make QScriptEngine::setGlobalObject() work to some extent

JSC requires that the global object is actually a
JSGlobalObject instance, whereas QScriptEngine::setGlobalObject()
allows any object to be set as the global object. The way we
solve this is by proxying from an internal global object to the
custom (user-set) object.

We need to take care that the internal global object is never
actually exposed through our API; a brilliantly named helper
function, toUsableValue(), makes that happen.

Evaluating "var a = 10" with a custom global object doesn't work
yet; the variable always ends up in the internal Global Object.
For variable assignments, JSC appears to bypass the normal
JSObject::put() and instead use
JSGlobalObject::copyGlobals{From,To}(), which means I can't
intercept and proxy the assignments.

This commit enough to get the Context2D example working. There's
another bug with iteration of the built-in Global Object's
properties (non-enumerable properties are always skipped by the
JSC C++ API, whereas with QScriptValueIterator they should not
be), but that's a totally separate issue.

5 files changed, 165 insertions, 34 deletions

diff --git a/src/script/api/qscriptengine.cpp b/src/script/api/qscriptengine.cpp
index 2f7e976..1b7d0e4 100644
--- a/src/script/api/qscriptengine.cpp
+++ b/src/script/api/qscriptengine.cpp
@@ -321,7 +321,7 @@ struct GlobalClientData : public JSC::JSGlobalData::ClientData
 class GlobalObject : public JSC::JSGlobalObject
 {
 public:
-    GlobalObject(QScriptEnginePrivate*);
+    GlobalObject();
     virtual ~GlobalObject();
     virtual JSC::UString className() const { return "global"; }
     virtual void mark();
@@ -337,7 +337,44 @@ public:
     virtual void getPropertyNames(JSC::ExecState*, JSC::PropertyNameArray&);
 
 public:
-    QScriptEnginePrivate *engine;
+    JSC::JSObject *customGlobalObject;
+};
+
+class OriginalGlobalObjectProxy : public JSC::JSObject
+{
+public:
+    explicit OriginalGlobalObjectProxy(WTF::PassRefPtr<JSC::Structure> sid,
+                                       JSC::JSGlobalObject *object)
+        : JSC::JSObject(sid), originalGlobalObject(object)
+    {}
+    virtual ~OriginalGlobalObjectProxy()
+    {}
+    virtual JSC::UString className() const
+    { return originalGlobalObject->className(); }
+    virtual void mark()
+    {
+        Q_ASSERT(!marked());
+        if (!originalGlobalObject->marked())
+            originalGlobalObject->JSC::JSGlobalObject::mark();
+        JSC::JSObject::mark();
+    }
+    virtual bool getOwnPropertySlot(JSC::ExecState* exec,
+                                    const JSC::Identifier& propertyName,
+                                    JSC::PropertySlot& slot)
+    { return originalGlobalObject->JSC::JSGlobalObject::getOwnPropertySlot(exec, propertyName, slot); }
+    virtual void put(JSC::ExecState* exec, const JSC::Identifier& propertyName,
+                     JSC::JSValue value, JSC::PutPropertySlot& slot)
+    { originalGlobalObject->JSC::JSGlobalObject::put(exec, propertyName, value, slot); }
+    virtual bool deleteProperty(JSC::ExecState* exec,
+                                const JSC::Identifier& propertyName)
+    { return originalGlobalObject->JSC::JSGlobalObject::deleteProperty(exec, propertyName); }
+    virtual bool getPropertyAttributes(JSC::ExecState* exec, const JSC::Identifier& propertyName,
+                                       unsigned& attributes) const
+    { return originalGlobalObject->JSC::JSGlobalObject::getPropertyAttributes(exec, propertyName, attributes); }
+    virtual void getPropertyNames(JSC::ExecState* exec, JSC::PropertyNameArray& propertyNames)
+    { originalGlobalObject->JSC::JSGlobalObject::getPropertyNames(exec, propertyNames); }
+private:
+    JSC::JSGlobalObject *originalGlobalObject;
 };
 
 static int toDigit(char c)
@@ -585,8 +622,8 @@ JSC::JSValue functionConnect(JSC::ExecState *exec, JSC::JSObject */*callee*/, JS
 #endif // QT_NO_QOBJECT
 }
 
-GlobalObject::GlobalObject(QScriptEnginePrivate *eng)
-    : JSC::JSGlobalObject(), engine(eng)
+GlobalObject::GlobalObject()
+    : JSC::JSGlobalObject(), customGlobalObject(0)
 {
 }
 
