Paper/patches/api/0487-Add-FeatureFlag-API.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jake Potrebic <jake.m.potrebic@gmail.com>
Date: Thu, 9 Mar 2023 11:24:43 -0800
Subject: [PATCH] Add FeatureFlag API


diff --git a/src/main/java/io/papermc/paper/world/flag/FeatureDependant.java b/src/main/java/io/papermc/paper/world/flag/FeatureDependant.java
new file mode 100644
index 0000000000000000000000000000000000000000..0fda065100c17ee00060df16467c0f7f98984ea7
--- /dev/null
+++ b/src/main/java/io/papermc/paper/world/flag/FeatureDependant.java
@@ -0,0 +1,27 @@
+package io.papermc.paper.world.flag;
+
+import java.util.Set;
+import org.bukkit.FeatureFlag;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.Unmodifiable;
+
+/**
+ * Implemented by types in built-in registries that are controlled by {@link FeatureFlag FeatureFlags}.
+ * Types in data-driven registries that are controlled by feature flags just will not exist in that registry.
+ * @apiNote When a type that currently implements this interface transitions to being data-drive, this
+ * interface will be removed from that type in the following major version.
+ */
+@ApiStatus.NonExtendable
+public interface FeatureDependant {
+
+    /**
+     * Gets the set of required feature flags for this
+     * to be enabled.
+     *
+     * @return the immutable set of feature flags
+     */
+    default @Unmodifiable @NonNull Set<FeatureFlag> requiredFeatures() {
+        return FeatureFlagProvider.provider().requiredFeatures(this);
+    }
+}
diff --git a/src/main/java/io/papermc/paper/world/flag/FeatureFlagProvider.java b/src/main/java/io/papermc/paper/world/flag/FeatureFlagProvider.java
new file mode 100644
index 0000000000000000000000000000000000000000..f64cbee35fd3c6fe7b5f7391f6d118166d26dc18
--- /dev/null
+++ b/src/main/java/io/papermc/paper/world/flag/FeatureFlagProvider.java
@@ -0,0 +1,19 @@
+package io.papermc.paper.world.flag;
+
+import java.util.Optional;
+import java.util.ServiceLoader;
+import java.util.Set;
+import org.bukkit.FeatureFlag;
+import org.jetbrains.annotations.ApiStatus;
+
+@ApiStatus.Internal
+interface FeatureFlagProvider {
+
+    Optional<FeatureFlagProvider> PROVIDER = ServiceLoader.load(FeatureFlagProvider.class).findFirst();
+
+    static FeatureFlagProvider provider() {
+        return PROVIDER.orElseThrow();
+    }
+
+    Set<FeatureFlag> requiredFeatures(FeatureDependant dependant);
+}
diff --git a/src/main/java/io/papermc/paper/world/flag/FeatureFlagSetHolder.java b/src/main/java/io/papermc/paper/world/flag/FeatureFlagSetHolder.java
new file mode 100644
index 0000000000000000000000000000000000000000..c4432ee20872eeb127852159cf89ed00809fb00e
--- /dev/null
+++ b/src/main/java/io/papermc/paper/world/flag/FeatureFlagSetHolder.java
@@ -0,0 +1,31 @@
+package io.papermc.paper.world.flag;
+
+import java.util.Set;
+import org.bukkit.FeatureFlag;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.Unmodifiable;
+
+/**
+ * Implemented by types that hold {@link FeatureFlag FeatureFlags} like
+ * {@link org.bukkit.generator.WorldInfo} and {@link org.bukkit.RegionAccessor}.
+ */
+@ApiStatus.NonExtendable
+public interface FeatureFlagSetHolder {
+
+    /**
+     * Checks if this is enabled based on the loaded feature flags.
+     *
+     * @return true if enabled
+     */
+    default boolean isEnabled(final @NonNull FeatureDependant featureDependant) {
+        return this.getFeatureFlags().containsAll(featureDependant.requiredFeatures());
+    }
+
+    /**
+     * Get all {@link FeatureFlag FeatureFlags} enabled in this world.
+     *
+     * @return all enabled {@link FeatureFlag FeatureFlags}
+     */
+    @Unmodifiable @NonNull Set<FeatureFlag> getFeatureFlags();
+}
diff --git a/src/main/java/org/bukkit/FeatureFlag.java b/src/main/java/org/bukkit/FeatureFlag.java
index 026b1832bcd163ab89668c991bf002e608e36aef..8fab13dc12c8fd6181479ab6e31e2498a8a91ee5 100644
--- a/src/main/java/org/bukkit/FeatureFlag.java
+++ b/src/main/java/org/bukkit/FeatureFlag.java
@@ -1,37 +1,56 @@
 package org.bukkit;
 
