log/slog - Array of Errors as Contextual Parameter prints empty objects - JsonHandler

[SKumarSpace]

What version of Go are you using (go version)?

$ go version
go version go1.21.3 windows/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\Shrey\AppData\Local\go-build
set GOENV=C:\Users\Shrey\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\Shrey\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\Shrey\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=C:\Program Files\Go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLCHAIN=auto
set GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.21.3
set GCCGO=gccgo
set GOAMD64=v1
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=NUL
set GOWORK=
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=C:\Users\Shrey\AppData\Local\Temp\go-build232294602=/tmp/go-build -gno-record-gcc-switches

What did you do?

I'm trying to log an array of errors. When I use slog and pass the errors array as a contextual attribute, it prints an empty object.
If I convert the errors to a string array, it works as expected.

It only prints empty objects when using slog.NewJSONHandler.
slog.NewTextHandler works fine

https://go.dev/play/p/EXC2lftUuSq

package main

import (
	"fmt"
	"log/slog"
	"os"
)

func main() {
	slogger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
	slog.SetDefault(slogger)

	testErrors := []error{
		fmt.Errorf("test error 1"),
		fmt.Errorf("test error 2"),
		fmt.Errorf("test error 3"),
	}

	slog.Warn("This does not work", "errors", testErrors)
	//slog.Warn("This does", "errors", ToStringArray(testErrors)) // This works as intended as it's a string array
}

func ToStringArray(errs []error) []string {
	var errStrings []string
	for _, err := range errs {
		errStrings = append(errStrings, err.Error())
	}

	return errStrings
}

What did you expect to see?

{"time":"2009-11-10T23:00:00Z","level":"WARN","msg":"This does not work","errors":["test error 1","test error 2","test error 3"]}

What did you see instead?

{"time":"2009-11-10T23:00:00Z","level":"WARN","msg":"This does not work","errors":[{},{},{}]}

[callthingsoff]

func TestMarshalError(t *testing.T) {
	testErrors := []error{
		fmt.Errorf("test error 1"),
		fmt.Errorf("test error 2"),
		fmt.Errorf("test error 3"),
	}
	x, e := json.Marshal(testErrors)
	fmt.Println(string(x), e)
}

[{},{},{}] <nil>

Maybe it’s related to the json package.

[aimuz]

rel: #5161

[seankhliao]

see above