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

--- a/net/minecraft/world/level/block/BlockLeaves.java
+++ b/net/minecraft/world/level/block/BlockLeaves.java
@@ -21,6 +21,8 @@
 import net.minecraft.world.phys.shapes.VoxelShape;
 import net.minecraft.world.phys.shapes.VoxelShapes;
 
+import org.bukkit.event.block.LeavesDecayEvent; // CraftBukkit
+
 public class BlockLeaves extends Block {
 
     public static final int DECAY_DISTANCE = 7;
@@ -46,6 +48,14 @@
     @Override
     public void tick(IBlockData iblockdata, WorldServer worldserver, BlockPosition blockposition, Random random) {
         if (!(Boolean) iblockdata.get(BlockLeaves.PERSISTENT) && (Integer) iblockdata.get(BlockLeaves.DISTANCE) == 7) {
+            // CraftBukkit start
+            LeavesDecayEvent event = new LeavesDecayEvent(worldserver.getWorld().getBlockAt(blockposition.getX(), blockposition.getY(), blockposition.getZ()));
+            worldserver.getServer().getPluginManager().callEvent(event);
+
+            if (event.isCancelled() || worldserver.getType(blockposition).getBlock() != this) {
+                return;
+            }
+            // CraftBukkit end
             c(iblockdata, (World) worldserver, blockposition);
             worldserver.a(blockposition, false);
         }