Add WorldDifficultyChangeEvent (#12471)

paper-api/src/main/java/io/papermc/paper/event/world/WorldDifficultyChangeEvent.java

@@ -0,0 +1,59 @@
+package io.papermc.paper.event.world;
+
+import io.papermc.paper.command.brigadier.CommandSourceStack;
+import org.bukkit.Difficulty;
+import org.bukkit.World;
+import org.bukkit.event.HandlerList;
+import org.bukkit.event.world.WorldEvent;
+import org.jetbrains.annotations.ApiStatus;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
+
+/**
+ * Called when a world's difficulty is changed, either by command or by api.
+ * <p>
+ * If the world is in {@link World#isHardcore() hardcore}
+ * the resulting difficulty will always be {@link Difficulty#HARD}
+ */
+@NullMarked
+public class WorldDifficultyChangeEvent extends WorldEvent {
+
+    private static final HandlerList HANDLER_LIST = new HandlerList();
+
+    private final @Nullable CommandSourceStack commandSource;
+    private final Difficulty difficulty;
+
+    @ApiStatus.Internal
+    public WorldDifficultyChangeEvent(final World world, final @Nullable CommandSourceStack commandSource, final Difficulty difficulty) {
+        super(world);
+        this.commandSource = commandSource;
+        this.difficulty = difficulty;
+    }
+
+    /**
+     * Gets the command source associated with this event.
+     *
+     * @return {@code null} if the difficulty was changed via api, otherwise the {@link CommandSourceStack}.
+     */
+    public @Nullable CommandSourceStack getCommandSource() {
+        return commandSource;
+    }
+
+    /**
+     * Gets the new difficulty of the world.
+     *
+     * @return the new difficulty.
+     */
+    public Difficulty getDifficulty() {
+        return difficulty;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return HANDLER_LIST;
+    }
+
+    public static HandlerList getHandlerList() {
+        return HANDLER_LIST;
+    }
+}

paper-server/patches/features/0016-Moonrise-optimisation-patches.patch

@@ -23867,7 +23867,7 @@ index 46de98a6bbbae48c4837e1e588ba198a363d2dde..fd3553bdc1c3cdbf6aa3dc00e0a4987f
                  thread1 -> {
                      DedicatedServer dedicatedServer1 = new DedicatedServer(
 diff --git a/net/minecraft/server/MinecraftServer.java b/net/minecraft/server/MinecraftServer.java
-index 3527c39f3f95832d52aeda6205bbbb7161ecaf66..dc47259e40089a4793d950d4c3dc5bcc51ff680f 100644
+index f1346c2dc8fcf24a1ed945dbc57775daaa683b72..3b2b9d959e704abf87fd074418b47ff741a2a65e 100644
 --- a/net/minecraft/server/MinecraftServer.java
 +++ b/net/minecraft/server/MinecraftServer.java
 @@ -173,7 +173,7 @@ import net.minecraft.world.phys.Vec2;
@@ -24059,7 +24059,7 @@ index 3527c39f3f95832d52aeda6205bbbb7161ecaf66..dc47259e40089a4793d950d4c3dc5bcc
              return true;
          } else {
              boolean ret = false; // Paper - force execution of all worlds, do not just bias the first
-@@ -2479,6 +2567,12 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
+@@ -2482,6 +2570,12 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
          }
      }
  
@@ -28333,7 +28333,7 @@ index b30f56fbc1fd17259a1d05dc9155fffcab292ca1..11fed81a4696ba18440e755c3b8a5ca3
          this.generatingStep = generatingStep;
          this.cache = cache;
 diff --git a/net/minecraft/server/players/PlayerList.java b/net/minecraft/server/players/PlayerList.java
-index 774b597b34198d55bdec861e3ebabb36bac8e33e..d099b76082e59baf42de8e265eb2bc593c6e6f86 100644
+index fdfbfd535469affe755379911b6fdda695866849..9547000b6e41fab39b00ca55ebd41825d222592e 100644
 --- a/net/minecraft/server/players/PlayerList.java
 +++ b/net/minecraft/server/players/PlayerList.java
 @@ -1310,7 +1310,7 @@ public abstract class PlayerList {

paper-server/patches/sources/net/minecraft/server/MinecraftServer.java.patch

@@ -1112,7 +1112,7 @@
      }
  
      public KeyPair getKeyPair() {
-@@ -1244,11 +_,14 @@
+@@ -1244,11 +_,17 @@
          }
      }
  
