[Bug libstdc++/65229] New: pretty-printer exception on std::bitset<0>

["msebor at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65229

            Bug ID: 65229
           Summary: pretty-printer exception on std::bitset<0>
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org

The StdBitsetPrinter class assumes that objects of all std::bitset
specializations contain a member named _M_w.  However, std::bitset<0> is an
empty class, and attempting to print an object of std::bitset<0> in GDB causes
a Python exception.  A trivial patch to avoid the exception is below.

$ cat t.cpp && g++ -g t.cpp && gdb -batch -ex "b main" -ex r -ex "p b" -q a.out
#include <bitset>

int main (void) {
    std::bitset<0> b;
    (void)&b;
}
Breakpoint 1 at 0x4005b0: file t.cpp, line 4.

Breakpoint 1, main () at t.cpp:4
4        std::bitset<0> b;
Python Exception <class 'gdb.error'> There is no member or method named _M_w.: 
$1 = std::bitset


index 5a414c5..8c5354f 100644
--- a/libstdc++-v3/python/libstdcxx/v6/printers.py
+++ b/libstdc++-v3/python/libstdcxx/v6/printers.py
@@ -568,7 +568,13 @@ class StdBitsetPrinter:
         return '%s' % (self.typename)

     def children (self):
-        words = self.val['_M_w']
+        try:
+            # An empty bitset may not have any members which will
+            # result in an exception being thrown.
+            words = self.val['_M_w']
+        except:
+            return ""
+
         wtype = words.type

         # The _M_w member can be either an unsigned long, or an