xmlast.rb

require 'parser/current'
require 'rexml/document'

class XMLAST
  include REXML
  attr_reader :doc

  def initialize sexp
    @doc = Document.new "<root></root>"
    @sexp = sexp
    root = @doc.root
    populate_tree(root, sexp)
  end

  def populate_tree xml, sexp
    if sexp.is_a?(String) ||
        sexp.is_a?(Symbol) ||
        sexp.is_a?(Numeric) ||
        sexp.is_a?(NilClass)
      el = Element.new(sexp.class.to_s.downcase + "-val")
      el.add_attribute 'value', sexp.to_s
      xml.add_element el
    else
      el = Element.new(sexp.type.to_s)
      el.add_attribute('id', sexp.object_id)

      sexp.children.each{ |n| populate_tree(el, n) }
      xml.add_element el
    end
  end

  def treewalk sexp=@sexp
    return sexp unless sexp&.respond_to?(:children)
    [sexp, sexp.children.map {|n| treewalk(n) }].flatten
  end

  def xpath path
    results = XPath.match(doc, path)
    results.map do |n|
      if n.respond_to?(:attributes) && n.attributes['id']
        treewalk.find do |m| 
          m.object_id.to_s == n.attributes['id']
        end
      else
        n
      end
    end
  end
end

# snippet = 'f.text_field :attr, placeholder: "placeholder text"'
# exp = Parser::CurrentRuby.parse(snippet)
# xml = XMLAST.new(exp)
# xml.xpath('*/send/hash/pair[sym[symbol-val/@value="placeholder"]]/str')
# => [s(:str, "placeholder text")]