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/rustrogueliketutorial/chapter-61-townportal/src
    
    the code of the file until where you have to start completion: extern crate serde;
use rltk::{GameState, Rltk, Point};
use specs::prelude::*;
use specs::
    
    fn goto_level(&mut self, offset: i32) {
        freeze_level_entities(&mut self.ecs);

        // Build a new map and place the player
        let current_depth = self.ecs.fetch::<Map>().depth;
        self.generate_world_map(current_depth + offset, offset);

        // Notify the player
        let mut gamelog = self.ecs.fetch_mut::<gamelog::GameLog>();
        gamelog.entries.push("You change level.".to_string());
    }