Long live std::pair!

Make QPair an alias for std::pair, and qMakePair just a forwarder
towards std::make_pair.

Why? Fundamentally to ditch a bunch of NIH code; gain for free
structured bindings, std::tuple and std::reference_wrapper
compatibility, and so on.

Breakages:

* Some that code manually forward declares QPair.
We don't care about it (<QContainerFwd> is the proper way).

* Some code that overloads on std::pair and QPair. Luckily
it's mostly centralized: debug, metatypes, testing macros.
Just remove the QPair overload.

* Usages of qMakePair forcing the template type parameters.
There are a handful of these in qtbase, but only one was actually
broken.

* std::pair is NOT (and will never likely be) trivially copiable.
This is agreed to be a mistake done by practically all implementations
in C++11, can can't be fixed without breaking ABI.
Some code using QPair assuming it's trivially copiable may break;
exactly one occurrence was in qtbase.

* QMetaType logic extracts the type names in two different ways,
one by looking at the source code string (e.g. extracted by moc)
and one via some ad-hoc reflection in C++. We need to make
"QPair" (as spelled in the source code) be the same as "std::pair"
(gathered via reflection, which will see through the alias)
when compared. The way it's already done e.g. for QList is
by actually replacing the moc-extracted name with the name
of the actual type used in C++; do the same here.
On libc++, std::pair is actually in an inline namespace --
i.e. std::__1::pair; the reflection will extract and store
"std::__1::pair" so we need an ad-hoc fix to QMetaType.

[ChangeLog][QtCore][QPair] QPair is now an alias to std::pair,
and does not exist as a class in Qt any more. This may break
code such as functions overloaded for both QPair and std::pair.
Usually, the overload taking a QPair can be safely discarded,
leaving only the one taking a std::pair. QPair API has not changed,
and qMakePair is still available for compatibility (although
new code is encouraged to use std::pair and std::make_pair
directly instead).

Change-Id: I7725c751bf23946cde577b1406e86a336c0a3dcf
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

17 files changed, 63 insertions, 474 deletions

diff --git a/src/corelib/doc/snippets/code/doc_src_qpair.cpp b/src/corelib/doc/snippets/code/doc_src_qpair.cpp
deleted file mode 100644
index e62f91830c..0000000000
--- a/src/corelib/doc/snippets/code/doc_src_qpair.cpp
+++ /dev/null
@@ -1,75 +0,0 @@
-/****************************************************************************
-**
-** Copyright (C) 2016 The Qt Company Ltd.
-** Contact: https://www.qt.io/licensing/
-**
-** This file is part of the documentation of the Qt Toolkit.
-**
-** $QT_BEGIN_LICENSE:BSD$
-** Commercial License Usage
-** Licensees holding valid commercial Qt licenses may use this file in
-** accordance with the commercial license agreement provided with the
-** Software or, alternatively, in accordance with the terms contained in
-** a written agreement between you and The Qt Company. For licensing terms
-** and conditions see https://www.qt.io/terms-conditions. For further
-** information use the contact form at https://www.qt.io/contact-us.
-**
-** BSD License Usage
-** Alternatively, you may use this file under the terms of the BSD license
-** as follows:
-**
-** "Redistribution and use in source and binary forms, with or without
-** modification, are permitted provided that the following conditions are
-** met:
-**   * Redistributions of source code must retain the above copyright
-**     notice, this list of conditions and the following disclaimer.
-**   * Redistributions in binary form must reproduce the above copyright
-**     notice, this list of conditions and the following disclaimer in
-**     the documentation and/or other materials provided with the
-**     distribution.
-**   * Neither the name of The Qt Company Ltd nor the names of its
-**     contributors may be used to endorse or promote products derived
-**     from this software without specific prior written permission.
-**
-**
-** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
-**
-** $QT_END_LICENSE$
-**
-****************************************************************************/
-#include <qmath.h>
-
-//! [0]
-QPair<QString, double> pair;
-//! [0]
-
-
-//! [1]
-pair.first = "pi";
-pair.second = M_PI;
-//! [1]
-
-//! [struct]
-struct Variable {
-    QString name;
-    double value;
-};
-Variable v;
-v.name = "pi";
-v.value = M_PI;
-//! [struct]
-
-//! [2]
-QList<QPair<int, double> > list;
-list.append(qMakePair(66, M_PI));
-//! [2]
diff --git a/src/corelib/doc/src/containers.qdoc b/src/corelib/doc/src/containers.qdoc
index 537bd8c884..d73c9dd07b 100644
--- a/src/corelib/doc/src/containers.qdoc
+++ b/src/corelib/doc/src/containers.qdoc
@@ -608,8 +608,6 @@
 
