Paper/paper-server/nms-patches/net/minecraft/network/syncher/DataWatcher.patch

--- a/net/minecraft/network/syncher/DataWatcher.java
+++ b/net/minecraft/network/syncher/DataWatcher.java
@@ -24,6 +24,11 @@
 import org.apache.commons.lang3.ObjectUtils;
 import org.slf4j.Logger;
 
+// CraftBukkit start
+import net.minecraft.network.protocol.game.PacketPlayOutEntityMetadata;
+import net.minecraft.server.level.EntityPlayer;
+// CraftBukkit end
+
 public class DataWatcher {
 
     private static final Logger LOGGER = LogUtils.getLogger();
@@ -146,6 +151,13 @@
 
     }
 
+    // CraftBukkit start - add method from above
+    public <T> void markDirty(DataWatcherObject<T> datawatcherobject) {
+        this.getItem(datawatcherobject).setDirty(true);
+        this.isDirty = true;
+    }
+    // CraftBukkit end
+
     public boolean isDirty() {
         return this.isDirty;
     }
@@ -227,7 +239,7 @@
         if (!Objects.equals(datawatcher_b.serializer(), datawatcher_item.accessor.getSerializer())) {
             throw new IllegalStateException(String.format(Locale.ROOT, "Invalid entity data item type for field %d on entity %s: old=%s(%s), new=%s(%s)", datawatcher_item.accessor.getId(), this.entity, datawatcher_item.value, datawatcher_item.value.getClass(), datawatcher_b.value, datawatcher_b.value.getClass()));
         } else {
-            datawatcher_item.setValue(datawatcher_b.value);
+            datawatcher_item.setValue((T) datawatcher_b.value); // CraftBukkit - decompile error
         }
     }
 
@@ -235,6 +247,18 @@
         return this.itemsById.isEmpty();
     }
 
+    // CraftBukkit start
+    public void refresh(EntityPlayer to) {
+        if (!this.isEmpty()) {
+            List<DataWatcher.b<?>> list = this.getNonDefaultValues();
+
+            if (list != null) {
+                to.connection.send(new PacketPlayOutEntityMetadata(this.entity.getId(), list));
+            }
+        }
+    }
+    // CraftBukkit end
+
     public static class Item<T> {
 
         final DataWatcherObject<T> accessor;
@@ -277,7 +301,7 @@
         }
     }
 
-    public static record b<T> (int id, DataWatcherSerializer<T> serializer, T value) {
+    public static record b<T>(int id, DataWatcherSerializer<T> serializer, T value) { // CraftBukkit - decompile error
 
         public static <T> DataWatcher.b<T> create(DataWatcherObject<T> datawatcherobject, T t0) {
             DataWatcherSerializer<T> datawatcherserializer = datawatcherobject.getSerializer();