Add reflection for resources (#5175)

# Objective

We don't have reflection for resources.

## Solution

Introduce reflection for resources.

Continues #3580 (by @Davier), related to #3576.

---

## Changelog

### Added

* Reflection on a resource type (by adding `ReflectResource`):

```rust
#[derive(Reflect)]
#[reflect(Resource)]
struct MyResourse;
```

### Changed

* Rename `ReflectComponent::add_component` into `ReflectComponent::insert_component` for consistency.

## Migration Guide

* Rename `ReflectComponent::add_component` into `ReflectComponent::insert_component`.

crates/bevy_core_pipeline/src/clear_color.rs

@@ -17,7 +17,8 @@ pub enum ClearColorConfig {
 ///
 /// This color appears as the "background" color for simple apps, when
 /// there are portions of the screen with nothing rendered.
-#[derive(Component, Clone, Debug, Deref, DerefMut, ExtractResource)]
+#[derive(Component, Clone, Debug, Deref, DerefMut, ExtractResource, Reflect)]
+#[reflect(Resource)]
 pub struct ClearColor(pub Color);
 
 impl Default for ClearColor {

crates/bevy_core_pipeline/src/lib.rs

@@ -20,7 +20,8 @@ pub struct CorePipelinePlugin;
 
 impl Plugin for CorePipelinePlugin {
     fn build(&self, app: &mut App) {
-        app.init_resource::<ClearColor>()
+        app.register_type::<ClearColor>()
+            .init_resource::<ClearColor>()
             .add_plugin(ExtractResourcePlugin::<ClearColor>::default())
             .add_plugin(Core2dPlugin)
             .add_plugin(Core3dPlugin);

crates/bevy_ecs/src/change_detection.rs

@@ -216,7 +216,7 @@ change_detection_impl!(Mut<'a, T>, T,);
 impl_into_inner!(Mut<'a, T>, T,);
 impl_debug!(Mut<'a, T>,);
 
-/// Unique mutable borrow of a Reflected component
+/// Unique mutable borrow of a reflected component or resource
 #[cfg(feature = "bevy_reflect")]
 pub struct ReflectMut<'a> {
     pub(crate) value: &'a mut dyn Reflect,

crates/bevy_ecs/src/lib.rs

@@ -23,7 +23,7 @@ pub use bevy_ptr as ptr;
 pub mod prelude {
     #[doc(hidden)]
     #[cfg(feature = "bevy_reflect")]
-    pub use crate::reflect::ReflectComponent;
+    pub use crate::reflect::{ReflectComponent, ReflectResource};
     #[doc(hidden)]
     pub use crate::{
         bundle::Bundle,

crates/bevy_ecs/src/reflect.rs

@@ -4,6 +4,7 @@ pub use crate::change_detection::ReflectMut;
 use crate::{
     component::Component,
     entity::{Entity, EntityMap, MapEntities, MapEntitiesError},
+    system::Resource,
     world::{FromWorld, World},
 };
 use bevy_reflect::{
@@ -11,6 +12,10 @@ use bevy_reflect::{
     ReflectSerialize,
 };
 
+/// A struct used to operate on reflected [`Component`] of a type.
+///
+/// A [`ReflectComponent`] for type `T` can be obtained via
+/// [`bevy_reflect::TypeRegistration::data`].
 #[derive(Clone)]
 pub struct ReflectComponent {
     add_component: fn(&mut World, Entity, &dyn Reflect),
@@ -22,18 +27,34 @@ pub struct ReflectComponent {
 }
 
 impl ReflectComponent {
+    /// Insert a reflected [`Component`] into the entity like [`insert()`](crate::world::EntityMut::insert).
+    ///
+    /// # Panics
+    ///
+    /// Panics if there is no such entity.
     pub fn add_component(&self, world: &mut World, entity: Entity, component: &dyn Reflect) {
         (self.add_component)(world, entity, component);
     }
 
+    /// Uses reflection to set the value of this [`Component`] type in the entity to the given value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if there is no [`Component`] of the given type or the `entity` does not exist.
     pub fn apply_component(&self, world: &mut World, entity: Entity, component: &dyn Reflect) {
         (self.apply_component)(world, entity, component);
     }
 
+    /// Removes this [`Component`] type from the entity. Does nothing if it doesn't exist.
+    ///
+    /// # Panics
+    ///
+    /// Panics if there is no [`Component`] of the given type or the `entity` does not exist.
     pub fn remove_component(&self, world: &mut World, entity: Entity) {
         (self.remove_component)(world, entity);
     }
 
+    /// Gets the value of this [`Component`] type from the entity as a reflected reference.
     pub fn reflect_component<'a>(
         &self,
         world: &'a World,
@@ -42,6 +63,7 @@ impl ReflectComponent {
         (self.reflect_component)(world, entity)
     }
 
