From d0601e9eb3df15290103dfbdd9846e901d6be6eb 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 35ec15b392..7ded9bc6ce 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -68,6 +68,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
         }
     };
     List<Entity> entitySlice = null;
+    public org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason spawnReason;
     // Paper end
     static boolean isLevelAtLeast(NBTTagCompound tag, int level) {
         return tag.hasKey("Bukkit.updateLevel") && tag.getInt("Bukkit.updateLevel") >= level;
@@ -1592,6 +1593,9 @@ 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);
@@ -1726,6 +1730,26 @@ 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 ce66596c63..5645147dad 100644
--- a/src/main/java/net/minecraft/server/PlayerList.java
+++ b/src/main/java/net/minecraft/server/PlayerList.java
@@ -250,7 +250,7 @@ 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 9c4ef2e004..1a01e5e696 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -932,6 +932,7 @@ 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
         if (entity.valid) { MinecraftServer.LOGGER.error("Attempted Double World add on " + entity, new Throwable()); return true; } // Paper
         if (entity.dead) {
             // Paper start
diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
index 1cd3448e57..15042943c9 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
@@ -1053,5 +1053,10 @@ 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
 }
-- 
2.21.0