[Bug c++/108736] [concepts] multidimensional subscript operator inside requires with variable template arguments is broken

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108736

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[concepts] multidimensional |[concepts] multidimensional
                   |subscript operator reports  |subscript operator inside
                   |invalid error in requires   |requires with variable
                   |test                        |template arguments is
                   |                            |broken
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-02-09

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, even this is rejected:
```
    auto foo(auto a, auto... i) -> decltype(auto) {
        if constexpr (requires { a[i...]; }) {
            return a[i...];
        }
        else {
            return a;
        }
    }

    int x = foo(1, 1);
```

Note clang just ICEs.
Also the above works if it is not a variable argument auto ...

That is:
```
template<typename T, typename T1>
    auto foo(T a, T1 i) {
        if constexpr (requires { a[i]; }) {
            return a[i];
        }
        else {
            return a;
        }
    }

    int x = foo(1, 1);
```
Compiles just fine.