Request: PrettyPrint support for CommonMarker::Node

[gfx]

Debugging CommonMarker::Node is a pain because it doesn't support pp.

I have defined a monkey patch which is something like this:

class CommonMarker
  class Node
    # @param [PrettyPrint] pp
    def pretty_print(pp)
      pp.group(PP_INDENT_SIZE, "#<#{self.class}(#{type}): ", ">") do
        pp.breakable

        attrs = [
          :sourcepos,
          :string_content,
          :url,
          :title,
          :header_level,
          :list_type,
          :list_start,
          :list_tight,
          :fence_info, # the label for fenced code blocks
          :first_child,
        ].map do |name|
          [name, __send__(name)] rescue nil
        end.compact

        pp.seplist(attrs) do |name, value|
          if name != :first_child
            pp.text "#{name}="
            pp.pp value
          elsif value
            pp.group(PP_INDENT_SIZE) do
              children = []
              node = first_child
              while node
                children << node
                node = node.next
              end
              pp.text "children="
              pp.pp children
            end
          end
        end
      end
    end
  end
end

With this routine pp CommonMarker.render_doc("foo **bar** baz") results in:

#<CommonMarker::Node(document):
  sourcepos={:start_line=>1, :start_column=>1, :end_line=>1, :end_column=>15},
  children=[#<CommonMarker::Node(paragraph):
       sourcepos={:start_line=>1,
        :start_column=>1,
        :end_line=>1,
        :end_column=>15},
       children=[#<CommonMarker::Node(text):
            sourcepos={:start_line=>0,
             :start_column=>0,
             :end_line=>0,
             :end_column=>0},
            string_content="foo ",
            >,
          #<CommonMarker::Node(strong):
            sourcepos={:start_line=>0,
             :start_column=>0,
             :end_line=>0,
             :end_column=>0},
            children=[#<CommonMarker::Node(text):
                 sourcepos={:start_line=>0,
                  :start_column=>0,
                  :end_line=>0,
                  :end_column=>0},
                 string_content="bar",
                 >]>,
          #<CommonMarker::Node(text):
            sourcepos={:start_line=>0,
             :start_column=>0,
             :end_line=>0,
             :end_column=>0},
            string_content=" baz",
            >]>]>

[gjtorikian]

I'm afraid I don't know much about extending support for pretty print. Your code looks good to me, would you mind submitting a pull request?