NodaTimeDefaultJsonConverter doesn't seem to work with Interval

[kaydensigh]

Hi, I can't seem to get NodaTimeDefaultJsonConverter to work with Interval.

I added kaydensigh@ab0aef9 to NodaTimeDefaultJsonConverterAttributeTest.RoundTrip and the test fails with:

Message: 
  Assert.That(actual, Is.EqualTo(expected))
  Expected: 2023-05-29T14:11:23Z/2025-01-02T03:04:05Z
  But was:  1970-01-01T00:00:00Z/1970-01-01T00:00:00Z

Stack Trace: 
ClassicAssert.AreEqual(Object expected, Object actual)
NodaTimeDefaultJsonConverterAttributeTest.Roundtrip() line 32
1)    at NUnit.Framework.Legacy.ClassicAssert.AreEqual(Object expected, Object actual)
NodaTimeDefaultJsonConverterAttributeTest.Roundtrip() line 32

Is this expected?

[jskeet]

Will look into this over the weekend. It looks like it's expected to work, given that an interval converter is specified in https://github.com/nodatime/nodatime.serialization/blob/main/src/NodaTime.Serialization.SystemTextJson/NodaTimeDefaultJsonConverterFactory.cs

[jskeet]

Okay, I think I've worked out what's going on - ish. It does go into the NodaIntervalConverter, but then when we call options.WriteType with each of the instants, the JsonSerializerOptions don't have any converter registered for Instant, so it writes an empty string.

Basically I'll need to add a field to NodaIntervalConverter and NodaDateIntervalConverter so they each have a converter to use when reading/writing. It's not immediately clear to me what should happen if the caller has provided a JsonSerializerOptions which already has an InstantConverter though - will see what happens with other properties. (I don't know whether the defaulting is only applied as a fallback.)