[Bug c++/103943] New: ICE building qualified name inside class with variadic CTAD

["cbcode at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103943

            Bug ID: 103943
           Summary: ICE building qualified name inside class with variadic
                    CTAD
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cbcode at gmail dot com
  Target Milestone: ---

// gcc has known problems with variadic CTAD, not sure if this is related.
// regression (was fine in v8.3.0).

template<typename R, typename...AA> struct F0 { //OK
    R(*fun_ptr)(AA...);
};
template<typename R, typename...AA> struct F1 { //OK
    R(*fun_ptr)(AA...);
    F1(R(*fun_ptr)(AA...)) : fun_ptr(fun_ptr) {}
};
template<typename R, typename...AA> struct F2 { //OK
    R(*fun_ptr)(AA...);
    using fun_ptr_t = decltype(fun_ptr);
    F2(fun_ptr_t fun_ptr) : fun_ptr(fun_ptr) {}
};
template<typename R, typename...AA> struct F3 {
    R(*fun_ptr)(AA...);
//  using fun_ptr_t = decltype(fun_ptr); //OK as in F2
    using fun_ptr_t = decltype(F3::fun_ptr); //ICE: Segmentation fault
//  using fun_ptr_t = decltype(F3<R, AA...>::fun_ptr); //ICE: Segmentation
fault
    F3(fun_ptr_t fun_ptr) : fun_ptr(fun_ptr) {}
};
template<typename R, typename...AA> struct F4 {
    static R fun_not_implemented(AA...);
//  using fun_ptr_t = decltype(&fun_not_implemented); //OK
    using fun_ptr_t = decltype(&F4::fun_not_implemented); //OK with aggregate
initialization (no ctor)
//  using fun_ptr_t = decltype(&F4<R, AA...>::fun_not_implemented); //OK with
aggregate initialization (no ctor)
    fun_ptr_t fun_ptr;
};
template<typename R, typename...AA> struct F5 { //OK
    static R fun_not_implemented(AA...);
    using fun_ptr_t = decltype(&fun_not_implemented);
    fun_ptr_t fun_ptr;
    F5(fun_ptr_t fun_ptr) : fun_ptr(fun_ptr) {}
};
template<typename R, typename...AA> struct F6 {
    static R fun_not_implemented(AA...);
//  using fun_ptr_t = decltype(&fun_not_implemented); //OK as in F5
    using fun_ptr_t = decltype(&F6::fun_not_implemented); //ICE: in
build_qualified_name, at cp/tree.c:2238
//  using fun_ptr_t = decltype(&F6<R, AA...>::fun_not_implemented); //ICE: in
build_qualified_name, at cp/tree.c:2238
    fun_ptr_t fun_ptr;
    F6(fun_ptr_t fun_ptr) : fun_ptr(fun_ptr) {}
};
template<typename R, typename...AA> F0(R(*fun_ptr)(AA...)) -> F0<R, AA...>;
template<typename R, typename...AA> F1(R(*fun_ptr)(AA...)) -> F1<R, AA...>;
template<typename R, typename...AA> F2(R(*fun_ptr)(AA...)) -> F2<R, AA...>;
template<typename R, typename...AA> F3(R(*fun_ptr)(AA...)) -> F3<R, AA...>;
template<typename R, typename...AA> F4(R(*fun_ptr)(AA...)) -> F4<R, AA...>;
template<typename R, typename...AA> F5(R(*fun_ptr)(AA...)) -> F5<R, AA...>;
template<typename R, typename...AA> F6(R(*fun_ptr)(AA...)) -> F6<R, AA...>;

int fun(int a) {
    return a + 1;
}
#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
void test() {
    auto f0 = F0{&fun}; //OK
    auto f1 = F1{&fun}; //OK
    auto f2 = F2{&fun}; //OK
    auto f3 = F3{&fun}; //ICE: Segmentation fault
    auto f4 = F4{&fun}; //OK
    auto f5 = F5{&fun}; //OK
    auto f6 = F6{&fun}; //ICE: in build_qualified_name, at cp/tree.c:2238
}