Fix issues with client only commands in combination with server only commands not using MC's command system. (#8452)

src/main/java/net/minecraftforge/client/ClientCommandHandler.java

@@ -35,6 +35,7 @@ import com.mojang.brigadier.tree.RootCommandNode;
 import net.minecraft.ChatFormatting;
 import net.minecraft.Util;
 import net.minecraft.client.Minecraft;
+import net.minecraft.client.multiplayer.ClientPacketListener;
 import net.minecraft.client.player.LocalPlayer;
 import net.minecraft.commands.CommandRuntimeException;
 import net.minecraft.commands.CommandSourceStack;
@@ -46,6 +47,7 @@ import net.minecraft.network.chat.HoverEvent;
 import net.minecraft.network.chat.MutableComponent;
 import net.minecraft.network.chat.TextComponent;
 import net.minecraft.network.chat.TranslatableComponent;
+import net.minecraftforge.client.event.ClientPlayerNetworkEvent;
 import net.minecraftforge.client.event.RegisterClientCommandsEvent;
 import net.minecraftforge.common.MinecraftForge;
 import org.apache.logging.log4j.LogManager;
@@ -60,6 +62,22 @@ public class ClientCommandHandler
     private static final Logger LOGGER = LogManager.getLogger();
     private static CommandDispatcher<CommandSourceStack> commands = null;
 
+    public static void init()
+    {
+        MinecraftForge.EVENT_BUS.addListener(ClientCommandHandler::handleClientPlayerLogin);
+    }
+
+    private static void handleClientPlayerLogin(ClientPlayerNetworkEvent.LoggedInEvent event)
+    {
+        // some custom server implementations do not send ClientboundCommandsPacket, provide a fallback
+        var suggestionDispatcher = mergeServerCommands(new CommandDispatcher<>());
+        if (event.getConnection().getPacketListener() instanceof ClientPacketListener listener)
+        {
+            // Must set this, so that suggestions for client-only commands work, if server never sends commands packet
+            listener.commands = suggestionDispatcher;
+        }
+    }
+
     /*
      * For internal use
      * 
@@ -144,11 +162,17 @@ public class ClientCommandHandler
      */
     private static <S> void copy(CommandNode<S> sourceNode, CommandNode<S> resultNode)
     {
+        Map<CommandNode<S>, CommandNode<S>> newNodes = new IdentityHashMap<>();
+        newNodes.put(sourceNode, resultNode);
         for (CommandNode<S> child : sourceNode.getChildren())
         {
-            ArgumentBuilder<S, ?> builder = child.createBuilder();
-            CommandNode<S> copy = builder.build();
-            copy(child, copy);
+            CommandNode<S> copy = newNodes.computeIfAbsent(child, innerChild ->
+            {
+                ArgumentBuilder<S, ?> builder = innerChild.createBuilder();
+                CommandNode<S> innerCopy = builder.build();
+                copy(innerChild, innerCopy);
+                return innerCopy;
+            });
             resultNode.addChild(copy);
         }
     }
@@ -278,6 +302,11 @@ public class ClientCommandHandler
         }
         catch (CommandSyntaxException syntax)// Usually thrown by the CommandDispatcher
         {
+            if (syntax.getType() == CommandSyntaxException.BUILT_IN_EXCEPTIONS.dispatcherUnknownCommand())
+            {
+                // in case of unknown command, let the server try and handle it
+                return false;
+            }
             Minecraft.getInstance().player.sendMessage(
                     new TextComponent("").append(ComponentUtils.fromMessage(syntax.getRawMessage())).withStyle(ChatFormatting.RED), Util.NIL_UUID);
             if (syntax.getInput() != null && syntax.getCursor() >= 0)

src/main/java/net/minecraftforge/common/MinecraftForge.java

@@ -19,8 +19,11 @@
 
 package net.minecraftforge.common;
 
+import net.minecraftforge.api.distmarker.Dist;
+import net.minecraftforge.client.ClientCommandHandler;
 import net.minecraftforge.eventbus.api.BusBuilder;
 import net.minecraftforge.eventbus.api.IEventBus;
+import net.minecraftforge.fml.loading.FMLEnvironment;
 import net.minecraftforge.versions.forge.ForgeVersion;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -52,6 +55,7 @@ public class MinecraftForge
 
        UsernameCache.load();
        TierSortingRegistry.init();
+       if (FMLEnvironment.dist == Dist.CLIENT) ClientCommandHandler.init();
    }
 
 /*