Long live QPromise::addResults()!

Makes the pre-existing QFutureInterface functionality available via
the public QPromise API.

[ChangeLog][QtCore][QPromise] Added addResults() to report multiple
results at once.

Change-Id: I18e6ef2781df422020b9022d78d6c45107b01668
Reviewed-by: Sona Kurazyan <kurazyan.sona@gmail.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/corelib/thread/qpromise.h

@@ -51,6 +51,8 @@ public:
     {
         return d.reportResult(std::forward<U>(result), index);
     }
+    bool addResults(const QList<T> &result)
+    { return d.reportResults(result); }
 #ifndef QT_NO_EXCEPTIONS
     void setException(const QException &e) { d.reportException(e); }
 #if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)

src/corelib/thread/qpromise.qdoc

@@ -105,6 +105,29 @@
     For instance, iterative approaches that use QFuture::resultCount() or
     QFuture::const_iterator. In order to get all available results without
     thinking if there are index gaps or not, use QFuture::results().
+
+    \sa addResults()
+*/
+
+/*!
+    \fn template <typename T> bool QPromise<T>::addResults(const QList<T> &results)
+    \since 6.6
+
+    Adds \a results at the end of the internal result collection.
+
+    Returns \c true when \a results are added to the collection.
+
+    Returns \c false when this promise is in canceled or finished state.
+
+    This is more efficient than looping over addResult(), because associated
+    futures will be notified only once per addResults() call, instead of once
+    per element contained in \a results, as would be the case with individual
+    addResult() calls. But if the calculation of each element takes time, then
+    the code on the receiving end (future) cannot make progress until all
+    results are reported, so use this function only if the calculation of
+    consecutive elements is relatively fast.
+
+    \sa addResult()
 */
 
 /*! \fn template<typename T> void QPromise<T>::setException(const QException &e)

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

@@ -168,6 +168,15 @@ void tst_QPromise::addResult()
         QCOMPARE(f.resultCount(), 3);
         QCOMPARE(f.resultAt(2), result);
     }
+    // add multiple results in one go:
+    {
+        QList results = {42, 4242, 424242};
+        QVERIFY(promise.addResults(results));
+        QCOMPARE(f.resultCount(), 6);
+        QCOMPARE(f.resultAt(3), 42);
+        QCOMPARE(f.resultAt(4), 4242);
+        QCOMPARE(f.resultAt(5), 424242);
+    }
     // add as lvalue at position and overwrite
     {
         int result = -1;