Loader: Also drop engine when clearing contexts recursively

Simply clearing the expressions is not enough. We might have internal
signal/slot connections in addition. The main protagonists of such
behavior listen to context invalidation, though, and a context without
engine counts as invalid. At the same time, we leave the context object
in place so that we don't re-open QTBUG-66822. The currently running
binding will still be able to complete this way.

Fixes: QTBUG-118188
Change-Id: Ia973be26f0e4e3244adc71f95df7e0b4bef412c3
Reviewed-by: Sami Shalayel <sami.shalayel@qt.io>
(cherry picked from commit 054873dfea0ce07c94bb603edc3b7d61a6190c4f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 6b57107d908df535b04357e4fa9a716a03547429)
(cherry picked from commit f68cfe5ceb903f2091b2ce23032823a863f184c7)
(cherry picked from commit 26481958d806b2ca2f144a2667dc38e59df6ba7f)
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 87 insertions, 3 deletions

diff --git a/src/qml/qml/qqmlcontextdata.cpp b/src/qml/qml/qqmlcontextdata.cpp
index 6dc2f22a23..64fb3a5d30 100644
--- a/src/qml/qml/qqmlcontextdata.cpp
+++ b/src/qml/qml/qqmlcontextdata.cpp
@@ -100,7 +100,6 @@ void QQmlContextData::invalidate()
     }
 
     m_importedScripts.clear();
-
     m_engine = nullptr;
     clearParent();
 }
@@ -111,6 +110,8 @@ void QQmlContextData::clearContextRecursively()
 
     for (auto ctxIt = m_childContexts; ctxIt; ctxIt = ctxIt->m_nextChild)
         ctxIt->clearContextRecursively();
+
+    m_engine = nullptr;
 }
 
 void QQmlContextData::clearContext()
@@ -137,8 +138,7 @@ QQmlContextData::~QQmlContextData()
 
     // avoid recursion
     addref();
-    if (m_engine)
-        invalidate();
+    invalidate();
     m_linkedContext.reset();
 
     Q_ASSERT(refCount() == 1);
diff --git a/tests/auto/quick/qquickloader/data/invalidateContext.qml b/tests/auto/quick/qquickloader/data/invalidateContext.qml
new file mode 100644
index 0000000000..b5a28f5d0f
--- /dev/null
+++ b/tests/auto/quick/qquickloader/data/invalidateContext.qml
@@ -0,0 +1,28 @@
+import QtQuick
+
+Item  {
+    Loader {
+        active: loaderActive
+        sourceComponent: comp
+    }
+
+    Component {
+        id: comp
+        Column {
+            Repeater {
+                id: repeater
+                model: cppModel
+
+                Component.onCompleted: console.log("Repeater constructed");
+                Component.onDestruction: console.log("Repeater destroyed");
+
+                delegate: Text {
+                    text: {
+                        console.log("updating text");
+                        return display + rootData.getValue();
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/tests/auto/quick/qquickloader/tst_qquickloader.cpp b/tests/auto/quick/qquickloader/tst_qquickloader.cpp
index 389f037166..afc49fe74d 100644
--- a/tests/auto/quick/qquickloader/tst_qquickloader.cpp
+++ b/tests/auto/quick/qquickloader/tst_qquickloader.cpp
@@ -117,6 +117,8 @@ private slots:
     void stackOverflow();
     void stackOverflow2();
     void boundComponent();
+
+    void invalidateContext();
 };
 
 Q_DECLARE_METATYPE(QList<QQmlError>)
@@ -1585,6 +1587,60 @@ void tst_QQuickLoader::boundComponent()
     QCOMPARE(o->objectName(), QStringLiteral("loaded"));
 }
 
+class CppModel : public QAbstractListModel
+{
+public:
+    virtual int rowCount(const QModelIndex &) const override {return 1;}
+    virtual QVariant data(const QModelIndex &, int) const override { return "test"; }
+
+    void reset () {beginResetModel(); endResetModel();}
+};
+
+class RootData : public QObject
+{
+    Q_OBJECT
+public:
+    RootData() : object(std::make_unique<QObject>())
+    {
+        object->setObjectName("objectName");
+    }
+
+    Q_INVOKABLE QString getValue() const {  return object->objectName(); }
+
+    void deleteObject() { object.reset(); }
+
+private:
+    std::unique_ptr<QObject> object;
+};
+
+void tst_QQuickLoader::invalidateContext()
+{
+    CppModel model;
+    RootData rootData;
+
+    QQmlEngine engine;
+    QQmlContext *rootContext = engine.rootContext();
+    rootContext->setContextProperty("cppModel", &model);
+    rootContext->setContextProperty("loaderActive", true);
+    rootContext->setContextProperty("rootData", &rootData);
+
+    QQmlComponent component(&engine, testFileUrl("invalidateContext.qml"));\
+    QVERIFY2(component.isReady(), qPrintable(component.errorString()));
+
+    QTest::ignoreMessage(QtDebugMsg, "Repeater constructed");
+    QTest::ignoreMessage(QtDebugMsg, "updating text");
+    QScopedPointer<QObject> o(component.create());
+
+    QTest::ignoreMessage(QtDebugMsg, "Repeater destroyed");
+    rootContext->setContextProperty("loaderActive", false);
+
+    // The object should never be used anymore, as loader is inactive
+    rootData.deleteObject();
+
+    // Should not trigger any re-evaluation (which would crash in getValue())
+    model.reset();
+}
+
 QTEST_MAIN(tst_QQuickLoader)
 
 #include "tst_qquickloader.moc"