code: func ToQuery(from, to int64, matchers []*labels.Matcher, p *storage.SelectParams) (*prompb.Query, error) {
  	ms, err := toLabelMatchers(matchers)
  	if err != nil {
  		return nil, err
  	}
  
  	var rp *prompb.ReadHints
  	if p != nil {
  		rp = &prompb.ReadHints{
  			StepMs:  p.Step,
  			Func:    p.Func,
  			StartMs: p.Start,
  			EndMs:   p.End,
  		}
  	}
  
  	return &prompb.Query{
  		StartTimestampMs: from,
  		EndTimestampMs:   to,
  		Matchers:         ms,
  		Hints:            rp,
  	}, nil
  }
docs: // ToQuery builds a Query proto.