[libcxx-commits] [libcxx] [libc++] fixing missing forward declarations of uses_allocator_construction_args (PR #67044)

[Louis Dionne via libcxx-commits]

================
@@ -118,6 +118,15 @@ constexpr bool test() {
     assert(std::get<2>(std::get<1>(ret)) == 3);
     assert(std::get<0>(std::get<2>(ret)) == 4);
   }
+  {
----------------
ldionne wrote:

You can change the test to this:

```
{
    // See https://github.com/llvm/llvm-project/issues/66714
    {
      using NestedPairType = std::pair<int, std::pair<int, UsesAllocArgT>>;
      std::same_as<std::tuple<std::piecewise_construct_t,
                              std::tuple<>,
                              std::tuple<std::piecewise_construct_t,
                                         std::tuple<>,
                                         std::tuple<std::allocator_arg_t, const Alloc&>>>> auto ret =
          test_uses_allocator_construction_args<NestedPairType>(a);
          (void)ret;
    }
    {
      using NestedPairType = std::pair<int, std::pair<UsesAllocArgT, int>>;
      std::same_as<std::tuple<std::piecewise_construct_t,
                              std::tuple<>,
                              std::tuple<std::piecewise_construct_t,
                                         std::tuple<std::allocator_arg_t, const Alloc&>,
                                         std::tuple<>>>> auto ret =
        test_uses_allocator_construction_args<NestedPairType>(a);
        (void)ret;
    }
  }
```

It doesn't require using `std::pmr`.

https://github.com/llvm/llvm-project/pull/67044