PaperMC/paper-server/nms-patches/net/minecraft/world/entity/npc/EntityVillagerAbstract.patch

--- a/net/minecraft/world/entity/npc/EntityVillagerAbstract.java
+++ b/net/minecraft/world/entity/npc/EntityVillagerAbstract.java
@@ -35,8 +35,24 @@
 import net.minecraft.world.level.pathfinder.PathType;
 import net.minecraft.world.phys.Vec3D;
 
+// CraftBukkit start
+import org.bukkit.Bukkit;
+import org.bukkit.craftbukkit.inventory.CraftMerchant;
+import org.bukkit.craftbukkit.inventory.CraftMerchantRecipe;
+import org.bukkit.entity.AbstractVillager;
+import org.bukkit.event.entity.VillagerAcquireTradeEvent;
+// CraftBukkit end
+
 public abstract class EntityVillagerAbstract extends EntityAgeable implements InventoryCarrier, NPC, IMerchant {
 
+    // CraftBukkit start
+    private CraftMerchant craftMerchant;
+
+    @Override
+    public CraftMerchant getCraftMerchant() {
+        return (craftMerchant == null) ? craftMerchant = new CraftMerchant(this) : craftMerchant;
+    }
+    // CraftBukkit end
     private static final DataWatcherObject<Integer> DATA_UNHAPPY_COUNTER = DataWatcher.defineId(EntityVillagerAbstract.class, DataWatcherRegistry.INT);
     public static final int VILLAGER_SLOT_OFFSET = 300;
     private static final int VILLAGER_INVENTORY_SIZE = 8;
@@ -44,7 +60,7 @@
     private EntityHuman tradingPlayer;
     @Nullable
     protected MerchantRecipeList offers;
-    private final InventorySubcontainer inventory = new InventorySubcontainer(8);
+    private final InventorySubcontainer inventory = new InventorySubcontainer(8, (org.bukkit.craftbukkit.entity.CraftAbstractVillager) this.getBukkitEntity()); // CraftBukkit add argument
 
     public EntityVillagerAbstract(EntityTypes<? extends EntityVillagerAbstract> entitytypes, World world) {
         super(entitytypes, world);
@@ -233,7 +249,16 @@
             MerchantRecipe merchantrecipe = ((VillagerTrades.IMerchantRecipeOption) arraylist.remove(this.random.nextInt(arraylist.size()))).getOffer(this, this.random);
 
             if (merchantrecipe != null) {
-                merchantrecipelist.add(merchantrecipe);
+                // CraftBukkit start
+                VillagerAcquireTradeEvent event = new VillagerAcquireTradeEvent((AbstractVillager) getBukkitEntity(), merchantrecipe.asBukkit());
+                // Suppress during worldgen
+                if (this.valid) {
+                    Bukkit.getPluginManager().callEvent(event);
+                }
+                if (!event.isCancelled()) {
+                    merchantrecipelist.add(CraftMerchantRecipe.fromBukkit(event.getRecipe()).toMinecraft());
+                }
+                // CraftBukkit end
                 ++j;
             }
         }