yaml_tree_builder.rb

class YAMLTreeBuilder < YAML::TreeBuilder
  def initialize
    super

    @path_stack = []
  end

  def scalar(*)
    super.tap do
      if YAML::Nodes::Mapping === @last
        if @last.children.size.odd?
          @path_stack.push(@last.children.last.value)
        else
          @path_stack.pop
        end
      end
    end
  end

  def alias(*)
    super.tap do
      if YAML::Nodes::Mapping === @last
        if @last.children.size.odd?
          # noop
        else
          @path_stack.pop
        end
      end
    end
  end

  %w(end_mapping end_sequence).each do |m|
    define_method(m) do |*args|
      brothers = @stack[-2].children
      if Psych::Nodes::Scalar === brothers[brothers.index(@last) - 1]
        @path_stack.pop
      end
      super(*args)
    end
  end
end