@@ -596,37 +633,52 @@ GlobalObject::~GlobalObject()
 
 void GlobalObject::mark()
 {
+    Q_ASSERT(!marked());
     JSC::JSGlobalObject::mark();
+    if (customGlobalObject && !customGlobalObject->marked())
+        customGlobalObject->mark();
 }
 
 bool GlobalObject::getOwnPropertySlot(JSC::ExecState* exec,
                                       const JSC::Identifier& propertyName,
                                       JSC::PropertySlot& slot)
 {
+    if (customGlobalObject)
+        return customGlobalObject->getOwnPropertySlot(exec, propertyName, slot);
     return JSC::JSGlobalObject::getOwnPropertySlot(exec, propertyName, slot);
 }
 
 void GlobalObject::put(JSC::ExecState* exec, const JSC::Identifier& propertyName,
                        JSC::JSValue value, JSC::PutPropertySlot& slot)
 {
-    JSC::JSGlobalObject::put(exec, propertyName, value, slot);
+    if (customGlobalObject)
+        customGlobalObject->put(exec, propertyName, value, slot);
+    else
+        JSC::JSGlobalObject::put(exec, propertyName, value, slot);
 }
 
 bool GlobalObject::deleteProperty(JSC::ExecState* exec,
                                   const JSC::Identifier& propertyName)
 {
+    if (customGlobalObject)
+        return customGlobalObject->deleteProperty(exec, propertyName);
     return JSC::JSGlobalObject::deleteProperty(exec, propertyName);
 }
 
 bool GlobalObject::getPropertyAttributes(JSC::ExecState* exec, const JSC::Identifier& propertyName,
                                          unsigned& attributes) const
 {
+    if (customGlobalObject)
+        return customGlobalObject->getPropertyAttributes(exec, propertyName, attributes);
     return JSC::JSGlobalObject::getPropertyAttributes(exec, propertyName, attributes);
 }
 
 void GlobalObject::getPropertyNames(JSC::ExecState* exec, JSC::PropertyNameArray& propertyNames)
 {
-    JSC::JSGlobalObject::getPropertyNames(exec, propertyNames);
+    if (customGlobalObject)
+        customGlobalObject->getPropertyNames(exec, propertyNames);
+    else
+        JSC::JSGlobalObject::getPropertyNames(exec, propertyNames);
 }
 
 static JSC::JSValue JSC_HOST_CALL functionPrint(JSC::ExecState*, JSC::JSObject*, JSC::JSValue, const JSC::ArgList&);
@@ -785,6 +837,7 @@ JSC::JSValue stringProtoFuncArg(JSC::ExecState *exec, JSC::JSObject*, JSC::JSVal
 namespace JSC {
 
 ASSERT_CLASS_FITS_IN_CELL(QScript::GlobalObject);
+ASSERT_CLASS_FITS_IN_CELL(QScript::OriginalGlobalObjectProxy);
 
 } // namespace JSC
 
@@ -796,7 +849,7 @@ QScriptEnginePrivate::QScriptEnginePrivate() : idGenerator(1)
 
     globalData = JSC::JSGlobalData::create().releaseRef();
     globalData->clientData = new QScript::GlobalClientData(this);
-    JSC::JSGlobalObject *globalObject = new (globalData)QScript::GlobalObject(this);
+    JSC::JSGlobalObject *globalObject = new (globalData)QScript::GlobalObject();
 
     JSC::ExecState* exec = globalObject->globalExec();
 
@@ -821,7 +874,7 @@ QScriptEnginePrivate::QScriptEnginePrivate() : idGenerator(1)
 
     currentFrame = exec;
 
-    customGlobalObject = 0;
+    originalGlobalObjectProxy = 0;
     agent = 0;
     processEventsInterval = -1;
 }
@@ -1029,20 +1082,79 @@ void QScriptEnginePrivate::releaseContextForFrame(JSC::ExecState *frame)
     delete ctx;
 }
 
-JSC::JSGlobalObject *QScriptEnginePrivate::globalObject() const
+JSC::JSGlobalObject *QScriptEnginePrivate::originalGlobalObject() const
 {
     return globalData->head;
 }
 
