Update var property to null on object deletion

When a var property contains a pointer to a QObject-derived instance,
ensure that object deletion causes the property to be updated.

Task-number: QTBUG-26542
Change-Id: I67a59ffd7f09063328d45dc84889add55a5428e4
Reviewed-by: Martin Jones <martin.jones@nokia.com>

2 files changed, 52 insertions, 11 deletions

diff --git a/src/qml/qml/qqmlvmemetaobject.cpp b/src/qml/qml/qqmlvmemetaobject.cpp
index 5dcff3ea24..ce574875e3 100644
--- a/src/qml/qml/qqmlvmemetaobject.cpp
+++ b/src/qml/qml/qqmlvmemetaobject.cpp
@@ -57,8 +57,8 @@ Q_DECLARE_METATYPE(QJSValue);
 
 QT_BEGIN_NAMESPACE
 
-QQmlVMEVariantQObjectPtr::QQmlVMEVariantQObjectPtr()
-    : QQmlGuard<QObject>(0), m_target(0), m_index(-1)
+QQmlVMEVariantQObjectPtr::QQmlVMEVariantQObjectPtr(bool isVar)
+    : QQmlGuard<QObject>(0), m_target(0), m_isVar(isVar), m_index(-1)
 {
 }
 
@@ -66,10 +66,16 @@ QQmlVMEVariantQObjectPtr::~QQmlVMEVariantQObjectPtr()
 {
 }
 
-void QQmlVMEVariantQObjectPtr::objectDestroyed(QObject *)
+void QQmlVMEVariantQObjectPtr::objectDestroyed(QObject *o)
 {
-    if (m_target && m_index >= 0)
+    if (m_target && m_index >= 0) {
+        if (m_isVar && m_target->varPropertiesInitialized && !m_target->varProperties.IsEmpty()) {
+            // Set the var property to NULL
+            m_target->varProperties->Set(m_index - m_target->firstVarPropertyIndex, v8::Null());
+        }
+
         m_target->activate(m_target->object, m_target->methodOffset() + m_index, 0);
+    }
 }
 
 void QQmlVMEVariantQObjectPtr::setGuardedValue(QObject *obj, QQmlVMEMetaObject *target, int index)
@@ -336,7 +342,7 @@ void QQmlVMEVariant::setValue(QObject *v, QQmlVMEMetaObject *target, int index)
     if (type != QMetaType::QObjectStar) {
         cleanup();
         type = QMetaType::QObjectStar;
-        new (dataPtr()) QQmlVMEVariantQObjectPtr;
+        new (dataPtr()) QQmlVMEVariantQObjectPtr(false);
     }
     reinterpret_cast<QQmlVMEVariantQObjectPtr*>(dataPtr())->setGuardedValue(v, target, index);
 }
@@ -602,6 +608,8 @@ QQmlVMEMetaObject::~QQmlVMEMetaObject()
 
     if (metaData->varPropertyCount)
         qPersistentDispose(varProperties); // if not weak, will not have been cleaned up by the callback.
+
+    qDeleteAll(varObjectGuards);
 }
 
 int QQmlVMEMetaObject::metaCall(QMetaObject::Call c, int _id, void **a)
@@ -1036,15 +1044,30 @@ void QQmlVMEMetaObject::writeVarProperty(int id, v8::Handle<v8::Value> value)
         }
     }
 
-    // And, if the new value is a scarce resource, we need to ensure that it does not get
-    // automatically released by the engine until no other references to it exist.
+    QObject *valueObject = 0;
+    QQmlVMEVariantQObjectPtr *guard = getQObjectGuardForProperty(id);
+
     if (value->IsObject()) {
-        QV8VariantResource *r = v8_resource_cast<QV8VariantResource>(v8::Handle<v8::Object>::Cast(value));
-        if (r) {
+        // And, if the new value is a scarce resource, we need to ensure that it does not get
+        // automatically released by the engine until no other references to it exist.
+        if (QV8VariantResource *r = v8_resource_cast<QV8VariantResource>(v8::Handle<v8::Object>::Cast(value))) {
             r->addVmePropertyReference();
+        } else if (QV8QObjectResource *r = v8_resource_cast<QV8QObjectResource>(v8::Handle<v8::Object>::Cast(value))) {
+            // We need to track this QObject to signal its deletion
+            valueObject = r->object;
+
+            // Do we already have a QObject guard for this property?
+            if (valueObject && !guard) {
+                guard = new QQmlVMEVariantQObjectPtr(true);
+                varObjectGuards.append(guard);
+            }
         }
     }
 
+    if (guard) {
+        guard->setGuardedValue(valueObject, this, id);
+    }
+
     // Write the value and emit change signal as appropriate.
     varProperties->Set(id - firstVarPropertyIndex, value);
     activate(object, methodOffset() + id, 0);
@@ -1367,4 +1390,16 @@ QQmlVMEMetaObject *QQmlVMEMetaObject::getForSignal(QObject *o, int coreIndex)
     return vme;
 }
 
+QQmlVMEVariantQObjectPtr *QQmlVMEMetaObject::getQObjectGuardForProperty(int index) const
+{
+    QList<QQmlVMEVariantQObjectPtr *>::ConstIterator it = varObjectGuards.constBegin(), end = varObjectGuards.constEnd();
+    for ( ; it != end; ++it) {
+        if ((*it)->m_index == index) {
+            return *it;
+        }
+    }
+
+    return 0;
+}
+
 QT_END_NAMESPACE
diff --git a/src/qml/qml/qqmlvmemetaobject_p.h b/src/qml/qml/qqmlvmemetaobject_p.h
index 7a01b70b06..5751989b0c 100644
--- a/src/qml/qml/qqmlvmemetaobject_p.h
+++ b/src/qml/qml/qqmlvmemetaobject_p.h
@@ -141,13 +141,15 @@ class QQmlVMEMetaObject;
 class QQmlVMEVariantQObjectPtr : public QQmlGuard<QObject>
 {
 public:
-    inline QQmlVMEVariantQObjectPtr();
+    inline QQmlVMEVariantQObjectPtr(bool isVar);
     inline ~QQmlVMEVariantQObjectPtr();
+
     inline void objectDestroyed(QObject *);
     inline void setGuardedValue(QObject *obj, QQmlVMEMetaObject *target, int index);
 
     QQmlVMEMetaObject *m_target;
-    int m_index;
+    unsigned m_isVar : 1;
+    int m_index : 31;
 };
 
 class QV8QObjectWrapper;
@@ -238,6 +240,10 @@ public:
 
     void activate(QObject *, int, void **);
 
+    QList<QQmlVMEVariantQObjectPtr *> varObjectGuards;
+
+    QQmlVMEVariantQObjectPtr *getQObjectGuardForProperty(int) const;
+
     friend class QV8GCCallback;
     friend class QV8QObjectWrapper;
 };