QtConcurrent: prevent conversion of ReduceOption to initial value

QtConcurrent map- and filter-reduce functions take an initial value,
which can be of any type that is convertable to the result type. The
side-effect of this is that the enum values passed as ReduceOptions can
be treated as an initial value (if they are convertable to the result
type) which will result into a wrong overload call. To avoid this, added
additional check to make sure that the initial value type doesn't match
with ReduceOption enum.

Note that this required including the qtconcurrentreducekernel.h header
in qtconcurrentfunctionwrappers.h (which contains compiler checks for
QtConcurrent) for accessing ReduceOption enum, so I had to get rid of
qtconcurrentfunctionwrappers.h include from qtconcurrentreducekernel.h
to avoid circular header includes. This, in turn, required moving the
QtPrivate::SequenceHolder helper type to qtconcurrentreducekernel.h,
which didn't belong to qtconcurrentfunctionwrappers.h anyway.

Pick-to: 6.3 6.2
Fixes: QTBUG-102999
Change-Id: Ieaa8ef2e4bd82ce2ada2e0af9a47b87b51d59e87
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

4 files changed, 81 insertions, 41 deletions

diff --git a/src/concurrent/qtconcurrentfilter.h b/src/concurrent/qtconcurrentfilter.h
index 86e9a531d2..e35c445b94 100644
--- a/src/concurrent/qtconcurrentfilter.h
+++ b/src/concurrent/qtconcurrentfilter.h
@@ -73,7 +73,8 @@ template <typename ResultType, typename Sequence, typename KeepFunctor, typename
 #else
 template <typename ResultType, typename Sequence, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> filteredReduced(QThreadPool *pool,
                                     Sequence &&sequence,
@@ -95,7 +96,8 @@ template <typename ResultType, typename Sequence, typename KeepFunctor, typename
 #else
 template <typename ResultType, typename Sequence, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> filteredReduced(Sequence &&sequence,
                                     KeepFunctor &&keep,
@@ -144,7 +146,8 @@ template <typename Sequence, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
           std::enable_if_t<QtPrivate::isInvocable<KeepFunctor, Sequence>::value, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 QFuture<ResultType> filteredReduced(QThreadPool *pool,
                                     Sequence &&sequence,
                                     KeepFunctor &&keep,
@@ -163,7 +166,8 @@ template <typename Sequence, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
           std::enable_if_t<QtPrivate::isInvocable<KeepFunctor, Sequence>::value, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 QFuture<ResultType> filteredReduced(Sequence &&sequence,
                                     KeepFunctor &&keep,
                                     ReduceFunctor &&reduce,
@@ -211,7 +215,8 @@ template <typename ResultType, typename Iterator, typename KeepFunctor, typename
 #else
 template <typename ResultType, typename Iterator, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> filteredReduced(QThreadPool *pool,
                                     Iterator begin,
@@ -233,7 +238,8 @@ template <typename ResultType, typename Iterator, typename KeepFunctor, typename
 #else
 template <typename ResultType, typename Iterator, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> filteredReduced(Iterator begin,
                                     Iterator end,
@@ -281,7 +287,8 @@ QFuture<ResultType> filteredReduced(Iterator begin,
 template <typename Iterator, typename KeepFunctor, typename ReduceFunctor,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 QFuture<ResultType> filteredReduced(QThreadPool *pool,
                                     Iterator begin,
                                     Iterator end,
@@ -300,7 +307,8 @@ template <typename Iterator, typename KeepFunctor, typename ReduceFunctor,
           std::enable_if_t<QtPrivate::isIterator_v<Iterator>, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 QFuture<ResultType> filteredReduced(Iterator begin,
                                     Iterator end,
                                     KeepFunctor &&keep,
@@ -400,7 +408,8 @@ template <typename ResultType, typename Sequence, typename KeepFunctor, typename
 #else
 template <typename ResultType, typename Sequence, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingFilteredReduced(QThreadPool *pool,
                                    Sequence &&sequence,
@@ -423,7 +432,8 @@ template <typename ResultType, typename Sequence, typename KeepFunctor, typename
 #else
 template <typename ResultType, typename Sequence, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingFilteredReduced(Sequence &&sequence,
                                    KeepFunctor &&keep,
@@ -475,7 +485,8 @@ template <typename Sequence, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
           std::enable_if_t<QtPrivate::isInvocable<KeepFunctor, Sequence>::value, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 ResultType blockingFilteredReduced(QThreadPool *pool,
                                    Sequence &&sequence,
                                    KeepFunctor &&keep,
@@ -495,7 +506,8 @@ template <typename Sequence, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
           std::enable_if_t<QtPrivate::isInvocable<KeepFunctor, Sequence>::value, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 ResultType blockingFilteredReduced(Sequence &&sequence,
                                    KeepFunctor &&keep,
                                    ReduceFunctor &&reduce,
@@ -547,7 +559,8 @@ template <typename ResultType, typename Iterator, typename KeepFunctor, typename
 #else
 template <typename ResultType, typename Iterator, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingFilteredReduced(QThreadPool *pool,
                                    Iterator begin,
@@ -570,7 +583,8 @@ template <typename ResultType, typename Iterator, typename KeepFunctor, typename
 #else
 template <typename ResultType, typename Iterator, typename KeepFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingFilteredReduced(Iterator begin,
                                    Iterator end,
@@ -621,7 +635,8 @@ ResultType blockingFilteredReduced(Iterator begin,
 template <typename Iterator, typename KeepFunctor, typename ReduceFunctor,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 ResultType blockingFilteredReduced(QThreadPool *pool,
                                    Iterator begin,
                                    Iterator end, KeepFunctor &&keep,
@@ -640,7 +655,8 @@ template <typename Iterator, typename KeepFunctor, typename ReduceFunctor,
           std::enable_if_t<QtPrivate::isIterator_v<Iterator>, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 ResultType blockingFilteredReduced(Iterator begin,
                                    Iterator end,
                                    KeepFunctor &&keep,
diff --git a/src/concurrent/qtconcurrentfunctionwrappers.h b/src/concurrent/qtconcurrentfunctionwrappers.h
index b337b90e0a..4882ed8d89 100644
--- a/src/concurrent/qtconcurrentfunctionwrappers.h
+++ b/src/concurrent/qtconcurrentfunctionwrappers.h
@@ -5,6 +5,7 @@
 #define QTCONCURRENT_FUNCTIONWRAPPERS_H
 
