Formatting long with FMT_BUILTIN_TYPES=0

[montekarlos]

Consider the following code sample using fmtlib v11.1.4 or master

#define FMT_BUILTIN_TYPES 0

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

int main() {
    long n(1234);
    fmt::print("1234!={}", n);    
}

The expected output of this is 1234!=1234 however when built and run using FMT_BUILTIN_TYPES=0 the results are 1234!=536895556 (your results will vary)

Note that changing long to int will resolve this

I'm hitting this issue on non-eabi (defines int32_t as long) but I can also create on x64 MSVC.

My understand is of this is that during argument processing custom.value and custom.format are set, but then basic_format_args::type detects as detail::type::int_type so then during formatting (visit) the wrong member of the union is used.

[vitaut]

Could you provide a godbolt repro?

[montekarlos]

Sadly godbolt doesn't provide libfmt library support for msvc and unknown-eabi fails linking fmtlib

https://godbolt.org/z/s7ba4Wvf3

[montekarlos]

I don't fully understand what is happening

However when FMT_BUILTIN_TYPES=0 I see this behaviour

fmtlib v11.1.4:

base.1121:

using stored_type_constant = std::integral_constant<
    type, Context::builtin_types || TYPE == type::int_type ? TYPE
                                                           : type::custom_type>;

Is returning int_type even though

However base:2138
FMT_CONSTEXPR FMT_INLINE value(long x FMT_BUILTIN) : value(long_type(x)) {} has been disabled so will be compiled via

  template <typename T,
            FMT_ENABLE_IF(use_formatter<T>::value || !FMT_BUILTIN_TYPES)>
  FMT_CONSTEXPR20 FMT_INLINE value(T& x) : value(x, custom_tag()) {}

Which results in a custom with an integer type.