hiredis included through FetchContent should not include CPack

[koenvandesande]

When you include hiredis through FetchContent, it causes a warning when the main project also uses CPack:

CMake Warning at /usr/local/lib/python3.12/dist-packages/cmake/data/share/cmake-3.31/Modules/CPack.cmake:510 (message):
  CPack.cmake has already been included!!
Call Stack (most recent call first):
  cmake-build-debug-wsl/_deps/hiredis/CMakeLists.txt:98 (include)

Could you prevent this by guarding the inclusion of CPack with a check on whether it is the top-level project?

if(PROJECT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
  include(CPack)
endif()

If needed I could turn this into a PR if that is easier for you.

[michael-grunder]

Disclaimer: My knowledge of CMake is limited (nonexistent 😄)

Your solution looks like it's right, but it seems like people sumetimes add a second conditional

if (PROJECT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
  if (NOT CPack_CMake_INCLUDED)
    include(CPack)
  endif()
endif()

Also I wonder if we are excluding CPack should we also exclude all of the lines setting cpack vendor, description, etc? I honestly don't know what's idiomatic.

If it is correct to exclude everything we would just move all of the cpack lines into the if block with the include(CPack).

[koenvandesande]

I think it is cleanest to put all cpack variables behind the guard. I also named the guard MAIN_PROJECT, as I've seen that in nlohmann/json
And I've updated the CMake version range to silence CMake warnings