Allow QQmlEngine to load the compilation unit from url

This seems fairly essential one way or another since e.g. QQmlContext
uses the compilation unit to set up some of the internal data members.
Add a new method to the private API of QQmlEngine. This API could be
used by the object creation compiler to set up different parts of the
object (again, QQmlContext)

Change-Id: I25894ab74606793ade391bafd8eb5b1cbfbe0952
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/qml/qml/qqmlengine.cpp

@@ -2262,16 +2262,13 @@ void QQmlEnginePrivate::executeRuntimeFunction(const QUrl &url, qsizetype functi
                                                QMetaType *types)
 {
     Q_Q(QQmlEngine);
-    const auto unit = typeLoader.getType(url)->compilationUnit();
+    const auto unit = compilationUnitFromUrl(url);
     if (!unit)
         return;
 
     Q_ASSERT(functionIndex >= 0);
     Q_ASSERT(thisObject);
 
-    if (!unit->engine)
-        unit->linkToEngine(q->handle());
-
     if (unit->runtimeFunctions.length() <= functionIndex)
         return;
 
@@ -2284,6 +2281,16 @@ void QQmlEnginePrivate::executeRuntimeFunction(const QUrl &url, qsizetype functi
                                QQmlContextData::get(ctx), argc, args, types);
 }
 
+QV4::ExecutableCompilationUnit *QQmlEnginePrivate::compilationUnitFromUrl(const QUrl &url)
+{
+    auto unit = typeLoader.getType(url)->compilationUnit();
+    if (!unit)
+        return nullptr;
+    if (!unit->engine)
+        unit->linkToEngine(v4engine());
+    return unit;
+}
+
 #if defined(Q_OS_WIN)
 // Normalize a file name using Shell API. As opposed to converting it
 // to a short 8.3 name and back, this also works for drives where 8.3 notation

src/qml/qml/qqmlengine_p.h

@@ -297,6 +297,7 @@ public:
 
     void executeRuntimeFunction(const QUrl &url, qsizetype functionIndex, QObject *thisObject,
                                 int argc = 0, void **args = nullptr, QMetaType *types = nullptr);
+    QV4::ExecutableCompilationUnit *compilationUnitFromUrl(const QUrl &url);
 
 private:
     class SingletonInstances : private QHash<QQmlType, QJSValue>