[CMake] Changes to cmake_minimum_required() for 3.12

[Hendrik Sattler]

Thanks for the link.
The backwards compatibility is something worth mentioning in the release notes, so that people can use it right away.


Am 1. Juli 2018 00:12:19 MESZ schrieb Craig Scott <craig.scott at crascit.com>:
>(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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