Extend cloning functionality and add convenience methods to EntityWorldMut and EntityCommands (bevyengine#16826)

## Objective

Thanks to @eugineerd's work on entity cloning (bevyengine#16132), we now have a
robust way to copy components between entities. We can extend this to
implement some useful functionality that would have been more
complicated before.

Closes bevyengine#15350.

## Solution

`EntityCloneBuilder` now automatically includes required components
alongside any component added/removed from the component filter.

Added the following methods to `EntityCloneBuilder`:
- `move_components`
- `without_required_components`

Added the following methods to `EntityWorldMut` and `EntityCommands`:
- `clone_with`
- `clone_components`
- `move_components`

Also added `clone_and_spawn` and `clone_and_spawn_with` to
`EntityWorldMut` (`EntityCommands` already had them).

## Showcase

```
assert_eq!(world.entity(entity_a).get::<B>(), Some(&B));
assert_eq!(world.entity(entity_b).get::<B>(), None);
world.entity_mut(entity_a).clone_components::<B>(entity_b);
assert_eq!(world.entity(entity_a).get::<B>(), Some(&B));
assert_eq!(world.entity(entity_b).get::<B>(), Some(&B));

assert_eq!(world.entity(entity_a).get::<C>(), Some(&C(5)));
assert_eq!(world.entity(entity_b).get::<C>(), None);
world.entity_mut(entity_a).move_components::<C>(entity_b);
assert_eq!(world.entity(entity_a).get::<C>(), None);
assert_eq!(world.entity(entity_b).get::<C>(), Some(&C(5)));
```

Author: JaySpruce

crates/bevy_ecs/src/entity/clone_entities.rs

@@ -18,6 +18,7 @@ pub struct EntityCloner {
     filter_allows_components: bool,
     filter: Arc<HashSet<ComponentId>>,
     clone_handlers_overrides: Arc<HashMap<ComponentId, ComponentCloneHandler>>,
+    move_components: bool,
 }
 
 impl EntityCloner {
@@ -35,17 +36,21 @@ impl EntityCloner {
                 .filter(|id| self.is_cloning_allowed(id)),
         );
 
-        for component in components {
+        for component in &components {
             let global_handlers = world.components().get_component_clone_handlers();
-            let handler = match self.clone_handlers_overrides.get(&component) {
-                None => global_handlers.get_handler(component),
+            let handler = match self.clone_handlers_overrides.get(component) {
+                None => global_handlers.get_handler(*component),
                 Some(ComponentCloneHandler::Default) => global_handlers.get_default_handler(),
                 Some(ComponentCloneHandler::Ignore) => component_clone_ignore,
                 Some(ComponentCloneHandler::Custom(handler)) => *handler,
             };
-            self.component_id = Some(component);
+            self.component_id = Some(*component);
             (handler)(&mut world.into(), self);
         }
+
+        if self.move_components {
+            world.entity_mut(self.source).remove_by_ids(&components);
+        }
     }
 
     fn is_cloning_allowed(&self, component: &ComponentId) -> bool {
@@ -145,6 +150,8 @@ pub struct EntityCloneBuilder<'w> {
     filter_allows_components: bool,
     filter: HashSet<ComponentId>,
     clone_handlers_overrides: HashMap<ComponentId, ComponentCloneHandler>,
+    attach_required_components: bool,
+    move_components: bool,
 }
 
 impl<'w> EntityCloneBuilder<'w> {
@@ -155,6 +162,8 @@ impl<'w> EntityCloneBuilder<'w> {
             filter_allows_components: false,
             filter: Default::default(),
             clone_handlers_overrides: Default::default(),
+            attach_required_components: true,
+            move_components: false,
         }
     }
 
@@ -165,6 +174,7 @@ impl<'w> EntityCloneBuilder<'w> {
             filter_allows_components,
             filter,
             clone_handlers_overrides,
+            move_components,
             ..
         } = self;
 