     \li QContiguousCache<T> provides an efficient way of caching data
     that is typically accessed in a contiguous way.
-
-    \li QPair<T1, T2> stores a pair of elements.
     \endlist
 
     Additional non-template types that compete with Qt's template
diff --git a/src/corelib/io/qdebug.h b/src/corelib/io/qdebug.h
index 723bb478ad..22ba3879f4 100644
--- a/src/corelib/io/qdebug.h
+++ b/src/corelib/io/qdebug.h
@@ -45,7 +45,6 @@
 #include <QtCore/qhash.h>
 #include <QtCore/qlist.h>
 #include <QtCore/qmap.h>
-#include <QtCore/qpair.h>
 #include <QtCore/qtextstream.h>
 #include <QtCore/qstring.h>
 #include <QtCore/qvector.h>
@@ -319,15 +318,6 @@ inline QDebug operator<<(QDebug debug, const QMultiHash<Key, T> &hash)
 }
 
 template <class T1, class T2>
-inline QDebug operator<<(QDebug debug, const QPair<T1, T2> &pair)
-{
-    const bool oldSetting = debug.autoInsertSpaces();
-    debug.nospace() << "QPair(" << pair.first << ',' << pair.second << ')';
-    debug.setAutoInsertSpaces(oldSetting);
-    return debug.maybeSpace();
-}
-
-template <class T1, class T2>
 inline QDebug operator<<(QDebug debug, const std::pair<T1, T2> &pair)
 {
     const QDebugStateSaver saver(debug);
diff --git a/src/corelib/kernel/qmetatype.h b/src/corelib/kernel/qmetatype.h
index d8b547c8e2..d964c16915 100644
--- a/src/corelib/kernel/qmetatype.h
+++ b/src/corelib/kernel/qmetatype.h
@@ -240,8 +240,7 @@ inline Q_DECL_CONSTEXPR int qMetaTypeId();
 
 #define QT_FOR_EACH_AUTOMATIC_TEMPLATE_2ARG(F) \
     F(QHash, class) \
-    F(QMap, class) \
-    F(QPair, struct)
+    F(QMap, class)
 
 #define QT_FOR_EACH_AUTOMATIC_TEMPLATE_SMART_POINTER(F) \
     F(QSharedPointer) \
@@ -1392,15 +1391,6 @@ template<typename From>
 struct QPairVariantInterfaceConvertFunctor;
 
 template<typename T, typename U>
-struct QPairVariantInterfaceConvertFunctor<QPair<T, U> >
-{
-    QPairVariantInterfaceImpl operator()(const QPair<T, U>& f) const
-    {
-        return QPairVariantInterfaceImpl(&f);
-    }
-};
-
-template<typename T, typename U>
 struct QPairVariantInterfaceConvertFunctor<std::pair<T, U> >
 {
     QPairVariantInterfaceImpl operator()(const std::pair<T, U>& f) const
@@ -1670,8 +1660,6 @@ namespace QtPrivate
         }
     };
     template<typename T, typename U>
-    struct IsPair<QPair<T, U> > : IsMetaTypePair<QPair<T, U> > {};
-    template<typename T, typename U>
     struct IsPair<std::pair<T, U> > : IsMetaTypePair<std::pair<T, U> > {};
 
     template<typename T>
@@ -2209,7 +2197,6 @@ Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE(QHash)
 Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE(QMap)
 Q_DECLARE_ASSOCIATIVE_CONTAINER_METATYPE(std::map)
 
-Q_DECLARE_METATYPE_TEMPLATE_2ARG(QPair)
 Q_DECLARE_METATYPE_TEMPLATE_2ARG(std::pair)
 
