Use long for numeric dates

[martincostello]

Use long instead of int to avoid an implicit conversion and the Y2038 bug.

Resolves #590.

---

Before the change?

• An implicit conversion from int to long occurs when creating a DateTimeOffset from a JSON number.
• Numeric timestamps beyond 2038-01-19T03:14:07Z cannot be deserialized:

System.Text.Json.JsonException : The JSON value could not be converted to System.DateTimeOffset. Path: $ | LineNumber: 0 | BytePositionInLine: 10.
---- System.FormatException : Either the JSON value is not in a supported format, or is out of bounds for an Int32.

ThrowHelper.ReThrowWithPath(ReadStack& state, Utf8JsonReader& reader, Exception ex)
JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan`1 utf8Json, JsonTypeInfo jsonTypeInfo, Nullable`1 actualByteCount)
JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan`1 json, JsonTypeInfo jsonTypeInfo)
JsonSerializer.Deserialize[TValue](String json, JsonSerializerOptions options)
DateTimeOffsetConverterTests.CanDeserializeNumberY2038() line 50
----- Inner Stack Trace -----
Utf8JsonReader.GetInt32()
DateTimeOffsetConverter.HandleNumber(Utf8JsonReader reader) line 28
DateTimeOffsetConverter.ReadInternal(Utf8JsonReader& reader) line 14
DateTimeOffsetConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options) line 6
JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)

After the change?

• No implicit conversion occurs.
• Values after 2038-01-19T03:14:07Z can be deserialized

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

• Yes
• No

---

[github-actions]

👋 Hi! Thank you for this contribution! Just to let you know, our GitHub SDK team does a round of issue and PR reviews twice a week, every Monday and Friday! We have a process in place for prioritizing and responding to your input. Because you are a part of this community please feel free to comment, add to, or pick up any issues/PRs that are labeled with Status: Up for grabs. You & others like you are the reason all of this works! So thank you & happy coding! 🚀

[JamieMagee]

Thanks for catching this! I wonder if anyone will be using this code in 2038 😅

I wonder if this would be a good Roslyn analyzer?

[martincostello]

I wonder if anyone will be using this code in 2038 😅

I had the same thought, but you know what they say:

I wonder if this would be a good Roslyn analyzer?

🤔 maybe - I'll raise an issue with the suggestion and see what folks think.

[martincostello]

I'll raise an issue with the suggestion and see what folks think.

dotnet/runtime#108712