ENH: Update compiler versions for C++14

[N-Dekker]

Following pull request InsightSoftwareConsortium/ITK#2563
"ENH: Upgrade ITK from C++11 to C++14"

Suggested by Jon Haitz Legarreta Gorroño (@jhlegarreta) at InsightSoftwareConsortium/ITK#2563

[jhlegarreta]

Looks good to me. I'd say that wisest would be to wait until the changes are agreed upon and merged in ITK before merging.

[N-Dekker]

Note to maintainers: this pull request should only be merged once ITK has indeed moved from C++11 to C++14 (possibly by pull request InsightSoftwareConsortium/ITK#2563 ), as commented by @jhlegarreta

[thewtex]

Thanks for adding this @N-Dekker !

[N-Dekker]

@thewtex You're welcome, but I'm not entirely sure if my pull request is OK. Looking at:

ITKSoftwareGuide/SoftwareGuide/Latex/Introduction/Installation.tex

Lines 32 to 40 in ae7db1a

	%% The following compilers should have nightly dashboard in the "Expected builds"
	%% to ensure that support is maintained.
	%%
	\begin{itemize}
	\item GCC 4.8 and newer
	\item Visual Studio 2015, 2017, 2019, toolsets 14.x, 15.0, 16.0
	\item Apple Clang 7.0 and newer
	\item Clang 6 and newer
	\end{itemize}

Versus:

https://github.com/InsightSoftwareConsortium/ITK/blob/master/Documentation/SupportedCompilers.md

Should they be the same? Because now they are different! Even after my pull request 🤔

Apparently ITK already required AppleClang 7.0.2 and later (from Xcode 7.2.1) before the upgrade to C++14! Should that requirement still be adjusted for C++14?

[N-Dekker]

I think this PR ("ENH: Update compiler versions for C++14") does not need to adjust the Clang versions, as Clang 6 and Apple Clang 7.0 should already support C++14. Right, @seanm ? Note that these are the compilers that "should have nightly dashboard". ITK might still compile fine on other compiler versions 😃

I'm not against upgrading Clang, it's just that it seems beyond the scope of this pull request.

[thewtex]

Should they be the same? Because now they are different!

Yes, could they please be synchronized?

[N-Dekker]

@thewtex

Yes, could they please be synchronized?

They may not mean exactly the same thing: The compilers that "should have nightly dashboard" and the "supported" compilers. Or should they be exactly the same compilers?

Anyway, this pull request does already synchronize MSVC and GCC. For (Apple) Clang I just do not know the preferred minimum. We AppleClang 12.0.0.12000032 Xcode 12.4 (on GitHub Actions) and Apple clang version 12.0.5 (clang-1205.0.22.9) (as @ViktorvdValk told me). Sean (@seanm) wrote at https://discourse.itk.org/t/may-we-start-using-c-14-at-the-master-branch/4172/23?u=niels_dekker that he is ok with Xcode 7.2.1 being the minimum.

[seanm]

You may as well put Xcode 7.2.1 as the minimum.

It's the newest possible Xcode on macOS 10.10.x, which is the oldest version of macOS that I have a bot for. I don't think anyone else runs any Mac bot older than that.

[N-Dekker]

You may as well put Xcode 7.2.1 as the minimum.

Thanks @seanm Please check f65f786 !

[thewtex]

They may not mean exactly the same thing: The compilers that "should have nightly dashboard" and the "supported" compilers. Or should they be exactly the same compilers?

They should be the same compilers. We likely could use more dashboard builds, but that is a separate issue.