[capnproto] RFC for 0.7: Require C++14, GCC 4.9+, Clang 3.6+, Visual Studio 2017+

['Kenton Varda' via Cap'n Proto]

Hi all,

I expect to release 0.7 of Cap'n Proto in mid-July, and possibly shoot for
1.0 by the end of this year.

In 0.7, I've decided to bump the minimum versions of compilers and language
standards we require, as follows:

- We will require C++14. Previously, we required only C++11. C++14 fixes
some serious pain points from C++11, and working around those pain points
for compatibility reasons has become too painful. GCC 4.9 and Clang 3.6
appear to be the minimum compiler versions supporting C++14 to the extend
we need.

- We will drop support for Visual Studio 2015, requiring Visual Studio
2017+. This is not related to the C++14 change, but rather because we have
found it very difficult to work around bugs in VS 2015 in general. It seems
like every time I touch a template or use constexpr, VS 2015 breaks and
requires a work-around. In PR#698
<https://github.com/capnproto/capnproto/pull/698> I find myself stumped. If
we dropped VS 2015 support, then I could move on, and could also eliminate
a lot of ugly hacks from the codebase.

Are there any objections to these changes?

-Kenton

['Kenton Varda' via Cap'n Proto]

Since there are no objections, I am moving forward with this.

-Kenton

Post by 'Kenton Varda' via Cap'n Proto
Hi all,
I expect to release 0.7 of Cap'n Proto in mid-July, and possibly shoot for
1.0 by the end of this year.
In 0.7, I've decided to bump the minimum versions of compilers and
- We will require C++14. Previously, we required only C++11. C++14 fixes
some serious pain points from C++11, and working around those pain points
for compatibility reasons has become too painful. GCC 4.9 and Clang 3.6
appear to be the minimum compiler versions supporting C++14 to the extend
we need.
- We will drop support for Visual Studio 2015, requiring Visual Studio
2017+. This is not related to the C++14 change, but rather because we have
found it very difficult to work around bugs in VS 2015 in general. It seems
like every time I touch a template or use constexpr, VS 2015 breaks and
requires a work-around. In PR#698
<https://github.com/capnproto/capnproto/pull/698> I find myself stumped.
If we dropped VS 2015 support, then I could move on, and could also
eliminate a lot of ugly hacks from the codebase.
Are there any objections to these changes?
-Kenton