[Bug libstdc++/79243] [7 Regression] Ambiguity with <string_view> and versioned namespaces

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79243

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Thu Jan 26 18:32:55 2017
New Revision: 244945

URL: https://gcc.gnu.org/viewcvs?rev=244945&root=gcc&view=rev
Log:
Fix namespace versioning and remove __detail::__identity helpers

        PR libstdc++/79243
        * include/bits/c++config (literals::string_view_literals::__7): Add.
        Only declare versioned namespaces for the relevant C++ dialects.
        * include/experimental/bits/erase_if.h (fundamentals_v2::__detail):
        Add versioning macros.
        * include/experimental/bits/lfts_config.h:
        (fundamentals_v1::__detail::__7, fundamentals_v2::__detail::__7): Add.
        * include/experimental/string_view (fundamentals_v2::__detail):
        Add versioning macros.
        (fundamentals_v2::__detail::__identity): Remove.
        (fundamentals_v2::__detail::__idt): Use common_type instead of
        __detail::__identity.
        * include/std/string_view (__detail::__identity, __detail::__idt):
        Likewise.
        (literals::string_view_literals): Fix nesting of versioning macros.

Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/bits/c++config
    trunk/libstdc++-v3/include/experimental/bits/erase_if.h
    trunk/libstdc++-v3/include/experimental/bits/lfts_config.h
    trunk/libstdc++-v3/include/experimental/string_view
    trunk/libstdc++-v3/include/std/string_view