#971: Remove strong chunk reference in PDC

A previous fix for SPIGOT-6814 implemented a callback function for the
PDC implementation that could be set to actively define a chunk as
unsaved, allowing chunks that have not been mutated through block
changes to still require saving if the chunks pdc was mutated.

This implementation however would pass a callback that references the
chunk access internally, meaning the PDC now actively holds onto a
callback that holds a reference to the entire chunk.

Aditionally, this change also impacted the pdc for item metas and
entities for really no reason whatsoever.

This commit re-implements the fix by introducing a new child of the pdc
implementation that the chunk now uses as its pdc. This specific
implementation maintains a dirty flag that is set to `true` on any form
of mutation and set back to false by the chunk that owns the PDC
whenever the chunk itself is flag as no longer dirty.

By: Bjarne Koll <lynxplay101@gmail.com>

paper-server/src/main/java/org/bukkit/craftbukkit/persistence/CraftPersistentDataContainer.java

@@ -15,13 +15,11 @@ import org.bukkit.persistence.PersistentDataAdapterContext;
 import org.bukkit.persistence.PersistentDataContainer;
 import org.bukkit.persistence.PersistentDataType;
 
-public final class CraftPersistentDataContainer implements PersistentDataContainer {
+public class CraftPersistentDataContainer implements PersistentDataContainer {
 
-    private static final Callback EMPTY = () -> { };
     private final Map<String, NBTBase> customDataTags = new HashMap<>();
     private final CraftPersistentDataTypeRegistry registry;
     private final CraftPersistentDataAdapterContext adapterContext;
-    private Callback callback = EMPTY;
 
     public CraftPersistentDataContainer(Map<String, NBTBase> customTags, CraftPersistentDataTypeRegistry registry) {
         this(registry);
@@ -33,14 +31,6 @@ public final class CraftPersistentDataContainer implements PersistentDataContain
         this.adapterContext = new CraftPersistentDataAdapterContext(this.registry);
     }
 
-    public void setCallback(Callback callback) {
-        if (callback == null) {
-            this.callback = EMPTY;
-            return;
-        }
-
-        this.callback = callback;
-    }
 
     @Override
     public <T, Z> void set(NamespacedKey key, PersistentDataType<T, Z> type, Z value) {
@@ -49,7 +39,6 @@ public final class CraftPersistentDataContainer implements PersistentDataContain
         Validate.notNull(value, "The provided value for the custom value was null");
 
         this.customDataTags.put(key.toString(), registry.wrap(type.getPrimitiveType(), type.toPrimitive(value, adapterContext)));
-        callback.onValueChange();
     }
 
     @Override
@@ -103,7 +92,6 @@ public final class CraftPersistentDataContainer implements PersistentDataContain
         Validate.notNull(key, "The provided key for the custom value was null");
 
         this.customDataTags.remove(key.toString());
-        callback.onValueChange();
     }
 
     @Override
@@ -138,19 +126,16 @@ public final class CraftPersistentDataContainer implements PersistentDataContain
 
     public void put(String key, NBTBase base) {
         this.customDataTags.put(key, base);
-        callback.onValueChange();
     }
 
     public void putAll(Map<String, NBTBase> map) {
         this.customDataTags.putAll(map);
-        callback.onValueChange();
     }
 
     public void putAll(NBTTagCompound compound) {
         for (String key : compound.getAllKeys()) {
             this.customDataTags.put(key, compound.get(key));
         }
-        callback.onValueChange();
     }
 
     public Map<String, NBTBase> getRaw() {
@@ -171,9 +156,4 @@ public final class CraftPersistentDataContainer implements PersistentDataContain
     public Map<String, Object> serialize() {
         return (Map<String, Object>) CraftNBTTagConfigSerializer.serialize(toTagCompound());
     }
-
-    @FunctionalInterface
-    public interface Callback {
-        void onValueChange();
-    }
 }

paper-server/src/main/java/org/bukkit/craftbukkit/persistence/DirtyCraftPersistentDataContainer.java

@@ -0,0 +1,62 @@
+package org.bukkit.craftbukkit.persistence;
+
+import java.util.Map;
+import net.minecraft.nbt.NBTBase;
+import net.minecraft.nbt.NBTTagCompound;
+import org.bukkit.NamespacedKey;
+import org.bukkit.persistence.PersistentDataType;
+
+/**
+ * A child class of the persistent data container that recalls if it has been
+ * mutated from an external caller.
+ */
+public final class DirtyCraftPersistentDataContainer extends CraftPersistentDataContainer {
+
+    private boolean dirty;
+
+    public DirtyCraftPersistentDataContainer(Map<String, NBTBase> customTags, CraftPersistentDataTypeRegistry registry) {
+        super(customTags, registry);
+    }
+
+    public DirtyCraftPersistentDataContainer(CraftPersistentDataTypeRegistry registry) {
+        super(registry);
+    }
+
+    public boolean dirty() {
+        return this.dirty;
+    }
+
+    public void dirty(final boolean dirty) {
+        this.dirty = dirty;
+    }
+
+    @Override
+    public <T, Z> void set(NamespacedKey key, PersistentDataType<T, Z> type, Z value) {
+        super.set(key, type, value);
+        this.dirty(true);
+    }
+
+    @Override
+    public void remove(NamespacedKey key) {
+        super.remove(key);
+        this.dirty(true);
+    }
+
+    @Override
+    public void put(String key, NBTBase base) {
+        super.put(key, base);
+        this.dirty(true);
+    }
+
+    @Override
+    public void putAll(NBTTagCompound compound) {
+        super.putAll(compound);
+        this.dirty(true);
+    }
+
+    @Override
+    public void putAll(Map<String, NBTBase> map) {
+        super.putAll(map);
+        this.dirty(true);
+    }
+}