Rust config_struct crate build script with check for the existence of the config file

build.rs

use config_struct::{Error, StructOptions};
use std::fs;

const CONFIG_FILE_DST: &str = "src/config.rs";

fn main() -> Result<(), Error> {
    println!("cargo:rerun-if-changed=build.rs");
    println!("cargo:rerun-if-changed=config.toml");

    let mut config_file_src = "config.toml";

    let metadata = fs::metadata(config_file_src);

    if metadata.is_err() || !metadata.unwrap().is_file() {
        println!("cargo:warning={} not found!", config_file_src);
        config_file_src = "config-example.toml";
        println!("cargo:warning=Using {} instead!", config_file_src);
    }

    config_struct::create_config(
        config_file_src,
        CONFIG_FILE_DST,
        &StructOptions::default()
    )
}