From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sun, 19 Apr 2020 00:05:46 -0400
Subject: [PATCH] Fix Longstanding Broken behavior of PlayerJoinEvent

For years, plugin developers have had to delay many things they do
inside of the PlayerJoinEvent by 1 tick to make it actually work.

This all boiled down to 1 reason why: The event fired before the
player was fully ready and joined to the world!

Additionally, if that player logged out on a vehicle, the event
fired before the vehicle was even loaded, so that plugins had no
access to the vehicle during this event either.

This change finally fixes this issue, fully preparing the player
into the world as a fully ready entity, vehicle included.

There should be no plugins that break because of this change, but might
improve consistency with other plugins instead.

For example, if 2 plugins listens to this event, and the first one
teleported the player in the event, then the 2nd plugin actually
would be getting a valid player!

This was very non deterministic. This change will ensure every plugin
receives a deterministic result, and should no longer require 1 tick
delays anymore.

diff --git a/src/main/java/net/minecraft/server/EntityPlayer.java b/src/main/java/net/minecraft/server/EntityPlayer.java
index ef35e07fd8b27a66710140c1422f88ad512e774f..56cf64709ae520287f6687fe7c2f55040cc769a1 100644
--- a/src/main/java/net/minecraft/server/EntityPlayer.java
+++ b/src/main/java/net/minecraft/server/EntityPlayer.java
@@ -104,6 +104,7 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
     public double maxHealthCache;
     public boolean joining = true;
     public boolean sentListPacket = false;
+    public boolean supressTrackerForLogin = false; // Paper
     public Integer clientViewDistance;
     // CraftBukkit end
     public PlayerNaturallySpawnCreaturesEvent playerNaturallySpawnedEvent; // Paper
diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
index 4ab719930f5b35c0ae221e9345f1e2eda7d9d719..8de86684dda275585826617b41d6792f233b814c 100644
--- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
@@ -1535,6 +1535,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
                 .printStackTrace();
             return;
         }
+        if (entity instanceof EntityPlayer && ((EntityPlayer) entity).supressTrackerForLogin) return; // Delay adding to tracker until after list packets
         // Paper end
         if (!(entity instanceof EntityComplexPart)) {
             EntityTypes<?> entitytypes = entity.getEntityType();
diff --git a/src/main/java/net/minecraft/server/PlayerList.java b/src/main/java/net/minecraft/server/PlayerList.java
index 06c675ce3b61766dbb7b456fd6aa46f55357e1b8..a2c9cb6b5c06a76b5fafb75ef51293832f0f4620 100644
--- a/src/main/java/net/minecraft/server/PlayerList.java
+++ b/src/main/java/net/minecraft/server/PlayerList.java
@@ -202,6 +202,12 @@ public abstract class PlayerList {
         this.j.put(entityplayer.getUniqueID(), entityplayer);
         // this.sendAll(new PacketPlayOutPlayerInfo(PacketPlayOutPlayerInfo.EnumPlayerInfoAction.ADD_PLAYER, new EntityPlayer[]{entityplayer})); // CraftBukkit - replaced with loop below
 
+        // Paper start - correctly register player BEFORE PlayerJoinEvent, so the entity is valid and doesn't require tick delay hacks
+        entityplayer.supressTrackerForLogin = true;
+        worldserver.addPlayerJoin(entityplayer);
+        this.server.getBossBattleCustomData().a(entityplayer); // see commented out section below worldserver.addPlayerJoin(entityplayer);
+        mountSavedVehicle(entityplayer, worldserver, nbttagcompound);
+        // Paper end
         // CraftBukkit start
         PlayerJoinEvent playerJoinEvent = new PlayerJoinEvent(cserver.getPlayer(entityplayer), joinMessage);
         cserver.getPluginManager().callEvent(playerJoinEvent);
@@ -236,6 +242,8 @@ public abstract class PlayerList {
             entityplayer.playerConnection.sendPacket(new PacketPlayOutPlayerInfo(PacketPlayOutPlayerInfo.EnumPlayerInfoAction.ADD_PLAYER, new EntityPlayer[] { entityplayer1}));
         }
         entityplayer.sentListPacket = true;
+        entityplayer.supressTrackerForLogin = false; // Paper
+        ((WorldServer)entityplayer.world).getChunkProvider().playerChunkMap.addEntity(entityplayer); // Paper - track entity now
         // CraftBukkit end
 
         entityplayer.playerConnection.sendPacket(new PacketPlayOutEntityMetadata(entityplayer.getId(), entityplayer.datawatcher, true)); // CraftBukkit - BungeeCord#2321, send complete data to self on spawn
@@ -261,6 +269,11 @@ public abstract class PlayerList {
             playerconnection.sendPacket(new PacketPlayOutEntityEffect(entityplayer.getId(), mobeffect));
         }
 
+        // Paper start - move vehicle into method so it can be called above - short circuit around that code
+        onPlayerJoinFinish(entityplayer, worldserver, s1);
+    }
+    private void mountSavedVehicle(EntityPlayer entityplayer, WorldServer worldserver, NBTTagCompound nbttagcompound) {
+        // Paper end
         if (nbttagcompound != null && nbttagcompound.hasKeyOfType("RootVehicle", 10)) {
             NBTTagCompound nbttagcompound1 = nbttagcompound.getCompound("RootVehicle");
             // CraftBukkit start
@@ -309,6 +322,10 @@ public abstract class PlayerList {
             }
         }
 
+        // Paper start
+    }
+    public void onPlayerJoinFinish(EntityPlayer entityplayer, WorldServer worldserver1, String s1) {
+        // Paper end
         entityplayer.syncInventory();
         // Paper start - Add to collideRule team if needed
         final Scoreboard scoreboard = this.getServer().getWorldServer(World.OVERWORLD).getScoreboard();