Warning "'return' : conversion from 'size_t' to 'int'" while connecting signal wtih std::vector to a lambda function.

Steps to reproduce:

• create a new Qt Application with Widgets in QtCreator
• add this signal to the MainWidow class (mainwindow.h):
  signals: void sigUS_selectionItemChange(std::vector<int> const&);
• add this connection in the MainWindow ctor (mainwindow.cpp):
  QObject::connect(this, &MainWindow::sigUS_selectionItemChange,
  [this](std::vector<int> const&) { });
• Compile the project.

Suggestion to correct: modify qmetatype.h file like this (note the added "static_cast<int>("...")"):
template<typename T>
struct ContainerAPI<QList<T> > : CapabilitiesImpl<QList<T> >
{ static int size(const QList<T> *t)

{ return static_cast<int>(t->size()); } };

template<typename T>
struct ContainerAPI<QVector<T> > : CapabilitiesImpl<QVector<T> >
{ static int size(const QVector<T> *t) { return static_cast<int>(t->size()); }

};

template<typename T>
struct ContainerAPI<std::vector<T> > : CapabilitiesImpl<std::vector<T> >
{ static int size(const std::vector<T> *t)

{ return static_cast<int>(t->size()); } };

template<typename T>
struct ContainerAPI<std::list<T> > : CapabilitiesImpl<std::list<T> >
{ static int size(const std::list<T> *t) { return static_cast<int>(t->size()); }

};