Struct with flatten field serialized as JSON, but not as struct

[apatrushev]

Struct without flatten field serialized as struct:

use serde::{Deserialize, Serialize};
use serde_json::json;


#[derive(Debug, Deserialize, Serialize)]
struct Event {
    sender: String,
}


fn main() {
    let event = json!({
        "sender": "foobar",
    });
    let event = event.to_string();
    let event = serde_json::from_str::<Event>(&event).unwrap();
    let value = ron::to_string(&event).unwrap();
    println!("{}", value);
}

Result:

(sender:"foobar")

Struct containing flatten field serialized as JSON:

use std::collections::HashMap;

use serde::{Deserialize, Serialize};
use serde_json::json;


#[derive(Debug, Deserialize, Serialize)]
struct Event {
    sender: String,

    #[serde(flatten)]
    extra: HashMap<String, String>,
}


fn main() {
    let event = json!({
        "sender": "foobar",
        "info": "test"
    });
    let event = event.to_string();
    let event = serde_json::from_str::<Event>(&event).unwrap();
    let value = ron::to_string(&event).unwrap();
    println!("{}", value);
}

Result:

{"sender":"foobar","info":"test"}

May be it would be better to see it as (literally ignore the flatten attribute for the fields on serialization may be optionally):

(sender:"foobar", extra: {"info":"test"})

[juntyr]

This is unfortunately serde's fault and ron cannot do anything about it.

When a struct contains any flattened fields, serde serializes it as a map (since serializing a struct requires having statically known field names) and not a struct. From ron's point of view, we just get a map from serde and have no idea that it was ever a struct.