feat: Add support for omitting empty and zero values in validation (including nil pointer and empty content of pointer) (#1289)

## Fixes Or Enhances

**Add the `omitzero` Tag:**
- It allows you to ignore the subsequent validations if the value of a
field is empty
- If the field is a pointer and the pointer is nil, ignore the
subsequent validations
- If the field is a pointer and the pointer is not nil, but the content
value of the pointer is zero, the subsequent validations will be ignored


**Make sure that you've checked the boxes below before you submit PR:**
- [x] Tests exist or have been written that cover this particular
change.

@go-playground/validator-maintainers

Author: zeewell

baked_in.go

@@ -50,6 +50,7 @@ var (
 		keysTag:           {},
 		endKeysTag:        {},
 		structOnlyTag:     {},
+		omitzero:          {},
 		omitempty:         {},
 		omitnil:           {},
 		skipValidationTag: {},
@@ -1797,6 +1798,20 @@ func hasValue(fl FieldLevel) bool {
 	}
 }
 
+// hasNotZeroValue is the validation function for validating if the current field's value is not the zero value for its type.
+func hasNotZeroValue(fl FieldLevel) bool {
+	field := fl.Field()
+	switch field.Kind() {
+	case reflect.Slice, reflect.Map, reflect.Ptr, reflect.Interface, reflect.Chan, reflect.Func:
+		return !field.IsNil()
+	default:
+		if fl.(*validate).fldIsPointer && field.Interface() != nil {
+			return !field.IsZero()
+		}
+		return field.IsValid() && !field.IsZero()
+	}
+}
+
 // requireCheckFieldKind is a func for check field kind
 func requireCheckFieldKind(fl FieldLevel, param string, defaultNotFoundValue bool) bool {
 	field := fl.Field()

cache.go

@@ -21,6 +21,7 @@ const (
 	typeKeys
 	typeEndKeys
 	typeOmitNil
+	typeOmitZero
 )
 
 const (
@@ -249,6 +250,10 @@ func (v *Validate) parseFieldTagsRecursive(tag string, fieldName string, alias s
 			}
 			return
 
+		case omitzero:
+			current.typeof = typeOmitZero
+			continue
+
 		case omitempty:
 			current.typeof = typeOmitEmpty
 			continue

validator.go

@@ -117,6 +117,10 @@ func (v *validate) traverseField(ctx context.Context, parent reflect.Value, curr
 			return
 		}
 
+		if ct.typeof == typeOmitZero {
+			return
+		}
+
 		if ct.hasTag {
 			if kind == reflect.Invalid {
 				v.str1 = string(append(ns, cf.altName...))
@@ -238,6 +242,19 @@ OUTER:
 			ct = ct.next
 			continue
 
+		case typeOmitZero:
+			v.slflParent = parent
+			v.flField = current
+			v.cf = cf
+			v.ct = ct
+
+			if !hasNotZeroValue(v) {
+				return
+			}
+
+			ct = ct.next
+			continue
+
 		case typeOmitNil:
 			v.slflParent = parent
 			v.flField = current

validator_instance.go

@@ -21,6 +21,7 @@ const (
 	tagKeySeparator       = "="
 	structOnlyTag         = "structonly"
 	noStructLevelTag      = "nostructlevel"
+	omitzero              = "omitzero"
 	omitempty             = "omitempty"
 	omitnil               = "omitnil"
 	isdefault             = "isdefault"

validator_test.go

@@ -14022,6 +14022,57 @@ func TestOmitNilAndRequired(t *testing.T) {
 	})
 }
 
+func TestOmitZero(t *testing.T) {
+	type (
+		OmitEmpty struct {
+			Str    string  `validate:"omitempty,min=10"`
+			StrPtr *string `validate:"omitempty,min=10"`
+		}
+		OmitZero struct {
+			Str    string  `validate:"omitzero,min=10"`
+			StrPtr *string `validate:"omitzero,min=10"`
+		}
+	)
+
+	var (
+		validate = New()
+		valid    = "this is the long string to pass the validation rule"
+		empty    = ""
+	)
+
+	t.Run("compare using valid data", func(t *testing.T) {
+		err1 := validate.Struct(OmitEmpty{Str: valid, StrPtr: &valid})
+		err2 := validate.Struct(OmitZero{Str: valid, StrPtr: &valid})
+
+		Equal(t, err1, nil)
+		Equal(t, err2, nil)
+	})
+
+	t.Run("compare fully empty omitempty and omitzero", func(t *testing.T) {
+		err1 := validate.Struct(OmitEmpty{})
+		err2 := validate.Struct(OmitZero{})
+
+		Equal(t, err1, nil)
+		Equal(t, err2, nil)
+	})
+
+	t.Run("compare with zero value", func(t *testing.T) {
+		err1 := validate.Struct(OmitEmpty{Str: "", StrPtr: nil})
+		err2 := validate.Struct(OmitZero{Str: "", StrPtr: nil})
+
+		Equal(t, err1, nil)
+		Equal(t, err2, nil)
+	})
+
+	t.Run("compare with empty value", func(t *testing.T) {
+		err1 := validate.Struct(OmitEmpty{Str: empty, StrPtr: &empty})
+		err2 := validate.Struct(OmitZero{Str: empty, StrPtr: &empty})
+
+		AssertError(t, err1, "OmitEmpty.StrPtr", "OmitEmpty.StrPtr", "StrPtr", "StrPtr", "min")
+		Equal(t, err2, nil)
+	})
+}
+
 func TestPrivateFieldsStruct(t *testing.T) {
 	type tc struct {
 		stct     interface{}