Connections: Don't crash when target is deleted

Pick-to: 6.4 6.2
Fixes: QTBUG-108697
Change-Id: I019edf3a0a702ad1dca340473265933e4d131e99
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/qml/types/qqmlconnections.cpp

@@ -24,15 +24,13 @@ Q_LOGGING_CATEGORY(lcQmlConnections, "qt.qml.connections")
 class QQmlConnectionsPrivate : public QObjectPrivate
 {
 public:
-    QQmlConnectionsPrivate() : target(nullptr), enabled(true), targetSet(false), ignoreUnknownSignals(false), componentcomplete(true) {}
-
     QList<QQmlBoundSignal*> boundsignals;
-    QObject *target;
+    QQmlGuard<QObject> target;
 
-    bool enabled;
-    bool targetSet;
-    bool ignoreUnknownSignals;
-    bool componentcomplete;
+    bool enabled = true;
+    bool targetSet = false;
+    bool ignoreUnknownSignals = false;
+    bool componentcomplete = true;
 
     QQmlRefPointer<QV4::ExecutableCompilationUnit> compilationUnit;
     QList<const QV4::CompiledData::Binding *> bindings;
@@ -119,7 +117,7 @@ QQmlConnections::QQmlConnections(QObject *parent) :
 QObject *QQmlConnections::target() const
 {
     Q_D(const QQmlConnections);
-    return d->targetSet ? d->target : parent();
+    return d->targetSet ? d->target.data() : parent();
 }
 
 class QQmlBoundSignalDeleter : public QObject

tests/auto/qml/qqmlconnections/data/invalidTarget.qml

@@ -0,0 +1,31 @@
+import QtQml
+
+QtObject {
+    id: root
+    objectName: button.objectName
+
+    property QtObject b: QtObject {
+        objectName: "button"
+        id: button
+        signal clicked
+    }
+
+    property Connections c: Connections {
+        id: connections
+        target: null
+        function onClicked() { button.destroy(); }
+    }
+
+    property Timer t: Timer {
+       interval: 10
+       running: true
+       onTriggered: {
+           root.objectName = connections.target.objectName
+       }
+    }
+
+    Component.onCompleted: {
+        connections.target = button;
+        button.clicked()
+    }
+}

tests/auto/qml/qqmlconnections/tst_qqmlconnections.cpp

@@ -53,6 +53,7 @@ private slots:
     void noAcceleratedGlobalLookup();
 
     void bindToPropertyWithUnderscoreChangeHandler();
+    void invalidTarget();
 
 private:
     QQmlEngine engine;
@@ -465,6 +466,25 @@ void tst_qqmlconnections::bindToPropertyWithUnderscoreChangeHandler()
     QVERIFY(root->property("success").toBool());
 }
 
+void tst_qqmlconnections::invalidTarget()
+{
+    QQmlEngine engine;
+    const QUrl url = testFileUrl("invalidTarget.qml");
+    QQmlComponent component(&engine, url);
+    QVERIFY2(component.isReady(), qPrintable(component.errorString()));
+
+    QScopedPointer<QObject> root {component.create()};
+    QVERIFY(root);
+    QCOMPARE(root->objectName(), QStringLiteral("button"));
+
+    QTest::ignoreMessage(
+                QtWarningMsg,
+                qPrintable(
+                    url.toString()
+                    + QLatin1String(":5:5: TypeError: Cannot read property 'objectName' of null")));
+    QTRY_VERIFY(root->objectName().isEmpty());
+}
+
 QTEST_MAIN(tst_qqmlconnections)
 
 #include "tst_qqmlconnections.moc"