[libcxx-commits] [libcxx] [libc++][NFC] Reduce workaround in a `in_place_t` constructor of `optional` (PR #174306)

[A. Jiang via libcxx-commits]

================
@@ -895,11 +896,9 @@ public:
   _LIBCPP_HIDE_FROM_ABI constexpr optional(optional&&)      = default;
   _LIBCPP_HIDE_FROM_ABI constexpr optional(nullopt_t) noexcept {}
 
-  template <
-      class _InPlaceT,
-      class... _Args,
-      enable_if_t<_And<_IsSame<_InPlaceT, in_place_t>, __is_constructible_for_optional<_Tp, _Args...>>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI constexpr explicit optional(_InPlaceT, _Args&&... __args)
+  // TODO(LLVM 23): Use _v instead of ::value.
----------------
frederick-vs-ja wrote:

The error messages are the following ([demo](https://godbolt.org/z/czW9PM9Yz), where test copied and correspondingly modified LLVM 20's `<optional>`):
```
<source>:1347:11: error: no matching member function for call to 'emplace'
 1347 |   w.inner.emplace();
      |   ~~~~~~~~^~~~~~~
<source>:764:60: note: candidate template ignored: requirement 'is_constructible_v<Wrapped::Inner>' was not satisfied [with _Args = <>]
  764 |   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& emplace(_Args&&... __args) {
```

https://github.com/llvm/llvm-project/pull/174306