Compile failure for fmt::sprintf on gcc9.2.0 if using -std:c++17 and above

[hkAlice]

Example code:

#include <string>
#include <fmt/printf.h>

int main( int argc, char *argv[] )
{
    std::string testStr = "fmt::sprintf test: %03d";
    
    uint32_t idx = 1;
    std::string fmtTestStr = fmt::sprintf( testStr, idx );

    return 0;
}

In file included from /run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/format.h:46,
                 from /run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/ostream.h:12,
                 from /run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/printf.h:14,
                 from /run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/src/main.cpp:2:
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/core.h: In instantiation of ‘constexpr decltype (vis(0)) fmt::v6::visit_format_arg(Visitor&&, const fmt::v6::basic_format_arg<Context>&) [with Visitor = fmt::v6::printf_arg_formatter<fmt::v6::buffer_range<char> >; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>; decltype (vis(0)) = std::back_insert_iterator<fmt::v6::internal::buffer<char> >]’:
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/printf.h:562:5:   required from ‘OutputIt fmt::v6::basic_printf_context<OutputIt, Char>::format() [with ArgFormatter = fmt::v6::printf_arg_formatter<fmt::v6::buffer_range<char> >; OutputIt = std::back_insert_iterator<fmt::v6::internal::buffer<char> >; Char = char]’
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/printf.h:181:3:   required from ‘void fmt::v6::internal::printf(fmt::v6::internal::buffer<Char>&, fmt::v6::basic_string_view<Char>, fmt::v6::basic_format_args<Context>) [with Char = char; Context = fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<char> >, char>]’
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/printf.h:606:9:   required from ‘std::__cxx11::basic_string<Char> fmt::v6::vsprintf(const S&, fmt::v6::basic_format_args<fmt::v6::basic_printf_context<std::back_insert_iterator<fmt::v6::internal::buffer<Char> >, Char> >) [with S = fmt::v6::basic_string_view<char>; Char = char]’
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/printf.h:623:18:   required from ‘std::__cxx11::basic_string<Char> fmt::v6::sprintf(const S&, const Args& ...) [with S = std::__cxx11::basic_string<char>; Args = {unsigned int}; Char = char]’
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/src/main.cpp:9:57:   required from here
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/core.h:972:15: error: no match for call to ‘(fmt::v6::printf_arg_formatter<fmt::v6::buffer_range<char> >) (const int128_t&)’
  972 |     return vis(arg.value_.int128_value);
      |            ~~~^~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/src/main.cpp:2:
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/printf.h:239:12: note: candidate: ‘template<class T, typename std::enable_if<std::is_integral<_Tp>::value, int>::type <anonymous> > fmt::v6::printf_arg_formatter<Range>::iterator fmt::v6::printf_arg_formatter<Range>::operator()(T) [with T = T; typename std::enable_if<std::is_integral<U>::value, int>::type <anonymous> = <enumerator>; Range = fmt::v6::buffer_range<char>]’
  239 |   iterator operator()(T value) {
      |            ^~~~~~~~
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/printf.h:239:12: note:   template argument deduction/substitution failed:
In file included from /run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/format.h:46,
                 from /run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/ostream.h:12,
                 from /run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/printf.h:14,
                 from /run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/src/main.cpp:2:
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/core.h:218:62: error: no type named ‘type’ in ‘struct std::enable_if<false, int>’
  218 | #define FMT_ENABLE_IF(...) enable_if_t<(__VA_ARGS__), int> = 0
      |                                                              ^
/run/media/maru/Shiki/Data/Dev/fmt-gcc9-test/lib/fmt/include/fmt/printf.h:238:25: note: in expansion of macro ‘FMT_ENABLE_IF’
  238 |   template <typename T, FMT_ENABLE_IF(std::is_integral<T>::value)>

The snippet fails to compile on gcc9.2.0 when using flags -std=c++17, -std=c++1z-, -std=c++2a etc. It works fine on gcc8 as well as VS2019 MSVC.

Thank you!

[vitaut]

Should be fixed in 2730e90. Thanks for reporting.