Add runtime warnings

route/rule_user_id.go

@@ -4,9 +4,16 @@ import (
 	"strings"
 
 	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing-box/common/warning"
+	C "github.com/sagernet/sing-box/constant"
 	F "github.com/sagernet/sing/common/format"
 )
 
+var warnUserIDOnNonLinux = warning.New(
+	func() bool { return !C.IsLinux },
+	"rule item `user_id` is only supported on Linux",
+)
+
 var _ RuleItem = (*UserIdItem)(nil)
 
 type UserIdItem struct {
@@ -15,6 +22,7 @@ type UserIdItem struct {
 }
 
 func NewUserIDItem(userIdList []int32) *UserIdItem {
+	warnUserIDOnNonLinux.Check()
 	rule := &UserIdItem{
 		userIds:   userIdList,
 		userIdMap: make(map[int32]bool),