add-custom-command

I'm using an external library which provides a CMake function for automatic code generation, to be used in my CMakeLists. The problem is that whenever I modify a CMakeLists then the function is run again, triggering the recompilation of the newly generated but unchanged sources. I'd need something like add_custom_command with the possibility to specify the CMake function as COMMAND instead of an executable, so that the function is run only if the automatically generated files are not already present. Is this feasible? If not, does it exist another way to obtain the same result? Thanks. To

See last status update Initial conditions code generator that generates set of c++ sources taking one input file as parameter input file may include other input files already solved task of getting list of output files, parsing input codegen files to get full list of codegen inputs. I.e. add_custom_command is provided with correct set of dependencies for the first time: add_custom_command(OUTPUT ${generatedSources} COMMAND ${codegenCommand} ARGS ${codegenArgs} DEPENDS ${codegenInputFiles}) Problem scenario current system works well until someone modifies one of codegen input files to include