validate/error.go

package validate

import "fmt"

// Err is the zero Error. It carries no message, so errors.Is(x, Err) is
// true for any error produced by this package.
var Err = Error{}

// Error represents a validation error.
type Error struct {
	Message string
	Data    []any
}

// Error returns the error message. If Data is non-empty, Message is used
// as an fmt.Sprintf format string and Data as its arguments (this is how
// the sentinels with %d/%q verbs are filled in, e.g. via With).
func (e Error) Error() string {
	if len(e.Data) > 0 {
		return fmt.Sprintf(e.Message, e.Data...)
	}
	return e.Message
}

// Is determines whether the Error is an instance of the target.
// https://pkg.go.dev/errors#Is
//
// If the target is a validation error and specifies a message, this function returns true if the messages match.
// If the target is an empty validation error, this function always returns true.
func (e Error) Is(target error) bool {
	if t, ok := target.(Error); ok {
		return t.Message == e.Message || t.Message == ""
	}
	return false
}

// With returns a copy of the Error with value appended to Data, so it
// lands in the message when Message contains a formatting verb:
//
//	ErrMustBeLonger.With(4) // "must contain at least 4 characters"
func (e Error) With(value any) Error {
	if e.Data == nil {
		e.Data = []any{}
	}
	e.Data = append(e.Data, value)
	return e
}

// NewError creates a new validation error.
func NewError(message string) Error {
	return Error{
		Message: message,
	}
}