On Fri, 21 Jan 2022 at 17:42, Jonathan Wakely <jwakely@xxxxxxxxxx> wrote:
>
> On Fri, 21 Jan 2022 at 16:37, Robert-André Mauchin <zebob.m@xxxxxxxxx> wrote:
> >
> > On 1/21/22 14:46, Robert-André Mauchin wrote:
> > > Hello,
> > >
> > > So I built Clementine last week with no issue, but it failed during
> > > the mass rebuild with the folloing error:
> > >
> > > In file included from /builddir/build/BUILD/Clementine-0be314337d5bbd6fc7f5c76c31d7b87e37ba3a04/src/core/tagreaderclient.h:29,
> > > from /builddir/build/BUILD/Clementine-0be314337d5bbd6fc7f5c76c31d7b87e37ba3a04/src/core/tagreaderclient.cpp:21:
> > > /builddir/build/BUILD/Clementine-0be314337d5bbd6fc7f5c76c31d7b87e37ba3a04/ext/libclementine-common/core/workerpool.h: In instantiation of 'WorkerPool<HandlerType>::WorkerPool(QObject*) [with HandlerType = AbstractMessageHandler<cpb::tagreader::Message>]':
> > > /builddir/build/BUILD/Clementine-0be314337d5bbd6fc7f5c76c31d7b87e37ba3a04/src/core/tagreaderclient.cpp:40:52: required from here
> > > /builddir/build/BUILD/Clementine-0be314337d5bbd6fc7f5c76c31d7b87e37ba3a04/ext/libclementine-common/core/workerpool.h:168:55: error: passing 'QString' as 'this' argument discards qualifiers [-fpermissive]
> > > 168 | local_server_name_ = qApp->applicationName().toLower();
> > > | ^
> > > In file included from /usr/include/qt5/QtCore/qhashfunctions.h:44,
> > > from /usr/include/qt5/QtCore/qlist.h:47,
> > > from /usr/include/qt5/QtCore/qstringlist.h:41,
> > > from /usr/include/qt5/QtCore/QStringList:1,
> > > from /builddir/build/BUILD/Clementine-0be314337d5bbd6fc7f5c76c31d7b87e37ba3a04/src/core/tagreaderclient.h:26:
> > > /usr/include/qt5/QtCore/qstring.h:510:31: note: in call to 'QString QString::toLower() &&'
> > > 510 | Q_REQUIRED_RESULT QString toLower() &&
> > > | ^~~~~~~
> > >
> > >
> > > Nothing stands up to me in the linked code:
> > >
> > > template <typename HandlerType>
> > > WorkerPool<HandlerType>::WorkerPool(QObject* parent)
> > > : _WorkerPoolBase(parent), next_worker_(0), next_id_(0) {
> > > worker_count_ = qBound(1, QThread::idealThreadCount() / 2, 2);
> > > local_server_name_ = qApp->applicationName().toLower();
> > >
> > > if (local_server_name_.isEmpty()) local_server_name_ = "workerpool";
> > > }
> > >
> > >
> > > Anyone knows if a flag, or compiler, has changed since last week? Or have any input at all?
> > >
> > > Best regards,
> > >
> > > Robert-André
> >
> > So the problem is specific to GCC 12 but I can't find anything in the changelog related to this.
> > It seems toLower() takes a const as input and qApp->applicationName() is not a const.
>
> No, you have it backwards.
>
> QString::toLower() && can only be called on a non-const rvalue, and
> applicationName() is apparently returning a const object.
>
> >
> > I solved by replacing
> > local_server_name_ = qApp->applicationName().toLower();
> > to
> > local_server_name_ = QString(qApp->applicationName()).toLower();
>
> This creates an rvalue, which allows the call to toLower().
>
> > Still I would love for a GCC specialist to point me to the relevant change in GCC 12 so I can
> > send a patch upstream with explanation for the change.
>
> The Qt code has two overloads:
>
> Q_REQUIRED_RESULT QString toLower() const &
> { return toLower_helper(*this); }
> Q_REQUIRED_RESULT QString toLower() &&
> { return toLower_helper(*this); }
>
> For some reason, the second one is being used when it should be the first.
>
> I don't think this is a GCC change though.
I was wrong, this is a weird GCC overload resolution bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104173
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