Generate multiple C files by custom command in CMake then compile them

Question

I'm trying to make a single CMakeLists.txt that calls an external command to generate a bunch of C files in a folder, then compile those C files. Currently it looks like this:

set (OUTPUT_DIR ${CMAKE_CURRENT_SOURCE_DIR}/Generated)
set (OUTPUT_FILES
  ${OUTPUT_DIR}/*.c
  ${OUTPUT_DIR}/*.h
)

add_custom_command(OUTPUT ${OUTPUT_FILES}
  COMMAND external_c_files_generator --output-folder ${PYTHON_WRAPPER_OUTPUT_DIR}
  COMMENT "Generating C code..."
)

add_executable (my_executable ${OUTPUT_FILES})

Problem: the sample above obviously doesn't work because CMake doesn't support wildcards this way. It does work if I don't use wildcards. But I need to allow my external C files generator to generate "whatever it wants", including multiple C files which names I can't predict, and just take all the files it generates and compile them.

A very common solution that can be found regarding usage of wildcards in CMake is file(GLOB). Unfortunately it's not applicable in this case because file(GLOB) is called during the build system generation, not during the build itself.

Other solutions that can't be employed:

• Generate the files outside cmake, and generate the CMakeLists.txt along it, then finally call CMake: can't be done in my case because my custom command actually relies on other CMake steps that generate other files.

Everything in in the details.