add fmt.Stringer support

devslog.go

@@ -58,6 +58,9 @@ type Options struct {
 
 	// Max stack trace frames when unwrapping errors
 	MaxErrorStackTrace uint
+
+	// Use method String() for formatting value
+	StringerFormatter bool
 }
 
 type groupOrAttrs struct {
@@ -311,6 +314,13 @@ func (h *developHandler) colorize(b []byte, as attributes, l int, g []string) []
 				break
 			}
 
+			if h.opts.StringerFormatter {
+				if stringer, ok := av.(fmt.Stringer); ok {
+					v = []byte(stringer.String())
+					break
+				}
+			}
+
 			avt := reflect.TypeOf(av)
 			avv := reflect.ValueOf(av)
 			if avt == nil {
@@ -547,6 +557,12 @@ func (h *developHandler) elementType(t reflect.Type, v reflect.Value, l int, p i
 		return atb(v)
 	}
 
+	if h.opts.StringerFormatter {
+		if stringer, ok := v.Interface().(fmt.Stringer); ok {
+			return []byte(stringer.String())
+		}
+	}
+
 	switch v.Kind() {
 	case reflect.Array:
 		b = h.formatSlice(t, v, l+1)

devslog_test.go

@@ -57,6 +57,7 @@ func Test_Types(t *testing.T) {
 		SortKeys:          true,
 		TimeFormat:        "[]",
 		NewLineAfterLog:   true,
+		StringerFormatter: true,
 	}
 
 	test_String(t, opts)
@@ -73,6 +74,8 @@ func Test_Types(t *testing.T) {
 	test_Group(t, opts)
 	test_LogValuer(t, opts)
 	test_LogValuerPanic(t, opts)
+	test_Stringer(t, opts)
+	test_StringerInner(t, opts)
 }
 
 func test_NewHandlerDefaults(t *testing.T) {
@@ -808,3 +811,53 @@ func test_LogValuerPanic(t *testing.T, o *Options) {
 		t.Errorf("\nGot:\n%s\n , %[1]q expected it to contain panic stack trace", w.WrittenData)
 	}
 }
+
+type logStringerExample1 struct {
+	A []byte
+}
+
+func (item logStringerExample1) String() string {
+	return fmt.Sprintf("A: %s", item.A)
+}
+
+func test_Stringer(t *testing.T, o *Options) {
+	w := &MockWriter{}
+	logger := slog.New(NewHandler(w, o))
+	item1 := logStringerExample1{
+		A: []byte("test"),
+	}
+	logger.Info("test_stringer",
+		slog.Any("item1", item1),
+	)
+
+	expected := []byte("\x1b[2m\x1b[37m[]\x1b[0m \x1b[42m\x1b[30m INFO \x1b[0m \x1b[32mtest_stringer\x1b[0m\n  \x1b[35mitem1\x1b[0m: A: test\n\n")
+
+	if !bytes.Equal(w.WrittenData, expected) {
+		t.Errorf("\nExpected:\n%s\nGot:\n%s\nExpected:\n%[1]q\nGot:\n%[2]q", expected, w.WrittenData)
+	}
+}
+
+type logStringerExample2 struct {
+	Inner logStringerExample1
+	Other int
+}
+
+func test_StringerInner(t *testing.T, o *Options) {
+	w := &MockWriter{}
+	logger := slog.New(NewHandler(w, o))
+	item1 := logStringerExample2{
+		Inner: logStringerExample1{
+			A: []byte("test"),
+		},
+		Other: 42,
+	}
+	logger.Info("test_stringer_inner",
+		slog.Any("item1", item1),
+	)
+
+	expected := []byte("\x1b[2m\x1b[37m[]\x1b[0m \x1b[42m\x1b[30m INFO \x1b[0m \x1b[32mtest_stringer_inner\x1b[0m\n\x1b[33mS\x1b[0m \x1b[35mitem1\x1b[0m: \x1b[33md\x1b[0m\x1b[33me\x1b[0m\x1b[33mv\x1b[0m\x1b[33ms\x1b[0m\x1b[33ml\x1b[0m\x1b[33mo\x1b[0m\x1b[33mg\x1b[0m\x1b[33m.\x1b[0m\x1b[33ml\x1b[0m\x1b[33mo\x1b[0m\x1b[33mg\x1b[0m\x1b[33mS\x1b[0m\x1b[33mt\x1b[0m\x1b[33mr\x1b[0m\x1b[33mi\x1b[0m\x1b[33mn\x1b[0m\x1b[33mg\x1b[0m\x1b[33me\x1b[0m\x1b[33mr\x1b[0m\x1b[33mE\x1b[0m\x1b[33mx\x1b[0m\x1b[33ma\x1b[0m\x1b[33mm\x1b[0m\x1b[33mp\x1b[0m\x1b[33ml\x1b[0m\x1b[33me\x1b[0m\x1b[33m2\x1b[0m\n    \x1b[32mInner\x1b[0m: A: test\n    \x1b[32mOther\x1b[0m: \x1b[33m42\x1b[0m\n\n")
+
+	if !bytes.Equal(w.WrittenData, expected) {
+		t.Errorf("\nExpected:\n%s\nGot:\n%s\nExpected:\n%[1]q\nGot:\n%[2]q", expected, w.WrittenData)
+	}
+}