Enable support for Solidus engines conditionally

lib/solidus_support/engine_extensions/decorators.rb

@@ -4,33 +4,62 @@ module SolidusSupport
   module EngineExtensions
     module Decorators
       def self.included(engine)
+        engine.extend ClassMethods
+
         engine.class_eval do
-          extend ClassMethods
           config.to_prepare(&method(:activate).to_proc)
         end
       end
 
       module ClassMethods
         def activate
-          base_path = root.join('app/decorators')
-
           if Rails.respond_to?(:autoloaders) && Rails.autoloaders.main
-            # Add decorators folder to the Rails autoloader. This
-            # allows Zeitwerk to resolve decorators paths correctly,
-            # when used.
-            Dir.glob(base_path.join('*')) do |decorators_folder|
+            # Add decorators folder to the Rails autoloader. This tells Zeitwerk to treat paths
+            # such as app/decorators/controllers as roots.
+            Dir.glob(decorators_root.join('*')) do |decorators_folder|
               Rails.autoloaders.main.push_dir(decorators_folder)
             end
           end
 
-          # Load decorator files. This is needed since they are
-          # never explicitely referenced in the application code
-          # and won't be loaded by default. We need them to be
-          # executed anyway to extend exisiting classes.
-          Dir.glob(base_path.join('**/*.rb')) do |decorator_path|
+          load_decorators_from(decorators_root)
+
+          enable_engine_support('backend') if SolidusSupport.backend_available?
+          enable_engine_support('frontend') if SolidusSupport.frontend_available?
+          enable_engine_support('api') if SolidusSupport.api_available?
+        end
+
+        private
+
+        # Loads decorator files.
+        #
+        # This is needed since they are never explicitly referenced in the application code and
+        # won't be loaded by default. We need them to be executed regardless in order to decorate
+        # existing classes.
+        def load_decorators_from(path)
+          Dir.glob(path.join('**/*.rb')) do |decorator_path|
             require_dependency(decorator_path)
           end
         end
+
+        # Returns the root for this engine's decorators.
+        #
+        # @return [Path]
+        def decorators_root
+          root.join('app/decorators')
+        end
+
+        # Enables support for a Solidus engine.
+        #
+        # This will simply tell Rails to load lib/controllers/[engine] and lib/views/[engine], as
+        # well as loading the decorators from lib/decorators/[engine].
+        #
+        # @see #load_decorators_path
+        def enable_engine_support(engine)
+          paths['app/controllers'] << "lib/controllers/#{engine}"
+          paths['app/views'] << "lib/views/#{engine}"
+
+          load_decorators_from(root.join("lib/decorators/#{engine}"))
+        end
       end
     end
   end