[Bug c++/105921] New: internal compiler error: in cp_parser_template_id, at cp/parser.cc:18362

[Bug c++/105921] New: internal compiler error: in cp_parser_template_id, at cp/parser.cc:18362

[orbisvicis+gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105921

            Bug ID: 105921
           Summary: internal compiler error: in cp_parser_template_id, at
                    cp/parser.cc:18362
           Product: gcc
           Version: 12.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: orbisvicis+gcc at gmail dot com
  Target Milestone: ---

Created attachment 53117
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53117&action=edit
bug.cxx.i

[Bug c++/105921] internal compiler error: in cp_parser_template_id, at cp/parser.cc:18362

[orbisvicis+gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105921

--- Comment #1 from Yclept Nemo <orbisvicis+gcc at gmail dot com> ---
AFAICT, the attachment includes everything needed in a bug report. Inlining the
code here for convenience:

#include <utility>

template <typename T, int N>
auto a = (struct A {
    template <class T1, int>
    using Temp = T1;

    template <int... I>
    auto get(std::index_sequence<I...>){
        return (int (*)( Temp<T,N>... ))nullptr;
    }
}){}.get(std::make_index_sequence<N>{});

int main () {
    a<int, 4>;
}

[Bug c++/105921] internal compiler error: in cp_parser_template_id, at cp/parser.cc:18362

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105921

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-06-16
     Ever confirmed|0                           |1
                 CC|                            |marxin at gcc dot gnu.org

[Bug c++/105921] internal compiler error: in cp_parser_template_id, at cp/parser.cc:18362

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105921

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |11.1.0, 6.1.0, 9.1.0
           Keywords|ice-on-valid-code           |

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
template <int T>
auto a = (struct A {}){};

int main () {
    a<4>;
}

So GCC declares this as a compound literal where the new type is defined in the
(). It turns out for template variables, GCC is not ready for this.

Note clang rejects this code in both the non-template case and the template
case where defining a new struct is not allowed.

I don't know if we should restrict defining the new struct here or not.

This is not a regression either.