[libcxx-commits] [libcxx] [libc++] Fix the mdspan ElementType complete object type mandate (PR #191703)

[Hewill Kang via libcxx-commits]

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@@ -66,6 +67,9 @@ class mdspan {
 private:
   static_assert(__mdspan_detail::__is_extents_v<_Extents>,
                 "mdspan: Extents template parameter must be a specialization of extents.");
+  static_assert(
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hewillk wrote:

I don't think we want `requires { sizeof(_ElementType); }` here.

`!is_abstract_v<_ElementType>` would already cause a hard error if `_ElementType` is an incomplete type.

https://github.com/llvm/llvm-project/pull/191703