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From: "jason at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/98939] [C++23] Implement P1787R6 "Declarations and where to
 find them"
Date: Thu, 18 Nov 2021 17:38:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98939

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #2)
> class C {
>   template <typename...> struct _List;
>=20
>   template <unsigned long, typename, bool B =3D value> struct S; // #1
>=20
>   template <unsigned long _Sz, typename _Uint, typename... _UInts>
>   struct S<_Sz, _List<_Uint, _UInts...>>; // #2
>=20
>   static constexpr bool value =3D false;
> };
>=20
> #2 wants to lookup_template_class S, but S can contain a DEFERRED_PARSE, =
so
> that's not going to work.  Perhaps we have to delay finish_template_type
> until the end of class somehow...

As I was saying in our meeting, I think in this testcase #2 is ill-formed
because it depends on a default argument that hasn't been parsed yet.=