lookup_ancestor

# File lib/rdoc/ri/driver.rb, line 513
  def lookup_ancestor(klass, orig_klass)
    # This is a bit hacky, but ri will go into an infinite
    # loop otherwise, since Object has an Object ancestor
    # for some reason.  Depending on the documentation state, I've seen
    # Kernel as an ancestor of Object and not as an ancestor of Object.
    if ((orig_klass == "Object") &&
        ((klass == "Kernel") || (klass == "Object")))
      return nil
    end

    cache = class_cache[orig_klass]

    return nil unless cache

    ancestors = [orig_klass]
    ancestors.push(*cache.includes.map { |inc| inc['name'] })
    ancestors << cache.superclass
    
    ancestor_index = ancestors.index(klass)

    if ancestor_index
      ancestor = ancestors[ancestors.index(klass) + 1]
      return ancestor if ancestor
    end

    lookup_ancestor klass, cache.superclass
  end