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From: "jlame646 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107111] New: GCC accepts invalid program involving function
 declaration with pack expansion
Date: Sat, 01 Oct 2022 17:05:30 +0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 12.1.1
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: jlame646 at gmail dot com
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107111

            Bug ID: 107111
           Summary: GCC accepts invalid program involving function
                    declaration with pack expansion
           Product: gcc
           Version: 12.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jlame646 at gmail dot com
  Target Milestone: ---

The following program is incorrectly accepted by gcc. Demo:
https://godbolt.org/z/rvfqzo5YW

```
template<typename T, typename... V>=20
struct C=20
{
    T v(V()...);;
};
int main()
{

    C<int> c; //works with gcc but rejected in clang=20
    C<int, double, int, int> c2; //same here: works with gcc but rejected in
clang
}
```
This is invalid because the construct `V()...` is actually equivalent to
`V(),...`. So `V` is not expanded and this must be rejected.=