RFC: What should go in our <version> header?

[Ed Smith-Rowland]

On 06/15/2018 11:52 AM, Jonathan Wakely wrote:
> C++20 adds a <version> header, which should define all the library
> feature test macros, as well as implementation-specific macros like
> _GLIBCXX_RELEASE and __GLIBCXX__.
>
> We should decide whether to implement <version> by simply including
> <bits/c++config.h> and then adding the feature test macros, or if we
> should keep it minimal and *only* define _GLIBCXX_RELEASE and
> __GLIBCXX__ and the feature tests (and then have <bits/c++config.h>
> include <version>?)
>
> I think I prefer to make <version> just include <bits/c++config.h>.
>
> I think we should define the feature-test macros in both <version> and
> the relevant header (e.g. __cpp_string_view in <string_view>). We
> could make everything include <version> and then every header would
> define every feature test macro, but I don't think that's good for
> portability.
>
> My preference is implemented by the attached patch.
>
This is pretty much what I was looking at doing.  I say go!
>
> While on the subject, should we just delete some of this autoconf-junk
> from our c++config.h headers?
>
> /* Name of package */
> /* #undef _GLIBCXX_PACKAGE */
>
> /* Define to the address where bug reports for this package should be 
> sent. */
> #define _GLIBCXX_PACKAGE_BUGREPORT ""
>
> /* Define to the full name of this package. */
> #define _GLIBCXX_PACKAGE_NAME "package-unused"
>
> /* Define to the full name and version of this package. */
> #define _GLIBCXX_PACKAGE_STRING "package-unused version-unused"
>
> /* Define to the one symbol short name of this package. */
> #define _GLIBCXX_PACKAGE_TARNAME "libstdc++"
>
> /* Define to the home page for this package. */
> #define _GLIBCXX_PACKAGE_URL ""
>
> /* Define to the version of this package. */
> #define _GLIBCXX_PACKAGE__GLIBCXX_VERSION "version-unused"
>
I don't have an opinion here except if this is unused cruft let's lose 
it.  I think we *are* supposed to have some project and version 
identification.  We have _GLIBCXX_* everywhere.  The folks that use 
libstdc++ *outside* of g++ might have some opinions about this too.

Ed