Add world to Entity AddTo/RemoveFrom Events (#10183)

When a plugin listens to the EntityAddToWorld and EntityRemoveFromWorld events, I don't believe there is currently any method of directly obtaining which world the entity was actually added to/removed from. Using event.getEntity().getWorld() works in many cases, but not all. Specifically, when an entity is teleported from one world to another, the location of the entity is updated prior to the removal event being called. This means that when an entity goes through a nether/end portal or is teleported between worlds with a command, a plugin listening to the EntityRemoveFromWorldEvent has no way of determining which world the entity was actually removed from (without relying on other events).

To resolve this, I've added the world as a field in the events along with a getter to retrieve it. I also removed an unused import and made the documentation more clear on the event behaviour when chunks load/unload.

patches/api/Entity-AddTo-RemoveFrom-World-Events.patch

@@ -12,22 +12,31 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 @@ -0,0 +0,0 @@
 +package com.destroystokyo.paper.event.entity;
 +
++import org.bukkit.World;
 +import org.bukkit.entity.Entity;
-+import org.bukkit.event.Event;
 +import org.bukkit.event.HandlerList;
 +import org.bukkit.event.entity.EntityEvent;
 +import org.jetbrains.annotations.NotNull;
 +
 +/**
-+ * Fired any time an entity is being added to the world for any reason.
++ * Fired any time an entity is being added to the world for any reason (including a chunk loading).
 + *
 + * Not to be confused with {@link org.bukkit.event.entity.CreatureSpawnEvent}
-+ * This will fire anytime a chunk is reloaded too.
 + */
 +public class EntityAddToWorldEvent extends EntityEvent {
++    @NotNull private final World world;
 +
-+    public EntityAddToWorldEvent(@NotNull Entity entity) {
++    public EntityAddToWorldEvent(@NotNull Entity entity, @NotNull World world) {
 +        super(entity);
++        this.world = world;
++    }
++
++    /**
++     * @return The world that the entity is being added to
++     */
++    @NotNull
++    public World getWorld() {
++        return world;
 +    }
 +
 +    private static final HandlerList handlers = new HandlerList();
@@ -50,19 +59,30 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 @@ -0,0 +0,0 @@
 +package com.destroystokyo.paper.event.entity;
 +
++import org.bukkit.World;
 +import org.bukkit.entity.Entity;
-+import org.bukkit.event.Event;
 +import org.bukkit.event.HandlerList;
 +import org.bukkit.event.entity.EntityEvent;
 +import org.jetbrains.annotations.NotNull;
 +
 +/**
-+ * Fired any time an entity is being removed from a world for any reason
++ * Fired any time an entity is being removed from a world for any reason (including a chunk unloading).
++ * Note: The entity is updated prior to this event being called, as such, the entity's world may not be equal to {@link #getWorld()}.
 + */
 +public class EntityRemoveFromWorldEvent extends EntityEvent {
++    @NotNull private final World world;
 +
-+    public EntityRemoveFromWorldEvent(@NotNull Entity entity) {
++    public EntityRemoveFromWorldEvent(@NotNull Entity entity, @NotNull World world) {
 +        super(entity);
++        this.world = world;
++    }
++
++    /**
++     * @return The world that the entity is being removed from
++     */
++    @NotNull
++    public World getWorld() {
++        return world;
 +    }
 +
 +    private static final HandlerList handlers = new HandlerList();

patches/server/Entity-AddTo-RemoveFrom-World-Events.patch

@@ -12,7 +12,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
                  entity.setOrigin(entity.getOriginVector().toLocation(getWorld()));
              }
              // Paper end
-+            new com.destroystokyo.paper.event.entity.EntityAddToWorldEvent(entity.getBukkitEntity()).callEvent(); // Paper - fire while valid
++            new com.destroystokyo.paper.event.entity.EntityAddToWorldEvent(entity.getBukkitEntity(), ServerLevel.this.getWorld()).callEvent(); // Paper - fire while valid
          }
  
          public void onTrackingEnd(Entity entity) {
@@ -20,7 +20,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
                  }
              }
              // CraftBukkit end
-+            new com.destroystokyo.paper.event.entity.EntityRemoveFromWorldEvent(entity.getBukkitEntity()).callEvent(); // Paper - fire while valid
++            new com.destroystokyo.paper.event.entity.EntityRemoveFromWorldEvent(entity.getBukkitEntity(), ServerLevel.this.getWorld()).callEvent(); // Paper - fire while valid
          }
  
          public void onSectionChange(Entity entity) {