class IRB::Irb

def handle_exception(exc)
  if exc.backtrace && exc.backtrace[0] =~ /\/irb(2)?(\/.*|-.*|\.rb)?:/ && exc.class.to_s !~ /^IRB/ &&
     !(SyntaxError === exc) && !(EncodingError === exc)
    # The backtrace of invalid encoding hash (ex. {"\xAE": 1}) raises EncodingError without lineno.
    irb_bug = true
  else
    irb_bug = false
  end
  if exc.backtrace
    order = nil
    if RUBY_VERSION < '3.0.0'
      if STDOUT.tty?
        message = exc.full_message(order: :bottom)
        order = :bottom
      else
        message = exc.full_message(order: :top)
        order = :top
      end
    else # '3.0.0' <= RUBY_VERSION
      message = exc.full_message(order: :top)
      order = :top
    end
    message = convert_invalid_byte_sequence(message, exc.message.encoding)
    message = encode_with_invalid_byte_sequence(message, IRB.conf[:LC_MESSAGES].encoding) unless message.encoding.to_s.casecmp?(IRB.conf[:LC_MESSAGES].encoding.to_s)
    message = message.gsub(/((?:^\t.+$\n)+)/)  { |m|
      case order
      when :top
        lines = m.split("\n")
      when :bottom
        lines = m.split("\n").reverse
      end
      unless irb_bug
        lines = lines.map { |l| @context.workspace.filter_backtrace(l) }.compact
        if lines.size > @context.back_trace_limit
          omit = lines.size - @context.back_trace_limit
          lines = lines[0..(@context.back_trace_limit - 1)]
          lines << "\t... %d levels..." % omit
        end
      end
      lines = lines.reverse if order == :bottom
      lines.map{ |l| l + "\n" }.join
    }
    # The "<top (required)>" in "(irb)" may be the top level of IRB so imitate the main object.
    message = message.gsub(/\(irb\):(?<num>\d+):in `<(?<frame>top \(required\))>'/)  { "(irb):#{$~[:num]}:in `<main>'" }
    puts message
  end
  print "Maybe IRB bug!\n" if irb_bug
end