QMetaType: Support converting any QFuture<T> to QFuture<void>

QMetaType now implicitly knows how to convert any QFuture<T> to
QFuture<void> without needing to manually register a converter
function.

QtWebChannel will make use of this to transparently support QFuture<T>
return types.

[ChangeLog][QtCore][QMetaType] QMetaType now supports converting any
QFuture<T> to QFuture<void>.

Task-number: QTBUG-92903
Change-Id: Ied7e71be37c346cc3d2c274ffb0d91a6821ab4d4
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 18 insertions, 0 deletions

diff --git a/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp b/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
index 8eadaee62a..af83ee3b95 100644
--- a/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
+++ b/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
@@ -164,6 +164,7 @@ private slots:
     void createReadyFutures();
 
     void getFutureInterface();
+    void convertQMetaType();
 
 private:
     using size_type = std::vector<int>::size_type;
@@ -3532,5 +3533,22 @@ void tst_QFuture::getFutureInterface()
     QCOMPARE(interface.resultCount(), 1);
 }
 
+void tst_QFuture::convertQMetaType()
+{
+    const auto intType = QMetaType::fromType<QFuture<int>>();
+    const auto voidType = QMetaType::fromType<QFuture<void>>();
+
+    QVERIFY(QMetaType::canConvert(intType, voidType));
+
+    const int val = 42;
+    QFuture<int> f = QtFuture::makeReadyFuture(val);
+    auto variant = QVariant::fromValue(f);
+    QVERIFY(variant.convert(voidType));
+
+    const auto voidFuture = variant.value<QFuture<void>>();
+    QVERIFY(voidFuture.isValid());
+    QVERIFY(voidFuture.isFinished());
+}
+
 QTEST_MAIN(tst_QFuture)
 #include "tst_qfuture.moc"