QJniArray: add arithmetic operators

Required for making the iterator random access.

Based on review comments.

Task-number: QTBUG-126150
Change-Id: I80ee8ed584747759acb17ee956551caba4d5bdaa
Reviewed-by: Soheil Armin <soheil.armin@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit c4e406e3792405cfc0b8cc97a29f136c0fd44a2e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qjniarray.h

@@ -48,23 +48,54 @@ struct QJniArrayIterator
         ++that.m_index;
         return that;
     }
-    friend QJniArrayIterator operator++(QJniArrayIterator &that, int) noexcept
+    friend QJniArrayIterator operator++(QJniArrayIterator &that, difference_type) noexcept
     {
         auto copy = that;
         ++that;
         return copy;
     }
+    friend QJniArrayIterator operator+(const QJniArrayIterator &that, difference_type n) noexcept
+    {
+        return {that.m_index + n, that.m_array};
+    }
+    friend QJniArrayIterator operator+(difference_type n, const QJniArrayIterator &that) noexcept
+    {
+        return that + n;
+    }
+    friend QJniArrayIterator &operator+=(QJniArrayIterator &that, difference_type n) noexcept
+    {
+        that.m_index += n;
+        return that;
+    }
     friend QJniArrayIterator &operator--(QJniArrayIterator &that) noexcept
     {
         --that.m_index;
         return that;
     }
-    friend QJniArrayIterator operator--(QJniArrayIterator &that, int) noexcept
+    friend QJniArrayIterator operator--(QJniArrayIterator &that, difference_type) noexcept
     {
         auto copy = that;
         --that;
         return copy;
     }
+    friend QJniArrayIterator operator-(const QJniArrayIterator &that, difference_type n) noexcept
+    {
+        return {that.m_index - n, that.m_array};
+    }
+    friend QJniArrayIterator operator-(difference_type n, const QJniArrayIterator &that) noexcept
+    {
+        return {n - that.m_index, that.m_array};
+    }
+    friend QJniArrayIterator &operator-=(QJniArrayIterator &that, difference_type n) noexcept
+    {
+        that.m_index -= n;
+        return that;
+    }
+    friend difference_type operator-(const QJniArrayIterator &lhs, const QJniArrayIterator &rhs)
+    {
+        Q_ASSERT(lhs.m_array == rhs.m_array);
+        return lhs.m_index - rhs.m_index;
+    }
     void swap(QJniArrayIterator &other) noexcept
     {
         std::swap(m_index, other.m_index);

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

@@ -234,6 +234,23 @@ void tst_QJniArray::operators()
         it++;
         QCOMPARE(*it, 'e');
         QCOMPARE(++it, array.end());
+
+        it -= array.size();
+        QCOMPARE(it, array.begin());
+        it += 2;
+        QCOMPARE(*it, 'c');
+
+        const auto it2 = it + 2;
+        QCOMPARE(*it2, 'e');
+        QCOMPARE(it2 - it, 2);
+
+        it = it2 - 2;
+        QCOMPARE(*it, 'c');
+
+        it = 1 + it;
+        QCOMPARE(*it, 'd');
+        it = array.size() - it;
+        QCOMPARE(*it, 'c');
     }
     {
         auto it = array.rbegin();