railties/lib/rails/engine.rb
# frozen_string_literal: true
require "rails/railtie"
require "rails/engine/railties"
require "active_support/callbacks"
require "active_support/core_ext/module/delegation"
require "active_support/core_ext/object/try"
require "pathname"
require "thread"
module Rails
# +Rails::Engine+ allows you to wrap a specific \Rails application or subset of
# functionality and share it with other applications or within a larger packaged application.
# Every Rails::Application is just an engine, which allows for simple
# feature and application sharing.
#
# Any +Rails::Engine+ is also a Rails::Railtie, so the same
# methods (like {rake_tasks}[rdoc-ref:Rails::Railtie::rake_tasks] and
# {generators}[rdoc-ref:Rails::Railtie::generators]) and configuration
# options that are available in railties can also be used in engines.
#
# == Creating an Engine
#
# If you want a gem to behave as an engine, you have to specify an +Engine+
# for it somewhere inside your plugin's +lib+ folder (similar to how we
# specify a +Railtie+):
#
# # lib/my_engine.rb
# module MyEngine
# class Engine < Rails::Engine
# end
# end
#
# Then ensure that this file is loaded at the top of your <tt>config/application.rb</tt>
# (or in your +Gemfile+), and it will automatically load models, controllers, and helpers
# inside +app+, load routes at <tt>config/routes.rb</tt>, load locales at
# <tt>config/locales/**/*</tt>, and load tasks at <tt>lib/tasks/**/*</tt>.
#
# == Configuration
#
# Like railties, engines can access a config object which contains configuration shared by
# all railties and the application.
# Additionally, each engine can access <tt>autoload_paths</tt>, <tt>eager_load_paths</tt> and
# <tt>autoload_once_paths</tt> settings which are scoped to that engine.
#
# class MyEngine < Rails::Engine
# # Add a load path for this specific Engine
# config.autoload_paths << File.expand_path("lib/some/path", __dir__)
#
# initializer "my_engine.add_middleware" do |app|
# app.middleware.use MyEngine::Middleware
# end
# end
#
# == Generators
#
# You can set up generators for engines with <tt>config.generators</tt> method:
#
# class MyEngine < Rails::Engine
# config.generators do |g|
# g.orm :active_record
# g.template_engine :erb
# g.test_framework :test_unit
# end
# end
#
# You can also set generators for an application by using <tt>config.app_generators</tt>:
#
# class MyEngine < Rails::Engine
# # note that you can also pass block to app_generators in the same way you
# # can pass it to generators method
# config.app_generators.orm :datamapper
# end
#
# == Paths
#
# Applications and engines have flexible path configuration, meaning that you
# are not required to place your controllers at <tt>app/controllers</tt>, but
# in any place which you find convenient.
#
# For example, let's suppose you want to place your controllers in <tt>lib/controllers</tt>.
# You can set that as an option:
#
# class MyEngine < Rails::Engine
# paths["app/controllers"] = "lib/controllers"
# end
#
# You can also have your controllers loaded from both <tt>app/controllers</tt> and
# <tt>lib/controllers</tt>:
#
# class MyEngine < Rails::Engine
# paths["app/controllers"] << "lib/controllers"
# end
#
# The available paths in an engine are:
#
# class MyEngine < Rails::Engine
# paths["app"] # => ["app"]
# paths["app/controllers"] # => ["app/controllers"]
# paths["app/helpers"] # => ["app/helpers"]
# paths["app/models"] # => ["app/models"]
# paths["app/views"] # => ["app/views"]
# paths["lib"] # => ["lib"]
# paths["lib/tasks"] # => ["lib/tasks"]
# paths["config"] # => ["config"]
# paths["config/initializers"] # => ["config/initializers"]
# paths["config/locales"] # => ["config/locales"]
# paths["config/routes.rb"] # => ["config/routes.rb"]
# end
#
# The <tt>Application</tt> class adds a couple more paths to this set. And as in your
# <tt>Application</tt>, all folders under +app+ are automatically added to the load path.
# If you have an <tt>app/services</tt> folder for example, it will be added by default.
#
# == Endpoint
#
# An engine can also be a Rack application. It can be useful if you have a Rack application that
# you would like to provide with some of the +Engine+'s features.
