[tests, Fatbuffers, v2.0.7] Building tests fails with GCC 4.8.5

[flukeborder]

Building Flatbuffers tests v2.0.7 with GCC 4.8.5 (CentOS 7) fails with a series of errors pertaining to the initialiser list / explicit constructor. One example:

.../flatbuffers/tests/test.cpp: In function ‘void {anonymous}::UtilConvertCase()’: .../flatbuffers/tests/test.cpp:1509:9: error: converting to ‘std::tuple<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, flatbuffers::Case, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >’ from initializer list would use explicit constructor ‘constexpr std::tuple< <template-parameter-1-1> >::tuple(_UElements&& ...) [with _UElements = {const char (&)[20], flatbuffers::Case, const char (&)[17]}; <template-parameter-2-2> = void; _Elements = {std::basic_string<char, std::char_traits<char>, std::allocator<char> >, flatbuffers::Case, std::basic_string<char, std::char_traits<char>, std::allocator<char> >}]’ };

It appears that the tests are written using the initialiser list sytax compatible with C++14 standard library and above, and not the one compatible with C++11.

See e.g. https://stackoverflow.com/questions/26947704/implicit-conversion-failure-from-initializer-list

[dbaileychess]

Thanks, Looks like we need CI for gcc with --std=c++11 explicitly set. Most users are probably compiling with a later standard and don't have the error.

[flukeborder]

You might consider being more strict regarding the C++ standard to be used by the individual targets - that is, using the CMAKE_CXX_STANDARD approach rather than the "compiler features" approach (the former translates to --std=c++11 with GCC).
The "compiler features" approach is more suitable for an "end user project", whereas Flatbuffers is a rather special case - it's not even a library, but more of a compile-time code generation utility.
Obviously, you want the generated Flatbuffers C++ code to conform to the specific C++ standard, in order to establish the minimum C++ standard required for projects that use Flatbuffers. In the view of that, it makes sense to force a specific standard (i.e. not to allow a higher standard) for the test targets. CMAKE_CXX_STANDARD can be defined on a target-per-target basis, so having C++17-specific tests should not be an issue.

[dbaileychess]

This should be fixed by #7487, since I ran into that issue while refactoring.