An API to deprecate some functionality exported into QML and warn a user when this functionality is still used

There are a few techniques available to manage versions and API evolution in Qt:

• Q_DECL_DEPRECATED macro
• [[deprecated]] attribute in C++14
• Versioning in QML modules, incl. new additions for this in Qt 6.2 (https://www.qt.io/blog/qml-modules-in-qt-6.2)
• The new @Deprecated statement used by QML Lint (https://www.qt.io/blog/whats-new-in-qml-tooling-in-qt-6.2)

Yet, this is not sufficient for use cases when a user provides QML API in a C++-only plugin and wants to warn other users that some parts of this API (and not the whole module) are deprecated.

An idea for a solution would be to extend the existing ways of exporting C++ attributes into QML (https://doc.qt.io/qt-6/qtqml-cppintegration-exposecppattributes.html)