Logging

The goal: print messages from Rust code to the Output Log.

#![allow(unused)]
fn main() {
log::info!("[MyGame] wave {wave} started");
log::warn!("[MyGame] no spawn points in the level");
log::error!("[MyGame] could not load the save: {e}");
}

Rusteal logs through the log crate, the logging facade of the Rust ecosystem: the projects Rusteal creates depend on it (log = { workspace = true } in the game crate), and the library routes it to the Output Log when it loads. Its messages go under the LogRusteal category, with the level’s color: plain for info!, yellow for warn!, red for error!.

LogRusteal: [MyGame] wave 3 started
LogRusteal: Warning: [MyGame] no spawn points in the level

debug! and trace! are off by default. Turn them on, for the whole library, where it starts:

#![allow(unused)]
fn main() {
fn verbose_logs() {
    log::set_max_level(log::LevelFilter::Debug);
}

rusteal_runtime::on_load!(verbose_logs);
}

They show at the display level, like info!. The crates your game depends on that log through log (most do) show in the Output Log the same way.

A project made before Rusteal routed log has no log dependency: add log = "0.4" to [workspace.dependencies] in Rust/Cargo.toml and log = { workspace = true } to the game crate’s [dependencies]. Its ulog! calls keep working.

Filtering

In the Output Log tab, Filters > Categories can show LogRusteal alone. A prefix of your own at the start of each message ([MyGame], [Inventory]) makes them easy to find with the search box as well.

Screenshot: the Output Log filtered to the LogRusteal category. (images/iteration/output_log_filter.png)

Errors that reach the log by themselves

Some failures are logged without any code of yours:

• A panic in your code is caught where the engine called into Rust, and logged as an error. The editor keeps running; the function that panicked stops there.
• A function bound by name (an input action, a delegate, a timer) that does not exist is logged with its name.
• A library built against another Rusteal version is refused, with both versions in the log.

Logging a RustealResult

Engine calls that can fail return a RustealResult. A common pattern is to put the work in a method that returns one, and log the error in the event that calls it:

#![allow(unused)]
fn main() {
#[ufunction(Override)]
fn receive_begin_play(&mut self) {
    if let Err(e) = self.setup() {
        log::warn!("[MyGame] setup failed: {e}");
    }
}
}

See Errors.