 #define Q_DECLARE_METATYPE_TEMPLATE_SMART_POINTER_ITER(TEMPLATENAME) \
@@ -2532,6 +2519,16 @@ public:
             // Replace QList by QVector
             appendStr("QVector");
         }
+
+        if (skipToken(begin, end, "QPair")) {
+            // replace QPair by std::pair
+#ifdef _LIBCPP_VERSION
+            appendStr("std::" QT_STRINGIFY(_LIBCPP_ABI_NAMESPACE) "::pair");
+#else
+            appendStr("std::pair");
+#endif
+        }
+
         if (!hasMiddleConst) {
             // Normalize the integer types
             int numLong = 0;
diff --git a/src/corelib/serialization/qdatastream.cpp b/src/corelib/serialization/qdatastream.cpp
index 3026e554bf..316a164c6d 100644
--- a/src/corelib/serialization/qdatastream.cpp
+++ b/src/corelib/serialization/qdatastream.cpp
@@ -1119,6 +1119,16 @@ int QDataStream::readRawData(char *s, int len)
     return readBlock(s, len);
 }
 
+/*! \fn template <class T1, class T2> QDataStream &operator>>(QDataStream &in, std::pair<T1, T2> &pair)
+    \since 6.0
+    \relates QDataStream
+
+    Reads a pair from stream \a in into \a pair.
+
+    This function requires the T1 and T2 types to implement \c operator>>().
+
+    \sa {Serializing Qt Data Types}
+*/
 
 /*****************************************************************************
   QDataStream write functions
@@ -1446,6 +1456,18 @@ int QDataStream::skipRawData(int len)
     return skipResult;
 }
 
+/*!
+    \fn template <class T1, class T2> QDataStream &operator<<(QDataStream &out, const std::pair<T1, T2> &pair)
+    \since 6.0
+    \relates QDataStream
+
+    Writes the pair \a pair to stream \a out.
+
+    This function requires the T1 and T2 types to implement \c operator<<().
+
+    \sa {Serializing Qt Data Types}
+*/
+
 QT_END_NAMESPACE
 
 #endif // QT_NO_DATASTREAM
diff --git a/src/corelib/serialization/qdatastream.h b/src/corelib/serialization/qdatastream.h
index 4568ba3a84..c11d6803ac 100644
--- a/src/corelib/serialization/qdatastream.h
+++ b/src/corelib/serialization/qdatastream.h
@@ -480,14 +480,14 @@ inline QDataStream &operator<<(QDataStream &s, const QMultiMap<Key, T> &map)
 
 #ifndef QT_NO_DATASTREAM
 template <class T1, class T2>
-inline QDataStream& operator>>(QDataStream& s, QPair<T1, T2>& p)
+inline QDataStream& 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 QPair<T1, T2>& p)
+inline QDataStream& operator<<(QDataStream& s, const std::pair<T1, T2> &p)
 {
     s << p.first << p.second;
     return s;
diff --git a/src/corelib/tools/qcontainerfwd.h b/src/corelib/tools/qcontainerfwd.h
index bdf9e0dcc0..fd4701a8b1 100644
--- a/src/corelib/tools/qcontainerfwd.h
+++ b/src/corelib/tools/qcontainerfwd.h
@@ -50,7 +50,8 @@ template <class Key, class T> class QHash;
 template <class Key, class T> class QMap;
 template <class Key, class T> class QMultiHash;
 template <class Key, class T> class QMultiMap;
-template <class T1, class T2> struct QPair;
+template <typename T1, typename T2>
+using QPair = std::pair<T1, T2>;
 template <class T> class QQueue;
 template <class T> class QSet;
 template <class T> class QStack;
diff --git a/src/corelib/tools/qhashfunctions.h b/src/corelib/tools/qhashfunctions.h
index 5742540061..38e799e78b 100644
--- a/src/corelib/tools/qhashfunctions.h
+++ b/src/corelib/tools/qhashfunctions.h
@@ -252,15 +252,6 @@ inline size_t qHashRangeCommutative(InputIterator first, InputIterator last, siz
     return std::accumulate(first, last, seed, QtPrivate::QHashCombineCommutative());
 }
 
-template <typename T1, typename T2> inline size_t qHash(const QPair<T1, T2> &key, size_t seed = 0)
-    noexcept(noexcept(qHash(key.first, seed)) && noexcept(qHash(key.second, seed)))
-{
-    QtPrivate::QHashCombine hash;
-    seed = hash(seed, key.first);
-    seed = hash(seed, key.second);
-    return seed;
-}
-
 template <typename T1, typename T2> inline size_t qHash(const std::pair<T1, T2> &key, size_t seed = 0)
     noexcept(noexcept(qHash(key.first, seed)) && noexcept(qHash(key.second, seed)))
 {
diff --git a/src/corelib/tools/qpair.h b/src/corelib/tools/qpair.h
index 9ebf88bc8f..6cb7fc5079 100644
--- a/src/corelib/tools/qpair.h
+++ b/src/corelib/tools/qpair.h
@@ -44,115 +44,22 @@
 
