When deactivating a loader, do not immediately clear its context

In 2eb2d6386da304cd1164264ae0bff685c796d89c, deactivating/clearing the
loader would now prevent any subsequent bindings from being evaluated.
The problem there was that the item created by the loader wouldn't have
a parent item (among things) anymore, so references to it in the
bindings would result in errors.

The way to prevent it was done by invalidating the context of the item,
which in turn would detach it from the root context. This is a problem
if objects in the root context are referenced after
deactivating/clearing the loader:

  onSomethingChanged: {
    loader.source = ""
    objectInRootContext.doIt()
  }

This would result in a ReferenceError when resolving objectInRootContext
and break the behavior present before the fix mentioned above. The
correct way is to recursively clear the context set on all bindings, but
leave everything in place. This way, no subsequent bindings will be
evaluated, but the currently "running" scripts will still be able to
reach the root context.

Task-number: QTBUG-66822
Change-Id: Ic9c2ab0a752093a26967da4783cb4c29cf83d2ca
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Michael Brasser <michael.brasser@live.com>

5 files changed, 127 insertions, 2 deletions

diff --git a/src/qml/qml/qqmlcontext.cpp b/src/qml/qml/qqmlcontext.cpp
index 6e43bc735f..5dd3278b4c 100644
--- a/src/qml/qml/qqmlcontext.cpp
+++ b/src/qml/qml/qqmlcontext.cpp
@@ -593,6 +593,14 @@ void QQmlContextData::invalidate()
     parent = nullptr;
 }
 
+void QQmlContextData::clearContextRecursively()
+{
+    clearContext();
+
+    for (auto ctxIt = childContexts; ctxIt; ctxIt = ctxIt->nextChild)
+        ctxIt->clearContextRecursively();
+}
+
 void QQmlContextData::clearContext()
 {
     emitDestruction();
diff --git a/src/qml/qml/qqmlcontext_p.h b/src/qml/qml/qqmlcontext_p.h
index ff36d6c9a8..5dfee48848 100644
--- a/src/qml/qml/qqmlcontext_p.h
+++ b/src/qml/qml/qqmlcontext_p.h
@@ -115,6 +115,7 @@ public:
     QQmlContextData(QQmlContext *);
     void emitDestruction();
     void clearContext();
+    void clearContextRecursively();
     void invalidate();
 
     inline bool isValid() const {
diff --git a/src/quick/items/qquickloader.cpp b/src/quick/items/qquickloader.cpp
index 34f30e81a3..6960e16bd9 100644
--- a/src/quick/items/qquickloader.cpp
+++ b/src/quick/items/qquickloader.cpp
@@ -102,7 +102,7 @@ void QQuickLoaderPrivate::clear()
     // this we may get transient errors from use of 'parent', for example.
     QQmlContext *context = qmlContext(object);
     if (context)
-        QQmlContextData::get(context)->invalidate();
+        QQmlContextData::get(context)->clearContextRecursively();
 
     if (loadingFromSource && component) {
         // disconnect since we deleteLater
@@ -363,7 +363,7 @@ void QQuickLoader::setActive(bool newVal)
         // this we may get transient errors from use of 'parent', for example.
         QQmlContext *context = qmlContext(d->object);
         if (context)
-            QQmlContextData::get(context)->invalidate();
+            QQmlContextData::get(context)->clearContextRecursively();
 
