(De) serialize resources in scenes (#6846)

# Objective

Co-Authored-By: davier
[bricedavier@gmail.com](mailto:bricedavier@gmail.com)
Fixes #3576.
Adds a `resources` field in scene serialization data to allow
de/serializing resources that have reflection enabled.

## Solution

Most of this code is taken from a previous closed PR:
https://github.com/bevyengine/bevy/pull/3580. Most of the credit goes to
@Davier , what I did was mostly getting it to work on the latest main
branch of Bevy, along with adding a few asserts in the currently
existing tests to be sure everything is working properly.

This PR changes the scene format to include resources in this way:
```
(
  resources: {
    // List of resources here, keyed by resource type name.
  },
  entities: [
    // Previous scene format here
  ],
)
```

An example taken from the tests:
```
(
  resources: {
    "bevy_scene::serde::tests::MyResource": (
      foo: 123,
    ),
  },
  entities: {
    // Previous scene format here
  },
)
```
For this, a `resources` fields has been added on the `DynamicScene` and
the `DynamicSceneBuilder` structs. The latter now also has a method
named `extract_resources` to properly extract the existing resources
registered in the local type registry, in a similar way to
`extract_entities`.


---

## Changelog


Added: Reflect resources registered in the type registry used by dynamic
scenes will now be properly de/serialized in scene data.

## Migration Guide

Since the scene format has been changed, the user may not be able to use
scenes saved prior to this PR due to the `resources` scene field being
missing. ~~To preserve backwards compatibility, I will try to make the
`resources` fully optional so that old scenes can be loaded without
issue.~~

## TODOs

- [x] I may have to update a few doc blocks still referring to dynamic
scenes as mere container of entities, since they now include resources
as well.
- [x] ~~I want to make the `resources` key optional, as specified in the
Migration Guide, so that old scenes will be compatible with this
change.~~ Since this would only be trivial for ron format, I think it
might be better to consider it in a separate PR/discussion to figure out
if it could be done for binary serialization too.
- [x] I suppose it might be a good idea to add a resources in the scene
example so that users will quickly notice they can serialize resources
just like entities.

---------

Co-authored-by: Carter Anderson <mcanders1@gmail.com>

assets/scenes/load_scene_example.scn.ron

@@ -1,4 +1,9 @@
 (
+  resources: {
+    "scene::ResourceA": (
+      score: 2,
+    ),
+  },
   entities: {
     0: (
       components: {

crates/bevy_scene/src/dynamic_scene.rs

@@ -10,10 +10,13 @@ use bevy_reflect::{Reflect, TypeRegistryArc, TypeUuid};
 
 #[cfg(feature = "serialize")]
 use crate::serde::SceneSerializer;
+use bevy_ecs::reflect::ReflectResource;
 #[cfg(feature = "serialize")]
 use serde::Serialize;
 
-/// A collection of serializable dynamic entities, each with its own run-time defined set of components.
+/// A collection of serializable resources and dynamic entities.
+///
+/// Each dynamic entity in the collection contains its own run-time defined set of components.
 /// To spawn a dynamic scene, you can use either:
 /// * [`SceneSpawner::spawn_dynamic`](crate::SceneSpawner::spawn_dynamic)
 /// * adding the [`DynamicSceneBundle`](crate::DynamicSceneBundle) to an entity
@@ -23,6 +26,7 @@ use serde::Serialize;
 #[derive(Default, TypeUuid)]
 #[uuid = "749479b1-fb8c-4ff8-a775-623aa76014f5"]
 pub struct DynamicScene {
+    pub resources: Vec<Box<dyn Reflect>>,
     pub entities: Vec<DynamicEntity>,
 }
 
