Literal-based API: error: ‘struct fmt::v5::formatter<UUID, char, void>’ has no member named ‘parse’

[chronoxor]

"{}"_format(UUID()) failed to compile under GCC 8.2.0 (Ubuntu 18.04.2 x64) for user classe with ostream friend operator (VS 2017 is ok):

// Compiles fine!
fmt::format("{}", UUID());
// error: ‘struct fmt::v5::formatter<CppCommon::UUID, char, void>’ has no member named ‘parse’
"{}"_format(UUID());

fmt/format.h:2140:12: error: ‘struct fmt::v5::formatter<UUID, char, void>’ has no member named ‘parse’
   return f.parse(ctx);
          ~~^~~~~

where UUID is my custom class with ostream operator:

class UUID
{
public:
    UUID() : _data() { _data.fill(0); }
    explicit UUID(const std::string& uuid);
    explicit UUID(const std::array<uint8_t, 16>& data) : _data(data) {}
    UUID(const UUID&) = default;
    UUID(UUID&&) noexcept = default;
    ~UUID() = default;

    UUID& operator=(const std::string& uuid)
    { _data = UUID(uuid).data(); return *this; }
    UUID& operator=(const std::array<uint8_t, 16>& data)
    { _data = data; return *this; }
    UUID& operator=(const UUID&) = default;
    UUID& operator=(UUID&&) noexcept = default;

    //! Get string from the current UUID in format "00000000-0000-0000-0000-000000000000"
    std::string string() const;

    //! Output instance into the given output stream
    friend std::ostream& operator<<(std::ostream& os, const UUID& uuid)
    { os << uuid.string(); return os; }

private:
    std::array<uint8_t, 16> _data;
};

[vitaut]

Thanks for reporting. This is an unfortunate side effect of the fix to #952. Need to plug in the fallback formatter that implements operator<< support into the compile-time check machinery.

[vitaut]

Should be fixed in da0ea41.