[Bug c++/49604] New: forward-declared enum in class scope is private in context of constexpr

["b.r.longbons at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49604

           Summary: forward-declared enum in class scope is private in
                    context of constexpr
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: b.r.longbons@gmail.com


Created attachment 24652
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24652
Minimal testcase

If an enum is forward-declared as a public member of a class (but not a
struct), and the values are defined afterward, then the enum values cannot be
be used in the context of a constexpr:

enum-broken.cpp:9:26: error: 'Foo::impl_t Foo::X' is private
enum-broken.cpp:11:27: error: within this context

(see attachment)

Workaround:
Use 'struct' instead of 'class'.

What works:
It works fine if 'struct' is used instead of 'class'.
It works fine without the constexpr.
It works fine if the enum values are defined in the declaration.
It works find if the nested type is a struct with a static member.

Versions:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.6.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.6.0/work/gcc-4.6.0/configure
--prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.6.0
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.0/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.0
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.0/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.0/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.0/include/g++-v4
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec
--disable-fixed-point --without-ppl --without-cloog --enable-lto --disable-nls
--with-system-zlib --disable-werror --enable-secureplt --enable-multilib
--enable-libmudflap --disable-libssp --enable-libgomp --enable-cld
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.6.0/python
--enable-checking=release --disable-libgcj --enable-languages=c,c++,fortran
--enable-shared --enable-threads=posix --enable-__cxa_atexit
--enable-clocale=gnu --with-bugurl=http://bugs.gentoo.org/
--with-pkgversion='Gentoo 4.6.0 p1.2, pie-0.4.5'
Thread model: posix
gcc version 4.6.0 (Gentoo 4.6.0 p1.2, pie-0.4.5) 


Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.6.1/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.6.1-1'
--with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++,go --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-multiarch
--with-multiarch-defaults=x86_64-linux-gnu --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib/x86_64-linux-gnu
--without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.6 --libdir=/usr/lib/x86_64-linux-gnu
--enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-plugin --enable-objc-gc
--with-arch-32=i586 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.1 (Debian 4.6.1-1)