Add isdefault validation

README.md

@@ -1,7 +1,7 @@
 Package validator
 ================
 <img align="right" src="https://raw.githubusercontent.com/go-playground/validator/v9/logo.png">[![Join the chat at https://gitter.im/go-playground/validator](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/go-playground/validator?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-![Project status](https://img.shields.io/badge/version-9.6.0-green.svg)
+![Project status](https://img.shields.io/badge/version-9.7.0-green.svg)
 [![Build Status](https://semaphoreci.com/api/v1/joeybloggs/validator/branches/v9/badge.svg)](https://semaphoreci.com/joeybloggs/validator)
 [![Coverage Status](https://coveralls.io/repos/go-playground/validator/badge.svg?branch=v9&service=github)](https://coveralls.io/github/go-playground/validator?branch=v9)
 [![Go Report Card](https://goreportcard.com/badge/github.com/go-playground/validator)](https://goreportcard.com/report/github.com/go-playground/validator)

baked_in.go

@@ -37,6 +37,7 @@ var (
 		utf8Pipe:          {},
 		noStructLevelTag:  {},
 		requiredTag:       {},
+		isdefault:         {},
 	}
 
 	// BakedInAliasValidators is a default mapping of a single validation tag that
@@ -51,6 +52,7 @@ var (
 	// or even disregard and use your own map if so desired.
 	bakedInValidators = map[string]Func{
 		"required":        hasValue,
+		"isdefault":       isDefault,
 		"len":             hasLengthOf,
 		"min":             hasMinOf,
 		"max":             hasMaxOf,
@@ -903,6 +905,11 @@ func isAlphaUnicode(fl FieldLevel) bool {
 	return alphaUnicodeRegex.MatchString(fl.Field().String())
 }
 
+// isDefault is the opposite of required aka hasValue
+func isDefault(fl FieldLevel) bool {
+	return !hasValue(fl)
+}
+
 // HasValue is the validation function for validating if the current field's value is not the default static value.
 func hasValue(fl FieldLevel) bool {
 

cache.go

@@ -13,6 +13,7 @@ type tagType uint8
 const (
 	typeDefault tagType = iota
 	typeOmitEmpty
+	typeIsDefault
 	typeNoStructLevel
 	typeStructOnly
 	typeDive
@@ -224,6 +225,10 @@ func (v *Validate) parseFieldTagsRecursive(tag string, fieldName string, alias s
 
 		default:
 
+			if t == isdefault {
+				current.typeof = typeIsDefault
+			}
+
 			// if a pipe character is needed within the param you must use the utf8Pipe representation "0x7C"
 			orVals := strings.Split(t, orSeparator)
 

doc.go

@@ -220,6 +220,13 @@ ensures the value is not nil.
 
 	Usage: required
 
+Is Default
+
+This validates that the value is the default value and is almost the
+opposite of required.
+
+	Usage: isdefault
+
 Length
 
 For numbers, length will ensure that the value is

validator.go

@@ -112,7 +112,7 @@ func (v *validate) traverseField(ctx context.Context, parent reflect.Value, curr
 			return
 		}
 
-		if ct.typeof == typeOmitEmpty {
+		if ct.typeof == typeOmitEmpty || ct.typeof == typeIsDefault {
 			return
 		}
 
@@ -174,6 +174,39 @@ func (v *validate) traverseField(ctx context.Context, parent reflect.Value, curr
 
 				if ct.typeof == typeStructOnly {
 					goto CONTINUE
+				} else if ct.typeof == typeIsDefault {
+					// set Field Level fields
+					v.slflParent = parent
+					v.flField = current
+					v.cf = cf
+					v.ct = ct
+
+					if !ct.fn(ctx, v) {
+						v.str1 = string(append(ns, cf.altName...))
+
+						if v.v.hasTagNameFunc {
+							v.str2 = string(append(structNs, cf.name...))
+						} else {
+							v.str2 = v.str1
+						}
+
+						v.errs = append(v.errs,
+							&fieldError{
+								v:              v.v,
+								tag:            ct.aliasTag,
+								actualTag:      ct.tag,
+								ns:             v.str1,
+								structNs:       v.str2,
+								fieldLen:       uint8(len(cf.altName)),
+								structfieldLen: uint8(len(cf.name)),
+								value:          current.Interface(),
+								param:          ct.param,
+								kind:           kind,
+								typ:            typ,
+							},
+						)
+						return
+					}
 				}
 
 				ct = ct.next
@@ -404,10 +437,6 @@ OUTER:
 			v.cf = cf
 			v.ct = ct
 
-			// // report error interface functions need these
-			// v.ns = ns
-			// v.actualNs = structNs
-
 			if !ct.fn(ctx, v) {
 
 				v.str1 = string(append(ns, cf.altName...))

validator_instance.go

@@ -22,6 +22,7 @@ const (
 	structOnlyTag      = "structonly"
 	noStructLevelTag   = "nostructlevel"
 	omitempty          = "omitempty"
+	isdefault          = "isdefault"
 	skipValidationTag  = "-"
 	diveTag            = "dive"
 	requiredTag        = "required"

validator_test.go

@@ -7213,3 +7213,43 @@ func TestFQDNValidation(t *testing.T) {
 		}
 	}
 }
+
+func TestIsDefault(t *testing.T) {
+
+	validate := New()
+
+	type Inner struct {
+		String string `validate:"isdefault"`
+	}
+	type Test struct {
+		String string `validate:"isdefault"`
+		Inner  *Inner `validate:"isdefault"`
+	}
+
+	var tt Test
+
+	errs := validate.Struct(tt)
+	Equal(t, errs, nil)
+
+	tt.Inner = &Inner{String: ""}
+	errs = validate.Struct(tt)
+	NotEqual(t, errs, nil)
+
+	fe := errs.(ValidationErrors)[0]
+	Equal(t, fe.Field(), "Inner")
+	Equal(t, fe.Namespace(), "Test.Inner")
+	Equal(t, fe.Tag(), "isdefault")
+
+	type Test2 struct {
+		Inner Inner `validate:"isdefault"`
+	}
+
+	var t2 Test2
+	errs = validate.Struct(t2)
+	Equal(t, errs, nil)
+
+	t2.Inner.String = "Changed"
+	errs = validate.Struct(t2)
+	NotEqual(t, errs, nil)
+
+}