[llvm-bugs] [Bug 47452] New: compiler crashes without proper diagnostics upon bad recursive variadic template usage

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47452

            Bug ID: 47452
           Summary: compiler crashes without proper diagnostics upon bad
                    recursive variadic template usage
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: kirshamir at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

template<std::size_t INDEX, typename... Ts>
struct A;

template<std::size_t INDEX, typename T>
class A<INDEX, T> {
    T t;
public:
    template<typename U, typename = std::enable_if_t<std::is_constructible_v<T,
U>>>
    constexpr A(U&& u)
    : t{std::forward<U>(u)} {}
};

template<std::size_t INDEX, typename T, typename... Ts>
struct A<INDEX, T, Ts...>: A<INDEX+1, Ts...>, A<INDEX, T> {
    template<typename U, typename... Us>
    constexpr A(U&& u, Us&&... us) noexcept(noexcept(A<INDEX+1, T,
Ts...>{std::forward<U>(u), std::forward<Us>(us)...}))
    : A<INDEX+1, Ts...>{std::forward<Us>(us)...}, A<INDEX,
T>{std::forward<U>(u)} {}
};

int main() {
    A<0,int> a1{3};
    A<0,int,int> a2{3, 3};
}

---------

The noexcept expression on the ctor of struct A<INDEX, T, Ts...> is recursively
using the same method.

Compiler crashes without proper diagnostics.

Code: https://godbolt.org/z/KcbT13

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