 QT_BEGIN_NAMESPACE
 
-
-template <class T1, class T2>
-struct QPair
-{
-    typedef T1 first_type;
-    typedef T2 second_type;
-
-    Q_DECL_CONSTEXPR QPair()
-        noexcept((std::is_nothrow_default_constructible<T1>::value &&
-                              std::is_nothrow_default_constructible<T2>::value))
-        : first(), second() {}
-    Q_DECL_CONSTEXPR QPair(const T1 &t1, const T2 &t2)
-        noexcept((std::is_nothrow_copy_constructible<T1>::value &&
-                              std::is_nothrow_copy_constructible<T2>::value))
-        : first(t1), second(t2) {}
-    // compiler-generated copy/move ctor/assignment operators are fine!
-
-    template <typename TT1, typename TT2>
-    Q_DECL_CONSTEXPR QPair(const QPair<TT1, TT2> &p)
-        noexcept((std::is_nothrow_constructible<T1, TT1&>::value &&
-                              std::is_nothrow_constructible<T2, TT2&>::value))
-        : first(p.first), second(p.second) {}
-    template <typename TT1, typename TT2>
-    Q_DECL_RELAXED_CONSTEXPR QPair &operator=(const QPair<TT1, TT2> &p)
-        noexcept((std::is_nothrow_assignable<T1, TT1&>::value &&
-                              std::is_nothrow_assignable<T2, TT2&>::value))
-    { first = p.first; second = p.second; return *this; }
-    template <typename TT1, typename TT2>
-    Q_DECL_CONSTEXPR QPair(QPair<TT1, TT2> &&p)
-        noexcept((std::is_nothrow_constructible<T1, TT1>::value &&
-                              std::is_nothrow_constructible<T2, TT2>::value))
-        // can't use std::move here as it's not constexpr in C++11:
-        : first(static_cast<TT1 &&>(p.first)), second(static_cast<TT2 &&>(p.second)) {}
-    template <typename TT1, typename TT2>
-    Q_DECL_RELAXED_CONSTEXPR QPair &operator=(QPair<TT1, TT2> &&p)
-        noexcept((std::is_nothrow_assignable<T1, TT1>::value &&
-                              std::is_nothrow_assignable<T2, TT2>::value))
-    { first = std::move(p.first); second = std::move(p.second); return *this; }
-
-    Q_DECL_RELAXED_CONSTEXPR void swap(QPair &other)
-        noexcept(noexcept(qSwap(other.first, other.first)) && noexcept(qSwap(other.second, other.second)))
-    {
-        // use qSwap() to pick up ADL swaps automatically:
-        qSwap(first, other.first);
-        qSwap(second, other.second);
-    }
-
-    T1 first;
-    T2 second;
-};
-
-#if defined(__cpp_deduction_guides) && __cpp_deduction_guides >= 201606
-template<class T1, class T2>
-QPair(T1, T2) -> QPair<T1, T2>;
+#if 0
+#pragma qt_class(QPair)
 #endif
 
 template <typename T1, typename T2>
-void swap(QPair<T1, T2> &lhs, QPair<T1, T2> &rhs) noexcept(noexcept(lhs.swap(rhs)))
-{ lhs.swap(rhs); }
-
-// mark QPair<T1,T2> as complex/movable/primitive depending on the
-// typeinfos of the constituents:
-template<class T1, class T2>
-class QTypeInfo<QPair<T1, T2> > : public QTypeInfoMerger<QPair<T1, T2>, T1, T2> {}; // Q_DECLARE_TYPEINFO
+using QPair = std::pair<T1, T2>;
 
