Documentation for aux_source_directory() appears out of date
https://cmake.org/cmake/help/v3.23/command/aux_source_directory.html says
"there is no way for CMake to generate a build system that knows when a new source file has been added."
But this appears to be incorrect, as
file(GLOB CPP_FILES CONFIGURE_DEPENDS "${SOURCE_SUBDIR}*.cpp")
target_add_sources(${PROJECT_NAME} PUBLIC ${CPP_FILES})
appears to do just that.
Edited by Brad King