Add status.WithDescription (#20)

status/error.go

@@ -19,6 +19,11 @@ func (c Code) Error() string {
 	return codeToMsg[c]
 }
 
+// Is implements interface for errors.Is.
+func (c Code) Is(target error) bool {
+	return target == c //nolint:goerr113 // Target is expected to be plain status error.
+}
+
 type errorWithStatus struct {
 	err  error
 	code Code
@@ -55,3 +60,21 @@ func Wrap(err error, code Code) error {
 		code: code,
 	}
 }
+
+type codeWithDescription struct {
+	Code
+	desc string
+}
+
+func (e codeWithDescription) Description() string {
+	return e.desc
+}
+
+// WithDescription augments status Code with textual description.
+func WithDescription(code Code, description string) error {
+	e := codeWithDescription{}
+	e.Code = code
+	e.desc = description
+
+	return e
+}

status/error_test.go

@@ -20,3 +20,16 @@ func TestWrap(t *testing.T) {
 func TestCode_Error(t *testing.T) {
 	assert.Equal(t, "deadline exceeded", status.DeadlineExceeded.Error())
 }
+
+func TestWithDescription(t *testing.T) {
+	err := status.WithDescription(status.AlreadyExists, "This is a description.")
+	assert.EqualError(t, err, "already exists")
+	assert.True(t, errors.Is(err, status.AlreadyExists))
+	assert.False(t, errors.Is(err, status.NotFound))
+
+	d, ok := err.(interface {
+		Description() string
+	})
+	assert.True(t, ok)
+	assert.Equal(t, "This is a description.", d.Description())
+}