bevy/crates/bevy_asset/src/filesystem_watcher.rs

use crossbeam_channel::Receiver;
use notify::{Event, RecommendedWatcher, RecursiveMode, Result, Watcher};
use std::path::Path;

/// Watches for changes to assets on the filesystem. This is used by the `AssetServer` to reload them
pub struct FilesystemWatcher {
    pub watcher: RecommendedWatcher,
    pub receiver: Receiver<Result<Event>>,
}

impl Default for FilesystemWatcher {
    fn default() -> Self {
        let (sender, receiver) = crossbeam_channel::unbounded();
        let watcher: RecommendedWatcher = Watcher::new_immediate(move |res| {
            sender.send(res).expect("Watch event send failure.");
        })
        .expect("Failed to create filesystem watcher.");
        FilesystemWatcher { watcher, receiver }
    }
}

impl FilesystemWatcher {
    pub fn watch<P: AsRef<Path>>(&mut self, path: P) -> Result<()> {
        self.watcher.watch(path, RecursiveMode::Recursive)
    }
}