Fix Per World Difficulty / Remembering Difficulty

Fixes per world difficulty with /difficulty command and also
makes it so that the server keeps the last difficulty used instead
of restoring the server.properties every single load.

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

@@ -555,15 +555,17 @@
  
          if (!iworlddataserver.isInitialized()) {
              try {
-@@ -427,30 +717,8 @@
+@@ -425,32 +715,10 @@
-             iworlddataserver.setInitialized(true);
+             }
-         }
  
+             iworlddataserver.setInitialized(true);
+-        }
+-
 -        this.getPlayerList().addWorldborderListener(worldserver);
 -        if (this.worldData.getCustomBossEvents() != null) {
 -            this.getCustomBossEvents().load(this.worldData.getCustomBossEvents(), this.registryAccess());
--        }
+         }
--
+ 
 -        RandomSequences randomsequences = worldserver.getRandomSequences();
 -        Iterator iterator = iregistry.entrySet().iterator();
 -
@@ -672,7 +674,7 @@
 +        worldloadlistener.stop();
 +        // CraftBukkit start
 +        // this.updateMobSpawningFlags();
-+        worldserver.setSpawnSettings(this.isSpawningMonsters());
++        worldserver.setSpawnSettings(worldserver.serverLevelData.getDifficulty() != Difficulty.PEACEFUL && ((DedicatedServer) this).settings.getProperties().spawnMonsters); // Paper - per level difficulty (from setDifficulty(ServerLevel, Difficulty, boolean))
 +
 +        this.forceTicks = false;
 +        // CraftBukkit end
@@ -698,12 +700,10 @@
          if (flush) {
              Iterator iterator1 = this.getAllLevels().iterator();
  
-@@ -626,20 +925,47 @@
+@@ -628,18 +927,45 @@
-     @Override
-     public void close() {
          this.stopServer();
-+    }
+     }
-+
+ 
 +    // CraftBukkit start
 +    private boolean hasStopped = false;
 +    private boolean hasLoggedStop = false; // Paper - Debugging
@@ -712,9 +712,9 @@
 +        synchronized (this.stopLock) {
 +            return this.hasStopped;
 +        }
-     }
++    }
 +    // CraftBukkit end
- 
++
      public void stopServer() {
 +        // CraftBukkit start - prevent double stopping on multiple threads
 +        synchronized(this.stopLock) {
@@ -916,24 +916,22 @@
                  this.onServerExit();
              }
  
-@@ -889,9 +1325,16 @@
+@@ -889,7 +1325,14 @@
      }
  
      private boolean haveTime() {
 -        return this.runningTask() || Util.getNanos() < (this.mayHaveDelayedTasks ? this.delayedTasksMaxNextTickTimeNanos : this.nextTickTimeNanos);
 +        // CraftBukkit start
 +        return this.forceTicks || this.runningTask() || Util.getNanos() < (this.mayHaveDelayedTasks ? this.delayedTasksMaxNextTickTimeNanos : this.nextTickTimeNanos);
-     }
++    }
- 
++
 +    private void executeModerately() {
 +        this.runAllTasks();
 +        java.util.concurrent.locks.LockSupport.parkNanos("executing tasks", 1000L);
 +        // CraftBukkit end
-+    }
+     }
-+
-     public static boolean throwIfFatalException() {
-         RuntimeException runtimeexception = (RuntimeException) MinecraftServer.fatalException.get();
  
+     public static boolean throwIfFatalException() {
 @@ -903,7 +1346,7 @@
      }
  
