code: public static Matcher assignmentWithRhs(final Matcher rhsMatcher) {
      return new Matcher() {
        @Override public boolean matches(Node node, NodeMetadata metadata) {
          return node.isAssign() && rhsMatcher.matches(node.getLastChild(), metadata);
        }
      };
    }
docs: Returns a Matcher that matches an ASSIGN node where the RHS of the assignment matches the given
  rhsMatcher.