Including optional/optional_fwd.hpp then type_traits.hpp

[Tony Lewis <tonyelewis@…>]

1.61.0 beta introduces a new problem: the following code has started failing to compile since 1.60.0:

#include <boost/optional/optional_fwd.hpp>
#include <boost/type_traits.hpp>

This appears to be caused by a change to optional_fwd.hpp so that it now includes boost/config/suffix.hpp. It turns out that that already had the potential to cause problems in 1.60.0, eg the following fails to compile:

#include <boost/config/suffix.hpp>
#include <boost/type_traits.hpp>

Does Boost.Config allow other Boost libraries to include boost/config/suffix.hpp directly? If so, I think Config needs to fix the above problem. If not, optional_fwd.hpp needs to be changed to include boost/config.hpp not boost/config/suffix.hpp (and in that case it might be good to do the following).

1. scan for any other includes in any other Boost libraries
2. fix them
3. move suffix.hpp and similar in a detail subdirectory.

I'm seeing equivalent errors on both Clang 3.6.2-1 and GCC 5.2.1.

Command lines:

clang++ -std=c++11 -isystem /opt/boost_1_61_0_b1_clang_build/include a.cpp
g++     -std=c++11 -isystem /opt/boost_1_61_0_b1_gcc_build/include   a.cpp

[John Maddock]

No way should optional be including an internal Config header directly - that's just not supported.

[Tony Lewis <tonyelewis@…>]

I think this is related to ticket:12179.

[Tony Lewis <tonyelewis@…>]

Yes - the develop branch of the ​boostorg/optional !GitHub repo now works for me.

Thanks very much for your work on this.