Ensure that variant property references keep QObjects alive

Previously, only var property references could keep QObjects alive.
This meant that the garbage collector would collect QObject data
prematurely.

This commit ensures that variant properties keep QObjects alive as
required.

Task-number: QTBUG-24767
Change-Id: Ic98a06863251a3e7d6384ba9256810a78fb23406
Reviewed-by: Martin Jones <martin.jones@nokia.com>

1 files changed, 31 insertions, 3 deletions

diff --git a/src/qml/qml/qqmlvmemetaobject.cpp b/src/qml/qml/qqmlvmemetaobject.cpp
index 50fda6db39..2434ef0a2b 100644
--- a/src/qml/qml/qqmlvmemetaobject.cpp
+++ b/src/qml/qml/qqmlvmemetaobject.cpp
@@ -515,6 +515,9 @@ QQmlVMEMetaObject::QQmlVMEMetaObject(QObject *obj,
 
     aConnected.resize(metaData->aliasCount);
     int list_type = qMetaTypeId<QQmlListProperty<QObject> >();
+    int qobject_type = qMetaTypeId<QObject*>();
+    int variant_type = qMetaTypeId<QVariant>();
+    bool needsGcCallback = (metaData->varPropertyCount > 0);
 
     // ### Optimize
     for (int ii = 0; ii < metaData->propertyCount - metaData->varPropertyCount; ++ii) {
@@ -522,12 +525,20 @@ QQmlVMEMetaObject::QQmlVMEMetaObject(QObject *obj,
         if (t == list_type) {
             listProperties.append(List(methodOffset() + ii, this));
             data[ii].setValue(listProperties.count() - 1);
-        } 
+        } else if (!needsGcCallback && (t == qobject_type || t == variant_type)) {
+            needsGcCallback = true;
+        }
     }
 
     firstVarPropertyIndex = metaData->propertyCount - metaData->varPropertyCount;
-    if (metaData->varPropertyCount)
+
+    // both var properties and variant properties can keep references to
+    // other QObjects, and var properties can also keep references to
+    // JavaScript objects.  If we have any properties, we need to hook
+    // the gc() to ensure that references keep objects alive as needed.
+    if (needsGcCallback) {
         QV8GCCallback::addGcCallbackNode(this);
+    }
 }
 
 QQmlVMEMetaObject::~QQmlVMEMetaObject()
@@ -1121,9 +1132,26 @@ void QQmlVMEMetaObject::GcPrologueCallback(QV8GCCallback::Node *node)
 {
     QQmlVMEMetaObject *vmemo = static_cast<QQmlVMEMetaObject*>(node);
     Q_ASSERT(vmemo);
-    if (!vmemo->varPropertiesInitialized || vmemo->varProperties.IsEmpty() || !vmemo->ctxt || !vmemo->ctxt->engine)
+
+    if (!vmemo->ctxt || !vmemo->ctxt->engine)
         return;
     QQmlEnginePrivate *ep = QQmlEnginePrivate::get(vmemo->ctxt->engine);
+
+    // add references created by VMEVariant properties
+    int maxDataIdx = vmemo->metaData->propertyCount - vmemo->metaData->varPropertyCount;
+    for (int ii = 0; ii < maxDataIdx; ++ii) { // XXX TODO: optimise?
+        if (vmemo->data[ii].dataType() == QMetaType::QObjectStar) {
+            // possible QObject reference.
+            QObject *ref = vmemo->data[ii].asQObject();
+            if (ref) {
+                ep->v8engine()->addRelationshipForGC(vmemo->object, ref);
+            }
+        }
+    }
+
+    // add references created by var properties
+    if (!vmemo->varPropertiesInitialized || vmemo->varProperties.IsEmpty())
+        return;
     ep->v8engine()->addRelationshipForGC(vmemo->object, vmemo->varProperties);
 }