@@ -47,15 +51,16 @@ impl DynamicScene {
             DynamicSceneBuilder::from_world_with_type_registry(world, type_registry.clone());
 
         builder.extract_entities(world.iter_entities().map(|entity| entity.id()));
+        builder.extract_resources();
 
         builder.build()
     }
 
-    /// Write the dynamic entities and their corresponding components to the given world.
+    /// Write the resources, the dynamic entities, and their corresponding components to the given world.
     ///
     /// This method will return a [`SceneSpawnError`] if a type either is not registered
     /// in the provided [`AppTypeRegistry`] resource, or doesn't reflect the
-    /// [`Component`](bevy_ecs::component::Component) trait.
+    /// [`Component`](bevy_ecs::component::Component) or [`Resource`](bevy_ecs::prelude::Resource) trait.
     pub fn write_to_world_with(
         &self,
         world: &mut World,
@@ -64,6 +69,23 @@ impl DynamicScene {
     ) -> Result<(), SceneSpawnError> {
         let type_registry = type_registry.read();
 
+        for resource in &self.resources {
+            let registration = type_registry
+                .get_with_name(resource.type_name())
+                .ok_or_else(|| SceneSpawnError::UnregisteredType {
+                    type_name: resource.type_name().to_string(),
+                })?;
+            let reflect_resource = registration.data::<ReflectResource>().ok_or_else(|| {
+                SceneSpawnError::UnregisteredResource {
+                    type_name: resource.type_name().to_string(),
+                }
+            })?;
+
+            // If the world already contains an instance of the given resource
+            // just apply the (possibly) new value, otherwise insert the resource
+            reflect_resource.apply_or_insert(world, &**resource);
+        }
+
         for scene_entity in &self.entities {
             // Fetch the entity with the given entity id from the `entity_map`
             // or spawn a new entity with a transiently unique id if there is
@@ -105,7 +127,7 @@ impl DynamicScene {
         Ok(())
     }
 
-    /// Write the dynamic entities and their corresponding components to the given world.
+    /// Write the resources, the dynamic entities, and their corresponding components to the given world.
     ///
     /// This method will return a [`SceneSpawnError`] if a type either is not registered
     /// in the world's [`AppTypeRegistry`] resource, or doesn't reflect the

crates/bevy_scene/src/dynamic_scene_builder.rs

@@ -1,10 +1,16 @@
 use crate::{DynamicEntity, DynamicScene};
 use bevy_app::AppTypeRegistry;
-use bevy_ecs::{prelude::Entity, reflect::ReflectComponent, world::World};
+use bevy_ecs::component::ComponentId;
+use bevy_ecs::{
+    prelude::Entity,
+    reflect::{ReflectComponent, ReflectResource},
+    world::World,
+};
+use bevy_reflect::Reflect;
 use bevy_utils::default;
 use std::collections::BTreeMap;
 
-/// A [`DynamicScene`] builder, used to build a scene from a [`World`] by extracting some entities.
+/// A [`DynamicScene`] builder, used to build a scene from a [`World`] by extracting some entities and resources.
 ///
 /// # Entity Order
 ///
@@ -31,6 +37,7 @@ use std::collections::BTreeMap;
 /// let dynamic_scene = builder.build();
 /// ```
 pub struct DynamicSceneBuilder<'w> {
+    extracted_resources: BTreeMap<ComponentId, Box<dyn Reflect>>,
     extracted_scene: BTreeMap<u32, DynamicEntity>,
     type_registry: AppTypeRegistry,
     original_world: &'w World,
@@ -41,6 +48,7 @@ impl<'w> DynamicSceneBuilder<'w> {
     /// All components registered in that world's [`AppTypeRegistry`] resource will be extracted.
     pub fn from_world(world: &'w World) -> Self {
         Self {
+            extracted_resources: default(),
             extracted_scene: default(),
             type_registry: world.resource::<AppTypeRegistry>().clone(),
             original_world: world,
@@ -51,6 +59,7 @@ impl<'w> DynamicSceneBuilder<'w> {
     /// Only components registered in the given [`AppTypeRegistry`] will be extracted.
     pub fn from_world_with_type_registry(world: &'w World, type_registry: AppTypeRegistry) -> Self {
         Self {
+            extracted_resources: default(),
             extracted_scene: default(),
             type_registry,
             original_world: world,
@@ -63,6 +72,7 @@ impl<'w> DynamicSceneBuilder<'w> {
     /// [`Self::remove_empty_entities`] before building the scene.
     pub fn build(self) -> DynamicScene {
         DynamicScene {
+            resources: self.extracted_resources.into_values().collect(),
             entities: self.extracted_scene.into_values().collect(),
         }
     }
@@ -126,17 +136,20 @@ impl<'w> DynamicSceneBuilder<'w> {
 