+JSC::JSObject *QScriptEnginePrivate::customGlobalObject() const
+{
+    QScript::GlobalObject *glob = static_cast<QScript::GlobalObject*>(originalGlobalObject());
+    return glob->customGlobalObject;
+}
+
+JSC::JSObject *QScriptEnginePrivate::getOriginalGlobalObjectProxy()
+{
+    if (!originalGlobalObjectProxy) {
+        JSC::ExecState* exec = currentFrame;
+        originalGlobalObjectProxy = new (exec)QScript::OriginalGlobalObjectProxy(scriptObjectStructure, originalGlobalObject());
+    }
+    return originalGlobalObjectProxy;
+}
+
+JSC::JSObject *QScriptEnginePrivate::globalObject() const
+{
+    QScript::GlobalObject *glob = static_cast<QScript::GlobalObject*>(originalGlobalObject());
+    if (glob->customGlobalObject)
+        return glob->customGlobalObject;
+    return glob;
+}
+
+void QScriptEnginePrivate::setGlobalObject(JSC::JSObject *object)
+{
+    if (object == globalObject())
+        return;
+    QScript::GlobalObject *glob = static_cast<QScript::GlobalObject*>(originalGlobalObject());
+    if (object == originalGlobalObjectProxy)
+        glob->customGlobalObject = 0;
+    else {
+        Q_ASSERT(object != originalGlobalObject());
+        glob->customGlobalObject = object;
+    }
+}
+
 JSC::ExecState *QScriptEnginePrivate::globalExec() const
 {
-    return globalObject()->globalExec();
+    return originalGlobalObject()->globalExec();
+}
+
+/*!
+  \internal
+
+  If the given \a value is the original global object, returns the custom
+  global object or a proxy to the original global object; otherwise returns \a
+  value.
+*/
+JSC::JSValue QScriptEnginePrivate::toUsableValue(JSC::JSValue value)
+{
+    if (!value || !value.isObject() || !JSC::asObject(value)->isGlobalObject())
+        return value;
+    Q_ASSERT(JSC::asObject(value) == originalGlobalObject());
+    if (customGlobalObject())
+        return customGlobalObject();
+    if (!originalGlobalObjectProxy)
+        originalGlobalObjectProxy = new (currentFrame)QScript::OriginalGlobalObjectProxy(scriptObjectStructure, originalGlobalObject());
+    return originalGlobalObjectProxy;
 }
 
 void QScriptEnginePrivate::mark()
 {
-    if (customGlobalObject && !customGlobalObject->marked())
-        customGlobalObject->mark();
+    if (!originalGlobalObject()->marked())
+        originalGlobalObject()->mark();
+    if (!globalObject()->marked())
+        globalObject()->mark();
+    if (originalGlobalObjectProxy && !originalGlobalObjectProxy->marked())
+        originalGlobalObjectProxy->mark();
 
     if (qobjectPrototype && !qobjectPrototype->marked())
         qobjectPrototype->mark();
@@ -1086,9 +1198,6 @@ bool QScriptEnginePrivate::isCollecting() const
 
 void QScriptEnginePrivate::collectGarbage()
 {
-    // ### why isn't the global object always marked by the Collector?
-    if (!globalObject()->marked())
-        globalObject()->mark();
     JSC::JSLock lock(false);
     globalData->heap.collect();
 }
@@ -1385,11 +1494,10 @@ QScriptValue QScriptEngine::globalObject() const
 void QScriptEngine::setGlobalObject(const QScriptValue &object)
 {
     Q_D(QScriptEngine);
-    if (!object.isObject() || globalObject().strictlyEquals(object))
+    if (!object.isObject())
         return;
     JSC::JSObject *jscObject = JSC::asObject(d->scriptValueToJSCValue(object));
-    qWarning("QScriptEngine::setGlobalObject() is not implemented");
-//    d->customGlobalObject = jscObject;
+    d->setGlobalObject(jscObject);
 }
 
 /*!
@@ -2410,7 +2518,7 @@ QScriptValue QScriptEnginePrivate::create(int type, const void *ptr)
         }
     }
     if (result.isObject() && info && info->prototype
-        && JSC::JSValue::strictEqual(scriptValueToJSCValue(result.prototype()), globalObject()->objectPrototype())) {
+        && JSC::JSValue::strictEqual(scriptValueToJSCValue(result.prototype()), originalGlobalObject()->objectPrototype())) {
         result.setPrototype(scriptValueFromJSCValue(info->prototype));
     }
     return result;
@@ -2671,7 +2779,7 @@ void QScriptEngine::installTranslatorFunctions(const QScriptValue &object)
     Q_D(QScriptEngine);
     JSC::ExecState* exec = d->currentFrame;
     JSC::JSValue jscObject = d->scriptValueToJSCValue(object);
-    JSC::JSGlobalObject *glob = d->globalObject();
+    JSC::JSGlobalObject *glob = d->originalGlobalObject();
     if (!jscObject || !jscObject.isObject())
         jscObject = glob;
 //    unsigned attribs = JSC::DontEnum;
diff --git a/src/script/api/qscriptengine_p.h b/src/script/api/qscriptengine_p.h
index 4db77c0..c0f5e13 100644
--- a/src/script/api/qscriptengine_p.h
+++ b/src/script/api/qscriptengine_p.h
@@ -110,8 +110,13 @@ public:
     QScriptContext *contextForFrame(JSC::ExecState *frame);
     void releaseContextForFrame(JSC::ExecState *frame);
 
