QmlDesiger: add LazyUniquePtr

Creating a memory on heap is not cheap. To defer it LazyUniquePtr is
allocating as the type is cast.

Change-Id: Id3239da7136101040fcb47c9359c96d8ca236bb5
Reviewed-by: Vikas Pachdha <vikas.pachdha@qt.io>

src/plugins/qmldesigner/components/designsystemview/designsysteminterface.cpp

@@ -6,6 +6,8 @@
 
 #include <designsystem/dsconstants.h>
 #include <designsystem/dsthememanager.h>
+#include <qmldesignerutils/memory.h>
+
 #include <QQmlEngine>
 
 namespace QmlDesigner {
@@ -74,8 +76,8 @@ QStringList DesignSystemInterface::collections() const
 CollectionModel *DesignSystemInterface::createModel(const QString &typeName, DSThemeManager *collection)
 {
     auto [newItr, success] = m_models.try_emplace(typeName,
-                                                  std::make_unique<CollectionModel>(collection,
+                                                  makeLazyUniquePtr<CollectionModel>(collection,
-                                                                                    m_store));
+                                                                                     m_store));
     if (success) {
         // Otherwise the model will be deleted by the QML engine.
         QQmlEngine::setObjectOwnership(newItr->second.get(), QQmlEngine::CppOwnership);

src/plugins/qmldesigner/libs/designsystem/dsthememanager.cpp

@@ -263,9 +263,7 @@ void DSThemeManager::decorateThemeInterface(ModelNode rootNode) const
 
 DSThemeGroup *DSThemeManager::propertyGroup(GroupType type)
 {
-    auto itr = m_groups.find(type);
+    auto itr = m_groups.try_emplace(type, makeLazySharedPtr<DSThemeGroup>(type)).first;
-    if (itr == m_groups.end())
-        itr = m_groups.try_emplace(type, std::make_unique<DSThemeGroup>(type)).first;
 
     return itr->second.get();
 }

src/plugins/qmldesigner/libs/qmldesignerutils/CMakeLists.txt

@@ -8,6 +8,7 @@ add_qtc_library(QmlDesignerUtils STATIC
     asset.cpp asset.h
     designeralgorithm.h
     filedownloader.cpp filedownloader.h
+    memory.h
     multifiledownloader.cpp multifiledownloader.h
     fileextractor.cpp fileextractor.h
     hdrimage.cpp hdrimage.h

src/plugins/qmldesigner/libs/qmldesignerutils/memory.h

@@ -0,0 +1,52 @@
+// Copyright (C) 2023 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#pragma once
+
+#include <memory>
+#include <tuple>
+
+namespace QmlDesigner {
+
+template<typename Pointer, typename... Arguments>
+class LazyPtr
+{
+    using ResultType = Pointer::element_type;
+
+public:
+    LazyPtr(Arguments &&...arguments)
+        : m_arguments{std::forward_as_tuple(std::forward<Arguments>(arguments)...)}
+    {}
+
+    operator Pointer() const
+    {
+        return std::apply(
+            [](auto &&...arguments) {
+                return Pointer(new ResultType(std::forward<decltype(arguments)>(arguments)...));
+            },
+            m_arguments);
+    }
+
+private:
+    std::tuple<Arguments...> m_arguments;
+};
+
+template<typename ResultType, typename... Arguments>
+using LazyUniquePtr = LazyPtr<std::unique_ptr<ResultType>, Arguments...>;
+
+template<typename Result, typename... Arguments>
+LazyUniquePtr<Result, Arguments...> makeLazyUniquePtr(Arguments &&...arguments)
+{
+    return LazyUniquePtr<Result, Arguments...>(std::forward<Arguments>(arguments)...);
+}
+
+template<typename ResultType, typename... Arguments>
+using LazySharedPtr = LazyPtr<std::shared_ptr<ResultType>, Arguments...>;
+
+template<typename ResultType, typename... Arguments>
+LazySharedPtr<ResultType, Arguments...> makeLazySharedPtr(Arguments &&...arguments)
+{
+    return LazySharedPtr<ResultType, Arguments...>(std::forward<Arguments>(arguments)...);
+}
+
+} // namespace QmlDesigner