             let entity = self.original_world.entity(entity);
             for component_id in entity.archetype().components() {
-                let reflect_component = self
+                let mut extract_and_push = || {
-                    .original_world
+                    let type_id = self
-                    .components()
+                        .original_world
-                    .get_info(component_id)
+                        .components()
-                    .and_then(|info| type_registry.get(info.type_id().unwrap()))
+                        .get_info(component_id)?
-                    .and_then(|registration| registration.data::<ReflectComponent>())
+                        .type_id()?;
-                    .and_then(|reflect_component| reflect_component.reflect(entity));
+                    let component = type_registry
-
+                        .get(type_id)?
-                if let Some(reflect_component) = reflect_component {
+                        .data::<ReflectComponent>()?
-                    entry.components.push(reflect_component.clone_value());
+                        .reflect(entity)?;
-                }
+                    entry.components.push(component.clone_value());
+                    Some(())
+                };
+                extract_and_push();
             }
             self.extracted_scene.insert(index, entry);
         }
@@ -144,13 +157,59 @@ impl<'w> DynamicSceneBuilder<'w> {
         drop(type_registry);
         self
     }
+
+    /// Extract resources from the builder's [`World`].
+    ///
+    /// Only resources registered in the builder's [`AppTypeRegistry`] will be extracted.
+    /// Re-extracting a resource that was already extracted will have no effect.
+    /// ```
+    /// # use bevy_scene::DynamicSceneBuilder;
+    /// # use bevy_app::AppTypeRegistry;
+    /// # use bevy_ecs::prelude::{ReflectResource, Resource, World};
+    /// # use bevy_reflect::Reflect;
+    /// #[derive(Resource, Default, Reflect)]
+    /// #[reflect(Resource)]
+    /// struct MyResource;
+    ///
+    /// # let mut world = World::default();
+    /// # world.init_resource::<AppTypeRegistry>();
+    /// world.insert_resource(MyResource);
+    ///
+    /// let mut builder = DynamicSceneBuilder::from_world(&world);
+    /// builder.extract_resources();
+    /// let scene = builder.build();
+    /// ```
+    pub fn extract_resources(&mut self) -> &mut Self {
+        let type_registry = self.type_registry.read();
+        for (component_id, _) in self.original_world.storages().resources.iter() {
+            let mut extract_and_push = || {
+                let type_id = self
+                    .original_world
+                    .components()
+                    .get_info(component_id)?
+                    .type_id()?;
+                let resource = type_registry
+                    .get(type_id)?
+                    .data::<ReflectResource>()?
+                    .reflect(self.original_world)?;
+                self.extracted_resources
+                    .insert(component_id, resource.clone_value());
+                Some(())
+            };
+            extract_and_push();
+        }
+
+        drop(type_registry);
+        self
+    }
 }
 
 #[cfg(test)]
 mod tests {
     use bevy_app::AppTypeRegistry;
     use bevy_ecs::{
-        component::Component, prelude::Entity, query::With, reflect::ReflectComponent, world::World,
+        component::Component, prelude::Entity, prelude::Resource, query::With,
+        reflect::ReflectComponent, reflect::ReflectResource, world::World,
     };
 
     use bevy_reflect::Reflect;
@@ -160,10 +219,15 @@ mod tests {
     #[derive(Component, Reflect, Default, Eq, PartialEq, Debug)]
     #[reflect(Component)]
     struct ComponentA;
+
     #[derive(Component, Reflect, Default, Eq, PartialEq, Debug)]
     #[reflect(Component)]
     struct ComponentB;
 