-    JSC::JSGlobalObject *globalObject() const;
+    JSC::JSGlobalObject *originalGlobalObject() const;
+    JSC::JSObject *getOriginalGlobalObjectProxy();
+    JSC::JSObject *customGlobalObject() const;
+    JSC::JSObject *globalObject() const;
+    void setGlobalObject(JSC::JSObject *object);
     JSC::ExecState *globalExec() const;
+    JSC::JSValue toUsableValue(JSC::JSValue value);
 
     void mark();
     bool isCollecting() const;
@@ -162,7 +167,7 @@ public:
 #endif
 
     JSC::JSGlobalData *globalData;
-    JSC::JSObject *customGlobalObject;
+    JSC::JSObject *originalGlobalObjectProxy;
     JSC::ExecState *currentFrame;
     QHash<JSC::ExecState*, QScriptContext*> contextForFrameHash;
 
diff --git a/src/script/api/qscriptvalue.cpp b/src/script/api/qscriptvalue.cpp
index 5ace14d..59e6729 100644
--- a/src/script/api/qscriptvalue.cpp
+++ b/src/script/api/qscriptvalue.cpp
@@ -276,19 +276,20 @@ QScriptValuePrivate::QScriptValueAutoRegister& QScriptValuePrivate::QScriptValue
     return *this;
 };
 
-
 void QScriptValuePrivate::initFromJSCValue(JSC::JSValue value)
 {
-    type = JSC;
-    jscValue = value;
     if (value.isCell()) {
-        JSC::JSCell *cell = value.asCell();
         Q_ASSERT(engine != 0);
         QScriptEnginePrivate *eng_p = QScriptEnginePrivate::get(engine);
+        value = eng_p->toUsableValue(value);
+        JSC::JSCell *cell = JSC::asCell(value);
+        Q_ASSERT(cell != eng_p->originalGlobalObject());
         if (!eng_p->keepAliveValues.contains(cell))
             eng_p->keepAliveValues[cell] = 0;
         eng_p->keepAliveValues[cell].ref();
     }
+    type = JSC;
+    jscValue = value;
 }
 
 void QScriptValuePrivate::initFromNumber(double value)
diff --git a/src/script/bridge/qscriptqobject.cpp b/src/script/bridge/qscriptqobject.cpp
index b065f5c..94bd8f9 100644
--- a/src/script/bridge/qscriptqobject.cpp
+++ b/src/script/bridge/qscriptqobject.cpp
@@ -487,6 +487,7 @@ JSC::JSValue QtFunction::execute(JSC::ExecState *exec, JSC::JSValue thisValue,
 
     const QMetaObject *meta = qobj->metaObject();
     QObject *thisQObject = 0;
+    thisValue = engine->toUsableValue(thisValue);
     if (thisValue.isObject(&QScriptObject::info)) {
         delegate = static_cast<QScriptObject*>(JSC::asObject(thisValue))->delegate();
         if (delegate && (delegate->type() == QScriptObjectDelegate::QtObject))
@@ -1029,6 +1030,7 @@ JSC::JSValue QtPropertyFunction::execute(JSC::ExecState *exec,
 
