Trace all require calls. A late-resort debug option in Ruby 2.x.

trace_requires.rb

require 'pathname'
alias :require_original :require
def require(*args)
  called_by = caller_locations(1, 1).first

  home_relative_path = called_by.path.gsub Dir.home, '~'
  cwd = Pathname.new(Dir.pwd)
  cwd_relative_path = Pathname.new(called_by.path).relative_path_from(cwd).to_s

  shortest_path = if home_relative_path.length > cwd_relative_path.length
                    cwd_relative_path
                  else
                    home_relative_path
                  end

  STDERR.puts "'#{args.first}' required by #{shortest_path}:#{called_by.lineno}"

  require_original *args
end