WIP

❯  go test -bench BenchmarkAnyInGoroutine -benchmem -run Any   -test.cpuprofile ~/cpuprof

goos: darwin
goarch: arm64
pkg: go.uber.org/zap
BenchmarkAnyInGoroutine1/int-in-goroutine-with-stack-12                  3125690               376.5 ns/op            88 B/op          2 allocs/op
BenchmarkAnyInGoroutine1/any-in-goroutine-with-stack-12                  1763952               665.0 ns/op            88 B/op          2 allocs/op
BenchmarkAnyInGoroutine1/any-int-in-goroutine-with-stack-12              2904816               398.3 ns/op            88 B/op          2 allocs/op
BenchmarkAnyInGoroutine1/any-12                                          4141492               289.2 ns/op            64 B/op          1 allocs/op
BenchmarkAnyInGoroutine1/int-12                                          4395013               274.5 ns/op            64 B/op          1 allocs/op
BenchmarkAnyInGoroutine1/goroutine-12                                    5005946               217.9 ns/op             0 B/op          0 allocs/op
BenchmarkAnyInGoroutine1/int-in-goroutine-12                             2079958               594.9 ns/op            88 B/op          2 allocs/op
BenchmarkAnyInGoroutine1/any-in-goroutine-12                             1773802               649.9 ns/op            88 B/op          2 allocs/op

field.go

@@ -547,3 +547,13 @@ func Any(key string, value interface{}) Field {
 		return Reflect(key, val)
 	}
 }
+
+// AnyInt is a dummified version of Any that can handle ints.
+func AnyInt(key string, value interface{}) Field {
+	switch val := value.(type) {
+	case int:
+		return Int(key, val)
+	default:
+		return Reflect(key, val)
+	}
+}

logger_bench_test.go

@@ -22,6 +22,7 @@ package zap
 
 import (
 	"errors"
+	"sync"
 	"testing"
 	"time"
 
@@ -238,3 +239,112 @@ func Benchmark100Fields(b *testing.B) {
 		logger.With(first...).Info("Child loggers with lots of context.", second...)
 	}
 }
+
+func dummy(wg *sync.WaitGroup, s string, i int) string {
+	if i == 0 {
+		wg.Wait()
+		return "1" + s
+	}
+	return dummy(wg, s, i-1)
+}
+
+func stackGrower(n int) *sync.WaitGroup {
+	wg := sync.WaitGroup{}
+	wg.Add(1)
+
+	go dummy(&wg, "hi", n)
+	return &wg
+}
+
+func BenchmarkAnyInGoroutine1(b *testing.B) {
+	logger := New(
+		zapcore.NewCore(
+			zapcore.NewJSONEncoder(NewProductionConfig().EncoderConfig),
+			&ztest.Discarder{},
+			DebugLevel,
+		),
+	)
+
+	b.Run("int-in-goroutine-with-stack", func(b *testing.B) {
+		wg := sync.WaitGroup{}
+		wg.Add(b.N)
+		defer stackGrower(1000).Done()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			go func() {
+				logger.Info("", Int("one", 1))
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+		b.StopTimer()
+	})
+	b.Run("any-in-goroutine-with-stack", func(b *testing.B) {
+		wg := sync.WaitGroup{}
+		wg.Add(b.N)
+		defer stackGrower(1000).Done()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			go func() {
+				logger.Info("", Any("one", 1))
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+		b.StopTimer()
+	})
+	b.Run("any-int-in-goroutine-with-stack", func(b *testing.B) {
+		wg := sync.WaitGroup{}
+		wg.Add(b.N)
+		defer stackGrower(1000).Done()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			go func() {
+				logger.Info("", AnyInt("one", 1))
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+		b.StopTimer()
+	})
+	b.Run("any", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			logger.Info("", Any("one", 1))
+		}
+	})
+	b.Run("int", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			logger.Info("", Int("one", 1))
+		}
+	})
+	b.Run("goroutine", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			go func() {}()
+		}
+	})
+	b.Run("int-in-goroutine", func(b *testing.B) {
+		wg := sync.WaitGroup{}
+		wg.Add(b.N)
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			go func() {
+				logger.Info("", Int("one", 1))
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+	})
+	b.Run("any-in-goroutine", func(b *testing.B) {
+		wg := sync.WaitGroup{}
+		wg.Add(b.N)
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			go func() {
+				logger.Info("", Any("one", 1))
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+		b.StopTimer()
+	})
+}