CMake files use string(JOIN) while only requesting CMake >= 3.5

[coryan]

What version of protobuf and what language are you using?

Version: 22.4
Language: C++

What operating system (Linux, Windows, ...) and version?

Ubuntu 18.04

What runtime / compiler are you using (e.g., python version or gcc version)

GCC 7.5

What did you do?

I used this Dockerfile:

https://github.com/coryan/google-cloud-cpp/blob/414854fb53439c3d34ccb17766312c518afa9e3d/ci/cloudbuild/dockerfiles/demo-ubuntu-bionic.Dockerfile#L66-L76

What did you expect to see

A successful build.

What did you see instead?

Step #0: -- The C compiler identification is GNU 7.5.0
Step #0: -- The CXX compiler identification is GNU 7.5.0
Step #0: -- Check for working C compiler: /usr/bin/cc
Step #0: -- Check for working C compiler: /usr/bin/cc -- works
Step #0: -- Detecting C compiler ABI info
Step #0: -- Detecting C compiler ABI info - done
Step #0: -- Detecting C compile features
Step #0: -- Detecting C compile features - done
Step #0: -- Check for working CXX compiler: /usr/bin/c++
Step #0: -- Check for working CXX compiler: /usr/bin/c++ -- works
Step #0: -- Detecting CXX compiler ABI info
Step #0: -- Detecting CXX compiler ABI info - done
Step #0: -- Detecting CXX compile features
Step #0: -- Detecting CXX compile features - done
Step #0: -- 
Step #0: -- 22.4.0
Step #0: -- Performing Test protobuf_HAVE_LD_VERSION_SCRIPT
Step #0: -- Performing Test protobuf_HAVE_LD_VERSION_SCRIPT - Success
Step #0: -- Looking for pthread.h
Step #0: -- Looking for pthread.h - found
Step #0: -- Looking for pthread_create
Step #0: -- Looking for pthread_create - not found
Step #0: -- Looking for pthread_create in pthreads
Step #0: -- Looking for pthread_create in pthreads - not found
Step #0: -- Looking for pthread_create in pthread
Step #0: -- Looking for pthread_create in pthread - found
Step #0: -- Found Threads: TRUE  
Step #0: -- Found ZLIB: /usr/lib/x86_64-linux-gnu/libz.so (found version "1.2.11") 
Step #0: -- Performing Test protobuf_HAVE_BUILTIN_ATOMICS
Step #0: -- Performing Test protobuf_HAVE_BUILTIN_ATOMICS - SuccessStep #0: CMake Error at cmake/install.cmake:9 (string):
Step #0:   string does not recognize sub-command JOIN
Step #0: Call Stack (most recent call first):
Step #0:   CMakeLists.txt:409 (include)

Anything else we should know about your project / environment

string(JOIN) ships with CMake >= 3.12:

https://cmake.org/cmake/help/latest/command/string.html#join

However Protobuf 22.4 requires CMake >= 3.5:

protobuf/CMakeLists.txt

Line 2 in dbb9f9b

cmake_minimum_required(VERSION 3.5)

You could bump the CMake requirements but notice that the overall foundations matrix still says CMake >= 3.10:

https://github.com/google/oss-policies-info/blob/6587f128170c23282eb40949c914403a4010079a/foundational-cxx-support-matrix.md?plain=1#L6

[fowles]

Somewhere around here:

protobuf/cmake/install.cmake

Line 9 in dbb9f9b

string(JOIN " " _pc_target_list ${_pc_targets})

One needs to write a loop

CMake
  set(_protobuf_PC_REQUIRES "")
  set(_sep "")
  foreach (_target IN LISTS _pc_target_list)
    string(CONCAT _protobuf_PC_REQUIRES "${_protobuf_PC_REQUIRES}" "${_sep}" "${_target}")
    set(_sep " ")
  endforeach ()