Can't deserialize some cases when using #[serde(flatten)]

[kardeiz]

Hi! When using serde's relatively new #[serde(flatten)] feature, nested values are sometimes not parsed correctly. It seems like values that have to be parsed from strings (e.g., numbers) are failing; it seems like they are deserialized too early into a string, rather than the final value type.

For example, here is a failing test

#[test]
fn flattened_struct() {
    #[derive(Debug,Serialize,Deserialize,PartialEq)]
    struct InnerQuery {
        name: String,
        age: u32
    }

    #[derive(Debug,Serialize,Deserialize,PartialEq)]
    struct Query {
        #[serde(flatten)]
        inner: InnerQuery,
    }

    let query = Query {
        inner: InnerQuery {
            name: "Carrot".into(),
            age: 45
        }
    };

    let params = "name=Carrot&age=45";

    let rec_params: Query = qs::from_str(params).unwrap();

    assert_eq!(rec_params, query);
}

This panics with "invalid type: string \"45\", expected u32".

Have you encountered this? Any thoughts or workarounds?

[kardeiz]

Nevermind, this appears to be a problem higher up: serde-rs/serde#1183 and nox/serde_urlencoded#33. Closing.

[samscott89]

Happened to come across this again today, and proposed this workaround. Leaving here for future interest.

[maxcountryman]

Happened to come across this again today, and proposed this workaround. Leaving here for future interest.

Very helpful--thank you! I wonder if it isn't better to suggest the serde_with crate as an alternative to rolling your own fromstr?

[samscott89]

Happened to come across this again today, and proposed this workaround. Leaving here for future interest.

Very helpful--thank you! I wonder if it isn't better to suggest the serde_with crate as an alternative to rolling your own fromstr?

Thanks for the suggestion, yes that looks like a better approach!