MouseArea: don't override preventStealing on mouse release

In setPreventStealing() we call setKeepMouseGrab(); so it does not make
sense to override setKeepMouseGrab() in other places without even
checking the state of the preventStealing property.

Pick-to: 5.15 6.2 6.3
Fixes: QTBUG-103522
Change-Id: Ib4a2b01b814835715642aec83fac0a84debe2461
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/quick/items/qquickmousearea.cpp

@@ -808,7 +808,8 @@ void QQuickMouseArea::mouseReleaseEvent(QMouseEvent *event)
             QQuickWindow *w = window();
             if (w && w->mouseGrabberItem() == this)
                 ungrabMouse();
-            setKeepMouseGrab(false);
+            if (!d->preventStealing)
+                setKeepMouseGrab(false);
         }
     }
     d->doubleClick = false;

tests/auto/quick/qquickmousearea/data/preventStealingListViewChild.qml

@@ -0,0 +1,31 @@
+import QtQuick 2.15
+
+ListView {
+    id: flick
+    width: 640
+    height: 480
+    model: 100
+
+    delegate: Rectangle {
+        border.color: "#81e889"
+        width: 640; height: 100
+        Text { text: "Row " + index }
+    }
+
+    Rectangle {
+        anchors.right: parent.right
+        anchors.margins: 2
+        color: ma.pressed ? "#81e889" : "#c2f4c6"
+        width: 50; height: 50
+        radius: 5
+        MouseArea {
+            id: ma
+            anchors.fill: parent
+            preventStealing: true
+            drag {
+                target: parent
+                axis: Drag.YAxis
+            }
+        }
+    }
+}

tests/auto/quick/qquickmousearea/tst_qquickmousearea.cpp

@@ -125,6 +125,7 @@ private slots:
     void invalidClick();
     void pressedOrdering();
     void preventStealing();
+    void preventStealingListViewChild();
     void clickThrough();
     void hoverPosition();
     void hoverPropagation();
@@ -1108,6 +1109,36 @@ void tst_QQuickMouseArea::preventStealing()
     QTest::mouseRelease(&window, Qt::LeftButton, Qt::NoModifier, p);
 }
 
+// QTBUG-103522
+void tst_QQuickMouseArea::preventStealingListViewChild()
+{
+    QQuickView window;
+    QVERIFY(QQuickTest::showView(window, testFileUrl("preventStealingListViewChild.qml")));
+    QQuickFlickable *flickable = qobject_cast<QQuickFlickable*>(window.rootObject());
+    QVERIFY(flickable);
+    QQuickMouseArea *mouseArea = flickable->findChild<QQuickMouseArea*>();
+    QVERIFY(mouseArea);
+    QPoint p = mouseArea->mapToScene(mouseArea->boundingRect().center()).toPoint();
+    const int threshold = qApp->styleHints()->startDragDistance();
+
+    flickable->flick(0, -10000);
+    for (int i = 0; i < 2; ++i) {
+        QVERIFY(flickable->isMovingVertically());
+        QTest::touchEvent(&window, device).press(0, p);
+        QQuickTouchUtils::flush(&window);
+        for (int j = 0; j < 4 && !mouseArea->drag()->active(); ++j) {
+            p += QPoint(0, threshold);
+            QTest::touchEvent(&window, device).move(0, p);
+            QQuickTouchUtils::flush(&window);
+        }
+        // MouseArea should be dragged because of preventStealing; ListView does not steal the grab.
+        QVERIFY(mouseArea->drag()->active());
+        QCOMPARE(flickable->isDragging(), false);
+        QTest::touchEvent(&window, device).release(0, p);
+        QCOMPARE(mouseArea->drag()->active(), false);
+    }
+}
+
 void tst_QQuickMouseArea::clickThrough()
 {
     // timestamp delay to avoid generating a double click