Generate Build Database is Empty

I am attempting to experiment with the experimental CMAKE_EXPORT_BUILD_DATABASE flag. I think I got it up and running to the point where the cmake_build_database target is generating a build_database.json. However the sets list is empty. Is there something I am missing to make sure this database includes all of my targets?

Repro:

Dowload cmake 4.3.2

Install clang-22

mkdir build
cd build
cmake .. -G Ninja
cd ..
cmake --build build --target cmake_build_database app

@ben.boeckel