[Dune-devel] Required CMake version

[Christoph Grüninger]

Dear all,
some facts, as I recollect them:

1) We decided 2015 in Heidelberg at our Dev Meeting to require CMake
3.0. We did not bump the version to 3.0 because 2.8.12 was enough.
Later, we decided to use 3.1 and thus I was cleaning up code doing so.
2) Steffen and Dominic found some bugs in older CMake version, and they
wished to switch to CMake 3.1 already in 2015. Having the switch with
Dune 2.6 seems reasonable.
3) Working with CMake pre-3.0 is more painful as the documentation is
cumbersome.
4) The increased required CMake version was not announced by a merge
request. I asked on the mailing list and nobody answered. Nobody.
http://lists.dune-project.org/pipermail/dune/2017-September/014638.html

So, I don't have a specific command to increase the version to 2.8.12.
But we decided to switch to 3.1 and I don't see an argument so stay with
2.8.12.
Who are these ominous users? Once, Alf used Red Hat 5 and we wanted to
stay compatible. Please provide an actual platform. Then we can decide
whether we want to support it or not.
I hate this discussion popping up whenever we want to materialize our
decisions. Based on our decision, we could rely on CMake >= 3.0 for more
than two years! What system does provide GCC 5 but not CMake 3.0?

What is dangerous, if dune-common requests 3.1 but downstream modules
use 2.8.12. Then CMake is in the wrong mode and will interpret things
differently. That is what we called "subtle bugs".

As CMake is easily installed, having included any version in our CI
should be a no-brainer (without me doing the actual work…).

Overall, if we have a formal vote to stay compatible to 2.8.12 I will
shut up. Until then I veto anything snatching my CMake version away from me.

Bye
Christoph

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