# File lib/staticmatic/template_error.rb, line 26
  def source_extract(indentation = 0)
    return "" unless num = line_number
    num = num.to_i

    source_code = @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 = ' ' * indentation
    line_counter = start_on_line
    return unless source_code = source_code[start_on_line..end_on_line]

    source_code.collect do |line|
      line_counter += 1
      "#{indent}#{line_counter}: #{line}\n"
    end.to_s
  end