Demonstration of MarshalLog errors

main.go

package main

import (
	"fmt"
	"log"
	"os"

	"github.com/go-logr/logr"
	"github.com/go-logr/stdr"
	"github.com/go-logr/zapr"
	"go.uber.org/zap"
)

type testMarshler struct {
	value int
}

func (m testMarshler) MarshalLog() interface{} {
	return struct {
		Value int
	}{
		Value: m.value,
	}
}

func main() {
	stdLogr := stdr.New(log.New(os.Stdout, "", log.Default().Flags()))
	zapLogr := zapr.NewLogger(zap.NewExample())

	printLogr(stdLogr)
	printLogr(zapLogr)

}

func printLogr(l logr.Logger) {
	x := testMarshler{1}
	y := []testMarshler{{2}, {3}}
	z := map[string]testMarshler{"foo": {4}, "bar": {5}}
	a := struct{ Embed testMarshler }{Embed: testMarshler{6}}

	fmt.Println("=====================")
	l.Info("bare struct", "x", x)
	l.Info("slice", "y", y)
	l.Info("map", "z", z)
	l.Info("object", "a", a)
}

shell-output

$ go run .
=====================
2022/01/24 17:58:42 "level"=0 "msg"="bare struct" "x"={"Value":1}
2022/01/24 17:58:42 "level"=0 "msg"="slice" "y"=[{"Value":2},{"Value":3}]
2022/01/24 17:58:42 "level"=0 "msg"="map" "z"={"foo":{"Value":4},"bar":{"Value":5}}
2022/01/24 17:58:42 "level"=0 "msg"="object" "a"={"Embed":{"Value":6}}
=====================
{"level":"info","msg":"bare struct","x":{"Value":1}}
{"level":"info","msg":"slice","y":[{},{}]}
{"level":"info","msg":"map","z":{"bar":{},"foo":{}}}
{"level":"info","msg":"object","a":{"Embed":{}}}