-template <class T1, class T2>
-Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator==(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-    noexcept(noexcept(p1.first == p2.first && p1.second == p2.second))
-{ return p1.first == p2.first && p1.second == p2.second; }
-
-template <class T1, class T2>
-Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator!=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-    noexcept(noexcept(!(p1 == p2)))
-{ return !(p1 == p2); }
-
-template <class T1, class T2>
-Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator<(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-    noexcept(noexcept(p1.first < p2.first || (!(p2.first < p1.first) && p1.second < p2.second)))
-{
-    return p1.first < p2.first || (!(p2.first < p1.first) && p1.second < p2.second);
-}
-
-template <class T1, class T2>
-Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator>(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-    noexcept(noexcept(p2 < p1))
-{
-    return p2 < p1;
-}
-
-template <class T1, class T2>
-Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator<=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-    noexcept(noexcept(!(p2 < p1)))
-{
-    return !(p2 < p1);
-}
-
-template <class T1, class T2>
-Q_DECL_CONSTEXPR Q_INLINE_TEMPLATE bool operator>=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-    noexcept(noexcept(!(p1 < p2)))
+template <typename T1, typename T2>
+constexpr decltype(auto) qMakePair(T1 &&value1, T2 &&value2)
+    noexcept(noexcept(std::make_pair(std::forward<T1>(value1), std::forward<T2>(value2))))
 {
-    return !(p1 < p2);
+    return std::make_pair(std::forward<T1>(value1), std::forward<T2>(value2));
 }
 
-template <class T1, class T2>
-Q_DECL_CONSTEXPR Q_OUTOFLINE_TEMPLATE QPair<T1, T2> qMakePair(const T1 &x, const T2 &y)
-    noexcept(noexcept(QPair<T1, T2>(x, y)))
-{
-    return QPair<T1, T2>(x, y);
-}
+template<class T1, class T2>
+class QTypeInfo<std::pair<T1, T2>> : public QTypeInfoMerger<std::pair<T1, T2>, T1, T2> {};
 
 QT_END_NAMESPACE
 
diff --git a/src/corelib/tools/qpair.qdoc b/src/corelib/tools/qpair.qdoc
index 65576ef2e6..0e17b6c3b9 100644
--- a/src/corelib/tools/qpair.qdoc
+++ b/src/corelib/tools/qpair.qdoc
@@ -28,255 +28,24 @@
 /*!
     \class QPair
     \inmodule QtCore
-    \reentrant
-    \brief The QPair class is a template class that stores a pair of items.
+    \obsolete
+    \brief QPair is an alias for std::pair.
 
     \ingroup tools
 
-    QPair\<T1, T2\> can be used in your application if the STL \c
-    pair type is not available. It stores one value of type T1 and
-    one value of type T2. It can be used as a return value for a
-    function that needs to return two values, or as the value type of
-    a \l{Container classes}{generic container}.
-
-    Here's an example of a QPair that stores one QString and one \c
-    double value:
-
-    \snippet code/doc_src_qpair.cpp 0
-
-    The components are accessible as public data members called \l
-    first and \l second. For example:
-
-    \snippet code/doc_src_qpair.cpp 1
-
-    Note, however, that it is almost always preferable to define a small struct
-    to hold the result of a function with multiple return values. A struct
-    trivially generalizes to more than two values, and allows more descriptive
-    member names than \c{first} and \c{second}:
-
-    \snippet code/doc_src_qpair.cpp struct
-
-    The advent of C++11 automatic variable type deduction (\c{auto}) shifts the
-    emphasis from the type name to the name of functions and members. Thus, QPair,
-    like \c{std::pair} and \c{std::tuple}, is mostly useful in generic (template)
-    code, where defining a dedicated type is not possible.
-
-    QPair's template data types (T1 and T2) must be \l{assignable
-    data types}. You cannot, for example, store a QWidget as a value;
-    instead, store a QWidget *. A few functions have additional
-    requirements; these requirements are documented on a per-function
-    basis.
+    QPair\<T1, T2\> is a typedef for std::pair\<T1, T2\>.
+    It is provided for backwards compatibility. Use std::pair directly
+    instead.
 
