Revert "qxp::function_ref: drop use of q23::invoke_r"

This reverts commit b9cce12e76796962e5e5ad0d5408370af56af459, which
broke

    function_ref<void(int)> f = [](int i) { return i; };

ie. swallowing of return types.

We could maybe implement the same without invoke_r, with the same
manual if-constexpr that invoke_r has, but it would be a pointless
duplication across the two thunks we have, so just use invoke_r.

Add tests.

Pick-to: 6.4
Task-number: QTBUG-103739
Change-Id: I6034f05d813c06a25e8058ded5b6b62f3ca858b4
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 5 insertions, 3 deletions

diff --git a/src/corelib/global/qxpfunctional.h b/src/corelib/global/qxpfunctional.h
index ca015be22e..67350c56ed 100644
--- a/src/corelib/global/qxpfunctional.h
+++ b/src/corelib/global/qxpfunctional.h
@@ -21,7 +21,7 @@
 // We mean it.
 //
 
-#include <QtCore/q20functional.h>
+#include <QtCore/q23functional.h>
 #include <type_traits>
 #include <utility>
 
@@ -99,7 +99,8 @@ public:
     Q_IMPLICIT function_ref_base(F* f) noexcept
         : m_bound_entity(f),
           m_thunk_ptr([](BoundEntityType ctx, ArgTypes&&... args) noexcept(noex) -> R {
-                return reinterpret_cast<F*>(ctx.fun)(std::forward<ArgTypes>(args)...);
+                return q23::invoke_r<R>(reinterpret_cast<F*>(ctx.fun),
+                                        std::forward<ArgTypes>(args)...);
             })
     {}
 
@@ -115,7 +116,8 @@ public:
         : m_bound_entity(std::addressof(f)),
           m_thunk_ptr([](BoundEntityType ctx, ArgTypes&&... args) noexcept(noex) -> R {
                 using That = copy_const_t<Const, std::remove_reference_t<F>>;
-                return (*static_cast<That*>(ctx.obj))(std::forward<ArgTypes>(args)...);
+                return q23::invoke_r<R>(*static_cast<That*>(ctx.obj),
+                                        std::forward<ArgTypes>(args)...);
             })
     {}