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: trees.rs
    path of file: ./repos/noxfutura/nox_planet/src/region/builder
    
    the code of the file until where you have to start completion: use crate::{ground_z, Region, TileType};
use bengine::geometry::*;
use bengine::random::*;
use legion::*;
use nox_raws::*;
use nox_spatial::*;
use parking_lot::RwLock;

lazy_static! {
    static
    
fn can_see_sky(region: &Region, x: usize, y: usize, z: usize) -> bool {
    let mut sz = z + 1;
    while sz < REGION_DEPTH {
        if region.tile_types[mapidx(x, y, sz)] != TileType::Empty {
            return false;
        }
        sz += 1;
    }
    true
}