code: func (p *Provider) ReadDataDiff(
  	info *terraform.InstanceInfo,
  	c *terraform.ResourceConfig) (*terraform.InstanceDiff, error) {
  
  	r, ok := p.DataSourcesMap[info.Type]
  	if !ok {
  		return nil, fmt.Errorf("unknown data source: %s", info.Type)
  	}
  
  	return r.Diff(nil, c, p.meta)
  }
docs: // ReadDataDiff implementation of terraform.ResourceProvider interface.