This may not be a new issue, as I'm trying to update a project from Boost 1.68 to 1.80 (big jump!), but in trying to compile I'm being hit with this lengthy warning (and this particular project is building with warnings as errors, so this is problematic): warning C4714: function 'class boost::variant __cdecl boost::detail::variant::visitation_impl,struct boost::detail::variant::visitation_impl_step,class boost::weak_ptr<class boost::signals2::detail::trackable_pointee>,struct boost::mpl::l_item,class boost::weak_ptr<void>,struct boost::mpl::l_item,class boost::signals2::detail::foreign_void_weak_ptr,struct boost::mpl::l_end>

...

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,struct boost::mpl::l_iter<struct boost::mpl::l_end> >,class boost::detail::variant::invoke_visitor,void const *,struct boost::variant::has_fallback_type_>(int,int,class boost::detail::variant::invoke_visitor &,void const *,struct boost::mpl::bool_<0>,struct boost::variant::has_fallback_type_,struct boost::mpl::int_<0> *,struct boost::detail::variant::visitation_impl_step,class boost::weak_ptr<class boost::signals2::detail::trackable_pointee>,struct boost::mpl::l_item,class boost::weak_ptr<void>,struct boost::mpl::l_item,class boost::signals2::detail::foreign_void_weak_ptr,struct boost::mpl::l_end> ,struct boost::mpl::l_iter<struct boost::mpl::l_end> > *)' marked as __forceinline not inlined

I'm not sure whether the Real Bug™ is in signals2 or in variant, but I don't think it's in any of my code since it doesn't name any of my types above that I can see. I tried the big stick of setting all of Boost to "external" (and set the external warning level to 0), but sadly this did not suppress the warning. Wrapping it in a #pragma suppression does hide the warning, which makes me sufficiently happy. But perhaps someone might be interested to poke at it?