Add initial support for deep aliases

This patch reuses the existing support for value types to support
aliases of depth 2. This covers the initial use case in QTBUG-48150.

Adding support for "deeper" aliases would require storing the complete
"property path", which in turn would require increasing the size of the
Alias data. This is currently considered out of scope, at least until a
clear use-case appears.

Fixes: QTBUG-48150
Change-Id: Id2ac4dd175003a37eba2919e7604d0a3be54d29f
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 25 insertions, 8 deletions

diff --git a/src/qml/qml/qqmlvmemetaobject.cpp b/src/qml/qml/qqmlvmemetaobject.cpp
index b9d8fed243..abdc686ec2 100644
--- a/src/qml/qml/qqmlvmemetaobject.cpp
+++ b/src/qml/qml/qqmlvmemetaobject.cpp
@@ -164,8 +164,19 @@ void QQmlVMEMetaObjectEndpoint::tryConnect()
             QQmlData *targetDData = QQmlData::get(target, /*create*/false);
             if (!targetDData)
                 return;
-            int coreIndex = QQmlPropertyIndex::fromEncoded(aliasData->encodedMetaPropertyIndex).coreIndex();
+            QQmlPropertyIndex encodedIndex = QQmlPropertyIndex::fromEncoded(aliasData->encodedMetaPropertyIndex);
+            int coreIndex = encodedIndex.coreIndex();
+            int valueTypeIndex = encodedIndex.valueTypeIndex();
             const QQmlPropertyData *pd = targetDData->propertyCache->property(coreIndex);
+            if (pd && valueTypeIndex != -1 && !QQmlValueTypeFactory::valueType(pd->propType())) {
+                // deep alias
+                QQmlEnginePrivate *enginePriv = QQmlEnginePrivate::get(metaObject->compilationUnit->engine->qmlEngine());
+                auto const *newPropertyCache = enginePriv->propertyCacheForType(pd->propType());
+                void *argv[1] = { &target };
+                QMetaObject::metacall(target, QMetaObject::ReadProperty, coreIndex, argv);
+                Q_ASSERT(newPropertyCache);
+                pd = newPropertyCache->property(valueTypeIndex);
+            }
             if (!pd)
                 return;
 
@@ -858,17 +869,23 @@ int QQmlVMEMetaObject::metaCall(QObject *o, QMetaObject::Call c, int _id, void *
                     if (!targetDData->propertyCache)
                         return -1;
                     const QQmlPropertyData *pd = targetDData->propertyCache->property(coreIndex);
-                    // Value type property
+                    // Value type property or deep alias
                     QQmlValueType *valueType = QQmlValueTypeFactory::valueType(pd->propType());
-                    Q_ASSERT(valueType);
+                    if (valueType) {
 
-                    valueType->read(target, coreIndex);
-                    int rv = QMetaObject::metacall(valueType, c, valueTypePropertyIndex, a);
+                        valueType->read(target, coreIndex);
+                        int rv = QMetaObject::metacall(valueType, c, valueTypePropertyIndex, a);
 
-                    if (c == QMetaObject::WriteProperty)
-                        valueType->write(target, coreIndex, nullptr);
+                        if (c == QMetaObject::WriteProperty)
+                            valueType->write(target, coreIndex, nullptr);
 
-                    return rv;
+                        return rv;
+                    } else {
+                        // deep alias
+                        void *argv[1] = { &target };
+                        QMetaObject::metacall(target, QMetaObject::ReadProperty, coreIndex, argv);
+                        return QMetaObject::metacall(target, c, valueTypePropertyIndex, a);
+                    }
 
                 } else {
                     return QMetaObject::metacall(target, c, coreIndex, a);