#
# To do that, use the ::endpoint method:
#
# module MyEngine
# class Engine < Rails::Engine
# endpoint MyRackApplication
# end
# end
#
# Now you can mount your engine in application's routes:
#
# Rails.application.routes.draw do
# mount MyEngine::Engine => "/engine"
# end
#
# == Middleware stack
#
# As an engine can now be a Rack endpoint, it can also have a middleware
# stack. The usage is exactly the same as in <tt>Application</tt>:
#
# module MyEngine
# class Engine < Rails::Engine
# middleware.use SomeMiddleware
# end
# end
#
# == Routes
#
# If you don't specify an endpoint, routes will be used as the default
# endpoint. You can use them just like you use an application's routes:
#
# # ENGINE/config/routes.rb
# MyEngine::Engine.routes.draw do
# get "/" => "posts#index"
# end
#
# == Mount priority
#
# Note that now there can be more than one router in your application, and it's better to avoid
# passing requests through many routers. Consider this situation:
#
# Rails.application.routes.draw do
# mount MyEngine::Engine => "/blog"
# get "/blog/omg" => "main#omg"
# end
#
# +MyEngine+ is mounted at <tt>/blog</tt>, and <tt>/blog/omg</tt> points to application's
# controller. In such a situation, requests to <tt>/blog/omg</tt> will go through +MyEngine+,
# and if there is no such route in +Engine+'s routes, it will be dispatched to <tt>main#omg</tt>.
# It's much better to swap that:
#
# Rails.application.routes.draw do
# get "/blog/omg" => "main#omg"
# mount MyEngine::Engine => "/blog"
# end
#
# Now, +Engine+ will get only requests that were not handled by +Application+.
#
# == Engine name
#
# There are some places where an Engine's name is used:
#
# * routes: when you mount an Engine with <tt>mount(MyEngine::Engine => '/my_engine')</tt>,
# it's used as default <tt>:as</tt> option
# * rake task for installing migrations <tt>my_engine:install:migrations</tt>
#
# Engine name is set by default based on class name. For +MyEngine::Engine+ it will be
# <tt>my_engine_engine</tt>. You can change it manually using the <tt>engine_name</tt> method:
#
# module MyEngine
# class Engine < Rails::Engine
# engine_name "my_engine"
# end
# end
#
# == Isolated Engine
#
# Normally when you create controllers, helpers, and models inside an engine, they are treated
# as if they were created inside the application itself. This means that all helpers and
# named routes from the application will be available to your engine's controllers as well.
#
# However, sometimes you want to isolate your engine from the application, especially if your engine
# has its own router. To do that, you simply need to call ::isolate_namespace. This method requires
# you to pass a module where all your controllers, helpers, and models should be nested to:
#
# module MyEngine
# class Engine < Rails::Engine
# isolate_namespace MyEngine
# end
# end
#
# With such an engine, everything that is inside the +MyEngine+ module will be isolated from
# the application.
#
# Consider this controller:
#
# module MyEngine
# class FooController < ActionController::Base
# end
# end
#
# If the +MyEngine+ engine is marked as isolated, +FooController+ only has
# access to helpers from +MyEngine+, and <tt>url_helpers</tt> from
# <tt>MyEngine::Engine.routes</tt>.
#
# The next thing that changes in isolated engines is the behavior of routes.
# Normally, when you namespace your controllers, you also need to namespace
# the related routes. With an isolated engine, the engine's namespace is
# automatically applied, so you don't need to specify it explicitly in your
# routes:
#
# MyEngine::Engine.routes.draw do
# resources :articles
# end
#
# If +MyEngine+ is isolated, the routes above will point to
# +MyEngine::ArticlesController+. You also don't need to use longer
# URL helpers like +my_engine_articles_path+. Instead, you should simply use
# +articles_path+, like you would do with your main application.
#
# To make this behavior consistent with other parts of the framework,
# isolated engines also have an effect on ActiveModel::Naming. In a
# normal \Rails app, when you use a namespaced model such as
# +Namespace::Article+, ActiveModel::Naming will generate
# names with the prefix "namespace". In an isolated engine, the prefix will
# be omitted in URL helpers and form fields, for convenience.
#
# polymorphic_url(MyEngine::Article.new)
# # => "articles_path" # not "my_engine_articles_path"
#
# form_for(MyEngine::Article.new) do
# text_field :title # => <input type="text" name="article[title]" id="article_title" />
# end
#
# Additionally, an isolated engine will set its own name according to its
# namespace, so <tt>MyEngine::Engine.engine_name</tt> will return
# "my_engine". It will also set +MyEngine.table_name_prefix+ to "my_engine_",
# meaning for example that +MyEngine::Article+ will use the
# +my_engine_articles+ database table by default.
