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: assume-role.rs
    path of file: ./repos/aws-doc-sdk-examples/rustv1/examples/sts/src/bin
    
    the code of the file until where you have to start completion: // Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

#![allow(clippy::result_large_err)]

use aws_config::meta::region::RegionProviderChain;
use aws_sdk_sts::{meta::PKG_VERSION, Client, Error};
use aws_types::region::Region;
use aws_types::sdk_config::SdkConfig;
use clap::Parser;

#[derive(Debug, Parser)]
struct Opt {
    /// The AWS Region.
    #[structopt(short, long)]
    region: Option<String>,

    /// Whether to display additional information.
    #[structopt(short, long)]
    verbose: bool,

    /// Whether to display additional information.
    #[structopt(long)]
    role_arn: String,

    /// Whether to display additional information.
    #[structopt(long)]
    role_session_name
    
async fn assume_role(config: &SdkConfig, role_name: String, session_name: Option<String>) {
    let provider = aws_config::sts::AssumeRoleProvider::builder(role_name)
        .session_name(session_name.unwrap_or("rust_sdk_example_session".into()))
        .configure(config)
        .build()
        .await;

    let local_config = aws_config::from_env()
        .credentials_provider(provider)
        .load()
        .await;
    let client = Client::new(&local_config);
    let req = client.get_caller_identity();
    let resp = req.send().await;
    match resp {
        Ok(e) => {
            println!("UserID :               {}", e.user_id().unwrap_or_default());
            println!("Account:               {}", e.account().unwrap_or_default());
            println!("Arn    :               {}", e.arn().unwrap_or_default());
        }
        Err(e) => println!("{:?}", e),
    }
}