     \sa {Container Classes}
 */
 
-/*! \typedef QPair::first_type
-
-    The type of the first element in the pair (T1).
-
-    \sa first
-*/
-
-/*! \typedef QPair::second_type
-
-    The type of the second element in the pair (T2).
-
-    \sa second
-*/
-
-/*! \variable QPair::first
-
-    The first element in the pair.
-*/
-
-/*! \variable QPair::second
-
-    The second element in the pair.
-*/
-
-/*! \fn template <class T1, class T2> QPair<T1, T2>::QPair()
-
-    Constructs an empty pair. The \c first and \c second elements are
-    initialized with \l{default-constructed value}s.
-*/
-
-/*!
-    \fn template <class T1, class T2> QPair<T1, T2>::QPair(const T1 &value1, const T2 &value2)
-
-    Constructs a pair and initializes the \c first element with \a
-    value1 and the \c second element with \a value2.
-
-    \sa qMakePair()
-*/
-
-/*!
-\fn template <class T1, class T2> void QPair<T1, T2>::swap(QPair &other)
-
-    \since 5.5
-    Swaps this pair with \a other.
-
-    Equivalent to
-    \code
-        qSwap(this->first, other.first);
-        qSwap(this->second, other.second);
-    \endcode
-
-    Swap overloads are found in namespace \c std as well as via
-    argument-dependent lookup (ADL) in the namespace of \c{T} .
-*/
-
-/*!
-\fn template <class T1, class T2> void swap(QPair<T1, T2> &lhs, QPair<T1, T2> &rhs)
-    \overload
-    \relates QPair
-    \since 5.5
-
-    Swaps \a lhs with \a rhs.
-*/
-
-/*!
-    \fn template <class T1, class T2> template <typename TT1, typename TT2> QPair<T1, T2>::QPair(const QPair<TT1, TT2> &p)
-    \since 5.2
-
-    Constructs a pair from the other pair \a p, of types TT1 and TT2. This
-    constructor will fail if \c first cannot be initialized from \c p.first or
-    if \c second cannot be initialized from \c p.second.
-
-    \sa qMakePair()
-*/
-
-/*!
-    \fn template <class T1, class T2> template <typename TT1, typename TT2> QPair<T1, T2>::QPair(QPair<TT1, TT2> &&p)
-    \since 5.2
-
-    Move-constructs a QPair instance, making it point to the same object that \a p was pointing to.
-*/
-
-/*!
-    \fn template <class T1, class T2> template <typename TT1, typename TT2> QPair & QPair<T1, T2>::operator=(const QPair<TT1, TT2> &p)
-    \since 5.2
-
-    Copies pair \a p into this pair.
-
-    \sa qMakePair()
-*/
-
-/*!
-    \fn template <class T1, class T2> template <typename TT1, typename TT2> QPair & QPair<T1, T2>::operator=(QPair<TT1, TT2> &&p)
-    \since 5.2
-
-    Move-assigns pair \a p into this pair instance.
-*/
-
-/*! \fn template <class T1, class T2> bool operator==(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-
-    \relates QPair
-
-    Returns \c true if \a p1 is equal to \a p2; otherwise returns \c false.
-    Two pairs compare equal if their \c first data members compare
-    equal and if their \c second data members compare equal.
-
-    This function requires the T1 and T2 types to have an
-    implementation of \c operator==().
-*/
-
-/*! \fn template <class T1, class T2> bool operator!=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-
-    \relates QPair
-
-    Returns \c true if \a p1 is not equal to \a p2; otherwise returns
-    false. Two pairs compare as not equal if their \c first data
-    members are not equal or if their \c second data members are not
-    equal.
-
-    This function requires the T1 and T2 types to have an
-    implementation of \c operator==().
-*/
-
-/*! \fn template <class T1, class T2> bool operator<(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-
-    \relates QPair
-
-    Returns \c true if \a p1 is less than \a p2; otherwise returns
-    false. The comparison is done on the \c first members of \a p1
-    and \a p2; if they compare equal, the \c second members are
-    compared to break the tie.
-
-    This function requires the T1 and T2 types to have an
-    implementation of \c operator<().
-*/
-
-/*! \fn template <class T1, class T2> bool operator>(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-
-    \relates QPair
-
-    Returns \c true if \a p1 is greater than \a p2; otherwise returns
-    false. The comparison is done on the \c first members of \a p1
-    and \a p2; if they compare equal, the \c second members are
-    compared to break the tie.
-
-    This function requires the T1 and T2 types to have an
-    implementation of \c operator<().
-*/
-
-/*! \fn template <class T1, class T2> bool operator<=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-
-    \relates QPair
-
-    Returns \c true if \a p1 is less than or equal to \a p2; otherwise
-    returns \c false. The comparison is done on the \c first members of
-    \a p1 and \a p2; if they compare equal, the \c second members are
-    compared to break the tie.
-
-    This function requires the T1 and T2 types to have an
-    implementation of \c operator<().
-*/
-
-/*! \fn template <class T1, class T2> bool operator>=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)
-
-    \relates QPair
-
-    Returns \c true if \a p1 is greater than or equal to \a p2;
-    otherwise returns \c false. The comparison is done on the \c first
-    members of \a p1 and \a p2; if they compare equal, the \c second
-    members are compared to break the tie.
-
-    This function requires the T1 and T2 types to have an
-    implementation of \c operator<().
-*/
-
 /*!
-    \fn template <class T1, class T2> QPair<T1, T2> qMakePair(const T1 &value1, const T2 &value2)
-
-    \relates QPair
-
-    Returns a QPair\<T1, T2\> that contains \a value1 and \a value2.
-    Example:
-
-    \snippet code/doc_src_qpair.cpp 2
-
-    This is equivalent to QPair<T1, T2>(\a value1, \a value2), but
-    usually requires less typing.
-*/
-
-/*! \fn template <class T1, class T2> QDataStream &operator>>(QDataStream &in, QPair<T1, T2> &pair)
-
-    \relates QPair
-
-    Reads a pair from stream \a in into \a pair.
-
-    This function requires the T1 and T2 types to implement \c operator>>().
-
-    \sa {Serializing Qt Data Types}
-*/
-
-/*! \fn template <class T1, class T2> QDataStream &operator<<(QDataStream &out, const QPair<T1, T2> &pair)
-
+    \fn template <class T1, class T2> QPair<T1, T2> qMakePair(T1 &&value1, T2 &&value2)
+    \obsolete
     \relates QPair
 
