fix panic when receiving add_entity and start_configuration in the same update

azalea-client/tests/receive_spawn_entity_and_start_config_packet.rs

@@ -0,0 +1,42 @@
+use azalea_client::{InConfigState, test_simulation::*};
+use azalea_core::{position::Vec3, resource_location::ResourceLocation};
+use azalea_protocol::packets::{
+    ConnectionProtocol,
+    game::{ClientboundAddEntity, ClientboundStartConfiguration},
+};
+use azalea_registry::{DataRegistry, DimensionType, EntityKind};
+use azalea_world::InstanceName;
+use bevy_log::tracing_subscriber;
+use uuid::Uuid;
+
+#[test]
+fn test_receive_spawn_entity_and_start_config_packet() {
+    let _ = tracing_subscriber::fmt::try_init();
+
+    let mut simulation = Simulation::new(ConnectionProtocol::Game);
+    simulation.receive_packet(make_basic_login_packet(
+        DimensionType::new_raw(0),
+        ResourceLocation::new("minecraft:overworld"),
+    ));
+    simulation.tick();
+    assert!(simulation.has_component::<InstanceName>());
+    simulation.tick();
+
+    simulation.receive_packet(ClientboundAddEntity {
+        id: 123.into(),
+        uuid: Uuid::new_v4(),
+        entity_type: EntityKind::ArmorStand,
+        position: Vec3::ZERO,
+        x_rot: 0,
+        y_rot: 0,
+        y_head_rot: 0,
+        data: 0,
+        velocity: Default::default(),
+    });
+    simulation.receive_packet(ClientboundStartConfiguration);
+
+    simulation.tick();
+    assert!(simulation.has_component::<InConfigState>());
+
+    // make sure that the entity is despawned
+}

azalea-entity/src/plugin/mod.rs

@@ -46,6 +46,11 @@ impl Plugin for EntityPlugin {
             Update,
             (
                 (
+                    // remove_despawned_entities_from_indexes is done again here to correctly
+                    // handle the case where an entity is spawned and then the world is removed at
+                    // the same time (like with ClientboundStartConfiguration).
+                    indexing::remove_despawned_entities_from_indexes
+                        .in_set(EntityUpdateSet::Deindex),
                     indexing::update_entity_chunk_positions,
                     indexing::insert_entity_chunk_position,
                 )