From e8193ba5787a980b65b217dca1a15eb32cebbf81 Mon Sep 17 00:00:00 2001
From: Bruno Ploumhans <13494793+Technici4n@users.noreply.github.com>
Date: Sun, 22 Dec 2024 21:17:50 +0100
Subject: [PATCH] Fix #8295: CPU IGridMultiblock returning null nodes (#8298)

Confirmed to be an issue with our CPUs too. Going for the easy fix for
now.

(cherry picked from commit 5712d726882183bd1d83857f53004b970f11fb84)
---
 .../blockentity/crafting/CraftingBlockEntity.java | 15 ++++++++++++---
 .../appeng/me/pathfinding/PathingCalculation.java | 12 +++++++++++-
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/src/main/java/appeng/blockentity/crafting/CraftingBlockEntity.java b/src/main/java/appeng/blockentity/crafting/CraftingBlockEntity.java
index c5639290481..dda7b18ed91 100644
--- a/src/main/java/appeng/blockentity/crafting/CraftingBlockEntity.java
+++ b/src/main/java/appeng/blockentity/crafting/CraftingBlockEntity.java
@@ -23,8 +23,6 @@
 import java.util.Iterator;
 import java.util.Set;
 
-import com.google.common.collect.Iterators;
-
 import net.minecraft.Util;
 import net.minecraft.core.BlockPos;
 import net.minecraft.core.Direction;
@@ -331,7 +329,18 @@ private Iterator<IGridNode> getMultiblockNodes() {
         if (this.getCluster() == null) {
             return new ChainedIterator<>();
         }
-        return Iterators.transform(this.getCluster().getBlockEntities(), CraftingBlockEntity::getGridNode);
+        var nodes = new ArrayList<IGridNode>();
+        var it = this.getCluster().getBlockEntities();
+        while (it.hasNext()) {
+            var node = it.next().getGridNode();
+            if (node != null) {
+                // We might have built the multiblock before all nodes have been initialized.
+                // As a quick fix just ignore null nodes, which matches previous pathing behavior.
+                // See https://github.com/AppliedEnergistics/Applied-Energistics-2/issues/8295
+                nodes.add(node);
+            }
+        }
+        return nodes.iterator();
     }
 
     @Override
diff --git a/src/main/java/appeng/me/pathfinding/PathingCalculation.java b/src/main/java/appeng/me/pathfinding/PathingCalculation.java
index 56c23fa849c..0cfa2546225 100644
--- a/src/main/java/appeng/me/pathfinding/PathingCalculation.java
+++ b/src/main/java/appeng/me/pathfinding/PathingCalculation.java
@@ -25,6 +25,9 @@
 import java.util.Queue;
 import java.util.Set;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import it.unimi.dsi.fastutil.objects.Reference2IntOpenHashMap;
 
 import appeng.api.networking.GridFlags;
@@ -46,6 +49,8 @@
  * Second, a DFS is performed to propagate the channel count upwards.
  */
 public class PathingCalculation {
+    private static final Logger LOG = LoggerFactory.getLogger(PathingCalculation.class);
+
     private final IGrid grid;
     /**
      * Path items that are part of a multiblock that was already granted a channel.
@@ -152,7 +157,12 @@ private void processQueue(Queue<IPathItem> oldOpen, int queueIndex) {
                                     var oni = multiblock.getMultiblockNodes();
                                     while (oni.hasNext()) {
                                         final IGridNode otherNodes = oni.next();
-                                        if (otherNodes != pi) {
+                                        if (otherNodes == null) {
+                                            // Only a log for now until addons are fixed too. See
+                                            // https://github.com/AppliedEnergistics/Applied-Energistics-2/issues/8295
+                                            LOG.error("Skipping null node returned by grid multiblock node {}",
+                                                    multiblock);
+                                        } else if (otherNodes != pi) {
                                             this.multiblocksWithChannel.add((GridNode) otherNodes);
                                         }
                                     }