X3 doesn't compile on g++ 4.8 cxxstd=11

[pdimov]

https://travis-ci.org/boostorg/boost/jobs/308195225

./boost/spirit/home/x3/support/context.hpp:28:18: error: expected primary-expression before ‘auto’
         decltype(auto) get(ID_ id) const
                  ^

These tests should probably be guarded by requires.

Also,

In file included from libs/spirit/test/x3/x3_variant.cpp:9:
./boost/spirit/home/x3/support/ast/variant.hpp:134:50: error: no template named 'remove_reference_t' in namespace 'std'; did you mean simply 'remove_reference_t'?
                                                ,std::remove_reference_t<T>

Looks like X3 wants C++14.

[Kojoley]

Yeah, X3 requires c++14. I do not know why https://github.com/boostorg/spirit/blob/0917fca9fdcf3b42a3f5dedd595217164d94a3fb/test/x3/Jamfile#L17-L24 is not working, I did not touch this and thought it worked.

[pdimov]

That's not the correct way to do it even if it worked, as it would've overridden cxxstd=17 and you do want to be able to test on C++17; use [ requires cxx14_something ].

[Kojoley]

Yes, this was my plan. I just actually turned on x3 tests to see a feedback from regression matrix while knew that x3 tests not in a good condition.

[djowel]

That was a really old commit, before gcc even had std=c++14, IIRC. Yes, X3 requires at least C++14.