From 58a367276cfc99d6bbaf4a14e881976c2fc2e248 Mon Sep 17 00:00:00 2001
From: junya koyama <arukiidou@yahoo.co.jp>
Date: Sun, 4 Feb 2024 23:36:53 +0900
Subject: [PATCH] zapslog: fix handler state management problems.

Signed-off-by: junya koyama <arukiidou@yahoo.co.jp>
---
 exp/zapslog/handler.go | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/exp/zapslog/handler.go b/exp/zapslog/handler.go
index 6445aca5f..6e6f491c1 100644
--- a/exp/zapslog/handler.go
+++ b/exp/zapslog/handler.go
@@ -26,6 +26,7 @@ import (
 	"context"
 	"log/slog"
 	"runtime"
+	"slices"
 
 	"go.uber.org/zap"
 	"go.uber.org/zap/internal/stacktrace"
@@ -163,15 +164,19 @@ func (h *Handler) Handle(ctx context.Context, record slog.Record) error {
 	}
 
 	fields := make([]zapcore.Field, 0, record.NumAttrs()+1)
+	var addedNamespace bool
 	record.Attrs(func(attr slog.Attr) bool {
 		f := convertAttrToField(attr)
-		if h.holdGroup != "" && f != zap.Skip() {
-			fields = append(fields, zap.Namespace(h.holdGroup))
-			h.holdGroup = ""
+		if !addedNamespace && f != zap.Skip() {
+			addedNamespace = true
 		}
 		fields = append(fields, f)
 		return true
 	})
+	if h.holdGroup != "" && addedNamespace {
+		// group is before than other fields.
+		fields = slices.Insert(fields, 0, zap.Namespace(h.holdGroup))
+	}
 
 	ce.Write(fields...)
 	return nil
@@ -181,28 +186,41 @@ func (h *Handler) Handle(ctx context.Context, record slog.Record) error {
 // both the receiver's attributes and the arguments.
 func (h *Handler) WithAttrs(attrs []slog.Attr) slog.Handler {
 	fields := make([]zapcore.Field, 0, len(attrs)+1)
+	var addedNamespace bool
 	for _, attr := range attrs {
 		f := convertAttrToField(attr)
-		if h.holdGroup != "" && f != zap.Skip() {
-			fields = append(fields, zap.Namespace(h.holdGroup))
-			h.holdGroup = ""
+		if !addedNamespace && f != zap.Skip() {
+			addedNamespace = true
 		}
 		fields = append(fields, f)
 	}
+	if h.holdGroup != "" && addedNamespace {
+		// group is before than other fields.
+		fields = slices.Insert(fields, 0, zap.Namespace(h.holdGroup))
+		return h.withFieldsAndUpdateGroup("", fields...)
+	}
 	return h.withFields(fields...)
 }
 
 // WithGroup returns a new Handler with the given group appended to
 // the receiver's existing groups.
 func (h *Handler) WithGroup(group string) slog.Handler {
-	cloned := *h
 	if h.holdGroup != "" {
-		cloned.core = h.core.With([]zapcore.Field{zap.Namespace(h.holdGroup)})
+		return h.withFieldsAndUpdateGroup(group, zap.Namespace(h.holdGroup))
 	}
+	cloned := *h
 	cloned.holdGroup = group
 	return &cloned
 }
 
+// withFieldsAndUpdateGroup returns a cloned Handler with the given fields and set new group.
+func (h *Handler) withFieldsAndUpdateGroup(newGroup string, fields ...zapcore.Field) *Handler {
+	cloned := *h
+	cloned.core = h.core.With(fields)
+	cloned.holdGroup = newGroup
+	return &cloned
+}
+
 // withFields returns a cloned Handler with the given fields.
 func (h *Handler) withFields(fields ...zapcore.Field) *Handler {
 	cloned := *h