JNI: Fix native functions that take a declared QtJniTypes class

Now that QtJniTypes::Objects are no longer primitive types that are the
same as a jobject, using those types in registered native functions
breaks. JNI will call those function with a jobject on the function
pointer, and lacking any type safety, the call to the registered
function will proceed with a wrong type of object on the stack.

To fix that, register the native function via a proxy that is a variadic
argument function, and unpack the variadic arguments into a list of
typed arguments, using the types we know the user-code function wants.
Then call the function with a tuple of those types using std::apply,
which gives us type safety and implicit conversion for free.

Add a test that exercises this.

Change-Id: I9f980e55d3d13f8fc16c410dc0d17dbdc200cb47
Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>

3 files changed, 63 insertions, 6 deletions

diff --git a/tests/auto/corelib/kernel/qjniobject/testdata/src/org/qtproject/qt/android/testdata/QtJniObjectTestClass.java b/tests/auto/corelib/kernel/qjniobject/testdata/src/org/qtproject/qt/android/testdata/QtJniObjectTestClass.java
index dc55ad0f89..813aaf2bbf 100644
--- a/tests/auto/corelib/kernel/qjniobject/testdata/src/org/qtproject/qt/android/testdata/QtJniObjectTestClass.java
+++ b/tests/auto/corelib/kernel/qjniobject/testdata/src/org/qtproject/qt/android/testdata/QtJniObjectTestClass.java
@@ -170,5 +170,12 @@ public class QtJniObjectTestClass
     public static double[] staticDoubleArrayMethod()
     { double[] array = { 3.0, 2.0, 1.0 }; return array; }
     public double[] doubleArrayMethod() { return staticDoubleArrayMethod(); }
-}
 
+    // --------------------------------------------------------------------------------------------
+    native public int callbackWithObject(QtJniObjectTestClass that);
+
+    public int callMeBackWithObject(QtJniObjectTestClass that)
+    {
+        return callbackWithObject(that);
+    }
+}
diff --git a/tests/auto/corelib/kernel/qjniobject/tst_qjniobject.cpp b/tests/auto/corelib/kernel/qjniobject/tst_qjniobject.cpp
index 49a814f122..65c9680d4e 100644
--- a/tests/auto/corelib/kernel/qjniobject/tst_qjniobject.cpp
+++ b/tests/auto/corelib/kernel/qjniobject/tst_qjniobject.cpp
@@ -10,7 +10,7 @@
 
 using namespace Qt::StringLiterals;
 
-static const char testClassName[] = "org/qtproject/qt/android/testdatapackage/QtJniObjectTestClass";
+static constexpr const char testClassName[] = "org/qtproject/qt/android/testdatapackage/QtJniObjectTestClass";
 Q_DECLARE_JNI_CLASS(QtJniObjectTestClass, testClassName)
 using TestClass = QtJniTypes::QtJniObjectTestClass;
 
@@ -113,6 +113,8 @@ private slots:
     void isClassAvailable();
     void fromLocalRef();
 
+    void callback();
+
     void cleanupTestCase();
 };
 
@@ -1664,6 +1666,31 @@ void tst_QJniObject::fromLocalRef()
         QJniObject o = QJniObject::fromLocalRef(env->FindClass("java/lang/String"));
 }
 
+
+static std::optional<TestClass> calledWithObject;
+static int callbackWithObject(JNIEnv *env, jobject thiz, TestClass that)
+{
+    Q_UNUSED(env);
+    Q_UNUSED(thiz);
+    calledWithObject.emplace(that);
+    return 42;
+}
+
+Q_DECLARE_JNI_NATIVE_METHOD(callbackWithObject)
+
+void tst_QJniObject::callback()
+{
+    TestClass testObject;
+    QJniEnvironment env;
+    QVERIFY(env.registerNativeMethods(testObject.objectClass(), {
+        Q_JNI_NATIVE_METHOD(callbackWithObject)
+    }));
+    int result = testObject.callMethod<int>("callMeBackWithObject", testObject);
+    QVERIFY(calledWithObject);
+    QVERIFY(calledWithObject.value() == testObject);
+    QCOMPARE(result, 42);
+}
+
 QTEST_MAIN(tst_QJniObject)
 
 #include "tst_qjniobject.moc"
diff --git a/tests/auto/corelib/kernel/qjnitypes/tst_qjnitypes.cpp b/tests/auto/corelib/kernel/qjnitypes/tst_qjnitypes.cpp
index 0ce2295092..a499b6f2d2 100644
--- a/tests/auto/corelib/kernel/qjnitypes/tst_qjnitypes.cpp
+++ b/tests/auto/corelib/kernel/qjnitypes/tst_qjnitypes.cpp
@@ -14,6 +14,9 @@ class tst_QJniTypes : public QObject
 public:
     tst_QJniTypes() = default;
 
+    static void nativeClassMethod(JNIEnv *, jclass, int);
+    Q_DECLARE_JNI_NATIVE_METHOD_IN_CURRENT_SCOPE(nativeClassMethod);
+
 private slots:
     void initTestCase();
     void nativeMethod();
@@ -154,12 +157,32 @@ Q_DECLARE_JNI_NATIVE_METHOD(nativeFunction)
 
 static_assert(QtJniTypes::nativeMethodSignature(nativeFunction) == "(ILjava/lang/String;J)Z");
 
+static int forwardDeclaredNativeFunction(JNIEnv *, jobject, bool);
+Q_DECLARE_JNI_NATIVE_METHOD(forwardDeclaredNativeFunction)
+static int forwardDeclaredNativeFunction(JNIEnv *, jobject, bool) { return 0; }
+static_assert(QtJniTypes::nativeMethodSignature(forwardDeclaredNativeFunction) == "(Z)I");
+
+static_assert(QtJniTypes::nativeMethodSignature(tst_QJniTypes::nativeClassMethod) == "(I)V");
+void tst_QJniTypes::nativeClassMethod(JNIEnv *, jclass, int) {}
+
 void tst_QJniTypes::nativeMethod()
 {
-    const auto method = Q_JNI_NATIVE_METHOD(nativeFunction);
-    QVERIFY(method.fnPtr == nativeFunction);
-    QCOMPARE(method.name, "nativeFunction");
-    QCOMPARE(method.signature, "(ILjava/lang/String;J)Z");
+    {
+        const auto method = Q_JNI_NATIVE_METHOD(nativeFunction);
+        QVERIFY(method.fnPtr == QtJniMethods::va_nativeFunction);
+        QCOMPARE(method.name, "nativeFunction");
+        QCOMPARE(method.signature, "(ILjava/lang/String;J)Z");
+    }
+
+    {
+        const auto method = Q_JNI_NATIVE_METHOD(forwardDeclaredNativeFunction);
+        QVERIFY(method.fnPtr == QtJniMethods::va_forwardDeclaredNativeFunction);
+    }
+
+    {
+        const auto method = Q_JNI_NATIVE_SCOPED_METHOD(nativeClassMethod, tst_QJniTypes);
+        QVERIFY(method.fnPtr == va_nativeClassMethod);
+    }
 }
 
 void tst_QJniTypes::construct()