Attribute Modifier API improvements

Co-authored-by: Malfrador <malfrador@gmail.com>

paper-api/src/main/java/org/bukkit/attribute/AttributeInstance.java

@@ -39,6 +39,42 @@ public interface AttributeInstance {
     @NotNull
     Collection<AttributeModifier> getModifiers();
 
+    // Paper start
+    /**
+     * Gets the modifier with the corresponding key.
+     *
+     * @param key the jey of the modifier
+     * @return the modifier, if it exists
+     */
+    @org.jetbrains.annotations.Nullable AttributeModifier getModifier(@NotNull net.kyori.adventure.key.Key key);
+
+    /**
+     * Remove a modifier with the corresponding key from this instance.
+     *
+     * @param key the key of the modifier
+     */
+    void removeModifier(@NotNull net.kyori.adventure.key.Key key);
+
+    /**
+     * Gets the modifier with the corresponding UUID.
+     *
+     * @param uuid the UUID of the modifier
+     * @return the modifier, if it exists
+     * @deprecated use {@link #getModifier(net.kyori.adventure.key.Key)}, modifiers are no longer stored by UUID
+     */
+    @Deprecated(forRemoval = true, since = "1.21")
+    @org.jetbrains.annotations.Nullable AttributeModifier getModifier(@NotNull java.util.UUID uuid);
+
+    /**
+     * Remove a modifier with the corresponding UUID from this instance.
+     *
+     * @param uuid the UUID of the modifier
+     * @deprecated use {@link #removeModifier(net.kyori.adventure.key.Key)}, modifiers are no longer stored by UUID
+     */
+    @Deprecated(forRemoval = true, since = "1.21")
+    void removeModifier(@NotNull java.util.UUID uuid);
+    // Paper end
+
     /**
      * Add a modifier to this instance.
      *
@@ -46,6 +82,16 @@ public interface AttributeInstance {
      */
     void addModifier(@NotNull AttributeModifier modifier);
 
+    // Paper start - Transient modifier API
+    /**
+     * Add a transient modifier to this instance.
+     * Transient modifiers are not persisted (saved with the NBT data)
+     *
+     * @param modifier to add
+     */
+    void addTransientModifier(@NotNull AttributeModifier modifier);
+    // Paper end
+
     /**
      * Remove a modifier from this instance.
      *