Few issues with fallback_formatter

[sitano]

seastar does not compile with 6.2.0-1 fmt on my machine.

I have reproduced the errors with the following code:

#include <fmt/core.h>
#include <fmt/format.h>
#include <fmt/printf.h>
#include <sstream>
#include <iostream>

namespace db {
  enum class consistency_level {};

  std::ostream& operator<<(std::ostream& os, consistency_level cl);
}

std::string unavailable_exception(db::consistency_level cl) {
  return fmt::sprintf("%s", cl);
}


int main() {
  std::cout << unavailable_exception(does_not_matter);
}

Output:

In file included from 1.cc:2:
/usr/include/fmt/format.h: In instantiation of ‘decltype (ctx.out()) fmt::v6::formatter<T, Char, typename std::enable_if<(fmt::v6::internal::type_constant<T, Char>::value != fmt::v6::internal::type::custom_type), void>::type>::format(const T&, FormatContext&) [with FormatContext = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; T = fmt::v6::basic_string_view<char>; Char = char; typename std::enable_if<(fmt::v6::internal::type_constant<T, Char>::value != fmt::v6::internal::type::custom_type), void>::type = void; decltype (ctx.out()) = std::back_insert_iterator<fmt::v6::internal::buffer<char> >]’:
/usr/include/fmt/ostream.h:113:60:   required from ‘decltype (ctx.out()) fmt::v6::internal::fallback_formatter<T, Char, typename std::enable_if<fmt::v6::internal::is_streamable<T, Char>::value, void>::type>::format(const T&, Context&) [with Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; T = db::consistency_level; Char = char; typename std::enable_if<fmt::v6::internal::is_streamable<T, Char>::value, void>::type = void; decltype (ctx.out()) = std::back_insert_iterator<fmt::v6::internal::buffer<char> >]’
/usr/include/fmt/core.h:898:5:   required from ‘static void fmt::v6::internal::value<Context>::format_custom_arg(const void*, fmt::v6::basic_format_parse_context<typename Context::char_type>&, Context&) [with T = db::consistency_level; Formatter = fmt::v6::internal::fallback_formatter<db::consistency_level, char, void>; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; typename Context::char_type = char]’
/usr/include/fmt/core.h:882:19:   required from ‘fmt::v6::internal::value<Context>::value(const T&) [with T = db::consistency_level; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>]’
/usr/include/fmt/core.h:1213:39:   required from ‘fmt::v6::internal::value<Context> fmt::v6::internal::make_arg(const T&) [with bool IS_PACKED = true; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; T = db::consistency_level; typename std::enable_if<IS_PACKED, int>::type <anonymous> = 0]’
/usr/include/fmt/core.h:1349:53:   required from ‘fmt::v6::format_arg_store<Context, Args>::format_arg_store(const Args& ...) [with Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; Args = {db::consistency_level}]’
/usr/include/fmt/core.h:1364:18:   required from ‘fmt::v6::format_arg_store<Context, Args ...> fmt::v6::make_format_args(const Args& ...) [with Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; Args = {db::consistency_level}]’
/usr/include/fmt/printf.h:627:68:   required from ‘std::__cxx11::basic_string<Char> fmt::v6::sprintf(const S&, const Args& ...) [with S = char [3]; Args = {db::consistency_level}; Char = char]’
1.cc:14:31:   required from here
/usr/include/fmt/format.h:3012:29: error: no matching function for call to ‘fmt::v6::arg_formatter<fmt::v6::internal::output_range<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char> >::arg_formatter(fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>&, std::nullptr_t, fmt::v6::internal::dynamic_format_specs<char>*)’
 3012 |     return visit_format_arg(arg_formatter<range_type>(ctx, nullptr, &specs_),
      |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/fmt/format.h:2764:12: note: candidate: ‘fmt::v6::arg_formatter<Range>::arg_formatter(fmt::v6::arg_formatter<Range>::context_type&, fmt::v6::basic_format_parse_context<typename Range::value_type>*, fmt::v6::arg_formatter<Range>::format_specs*) [with Range = fmt::v6::internal::output_range<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; fmt::v6::arg_formatter<Range>::context_type = fmt::v6::basic_format_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; typename Range::value_type = char; typename fmt::v6::internal::arg_formatter_base<Range>::iterator = std::back_insert_iterator<fmt::v6::internal::buffer<char> >; fmt::v6::arg_formatter<Range>::format_specs = fmt::v6::basic_format_specs<char>]’
 2764 |   explicit arg_formatter(
      |            ^~~~~~~~~~~~~
/usr/include/fmt/format.h:2765:21: note:   no known conversion for argument 1 from ‘fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>’ to ‘fmt::v6::arg_formatter<fmt::v6::internal::output_range<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char> >::context_type&’ {aka ‘fmt::v6::basic_format_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>&’}
 2765 |       context_type& ctx,
      |       ~~~~~~~~~~~~~~^~~
