https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95945
--- Comment #1 from Haoxin Tu <haoxintu at gmail dot com> ---
Add a more meaningful case
$cat p.cc
int a ( auto struct x { int b ();}) {}
$g++ -w p.cc
p.cc:1:23: error: types may not be defined in parameter types
1 | int a ( auto struct x { int b ();}) {}
| ^
p.cc:1:32: internal compiler error: in poplevel, at cp/decl.c:585
1 | int a ( auto struct x { int b ();}) {}
| ^
0x683eae poplevel(int, int, int)
../../gcc/cp/decl.c:585
0xa45d68 end_template_decl()
../../gcc/cp/pt.c:4688
0x9f86c2 finish_fully_implicit_template
../../gcc/cp/parser.c:44280
0xa3a12a cp_parser_member_declaration
../../gcc/cp/parser.c:25414
0xa0e061 cp_parser_member_specification_opt
../../gcc/cp/parser.c:24850
0xa0e061 cp_parser_class_specifier_1
../../gcc/cp/parser.c:23947
0xa10213 cp_parser_class_specifier
../../gcc/cp/parser.c:24254
0xa10213 cp_parser_type_specifier
../../gcc/cp/parser.c:17762
0xa11172 cp_parser_decl_specifier_seq
../../gcc/cp/parser.c:14410
0xa2db8f cp_parser_parameter_declaration
../../gcc/cp/parser.c:22818
0xa2e582 cp_parser_parameter_declaration_list
../../gcc/cp/parser.c:22641
0xa2e95c cp_parser_parameter_declaration_clause
../../gcc/cp/parser.c:22568
0xa1bda7 cp_parser_direct_declarator
../../gcc/cp/parser.c:21245
0xa1bda7 cp_parser_declarator
../../gcc/cp/parser.c:21109
0xa30346 cp_parser_init_declarator
../../gcc/cp/parser.c:20609
0xa11e42 cp_parser_simple_declaration
../../gcc/cp/parser.c:13785
0xa3b0b6 cp_parser_declaration
../../gcc/cp/parser.c:13484
0xa3b7fa cp_parser_translation_unit
../../gcc/cp/parser.c:4761
0xa3b7fa c_parse_file()
../../gcc/cp/parser.c:44043
0xb5473b c_common_parse_file()
../../gcc/c-family/c-opts.c:1190
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
In Clang
$clang++ -w p.cc
p.cc:1:21: error: 'x' cannot be defined in a parameter type
int a ( auto struct x { int b ();}) {}
^
1 error generated.