+    /// Gets the value of this [`Component`] type from the entity as a mutable reflected reference.
     pub fn reflect_component_mut<'a>(
         &self,
         world: &'a mut World,
@@ -56,7 +78,7 @@ impl ReflectComponent {
     /// violating Rust's aliasing rules. To avoid this:
     /// * Only call this method in an exclusive system to avoid sharing across threads (or use a
     ///   scheduler that enforces safe memory access).
-    /// * Don't call this method more than once in the same scope for a given component.
+    /// * Don't call this method more than once in the same scope for a given [`Component`].
     pub unsafe fn reflect_component_unchecked_mut<'a>(
         &self,
         world: &'a World,
@@ -65,6 +87,11 @@ impl ReflectComponent {
         (self.reflect_component_mut)(world, entity)
     }
 
+    /// Gets the value of this [`Component`] type from entity from `source_world` and [applies](Self::apply_component()) it to the value of this [`Component`] type in entity in `destination_world`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if there is no [`Component`] of the given type or either entity does not exist.
     pub fn copy_component(
         &self,
         source_world: &World,
@@ -123,6 +150,108 @@ impl<C: Component + Reflect + FromWorld> FromType<C> for ReflectComponent {
     }
 }
 
+/// A struct used to operate on reflected [`Resource`] of a type.
+///
+/// A [`ReflectResource`] for type `T` can be obtained via
+/// [`bevy_reflect::TypeRegistration::data`].
+#[derive(Clone)]
+pub struct ReflectResource {
+    insert_resource: fn(&mut World, &dyn Reflect),
+    apply_resource: fn(&mut World, &dyn Reflect),
+    remove_resource: fn(&mut World),
+    reflect_resource: fn(&World) -> Option<&dyn Reflect>,
+    reflect_resource_unchecked_mut: unsafe fn(&World) -> Option<ReflectMut>,
+    copy_resource: fn(&World, &mut World),
+}
+
+impl ReflectResource {
+    /// Insert a reflected [`Resource`] into the world like [`insert_resource()`](World::insert_resource).
+    pub fn insert_resource(&self, world: &mut World, resource: &dyn Reflect) {
+        (self.insert_resource)(world, resource);
+    }
+
+    /// Uses reflection to set the value of this [`Resource`] type in the world to the given value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if there is no [`Resource`] of the given type.
+    pub fn apply_resource(&self, world: &mut World, resource: &dyn Reflect) {
+        (self.apply_resource)(world, resource);
+    }
+
+    /// Removes this [`Resource`] type from the world. Does nothing if it doesn't exist.
+    pub fn remove_resource(&self, world: &mut World) {
+        (self.remove_resource)(world);
+    }
+
+    /// Gets the value of this [`Resource`] type from the world as a reflected reference.
+    pub fn reflect_resource<'a>(&self, world: &'a World) -> Option<&'a dyn Reflect> {
+        (self.reflect_resource)(world)
+    }
+
+    /// Gets the value of this [`Resource`] type from the world as a mutable reflected reference.
+    pub fn reflect_resource_mut<'a>(&self, world: &'a mut World) -> Option<ReflectMut<'a>> {
+        // SAFE: unique world access
+        unsafe { (self.reflect_resource_unchecked_mut)(world) }
+    }
+
+    /// # Safety
+    /// This method does not prevent you from having two mutable pointers to the same data,
+    /// violating Rust's aliasing rules. To avoid this:
+    /// * Only call this method in an exclusive system to avoid sharing across threads (or use a
+    ///   scheduler that enforces safe memory access).
+    /// * Don't call this method more than once in the same scope for a given [`Resource`].
+    pub unsafe fn reflect_resource_unckecked_mut<'a>(
+        &self,
+        world: &'a World,
+    ) -> Option<ReflectMut<'a>> {
+        (self.reflect_resource_unchecked_mut)(world)
+    }
+
+    /// Gets the value of this [`Resource`] type from `source_world` and [applies](Self::apply_resource()) it to the value of this [`Resource`] type in `destination_world`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if there is no [`Resource`] of the given type.
+    pub fn copy_resource(&self, source_world: &World, destination_world: &mut World) {
+        (self.copy_resource)(source_world, destination_world);
+    }
+}
+
+impl<C: Resource + Reflect + FromWorld> FromType<C> for ReflectResource {
+    fn from_type() -> Self {
+        ReflectResource {
+            insert_resource: |world, reflected_resource| {
+                let mut resource = C::from_world(world);
+                resource.apply(reflected_resource);
+                world.insert_resource(resource);
+            },
+            apply_resource: |world, reflected_resource| {
+                let mut resource = world.resource_mut::<C>();
+                resource.apply(reflected_resource);
+            },
+            remove_resource: |world| {
+                world.remove_resource::<C>();
+            },
+            reflect_resource: |world| world.get_resource::<C>().map(|res| res as &dyn Reflect),
+            reflect_resource_unchecked_mut: |world| unsafe {
+                world
+                    .get_resource_unchecked_mut::<C>()
+                    .map(|res| ReflectMut {
+                        value: res.value as &mut dyn Reflect,
+                        ticks: res.ticks,
+                    })
+            },
+            copy_resource: |source_world, destination_world| {
+                let source_resource = source_world.resource::<C>();
+                let mut destination_resource = C::from_world(destination_world);
+                destination_resource.apply(source_resource);
+                destination_world.insert_resource(destination_resource);
+            },
+        }
+    }
+}
+
 impl_reflect_value!(Entity(Hash, PartialEq, Serialize, Deserialize));
 impl_from_reflect_value!(Entity);
 