@@ -1121,10 +1121,13 @@
 -            this.worldData.setDifficulty(this.worldData.isHardcore() ? Difficulty.HARD : difficulty);
 -            this.updateMobSpawningFlags();
 -            this.getPlayerList().getPlayers().forEach(this::sendDifficultyUpdate);
-+    // Paper start - per level difficulty
++    // Paper start - per level difficulty, WorldDifficultyChangeEvent
-+    public void setDifficulty(ServerLevel level, Difficulty difficulty, boolean forced) {
++    public void setDifficulty(ServerLevel level, Difficulty difficulty, @Nullable CommandSourceStack source, boolean forced) {
 +        net.minecraft.world.level.storage.PrimaryLevelData worldData = level.serverLevelData;
 +        if (forced || !worldData.isDifficultyLocked()) {
++            new io.papermc.paper.event.world.WorldDifficultyChangeEvent(
++                level.getWorld(), source, org.bukkit.craftbukkit.util.CraftDifficulty.toBukkit(difficulty)
++            ).callEvent();
 +            worldData.setDifficulty(worldData.isHardcore() ? Difficulty.HARD : difficulty);
 +            level.setSpawnSettings(worldData.getDifficulty() != Difficulty.PEACEFUL && ((net.minecraft.server.dedicated.DedicatedServer) this).settings.getProperties().spawnMonsters);
 +            // this.getPlayerList().getPlayers().forEach(this::sendDifficultyUpdate);

paper-server/patches/sources/net/minecraft/server/commands/DifficultyCommand.java.patch

@@ -9,7 +9,7 @@
              throw ERROR_ALREADY_DIFFICULT.create(difficulty.getKey());
          } else {
 -            server.setDifficulty(difficulty, true);
-+            server.setDifficulty(source.getLevel(), difficulty, true); // Paper - per level difficulty; don't skip other difficulty-changing logic (fix upstream's fix)
++            server.setDifficulty(source.getLevel(), difficulty, source, true); // Paper - per level difficulty; don't skip other difficulty-changing logic (fix upstream's fix); WorldDifficultyChangeEvent
              source.sendSuccess(() -> Component.translatable("commands.difficulty.success", difficulty.getDisplayName()), true);
              return 0;
          }

paper-server/src/main/java/org/bukkit/craftbukkit/CraftWorld.java

@@ -113,6 +113,7 @@ import org.bukkit.craftbukkit.metadata.BlockMetadataStore;
 import org.bukkit.craftbukkit.persistence.CraftPersistentDataContainer;
 import org.bukkit.craftbukkit.persistence.CraftPersistentDataTypeRegistry;
 import org.bukkit.craftbukkit.util.CraftBiomeSearchResult;
+import org.bukkit.craftbukkit.util.CraftDifficulty;
 import org.bukkit.craftbukkit.util.CraftLocation;
 import org.bukkit.craftbukkit.util.CraftNamespacedKey;
 import org.bukkit.craftbukkit.util.CraftRayTraceResult;
@@ -1310,12 +1311,12 @@ public class CraftWorld extends CraftRegionAccessor implements World {
 
     @Override
     public void setDifficulty(Difficulty difficulty) {
-        this.getHandle().getServer().setDifficulty(this.getHandle(), net.minecraft.world.Difficulty.byId(difficulty.getValue()), true); // Paper - per level difficulty; don't skip other difficulty-changing logic
+        this.getHandle().getServer().setDifficulty(this.getHandle(), CraftDifficulty.toMinecraft(difficulty), null, true);
     }
 
     @Override
     public Difficulty getDifficulty() {
-        return Difficulty.getByValue(this.getHandle().getDifficulty().ordinal());
+        return CraftDifficulty.toBukkit(this.getHandle().getDifficulty());
     }
 
     @Override

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

@@ -0,0 +1,24 @@
+package org.bukkit.craftbukkit.util;
+
+import org.jspecify.annotations.NullMarked;
+
+@NullMarked
+public final class CraftDifficulty {
+    public static org.bukkit.Difficulty toBukkit(net.minecraft.world.Difficulty difficulty) {
+        return switch (difficulty) {
+            case EASY -> org.bukkit.Difficulty.EASY;
+            case HARD -> org.bukkit.Difficulty.HARD;
+            case NORMAL -> org.bukkit.Difficulty.NORMAL;
+            case PEACEFUL -> org.bukkit.Difficulty.PEACEFUL;
+        };
+    }
+
+    public static net.minecraft.world.Difficulty toMinecraft(org.bukkit.Difficulty difficulty) {
+        return switch (difficulty) {
+            case EASY -> net.minecraft.world.Difficulty.EASY;
+            case HARD -> net.minecraft.world.Difficulty.HARD;
+            case NORMAL -> net.minecraft.world.Difficulty.NORMAL;
+            case PEACEFUL -> net.minecraft.world.Difficulty.PEACEFUL;
+        };
+    }
+}