add a visualizer for _Ref_count_obj_alloc3 and _Ref_count_obj2

[Igor Zhukov (fsb4000)]

Fixes #2787

test:

#include <memory>

int main() {
	std::allocator<int> alloc{};
	auto ms = std::make_shared<int>();
	auto as = std::allocate_shared<int>(alloc, 10);
        return 0;
}

Do we need some comments for them like ?

[Stephan T. Lavavej (StephanTLavavej)]

Programmer-archaeology:

MSVC-PR-179257 "Comply with The Rules for allocator::construct.", merged 2019-05-08, shipped in VS 2019 16.3, introduced _Ref_count_obj2 and _Ref_count_obj_alloc2.

#309, merged 2020-04-08, shipped in VS 2019 16.7, introduced _Ref_count_obj_alloc3.

I don't think we absolutely need version comments, but I wouldn't object to them.

[Igor Zhukov (fsb4000)]

test code:

#include <memory>

template <typename T>
struct stateful_allocator
    : std::allocator
{
    stateful_allocator() {}
    template <typename U> stateful_allocator(stateful_allocator const&) {}

    typedef T value_type;
    template <typename U> struct rebind { typedef stateful_allocator other; };
    T* allocate(size_t n) {
        return static_cast(operator new(n * sizeof(T)));
    }
    void deallocate(T* p, size_t) { operator delete(p); }
    int state = 0;
};

int main() {
	std::allocator<int> alloc{};
        stateful_allocator<int> salloc{};
	auto ms = std::make_shared<int>();
	auto as = std::allocate_shared<int>(alloc, 10);
        auto as2 = std::allocate_shared<int>(salloc, 10);
	return 0;
}

[Igor Zhukov (fsb4000)]

I didn't test _Ref_count_obj_alloc2 but I hope it is correct because _Ref_count_obj_alloc2inherits from _Ebco_base, similar to _Ref_count_obj_alloc3

 class __declspec(empty_bases) _Ref_count_obj_alloc2 : public _Ebco_base<_Alloc>, public _Ref_count_base {

class _Ref_count_obj_alloc3 : public _Ebco_base<_Rebind_alloc_t<_Alloc, _Ty>>, public _Ref_count_base {

[Michael Schellenberger Costa (miscco)]

Can we add a fixed string to a _Uses == 0 condition?

[Stephan T. Lavavej (StephanTLavavej)]

Why would we need to show a child item for an empty shared_ptr? (weak_ptrs will display themselves as expired, IIRC)

[Stephan T. Lavavej (StephanTLavavej)]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[Stephan T. Lavavej (StephanTLavavej)]

I've resolved a trivial merge conflict where #2804 deleted code next to this PR's addition.

[Stephan T. Lavavej (StephanTLavavej)]

Thanks for fixing these important visualizers! 🎉 🚀 😸