find_unused_views.rake

desc 'Finds unused views (i.e. view files not starting with "_"). '\
     'May find false positives (programmatically chosen views).'
task find_unused_views: :environment do
  UnusedViewFinder.run
end

module UnusedViewFinder
  module_function

  ALLOWLISTED_PATHS_REGEX = %r{
    /debug/
    |
    /layouts/
  }x

  def run
    result = unused_views
    puts '-' * 30, result, '=' * 30, "#{result.size} potentially unused views"
  end

  def unused_views
    view_files.grep_v(ALLOWLISTED_PATHS_REGEX).select(&method(:unused?))
  end

  def unused?(full_path)
    (%r{/app/views/(?<path>.+)/(?<name>[^_.][^/.]*)\.[^/]+\z}x =~ full_path) &&
      !view_implicitly_used_in_own_controller?(path, name) &&
      !view_explicitly_used_in_any_controller?(path, name)
  end

  def view_implicitly_used_in_own_controller?(path, name)
    name.to_sym.in?(controller_class(path)&.public_instance_methods || [])
  end

  def view_explicitly_used_in_any_controller?(path, name)
    view_explicitly_used_in_own_controller?(path, name) ||
    view_explicitly_used_in_other_controller?(path, name)
  end

  def view_explicitly_used_in_own_controller?(path, name)
    regex = /render[^\n]+#{name}/
    controller_files.grep(/#{path}/).any? { |cf| regex.match?(File.read(cf)) }
  end

  def view_explicitly_used_in_other_controller?(path, name)
    regex = /render[^\n]+#{[path, name].join(?/)}/
    controller_files.any? { |cf| regex.match?(File.read(cf)) }
  end

  def controller_class(view_path)
    dirs = view_path.split(?/)
    controller_name = dirs.last.classify.pluralize.gsub(/(Volunteering)s/, '\1')
    controller_name.prepend("#{dirs[0..-2] * ?/}/".classify) if dirs.many?
    "#{controller_name}Controller".constantize rescue nil
  end

  def view_files
    @v_files ||= Dir[Rails.root.join('app', 'views', '**', '*.html.*')]
  end

  def controller_files
    @c_files ||= Dir[Rails.root.join('app', 'controllers', '**', '*.rb')]
  end
end