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: custom_diagnostic.rs
    path of file: ./repos/bevy/examples/diagnostics
    
    the code of the file until where you have to start completion: //! This example illustrates how to create a custom diagnostic.

use bevy::{
    diagnostic::{
        Diagnostic, DiagnosticPath, Diagnostics, LogDiagnosticsPlugin, RegisterDiagnostic,
    },
    prelude::*,
};

fn main() {
    App::new()
        .add_plugin
    
fn main() {
    App::new()
        .add_plugins((
            DefaultPlugins,
            // The "print diagnostics" plugin is optional.
            // It just visualizes our diagnostics in the console.
            LogDiagnosticsPlugin::default(),
        ))
        // Diagnostics must be initialized before measurements can be added.
        .register_diagnostic(Diagnostic::new(SYSTEM_ITERATION_COUNT).with_suffix(" iterations"))
        .add_systems(Update, my_system)
        .run();
}