[Bug libstdc++/80675] Incorrect implementation of LWG 2534

[ville at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80675

--- Comment #3 from ville at gcc dot gnu.org ---
Author: ville
Date: Wed Jun 21 21:09:46 2017
New Revision: 249471

URL: https://gcc.gnu.org/viewcvs?rev=249471&root=gcc&view=rev
Log:
PR libstdc++/80675, PR libstdc++/80940

Backport from mainline
2017-06-21  Ville Voutilainen  <ville.voutilainen@gmail.com>

PR libstdc++/80675
PR libstdc++/80940
* include/std/istream:
(__is_convertible_to_basic_istream_test(basic_istream<_Ch, _Up>*)): New.
(__do_is_convertible_to_basic_istream_impl): Likewise.
(__is_convertible_to_basic_istream_impl): Likewise.
(__is_convertible_to_basic_istream): Use the new base.
(__rvalue_istream_type): New.
(operator>>(_Istream&&, _Tp&&)): Use the new helper alias
for the SFINAE check, convert to the helper alias type before
doing the actual extraction.
* include/std/ostream:
(__is_convertible_to_basic_ostream_test(basic_ostream<_Ch, _Up>*)): New.
(__do_is_convertible_to_basic_ostream_impl): Likewise.
(__is_convertible_to_basic_ostream_impl): Likewise.
(__is_convertible_to_basic_ostream): Use the new base.
(__rvalue_ostream_type): New.
(operator<<(_Ostream&&, const _Tp&)): Use the new helper alias
for the SFINAE check, convert to the helper alias type before
doing the actual insertion.
* testsuite/27_io/rvalue_streams-2.cc: Add new tests.

Modified:
    branches/gcc-7-branch/libstdc++-v3/ChangeLog
    branches/gcc-7-branch/libstdc++-v3/include/std/istream
    branches/gcc-7-branch/libstdc++-v3/include/std/ostream
    branches/gcc-7-branch/libstdc++-v3/testsuite/27_io/rvalue_streams-2.cc