class IRB::ExtendCommand::ShowSource

def find_source(str, irb_context)
  case str
  when /\A[A-Z]\w*(::[A-Z]\w*)*\z/ # Const::Name
    eval(str, irb_context.workspace.binding) # trigger autoload
    base = irb_context.workspace.binding.receiver.yield_self { |r| r.is_a?(Module) ? r : Object }
    file, line = base.const_source_location(str)
  when /\A(?<owner>[A-Z]\w*(::[A-Z]\w*)*)#(?<method>[^ :.]+)\z/ # Class#method
    owner = eval(Regexp.last_match[:owner], irb_context.workspace.binding)
    method = Regexp.last_match[:method]
    if owner.respond_to?(:instance_method)
      methods = owner.instance_methods + owner.private_instance_methods
      file, line = owner.instance_method(method).source_location if methods.include?(method.to_sym)
    end
  when /\A((?<receiver>.+)(\.|::))?(?<method>[^ :.]+)\z/ # method, receiver.method, receiver::method
    receiver = eval(Regexp.last_match[:receiver] || 'self', irb_context.workspace.binding)
    method = Regexp.last_match[:method]
    file, line = receiver.method(method).source_location if receiver.respond_to?(method, true)
  end
  if file && line
    Source.new(file: file, first_line: line, last_line: find_end(file, line, irb_context))
  end
end