Constrain the data stream operators for containers

Check that we can successfully instantiate the data
stream operator for a container before we actually try.

This is required so we can automate registration of debug
stream operators with QMetaType.

Change-Id: Ib100a5242470d7fc8067058cc4d81af2fa9354b0
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

4 files changed, 46 insertions, 18 deletions

diff --git a/src/corelib/global/qtypeinfo.h b/src/corelib/global/qtypeinfo.h
index 2f7bb414b5..e45347ee10 100644
--- a/src/corelib/global/qtypeinfo.h
+++ b/src/corelib/global/qtypeinfo.h
@@ -464,6 +464,17 @@ struct has_ostream_operator<Stream, T, std::void_t<decltype(detail::reference<St
 template <typename Stream, typename T>
 constexpr bool has_ostream_operator_v = has_ostream_operator<Stream, T>::value;
 
+template <typename Stream, typename, typename = void>
+struct has_istream_operator : std::false_type {};
+template <typename Stream, typename T>
+struct has_istream_operator<Stream, T, std::void_t<decltype(detail::reference<Stream>() >> detail::reference<T>())>>
+        : std::true_type {};
+template <typename Stream, typename T>
+constexpr bool has_istream_operator_v = has_istream_operator<Stream, T>::value;
+
+template <typename Stream, typename T>
+constexpr bool has_stream_operator_v = has_ostream_operator_v<Stream, T> && has_istream_operator_v<Stream, T>;
+
 }
 
 
diff --git a/src/corelib/serialization/qdatastream.h b/src/corelib/serialization/qdatastream.h
index d00fb5e7d8..48e96cb4c5 100644
--- a/src/corelib/serialization/qdatastream.h
+++ b/src/corelib/serialization/qdatastream.h
@@ -347,6 +347,13 @@ QDataStream &writeAssociativeMultiContainer(QDataStream &s, const Container &c)
 
 } // QtPrivate namespace
 
+template<typename ...T>
+using QDataStreamIfHasOStreamOperators =
+    std::enable_if_t<std::conjunction_v<QTypeTraits::has_ostream_operator<QDataStream, T>...>, QDataStream &>;
+template<typename ...T>
+using QDataStreamIfHasIStreamOperators =
+    std::enable_if_t<std::conjunction_v<QTypeTraits::has_istream_operator<QDataStream, T>...>, QDataStream &>;
+
 /*****************************************************************************
   QDataStream inline functions
  *****************************************************************************/
@@ -406,88 +413,88 @@ operator>>(QDataStream &s, T &t)
 { return s >> reinterpret_cast<typename std::underlying_type<T>::type &>(t); }
 
 template<typename T>
-inline QDataStream &operator>>(QDataStream &s, QList<T> &v)
+inline QDataStreamIfHasIStreamOperators<T> operator>>(QDataStream &s, QList<T> &v)
 {
     return QtPrivate::readArrayBasedContainer(s, v);
 }
 
 template<typename T>
-inline QDataStream &operator<<(QDataStream &s, const QList<T> &v)
+inline QDataStreamIfHasOStreamOperators<T> operator<<(QDataStream &s, const QList<T> &v)
 {
     return QtPrivate::writeSequentialContainer(s, v);
 }
 
 template <typename T>
-inline QDataStream &operator>>(QDataStream &s, QSet<T> &set)
+inline QDataStreamIfHasIStreamOperators<T> operator>>(QDataStream &s, QSet<T> &set)
 {
     return QtPrivate::readListBasedContainer(s, set);
 }
 
 template <typename T>
-inline QDataStream &operator<<(QDataStream &s, const QSet<T> &set)
+inline QDataStreamIfHasOStreamOperators<T> operator<<(QDataStream &s, const QSet<T> &set)
 {
     return QtPrivate::writeSequentialContainer(s, set);
 }
 
 template <class Key, class T>
-inline QDataStream &operator>>(QDataStream &s, QHash<Key, T> &hash)
+inline QDataStreamIfHasIStreamOperators<Key, T> operator>>(QDataStream &s, QHash<Key, T> &hash)
 {
     return QtPrivate::readAssociativeContainer(s, hash);
 }
 
 template <class Key, class T>
 
-inline QDataStream &operator<<(QDataStream &s, const QHash<Key, T> &hash)
+inline QDataStreamIfHasOStreamOperators<Key, T> operator<<(QDataStream &s, const QHash<Key, T> &hash)
 {
     return QtPrivate::writeAssociativeContainer(s, hash);
 }
 
 template <class Key, class T>
-inline QDataStream &operator>>(QDataStream &s, QMultiHash<Key, T> &hash)
+inline QDataStreamIfHasIStreamOperators<Key, T> operator>>(QDataStream &s, QMultiHash<Key, T> &hash)
 {
     return QtPrivate::readAssociativeContainer(s, hash);
 }
 
