sys-devel/make: default CXX to c++ instead of g++

[lei-april]

Bug #589894

Package-Manager: portage-2.2.28

[mgorny]

While I agree this is in line with how CC is defined, I don't think we ought to change this without upstream doing the same. It's not good for Gentoo make to behave different from make on other distributions.

[blueness]

I agree with @mgorny Can you help me understand precisely why this is a problem as you say in bug #589894. Does invoking g++ on a musl/clang system fail?

[mgorny]

I think his point is that if we implement the eselect logic to symlink c++ to clang++, make will still default to g++ rather than c++/clang++.

[blueness]

@zzlei Have bounced this by upstream? GNU make releases move slowly, but if upstream OK's it, we can legitimately backport it.

[lei-april]

@blueness I asked about this upstream and their rationale is: cc is the C compiler name required by POSIX (actually in the latest standard it's changed to c99), but there's no requirement for a C++ compiler. And it seems in the early days, there's only g++ but no c++ (which I don't think is valid on modern systems), so GNU Make simply picked g++ as the C++ compiler.

I've checked macOS and FreeBSD; their Make systems both default CXX to c++, and I think there're good reasons to do so on Linux as well. What about a USE flag that enables this feature optionally? @mgorny

[mgorny]

Nah, this is not worth the confusion associated with USE flags. I'd say the change makes sense since CC defaults to cc and not gcc, and we can guarantee c++ will be valid. We could take this as Gentoo customization. @blueness, what do you think?

[blueness]

I think upstream's reasoning is bad. I'd like to see it be c++. If we make the change then, yes, we as a distro will have to make sure c++ is correct. I'm not sure how to do that if a system has both clang and gcc installed since I haven't played with clang much, but I can't imagine it being difficult.

[mgorny]

I agree. While this is not strictly necessary, I'd say we should ensure that cc/c++ point to the same compiler. Normally both point at gcc but if we start supporting switching that (e.g. using eselect-compiler @zzlei proposed), make should default to matching compilers.

[lei-april]

FWIW, the latest POSIX spec replaces cc with c99, and GNU Make might make the switch in the future (http://lists.gnu.org/archive/html/bug-make/2016-07/msg00020.html).

The eselect-compiler module will need to handle this correctly.

[mgorny]

@blueness, ping. Can we merge this? ;-)

[jbergstroem]

I think Lei's argument makes sense here. Seeing how the standard doesn't define a requirement but recent (and even old) versions of gcc (g++) as well as other c++ compilers provide this I only see a win by doing so. Additionally (as Lei also mentioned), cmake defaults to it; meaning other people have also spent time thinking and validating (disqualifying) its effects.

[jbergstroem]

Just found this by running in to the same issue a few months later. Anyone thought more about this?