Address extension types in qmltc

Whenever working with properties (reading, writing, aliasing, etc.)
of the type that has extensions, prefer the same-named properties
from extension objects over type-owned properties (this is the internal
QML mechanism)

To achieve that, we need to query the extension object:
* for Q_GADGETs use a dummy model of assuming we can cast the object
  to the extension type and use that
* for Q_OBJECTs use a qmlExtendedObject() with additional logic of
  figuring out which extension should be picked in each specific case

Create QQmlProxyMetaObject via a custom dynamic meta object API for
qmltc-compiled objects that are derived from base types with
extensions

Task-number: QTBUG-91956
Change-Id: I5e783768ae2abdb9dddf894de7e79960244352bd
Reviewed-by: Ulf Hermann <[email protected]>

2 files changed, 120 insertions, 1 deletions

diff --git a/src/qml/qmltc/qqmltcobjectcreationhelper.cpp b/src/qml/qmltc/qqmltcobjectcreationhelper.cpp
new file mode 100644
index 0000000000..b88b43d7be
--- /dev/null
+++ b/src/qml/qmltc/qqmltcobjectcreationhelper.cpp
@@ -0,0 +1,98 @@
+/****************************************************************************
+**
+** Copyright (C) 2022 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQml module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qqmltcobjectcreationhelper_p.h"
+
+#include <private/qqmlmetatype_p.h>
+#include <private/qmetaobjectbuilder_p.h>
+#include <private/qobject_p.h>
+#include <private/qqmltype_p_p.h>
+
+QT_BEGIN_NAMESPACE
+
+void qmltcCreateDynamicMetaObject(QObject *object, const QMetaObject *staticMetaObject,
+                                  const QmltcTypeData &data)
+{
+    // TODO: when/if qmltc-compiled types would be registered via
+    // qmltyperegistrar, instead of creating a dummy QQmlTypePrivate, fetch the
+    // good QQmlType via QQmlMetaType::qmlType(). to do it correctly, one needs,
+    // along with the meta object, module name and revision. all that should be
+    // available ahead-of-time to qmltc.
+    auto qmlTypePrivate = new QQmlTypePrivate(data.regType);
+    // place the newly created QQmlTypePrivate into the qml meta data storage so
+    // that it is properly deleted
+    QQmlMetaType::registerMetaObjectForType(staticMetaObject, qmlTypePrivate);
+
+    // initialize QQmlType::QQmlCppTypeData
+    Q_ASSERT(data.regType == QQmlType::CppType);
+    qmlTypePrivate->extraData.cd->allocationSize = data.allocationSize;
+    qmlTypePrivate->extraData.cd->newFunc = nullptr;
+    qmlTypePrivate->extraData.cd->userdata = nullptr;
+    qmlTypePrivate->extraData.cd->noCreationReason =
+            QStringLiteral("Qmltc-compiled type is not creatable via QQmlType");
+    qmlTypePrivate->extraData.cd->createValueTypeFunc = nullptr;
+    qmlTypePrivate->extraData.cd->parserStatusCast = -1;
+    qmlTypePrivate->extraData.cd->extFunc = nullptr;
+    qmlTypePrivate->extraData.cd->extMetaObject = nullptr;
+    qmlTypePrivate->extraData.cd->customParser = nullptr;
+    qmlTypePrivate->extraData.cd->attachedPropertiesFunc = nullptr;
+    qmlTypePrivate->extraData.cd->attachedPropertiesType = nullptr;
+    qmlTypePrivate->extraData.cd->propertyValueSourceCast = -1;
+    qmlTypePrivate->extraData.cd->propertyValueInterceptorCast = -1;
+    qmlTypePrivate->extraData.cd->finalizerCast = -1;
+    qmlTypePrivate->extraData.cd->registerEnumClassesUnscoped = false;
+    qmlTypePrivate->extraData.cd->registerEnumsFromRelatedTypes = false;
+
+    qmlTypePrivate->baseMetaObject = data.metaObject;
+    qmlTypePrivate->init();
+
+    QQmlType qmlType(qmlTypePrivate);
+    Q_ASSERT(qmlType.isValid());
+
+    QObjectPrivate *op = QObjectPrivate::get(object);
+    // ### inefficient - rather, call this function only once for the leaf type
+    if (op->metaObject) {
+        delete op->metaObject;
+        op->metaObject = nullptr;
+    }
+
+    qmlType.createProxy(object);
+}
+
+QT_END_NAMESPACE
diff --git a/src/qml/qmltc/qqmltcobjectcreationhelper_p.h b/src/qml/qmltc/qqmltcobjectcreationhelper_p.h
index 6aa37b1e53..56b89925da 100644
--- a/src/qml/qmltc/qqmltcobjectcreationhelper_p.h
+++ b/src/qml/qmltc/qqmltcobjectcreationhelper_p.h
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2021 The Qt Company Ltd.
+** Copyright (C) 2022 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtQml module of the Qt Toolkit.
@@ -53,6 +53,9 @@
 
 #include <QtQml/qqml.h>
 #include <QtCore/private/qglobal_p.h>
+#include <QtCore/qversionnumber.h>
+#include <private/qtqmlglobal_p.h>
+#include <private/qqmltype_p.h>
 
 #include <array>
 
@@ -137,6 +140,24 @@ public:
     }
 };
 
+struct QmltcTypeData
+{
+    QQmlType::RegistrationType regType = QQmlType::CppType;
+    int allocationSize = 0;
+    const QMetaObject *metaObject = nullptr;
+
+    template<typename QmltcGeneratedType>
+    QmltcTypeData(QmltcGeneratedType *)
+        : allocationSize(sizeof(QmltcGeneratedType)),
+          metaObject(&QmltcGeneratedType::staticMetaObject)
+    {
+    }
+};
+
+Q_QML_PRIVATE_EXPORT void qmltcCreateDynamicMetaObject(QObject *object,
+                                                       const QMetaObject *staticMetaObject,
+                                                       const QmltcTypeData &data);
+
 QT_END_NAMESPACE
 
 #endif // QQMLTCOBJECTCREATIONHELPER_P_H