Improve declarative Plugin definition interface

env.sh

@@ -1,2 +1,2 @@
 #!/bin/sh
-export GITBUCKET_VERSION=3.4.0
+export GITBUCKET_VERSION=3.4.1-SNAPSHOT

src/main/scala/gitbucket/core/plugin/Plugin.scala

@@ -22,36 +22,56 @@ trait Plugin {
    */
   val images: Seq[(String, Array[Byte])] = Nil
 
+  /**
+   * Override to declare this plug-in provides images.
+   */
+  def images(registry: PluginRegistry, context: ServletContext, settings: SystemSettings): Seq[(String, Array[Byte])] = Nil
+
   /**
    * Override to declare this plug-in provides controllers.
    */
   val controllers: Seq[(String, ControllerBase)] = Nil
 
+  /**
+   * Override to declare this plug-in provides controllers.
+   */
+  def controllers(registry: PluginRegistry, context: ServletContext, settings: SystemSettings): Seq[(String, ControllerBase)] = Nil
+
   /**
    * Override to declare this plug-in provides JavaScript.
    */
   val javaScripts: Seq[(String, String)] = Nil
 
+  /**
+   * Override to declare this plug-in provides JavaScript.
+   */
+  def javaScripts(registry: PluginRegistry, context: ServletContext, settings: SystemSettings): Seq[(String, String)] = Nil
+
   /**
    * Override to declare this plug-in provides renderers.
    */
   val renderers: Seq[(String, Renderer)] = Nil
 
+  /**
+   * Override to declare this plug-in provides renderers.
+   */
+  def renderers(registry: PluginRegistry, context: ServletContext, settings: SystemSettings): Seq[(String, Renderer)] = Nil
+
   /**
    * This method is invoked in initialization of plugin system.
    * Register plugin functionality to PluginRegistry.
    */
   def initialize(registry: PluginRegistry, context: ServletContext, settings: SystemSettings): Unit = {
-    images.foreach { case (id, in) =>
+    (images ++ images(registry, context, settings)).foreach { case (id, in) =>
       registry.addImage(id, in)
     }
-    controllers.foreach { case (path, controller) =>
+    (controllers ++ controllers(registry, context, settings)).foreach { case (path, controller) =>
       registry.addController(path, controller)
     }
-    javaScripts.foreach { case (path, script) =>
+    (javaScripts ++ javaScripts(registry, context, settings)).foreach { case (path, script) =>
       registry.addJavaScript(path, script)
     }
-    renderers.foreach { case (extension, renderer) =>
+    (renderers ++ renderers(registry, context, settings)).foreach { case (extension, renderer) =>
       registry.addRenderer(extension, renderer)
     }
   }