Name resolution for function declared in anonymous struct

Question

Should name resolution work for A , B , C in the following code in parameter list of f definition?

namespace ns
{
struct A {};
struct S
{
    struct B {};
    struct
    {
        struct C {};
        void f(A, B, C);
    } x;
};
}

#include <type_traits>

void std::type_identity_t<decltype(ns::S::x)>::f(A, B, C) {}

int main()
{
}

Actually it works in latest clang .

Answer 1

[basic.lookup.unqual]/8 For the members of a class X , a name used ... in the definition of a class member outside of the definition of X , following the member's declarator-id (24), shall be declared in one of the following ways:
...
(8.2) — shall be a member of class X ..., or
(8.3) — if X is a nested class of class Y (11.4.10), shall be a member of Y ,... or
...
(8.5) — if X is a member of namespace N , or is a nested class of a class that is a member of N , ... before the use of the name, in namespace N or in one of N 's enclosing namespaces.

Footnote 24) That is, an unqualified name that occurs, for instance, in a type in the parameter-declaration-clause or in the noexcept-specifier .

Here X is decltype(ns::S::x) , Y is S , N is ns . Therefore, A is found via (8.5), B via (8.3), C via (8.2).