Optional Options should have a `null` type

[ryanw]

Optional Options should have a `null` type

[petersn]

I agree that | null and ? are sort of orthogonal, and probably there should be finer grained control here. Analogously, currently #[serde(skip_serializing_if = "...")] only checks for Option::is_none, because ts-rs's "optional" field simply means replacing an Option<T> field with a T field and slapping a ? on it. This means that ts-rs doesn't emit ?s for other skip_serializing_if fields, because it can't know that they're on Option types.

I propose we replace this with two concepts: optional (?), and nullable (| null). By default Option<T> produces a nullable field, and skip_serializing_if always produces an optional field. We can even make it so that if it detects skip_serializing_if = "Option::is_none" that it becomes optional and not nullable, which would make this proposal be a backwards-compatible extension of the current behavior.

I have a patch that does something sort of like this (main...petersn:ts-rs:optional-changes although it's mixed in with other changes), but I'm curious what the maintainers think is the right behavior here.