Bug: alias and flatten don't work together

[wcarmon]

The code below demonstrates that flatten and alias features of serde don't work together.

Below shows examples from both serde_json and toml library.

Env

• lib version: toml = "0.5.9"
• lib version: serde_json = "1.0.89"
• 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_in_toml() {
        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_in_toml() {
        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);
    }

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

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

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

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

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

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

Related

• Bug: alias and flatten don't work together toml-rs/toml#389
• (Maybe related): Suggest #[serde(flatten)] in error message when writing #[serde(inline)] #2236

[jonasbb]

This is a known problem: #1504.

[Mingun]

This was fixed (partially) by #2387, the in-place part is fixed in #2443

[dtolnay]

Closing as a duplicate of #2188.