[Bug libstdc++/121765] `std::formatter` specialization for user-defined type inheriting from `std::formatter` fails concept `std::formattable` check unexpectedly

[tkaminsk at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121765

Tomasz Kamiński <tkaminsk at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tkaminsk at gcc dot gnu.org

--- Comment #2 from Tomasz Kamiński <tkaminsk at gcc dot gnu.org> ---
As a workaround until the issue is fixed consider specifying return type
explicitly,
instead of using auto:
template <>
struct std::formatter<S> : std::formatter<std::pair<int, double>> {
    template <typename FormatContext>
    typename FormatContext::iterator 
    format(const S& s, FormatContext& ctx) const {
        return std::formatter<std::pair<int, double>>::format(
            std::make_pair(s.i, s.d), ctx);
    }
};

Example: https://godbolt.org/z/Ga3PKWGjE