 template <class Key, class T>
-inline QDataStream &operator<<(QDataStream &s, const QMultiHash<Key, T> &hash)
+inline QDataStreamIfHasOStreamOperators<Key, T> operator<<(QDataStream &s, const QMultiHash<Key, T> &hash)
 {
     return QtPrivate::writeAssociativeMultiContainer(s, hash);
 }
 
 template <class Key, class T>
-inline QDataStream &operator>>(QDataStream &s, QMap<Key, T> &map)
+inline QDataStreamIfHasIStreamOperators<Key, T> operator>>(QDataStream &s, QMap<Key, T> &map)
 {
     return QtPrivate::readAssociativeContainer(s, map);
 }
 
 template <class Key, class T>
-inline QDataStream &operator<<(QDataStream &s, const QMap<Key, T> &map)
+inline QDataStreamIfHasOStreamOperators<Key, T> operator<<(QDataStream &s, const QMap<Key, T> &map)
 {
     return QtPrivate::writeAssociativeContainer(s, map);
 }
 
 template <class Key, class T>
-inline QDataStream &operator>>(QDataStream &s, QMultiMap<Key, T> &map)
+inline QDataStreamIfHasIStreamOperators<Key, T> operator>>(QDataStream &s, QMultiMap<Key, T> &map)
 {
     return QtPrivate::readAssociativeContainer(s, map);
 }
 
 template <class Key, class T>
-inline QDataStream &operator<<(QDataStream &s, const QMultiMap<Key, T> &map)
+inline QDataStreamIfHasOStreamOperators<Key, T> operator<<(QDataStream &s, const QMultiMap<Key, T> &map)
 {
     return QtPrivate::writeAssociativeMultiContainer(s, map);
 }
 
 #ifndef QT_NO_DATASTREAM
 template <class T1, class T2>
-inline QDataStream& operator>>(QDataStream& s, std::pair<T1, T2> &p)
+inline QDataStreamIfHasIStreamOperators<T1, T2> operator>>(QDataStream& s, std::pair<T1, T2> &p)
 {
     s >> p.first >> p.second;
     return s;
 }
 
 template <class T1, class T2>
-inline QDataStream& operator<<(QDataStream& s, const std::pair<T1, T2> &p)
+inline QDataStreamIfHasOStreamOperators<T1, T2> operator<<(QDataStream& s, const std::pair<T1, T2> &p)
 {
     s << p.first << p.second;
     return s;
diff --git a/tests/auto/corelib/io/qdebug/tst_qdebug.cpp b/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
index 72412aa44d..0b54f53517 100644
--- a/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
+++ b/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
@@ -35,11 +35,13 @@
 #include <QtConcurrentRun>
 #include <QFutureSynchronizer>
 
-static_assert(QTypeTraits::has_ostream_v<QDebug, int>);
-static_assert(QTypeTraits::has_ostream_v<QDebug, QList<int>>);
+static_assert(QTypeTraits::has_ostream_operator_v<QDebug, int>);
+static_assert(QTypeTraits::has_ostream_operator_v<QDebug, QList<int>>);
+static_assert(QTypeTraits::has_ostream_operator_v<QDebug, QMap<int, QString>>);
 struct NonStreamable {};
-static_assert(!QTypeTraits::has_ostream_v<QDebug, NonStreamable>);
-static_assert(!QTypeTraits::has_ostream_v<QDebug, QList<NonStreamable>>);
+static_assert(!QTypeTraits::has_ostream_operator_v<QDebug, NonStreamable>);
+static_assert(!QTypeTraits::has_ostream_operator_v<QDebug, QList<NonStreamable>>);
+static_assert(!QTypeTraits::has_ostream_operator_v<QDebug, QMap<int, NonStreamable>>);
 
 class tst_QDebug: public QObject
 {
diff --git a/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp b/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp
index 932c4d25d2..bd7100adec 100644
--- a/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp
+++ b/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp
@@ -36,6 +36,14 @@
 #include <QtGui/QPixmap>
 #include <QtGui/QTextLength>
 
+static_assert(QTypeTraits::has_ostream_operator_v<QDataStream, int>);
+static_assert(QTypeTraits::has_ostream_operator_v<QDataStream, QList<int>>);
+static_assert(QTypeTraits::has_ostream_operator_v<QDataStream, QMap<int, QString>>);
+struct NonStreamable {};
+static_assert(!QTypeTraits::has_ostream_operator_v<QDataStream, NonStreamable>);
+static_assert(!QTypeTraits::has_ostream_operator_v<QDataStream, QList<NonStreamable>>);
+static_assert(!QTypeTraits::has_ostream_operator_v<QDataStream, QMap<int, NonStreamable>>);
+
 class tst_QDataStream : public QObject
 {
 Q_OBJECT