warning in BOOST_BIMAP_STATIC_ERROR with clang trunk

[Nathan Ridge]

The following code:

#include <boost/bimap/detail/debug/static_error.hpp>

template <typename T>
struct S
{
    BOOST_BIMAP_STATIC_ERROR(SOME_MESSAGE, (T));
};

produces a warning with clang trunk:

test.cpp:6:5: warning: class member cannot be redeclared [-Wgnu]
    BOOST_BIMAP_STATIC_ERROR(SOME_MESSAGE, (T));
    ^
boost/bimap/detail/debug/static_error.hpp:30:30: note: expanded from macro 'BOOST_BIMAP_STATIC_ERROR'
                             BOOST_PP_CAT(BIMAP_STATIC_ERROR__,MESSAGE),      \
                             ^
boost/preprocessor/cat.hpp:22:32: note: expanded from macro 'BOOST_PP_CAT'
#    define BOOST_PP_CAT(a, b) BOOST_PP_CAT_I(a, b)
                               ^
boost/preprocessor/cat.hpp:29:34: note: expanded from macro 'BOOST_PP_CAT_I'
#    define BOOST_PP_CAT_I(a, b) a ## b
                                 ^
<scratch space>:167:1: note: expanded from here
BIMAP_STATIC_ERROR__SOME_MESSAGE
^
boost/mpl/assert.hpp:435:59: note: expanded from macro 'BOOST_MPL_ASSERT_MSG'
BOOST_MPL_ASSERT_MSG_IMPL( BOOST_MPL_AUX_PP_COUNTER(), c, msg, types_ ) \
                                                          ^
boost/mpl/assert.hpp:419:8: note: expanded from macro '\
BOOST_MPL_ASSERT_MSG_IMPL'
struct msg; \
       ^
test.cpp:6:5: note: previous declaration is here
boost/bimap/detail/debug/static_error.hpp:28:16: note: expanded from macro 'BOOST_BIMAP_STATIC_ERROR'
        struct BOOST_PP_CAT(BIMAP_STATIC_ERROR__,MESSAGE) {};                 \
               ^
boost/preprocessor/cat.hpp:22:32: note: expanded from macro 'BOOST_PP_CAT'
#    define BOOST_PP_CAT(a, b) BOOST_PP_CAT_I(a, b)
                               ^
boost/preprocessor/cat.hpp:29:34: note: expanded from macro 'BOOST_PP_CAT_I'
#    define BOOST_PP_CAT_I(a, b) a ## b
                                 ^
<scratch space>:166:1: note: expanded from here
BIMAP_STATIC_ERROR__SOME_MESSAGE
^

The reason is that the macro expands to the following:

template <typename T>
struct S
{
    struct BIMAP_STATIC_ERROR__SOME_MESSAGE {};                 
    struct BIMAP_STATIC_ERROR__SOME_MESSAGE;
    // <snip rest of expansion>
};

The nested structure 'BIMAP_STATIC_ERROR_SOME_MESSAGE' is defined, and then redeclared. Such redeclaration is, apparently, not allowed. GCC accepts it as an extension, but the trunk version of clang warns about it.

As a result, any code that uses Bimap is littered with warnings of this sort (since the library uses BOOST_BIMAP_STATIC_ERROR in multiple places).

The fix is simple: modify BOOST_BIMAP_STATIC_ERROR to omit the definition, which is not necessary. The declaration emitted by BOOST_MPL_ASSERT_MSG is sufficient.

Patch attached.

[Nathan Ridge]

patch that fixes the warning

[Jim King <jim.king@…>]

I also ran into this with the boost "master" tip for 1.56 plus the latest clang-3.5.0. If you use -Wall -Werror in your projects this becomes a build error.

[anonymous]

doesn't clear the issue.. created a lot of warnings and issues

[Nathan Ridge]

Replying to anonymous:

doesn't clear the issue.. created a lot of warnings and issues

Are you referring to my patch from comment 1?

[anonymous]

This patch fixes using bimap on clang with option -Wall -Werror perfectly; should be applied to upstream.

[anonymous]

Why hasn't this patch been merged yet?

[Finomnis]

+1, fixed my problems as well. Could one of the developers at least give some kind of a statement why this didn't get merged yet?

[anonymous]

+1, fixed my problem as well.

[Matias Capeletto]

Applied from pull-request: ​https://github.com/boostorg/bimap/commit/e4b46b3258f0a5be1484d9c507f6133930498925, thanks and sorry for the delay.