 #include <QtConcurrent/qtconcurrentcompilertest.h>
+#include <QtConcurrent/qtconcurrentreducekernel.h>
 #include <QtCore/qfuture.h>
 
 #include <tuple>
@@ -121,6 +122,11 @@ inline constexpr bool isIterator_v<T, std::void_t<typename std::iterator_traits<
 template <class Callable, class Sequence>
 using isInvocable = std::is_invocable<Callable, typename std::decay_t<Sequence>::value_type>;
 
+template <class InitialValueType, class ResultType>
+inline constexpr bool isInitialValueCompatible_v = std::conjunction_v<
+        std::is_convertible<InitialValueType, ResultType>,
+        std::negation<std::is_same<std::decay_t<InitialValueType>, QtConcurrent::ReduceOption>>>;
+
 template<class Callable, class Enable = void>
 struct ReduceResultTypeHelper
 {
@@ -163,14 +169,6 @@ struct MapSequenceResultType<InputSequence<T...>, MapFunctor>
 
 #endif // QT_NO_TEMPLATE_TEMPLATE_PARAMETER
 
-template<typename Sequence>
-struct SequenceHolder
-{
-    SequenceHolder(const Sequence &s) : sequence(s) { }
-    SequenceHolder(Sequence &&s) : sequence(std::move(s)) { }
-    Sequence sequence;
-};
-
 } // namespace QtPrivate.
 
