From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Trigary <trigary0@gmail.com>
Date: Sat, 27 Mar 2021 11:13:30 +0100
Subject: [PATCH] fix cancelling block falling causing client desync


diff --git a/src/main/java/net/minecraft/world/entity/item/EntityFallingBlock.java b/src/main/java/net/minecraft/world/entity/item/EntityFallingBlock.java
index 62d8b53c024888aa43b8fddf8a475dfb8284a4cc..2a61c24dd26edf4c72e977c6024fe233bab08a2f 100644
--- a/src/main/java/net/minecraft/world/entity/item/EntityFallingBlock.java
+++ b/src/main/java/net/minecraft/world/entity/item/EntityFallingBlock.java
@@ -14,6 +14,7 @@ import net.minecraft.network.protocol.game.PacketPlayOutSpawnEntity;
 import net.minecraft.network.syncher.DataWatcher;
 import net.minecraft.network.syncher.DataWatcherObject;
 import net.minecraft.network.syncher.DataWatcherRegistry;
+import net.minecraft.server.level.WorldServer;
 import net.minecraft.tags.Tag;
 import net.minecraft.tags.TagsBlock;
 import net.minecraft.tags.TagsFluid;
@@ -43,6 +44,7 @@ import net.minecraft.world.phys.MovingObjectPosition;
 import net.minecraft.world.phys.MovingObjectPositionBlock;
 import net.minecraft.world.phys.Vec3D;
 
+import org.bukkit.craftbukkit.block.CraftBlock;
 import org.bukkit.craftbukkit.event.CraftEventFactory; // CraftBukkit
 
 public class EntityFallingBlock extends Entity {
@@ -116,8 +118,18 @@ public class EntityFallingBlock extends Entity {
 
             if (this.ticksLived++ == 0) {
                 blockposition = this.getChunkCoordinates();
-                if (this.world.getType(blockposition).a(block) && !CraftEventFactory.callEntityChangeBlockEvent(this, blockposition, Blocks.AIR.getBlockData()).isCancelled()) {
-                    this.world.a(blockposition, false);
+                // Paper start - fix cancelling block falling causing client desync
+                if (this.world.getType(blockposition).isSameInstance(block)) {
+                    if (CraftEventFactory.callEntityChangeBlockEvent(this, blockposition, Blocks.AIR.getBlockData()).isCancelled()) {
+                        if (this.world.getType(blockposition).isSameInstance(block)) { //if listener didn't update the block
+                            ((WorldServer) world).getChunkProvider().flagDirty(blockposition);
+                        }
+                        this.die();
+                        return;
+                    } else {
+                        this.world.setAir(blockposition, false);
+                    }
+                    // Paper end - fix cancelling block falling causing client desync
                 } else if (!this.world.isClientSide) {
                     this.die();
                     return;
diff --git a/src/main/java/net/minecraft/world/level/block/state/BlockBase.java b/src/main/java/net/minecraft/world/level/block/state/BlockBase.java
index 3fdafc0ff0c4148ec844dbdc1455d17cdcb4a75a..0d26250887f80d0c250bcd6bc7de303362427d3e 100644
--- a/src/main/java/net/minecraft/world/level/block/state/BlockBase.java
+++ b/src/main/java/net/minecraft/world/level/block/state/BlockBase.java
@@ -683,6 +683,7 @@ public abstract class BlockBase {
             return this.getBlock().a(tag) && predicate.test(this);
         }
 
+        public final boolean isSameInstance(Block block) { return a(block); } // Paper - OBFHELPER
         public boolean a(Block block) {
             return this.getBlock().a(block);
         }