#
# == Using Engine's routes outside Engine
#
# Since you can now mount an engine inside application's routes, you do not have direct access to +Engine+'s
# <tt>url_helpers</tt> inside +Application+. When you mount an engine in an application's routes, a special helper is
# created to allow you to do that. Consider such a scenario:
#
# # config/routes.rb
# Rails.application.routes.draw do
# mount MyEngine::Engine => "/my_engine", as: "my_engine"
# get "/foo" => "foo#index"
# end
#
# Now, you can use the <tt>my_engine</tt> helper inside your application:
#
# class FooController < ApplicationController
# def index
# my_engine.root_url # => /my_engine/
# end
# end
#
# There is also a <tt>main_app</tt> helper that gives you access to application's routes inside Engine:
#
# module MyEngine
# class BarController
# def index
# main_app.foo_path # => /foo
# end
# end
# end
#
# Note that the <tt>:as</tt> option given to mount takes the <tt>engine_name</tt> as default, so most of the time
# you can simply omit it.
#
# Finally, if you want to generate a URL to an engine's route using
# <tt>polymorphic_url</tt>, you also need to pass the engine helper. Let's
# say that you want to create a form pointing to one of the engine's routes.
# All you need to do is pass the helper as the first element in array with
# attributes for URL:
#
# form_for([my_engine, @user])
#
# This code will use <tt>my_engine.user_path(@user)</tt> to generate the proper route.
#
# == Isolated engine's helpers
#
# Sometimes you may want to isolate an engine, but use helpers that are defined for it.
# If you want to share just a few specific helpers you can add them to application's
# helpers in ApplicationController:
#
# class ApplicationController < ActionController::Base
# helper MyEngine::SharedEngineHelper
# end
#
# If you want to include all of the engine's helpers, you can use the #helper method on an engine's
# instance:
#
# class ApplicationController < ActionController::Base
# helper MyEngine::Engine.helpers
# end
#
# It will include all of the helpers from engine's directory. Take into account this does
# not include helpers defined in controllers with helper_method or other similar solutions,
# only helpers defined in the helpers directory will be included.
#
# == Migrations & seed data
#
# Engines can have their own migrations. The default path for migrations is exactly the same
# as in application: <tt>db/migrate</tt>
#
# To use engine's migrations in application you can use the rake task below, which copies them to
# application's dir:
#
# $ rake ENGINE_NAME:install:migrations
#
# Note that some of the migrations may be skipped if a migration with the same name already exists
# in application. In such a situation you must decide whether to leave that migration or rename the
# migration in the application and rerun copying migrations.
#
# If your engine has migrations, you may also want to prepare data for the database in
# the <tt>db/seeds.rb</tt> file. You can load that data using the <tt>load_seed</tt> method, e.g.
#
# MyEngine::Engine.load_seed
#
# == Loading priority
#
# In order to change engine's priority you can use +config.railties_order+ in the main application.
# It will affect the priority of loading views, helpers, assets, and all the other files
# related to engine or application.
#
# # load Blog::Engine with highest priority, followed by application and other railties
# config.railties_order = [Blog::Engine, :main_app, :all]
class Engine < Railtie
autoload :Configuration, "rails/engine/configuration"
class << self
attr_accessor :called_from, :isolated
alias :isolated? :isolated
alias :engine_name :railtie_name
delegate :eager_load!, to: :instance
def inherited(base)
unless base.abstract_railtie?
Rails::Railtie::Configuration.eager_load_namespaces << base
base.called_from = begin
call_stack = caller_locations.map { |l| l.absolute_path || l.path }
File.dirname(call_stack.detect { |p| !p.match?(%r[railties[\w.-]*/lib/rails|rack[\w.-]*/lib/rack]) })
end
end
super
end
def find_root(from)
find_root_with_flag "lib", from
end
def endpoint(endpoint = nil)
@endpoint ||= nil
@endpoint = endpoint if endpoint
@endpoint
end
def isolate_namespace(mod)
engine_name(generate_railtie_name(mod.name))
routes.default_scope = { module: ActiveSupport::Inflector.underscore(mod.name) }
self.isolated = true
unless mod.respond_to?(:railtie_namespace)
name, railtie = engine_name, self
mod.singleton_class.instance_eval do
define_method(:railtie_namespace) { railtie }
unless mod.respond_to?(:table_name_prefix)
define_method(:table_name_prefix) { "#{name}_" }
ActiveSupport.on_load(:active_record) do
mod.singleton_class.redefine_method(:table_name_prefix) do
"#{ActiveRecord::Base.table_name_prefix}#{name}_"
end
end
end
unless mod.respond_to?(:use_relative_model_naming?)
