Dealing with Fortran include files

Code
1

I am building a Fortran project that contains numerous include files (extension .inc). These are not public include files, but rather implementation details which were generated by a template mechanism.

Where do these files belong?

Currently I am using this:

add_library(foo 
    src/foo.f90 
    src/foo_impl.inc
)

But I think alternatives such as:

# Alternative 1
add_library(foo
   src/foo.f90
)
target_include_directories(foo PRIVATE src/)

or,

# Alternative 2
add_library(foo src/foo.f90)
target_sources(foo PRIVATE foo_impl.inc)

would also work.

What are the differences? Which option would be best, if the generation of the *.inc were to be included in the CMake build?

2

I would put CMake-generated .inc under PROJECT_BINARY_DIR and target_include_directories() that subdirectory.