code: def fail(self, msg, lineno=None, exc=TemplateSyntaxError):
          
          if lineno is None:
              lineno = self.stream.current.lineno
          raise exc(msg, lineno, self.name, self.filename)
docs: Convenience method that raises `exc` with the message, passed
          line number or last line number as well as the current name and
          filename.