Add ValidationNotInEnumError

See kaitai-io/kaitai_struct#435 (comment)

kaitai/error.go

@@ -175,6 +175,32 @@ func (e ValidationNotAnyOfError) Error() string {
 	)
 }
 
+// ValidationNotInEnumError signals validation failure: we required "Actual" value
+// to be in the enum, but it turned out that it's not.
+type ValidationNotInEnumError struct {
+	actual interface{}
+	locationInfo
+}
+
+// NewValidationNotInEnumError creates a new ValidationNotInEnumError instance.
+func NewValidationNotInEnumError(actual interface{}, io *Stream, srcPath string) ValidationNotInEnumError {
+	return ValidationNotInEnumError{
+		actual,
+		newLocationInfo(io, srcPath),
+	}
+}
+
+// Actual is a getter of the actual value associated with the validation error.
+func (e ValidationNotInEnumError) Actual() interface{} { return e.actual }
+
+func (e ValidationNotInEnumError) Error() string {
+	return e.msgWithLocation(
+		validationFailedMsg(
+			fmt.Sprintf("not in the enum, got %v", e.actual),
+		),
+	)
+}
+
 // ValidationExprError signals validation failure: we required "Actual" value
 // to match the expression, but it turned out that it doesn't.
 type ValidationExprError struct {

kaitai/error_test.go

@@ -81,6 +81,7 @@ func TestValidationFailedError_interface(t *testing.T) {
 		{"ValidationLessThanError", NewValidationLessThanError(2, actual, io, srcPath)},
 		{"ValidationGreaterThanError", NewValidationGreaterThanError(2, actual, io, srcPath)},
 		{"ValidationNotAnyOfError", NewValidationNotAnyOfError(actual, io, srcPath)},
+		{"ValidationNotInEnumError", NewValidationNotInEnumError(actual, io, srcPath)},
 		{"ValidationExprError", NewValidationExprError(actual, io, srcPath)},
 	}
 	for _, tt := range tests {
@@ -270,6 +271,27 @@ func TestValidationNotAnyOfError_Error(t *testing.T) {
 	}
 }
 
+func TestValidationNotInEnumError_Error(t *testing.T) {
+	io := NewStream(bytes.NewReader([]byte("test")))
+	tests := []struct {
+		name string
+		e    ValidationNotInEnumError
+		want string
+	}{
+		{
+			"integer", NewValidationNotInEnumError(-42, io, "/seq/0"),
+			"/seq/0: at pos 0: validation failed: not in the enum, got -42",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := tt.e.Error(); got != tt.want {
+				t.Errorf("ValidationNotInEnumError.Error() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestValidationExprError_Error(t *testing.T) {
 	io := NewStream(bytes.NewReader([]byte("test")))
 	tests := []struct {