`jsoncppConfig.cmake.in` uses `cmake_policy(VERSION 3.0...)` which CMake 4.0+ rejects

[xuhdev]

jsoncppConfig.cmake.in contains:

jsoncpp/jsoncppConfig.cmake.in

Line 2 in cdc8483

cmake_policy(VERSION 3.0...3.26)

CMake 4.0 has removed compatibility with policy versions below 3.5:

Compatibility with versions of CMake older than 3.5 has been removed.

So any project using find_package(jsoncpp) with CMake 4.0+ fails with:

CMake Error at .../jsoncppConfig.cmake:2 (cmake_policy):
  Compatibility with CMake < 3.5 has been removed from CMake.

This was reported in #1604 but was closed based on a suggestion to bump the max instead of the min. That was a misunderstanding -- the error is about the min (3.0), not the max. CMake 4.0 rejects any cmake_policy(VERSION) or cmake_minimum_required(VERSION) with a minimum below 3.5, regardless of the max.

[oold]

I don't think that is intended behavior on CMake's part. CMake should never fail if there is a supported policy version within the min-max range given to cmake_minimum_required(VERSION) or cmake_policy(VERSION).

Note that calls to those commands can still support older versions of CMake by using their VERSION arguments' <min>...<max> syntax. This requires only the <min> version of CMake, but when running a newer version, sets policies up to the <max> version.