From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 11 Jul 2020 03:54:28 -0400
Subject: [PATCH] Thread Safe Vanilla Command permission checking

Datapacks check this on load and are built concurrently. This was breaking them badly due
to race conditions.

Plus, .canUse we want to be safe for async anyways.

diff --git a/src/main/java/com/mojang/brigadier/tree/CommandNode.java b/src/main/java/com/mojang/brigadier/tree/CommandNode.java
index 7ef6c99d2235eed38197aa76bc9553d7efbe52a4..c0fac7369b111e65b896a15848ae22457e5e8914 100644
--- a/src/main/java/com/mojang/brigadier/tree/CommandNode.java
+++ b/src/main/java/com/mojang/brigadier/tree/CommandNode.java
@@ -75,10 +75,10 @@ public abstract class CommandNode<S> implements Comparable<CommandNode<S>> {
     public synchronized boolean canUse(final S source) {
         if (source instanceof CommandListenerWrapper) {
             try {
-                ((CommandListenerWrapper) source).currentCommand = this;
+                ((CommandListenerWrapper) source).currentCommand.set(this); // Paper
                 return requirement.test(source);
             } finally {
-                ((CommandListenerWrapper) source).currentCommand = null;
+                ((CommandListenerWrapper) source).currentCommand.set(null); // Paper
             }
         }
         // CraftBukkit end
diff --git a/src/main/java/net/minecraft/commands/CommandListenerWrapper.java b/src/main/java/net/minecraft/commands/CommandListenerWrapper.java
index b5ee789c8dfb7f413ab60902ff3d2ef0cf8273cd..8402af32cc476d7f468842eb4f34c7521d72bcc8 100644
--- a/src/main/java/net/minecraft/commands/CommandListenerWrapper.java
+++ b/src/main/java/net/minecraft/commands/CommandListenerWrapper.java
@@ -55,7 +55,7 @@ public class CommandListenerWrapper implements ICompletionProvider, com.destroys
     private final ResultConsumer<CommandListenerWrapper> l;
     private final ArgumentAnchor.Anchor m;
     private final Vec2F n;
-    public volatile CommandNode currentCommand; // CraftBukkit
+    public ThreadLocal<CommandNode> currentCommand = new ThreadLocal<>(); // CraftBukkit // Paper
 
     public CommandListenerWrapper(ICommandListener icommandlistener, Vec3D vec3d, Vec2F vec2f, WorldServer worldserver, int i, String s, IChatBaseComponent ichatbasecomponent, MinecraftServer minecraftserver, @Nullable Entity entity) {
         this(icommandlistener, vec3d, vec2f, worldserver, i, s, ichatbasecomponent, minecraftserver, entity, false, (commandcontext, flag, j) -> {
@@ -172,9 +172,11 @@ public class CommandListenerWrapper implements ICompletionProvider, com.destroys
     @Override
     public boolean hasPermission(int i) {
         // CraftBukkit start
-        CommandNode currentCommand = this.currentCommand;
+        // Paper start - fix concurrency issue
+        CommandNode currentCommand = this.currentCommand.get();
         if (currentCommand != null) {
             return hasPermission(i, org.bukkit.craftbukkit.command.VanillaCommandWrapper.getPermission(currentCommand));
+            // Paper end
         }
         // CraftBukkit end