         if (d->item) {
             QQuickItemPrivate *p = QQuickItemPrivate::get(d->item);
diff --git a/tests/auto/quick/qquickloader/data/rootContext.qml b/tests/auto/quick/qquickloader/data/rootContext.qml
new file mode 100644
index 0000000000..277db43d57
--- /dev/null
+++ b/tests/auto/quick/qquickloader/data/rootContext.qml
@@ -0,0 +1,55 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the manual tests of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.0
+
+Rectangle {
+    width: 360
+    height: 360
+
+    property alias loader: loader
+
+    Loader {
+        id: loader
+    }
+
+    property Component component: Item {
+        property bool trigger: false
+        onTriggerChanged: {
+            objectInRootContext.doIt() // make sure we can resolve objectInRootContext
+            loader.active = false
+            objectInRootContext.doIt() // make sure we can STILL resolve objectInRootContext
+            anotherProperty = true // see if we can trigger subsequent signal handlers (we shouldn't)
+        }
+        property bool anotherProperty: false
+        onAnotherPropertyChanged: {
+            // this should never be executed
+            objectInRootContext.doIt()
+        }
+    }
+}
diff --git a/tests/auto/quick/qquickloader/tst_qquickloader.cpp b/tests/auto/quick/qquickloader/tst_qquickloader.cpp
index 30fc52f95a..7a176661e8 100644
--- a/tests/auto/quick/qquickloader/tst_qquickloader.cpp
+++ b/tests/auto/quick/qquickloader/tst_qquickloader.cpp
@@ -29,6 +29,7 @@
 
 #include <QSignalSpy>
 
+#include <QtQml/QQmlContext>
 #include <QtQml/qqmlengine.h>
 #include <QtQml/qqmlcomponent.h>
 #include <QtQml/qqmlincubator.h>
@@ -123,6 +124,8 @@ private slots:
 
     void bindings();
     void parentErrors();
+
+    void rootContext();
 };
 
 Q_DECLARE_METATYPE(QList<QQmlError>)
@@ -1327,6 +1330,64 @@ void tst_QQuickLoader::parentErrors()
     QVERIFY2(warningsSpy.isEmpty(), qPrintable(failureMessage));
 }
 
+class ObjectInRootContext: public QObject
+{
+    Q_OBJECT
+
+public:
+    int didIt = 0;
+
+public slots:
+    void doIt() {
+        didIt += 1;
+    }
+};
+
+void tst_QQuickLoader::rootContext()
+{
+    QQmlEngine engine;
+    ObjectInRootContext objectInRootContext;
+    engine.rootContext()->setContextProperty("objectInRootContext", &objectInRootContext);
+
+    QQmlComponent component(&engine, testFileUrl("rootContext.qml"));
+    QScopedPointer<QObject> object(component.create());
+    QVERIFY(!object.isNull());
+
+    QQuickLoader *loader = object->property("loader").value<QQuickLoader*>();
+    QVERIFY(loader);
+
+    QSignalSpy warningsSpy(&engine, SIGNAL(warnings(QList<QQmlError>)));
+
+    // Give the loader a component
+    loader->setSourceComponent(object->property("component").value<QQmlComponent*>());
+    QTRY_VERIFY(loader->active());
+    QTRY_VERIFY(loader->item());
+
+    QString failureMessage;
+    if (!warningsSpy.isEmpty()) {
+        QDebug stream(&failureMessage);
+        stream << warningsSpy.first().first().value<QList<QQmlError>>();
+    }
+    QVERIFY2(warningsSpy.isEmpty(), qPrintable(failureMessage));
+    QCOMPARE(objectInRootContext.didIt, 0);
+
+    // Deactivate the loader, which deletes the item.
+    // Check that a) there are no errors, and b) the objectInRootContext can still be resolved even
+    // after deactivating the loader. If it cannot, a ReferenceError for objectInRootContext is
+    // generated (and the 'doIt' counter in objectInRootContext will be 1 for the call before
+    // the deactivation).
+    loader->item()->setProperty("trigger", true);
+    QTRY_VERIFY(!loader->active());
+    QTRY_VERIFY(!loader->item());
+
+    if (!warningsSpy.isEmpty()) {
+        QDebug stream(&failureMessage);
+        stream << warningsSpy.first().first().value<QList<QQmlError>>();
+    }
+    QVERIFY2(warningsSpy.isEmpty(), qPrintable(failureMessage));
+    QCOMPARE(objectInRootContext.didIt, 2);
+}
+
 QTEST_MAIN(tst_QQuickLoader)
 
 #include "tst_qquickloader.moc"