Add Lifecycle Event system

This event system is separate from Bukkit's event system and is
meant for managing resources across reloads and from points in the
PluginBootstrap.

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

@@ -271,4 +271,12 @@ public interface UnsafeValues {
      */
     @Nullable org.bukkit.Color getSpawnEggLayerColor(org.bukkit.entity.EntityType entityType, int layer);
     // Paper end - spawn egg color visibility
+
+    // Paper start - lifecycle event API
+    /**
+     * @hidden
+     */
+    @org.jetbrains.annotations.ApiStatus.Internal
+    io.papermc.paper.plugin.lifecycle.event.LifecycleEventManager<org.bukkit.plugin.Plugin> createPluginLifecycleEventManager(final org.bukkit.plugin.java.JavaPlugin plugin, final java.util.function.BooleanSupplier registrationCheck);
+    // Paper end - lifecycle event API
 }

paper-api/src/main/java/org/bukkit/plugin/Plugin.java

@@ -16,7 +16,7 @@ import org.jetbrains.annotations.Nullable;
  * <p>
  * The use of {@link PluginBase} is recommended for actual Implementation
  */
-public interface Plugin extends TabExecutor {
+public interface Plugin extends TabExecutor, io.papermc.paper.plugin.lifecycle.event.LifecycleEventOwner { // Paper
     /**
      * Returns the folder that the plugin data files are located in. The
      * folder may not yet exist.
@@ -224,4 +224,14 @@ public interface Plugin extends TabExecutor {
      */
     @NotNull
     public String getName();
+
+    // Paper start - lifecycle events
+    /**
+     * Get the lifecycle event manager for registering handlers
+     * for lifecycle events allowed on the {@link Plugin}.
+     *
+     * @return the lifecycle event manager
+     */
+    io.papermc.paper.plugin.lifecycle.event.@NotNull LifecycleEventManager<Plugin> getLifecycleManager();
+    // Paper end - lifecycle events
 }

paper-api/src/main/java/org/bukkit/plugin/java/JavaPlugin.java

@@ -48,6 +48,11 @@ public abstract class JavaPlugin extends PluginBase {
     private FileConfiguration newConfig = null;
     private File configFile = null;
     private Logger logger = null; // Paper - PluginLogger -> Logger
+    // Paper start - lifecycle events
+    @SuppressWarnings("deprecation")
+    private final io.papermc.paper.plugin.lifecycle.event.LifecycleEventManager<org.bukkit.plugin.Plugin> lifecycleEventManager = org.bukkit.Bukkit.getUnsafe().createPluginLifecycleEventManager(this, () -> this.allowsLifecycleRegistration);
+    private boolean allowsLifecycleRegistration = true;
+    // Paper end
 
     public JavaPlugin() {
         // Paper start
@@ -279,7 +284,9 @@ public abstract class JavaPlugin extends PluginBase {
             isEnabled = enabled;
 
             if (isEnabled) {
+                try { // Paper - lifecycle events
                 onEnable();
+                } finally { this.allowsLifecycleRegistration = false; } // Paper - lifecycle events
             } else {
                 onDisable();
             }
@@ -457,4 +464,11 @@ public abstract class JavaPlugin extends PluginBase {
         }
         return plugin;
     }
+
+    // Paper start - lifecycle events
+    @Override
+    public final io.papermc.paper.plugin.lifecycle.event.@NotNull LifecycleEventManager<org.bukkit.plugin.Plugin> getLifecycleManager() {
+        return this.lifecycleEventManager;
+    }
+    // Paper end - lifecycle events
 }