+// Paper start - overhaul FeatureFlag API
+import com.google.common.base.Preconditions;
+import java.util.List;
+import net.kyori.adventure.key.Key;
+import net.kyori.adventure.util.Index;
+import org.intellij.lang.annotations.Subst;
+// Paper end - overhaul FeatureFlag API
 import org.jetbrains.annotations.ApiStatus;
 
 /**
  * This represents a Feature Flag for a World.
- * <br>
- * Flags which are unavailable in the current version will be null and/or
- * removed.
  */
-@ApiStatus.Experimental
 public interface FeatureFlag extends Keyed {
 
-    public static final FeatureFlag VANILLA = Bukkit.getUnsafe().getFeatureFlag(NamespacedKey.minecraft("vanilla"));
+    // Paper start - overhaul FeatureFlag API
+    /**
+     * The {@code vanilla} feature flag.
+     */
+    FeatureFlag VANILLA = create("vanilla");
 
+    /**
+     * The {@code bundle} feature flag.
+     */
     @ApiStatus.Experimental // Paper - add missing annotation
-    public static final FeatureFlag BUNDLE = Bukkit.getUnsafe().getFeatureFlag(NamespacedKey.minecraft("bundle"));
+    FeatureFlag BUNDLE = create("bundle");
 
     /**
-     * <strong>AVAILABLE BETWEEN VERSIONS:</strong> 1.19 - 1.19.4
-     *
-     * @deprecated not available since 1.20
+     * The {@code trade_rebalance} feature flag.
      */
-    @Deprecated
-    public static final FeatureFlag UPDATE_1_20 = Bukkit.getUnsafe().getFeatureFlag(NamespacedKey.minecraft("update_1_20"));
-
     @ApiStatus.Experimental // Paper - add missing annotation
-    public static final FeatureFlag TRADE_REBALANCE = Bukkit.getUnsafe().getFeatureFlag(NamespacedKey.minecraft("trade_rebalance"));
+    FeatureFlag TRADE_REBALANCE = create("trade_rebalance");
+
+    @Deprecated(since = "1.20")
+    FeatureFlag UPDATE_1_20 = deprecated("update_1_20");
+
+    @Deprecated(since = "1.21")
+    FeatureFlag UPDATE_121 = deprecated("update_1_21");
 
