[libcxx-commits] [libcxx] [libc++][mdspan] Fix extents CTAD (PR #68737)

[Louis Dionne via libcxx-commits]

================
@@ -21,6 +21,12 @@
 #include "../ConvertibleToIntegral.h"
 #include "test_macros.h"
 
+struct S {
----------------
ldionne wrote:

```
struct NonDefaultIndex {
   size_t value;
   constexpr NonDefaultIndex() = delete;
   constexpr NonDefaultIndex(size_t val) : value(val){}
   constexpr operator size_t() const noexcept { return value; }
 };
```

This will make it more obvious what we're testing.

https://github.com/llvm/llvm-project/pull/68737