Setting Connection's target to null should disconnect implicit target

Change-Id: Id7c8c7080e6db8bb6d09c1df13cddaef047cf611
Task-number: QTBUG-56499
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>

src/qml/types/qqmlconnections.cpp

@@ -159,9 +159,9 @@ private:
 void QQmlConnections::setTarget(QObject *obj)
 {
     Q_D(QQmlConnections);
-    d->targetSet = true; // even if setting to 0, it is *set*
-    if (d->target == obj)
+    if (d->targetSet && d->target == obj)
         return;
+    d->targetSet = true; // even if setting to 0, it is *set*
     foreach (QQmlBoundSignal *s, d->boundsignals) {
         // It is possible that target is being changed due to one of our signal
         // handlers -> use deleteLater().

tests/auto/qml/qqmlconnections/data/test-connection-implicit.qml

+import QtQuick 2.0
+
+Item {
+    width: 50
+
+    property bool tested: false
+
+    Connections { onWidthChanged: tested = true }
+}

tests/auto/qml/qqmlconnections/tst_qqmlconnections.cpp

@@ -56,6 +56,7 @@ private slots:
     void errors();
     void rewriteErrors();
     void singletonTypeTarget();
+    void clearImplicitTarget();
 
 private:
     QQmlEngine engine;
@@ -329,6 +330,32 @@ void tst_qqmlconnections::singletonTypeTarget()
     delete object;
 }
 
+//QTBUG-56499
+void tst_qqmlconnections::clearImplicitTarget()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("test-connection-implicit.qml"));
+    QQuickItem *item = qobject_cast<QQuickItem*>(c.create());
+
+    QVERIFY(item != 0);
+
+    // normal case: fire Connections
+    item->setWidth(100.);
+    QCOMPARE(item->property("tested").toBool(), true);
+
+    item->setProperty("tested", false);
+    // clear the implicit target
+    QQmlConnections *connections = item->findChild<QQmlConnections*>();
+    QVERIFY(connections);
+    connections->setTarget(0);
+
+    // target cleared: no longer fire Connections
+    item->setWidth(150.);
+    QCOMPARE(item->property("tested").toBool(), false);
+
+    delete item;
+}
+
 QTEST_MAIN(tst_qqmlconnections)
 
 #include "tst_qqmlconnections.moc"