GCC-9 build error

[phprus]

Commit with added GCC-9 CI: phprus@4e38606
Full build log: https://github.com/phprus/fmt/runs/8287290178?check_suite_focus=true

Error:

In file included from /home/runner/work/fmt/fmt/test/xchar-test.cc:8:
/home/runner/work/fmt/fmt/include/fmt/xchar.h: In instantiation of ‘bool fmt::v9::detail::write_loc(OutputIt, fmt::v9::basic_format_arg<fmt::v9::basic_format_context<std::back_insert_iterator<fmt::v9::detail::buffer<wchar_t> >, wchar_t> >, const fmt::v9::basic_format_specs<wchar_t>&, fmt::v9::detail::locale_ref) [with OutputIt = wchar_t*]’:
/home/runner/work/fmt/fmt/include/fmt/format.h:2200:16:   required from ‘constexpr OutputIt fmt::v9::detail::write(OutputIt, T, const fmt::v9::basic_format_specs<Char>&, fmt::v9::detail::locale_ref) [with Char = wchar_t; OutputIt = wchar_t*; T = int; typename std::enable_if<((fmt::v9::detail::is_integral<T>::value && (! std::is_same<T, bool>::value)) && (! std::is_same<OutputIt, typename std::conditional<std::is_same<Char, char>::value, fmt::v9::appender, std::back_insert_iterator<fmt::v9::detail::buffer<T> > >::type>::value)), int>::type <anonymous> = 0]’
/home/runner/work/fmt/fmt/include/fmt/format.h:3789:31:   required from ‘constexpr decltype (ctx.out()) fmt::v9::formatter<T, Char, typename std::enable_if<(fmt::v9::detail::type_constant<T, Char>::value != fmt::v9::detail::type::custom_type), void>::type>::format(const T&, FormatContext&) const [with FormatContext = fmt::v9::basic_format_context<wchar_t*, wchar_t>; T = int; Char = wchar_t; typename std::enable_if<(fmt::v9::detail::type_constant<T, Char>::value != fmt::v9::detail::type::custom_type), void>::type = void; decltype (ctx.out()) = wchar_t*]’
/home/runner/work/fmt/fmt/include/fmt/core.h:827:72:   required by substitution of ‘template<class Context, class T> constexpr decltype ((typename Context::formatter_type<T>().format(declval<const T&>(), declval<Context&>()), true)) fmt::v9::detail::has_const_formatter_impl(T*) [with Context = fmt::v9::basic_format_context<wchar_t*, wchar_t>; T = int]’
/home/runner/work/fmt/fmt/include/fmt/core.h:837:43:   required from ‘constexpr bool fmt::v9::detail::has_const_formatter() [with T = int; Context = fmt::v9::basic_format_context<wchar_t*, wchar_t>]’
/home/runner/work/fmt/fmt/include/fmt/core.h:1498:54:   [ skipping 2 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]
/home/runner/work/fmt/fmt/include/fmt/core.h:1526:33:   required by substitution of ‘template<class T, class U, typename std::enable_if<((((((! fmt::v9::detail::is_string<S>::value) && (! fmt::v9::is_char<U>::value)) && (! std::is_array<_To>::value)) && (! std::is_pointer<_Dp>::value)) && (! fmt::v9::detail::has_format_as<U>::value)) && (std::is_constructible<fmt::v9::formatter<U, wchar_t, void> >::value || fmt::v9::detail::has_fallback_formatter<U, wchar_t>::value)), int>::type <anonymous> > constexpr decltype (((fmt::v9::detail::arg_mapper<fmt::v9::basic_format_context<wchar_t*, wchar_t> >*)this)->fmt::v9::detail::arg_mapper<fmt::v9::basic_format_context<wchar_t*, wchar_t> >::do_map(forward<T>(val))) fmt::v9::detail::arg_mapper<fmt::v9::basic_format_context<wchar_t*, wchar_t> >::map<T, U, <enumerator> >(T&&) [with T = const int&; U = int; typename std::enable_if<((((((! fmt::v9::detail::is_string<S>::value) && (! fmt::v9::is_char<U>::value)) && (! std::is_array<_To>::value)) && (! std::is_pointer<_Dp>::value)) && (! fmt::v9::detail::has_format_as<U>::value)) && (std::is_constructible<fmt::v9::formatter<U, wchar_t, void> >::value || fmt::v9::detail::has_fallback_formatter<U, wchar_t>::value)), int>::type <anonymous> = 0]’
/home/runner/work/fmt/fmt/include/fmt/core.h:1542:7:   required by substitution of ‘template<class T, class Context> using mapped_type_constant = fmt::v9::detail::type_constant<decltype (fmt::v9::detail::arg_mapper<Context>().map(declval<const T&>())), typename Context::char_type> [with T = int; Context = fmt::v9::basic_format_context<wchar_t*, wchar_t>]’
/home/runner/work/fmt/fmt/include/fmt/core.h:2971:78:   required from ‘constexpr fmt::v9::detail::format_string_checker<Char, ErrorHandler, Args>::format_string_checker(fmt::v9::basic_string_view<Char>, ErrorHandler) [with Char = wchar_t; ErrorHandler = fmt::v9::detail::error_handler; Args = {int}]’
/home/runner/work/fmt/fmt/include/fmt/core.h:3022:33:   required from ‘void fmt::v9::detail::check_format_string(S) [with Args = {int}; S = xchar_test_compile_time_string_Test::TestBody()::<lambda()>::FMT_COMPILE_STRING; typename std::enable_if<fmt::v9::detail::is_compile_string<S>::value, int>::type <anonymous> = 0]’
/home/runner/work/fmt/fmt/include/fmt/core.h:3176:41:   required from ‘fmt::v9::basic_format_string<Char, Args>::basic_format_string(const S&) [with S = xchar_test_compile_time_string_Test::TestBody()::<lambda()>::FMT_COMPILE_STRING; typename std::enable_if<std::is_convertible<const S&, fmt::v9::basic_string_view<Char> >::value, int>::type <anonymous> = 0; Char = wchar_t; Args = {int}]’
/home/runner/work/fmt/fmt/test/xchar-test.cc:104:3:   required from here
/home/runner/work/fmt/fmt/include/fmt/xchar.h:36:27: error: could not convert ‘out’ from ‘wchar_t*’ to ‘fmt::v9::detail::buffer_appender<wchar_t>’ {aka ‘std::back_insert_iterator<fmt::v9::detail::buffer<wchar_t> >’}
   36 |       loc_writer<wchar_t>{out, specs, separator, grouping, {}}, val);
      |                           ^~~
      |                           |
      |                           wchar_t*