Clang Compiler warning: [-Wfloat-equal]

[abdes]

third_party_deps/fmtlib-src/include/fmt/format.h:2299:53: warning: comparing floating point with == or != is unsafe [-Wfloat-equal]
  if (is_constant_evaluated()) return value - value == 0;
                                      ~~~~~~~~~~~~~ ^  ~

please consider disabling the warning in fmtlib itself or defining a float_equal_no_warning function or similar, or using std::equal_to, or comparing to epsilon, etc.

[vitaut]

A PR to silence this warning would be welcome.

[abdes]

As it stands today in the current implementation, it does not look like you are doing very accurate floating point comparison. Such comparison is much more complicated, and would require a lot more code, similar to what boost.Math is doing for example.

Let me know if just silencing the warning is ok, or if you intend to have very accurate floating point comparison.

[vitaut]

It is not a comparison but a fallback implementation of isfinite. The warning is meaningless and should simply be suppressed.

[vitaut]

Suppressed this false positive in ef54f9a.

[abdes]

Sorry, but you only partially solved the problem:

[ 33%] Building CXX object test/CMakeFiles/format-test.dir/format-test.cc.o
In file included from /home/xxx/projects/fmt/test/format-test.cc:13:
/home/xxx/projects/fmt/include/fmt/format.h: In instantiation of ‘constexpr bool fmt::v8::detail::isfinite(T) [with T = __float128; typename std::enable_if<std::is_same<T, __float128>::value, int>::type <anonymous> = 0]’:
/home/xxx/projects/fmt/test/format-test.cc:80:3:   required from ‘void check_isfinite() [with Float = __float128]’
/home/xxx/projects/fmt/test/format-test.cc:95:40:   required from here
/home/xxx/projects/fmt/include/fmt/format.h:2308:24: warning: comparing floating-point with ‘==’ or ‘!=’ is unsafe [-Wfloat-equal]
 2308 |   return value - value == 0;  // std::isfinite doesn't support __float128.
      |          ~~~~~~~~~~~~~~^~~~

Additionally, not in the API, but in a test file:

[ 83%] Building CXX object test/CMakeFiles/xchar-test.dir/xchar-test.cc.o
/home/xxx/projects/fmt/test/xchar-test.cc: In member function ‘typename FormatContext::iterator fmt::v8::formatter<std::complex<double>, charT>::format(const std::complex<double>&, FormatContext&)’:
/home/xxx/projects/fmt/test/xchar-test.cc:483:31: warning: comparing floating-point with ‘==’ or ‘!=’ is unsafe [-Wfloat-equal]
  483 |                      c.real() != 0 ? fmt::format("({}+{}i)", real, imag)
      |                      ~~~~~~~~~^~~~
/home/xxx/projects/fmt/test/xchar-test.cc: In instantiation of ‘typename FormatContext::iterator fmt::v8::formatter<std::complex<double>, charT>::format(const std::complex<double>&, FormatContext&) [with FormatContext = fmt::v8::basic_format_context<fmt::v8::appender, char>; charT = char; typename FormatContext::iterator = fmt::v8::appender]’:
/home/xxx/projects/fmt/include/fmt/core.h:1266:28:   required from ‘static void fmt::v8::detail::value<Context>::format_custom_arg(void*, typename Context::parse_context_type&, Context&) [with T = std::complex<double>; Formatter = fmt::v8::formatter<std::complex<double>, char, void>; Context = fmt::v8::basic_format_context<fmt::v8::appender, char>; typename Context::parse_context_type = fmt::v8::basic_format_parse_context<char>]’
/home/xxx/projects/fmt/include/fmt/core.h:1245:19:   required from ‘fmt::v8::detail::value<Context>::value(T&) [with T = const std::complex<double>; Context = fmt::v8::basic_format_context<fmt::v8::appender, char>]’
/home/xxx/projects/fmt/include/fmt/core.h:1727:14:   required from ‘fmt::v8::detail::value<Context> fmt::v8::detail::make_value(T&&) [with Context = fmt::v8::basic_format_context<fmt::v8::appender, char>; T = std::complex<double>&]’
/home/xxx/projects/fmt/include/fmt/core.h:1744:29:   required from ‘fmt::v8::detail::value<Context> fmt::v8::detail::make_arg(T&&) [with bool IS_PACKED = true; Context = fmt::v8::basic_format_context<fmt::v8::appender, char>; fmt::v8::detail::type <anonymous> = fmt::v8::detail::type::custom_type; T = std::complex<double>&; typename std::enable_if<IS_PACKED, int>::type <anonymous> = 0]’
/home/xxx/projects/fmt/include/fmt/core.h:1868:77:   required from ‘fmt::v8::format_arg_store<Context, Args>::format_arg_store(T&& ...) [with T = {std::complex<double>&}; Context = fmt::v8::basic_format_context<fmt::v8::appender, char>; Args = {std::complex<double>}]’
/home/xxx/projects/fmt/include/fmt/core.h:1885:38:   required from ‘constexpr fmt::v8::format_arg_store<Context, typename std::remove_cv<typename std::remove_reference<Args>::type>::type ...> fmt::v8::make_format_args(Args&& ...) [with Context = fmt::v8::basic_format_context<fmt::v8::appender, char>; Args = {std::complex<double>&}]’
/home/xxx/projects/fmt/include/fmt/core.h:3167:44:   required from ‘std::string fmt::v8::format(fmt::v8::format_string<T ...>, T&& ...) [with T = {std::complex<double>}; std::string = std::__cxx11::basic_string<char>; fmt::v8::format_string<T ...> = fmt::v8::basic_format_string<char, std::complex<double> >]’
/home/xxx/projects/fmt/test/xchar-test.cc:490:30:   required from here
/home/xxx/projects/fmt/test/xchar-test.cc:483:31: warning: comparing floating-point with ‘==’ or ‘!=’ is unsafe [-Wfloat-equal]

[vitaut]

In general fixing all possible warnings is a non-goal but a PR similar to ef54f9a would be welcome. You can also suppress warnings with FMT_SYSTEM_HEADERS.