println!("\n\nReading World Data...\n\n");
let mut world_data_string = String::new();
world.read_to_string(&mut world_data_string).unwrap();
let mut world_data: Vec<char> = world_data_string.chars().collect();
let mut tile_list_pusher = vec![];
for o in file_list_indexer {
tile_list_pusher.push(&world_data[0..o * 5000 + 1]);
}
A reproduction is more like this -- i.e. it reproduces the same error. I had some time to thin it down, but you'll generally get better (free) help if you put some more effort in yourself.
Anyway, you declare tile_set but never use it. Rust is statically typed, and the compiler will error if it can't determine the type at compile time. Either comment it out for now, give it an explicit type, or use it in such a way that the compiler can see what you're going to put into it.
// Will need this later
// let mut tile_list = vec![];