QQuickLoader: Check for QQmlEngine before using it

The loader's context may have been removed from the context hierarchy or
it may not have a context in the first place. We should not crash then.

Fixes: QTBUG-67950
Change-Id: I1058d5b1f978aa040f8b2f018c4357dd7a3ef333
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 79e885537f8546a18d7d9d902d6efe40b1915c96)

2 files changed, 20 insertions, 7 deletions

diff --git a/src/quick/items/qquickloader.cpp b/src/quick/items/qquickloader.cpp
index 93cff95b7b..7b08ec5a66 100644
--- a/src/quick/items/qquickloader.cpp
+++ b/src/quick/items/qquickloader.cpp
@@ -439,9 +439,8 @@ void QQuickLoader::loadFromSource()
     }
 
     if (isComponentComplete()) {
-        QQmlComponent::CompilationMode mode = d->asynchronous ? QQmlComponent::Asynchronous : QQmlComponent::PreferSynchronous;
         if (!d->component)
-            d->component.setObject(new QQmlComponent(qmlEngine(this), d->source, mode, this), this);
+            d->createComponent();
         d->load();
     }
 }
@@ -806,11 +805,8 @@ void QQuickLoader::componentComplete()
     Q_D(QQuickLoader);
     QQuickItem::componentComplete();
     if (active()) {
-        if (d->loadingFromSource) {
-            QQmlComponent::CompilationMode mode = d->asynchronous ? QQmlComponent::Asynchronous : QQmlComponent::PreferSynchronous;
-            if (!d->component)
-                d->component.setObject(new QQmlComponent(qmlEngine(this), d->source, mode, this), this);
-        }
+        if (d->loadingFromSource && !d->component)
+            d->createComponent();
         d->load();
     }
 }
@@ -1044,6 +1040,22 @@ void QQuickLoaderPrivate::updateStatus()
     }
 }
 
+void QQuickLoaderPrivate::createComponent()
+{
+    Q_Q(QQuickLoader);
+    const QQmlComponent::CompilationMode mode = asynchronous
+            ? QQmlComponent::Asynchronous
+            : QQmlComponent::PreferSynchronous;
+    if (QQmlContext *context = qmlContext(q)) {
+        if (QQmlEngine *engine = context->engine()) {
+            component.setObject(new QQmlComponent(engine, source, mode, q), q);
+            return;
+        }
+    }
+
+    qmlWarning(q) << "createComponent: Cannot find a QML engine.";
+}
+
 #include <moc_qquickloader_p.cpp>
 
 QT_END_NAMESPACE
diff --git a/src/quick/items/qquickloader_p_p.h b/src/quick/items/qquickloader_p_p.h
index 5fc231a8e6..4c63b82b6a 100644
--- a/src/quick/items/qquickloader_p_p.h
+++ b/src/quick/items/qquickloader_p_p.h
@@ -98,6 +98,7 @@ public:
     QV4::ReturnedValue extractInitialPropertyValues(QQmlV4Function *args, QObject *loader, bool *error);
     QQuickLoader::Status computeStatus() const;
     void updateStatus();
+    void createComponent();
 
     qreal getImplicitWidth() const override;
     qreal getImplicitHeight() const override;