     /**
-     * <strong>AVAILABLE BETWEEN VERSIONS:</strong> 1.20.5 - 1.20.6
-     *
-     * @deprecated not available since 1.21
+     * An index of all feature flags.
      */
-    @Deprecated
-    public static final FeatureFlag UPDATE_121 = Bukkit.getUnsafe().getFeatureFlag(NamespacedKey.minecraft("update_1_21"));
+    Index<Key, FeatureFlag> ALL_FLAGS = Index.create(FeatureFlag::key, List.copyOf(FeatureFlagImpl.ALL_FLAGS));
+
+    private static FeatureFlag create(@Subst("vanilla") final String name) {
+        final FeatureFlag flag = new FeatureFlagImpl(NamespacedKey.minecraft(name));
+        Preconditions.checkState(FeatureFlagImpl.ALL_FLAGS.add(flag), "Tried to add duplicate feature flag: " + name);
+        return flag;
+    }
+
+    private static FeatureFlag deprecated(@Subst("vanilla") final String name) {
+        return new FeatureFlagImpl.Deprecated(NamespacedKey.minecraft(name));
+    }
+    // Paper end - overhaul FeatureFlag API
 }
diff --git a/src/main/java/org/bukkit/FeatureFlagImpl.java b/src/main/java/org/bukkit/FeatureFlagImpl.java
new file mode 100644
index 0000000000000000000000000000000000000000..a33517dbd69021fde8246836720b6247800ee43c
--- /dev/null
+++ b/src/main/java/org/bukkit/FeatureFlagImpl.java
@@ -0,0 +1,29 @@
+package org.bukkit;
+
+import java.util.HashSet;
+import java.util.Set;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+import org.jetbrains.annotations.ApiStatus;
+
+@ApiStatus.Internal
+@DefaultQualifier(NonNull.class)
+record FeatureFlagImpl(NamespacedKey key) implements FeatureFlag {
+
+    static final Set<FeatureFlag> ALL_FLAGS = new HashSet<>();
+
+    @Override
+    public NamespacedKey getKey() {
+        return this.key;
+    }
+
+    @ApiStatus.Internal
+    @DefaultQualifier(NonNull.class)
+    record Deprecated(NamespacedKey key) implements FeatureFlag {
+
+        @Override
+        public NamespacedKey getKey() {
+            return this.key;
+        }
+    }
+}
diff --git a/src/main/java/org/bukkit/RegionAccessor.java b/src/main/java/org/bukkit/RegionAccessor.java
index eb33e8e671972aa308ad75a7ce9aa9ac526f470f..05ecf3cb38ff42c8b52405d900197e6bf47dd1e6 100644
--- a/src/main/java/org/bukkit/RegionAccessor.java
+++ b/src/main/java/org/bukkit/RegionAccessor.java
@@ -18,7 +18,7 @@ import org.jetbrains.annotations.Nullable;
  * A RegionAccessor gives access to getting, modifying and spawning {@link Biome}, {@link BlockState} and {@link Entity},
  * as well as generating some basic structures.
  */
-public interface RegionAccessor extends Keyed { // Paper
+public interface RegionAccessor extends Keyed, io.papermc.paper.world.flag.FeatureFlagSetHolder { // Paper - feature flag API
 
     /**
      * Gets the {@link Biome} at the given {@link Location}.
diff --git a/src/main/java/org/bukkit/UnsafeValues.java b/src/main/java/org/bukkit/UnsafeValues.java
index 330e3013eda204aa9b33d5e1c3104e0b595abdbc..c80e0ef587a001ee6de3f5c182cc9696d58bafeb 100644
--- a/src/main/java/org/bukkit/UnsafeValues.java
+++ b/src/main/java/org/bukkit/UnsafeValues.java
@@ -114,8 +114,7 @@ public interface UnsafeValues {
 
     String getTranslationKey(Attribute attribute);
 
-    @Nullable
-    FeatureFlag getFeatureFlag(@NotNull NamespacedKey key);
+    // Paper - replace with better system
 
     /**
      * Do not use, method will get removed, and the plugin won't run
diff --git a/src/main/java/org/bukkit/block/BlockType.java b/src/main/java/org/bukkit/block/BlockType.java
index 8f430a4067fc722ebfbca846cccded4fb0a3a4e5..4aa79016eb5f7edf930c82d30ff25078fdb88436 100644
--- a/src/main/java/org/bukkit/block/BlockType.java
+++ b/src/main/java/org/bukkit/block/BlockType.java
@@ -123,7 +123,7 @@ import org.jetbrains.annotations.Nullable;
  * changes may occur. Do not use this API in plugins.
  */
 @ApiStatus.Internal
-public interface BlockType extends Keyed, Translatable, net.kyori.adventure.translation.Translatable { // Paper - add translatable
+public interface BlockType extends Keyed, Translatable, net.kyori.adventure.translation.Translatable, io.papermc.paper.world.flag.FeatureDependant { // Paper - add translatable & feature flag API
 
     /**
      * Typed represents a subtype of {@link BlockType}s that have a known block
diff --git a/src/main/java/org/bukkit/entity/EntityType.java b/src/main/java/org/bukkit/entity/EntityType.java
index ba605ad75d4ed920c0dc4527529998041a58676b..a78e1c431a6ea46ba7c44880e25a871f473bef41 100644
--- a/src/main/java/org/bukkit/entity/EntityType.java
+++ b/src/main/java/org/bukkit/entity/EntityType.java
@@ -23,7 +23,7 @@ import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-public enum EntityType implements Keyed, Translatable, net.kyori.adventure.translation.Translatable { // Paper - translatable
+public enum EntityType implements Keyed, Translatable, net.kyori.adventure.translation.Translatable, io.papermc.paper.world.flag.FeatureDependant { // Paper - translatable
 
