Use std::addressof to get the address of QMaybe wrapped type

Using QMaybe with types that overloads operator& can have unintended
effects because QMaybe::operator-> would call the overload. This could
cause problems with types such as WRL::ComPtr which resets its pointer
when taking its address.

To ensure that we get the address of the instance, we should use
std::addressof instead of calling operator& to get the wrapped object's
address.

This fixes an issue where QMaybe<ComPtr> resets the COM pointer and
returns nullptr when attempting to extract the raw interface pointer
like this:

    QMaybe<ComPtr<Interface>, HRESULT> instance = foo();
    Interface *rawIf = instance->Get(); // Reset instance and return 0

Pick-to: 6.5
Change-Id: I544dec6dc0cf59c2b3a46fe6d9ebbf08aac80737
Reviewed-by: Tim Blechmann <tim@klingt.org>
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit 3367b137e3aeec76b7edb7d14bde1a6cec7a64f4)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 08b52a310244d299dddf01128493bdadc32325cf)

1 files changed, 3 insertions, 2 deletions

diff --git a/src/multimedia/qmaybe_p.h b/src/multimedia/qmaybe_p.h
index f35d2c329..5fe2d4d6c 100644
--- a/src/multimedia/qmaybe_p.h
+++ b/src/multimedia/qmaybe_p.h
@@ -19,6 +19,7 @@
 #include <qstring.h>
 #include <optional>
 #include <utility>
+#include <memory>
 
 QT_BEGIN_NAMESPACE
 
@@ -77,8 +78,8 @@ public:
         return *m_value;
     }
 
-    constexpr Value *operator->() noexcept { return &value(); }
-    constexpr const Value *operator->() const noexcept { return &value(); }
+    constexpr Value *operator->() noexcept { return std::addressof(value()); }
+    constexpr const Value *operator->() const noexcept { return std::addressof(value()); }
 
     constexpr Value &operator*() &noexcept { return value(); }
     constexpr const Value &operator*() const &noexcept { return value(); }