add const function (#8)

annotator.go

@@ -35,3 +35,9 @@ func WithAttrs(attrs ...Attribute) AnnotatorFunc {
 		}
 	}
 }
+
+func WithNoStackTrace() AnnotatorFunc {
+	return func(err *Error) {
+		err.stack = nil
+	}
+}

error.go

@@ -56,6 +56,10 @@ func New(message string, annotators ...any) error {
 	return wrap(err, annotators...)
 }
 
+func Const(message string) error {
+	return New(message, WithNoStackTrace())
+}
+
 func Is(err, target error) bool {
 	return errors.Is(err, target)
 }

errors_test.go

@@ -310,3 +310,17 @@ func TestJoin(t *testing.T) {
 		})
 	}
 }
+
+func TestConst(t *testing.T) {
+	err := errors.Const("test")
+	if err == nil {
+		t.Fatal("got nil error")
+	}
+	if err.Error() != "test" {
+		t.Errorf("expected test, got %s", err.Error())
+	}
+	cErr := mustCast(t, err)
+	if len(cErr.StackTrace()) != 0 {
+		t.Errorf("expected no stack trace, got %d", len(cErr.StackTrace()))
+	}
+}