C++/Qt false positive: qRegisterMetatype is not a noop

[tcanabrava]

The tool complains that qRegisterMetatype is a noop, it's not.

https://lgtm.com/projects/g/KDE/okular/snapshot/9755abc39706567915f1d1b757b70e2a0f8e3f3a/files/autotests/parttest.cpp?sort=name&dir=ASC&mode=heatmap#x9525a92bb944ee97:1

[rdmarsh2]

I agreed with you at first and went digging to find what we did wrong, but I wound up convincing myself that the result is correct. qRegisterMetatype<T> calls qMetaTypeId<T>(), which calls QMetaTypeId2<T>::qt_metatype_id(). That would normally call QMetaTypeId<T>::qt_metatype_id(), but there's a specialization of QMetaTypeId2 for QUrl declared via QT_FOR_EACH_STATIC_TYPE(Q_DECLARE_BUILTIN_METATYPE). Q_DECLARE_BUILTIN_METATYPE declares a qt_metatype_id() with no side effects. As a result, the call to qRegisterMetatype<QUrl>() has no side effects.

[tcanabrava]

Learning a thing everyday. :)
Thanks for the proactiveness.