class ActionView::Template::Error

def source_extract(indentation = 0, output = :console)
  return unless num = line_number
  num = num.to_i
  source_code = @template.source.split("\n")
  start_on_line = [ num - SOURCE_CODE_RADIUS - 1, 0 ].max
  end_on_line   = [ num + SOURCE_CODE_RADIUS - 1, source_code.length].min
  indent = end_on_line.to_s.size + indentation
  return unless source_code = source_code[start_on_line..end_on_line]
  formatted_code_for(source_code, start_on_line, indent, output)
end