crates/bevy_pbr/src/lib.rs

@@ -125,6 +125,9 @@ impl Plugin for PbrPlugin {
             .register_type::<PointLight>()
             .add_plugin(MeshRenderPlugin)
             .add_plugin(MaterialPlugin::<StandardMaterial>::default())
+            .register_type::<AmbientLight>()
+            .register_type::<DirectionalLightShadowMap>()
+            .register_type::<PointLightShadowMap>()
             .init_resource::<AmbientLight>()
             .init_resource::<GlobalVisiblePointLights>()
             .init_resource::<DirectionalLightShadowMap>()

crates/bevy_pbr/src/light.rs

@@ -73,7 +73,8 @@ impl PointLight {
     pub const DEFAULT_SHADOW_NORMAL_BIAS: f32 = 0.6;
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Reflect)]
+#[reflect(Resource)]
 pub struct PointLightShadowMap {
     pub size: usize,
 }
@@ -151,7 +152,8 @@ impl DirectionalLight {
     pub const DEFAULT_SHADOW_NORMAL_BIAS: f32 = 0.6;
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Reflect)]
+#[reflect(Resource)]
 pub struct DirectionalLightShadowMap {
     pub size: usize,
 }
@@ -166,7 +168,8 @@ impl Default for DirectionalLightShadowMap {
 }
 
 /// An ambient light, which lights the entire scene equally.
-#[derive(Clone, Debug, ExtractResource)]
+#[derive(Clone, Debug, ExtractResource, Reflect)]
+#[reflect(Resource)]
 pub struct AmbientLight {
     pub color: Color,
     /// A direct scale factor multiplied with `color` before being passed to the shader.

crates/bevy_pbr/src/wireframe.rs

@@ -35,7 +35,8 @@ impl Plugin for WireframePlugin {
             Shader::from_wgsl
         );
 
-        app.init_resource::<WireframeConfig>()
+        app.register_type::<WireframeConfig>()
+            .init_resource::<WireframeConfig>()
             .add_plugin(ExtractResourcePlugin::<WireframeConfig>::default());
 
         if let Ok(render_app) = app.get_sub_app_mut(RenderApp) {
@@ -60,7 +61,8 @@ fn extract_wireframes(mut commands: Commands, query: Query<Entity, With<Wirefram
 #[reflect(Component, Default)]
 pub struct Wireframe;
 
-#[derive(Debug, Clone, Default, ExtractResource)]
+#[derive(Debug, Clone, Default, ExtractResource, Reflect)]
+#[reflect(Resource)]
 pub struct WireframeConfig {
     /// Whether to show wireframes for all meshes. If `false`, only meshes with a [Wireframe] component will be rendered.
     pub global: bool,

crates/bevy_render/src/view/mod.rs

@@ -21,6 +21,7 @@ use crate::{
 use bevy_app::{App, Plugin};
 use bevy_ecs::prelude::*;
 use bevy_math::{Mat4, Vec3};
+use bevy_reflect::Reflect;
 use bevy_transform::components::GlobalTransform;
 use bevy_utils::HashMap;
 
@@ -28,7 +29,8 @@ pub struct ViewPlugin;
 
 impl Plugin for ViewPlugin {
     fn build(&self, app: &mut App) {
-        app.init_resource::<Msaa>()
+        app.register_type::<Msaa>()
+            .init_resource::<Msaa>()
             // NOTE: windows.is_changed() handles cases where a window was resized
             .add_plugin(ExtractResourcePlugin::<Msaa>::default())
             .add_plugin(VisibilityPlugin);
@@ -45,7 +47,6 @@ impl Plugin for ViewPlugin {
     }
 }
 
-#[derive(Clone, ExtractResource)]
 /// Configuration resource for [Multi-Sample Anti-Aliasing](https://en.wikipedia.org/wiki/Multisample_anti-aliasing).
 ///
 /// # Example
@@ -56,6 +57,8 @@ impl Plugin for ViewPlugin {
 ///     .insert_resource(Msaa { samples: 4 })
 ///     .run();
 /// ```
+#[derive(Clone, ExtractResource, Reflect)]
+#[reflect(Resource)]
 pub struct Msaa {
     /// The number of samples to run for Multi-Sample Anti-Aliasing. Higher numbers result in
     /// smoother edges.