Install Generator to Properly Install Engine in Host Apps

app/controllers/maintenance_tasks/runs_controller.rb

@@ -8,7 +8,7 @@ module MaintenanceTasks
   class RunsController < ApplicationController
     # Renders the /maintenance_tasks page, displaying available tasks to users.
     def index
-      @available_tasks = Task.descendants
+      @available_tasks = Task.available_tasks
     end
 
     # POST /maintenance_tasks/runs

app/jobs/maintenance_tasks/task.rb

@@ -8,6 +8,18 @@ class Task < ActiveJob::Base
     extend ActiveSupport::DescendantsTracker
 
     class << self
+      # Controls the value of abstract_class, which indicates whether the class
+      # is abstract or not. Abstract classes are excluded from the list of
+      # available_tasks.
+      #
+      # @return [Boolean] the value of abstract_class
+      attr_accessor :abstract_class
+
+      # @return [Boolean] whether or not the class is abstract
+      def abstract_class?
+        defined?(@abstract_class) && @abstract_class == true
+      end
+
       # Given the name of a Task, returns the Task subclass. Returns nil if
       # there's no task with that name.
       def named(name)
@@ -16,12 +28,13 @@ def named(name)
         nil
       end
 
-      # Returns a list of classes that inherit from the Task superclass.
+      # Returns a list of concrete classes that inherit from
+      # the Task superclass.
       #
       # @return [Array<Class>] the list of classes.
-      def descendants
+      def available_tasks
         load_constants
-        super
+        descendants.reject(&:abstract_class?)
       end
 
       private

lib/generators/maintenance_tasks/install_generator.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+module MaintenanceTasks
+  # Generator used to set up the engine in the host application.
+  # It handles mounting the engine, installing migrations
+  # and creating some required files.
+  class InstallGenerator < Rails::Generators::Base
+    source_root File.expand_path('templates', __dir__)
+
+    # Mounts the engine in the host application's config/routes.rb
+    def mount_engine
+      route("mount MaintenanceTasks::Engine => '/maintenance_tasks'")
+    end
+
+    # Copies engine migrations to host application and migrates the database
+    def install_migrations
+      rake('maintenance_tasks:install:migrations')
+      rake('db:migrate')
+    end
+
+    # Creates an initializer file for the engine in the host application
+    def create_initializer
+      template(
+        'maintenance_tasks.rb',
+        'config/initializers/maintenance_tasks.rb'
+      )
+    end
+
+    # Creates ApplicationTask class for task classes to subclass
+    def create_application_task
+      template(
+        'application_task.rb',
+        'app/jobs/maintenance/application_task.rb'
+      )
+    end
+  end
+end

lib/generators/maintenance_tasks/templates/application_task.rb.tt

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+module Maintenance
+  class ApplicationTask < MaintenanceTasks::Task
+    self.abstract_class = true
+  end
+end

lib/generators/maintenance_tasks/templates/maintenance_tasks.rb.tt

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+# Custom configuration for the tasks namespace can be defined here, ie.
+# MaintenanceTasks.tasks_module = 'Maintenance'
+<% unless Rails.autoloaders.zeitwerk_enabled? -%>
+
+# Your application does not use Zeitwerk, so task dependencies must be
+# manually required. This block can be removed if zeitwerk mode is enabled.
+# For more information on Zeitwerk, see https://guides.rubyonrails.org/autoloading_and_reloading_constants.html
+Rails.application.config.to_prepare do
+  Dir["#{Rails.root}/app/jobs/maintenance/*.rb"].each do |file|
+    require_dependency(file)
+  end
+end
+<% end -%>

test/dummy/app/jobs/maintenance/application_task.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+module Maintenance
+  class ApplicationTask < MaintenanceTasks::Task
+    self.abstract_class = true
+  end
+end

test/dummy/config/initializers/maintenance_tasks.rb

@@ -2,10 +2,3 @@
 
 # Custom configuration for the tasks namespace can be defined here, ie.
 # MaintenanceTasks.tasks_module = 'Maintenance'
-
-# If autoloader is not Zeitwerk, tasks must be manually required
-# Rails.application.config.to_prepare do
-#   Dir["#{Rails.root}/app/jobs/maintenance/*.rb"].each do |file|
-#     require_dependency(file)
-#   end
-# end

test/dummy/db/schema.rb

@@ -32,5 +32,4 @@
     t.datetime "created_at", precision: 6, null: false
     t.datetime "updated_at", precision: 6, null: false
   end
-
 end

test/jobs/maintenance_tasks/task_test.rb

@@ -3,9 +3,9 @@
 
 module MaintenanceTasks
   class TaskTest < ActiveJob::TestCase
-    test '.descendants returns list of tasks that inherit from the Task superclass' do
-      expected_tasks = [Maintenance::UpdatePostsTask]
-      assert_equal expected_tasks, MaintenanceTasks::Task.descendants
+    test '.available_tasks returns list of tasks that inherit from the Task superclass' do
+      expected = ['Maintenance::UpdatePostsTask']
+      assert_equal expected, MaintenanceTasks::Task.available_tasks.map(&:name)
     end
 
     test '.named returns the task based on its name' do

test/lib/generators/maintenance_tasks/install_generator_test.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+require 'test_helper'
+require 'generators/maintenance_tasks/install_generator'
+
+module MaintenanceTasks
+  class InstallGeneratorTest < Rails::Generators::TestCase
+    tests InstallGenerator
+    SAMPLE_APP_PATH = Engine.root.join('tmp/sample_app')
+    destination SAMPLE_APP_PATH
+    setup :prepare_destination
+
+    def setup
+      super
+      setup_sample_app
+    end
+
+    def teardown
+      FileUtils.rm_rf(SAMPLE_APP_PATH)
+    end
+
+    test 'generator mounts engine, runs migrations, and creates required files' do
+      Dir.chdir(SAMPLE_APP_PATH) do
+        run_generator
+
+        assert_file('config/routes.rb') do |contents|
+          assert_match(
+            %r{mount MaintenanceTasks::Engine => '/maintenance_tasks'},
+            contents
+          )
+        end
+
+        mig = 'db/migrate/create_maintenance_tasks_runs.maintenance_tasks.rb'
+        assert_migration(mig)
+        assert_file('db/schema.rb') do |contents|
+          assert_match(/create_table "maintenance_tasks_runs"/, contents)
+        end
+
+        assert_file('app/jobs/maintenance/application_task.rb')
+        assert_file('config/initializers/maintenance_tasks.rb')
+      end
+    end
+
+    private
+
+    def setup_sample_app
+      FileUtils.copy_entry(Rails.root, SAMPLE_APP_PATH)
+
+      Dir.chdir(SAMPLE_APP_PATH) do
+        FileUtils.rm_r('db')
+        FileUtils.rm('config/initializers/maintenance_tasks.rb')
+        FileUtils.rm('app/jobs/maintenance/application_task.rb')
+      end
+    end
+  end
+end