[Bug c++/78637] New: ICE on invalid C++ code on x86_64-linux-gnu (internal compiler error: in pop_namespace, at cp/name-lookup.c:3826)

["chengniansun at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78637

            Bug ID: 78637
           Summary: ICE on invalid C++ code on x86_64-linux-gnu (internal
                    compiler error: in pop_namespace, at
                    cp/name-lookup.c:3826)
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chengniansun at gmail dot com
  Target Milestone: ---

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-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 20161201 (experimental) [trunk revision 243118] (GCC)
$
$ gcc-trunk small.C
small.C:4:14: error: ‘namespace X::Y { }’ redeclared as different kind of
symbol
 namespace X::Y z;
              ^
small.C:2:7: note: previous declaration ‘class X::Y’
 class Y;
       ^
small.C:4:16: error: expected ‘{’ before ‘z’
 namespace X::Y z;
                ^
small.C:4:16: error: ‘z’ does not name a type
small.C:4:17: internal compiler error: in pop_namespace, at
cp/name-lookup.c:3826
 namespace X::Y z;
                 ^
0x890072 pop_namespace()
        ../../gcc-source-trunk/gcc/cp/name-lookup.c:3826
0x7d11bf cp_parser_namespace_definition
        ../../gcc-source-trunk/gcc/cp/parser.c:18226
0x7d07db cp_parser_declaration
        ../../gcc-source-trunk/gcc/cp/parser.c:12472
0x7d0ab4 cp_parser_declaration_seq_opt
        ../../gcc-source-trunk/gcc/cp/parser.c:12364
0x7d0df8 cp_parser_translation_unit
        ../../gcc-source-trunk/gcc/cp/parser.c:4368
0x7d0df8 c_parse_file()
        ../../gcc-source-trunk/gcc/cp/parser.c:38262
0x935c32 c_common_parse_file()
        ../../gcc-source-trunk/gcc/c-family/c-opts.c:1098
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.
$
$ cat small.C
namespace X {
class Y;
}
namespace X::Y z;
$