fmt 11 cannot format string_view

[aminya]

I updated the following code to fmt 11, and it no longer compiles with the below error. Do you know what could be the reason?

Unfortunately, I can't reproduce it on Godbolt, but here's the link anyway. I included all the calls to the function. My suspect is that other libraries or headers break fmt.
https://godbolt.org/z/Gvabcz5Ex

#include <fmt/core.h>
#include <stdexcept>

#include <string>
#include <string_view>

using std::string_view, std::exception, std::runtime_error, std::string;

[[noreturn]] inline void print_string_view(string_view message) {
  fmt::print(stderr, "{}\n", message);
}


int main() {
    try {
        throw runtime_error("test");
    } catch (const exception& err) {
        print_string_view(err.what());
    }

    print_string_view("sss" + string("sss"));
}

build/vcpkg_installed/x64-linux/include/fmt/base.h:1518:68: error: no matching member function for call to 'map'
 1518 |   FMT_MAP_API auto map(const T& val) -> decltype(FMT_DECLTYPE_THIS map(U())) {
      |                                                                    ^~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1560:28: note: in instantiation of template class 'fmt::detail::arg_mapper<fmt::context>' requested here
 1560 |     type_constant<decltype(arg_mapper<Context>().map(std::declval<const T&>())),
      |                            ^
build/vcpkg_installed/x64-linux/include/fmt/base.h:2733:16: note: in instantiation of template type alias 'mapped_type_constant' requested here
 2733 |       : types_{mapped_type_constant<Args, buffered_context<Char>>::value...},
      |                ^
build/vcpkg_installed/x64-linux/include/fmt/base.h:2884:47: note: in instantiation of member function 'fmt::detail::format_string_checker<char, std::basic_string_view<char>>::format_string_checker' requested here
 2884 |       detail::parse_format_string<true>(str_, checker(s));
      |                                               ^
packages/stdx/include/stdx/errors.hpp:18:22: note: in instantiation of function template specialization 'fmt::basic_format_string<char, std::basic_string_view<char> &>::basic_format_string<char[4], 0>' requested here
   18 |   fmt::print(stderr, "{}\n", message);
      |                      ^
build/vcpkg_installed/x64-linux/include/fmt/base.h:1511:20: note: candidate function template not viable: requires single argument 'values', but no arguments were provided
 1511 |   FMT_MAP_API auto map(const T (&values)[N]) -> const T (&)[N] {
      |                    ^   ~~~~~~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1505:22: note: candidate function template not viable: requires 1 argument, but 0 were provided
 1505 |   FMT_CONSTEXPR auto map(const T&) -> unformattable_pointer {
      |                      ^   ~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1494:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1494 |   FMT_MAP_API auto map(std::nullptr_t val) -> const void* { return val; }
      |                    ^   ~~~~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1491:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1491 |   FMT_MAP_API auto map(const volatile void* val) -> const void* {
      |                    ^   ~~~~~~~~~~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1488:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1488 |   FMT_MAP_API auto map(volatile void* val) -> const void* {
      |                    ^   ~~~~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1487:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1487 |   FMT_MAP_API auto map(const void* val) -> const void* { return val; }
      |                    ^   ~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1486:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1486 |   FMT_MAP_API auto map(void* val) -> const void* { return val; }
      |                    ^   ~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1482:20: note: candidate function template not viable: requires 1 argument, but 0 were provided
 1482 |   FMT_MAP_API auto map(const T&) -> unformattable_char {
      |                    ^   ~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1476:20: note: candidate function template not viable: requires single argument 'val', but no arguments were provided
 1476 |   FMT_MAP_API auto map(const T& val) -> basic_string_view<Char> {
      |                    ^   ~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1472:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1472 |   FMT_MAP_API auto map(const char_type* val) -> const char_type* { return val; }
      |                    ^   ~~~~~~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1471:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1471 |   FMT_MAP_API auto map(char_type* val) -> const char_type* { return val; }
      |                    ^   ~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1469:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1469 |   FMT_MAP_API auto map(long double val) -> long double { return val; }
