Improve GameRule API (#13668)

Co-authored-by: Jake Potrebic <jake.m.potrebic@gmail.com>

Author: Lulu13022002

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

@@ -488,6 +488,14 @@ private static UnaryOperator<Boolean> inverseBool() {
     @NotNull
     public abstract Class<T> getType();
 
+    /**
+     * Get the default value of this rule.
+     *
+     * @return the default value
+     */
+    @NotNull
+    public abstract T getDefaultValue();
+
     /**
      * Get a {@link GameRule} by its name.
      *

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

@@ -3802,8 +3802,7 @@ default void playSound(@NotNull Entity entity, @NotNull String sound, float volu
      * @param <T> the GameRule's type
      * @return the current value
      */
-    @Nullable
-    public <T> T getGameRuleValue(@NotNull GameRule<T> rule);
+    public @NotNull <T> T getGameRuleValue(@NotNull GameRule<T> rule);
 
     /**
      * Get the default value for a given {@link GameRule}. This value is not
@@ -3812,9 +3811,12 @@ default void playSound(@NotNull Entity entity, @NotNull String sound, float volu
      * @param rule the rule to return a default value for
      * @param <T> the type of GameRule
      * @return the default value
+     * @deprecated use {@link GameRule#getDefaultValue()} instead
      */
-    @Nullable
-    public <T> T getGameRuleDefault(@NotNull GameRule<T> rule);
+    @Deprecated(since = "26.1.2")
+    default <T> @NotNull T getGameRuleDefault(@NotNull GameRule<T> rule) {
+        return rule.getDefaultValue();
+    }
 
     /**
      * Set the given {@link GameRule}'s new value.

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

@@ -76,11 +76,24 @@ public Class<T> getType() {
         };
     }
 
+    @Override
+    public T getDefaultValue() {
+        return shimLegacyValue(this.getHandle().defaultValue(), this);
+    }
+
     @Override
     public String translationKey() {
         return this.getHandle().getDescriptionId();
     }
 
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    public static <T> T shimLegacyValue(T value, GameRule<?> rule) {
+        if (rule instanceof LegacyGameRuleWrapper wrapper) {
+            return (T) wrapper.getToLegacyFromModern().apply(value);
+        }
+        return value;
+    }
+
     public static class LegacyGameRuleWrapper<LEGACY, MODERN> extends CraftGameRule<LEGACY> {
 
         private final Class<LEGACY> typeOverride;

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

@@ -1688,30 +1688,12 @@ public boolean isGameRule(String rule) {
         return this.getHandle().getGameRules().rules.has(CraftGameRule.bukkitToMinecraft(bukkit));
     }
 
-    public static <T> T shimLegacyValue(T value, org.bukkit.GameRule<?> gameRule){
-        //noinspection rawtypes unchecked
-        if (gameRule instanceof CraftGameRule.LegacyGameRuleWrapper legacyGameRuleWrapper) {
-            //noinspection unchecked
-            return (T) legacyGameRuleWrapper.getToLegacyFromModern().apply(value);
-        }
-
-        return value;
-    }
-
     @Override
-    public <T> @Nullable T getGameRuleValue(org.bukkit.@NotNull GameRule<T> rule) {
+    public <T> @NotNull T getGameRuleValue(org.bukkit.@NotNull GameRule<T> rule) {
         Preconditions.checkArgument(rule != null, "GameRule cannot be null");
 
         T value = this.getHandle().getGameRules().get(CraftGameRule.bukkitToMinecraft(rule));
-        return shimLegacyValue(value, rule);
-    }
-
-    @Override
-    public <T> @Nullable T getGameRuleDefault(org.bukkit.@NotNull GameRule<T> rule) {
-        Preconditions.checkArgument(rule != null, "GameRule cannot be null");
-        T value = CraftGameRule.bukkitToMinecraft(rule).defaultValue();
-
-        return shimLegacyValue(value, rule);
+        return CraftGameRule.shimLegacyValue(value, rule);
     }
 
     @Override