Find unused helpers in a Rails app

find_unused_helpers.rb

#!/usr/bin/env ruby
#
# Shotgun approach (read: slow and dirty hack) to help find unused helpers in a Rails application
#

start = Time.now

# Build an array of filename globs to process.
# Only search file types that might use or define a helper.
extensions = %w[rb js haml erb jbuilder].map { |ext| "app/**/**/*.#{ext}" }

# Build a hash of all the source files to search.
# Key is filename, value is an array of the lines.
source_files = {}
Dir.glob(extensions).each do |filename|
  source_files[filename] = File.readlines(filename)
end

# Build an array of method names defined in app/helper/* files.
helpers = source_files.keys.grep(/app\/helpers/).map do |filename|
  source_files[filename].map do |line|
    Regexp.last_match(1).chomp if line =~ /def ([^\(\s]+)/
  end
end.flatten.reject(&:nil?)

puts "Scanning #{source_files.size} files for #{helpers.size} helpers..."

# Combine all the source code into a giant array of lines.
source_code = source_files.values.flatten

# Iterate over all the helpers and reject any that appear anywhere in the complete source.
unused = helpers.reject do |helper|
  source_code.any? do |line|
    line.match?(/#{helper}/) && !line.match?(/def #{helper}/)
  end
end

finish = Time.now

if unused
  puts "\nFound #{unused.size} unused helpers:\n\n"
  unused.each { |helper| puts "  - #{helper}" }
  puts "\n"
else
  puts 'No unused helpers were found.'
end

puts "Finished in #{finish - start} seconds."