Simplify the ComponentIdFor type

[JoJoJet]

Objective

ComponentIdFor is a type that gives you access to a component's ComponentId in a system. It is currently awkward to use, since it must be wrapped in a Local<> to be used.

Solution

Make ComponentIdFor a proper SystemParam.

---

Changelog

• Refactored the type ComponentIdFor in order to simplify how it is used.

Migration Guide

The type ComponentIdFor<T> now implements SystemParam instead of FromWorld -- this means it should be used as the parameter for a system directly instead of being used in a Local.

// Before:
fn my_system(
    component_id: Local<ComponentIdFor<MyComponent>>,
) {
    let component_id = **component_id;
}

// After:
fn my_system(
    component_id: ComponentIdFor<MyComponent>,
) {
    let component_id = component_id.get();
}

[Aceeri]

What this bein used for?

[JoJoJet]

Our derive macros don't know the difference between bevy_ecs and a third party crate, so we need to include this anytime we use a derive from within bevy_ecs. It's a very annoying issue that, as far as I know, can't be fixed without changes to rustc.

[alice-i-cecile]

Yeah I've run into this before and never found a satisfying workaround.

[Aceeri]

Ah ya, forgot about that req, looks good to me :)

[alice-i-cecile]

Agreed: this is cleaner.

[MrGVSV]

Had no idea this even existed 😳