Add runtime warnings

route/rule_package_name.go

@@ -4,6 +4,13 @@ import (
 	"strings"
 
 	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing-box/common/warning"
+	C "github.com/sagernet/sing-box/constant"
+)
+
+var warnPackageNameOnNonAndroid = warning.New(
+	func() bool { return !C.IsAndroid },
+	"rule item `package_name` is only supported on Android",
 )
 
 var _ RuleItem = (*PackageNameItem)(nil)
@@ -14,6 +21,7 @@ type PackageNameItem struct {
 }
 
 func NewPackageNameItem(packageNameList []string) *PackageNameItem {
+	warnPackageNameOnNonAndroid.Check()
 	rule := &PackageNameItem{
 		packageNames: packageNameList,
 		packageMap:   make(map[string]bool),