[CMake] Adding Cmake version in online documentation

[Alexander Neundorf]

On Wednesday 09 November 2016 00:47:39 Albrecht Schlosser wrote:
> On 08.11.2016 23:01 Nils Gladitz wrote:
> > On 08.11.2016 20:26, Albrecht Schlosser wrote:
> >> I'm a developer of a public GUI library (FLTK). In this position you
> >> don't know anything about the availability of CMake versions on your
> >> target platforms. Our intention is to keep cmake_minimum_required() as
> >> low as possible.
> > 
> > If you are intending to keep the required version as low as possible
> > you'll already have a justification / reason for doing so.
> > I can only assume that the reason is that you need to support ancient
> > platforms which ship equally ancient versions of CMake and you don't
> > want to bother your users to build or install custom newer versions of
> > CMake.
> > 
> > It doesn't matter what your reasons or justifications for it are (though
> > I would hope they are valid and verified) but you have to decide on a
> > minimum version that you can life with in the end.
> 
> Basically that's a floating target. We need to evaluate this from time
> to time and maybe adjust the required version.

You could have a look at the major distributions and what they ship.
The oldest I have to support is RHEL 5, released first 2007, and that feels 
really ancient. But there are people out there which still run such systems.
Centos 5 comes with CMake 2.6.4, Centos 6 with 2.8.12.
OTOH, installing additional versions of CMake is really easy, thanks to the 
binary packages provided by Kitware (... which IIRC are built in a Docker 
Centos 5 container).

Btw. I really appreciate your idea to keep the requirements low. :-)
 
> >> That said, whenever you change a CMakeLists.txt file you should be
> >> aware if the commands you use are compatible with the CMake version
> >> you "require". There should be an easy way to find out in which
> >> version a particular CMake command has been introduced. Only with this
> >> information you can decide if you should use this fine command or
> >> better find another way to do the task you're going to do.
> > 
> > At this point you only have to refer to the documentation that actually
> > corresponds to the version you decided to require.
> > You'll only find commands and behaviours in that documentation that'll
> > actually be available in your minimum version.
> 
> Yep, that's simple, of course. But if there is a (new) command you want
> to use it would be interesting to know the CMake version it was
> introduced to _decide_ if you can or want to do without it or raise the
> required version. I'm sure that we will raise the required version when
> CMake gets (or got) a new feature we need to use. But we need the facts
> to decide...

You can have a look here, there is the documentation for all cmake versions 
back to 2.6: https://cmake.org/documentation/

Alex