JNI: don't inherit declared types from JObject

JObjectBase has a protected destructor, but JObject doesn't, so
inheriting from it might result in UB. Declare the Type as an alias to
JObject<TypeTag> instead. Specialize the traits for the TypeTag, and
add a partial specialization of the traits for JObject<T>.

Adjust the return type of the named constructors of JObject.

Pick-to: 6.8
Change-Id: Ibe74c3cd3b3a2a81779117dd2d228684c365a845
Reviewed-by: Assam Boudjelthia <[email protected]>

2 files changed, 22 insertions, 10 deletions

diff --git a/src/corelib/kernel/qjniobject.h b/src/corelib/kernel/qjniobject.h
index af6c54e5aac..45f84afd0d6 100644
--- a/src/corelib/kernel/qjniobject.h
+++ b/src/corelib/kernel/qjniobject.h
@@ -720,7 +720,7 @@ public:
     ~JObject() = default;
 
     template<typename Arg, typename ...Args
-            , std::enable_if_t<!std::is_same_v<Arg, JObject>, bool> = true
+            , std::enable_if_t<!std::is_same_v<q20::remove_cvref_t<Arg>, JObject>, bool> = true
             , IfValidSignatureTypes<Arg, Args...> = true
     >
     explicit JObject(Arg && arg, Args &&...args)
@@ -729,10 +729,19 @@ public:
     {}
 
     // named constructors avoid ambiguities
-    static Type fromJObject(jobject object) { return Type(object); }
+    static JObject fromJObject(jobject object)
+    {
+        return JObject(object);
+    }
     template <typename ...Args>
-    static Type construct(Args &&...args) { return Type(std::forward<Args>(args)...); }
-    static Type fromLocalRef(jobject lref) { return Type(QJniObject::fromLocalRef(lref)); }
+    static JObject construct(Args &&...args)
+    {
+        return JObject(std::forward<Args>(args)...);
+    }
+    static JObject fromLocalRef(jobject lref)
+    {
+        return JObject(QJniObject::fromLocalRef(lref));
+    }
 
     static bool registerNativeMethods(std::initializer_list<JNINativeMethod> methods)
     {
@@ -809,6 +818,11 @@ private:
     { return lhs.m_object == rhs.m_object; }
     Q_DECLARE_EQUALITY_COMPARABLE_LITERAL_TYPE(JObject);
 };
+
+template <typename T> struct Traits<JObject<T>> {
+    static constexpr auto signature() { return Traits<T>::signature(); }
+    static constexpr auto className() { return Traits<T>::className(); }
+};
 }
 
 // This cannot be included earlier as QJniArray is a QJniObject subclass, but it
diff --git a/src/corelib/kernel/qjnitypes.h b/src/corelib/kernel/qjnitypes.h
index 033445be6a7..5ad63badcd9 100644
--- a/src/corelib/kernel/qjnitypes.h
+++ b/src/corelib/kernel/qjnitypes.h
@@ -14,17 +14,15 @@ QT_BEGIN_NAMESPACE
 // QT_TECH_PREVIEW_API
 #define Q_DECLARE_JNI_TYPE_HELPER(Type)                         \
 namespace QtJniTypes {                                          \
-struct Type : JObject<Type>                                     \
-{                                                               \
-    using JObject::JObject;                                     \
-};                                                              \
+struct Type##Tag { explicit Type##Tag() = default; };           \
+using Type = JObject<Type##Tag>;                                \
 }                                                               \
 
 // QT_TECH_PREVIEW_API
 #define Q_DECLARE_JNI_TYPE(Type, Signature)                     \
 Q_DECLARE_JNI_TYPE_HELPER(Type)                                 \
 template<>                                                      \
-struct QtJniTypes::Traits<QtJniTypes::Type> {                   \
+struct QtJniTypes::Traits<QtJniTypes::Type##Tag> {              \
     static constexpr auto signature()                           \
     {                                                           \
         constexpr QtJniTypes::CTString sig(Signature);          \
@@ -39,7 +37,7 @@ struct QtJniTypes::Traits<QtJniTypes::Type> {                   \
 #define Q_DECLARE_JNI_CLASS(Type, Signature)                    \
 Q_DECLARE_JNI_TYPE_HELPER(Type)                                 \
 template<>                                                      \
-struct QtJniTypes::Traits<QtJniTypes::Type> {                   \
+struct QtJniTypes::Traits<QtJniTypes::Type##Tag> {              \
     static constexpr auto className()                           \
     {                                                           \
         return QtJniTypes::CTString(Signature);                 \