MouseArea: don't get stuck in pressed state when disabling in press

In 8ace780b5a we fixed the case when
MouseArea hides itself on press. This time, the concern is when it
becomes _effectively_ disabled by disabling its parent on press.
(As explained in a comment on QTBUG-38364, the MouseArea.enabled state
is independent, but we can nevertheless also find out when the effective
enabled state changes.)

[ChangeLog][QtQuick][MouseArea] When a MouseArea becomes effectively
disabled due to a parent's enabled property being set false while the
mouse is pressed, the press will now be canceled.

Fixes: QTBUG-39806
Fixes: QTBUG-103788
Change-Id: I8d69b535b6e1b5d51ad1e030f52217de9ab541f1
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/quick/items/qquickmousearea.cpp

@@ -1038,6 +1038,12 @@ void QQuickMouseArea::itemChange(ItemChange change, const ItemChangeData &value)
 {
     Q_D(QQuickMouseArea);
     switch (change) {
+    case ItemEnabledHasChanged:
+        // If MouseArea becomes effectively disabled by disabling a parent
+        // (for example, onPressed: parent.enabled = false), cancel the pressed state.
+        if (d->pressed && !d->effectiveEnable)
+            ungrabMouse();
+        break;
     case ItemVisibleHasChanged:
         if (d->effectiveEnable && d->enabled && hoverEnabled() && d->hovered != (isVisible() && isUnderMouse())) {
             if (!d->hovered) {
@@ -1048,7 +1054,7 @@ void QQuickMouseArea::itemChange(ItemChange change, const ItemChangeData &value)
             setHovered(!d->hovered);
         }
         if (d->pressed && (!isVisible())) {
-            // This happens when the mouse area sets itself disabled or hidden
+            // This happens when the mouse area hides itself
             // inside the press handler. In that case we should not keep the internal
             // state as pressed, since we never became the mouse grabber.
             ungrabMouse();

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

@@ -0,0 +1,14 @@
+import QtQuick
+
+Rectangle {
+    id: whiteRect
+    width: 200
+    height: 200
+    color: ma.pressed ? "lightsteelblue" : "white"
+    MouseArea {
+        id: ma
+        objectName: "mousearea"
+        anchors.fill: parent
+        onPressed: parent.enabled = false
+    }
+}

tests/auto/quick/qquickmousearea/tst_qquickmousearea.cpp

@@ -110,6 +110,8 @@ private slots:
     void subtreeHoverEnabled();
     void hoverWhenDisabled();
     void disableAfterPress();
+    void disableParentOnPress_data();
+    void disableParentOnPress();
     void onWheel();
     void transformedMouseArea_data();
     void transformedMouseArea();
@@ -1532,6 +1534,53 @@ void tst_QQuickMouseArea::disableAfterPress()
     QCOMPARE(mouseReleaseSpy.size(), 0);
 }
 
+void tst_QQuickMouseArea::disableParentOnPress_data()
+{
+    QTest::addColumn<const QPointingDevice *>("device");
+
+    QTest::newRow("core pointer") << QPointingDevice::primaryPointingDevice();
+    QTest::newRow("touch") << device;
+}
+
+void tst_QQuickMouseArea::disableParentOnPress() // QTBUG-39806 and QTBUG-103788
+{
+    QFETCH(const QPointingDevice *, device);
+
+    QQuickView window;
+    QVERIFY(QQuickTest::showView(window, testFileUrl("disableParentOnPress.qml")));
+    QQuickItem *root = window.rootObject();
+    QVERIFY(root);
+    QQuickMouseArea *mouseArea = root->findChild<QQuickMouseArea*>();
+    QVERIFY(mouseArea);
+
+    QSignalSpy pressedChangedSpy(mouseArea, &QQuickMouseArea::pressedChanged);
+    QSignalSpy canceledSpy(mouseArea, &QQuickMouseArea::canceled);
+    QSignalSpy enabledSpy(mouseArea, &QQuickMouseArea::enabledChanged);
+    QSignalSpy parentEnabledSpy(root, &QQuickItem::enabledChanged);
+    const QPoint p(100, 100);
+
+    QQuickTest::pointerPress(device, &window, 0, p);
+    QTRY_COMPARE(parentEnabledSpy.size(), 1);
+    QCOMPARE(root->isEnabled(), false);
+    QCOMPARE(mouseArea->isEnabled(), true); // enabled is independent, unfortunately (inverse of QTBUG-38364)
+    QCOMPARE(QQuickItemPrivate::get(mouseArea)->effectiveEnable, false);
+    // bug fix: it knows it got effectively disabled, so now it's no longer pressed
+    QCOMPARE(mouseArea->pressed(), false);
+    QCOMPARE(canceledSpy.size(), 1); // ...because the press was canceled
+    QCOMPARE(pressedChangedSpy.size(), 2); // kerchunk
+    QQuickTest::pointerRelease(device, &window, 0, p);
+
+    // now re-enable it and try again
+    root->setEnabled(true);
+    QQuickTest::pointerPress(device, &window, 0, p);
+    QTRY_COMPARE(root->isEnabled(), false);
+    QCOMPARE(QQuickItemPrivate::get(mouseArea)->effectiveEnable, false);
+    QCOMPARE(mouseArea->pressed(), false);
+    QCOMPARE(canceledSpy.size(), 2);
+    QCOMPARE(pressedChangedSpy.size(), 4);
+    QQuickTest::pointerRelease(device, &window, 0, p);
+}
+
 void tst_QQuickMouseArea::onWheel()
 {
     QQuickView window;