Find unused routes in Rails

unused_routes.rb

#!/usr/bin/env ruby
# Extracted from traceroute gem + checking the presence of views as well

require_relative './config/environment.rb'

class Traceroute
  def initialize(app)
    @app = app
  end

  def load_everything!
    @app.eager_load!
    ::Rails::InfoController rescue NameError
    ::Rails::WelcomeController rescue NameError
    ::Rails::MailersController rescue NameError
    @app.reload_routes!

    Rails::Engine.subclasses.each(&:eager_load!)
  end

  def unused_routes
    views = Dir.glob("#{Rails.root}/app/views/**/*").each do |view|
      view.gsub!(/(.*\/[^\/\.]+)[^\/]+/, '\\1')
    end

    (routed_actions - defined_action_methods).reject do |path|
      views.include? "#{Rails.root}/app/views/#{path.gsub('#','/')}"
    end
  end

  def defined_action_methods
    ActionController::Base.descendants.map do |controller|
      controller.action_methods.reject {|a| (a =~ /\A(_conditional)?_callback_/) || (a == '_layout_from_proc')}.map do |action|
        "#{controller.controller_path}##{action}"
      end
    end.flatten.reject {|r| r.start_with? 'rails/'}
  end

  def routed_actions
    routes.map do |r|
      if r.requirements[:controller].blank? && r.requirements[:action].blank? && (r.path == '/:controller(/:action(/:id(.:format)))')
        %Q["#{r.path}"  This is a legacy wild controller route that's not recommended for RESTful applications.]
      else
        "#{r.requirements[:controller]}##{r.requirements[:action]}"
      end
    end.reject {|r| r.start_with? 'rails/'}
  end

  private

  def routes
    routes = @app.routes.routes.reject {|r| r.name.nil? && r.requirements.blank?}

    routes.reject! {|r| r.app.is_a?(ActionDispatch::Routing::Mapper::Constraints) && r.app.app.respond_to?(:call)}

    routes.reject! {|r| r.app.is_a?(ActionDispatch::Routing::Redirect)}

    if @app.config.respond_to?(:assets)
      exclusion_regexp = %r{^#{@app.config.assets.prefix}}

      routes.reject! do |route|
        path = (defined?(ActionDispatch::Journey::Route) || defined?(Journey::Route)) ? route.path.spec.to_s : route.path
        path =~ exclusion_regexp
      end
    end
    routes
  end
end

traceroute = Traceroute.new Rails.application
traceroute.load_everything!
unused_routes = traceroute.unused_routes

puts "Unused routes (#{unused_routes.count}):"
unused_routes.each {|route| puts "  #{route}"}

unless unused_routes.empty? || ENV['FAIL_ON_ERROR'].blank?
  fail "Unused routes detected."
end