[Bug c++/106026] New: ICE: error reporting routines re-entered.

[ldalessandro at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106026

            Bug ID: 106026
           Summary: ICE: error reporting routines re-entered.
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ldalessandro at gmail dot com
  Target Milestone: ---

Created attachment 53163
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53163&action=edit
Eric's tag_invoke implementation.

Triggered with complicated tag_invoke + concepts. This code is erroneous (the
friend function with "requires requires" in cpos::extent and the free function
with "concepts::has_static_extent" should not both be possible.

This requires Eric Niebler's tag_invoke gist, which is somewhat complex, so I
left it in as an #include. I attached an actual copy as tag_invoke.hpp to this
PR as well.

https://godbolt.org/z/fzqEG6bnW

    #include
<https://gist.githubusercontent.com/ericniebler/056f5459cf259da526d9ea2279c386bb/raw/6c63fa81442e811fea8bd6920a95c0b8229dca6c/tag_invoke.hpp>
    #include <array>
    #include <concepts>

    #define FWD(x) static_cast<decltype(x)&&>(x)

    namespace traits {
        template <class T>
        inline constexpr auto extents_v = not defined(extents_v<T>);
    }

    namespace cpos {
        struct extents
        {
            template <class T>
            requires requires {
                { traits::extents_v<std::remove_cvref_t<T>> };
            }
            constexpr friend auto tag_invoke(extents, T&&) {
                return traits::extents_v<std::remove_cvref_t<T>>;
            }

            constexpr auto operator()(auto&& x) const {
                return tag_invoke(*this, FWD(x));
            }
        };
    }

    constexpr cpos::extents extents;

    namespace concepts {
        template <class T>
        concept has_extents = requires (T t) {
            { extents(t) };
        };

        template <class T>
        concept has_static_extents = has_extents<T> and requires {
            { traits::extents_v<std::remove_cvref_t<T>> };
        };
    }

    template <concepts::has_static_extents T>
    constexpr auto tag_invoke(cpos::extents, T&&) {
        return traits::extents_v<std::remove_cvref_t<T>>;
    }

    template <auto _shape>
    struct static_tensor {
    };

    namespace traits {
        template <auto _shape>
        inline constexpr auto extents_v<static_tensor<_shape>> = _shape;
    }

    constexpr std::array matrix_shape = { 3, 3 };
    auto x = static_tensor<matrix_shape>{};

    static_assert(concepts::has_static_extents<decltype(x)>);