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Fix rvalue overload of qobject_pointer_cast for GCC 9.3

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The code assumed that any C++ implementation would implement the
resolution for LWG2996 in C++20 mode. While that may be the case in
the future, the current state in GCC 9.3 as shipped in Ubuntu 20.04
LTS is that it doesn't, which leads to tst_qsharedpointer fail there.

Fix by using the safe version of std::move, std::exchange, which
guarantees the state of the src object, no matter what the callee
does.

Change-Id: Icc39b527df4d3a7b398ff2b44bcbdf9082b81f2f
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
(cherry picked from commit 0632494bd47e924ce7914b6457791d4612599e5f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Marc Mutz 2021-07-02 08:55:14 +02:00 committed by Qt Cherry-pick Bot
parent e474183059
commit 20b805f30f
1 changed files with 1 additions and 5 deletions
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6
src/corelib/tools/qsharedpointer_impl.h
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@ -925,15 +925,11 @@ std::shared_ptr<X> qobject_pointer_cast(std::shared_ptr<T> &&src)
using element_type = typename std::shared_ptr<X>::element_type;
auto castResult = qobject_cast<element_type *>(src.get());
if (castResult) {
auto result = std::shared_ptr<X>(std::move(src), castResult);
#if __cplusplus <= 201703L
// C++2a's move aliasing constructor will leave src empty.
// Before C++2a we don't really know if the compiler has support for it.
// The move aliasing constructor is the resolution for LWG2996,
// which does not impose a feature-testing macro. So: clear src.
src.reset();
#endif
return result;
return std::shared_ptr<X>(std::exchange(src, nullptr), castResult);
}
return std::shared_ptr<X>();
}