PaperMC/paper-server/nms-patches/net/minecraft/world/level/block/LayeredCauldronBlock.patch

--- a/net/minecraft/world/level/block/LayeredCauldronBlock.java
+++ b/net/minecraft/world/level/block/LayeredCauldronBlock.java
@@ -17,6 +17,11 @@
 import net.minecraft.world.level.material.FluidType;
 import net.minecraft.world.level.material.FluidTypes;
 
+// CraftBukkit start
+import org.bukkit.craftbukkit.block.CraftBlockState;
+import org.bukkit.event.block.CauldronLevelChangeEvent;
+// CraftBukkit end
+
 public class LayeredCauldronBlock extends AbstractCauldronBlock {
 
     public static final int MIN_FILL_LEVEL = 1;
@@ -56,10 +61,14 @@
     @Override
     public void a(IBlockData iblockdata, World world, BlockPosition blockposition, Entity entity) {
         if (!world.isClientSide && entity.isBurning() && this.a(iblockdata, blockposition, entity)) {
-            entity.extinguish();
+            // CraftBukkit start
             if (entity.a(world, blockposition)) {
-                this.d(iblockdata, world, blockposition);
+                if (!decreaseLevel(iblockdata, world, blockposition, entity, CauldronLevelChangeEvent.ChangeReason.EXTINGUISH)) {
+                    return;
+                }
             }
+            entity.extinguish();
+            // CraftBukkit end
         }
 
     }
@@ -69,15 +78,38 @@
     }
 
     public static void e(IBlockData iblockdata, World world, BlockPosition blockposition) {
+        // CraftBukkit start
+        decreaseLevel(iblockdata, world, blockposition, null, CauldronLevelChangeEvent.ChangeReason.UNKNOWN);
+    }
+
+    public static boolean decreaseLevel(IBlockData iblockdata, World world, BlockPosition blockposition, Entity entity, CauldronLevelChangeEvent.ChangeReason reason) {
         int i = (Integer) iblockdata.get(LayeredCauldronBlock.LEVEL) - 1;
 
-        world.setTypeUpdate(blockposition, i == 0 ? Blocks.CAULDRON.getBlockData() : (IBlockData) iblockdata.set(LayeredCauldronBlock.LEVEL, i));
+        return changeLevel(iblockdata, world, blockposition, i == 0 ? Blocks.CAULDRON.getBlockData() : iblockdata.set(LayeredCauldronBlock.LEVEL, i), entity, reason);
     }
 
+    // CraftBukkit start
+    public static boolean changeLevel(IBlockData iblockdata, World world, BlockPosition blockposition, IBlockData newBlock, Entity entity, CauldronLevelChangeEvent.ChangeReason reason) {
+        CraftBlockState newState = CraftBlockState.getBlockState(world, blockposition);
+        newState.setData(newBlock);
+
+        CauldronLevelChangeEvent event = new CauldronLevelChangeEvent(
+                world.getWorld().getBlockAt(blockposition.getX(), blockposition.getY(), blockposition.getZ()),
+                (entity == null) ? null : entity.getBukkitEntity(), reason, newState
+        );
+        world.getCraftServer().getPluginManager().callEvent(event);
+        if (event.isCancelled()) {
+            return false;
+        }
+        newState.update(true);
+        return true;
+    }
+    // CraftBukkit end
+
     @Override
     public void a(IBlockData iblockdata, World world, BlockPosition blockposition, BiomeBase.Precipitation biomebase_precipitation) {
         if (BlockCauldron.a(world, biomebase_precipitation) && (Integer) iblockdata.get(LayeredCauldronBlock.LEVEL) != 3 && this.fillPredicate.test(biomebase_precipitation)) {
-            world.setTypeUpdate(blockposition, (IBlockData) iblockdata.a((IBlockState) LayeredCauldronBlock.LEVEL));
+            changeLevel(iblockdata, world, blockposition, (IBlockData) iblockdata.a((IBlockState) LayeredCauldronBlock.LEVEL), null, CauldronLevelChangeEvent.ChangeReason.NATURAL_FILL); // CraftBukkit
         }
     }
 
@@ -94,7 +126,11 @@
     @Override
     protected void a(IBlockData iblockdata, World world, BlockPosition blockposition, FluidType fluidtype) {
         if (!this.c(iblockdata)) {
-            world.setTypeUpdate(blockposition, (IBlockData) iblockdata.set(LayeredCauldronBlock.LEVEL, (Integer) iblockdata.get(LayeredCauldronBlock.LEVEL) + 1));
+            // CraftBukkit start
+            if (!changeLevel(iblockdata, world, blockposition, (IBlockData) iblockdata.set(LayeredCauldronBlock.LEVEL, (Integer) iblockdata.get(LayeredCauldronBlock.LEVEL) + 1), null, CauldronLevelChangeEvent.ChangeReason.NATURAL_FILL)) {
+                return;
+            }
+            // CraftBukkit end
             world.triggerEffect(1047, blockposition, 0);
         }
     }