Make UNSET enums' String() return "UNSET"

ygen/gogen.go

@@ -2111,7 +2111,7 @@ func writeGoEnum(inputEnum *yangEnum) (goEnumCodeSnippet, error) {
 	// initialised to be UNSET, such that it is possible to determine that the enumerated value
 	// was not modified.
 	values := map[int64]string{
-		0: "UNSET",
+		0: ygot.GoEnumZeroName,
 	}
 
 	// origValues stores the original set of value names, these are not maintained to be

ygen/schema_tests/schema_test.go

@@ -228,7 +228,7 @@ func TestEnumStringFunction(t *testing.T) {
 	}, {
 		desc:   "out-of-range: UNSET",
 		inEnum: exampleoc.Interface_OperStatus_UNSET,
-		want:   "out-of-range E_Interface_OperStatus enum value: 0",
+		want:   "UNSET",
 	}, {
 		desc:   "out-of-range: too high",
 		inEnum: exampleoc.E_Interface_OperStatus(100),

ygot/struct_validation_map.go

@@ -34,6 +34,9 @@ import (
 )
 
 const (
+	// GoEnumZeroName is the string value used to represent an unset
+	// enumeration/identity value in Go.
+	GoEnumZeroName = "UNSET"
 	// indentString represents the default indentation string used for
 	// JSON. Three spaces are used based on the legacy use of EmitJSON.
 	indentString string = "   "
@@ -187,6 +190,9 @@ func enumFieldToString(field reflect.Value, appendModuleName bool) (string, bool
 func EnumLogString(e GoEnum, val int64, enumTypeName string) string {
 	enumDef, ok := e.ΛMap()[enumTypeName][val]
 	if !ok {
+		if val == 0 {
+			return GoEnumZeroName
+		}
 		return fmt.Sprintf("out-of-range %s enum value: %v", enumTypeName, val)
 	}
 	return enumDef.Name

ygot/struct_validation_map_test.go

@@ -446,7 +446,7 @@ func TestEnumLogString(t *testing.T) {
 		inEnum:         EUNSET,
 		inVal:          int64(EUNSET),
 		inEnumTypeName: "enumTest",
-		want:           "out-of-range enumTest enum value: 0",
+		want:           "UNSET",
 	}, {
 		desc:           "way out of range",
 		inEnum:         EONE,