Re: CMake minimum version to support

From: Deniz Bahadir (deniz.bahadir_at_[hidden])
Date: 2021-06-03 09:37:39

Am 02.06.21 um 18:32 schrieb Peter Dimov via Boost:
> I suppose the time has come to have the discussion on
> the minimum CMake version we will support for building
> Boost. Currently that's set to 3.5, which kind of works, but
> is fairly inconvenient.
>
> The interesting options are
>
> - CMake 3.8: required for use of the compile features
>    cxx_std_11, cxx_std_14, cxx_std_17, etc. Also allows
>    source_group(TREE, which is used by Json and
>    PropertyTree.
>
> - CMake 3.9: required by Nowide, I'm not sure why.
>    Also, required for FindMPI to define an imported
>    target. Building Boost.MPI is optional though.
>
> - CMake 3.13: required for Boost installation support.
>
> - CMake 3.14: required for FindPython to be modern
>    enough to make building Boost.Python reasonably
>    easy. (Building Boost.Python is optional, though.)
>
> There are also less important nice-to-have things such as
>
> - CMake 3.10: adds include_guard()
> - CMake 3.12: adds CONFIGURE_DEPENDS to file(GLOB
> - CMake 3.15: adds VERBOSE/DEBUG to message(
>
> Opinions?

I never understood why users were so lazy to get the latest CMake 
version and insist on using old, outdated and buggy versions which were 
supplied with older Linux distributions.
I always recommend to users to use the latest CMake version. (They are 
very good with keeping backwards-compatibility.)
Kitware provides binaries for Windows, Mac and Linux and even has an APT 
repository for Debian-based Linux distributions. And even building CMake 
oneself is also quite simple.

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.

Something I always recommended was to go with at least CMake 3.13.
This one is able to treat OBJECT library targets (almost) identical to 
other types of CMake targets and also contains some 
simplifications/unifications to the `target_*` commands.

If, however, for example generated files are used and therefore the 
`GENERATED` property, I recommend to take at least CMake 3.20, because 
that one makes it possible to see that property from any directory.

My 2 ct.
Deniz

PS: A short note/disclaimer: I know about and especially mentioned these 
specific features, because I provided them to CMake. (I needed them and 
they were missing from CMake.)

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