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From: "arthur.j.odwyer at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/96213] GCC doesn't complain about ill-formed non-dependent
 template default argument
Date: Thu, 23 Jul 2020 20:27:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96213

--- Comment #2 from Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> ---
Here's a similar situation I just ran into again, somehow!

// https://godbolt.org/z/3TKG1z
struct S {};
template<class =3D decltype(S(42), void())> void f() {}
template<int I=3D42, class =3D decltype(S(I), void())> void g() {}
int main() {
    f();  // correctly errors out
    g();  // incorrectly accepted by GCC
}

GCC is happy to treat `S(I)` as well-formed when `I` is a template paramete=
r.
Obviously `decltype(S(I), void())` can't be anything because `S(I)` is
ill-formed, so I'm not sure what GCC is doing to compile this.=