Description of problem:
Compiling a program that includes a Boost ICL (interval container library) yields an error when C++17 is selected. It works when using other standard switches (e.g. C++14).


Version-Release number of selected component (if applicable):
boost-devel-1.63.0-6.fc26.x86_64

How reproducible:
always

Steps to Reproduce:
1. $ cat > test_icl.cc 
#include <boost/icl/interval_set.hpp>

int main()
{
  return 0;
}
2. $ g++ -std=c++1z test_icl.cc
3.

Actual results:
In file included from /usr/include/boost/icl/type_traits/identity_element.hpp:11:0,
                 from /usr/include/boost/icl/type_traits/unit_element.hpp:12,
                 from /usr/include/boost/icl/concept/interval.hpp:17,
                 from /usr/include/boost/icl/concept/joinable.hpp:12,
                 from /usr/include/boost/icl/associative_interval_container.hpp:13,
                 from /usr/include/boost/icl/interval_base_set.hpp:24,
                 from /usr/include/boost/icl/interval_set.hpp:14,
                 from test_icl.cc:1:
/usr/include/boost/icl/type_traits/type_to_string.hpp:56:12: error: partial specialization of ‘struct boost::icl::type_to_string<Unary<Type> >’ after instantiation of ‘struct boost::icl::type_to_string<std::__cxx11::basic_string<char> >’ [-fpermissive]
     struct type_to_string<Unary<Type> >
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/boost/icl/type_traits/type_to_string.hpp:72:12: error: partial specialization of ‘struct boost::icl::type_to_string<Binary<Type1, Type2> >’ after instantiation of ‘struct boost::icl::type_to_string<std::__cxx11::basic_string<char> >’ [-fpermissive]
     struct type_to_string<Binary<Type1, Type2> >
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Expected results:
No error output, successful compilation.

Additional info:

What does work:

$ g++ -std=c++14 test_icl.cc


Unfortunately, although clang++ has some C++17 support, it can't be used as a drop-in replacement, because it hasn't enough support for compiling libstdc++ std::optional implementation which is included by Boost ICL:

$ clang++ -std=c++1z test_icl.cc
In file included from test_icl.cc:1:
In file included from /usr/include/boost/icl/interval_set.hpp:14:
In file included from /usr/include/boost/icl/interval_base_set.hpp:19:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7/set:60:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7/bits/stl_tree.h:72:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7/bits/node_handle.h:39:
/usr/bin/../lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7/optional:1032:27: error: use of class template 'optional' requires template arguments
  template <typename _Tp> optional(_Tp) -> optional<_Tp>;
                          ^
/usr/bin/../lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7/optional:451:11: note: template is declared here
    class optional
          ^
/usr/bin/../lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7/optional:1032:40: error: expected ';' at end of declaration
  template <typename _Tp> optional(_Tp) -> optional<_Tp>;
                                       ^
/usr/bin/../lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7/optional:1032:41: error: cannot use arrow operator on a type
  template <typename _Tp> optional(_Tp) -> optional<_Tp>;
                                        ^
3 errors generated.