@@ -1136,7 +1134,36 @@
      }
  
      public KeyPair getKeyPair() {
-@@ -1481,10 +1986,20 @@
+@@ -1385,11 +1890,14 @@
+         }
+     }
+ 
+-    public void setDifficulty(Difficulty difficulty, boolean forceUpdate) {
+-        if (forceUpdate || !this.worldData.isDifficultyLocked()) {
+-            this.worldData.setDifficulty(this.worldData.isHardcore() ? Difficulty.HARD : difficulty);
+-            this.updateMobSpawningFlags();
+-            this.getPlayerList().getPlayers().forEach(this::sendDifficultyUpdate);
++    // Paper start - per level difficulty
++    public void setDifficulty(ServerLevel level, Difficulty difficulty, boolean forceUpdate) {
++        PrimaryLevelData worldData = level.serverLevelData;
++        if (forceUpdate || !worldData.isDifficultyLocked()) {
++            worldData.setDifficulty(worldData.isHardcore() ? Difficulty.HARD : difficulty);
++            level.setSpawnSettings(worldData.getDifficulty() != Difficulty.PEACEFUL && ((DedicatedServer) this).settings.getProperties().spawnMonsters);
++            // this.getPlayerList().getPlayers().forEach(this::sendDifficultyUpdate);
++            // Paper end - per level difficulty
+         }
+     }
+ 
+@@ -1403,7 +1911,7 @@
+         while (iterator.hasNext()) {
+             ServerLevel worldserver = (ServerLevel) iterator.next();
+ 
+-            worldserver.setSpawnSettings(this.isSpawningMonsters());
++            worldserver.setSpawnSettings(worldserver.serverLevelData.getDifficulty() != Difficulty.PEACEFUL && ((DedicatedServer) this).settings.getProperties().spawnMonsters); // Paper - per level difficulty (from setDifficulty(ServerLevel, Difficulty, boolean))
+         }
+ 
+     }
+@@ -1481,10 +1989,20 @@
  
      @Override
      public String getMotd() {
@@ -1158,7 +1185,7 @@
          this.motd = motd;
      }
  
-@@ -1507,7 +2022,7 @@
+@@ -1507,7 +2025,7 @@
      }
  
      public ServerConnectionListener getConnection() {
@@ -1167,7 +1194,7 @@
      }
  
      public boolean isReady() {
-@@ -1634,11 +2149,11 @@
+@@ -1634,11 +2152,11 @@
  
      public CompletableFuture<Void> reloadResources(Collection<String> dataPacks) {
          CompletableFuture<Void> completablefuture = CompletableFuture.supplyAsync(() -> {
@@ -1181,7 +1208,7 @@
          }, this).thenCompose((immutablelist) -> {
              MultiPackResourceManager resourcemanager = new MultiPackResourceManager(PackType.SERVER_DATA, immutablelist);
              List<Registry.PendingTags<?>> list = TagLoader.loadTagsForExistingRegistries(resourcemanager, this.registries.compositeAccess());
-@@ -1654,6 +2169,7 @@
+@@ -1654,6 +2172,7 @@
          }).thenAcceptAsync((minecraftserver_reloadableresources) -> {
              this.resources.close();
              this.resources = minecraftserver_reloadableresources;
@@ -1189,7 +1216,7 @@
              this.packRepository.setSelected(dataPacks);
              WorldDataConfiguration worlddataconfiguration = new WorldDataConfiguration(MinecraftServer.getSelectedPacks(this.packRepository, true), this.worldData.enabledFeatures());
  
-@@ -1952,7 +2468,7 @@
+@@ -1952,7 +2471,7 @@
              final List<String> list = Lists.newArrayList();
              final GameRules gamerules = this.getGameRules();
  
@@ -1198,7 +1225,7 @@
                  @Override
                  public <T extends GameRules.Value<T>> void visit(GameRules.Key<T> key, GameRules.Type<T> type) {
                      list.add(String.format(Locale.ROOT, "%s=%s\n", key.getId(), gamerules.getRule(key)));
-@@ -2058,7 +2574,7 @@
+@@ -2058,7 +2577,7 @@
              try {
                  label51:
                  {
@@ -1207,18 +1234,15 @@
  
                      try {
                          arraylist = Lists.newArrayList(NativeModuleLister.listModules());
-@@ -2105,9 +2621,24 @@
+@@ -2108,6 +2627,21 @@
-         if (bufferedwriter != null) {
+ 
-             bufferedwriter.close();
+     }
-         }
-+
-+    }
  