-    Writes the pair \a pair to stream \a out.
-
-    This function requires the T1 and T2 types to implement \c operator<<().
-
-    \sa {Serializing Qt Data Types}
+    qMakePair forwards its arguments to std::make_pair, and returns
+    the resulting std::pair. It is provided for backwards compatibility.
+    Use std::make_pair directly instead.
 */
diff --git a/src/network/ssl/qsslkey.h b/src/network/ssl/qsslkey.h
index 74be406539..9e70554716 100644
--- a/src/network/ssl/qsslkey.h
+++ b/src/network/ssl/qsslkey.h
@@ -52,8 +52,6 @@ QT_BEGIN_NAMESPACE
 
 #ifndef QT_NO_SSL
 
-template <typename A, typename B> struct QPair;
-
 class QIODevice;
 
 class QSslKeyPrivate;
diff --git a/src/opengl/qopengltimerquery.cpp b/src/opengl/qopengltimerquery.cpp
index 44955d48fc..d5ef875efa 100644
--- a/src/opengl/qopengltimerquery.cpp
+++ b/src/opengl/qopengltimerquery.cpp
@@ -143,11 +143,11 @@ bool QOpenGLTimerQueryPrivate::create()
 
     // Check to see if we also need to resolve the functions for EXT_timer_query
     QSurfaceFormat f = context->format();
-    if (f.version() <= qMakePair<int, int>(3, 2)
+    if (f.version() <= qMakePair(3, 2)
         && !context->hasExtension(QByteArrayLiteral("GL_ARB_timer_query"))
         && context->hasExtension(QByteArrayLiteral("GL_EXT_timer_query"))) {
         ext = new QExtTimerQueryHelper(context);
-    } else if (f.version() <= qMakePair<int, int>(3, 2)
+    } else if (f.version() <= qMakePair(3, 2)
                && !context->hasExtension(QByteArrayLiteral("GL_ARB_timer_query"))
                && !context->hasExtension(QByteArrayLiteral("GL_EXT_timer_query"))) {
         qWarning("QOpenGLTimerQuery requires one of:\n"
@@ -530,11 +530,11 @@ bool QOpenGLTimeMonitorPrivate::create()
 
