JNI: add test coverage to confirm assumptions about array validity

When the Java array that we hold a reference to is changed on the Java
side, then our reference continues to be valid, and references a
different object than the new array in Java.

Pick-to: 6.8
Change-Id: If8743cc1b2fabb254b9c0009f41377455719ec3e
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

tests/auto/corelib/kernel/qjniobject/testdata/src/org/qtproject/qt/android/testdata/QtJniObjectTestClass.java

@@ -43,6 +43,8 @@ public class QtJniObjectTestClass
     static char S_CHAR_VAR;
     static String S_STRING_OBJECT_VAR;
 
+    static char[] S_CHAR_ARRAY = A_STRING_OBJECT.toCharArray();
+
     // --------------------------------------------------------------------------------------------
     public static void staticVoidMethod() { return; }
     public static void staticVoidMethodWithArgs(int a, boolean b, char c) { return; }
@@ -198,6 +200,18 @@ public class QtJniObjectTestClass
     public char[] reverseCharArray(char[] array)
     { return staticReverseCharArray(array); }
 
+    // --------------------------------------------------------------------------------------------
+    public static char[] getStaticCharArray()
+    { return S_CHAR_ARRAY; }
+    public static void mutateStaticCharArray(char [] values)
+    {
+        for (int i = 0; i < values.length; ++i) {
+            S_CHAR_ARRAY[i] = values[i];
+        }
+    }
+    public static void replaceStaticCharArray(char[] array)
+    { S_CHAR_ARRAY = array; }
+
     // --------------------------------------------------------------------------------------------
     public static short[] staticShortArrayMethod() { short[] array = { 3, 2, 1 }; return array; }
     public short[] shortArrayMethod() { return staticShortArrayMethod(); }

tests/auto/corelib/kernel/qjniobject/tst_qjniobject.cpp

@@ -116,6 +116,7 @@ private slots:
     void isClassAvailable();
     void fromLocalRef();
     void largeObjectArray();
+    void arrayLifetime();
 
     void callback_data();
     void callback();
@@ -1884,6 +1885,42 @@ void tst_QJniObject::largeObjectArray()
     }
 }
 
+void tst_QJniObject::arrayLifetime()
+{
+    const auto stringData = A_STRING_OBJECT();
+
+    QJniArray oldChars = TestClass::callStaticMethod<jchar[]>("getStaticCharArray");
+    QVERIFY(oldChars.isValid());
+    QCOMPARE(oldChars.size(), stringData.size());
+    QCOMPARE(QChar(oldChars.toContainer().at(0)), stringData.at(0));
+
+    QJniArray<jchar> newChars{'a', 'b', 'c'};
+    // replace the first three characters in the array
+    TestClass::callStaticMethod<void>("mutateStaticCharArray", newChars);
+    // the old jcharArray is still valid and the size is unchanged
+    QVERIFY(oldChars.isValid());
+    QCOMPARE(oldChars.size(), A_STRING_OBJECT().size());
+    QCOMPARE(oldChars.toContainer().at(0), jchar('a'));
+
+    // get a second reference to the Java array
+    QJniArray updatedChars = TestClass::getStaticField<jchar[]>("S_CHAR_ARRAY");
+    // the two QJniArrays reference the same jobject
+    QCOMPARE(updatedChars.size(), oldChars.size());
+    QCOMPARE(updatedChars, oldChars);
+
+    // replace the Java array; the old jcharArray is still valid and unchanged
+    TestClass::callStaticMethod<void>("replaceStaticCharArray", newChars);
+    // the old jcharArray is still valid and unchanged
+    QVERIFY(oldChars.isValid());
+    QCOMPARE(oldChars.size(), stringData.size());
+    QCOMPARE(oldChars, updatedChars);
+
+    // we get the same object that we set
+    updatedChars = TestClass::getStaticField<jchar[]>("S_CHAR_ARRAY");
+    QCOMPARE(updatedChars, newChars);
+    QCOMPARE_NE(updatedChars, oldChars);
+}
+
 enum class CallbackParameterType
 {
     Object,