feat: support slog attributes (charmbracelet#127)

json.go

@@ -11,16 +11,26 @@ 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.jsonFormatterRoot(jw, kv.Key, kv.Value)
+			i++
+		default:
+			if i+1 < len(keyvals) {
+				l.jsonFormatterRoot(jw, keyvals[i], keyvals[i+1])
+			}
+			i += 2
+		}
 	}
 
 	jw.end()
 	l.b.WriteRune('\n')
 }
 
-func (l *Logger) jsonFormatterKeyVal(jw *jsonWriter, anyKey, value any) {
-	switch anyKey {
+func (l *Logger) jsonFormatterRoot(jw *jsonWriter, key, value any) {
+	switch key {
 	case TimestampKey:
 		if t, ok := value.(time.Time); ok {
 			jw.objectItem(TimestampKey, t.Format(l.timeFormat))
@@ -42,22 +52,43 @@ func (l *Logger) jsonFormatterKeyVal(jw *jsonWriter, anyKey, value any) {
 			jw.objectItem(MessageKey, fmt.Sprint(msg))
 		}
 	default:
-		switch k := anyKey.(type) {
-		case fmt.Stringer:
-			jw.objectKey(k.String())
-		case error:
-			jw.objectKey(k.Error())
-		default:
-			jw.objectKey(fmt.Sprint(k))
-		}
-		switch v := value.(type) {
-		case error:
-			jw.objectValue(v.Error())
-		case fmt.Stringer:
-			jw.objectValue(v.String())
-		default:
-			jw.objectValue(v)
+		l.jsonFormatterItem(jw, key, value)
+	}
+}
+
+func (l *Logger) jsonFormatterItem(jw *jsonWriter, key, value any) {
+	switch k := key.(type) {
+	case fmt.Stringer:
+		jw.objectKey(k.String())
+	case error:
+		jw.objectKey(k.Error())
+	default:
+		jw.objectKey(fmt.Sprint(k))
+	}
+	switch v := value.(type) {
+	case error:
+		jw.objectValue(v.Error())
+	case slogLogValuer:
+		l.writeSlogValue(jw, v.LogValue())
+	case slogValue:
+		l.writeSlogValue(jw, v.Resolve())
+	case fmt.Stringer:
+		jw.objectValue(v.String())
+	default:
+		jw.objectValue(v)
+	}
+}
+
+func (l *Logger) writeSlogValue(jw *jsonWriter, v slogValue) {
+	switch v.Kind() {
+	case slogKindGroup:
+		jw.start()
+		for _, attr := range v.Group() {
+			l.jsonFormatterItem(jw, attr.Key, attr.Value)
 		}
+		jw.end()
+	default:
+		jw.objectValue(v.Any())
 	}
 }
 

logger_121.go

@@ -10,6 +10,15 @@ import (
 	"sync/atomic"
 )
 
+// type aliases for slog.
+type (
+	slogAttr      = slog.Attr
+	slogValue     = slog.Value
+	slogLogValuer = slog.LogValuer
+)
+
+const slogKindGroup = slog.KindGroup
+
 // Enabled reports whether the logger is enabled for the given level.
 //
 // Implements slog.Handler.
@@ -27,7 +36,7 @@ func (l *Logger) Handle(ctx context.Context, record slog.Record) error {
 
 	fields := make([]interface{}, 0, record.NumAttrs()*2)
 	record.Attrs(func(a slog.Attr) bool {
-		fields = append(fields, a.Key, a.Value.String())
+		fields = append(fields, a.Key, a.Value)
 		return true
 	})
 	// Get the caller frame using the record's PC.

