Find (maybe) unused functions in Ruby

find_unused_functions.rb

#!/usr/bin/env ruby

require 'optparse'

module CLI
  extend self

  PATHS_TO_CHECK = %w(app bin config engines lib script)
  EXTENSIONS_TO_CHECK_FOR_DEFINITIONS = %w(.rb .rake)
  EXTENSIONS_TO_CHECK_FOR_USAGE = EXTENSIONS_TO_CHECK_FOR_DEFINITIONS + %w(.yml .yaml .erb)

  FUNCTION_DEF_REGEX = /def\s+(\w+[!?]?)\s*\(?/
  FUNCTION_USE_REGEX = /(?<!def )\w+[?!]?/

  def main(at_most: 2**30)
    maybe_unused_methods = {}

    # Gather all function definitions
    PATHS_TO_CHECK.each do |path|
      Dir.glob("#{path}/**/*").each do |file|
        if EXTENSIONS_TO_CHECK_FOR_DEFINITIONS.include?(File.extname(file))
          File.read(file).scan(FUNCTION_DEF_REGEX).flatten.each do |method_name|
            # Same method name may exist across files, but this is a pretty dumb script, so that's okay
            maybe_unused_methods[method_name] ||= []
            maybe_unused_methods[method_name] << file
          end
        end
      end
    end

    # If a symbol exists (and not part of a 'def <sym>') then remove it from the list of methods
    PATHS_TO_CHECK.each do |path|
      Dir.glob("#{path}/**/*").each do |file|
        if EXTENSIONS_TO_CHECK_FOR_USAGE.include?(File.extname(file))
          File.read(file).scan(FUNCTION_USE_REGEX).flatten.each do |symbol|
            maybe_unused_methods.delete(symbol)
          end
        end
      end
    end

    maybe_unused_methods.each do |method_name, defined_in|
      puts "#{method_name} #{defined_in.join(',')}" if defined_in.length <= at_most
    end
  end
end


if __FILE__ == $0
  options = {}
  OptionParser.new do |opts|
    opts.banner = "Usage: #{$0} [options]"

    # If a method name is used across files, there's a good chance it's part of some library or
    # superclass that we're not seeing in this codebase
    opts.on("-n", "--at-most N", Integer, "Only output entries defined in at most N files") do |value|
      options[:at_most] = value
    end
  end.parse!

  CLI.main(**options)
end