chrono::time_zone::to_sys() on 'nonexistent time' deviates

[chrisse74]

When calling the (experimental-library feature) std::chrono::time_zone::to_sys() with a 'nonexistent time' (daylight saving) the hour is corrected, but the minute part remains.

According to https://en.cppreference.com/w/cpp/chrono/time_zone/to_sys the correct behaviour would be: "If tp represents a nonexistent time between two UTC time_points, those two time_points will be the same, and that time_point will be returned."

Example

int main()
{
    using namespace std::literals;
    const std::chrono::time_zone* specificTimeZone = std::chrono::get_tzdb().locate_zone("Europe/Vienna");
    {
        const std::chrono::local_seconds inpTime{ std::chrono::local_days{ 2024y / std::chrono::March / 31d } + 2h + 0min };
        const std::chrono::sys_seconds experimentalSystemTimestamp = specificTimeZone->to_sys(inpTime, std::chrono::choose::earliest);
        std::cout << "UTC Timestamp: " << experimentalSystemTimestamp << std::endl;
    }

    {
        const std::chrono::local_seconds inpTime{ std::chrono::local_days{ 2024y / std::chrono::March / 31d } + 2h + 30min };
        const std::chrono::sys_seconds experimentalSystemTimestamp = specificTimeZone->to_sys(inpTime, std::chrono::choose::earliest);
        std::cout << "UTC Timestamp: " << experimentalSystemTimestamp << std::endl;
    }

    {
        const std::chrono::local_seconds inpTime{ std::chrono::local_days{ 2024y / std::chrono::March / 31d } + 3h + 0min };
        const std::chrono::sys_seconds experimentalSystemTimestamp = specificTimeZone->to_sys(inpTime, std::chrono::choose::earliest);
        std::cout << "UTC Timestamp: " << experimentalSystemTimestamp << std::endl;
    }

Output

UTC Timestamp: 2024-03-31 01:00:00
UTC Timestamp: 2024-03-31 01:30:00
UTC Timestamp: 2024-03-31 01:00:00

Expected output

I would expect all the local timestamps between 31.03.2024 02:00 and 3:00 being converted to the same UTC timestamp (2024-03-31 01:00:00).

Environment

• clang version 19.1.2
• compiled using -fexperimental-library
• RHEL 9.4

[mordante]

Thanks for the detailed bug report. I've just created a PR to fix this.