Paper/nms-patches/ChunkRegionLoader.patch

--- a/net/minecraft/server/ChunkRegionLoader.java
+++ b/net/minecraft/server/ChunkRegionLoader.java
@@ -29,8 +29,36 @@
         this.e = dataconvertermanager;
     }
 
+    // CraftBukkit start
+    public boolean chunkExists(World world, int i, int j) {
+        ChunkCoordIntPair chunkcoordintpair = new ChunkCoordIntPair(i, j);
+
+        if (this.c.contains(chunkcoordintpair)) {
+            if (this.b.containsKey(chunkcoordintpair)) {
+                return true;
+            }
+        }
+
+        return RegionFileCache.a(this.d, i, j).chunkExists(i & 31, j & 31);
+    }
+    // CraftBukkit end
+
+    // CraftBukkit start - Add async variant, provide compatibility
     @Nullable
     public Chunk a(World world, int i, int j) throws IOException {
+        Object[] data = loadChunk(world, i, j);
+        if (data != null) {
+            Chunk chunk = (Chunk) data[0];
+            NBTTagCompound nbttagcompound = (NBTTagCompound) data[1];
+            loadEntities(chunk, nbttagcompound.getCompound("Level"), world);
+            return chunk;
+        }
+
+        return null;
+    }
+
+    public Object[] loadChunk(World world, int i, int j) throws IOException {
+        // CraftBukkit end
         ChunkCoordIntPair chunkcoordintpair = new ChunkCoordIntPair(i, j);
         NBTTagCompound nbttagcompound = (NBTTagCompound) this.b.get(chunkcoordintpair);
 
@@ -47,7 +75,7 @@
         return this.a(world, i, j, nbttagcompound);
     }
 
-    protected Chunk a(World world, int i, int j, NBTTagCompound nbttagcompound) {
+    protected Object[] a(World world, int i, int j, NBTTagCompound nbttagcompound) { // CraftBukkit - return Chunk -> Object[]
         if (!nbttagcompound.hasKeyOfType("Level", 10)) {
             ChunkRegionLoader.a.error("Chunk file at " + i + "," + j + " is missing level data, skipping");
             return null;
@@ -64,10 +92,28 @@
                     ChunkRegionLoader.a.error("Chunk file at " + i + "," + j + " is in the wrong location; relocating. (Expected " + i + ", " + j + ", got " + chunk.locX + ", " + chunk.locZ + ")");
                     nbttagcompound1.setInt("xPos", i);
                     nbttagcompound1.setInt("zPos", j);
+
+                    // CraftBukkit start - Have to move tile entities since we don't load them at this stage
+                    NBTTagList tileEntities = nbttagcompound.getCompound("Level").getList("TileEntities", 10);
+                    if (tileEntities != null) {
+                        for (int te = 0; te < tileEntities.size(); te++) {
+                            NBTTagCompound tileEntity = (NBTTagCompound) tileEntities.get(te);
+                            int x = tileEntity.getInt("x") - chunk.locX * 16;
+                            int z = tileEntity.getInt("z") - chunk.locZ * 16;
+                            tileEntity.setInt("x", i * 16 + x);
+                            tileEntity.setInt("z", j * 16 + z);
+                        }
+                    }
+                    // CraftBukkit end
                     chunk = this.a(world, nbttagcompound1);
                 }
 
-                return chunk;
+                // CraftBukkit start
+                Object[] data = new Object[2];
+                data[0] = chunk;
+                data[1] = nbttagcompound;
+                return data;
+                // CraftBukkit end
             }
         }
     }
@@ -296,6 +342,13 @@
             chunk.a(nbttagcompound.getByteArray("Biomes"));
         }
 
+        // CraftBukkit start - End this method here and split off entity loading to another method
+        return chunk;
+    }
+
+    public void loadEntities(Chunk chunk, NBTTagCompound nbttagcompound, World world) {
+        // CraftBukkit end
+
         NBTTagList nbttaglist1 = nbttagcompound.getList("Entities", 10);
 
         if (nbttaglist1 != null) {
@@ -339,7 +392,7 @@
             }
         }
 
-        return chunk;
+        // return chunk; // CraftBukkit
     }
 
     @Nullable
@@ -403,8 +456,14 @@
         }
     }
 
+    // CraftBukkit start
     public static void a(Entity entity, World world) {
-        if (world.addEntity(entity) && entity.isVehicle()) {
+        a(entity, world, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.DEFAULT);
+    }
+
+    public static void a(Entity entity, World world, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason reason) {
+        if (world.addEntity(entity, reason) && entity.isVehicle()) {
+            // CraftBukkit end
             Iterator iterator = entity.bv().iterator();
 
             while (iterator.hasNext()) {