The C++ syncqt tool that replaced the Perl script has severe buildsystem problems:

1. it is compiled during CMake time, instead of Ninja time
2. It has no NInja target to build it
3. it is an always-optimised build

I understand the first one may be difficult to solve, as we may need it during generation time. I don't see why, because after a CMake run on a clean build dir, the include hierarchy is pretty empty:

$ find include/QtCore -type f 
include/QtCore/QtCoreDepends
include/QtCore/qtcoreexports.h

This tells me that syncqt hasn't been run yet, so it needn't have been built yet.

Regardless, there has to be a target to rebuild it without having to rerun CMake, otherwise iterating on it is very time-consuming.

Finally, it needs to obey the user's choice of compiler flags and build types, like moc does. That means a debug build of qtbase must produce a debug build of syncqt, so we can actually debug the tool. The impact on time execution is minimal for this tool, especially compared to the cmake_automoc and moc tools, which do far more processing and are run far more often. Besides, there's QT_FORCE_FIND_TOOLS to avoid such problems.