/usr/include/fmt/format.h:2743:7: note: candidate: ‘constexpr fmt::v6::arg_formatter<fmt::v6::internal::output_range<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char> >::arg_formatter(const fmt::v6::arg_formatter<fmt::v6::internal::output_range<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char> >&)’
 2743 | class arg_formatter : public internal::arg_formatter_base<Range> {
      |       ^~~~~~~~~~~~~
/usr/include/fmt/format.h:2743:7: note:   candidate expects 1 argument, 3 provided
/usr/include/fmt/format.h:2743:7: note: candidate: ‘constexpr fmt::v6::arg_formatter<fmt::v6::internal::output_range<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char> >::arg_formatter(fmt::v6::arg_formatter<fmt::v6::internal::output_range<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char> >&&)’
/usr/include/fmt/format.h:2743:7: note:   candidate expects 1 argument, 3 provided
/usr/include/fmt/format.h: In instantiation of ‘void fmt::v6::internal::handle_dynamic_spec(int&, fmt::v6::internal::arg_ref<typename Context::char_type>, Context&) [with Handler = fmt::v6::internal::width_checker; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; typename Context::char_type = char]’:
/usr/include/fmt/format.h:3005:59:   required from ‘decltype (ctx.out()) fmt::v6::formatter<T, Char, typename std::enable_if<(fmt::v6::internal::type_constant<T, Char>::value != fmt::v6::internal::type::custom_type), void>::type>::format(const T&, FormatContext&) [with FormatContext = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; T = fmt::v6::basic_string_view<char>; Char = char; typename std::enable_if<(fmt::v6::internal::type_constant<T, Char>::value != fmt::v6::internal::type::custom_type), void>::type = void; decltype (ctx.out()) = std::back_insert_iterator<fmt::v6::internal::buffer<char> >]’
/usr/include/fmt/ostream.h:113:60:   required from ‘decltype (ctx.out()) fmt::v6::internal::fallback_formatter<T, Char, typename std::enable_if<fmt::v6::internal::is_streamable<T, Char>::value, void>::type>::format(const T&, Context&) [with Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; T = db::consistency_level; Char = char; typename std::enable_if<fmt::v6::internal::is_streamable<T, Char>::value, void>::type = void; decltype (ctx.out()) = std::back_insert_iterator<fmt::v6::internal::buffer<char> >]’
/usr/include/fmt/core.h:898:5:   required from ‘static void fmt::v6::internal::value<Context>::format_custom_arg(const void*, fmt::v6::basic_format_parse_context<typename Context::char_type>&, Context&) [with T = db::consistency_level; Formatter = fmt::v6::internal::fallback_formatter<db::consistency_level, char, void>; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; typename Context::char_type = char]’
/usr/include/fmt/core.h:882:19:   required from ‘fmt::v6::internal::value<Context>::value(const T&) [with T = db::consistency_level; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>]’
/usr/include/fmt/core.h:1213:39:   required from ‘fmt::v6::internal::value<Context> fmt::v6::internal::make_arg(const T&) [with bool IS_PACKED = true; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; T = db::consistency_level; typename std::enable_if<IS_PACKED, int>::type <anonymous> = 0]’
/usr/include/fmt/core.h:1349:53:   required from ‘fmt::v6::format_arg_store<Context, Args>::format_arg_store(const Args& ...) [with Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; Args = {db::consistency_level}]’
/usr/include/fmt/core.h:1364:18:   required from ‘fmt::v6::format_arg_store<Context, Args ...> fmt::v6::make_format_args(const Args& ...) [with Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; Args = {db::consistency_level}]’
/usr/include/fmt/printf.h:627:68:   required from ‘std::__cxx11::basic_string<Char> fmt::v6::sprintf(const S&, const Args& ...) [with S = char [3]; Args = {db::consistency_level}; Char = char]’
1.cc:14:31:   required from here
/usr/include/fmt/format.h:2717:53: error: ‘class fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>’ has no member named ‘error_handler’
 2717 |                                                 ctx.error_handler());
      |                                                 ~~~~^~~~~~~~~~~~~
/usr/include/fmt/format.h:2720:65: error: cannot convert ‘fmt::v6::basic_string_view<char>’ to ‘int’
 2720 |     value = internal::get_dynamic_spec<Handler>(ctx.arg(ref.val.name),
      |                                                         ~~~~~~~~^~~~
      |                                                                 |
      |                                                                 fmt::v6::basic_string_view<char>
In file included from 1.cc:3:
/usr/include/fmt/printf.h:363:22: note:   initializing argument 1 of ‘fmt::v6::basic_printf_context<OutputIt, Char>::format_arg fmt::v6::basic_printf_context<OutputIt, Char>::arg(int) const [with OutputIt = std::back_insert_iterator<fmt::v6::internal::buffer<char> >; Char = char; fmt::v6::basic_printf_context<OutputIt, Char>::format_arg = fmt::v6::basic_format_arg<fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char> >]’
  363 |   format_arg arg(int id) const { return args_.get(id); }
      |                  ~~~~^~
In file included from 1.cc:2:
