[Bug c++/66712] New: [concepts] variadic concepts cause havoc

["eric.niebler at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66712

            Bug ID: 66712
           Summary: [concepts] variadic concepts cause havoc
           Product: gcc
           Version: c++-concepts
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eric.niebler at gmail dot com
  Target Milestone: ---

template <class T, class...Args>
concept bool _Constructible_ =
  requires (Args&&...args)
  {
    T{ ((Args&&)(args))... };
  };

template <class T, class...Args>
constexpr bool _constructible_() { return false; }

_Constructible_{T, ...Args...}
constexpr bool _constructible_() { return true; }

struct S
{
  S(int, char const *);
};

int main()
{
  static_assert(_constructible_<S, int, char const *>(), "");
}


Result:

temp.cpp: In function âint main()â:
temp.cpp:22:55: internal compiler error: tree check: expected record_type or
union_type or qual_union_type, have template_type_parm in lookup_base, at
cp/search.c:224
   static_assert(_constructible_<S, int, char const *>(), "");
                                                       ^

temp.cpp:22:55: internal compiler error: Aborted
g++: internal compiler error: Aborted (program cc1plus)
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.


The trouble with variadic concepts is a blocker for STL2.