Failure with cmake 4.1

[hsdk123]

Description

The latest cmake version is 4.1.2, and thus seems to fail
https://github.com/nlohmann/json/blob/develop/CMakeLists.txt#L1

Is there a reason why there's a cmake max check defined?

Reproduction steps

Use cmake 4.1

Expected vs. actual results

No error expected.
CMake's error in these situations is also confusing as it doesn't highlight the maximum version:

CMake Error at /Users/runner/work/Light.vn-core/Light.vn-core/_deps/json/230202b6f5267cbf0c8e5a2f17301964d95f83ff/CMakeLists.txt:1 (cmake_minimum_required):
-- Configuring incomplete, errors occurred!
  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.

Minimal code example

Error messages

Compiler and operating system

emscripten, Windows

Library version

develop

Validation

• The bug also occurs if the latest version from the develop branch is used.
• I can successfully compile and run the unit tests.

[gregmarr]

The second number is not "the max CMake version supported", it is "Use the policies as of this CMake version", so this says that we want 3.5 as the minimum, but the policies as of 4.0.

[hsdk123]

The second number is not "the max CMake version supported", it is "Use the policies as of this CMake version", so this says that we want 3.5 as the minimum, but the policies as of 4.0.

This is awfully odd then, my logs are stating: CMAKE_VERSION: 4.1.1 and the issue is coming from the cmake_minimum_required statement as per the log line

[nlohmann]

I cannot reproduce the issue on the latest develop branch:

$ cmake --version
cmake version 4.1.2

CMake suite maintained and supported by Kitware (kitware.com/cmake).


$ cmake .. -DJSON_BuildTests=ON
-- The CXX compiler identification is AppleClang 17.0.0.17000319
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Using the multi-header code from /Users/niels.lohmann/Code/json/include/
-- Operating system: Darwin-24.6.0; ProductName:		macOS; ProductVersion:		15.7.1; BuildVersion:		24G231; Darwin M-CVFVWL25KQ 24.6.0 Darwin Kernel Version 24.6.0: Mon Aug 11 21:16:31 PDT 2025; root:xnu-11417.140.69.701.11~1/RELEASE_ARM64_T6030 arm64
-- Compiler: Apple clang version 17.0.0 (clang-1700.3.19.1); Target: arm64-apple-darwin24.6.0; Thread model: posix; InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
-- C++ standard library: LLVM C++ Standard Library (libc++), _LIBCPP_VERSION=200100
-- Testing standards: 11 14 17 20 23
-- Looking for C++ include sys/types.h
-- Looking for C++ include sys/types.h - found
-- Looking for C++ include stdint.h
-- Looking for C++ include stdint.h - found
-- Looking for C++ include stddef.h
-- Looking for C++ include stddef.h - found
-- Check size of size_t
-- Check size of size_t - done
-- Configuring done (2.2s)
-- Generating done (0.3s)
-- Build files have been written to: /Users/niels.lohmann/Code/json/build