Add new x/errors/validation package to make your life even more easier (using Generics)

x/errors/validation/error.go

@@ -0,0 +1,92 @@
+package validation
+
+import (
+	"fmt"
+
+	"github.com/kataras/iris/v12/x/errors"
+)
+
+// FieldError describes a field validation error.
+// It completes the errors.ValidationError interface.
+type FieldError[T any] struct {
+	Field  string `json:"field"`
+	Value  T      `json:"value"`
+	Reason string `json:"reason"`
+}
+
+// Field returns a new validation error.
+//
+// Use its Func method to add validations over this field.
+func Field[T any](field string, value T) *FieldError[T] {
+	return &FieldError[T]{Field: field, Value: value}
+}
+
+// Error completes the standard error interface.
+func (e *FieldError[T]) Error() string {
+	return fmt.Sprintf("field %q got invalid value of %v: reason: %s", e.Field, e.Value, e.Reason)
+}
+
+// GetField returns the field name.
+func (e *FieldError[T]) GetField() string {
+	return e.Field
+}
+
+// GetValue returns the value of the field.
+func (e *FieldError[T]) GetValue() any {
+	return e.Value
+}
+
+// GetReason returns the reason of the validation error.
+func (e *FieldError[T]) GetReason() string {
+	return e.Reason
+}
+
+// IsZero reports whether the error is nil or has an empty reason.
+func (e *FieldError[T]) IsZero() bool {
+	return e == nil || e.Reason == ""
+}
+
+func (e *FieldError[T]) joinReason(reason string) {
+	if reason == "" {
+		return
+	}
+
+	if e.Reason == "" {
+		e.Reason = reason
+	} else {
+		e.Reason += ", " + reason
+	}
+}
+
+// Func accepts a variadic number of functions which accept the value of the field
+// and return a string message if the value is invalid.
+// It joins the reasons into one.
+func (e *FieldError[T]) Func(fns ...func(value T) string) *FieldError[T] {
+	for _, fn := range fns {
+		e.joinReason(fn(e.Value))
+	}
+
+	return e
+}
+
+// Join joins the given validation errors into one.
+func Join(errs ...errors.ValidationError) error { // note that here we return the standard error type instead of the errors.ValidationError in order to make the error nil instead of ValidationErrors(nil) on empty slice.
+	if len(errs) == 0 {
+		return nil
+	}
+
+	joinedErrs := make(errors.ValidationErrors, 0, len(errs))
+	for _, err := range errs {
+		if err == nil || err.GetReason() == "" {
+			continue
+		}
+
+		joinedErrs = append(joinedErrs, err)
+	}
+
+	if len(joinedErrs) == 0 {
+		return nil
+	}
+
+	return joinedErrs
+}