Compiler Error on `#[derive(Bundle)]` for Generic Bundles in 0.16

[Zeenobit]

Bevy version

Bevy 0.16

What you did

This is a follow up to this discussion.

The following code no longer compiles as of Bevy 0.16:

use bevy::prelude::*;

#[derive(Bundle)]
struct Foo<T: Bundle>(T);

error[E0277]: the trait bound `T: BundleFromComponents` is not satisfied

I understand this requires BundleFromComponent trait bound to work because of the new changes to Bundles:

use bevy::prelude::*;
use bevy::ecs::bundle::BundleFromComponents;

#[derive(Bundle)]
struct Foo<T: Bundle + BundleFromComponents>(T);

However, as discussed, this feels like a regression since BundleFromComponents is mostly an implementation detail (to me, at least).

Additional information

Some solutions that come to my mind:

• We could have Bundle require BundleFromComponents as a trait bound. But this makes me wonder why this trait was split out to begin with.
• We could introduce a new CompleteBundle trait (naming is hard) which does require BundleFromComponent and change derive(Bundle) to derive(CompleteBundle) instead.

[alice-i-cecile]

#3227 is related, as both involve refactors to the Bundle family of traits.