MetaType: Fix operator{+,-}(int) with the type-erased const_iterators.

Make sure we don't modify the lhs. Instead copy it and advance the
copy.

Change-Id: I3440e8e175bfc299f8f83b816faca54fa3f79e43
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/corelib/kernel/qmetatype.h

@@ -892,6 +892,7 @@ public:
     typedef VariantData (*getFunc)( void * const *p, int metaTypeId, uint flags);
     typedef void (*destroyIterFunc)(void **p);
     typedef bool (*equalIterFunc)(void * const *p, void * const *other);
+    typedef void (*copyIterFunc)(void **, void * const *);
 
     sizeFunc _size;
     atFunc _at;
@@ -901,6 +902,7 @@ public:
     getFunc _get;
     destroyIterFunc _destroyIter;
     equalIterFunc _equalIter;
+    copyIterFunc _copyIter;
 
     template<class T>
     static int sizeImpl(const void *p)
@@ -938,6 +940,10 @@ public:
     static VariantData getImpl(void * const *iterator, int metaTypeId, uint flags)
     { return VariantData(metaTypeId, IteratorOwner<typename T::const_iterator>::getData(iterator), flags); }
 
+    template<class T>
+    static void copyIterImpl(void **dest, void * const * src)
+    { IteratorOwner<typename T::const_iterator>::assign(dest, *static_cast<typename T::const_iterator*>(*src)); }
+
 public:
     template<class T> QSequentialIterableImpl(const T*p)
       : _iterable(p)
@@ -953,6 +959,7 @@ public:
       , _get(getImpl<T>)
       , _destroyIter(destroyIterImpl<T>)
       , _equalIter(equalIterImpl<T>)
+      , _copyIter(copyIterImpl<T>)
     {
     }
 
@@ -970,6 +977,7 @@ public:
       , _get(0)
       , _destroyIter(0)
       , _equalIter(0)
+      , _copyIter(0)
     {
     }
 
@@ -990,6 +998,12 @@ public:
     int size() const { Q_ASSERT(_iterable); return _size(_iterable); }
 
     inline void destroyIter() { _destroyIter(&_iterator); }
+
+    void copy(const QSequentialIterableImpl &other)
+    {
+      *this = other;
+      _copyIter(&_iterator, &other._iterator);
+    }
 };
 
 template<typename From>
@@ -1055,6 +1069,7 @@ public:
     typedef VariantData (*getFunc)(void * const *p, int metaTypeId, uint flags);
     typedef void (*destroyIterFunc)(void **p);
     typedef bool (*equalIterFunc)(void * const *p, void * const *other);
+    typedef void (*copyIterFunc)(void **, void * const *);
 
     sizeFunc _size;
     findFunc _find;
@@ -1065,6 +1080,7 @@ public:
     getFunc _getValue;
     destroyIterFunc _destroyIter;
     equalIterFunc _equalIter;
+    copyIterFunc _copyIter;
 
     template<class T>
     static int sizeImpl(const void *p)
@@ -1104,6 +1120,10 @@ public:
     static bool equalIterImpl(void * const *iterator, void * const *other)
     { return *static_cast<typename T::const_iterator*>(*iterator) == *static_cast<typename T::const_iterator*>(*other); }
 
+    template<class T>
+    static void copyIterImpl(void **dest, void * const * src)
+    { IteratorOwner<typename T::const_iterator>::assign(dest, *static_cast<typename T::const_iterator*>(*src)); }
+
 public:
     template<class T> QAssociativeIterableImpl(const T*p)
       : _iterable(p)
@@ -1120,6 +1140,7 @@ public:
       , _getValue(getValueImpl<T>)
       , _destroyIter(destroyIterImpl<T>)
       , _equalIter(equalIterImpl<T>)
+      , _copyIter(copyIterImpl<T>)
     {
     }
 
@@ -1138,6 +1159,7 @@ public:
       , _getValue(0)
       , _destroyIter(0)
       , _equalIter(0)
+      , _copyIter(0)
     {
     }
 
