From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: commandblockguy <commandblockguy1@gmail.com>
Date: Fri, 14 Aug 2020 14:44:14 -0500
Subject: [PATCH] Prevent headless pistons from being created

Prevent headless pistons from being created by explosions or tree/mushroom growth.

diff --git a/src/main/java/net/minecraft/world/level/Explosion.java b/src/main/java/net/minecraft/world/level/Explosion.java
index 1350c8df69b4ffcf9daa73549e496627db8bc6f7..69914a048987c21ee2ed2c489aab269862fda8f2 100644
--- a/src/main/java/net/minecraft/world/level/Explosion.java
+++ b/src/main/java/net/minecraft/world/level/Explosion.java
@@ -207,6 +207,15 @@ public class Explosion {
 
                             if (f > 0.0F && this.damageCalculator.shouldBlockExplode(this, this.level, blockposition, iblockdata, f)) {
                                 set.add(blockposition);
+                                // Paper start - prevent headless pistons from forming
+                                if (!io.papermc.paper.configuration.GlobalConfiguration.get().unsupportedSettings.allowHeadlessPistons && iblockdata.getBlock() == Blocks.MOVING_PISTON) {
+                                    net.minecraft.world.level.block.entity.BlockEntity extension = this.level.getBlockEntity(blockposition);
+                                    if (extension instanceof net.minecraft.world.level.block.piston.PistonMovingBlockEntity blockEntity && blockEntity.isSourcePiston()) {
+                                       net.minecraft.core.Direction direction = iblockdata.getValue(net.minecraft.world.level.block.piston.PistonHeadBlock.FACING);
+                                       set.add(blockposition.relative(direction.getOpposite()));
+                                    }
+                                }
+                                // Paper end - prevent headless pistons from forming
                             }
 
                             d4 += d0 * 0.30000001192092896D;