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 +182,95 @@ func TestSlogCustomLevel(t *testing.T) {
 		})
 	}
 }
+
+type testLogValue struct {
+	v slog.Value
+}
+
+func (v testLogValue) LogValue() slog.Value {
+	return v.v
+}
+
+func TestSlogAttr(t *testing.T) {
+	cases := []struct {
+		name     string
+		expected string
+		kvs      []interface{}
+	}{
+		{
+			name:     "any",
+			expected: `{"level":"info","msg":"message","any":42}` + "\n",
+			kvs:      []any{"any", slog.AnyValue(42)},
+		},
+		{
+			name:     "bool",
+			expected: `{"level":"info","msg":"message","bool":false}` + "\n",
+			kvs:      []any{"bool", slog.BoolValue(false)},
+		},
+		{
+			name:     "duration",
+			expected: `{"level":"info","msg":"message","duration":10800000000000}` + "\n",
+			kvs:      []any{"duration", slog.DurationValue(3 * time.Hour)},
+		},
+		{
+			name:     "float64",
+			expected: `{"level":"info","msg":"message","float64":123}` + "\n",
+			kvs:      []any{"float64", slog.Float64Value(123)},
+		},
+		{
+			name:     "string",
+			expected: `{"level":"info","msg":"message","string":"hello"}` + "\n",
+			kvs:      []any{"string", slog.StringValue("hello")},
+		},
+		{
+			name:     "time",
+			expected: `{"level":"info","msg":"message","_time":"1970-01-01T00:00:00Z"}` + "\n",
+			kvs:      []any{"_time", slog.TimeValue(time.Unix(0, 0).UTC())},
+		},
+		{
+			name:     "uint64",
+			expected: `{"level":"info","msg":"message","uint64":42}` + "\n",
+			kvs:      []any{"uint64", slog.Uint64Value(42)},
+		},
+		{
+			name:     "group",
+			expected: `{"level":"info","msg":"message","g":{"b":true}}` + "\n",
+			kvs:      []any{slog.Group("g", slog.Bool("b", true))},
+		},
+		{
+			name:     "log valuer",
+			expected: `{"level":"info","msg":"message","lv":42}` + "\n",
+			kvs: []any{
+				"lv", testLogValue{slog.AnyValue(42)},
+			},
+		},
+		{
+			name:     "log valuer",
+			expected: `{"level":"info","msg":"message","lv":{"first":"hello","last":"world"}}` + "\n",
+			kvs: []any{
+				"lv", testLogValue{slog.GroupValue(
+					slog.String("first", "hello"),
+					slog.String("last", "world"),
+				)},
+			},
+		},
+	}
+
+	for _, c := range cases {
+		c := c
+		t.Run(c.name, func(t *testing.T) {
+			t.Parallel()
+
+			// expect same output from slog and log
+			var buf bytes.Buffer
+			l := NewWithOptions(&buf, Options{Formatter: JSONFormatter})
+			l.Info("message", c.kvs...)
+			assert.Equal(t, c.expected, buf.String())
+
+			buf.Truncate(0)
+			sl := slog.New(l)
+			sl.Info("message", c.kvs...)
+			assert.Equal(t, c.expected, buf.String())
+		})
+	}
+}

logger_no121.go

@@ -11,6 +11,15 @@ import (
 	"golang.org/x/exp/slog"
 )
 
+// type alises for slog.
+type (
+	slogAttr      = slog.Attr
+	slogValue     = slog.Value
+	slogLogValuer = slog.LogValuer
+)
+
+const slogKindGroup = slog.KindGroup
+
 // Enabled reports whether the logger is enabled for the given level.
 //
 // Implements slog.Handler.
@@ -24,7 +33,7 @@ func (l *Logger) Enabled(_ context.Context, level slog.Level) bool {
 func (l *Logger) Handle(_ context.Context, record slog.Record) error {
 	fields := make([]interface{}, 0, record.NumAttrs()*2)
 	record.Attrs(func(a slog.Attr) bool {
-		fields = append(fields, a.Key, a.Value.String())
+		fields = append(fields, a.Key, a.Value)
 		return true
 	})
 	// Get the caller frame using the record's PC.