Add support for Rails::Engine

Gemfile

@@ -14,6 +14,7 @@ end
 
 group :test do
   gem "rspec-rails"
+  gem "super_engine", path: "spec/dummies/with-engine/dummy/engines/super_engine", require: false
 end
 
 group :tools do

dry-rails.gemspec

@@ -36,4 +36,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "bundler"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec"
+
+  # our super engine used in specs
+  spec.add_development_dependency "super_engine"
 end

lib/dry/rails.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 require "dry/rails/railtie"
+require "dry/rails/engine"
+require "dry/rails/finalizer"
 require "dry/rails/container"
 require "dry/rails/components"
 
@@ -20,14 +22,24 @@ module Dry
   #
   # @api public
   module Rails
+    extend Configurable
+    # Set to true to turn off dry-system for main application
+    # Meant to be used in setup where dry-system is only used within Rails::Engine(s)
+    #
+    # @api public
+    setting :main_app_disabled, default: false
+
+    # This is being injected by main app Railtie
+    # @api private
+    setting :main_app_name
+
     # Set container block that will be evaluated in the context of the container
     #
     # @return [self]
     #
     # @api public
     def self.container(&block)
-      _container_blocks << block
-      self
+      Engine.container(config.main_app_name, &block)
     end
 
     # Create a new container class
@@ -40,19 +52,12 @@ def self.container(&block)
     #
     # @api private
     def self.create_container(options = {})
-      Class.new(Container) { config.update(options) }
+      Engine.create_container(options)
     end
 
     # @api private
     def self.evaluate_initializer(container)
-      _container_blocks.each do |block|
-        container.class_eval(&block)
-      end
-    end
-
-    # @api private
-    def self._container_blocks
-      @_container_blocks ||= []
+      Engine.evaluate_initializer(config.main_app_name, container)
     end
   end
 end

lib/dry/rails/boot/safe_params.rb

@@ -6,7 +6,7 @@
   end
 
   start do
-    ApplicationController.include(Dry::Rails::Features::SafeParams)
+    ActionController::Base.include(Dry::Rails::Features::SafeParams)
 
     if defined?(ActionController::API)
       ActionController::API.include(Dry::Rails::Features::SafeParams)

lib/dry/rails/engine.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module Dry
+  module Rails
+    module Engine
+      # Set container block that will be evaluated in the context of the container
+      #
+      # @param name [Symbol]
+      # @return [self]
+      #
+      # @api public
+      def self.container(name, &block)
+        _container_blocks[name] << block
+        self
+      end
+
+      # Create a new container class
+      #
+      # This is used during booting and reloading
+      #
+      # @param name [Symbol]
+      # @param options [Hash] Container configuration settings
+      #
+      # @return [Class]
+      #
+      # @api private
+      def self.create_container(options = {})
+        Class.new(Container) { config.update(options) }
+      end
+
+      # @api private
+      def self.evaluate_initializer(name, container)
+        _container_blocks[name].each do |block|
+          container.class_eval(&block)
+        end
+      end
+
+      # @api private
+      def self._container_blocks
+        @_container_blocks ||= Hash.new { |h, k| h[k] = [] }
+      end
+    end
+  end
+end