     // ### don't go via QScriptValue
     QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
+    thisValue = engine->toUsableValue(thisValue);
     QScriptValue object = engine->scriptValueFromJSCValue(thisValue);
     QObject *qobject = object.toQObject();
     while ((!qobject || (qobject->metaObject() != data->meta))
@@ -1168,7 +1170,7 @@ bool QObjectDelegate::getOwnPropertySlot(QScriptObject *object, JSC::ExecState *
                     || (index >= meta->methodOffset())) {
                     QtFunction *fun = new (exec)QtFunction(
                         object, index, /*maybeOverloaded=*/false,
-                        &exec->globalData(), eng->globalObject()->functionStructure(),
+                        &exec->globalData(), eng->originalGlobalObject()->functionStructure(),
                         propertyName);
                     slot.setValue(fun);
                     data->cachedMembers.insert(name, fun);
@@ -1187,7 +1189,7 @@ bool QObjectDelegate::getOwnPropertySlot(QScriptObject *object, JSC::ExecState *
                 if (GeneratePropertyFunctions) {
                     QtPropertyFunction *fun = new (exec)QtPropertyFunction(
                         meta, index, &exec->globalData(),
-                        eng->globalObject()->functionStructure(),
+                        eng->originalGlobalObject()->functionStructure(),
                         propertyName);
                     data->cachedMembers.insert(name, fun);
                     slot.setGetterSlot(fun);
@@ -1219,7 +1221,7 @@ bool QObjectDelegate::getOwnPropertySlot(QScriptObject *object, JSC::ExecState *
             && (methodName(method) == name)) {
             QtFunction *fun = new (exec)QtFunction(
                 object, index, /*maybeOverloaded=*/true,
-                &exec->globalData(), eng->globalObject()->functionStructure(),
+                &exec->globalData(), eng->originalGlobalObject()->functionStructure(),
                 propertyName);
             slot.setValue(fun);
             data->cachedMembers.insert(name, fun);
@@ -1292,7 +1294,7 @@ void QObjectDelegate::put(QScriptObject *object, JSC::ExecState* exec,
                     } else {
                         fun = new (exec)QtPropertyFunction(
                             meta, index, &exec->globalData(),
-                            eng->globalObject()->functionStructure(),
+                            eng->originalGlobalObject()->functionStructure(),
                             propertyName);
                         data->cachedMembers.insert(name, fun);
                     }
@@ -1520,6 +1522,8 @@ void QObjectDelegate::mark(QScriptObject *object)
 static JSC::JSValue JSC_HOST_CALL qobjectProtoFuncFindChild(JSC::ExecState *exec, JSC::JSObject*,
                                                             JSC::JSValue thisValue, const JSC::ArgList &args)
 {
+    QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
+    thisValue = engine->toUsableValue(thisValue);
     if (!thisValue.isObject(&QScriptObject::info))
         return throwError(exec, JSC::TypeError, "this object is not a QObject");
     QScriptObject *scriptObject = static_cast<QScriptObject*>(JSC::asObject(thisValue));
@@ -1532,13 +1536,14 @@ static JSC::JSValue JSC_HOST_CALL qobjectProtoFuncFindChild(JSC::ExecState *exec
         name = QScript::qtStringFromJSCUString(args.at(0).toString(exec));
     QObject *child = qFindChild<QObject*>(obj, name);
     QScriptEngine::QObjectWrapOptions opt = QScriptEngine::PreferExistingWrapperObject;
-    QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
     return engine->newQObject(child, QScriptEngine::QtOwnership, opt);
 }
 
 static JSC::JSValue JSC_HOST_CALL qobjectProtoFuncFindChildren(JSC::ExecState *exec, JSC::JSObject*,
                                                                JSC::JSValue thisValue, const JSC::ArgList &args)
 {
+    QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
+    thisValue = engine->toUsableValue(thisValue);
     // extract the QObject
     if (!thisValue.isObject(&QScriptObject::info))
         return throwError(exec, JSC::TypeError, "this object is not a QObject");
@@ -1547,7 +1552,6 @@ static JSC::JSValue JSC_HOST_CALL qobjectProtoFuncFindChildren(JSC::ExecState *e
     if (!delegate || (delegate->type() != QScriptObjectDelegate::QtObject))
         return throwError(exec, JSC::TypeError, "this object is not a QObject");
     const QObject *const obj = static_cast<QObjectDelegate*>(delegate)->value();
-    QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
 