class_eval "def use_relative_model_naming?; true; end", __FILE__, __LINE__
end
unless mod.respond_to?(:railtie_helpers_paths)
define_method(:railtie_helpers_paths) { railtie.helpers_paths }
end
unless mod.respond_to?(:railtie_routes_url_helpers)
define_method(:railtie_routes_url_helpers) { |include_path_helpers = true| railtie.routes.url_helpers(include_path_helpers) }
end
end
end
end
# Finds engine with given path.
def find(path)
expanded_path = File.expand_path path
Rails::Engine.subclasses.each do |klass|
engine = klass.instance
return engine if File.expand_path(engine.root) == expanded_path
end
nil
end
end
include ActiveSupport::Callbacks
define_callbacks :load_seed
delegate :middleware, :root, :paths, to: :config
delegate :engine_name, :isolated?, to: :class
def initialize
@_all_autoload_paths = nil
@_all_load_paths = nil
@app = nil
@config = nil
@env_config = nil
@helpers = nil
@routes = nil
@app_build_lock = Mutex.new
super
end
# Load console and invoke the registered hooks.
# Check Rails::Railtie.console for more info.
def load_console(app = self)
require "rails/console/methods"
run_console_blocks(app)
self
end
# Load \Rails runner and invoke the registered hooks.
# Check Rails::Railtie.runner for more info.
def load_runner(app = self)
run_runner_blocks(app)
self
end
# Load Rake and railties tasks, and invoke the registered hooks.
# Check Rails::Railtie.rake_tasks for more info.
def load_tasks(app = self)
require "rake"
run_tasks_blocks(app)
self
end
# Load \Rails generators and invoke the registered hooks.
# Check Rails::Railtie.generators for more info.
def load_generators(app = self)
require "rails/generators"
run_generators_blocks(app)
Rails::Generators.configure!(app.config.generators)
self
end
# Invoke the server registered hooks.
# Check Rails::Railtie.server for more info.
def load_server(app = self)
run_server_blocks(app)
self
end
def eager_load!
# Already done by Zeitwerk::Loader.eager_load_all. By now, we leave the
# method as a no-op for backwards compatibility.
end
def railties
@railties ||= Railties.new
end
# Returns a module with all the helpers defined for the engine.
def helpers
@helpers ||= begin
helpers = Module.new
AbstractController::Helpers.helper_modules_from_paths(helpers_paths).each do |mod|
helpers.include(mod)
end
helpers
end
end
# Returns all registered helpers paths.
def helpers_paths
paths["app/helpers"].existent
end
# Returns the underlying Rack application for this engine.
def app
@app || @app_build_lock.synchronize {
@app ||= begin
stack = default_middleware_stack
config.middleware = build_middleware.merge_into(stack)
config.middleware.build(endpoint)
end
}
end
# Returns the endpoint for this engine. If none is registered,
# defaults to an ActionDispatch::Routing::RouteSet.
def endpoint
self.class.endpoint || routes
end
# Define the Rack API for this engine.
def call(env)
req = build_request env
app.call req.env
end
# Defines additional Rack env configuration that is added on each call.
def env_config
@env_config ||= {}
end
# Defines the routes for this engine. If a block is given to
# routes, it is appended to the engine.
def routes(&block)
@routes ||= ActionDispatch::Routing::RouteSet.new_with_config(config)
@routes.append(&block) if block_given?
@routes
end
# Define the configuration object for the engine.
def config
@config ||= Engine::Configuration.new(self.class.find_root(self.class.called_from))
end
# Load data from db/seeds.rb file. It can be used in to load engines'
# seeds, e.g.:
#
# Blog::Engine.load_seed
def load_seed
seed_file = paths["db/seeds.rb"].existent.first
run_callbacks(:load_seed) { load(seed_file) } if seed_file
end
initializer :load_environment_config, before: :load_environment_hook, group: :all do
paths["config/environments"].existent.each do |environment|
require environment
end
end
initializer :set_load_path, before: :bootstrap_hook do |app|
_all_load_paths(app.config.add_autoload_paths_to_load_path).reverse_each do |path|
$LOAD_PATH.unshift(path) if File.directory?(path)
end
$LOAD_PATH.uniq!
end
initializer :set_autoload_paths, before: :bootstrap_hook do
ActiveSupport::Dependencies.autoload_paths.unshift(*_all_autoload_paths)
ActiveSupport::Dependencies.autoload_once_paths.unshift(*_all_autoload_once_paths)
config.autoload_paths.freeze
config.autoload_once_paths.freeze
end
initializer :set_eager_load_paths, before: :bootstrap_hook do
ActiveSupport::Dependencies._eager_load_paths.merge(config.all_eager_load_paths)
config.eager_load_paths.freeze
end
initializer :add_routing_paths do |app|
routing_paths = paths["config/routes.rb"].existent
external_paths = self.paths["config/routes"].paths
routes.draw_paths.concat(external_paths)
app.routes.draw_paths.concat(external_paths)
if routes? || routing_paths.any?
app.routes_reloader.paths.unshift(*routing_paths)
app.routes_reloader.route_sets << routes
app.routes_reloader.external_routes.unshift(*external_paths)
end
end
# I18n load paths are a special case since the ones added
# later have higher priority.
initializer :add_locales do
config.i18n.railties_load_path << paths["config/locales"]
end
initializer :add_view_paths do
views = paths["app/views"].existent
unless views.empty?
