code: def tool_jar(self, key, scope=None):
      
      return self.tool_jar_from_products(self.context.products, key, scope=self._scope(scope))
docs: Get the jar for the tool previously registered under key in the given scope.
  
      :param string key: The key the tool configuration was registered under.
      :param string scope: The scope the tool configuration was registered under; the task scope by
                           default.
      :returns: A single jar path.
      :rtype: string
      :raises: `JvmToolMixin.InvalidToolClasspath` when the tool classpath is not composed of exactly
               one jar.