CMake minimum version 3.10

[scivision]

This mitigates maintenance burden as CMake minimum version isn't
relevant for these tests. CMake >= 3.31 warns if CMake minimum version
is less than 3.10.

ref: https://gitlab.kitware.com/cmake/cmake/-/merge_requests/9875

[eli-schwartz]

Overall this change seems quite reasonable. And 3.5 is certainly not necessary for us anymore since if I recall correctly meson no longer supports versions of cmake below 3.14 for use in subproject() -- which I think is what all this code is related to anyway.

[eli-schwartz]

Are we able to get away with the same "whatever the current version is" trick here too?

[dg0yt]

I wonder if this is a good idea. This command is not about the actual version of CMake but about the behavior of CMake.

Before this change, it set a fixed set of CMake policies to NEW.
With this change, it will set a variable set of policies to NEW, subject to the version of CMake which is being run. This may be more fragile: users that run tests with a different version of CMake may get different results. CMake policies should limit this variation, but this PR disables that instrument.

To reduce maintenance burden without allowing allowing umlimited future policies, there is

cmake_minimum_required(VERSION 3.14...3.30)

[eli-schwartz]

With this change, it will set a variable set of policies to NEW, subject to the version of CMake which is being run. This may be more fragile: users that run tests with a different version of CMake may get different results. CMake policies should limit this variation, but this PR disables that instrument.

This PR makes meson's own unittests run using those variable policies, and makes the "CMake Toolchain: Calling CMake once to generate the compiler state" internal code use a fixed version of 3.10, having upgraded that from 3.7.

No user code should be affected at any time, but people packaging meson and running the meson testsuite might see the issues you theorized.

Has that happened? Does this indicate something that our testsuite files need to adapt to?

[dg0yt]

I'm aware that this is only test code. The package manager I look at doesn't run such tests so it isn't affected. So indeed I "theorized" that only with other "people packaging meson" in mind. And contributors, too, if they can and do run the tests.