// This should serialize and deserialize directly as String, rather than as newtype.
#[derive(Serialize, Deserialize)]
#[serde(transparent)]
struct Transparent(String);

// Generated code.
impl Serialize for Transparent {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
        where S: Serializer
    {
        self.0.serialize(serializer)
    }
}

impl<'de> Deserialize<'de> for Transparent {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where D: Deserializer<'de>
    {
        Deserialize::deserialize(deserializer).map(Transparent)
    }
}