[Bug c/107177] New: ICE: tree check: expected type_argument_pack or nontype_argument_pack, have integer_type in unify_pack_expansion, at cp/pt.cc:23912

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107177

            Bug ID: 107177
           Summary: ICE: tree check: expected type_argument_pack or
                    nontype_argument_pack, have integer_type in
                    unify_pack_expansion, at cp/pt.cc:23912
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---

g++ 13.0.0 20220925 snapshot (g:77bbf69d2981dafc2ef3e59bfbefb645d88bab9d) ICEs
when compiling the following testcase, reduced from
test/SemaTemplate/pack-deduction.cpp from the clang 15.0.1 test suite:

template<typename ...T> struct X {};
template<typename ...T> int f1(X<T, T...>... a);

int a1 = f1(X<int, int, double>(), X<double, int, double>());

% g++-13.0.0 -c r6lgqt43.cpp
r6lgqt43.cpp: In substitution of 'template<class ... T> int f1(X<T, T ...>...)
[with T = <missing>]':
r6lgqt43.cpp:6:14:   required from here
r6lgqt43.cpp:6:14: internal compiler error: tree check: expected
type_argument_pack or nontype_argument_pack, have integer_type in
unify_pack_expansion, at cp/pt.cc:23912
    6 |   int a1 = f1(X<int, int, double>(), X<double, int, double>());
      |            ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0x89062a tree_check_failed(tree_node const*, char const*, int, char const*,
...)
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/tree.cc:8827
0x71cbda tree_check2(tree_node*, char const*, int, char const*, tree_code,
tree_code)
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/tree.h:3539
0x71cbda unify_pack_expansion
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:23912
0xb60eb5 unify
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:24728
0xb60ce5 unify
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:24925
0xb60e73 unify
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:24722
0xb605b9 try_class_unification
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:23679
0xb61253 unify
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:24759
0xb5e1bc unify_one_argument
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:22894
0xb5eefa unify_pack_expansion
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:23943
0xb73e50 type_unification_real
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:23037
0xb8a74a fn_type_unification(tree_node*, tree_node*, tree_node*, tree_node*
const*, unsigned int, tree_node*, unification_kind_t, int, conversion**, bool,
bool)
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/pt.cc:22341
0x9722cf add_template_candidate_real
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/call.cc:3573
0x97339a add_template_candidate
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/call.cc:3661
0x97339a add_candidates
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/call.cc:6219
0x979969 add_candidates
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/call.cc:4726
0x979969 perform_overload_resolution
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/call.cc:4743
0x97f1f2 build_new_function_call(tree_node*, vec<tree_node*, va_gc,
vl_embed>**, int)
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/call.cc:4850
0xbac94a finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool,
bool, int)
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/semantics.cc:2904
0xb051fb cp_parser_postfix_expression
       
/var/tmp/portage/sys-devel/gcc-13.0.0_p20220925/work/gcc-13-20220925/gcc/cp/parser.cc:7965

Previous gcc releases ICE (down to at leaset 4.7) in tsubst, at cp/pt.cc:15867.
clang accepts this snippet.