cmake: pass include directories to external project

Question

I'm using cmake and external project module via ExternalProject_Add.

I'd like to specify custom header location for external project (just exactly as if I use include_directories in that project, but I am not able to modify its CMakeLists.txt and don't want to apply patch).

Is there any possibility to pass some include path to my external project?

I tried CMAKE_ARGS -DCMAKE_INCLUDE_PATH=<required path> without success.

Answer 1

You may execute additional CMake script for external project by assigning path to this script to variable CMAKE_PROJECT_<PROJECT-NAME>_INCLUDE (documentation).

Let external project uses CMake command

project(e_cool)

and you want to execute

include_directories(/path/to/additional/include)

at that moment.

For doing that, you need to prepare cmake script with corresponded content:

fix_e_cool.cmake:

include_directories(/path/to/additional/include)

And pass this script via CMAKE_ARGS option of ExternalProject_Add in the main project:

CMakeLists.txt:

...
ExternalProject_Add(<name>
    ...
    CMAKE_ARGS -DCMAKE_PROJECT_e_cool_INCLUDE=${CMAKE_SOURCE_DIR}/fix_e_cool.cmake
)