 +    // CraftBukkit start
 +    public boolean isDebugging() {
 +        return false;
-     }
++    }
- 
++
 +    public static MinecraftServer getServer() {
 +        return SERVER; // Paper
 +    }
@@ -1232,7 +1256,7 @@
      private ProfilerFiller createProfiler() {
          if (this.willStartRecordingMetrics) {
              this.metricsRecorder = ActiveMetricsRecorder.createStarted(new ServerMetricsSamplersProvider(Util.timeSource, this.isDedicatedServer()), Util.timeSource, Util.ioPool(), new MetricsPersister("server"), this.onMetricsRecordingStopped, (path) -> {
-@@ -2225,18 +2756,24 @@
+@@ -2225,18 +2759,24 @@
      }
  
      public void logChatMessage(Component message, ChatType.Bound params, @Nullable String prefix) {
@@ -1261,15 +1285,17 @@
      }
  
      public boolean logIPs() {
-@@ -2379,4 +2916,30 @@
+@@ -2377,6 +2917,32 @@
-     public static record ServerResourcePackInfo(UUID id, String url, String hash, boolean isRequired, @Nullable Component prompt) {
- 
      }
+ 
+     public static record ServerResourcePackInfo(UUID id, String url, String hash, boolean isRequired, @Nullable Component prompt) {
++
++    }
 +
 +    // Paper start - Add tick times API and /mspt command
 +    public static class TickTimes {
 +        private final long[] times;
-+
+ 
 +        public TickTimes(int length) {
 +            times = new long[length];
 +        }
@@ -1289,6 +1315,6 @@
 +            }
 +            return ((double) total / (double) times.length) * 1.0E-6D;
 +        }
-+    }
+     }
 +    // Paper end - Add tick times API and /mspt command
  }

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

@@ -11,7 +11,7 @@
              throw DifficultyCommand.ERROR_ALREADY_DIFFICULT.create(difficulty.getKey());
          } else {
 -            minecraftserver.setDifficulty(difficulty, true);
-+            worldServer.serverLevelData.setDifficulty(difficulty); // CraftBukkit
++            minecraftserver.setDifficulty(worldServer, difficulty, true); // Paper - per level difficulty; don't skip other difficulty-changing logic (fix upstream's fix)
              source.sendSuccess(() -> {
                  return Component.translatable("commands.difficulty.success", difficulty.getDisplayName());
              }, true);

paper-server/patches/sources/net/minecraft/server/dedicated/DedicatedServer.java.patch

@@ -250,6 +250,15 @@
      @Override
      public boolean isSpawningMonsters() {
          return this.settings.getProperties().spawnMonsters && super.isSpawningMonsters();
+@@ -227,7 +337,7 @@
+ 
+     @Override
+     public void forceDifficulty() {
+-        this.setDifficulty(this.getProperties().difficulty, true);
++        // this.setDifficulty(this.getProperties().difficulty, true); // Paper - per level difficulty; Don't overwrite level.dat's difficulty, keep current
+     }
+ 
+     @Override
 @@ -286,13 +396,14 @@
          }
  

paper-server/patches/sources/net/minecraft/server/network/ServerGamePacketListenerImpl.java.patch

@@ -629,8 +629,8 @@
 +                                if (i > Math.max(this.allowedPlayerTicks, 5)) {
                                      ServerGamePacketListenerImpl.LOGGER.debug("{} is sending move packets too frequently ({} packets since last tick)", this.player.getName().getString(), i);
                                      i = 1;
-+                                }
+                                 }
-+
+ 
 +                                if (packet.hasRot || d10 > 0) {
 +                                    this.allowedPlayerTicks -= 1;
 +                                } else {
@@ -646,9 +646,9 @@
 +                                if (this.player.level().paperConfig().chunks.preventMovingIntoUnloadedChunks && (this.player.getX() != toX || this.player.getZ() != toZ) && !worldserver.areChunksLoadedForMove(this.player.getBoundingBox().expandTowards(new Vec3(toX, toY, toZ).subtract(this.player.position())))) {
 +                                    this.internalTeleport(PositionMoveRotation.of(this.player), Collections.emptySet());
 +                                    return;
-                                 }
++                                }
 +                                // Paper end - Prevent moving into unloaded chunks
- 
++
                                  if (this.shouldCheckPlayerMovement(flag)) {
                                      float f2 = flag ? 300.0F : 100.0F;
  
