Compile Error "error C2668" when try formatting user-defined type.

[XiangYyang]

A simple code from https://fmt.dev/latest/api.html?highlight=formatter:

#include ...

struct point { double x, y; };

template <> struct fmt::formatter<point> {
  // Presentation format: 'f' - fixed, 'e' - exponential.
  char presentation = 'f';

  // Parses format specifications of the form ['f' | 'e'].
  constexpr auto parse(format_parse_context& ctx) -> decltype(ctx.begin()) {
    // [ctx.begin(), ctx.end()) is a character range that contains a part of
    // the format string starting from the format specifications to be parsed,
    // e.g. in
    //
    //   fmt::format("{:f} - point of interest", point{1, 2});
    //
    // the range will contain "f} - point of interest". The formatter should
    // parse specifiers until '}' or the end of the range. In this example
    // the formatter should parse the 'f' specifier and return an iterator
    // pointing to '}'.

    // Parse the presentation format and store it in the formatter:
    auto it = ctx.begin(), end = ctx.end();
    if (it != end && (*it == 'f' || *it == 'e')) presentation = *it++;

    // Check if reached the end of the range:
    if (it != end && *it != '}')
      throw format_error("invalid format");

    // Return an iterator past the end of the parsed range:
    return it;
  }

  // Formats the point p using the parsed format specification (presentation)
  // stored in this formatter.
  template <typename FormatContext>
  auto format(const point& p, FormatContext& ctx) -> decltype(ctx.out()) {
    // ctx.out() is an output iterator to write to.
    return format_to(
        ctx.out(),
        presentation == 'f' ? "({:.1f}, {:.1f})" : "({:.1e}, {:.1e})",
        p.x, p.y);
  }
};

then

point fuck = { 1, 2 };
fmt::print("{}\n", fuck);

Using MSVC++ Compiler 16.11.0 to build with C++20 (I use consteval in my code, so, I must use C++20), cause an compile error:

error C2668: “fmt::v8::format_to”: ambiguous call to overloaded function

It said that there are two functions can be called:

OutputIt fmt::v8::format_to<OutputIt,const double&,const double&,0>(OutputIt,fmt::v8::basic_format_string<char,const double &,const double &>,const double &,const double &)
          with
          [
              OutputIt=fmt::v8::appender
          ]

OR:

_OutputIt std::format_to<OutputIt,double,double>(_OutputIt,const std::string_view,const double &,const double &)
          with
          [
              _OutputIt=fmt::v8::appender,
              OutputIt=fmt::v8::appender
          ]

I don't know what happend, I need a help.

Thanks.

[vitaut]

Looks like the same issue as #2522. Please use an updated example from https://fmt.dev/dev/api.html#formatting-user-defined-types.