[Bug libstdc++/62154] New: std::throw_with_nested should not require a polymorphic type

["jaak at ristioja dot ee" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62154

            Bug ID: 62154
           Summary: std::throw_with_nested should not require a
                    polymorphic type
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jaak at ristioja dot ee

#include <exception>
struct E { E(int) {} };
int main() { std::throw_with_nested(E(42)); return 0; }

Compiling with "g++ -std=c++11 -Wall -Wextra". Tried with GCC 4.7.4, 4.8.3 and
4.9.1 and Clang.

In file included from
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.1/include/g++-v4/exception:163:0,
                 from test.cpp:1:
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.1/include/g++-v4/bits/nested_exception.h:
In instantiation of 'static const std::nested_exception*
std::__get_nested_helper<_Ex>::_S_get(const _Ex&) [with _Ex = E]':
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.1/include/g++-v4/bits/nested_exception.h:104:51:
  required from 'const std::nested_exception* std::__get_nested_exception(const
_Ex&) [with _Ex = E]'
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.1/include/g++-v4/bits/nested_exception.h:138:38:
  required from 'void std::throw_with_nested(_Ex) [with _Ex = E]'
test.cpp:6:31:   required from here
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.1/include/g++-v4/bits/nested_exception.h:90:59:
error: cannot dynamic_cast '& __ex' (of type 'const struct E*') to type 'const
class std::nested_exception*' (source type is not polymorphic)
       { return dynamic_cast<const nested_exception*>(&__ex); }
                                                           ^