How to make directory by generator expressions in CMake?

Question

I want to create a directory by using the file(MAKE_DIRECTORY but it doesn't work with the generator expressions.

I'm trying to use the generator expression inside another CMake module, as a rough code snippet:

function_from_another_module(target_name)

and in that module:

file(MAKE_DIRECTORY $<TARGET_FILE_DIR:${target_name}>/foo/bar)

And in my real case, I'm trying to do some management on my exe targets, copy assets, generate files and some other platform based configurations.

Answer 1

The file() command is executed at configuration time and at that time and at that time generator expressions aren't evaluated yet. Furthermore the result may depend which is never available during the configuration process, just during the build.

You may be able to get the desired outcome by using adding build event logic via add_custom_command though:

add_custom_command(TARGET ${target_name} # correct target to attach logic to?
                   PRE_BUILD             # or PRE_LINK/POST_BUILD ? 
                   COMMAND ${CMAKE_COMMAND} -E make_directory "$<TARGET_FILE_DIR:${target_name}>/foo/bar")

Depending on your asset management logic you may want to create a cmake script doing the copying, execute it using ${CMAKE_COMMAND} -P script_file.cmake ... and pass necessary parameters using -D options, see CMake Command Line Tool: Run a Script