Annotate System.Text.Json for nullable

[buyaa-n]

Recreating PR as old one #114 no more accessible, gone with old private fork

CC @ahsonkhan@steveharter@stephentoub@safern

[ahsonkhan]

48/125 files reviewed (JsonDocument, JsonElement, JsonNode, and related types).

Here's some feedback so far.

[buyaa-n]

Failed CI legs doesn't look like caused from this PR changes, gonna merge this

[danmoseley]

Yay!

[ahsonkhan]

gonna merge this

Awesome! Thanks for your patience and effort in getting this merged, @buyaa-n. I appreciate you taking your time with it and getting the details right. Nullability annotations of a complex library like JSON hopefully help explore and refine the guidelines.

[buyaa-n]

Awesome! Thanks for your patience and effort in getting this merged, @buyaa-n. I appreciate you taking your time with it and getting the details right. Nullability annotations of a complex library like JSON hopefully help explore and refine the guidelines.

Thanks for your delicate review, learnt a lot. Have fun with nullability aware coding 😄

[ahsonkhan]

Moving comment from #114 (comment) (since that PR was closed).

Highlighting the breaking change here (which became visible when enabling nullability analysis).

Deserializing into a char is now more strict to match user expectations. The payload must contain a single-character string for deserialization to succeed:

publicclassMyPoco{publiccharCharacter{get;set;}}publicstaticvoidTestDeserializeToChar(){// Before (3.1): NullReferenceException// After (5.0): JsonExceptionJsonSerializer.Deserialize<MyPoco>("{\"Character\": null}");// Before (3.1): IndexOutOfRangeException// After (5.0): JsonExceptionJsonSerializer.Deserialize<MyPoco>("{\"Character\": \"\"}");// Before (3.1): Set Character to the first character - 'a'// After (5.0): JsonExceptionJsonSerializer.Deserialize<MyPoco>("{\"Character\": \"abc\"}");}

Passing in null for the Type parameter while serializing now correctly throws ArgumentNullException rather than returning "null" JSON:

publicstaticvoidTestSerializeNullType(){// Before (3.1): Returned a string with value "null"// After (5.0): ArgumentNullException: Value cannot be null. (Parameter 'type')JsonSerializer.Serialize(null,null);// Same with other Serialize{Async} overloads// Before (3.1): Returned a byte[] with value "null"// After (5.0): ArgumentNullException: Value cannot be null. (Parameter 'type')JsonSerializer.SerializeToUtf8Bytes(null,null);}

[danmoseley]

@buyaa-n@layomia Does this need a breaking change issue?