lib/dry/rails/finalizer.rb

@@ -0,0 +1,172 @@
+# frozen_string_literal: true
+
+module Dry
+  module Rails
+    class Finalizer
+      def self.app_namespace_to_name(app_namespace)
+        app_namespace.name.underscore.to_sym
+      end
+
+      # rubocop:disable Metrics/ParameterLists
+      def initialize(
+        railtie:,
+        app_namespace:,
+        root_path:,
+        name: Dry::Rails.config.main_app_name,
+        container_const_name: Dry::Rails::Container.container_constant,
+        default_inflector: ActiveSupport::Inflector
+      )
+        @railtie = railtie
+        @app_namespace = app_namespace
+        @root_path = root_path
+        @name = name
+        @container_const_name = container_const_name
+        @default_inflector = default_inflector
+      end
+      # rubocop:enable Metrics/ParameterLists
+
+      attr_reader :railtie,
+                  :root_path,
+                  :container_const_name
+
+      # Infer the default application namespace
+      #
+      # TODO: we had to rename namespace=>app_namespace because
+      #       Rake::DSL's Kernel#namespace *sometimes* breaks things.
+      #       Currently we are missing specs verifying that rake tasks work
+      #       correctly and those must be added!
+      #
+      # @return [Module]
+      #
+      # @api public
+      attr_reader :app_namespace
+
+      # Code-reloading-aware finalization process
+      #
+      # This sets up `Container` and `Deps` constants, reloads them if this is in reloading mode,
+      # and registers default components like the railtie itself or the inflector
+      #
+      # @api public
+      #
+      # rubocop:disable Metrics/AbcSize
+      def finalize!
+        stop_features if reloading?
+
+        container = Dry::Rails::Engine.create_container(
+          root: root_path,
+          inflector: default_inflector,
+          system_dir: root_path.join("config/system"),
+          bootable_dirs: [root_path.join("config/system/boot")]
+        )
+
+        # Enable :env plugin by default because it is a very common requirement
+        container.use :env, inferrer: -> { ::Rails.env }
+
+        container.register(:railtie, railtie)
+        container.register(:inflector, default_inflector)
+
+        # Remove previously defined constants, if any, so we don't end up with
+        # unsused constants in app's namespace when a name change happens.
+        remove_constant(container.auto_inject_constant)
+        remove_constant(container.container_constant)
+
+        Dry::Rails::Engine.evaluate_initializer(name, container)
+
+        @container_const_name = container.container_constant
+
+        set_or_reload(container.container_constant, container)
+        set_or_reload(container.auto_inject_constant, container.injector)
+
+        container.features.each do |feature|
+          container.boot(feature, from: :rails)
+        end
+
+        container.refresh_boot_files if reloading?
+
+        container.finalize!(freeze: !::Rails.env.test?)
+      end
+      # rubocop:enable Metrics/AbcSize
+
+      # Stops all configured features (bootable components)
+      #
+      # This is *crucial* when reloading code in development mode. Every bootable component
+      # should be able to clear the runtime from any constants that it created in its `stop`
+      # lifecycle step
+      #
+      # @api public
+      def stop_features
+        container.features.each do |feature|
+          container.stop(feature) if container.booted?(feature)
+        end
+      end
+
+      # Exposes the container constant
+      #
+      # @return [Dry::Rails::Container]
+      #
+      # @api public
+      def container
+        app_namespace.const_get(container_const_name, false)
+      end
+
+      # Return true if we're in code-reloading mode
+      #
+      # @api private
+      def reloading?
+        app_namespace.const_defined?(container_const_name, false)
+      end
+
+      # Return the default system name
+      #
+      # In the dry-system world containers are explicitly named using symbols, so that you can
+      # refer to them easily when ie importing one container into another
+      #
+      # @return [Symbol]
+      #
+      # @api private
+      attr_reader :name
+
+      # Sets or reloads a constant within the application namespace
+      #
+      # @api private
+      attr_reader :default_inflector
+
+      # @api private
+      def set_or_reload(const_name, const)
+        remove_constant(const_name)
+        app_namespace.const_set(const_name, const)
+      end
+
+      # @api private
+      def remove_constant(const_name)
+        if app_namespace.const_defined?(const_name, false)
+          app_namespace.__send__(:remove_const, const_name)
+        end
+      end
+    end
+
+    module Engine
+      class Finalizer
+        # rubocop:disable Metrics/ParameterLists
+        def self.new(
+          railtie:,
+          app_namespace:,
+          root_path:,
+          name: nil,
+          container_const_name: Dry::Rails::Container.container_constant,
+          default_inflector: ActiveSupport::Inflector
+        )
+          Dry::Rails::Finalizer.new(
+            railtie: railtie,
+            app_namespace: app_namespace,
+            root_path: root_path,
+            name: name || ::Dry::Rails::Finalizer.app_namespace_to_name(app_namespace),
+            container_const_name: container_const_name,
+            default_inflector: default_inflector
+          )
+        end
+        # rubocop:enable Metrics/ParameterLists
+      end
+    end
+  end
+end