Details
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Bug
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Resolution: Unresolved
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P2: Important
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None
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5.13.2, 5.15.19, 6.10.0 Beta1
Description
(git blame fingers 014d7ac65417ed9b5ffb85cca24d16564ff5005a (https://codereview.qt-project.org/c/qt/qtbase/+/272844))
The IfCompatible constraints do not exclude X == T, which is fine for the (X*) ctor, but causes the QSharedPointer<X> && and const QSharedPointer<X>& to be move/copy ctors; ditto assignment operators, ditto QWeakPointer.
The problem is that some of these have additional constrains, e.g. QWeakPointer(QWeakPointer<X> &&), which also checks IfNotVirtualBase<X>, and that fails to compile when qxp::is_virtual_base is actually std::is_virtual_base, which requires X to be a complete type:
In file included from /d/gcc/15/include/c++/15.1.1/bits/stl_pair.h:60,
from /d/gcc/15/include/c++/15.1.1/utility:71,
from /home/marc/Qt/qt5/qtbase/src/corelib/global/qcompilerdetection.h:879,
from /home/marc/Qt/qt5-build-2/qtbase/include/QtCore/qcompilerdetection.h:1,
from /home/marc/Qt/qt5-build-2/qtbase/include/QtQmlCompiler/qtqmlcompilerexports.h:7,
from /home/marc/Qt/qt5/qtdeclarative/src/qmlcompiler/qqmljslogger_p.h:18,
from /home/marc/Qt/qt5-build-2/qtbase/include/QtQmlCompiler/6.11.0/QtQmlCompiler/private/qqmljslogger_p.h:1,
from /home/marc/Qt/qt5/qtdeclarative/src/qmlcompiler/qqmljscompilepass_p.h:18,
from /home/marc/Qt/qt5-build-2/qtbase/include/QtQmlCompiler/6.11.0/QtQmlCompiler/private/qqmljscompilepass_p.h:1,
from /home/marc/Qt/qt5/qtdeclarative/src/qmlcompiler/qqmljsoptimizations_p.h:17,
from /home/marc/Qt/qt5/qtdeclarative/src/qmlcompiler/qqmljsoptimizations.cpp:4:
/d/gcc/15/include/c++/15.1.1/type_traits: In instantiation of ‘constexpr const bool std::is_virtual_base_of_v<const QQmlJSScope, const QQmlJSScope>’:
/home/marc/Qt/qt5/qtbase/src/corelib/tools/qsharedpointer_impl.h:601:54: required by substitution of ‘template<class X, typename std::enable_if<std::is_convertible<_Up*, const QQmlJSScope*>::value, bool>::type <anonymous>, typename std::enable_if<(! is_virtual_base_of_v<const QQmlJSScope, X>), bool>::type <anonymous> > QWeakPointer<const QQmlJSScope>::QWeakPointer(QWeakPointer<T>&&) [with X = const QQmlJSScope; typename std::enable_if<std::is_convertible<_Up*, const QQmlJSScope*>::value, bool>::type <anonymous> = <missing>; typename std::enable_if<(! is_virtual_base_of_v<const QQmlJSScope, X>), bool>::type <anonymous> = <missing>]’
601 | using IfNotVirtualBase = typename std::enable_if<!qxp::is_virtual_base_of_v<T, X>, bool>::type;
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/marc/Qt/qt5/qtdeclarative/src/qmlcompiler/qqmljsmetatypes_p.h:145:11: required from here
145 | m_type(type),
| ^~~~~~~~~~~~
/d/gcc/15/include/c++/15.1.1/type_traits:3697:48: error: invalid use of incomplete type ‘const class QQmlJSScope’
3697 | inline constexpr bool is_virtual_base_of_v = __builtin_is_virtual_base_of(_Base, _Derived);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/marc/Qt/qt5/qtdeclarative/src/qmlcompiler/qqmljsloggingutils_p.h:21,
from /home/marc/Qt/qt5/qtdeclarative/src/qmlcompiler/qqmljslogger_p.h:21:
/home/marc/Qt/qt5/qtdeclarative/src/qmlcompiler/qqmljsloggingutils.h:13:7: note: forward declaration of ‘class QQmlJSScope’
13 | class QQmlJSScope;
| ^~~~~~~~~~~
There are several layers of fixes here:
- our impl of qxp::is_virtual_base should mandate that the arguments are complete types if C++26 std::is_virtual_base_of does
- QSharedPointer and QWeakPointer should not be making accidental copy and move SMFs
- also, there seems to be something fishy with the overload set, since QWeakPointer(QWeakPointer<X>&&) makes a distinction between virtual and non-virtual bases, but QWeakPointer(const QWeakPointer<X> &) does not, and neither do the assignment operators.
Attachments
Gerrit Reviews
| For Gerrit Dashboard: QTBUG-138246 | ||||||
|---|---|---|---|---|---|---|
| # | Subject | Branch | Project | Status | CR | V |
| 658768,4 | QWeakPointer: don't let IfCompatible<X> make accidental SMFs | dev | qt/qtbase | Status: NEW | 0 | +1 |