Clang fails to match the out-of-line member function specialization's noexcept specifier containing packs

[zyn0217]

I stumbled upon this case when I was trying to clean up the uses of getTemplateInstantiationArgs(), which is in preparation for my CWG 2369 implementation.

https://clang.godbolt.org/z/MnYbGKoqP

template <typename T> struct S {
  template <typename... U>
  constexpr int UseAlignOf(int param = 1) noexcept(sizeof...(U) == 4);
};

template <>
template <typename... U>
constexpr int S<int>::UseAlignOf(int param) noexcept(sizeof...(U) == 4) {
  return param;
}

static_assert(S<int>().UseAlignOf<char>(), "");

Tested with @jcsxky's #102267 but everything persists.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Younan Zhang (zyn0217)

I stumbled upon this case when I was trying to [clean up](https://github.com//pull/104911) the uses of `getTemplateInstantiationArgs()`, which is in preparation for my CWG 2369 implementation.

https://clang.godbolt.org/z/MnYbGKoqP

template <typename T> struct S {
  template <typename... U>
  constexpr int UseAlignOf(int param = 1) noexcept(sizeof...(U) == 4);
};

template <>
template <typename... U>
constexpr int S<int>::UseAlignOf(int param) noexcept(sizeof...(U) == 4) {
  return param;
}

static_assert(S<int>().UseAlignOf<char>(), "");

Tested with @jcsxky's #102267 but everything persists.

[jcsxky]

Same as issue #101330 , clang can't find the instantiated template parameter. The difference is LocalInstantiationScope exits this time and we can't get instantiated template parameter from outer scope as well. Maybe it's too late in exception specifier equivalence checking?

[shafik]

Note edg also does not accept: https://clang.godbolt.org/z/n53cs3ev4

but if we don't use packs then clang accepts: https://clang.godbolt.org/z/hn5zjsY98