Lift restriction for type registrations in QML module plugins

During the registerTypes() callback in a QML module plugin we only allow
types to be registered that match the module URI specified in the
qmldir.

We can observe in QtQuickControls 2 that sometimes we need to register
types outside of the namespace of the module itself. QQC2 is in
QtQuick.Controls but the module has internal types that are in
QtQuick.Controls.impl.

Types are intended to be registered once in the virtual registerTypes()
function. However as we don't allow for the registration of .impl to
happen in registerTypes(), QQC2 works around this by registering the
types in initializeEngine(), during which the namespace restriction is
not in place.

This workaround means that every time an application creates a
QQuickView (and thus new QML engine) and loads a QML file that imports
QQC2, we end up calling initializeEngine(), as opposed to
registerTypes() that is called only one single time in the application
process. As a consequence each time this happens we and up calling
qmlRegisterTypes() with the same times and leak memory this way, as
qmlRegisterType*() is supposed to register a new type and return a new
type id that can be passed to qmlUnregisterType.

To solve this this patch lifts the restriction on namespaces for
registered types during registerTypes(). The real world case of QQC2
shows that the restriction is limiting and also easy to work around.
With the restriction lifted QQC2 can now register all types once in
registerTypes() instead.

[ChangeLog][QtQml][Important Behavior Changes] QML module plugins used
to be limited to type registrations in the primary module namespace in
the virtual registerTypes() function. Module authors worked around this
limitation by placing necessary internal type registrations into
initializeEngine() that may cause memory leaks. Therefore this
restriction has been moved and types in any (non-protected) namespaces
can be registered in the registerTypes() function.

Change-Id: I5baf9718a0b0a591f6eb6d7e2dc83e13b204800d
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 1 insertions, 9 deletions

diff --git a/src/qml/qml/qqmlmetatype.cpp b/src/qml/qml/qqmlmetatype.cpp
index 40864de366..b324386bf5 100644
--- a/src/qml/qml/qqmlmetatype.cpp
+++ b/src/qml/qml/qqmlmetatype.cpp
@@ -1579,15 +1579,7 @@ bool checkRegistration(QQmlType::RegistrationType typeType, QQmlMetaTypeData *da
     if (uri && !typeName.isEmpty()) {
         QString nameSpace = QString::fromUtf8(uri);
 
-        if (!data->typeRegistrationNamespace.isEmpty()) {
-            // We can only install types into the registered namespace
-            if (nameSpace != data->typeRegistrationNamespace) {
-                QString failure(QCoreApplication::translate("qmlRegisterType",
-                                                            "Cannot install %1 '%2' into unregistered namespace '%3'"));
-                data->typeRegistrationFailures.append(failure.arg(registrationTypeString(typeType)).arg(typeName).arg(nameSpace));
-                return false;
-            }
-        } else if (data->typeRegistrationNamespace != nameSpace) {
+        if (data->typeRegistrationNamespace.isEmpty() && !nameSpace.isEmpty()) {
             // Is the target namespace protected against further registrations?
             if (data->protectedNamespaces.contains(nameSpace)) {
                 QString failure(QCoreApplication::translate("qmlRegisterType",