code: func UnwrapErrorWithFileContext(err error) *ErrorWithFileContext {
  	for err != nil {
  		switch v := err.(type) {
  		case *ErrorWithFileContext:
  			return v
  		case causer:
  			err = v.Cause()
  		default:
  			return nil
  		}
  	}
  	return nil
  }
docs: // UnwrapErrorWithFileContext tries to unwrap an ErrorWithFileContext from err.
  // It returns nil if this is not possible.