      |                    ^   ~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1468:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1468 |   FMT_MAP_API auto map(double val) -> double { return val; }
      |                    ^   ~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1467:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1467 |   FMT_MAP_API auto map(float val) -> float { return val; }
      |                    ^   ~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1463:20: note: candidate function template not viable: requires 1 argument, but 0 were provided
 1463 |   FMT_MAP_API auto map(T) -> unformattable_char {
      |                    ^   ~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1452:20: note: candidate function template not viable: requires single argument 'val', but no arguments were provided
 1452 |   FMT_MAP_API auto map(T val) -> char_type {
      |                    ^   ~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1448:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1448 |   FMT_MAP_API auto map(bool val) -> bool { return val; }
      |                    ^   ~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1447:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1447 |   FMT_MAP_API auto map(uint128_opt val) -> uint128_opt { return val; }
      |                    ^   ~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1446:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1446 |   FMT_MAP_API auto map(int128_opt val) -> int128_opt { return val; }
      |                    ^   ~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1443:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1443 |   FMT_MAP_API auto map(unsigned long long val) -> unsigned long long {
      |                    ^   ~~~~~~~~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1442:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1442 |   FMT_MAP_API auto map(long long val) -> long long { return val; }
      |                    ^   ~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1441:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1441 |   FMT_MAP_API auto map(unsigned long val) -> ulong_type { return val; }
      |                    ^   ~~~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1440:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1440 |   FMT_MAP_API auto map(long val) -> long_type { return val; }
      |                    ^   ~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1439:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1439 |   FMT_MAP_API auto map(unsigned val) -> unsigned { return val; }
      |                    ^   ~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1438:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1438 |   FMT_MAP_API auto map(int val) -> int { return val; }
      |                    ^   ~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1437:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1437 |   FMT_MAP_API auto map(unsigned short val) -> unsigned { return val; }
      |                    ^   ~~~~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1436:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1436 |   FMT_MAP_API auto map(short val) -> int { return val; }
      |                    ^   ~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1435:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1435 |   FMT_MAP_API auto map(unsigned char val) -> unsigned { return val; }
      |                    ^   ~~~~~~~~~~~~~~~~~
build/vcpkg_installed/x64-linux/include/fmt/base.h:1434:20: note: candidate function not viable: requires single argument 'val', but no arguments were provided
 1434 |   FMT_MAP_API auto map(signed char val) -> int { return val; }
      |                    ^   ~~~~~~~~~~~~~~~
1 error generated.

[aminya]

Okay, I found the reason. It's cpprest headers. Including fmt after cpprest causes these issues.

Cpprest does some questionable macro definitions here.
https://github.com/microsoft/cpprestsdk/blob/411a109150b270f23c8c97fa4ec9a0a4a98cdecf/Release/include/cpprest/details/basic_types.h#L87

The U Macro overrides the U typename in fmt!!

  template <typename T, typename U = format_as_t<T>,
            FMT_ENABLE_IF(std::is_arithmetic<U>::value)>
  FMT_MAP_API auto map(const T& val) -> decltype(FMT_DECLTYPE_THIS map(U())) {
    return map(format_as(val));
  }

I think we have to make a PR to fix this upstream.

As a workaround _TURN_OFF_PLATFORM_STRING can be defined before including cpprest headers.

[aminya]

A better workaround is to undef U after including any headers that include cpprest

// include some header that includes cpprest
// immediately after:
#if defined(U)
#undef U
#endif

This applies to any client generated by OpenAPI

https://github.com/OpenAPITools/openapi-generator/blob/673cd15e72d8dc110bcb685a36a4e0b4c8dfe67c/modules/openapi-generator/src/main/resources/cpp-rest-sdk-client/model-source.mustache#L83