 
diff --git a/src/concurrent/qtconcurrentmap.h b/src/concurrent/qtconcurrentmap.h
index 3358d93a4e..2d829daca4 100644
--- a/src/concurrent/qtconcurrentmap.h
+++ b/src/concurrent/qtconcurrentmap.h
@@ -77,7 +77,8 @@ template <typename ResultType, typename Sequence, typename MapFunctor, typename
 #else
 template <typename ResultType, typename Sequence, typename MapFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> mappedReduced(QThreadPool *pool,
                                   Sequence &&sequence,
@@ -98,7 +99,8 @@ template <typename ResultType, typename Sequence, typename MapFunctor, typename
 #else
 template <typename ResultType, typename Sequence, typename MapFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> mappedReduced(Sequence &&sequence,
                                   MapFunctor &&map,
@@ -149,7 +151,8 @@ template <typename Sequence, typename MapFunctor, typename ReduceFunctor, typena
 template <typename Sequence, typename MapFunctor, typename ReduceFunctor, typename InitialValueType,
           std::enable_if_t<QtPrivate::isInvocable<MapFunctor, Sequence>::value, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> mappedReduced(QThreadPool *pool,
                                   Sequence &&sequence,
@@ -172,7 +175,8 @@ template <typename Sequence, typename MapFunctor, typename ReduceFunctor, typena
 template <typename Sequence, typename MapFunctor, typename ReduceFunctor, typename InitialValueType,
           std::enable_if_t<QtPrivate::isInvocable<MapFunctor, Sequence>::value, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> mappedReduced(Sequence &&sequence,
                                   MapFunctor &&map,
@@ -221,7 +225,8 @@ template <typename ResultType, typename Iterator, typename MapFunctor, typename
 #else
 template <typename ResultType, typename Iterator, typename MapFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> mappedReduced(QThreadPool *pool,
                                   Iterator begin,
@@ -243,7 +248,8 @@ template <typename ResultType, typename Iterator, typename MapFunctor, typename
 #else
 template <typename ResultType, typename Iterator, typename MapFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> mappedReduced(Iterator begin,
                                   Iterator end,
@@ -295,7 +301,8 @@ template <typename Iterator, typename MapFunctor, typename ReduceFunctor, typena
 template <typename Iterator, typename MapFunctor, typename ReduceFunctor,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 QFuture<ResultType> mappedReduced(QThreadPool *pool,
                                   Iterator begin,
@@ -319,7 +326,8 @@ template<typename Iterator, typename MapFunctor, typename ReduceFunctor,
          std::enable_if_t<QtPrivate::isIterator_v<Iterator>, int> = 0,
          typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
          typename InitialValueType,
-         std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+         std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                          int> = 0>
 #endif
 QFuture<ResultType> mappedReduced(Iterator begin,
                                   Iterator end,
@@ -447,7 +455,8 @@ template <typename ResultType, typename Sequence, typename MapFunctor, typename
 #else
 template <typename ResultType, typename Sequence, typename MapFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingMappedReduced(QThreadPool *pool,
                                  Sequence &&sequence,
@@ -470,7 +479,8 @@ template <typename ResultType, typename Sequence, typename MapFunctor, typename
 #else
 template <typename ResultType, typename Sequence, typename MapFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingMappedReduced(Sequence &&sequence,
                                  MapFunctor &&map,
@@ -526,7 +536,8 @@ template <typename MapFunctor, typename ReduceFunctor, typename Sequence, typena
 template <typename MapFunctor, typename ReduceFunctor, typename Sequence, typename InitialValueType,
           std::enable_if_t<QtPrivate::isInvocable<MapFunctor, Sequence>::value, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingMappedReduced(QThreadPool *pool,
                                  Sequence &&sequence,
@@ -550,7 +561,8 @@ template <typename MapFunctor, typename ReduceFunctor, typename Sequence, typena
 template<typename MapFunctor, typename ReduceFunctor, typename Sequence, typename InitialValueType,
          std::enable_if_t<QtPrivate::isInvocable<MapFunctor, Sequence>::value, int> = 0,
          typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
-         std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+         std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                          int> = 0>
 #endif
 ResultType blockingMappedReduced(Sequence &&sequence,
                                  MapFunctor &&map,
@@ -602,7 +614,8 @@ template <typename ResultType, typename Iterator, typename MapFunctor, typename
 #else
 template <typename ResultType, typename Iterator, typename MapFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingMappedReduced(QThreadPool *pool,
                                  Iterator begin,
@@ -626,7 +639,8 @@ template <typename ResultType, typename Iterator, typename MapFunctor, typename
 #else
 template <typename ResultType, typename Iterator, typename MapFunctor, typename ReduceFunctor,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingMappedReduced(Iterator begin,
                                  Iterator end,
@@ -681,7 +695,8 @@ template <typename Iterator, typename MapFunctor, typename ReduceFunctor, typena
 template <typename Iterator, typename MapFunctor, typename ReduceFunctor,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingMappedReduced(QThreadPool *pool,
                                  Iterator begin,
@@ -706,7 +721,8 @@ template <typename Iterator, typename MapFunctor, typename ReduceFunctor,
           std::enable_if_t<QtPrivate::isIterator_v<Iterator>, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
-          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
+          std::enable_if_t<QtPrivate::isInitialValueCompatible_v<InitialValueType, ResultType>,
+                           int> = 0>
 #endif
 ResultType blockingMappedReduced(Iterator begin,
                                  Iterator end,
diff --git a/src/concurrent/qtconcurrentreducekernel.h b/src/concurrent/qtconcurrentreducekernel.h
index 9ea0f33f91..a58739fc41 100644
--- a/src/concurrent/qtconcurrentreducekernel.h
+++ b/src/concurrent/qtconcurrentreducekernel.h
@@ -5,7 +5,6 @@
 #define QTCONCURRENT_REDUCEKERNEL_H
 
 #include <QtConcurrent/qtconcurrent_global.h>
-#include <QtConcurrent/qtconcurrentfunctionwrappers.h>
 
 #if !defined(QT_NO_CONCURRENT) || defined(Q_CLANG_QDOC)
 
@@ -20,6 +19,17 @@
 
 QT_BEGIN_NAMESPACE
 
+namespace QtPrivate {
+
+template<typename Sequence>
+struct SequenceHolder
+{
+    SequenceHolder(const Sequence &s) : sequence(s) { }
+    SequenceHolder(Sequence &&s) : sequence(std::move(s)) { }
+    Sequence sequence;
+};
+
+}
 
 namespace QtConcurrent {