Bug in partial class template specialization

[vladon]

template <class A>
struct Foo {
  template <class Bar>
  constexpr auto a_method();
};

template <class A>
template <class Bar>
constexpr auto Foo<A>::a_method() {
    return 42;
}

template <>
template <class Bar>
constexpr auto Foo<void>::a_method() {
    return 42;
}

It can be compiled with GCC, but not with Clang.
If we first provide explicit specialization, Clang will compile it.
Seems like a bug in Clang.

See also:
https://stackoverflow.com/questions/70670212/is-this-partial-class-specialization-buggy-or-is-it-a-bug-in-clang-or-gcc

[zygoloid]

Looks like we're probably comparing the resolved type instead of the declared type, so the unresolved auto in the explicit member specialization doesn't match the resolved auto in the member of the primary template.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[llvmbot]

@llvm/issue-subscribers-bug