qmlRegisterSingletonInstance: Do not crash if instance gets deleted

Use a QPointer, so that we notice if the object has been deleted.
Also ensure that in the documentation the function is in a single line,
as qdoc will otherwise silently omit it.

Change-Id: Idecd370d00089997cd18b3247ad2290a561b2b69
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/qml/qml/qqml.cpp b/src/qml/qml/qqml.cpp
index 8a50b51b5d..5b16a3c9e2 100644
--- a/src/qml/qml/qqml.cpp
+++ b/src/qml/qml/qqml.cpp
@@ -79,6 +79,13 @@ int qmlTypeId(const char *uri, int versionMajor, int versionMinor, const char *q
 // From qqmlprivate.h
 QObject *QQmlPrivate::RegisterSingletonFunctor::operator()(QQmlEngine *qeng, QJSEngine *)
 {
+    if (!m_object) {
+        QQmlError error;
+        error.setDescription(QLatin1String("The registered singleton has already been deleted. Ensure that it outlives the engine."));
+        QQmlEnginePrivate::get(qeng)->warning(qeng, error);
+        return nullptr;
+    }
+
     if (qeng->thread() != m_object->thread()) {
         QQmlError error;
         error.setDescription(QLatin1String("Registered object must live in the same thread as the engine it was registered with"));