     // These strings MUST match the strings in nms.EntityTypes and are case sensitive.
     /**
diff --git a/src/main/java/org/bukkit/generator/WorldInfo.java b/src/main/java/org/bukkit/generator/WorldInfo.java
index 5067f1371433cccd3287af7f03e152f2c3c1ece3..e0cb282541548ac3bd24cce86b3413f5748ea8bc 100644
--- a/src/main/java/org/bukkit/generator/WorldInfo.java
+++ b/src/main/java/org/bukkit/generator/WorldInfo.java
@@ -7,7 +7,7 @@ import org.jetbrains.annotations.NotNull;
 /**
  * Holds various information of a World
  */
-public interface WorldInfo {
+public interface WorldInfo extends io.papermc.paper.world.flag.FeatureFlagSetHolder { // Paper - feature flag API
 
     /**
      * Gets the unique name of this world
diff --git a/src/main/java/org/bukkit/inventory/ItemType.java b/src/main/java/org/bukkit/inventory/ItemType.java
index 0168f0a14a3e899e84c5e36963ff79950ab580fb..86887e8b20288b8204adcc64993b39f94269a0eb 100644
--- a/src/main/java/org/bukkit/inventory/ItemType.java
+++ b/src/main/java/org/bukkit/inventory/ItemType.java
@@ -48,7 +48,7 @@ import org.jetbrains.annotations.Nullable;
  * changes may occur. Do not use this API in plugins.
  */
 @ApiStatus.Experimental // Paper - already required for registry builders
-public interface ItemType extends Keyed, Translatable, net.kyori.adventure.translation.Translatable { // Paper - add Translatable
+public interface ItemType extends Keyed, Translatable, net.kyori.adventure.translation.Translatable, io.papermc.paper.world.flag.FeatureDependant { // Paper - add Translatable & feature flag API
 
     /**
      * Typed represents a subtype of {@link ItemType}s that have a known item meta type
diff --git a/src/main/java/org/bukkit/potion/PotionEffectType.java b/src/main/java/org/bukkit/potion/PotionEffectType.java
index 10fa51d116b40450b51af9110d5637f3505ebf65..647452f16e4bf7e5a61520123e62d9408ec9adfb 100644
--- a/src/main/java/org/bukkit/potion/PotionEffectType.java
+++ b/src/main/java/org/bukkit/potion/PotionEffectType.java
@@ -17,7 +17,7 @@ import org.jetbrains.annotations.Nullable;
 /**
  * Represents a type of potion and its effect on an entity.
  */
-public abstract class PotionEffectType implements Keyed, Translatable, net.kyori.adventure.translation.Translatable { // Paper - implement Translatable
+public abstract class PotionEffectType implements Keyed, Translatable, net.kyori.adventure.translation.Translatable, io.papermc.paper.world.flag.FeatureDependant { // Paper - implement Translatable & feature flag API
     private static final BiMap<Integer, PotionEffectType> ID_MAP = HashBiMap.create();
 
     /**
diff --git a/src/main/java/org/bukkit/potion/PotionType.java b/src/main/java/org/bukkit/potion/PotionType.java
index 453c626092caa734a0af5800699f299fc6fd0e43..c82cc9d9db5cb0e0e3c02f6a9564fc935ee594aa 100644
--- a/src/main/java/org/bukkit/potion/PotionType.java
+++ b/src/main/java/org/bukkit/potion/PotionType.java
@@ -14,7 +14,7 @@ import org.jetbrains.annotations.Nullable;
  * This enum reflects and matches each potion state that can be obtained from
  * the Creative mode inventory
  */
-public enum PotionType implements Keyed {
+public enum PotionType implements Keyed, io.papermc.paper.world.flag.FeatureDependant { // Paper - feature flag API
     WATER("water"),
     MUNDANE("mundane"),
     THICK("thick"),