Single file working Rails 8 app, with dependancies spec inside

rails_minimal.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  ruby '3.3.0'

  gem 'rails', '~> 8.0.0'
  gem 'puma'
  gem 'rackup'
end

require 'action_controller/railtie'

module Controllers
  class HomeController < ActionController::Metal
    def index
      self.response_body = '<h1>Hello from Rails 8!</h1>'
    end
  end
end

class MinimalApp < Rails::Application
  # Set Rails configuration
  config.root = __dir__
  config.secret_key_base = 'random_secret_key_base'

  # Initialize configuration defaults for Rails 8.0
  config.load_defaults 8.0

  # Disable unnecessary Rails features
  config.eager_load = false
  config.logger = Logger.new($stdout)
  config.log_level = :debug

  # Initialize and run the application
  initialize!

  # Register our controller
  ActiveSupport.on_load(:action_controller) do
    include Controllers
  end
end

# Routes configuration
MinimalApp.routes.draw do
  root to: Controllers::HomeController.action(:index)
end

# Rackup configuration
if __FILE__ == $0
  require 'rackup'
  Rackup::Server.start(
    app: MinimalApp, 
    Port: 3000,
    Host: '0.0.0.0'
  )
end