Re: CMake minimum version to support

From: Alexander Grund (alexander.grund_at_[hidden])
Date: 2021-06-03 09:57:18

> If Boost is really hesitant to require this of its users I recommend 
> to collect the features that you need and require at least the latest 
> version of CMake which brings in these features.

^This

While I agree that upgrading CMake is easy, needlessly requiring the 
latest version is counterproductive.

I know if one instance at least where I can given an example: For 
automated installations on HPC systems "toolchain generations" are 
defined. And in each generation only 1 version of each software can 
exist. The base is then e.g. GCC 9.3.0 and OpenMPI 4.1.0 and then 
software gets successively added as needed.
Hence when CMake X is added and later Boost is released and that is 
added but requires CMake Y (with Y > X) it would mean that it cannot be 
used in this toolchain generation and people need to wait till the next 
update.

So I'd focus on 2 points:
- Use the CMake version that is required for what is used
- Try to avoid CMake versions more recent than, say, 1 year, maybe 2. 
This has also the benefit that things may stabilize with patch releases.

And for completeness: CMake does deprecate and eventually remove stuff. 
So there are (rare) instances where it is not backwards compatible. And 
even though often policies are used for such breaking changes, I'm quite 
certain even projects claiming they support CMake X do in fact not. Also 
note that requiring a more recent CMake enables all policies introduced 
until then, so behavior may change just by upgrading the required cmake 
version.