Compiler fails to find custom formatter when target is wide string (fmt 8.1.1)

[artemyv]

We have recently switched from fmt lib 8.0.1 to 8.1.1
Formatting class enums stopped working by default (as int)

I was trying to use answers from #391 (comment) to create a custom formatter.
It works when target is string and does not find the proper function when target is wstring.

What is wrong with my code?

#include <string_view>
#include <fmt/xchar.h>

namespace CoreCommon {
    enum class RDSRole {
        AutoDetect,
        Enabled,
        Disabled
    };
}

template <typename Char>
struct fmt::formatter<CoreCommon::RDSRole, Char> : formatter<std::basic_string_view<Char>>
{
    template <typename FormatContext>
    auto format(CoreCommon::RDSRole role, FormatContext &ctx)
    {
        std::basic_string_view<Char> name;
        switch (role)
        {
        case CoreCommon::RDSRole::AutoDetect:
            if constexpr (std::is_same<Char, char>::value)
                name = "auto";
            else
                name = L"auto";
            break;
        case CoreCommon::RDSRole::Enabled:
            if constexpr (std::is_same<Char, char>::value)
                name = "enabled";
            else
                name = L"enabled";
            break;
        case CoreCommon::RDSRole::Disabled:
            if constexpr (std::is_same<Char, char>::value)
                name = "disabled";
            else
                name = L"disabled";
            break;
        default:
            if constexpr (std::is_same<Char, char>::value)
                name = "unknown";
            else
                name = L"unknown";
            break;
        }
        return formatter<std::basic_string_view<Char>>::format(name, ctx);
    }
};
int main()
{
    fmt::print("Hello {}!\n", "World");
    fmt::print(L"Hello {}!\n", L"World");

    auto role = CoreCommon::RDSRole::AutoDetect;
    auto msg = fmt::format("RDS={}", role);

    fmt::print("Role {}!\n", msg);
    auto wmsg = fmt::format(L"RDS={}", role); //this line fails (or formats as int in older fmt lib

    fmt::print(L"Role {}!\n", wmsg);
    return 0;
}

Could you give me a hint how to resolve the issue?

[artemyv]

BTW - I'm compiling as c++17 under MSVC 2017 and 2019

[vitaut]

Your formatter specialization is defined incorrectly because it inherits from formatter<std::basic_string_view<Char>> instead of formatter<std::basic_string_view<Char>, Char>. Fixing this will make the enum formattable with wide format.

[artemyv]

Thanks, that has solved my issue