[Bug c++/80664] New: Destructor not called upon exception while initializing a vector

["akrzemi1 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80664

            Bug ID: 80664
           Summary: Destructor not called upon exception while
                    initializing a vector
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: akrzemi1 at gmail dot com
  Target Milestone: ---

The following program logs calls to successful constructors and destructors of
class `R`. I expect the number of constructions to equal the number of
destructions. But when second construction fails, the destructor of the
previously fully created object is not called. This is becayse shared_ptr's
destructor is skipped! This happens when list-initializing a vector of
shared_ptr's: 

```
#include <cstdio>
#include <memory>
#include <stdexcept>
#include <vector>

void acquire_resource() // emulates failure to acquire the second resource
{
  static int resources_exhausted = 0;
  if (resources_exhausted) 
    throw std::runtime_error("failed");
  else
    ++resources_exhausted;
}

struct R
{
  explicit R(int)
  {
      acquire_resource();
      std::puts("create"); 
  }

  R(R const&) = delete; // no copying, no moving

  ~R() { std::puts("destroy"); }
};

int main()
{
  try {
    std::vector<std::shared_ptr<R>> v {
      std::make_shared<R>(1), // created, but never destroyed
      std::make_shared<R>(2)  // creation fails for this one
    };
  }
  catch (...) {}
}
```

I consider the bug serious as it undermines the trust in C++'s "RAII
philosophy".