@@ -1155,6 +1177,12 @@ public:
     { _find(_iterable, key.data, &_iterator); }
 
     int size() const { Q_ASSERT(_iterable); return _size(_iterable); }
+
+    void copy(const QAssociativeIterableImpl &other)
+    {
+      *this = other;
+      _copyIter(&_iterator, &other._iterator);
+    }
 };
 
 template<typename From>

src/corelib/kernel/qvariant.h

@@ -615,8 +615,8 @@ public:
         inline const_iterator operator--(int) { QtMetaTypePrivate::QSequentialIterableImpl impl = m_impl; m_impl.advance(-1); return const_iterator(impl, this->ref); }
         inline const_iterator &operator+=(int j) { m_impl.advance(j); return *this; }
         inline const_iterator &operator-=(int j) { m_impl.advance(-j); return *this; }
-        inline const_iterator operator+(int j) const { QtMetaTypePrivate::QSequentialIterableImpl impl = m_impl; impl.advance(j); return const_iterator(impl, this->ref);  }
+        inline const_iterator operator+(int j) const { QtMetaTypePrivate::QSequentialIterableImpl impl; impl.copy(m_impl); impl.advance(j); return const_iterator(impl, new QAtomicInt(0));  }
-        inline const_iterator operator-(int j) const { QtMetaTypePrivate::QSequentialIterableImpl impl = m_impl; impl.advance(-j); return const_iterator(impl, this->ref);  }
+        inline const_iterator operator-(int j) const { QtMetaTypePrivate::QSequentialIterableImpl impl; impl.copy(m_impl); impl.advance(-j); return const_iterator(impl, new QAtomicInt(0));  }
     };
 
     friend struct const_iterator;
@@ -700,8 +700,8 @@ public:
         inline const_iterator operator--(int) { QtMetaTypePrivate::QAssociativeIterableImpl impl = m_impl; m_impl.advance(-1); return const_iterator(impl, this->ref); }
         inline const_iterator &operator+=(int j) { m_impl.advance(j); return *this; }
         inline const_iterator &operator-=(int j) { m_impl.advance(-j); return *this; }
-        inline const_iterator operator+(int j) const { QtMetaTypePrivate::QAssociativeIterableImpl impl = m_impl; impl.advance(j); return const_iterator(impl, this->ref);  }
+        inline const_iterator operator+(int j) const { QtMetaTypePrivate::QAssociativeIterableImpl impl; impl.copy(m_impl); impl.advance(j); return const_iterator(impl, new QAtomicInt(0));  }
-        inline const_iterator operator-(int j) const { QtMetaTypePrivate::QAssociativeIterableImpl impl = m_impl; impl.advance(-j); return const_iterator(impl, this->ref);  }
+        inline const_iterator operator-(int j) const { QtMetaTypePrivate::QAssociativeIterableImpl impl; impl.copy(m_impl); impl.advance(-j); return const_iterator(impl, new QAtomicInt(0));  }
     };
 
     friend struct const_iterator;

tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp

@@ -3818,6 +3818,20 @@ void tst_QVariant::iterateContainerElements()
     TEST_SEQUENTIAL_ITERATION(std::forward_list, QString)
 #endif
 
+    {
+        QVariantList ints;
+        ints << 1 << 2 << 3;
+        QVariant var = QVariant::fromValue(ints);
+        QSequentialIterable iter = var.value<QSequentialIterable>();
+        QSequentialIterable::const_iterator it = iter.begin();
+        QSequentialIterable::const_iterator end = iter.end();
+        QCOMPARE(ints.at(1), *(it + 1));
+        int i = 0;
+        for ( ; it != end; ++it, ++i) {
+            QCOMPARE(ints.at(i), *it);
+        }
+    }
+
 #define TEST_ASSOCIATIVE_ITERATION(CONTAINER, KEY_TYPE, MAPPED_TYPE) \
     { \
         int numSeen = 0; \
@@ -3852,6 +3866,22 @@ void tst_QVariant::iterateContainerElements()
 #ifdef TEST_UNORDERED_MAP
     TEST_ASSOCIATIVE_ITERATION(std::unordered_map, int, bool)
 #endif
+
+    {
+        QMap<int, QString> mapping;
+        mapping.insert(1, "one");
+        mapping.insert(2, "two");
+        mapping.insert(3, "three");
+        QVariant var = QVariant::fromValue(mapping);
+        QAssociativeIterable iter = var.value<QAssociativeIterable>();
+        QAssociativeIterable::const_iterator it = iter.begin();
+        QAssociativeIterable::const_iterator end = iter.end();
+        QCOMPARE(*(mapping.begin() + 1), (*(it + 1)).toString());
+        int i = 0;
+        for ( ; it != end; ++it, ++i) {
+            QCOMPARE(*(mapping.begin() + i), (*it).toString());
+        }
+    }
 }
 
 void tst_QVariant::pairElements()