[Bug c++/66844] [c++-concepts] Requires-expression parameter with void type

["Casey at Carter dot net" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66844

--- Comment #2 from Casey Carter <Casey at Carter dot net> ---
If the intent is to allow parameters of void type - and I admit the wording of
5.1.4/5 is unclear as to exactly which of the rules of 8.3.5 are intended to
apply to the parameter-declaration-clause of a requires-expression - then this
program should be well-formed:

template <class T, class U>
concept bool Same = __is_same_as(T, U);

template <class T>
concept bool C =
  requires (T t, void v) {
    requires Same<decltype(t), decltype(v)>;
  };

template <C>
constexpr bool is_c() { return true; }

static_assert(is_c<void>(), "");

int main() {}

which the compiler diagnoses with "error: invalid use of type ‘void’ in
parameter declaration".
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Subject: [Bug bootstrap/66898] [6 Regression] profiledbootstrap failure on x86
Date: Thu, 16 Jul 2015 18:02:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idf898

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE
   Target Milestone|---                         |6.0

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
Dup.

*** This bug has been marked as a duplicate of bug 66891 ***