+    #[derive(Resource, Reflect, Default, Eq, PartialEq, Debug)]
+    #[reflect(Resource)]
+    struct ResourceA;
+
     #[test]
     fn extract_one_entity() {
         let mut world = World::default();
@@ -303,4 +367,41 @@ mod tests {
         assert_eq!(scene.entities.len(), 1);
         assert_eq!(scene.entities[0].entity, entity_a.index());
     }
+
+    #[test]
+    fn extract_one_resource() {
+        let mut world = World::default();
+
+        let atr = AppTypeRegistry::default();
+        atr.write().register::<ResourceA>();
+        world.insert_resource(atr);
+
+        world.insert_resource(ResourceA);
+
+        let mut builder = DynamicSceneBuilder::from_world(&world);
+        builder.extract_resources();
+        let scene = builder.build();
+
+        assert_eq!(scene.resources.len(), 1);
+        assert!(scene.resources[0].represents::<ResourceA>());
+    }
+
+    #[test]
+    fn extract_one_resource_twice() {
+        let mut world = World::default();
+
+        let atr = AppTypeRegistry::default();
+        atr.write().register::<ResourceA>();
+        world.insert_resource(atr);
+
+        world.insert_resource(ResourceA);
+
+        let mut builder = DynamicSceneBuilder::from_world(&world);
+        builder.extract_resources();
+        builder.extract_resources();
+        let scene = builder.build();
+
+        assert_eq!(scene.resources.len(), 1);
+        assert!(scene.resources[0].represents::<ResourceA>());
+    }
 }

crates/bevy_scene/src/scene.rs

@@ -1,7 +1,7 @@
 use bevy_app::AppTypeRegistry;
 use bevy_ecs::{
     entity::EntityMap,
-    reflect::{ReflectComponent, ReflectMapEntities},
+    reflect::{ReflectComponent, ReflectMapEntities, ReflectResource},
     world::World,
 };
 use bevy_reflect::TypeUuid;
@@ -61,6 +61,33 @@ impl Scene {
         };
 
         let type_registry = type_registry.read();
+
+        // Resources archetype
+        for (component_id, _) in self.world.storages().resources.iter() {
+            let component_info = self
+                .world
+                .components()
+                .get_info(component_id)
+                .expect("component_ids in archetypes should have ComponentInfo");
+
+            let type_id = component_info
+                .type_id()
+                .expect("reflected resources must have a type_id");
+
+            let registration =
+                type_registry
+                    .get(type_id)
+                    .ok_or_else(|| SceneSpawnError::UnregisteredType {
+                        type_name: component_info.name().to_string(),
+                    })?;
+            let reflect_resource = registration.data::<ReflectResource>().ok_or_else(|| {
+                SceneSpawnError::UnregisteredResource {
+                    type_name: component_info.name().to_string(),
+                }
+            })?;
+            reflect_resource.copy(&self.world, world);
+        }
+
         for archetype in self.world.archetypes().iter() {
             for scene_entity in archetype.entities() {
                 let entity = *instance_info

crates/bevy_scene/src/scene_spawner.rs

@@ -45,6 +45,8 @@ pub struct SceneSpawner {
 pub enum SceneSpawnError {
     #[error("scene contains the unregistered component `{type_name}`. consider adding `#[reflect(Component)]` to your type")]
     UnregisteredComponent { type_name: String },
+    #[error("scene contains the unregistered resource `{type_name}`. consider adding `#[reflect(Resource)]` to your type")]
+    UnregisteredResource { type_name: String },
     #[error("scene contains the unregistered type `{type_name}`. consider registering the type using `app.register_type::<T>()`")]
     UnregisteredType { type_name: String },
     #[error("scene does not exist")]

crates/bevy_scene/src/serde.rs

@@ -15,6 +15,7 @@ use serde::{
 use std::fmt::Formatter;
 
 pub const SCENE_STRUCT: &str = "Scene";
+pub const SCENE_RESOURCES: &str = "resources";
 pub const SCENE_ENTITIES: &str = "entities";
 
 pub const ENTITY_STRUCT: &str = "Entity";
@@ -36,7 +37,14 @@ impl<'a> Serialize for SceneSerializer<'a> {
     where
         S: serde::Serializer,
     {
-        let mut state = serializer.serialize_struct(SCENE_STRUCT, 1)?;
+        let mut state = serializer.serialize_struct(SCENE_STRUCT, 2)?;
+        state.serialize_field(
+            SCENE_RESOURCES,
+            &SceneMapSerializer {
+                entries: &self.scene.resources,
+                registry: self.registry,
+            },
+        )?;
         state.serialize_field(
             SCENE_ENTITIES,
             &EntitiesSerializer {
@@ -85,8 +93,8 @@ impl<'a> Serialize for EntitySerializer<'a> {
         let mut state = serializer.serialize_struct(ENTITY_STRUCT, 1)?;
         state.serialize_field(
             ENTITY_FIELD_COMPONENTS,
-            &ComponentsSerializer {
+            &SceneMapSerializer {
-                components: &self.entity.components,
+                entries: &self.entity.components,
                 registry: self.registry,
             },
         )?;
@@ -94,21 +102,21 @@ impl<'a> Serialize for EntitySerializer<'a> {
     }
 }
 
