[Bug c++/103273] New: [12 Regression] internal compiler error: in cp_parser_type_id_1, at cp/parser.c:24010

["steinar+gcc at gunderson dot no" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103273

            Bug ID: 103273
           Summary: [12 Regression] internal compiler error: in
                    cp_parser_type_id_1, at cp/parser.c:24010
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: steinar+gcc at gunderson dot no
  Target Milestone: ---

Found while minimizing another regression:

gcc version 12.0.0 20210918 (experimental) [master r12-3644-g7afcb534239]
(Debian 20210918-1) 

bigscreen:~/creduce> cat fts0opt.i
template <class a> struct b;
b < b struct {

bigscreen:~/creduce> /usr/lib/gcc-snapshot/bin/g++ -c fts0opt.i
fts0opt.i:2:14: error: types may not be defined in template arguments
    2 | b < b struct {
      |              ^
fts0opt.i:2:15: error: expected '}' at end of input
    2 | b < b struct {
      |              ~^
fts0opt.i:2:15: internal compiler error: in cp_parser_type_id_1, at
cp/parser.c:24010
0x6fa6a2 cp_parser_type_id_1
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:24010
0xf578c3 cp_parser_template_type_arg
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:24105
0xf579ef cp_parser_template_argument
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:18660
0xf579ef cp_parser_template_argument_list
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:18571
0xf579ef cp_parser_enclosed_template_argument_list
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:31853
0xf58e76 cp_parser_template_id
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:18108
0xf5969b cp_parser_class_name
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:25535
0xf5035a cp_parser_qualifying_entity
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:7048
0xf5035a cp_parser_nested_name_specifier_opt
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:6730
0xf45f4d cp_parser_constructor_declarator_p
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:30712
0xf45f4d cp_parser_decl_specifier_seq
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:15743
0xf469b4 cp_parser_simple_declaration
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:15006
0xf76f25 cp_parser_declaration
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:14819
0xf778fe cp_parser_toplevel_declaration
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:14840
0xf778fe cp_parser_translation_unit
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:4978
0xf778fe c_parse_file()
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/cp/parser.c:47653
0x10a4a4d c_common_parse_file()
       
/build/gcc-snapshot-FKpLPc/gcc-snapshot-20210918/src/gcc/c-family/c-opts.c:1236
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