def read_ast(file)
      @ast_cache ||= Rufus::Lru::Hash.new(5)
      if @ast_cache.include?(file)
        @ast_cache[file]
      else
        @ast_cache[file] = uncached_read_ast(file)
      end
    end
def read_ast(file)
      @ast_cache ||= Rufus::Lru::Hash.new(5)
      if @ast_cache.include?(file)
        @ast_cache[file]
      else
        @ast_cache[file] = uncached_read_ast(file)
      end
    end
Read the AST for the given Ruby source file