[CMake] Changes to cmake_minimum_required() for 3.12

[Craig Scott]

(Subject changed to be specific to this discussion)

On Sat, Jun 30, 2018 at 3:13 PM, Hendrik Sattler <post at hendrik-sattler.de>
wrote:

> It would actually make even more sense to rename cmake_minimum_required()
> to cmake_version_required() with the new syntax or something similar. Users
> of the old function cannot use the new syntax in older cmake versions and
> the old name does not actually fit the new functionality.
>

Actually older versions can use the new syntax and this is indeed the
specific reason why the new syntax is the way it is. Older CMake versions
will see the extra dots as being version component separators and will end
up effectively ignoring the max part. The nett result is that older
versions will continue to treat the min version as the policy setting just
like they have been to date. Newer versions of CMake will be able to take
advantage of the extra information provided by the max part to allow newer
policies to be enforced.

Regarding the renaming, a very similar discussion took place in the merge
request itself, so I'll refer you to there for details:

https://gitlab.kitware.com/cmake/cmake/merge_requests/1864#note_389157




>
> Am 30. Juni 2018 00:05:25 MESZ schrieb "Alan W. Irwin" <
> irwin at beluga.phys.uvic.ca>:
> >On 2018-06-29 14:46-0400 Robert Maynard wrote:
> >[...]
> >> * The "cmake_minimum_required()" and "cmake_policy(VERSION)"
> >>  commands now accept a version range using the form
> >>  "<min>[...<max>]". The "<min>" version is required but policies are
> >>  set based on the "<max>" version.  This allows projects to specify a
> >>  range of versions for which they have been updated and avoid
> >>  explicit policy settings.
> >[...]
> >
> >I suggest the following change to the above description:
> >
> >but policies are set based on the "<max>" version.
> >
> >==>
> >
> >but policies are set based on the minimum of the running CMake and
> >"<max>" versions.
> >
> >I prefer the latter because it immediately answers the question implied
> >by the former, i.e.,
> >what happens if the running version is less than max?
>

Seems reasonable. I've created a MR with a slight tweak to your wording for
this here <https://gitlab.kitware.com/cmake/cmake/merge_requests/2180>.

-- 
Craig Scott
Melbourne, Australia
https://crascit.com
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