code: func (d *Flags) StartTracing() (io.Closer, error) {
  	if d.TracePath == "" {
  		return &tracingState{}, nil
  	}
  	f, err := os.Create(d.TracePath)
  	if err != nil {
  		return &tracingState{}, err
  	}
  	if err = tracer.Start(f, 0); err != nil {
  		_ = f.Close()
  		return &tracingState{}, err
  	}
  	return &tracingState{f}, nil
  }
docs: // StartTracing enables tracing and returns a closer that must be called on
  // process termination.