-pub struct ComponentsSerializer<'a> {
+pub struct SceneMapSerializer<'a> {
-    pub components: &'a [Box<dyn Reflect>],
+    pub entries: &'a [Box<dyn Reflect>],
     pub registry: &'a TypeRegistryArc,
 }
 
-impl<'a> Serialize for ComponentsSerializer<'a> {
+impl<'a> Serialize for SceneMapSerializer<'a> {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
         S: serde::Serializer,
     {
-        let mut state = serializer.serialize_map(Some(self.components.len()))?;
+        let mut state = serializer.serialize_map(Some(self.entries.len()))?;
-        for component in self.components {
+        for reflect in self.entries {
             state.serialize_entry(
-                component.type_name(),
+                reflect.type_name(),
-                &TypedReflectSerializer::new(&**component, &self.registry.read()),
+                &TypedReflectSerializer::new(&**reflect, &self.registry.read()),
             )?;
         }
         state.end()
@@ -118,6 +126,7 @@ impl<'a> Serialize for ComponentsSerializer<'a> {
 #[derive(Deserialize)]
 #[serde(field_identifier, rename_all = "lowercase")]
 enum SceneField {
+    Resources,
     Entities,
 }
 
@@ -140,7 +149,7 @@ impl<'a, 'de> DeserializeSeed<'de> for SceneDeserializer<'a> {
     {
         deserializer.deserialize_struct(
             SCENE_STRUCT,
-            &[SCENE_ENTITIES],
+            &[SCENE_RESOURCES, SCENE_ENTITIES],
             SceneVisitor {
                 type_registry: self.type_registry,
             },
@@ -163,9 +172,18 @@ impl<'a, 'de> Visitor<'de> for SceneVisitor<'a> {
     where
         A: MapAccess<'de>,
     {
+        let mut resources = None;
         let mut entities = None;
         while let Some(key) = map.next_key()? {
             match key {
+                SceneField::Resources => {
+                    if resources.is_some() {
+                        return Err(Error::duplicate_field(SCENE_RESOURCES));
+                    }
+                    resources = Some(map.next_value_seed(SceneMapDeserializer {
+                        registry: self.type_registry,
+                    })?);
+                }
                 SceneField::Entities => {
                     if entities.is_some() {
                         return Err(Error::duplicate_field(SCENE_ENTITIES));
@@ -177,22 +195,35 @@ impl<'a, 'de> Visitor<'de> for SceneVisitor<'a> {
             }
         }
 
+        let resources = resources.ok_or_else(|| Error::missing_field(SCENE_RESOURCES))?;
         let entities = entities.ok_or_else(|| Error::missing_field(SCENE_ENTITIES))?;
 
-        Ok(DynamicScene { entities })
+        Ok(DynamicScene {
+            resources,
+            entities,
+        })
     }
 
     fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
     where
         A: SeqAccess<'de>,
     {
+        let resources = seq
+            .next_element_seed(SceneMapDeserializer {
+                registry: self.type_registry,
+            })?
+            .ok_or_else(|| Error::missing_field(SCENE_RESOURCES))?;
+
         let entities = seq
             .next_element_seed(SceneEntitiesDeserializer {
                 type_registry: self.type_registry,
             })?
             .ok_or_else(|| Error::missing_field(SCENE_ENTITIES))?;
 
-        Ok(DynamicScene { entities })
+        Ok(DynamicScene {
+            resources,
+            entities,
+        })
     }
 }
 
