QJniArray: add deduction guide for direct construction from container

That way,

QList list{1, 2, 3};
QJniArray array(list);

works.

Change-Id: If04f8115c51fce533cb4287bf36841ff0daeb11b
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit f199d4f78d528f7a70170d2469ae4807e4a5e765)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qjniarray.h

@@ -363,6 +363,13 @@ public:
     }
 };
 
+// Deduction guide so that we can construct as 'QJniArray list(Container<T>)'. Since
+// fromContainer() maps several C++ types to the same JNI type (e.g. both jboolean and
+// bool become QJniArray<jboolean>), we have to deduce to what fromContainer() would
+// give us.
+template <typename Container, QJniArrayBase::if_contiguous_container<Container> = true>
+QJniArray(Container) -> QJniArray<typename decltype(QJniArrayBase::fromContainer(std::declval<Container>()))::value_type>;
+
 template <typename ElementType, typename List, typename NewFn, typename SetFn>
 auto QJniArrayBase::makeArray(List &&list, NewFn &&newArray, SetFn &&setRegion)
 {

tests/auto/corelib/kernel/qjniarray/tst_qjniarray.cpp

@@ -81,6 +81,7 @@ VERIFY_RETURN_FOR_TYPE(QJniArray<List>, QJniArray<List>);
 
 void tst_QJniArray::construct()
 {
+    // explicit
     {
         QStringList strings;
         for (int i = 0; i < 10000; ++i)
@@ -89,13 +90,36 @@ void tst_QJniArray::construct()
         QCOMPARE(list.size(), 10000);
     }
     {
-        QJniArray<jint> list{1, 2, 3};
+        QJniArray bytes = QJniArrayBase::fromContainer(QByteArray("abc"));
+        static_assert(std::is_same_v<decltype(bytes)::value_type, jbyte>);
+        QCOMPARE(bytes.size(), 3);
+    }
+    {
+        QJniArray list{1, 2, 3};
+        static_assert(std::is_same_v<decltype(list), QJniArray<int>>);
         QCOMPARE(list.size(), 3);
+        list = {4, 5};
+        QCOMPARE(list.size(), 2);
     }
     {
         QJniArray<jint> list(QList<int>{1, 2, 3});
         QCOMPARE(list.size(), 3);
     }
+    // CTAD with deduction guide
+    {
+        QJniArray list(QList<int>{1, 2, 3});
+        QCOMPARE(list.size(), 3);
+    }
+    {
+        QJniArray bytes(QByteArray("abc"));
+        static_assert(std::is_same_v<decltype(bytes)::value_type, jbyte>);
+        QCOMPARE(bytes.size(), 3);
+    }
+    {
+        QStringList strings{"a", "b", "c"};
+        QJniArray list(strings);
+        QCOMPARE(list.size(), 3);
+    }
     {
         QJniArray<jint> list{QList<int>{1, 2, 3}};
         QCOMPARE(list.size(), 3);
@@ -110,7 +134,7 @@ void tst_QJniArray::size()
 
     QList<int> intList;
     intList.resize(10);
-    auto intArray = QJniArrayBase::fromContainer(intList);
+    auto intArray = QJniArray(intList);
     QCOMPARE(intArray.size(), 10);
 }
 

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

@@ -1627,7 +1627,7 @@ void tst_QJniObject::templateApiCheck()
         QCOMPARE(array.size(), 3);
         QCOMPARE(array.toContainer(), "abc");
 
-        QJniArray<jbyte> newArray = QJniArrayBase::fromContainer(QByteArray{"cba"});
+        QJniArray newArray = QJniArray(QByteArray{"cba"});
         QVERIFY(newArray.isValid());
         const auto reverse = testClass.callMethod<jbyte[]>("reverseByteArray", newArray);
         QVERIFY(reverse.isValid());