Allow to output nested goerr logging

errors.go

@@ -205,7 +205,13 @@ func (x *Error) LogValue() slog.Value {
 	attrs = append(attrs, slog.Any("stacktrace", stacktrace))
 
 	if x.cause != nil {
-		attrs = append(attrs, slog.Any("cause", x.cause))
+		var errAttr slog.Attr
+		if lv, ok := x.cause.(slog.LogValuer); ok {
+			errAttr = slog.Any("cause", lv.LogValue())
+		} else {
+			errAttr = slog.Any("cause", x.cause)
+		}
+		attrs = append(attrs, errAttr)
 	}
 
 	return slog.GroupValue(attrs...)

test/errors_test.go

@@ -1,7 +1,9 @@
 package main_test
 
 import (
+	"bytes"
 	"fmt"
+	"log/slog"
 	"testing"
 
 	"github.com/m-mizutani/goerr"
@@ -44,7 +46,7 @@ func TestStackTrace(t *testing.T) {
 	require.Equal(t, 4, len(st))
 	assert.Equal(t, "github.com/m-mizutani/goerr/test_test.oops", st[0].Func)
 	assert.Regexp(t, `/goerr/test/errors_test\.go$`, st[0].File)
-	assert.Equal(t, 14, st[0].Line)
+	assert.Equal(t, 16, st[0].Line)
 }
 
 func TestMultileWrap(t *testing.T) {
@@ -101,3 +103,13 @@ func TestErrorString(t *testing.T) {
 	err := goerr.Wrap(goerr.Wrap(goerr.New("blue"), "orange"), "red")
 	assert.Equal(t, "red: orange: blue", err.Error())
 }
+
+func TestLoggingNestedError(t *testing.T) {
+	err1 := goerr.New("e1").With("color", "orange")
+	err2 := goerr.Wrap(err1, "e2").With("number", "five")
+	out := &bytes.Buffer{}
+	logger := slog.New(slog.NewJSONHandler(out, nil))
+	logger.Error("fail", slog.Any("error", err2))
+	assert.Contains(t, out.String(), `"number":"five"`)
+	assert.Contains(t, out.String(), `"color":"orange"`)
+}