CMake Config checks for system architecture causes problems on Conan

[cjdb]

Description

While trying to build something with Conan (that uses Catch2), I encountered this diagnostic:

CMake Error at CMakeLists.txt:28 (find_package):
  Could not find a configuration file for package "Catch2" that is compatible
  with requested version "2.3.0".

  The following configuration files were considered but not accepted:

    /home/cjdb/.conan/data/catch2/2.3.0/bincrafters/stable/package/5ab84d6acfe1f23c4fae0ab88f26e3a396351ac9/lib/cmake/Catch2/Catch2Config.cmake, version: 2.3.0 (32bit)

@mmha identified that the call to write_basic_package_version_file in the root CMakeLists.txt generates something that checks the system architecture. By commenting out the following lines in /home/cjdb/.conan/data/catch2/2.3.0/bincrafters/stable/package/5ab84d6acfe1f23c4fae0ab88f26e3a396351ac9/lib/cmake/Catch2/Catch2ConfigVersion.cmake, we were able to kill the error:

# check that the installed version has the same 32/64bit-ness as the one which is currently searching:
#if(NOT CMAKE_SIZEOF_VOID_P STREQUAL "4")
#  math(EXPR installedBits "4 * 8")
#  set(PACKAGE_VERSION "${PACKAGE_VERSION} (${installedBits}bit)")
#  set(PACKAGE_VERSION_UNSUITABLE TRUE)

I'm using a 64-bit machine, which is appears to be different to the bincrafters' machine (as it is expecting a 32-bit machine).

Steps to reproduce

Add this to your project's CMakeLists.txt

find_package(Catch2 2.3.0 REQUIRED)

Extra information

# conanfile.txt
[requires]
boost/1.68.0@conan/stable
range-v3/0.3.6@ericniebler/stable
catch2/2.3.0@bincrafters/stable

[generators]
cmake_paths
virtualenv

[mmha]

There is an issue on the Kitware Gitlab open for this limitation: https://gitlab.kitware.com/cmake/cmake/issues/16184

[horenmar]

So, if I understand this correctly, the problem is that CMake automatically encodes and checks what "bitness" a package is when using PackageConfig, and Conan generates the package on a 32bit machine, which means that 64bit machines cannot use the package?

[mmha]

@horenmar That is correct. It's more of an upstream CMake issue than a Catch issue, but as it stands right now the version check for the config file makes the CMake package nonportable.

[horenmar]

Yeah, I am gonna say that either of the upstreams (CMake/conan) need to fix this. Catch2ConfigVersion.cmake is completely autogenerated using CMake facilities, so either conan needs to provide properly configured files, or CMake needs to provide the ability to mark a package as platform-independent, but I don't want to change our CMake files to write our bespoke ConfigVersion file.

[horenmar]

As it turns out, there is a fairly reasonable workaround.