[clazy] [Bug 389994] New: new-check: Avoid explicit qRegisterMetaType / Q_DECLARE_METATYPE

[bugzilla_noreply at kde.org]

https://bugs.kde.org/show_bug.cgi?id=389994

            Bug ID: 389994
           Summary: new-check: Avoid explicit qRegisterMetaType /
                    Q_DECLARE_METATYPE
           Product: clazy
           Version: unspecified
          Platform: Other
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: aklitzing at gmail.com
                CC: smartins at kde.org
  Target Milestone: ---

It would be helpful if clazy could check if a class is able to register itself
in Qt's meta-object-system.

Sometimes it is a forgotten include (forward declared) or something like this
that the moc cannot see the whole class and won't generate the
"qRegisterMetaType" itself. Most times the developer will add qRegisterMetaType
somewhere because Qt said it at runtime. But clazy could help here to warn if a
class is used in signal/slot and moc is not able to generate the registration
as it is the better way to let moc do the registration.

moc can generate q qt_static_metacall with stuff like this:

    } else if (_c == QMetaObject::RegisterMethodArgumentMetaType) {
        switch (_id) {
        default: *reinterpret_cast<int*>(_a[0]) = -1; break;
        case 0:
            switch (*reinterpret_cast<int*>(_a[1])) {
            default: *reinterpret_cast<int*>(_a[0]) = -1; break;
            case 1:
                *reinterpret_cast<int*>(_a[0]) = qRegisterMetaType<
QSharedPointer<CUSTOM_CLASS> >(); break;
            }
            break;


moc has some more possibilities to detect own types like Q_PROPERTY usage.

See:
https://code.qt.io/cgit/qt/qtbase.git/tree/src/tools/moc/generator.cpp
https://woboq.com/blog/qmetatype-knows-your-types.html

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