From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: dfsek <dfsek@protonmail.com>
Date: Sat, 19 Jun 2021 20:15:59 -0700
Subject: [PATCH] Add Feature Generation API


diff --git a/src/main/java/io/papermc/paper/world/gen/CraftProtoWorld.java b/src/main/java/io/papermc/paper/world/gen/CraftProtoWorld.java
new file mode 100644
index 0000000000000000000000000000000000000000..33de2d14a90b405c6c0057e1f01d38a5c9e0d3f2
--- /dev/null
+++ b/src/main/java/io/papermc/paper/world/gen/CraftProtoWorld.java
@@ -0,0 +1,94 @@
+package io.papermc.paper.world.gen;
+
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.WorldGenRegion;
+import net.minecraft.world.entity.Mob;
+import net.minecraft.world.entity.MobSpawnType;
+import net.minecraft.world.entity.SpawnGroupData;
+import org.bukkit.World;
+import org.bukkit.block.data.BlockData;
+import org.bukkit.craftbukkit.block.data.CraftBlockData;
+import org.bukkit.entity.Entity;
+import org.bukkit.event.entity.CreatureSpawnEvent;
+import org.bukkit.util.Vector;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Objects;
+import java.util.function.Consumer;
+
+public class CraftProtoWorld implements ProtoWorld {
+    private WorldGenRegion region;
+
+    public CraftProtoWorld(WorldGenRegion region) {
+        this.region = region;
+    }
+
+    public void clearReference() {
+        region = null;
+    }
+
+    @Override
+    public void setBlockData(int x, int y, int z, @NotNull BlockData data) {
+        BlockPos position = new BlockPos(x, y, z);
+        getDelegate().setBlock(position, ((CraftBlockData) data).getState(), 3);
+    }
+
+    @Override
+    public void scheduleBlockUpdate(int x, int y, int z) {
+        BlockPos position = new BlockPos(x, y, z);
+        getDelegate().getBlockTicks().scheduleTick(position, getDelegate().getBlockIfLoaded(position), 0);
+    }
+
+    @Override
+    public void scheduleFluidUpdate(int x, int y, int z) {
+        BlockPos position = new BlockPos(x, y, z);
+        getDelegate().getLiquidTicks().scheduleTick(position, getDelegate().getFluidState(position).getType(), 0);
+    }
+
+    @Override
+    public @NotNull World getWorld() {
+        // reading/writing the returned Minecraft world causes a deadlock.
+        // By implementing this, and covering it in warnings, we're assuming people won't be stupid, and
+        // if they are stupid, they'll figure it out pretty fast.
+        return getDelegate().getMinecraftWorld().getWorld();
+    }
+
+    @Override
+    public @NotNull BlockData getBlockData(int x, int y, int z) {
+        return CraftBlockData.fromData(getDelegate().getBlockState(new BlockPos(x, y, z)));
+    }
+
+    @Override
+    public int getCenterChunkX() {
+        return getDelegate().getCenter().x;
+    }
+
+    @Override
+    public int getCenterChunkZ() {
+        return getDelegate().getCenter().z;
+    }
+
+    @SuppressWarnings({"unchecked", "deprecation"})
+    @Override
+    public <T extends Entity> @NotNull T spawn(@NotNull Vector location, @NotNull Class<T> clazz, @Nullable Consumer<T> function, CreatureSpawnEvent.@NotNull SpawnReason reason) throws IllegalArgumentException {
+        net.minecraft.world.entity.Entity entity = getDelegate().getMinecraftWorld().getWorld().createEntity(location.toLocation(getWorld()), clazz);
+        Objects.requireNonNull(entity, "Cannot spawn null entity");
+        if (entity instanceof Mob) {
+            ((Mob) entity).finalizeSpawn(getDelegate(), getDelegate().getCurrentDifficultyAt(entity.blockPosition()), MobSpawnType.COMMAND, (SpawnGroupData) null, null);
+        }
+
+        if (function != null) {
+            function.accept((T) entity.getBukkitEntity());
+        }
+
+        getDelegate().addEntity(entity, reason);
+        return (T) entity.getBukkitEntity();
+    }
+
+    @NotNull
+    private WorldGenRegion getDelegate() {
+        return Objects.requireNonNull(region, "Cannot access ProtoWorld after generation!");
+    }
+}
+
diff --git a/src/main/java/org/bukkit/craftbukkit/generator/CustomChunkGenerator.java b/src/main/java/org/bukkit/craftbukkit/generator/CustomChunkGenerator.java
index 46ce973ca68420825316352ad4df907edf52bfec..bd1794ac7c7d736457203b4773f89af23d21a63d 100644
--- a/src/main/java/org/bukkit/craftbukkit/generator/CustomChunkGenerator.java
+++ b/src/main/java/org/bukkit/craftbukkit/generator/CustomChunkGenerator.java
@@ -191,6 +191,12 @@ public class CustomChunkGenerator extends InternalChunkGenerator {
         if (this.generator.shouldGenerateDecorations()) {
             this.delegate.applyBiomeDecoration(region, accessor);
         }
+
+        // Paper start
+        io.papermc.paper.world.gen.CraftProtoWorld protoWorld = new io.papermc.paper.world.gen.CraftProtoWorld(region);
+        generator.generateDecorations(protoWorld);
+        protoWorld.clearReference(); // make sure people dont try to use the ProtoWorld after we're done with it.
+        // Paper end
     }
 
     @Override