vendor/github.com/hashicorp/go-multierror/append.go

package multierror

// Append is a helper function that will append more errors
// onto an Error in order to create a larger multi-error.
//
// If err is not a multierror.Error, then it will be turned into
// one. If any of the errs are multierr.Error, they will be flattened
// one level into err.
func Append(err error, errs ...error) *Error {
	switch err := err.(type) {
	case *Error:
		// Typed nils can reach here, so initialize if we are nil
		if err == nil {
			err = new(Error)
		}

		// Go through each error and flatten
		for _, e := range errs {
			switch e := e.(type) {
			case *Error:
				if e != nil {
					err.Errors = append(err.Errors, e.Errors...)
				}
			default:
				if e != nil {
					err.Errors = append(err.Errors, e)
				}
			}
		}

		return err
	default:
		newErrs := make([]error, 0, len(errs)+1)
		if err != nil {
			newErrs = append(newErrs, err)
		}
		newErrs = append(newErrs, errs...)

		return Append(&Error{}, newErrs...)
	}
}