fmt::vformat() throws an exception on Clang in x86 mode during chrono formatting.

[TheStormN]

Hello,

I believe I've discovered a bug in latest version of fmt when compiled using Clang in x86 targeting mode. We have a legacy codebase with some Time functions wrappers which we try to refactor by using more modern tooling. We use fmt as polyfill for platforms which still don't have proper std:;format() support.

The current issue is reproducible only on our Clang x86 targeting pipeline, on all other mobile and desktop platforms the code works as expected. The exception being thrown is fmt::v11::format_error. I've managed to strip down the code to a small reproducible example. Here's the CompilerExplorer link: https://godbolt.org/z/v1Mezdd8T

The moment you remove the -m32 flag the program executes successfully.

#include <chrono>
#include <iostream>

#include <cassert>

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

template <class Clock, class Duration = typename Clock::duration>
std::string formatTime(const std::string& format, const std::chrono::time_point<Clock, Duration>& time)
{
    return fmt::vformat("{:" + format + '}', fmt::make_format_args(time));
}

std::string fromUnixEpochToRFC1123(const int64_t epoch)
{
    std::chrono::system_clock::time_point timePoint{ std::chrono::seconds(epoch / 1000) };

    return formatTime("%a, %d %b %Y %H:%M:%S GMT", std::chrono::floor<std::chrono::seconds>(timePoint));
}

int main() {
    auto result = fromUnixEpochToRFC1123(32536850400000);
    bool isResultExpected = result == "Mon, 19 Jan 3001 22:00:00 GMT";
    assert(isResultExpected);
    std::cout << result << std::endl;
}

EDIT: Switching from fmt to std works on the same compiler with same flags: https://godbolt.org/z/v8EnYzaWq

[vitaut]

The error is expected: 19 Jan 3001 is not representable as 32-bit time_t, see https://en.wikipedia.org/wiki/Year_2038_problem.

[TheStormN]

@vitaut Ok then, how the std::vformat handles that without an issue: https://godbolt.org/z/v8EnYzaWq
Same compiler version and flags as in the original example, just switched from fmt to std.

[vitaut]

I am not sure how they avoid conversion to time_t but if their method is implementable in {fmt} a PR would be welcome.

[TheStormN]

@vitaut Ok, could you at least reopen the issue, so it is known that some work can be done here.

[vitaut]

Sure, we can keep it open in case anyone is interested in investigating this further.

[TheStormN]

Thanks, I've updated the title and description a bit, because it it seems to be a generic issue with Clang in x86 targeting mode.