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 2b87c6eb28d4db634dd6d8ee42ff3aa78ed7cb68..f64aa22ed6fcb4af67317b99f459ee5296392548 100644
--- a/src/main/java/com/mojang/brigadier/tree/CommandNode.java
+++ b/src/main/java/com/mojang/brigadier/tree/CommandNode.java
@@ -74,10 +74,10 @@ public abstract class CommandNode<S> implements Comparable<CommandNode<S>> {
     public synchronized boolean canUse(final S source) {
         if (source instanceof CommandSourceStack) {
             try {
-                ((CommandSourceStack) source).currentCommand = this;
+                ((CommandSourceStack) source).currentCommand.put(Thread.currentThread(), this); // Paper
                 return this.requirement.test(source);
             } finally {
-                ((CommandSourceStack) source).currentCommand = null;
+                ((CommandSourceStack) source).currentCommand.remove(Thread.currentThread()); // Paper
             }
         }
         // CraftBukkit end
diff --git a/src/main/java/net/minecraft/commands/CommandSourceStack.java b/src/main/java/net/minecraft/commands/CommandSourceStack.java
index 31aaad639b6c285226ca7aca1bd2285cfe0d9117..db26d834d9a59c4fd60f99077f0118c08293678f 100644
--- a/src/main/java/net/minecraft/commands/CommandSourceStack.java
+++ b/src/main/java/net/minecraft/commands/CommandSourceStack.java
@@ -56,7 +56,7 @@ public class CommandSourceStack implements SharedSuggestionProvider, com.destroy
     private final ResultConsumer<CommandSourceStack> consumer;
     private final EntityAnchorArgument.Anchor anchor;
     private final Vec2 rotation;
-    public volatile CommandNode currentCommand; // CraftBukkit
+    public java.util.Map<Thread, CommandNode> currentCommand = new java.util.concurrent.ConcurrentHashMap<>(); // CraftBukkit // Paper
 
     public CommandSourceStack(CommandSource output, Vec3 pos, Vec2 rot, ServerLevel world, int level, String name, Component displayName, MinecraftServer server, @Nullable Entity entity) {
         this(output, pos, rot, world, level, name, displayName, server, entity, false, (commandcontext, flag, j) -> {
@@ -177,9 +177,11 @@ public class CommandSourceStack implements SharedSuggestionProvider, com.destroy
     @Override
     public boolean hasPermission(int level) {
         // CraftBukkit start
-        CommandNode currentCommand = this.currentCommand;
+        // Paper start - fix concurrency issue
+        CommandNode currentCommand = this.currentCommand.get(Thread.currentThread());
         if (currentCommand != null) {
             return this.hasPermission(level, org.bukkit.craftbukkit.command.VanillaCommandWrapper.getPermission(currentCommand));
+            // Paper end
         }
         // CraftBukkit end