PaperMC/nms-patches/ItemWorldMap.patch

--- a/net/minecraft/server/ItemWorldMap.java
+++ b/net/minecraft/server/ItemWorldMap.java
@@ -4,6 +4,11 @@
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Multisets;
 
+// CraftBukkit start
+import org.bukkit.Bukkit;
+import org.bukkit.event.server.MapInitializeEvent;
+// CraftBukkit end
+
 public class ItemWorldMap extends ItemWorldMapBase {
 
     protected ItemWorldMap() {
@@ -11,25 +16,32 @@
     }
 
     public WorldMap getSavedMap(ItemStack itemstack, World world) {
+        World worldMain = world.getServer().getServer().worlds.get(0); // CraftBukkit - store reference to primary world
         String s = "map_" + itemstack.getData();
-        WorldMap worldmap = (WorldMap) world.a(WorldMap.class, s);
+        WorldMap worldmap = (WorldMap) worldMain.a(WorldMap.class, s); // CraftBukkit - use primary world for maps
 
         if (worldmap == null && !world.isClientSide) {
-            itemstack.setData(world.b("map"));
+            itemstack.setData(worldMain.b("map")); // CraftBukkit - use primary world for maps
             s = "map_" + itemstack.getData();
             worldmap = new WorldMap(s);
             worldmap.scale = 3;
             worldmap.a((double) world.getWorldData().c(), (double) world.getWorldData().e(), worldmap.scale);
-            worldmap.map = (byte) world.worldProvider.getDimension();
+            worldmap.map = (byte) ((WorldServer) world).dimension; // CraftBukkit - fixes Bukkit multiworld maps
             worldmap.c();
-            world.a(s, (PersistentBase) worldmap);
+            worldMain.a(s, (PersistentBase) worldmap); // CraftBukkit - use primary world for maps
+
+            // CraftBukkit start
+            MapInitializeEvent event = new MapInitializeEvent(worldmap.mapView);
+            Bukkit.getServer().getPluginManager().callEvent(event);
+            // CraftBukkit end
         }
 
         return worldmap;
     }
 
     public void a(World world, Entity entity, WorldMap worldmap) {
-        if (world.worldProvider.getDimension() == worldmap.map && entity instanceof EntityHuman) {
+        // CraftBukkit - world.worldProvider -> ((WorldServer) world)
+        if (((WorldServer) world).dimension == worldmap.map && entity instanceof EntityHuman) {
             int i = 1 << worldmap.scale;
             int j = worldmap.centerX;
             int k = worldmap.centerZ;
@@ -181,6 +193,8 @@
         if (itemstack.hasTag() && itemstack.getTag().getBoolean("map_is_scaling")) {
             WorldMap worldmap = Items.FILLED_MAP.getSavedMap(itemstack, world);
 
+            world = world.getServer().getServer().worlds.get(0); // CraftBukkit - use primary world for maps
+
             itemstack.setData(world.b("map"));
             WorldMap worldmap1 = new WorldMap("map_" + itemstack.getData());
 
@@ -193,6 +207,11 @@
             worldmap1.map = worldmap.map;
             worldmap1.c();
             world.a("map_" + itemstack.getData(), (PersistentBase) worldmap1);
+
+            // CraftBukkit start
+            MapInitializeEvent event = new MapInitializeEvent(worldmap1.mapView);
+            Bukkit.getServer().getPluginManager().callEvent(event);
+            // CraftBukkit end
         }
 
     }