code: func SetSwarming(ctx context.Context, swarm *Swarming) context.Context {
  	var raw interface{}
  	if swarm != nil {
  		raw = swarm
  	}
  	ctx, err := Set(ctx, "swarming", raw)
  	if err != nil {
  		panic(fmt.Errorf("impossible: %s", err))
  	}
  	return ctx
  }
docs: // SetSwarming Sets the Swarming in the LUCI_CONTEXT.