I'm sure you can design schemas screwy enough that Rust can not even express them[0] but that one seems straightforward enough:

    #[derive(Serialize, Deserialize)]
    #[serde(tag = "kind", rename_all = "lowercase")]
    enum X {
        Foo { foobar: String },
        Bar {
            #[serde(skip_serializing_if = "Option::is_none")]
            foobar: Option<f64>, 
            barbaz: String
        }
    }

[0] an enum of numbers would be an issue for instance, though I guess you could always use a `repr(C)` enum it might look a bit odd and naming would be difficult.