accepts-invalid accessing private member of C++ class from scope specifier

[efriedma-quic]

template<int x> class A { static const int xx = 3; template<int y> class B; };
template<int x> template<int y> class A<x>::B { };
template<typename T> T f();
template<> int A<1>::B<A<1>::xx>::* f(){return nullptr;}

clang accepts.

gcc produces:

<source>: In function 'T f() [with T = int A<1>::B<3>::*]':
<source>:4:22: error: 'template<int y> class A<1>::B' is private within this context
    4 | template<> int A<1>::B<A<1>::xx>::* f(){return nullptr;}
      |                      ^
<source>:1:74: note: declared private here
    1 | template<int x> class A { static const int xx = 3; template<int y> class B; };
      |                                                                          ^
<source>:4:30: error: 'const int A<1>::xx' is private within this context
    4 | template<> int A<1>::B<A<1>::xx>::* f(){return nullptr;}
      |                              ^~
<source>:1:44: note: declared private here
    1 | template<int x> class A { static const int xx = 3; template<int y> class B; };
      |                                            ^~

I think clang is accidentally suppressing the access checks while disambiguating between a template function and a template member.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Eli Friedman (efriedma-quic)

``` template<int x> class A { static const int xx = 3; template<int y> class B; }; template<int x> template<int y> class A<x>::B { }; template<typename T> T f(); template<> int A<1>::B<A<1>::xx>::* f(){return nullptr;} ```

clang accepts.

gcc produces:

<source>: In function 'T f() [with T = int A<1>::B<3>::*]':
<source>:4:22: error: 'template<int y> class A<1>::B' is private within this context
    4 | template<> int A<1>::B<A<1>::xx>::* f(){return nullptr;}
      |                      ^
<source>:1:74: note: declared private here
    1 | template<int x> class A { static const int xx = 3; template<int y> class B; };
      |                                                                          ^
<source>:4:30: error: 'const int A<1>::xx' is private within this context
    4 | template<> int A<1>::B<A<1>::xx>::* f(){return nullptr;}
      |                              ^~
<source>:1:44: note: declared private here
    1 | template<int x> class A { static const int xx = 3; template<int y> class B; };
      |                                            ^~

I think clang is accidentally suppressing the access checks while disambiguating between a template function and a template member.