class Sass::Tree::Visitors::Extend

def self.check_extends_fired!(extends)
  extends.each_value do |ex|
    next if ex.result == :succeeded || ex.node.optional?
    message = "\"#{ex.extender}\" failed to @extend \"#{ex.target.join}\"."
    reason =
      if ex.result == :not_found
        "The selector \"#{ex.target.join}\" was not found."
      else
        "No selectors matching \"#{ex.target.join}\" could be unified with \"#{ex.extender}\"."
      end
    # TODO(nweiz): this should use the Sass stack trace of the extend node.
    raise Sass::SyntaxError.new(<<MESSAGE, :filename => ex.node.filename, :line => ex.node.line)
message}
reason}
e "@extend #{ex.target.join} !optional" if the extend should be able to fail.
SSAGE
  end
end