ActiveSupport.on_load(:action_controller) { prepend_view_path(views) if respond_to?(:prepend_view_path) }
ActiveSupport.on_load(:action_mailer) { prepend_view_path(views) }
end
end
initializer :add_mailer_preview_paths do
previews = paths["test/mailers/previews"].existent
unless previews.empty?
ActiveSupport.on_load(:action_mailer) { self.preview_paths |= previews }
end
end
initializer :add_fixture_paths do
next if is_a?(Rails::Application)
fixtures = config.root.join("test", "fixtures")
if fixtures_in_root_and_not_in_vendor_or_dot_dir?(fixtures)
ActiveSupport.on_load(:active_record_fixtures) { self.fixture_paths |= ["#{fixtures}/"] }
end
end
initializer :prepend_helpers_path do |app|
if !isolated? || (app == self)
app.config.helpers_paths.unshift(*paths["app/helpers"].existent)
end
end
initializer :load_config_initializers do
config.paths["config/initializers"].existent.sort.each do |initializer|
load_config_initializer(initializer)
end
end
initializer :wrap_executor_around_load_seed do |app|
self.class.set_callback(:load_seed, :around) do |engine, seeds_block|
app.executor.wrap(&seeds_block)
end
end
initializer :engines_blank_point do
# We need this initializer so all extra initializers added in engines are
# consistently executed after all the initializers above across all engines.
end
rake_tasks do
next if is_a?(Rails::Application)
next unless has_migrations?
namespace railtie_name do
namespace :install do
desc "Copy migrations from #{railtie_name} to application"
task :migrations do
ENV["FROM"] = railtie_name
if Rake::Task.task_defined?("railties:install:migrations")
Rake::Task["railties:install:migrations"].invoke
else
Rake::Task["app:railties:install:migrations"].invoke
end
end
end
end
end
def routes? # :nodoc:
@routes
end
protected
def run_tasks_blocks(*) # :nodoc:
super
paths["lib/tasks"].existent.sort.each { |ext| load(ext) }
end
private
def load_config_initializer(initializer) # :doc:
ActiveSupport::Notifications.instrument("load_config_initializer.railties", initializer: initializer) do
load(initializer)
end
end
def has_migrations?
paths["db/migrate"].existent.any?
end
def self.find_root_with_flag(flag, root_path, default = nil) # :nodoc:
while root_path && File.directory?(root_path) && !File.exist?("#{root_path}/#{flag}")
parent = File.dirname(root_path)
root_path = parent != root_path && parent
end
root = File.exist?("#{root_path}/#{flag}") ? root_path : default
raise "Could not find root path for #{self}" unless root
Pathname.new File.realpath root
end
def default_middleware_stack
ActionDispatch::MiddlewareStack.new
end
def _all_autoload_once_paths
config.all_autoload_once_paths.uniq
end
def _all_autoload_paths
@_all_autoload_paths ||= begin
autoload_paths = config.all_autoload_paths
autoload_paths += config.all_eager_load_paths
autoload_paths -= config.all_autoload_once_paths
autoload_paths.uniq
end
end
def _all_load_paths(add_autoload_paths_to_load_path)
@_all_load_paths ||= begin
load_paths = config.paths.load_paths
if add_autoload_paths_to_load_path
load_paths += _all_autoload_paths
load_paths += _all_autoload_once_paths
end
load_paths.uniq
end
end
def fixtures_in_root_and_not_in_vendor_or_dot_dir?(fixtures)
fixtures.exist? && fixtures.to_s.start_with?(Rails.root.to_s) &&
!fixtures.to_s.start_with?(Rails.root.join("vendor").to_s) &&
!fixtures.to_s.start_with?("#{Rails.root}/.".to_s)
end
def build_request(env)
env.merge!(env_config)
req = ActionDispatch::Request.new env
req.routes = routes
req.engine_script_name = req.script_name
req
end
def build_middleware
config.middleware
end
end
end