remove duplicate Parent update, properly set PreviousParent

Author: siler

crates/bevy_transform/src/hierarchy/child_builder.rs

@@ -47,8 +47,12 @@ pub struct ChildBuilder<'a> {
 impl Command for PushChildren {
     fn write(self: Box<Self>, world: &mut World, _resources: &mut Resources) {
         for child in self.children.iter() {
+            let previous = match world.get::<Parent>(*child) {
+                Ok(Parent(previous)) => *previous,
+                Err(_) => self.parent,
+            };
             world
-                .insert(*child, (Parent(self.parent), PreviousParent(self.parent)))
+                .insert(*child, (Parent(self.parent), PreviousParent(previous)))
                 .unwrap();
         }
         {

crates/bevy_transform/src/hierarchy/hierarchy_maintenance_system.rs

@@ -20,9 +20,6 @@ pub fn parent_update_system(
         }
     }
 
-    // Tracks all newly created `Children` Components this frame.
-    let mut children_additions = HashMap::<Entity, SmallVec<[Entity; 8]>>::default();
-
     // Entities with a changed Parent (that also have a PreviousParent, even if None)
     for (entity, parent, possible_previous_parent) in parent_query.iter_mut() {
         if let Some(mut previous_parent) = possible_previous_parent {
@@ -41,31 +38,7 @@ pub fn parent_update_system(
         } else {
             commands.insert_one(entity, PreviousParent(parent.0));
         };
-
-        // Add to the parent's `Children` (either the real component, or
-        // `children_additions`).
-        if let Ok(mut new_parent_children) = children_query.get_mut(parent.0) {
-            // This is the parent
-            debug_assert!(
-                !(*new_parent_children).0.contains(&entity),
-                "children already added"
-            );
-            (*new_parent_children).0.push(entity);
-        } else {
-            // The parent doesn't have a children entity, lets add it
-            children_additions
-                .entry(parent.0)
-                .or_insert_with(Default::default)
-                .push(entity);
-        }
     }
-
-    // Flush the `children_additions` to the command buffer. It is stored separate to
-    // collect multiple new children that point to the same parent into the same
-    // SmallVec, and to prevent redundant add+remove operations.
-    children_additions.iter().for_each(|(k, v)| {
-        commands.insert_one(*k, Children::with(v));
-    });
 }
 #[cfg(test)]
 mod test {