The crate serde_with provides the SerializeAs and DeserializeAs traits, which we can implement on our types to allow for composable serde(with = "") attributes. These currently aren't supported in vanilla serde.

This will enable the following (which currently isn't possible):

#[serde_as]
#[derive(Debug, Serialize, Deserialize)]
struct MyData {
    #[serde_as(as = "Option<bson::DateTime>")
    date: Option<chrono::DateTime<Utc>>
}

And this struct will serialize to / from BSON, even though there's an Option wrapper.

Originally reported in GH issue: https://github.com/mongodb/bson-rust/issues/303