NLohmann doesn't compile when enabling strict warning policies

[Wittmaxi]

• What is the issue you have?
  Project including nlohmann doesn't compile with strict warning options:

g++ *.cpp -g -o test -pedantic -Wall -Wextra -Wcast-align -Wcast-qual -Wctor-dtor-privacy -Wdisabled-optimization -Wformat=2 -Winit-self -Wlogical-op -Wmissing-declarations -Wmissing-include-dirs -Wnoexcept -Wold-style-cast -Woverloaded-virtual -Wredundant-decls -Wshadow -Wsign-conversion -Wsign-promo -Wstrict-null-sentinel -Wstrict-overflow=5 -Wswitch-default -Wundef -Werror -Wno-unused

• Please describe the steps to reproduce the issue. Can you provide a small but working code example?

#include "json.hpp"

int main();

• What is the expected behavior?

Clean compile, no warnings

• And what is the actual behavior instead?
  Getting following warnings:

$ g++ *.cpp -g -o test -pedantic -Wall -Wextra -Wcast-align -Wcast-qual -Wctor-dtor-privacy -Wdisabled-optimization -Wformat=2 -Winit-self -Wlogical-op -Wmissing-declarations -Wmissing-include-dirs -Wnoexcept -Wold-style-cast -Woverloaded-virtual -Wredundant-decls -Wshadow -Wsign-conversion -Wsign-promo -Wstrict-null-sentinel -Wstrict-overflow=5 -Wswitch-default -Wundef -Werror -Wno-unused


In file included from main.cpp:1:0:
json.hpp:231:33: error: all member functions in class ‘nlohmann::detail::has_mapped_type<T>’ are private [-Werror=ctor-dtor-privacy]
     template<typename T> struct has_##type {                                  \
                                 ^
json.hpp:374:1: note: in expansion of macro ‘NLOHMANN_JSON_HAS_HELPER’
 NLOHMANN_JSON_HAS_HELPER(mapped_type);
 ^~~~~~~~~~~~~~~~~~~~~~~~
json.hpp:231:33: error: all member functions in class ‘nlohmann::detail::has_key_type<T>’ are private [-Werror=ctor-dtor-privacy]
     template<typename T> struct has_##type {                                  \
                                 ^
json.hpp:375:1: note: in expansion of macro ‘NLOHMANN_JSON_HAS_HELPER’
 NLOHMANN_JSON_HAS_HELPER(key_type);
 ^~~~~~~~~~~~~~~~~~~~~~~~
json.hpp:231:33: error: all member functions in class ‘nlohmann::detail::has_value_type<T>’ are private [-Werror=ctor-dtor-privacy]
     template<typename T> struct has_##type {                                  \
                                 ^
json.hpp:376:1: note: in expansion of macro ‘NLOHMANN_JSON_HAS_HELPER’
 NLOHMANN_JSON_HAS_HELPER(value_type);
 ^~~~~~~~~~~~~~~~~~~~~~~~
json.hpp:231:33: error: all member functions in class ‘nlohmann::detail::has_iterator<T>’ are private [-Werror=ctor-dtor-privacy]
     template<typename T> struct has_##type {                                  \
                                 ^
json.hpp:377:1: note: in expansion of macro ‘NLOHMANN_JSON_HAS_HELPER’
 NLOHMANN_JSON_HAS_HELPER(iterator);
 ^~~~~~~~~~~~~~~~~~~~~~~~
In file included from main.cpp:1:0:
json.hpp:471:8: error: all member functions in class ‘nlohmann::detail::has_from_json<BasicJsonType, T>’ are private [-Werror=ctor-dtor-privacy]
 struct has_from_json
        ^~~~~~~~~~~~~
json.hpp:488:8: error: all member functions in class ‘nlohmann::detail::has_non_default_from_json<BasicJsonType, T>’ are private [-Werror=ctor-dtor-privacy]
 struct has_non_default_from_json
        ^~~~~~~~~~~~~~~~~~~~~~~~~
json.hpp:505:8: error: all member functions in class ‘nlohmann::detail::has_to_json<BasicJsonType, T>’ are private [-Werror=ctor-dtor-privacy]
 struct has_to_json
        ^~~~~~~~~~~
In file included from main.cpp:1:0:
json.hpp: In instantiation of ‘void nlohmann::detail::serializer<BasicJsonType>::dump(const BasicJsonType&, bool, bool, unsigned int, unsigned int) [with BasicJsonType = nlohmann::basic_json<>]’:
json.hpp:13069:13:   required from ‘nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::string_t nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::dump(int, char, bool) const [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; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::string_t = std::__cxx11::basic_string<char>]’
json.hpp:18827:25:   required from here
json.hpp:9809:9: error: switch missing default case [-Werror=switch-default]
         switch (val.m_type)
         ^~~~~~
cc1plus: all warnings being treated as errors

• Which compiler and operating system are you using? Is it a supported compiler?

GNU/Linux/Fedora, gcc

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl --enable-libmpx --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 7.3.1 20180712 (Red Hat 7.3.1-6) (GCC) 

• Did you use a released version of the library or the version from the develop branch?
  I used the newest release, as downloadable here: https://github.com/nlohmann/json/releases/download/v3.2.0/json.hpp

• If you experience a compilation error: can you compile and run the unit tests?
  Doesn't apply as I use the header only version.

• Additional:
  Strict warnings are very important to me as I want to ensure that I don't commit stupid mistakes (like we all do sometimes ;) ).

[Wittmaxi]

Putting a #pragma GCC system_header at top of json.hpp did the trick. You should consider releasing the file with that pragma and/or fixing those warnings.

Keep up the great work :-)!

[gregmarr]

There are multiple options as far as switch handling of enums, and it is impossible to make code clean to all of them at once, as one warns when there is no default case, and one warns when the default case is used when all the elements of an enum are also specified. See #889 and #555

You should be able to do the same as #pragma GCC system_header by including it with <json.hpp> instead of "json.hpp".

[Wittmaxi]

Okay that makes perfect sense! I can't include it with <json.hpp> because I need the file to be in the project folder

[theodelrieu]

I would put it in a third_party folder, then adding -isystem third_party to compiler options

[Wittmaxi]

Mhh. that might work as well.

[nlohmann]

I fixed the "all member functions are private" warning. As @gregmarr wrote, there is nothing consistent we can do about warnings in switches.

[Wittmaxi]

Thank you! I will close the issue now, I think all that CAN be done was done.