Long live QPromise::emplaceResult/At()!

And implement the rvalue overload of addResult() using it.

[ChangeLog][QtCore][QPromise] Added emplaceResult() and
emplaceResultAt() member functions.

Fixes: QTBUG-112270
Change-Id: Id369542215a60c0818f1afa8d564498be84732e8
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/thread/qpromise.h

@@ -46,10 +46,20 @@ public:
 
     // Core QPromise APIs
     QFuture<T> future() const { return d.future(); }
+    template<typename...Args, std::enable_if_t<std::is_constructible_v<T, Args...>, bool> = true>
+    bool emplaceResultAt(int index, Args&&...args)
+    {
+        return d.reportAndEmplaceResult(index, std::forward<Args>(args)...);
+    }
+    template<typename...Args, std::enable_if_t<std::is_constructible_v<T, Args...>, bool> = true>
+    bool emplaceResult(Args&&...args)
+    {
+        return d.reportAndEmplaceResult(-1, std::forward<Args>(args)...);
+    }
     template<typename U = T, typename = QtPrivate::EnableIfSameOrConvertible<U, T>>
     bool addResult(U &&result, int index = -1)
     {
-        return d.reportResult(std::forward<U>(result), index);
+        return d.reportAndEmplaceResult(index, std::forward<U>(result));
     }
     bool addResults(const QList<T> &result)
     { return d.reportResults(result); }

src/corelib/thread/qpromise.qdoc

@@ -91,15 +91,38 @@
 /*! \fn template <typename T> bool QPromise<T>::addResult(const T &result, int index = -1)
     \fn template <typename T> bool QPromise<T>::addResult(T &&result, int index = -1)
 
-    Adds \a result to the internal result collection at \a index position. If
-    index is unspecified, \a result is added to the end of the collection.
+    Same as
+    \code
+    emplaceResultAt(index, result);            // first overload
+    emplaceResultAt(index, std::move(result)); // second overload
+    \endcode
+    or, if \c{index == -1} (the default)
+    \code
+    emplaceResult(result);            // first overload
+    emplaceResult(std::move(result)); // second overload
+    \endcode
 
-    Returns \c true when \a result is added to the collection.
+    \sa emplaceResultAt(), emplaceResult(), addResults()
+*/
+
+/*!
+    \fn template <typename T> template <typename...Args, std::enable_if_t<std::is_constructible_v<T, Args...>, bool> = true> QPromise<T>::emplaceResultAt(int index, Args&&...args)
+    \fn template <typename T> template <typename...Args, std::enable_if_t<std::is_constructible_v<T, Args...>, bool> = true> QPromise<T>::emplaceResult(Args&&...args)
+    \since 6.6
+
+    Adds a result constructed from \a args... to the internal result collection
+    at \a index position (emplaceResultAt()) or the end of of the collection
+    (emplaceResult()).
+
+    Returns \c true when the result was added to the collection.
 
     Returns \c false when this promise is in canceled or finished state or when
-    \a result is rejected. addResult() rejects \a result if there's already
+    the result was rejected. addResult() rejects to add a result if there's already
     another result in the collection stored at the same index.
 
+    These functions only participate in overload resolutions if \c T is
+    constructible from \a args....
+
     You can get a result at a specific index by calling QFuture::resultAt().
 
     \note It is possible to specify an arbitrary index and request result at
@@ -108,7 +131,7 @@
     QFuture::const_iterator. In order to get all available results without
     thinking if there are index gaps or not, use QFuture::results().
 
-    \sa addResults()
+    \sa addResult(), addResults()
 */
 
 /*!

tests/auto/corelib/thread/qpromise/tst_qpromise.cpp

@@ -203,12 +203,20 @@ void tst_QPromise::addResultWithBracedInitializer() // QTBUG-111826
     {
         QString strValue;
         int intValue = 0;
+#ifndef __cpp_aggregate_paren_init // make emplacement work with MyClass
+        MyClass(QString s, int i) : strValue(std::move(s)), intValue(i) {}
+#endif
     };
 
     {
         QPromise<MyClass> myPromise;
         myPromise.addResult({"bar", 1});
     }
+
+    {
+        QPromise<MyClass> myPromise;
+        myPromise.emplaceResult("bar", 1);
+    }
 }
 
 void tst_QPromise::addResultOutOfOrder()