I have this function:

pub async fn start_file_server(
    stop_signal: Arc<watch::Receiver<bool>>, // Receiver used to monitor stop signal
) -> Result<(), Box<dyn std::error::Error>> {
    // Define the filter for Warp
    let filter = warp::path("ws")
        .and(warp::ws())
        .map(|ws: warp::ws::Ws| ws.on_upgrade(|socket| handle_ws_connection(socket)));

    // Start the Warp server
    let server = warp::serve(filter).run(([127, 0, 0, 1], 3030));

    // Spawn a task to monitor the stop signal
    let stop_signal_task = tokio::spawn(async move {
        // Wait for the stop signal to change
        let _ = stop_signal.changed().await;
        println!("Stop signal received, shutting down...");
    });

    // Use tokio::select! to wait for either the server to stop or the stop signal to be received
    tokio::select! {
        _ = server => {
            println!("Server stopped.");
        },
        _ = stop_signal_task => {
            // This will be triggered when the stop signal changes
            println!("Received stop signal, exiting...");
        }
    }

    Ok(())
}

stop_signal is a Receiver, but for some reason in let _ = stop_signal.changed().await; I’m getting error:

cannot borrow data in an `Arc` as mutable
trait `DerefMut` is required to modify through a dereference, but it is not implemented for `Arc<tokio::sync::watch::Receiver<bool>>` 

which is weird cause .changed() is not modifying anything and as of my understanding does not borrow anything.

Simplified version of function logic where start_file_server() is called:

let (stop_tx, stop_rx) = watch::channel(false);
let stop_signal = Arc::new(stop_rx);

let file_server_task = {
        let stop_signal = Arc::clone(&stop_signal);

        tokio::spawn(async move {
            if let Err(e) = start_file_server(stop_signal).await {
                eprintln!("Failed to start file server: {}", e);
            }
        })
};

Arc here is only for future where I may use stop_signal in another task. I tested code without using Arc and passing stop_rx to start_file_server() directly, the error stayed.