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 a4f97c1df86c574af9b9824a38034a3d76d6e357..d65defd5fc54086a969c568b93dfb05f40dd5a44 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 981f08a537253516a6ce8b78f6cd04d7e5e1b546..b14773074fc4b10ef427eb0ad9e21601a7287901 100644
--- a/src/main/java/net/minecraft/commands/CommandSourceStack.java
+++ b/src/main/java/net/minecraft/commands/CommandSourceStack.java
@@ -59,7 +59,7 @@ public class CommandSourceStack implements SharedSuggestionProvider, com.destroy
     private final Vec2 rotation;
     private final CommandSigningContext signingContext;
     private final TaskChainer chatMessageChainer;
-    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) -> {
@@ -195,9 +195,11 @@ 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
 
