code: func (bld *builder) maybePanic() {
  	if len(bld.results) == 0 {
  		return
  	}
  	res := bld.results[len(bld.results)-1]
  	if res == nil {
  		return
  	}
  	for _, f := range res.List {
  		for _, id := range f.Names {
  			bld.use(id)
  		}
  	}
  }
docs: // An operation that might panic marks named function results as used.