QJniArray: make reverse-iterable

Add rbeing/rend overload, relevant typedefs, and decrement operators.
As a drive-by, add noexcept to begin/end functions.

Found during header review.

Pick-to: 6.7
Task-number: QTBUG-119952
Change-Id: I32d9a7d50a1f03550944c2247516c455d4822fe7
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/corelib/kernel/qjniarray.h

@@ -31,7 +31,7 @@ struct QJniArrayIterator
     using pointer = T *;
     using reference = T; // difference to container requirements
     using const_reference = reference;
-    using iterator_category = std::forward_iterator_tag;
+    using iterator_category = std::bidirectional_iterator_tag;
 
     friend bool operator==(const QJniArrayIterator &lhs, const QJniArrayIterator &rhs) noexcept
     {
@@ -56,7 +56,17 @@ struct QJniArrayIterator
         ++that;
         return copy;
     }
-
+    friend QJniArrayIterator &operator--(QJniArrayIterator &that) noexcept
+    {
+        --that.m_index;
+        return that;
+    }
+    friend QJniArrayIterator operator--(QJniArrayIterator &that, int) noexcept
+    {
+        auto copy = that;
+        --that;
+        return copy;
+    }
     void swap(QJniArrayIterator &other) noexcept
     {
         std::swap(m_index, other.m_index);
@@ -178,6 +188,7 @@ public:
 
     // read-only container, so no iterator typedef
     using const_iterator = QJniArrayIterator<const T>;
+    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 
     QJniArray() = default;
     explicit QJniArray(jarray array) : QJniArrayBase(array) {}
@@ -226,12 +237,17 @@ public:
             return object<jarray>();
     }
 
-    const_iterator begin() const { return {0, this}; }
-    const_iterator constBegin() const { return begin(); }
-    const_iterator cbegin() const { return begin(); }
-    const_iterator end() const { return {size(), this}; }
-    const_iterator constEnd() const { return {end()}; }
-    const_iterator cend() const { return {end()}; }
+    const_iterator begin() const noexcept { return {0, this}; }
+    const_iterator constBegin() const noexcept { return begin(); }
+    const_iterator cbegin() const noexcept { return begin(); }
+    const_iterator end() const noexcept { return {size(), this}; }
+    const_iterator constEnd() const noexcept { return {end()}; }
+    const_iterator cend() const noexcept { return {end()}; }
+
+    const_reverse_iterator rbegin() const noexcept { return const_reverse_iterator(end()); }
+    const_reverse_iterator rend() const noexcept { return const_reverse_iterator(begin()); }
+    const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator(end()); }
+    const_reverse_iterator crend() const noexcept { return const_reverse_iterator(begin()); }
 
     const_reference operator[](size_type i) const { return at(i); }
     const_reference at(size_type i) const

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

@@ -103,6 +103,17 @@ void tst_QJniArray::operators()
         QCOMPARE(*it, 'e');
         QCOMPARE(++it, array.end());
     }
+    {
+        auto it = array.rbegin();
+        QCOMPARE(*it, 'e');
+        QCOMPARE(*++it, 'd');
+        QCOMPARE(*it++, 'd');
+        QCOMPARE(*it, 'c');
+        ++it;
+        it++;
+        QCOMPARE(*it, 'a');
+        QCOMPARE(++it, array.rend());
+    }
     {
         QJniArray<jbyte>::const_iterator it = {};
         QCOMPARE(it, QJniArray<jbyte>::const_iterator{});