Serde_json: Flatten nested internally-tagged enums?

help
2

There is no built-in way until we implement a flatten attribute -- I see you commented on serde-rs/serde#119.

For now you need to deserialize these yourself. Using your data structures from above, something like:

use serde::de::{self, Deserialize, Deserializer};
use serde_json::Value;

impl<'de> Deserialize<'de> for Message {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where D: Deserializer<'de>
    {
        #[derive(Deserialize)]
        #[serde(tag = "type", rename_all = "snake_case")]
        enum MessageHelper {
            EmotionLevel { message_id: usize },
            Car { message_id: usize },
        }

        let v = Value::deserialize(deserializer)?;
        let m = MessageHelper::deserialize(&v).map_err(de::Error::custom)?;
        match m {
            MessageHelper::EmotionLevel { message_id } => {
                Ok(Message::EmotionLevel {
                    message_id,
                    emotion: Emotion::deserialize(&v).map_err(de::Error::custom)?,
                })
            }
            MessageHelper::Car { message_id } => {
                Ok(Message::Car {
                    message_id,
                    part: CarPart::deserialize(&v).map_err(de::Error::custom)?,
                })
            }
        }
    }
}