Another compilation failure with Visual Studio

[garethsb]

The following new test case fails to compile with at least Visual Studio 2015 14.0.25431.01 Update 3, and Visual Studio 2019 16.5.0. Related to #167.

#include <nlohmann/json.hpp>
TEST_CASE("JSON pointers")
{
    SECTION("op<<")
    {
        nlohmann::basic_json<std::map, std::vector, std::string, bool, int32_t> a_different_instantiation_of_basic_json;
        nlohmann::json::json_pointer ptr;
        CHECK(ptr == ptr);
    }
}

The error message is:

nlohmann-json\test\thirdparty\doctest\doctest.h(782,1): error C2593: 'operator <<' is ambiguous
nlohmann-json\single_include\nlohmann/json.hpp(20642,26): message : could be 'std::ostream &nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::operator <<(std::ostream &,const nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer> &)' [found using argument-dependent lookup]
nlohmann-json\single_include\nlohmann/json.hpp(20642,26): message : or       'std::ostream &nlohmann::basic_json<std::map,std::vector,std::string,bool,int32_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>::operator <<(std::ostream &,const nlohmann::basic_json<std::map,std::vector,std::string,bool,int32_t,uint64_t,double,std::allocator,nlohmann::adl_serializer> &)' [found using argument-dependent lookup]
nlohmann-json\test\thirdparty\doctest\doctest.h(782,1): message : while trying to match the argument list '(std::ostream, const T)'
        with
        [
            T=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>
        ]
nlohmann-json\test\thirdparty\doctest\doctest.h(788): message : see reference to class template instantiation 'doctest::detail::has_insertion_operator_impl::has_insertion_operator<T>' being compiled
        with
        [
            T=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>
        ]
nlohmann-json\test\thirdparty\doctest\doctest.h(828): message : see reference to class template instantiation 'doctest::detail::has_insertion_operator<T>' being compiled
        with
        [
            T=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>
        ]
nlohmann-json\test\thirdparty\doctest\doctest.h(854): message : see reference to class template instantiation 'doctest::StringMaker<T>' being compiled
        with
        [
            T=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>
        ]
nlohmann-json\test\thirdparty\doctest\doctest.h(1011): message : see reference to function template instantiation 'doctest::String doctest::toString<L>(const T &)' being compiled
        with
        [
            L=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>,
            T=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>
        ]
nlohmann-json\test\thirdparty\doctest\doctest.h(1159): message : see reference to function template instantiation 'doctest::String doctest::detail::stringifyBinaryExpr<nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>,R>(const L &,const char *,const R &)' being compiled
        with
        [
            R=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>,
            L=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>
        ]
nlohmann-json\test\src\foo.cpp(8): message : see reference to function template instantiation 'doctest::detail::Result doctest::detail::Expression_lhs<const nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>> &>::operator ==<nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>>(const R &)' being compiled
        with
        [
            R=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>
        ]
nlohmann-json\test\src\foo.cpp(8): message : see reference to function template instantiation 'doctest::detail::Result doctest::detail::Expression_lhs<const nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>> &>::operator ==<nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>>(const R &)' being compiled
        with
        [
            R=nlohmann::json_pointer<nlohmann::basic_json<std::map,std::vector,std::string,bool,int64_t,uint64_t,double,std::allocator,nlohmann::adl_serializer>>
        ]

[emmenlau]

Yep, we get the same problem after switching from VS2019.3 to VS2019.5.

[MarvinSchultz]

Is there any known workaround?

[bhardwajs]

Just spent couple of hours on this issue and I can confirm I have a repro. I don't have a good reason why this is happening. Let me invest more time over the weekend and next week and see I can figure out why ADL is making this break.

As for workaround @MarvinSchultz , this compiled for me:

 SECTION("op<<")
    {
        nlohmann::basic_json<std::map, std::vector, std::string, bool, int64_t> a_different_instantiation_of_basic_json;
        nlohmann::json::json_pointer ptr;
        CHECK(ptr == ptr);
    }

Does this work for you? I am running VS 16.5.3 and cl.exe 19.25.28612.0.

If there is another MSVC issue, please do tag me. Thank you!

[garethsb]

That "workaround" isn't really a workaround, really, because by changing int32_t to int64_t, the type a_different_instantiation_of_basic_json is not actually different.

[t-b]

How about adding a PR with that new test case and then we can check which compilers accept that and which not?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.