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: main.rs
    path of file: ./repos/rust-playground/top-crates/src
    
    the code of the file until where you have to start completion: #![deny(rust_2018_idioms)]

use rust_playground_top_crates::*;
use serde::Serialize;
use std::{
    collections::BTreeMap,
    fs::{self, File},
    path::{Path, PathBuf},
};

/// A Cargo.toml file.
#[derive(Serialize)]
struct TomlManifest {
    package: TomlPackage,
    profile: Profiles,
    dependencies: BTreeMap<String, DependencySpec>,
    build_dependencies: BTreeMap<String, DependencySpec>,
}

/// Header of Cargo.toml file.
#[derive(Serialize)]
struct TomlPackage {
    name: String,
    version: String,
    authors: Vec<String>,
    resolver: String,
}

/// Profile used for build dependencies (build scripts, proc macro
    
fn main() {
    let d = fs::read_to_string("crate-modifications.toml")
        .expect("unable to read crate modifications file");

    let modifications: Modifications =
        toml::from_str(&d).expect("unable to parse crate modifications file");

    let (dependencies, infos) = rust_playground_top_crates::generate_info(&modifications);

    // Construct playground's Cargo.toml.
    let manifest = TomlManifest {
        package: TomlPackage {
            name: "playground".to_owned(),
            version: "0.0.1".to_owned(),
            authors: vec!["The Rust Playground".to_owned()],
            resolver: "2".to_owned(),
        },
        profile: Profiles {
            dev: Profile {
                codegen_units: 1,
                incremental: false,
                build_override: BuildOverride {
                    codegen_units: 1,
                    debug: true,
                },
            },
            release: Profile {
                codegen_units: 1,
                incremental: false,
                build_override: BuildOverride {
                    codegen_units: 1,
                    debug: false,
                },
            },
        },
        dependencies: dependencies.clone(),
        build_dependencies: dependencies,
    };

    // Write manifest file.
    let base_directory: PathBuf = std::env::args_os()
        .nth(1)
        .unwrap_or_else(|| "../compiler/base".into())
        .into();

    let cargo_toml = base_directory.join("Cargo.toml");
    write_manifest(manifest, &cargo_toml);
    println!("wrote {}", cargo_toml.display());

    let path = base_directory.join("crate-information.json");
    let mut f = File::create(&path)
        .unwrap_or_else(|e| panic!("Unable to create {}: {}", path.display(), e));
    serde_json::to_writer_pretty(&mut f, &infos)
        .unwrap_or_else(|e| panic!("Unable to write {}: {}", path.display(), e));
    println!("Wrote {}", path.display());
}