Fix issues in VillagerTrades.EmeraldsForVillagerTypeItem related to custom Villager Types (#10358)

Add VillagerType#registerBiomeType
Co-authored-by: Joseph T. McQuigg <J.T.McQuigg12@gmail.com>

patches/minecraft/net/minecraft/world/entity/npc/VillagerTrades.java.patch

@@ -0,0 +1,21 @@
+--- a/net/minecraft/world/entity/npc/VillagerTrades.java
++++ b/net/minecraft/world/entity/npc/VillagerTrades.java
+@@ -191,6 +_,7 @@
+       private final int villagerXp;
+ 
+       public EmeraldsForVillagerTypeItem(int p_35669_, int p_35670_, int p_35671_, Map<VillagerType, Item> p_35672_) {
++         if (false) // FORGE: Modders can add custom villager types, so remove this validation
+          BuiltInRegistries.VILLAGER_TYPE.stream().filter((p_35680_) -> {
+             return !p_35672_.containsKey(p_35680_);
+          }).findAny().ifPresent((p_258962_) -> {
+@@ -205,7 +_,9 @@
+       @Nullable
+       public MerchantOffer getOffer(Entity p_219685_, RandomSource p_219686_) {
+          if (p_219685_ instanceof VillagerDataHolder villagerdataholder) {
+-            ItemStack itemstack = new ItemStack(this.trades.get(villagerdataholder.getVillagerData().getType()), this.cost);
++            Item item = this.trades.get(villagerdataholder.getVillagerData().getType());
++            if (item == null) return null; // FORGE: Account for modded villager types by returning null if there is no trade
++            ItemStack itemstack = new ItemStack(item, this.cost);
+             return new MerchantOffer(itemstack, new ItemStack(Items.EMERALD), this.maxUses, this.villagerXp, 0.05F);
+          } else {
+             return null;

patches/minecraft/net/minecraft/world/entity/npc/VillagerType.java.patch

@@ -0,0 +1,12 @@
+--- a/net/minecraft/world/entity/npc/VillagerType.java
++++ b/net/minecraft/world/entity/npc/VillagerType.java
+@@ -67,4 +_,9 @@
+    public static VillagerType byBiome(Holder<Biome> p_204074_) {
+       return p_204074_.unwrapKey().map(BY_BIOME::get).orElse(PLAINS);
+    }
++
++   /** FORGE: Registers the VillagerType that will spawn in the given biome. This method should be called during FMLCommonSetupEvent using event.enqueueWork() */
++   public static void registerBiomeType(ResourceKey<Biome> biomeKey, VillagerType villagerType) {
++      BY_BIOME.put(biomeKey, villagerType);
++   }
+ }

src/test/java/net/minecraftforge/debug/gameplay/villager/VillagerTypeTestMod.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) Forge Development LLC and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.minecraftforge.debug.gameplay.villager;
+
+import net.minecraft.core.Holder;
+import net.minecraft.core.RegistryAccess;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.gametest.framework.GameTest;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.world.entity.EntityType;
+import net.minecraft.world.entity.npc.Villager;
+import net.minecraft.world.entity.npc.VillagerTrades;
+import net.minecraft.world.entity.npc.VillagerType;
+import net.minecraft.world.item.Items;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.Biomes;
+import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.event.lifecycle.FMLCommonSetupEvent;
+import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
+import net.minecraftforge.gametest.GameTestHolder;
+import net.minecraftforge.registries.DeferredRegister;
+import net.minecraftforge.registries.RegistryObject;
+import net.minecraftforge.test.BaseTestMod;
+
+import java.util.Map;
+
+@GameTestHolder("forge." + VillagerTypeTestMod.MOD_ID)
+@Mod(VillagerTypeTestMod.MOD_ID)
+public class VillagerTypeTestMod extends BaseTestMod {
+    public static final String MOD_ID = "villager_type_test";
+
+    private static final DeferredRegister<VillagerType> VILLAGER_TYPES = DeferredRegister.create(Registries.VILLAGER_TYPE, MOD_ID);
+
+    private static final RegistryObject<VillagerType> TEST_VILLAGER_TYPE = VILLAGER_TYPES.register("test_villager_type", () -> new VillagerType("test_villager_type"));
+
+    public VillagerTypeTestMod(FMLJavaModLoadingContext context) {
+        context.getModEventBus().addListener(this::onCommonSetup);
+    }
+
+    private void onCommonSetup(final FMLCommonSetupEvent event) {
+        event.enqueueWork(() -> VillagerType.registerBiomeType(Biomes.PLAINS, TEST_VILLAGER_TYPE.get()));
+    }
+
+    @GameTest(template = "forge:empty3x3x3")
+    public static void biome_type(GameTestHelper helper) {
+        RegistryAccess access = helper.getLevel().registryAccess();
+        VillagerType type = access.registryOrThrow(Registries.VILLAGER_TYPE).get(TEST_VILLAGER_TYPE.getId());
+        if (type == null)
+            helper.fail("Failed to find test_villager_type");
+        helper.assertValueEqual(type, TEST_VILLAGER_TYPE.get(), "Loaded entry does not contain expected value");
+
+        Holder<Biome> biome = access.lookupOrThrow(Registries.BIOME).getOrThrow(Biomes.PLAINS);
+        helper.assertValueEqual(VillagerType.byBiome(biome), TEST_VILLAGER_TYPE.get(), "VillagerType.byBiome did not return the expected value");
+
+        helper.succeed();
+    }
+
+    /** Test verifies NPE not thrown when looking up a villager type in the trade that doesn't contain that type.*/
+    @GameTest(template = "forge:empty3x3x3")
+    public static void emeralds_for_villager_type(GameTestHelper helper) {
+        var trade = new VillagerTrades.EmeraldsForVillagerTypeItem(1, 12, 30, Map.of(TEST_VILLAGER_TYPE.get(), Items.DIRT));
+        var rnd = helper.getLevel().getRandom();
+
+        // Should be a successful trade for dirt for our test villager
+        var test = new Villager(EntityType.VILLAGER, helper.getLevel(), TEST_VILLAGER_TYPE.get());
+        var test_offer = trade.getOffer(test, rnd);
+        helper.assertFalse(test_offer == null, "Failed to retreive trade value for test profession");
+        helper.assertValueEqual(test_offer.getItemCostA().itemStack().getItem(), Items.DIRT, "Offer did not return the expected item");
+
+        var plains = new Villager(EntityType.VILLAGER, helper.getLevel(), VillagerType.PLAINS);
+        // This will NPE on unpatched code, we need to test that it returns null correctly
+        var plains_offer = trade.getOffer(plains, rnd);
+        helper.assertTrue(plains_offer == null, "Offer should not be available for a plains villager");
+
+        helper.succeed();
+    }
+}