Proposal: improve error descriptions (capitalize variables and respect prefix)

[tomkarw]

Hey @softprops,
I encountered the problem of error accuracy when working with envy.

This issue seems vaguely relevant, but it's missing any description, so I decided to create a new one.

The problem

Basically given code like this

struct Env {
    pub some_var: String
}

fn main() {
    let _env = envy::prefixed("ABC_")
        .from_env::<Env>().unwrap();
}

I'm getting an error like this:

MissingValue("some_var")

where I'd like to see an error like this:

MissingValue("ABC_SOME_VAR")

Quick solution

I was able to overcome this in my project by a quick hack:

panic!("Missing value: ABC_{}", err.to_string().split_whitespace().last().unwrap().to_uppercase());

but obviously it would be better if envy just had nicer errors in the first place.

Proposal

I would be happy to introduce a PR, improving the error messages and adjusting the behavior for prefixed variables. Let me know if you're interested in seeing this, is the proposed improvement acceptable, and I'll work on it.

[flxdot]

I just stumbled across the same issue and wrote a thin wrapper around it:

use serde::de::DeserializeOwned;

#[derive(Debug)]
pub enum FromEnvError {
    MissingValue(String),
    Custom(String),
}

pub trait FromEnv: DeserializeOwned {
    fn from_env(prefix: &str) -> Result<Self, FromEnvError> {
        match envy::prefixed(prefix).from_env::<Self>() {
            Ok(config) => Ok(config),
            Err(error) => match error {
                envy::Error::MissingValue(key) => {
                    Err(FromEnvError::MissingValue(format!(
                        "Missing environment variable: {}{}",
                        prefix,
                        key.to_uppercase().as_str()
                    )))
                }
                envy::Error::Custom(error) => Err(FromEnvError::Custom(format!(
                    "Failed to load config from environment: {}",
                    error
                ))),
            },
        }
    }
}