The refactoring function "Move Class to a Dedicated Set of Source Files" from right click context menu on class declaration may move the definition "class Q_CORE_EXPORT QObject {...}" from qobject.h in the tool chain to the newly created source file leaving behind an unusable tool chain.

If  QtCreator has no write permission on qobject.h it will spawn a dialog window to ask for these permissions.

Inheriting from a QObject derived class seems necessary. See the attached example with Readme

If you run this on a toolchain where the user running QtCreator has no write permissions on the toolchain:
* open QtCreatorProject/QtCreatorBugMinimalExample/QtCreatorBugMinimalExample.pro in QtCreator
* open the file class.hpp
* right click on the class name "classB" in the class declaration
  * select "refactor"
  * select "Move class to a dedicated set of source files"
  * confirm the **first** following dialog
  * you will now see a dialog prompting you to give write permissions on qobject.h - ABORT THIS!
  * now look at the newly created source file and find definitions for Qobject

This has been encountered with with QtCreator 18.0.0 from from qt-online-installer and the accompanying tool chain.

IMHO QtCreator should never write to headers in the tool chain. I even think write access outside project directory and build directory is suspicious. QtCreator already generates a notification if a header file from outside the project directory is opened in the editor (and rightfully so).