CMakeLists.txt requires only CMake 3.16 but project options use policy from 3.18

[dholmes215]

From this discussion on Discord: https://discord.com/channels/773320866993012746/954385320336556042/958776874895556698

A user encountered the error:

CMake Error at build/_deps/_project_options-src/src/PackageProject.cmake:4 (cmake_policy):
  Policy "CMP0103" is not known to this version of CMake.

That policy was added in CMake 3.18, but this project's main CMakeLists.txt uses cmake_minimum_required(VERSION 3.16).

[ddalcino]

There are two obvious ways to solve this (see discussion at cpp-best-practices/gui_starter_template#208):

• bump the minimum CMake dependency to 3.18, or
• bump the project_options version to 0.19.0+

From cpp-best-practices/gui_starter_template#208 (comment):

I think the larger issue here is that we should test the minimum required versions of our tools in CI, and keep these up-to-date in our documentation. Our README specifies that you can use clang 6 or gcc 7, or any compiler that supports C++17. This is no longer true, since the project requires C++20. Conceivably, you could manually set CMAKE_CXX_STANDARD to C++17 and expect the project to work, but since we aren't testing that, we don't know that it will work and we shouldn't tell our users that it will.

[lefticus]

@ddalcino very good point. I'll create a new branch that we can collaborate on to get the docs/dependencies in alignment, and test upgrading to project_options 0.20.0

We can also use that branch to discuss if we want our own fork of project_options.

[lefticus]

See #18

Looks like we have work to do. Seems conan is no longer running. Somehow was disabled in the dynamic_project_options defaults, perhaps?

[ddalcino]

Looks like it happened here: aminya/project_options#71

Should be easy enough to specify ENABLE_CONAN when we call dynamic_project_options() though.

[lefticus]

Fixed in e51378d I think