I developed a library with lib.c and lib.h, which has its own CMakeLists.txt file, but to properly operate, this library includes lib_options.h file from the lib.h header. lib_options.h file must be provided by the user.

lib.h:

#ifndef LIB_HDR_H
#define LIB_HDR_H

//This file is user provided and is project specific
#include "lib_options.h"

#ifdef ...

#endif /* ... */
typedef enum {...} enum_name_t;

#endif

lib.c

#include "lib.h"

By far the easiest way is in fact (but I suspect super wrong) to use the cmake with INTERFACE library type, like:

add_library(lib INTERFACE)
target_sources(lib INTERFACE lib.c)
target_include_directories(lib INTERFACE lib.h)

And then it can be used in top CMakeLists.txt as:

add_executable(exec_name)
add_subdirectory(path/to/my/lib)
target_link_libraries(exec_name lib)
target_include_directories(exec_name .)

and if I create a lib_options.h file in the root directory, this one will be automatically picked up and compilation will work.

Reading several posts, use of INTERFACE shall be used for I don’t need header, but whoever is calling me, may need it type of include.

But if I change the interface to PUBLIC, then lib won’t picked up paths where user’s lib_options.h is stored, and will return a missing file error during compilation

How to properly setup this?