     // Check to see if we also need to resolve the functions for EXT_timer_query
     QSurfaceFormat f = context->format();
-    if (f.version() <= qMakePair<int, int>(3, 2)
+    if (f.version() <= qMakePair(3, 2)
         && !context->hasExtension(QByteArrayLiteral("GL_ARB_timer_query"))
         && context->hasExtension(QByteArrayLiteral("GL_EXT_timer_query"))) {
         ext = new QExtTimerQueryHelper(context);
-    } else if (f.version() <= qMakePair<int, int>(3, 2)
+    } else if (f.version() <= qMakePair(3, 2)
                && !context->hasExtension(QByteArrayLiteral("GL_ARB_timer_query"))
                && !context->hasExtension(QByteArrayLiteral("GL_EXT_timer_query"))) {
         qWarning("QOpenGLTimeMonitor requires one of:\n"
diff --git a/src/opengl/qopenglvertexarrayobject.cpp b/src/opengl/qopenglvertexarrayobject.cpp
index 7f28a0bc61..44a0640567 100644
--- a/src/opengl/qopenglvertexarrayobject.cpp
+++ b/src/opengl/qopenglvertexarrayobject.cpp
@@ -176,7 +176,7 @@ bool QOpenGLVertexArrayObjectPrivate::create()
         vaoFuncsType = NotSupported;
         QSurfaceFormat format = ctx->format();
 #if !QT_CONFIG(opengles2)
-        if (format.version() >= qMakePair<int, int>(3,2)) {
+        if (format.version() >= qMakePair(3,2)) {
             vaoFuncs.core_3_2 = QOpenGLVersionFunctionsFactory::get<QOpenGLFunctions_3_2_Core>(ctx);
             vaoFuncsType = Core_3_2;
             vaoFuncs.core_3_2->glGenVertexArrays(1, &vao);
diff --git a/src/plugins/platforms/ios/qiostextinputoverlay.mm b/src/plugins/platforms/ios/qiostextinputoverlay.mm
index 3da4ba5480..92c11cd5e9 100644
--- a/src/plugins/platforms/ios/qiostextinputoverlay.mm
+++ b/src/plugins/platforms/ios/qiostextinputoverlay.mm
@@ -67,7 +67,7 @@ static SelectionPair querySelection()
     QGuiApplication::sendEvent(QGuiApplication::focusObject(), &query);
     int anchorPos = query.value(Qt::ImAnchorPosition).toInt();
     int cursorPos = query.value(Qt::ImCursorPosition).toInt();
-    return qMakePair<int, int>(anchorPos, cursorPos);
+    return qMakePair(anchorPos, cursorPos);
 }
 
 static bool hasSelection()
diff --git a/src/testlib/qtest.h b/src/testlib/qtest.h
index 18175196ff..9455a66fdd 100644
--- a/src/testlib/qtest.h
+++ b/src/testlib/qtest.h
@@ -232,14 +232,6 @@ template<> inline char *toString(const QVariant &v)
 }
 
 template <typename T1, typename T2>
-inline char *toString(const QPair<T1, T2> &pair)
-{
-    const QScopedArrayPointer<char> first(toString(pair.first));
-    const QScopedArrayPointer<char> second(toString(pair.second));
-    return toString(QString::asprintf("QPair(%s,%s)", first.data(), second.data()));
-}
-
-template <typename T1, typename T2>
 inline char *toString(const std::pair<T1, T2> &pair)
 {
     const QScopedArrayPointer<char> first(toString(pair.first));
diff --git a/src/widgets/graphicsview/qgraphicsitemanimation.h b/src/widgets/graphicsview/qgraphicsitemanimation.h
index 2bd9206574..8165532366 100644
--- a/src/widgets/graphicsview/qgraphicsitemanimation.h
+++ b/src/widgets/graphicsview/qgraphicsitemanimation.h
@@ -51,7 +51,6 @@ class QGraphicsItem;
 class QPointF;
 class QTimeLine;
 class QTransform;
-template <class T1, class T2> struct QPair;
 
 class QGraphicsItemAnimationPrivate;
 class Q_WIDGETS_EXPORT QGraphicsItemAnimation : public QObject
diff --git a/src/widgets/itemviews/qtreeview.cpp b/src/widgets/itemviews/qtreeview.cpp
index 6606b3f2f9..41928ddf1e 100644
--- a/src/widgets/itemviews/qtreeview.cpp
+++ b/src/widgets/itemviews/qtreeview.cpp
@@ -3918,7 +3918,7 @@ QPair<int,int> QTreeViewPrivate::startAndEndColumns(const QRect &rect) const
         start = (start == -1 ? 0 : start);
         end = (end == -1 ? header->count() - 1 : end);
     }
-    return qMakePair<int,int>(qMin(start, end), qMax(start, end));
+    return qMakePair(qMin(start, end), qMax(start, end));
 }
 
 bool QTreeViewPrivate::hasVisibleChildren(const QModelIndex& parent) const