CMake build on Linux does not export ZMQ_BUILD_DRAFT_API as a compile_definition with the target

[datax1969]

libzmq version = 4.3.4

• OS:
  Ubuntu 20.04 with cmake 3.16.3

Building with the following command after extracting the tarball and mkdir build; cd build.

cmake -D BUILD_SHARED=OFF -D ENABLE_CURVE=OFF -D ENABLE_DRAFTS=ON =WITH_LIBBSD=OFF -D WITH_LIBSODIUM=OFF ..
sudo make install

The FindPackage config module in /usr/local/lib/cmake/ZeroMQ has no mention of ZMQ_BUILD_DRAFT_API even though you now need it to use the cmake target libzmq-static.

I add the compile definition in my own CMakeLists.txt but the general idea of CMake is that I shouldn't need to. This is further exacerbated when using cppzmq which also requires the definition.

[bluca]

It's exported in pkgconfig, you can use that instead. If you want something cmake specific, please send a PR to implement it.

[datax1969]

The difficulty arises through a combination of two slightly different issues:

1. Building and installing using cmake has a different effect to building and installing using autconf/configure. With a CMake build on Linux you get a pkgconfig.pc file and a ZeroMQConfig.cmake file installed in the correct places. With autoconf/configure you only get the .pc file.
2. The .pc file correctly exports ZMQ_BUILD_DRAFT_API. The .cmake file, if present, does not. This also means that all Windows builds (where cmake is forced) will not export that define.

CMake does not have a tight integration between when finding packages using its own mechanisms or that provided by pkg-config. cppzmq for instance tries first using find_package() and if that fails then falls back to the pkg-config method using pkg_check_modules().

So when I want to use libzmq in my project its much cleaner to know that either find_package() will work OR that I have to use the pkg-config method.

With Windows builds only supporting cmake and Windows not having pkg-config, I believe the proper multi-platform solution is to fix both these problems by ALWAYS installing ZeroMQConfig.cmake regardless of build method and fixing it to export the necessary #defines.

I can probably raise a PR to fix the ZeroMQConfig.cmake but autoconf is absolute black magic to me and I would not feel confident in doing this.

[bluca]

We can't support cmake stuff in autotools, that's not supported upstream and just too much work to do these kind of bol-ons. It's cmake-specific stuff, so to keep maintenance overhead down it's better to leave it with cmake alone. Please do send a PR to fix the variable exporting if you can.