@@ -1002,12 +1002,10 @@
          if (this.player.hasClientLoaded()) {
              this.ackBlockChangesUpTo(packet.getSequence());
              ServerLevel worldserver = this.player.serverLevel();
-@@ -1294,8 +1861,49 @@
+@@ -1296,6 +1863,47 @@
- 
-                 if (f1 != this.player.getXRot() || f != this.player.getYRot()) {
                      this.player.absRotateTo(f, f1);
-+                }
+                 }
-+
+ 
 +                // CraftBukkit start
 +                // Raytrace to look for 'rogue armswings'
 +                double d0 = this.player.getX();
@@ -1038,8 +1036,8 @@
 +                        cancelled = event.useItemInHand() == Event.Result.DENY;
 +                    }
 +                    this.player.gameMode.firedInteract = false;
-                 }
++                }
- 
++
 +                if (cancelled) {
 +                    this.player.getBukkitEntity().updateInventory(); // SPIGOT-2524
 +                    return;
@@ -1587,12 +1585,12 @@
 +                                    entity.getBukkitEntity().update(ServerGamePacketListenerImpl.this.player);
 +                                    ServerGamePacketListenerImpl.this.player.containerMenu.sendAllDataToRemote();
 +                                }
- 
++
 +                                if (triggerLeashUpdate && (event.isCancelled() || ServerGamePacketListenerImpl.this.player.getInventory().getSelected() == null || ServerGamePacketListenerImpl.this.player.getInventory().getSelected().getItem() != origItem)) {
 +                                    // Refresh the current leash state
 +                                    ServerGamePacketListenerImpl.this.send(new ClientboundSetEntityLinkPacket(entity, ((Mob) entity).getLeashHolder()));
 +                                }
-+
+ 
 +                                if (event.isCancelled() || ServerGamePacketListenerImpl.this.player.getInventory().getSelected() == null || ServerGamePacketListenerImpl.this.player.getInventory().getSelected().getItem() != origItem) {
 +                                    // Refresh the current entity metadata
 +                                    entity.refreshEntityData(ServerGamePacketListenerImpl.this.player);
@@ -2182,6 +2180,15 @@
          if (this.player.isModelPartShown(PlayerModelPart.HAT) != flag) {
              this.server.getPlayerList().broadcastAll(new ClientboundPlayerInfoUpdatePacket(ClientboundPlayerInfoUpdatePacket.Action.UPDATE_HAT, this.player));
          }
+@@ -2012,7 +3366,7 @@
+     public void handleChangeDifficulty(ServerboundChangeDifficultyPacket packet) {
+         PacketUtils.ensureRunningOnSameThread(packet, this, this.player.serverLevel());
+         if (this.player.hasPermissions(2) || this.isSingleplayerOwner()) {
+-            this.server.setDifficulty(packet.getDifficulty(), false);
++            // this.server.setDifficulty(packet.getDifficulty(), false); // Paper - per level difficulty; don't allow clients to change this
+         }
+     }
+ 
 @@ -2058,7 +3412,7 @@
          if (!this.waitingForSwitchToConfig) {
              throw new IllegalStateException("Client acknowledged config, but none was requested");

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

@@ -1000,8 +1000,8 @@ public final class CraftServer implements Server {
         org.spigotmc.SpigotConfig.init((File) this.console.options.valueOf("spigot-settings")); // Spigot
         this.console.paperConfigurations.reloadConfigs(this.console);
         for (ServerLevel world : this.console.getAllLevels()) {
-            world.serverLevelData.setDifficulty(config.difficulty);
+            // world.serverLevelData.setDifficulty(config.difficulty); // Paper - per level difficulty
-            world.setSpawnSettings(config.spawnMonsters);
+            world.setSpawnSettings(world.serverLevelData.getDifficulty() != Difficulty.PEACEFUL && config.spawnMonsters); // Paper - per level difficulty (from MinecraftServer#setDifficulty(ServerLevel, Difficulty, boolean))
 
             for (SpawnCategory spawnCategory : SpawnCategory.values()) {
                 if (CraftSpawnCategory.isValidForLimits(spawnCategory)) {

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

@@ -1170,7 +1170,7 @@ public class CraftWorld extends CraftRegionAccessor implements World {
 
     @Override
     public void setDifficulty(Difficulty difficulty) {
-        this.getHandle().serverLevelData.setDifficulty(net.minecraft.world.Difficulty.byId(difficulty.getValue()));
+        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
     }
 
     @Override