Json: Conflicts with std <any> compiling with GCC 10

[afowles]

What is the issue you have?

Attempting to upgrade code from fedora 30 to fedora 32. With GCC 10 on f32 programs fail to compile that include <any> before <nlohmann/json.hpp>. With GCC 9.3.1 on f30 (and an older version 3.7.0) the provided example compiles.

[~]$ g++ --version
g++ (GCC) 10.0.1 20200328 (Red Hat 10.0.1-0.11)
[~]$ sudo dnf list --installed | grep json-devel
json-devel.x86_64                               3.7.3-2.fc32

Please describe the steps to reproduce the issue.

With GCC 10 attempt to compile the provided example

1. g++ --std=c++17 -o test test.cpp

Where test.cpp is the following

Can you provide a small but working code example?

#include <any>
#include <nlohmann/json.hpp>

using namespace nlohmann;

int main() {
  json j;
  return 0;
}

What is the expected behavior?

Compiles

And what is the actual behavior instead?

In file included from /usr/include/c++/10/bits/move.h:57,
                 from /usr/include/c++/10/bits/nested_exception.h:40,
                 from /usr/include/c++/10/exception:148,
                 from /usr/include/c++/10/new:41,
                 from /usr/include/c++/10/any:37,
                 from test.cpp:1:
/usr/include/c++/10/type_traits: In instantiation of ‘struct std::is_constructible<nlohmann::basic_json<>, const nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer>&>’:
/usr/include/nlohmann/json.hpp:11120:79:   required by substitution of ‘template<class ... Args, typename std::enable_if<std::is_constructible<nlohmann::basic_json<>, Args ...>::value, int>::type <anonymous> > nlohmann::detail::json_ref<nlohmann::basic_json<> >::json_ref(Args&& ...) [with Args = {const nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer>&}; typename std::enable_if<std::is_constructible<nlohmann::basic_json<>, Args ...>::value, int>::type <anonymous> = <missing>]’
/usr/include/c++/10/type_traits:901:30:   required from ‘struct std::__is_constructible_impl<nlohmann::basic_json<>, const nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer>&>’
/usr/include/c++/10/type_traits:930:12:   required from ‘struct std::__is_copy_constructible_impl<nlohmann::basic_json<>, true>’
/usr/include/c++/10/type_traits:936:12:   required from ‘struct std::is_copy_constructible<nlohmann::basic_json<> >’
/usr/include/c++/10/type_traits:138:12:   [ skipping 2 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]
/usr/include/c++/10/type_traits:2657:31:   required by substitution of ‘template<class _Tp, class> static std::true_type std::__swappable_details::__do_is_swappable_impl::__test(int) [with _Tp = nlohmann::basic_json<>; <template-parameter-1-2> = <missing>]’
/usr/include/c++/10/type_traits:2681:35:   required from ‘struct std::__is_swappable_impl<nlohmann::basic_json<> >’
/usr/include/c++/10/type_traits:2707:12:   required from ‘struct std::is_swappable<nlohmann::basic_json<> >’
/usr/include/c++/10/type_traits:2727:26:   required from ‘constexpr const bool std::is_swappable_v<nlohmann::basic_json<> >’
/usr/include/c++/10/optional:1201:51:   required by substitution of ‘template<class _Tp> std::enable_if_t<(!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>))> std::swap(std::optional<_Tp>&, std::optional<_Tp>&) [with _Tp = nlohmann::basic_json<>]’
/usr/include/nlohmann/json.hpp:22677:1:   required from here
/usr/include/c++/10/type_traits:906:12: error: invalid use of incomplete type ‘struct std::__is_constructible_impl<nlohmann::basic_json<>, const nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer>&>’
  906 |     struct is_constructible
      |            ^~~~~~~~~~~~~~~~
/usr/include/c++/10/type_traits:900:12: note: declaration of ‘struct std::__is_constructible_impl<nlohmann::basic_json<>, const nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer>&>’
  900 |     struct __is_constructible_impl
      |            ^~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/10/vector:66,
                 from /usr/include/c++/10/functional:62,
                 from /usr/include/c++/10/pstl/glue_algorithm_defs.h:13,
                 from /usr/include/c++/10/algorithm:74,
                 from /usr/include/nlohmann/json.hpp:37,
                 from test.cpp:2:
/usr/include/c++/10/bits/stl_uninitialized.h: In instantiation of ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<const nlohmann::basic_json<>*, std::vector<nlohmann::basic_json<>, std::allocator<nlohmann::basic_json<> > > >; _ForwardIterator = nlohmann::basic_json<>*]’:
/usr/include/c++/10/bits/stl_uninitialized.h:325:37:   required from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = __gnu_cxx::__normal_iterator<const nlohmann::basic_json<>*, std::vector<nlohmann::basic_json<>, std::allocator<nlohmann::basic_json<> > > >; _ForwardIterator = nlohmann::basic_json<>*; _Tp = nlohmann::basic_json<>]’
