Display bug in LocalDate

I have found an interesting bug in how LocalDate is displayed/ToStringed

To showcase it, take the following code:

var lateDate = new LocalDate(9999, 01, 01);
var minimumYear = minimumDate.Year;
var longDateInterval = new DateInterval(minimumDate, new LocalDate(2021, 09, 01));
var allDays = longDateInterval.ToList();
var firstYear = longDateInterval.First().Year;

When inspecting the variables, the below is what is shown. minimumYear and firstYear are both correctly -9998, yet according to what the debugger displays, LocalDate.MinIsoValue is 9999-01-01 and the next days appear to be the following days, until you appear to go from 9999-12-31 to 9998-01-01.

The day of the week, however, does seem to be correct, given that it is different for LocalDate.MinIsoValue and new LocalDate(9999, 01, 01).

[jskeet]

Actually, I take that back about not having to distinguish between year-of-era and absolute year: the Japanese calendar supports multiple eras, and “yyyy” returns the year-of-era. Here’s an example:

using System;
using System.Globalization;

class Program
{
    static void Main()
    {
        var date = new DateTime(2021, 6, 9);
        var culture = CultureInfo.CreateSpecificCulture("jp-JP");
        var calendar = new JapaneseCalendar();
        culture.DateTimeFormat.Calendar = calendar;
        Console.WriteLine(date.ToString("yyyy-MM-dd", culture));
    }
}

The result is 03-06-09, because we’re in year 3 of the current era.

So while the result may be unexpected, I believe NodaTime is actually behaving correctly here. I would recommend users who want to deal with BCE dates should probably use LocalDatePattern.Iso, or a custom date/time format that uses uuuu instead of yyyy.

[jskeet]

Closing, as I believe there’s nothing here to change in Noda Time.