[Bug c++/72801] New: ICE on invalid C++ code with ill-formed class member specialization: tree check: expected class ‘expression’, have ‘type’ (integer_type) in tree_operand_check, at tree.h:3521

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72801

            Bug ID: 72801
           Summary: ICE on invalid C++ code with ill-formed class member
                    specialization: tree check: expected class
                    ‘expression’, have ‘type’ (integer_type) in
                    tree_operand_check, at tree.h:3521
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

This is a regression from 6.1.x.


$ g++-trunk -v
Using built-in specs.
COLLECT_GCC=g++-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 7.0.0 20160802 (experimental) [trunk revision 238983] (GCC)
$
$ g++-trunk -c small.cpp
small.cpp:17:50: internal compiler error: tree check: expected class
‘expression’, have ‘type’ (integer_type) in tree_operand_check, at tree.h:3521
 template <> const int B <>::template C < int () >::a;
                                                  ^~
0x1071a07 tree_class_check_failed(tree_node const*, tree_code_class, char
const*, int, char const*)
        ../../gcc-source-trunk/gcc/tree.c:9793
0x5da8f1 expr_check
        ../../gcc-source-trunk/gcc/tree.h:3192
0x5da8f1 tree_operand_check
        ../../gcc-source-trunk/gcc/tree.h:3521
0x709be5 tree_operand_check
        ../../gcc-source-trunk/gcc/tree.h:3244
0x709be5 unify_pack_expansion
        ../../gcc-source-trunk/gcc/cp/pt.c:19337
0x70a7b9 type_unification_real
        ../../gcc-source-trunk/gcc/cp/pt.c:18481
0x70c2fe unify
        ../../gcc-source-trunk/gcc/cp/pt.c:20176
0x70c516 unify
        ../../gcc-source-trunk/gcc/cp/pt.c:20056
0x70ed47 get_partial_spec_bindings
        ../../gcc-source-trunk/gcc/cp/pt.c:20826
0x7066c6 most_specialized_partial_spec
        ../../gcc-source-trunk/gcc/cp/pt.c:21082
0x721993 instantiate_class_template_1
        ../../gcc-source-trunk/gcc/cp/pt.c:9847
0x721993 instantiate_class_template(tree_node*)
        ../../gcc-source-trunk/gcc/cp/pt.c:10412
0x7c7363 complete_type(tree_node*)
        ../../gcc-source-trunk/gcc/cp/typeck.c:133
0x79954c cp_parser_nested_name_specifier_opt
        ../../gcc-source-trunk/gcc/cp/parser.c:6131
0x79a05e cp_parser_nested_name_specifier
        ../../gcc-source-trunk/gcc/cp/parser.c:6194
0x7a7cf6 cp_parser_ptr_operator
        ../../gcc-source-trunk/gcc/cp/parser.c:19525
0x79e67b cp_parser_declarator
        ../../gcc-source-trunk/gcc/cp/parser.c:18841
0x7b38b5 cp_parser_init_declarator
        ../../gcc-source-trunk/gcc/cp/parser.c:18424
0x7b57d1 cp_parser_single_declaration
        ../../gcc-source-trunk/gcc/cp/parser.c:25938
0x7b65e3 cp_parser_explicit_specialization
        ../../gcc-source-trunk/gcc/cp/parser.c:15779
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.
$


-------------------------------------------------------


template < typename, typename > struct A {};

template < typename ... T > struct B
{ 
  template < typename > struct C
  { 
    static const int a = 0;
  };

  template < typename R, typename ... S >
  struct C < R (A < T, S > ...) >
  { 
    static const int a = 1;
  };
};

template <> const int B <>::template C < int () >::a;