@@ -281,7 +312,7 @@ impl<'a, 'de> Visitor<'de> for SceneEntityVisitor<'a> {
         A: SeqAccess<'de>,
     {
         let components = seq
-            .next_element_seed(ComponentDeserializer {
+            .next_element_seed(SceneMapDeserializer {
                 registry: self.registry,
             })?
             .ok_or_else(|| Error::missing_field(ENTITY_FIELD_COMPONENTS))?;
@@ -304,7 +335,7 @@ impl<'a, 'de> Visitor<'de> for SceneEntityVisitor<'a> {
                         return Err(Error::duplicate_field(ENTITY_FIELD_COMPONENTS));
                     }
 
-                    components = Some(map.next_value_seed(ComponentDeserializer {
+                    components = Some(map.next_value_seed(SceneMapDeserializer {
                         registry: self.registry,
                     })?);
                 }
@@ -321,32 +352,32 @@ impl<'a, 'de> Visitor<'de> for SceneEntityVisitor<'a> {
     }
 }
 
-pub struct ComponentDeserializer<'a> {
+pub struct SceneMapDeserializer<'a> {
     pub registry: &'a TypeRegistry,
 }
 
-impl<'a, 'de> DeserializeSeed<'de> for ComponentDeserializer<'a> {
+impl<'a, 'de> DeserializeSeed<'de> for SceneMapDeserializer<'a> {
     type Value = Vec<Box<dyn Reflect>>;
 
     fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
     where
         D: serde::Deserializer<'de>,
     {
-        deserializer.deserialize_map(ComponentVisitor {
+        deserializer.deserialize_map(SceneMapVisitor {
             registry: self.registry,
         })
     }
 }
 
-struct ComponentVisitor<'a> {
+struct SceneMapVisitor<'a> {
     pub registry: &'a TypeRegistry,
 }
 
-impl<'a, 'de> Visitor<'de> for ComponentVisitor<'a> {
+impl<'a, 'de> Visitor<'de> for SceneMapVisitor<'a> {
     type Value = Vec<Box<dyn Reflect>>;
 
     fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
-        formatter.write_str("map of components")
+        formatter.write_str("map of reflect types")
     }
 
     fn visit_map<A>(self, mut map: A) -> std::result::Result<Self::Value, A::Error>
@@ -354,23 +385,23 @@ impl<'a, 'de> Visitor<'de> for ComponentVisitor<'a> {
         A: MapAccess<'de>,
     {
         let mut added = HashSet::new();
-        let mut components = Vec::new();
+        let mut entries = Vec::new();
         while let Some(registration) =
             map.next_key_seed(TypeRegistrationDeserializer::new(self.registry))?
         {
             if !added.insert(registration.type_id()) {
                 return Err(Error::custom(format_args!(
-                    "duplicate component: `{}`",
+                    "duplicate reflect type: `{}`",
                     registration.type_name()
                 )));
             }
 
-            components.push(
+            entries.push(
                 map.next_value_seed(TypedReflectDeserializer::new(registration, self.registry))?,
             );
         }
 
-        Ok(components)
+        Ok(entries)
     }
 
     fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
@@ -394,7 +425,7 @@ mod tests {
     use crate::{DynamicScene, DynamicSceneBuilder};
     use bevy_app::AppTypeRegistry;
     use bevy_ecs::entity::EntityMap;
-    use bevy_ecs::prelude::{Component, ReflectComponent, World};
+    use bevy_ecs::prelude::{Component, ReflectComponent, ReflectResource, Resource, World};
     use bevy_reflect::{FromReflect, Reflect, ReflectSerialize};
     use bincode::Options;
     use serde::de::DeserializeSeed;
@@ -429,6 +460,12 @@ mod tests {
         },
     }
 
+    #[derive(Resource, Reflect, Default)]
+    #[reflect(Resource)]
+    struct MyResource {
+        foo: i32,
+    }
+
     fn create_world() -> World {
         let mut world = World::new();
         let registry = AppTypeRegistry::default();
@@ -443,6 +480,7 @@ mod tests {
             registry.register_type_data::<String, ReflectSerialize>();
             registry.register::<[usize; 3]>();
             registry.register::<(f32, f32)>();
+            registry.register::<MyResource>();
         }
         world.insert_resource(registry);
         world
@@ -456,11 +494,19 @@ mod tests {
         let b = world.spawn((Foo(123), Bar(345))).id();
         let c = world.spawn((Foo(123), Bar(345), Baz(789))).id();
 
