[question] Does Conan take any step regarding the 'compiler' setting with CMake helper

We have a simple library, whose build is managed by CMake.

After adding a Conan test package, we are now observing surprising behaviours when calling conan create -s compiler=clang with a compiler setting that is not the value in the default profile (gcc):

CMake Error at build/22a957f739c44641d9703aa35ab1d4431991e8cf/conanbuildinfo.cmake:585 (message):
  Incorrect 'clang', is not the one detected by CMake: 'GNU'

Which raises the question: when providing a compiler setting, does the CMake build helper take any measure to use said compiler? If not, what is the best practice for the recipe implementers to forward this setting to the CMake helper?

[jgsogo]

Hi, @Adnn. We are working on a POC to start using toolchains for CMake (follow the issue here: https://github.com/conan-io/conan/issues/5737) as it is the best way to avoid this kind of errors.

Right now, the best thing you can do is to use profiles and add the environment variables CXX and CC to your profiles, and CMake will use them to populate CMAKE_CXX_COMPILER and CMAKE_C_COMPILER.

For example, a profile for Clang:

[settings]
os=Linux
os_build=Linux
arch=x86_64
arch_build=x86_64
compiler=clang
compiler.version=6.0
compiler.libcxx=libstdc++11
build_type=Release
[options]
[build_requires]
[env]
CXX=clang++
CC=clang

Other option is to populate the CMAKE_<LANG>_COMPILER variables yourself inside the recipe, using cmake.definitions, but I wouldn’t recommend this way over the profiles one.

[jgsogo]

Thanks a lot! 😊

With the effort in #5919 CMake integration in Conan should be easier to handle:

• the toolchain will take care of the compiler, flags,…
• the toolchain, via CMAKE_PROJECT_INCLUDE, will adjust some flags (like VS runtime)
• the information about dependencies will be consumed using a generator like find_package or find_package_multi,… or even cmake_paths if you just want the paths.

Decoupling the settings from the dependencies will make it more clear.