LibZMQ cannot be built with CMake Version 4.0.1 on Windows

[uelkue]

Issue description

LibZMQ does not build with CMake version 4.0.1 on Windows.

Environment

• libzmq version (commit hash if unreleased): 4.3.5, released on Oct 9, 2023
• OS: Windows 10 (22H2)
• CMake version: 4.0.1

Minimal test code / Steps to reproduce the issue

1. Create a build folder and change to this folder.
2. Build LibZMQ with the command cmake -G"MinGW Makefiles" -DCMAKE_SYSTEM_NAME=WindowsStore -DCMAKE_SYSTEM_VERSION=10.0 -DENABLE_CURVE=OFF -DZMQ_BUILD_TESTS=OFF -DMINGW=ON ..

What's the actual result? (include assertion message & call stack if applicable)

Build fails with the message:

CMake Warning (dev) at CMakeLists.txt:2 (project):
  cmake_minimum_required() should be called prior to this top-level project()
  call.  Please see the cmake-commands(7) manual for usage documentation of
  both commands.
This warning is for project developers.  Use -Wno-dev to suppress it.

-- The C compiler identification is GNU 14.2.0
-- The CXX compiler identification is GNU 14.2.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: C:/mingw64/bin/gcc.exe - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/mingw64/bin/c++.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Error at CMakeLists.txt:7 (cmake_minimum_required):
  Compatibility with CMake < 3.5 has been removed from CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.

  Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.

-- Configuring incomplete, errors occurred!

What's the expected result?

LibZMQ builds successfully with CMake.

[uelkue]

As indicated by the error message, setting -DCMAKE_POLICY_VERSION_MINIMUM=3.5 allows to build without any errors, although the warning persists.

[a4z]

This is not just a problem for Windows, but all platforms.

Since that breaks all CI systems that update CMake.
I think the proper solution is to set the minimum version to a reasonable one. The technical value if keeping 2.8 around is basically zero. CMake is easy to update, and I would argue there are more users on recent CMake versions than users on CMake versions that only exist in the museum.

PR is up

[uelkue]

Thank you @a4z . Yes, I totally agree, as 2.8 belongs to the museum and even the 3.0 is give or take 10 years old at this point. I will close the issue once your PR #4789 is closed.