`rake assets:stats`

assets.rake

namespace :assets do
  # Display all precompiled assets and their included
  # dependencies.
  #
  # Arguments:
  # * '--sort' sort the included deps list by their file size.
  #
  # bin/rake assets:stats [-- --sort]
  desc 'List file size for precompiled assets'
  task stats: :environment do
    sort = ARGV.include?('--sort')

    include ActiveSupport::NumberHelper
    environment = Rails.application.assets
    shell = Thor::Base.shell.new
    assets = Rails.application.assets_manifest.find(Rails.application.config.assets.precompile)

    assets.each do |asset|
      length = asset.length
      puts "#{asset.filename.remove("#{Rails.root}/")}: #{number_to_human_size(length)} total."

      # NOTE: `included` does not account for `.scss` files that were `@import`ed.
      if asset.metadata[:included] && asset.metadata[:included].length > 1
        deps = (asset.metadata[:included]).map do |uri|
          included = environment.load(uri)
          name = included.logical_path.remove('.self')
          size = number_to_human_size(included.length)

          [included.length, ['⎿', name, size]]
        end

        deps.sort_by!(&:first) if sort

        puts "Included assets:"
        shell.print_table(deps.map(&:last))
      end
      puts "\n"
    end
  end
end