+        world.insert_resource(MyResource { foo: 123 });
+
         let mut builder = DynamicSceneBuilder::from_world(&world);
         builder.extract_entities([a, b, c].into_iter());
+        builder.extract_resources();
         let scene = builder.build();
 
         let expected = r#"(
+  resources: {
+    "bevy_scene::serde::tests::MyResource": (
+      foo: 123,
+    ),
+  },
   entities: {
     0: (
       components: {
@@ -493,6 +539,11 @@ mod tests {
         let world = create_world();
 
         let input = r#"(
+  resources: {
+    "bevy_scene::serde::tests::MyResource": (
+      foo: 123,
+    ),
+  },
   entities: {
     0: (
       components: {
@@ -520,6 +571,11 @@ mod tests {
         };
         let scene = scene_deserializer.deserialize(&mut deserializer).unwrap();
 
+        assert_eq!(
+            1,
+            scene.resources.len(),
+            "expected `resources` to contain 1 resource"
+        );
         assert_eq!(
             3,
             scene.entities.len(),
@@ -530,6 +586,11 @@ mod tests {
         let mut dst_world = create_world();
         scene.write_to_world(&mut dst_world, &mut map).unwrap();
 
+        let my_resource = dst_world.get_resource::<MyResource>();
+        assert!(my_resource.is_some());
+        let my_resource = my_resource.unwrap();
+        assert_eq!(my_resource.foo, 123);
+
         assert_eq!(3, dst_world.query::<&Foo>().iter(&dst_world).count());
         assert_eq!(2, dst_world.query::<&Bar>().iter(&dst_world).count());
         assert_eq!(1, dst_world.query::<&Baz>().iter(&dst_world).count());
@@ -554,10 +615,10 @@ mod tests {
 
         assert_eq!(
             vec![
-                1, 0, 1, 37, 98, 101, 118, 121, 95, 115, 99, 101, 110, 101, 58, 58, 115, 101, 114,
+                0, 1, 0, 1, 37, 98, 101, 118, 121, 95, 115, 99, 101, 110, 101, 58, 58, 115, 101,
-                100, 101, 58, 58, 116, 101, 115, 116, 115, 58, 58, 77, 121, 67, 111, 109, 112, 111,
+                114, 100, 101, 58, 58, 116, 101, 115, 116, 115, 58, 58, 77, 121, 67, 111, 109, 112,
-                110, 101, 110, 116, 1, 2, 3, 102, 102, 166, 63, 205, 204, 108, 64, 1, 12, 72, 101,
+                111, 110, 101, 110, 116, 1, 2, 3, 102, 102, 166, 63, 205, 204, 108, 64, 1, 12, 72,
-                108, 108, 111, 32, 87, 111, 114, 108, 100, 33
+                101, 108, 108, 111, 32, 87, 111, 114, 108, 100, 33
             ],
             serialized_scene
         );
@@ -594,11 +655,11 @@ mod tests {
 
         assert_eq!(
             vec![
-                145, 129, 0, 145, 129, 217, 37, 98, 101, 118, 121, 95, 115, 99, 101, 110, 101, 58,
+                146, 128, 129, 0, 145, 129, 217, 37, 98, 101, 118, 121, 95, 115, 99, 101, 110, 101,
-                58, 115, 101, 114, 100, 101, 58, 58, 116, 101, 115, 116, 115, 58, 58, 77, 121, 67,
+                58, 58, 115, 101, 114, 100, 101, 58, 58, 116, 101, 115, 116, 115, 58, 58, 77, 121,
-                111, 109, 112, 111, 110, 101, 110, 116, 147, 147, 1, 2, 3, 146, 202, 63, 166, 102,
+                67, 111, 109, 112, 111, 110, 101, 110, 116, 147, 147, 1, 2, 3, 146, 202, 63, 166,
-                102, 202, 64, 108, 204, 205, 129, 165, 84, 117, 112, 108, 101, 172, 72, 101, 108,
+                102, 102, 202, 64, 108, 204, 205, 129, 165, 84, 117, 112, 108, 101, 172, 72, 101,
-                108, 111, 32, 87, 111, 114, 108, 100, 33
+                108, 108, 111, 32, 87, 111, 114, 108, 100, 33
             ],
             buf
         );
@@ -635,12 +696,12 @@ mod tests {
 
