From 1a338ddfa521b1e56ca2a8b6aad3297d38df88bf Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sun, 24 Mar 2019 00:24:52 -0400
Subject: [PATCH] Entity#getEntitySpawnReason

Allows you to return the SpawnReason for why an Entity Spawned

Pre existing entities will return NATURAL if it was a non
persistenting Living Entity, SPAWNER for spawners,
or DEFAULT since data was not stored.

diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
index 69bc9dae0d..1a20f105b5 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -72,6 +72,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
         }
     };
     List<Entity> entitySlice = null;
+    public org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason spawnReason;
     // Paper end
 
     public com.destroystokyo.paper.loottable.PaperLootableInventoryData lootableData; // Paper
@@ -1628,6 +1629,9 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
             if (this.origin != null) {
                 nbttagcompound.set("Paper.Origin", this.createList(origin.getX(), origin.getY(), origin.getZ()));
             }
+            if (spawnReason != null) {
+                nbttagcompound.setString("Paper.SpawnReason", spawnReason.name());
+            }
             // Save entity's from mob spawner status
             if (spawnedViaMobSpawner) {
                 nbttagcompound.setBoolean("Paper.FromMobSpawner", true);
@@ -1754,6 +1758,26 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
             }
 
             spawnedViaMobSpawner = nbttagcompound.getBoolean("Paper.FromMobSpawner"); // Restore entity's from mob spawner status
+            if (nbttagcompound.hasKey("Paper.SpawnReason")) {
+                String spawnReasonName = nbttagcompound.getString("Paper.SpawnReason");
+                try {
+                    spawnReason = org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.valueOf(spawnReasonName);
+                } catch (Exception ignored) {
+                    LogManager.getLogger().error("Unknown SpawnReason " + spawnReasonName + " for " + this);
+                }
+            }
+            if (spawnReason == null) {
+                if (spawnedViaMobSpawner) {
+                    spawnReason = org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.SPAWNER;
+                } else if (this instanceof EntityInsentient && (this instanceof EntityAnimal || this instanceof EntityFish) && !((EntityInsentient) this).isTypeNotPersistent(0.0)) {
+                    if (!nbttagcompound.getBoolean("PersistenceRequired")) {
+                        spawnReason = org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.NATURAL;
+                    }
+                }
+            }
+            if (spawnReason == null) {
+                spawnReason = org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.DEFAULT;
+            }
             // Paper end
 
         } catch (Throwable throwable) {
diff --git a/src/main/java/net/minecraft/server/PlayerList.java b/src/main/java/net/minecraft/server/PlayerList.java
index 9d715d891d..49437f2124 100644
--- a/src/main/java/net/minecraft/server/PlayerList.java
+++ b/src/main/java/net/minecraft/server/PlayerList.java
@@ -251,7 +251,7 @@ public abstract class PlayerList {
             // CraftBukkit start
             WorldServer finalWorldServer = worldserver;
             Entity entity = EntityTypes.a(nbttagcompound1.getCompound("Entity"), finalWorldServer, (entity1) -> {
-                return !finalWorldServer.addEntitySerialized(entity1) ? null : entity1;
+                return !finalWorldServer.addEntitySerialized(entity1, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.MOUNT) ? null : entity1; // Paper
                 // CraftBukkit end
             });
 
diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
index 7364f48210..64bd41f1e3 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -1001,6 +1001,7 @@ public class WorldServer extends World {
     // CraftBukkit start
     private boolean addEntity0(Entity entity, CreatureSpawnEvent.SpawnReason spawnReason) {
         org.spigotmc.AsyncCatcher.catchOp("entity add"); // Spigot
+        if (entity.spawnReason == null) entity.spawnReason = spawnReason; // Paper
         // Paper start
         if (entity.valid) {
             MinecraftServer.LOGGER.error("Attempted Double World add on " + entity, new Throwable());
diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
index 915ccb1807..dfa15372b8 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
@@ -1051,5 +1051,10 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
     public boolean fromMobSpawner() {
         return getHandle().spawnedViaMobSpawner;
     }
+
+    @Override
+    public org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason getEntitySpawnReason() {
+        return getHandle().spawnReason;
+    }
     // Paper end
 }
-- 
2.25.1