Round trip serialization and deserialization fails when storing an Option<UnitStruct>

[alice-i-cecile]

When writing to JSON, Some(UnitStruct) is serialized the same as None. This only seems to occur for structs with no data / fields.

I haven't investigated if this is a problem in other file formats.

This then causes the deserialization to not match the original value.

[alice-i-cecile]

The field gets serialized as field: null. I suspect this is a JSON-specific limitation around handling enum values.

[dtolnay]

Neither serde nor serde_json makes round trip guarantees in general.

What JSON would you expect to get for each of the two values?

[alice-i-cecile]

Given that unit structs are represented as null per the serde-json spec, I don't think there's a good solution. I'm very fine to leave this as "Won't Fix": this was merely a surprise that I felt was worth poking at and adding to the Google search results :)