/usr/include/fmt/format.h:2721:53: error: ‘class fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>’ has no member named ‘error_handler’
 2721 |                                                 ctx.error_handler());
      |                                                 ~~~~^~~~~~~~~~~~~
/usr/include/fmt/format.h: In instantiation of ‘void fmt::v6::internal::handle_dynamic_spec(int&, fmt::v6::internal::arg_ref<typename Context::char_type>, Context&) [with Handler = fmt::v6::internal::precision_checker; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; typename Context::char_type = char]’:
/usr/include/fmt/format.h:3007:63:   required from ‘decltype (ctx.out()) fmt::v6::formatter<T, Char, typename std::enable_if<(fmt::v6::internal::type_constant<T, Char>::value != fmt::v6::internal::type::custom_type), void>::type>::format(const T&, FormatContext&) [with FormatContext = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; T = fmt::v6::basic_string_view<char>; Char = char; typename std::enable_if<(fmt::v6::internal::type_constant<T, Char>::value != fmt::v6::internal::type::custom_type), void>::type = void; decltype (ctx.out()) = std::back_insert_iterator<fmt::v6::internal::buffer<char> >]’
/usr/include/fmt/ostream.h:113:60:   required from ‘decltype (ctx.out()) fmt::v6::internal::fallback_formatter<T, Char, typename std::enable_if<fmt::v6::internal::is_streamable<T, Char>::value, void>::type>::format(const T&, Context&) [with Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; T = db::consistency_level; Char = char; typename std::enable_if<fmt::v6::internal::is_streamable<T, Char>::value, void>::type = void; decltype (ctx.out()) = std::back_insert_iterator<fmt::v6::internal::buffer<char> >]’
/usr/include/fmt/core.h:898:5:   required from ‘static void fmt::v6::internal::value<Context>::format_custom_arg(const void*, fmt::v6::basic_format_parse_context<typename Context::char_type>&, Context&) [with T = db::consistency_level; Formatter = fmt::v6::internal::fallback_formatter<db::consistency_level, char, void>; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; typename Context::char_type = char]’
/usr/include/fmt/core.h:882:19:   required from ‘fmt::v6::internal::value<Context>::value(const T&) [with T = db::consistency_level; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>]’
/usr/include/fmt/core.h:1213:39:   required from ‘fmt::v6::internal::value<Context> fmt::v6::internal::make_arg(const T&) [with bool IS_PACKED = true; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; T = db::consistency_level; typename std::enable_if<IS_PACKED, int>::type <anonymous> = 0]’
/usr/include/fmt/core.h:1349:53:   required from ‘fmt::v6::format_arg_store<Context, Args>::format_arg_store(const Args& ...) [with Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; Args = {db::consistency_level}]’
/usr/include/fmt/core.h:1364:18:   required from ‘fmt::v6::format_arg_store<Context, Args ...> fmt::v6::make_format_args(const Args& ...) [with Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; Args = {db::consistency_level}]’
/usr/include/fmt/printf.h:627:68:   required from ‘std::__cxx11::basic_string<Char> fmt::v6::sprintf(const S&, const Args& ...) [with S = char [3]; Args = {db::consistency_level}; Char = char]’
1.cc:14:31:   required from here
/usr/include/fmt/format.h:2717:53: error: ‘class fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>’ has no member named ‘error_handler’
 2717 |                                                 ctx.error_handler());
      |                                                 ~~~~^~~~~~~~~~~~~
/usr/include/fmt/format.h:2720:65: error: cannot convert ‘fmt::v6::basic_string_view<char>’ to ‘int’
 2720 |     value = internal::get_dynamic_spec<Handler>(ctx.arg(ref.val.name),
      |                                                         ~~~~~~~~^~~~
      |                                                                 |
      |                                                                 fmt::v6::basic_string_view<char>
In file included from 1.cc:3:
/usr/include/fmt/printf.h:363:22: note:   initializing argument 1 of ‘fmt::v6::basic_printf_context<OutputIt, Char>::format_arg fmt::v6::basic_printf_context<OutputIt, Char>::arg(int) const [with OutputIt = std::back_insert_iterator<fmt::v6::internal::buffer<char> >; Char = char; fmt::v6::basic_printf_context<OutputIt, Char>::format_arg = fmt::v6::basic_format_arg<fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char> >]’
  363 |   format_arg arg(int id) const { return args_.get(id); }
      |                  ~~~~^~
In file included from 1.cc:2:
/usr/include/fmt/format.h:2721:53: error: ‘class fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>’ has no member named ‘error_handler’
 2721 |                                                 ctx.error_handler());

Indeed:

• basic_printf_context does not have an error_handler()
• arg(fmt::v6::basic_string_view<char>) does not exists in basic_printf_context
• arg_formatter can't explicitly cast wrong super type

[vitaut]

This has been fixed in master already (#1631): https://godbolt.org/z/br6fvT