code: func (w *Wrapper) CheckCycles() error {
  	w.sccs = w.tarjan()
  	cycles := []string{}
  	for _, scc := range w.sccs {
  		if len(scc) > 1 {
  			cycles = append(cycles, w.showComponent(scc))
  		}
  	}
  	if len(cycles) > 0 {
  		return fmt.Errorf("cycles found:\n%s\n", strings.Join(cycles, "\n"))
  	}
  	return nil
  }
docs: // CheckCycles checks for proto import structures that would result in
  // Go package cycles.