[Bug c++/120775] [C++26] P2996R13 - Reflection

[cooky.ykooc922 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120775

--- Comment #9 from Desmond Gold <cooky.ykooc922 at gmail dot com> ---
I tried to wrap the declarations using "if not consteval { ... }" which seems
to silence the ICE:

using info = decltype(^^::);

consteval info identity(info i) { return i; }
consteval int something_of(info) { return 10; }
consteval void do_something(info) {}

void fox() {
  if not consteval {
    constexpr info X {};
    constexpr info A = ^^::;
    constexpr info B = identity(A);
    static constexpr info D = ^^::;

    static_assert(X == info{});
    static_assert(A == ^^::);
    static_assert(B == ^^::);
    static_assert(D == ^^::);

    consteval { 
      do_something(X);
      do_something(A);
      int H = something_of(A);
      constexpr int I = something_of(A);
    }
  }
}

However, the ICE resurfaces when referencing the constexpr variable of a
consteval-only type:

using info = decltype(^^::);

consteval info identity(info i) { return i; }
consteval int something_of(info) { return 10; }
consteval void do_something(info) {}

void fox() {
  if not consteval {
    constexpr info X {};
    constexpr info A = ^^::;
    constexpr info B = identity(A);
    static constexpr info D = ^^::;

    static_assert(X == info{});
    static_assert(A == ^^::);
    static_assert(B == ^^::);
    static_assert(D == ^^::);

    consteval { 
      do_something(X);
      do_something(A);
      int H = something_of(A);
      constexpr int I = something_of(A);
    }

    // ICE
    // do_something(X);
    // do_something(A);
    // do_something_runtime<X>();
    // do_something_runtime<A>();
    // int C = something_of(A);
    // constexpr int E = something_of(A);
    // identity(A);
    // identity(B);
  }
}

Uncommenting the line one at a time will produce an ICE output 

https://godbolt.org/z/9xWhbYhbz