code: func (cli *Client) BuildCachePrune(ctx context.Context, opts types.BuildCachePruneOptions) (*types.BuildCachePruneReport, error) {
  	if err := cli.NewVersionError("1.31", "build prune"); err != nil {
  		return nil, err
  	}
  
  	report := types.BuildCachePruneReport{}
  
  	query := url.Values{}
  	if opts.All {
  		query.Set("all", "1")
  	}
  	query.Set("keep-storage", fmt.Sprintf("%d", opts.KeepStorage))
  	filters, err := filters.ToJSON(opts.Filters)
  	if err != nil {
  		return nil, errors.Wrap(err, "prune could not marshal filters option")
  	}
  	query.Set("filters", filters)
  
  	serverResp, err := cli.post(ctx, "/build/prune", query, nil, nil)
  	defer ensureReaderClosed(serverResp)
  
  	if err != nil {
  		return nil, err
  	}
  
  	if err := json.NewDecoder(serverResp.body).Decode(&report); err != nil {
  		return nil, fmt.Errorf("Error retrieving disk usage: %v", err)
  	}
  
  	return &report, nil
  }
docs: // BuildCachePrune requests the daemon to delete unused cache data