Improper deserialization for #[serde(flatten)] field

[dsgallups]

use serde::{Deserialize, Serialize};

#[derive(Serialize, Deserialize, PartialEq)]
pub struct Outer {
    value_a: i32,
    #[serde(flatten)]
    inner: Inner,
}

#[derive(Serialize, Deserialize, PartialEq)]
pub struct Inner {
    value_b: i32,
}

fn main() {
    let params = Outer {
        value_a: 3,
        inner: Inner { value_b: 6 },
    };

    let ser_params = serde_qs::to_string(&params).unwrap();

    assert_eq!("value_a=3&value_b=6", &ser_params);
    let output = serde_qs::from_str::<Outer>(&ser_params);

    let Err(serde_qs::Error::Custom(error)) = output else {
        unreachable!()
    };

    assert_eq!(error, r#"invalid type: string "6", expected i32"#)
}

Only Strings and Option<String>s appear to be supported in flattened structures :(

This might be a related issue of #153 and hence serde-rs/serde#1183. Let me know how I can help if it is possible to fix!

[samscott89]

Hey @dsgallups . Yep, unfortunately it's that same issue again.

I've tried many, many time to find a fix but it seems fundamentally impossible due to the serde issue.

In the meantime, the best known workaround is still https://docs.rs/serde_qs/latest/serde_qs/#flattenuntagged-workaround e.g.

#[test]
fn issue_159() {
    #[derive(Debug, Serialize, Deserialize, PartialEq)]
    pub struct Outer {
        value_a: i32,
        #[serde(flatten)]
        inner: Inner,
    }

    #[serde_with::serde_as]
    #[derive(Debug, Serialize, Deserialize, PartialEq)]
    pub struct Inner {
        #[serde_as(as = "serde_with::DisplayFromStr")]
        value_b: i32,
    }

    roundtrip_test!(Outer {
        value_a: 3,
        inner: Inner { value_b: 6 },
    });
}

(that macro is from the test suite that checks it roundtrip de/serializes)

[samscott89]

I'll keep this open and pinned for discoverability