Fix QFuture continuations/handlers to work with move-only callables

std::function, which is used to store the type-erased continuation
lambdas, requires the passed callable to be copy-constructible. This
makes impossible to use move-only callables with continuations/handlers.
In particular, it makes impossible passing lambdas that are capturing
move-only objects. The workaround is to store the continuation lambda
inside a wrapper for the callable, which stores the move-only lambda in
a QSharedPtr and can be stored in std::function, since it's copyable.

Pick-to: 6.2
Fixes: QTBUG-98493
Change-Id: I8b7a22fcf68dc132b3c533216a7a1665e9f9fb0a
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

2 files changed, 71 insertions, 0 deletions

diff --git a/tests/auto/corelib/thread/qfuture/CMakeLists.txt b/tests/auto/corelib/thread/qfuture/CMakeLists.txt
index dcf7846fd2..df5826032d 100644
--- a/tests/auto/corelib/thread/qfuture/CMakeLists.txt
+++ b/tests/auto/corelib/thread/qfuture/CMakeLists.txt
@@ -12,3 +12,8 @@ qt_internal_add_test(tst_qfuture
     PUBLIC_LIBRARIES
         Qt::CorePrivate
 )
+
+qt_internal_extend_target(tst_qmetatype CONDITION MSVC
+    COMPILE_OPTIONS
+        /bigobj
+)
diff --git a/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp b/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
index 385fbe7fca..f97caa0633 100644
--- a/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
+++ b/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
@@ -145,6 +145,7 @@ private slots:
     void onCanceled();
     void cancelContinuations();
     void continuationsWithContext();
+    void continuationsWithMoveOnlyLambda();
 #if 0
     // TODO: enable when QFuture::takeResults() is enabled
     void takeResults();
@@ -3111,6 +3112,71 @@ void tst_QFuture::continuationsWithContext()
     thread.wait();
 }
 
+void tst_QFuture::continuationsWithMoveOnlyLambda()
+{
+    // .then()
+    {
+        std::unique_ptr<int> uniquePtr(new int(42));
+        auto future = QtFuture::makeReadyFuture().then([p = std::move(uniquePtr)] { return *p; });
+        QCOMPARE(future.result(), 42);
+    }
+    // .then() with thread pool
+    {
+        QThreadPool pool;
+
+        std::unique_ptr<int> uniquePtr(new int(42));
+        auto future =
+                QtFuture::makeReadyFuture().then(&pool, [p = std::move(uniquePtr)] { return *p; });
+        QCOMPARE(future.result(), 42);
+    }
+    // .then() with context
+    {
+        QObject object;
+
+        std::unique_ptr<int> uniquePtr(new int(42));
+        auto future = QtFuture::makeReadyFuture().then(&object,
+                                                       [p = std::move(uniquePtr)] { return *p; });
+        QCOMPARE(future.result(), 42);
+    }
+
+    // .onCanceled()
+    {
+        std::unique_ptr<int> uniquePtr(new int(42));
+        auto future =
+                createCanceledFuture<int>().onCanceled([p = std::move(uniquePtr)] { return *p; });
+        QCOMPARE(future.result(), 42);
+    }
+
+    // .onCanceled() with context
+    {
+        QObject object;
+
+        std::unique_ptr<int> uniquePtr(new int(42));
+        auto future = createCanceledFuture<int>().onCanceled(
+                &object, [p = std::move(uniquePtr)] { return *p; });
+        QCOMPARE(future.result(), 42);
+    }
+
+#ifndef QT_NO_EXCEPTIONS
+    // .onFailed()
+    {
+        std::unique_ptr<int> uniquePtr(new int(42));
+        auto future = QtFuture::makeExceptionalFuture<int>(QException())
+                              .onFailed([p = std::move(uniquePtr)] { return *p; });
+        QCOMPARE(future.result(), 42);
+    }
+    // .onFailed() with context
+    {
+        QObject object;
+
+        std::unique_ptr<int> uniquePtr(new int(42));
+        auto future = QtFuture::makeExceptionalFuture<int>(QException())
+                              .onFailed(&object, [p = std::move(uniquePtr)] { return *p; });
+        QCOMPARE(future.result(), 42);
+    }
+#endif // QT_NO_EXCEPTIONS
+}
+
 void tst_QFuture::testSingleResult(const UniquePtr &p)
 {
     QVERIFY(p.get() != nullptr);