Allow hiredis to be retrieved automatically by FetchContent

[sjanel]

Configure hiredis features file before find package of hiredis to avoid configuration error.

Fix issues encountered by this PR, and this issue.

Here's how to use FetchContent with redis++ as a dependency with modern CMake (>= v3.24):

CMakeLists.txt

cmake_minimum_required(VERSION 3.24)
project(examples LANGUAGES CXX)

include(FetchContent)

FetchContent_Declare(
  hiredis
  GIT_REPOSITORY https://github.com/redis/hiredis
  GIT_TAG origin/master
  GIT_SHALLOW TRUE
  SOURCE_DIR _deps/hiredis
  # Make sure redis++ finds fetched content with its find_package()
  OVERRIDE_FIND_PACKAGE
)

FetchContent_Declare(
  redis-plus-plus
  GIT_REPOSITORY https://github.com/sjanel/redis-plus-plus.git
  GIT_TAG bugfix/hiredis-fetch-configure-file-found
  GIT_SHALLOW TRUE
)
FetchContent_MakeAvailable(redis-plus-plus)


add_executable(main
  main.cc
)

target_link_libraries(main
  redis++
)

main.cc

#include <sw/redis++/redis++.h>
#include <iostream>

int main() {
  auto redis = sw::redis::Redis("tcp://127.0.0.1:6379");
  redis.set("key", "value");
  auto val = redis.get("key");
  if (val) {
    std::cout << "Got: " << *val << std::endl;
  }
  return 0;
}

(adapted from this gist)

[juwalter]

just tried this in our project and configure and build are successful. big help and very nice work!!

[sewenew]

Great job! Thanks a lot!

The only problem is that this solution requires minimum version of cmake is 3.24. Is it possible to make the CMakeLists.txt also works with older version cmake for those who don't require the FetchContent feature? I mean, if they want to use FetchContent feature, the upgrade cmake to 3.24, otherwise, they can use an older version to build.

Regards

[sjanel]

Hello @sewenew !

Indeed it requires CMake 3.24 because of OVERRIDE_FIND_PACKAGE, but only for the consumer of the library, not for redis-plus-plus itself. Unfortunately, I don't know how to make this work without OVERRIDE_FIND_PACKAGE without a full rewrite of the CMakeLists.txt.

[sewenew]

@sjanel Sorry, but I misunderstood the solution. User with older version cmake, can still build redis-plus-plus the old way.

Thanks a lot for your contribution!

Regards

[david-drinn]

I think the latest CMake (v4.2.1 at the latest) has moved the directory of FetchContent's dependencies to, e.g., _deps/hiredis-src, -build, and -subbuild. This breaks the search for hiredis.h in this case.