Load Solidus engine extension files automatically

README.md

@@ -38,7 +38,7 @@ module SolidusExtensionName
   class Engine < Rails::Engine
     engine_name 'solidus_extension_name'
 
-    include SolidusSupport::EngineExtensions::Decorators
+    include SolidusSupport::EngineExtensions
 
     # ...
   end
@@ -57,6 +57,26 @@ end
 config.to_prepare(&method(:activate).to_proc)
 ```
 
+#### Loading files conditionally
+
+If you include `EngineExtensions` in your extension and structure your files according to the
+expected paths, they will be loaded automagically only when the relevant Solidus engines are
+available.
+
+Here's what an example structure may look like:
+
+- `lib/views/backend`: will only be added to the view paths when `solidus_backend` is available.
+- `lib/controllers/backend`: will only be added to the controller paths when `solidus_backend` is
+  available.
+- `lib/decorators/backend`: will only be added to the decorator paths when `solidus_backend` is
+  available.
+
+The same goes for `frontend` and `api`.
+
+We strongly recommend following this structure and making your extensions so that they're not
+dependent on anything other than `solidus_core`, only augmenting the functionality of the other
+engines when they are available.
+
 ## Development
 
 To install this gem onto your local machine, run `bundle exec rake install`. To release a new

lib/solidus_support/engine_extensions.rb

@@ -1,3 +1,76 @@
 # frozen_string_literal: true
 
-require_relative 'engine_extensions/decorators'
+module SolidusSupport
+  module EngineExtensions
+    include ActiveSupport::Deprecation::DeprecatedConstantAccessor
+    deprecate_constant 'Decorators', 'SolidusSupport::EngineExtensions'
+
+    def self.included(engine)
+      engine.extend ClassMethods
+
+      engine.class_eval do
+        config.to_prepare(&method(:activate))
+
+        enable_solidus_engine_support('backend') if SolidusSupport.backend_available?
+        enable_solidus_engine_support('frontend') if SolidusSupport.frontend_available?
+        enable_solidus_engine_support('api') if SolidusSupport.api_available?
+      end
+    end
+
+    module ClassMethods
+      def activate
+        if Rails.respond_to?(:autoloaders) && Rails.autoloaders.main
+          # Add decorators folder to the Rails autoloader. This tells Zeitwerk to treat paths
+          # such as app/decorators/controllers as roots.
+          solidus_decorators_root.glob('*') do |decorators_folder|
+            Rails.autoloaders.main.push_dir(decorators_folder)
+          end
+        end
+
+        load_solidus_decorators_from(solidus_decorators_root)
+      end
+
+      # 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_solidus_decorators_from(path)
+        path.glob('**/*.rb') do |decorator_path|
+          require_dependency(decorator_path)
+        end
+      end
+
+      private
+
+      # Returns the root for this engine's decorators.
+      #
+      # @return [Path]
+      def solidus_decorators_root
+        root.join('app/decorators')
+      end
+
+      # Enables support for a Solidus engine.
+      #
+      # This will tell Rails to:
+      #
+      #   * add +lib/controllers/[engine]+ to the controller paths;
+      #   * add +lib/views/[engine]+ to the view paths;
+      #   * load the decorators in +lib/decorators/[engine]+.
+      #
+      # @see #load_solidus_decorators_from
+      def enable_solidus_engine_support(engine)
+        paths['app/controllers'] << "lib/controllers/#{engine}"
+        paths['app/views'] << "lib/views/#{engine}"
+
+        engine_context = self
+        config.to_prepare do
+          engine_context.instance_eval do
+            path = root.join("lib/decorators/#{engine}")
+            load_solidus_decorators_from(path)
+          end
+        end
+      end
+    end
+  end
+end

solidus_support.gemspec

@@ -21,6 +21,8 @@ Gem::Specification.new do |s|
   s.executables = s.files.grep(%r{^exe/}) { |f| File.basename(f) }
   s.require_paths = ["lib"]
 
+  s.add_dependency 'activesupport', ['>= 5.2', '< 7.0.x']
+
   s.add_development_dependency 'bundler'
   s.add_development_dependency 'rake'
   s.add_development_dependency 'rspec-rails'