Support Enum?

[quake]

Got this error when try it with config-rs:

Err(invalid type: string "master", expected enum Mode)

Below is the struct and toml file:

#[derive(Debug, Deserialize)]
struct Database {
    url: String,
    mode: Mode,
}

#[derive(Debug, Deserialize)]
enum Mode {
    Master,
    Slave,
}

[database]
url = "postgres://postgres@localhost"
mode = "master"

toml supports Enum
toml-rs/toml-rs#165

am I doing anything wrong?

[mehcode]

It just seems that we don't support it on our end probably due to oversight. This would be a bug that needs fixing.

[vorner]

I've hit this too and tried to report it to serde (because to me it looked like the generated Deserialize must have been wrong).

Anyway, I also have a workaround, look here ‒ the trick with flattening another structure in. I don't know why it helps yet, though.

[mehcode]

Huh. The code path for flatten might be strange. It's definitely our fault for the normal case though. Enums are handled different in the deserializer and we just are missing that.

[vorner]

I just wanted to ask, if the code is in master now, would it make sense to release it as part of 0.9.2, not waiting for full 0.10.0?

[mehcode]

Released as 0.9.2

[vorner]

This seems not to work fully yet, this still fails :-( :

use std::collections::HashMap;
use config::{Config, File, FileFormat};
use serde::Deserialize;

#[derive(Debug, Eq, PartialEq, Hash, Deserialize)]
enum X {
    A,
    B,
}

const CFG: &str = r#"
A = "hello"
B = "world"
"#;

fn main() {
    let mut config = Config::new();
    config.merge(File::from_str(CFG, FileFormat::Toml)).unwrap();
    let c: HashMap<X, String> = config.try_into().unwrap();
}

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: invalid type: string "b", expected enum X', src/libcore/result.rs:999:5

By the way… should I open a separate issue for the fact it tries to feed it with lower-case b instead of the B I put into the configuration? (but it still fails even if I rename the enum to accept lower-case version).

It does seem to work in value-position in a struct, though.

Can we reopen? Or should I open a new one?

[geniusisme]

Enums as keys are not supported yet and I doubt they will ever be. Configuration sources are transformed into simple intermediate representation, which is tree built of maps/arrays and strings/numbers as leafs. And keys can only be strings in these maps. Then this intermediate representation is transformed into whatever you ask, within certain limits imposed by simple config structure.

Enums with trivial constructors can be deserialized from string values with corresponding names. More complex enums are deserialized from config maps/arrays, as everything else.

If you want to get complex data structures deserialized from config, you will need to do additional work. In your example it is possible to get Map<String, String> first, and then simply deserialize enum from string.

With regards to lower-case - here is the issue about that #65

[vorner]

Right, I'm only interest in the case where it is a simple enum, without any carried data ‒ I just want to limit the choices of what might be used as the key. That sounds like something that should be possible in theory (the complex enums as keys is probably not possible because it doesn't make sense in the tree structure).

[vorner]

By the way, I discovered a workaround that works now (without additional post-processing of the config data structure). I can first try_into into a serde_json::Value and go from there.

[mehcode]

Hm.. enums as configuration keys is a bit out-of-scope but I think we could make it work though. I'll leave this open to think through that.