[Merged by Bors] - Fix label macro for types with generics

[TheRawMeatball]

Fixes #1497

[aevyrie]

I switched to this PR branch, but am still seeing a type error with the following code:

#[derive(Debug, Hash, PartialEq, Eq, Clone, SystemLabel)]
pub enum BoundingSystem<T> {
    UpdateBoundVols(PhantomData<T>),
    UpdateDebugMeshes(PhantomData<T>),
}

errors:

error[E0107]: wrong number of type arguments: expected 1, found 0
  --> src\lib.rs:17:10
   |
17 | pub enum BoundingSystem<T> {
   |          ^^^^^^^^^^^^^^ expected 1 type argument

error[E0107]: wrong number of type arguments: expected 0, found 1
  --> src\lib.rs:17:25
   |
17 | pub enum BoundingSystem<T> {
   |                         ^ unexpected type argument

error[E0277]: the trait bound `BoundingSystem<T>: bevy::prelude::SystemLabel` is not satisfied
  --> src\lib.rs:36:28
   |
36 |                     .label(BoundingSystem::UpdateBoundVols(PhantomData::<T>::default())),
   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `bevy::prelude::SystemLabel` is 
not implemented for `BoundingSystem<T>`

[aevyrie]

With the most recent change (and a lot of derives 🙂) this seems to fix the type errors.

However, from a useability standpoint, I'm finding it impossible to get this working due to all the trait bounds. My goal is to use my components as types in generic systems. However, when multiple generic systems are run that need labels, my system dependencies are between systems of the same type - my components being the type - but this adds a ton of trait bounds on my component types. Is there some way I could wrap my components in something like a Box<> that implements all the SystemLabel functionality, without my components exploding with trait bound complexity?

I think what I'm doing here is a natural extension of generic systems, and the issues I'm running into are a repercussion of using strongly typed labels.

[TheRawMeatball]

Hmm, can you post a snippet?

[aevyrie]

Hmm, can you post a snippet?

Here's an example: https://github.com/aevyrie/bevy_mod_bounding/blob/9f5a1169fd742f58bac342c883df2001881594a0/src/lib.rs#L17-L25

I pushed the broken code to master.

[aevyrie]

My issue has been resolved here: #1497

[Ratysz]

Hmm, can you post a snippet?

Here's an example: https://github.com/aevyrie/bevy_mod_bounding/blob/9f5a1169fd742f58bac342c883df2001881594a0/src/lib.rs#L17-L25

I pushed the broken code to master.

Changing

PhantomData<T>: 'static + Clone + Hash + Debug + Eq + Send + Sync + BoundingVolume,

to

T: 'static + Clone + Hash + Debug + Eq + Send + Sync + BoundingVolume,

allows this to compile.

EDIT: Oh, I see the problem. If you can't make the relevant BoundingVolume implementors satisfy all those requirements, you'll have to manually implement those traits on BoundingSystem - deriving them directly won't work.

[cart]

bors r+

[bors]

Pull request successfully merged into main.

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