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Compilation with -fmodules-ts and use inside of a module · Issue #3472 · nlohmann/json

Description

Hi,
When just including #include <nlohmann/json.hpp> in a module, the compiler complains about impossible references.
It is not happening when not inside a module.

Reproduction steps

Just include the header inside a module and compile with -fmodules-ts.

This is the triggering flag, really.

Expected vs. actual results

No error

Minimal code example

//mod.cxx:

module;
#include <iostream>
#include <string_view>
#include <string>
#include <nlohmann/json.hpp>
export module hello;

export {
        namespace X {

                void greeter ( std::string_view const &name ){
                        std::string h = "exported greeter";

                        std::cout << "Hello " << name << "!" << h << "\n";

                }

        }
}


// main.cpp
import hello;

int main ( void ){

        X::greeter("ok");
        return 0;
}

// compile with
~/gcc-12.1/g++ -fmodules-ts -std=c++20 -I/my_path/include/ mod.cxx main.cpp

Error messages

`/usr/include/nlohmann/adl_serializer.hpp:41:17: error: ‘static decltype ((nlohmann::{anonymous}::to_json(j, forward<ValueType>(val)), void())) nlohmann::adl_serializer<T, SFINAE>::to_json(BasicJsonType&, ValueType&&) [with BasicJsonType = nlohmann::basic_json<>; ValueType = bool&; <template-parameter-1-1> = bool; <template-parameter-1-2> = void; decltype ((nlohmann::{anonymous}::to_json(j, forward<ValueType>(val)), void())) = void]’ references internal linkage entity ‘constexpr const nlohmann::detail::to_json_fn& nlohmann::{anonymous}::to_json’
   41 |     static auto to_json(BasicJsonType& j, ValueType&& val) noexcept(`

Compiler and operating system

Linux GCC-12.1

Library version

Latest

Validation