Fix bubbling of runtime requirements for #[require(...)] attribute (#16410)

# Objective

Fixes #16406.

Currently, the `#[require(...)]` attribute internally registers
component requirements using `register_required_components_manual`. This
is done recursively in a way where every requirement in the "inheritance
tree" is added into a flat `RequiredComponents` hash map with component
constructors and inheritance depths stored.

However, this does not consider runtime requirements: if a plugins has
already registered `C` as required by `B`, and a component `A` requires
`B` through the macro attribute, spawning an entity with `A` won't add
`C`. The `required_by` hash set for `C` doesn't have `A`, and the
`RequiredComponents` of `A` don't have `C`.

Intuitively, I would've thought that the macro attribute's requirements
were always added *before* runtime requirements, and in that case I
believe this shouldn't have been an issue. But the macro requirements
are based on `Component::register_required_components`, which in a lot
of cases (I think) is only called *after* the first time a bundle with
the component is inserted. So if a runtime requirement is defined
*before* this (as is often the case, during `Plugin::build`), the macro
may not take it into account.

## Solution

Register requirements inherited from the `required` component in
`register_required_components_manual_unchecked`.

## Testing

I added a test, essentially the same as in #16406, and it now passes. I
also ran some of the tests in #16409, and they seem to work as expected.
All the existing tests for required components pass.

crates/bevy_ecs/src/component.rs

@@ -1159,15 +1159,14 @@ impl Components {
     // NOTE: This should maybe be private, but it is currently public so that `bevy_ecs_macros` can use it.
     //       We can't directly move this there either, because this uses `Components::get_required_by_mut`,
     //       which is private, and could be equally risky to expose to users.
-    /// Registers the given component `R` as a [required component] for `T`,
-    /// and adds `T` to the list of requirees for `R`.
+    /// Registers the given component `R` and [required components] inherited from it as required by `T`,
+    /// and adds `T` to their lists of requirees.
     ///
     /// The given `inheritance_depth` determines how many levels of inheritance deep the requirement is.
     /// A direct requirement has a depth of `0`, and each level of inheritance increases the depth by `1`.
     /// Lower depths are more specific requirements, and can override existing less specific registrations.
     ///
-    /// This method does *not* recursively register required components for components required by `R`,
-    /// nor does it register them for components that require `T`.
+    /// This method does *not* register any components as required by components that require `T`.
     ///
     /// Only use this method if you know what you are doing. In most cases, you should instead use [`World::register_required_components`],
     /// or the equivalent method in `bevy_app::App`.
@@ -1196,15 +1195,14 @@ impl Components {
         }
     }
 
-    /// Registers the given component `R` as a [required component] for `T`,
-    /// and adds `T` to the list of requirees for `R`.
+    /// Registers the given component `R` and [required components] inherited from it as required by `T`,
+    /// and adds `T` to their lists of requirees.
     ///
     /// The given `inheritance_depth` determines how many levels of inheritance deep the requirement is.
     /// A direct requirement has a depth of `0`, and each level of inheritance increases the depth by `1`.
     /// Lower depths are more specific requirements, and can override existing less specific registrations.
     ///
-    /// This method does *not* recursively register required components for components required by `R`,
-    /// nor does it register them for components that require `T`.
+    /// This method does *not* register any components as required by components that require `T`.
     ///
     /// [required component]: Component#required-components
     ///
@@ -1232,6 +1230,27 @@ impl Components {
         //         Assuming it is valid, the component is in the list of required components, so it must exist already.
         let required_by = unsafe { self.get_required_by_mut(required).debug_checked_unwrap() };
         required_by.insert(requiree);
+
+        // Register the inherited required components for the requiree.
+        let required: Vec<(ComponentId, RequiredComponent)> = self
+            .get_info(required)
+            .unwrap()
+            .required_components()
+            .0
+            .iter()
+            .map(|(id, component)| (*id, component.clone()))
+            .collect();
+
+        for (id, component) in required {
+            // Register the inherited required components for the requiree.
+            // The inheritance depth is increased by `1` since this is a component required by the original required component.
+            required_components.register_dynamic(
+                id,
+                component.constructor.clone(),
+                component.inheritance_depth + 1,
+            );
+            self.get_required_by_mut(id).unwrap().insert(requiree);
+        }
     }
 
     #[inline]

crates/bevy_ecs/src/lib.rs

@@ -2321,6 +2321,30 @@ mod tests {
         );
     }
 
+    #[test]
+    fn runtime_required_components_propagate_up() {
+        // `A` requires `B` directly.
+        #[derive(Component)]
+        #[require(B)]
+        struct A;
+
+        #[derive(Component, Default)]
+        struct B;
+
+        #[derive(Component, Default)]
+        struct C;
+
+        let mut world = World::new();
+
+        // `B` requires `C` with a runtime registration.
+        // `A` should also require `C` because it requires `B`.
+        world.register_required_components::<B, C>();
+
+        let id = world.spawn(A).id();
+
+        assert!(world.entity(id).get::<C>().is_some());
+    }
+
     #[test]
     fn runtime_required_components_existing_archetype() {
         #[derive(Component)]