Probable UB in basic_value<> constructor

[p-kalugin]

In several basic_value<> constructors the destructor is called on not-yet constructed object:

basic_value( ... )
{
   try {  ...  }
   catch( ... ) {
      this->~basic_value();  // <== here
      throw;
   }
}

This seems like UB, though I'm not prepared to cite the relevant part of the Standard now.
Anyway, this leads to destructors of base subobjects to be called twice: first time when you explicitly call ~basic_value() and second time after rethrow, when already constructed base subobject gets destructed.

[ColinH]

There's definitely something wrong, we'll check the details later today.

[ColinH]

Thanks for letting us know about this issue, we looked at all cases and even found a problem not related to the new base class feature. It should all be fixed now.

[d-frey]

@p-kalugin That was a really good catch, thank you! Could you review the fix, please? I think we covered all cases correctly now, but an additional pair of eyes won't hurt. :)

[p-kalugin]

LGTM, thanks!