#549: Add Fluid types / tags

By: Martoph <sager1018@gmail.com>

paper-api/src/main/java/org/bukkit/Fluid.java

@@ -0,0 +1,24 @@
+package org.bukkit;
+
+import java.util.Locale;
+import org.jetbrains.annotations.NotNull;
+
+public enum Fluid implements Keyed {
+
+    WATER,
+    FLOWING_WATER,
+    LAVA,
+    FLOWING_LAVA;
+
+    private final NamespacedKey key;
+
+    private Fluid() {
+        this.key = NamespacedKey.minecraft(this.name().toLowerCase(Locale.ROOT));
+    }
+
+    @NotNull
+    @Override
+    public NamespacedKey getKey() {
+        return key;
+    }
+}

paper-api/src/main/java/org/bukkit/Registry.java

@@ -158,6 +158,12 @@ public interface Registry<T extends Keyed> extends Iterable<T> {
             return MemoryKey.getByKey(key);
         }
     };
+    /**
+     * Server fluids.
+     *
+     * @see Fluid
+     */
+    Registry<Fluid> FLUID = new SimpleRegistry<>(Fluid.class);
 
     /**
      * Get the object by its key.

paper-api/src/main/java/org/bukkit/Tag.java

@@ -409,6 +409,18 @@ public interface Tag<T extends Keyed> extends Keyed {
      * Vanilla item tag representing all furnace materials.
      */
     Tag<Material> ITEMS_FURNACE_MATERIALS = Bukkit.getTag(REGISTRY_ITEMS, NamespacedKey.minecraft("furnace_materials"), Material.class);
+    /**
+     * Key for the built in fluid registry.
+     */
+    String REGISTRY_FLUIDS = "fluids";
+    /**
+     * Vanilla fluid tag representing lava and flowing lava.
+     */
+    Tag<Fluid> FLUIDS_LAVA = Bukkit.getTag(REGISTRY_FLUIDS, NamespacedKey.minecraft("lava"), Fluid.class);
+    /**
+     * Vanilla fluid tag representing water and flowing water.
+     */
+    Tag<Fluid> FLUIDS_WATER = Bukkit.getTag(REGISTRY_FLUIDS, NamespacedKey.minecraft("water"), Fluid.class);
 
     /**
      * Returns whether or not this tag has an entry for the specified item.