Bug: alias and flatten don't work together

[wcarmon]

The code below demonstrates that flatten and alias features of serde don't work in the toml library.

Env

• lib version: toml = "0.5.9"
• cargo version: cargo 1.67.0-nightly (ba607b23d 2022-11-22)
• serde version serde = { version = "1.0.147", features = ["derive"] }
• serde flattening feature
• serde alias feature

Here is an MWE which demonstrates the bug

use serde::Deserialize;

#[derive(Deserialize)]
struct Inner {
    #[serde(alias = "myBool")]
    b: bool,

    i: i64,
}

#[derive(Deserialize)]
struct Outer {
    #[serde(flatten)]
    a: Inner,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn works_as_expected() {
        let t_str = r#"
b = true
i = 7
"#;

        let res: Result<Outer, toml::de::Error> = toml::from_str(t_str);
        let got = res.unwrap();

        assert_eq!(true, got.a.b);
        assert_eq!(7, got.a.i);
    }

    #[test]
    fn shows_bug() {
        let t_str = r#"
myBool = true
i = 7
"#;

        let res: Result<Outer, toml::de::Error> = toml::from_str(t_str);
        let got = res.unwrap(); // *** incorrect behavior manifests here

        assert_eq!(true, got.a.b);
        assert_eq!(7, got.a.i);
    }
}

[epage]

Have you tried reproducing this with other serde formats? I have a feeling that alias is more on the serde_derive side than on the serde format side.

[wcarmon]

you are correct.

It it happens in serde_json too

use serde::Deserialize;

    #[derive(Deserialize)]
    struct Inner {
        #[serde(alias = "myBool")]
        b: bool,

        i: i64,
    }

    #[derive(Deserialize)]
    struct Outer {
        #[serde(flatten)]
        a: Inner,
    }

    #[test]
    fn works_as_expected() {
        let t_str = r#"
{
    "b": true,
    "i": 7
}
"#;

        let res = serde_json::from_str::<Outer>(t_str);
        let got = res.unwrap();

        assert_eq!(true, got.a.b);
        assert_eq!(7, got.a.i);
    }

    #[test]
    fn shows_bug() {
        let t_str = r#"
{
    "myBool": true,
    "i": 7
}
"#;

        let res = serde_json::from_str::<Outer>(t_str);
        let got = res.unwrap(); // *** incorrect behavior manifests here

        assert_eq!(true, got.a.b);
        assert_eq!(7, got.a.i);
    }