zapslog: fix all with slogtest, support inline group, ignore empty group.

exp/zapslog/handler.go

@@ -39,6 +39,7 @@
 	addCaller  bool
 	addStackAt slog.Level
 	callerSkip int
+	holdGroup  string // holds latest group.
 }
 
 // NewHandler builds a [Handler] that writes to the supplied [zapcore.Core]
@@ -88,6 +89,10 @@
 	case slog.KindUint64:
 		return zap.Uint64(attr.Key, attr.Value.Uint64())
 	case slog.KindGroup:
+		if attr.Key == "" {
+			// Inlines recursively.
+			return zap.Inline(groupObject(attr.Value.Group()))
+		}
 		return zap.Object(attr.Key, groupObject(attr.Value.Group()))
 	case slog.KindLogValuer:
 		return convertAttrToField(slog.Attr{
@@ -157,29 +162,45 @@
 		ce.Stack = stacktrace.Take(3 + h.callerSkip)
 	}
 
-	fields := make([]zapcore.Field, 0, record.NumAttrs())
+	fields := make([]zapcore.Field, 0, record.NumAttrs()+1)
 	record.Attrs(func(attr slog.Attr) bool {
-		fields = append(fields, convertAttrToField(attr))
+		f := convertAttrToField(attr)
+		if h.holdGroup != "" && f != zap.Skip() {
+			fields = append(fields, zap.Namespace(h.holdGroup))
+			h.holdGroup = ""
+		}
+		fields = append(fields, f)
 		return true
 	})
+
 	ce.Write(fields...)
 	return nil
 }
 
 // WithAttrs returns a new Handler whose attributes consist of
 // both the receiver's attributes and the arguments.
 func (h *Handler) WithAttrs(attrs []slog.Attr) slog.Handler {
-	fields := make([]zapcore.Field, 0, len(attrs))
+	fields := make([]zapcore.Field, 0, len(attrs)+1)
 	for _, attr := range attrs {
-		fields = append(fields, convertAttrToField(attr))
+		f := convertAttrToField(attr)
+		if h.holdGroup != "" && f != zap.Skip() {
+			fields = append(fields, zap.Namespace(h.holdGroup))
+			h.holdGroup = ""
+		}
+		fields = append(fields, f)
 	}
 	return h.withFields(fields...)
 }
 
 // WithGroup returns a new Handler with the given group appended to
 // the receiver's existing groups.
 func (h *Handler) WithGroup(group string) slog.Handler {
-	return h.withFields(zap.Namespace(group))
+	cloned := *h
+	if h.holdGroup != "" {
+		cloned.core = h.core.With([]zapcore.Field{zap.Namespace(group)})
+	}
+	cloned.holdGroup = group
+	return &cloned
 }
 
 // withFields returns a cloned Handler with the given fields.

exp/zapslog/handler_test.go

@@ -23,13 +23,17 @@
 package zapslog
 
 import (
+	"bytes"
+	"encoding/json"
 	"log/slog"
 	"testing"
+	"testing/slogtest"
 	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/zap/zapcore"
+	"go.uber.org/zap/zaptest"
 	"go.uber.org/zap/zaptest/observer"
 )
 
@@ -150,6 +154,69 @@ func TestWithName(t *testing.T) {
 	})
 }
 
+func TestInlineGroup(t *testing.T) {
+	t.Parallel()
+	fac, observedLogs := observer.New(zapcore.DebugLevel)
+	t.Run("inline-group", func(t *testing.T) {
+		sl := slog.New(NewHandler(fac))
+		sl.Info("msg", "a", "b", slog.Group("", slog.String("c", "d")), "e", "f")
+
+		logs := observedLogs.TakeAll()
+		require.Len(t, logs, 1, "Expected exactly one entry to be logged")
+		entry := logs[0]
+		assert.Equal(t, "", entry.LoggerName, "Unexpected logger name")
+		assert.Equal(t, map[string]any{
+			"a": "b",
+			"c": "d",
+			"e": "f",
+		}, logs[0].ContextMap(), "Unexpected context")
+	})
+	t.Run("inline-group-recursive", func(t *testing.T) {
+		sl := slog.New(NewHandler(fac))
+		sl.Info("msg", "a", "b", slog.Group("", slog.Group("", slog.Group("", slog.String("c", "d"))), slog.Group("", "e", "f")))
+
+		logs := observedLogs.TakeAll()
+		require.Len(t, logs, 1, "Expected exactly one entry to be logged")
+		entry := logs[0]
+		assert.Equal(t, "", entry.LoggerName, "Unexpected logger name")
+		assert.Equal(t, map[string]any{
+			"a": "b",
+			"c": "d",
+			"e": "f",
+		}, logs[0].ContextMap(), "Unexpected context")
+	})
+}
+
+func TestWithGroup(t *testing.T) {
+	t.Parallel()
+	fac, observedLogs := observer.New(zapcore.DebugLevel)
+	t.Run("empty-group-record", func(t *testing.T) {
+		sl := slog.New(NewHandler(fac))
+		sl.With("a", "b").WithGroup("G").With("c", "d").WithGroup("H").Info("msg")
+
+		logs := observedLogs.TakeAll()
+		require.Len(t, logs, 1, "Expected exactly one entry to be logged")
+		entry := logs[0]
+		assert.Equal(t, "", entry.LoggerName, "Unexpected logger name")
+		assert.Equal(t, map[string]any{
+			"G": map[string]any{
+				"c": "d",
+			},
+			"a": "b",
+		}, logs[0].ContextMap(), "Unexpected context")
+	})
+	t.Run("only-records-to-ignore", func(t *testing.T) {
+		sl := slog.New(NewHandler(fac))
+		sl.WithGroup("H").With(slog.Attr{}).Info("msg")
+
+		logs := observedLogs.TakeAll()
+		require.Len(t, logs, 1, "Expected exactly one entry to be logged")
+		entry := logs[0]
+		assert.Equal(t, "", entry.LoggerName, "Unexpected logger name")
+		assert.Equal(t, map[string]any{}, logs[0].ContextMap(), "Unexpected context")
+	})
+}
+
 type Token string
 
 func (Token) LogValue() slog.Value {
@@ -189,3 +256,41 @@ func TestAttrKinds(t *testing.T) {
 		},
 		entry.ContextMap())
 }
+
+func TestSlogtest(t *testing.T) {
+	var buff bytes.Buffer
+	core := zapcore.NewCore(
+		zapcore.NewJSONEncoder(zapcore.EncoderConfig{
+			TimeKey:     slog.TimeKey,
+			MessageKey:  slog.MessageKey,
+			LevelKey:    slog.LevelKey,
+			EncodeLevel: zapcore.CapitalLevelEncoder,
+			EncodeTime:  zapcore.RFC3339TimeEncoder,
+		}),
+		zapcore.AddSync(&buff),
+		zapcore.DebugLevel,
+	)
+
+	// zaptest doesn't expose the underlying core,
+	// so we'll extract it from the logger.
+	testCore := zaptest.NewLogger(t).Core()
+
+	handler := NewHandler(zapcore.NewTee(core, testCore))
+	err := slogtest.TestHandler(
+		handler,
+		func() []map[string]any {
+			// Parse the newline-delimted JSON in buff.
+			var entries []map[string]any
+
+			dec := json.NewDecoder(bytes.NewReader(buff.Bytes()))
+			for dec.More() {
+				var ent map[string]any
+				require.NoError(t, dec.Decode(&ent), "Error decoding log message")
+				entries = append(entries, ent)
+			}
+
+			return entries
+		},
+	)
+	require.NoError(t, err, "Unexpected error from slogtest.TestHandler")
+}