README.md

configloader-rs... loads your config.

configloader-rs serializes the environment into your struct through proc macros and struct "annotations".

Why? It makes it easy to not repeat yourself. The struct already has naming conventions we want (most of the time) out of the environment to get the correct details.

Imagine you have the following:

use configloader::ConfigLoader;

#[derive(Debug, PartialEq, ConfigLoader)]
#[prefix("APP")]
struct AppConfig {
    name: String,
    port: u16,

    // ENV wins when it exists, otherwise this kicks in.
    #[default("false")]
    debug: bool,

    // Default::default(), don't go looking in ENV for this.
    #[skip]
    runtime_only_secret: String,

    #[nested]
    database: DatabaseConfig,

    #[nested]
    cache: CacheConfig,
}

#[derive(Debug, PartialEq, ConfigLoader)]
struct DatabaseConfig {
    url: String,
    max_connections: u32,

    #[nested]
    credentials: CredentialsConfig,
}

#[derive(Debug, PartialEq, ConfigLoader)]
struct CredentialsConfig {
    username: String,
    password: String,
}

#[derive(Debug, PartialEq, ConfigLoader)]
struct CacheConfig {
    host: String,

    #[default("6379")]
    port: u16,
}

fn main() -> Result<(), configloader::ConfigError> {
    let config = AppConfig::load()?;

    assert_eq!(config.name, "boring-oidc");
    assert_eq!(config.port, 8080);
    assert_eq!(config.debug, false);
    assert_eq!(config.database.url, "postgres://localhost/app");
    assert_eq!(config.database.max_connections, 10);
    assert_eq!(config.database.credentials.username, "admin");
    assert_eq!(config.cache.host, "localhost");
    assert_eq!(config.cache.port, 6379);
    assert_eq!(config.runtime_only_secret, "");

    Ok(())
}

And then your env looks like this:

APP_NAME=boring-oidc
APP_PORT=8080
APP_DATABASE_URL=postgres://localhost/app
APP_DATABASE_MAX_CONNECTIONS=10
APP_DATABASE_CREDENTIALS_USERNAME=admin
APP_DATABASE_CREDENTIALS_PASSWORD=not-for-your-readme-probably
APP_CACHE_HOST=localhost

Names are just the field names uppercased. Nested structs get the parent field name slapped in front:

database.url -> DATABASE_URL
database.credentials.username -> DATABASE_CREDENTIALS_USERNAME

If you add #[prefix("APP")] at the top, everything starts with APP_.

Defaults are fallbacks, not hardcoded overrides. So this:

#[default("6379")]
port: u16,

means APP_CACHE_PORT wins if it exists, otherwise 6379 is used.

If you don't want a top level prefix, don't add one:

#[derive(ConfigLoader)]
struct AppConfig {
    port: u16,
}

That one reads PORT.