Deserialization of enums from config doesn't work

[vorner]

Hello

I'm using the config crate together with its serde support. This seems to be problematic together with enums.

Reproducer

In this code, the inner test fails. However, the outer and inner_direct tests pass, so I think I'm not doing something completely silly.

use serde_derive::Deserialize;

#[derive(Deserialize)]
enum X {
    A,
    B,
}

#[derive(Deserialize)]
struct Y {
    x: X,
}

#[derive(Deserialize, Default)]
struct Inner {
    #[serde(default)]
    y: Vec<Y>,
}

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

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

    use config::{Config, File, FileFormat};

    const TOML: &str = r#"
    [[y]]
    x = "A"

    [[y]]
    x = "B"
    "#;

    fn cfg() -> Config {
        let mut config = Config::new();
        config.merge(File::from_str(TOML, FileFormat::Toml)).unwrap();
        config
    }

    #[test]
    fn inner() {
        cfg().try_into::<Inner>().unwrap();
    }

    #[test]
    fn outer() {
        cfg().try_into::<Outer>().unwrap();
    }

    #[test]
    fn inner_direct() {
        toml::from_str::<Inner>(TOML).unwrap();
    }
}

Exact versions used, if they matter:

• config: 0.9.1
• serde: 1.0.80
• serde-derive: 1.0.80
• toml: 0.4.8

Guesses

To me it looks like the enum doesn't like to be deserialized from owned String, but doing it from &str is fine. And when going through the flattening, something on the way maybe goes from String to &str. But that's just a wild guess.

[dtolnay]

If inner_direct passes but inner fails, it sounds like this is an issue with the config crate rather than with Serde. Please follow up with them about it. Thanks!

[vorner]

OK, but still, the fact that Inner and Outer acts different seems strange. Flattening one structure into another as its only field should IMO make them kind of equivalent?