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| author | Ivan Solovev <ivan.solovev@qt.io> | 2023-04-06 13:00:25 +0200 |
|---|---|---|
| committer | Ivan Solovev <ivan.solovev@qt.io> | 2023-04-30 19:42:29 +0200 |
| commit | 959800f6de137f6a77c7d5a2741a5bae0638cbd9 (patch) | |
| tree | 653d5a29cccff9e560ec8d9c5ad06013b2023fd4 /src/corelib/thread/qmutex.h | |
| parent | d3b3fc538b52d2efb46f0578cd1d19580837e877 (diff) | |
Short live Q_NODISCARD_CTOR
[ChangeLog][QtCore] Introduced Q_NODISCARD_CTOR which resolves to
[[nodiscard]] attribute for constructors on compilers that support
it, and does nothing on other compilers.
Using [[nodiscard]] attribute on a constructor is a C++20 feature,
however in practice it is supported on most of the compilers that
we use in Qt 6. Clang generates a [-Wunused-value] warning, GCC
and MinGW generate a [-Wunused-result] warnings, and MSVC
generates a C4834 warning.
However, there are some exceptions.
The Integrity compiler provides the following warning:
"tst_qglobal.cpp", line 699: warning #3435-D:
the "nodiscard" attribute doesn't apply to constructors,
destructors, or routines with void return type
[[nodiscard]] explicit Test(int val) : m_val(val) {}
The QNX compiler (QCC 8.3.0) and GCC 9.3.1 on OpenSUSE generate
the [-Wattributes] warning:
tst_qglobal.cpp: In member function
'void tst_QGlobal::nodiscardConstructor()':
tst_qglobal.cpp:699:44: warning: 'nodiscard' attribute applied to
'tst_QGlobal::nodiscardConstructor()::Test::Test(int)' with void
return type [-Wattributes]
[[nodiscard]] explicit Test(int val) : m_val(val) {}
These warnings will lead to build failures when compiled with
-warnings-are-errors flag, so for these compilers the macro
does not do anything.
An attempt to use __attribute__((__warn_unused_result__)) was
also unsuccessful on these compilers, so this patch goes for
an easy solution, and simply checks
__has_cpp_attribute(nodiscard) >= 201907L
to decide if the attribute is supported or not.
This commit also introduces a syntax-only test, and also applies
the new macro to QMutexLocker, because not all platforms in the
CI build and run unit tests.
Fixes: QTBUG-104161
Change-Id: Ib4230661a5ad5e8af0d67b21b034486ebcd67562
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Diffstat (limited to 'src/corelib/thread/qmutex.h')
| -rw-r--r-- | src/corelib/thread/qmutex.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/src/corelib/thread/qmutex.h b/src/corelib/thread/qmutex.h index af77f556fd4..407473c799f 100644 --- a/src/corelib/thread/qmutex.h +++ b/src/corelib/thread/qmutex.h @@ -231,6 +231,7 @@ template <typename Mutex> class [[nodiscard]] QMutexLocker { public: + Q_NODISCARD_CTOR inline explicit QMutexLocker(Mutex *mutex) QT_MUTEX_LOCK_NOEXCEPT { m_mutex = mutex; @@ -240,6 +241,7 @@ public: } } + Q_NODISCARD_CTOR inline QMutexLocker(QMutexLocker &&other) noexcept : m_mutex(std::exchange(other.m_mutex, nullptr)), m_isLocked(std::exchange(other.m_isLocked, false)) @@ -326,6 +328,7 @@ template <typename Mutex> class [[nodiscard]] QMutexLocker { public: + Q_NODISCARD_CTOR inline explicit QMutexLocker(Mutex *) noexcept {} inline ~QMutexLocker() noexcept {} |