spdlog and fmt::join

[bouda1]

Hi,

I have made the upgrade to spdlog 1.8.1 with {fmt} 7.1.2. Previously, I was using {fmt} 6.2.0 and spdlog 1.5.0.

Sometimes, I have lines like the following one:

log->debug("message {}", fmt::join(v, ", "));
where v is for example a vector of strings.

This line does not compile anymore. The workaround I found is to call fmt::format like this:
log->debug("message {}", fmt::format("{}", fmt::join(v, ", ")));

It does not look great...
Maybe this is not a real issue and you recommend to do otherwise.
What would you suggest?
Thank you.

[tt4g]

There are issues that may be related: fmtlib/fmt#2040

EDIT: Can use fmt 7.x? The version of fmt bundled by spdlog 1.8.1 is 7.0.3.

[bouda1]

OK, thank you.

[lacc97]

I'm having a similar issue which I don't think is related to the fmtlib bug. I'm using spdlog-1.8.1 and external fmtlib-7.1.3 with gcc-10.2.0 on Gentoo.

When compiling the following minimal example,

#include <fmt/format.h>
#include <spdlog/spdlog.h>

int main() {
  int foo[] = {1, 2, 3};
  spdlog::info("[{}]", fmt::join(foo, ", "));
}

gcc fails with

In file included from /usr/include/fmt/format.h:44,
                 from test.cpp:1:
/usr/include/fmt/core.h: In instantiation of ‘fmt::v7::format_arg_store<fmt::v7::basic_format_context<fmt::v7::detail::buffer_appender<Char>, Char>, fmt::v7::remove_reference_t<Args>...> fmt::v7::make_args_checked(const S&, fmt::v7::remove_reference_t<Args>& ...) [with Args = {const fmt::v7::arg_join<int*, int*, char>&}; S = fmt::v7::basic_string_view<char>; Char = char]’:
/usr/include/fmt/format.h:3820:54:   required from ‘typename fmt::v7::buffer_context<Char>::iterator fmt::v7::format_to(fmt::v7::basic_memory_buffer<Char, SIZE>&, const S&, Args&& ...) [with S = fmt::v7::basic_string_view<char>; Args = {const fmt::v7::arg_join<int*, int*, char>&}; long unsigned int SIZE = 250; Char = char; typename fmt::v7::buffer_context<Char>::iterator = fmt::v7::detail::buffer_appender<char>]’
/usr/include/spdlog/logger.h:340:27:   required from ‘void spdlog::logger::log_(spdlog::source_loc, spdlog::level::level_enum, const FormatString&, const Args& ...) [with FormatString = fmt::v7::basic_string_view<char>; Args = {fmt::v7::arg_join<int*, int*, char>}]’
/usr/include/spdlog/logger.h:87:13:   required from ‘void spdlog::logger::log(spdlog::source_loc, spdlog::level::level_enum, spdlog::string_view_t, const Args& ...) [with Args = {fmt::v7::arg_join<int*, int*, char>}; spdlog::string_view_t = fmt::v7::basic_string_view<char>]’
/usr/include/spdlog/logger.h:93:12:   required from ‘void spdlog::logger::log(spdlog::level::level_enum, const FormatString&, const Args& ...) [with FormatString = char [5]; Args = {fmt::v7::arg_join<int*, int*, char>}]’
/usr/include/spdlog/logger.h:111:12:   required from ‘void spdlog::logger::info(const FormatString&, const Args& ...) [with FormatString = char [5]; Args = {fmt::v7::arg_join<int*, int*, char>}]’
/usr/include/spdlog/spdlog.h:157:31:   required from ‘void spdlog::info(const FormatString&, const Args& ...) [with FormatString = char [5]; Args = {fmt::v7::arg_join<int*, int*, char>}]’
test.cpp:6:44:   required from here
/usr/include/fmt/core.h:1623:53: error: static assertion failed: passing views as lvalues is disallowed
 1621 |       detail::count<(
      |       ~~~~~~~~~~~~~~~                                
 1622 |               std::is_base_of<detail::view, remove_reference_t<Args>>::value &&
      |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 1623 |               std::is_reference<Args>::value)...>() == 0,
      |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~

Even cherrypicking the fix for the fmtlib bug doesn't fix this, so that's why I don't think it's related.

[lacc97]

Issue seems to be that when calling fmt::format_to from spdlog::logger::log_, the Args type goes from {fmt::v7::arg_join<int*, int*, char>} to {const fmt::v7::arg_join<int*, int*, char>&}, so it may be a problem with forwarding parameters. Not sure how to fix it though.

[lacc97]

Just realised my issue got fixed with #1726.