[libcxx] r285382 - Add __libcpp_version file and __libcpp_library_version function.

[James Y Knight via cfe-commits]

This breaks code which is using module headers, and then does like this:
extern "C" {
#include <stdint.h>
}

because:

> In file included from include/c++/v1/stdint.h:102:
> include/c++/v1/__config:912:35: error: declaration of
> '__libcpp_library_version' has a different language linkage
> _LIBCPP_FUNC_VIS _LIBCPP_WEAK int __libcpp_library_version();
>                                   ^
> include/c++/v1/__config:912:35: note: previous declaration is here
> _LIBCPP_FUNC_VIS _LIBCPP_WEAK int __libcpp_library_version();



Yes, ideally people wouldn't put a stdint.h include inside an extern "C",
but it's very common -- especially because a lot of C-library headers don't
have the appropriate extern "C" around their own declarations, so you
*need* to surround the whole thing with an extern "C". So this breaks a
whole lot of code.

I think you need to either make these functions extern "C", or else not
provide them in __config.



On Fri, Oct 28, 2016 at 2:06 AM, Eric Fiselier via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: ericwf
> Date: Fri Oct 28 01:06:50 2016
> New Revision: 285382
>
> URL: http://llvm.org/viewvc/llvm-project?rev=285382&view=rev
> Log:
> Add __libcpp_version file and __libcpp_library_version function.
>
> This patch does two seperate things. First it adds a file called
> "__libcpp_version" which only contains the current libc++ version
> (currently 4000). This file is not intended for use as a header. This file
> is used by Clang in order to easily determine the installed libc++ version.
> This allows Clang to enable/disable certain language features only when the
> library supports them.
>
> The second change is the addition of _LIBCPP_LIBRARY_VERSION macro, which
> returns the version of the installed dylib since it may be different than
> the headers.
>
> Added:
>     libcxx/trunk/include/__libcpp_version
>     libcxx/trunk/src/libcpp_version.cpp
>     libcxx/trunk/test/libcxx/version.pass.cpp
> Modified:
>     libcxx/trunk/include/__config
>     libcxx/trunk/lib/abi/CHANGELOG.TXT
>     libcxx/trunk/lib/abi/x86_64-linux-gnu.abilist
>
> Modified: libcxx/trunk/include/__config
> URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/__
> config?rev=285382&r1=285381&r2=285382&view=diff
> ============================================================
> ==================
> --- libcxx/trunk/include/__config (original)
> +++ libcxx/trunk/include/__config Fri Oct 28 01:06:50 2016
> @@ -908,6 +908,13 @@ extern "C" void __sanitizer_annotate_con
>  #define _LIBCPP_HAS_NO_BUILTIN_ADDRESSOF
>  #endif
>
> +_LIBCPP_BEGIN_NAMESPACE_STD
> +_LIBCPP_FUNC_VIS _LIBCPP_WEAK int __libcpp_library_version();
> +_LIBCPP_END_NAMESPACE_STD
> +
> +#define _LIBCPP_LIBRARY_VERSION \
> + (_VSTD::__libcpp_library_version ? _VSTD::__libcpp_library_version() :
> -1)
> +
>  #endif // __cplusplus
>
>  #endif // _LIBCPP_CONFIG
>
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