// source can change over time - i.e. for watchCache circular
// buffer. When the circular buffer is full and an event needs
// to be popped off, watchCache::startIndex is incremented. In
// this case, an interval tracking that popped event is valid
// only if it has already been copied to its internal buffer.
// However, for efficiency we perform that lazily and we mark

	s.pop(n.Pos())
	*s = append((*s), n)
}

// pop pops all nodes that appear lexically before pos
// (i.e., whose lexical extent has ended before or at pos).
// It returns the last node popped.
func (s *nodeStack) pop(pos token.Pos) (top Node) {
	i := len(*s)
	for i > 0 && (*s)[i-1].End() <= pos {
		top = (*s)[i-1]
		i--
	}
	*s = (*s)[0:i]
	return top
}