Fields with camelCase doesn't work

[vjousse]

Hi there,
I'm new to rust and config-rs, and I'm facing an annoying problem: I can't get structs with #[serde(rename_all = "camelCase")] to work.
I've setup a simple demo repository here to illustrate my problem.
My Toml:

snakeTest = "foo"

My struct:

#[derive(Debug, Deserialize)]
#[serde(rename_all = "camelCase")]
struct Settings {
    snake_test: String,
}

My main:

fn main() {
    let mut c = config::Config::default();
    c.merge(config::File::new("Settings", config::FileFormat::Toml))
        .unwrap();

    // Deserialize the entire file as single struct
    let s: Settings = c.try_into::<Settings>().unwrap();

    println!("{:?}", s);
}

The error:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: missing field `snakeTest`', libcore/result.rs:916:5

Am I missing something? Thanks!

[vjousse]

This seems to be related to this to_lowercase call here: https://github.com/mehcode/config-rs/blob/master/src/file/format/toml.rs#L32

Any reason why your are lowercasing every key?

[mehcode]

The primary reason is it's not always straightforward what case the key is in when it comes into the application. Consider building your application targeting a configuration file where all keys are lower_case but the system administrator needs to override something with an environment variable as UPPER_CASE.

I'd be hesitant to start doing camelCase to camel_case conversions everywhere. It might make sense to allow uniformly changing keys from a specific source though. Perhaps something like this:

config.merge(
  File::new("Settings").key_replacer(|key| to_lower_case(key))
)?;

[vjousse]

IMHO, a first good step would be adding some documentation about that. For example, warning people that keys in the files should be lowercase when using automatic deserialization with try_into.
What's your guidelines regarding the main README.md? It seems pretty poor atm, and this is very confusing for the newcomers. I may contribute some documentation if you want. Just tell me if I can help in that area.
Anyway, thanks for the answer and the great work!

[bowbahdoe]

This is surprising behaviour to say the least. It makes reading in json written in camel case pretty hard and it seems like an unnessicary restriction.

I'm not very clear on why the to_lower_case() calls are in there also: without this open issue I would have no way of knowing why this struct wouldn't deserialize.

#[derive(Debug, Deserialize)]
pub struct Tcp {
    pub host: String,
    #[serde(rename = "userPort")]
    pub user_port: Option<u64>,
    pub adminPort: Option<u64>
}

[mehcode]

Being fixed for 0.10. Keys will be case-sensitive on a per-source basis (so keys coming from the environment will still be case-insensitive).

[ufoscout]

@mehcode
Is there any estimated date for 0.10.0 to be released? If not, would it be possible to have a patch for this in 0.9?
We use this library in each of my company's project, but we are forced to migrate to something else as this bug is a huge issue for us :(

[mehcode]

@ufoscout there is a fork that is strictly case sensitive. Check closed PRs. Sorry for the trouble caused. How I use config I need the case insensitive behavior. I'm planning on making lookup/merging case insensitive but having the string still remember it's case for deserialization.

[arsing]

It is also possible to implement your own config::Source that's similar to config::File but doesn't lower-case the keys. That's what we do in https://github.com/Azure/iotedge/blob/e70bc6d7c2a5c74b8e4c818ee34e332213dbcdc7/edgelet/edgelet-utils/src/yaml_file_source.rs