From 6c7c8d1e68b4354fb4bda9a38289abe7f7003044 Mon Sep 17 00:00:00 2001
From: Jonas <jonaspuksta@gmail.com>
Date: Wed, 10 Jul 2024 09:12:52 +0300
Subject: [PATCH 1/2] Fix `remove_ancestor_marker` crash if the entity is
 already despawned

---
 src/sync/ancestor_marker.rs | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/sync/ancestor_marker.rs b/src/sync/ancestor_marker.rs
index bf308495..2a5533ba 100644
--- a/src/sync/ancestor_marker.rs
+++ b/src/sync/ancestor_marker.rs
@@ -213,6 +213,13 @@ fn add_ancestor_markers<C: Component>(
     }
 }
 
+/// Remove the component from entity, unless it is already despawned.
+fn remove_component<T: Bundle>(commands: &mut Commands, entity: Entity) {
+    if let Some(mut entity_commands) = commands.get_entity(entity) {
+        entity_commands.remove::<T>();
+    }
+}
+
 #[allow(clippy::type_complexity)]
 fn remove_ancestor_markers<C: Component>(
     entity: Entity,
@@ -232,11 +239,11 @@ fn remove_ancestor_markers<C: Component>(
             if keep_marker {
                 return;
             } else {
-                commands.entity(entity).remove::<AncestorMarker<C>>();
+                remove_component::<AncestorMarker<C>>(commands, entity);
             }
         } else {
             // The parent has no children, so it cannot be an ancestor.
-            commands.entity(entity).remove::<AncestorMarker<C>>();
+            remove_component::<AncestorMarker<C>>(commands, entity);
         }
     }
 
@@ -254,11 +261,11 @@ fn remove_ancestor_markers<C: Component>(
             if keep_marker {
                 return;
             } else {
-                commands.entity(parent_entity).remove::<AncestorMarker<C>>();
+                remove_component::<AncestorMarker<C>>(commands, parent_entity);
             }
         } else {
             // The parent has no children, so it cannot be an ancestor.
-            commands.entity(parent_entity).remove::<AncestorMarker<C>>();
+            remove_component::<AncestorMarker<C>>(commands, entity);
         }
 
         previous_parent = parent_entity;

From 1f1edb821f9ba3888988f9ac51fbb9022eecf576 Mon Sep 17 00:00:00 2001
From: Jonas <jonaspuksta@gmail.com>
Date: Wed, 10 Jul 2024 10:54:30 +0300
Subject: [PATCH 2/2] added tests which (re)move children and despawn the
 previous parents.

---
 src/sync/ancestor_marker.rs | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/src/sync/ancestor_marker.rs b/src/sync/ancestor_marker.rs
index 2a5533ba..4d970c2f 100644
--- a/src/sync/ancestor_marker.rs
+++ b/src/sync/ancestor_marker.rs
@@ -421,6 +421,21 @@ mod tests {
         app.world_mut().run_schedule(PostUpdate);
 
         assert!(!app.world().entity(an).contains::<AncestorMarker<C>>());
+
+        // Make CY a child of AN again. The `AncestorMarker<C>` marker should
+        // now be added to AN.
+        let mut entity_mut = app.world_mut().entity_mut(an);
+        entity_mut.add_child(cy);
+
+        app.world_mut().run_schedule(PostUpdate);
+        assert!(app.world().entity(an).contains::<AncestorMarker<C>>());
+
+        // Make CY an orphan and delete AN. This must not crash.
+        let mut entity_mut = app.world_mut().entity_mut(an);
+        entity_mut.remove_children(&[cy]);
+        entity_mut.despawn();
+
+        app.world_mut().run_schedule(PostUpdate);
     }
 
     #[test]
@@ -496,5 +511,11 @@ mod tests {
         assert!(!app.world().entity(bn).contains::<AncestorMarker<C>>());
         assert!(app.world().entity(cy).contains::<AncestorMarker<C>>());
         assert!(app.world().entity(an).contains::<AncestorMarker<C>>());
+
+        // Move all children from CY to BN and remove CY. This must not crash.
+        let mut entity_mut = app.world_mut().entity_mut(bn);
+        entity_mut.push_children(&[dn, en, fy, gy]);
+
+        app.world_mut().run_schedule(PostUpdate);
     }
 }