Function any_with_component 

pub fn any_with_component<T: Component>(
    query: Query<'_, '_, (), With<T>>,
) -> bool

A SystemCondition-satisfying system that returns true if there are any entities with the given component type.

This is equivalent to any_match_filter::<With<T>>()

To skip a system with a Query parameter if the query is empty, you may instead use Populated, if the query may match multiple entities, or Single, if it will only match one.

Example

app.add_systems(
    my_system.run_if(any_with_component::<MyComponent>),
);

#[derive(Component)]
struct MyComponent;

fn my_system(mut counter: ResMut<Counter>) {
    counter.0 += 1;
}

// No entities exist yet with a `MyComponent` component so `my_system` won't run
app.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 0);

world.spawn(MyComponent);

// An entities with `MyComponent` now exists so `my_system` will run
app.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 1);