Autoconf

Overview

autoconf is a crate that enables easily managing rust application configuration by automatically deriving functionality to load settings from environment variables, configuration files, and default values. This is done by procedurally parsing struct fields to build environment variable keys as well as deserialization using serde from a provided config file path. Functionality is customizable through several macro attribute helpers.

Key Features

• Simplicity: Minimal boilerplate, as simple as annotating your struct and a struct with named fields and a single method.
• Flexibility: Supports loading configuration data from environment variables, a single toml, json, yaml, xml, ini, ron or json5 configuration file with default trait implementations as a fall-back.
• Integration: Integrates conveniently with other macros such as smart_default.

Usage

Here's a complete example with all the currently implemented attributes. First define a configuration struct that the derive macro will fill from specified sources:

use autoconf::prelude::*;
use smart_default::SmartDefault;

#[derive(Config, Clone, SmartDefault)]
#[config(prefix = "PREFIX", path = "tests/config")]
pub struct Test {
    #[config(key = "CUSTOM_KEY")]
    #[default = "World"]
    name: String,
    #[config(prefix = "APP")]
    #[default = 3]
    id: i32,
    #[config(nest)]
    nested: Nested,
    #[config(key = "TIMEOUT_MS")]
    #[default = 1000]
    timeout: u64,
    #[config(key = "FEATURE_ENABLED")]
    #[default = false]
    feature_enabled: bool,
    #[default = 1.5]
    ratio: f64,
    #[config(nest)]
    metadata: Metadata,
    #[config(skip)]
    #[default(Some("Unused".to_string()))]
    unused_field: Option<String>,
}

#[derive(Config, Default, Clone)]
pub struct Nested {
    name: String,
}

#[derive(Config, Default, Clone)]
#[config(prefix = "META", separator = "__")]
pub struct Metadata {
    description: String,
    version: i32,
}

Then you can load your settings like so:

fn main() {
   let settings = Test::config();
}

This is intended to easily be used inside of something like std::sync::OnceLock

Considerations

• Version Flexibility: This is an initial release (v0.1.0), and as such, it is not fully optimized. The implementation involves some cloning for simplicity, which may impact performance in large-scale applications.
• Production Use Caution: This is my first published Rust crate, while it is fully functional and useful for me, it's advisable not to rely heavily on this library in critical production environments without thorough testing, especially where guarantees of stability and performance are required.
• Contribution: Contributions are welcome! Whether it's feature requests, bug reports, or pull requests, i'd love some constructive feedback!

I highly recommend checking out the config crate as it is a feature complete non-proc-macro alternative. This crate actually relies on config for file parsing.