Re: [I] [C++] Address "Compatibility with CMake < 3.5 has been removed" error [arrow]

["KyleFromNVIDIA (via GitHub)" <gi...@apache.org>]

KyleFromNVIDIA commented on issue #48801:
URL: https://github.com/apache/arrow/issues/48801#issuecomment-4498889561

   Here's how one can quickly reproduce the error with an Arrow build:
   
   git clone https://github.com/apache/arrow.git
   mkdir arrow/cpp/build
   cd arrow/cpp/build
   cmake .. -G Ninja -DARROW_WITH_RAPIDJSON=ON
   cmake --build .
   cmake .
   
   Notice the second configure step at the end. In the first configure, Arrow downloads and unzips RapidJSON, and on the first build, it builds it. In the second configure, find_package(RapidJSON) "finds" the RapidJSON that was just built. The config file that it finds has the cmake_minimum_required(), thus triggering the error.
   
   I think the real bug is that Arrow should be using FetchContent rather than ExternalProject, which would result in this mistaken find step not happening. However, there's still a chance that it could find a RapidJSONConfig.cmake elsewhere with the cmake_minimum_required(), so I still think https://github.com/apache/arrow/pull/49993 is worth doing regardless. The misuse of ExternalProject and the policy version are orthogonal issues that can be solved independently of each other.


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