Confusing trait bounds on MaterialPlugin

[Lege19]

use bevy::{prelude::*, render::render_resource::AsBindGroup};

//#[derive(Clone, Copy, PartialEq, Eq, Hash)]
struct TestMaterialKey {
    data: u8,
}
impl From<&TestMaterial> for TestMaterialKey {
    fn from(value: &TestMaterial) -> Self {
        Self {
            data: value.data
        }
    }
}

#[derive(Clone, TypePath, AsBindGroup, Asset)]
#[bind_group_data(TestMaterialKey)]
struct TestMaterial {
    data: u8
}
impl Material for TestMaterial { }

fn main() {
    App::new().add_plugins(MaterialPlugin::<TestMaterial>::default()).run();
}

Does not compile, with the error:

error[E0277]: the trait bound `bevy::prelude::MaterialPlugin<TestMaterial>: Plugins<_>` is not satisfied
   --> src/main.rs:23:28
    |
23  |     App::new().add_plugins(MaterialPlugin::<TestMaterial>::default()).run();
    |                ----------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `bevy::bevy_app::plugin::sealed::Plugins<_>` is not implemented for `bevy::prelude::MaterialPlugin<TestMaterial>`
    |                |
    |                required by a bound introduced by this call
    |
    = help: the following other types implement trait `bevy::bevy_app::plugin::sealed::Plugins<Marker>`:
              `()` implements `bevy::bevy_app::plugin::sealed::Plugins<(bevy::bevy_app::plugin::sealed::PluginsTupleMarker,)>`
              `(S,)` implements `bevy::bevy_app::plugin::sealed::Plugins<(bevy::bevy_app::plugin::sealed::PluginsTupleMarker, P)>`
              `(S0, S1)` implements `bevy::bevy_app::plugin::sealed::Plugins<(bevy::bevy_app::plugin::sealed::PluginsTupleMarker, P0, P1)>`
              `(S0, S1, S2)` implements `bevy::bevy_app::plugin::sealed::Plugins<(bevy::bevy_app::plugin::sealed::PluginsTupleMarker, P0, P1, P2)>`
              `(S0, S1, S2, S3)` implements `bevy::bevy_app::plugin::sealed::Plugins<(bevy::bevy_app::plugin::sealed::PluginsTupleMarker, P0, P1, P2, P3)>`
              `(S0, S1, S2, S3, S4)` implements `bevy::bevy_app::plugin::sealed::Plugins<(bevy::bevy_app::plugin::sealed::PluginsTupleMarker, P0, P1, P2, P3, P4)>`
              `(S0, S1, S2, S3, S4, S5)` implements `bevy::bevy_app::plugin::sealed::Plugins<(bevy::bevy_app::plugin::sealed::PluginsTupleMarker, P0, P1, P2, P3, P4, P5)>`
              `(S0, S1, S2, S3, S4, S5, S6)` implements `bevy::bevy_app::plugin::sealed::Plugins<(bevy::bevy_app::plugin::sealed::PluginsTupleMarker, P0, P1, P2, P3, P4, P5, P6)>`
            and 8 others
    = note: required for `bevy::prelude::MaterialPlugin<TestMaterial>` to implement `Plugins<_>`
note: required by a bound in `bevy::prelude::App::add_plugins`
   --> /home/jacobs/.cargo/registry/src/index.crates.io-6f17d22bba15001f/bevy_app-0.15.1/src/app.rs:548:52
    |
548 |     pub fn add_plugins<M>(&mut self, plugins: impl Plugins<M>) -> &mut Self {
    |                                                    ^^^^^^^^^^ required by this bound in `App::add_plugins`

Uncommenting #[derive(Clone, Copy, PartialEq, Eq, Hash)] fixes the error.
The reason this does not work, is that impl Plugin for MaterialPlugin requires <M as AsBindGroup>::Data: PartialEq + Eq + Hash + Clone however this is a pretty sneaky trait bound that is very easy to look over. I think that it should be a trait bound on MaterialPlugin too so that when a user attempts to do this they get a much more useful error. Failing that, I think more attention should be drawn to this in the docs because currently it's very easy to assume that any MaterialPlugin you are allowed to construct would implement Plugin. It's in the name after all.

[BenjaminBrienen]

I think improving the error message without making MaterialPlugin more restrictive would be better. There is an attribute that we can put on the trait to give a better message: #[diagnostic::on_unimplemented()]. I'd try that first.

[Lege19]

I thought about the making it less restrictive thing, and I think I disagree. If something isn't MaterialPlugin only implements Plugin and Default, and has no methods. So the only thing you can do with it is add it as a plugin. It exists to be a plugin. If something is a problem, it should cause an error at the earliest possible "time", so that the error is as close to the source as possible.