     // find the children
     QList<QObject *> children;
@@ -1562,7 +1566,7 @@ static JSC::JSValue JSC_HOST_CALL qobjectProtoFuncFindChildren(JSC::ExecState *e
             for (int i = 0; i < allChildrenCount; ++i) {
                 QObject *const child = allChildren.at(i);
                 const JSC::UString childName = qtStringToJSCUString(child->objectName());
-                JSC::RegExpConstructor* regExpConstructor = engine->globalObject()->regExpConstructor();
+                JSC::RegExpConstructor* regExpConstructor = engine->originalGlobalObject()->regExpConstructor();
                 int position;
                 int length;
                 regExpConstructor->performMatch(regexp->regExp(), childName, 0, position, length);
@@ -1591,6 +1595,8 @@ static JSC::JSValue JSC_HOST_CALL qobjectProtoFuncFindChildren(JSC::ExecState *e
 static JSC::JSValue JSC_HOST_CALL qobjectProtoFuncToString(JSC::ExecState *exec, JSC::JSObject*,
                                                            JSC::JSValue thisValue, const JSC::ArgList&)
 {
+    QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
+    thisValue = engine->toUsableValue(thisValue);
     if (!thisValue.isObject(&QScriptObject::info))
         return JSC::jsUndefined();
     QScriptObject *scriptObject = static_cast<QScriptObject*>(JSC::asObject(thisValue));
@@ -1771,10 +1777,11 @@ JSC::JSValue JSC_HOST_CALL QMetaObjectWrapperObject::call(
     JSC::ExecState *exec, JSC::JSObject *callee,
     JSC::JSValue thisValue, const JSC::ArgList &args)
 {
+    QScriptEnginePrivate *eng_p = scriptEngineFromExec(exec);
+    thisValue = eng_p->toUsableValue(thisValue);
     if (!callee->isObject(&QMetaObjectWrapperObject::info))
         return throwError(exec, JSC::TypeError, "callee is not a QMetaObject");
     QMetaObjectWrapperObject *self =  static_cast<QMetaObjectWrapperObject*>(callee);
-    QScriptEnginePrivate *eng_p = scriptEngineFromExec(exec);
     JSC::ExecState *previousFrame = eng_p->currentFrame;
     eng_p->currentFrame = exec;
     JSC::JSValue result = self->execute(exec, args);
@@ -1832,6 +1839,8 @@ struct StaticQtMetaObject : public QObject
 static JSC::JSValue JSC_HOST_CALL qmetaobjectProtoFuncClassName(
     JSC::ExecState *exec, JSC::JSObject*, JSC::JSValue thisValue, const JSC::ArgList&)
 {
+    QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
+    thisValue = engine->toUsableValue(thisValue);
     if (!thisValue.isObject(&QMetaObjectWrapperObject::info))
         return throwError(exec, JSC::TypeError, "this object is not a QMetaObject");
     const QMetaObject *meta = static_cast<QMetaObjectWrapperObject*>(JSC::asObject(thisValue))->value();
diff --git a/src/script/bridge/qscriptvariant.cpp b/src/script/bridge/qscriptvariant.cpp
index 46da70a..752dd09 100644
--- a/src/script/bridge/qscriptvariant.cpp
+++ b/src/script/bridge/qscriptvariant.cpp
@@ -13,6 +13,9 @@
 
 #ifndef QT_NO_SCRIPT
 
+#include "../api/qscriptengine.h"
+#include "../api/qscriptengine_p.h"
+
 #include "Error.h"
 #include "PrototypeFunction.h"
 #include "JSString.h"
@@ -28,6 +31,7 @@ namespace QScript
 {
 
 JSC::UString qtStringToJSCUString(const QString &str);
+QScriptEnginePrivate *scriptEngineFromExec(JSC::ExecState*);
 
 QVariantDelegate::QVariantDelegate(const QVariant &value)
     : m_value(value)
@@ -56,6 +60,8 @@ QScriptObjectDelegate::Type QVariantDelegate::type() const
 static JSC::JSValue JSC_HOST_CALL variantProtoFuncToString(JSC::ExecState *exec, JSC::JSObject*,
                                                            JSC::JSValue thisValue, const JSC::ArgList&)
 {
+    QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
+    thisValue = engine->toUsableValue(thisValue);
     if (!thisValue.isObject(&QScriptObject::info))
         return throwError(exec, JSC::TypeError, "This object is not a QVariant");
     QScriptObjectDelegate *delegate = static_cast<QScriptObject*>(JSC::asObject(thisValue))->delegate();
@@ -69,6 +75,8 @@ static JSC::JSValue JSC_HOST_CALL variantProtoFuncToString(JSC::ExecState *exec,
 static JSC::JSValue JSC_HOST_CALL variantProtoFuncValueOf(JSC::ExecState *exec, JSC::JSObject*,
                                                           JSC::JSValue thisValue, const JSC::ArgList&)
 {
+    QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
+    thisValue = engine->toUsableValue(thisValue);
     if (!thisValue.isObject(&QScriptObject::info))
         return throwError(exec, JSC::TypeError);
     QScriptObjectDelegate *delegate = static_cast<QScriptObject*>(JSC::asObject(thisValue))->delegate();