Rewriting spec files to add `rails3: true`

mark_specs_as_rails_3.rb

# requires pry, parser, and ast gems
#
# It also expects that you have build a file of spec files that should be modified. This file
# should contain one path/to/file per line.
#
# Running:
#   cat list_of_passing_spec_files.txt | xargs ruby-rewrite --load 'mark_specs_as_rails_3.rb' -m

require 'pry'

class MarkSpecsAsRails_3 < ::Parser::TreeRewriter
  # Method calls are tagged as :send
  # We're only interested in method calls so hook into on_send.
  def on_send(node)
    return if @already_rewrote_top_level_describe

    method = node.children[1]
    return unless method == :describe

    @already_rewrote_top_level_describe = true

    hash_node = node.children.find { |child_node| child_node.is_a?(Parser::AST::Node) && child_node.type == :hash }

    if hash_node
      rails3_node = hash_node.children.map(&:children).find do |(key_sexp, _)|
        key_sexp == Parser::CurrentRuby.parse(":rails3")
      end

      return if rails3_node # already present, no need to do anything

      # always use the range of the last child otherwise we will
      # insert after the closing right bracket if the file explicitly uses { key: value, .. }
      # to define the hash
      insertion_point = hash_node.children.last.loc.expression.end
    else
      insertion_point = node.loc.expression.end
    end

    insert_after insertion_point, ", rails3: true"

    super
  end
end