Function input_just_pressed 

pub fn input_just_pressed<T>(
    input: T,
) -> impl FnMut(Res<'_, ButtonInput<T>>) -> bool + Clone
where
    T: Copy + Eq + Hash + Send + Sync + 'static,

Run condition that is active if ButtonInput::just_pressed is true for the given input.

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Update, jump.run_if(input_just_pressed(KeyCode::Space)))
        .run();
}