@@ -175,29 +185,49 @@ impl<'w> EntityCloneBuilder<'w> {
             filter_allows_components,
             filter: Arc::new(filter),
             clone_handlers_overrides: Arc::new(clone_handlers_overrides),
+            move_components,
         }
         .clone_entity(world);
 
         world.flush_commands();
     }
 
+    /// By default, any components allowed/denied through the filter will automatically
+    /// allow/deny all of their required components.
+    ///
+    /// This method allows for a scoped mode where any changes to the filter
+    /// will not involve required components.
+    pub fn without_required_components(
+        &mut self,
+        builder: impl FnOnce(&mut EntityCloneBuilder) + Send + Sync + 'static,
+    ) -> &mut Self {
+        self.attach_required_components = false;
+        builder(self);
+        self.attach_required_components = true;
+        self
+    }
+
+    /// Sets whether the cloner should remove any components that were cloned,
+    /// effectively moving them from the source entity to the target.
+    ///
+    /// This is disabled by default.
+    ///
+    /// The setting only applies to components that are allowed through the filter
+    /// at the time [`EntityCloneBuilder::clone_entity`] is called.
+    pub fn move_components(&mut self, enable: bool) -> &mut Self {
+        self.move_components = enable;
+        self
+    }
+
     /// Adds all components of the bundle to the list of components to clone.
     ///
     /// Note that all components are allowed by default, to clone only explicitly allowed components make sure to call
     /// [`deny_all`](`Self::deny_all`) before calling any of the `allow` methods.
     pub fn allow<T: Bundle>(&mut self) -> &mut Self {
-        if self.filter_allows_components {
-            T::get_component_ids(self.world.components(), &mut |id| {
-                if let Some(id) = id {
-                    self.filter.insert(id);
-                }
-            });
-        } else {
-            T::get_component_ids(self.world.components(), &mut |id| {
-                if let Some(id) = id {
-                    self.filter.remove(&id);
-                }
-            });
+        let bundle = self.world.register_bundle::<T>();
+        let ids = bundle.explicit_components().to_owned();
+        for id in ids {
+            self.filter_allow(id);
         }
         self
     }
@@ -207,12 +237,8 @@ impl<'w> EntityCloneBuilder<'w> {
     /// Note that all components are allowed by default, to clone only explicitly allowed components make sure to call
     /// [`deny_all`](`Self::deny_all`) before calling any of the `allow` methods.
     pub fn allow_by_ids(&mut self, ids: impl IntoIterator<Item = ComponentId>) -> &mut Self {
-        if self.filter_allows_components {
-            self.filter.extend(ids);
-        } else {
-            ids.into_iter().for_each(|id| {
-                self.filter.remove(&id);
-            });
+        for id in ids {
+            self.filter_allow(id);
         }
         self
     }
@@ -222,15 +248,10 @@ impl<'w> EntityCloneBuilder<'w> {
     /// Note that all components are allowed by default, to clone only explicitly allowed components make sure to call
     /// [`deny_all`](`Self::deny_all`) before calling any of the `allow` methods.
     pub fn allow_by_type_ids(&mut self, ids: impl IntoIterator<Item = TypeId>) -> &mut Self {
-        let ids = ids
-            .into_iter()
-            .filter_map(|id| self.world.components().get_id(id));
-        if self.filter_allows_components {
-            self.filter.extend(ids);
-        } else {
-            ids.into_iter().for_each(|id| {
-                self.filter.remove(&id);
-            });
+        for type_id in ids {
+            if let Some(id) = self.world.components().get_id(type_id) {
+                self.filter_allow(id);
+            }
         }
         self
     }
@@ -244,45 +265,28 @@ impl<'w> EntityCloneBuilder<'w> {
 
     /// Disallows all components of the bundle from being cloned.
     pub fn deny<T: Bundle>(&mut self) -> &mut Self {
-        if self.filter_allows_components {
-            T::get_component_ids(self.world.components(), &mut |id| {
-                if let Some(id) = id {
-                    self.filter.remove(&id);
-                }
-            });
-        } else {
-            T::get_component_ids(self.world.components(), &mut |id| {
-                if let Some(id) = id {
-                    self.filter.insert(id);
-                }
-            });
+        let bundle = self.world.register_bundle::<T>();
+        let ids = bundle.explicit_components().to_owned();
+        for id in ids {
+            self.filter_deny(id);
         }
         self
     }
 
