Crate rclap 

rclap is a Rust utility that helps you create command-line interfaces with the clap crate by reducing boilerplate code. It generates clap structures from a simple TOML configuration file, allowing you to define your application’s command-line arguments, environment variables, and default values in one place.

How it works

1- Create a TOML File: Define your configuration settings in a simple TOML file, specifying the argument name, type, default value, and associated environment variable.

port = { type = "u16", default = "8080", doc = "Server port number", env = "PORT" }
ip = {  default = "localhost", doc = "connection URL", env = "URL" }

2- Apply the Macro: Use the #config macro on an empty struct in your Rust code. The macro reads the TOML file and generates the complete clap::Parser implementation for you.

use clap::Parser;
use rclap::config;

#[config]
struct MyConfig;

3- Parse and Use: Your application can then simply call MyConfig::parse() to handle all command-line and environment variable parsing.

fn main() {
    let config = MyConfig::parse();
    println!("Config: {:#?}", config);
    println!("{}", &config.port);
}

rclap prioritizes a hierarchical approach to configuration, allowing you to set the ip and port via either environment variables or command-line arguments. If neither is specified, the predefined default values will be used.

For instance, you can use the command-line flags –ip and –port to pass values directly. This would generate a help message like the one below, which clearly shows the available options, their default values, and the corresponding environment variables.

Usage: example [OPTIONS]

Options:
      --"ip" <ip>      connection URL [env: URL=] [default: localhost]
      --"port" <port>  Server port number [env: PORT=120] [default: 8080]
  -h, --help           Print help

Attribute Macros

config