PaperMC/nms-patches/BlockWitherSkull.patch

--- a/net/minecraft/server/BlockWitherSkull.java
+++ b/net/minecraft/server/BlockWitherSkull.java
@@ -3,6 +3,11 @@
 import java.util.Iterator;
 import javax.annotation.Nullable;
 
+// CraftBukkit start
+import org.bukkit.craftbukkit.util.BlockStateListPopulator;
+import org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason;
+// CraftBukkit end
+
 public class BlockWitherSkull extends BlockSkull {
 
     @Nullable
@@ -26,6 +31,7 @@
     }
 
     public static void a(World world, BlockPosition blockposition, TileEntitySkull tileentityskull) {
+        if (world.captureBlockStates) return; // CraftBukkit
         if (!world.isClientSide) {
             Block block = tileentityskull.getBlock().getBlock();
             boolean flag = block == Blocks.WITHER_SKELETON_SKULL || block == Blocks.WITHER_SKELETON_WALL_SKULL;
@@ -35,12 +41,14 @@
                 ShapeDetector.ShapeDetectorCollection shapedetector_shapedetectorcollection = shapedetector.a(world, blockposition);
 
                 if (shapedetector_shapedetectorcollection != null) {
+                    // CraftBukkit start - Use BlockStateListPopulator
+                    BlockStateListPopulator blockList = new BlockStateListPopulator(world);
                     for (int i = 0; i < shapedetector.c(); ++i) {
                         for (int j = 0; j < shapedetector.b(); ++j) {
                             ShapeDetectorBlock shapedetectorblock = shapedetector_shapedetectorcollection.a(i, j, 0);
 
-                            world.setTypeAndData(shapedetectorblock.getPosition(), Blocks.AIR.getBlockData(), 2);
-                            world.triggerEffect(2001, shapedetectorblock.getPosition(), Block.getCombinedId(shapedetectorblock.a()));
+                            blockList.setTypeAndData(shapedetectorblock.getPosition(), Blocks.AIR.getBlockData(), 2); // CraftBukkit
+                            // world.triggerEffect(2001, shapedetectorblock.getPosition(), Block.getCombinedId(shapedetectorblock.a())); // CraftBukkit
                         }
                     }
 
@@ -50,6 +58,15 @@
                     entitywither.setPositionRotation((double) blockposition1.getX() + 0.5D, (double) blockposition1.getY() + 0.55D, (double) blockposition1.getZ() + 0.5D, shapedetector_shapedetectorcollection.getFacing().m() == EnumDirection.EnumAxis.X ? 0.0F : 90.0F, 0.0F);
                     entitywither.aI = shapedetector_shapedetectorcollection.getFacing().m() == EnumDirection.EnumAxis.X ? 0.0F : 90.0F;
                     entitywither.l();
+                    // CraftBukkit start
+                    if (!world.addEntity(entitywither, SpawnReason.BUILD_WITHER)) {
+                        return;
+                    }
+                    for (BlockPosition pos : blockList.getBlocks()) {
+                        world.triggerEffect(2001, pos, Block.getCombinedId(world.getType(pos)));
+                    }
+                    blockList.updateList();
+                    // CraftBukkit end
                     Iterator iterator = world.a(EntityPlayer.class, entitywither.getBoundingBox().g(50.0D)).iterator();
 
                     while (iterator.hasNext()) {
@@ -58,7 +75,7 @@
                         CriterionTriggers.n.a(entityplayer, (Entity) entitywither);
                     }
 
-                    world.addEntity(entitywither);
+                    // world.addEntity(entitywither); // CraftBukkit - moved up
 
                     for (int k = 0; k < shapedetector.c(); ++k) {
                         for (int l = 0; l < shapedetector.b(); ++l) {