[Bug libstdc++/83982] [6/7/8/9 Regression] Exception guarantee of C++14 vector::resize(size_type) is not met

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83982

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
      Known to work|                            |5.5.0
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org
            Summary|Exception guarantee of      |[6/7/8/9 Regression]
                   |C++14                       |Exception guarantee of
                   |vector::resize(size_type)   |C++14
                   |is not met                  |vector::resize(size_type)
                   |                            |is not met
      Known to fail|                            |6.4.0, 7.3.0, 8.1.0, 9.0

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This testcase passes when compiled by GCC 5 with no option (because that means
-std=gnu++98 and so elements are copied not moved):

#include <vector>
#include <assert.h>

struct X
{
  X() : data(1)
  {
    if (fail)
      throw 1;
  }

  static bool fail;

  std::vector<int> data;
};

bool X::fail = false;

void
test01()
{
  std::vector<X> v(2);
  X* const addr = &v[0];
  bool caught = false;
  try {
    X::fail = true;
    v.resize(v.capacity() + 1); // force reallocation
  } catch (int) {
    caught = true;
  }
  assert( caught );
  assert( v.size() == 2 );
  assert( &v[0] == addr );
  // PR libstdc++/83982
  assert( ! v[0].data.empty() );
  assert( ! v[1].data.empty() );
}

int
main()
{
  test01();
}

But it fails when compiled by GCC 6 or later (except in C++98 modes), because
the existing elements are moved from and left empty. That makes this a
regression.