Add exists tag

exists tag used to ensure that a Pointer, Interface or
Invalid has a value, but won't interfere with any other validation.

doc.go

@@ -167,6 +167,14 @@ Here is a list of the current built in validators:
 		inside of you program you know the struct will be valid, but need to
 		verify it has been assigned.
 
+	exists
+		Is a special tag without a validation function attached. It is used when a field
+		is a Pointer, Interface or Invalid and you wish to validate that it exists.
+		Example: want to ensure a bool exists if you define the bool as a pointer and
+		use exists it will ensure there is a value; couldn't use required as it would
+		fail when the bool was false. exists will fail is the value is a Pointer, Interface
+		or Invalid and is nil. (Usage: exists)
+
 	omitempty
 		Allows conditional validation, for example if a field is not set with
 		a value (Determined by the required validator) then other validation

validator.go

@@ -33,6 +33,7 @@ const (
 	mapErrMsg           = "Field validation for \"%s\" failed on key \"%v\" with error(s): %s"
 	structErrMsg        = "Struct:%s\n"
 	diveTag             = "dive"
+	existsTag           = "exists"
 	arrayIndexFieldName = "%s[%d]"
 	mapIndexFieldName   = "%s[%v]"
 )
@@ -722,7 +723,22 @@ func (v *Validate) fieldWithNameAndValue(val interface{}, current interface{}, f
 
 			for _, val := range cTag.keyVals {
 
+				// if (idxField.Kind() == reflect.Ptr || idxField.Kind() == reflect.Interface) && idxField.IsNil() {
+				// if val[0] == existsTag {
+				// 	if (cField.kind == reflect.Ptr || cField.kind == reflect.Interface) && valueField.IsNil() {
+				// 		fieldErr = &FieldError{
+				// 			Field: name,
+				// 			Tag:   val[0],
+				// 			Value: f,
+				// 			Param: val[1],
+				// 		}
+				// 		err = errors.New(fieldErr.Tag)
+				// 	}
+
+				// } else {
+
 				fieldErr, err = v.fieldWithNameAndSingleTag(val, current, f, val[0], val[1], name)
+				// }
 
 				if err == nil {
 					return nil
@@ -740,6 +756,18 @@ func (v *Validate) fieldWithNameAndValue(val interface{}, current interface{}, f
 			return fieldErr
 		}
 
+		if cTag.keyVals[0][0] == existsTag {
+			if (cField.kind == reflect.Ptr || cField.kind == reflect.Interface) && valueField.IsNil() {
+				return &FieldError{
+					Field: name,
+					Tag:   cTag.keyVals[0][0],
+					Value: f,
+					Param: cTag.keyVals[0][1],
+				}
+			}
+			continue
+		}
+
 		if fieldErr, err = v.fieldWithNameAndSingleTag(val, current, f, cTag.keyVals[0][0], cTag.keyVals[0][1], name); err != nil {
 
 			fieldErr.Kind = cField.kind
@@ -981,6 +1009,10 @@ func (v *Validate) fieldWithNameAndSingleTag(val interface{}, current interface{
 		return nil, nil
 	}
 
+	// if key == existsTag {
+	// 	continue
+	// }
+
 	valFunc, ok := v.validationFuncs[key]
 	if !ok {
 		panic(fmt.Sprintf("Undefined validation function on field %s", name))

validator_test.go

@@ -1,6 +1,7 @@
 package validator
 
 import (
+	"encoding/json"
 	"fmt"
 	"path"
 	"reflect"
@@ -231,6 +232,36 @@ func AssertMapFieldError(t *testing.T, s map[string]*FieldError, field string, e
 	EqualSkip(t, 2, val.Tag, expectedTag)
 }
 
+func TestExistsValidation(t *testing.T) {
+
+	jsonText := "{ \"truthiness2\": true }"
+
+	type Thing struct {
+		Truthiness *bool `json:"truthiness" validate:"exists,required"`
+	}
+
+	var ting Thing
+
+	err := json.Unmarshal([]byte(jsonText), &ting)
+	Equal(t, err, nil)
+	NotEqual(t, ting, nil)
+	Equal(t, ting.Truthiness, nil)
+
+	errs := validate.Struct(ting)
+	NotEqual(t, errs, nil)
+	AssertFieldError(t, errs, "Truthiness", "exists")
+
+	jsonText = "{ \"truthiness\": true }"
+
+	err = json.Unmarshal([]byte(jsonText), &ting)
+	Equal(t, err, nil)
+	NotEqual(t, ting, nil)
+	Equal(t, ting.Truthiness, true)
+
+	errs = validate.Struct(ting)
+	Equal(t, errs, nil)
+}
+
 func TestSliceMapArrayChanFuncPtrInterfaceRequiredValidation(t *testing.T) {
 
 	var m map[string]string