     /// Extends the list of components that shouldn't be cloned.
     pub fn deny_by_ids(&mut self, ids: impl IntoIterator<Item = ComponentId>) -> &mut Self {
-        if self.filter_allows_components {
-            ids.into_iter().for_each(|id| {
-                self.filter.remove(&id);
-            });
-        } else {
-            self.filter.extend(ids);
+        for id in ids {
+            self.filter_deny(id);
         }
         self
     }
 
     /// Extends the list of components that shouldn't be cloned by type ids.
     pub fn deny_by_type_ids(&mut self, ids: impl IntoIterator<Item = TypeId>) -> &mut Self {
-        let ids = ids
-            .into_iter()
-            .filter_map(|id| self.world.components().get_id(id));
-        if self.filter_allows_components {
-            ids.into_iter().for_each(|id| {
-                self.filter.remove(&id);
-            });
-        } else {
-            self.filter.extend(ids);
+        for type_id in ids {
+            if let Some(id) = self.world.components().get_id(type_id) {
+                self.filter_deny(id);
+            }
         }
         self
     }
@@ -315,11 +319,52 @@ impl<'w> EntityCloneBuilder<'w> {
         }
         self
     }
+
+    /// Helper function that allows a component through the filter.
+    fn filter_allow(&mut self, id: ComponentId) {
+        if self.filter_allows_components {
+            self.filter.insert(id);
+        } else {
+            self.filter.remove(&id);
+        }
+        if self.attach_required_components {
+            if let Some(info) = self.world.components().get_info(id) {
+                for required_id in info.required_components().iter_ids() {
+                    if self.filter_allows_components {
+                        self.filter.insert(required_id);
+                    } else {
+                        self.filter.remove(&required_id);
+                    }
+                }
+            }
+        }
+    }
+
+    /// Helper function that disallows a component through the filter.
+    fn filter_deny(&mut self, id: ComponentId) {
+        if self.filter_allows_components {
+            self.filter.remove(&id);
+        } else {
+            self.filter.insert(id);
+        }
+        if self.attach_required_components {
+            if let Some(info) = self.world.components().get_info(id) {
+                for required_id in info.required_components().iter_ids() {
+                    if self.filter_allows_components {
+                        self.filter.remove(&required_id);
+                    } else {
+                        self.filter.insert(required_id);
+                    }
+                }
+            }
+        }
+    }
 }
 
 #[cfg(test)]
 mod tests {
     use crate::{self as bevy_ecs, component::Component, entity::EntityCloneBuilder, world::World};
+    use bevy_ecs_macros::require;
 
     #[cfg(feature = "bevy_reflect")]
     #[test]
@@ -520,4 +565,34 @@ mod tests {
         assert!(world.get::<B>(e_clone).is_none());
         assert!(world.get::<C>(e_clone).is_none());
     }
+
+    #[test]
+    fn clone_entity_with_required_components() {
+        #[derive(Component, Clone, PartialEq, Debug)]
+        #[require(B)]
+        struct A;
+
+        #[derive(Component, Clone, PartialEq, Debug, Default)]
+        #[require(C(|| C(5)))]
+        struct B;
+
+        #[derive(Component, Clone, PartialEq, Debug)]
+        struct C(u32);
+
+        let mut world = World::default();
+
+        let e = world.spawn(A).id();
+        let e_clone = world.spawn_empty().id();
+
+        let mut builder = EntityCloneBuilder::new(&mut world);
+        builder.deny_all();
+        builder.without_required_components(|builder| {
+            builder.allow::<B>();
+        });
+        builder.clone_entity(e, e_clone);
+
+        assert_eq!(world.entity(e_clone).get::<A>(), None);
+        assert_eq!(world.entity(e_clone).get::<B>(), Some(&B));
+        assert_eq!(world.entity(e_clone).get::<C>(), Some(&C(5)));
+    }
 }