Rails 3.2 assets usage report

list_rails_assets_usage.rb

# This script will list asset files which are used and those which aren't for a Rails 3.2 application.
#
# It works by prefixing/suffixing all (js css less scss sass coffee) files. Then, after having run
# rake assets:precompile, you can run the script again and it will search in public/assets for
# those prefix to know if the file is definetly not used, or if it could be used.

root_dirs = %w(app/assets vendor)
file_endings = %w(js css less scss sass coffee)

file_paths_to_handle = root_dirs.flat_map {|d| file_endings.flat_map {|fe| Dir["#{d}/**/*.#{fe}"] } }.sort

# Good old random generated password :)
UNIQUE_STRING = "agF0T197HYwWTCXcjTDM46uB"

def prefix_each_paths(file_paths)
  file_paths.each do |file_path|
    next if File.directory?(file_path)
    content = File.read(file_path)

    if file_path.end_with?('.coffee')
      # Only block comments are kept in coffee files
      line = "\n###\n#{UNIQUE_STRING}#{file_path}#{UNIQUE_STRING.reverse}\n###\n"
    else
      line = "\n/*#{UNIQUE_STRING}#{file_path}#{UNIQUE_STRING.reverse}*/\n"
    end
    # For entry-point files, it seems the early comments are ignored, so putting the line at the end solves that
    content = "#{line}#{content}#{line}"
    File.write(file_path, content)
  end
end

def extract_paths
  file_paths_to_check = Dir['public/assets/**/*.js'] + Dir['public/assets/**/*.css']
  found_file_paths = file_paths_to_check.flat_map do |file_path|
    content = File.read(file_path)
    content.scan(%r{#{UNIQUE_STRING}(.*?)#{UNIQUE_STRING.reverse}}).flatten
  end
  found_file_paths.uniq.sort
end

if File.exist?('public/assets')
  puts "Precompiled assets found, searching for unused files"
  found_paths = extract_paths
  unused_paths = file_paths_to_handle - found_paths
  msg = "#{found_paths.size} used paths, #{unused_paths.size} unused paths"
  puts msg
  puts unused_paths.map { |p| "Unused: #{p}"}
  puts found_paths.map { |p| "Used: #{p}"}
  puts msg
else
  prefix_each_paths(file_paths_to_handle)
  puts "Prefixed all the files, now:"
  puts "1) Make sure config.assets.compress is set to false in config/environments/production.rb"
  puts "2) Run `rake assets:precompile`"
  puts "3) Execute this script again"
end