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From: "friedkeenan at protonmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/98500] ICE template template parameter with default
 parameter lambda
Date: Wed, 23 Feb 2022 08:14:30 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98500

friedkeenan at protonmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |friedkeenan at protonmail =
dot com

--- Comment #3 from friedkeenan at protonmail dot com ---
I've triggered this without a template template parameter:

#include <type_traits>

template<auto unique =3D [] {}>
struct unique_empty_type { };

template<bool IsPresent, typename T>
using maybe_present =3D std::conditional_t<IsPresent, T, unique_empty_type<=
>>;

using empty =3D maybe_present<false, int>;

Godbolt link: https://godbolt.org/z/hf9csv8ne

Upon instantiating `empty`, an ICE is thrown. To me this seems like the same
bug.=