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: connection.rs
    path of file: ./repos/graphql-rust-demo/auth-service/src/persistence
    
    the code of the file until where you have to start completion: use std::env;

use diesel::pg::PgConnection;
use diesel::r2d2::{ConnectionManager, Pool};

pub type PgPool = Pool<
    
pub fn create_connection_pool() -> PgPool {
    let db_url = env::var("DATABASE_URL").expect("Can't get DB URL");
    let manager = ConnectionManager::<PgConnection>::new(db_url);
    Pool::builder()
        .build(manager)
        .expect("Failed to create pool")
}