Fix issues with new ChunkGenerator API

- RegionAccessor#setType / RegionAccessor#setBlockData doesn't run entity removal logic
- RegionAccessor#generateTree crashes by bee nest (TreeType#TALL_BIRCH)

By: DerFrZocker <derrieple@gmail.com>

paper-server/src/main/java/org/bukkit/craftbukkit/util/BlockStateListPopulator.java

@@ -1,55 +1,97 @@
 package org.bukkit.craftbukkit.util;
 
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import java.util.function.Predicate;
 import net.minecraft.core.BlockPosition;
+import net.minecraft.server.level.WorldServer;
 import net.minecraft.world.level.GeneratorAccess;
+import net.minecraft.world.level.block.ITileEntity;
+import net.minecraft.world.level.block.entity.TileEntity;
 import net.minecraft.world.level.block.state.IBlockData;
 import net.minecraft.world.level.dimension.DimensionManager;
 import net.minecraft.world.level.material.Fluid;
 import org.bukkit.block.BlockState;
 import org.bukkit.craftbukkit.block.CraftBlock;
+import org.bukkit.craftbukkit.block.CraftBlockEntityState;
 import org.bukkit.craftbukkit.block.CraftBlockState;
 
 public class BlockStateListPopulator extends DummyGeneratorAccess {
     private final GeneratorAccess world;
+    private final Map<BlockPosition, IBlockData> dataMap = new HashMap<>();
+    private final Map<BlockPosition, TileEntity> entityMap = new HashMap<>();
     private final LinkedHashMap<BlockPosition, CraftBlockState> list;
 
     public BlockStateListPopulator(GeneratorAccess world) {
         this(world, new LinkedHashMap<>());
     }
 
-    public BlockStateListPopulator(GeneratorAccess world, LinkedHashMap<BlockPosition, CraftBlockState> list) {
+    private BlockStateListPopulator(GeneratorAccess world, LinkedHashMap<BlockPosition, CraftBlockState> list) {
         this.world = world;
         this.list = list;
     }
 
     @Override
     public IBlockData getType(BlockPosition bp) {
-        CraftBlockState state = list.get(bp);
-        return (state != null) ? state.getHandle() : world.getType(bp);
+        IBlockData blockData = dataMap.get(bp);
+        return (blockData != null) ? blockData : world.getType(bp);
     }
 
     @Override
     public Fluid getFluid(BlockPosition bp) {
-        CraftBlockState state = list.get(bp);
-        return (state != null) ? state.getHandle().getFluid() : world.getFluid(bp);
+        IBlockData blockData = dataMap.get(bp);
+        return (blockData != null) ? blockData.getFluid() : world.getFluid(bp);
+    }
+
+    @Override
+    public TileEntity getTileEntity(BlockPosition blockposition) {
+        // The contains is important to check for null values
+        if (entityMap.containsKey(blockposition)) {
+            return entityMap.get(blockposition);
+        }
+
+        return world.getTileEntity(blockposition);
     }
 
     @Override
     public boolean setTypeAndData(BlockPosition position, IBlockData data, int flag) {
-        CraftBlockState state = (CraftBlockState) CraftBlock.at(world, position).getState();
-        state.setFlag(flag);
-        state.setData(data);
+        position = position.immutableCopy();
         // remove first to keep insertion order
         list.remove(position);
-        list.put(position.immutableCopy(), state);
+
+        dataMap.put(position, data);
+        if (data.isTileEntity()) {
+            entityMap.put(position, ((ITileEntity) data.getBlock()).createTile(position, data));
+        } else {
+            entityMap.put(position, null);
+        }
+
+        // use 'this' to ensure that the block state is the correct TileState
+        CraftBlockState state = (CraftBlockState) CraftBlock.at(this, position).getState();
+        state.setFlag(flag);
+        // set world handle to ensure that updated calls are done to the world and not to this populator
+        state.setWorldHandle(world);
+        list.put(position, state);
         return true;
     }
 
+    @Override
+    public WorldServer getMinecraftWorld() {
+        return world.getMinecraftWorld();
+    }
+
+    public void refreshTiles() {
+        for (CraftBlockState state : list.values()) {
+            if (state instanceof CraftBlockEntityState) {
+                ((CraftBlockEntityState<?>) state).refreshSnapshot();
+            }
+        }
+    }
+
     public void updateList() {
         for (BlockState state : list.values()) {
             state.update(true);