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 74af1b6158394d66fe470f9b7db741871f2bb534..30274979d8dafc7c0a374c3e6b1d1b5dbd6cfe4c 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 a59d14e61fcbca7861a5593d0717b81262ccbdc5..71e29d29ed5c2d61832e2f124967bb223708406f 100644
--- a/src/main/java/net/minecraft/commands/CommandSourceStack.java
+++ b/src/main/java/net/minecraft/commands/CommandSourceStack.java
@@ -9,8 +9,10 @@ import com.mojang.brigadier.suggestion.Suggestions;
 import com.mojang.brigadier.suggestion.SuggestionsBuilder;
 import java.util.Collection;
 import java.util.Iterator;
+import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.BinaryOperator;
 import java.util.stream.Stream;
 import javax.annotation.Nullable;
@@ -54,7 +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 Map<Thread, CommandNode> currentCommand = new 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) -> {
@@ -175,9 +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