Paper/nms-patches/EntityVillagerTrader.patch

--- a/net/minecraft/server/EntityVillagerTrader.java
+++ b/net/minecraft/server/EntityVillagerTrader.java
@@ -2,6 +2,12 @@
 
 import java.util.EnumSet;
 import javax.annotation.Nullable;
+// CraftBukkit start
+import org.bukkit.Bukkit;
+import org.bukkit.craftbukkit.inventory.CraftMerchantRecipe;
+import org.bukkit.entity.AbstractVillager;
+import org.bukkit.event.entity.VillagerAcquireTradeEvent;
+// CraftBukkit end
 
 public class EntityVillagerTrader extends EntityVillagerAbstract {
 
@@ -92,7 +98,16 @@
             MerchantRecipe merchantrecipe = villagertrades_imerchantrecipeoption.a(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
             }
 
         }