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: build.rs
    path of file: ./repos/rules_rust/examples/env_locations
    
    the code of the file until where you have to start completion: use std::{env, fs};

fn main() {
    // our source file should be readable
    let path = env::var("SOURCE_FILE").unwrap();
    let generated_data = fs::read_to_string(&path).unwrap();
    assert_eq!(generated_data, "source\n");

    // our generated data file should be readable
    let path = env::var("GENERATED_DATA").unwrap();
    let generated_data = fs::read_to_str
    
fn main() {
    // our source file should be readable
    let path = env::var("SOURCE_FILE").unwrap();
    let generated_data = fs::read_to_string(&path).unwrap();
    assert_eq!(generated_data, "source\n");

    // our generated data file should be readable
    let path = env::var("GENERATED_DATA").unwrap();
    let generated_data = fs::read_to_string(&path).unwrap();
    assert_eq!(generated_data, "hello\n");

    // and we should be able to read (and thus execute) our tool
    let path = env::var("SOME_TOOL").unwrap();
    assert!(!fs::read(&path).unwrap().is_empty());
}