/usr/include/c++/10/bits/stl_vector.h:555:31:   required from ‘std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp, _Alloc>&) [with _Tp = nlohmann::basic_json<>; _Alloc = std::allocator<nlohmann::basic_json<> >]’
/usr/include/c++/10/ext/new_allocator.h:151:4:   required from ‘void __gnu_cxx::new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = std::vector<nlohmann::basic_json<>, std::allocator<nlohmann::basic_json<> > >; _Args = {const std::vector<nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer>, std::allocator<nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer> > >&}; _Tp = std::vector<nlohmann::basic_json<>, std::allocator<nlohmann::basic_json<> > >]’
/usr/include/c++/10/bits/alloc_traits.h:507:17:   required from ‘static void std::allocator_traits<std::allocator<_Tp1> >::construct(std::allocator_traits<std::allocator<_Tp1> >::allocator_type&, _Up*, _Args&& ...) [with _Up = std::vector<nlohmann::basic_json<>, std::allocator<nlohmann::basic_json<> > >; _Args = {const std::vector<nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer>, std::allocator<nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer> > >&}; _Tp = std::vector<nlohmann::basic_json<>, std::allocator<nlohmann::basic_json<> > >; std::allocator_traits<std::allocator<_Tp1> >::allocator_type = std::allocator<std::vector<nlohmann::basic_json<>, std::allocator<nlohmann::basic_json<> > > >]’
/usr/include/nlohmann/json.hpp:15381:35:   [ skipping 2 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]
/usr/include/nlohmann/json.hpp:16365:25:   required from ‘nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::basic_json(const nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>&) [with ObjectType = std::map; ArrayType = std::vector; StringType = std::__cxx11::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; JSONSerializer = nlohmann::adl_serializer]’
/usr/include/nlohmann/json.hpp:4737:31:   required from ‘bool nlohmann::detail::json_sax_dom_callback_parser<BasicJsonType>::end_object() [with BasicJsonType = nlohmann::basic_json<>]’
/usr/include/nlohmann/json.hpp:8847:33:   required from ‘bool nlohmann::detail::parser<BasicJsonType>::sax_parse_internal(SAX*) [with SAX = nlohmann::detail::json_sax_dom_callback_parser<nlohmann::basic_json<> >; BasicJsonType = nlohmann::basic_json<>]’
/usr/include/nlohmann/json.hpp:8738:31:   required from ‘void nlohmann::detail::parser<BasicJsonType>::parse(bool, BasicJsonType&) [with BasicJsonType = nlohmann::basic_json<>]’
/usr/include/nlohmann/json.hpp:20882:79:   required from ‘static nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer> nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::parse(IteratorType, IteratorType, nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::parser_callback_t, bool) [with IteratorType = const char*; typename std::enable_if<std::is_base_of<std::random_access_iterator_tag, typename std::iterator_traits<_InputIterator>::iterator_category>::value, int>::type <anonymous> = 0; ObjectType = std::map; ArrayType = std::vector; StringType = std::__cxx11::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; JSONSerializer = nlohmann::adl_serializer; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::parser_callback_t = std::function<bool(int, nlohmann::detail::parser<nlohmann::basic_json<> >::parse_event_t, nlohmann::basic_json<>&)>]’
/usr/include/nlohmann/json.hpp:22700:42:   required from here
/usr/include/c++/10/bits/stl_uninitialized.h:137:72: error: ‘value’ is not a member of ‘std::is_constructible<nlohmann::basic_json<>, const nlohmann::basic_json<std::map, std::vector, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, long int, long unsigned int, double, std::allocator, nlohmann::adl_serializer>&>’
  137 | static_assert(is_constructible<_ValueType2, decltype(*__first)>::value,
      |                                                                  ^~~~~

Which compiler and operating system are you using?

• Compiler: g++ (GCC) 10.0.1 20200328 (Red Hat 10.0.1-0.11)
• Operating system: Fedora 32

Which version of the library did you use?

• [x] latest release version 3.7.3
• [ ] other release - please state the version: ___
• [ ] the develop branch

If you experience a compilation error: can you compile and run the unit tests?

• [x] yes
• [ ] no - please copy/paste the error message below

[FrancoisChabot]

This is the same as #2129.

The next release will fix the issue, but it's not clear why. I looked a bit into it, and it's starting to look like a compiler bug to my eyes.

The error implies that some template substitution attempts are being performed before basic_json is complete, but the callstack strongly implies that this is being performed after the type is complete. Combine this with the fact that clang handles this fine and that there is no change between the current release and develop that should affect this and, yeah....

[afowles]

Ah my bad didn't see it since it was closed. Thanks!

[kuzkry]

@FrancoisChabot, perhaps it isn't a compiler bug. See this analysis.