feat: support slog attributes

json.go

@@ -11,8 +11,18 @@ func (l *Logger) jsonFormatter(keyvals ...interface{}) {
 	jw := &jsonWriter{w: &l.b}
 	jw.start()
 
-	for i := 0; i < len(keyvals); i += 2 {
-		l.jsonFormatterKeyVal(jw, keyvals[i], keyvals[i+1])
+	i := 0
+	for i < len(keyvals) {
+		switch kv := keyvals[i].(type) {
+		case slogAttr:
+			l.jsonFormatterKeyVal(jw, kv.Key, kv.Value)
+			i++
+		default:
+			if i+1 < len(keyvals) {
+				l.jsonFormatterKeyVal(jw, keyvals[i], keyvals[i+1])
+			}
+			i += 2
+		}
 	}
 
 	jw.end()
@@ -53,6 +63,17 @@ func (l *Logger) jsonFormatterKeyVal(jw *jsonWriter, anyKey, value any) {
 		switch v := value.(type) {
 		case error:
 			jw.objectValue(v.Error())
+		case slogValue:
+			switch v.Kind() {
+			case slogKindGroup:
+				jw.start()
+				for _, attr := range v.Group() {
+					l.jsonFormatterKeyVal(jw, attr.Key, attr.Value)
+				}
+				jw.end()
+			default:
+				jw.objectValue(v.String())
+			}
 		case fmt.Stringer:
 			jw.objectValue(v.String())
 		default:

json_121.go

@@ -0,0 +1,15 @@
+//go:build go1.21
+// +build go1.21
+
+package log
+
+import "log/slog"
+
+type (
+	slogAttr  = slog.Attr
+	slogValue = slog.Value
+)
+
+const (
+	slogKindGroup = slog.KindGroup
+)

json_no121.go

@@ -0,0 +1,27 @@
+//go:build !go1.21
+// +build !go1.21
+
+package log
+
+type (
+	slogAttr struct {
+		Key   string
+		Value slogValue
+	}
+	slogValue struct{}
+	slogKind  int
+)
+
+const slogKindGroup slogKind = iota
+
+func (slogValue) String() string {
+	panic("should not be reached")
+}
+
+func (slogValue) Group() []slogAttr {
+	panic("should not be reached")
+}
+
+func (slogValue) Kind() slogKind {
+	panic("should not be reached")
+}

logger_121_test.go

@@ -6,11 +6,10 @@ package log
 import (
 	"bytes"
 	"context"
+	"log/slog"
 	"testing"
 	"time"
 
-	"log/slog"
-
 	"github.com/stretchr/testify/assert"
 )
 
@@ -183,3 +182,28 @@ func TestSlogCustomLevel(t *testing.T) {
 		})
 	}
 }
+
+func TestSlogAttr(t *testing.T) {
+	cases := []struct {
+		name     string
+		expected string
+		keyvals  []interface{}
+	}{
+		{
+			name:     "group",
+			expected: `{"level":"info","msg":"message","g":{"b":"true"}}` + "\n",
+			keyvals:  []any{slog.Group("g", slog.Bool("b", true))},
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			t.Parallel()
+
+			var buf bytes.Buffer
+			l := NewWithOptions(&buf, Options{Formatter: JSONFormatter})
+			l.Info("message", c.keyvals...)
+			assert.Equal(t, c.expected, buf.String())
+		})
+	}
+}