[Bug c++/95932] New: ICE in redeclare_class_template, at cp/pt.c:6231

[Bug c++/95932] New: ICE in redeclare_class_template, at cp/pt.c:6231

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95932

            Bug ID: 95932
           Summary: ICE in redeclare_class_template, at cp/pt.c:6231
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: ice-on-invalid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: haoxintu at gmail dot com
  Target Milestone: ---

This code, bug.cc, reduced by C-Reduce, makes GCC-trunk ICE.

$cat bug.cc
template <template>> struct a < class b{}, struct b {

$g++ bug.cc
bug.cc:1:19: error: expected ‘<’ before ‘>>’ token
    1 | template <template>> struct a < class b{}, struct b {
      |                   ^~
bug.cc:1:19: error: expected identifier before ‘>>’ token
bug.cc:1:19: error: expected ‘>’ before ‘>>’ token
bug.cc:1:19: error: expected ‘class’ or ‘typename’ before ‘>>’ token
bug.cc:1:19: error: expected identifier before ‘>>’ token
bug.cc:1:19: error: expected ‘>’ before ‘>>’ token
bug.cc:1:29: error: ‘a’ is not a class template
    1 | template <template>> struct a < class b{}, struct b {
      |                             ^
bug.cc:1:40: error: types may not be defined in template arguments
    1 | template <template>> struct a < class b{}, struct b {
      |                                        ^
bug.cc:1:51: internal compiler error: in redeclare_class_template, at
cp/pt.c:6231
    1 | template <template>> struct a < class b{}, struct b {
      |                                                   ^
0x652319 redeclare_class_template(tree_node*, tree_node*, tree_node*)
        ../../gcc/cp/pt.c:6231
0x8fb2e7 xref_tag_1
        ../../gcc/cp/decl.c:15043
0x8fb440 xref_tag(tag_types, tree_node*, tag_scope, bool)
        ../../gcc/cp/decl.c:15085
0x9a1584 cp_parser_class_head
        ../../gcc/cp/parser.c:24658
0x9a1584 cp_parser_class_specifier_1
        ../../gcc/cp/parser.c:23880
0x9a1aa3 cp_parser_class_specifier
        ../../gcc/cp/parser.c:24254
0x9a1aa3 cp_parser_type_specifier
        ../../gcc/cp/parser.c:17762
0x9b6b53 cp_parser_type_specifier_seq
        ../../gcc/cp/parser.c:22439
0x9afa94 cp_parser_type_id_1
        ../../gcc/cp/parser.c:22256
0x9b2603 cp_parser_template_type_arg
        ../../gcc/cp/parser.c:22347
0x9b6ccf cp_parser_template_argument
        ../../gcc/cp/parser.c:17235
0x9b6ccf cp_parser_template_argument_list
        ../../gcc/cp/parser.c:17146
0x9b6ccf cp_parser_enclosed_template_argument_list
        ../../gcc/cp/parser.c:29832
0x9b8cd0 cp_parser_check_for_invalid_template_id
        ../../gcc/cp/parser.c:3202
0x99ff18 cp_parser_check_for_invalid_template_id
        ../../gcc/cp/parser.c:3181
0x99ff18 cp_parser_class_head
        ../../gcc/cp/parser.c:24437
0x99ff18 cp_parser_class_specifier_1
        ../../gcc/cp/parser.c:23880
0x9a1aa3 cp_parser_class_specifier
        ../../gcc/cp/parser.c:24254
0x9a1aa3 cp_parser_type_specifier
        ../../gcc/cp/parser.c:17762
0x9a2a02 cp_parser_decl_specifier_seq
        ../../gcc/cp/parser.c:14410
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.


$g++ --version
g++ (GCC) 11.0.0 20200626 (experimental)
Copyright (C) 2020 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[Bug c++/95932] ICE in redeclare_class_template, at cp/pt.c:6231

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95932

--- Comment #1 from Haoxin Tu <haoxintu at gmail dot com> ---
Add a more meaningful case.

$cat p.cc
template <class> class a {};
template <template <class> > 
struct a < class b{}, struct b {}>;

$g++ p.cc
p.cc:2:28: error: expected ‘class’ or ‘typename’ before ‘>’ token
    2 | template <template <class> >
      |                            ^
p.cc:3:19: error: types may not be defined in template arguments
    3 | struct a < class b{}, struct b {}>;
      |                   ^
p.cc:3:30: internal compiler error: in redeclare_class_template, at
cp/pt.c:6231
    3 | struct a < class b{}, struct b {}>;
      |                              ^
0x6be12f redeclare_class_template(tree_node*, tree_node*, tree_node*)
        ../../gcc/cp/pt.c:6231
...

While in Clang
$clang++ p.cc
p.cc:2:28: error: template template parameter requires 'class' after the
parameter list
template <template <class> > 
                           ^
                           class 
p.cc:3:18: error: 'b' cannot be defined in a type specifier
struct a < class b{}, struct b {}>;
                 ^
2 errors generated.

I guess this is also a possible issue that users may encounter in programming,
but it makes GCC crashed.

[Bug c++/95932] ICE in redeclare_class_template, at cp/pt.c:6231

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95932

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-07-08
           Priority|P3                          |P5
                 CC|                            |mpolacek at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW