You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: cargo_config.rs
    path of file: ./repos/rules_rust/crate_universe/src/splicing
    
    the code of the file until where you have to start completion: //! Tools for parsing [Cargo configuration](https://doc.rust-lang.org/cargo/reference/config.html) files

use std::collections::BTreeMap;
use std::fs;
use std::path::Path;
use std::str::FromStr;

use crate::utils;
use anyhow::{bail, Result};
use serde::{Deserialize, Serialize};

/// The [`[registry]`](https://doc.rust-lang.org/cargo/reference/config.html#registry)
/// table controls the default registry used when one is not specified.
#[derive(Debug, Deserialize, Serialize, PartialEq, Eq)]
pub(crate) struct Registry {
    /// name of the default registry
    pub(crate) default: String,

    /// authentication token for crates.io
    pub(crate) token: Option<String>,
}

/// The [`[source]`](https://doc.rust-lang.org/cargo/reference/config.html#source)
/// table defines the registry sources available.
#[derive(Debug, Deserialize, Serialize, PartialEq, Eq)]
pub(crate) struct Source {
    /// replace this source with the given named source
    #[serde(rename = "replace-with")]
    pub(crate) replace_with: Option<String>,

    /// URL to a registry source
    #[serde(default = "default_registry_url")]
    pub(crate) registry: String,
}

/// This is the default registry url per what's defined by Cargo.
fn default_registry_url() -> String {
    utils::CRATES_IO_INDEX_URL.to_owned()
}

#[derive(Debug, Deserialize, Serialize, PartialEq, Eq)]
/// registries other than crates.io
pub(crate) struct AdditionalRegistry {
 
    
    fn registry_settings() {
        let temp_dir = tempfile::tempdir().unwrap();
        let config = temp_dir.as_ref().join("config.toml");

        fs::write(&config, textwrap::dedent(
            r#"
                # Makes artifactory the default registry and saves passing --registry parameter
                [registry]
                default = "art-crates-remote"
                
                [registries]
                # Remote repository proxy in Artifactory (read-only)
                art-crates-remote = { index = "https://artprod.mycompany/artifactory/git/cargo-remote.git" }
                
                # Optional, use with --registry to publish to crates.io
                crates-io = { index = "https://github.com/rust-lang/crates.io-index" }

                [net]
                git-fetch-with-cli = true
            "#,
        )).unwrap();

        let config = CargoConfig::try_from_path(&config).unwrap();
        assert_eq!(
            config,
            CargoConfig {
                registries: BTreeMap::from([
                    (
                        "art-crates-remote".to_owned(),
                        AdditionalRegistry {
                            index: "https://artprod.mycompany/artifactory/git/cargo-remote.git"
                                .to_owned(),
                            token: None,
                        },
                    ),
                    (
                        "crates-io".to_owned(),
                        AdditionalRegistry {
                            index: "https://github.com/rust-lang/crates.io-index".to_owned(),
                            token: None,
                        },
                    ),
                ]),
                registry: Registry {
                    default: "art-crates-remote".to_owned(),
                    token: None,
                },
                source: BTreeMap::new(),
            },
        )
    }