         assert_eq!(
             vec![
-                1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 37, 0, 0, 0, 0, 0, 0,
+                0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
-                0, 98, 101, 118, 121, 95, 115, 99, 101, 110, 101, 58, 58, 115, 101, 114, 100, 101,
+                37, 0, 0, 0, 0, 0, 0, 0, 98, 101, 118, 121, 95, 115, 99, 101, 110, 101, 58, 58,
-                58, 58, 116, 101, 115, 116, 115, 58, 58, 77, 121, 67, 111, 109, 112, 111, 110, 101,
+                115, 101, 114, 100, 101, 58, 58, 116, 101, 115, 116, 115, 58, 58, 77, 121, 67, 111,
-                110, 116, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0,
+                109, 112, 111, 110, 101, 110, 116, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
-                102, 102, 166, 63, 205, 204, 108, 64, 1, 0, 0, 0, 12, 0, 0, 0, 0, 0, 0, 0, 72, 101,
+                3, 0, 0, 0, 0, 0, 0, 0, 102, 102, 166, 63, 205, 204, 108, 64, 1, 0, 0, 0, 12, 0, 0,
-                108, 108, 111, 32, 87, 111, 114, 108, 100, 33
+                0, 0, 0, 0, 0, 72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100, 33
             ],
             serialized_scene
         );

examples/scene/scene.rs

@@ -1,8 +1,6 @@
 //! This example illustrates loading scenes from files.
-use std::fs::File;
-use std::io::Write;
-
 use bevy::{prelude::*, tasks::IoTaskPool, utils::Duration};
+use std::{fs::File, io::Write};
 
 fn main() {
     App::new()
@@ -14,6 +12,7 @@ fn main() {
         }))
         .register_type::<ComponentA>()
         .register_type::<ComponentB>()
+        .register_type::<ResourceA>()
         .add_systems(
             Startup,
             (save_scene_system, load_scene_system, infotext_system),
@@ -57,6 +56,13 @@ impl FromWorld for ComponentB {
     }
 }
 
+// Resources can be serialized in scenes as well, with the same requirements `Component`s have.
+#[derive(Resource, Reflect, Default)]
+#[reflect(Resource)]
+struct ResourceA {
+    pub score: u32,
+}
+
 // The initial scene file will be loaded below and not change when the scene is saved
 const SCENE_FILE_PATH: &str = "scenes/load_scene_example.scn.ron";
 
@@ -75,7 +81,10 @@ fn load_scene_system(mut commands: Commands, asset_server: Res<AssetServer>) {
 
 // This system logs all ComponentA components in our world. Try making a change to a ComponentA in
 // load_scene_example.scn. You should immediately see the changes appear in the console.
-fn log_system(query: Query<(Entity, &ComponentA), Changed<ComponentA>>) {
+fn log_system(
+    query: Query<(Entity, &ComponentA), Changed<ComponentA>>,
+    res: Option<Res<ResourceA>>,
+) {
     for (entity, component_a) in &query {
         info!("  Entity({})", entity.index());
         info!(
@@ -83,6 +92,11 @@ fn log_system(query: Query<(Entity, &ComponentA), Changed<ComponentA>>) {
             component_a.x, component_a.y
         );
     }
+    if let Some(res) = res {
+        if res.is_added() {
+            info!("  New ResourceA: {{ score: {} }}\n", res.score);
+        }
+    }
 }
 
 fn save_scene_system(world: &mut World) {
@@ -97,6 +111,7 @@ fn save_scene_system(world: &mut World) {
         Transform::IDENTITY,
     ));
     scene_world.spawn(ComponentA { x: 3.0, y: 4.0 });
+    scene_world.insert_resource(ResourceA { score: 1 });
 
     // The TypeRegistry resource contains information about all registered types (including
     // components). This is used to construct scenes.