "    }\n"
+                      "    DropArea {\n"
+                      "    width: 100; height: 100\n"
+                      "    x: 0; y: 100\n"
+                      "    onEntered: eventOrder.push('entered2');\n"
+                      "    onExited: eventOrder.push('exited2');\n"
+                      "    }\n"
+                      "}",
+                      QUrl());
+
+    QScopedPointer<QObject> object(component.create());
+    QQuickItem *item = qobject_cast<QQuickItem *>(object.data());
+    QVERIFY(item);
+    item->setParentItem(window.contentItem());
+
+    QMimeData data;
+
+    QWindowSystemInterface::handleDrag(&window, &data, QPoint(50, 50), Qt::CopyAction,
+                                       Qt::MouseButtons(), Qt::KeyboardModifiers());
+    QWindowSystemInterface::handleDrag(&window, &data, QPoint(50, 150), Qt::CopyAction,
+                                       Qt::MouseButtons(), Qt::KeyboardModifiers());
+    QWindowSystemInterface::handleDrag(&window, &data, QPoint(50, 250), Qt::CopyAction,
+                                       Qt::MouseButtons(), Qt::KeyboardModifiers());
+
+    const QList<QVariant> eventOrder = item->property("eventOrder").toList();
+    QCOMPARE(eventOrder,
+             QList<QVariant>({ u"entered1"_qs, u"exited1"_qs, u"entered2"_qs, u"exited2"_qs }));
+}
+
 QTEST_MAIN(tst_QQuickDropArea)
 
 #include "tst_qquickdroparea.moc"