Add benchmark for Nest, remove extra alloc in BenchmarkMarshalerField (…

…#90)

* Remove unnecessary alloc in BenchmarkMarshalerField

* json encoder: Add a benchmark for Nest

When we replace Nest with some sort of LogMarshalerfunc (#87), we should
compare performance against the existing implementation.

json_encoder_bench_test.go

@@ -34,6 +34,19 @@ type logRecord struct {
 	Fields  map[string]interface{} `json:"fields"`
 }
 
+var s string
+
+func BenchmarkJSONEncoderNest(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		enc := newJSONEncoder()
+		enc.Nest("nested", func(kv KeyValue) error {
+			kv.AddInt("i", i)
+			return nil
+		})
+		enc.Free()
+	}
+}
+
 func BenchmarkZapJSON(b *testing.B) {
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {

logger_bench_test.go

@@ -34,14 +34,14 @@ type user struct {
 	CreatedAt time.Time
 }
 
-func (u user) MarshalLog(kv zap.KeyValue) error {
+func (u *user) MarshalLog(kv zap.KeyValue) error {
 	kv.AddString("name", u.Name)
 	kv.AddString("email", u.Email)
 	kv.AddInt64("created_at", u.CreatedAt.UnixNano())
 	return nil
 }
 
-var _jane = user{
+var _jane = &user{
 	Name:      "Jane Doe",
 	Email:     "jane@test.com",
 	CreatedAt: time.Date(1980, 1, 1, 12, 0, 0, 0, time.UTC),
@@ -126,8 +126,6 @@ func BenchmarkStackField(b *testing.B) {
 }
 
 func BenchmarkMarshalerField(b *testing.B) {
-	// Expect an extra allocation here, since casting the user struct to the
-	// zap.Marshaler interface costs an alloc.
 	withBenchedLogger(b, func(log zap.Logger) {
 		log.Info("Arbitrary zap.LogMarshaler.", zap.Marshaler("user", _jane))
 	})