[Bug c++/107450] New: GCC accepts invalid program involving multiple template parameter packs

[Bug c++/107450] New: GCC accepts invalid program involving multiple template parameter packs

[jlame646 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107450

            Bug ID: 107450
           Summary: GCC accepts invalid program involving multiple
                    template parameter packs
           Product: gcc
           Version: 13.0
            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 invalid program is accepted by gcc and clang but rejected by
msvc:
Demo: https://godbolt.org/z/Esbq4qK94
```
template<typename... T1, typename... T2, typename... T3>
void foo(T1&&...args1, T2&&... args2, T3&&... args3) {
    std::cout << "args1:\n", ((std::cout << args1 << " "), ...);
    std::cout << "args2:\n", ((std::cout << args2 << " "), ...);
    std::cout << "args3:\n", ((std::cout << args3 << " "), ...);
}

int main(int argc, char** argv)
{
    foo(1,2,3,4,5,6); //gcc and clang compiles this while msvc correctly
rejects this
}
```

[Bug c++/107450] GCC accepts invalid program involving multiple template parameter packs

[jlame646 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107450

--- Comment #1 from Jason Liam <jlame646 at gmail dot com> ---
Also if we remove one of the template parameter(say T3) then msvc starts
compiling this code as well. Demo: https://godbolt.org/z/qacMzoT3q


Additionally, this current bug is most probably a duplicate of:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69623

[Bug c++/107450] GCC accepts invalid program involving multiple template parameter packs

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107450

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced/simplified (using auto because I feel like it):
int i, j, k;
void f(auto){i++;}
void g(auto){j++;}
void h(auto){k++;}
void foo(auto&&...args1, auto&&... args2, auto&&... args3) {
    (f(args1), ...);
    (g(args2), ...);
    (h(args3), ...);
}

int main(int argc, char** argv)
{
    foo(1,2,3,4,5,6); //gcc and clang compiles this while msvc correctly
rejects this
    __builtin_printf("args1: %d, args2: %d, args3: %d.\n", i, j, k);
}